Integrated charging topologies supplied from a multiphase voltage source and based on a six-phase b five-phase [10] .... Power factor correction a Equivalent circuit in charging mode b i
Introduction
Recent years have seen increasing technological, industrial, and commercial interest in electric transportation, particularly electric and plug-in hybrid electric vehicles (EV/PHEVs), driven by consumer demand for environmental benefits A crucial component of electric transportation is the charging of the traction battery, with various charging technologies discussed in detail in Chapter 2 Innovations are focusing on integrating motor drive and on-board battery chargers into a single circuit to reduce system weight and volume, known as integrated drives Researchers have extensively studied EV traction motors and integrated drives based on induction machines, permanent magnet machines, and switched reluctance machines, with the latest advancements reviewed comprehensively in Chapter 2.
Permanent magnet synchronous motors (PMSMs) have been widely used in electric transportation for their high efficiency and power density However, their reliance on rare-earth materials presents environmental and economic challenges, including resource depletion and supply constraints Consequently, recent research has shifted toward developing rare-earth-free machines to enable sustainable, large-scale production in the future Among these alternatives, switched reluctance machines (SRMs) have gained prominence due to their simple structure, flexible control, high efficiency, robust mechanical design, and excellent temperature tolerance, as they lack rotor magnets.
Research Questions
This research project focuses on analyzing the integration of Switched Reluctance Motor (SRM) and electric drive components in charging systems to enhance efficiency and simplify design The study aims to reduce the number of components needed for both driving and charging processes while preserving key features such as drive fault tolerance, power factor correction (PFC), battery voltage equalization, constant current constant voltage (CCCV) charging, and fast charging capabilities By optimizing these elements, the project seeks to improve overall system reliability, performance, and cost-effectiveness in electric vehicle charging solutions.
This overall objective comprises of the following research questions and associated sub-objectives:
1.2.1 RQ1 – What is the best power stage topology of switched reluctance motor drive to perform functions of an integrated drive?
The Switched Reluctance Motor (SRM) has been extensively studied for electric vehicle (EV) traction applications due to its simple structure, flexible control capabilities, high efficiency, robust mechanical design, and excellent temperature endurance resulting from the absence of rotor magnets During integrated drive operation, where motor windings are used for charging, it is crucial to ensure that no unwanted torque is generated and that the rotor remains stationary, a concern addressed in RQ1 Since SRM inductance varies with rotor position, RQ1 also explores the necessary control strategies to account for this inductance variability in the charging process.
1.2.2 RQ2 – What is the best approach to achieve CCCV, PFC, and fault tolerance and battery voltage equalization using a new integrated
The most effective battery charging methods for lithium-ion batteries are constant-current (CC) and constant-voltage (CV) algorithms During CC charging, the dc–dc converter's output voltage varies significantly, while in the CV phase, the output current decreases from maximum to nearly zero Understanding the operation of the converter during these phases is essential for optimizing charging performance and is thoroughly investigated as part of research question 2 (RQ2).
Power quality is crucial for the efficient operation of electric vehicle (EV) chargers, which require high input current demand Implementing power factor correction (PFC) is highly advantageous to improve efficiency and reduce power quality issues Designing the boost inductor for a PFC rectifier to optimize converter performance remains a key challenge, extensively discussed in current literature.
Implementing both CCCV (Constant-Current Constant-Voltage) and PFC (Power Factor Correction) features simultaneously presents significant challenges for integrated drives, as they require concurrent control of input current and output power To address this complexity, various topologies will be investigated under RQ2 to integrate these functionalities into a single, efficient design.
Battery cells in EVs exhibit varying characteristics due to manufacturing differences, cell architecture, and degradation, leading to inconsistencies in voltage and state of charge (SoC) In traditional systems, cells are connected in series and charged or discharged simultaneously, causing disparities that require stopping the process once any single cell reaches its cut-off voltage, which reduces efficiency Additionally, a single damaged cell can compromise the entire battery pack, highlighting the need for cell screening and balancing solutions Voltage and SoC equalization circuits are essential in practical applications to prevent overcharging or over-discharging, ensuring optimal battery health and safety As part of ongoing research, integrated drive systems are also considered to enable effective balancing across multiple battery packs, enhancing overall performance and longevity.
The following section reviews the general state-of-the-art in integrated drives and focuses further on SR motor drives and integrated drives in detail.
List of Publication
[P1] Mehdi Niakinezhad, Inam Ullah Nutkani, Nuwantha Fernando, “A New Modular
Asymmetrical Half-Bridge Switched Reluctance Motor Integrated Drive for Electric Vehicle Application,” 27 th International Symposium on Industrial Electronics (ISIE), Cairn, June
Mehdi Niakinezhad, Junaid Saeed, Nuwantha Fernando, and Liuping Wang presented an innovative integrated SRM drive system designed specifically for electric vehicle applications at the 27th International Symposium on Industrial Electronics (ISIE) in Cairn, June 2018 Their research highlights the drive's capability to deliver both constant current and constant voltage charging, enhancing efficiency and reliability in EV charging processes This advanced SRM drive system offers a seamless solution for electric vehicle power management, addressing key challenges in EV infrastructure The study emphasizes the importance of integrated drive systems with versatile charging capabilities to optimize performance and extend battery life in electric vehicles.
Junaid Saeed, Mehdi Niakinezhad, Nuwantha Fernando, and Liuping Wang presented a study on the "Model Predictive Control of an Electric Vehicle Motor Drive Integrated Battery Charger" at the IEEE 13th International Conference on Compatibility, Power Electronics, and Power Engineering (CPE-POWERENG 2019) in Denmark, April 2018 Their research focuses on optimizing electric vehicle battery charging processes through advanced control strategies, aiming to enhance efficiency and reliability in EV motor drive systems This innovative approach leverages model predictive control techniques to seamlessly integrate motor drive operations with battery charging, contributing to improved energy management and performance in electric vehicle applications.
[P4] Junaid Saeed, Mehdi Niakinezhad, Liuping Wang, Nuwantha Fernando, “An Integrated
Charger with Hybrid Power Source Using PV Array for EV Application,” IEEE 13 th International Conference on Compatibility, Power Electronics and Power Engineering (CPE-POWERENG 2019), Denmark, April 2018
[P5] Nuwantha Fernando, Inam Ullah Nutkani, Subrato Saha, Mehdi Niakinezhad, “Flux switching machines: A review on design and applications”, 20th International Conference on Electrical Machines and Systems (ICEMS), Sydney, August 2017
The research presented in publications [P2], [P3], and [P4] was conducted collaboratively with Dr Junaid Saeed, a PhD student at RMIT University, Melbourne I would like to clarify that Dr Junaid Saeed holds the intellectual ownership of the model development and control design detailed in these publications My contributions to these works are limited to other specific aspects of the research.
• Developing the power electronic topology of the proposed circuits
• Making sure each topology can meet the specification required for integrated drive/charger
• Designing the switching sequence for each mode of operation
Authorship order in these publications was determined through mutual agreement among the authors, reflecting each individual's technical contribution and involvement in editing the technical content.
Chapter 3 of this thesis discusses about the circuit diagram and switching strategy of three different integrated charger topologies presented in [P1], [P2], [P3] and [P4] So, a significant part of this chapter including figures and content are directly extracted from those papers Section 3.1discusses the topology presented in [P1] and [P3] Section 3.2 relates to topology presented in [P2] and Section 3.3 is relevant to the circuit discussed in [P4]
Chapter 5 which discuses about simulation results is also extracted from simulation section of aforementioned papers So, tables, figures and testing results are the same as those papers Section 5.1 is extracted from simulation section of [P1] Section 5.2 comes from simulation section of [P2] and Section 5.3 is driven from simulation part of [P4].
Electric Vehicle Battery Chargers
2.1.1 Types of Electric Vehicle Battery Chargers
There are two main types of EV battery chargers: on-board chargers and off-board chargers Off-board chargers are positioned outside the vehicle and typically provide a DC output that connects directly to the battery pack, enabling rapid charging times However, since off-board chargers are heavy and bulky due to their high power ratings, their installation is limited by the high infrastructure costs Despite their speedy charging capabilities, the adoption of off-board chargers remains constrained primarily because of these expensive infrastructure requirements.
On-board chargers are the second main type of EV battery chargers, designed to be lightweight and compact for convenience They enable electric vehicles to be directly charged from a single-phase or multi-phase AC power grid, making them the easiest and most accessible charging solution for EV owners This simplicity and ease of use position on-board chargers as a popular choice for everyday EV charging needs.
AC sources are widely available, an on-board charger does not demand for expensive infrastructure
At present on-board chargers, however, are usually capable of slow charging only [6] This is mainly because of the size and weight constraints
Chargers can be classified based on their charging approach into contact (conductive) and contactless (inductive) methods, regardless of whether they are off-board or on-board Conductive chargers establish a hard-wire connection between the power supply and the converter, typically featuring a Power Factor Correction (PFC) circuit followed by a buck or boost converter for CCCV battery charging In contrast, contactless chargers operate with isolated power supplies that do not require a wired connection between the source and the converter, using inductive coupling for wireless energy transfer Both types of chargers have distinct internal components, as illustrated in Figure 2.1.
Fig 2.1 Typical Power Electronic interface inside a PEV [6]
Contactless charging techniques utilize magnetic induction to transfer power from a primary (transmitter) to a secondary (receiver) winding through a transformer Traditionally, these chargers relied on stationary transformer principles for energy transmission Recent advancements have incorporated resonant converters and high-frequency coupling to enable efficient wireless power transfer across larger air gaps An active rectifier is then used to convert the received power into usable electrical energy for battery charging (See Fig 2.2 for an example of inductive charging technology.)
Fig 2.2 Full-bridge LLC resonant converter and synchronous rectifier followed by boost PFC [1]
Researchers have proposed integrating on-board chargers with bidirectional DC/DC converters used for motor operation to reduce cost, size, weight, and volume of electric vehicle charging systems This single-stage converter design enables seamless switching between motoring, regenerative braking, and charging, eliminating the need for separate components Utilizing motor windings and the propulsion inverter for charging offers a viable solution since driving and charging do not occur simultaneously, allowing high charging power levels limited only by the drive component ratings Consequently, high power fast-charging can be achieved efficiently without additional cost or system weight, enhancing overall vehicle design and performance.
Integrating the charging process into drive components is challenging, especially for fast charging that requires a three-phase power source This complexity mainly arises from torque production by the motor during charging, which results from current passing through the motor windings acting as the main inductive element For instance, induction machines (IM) and permanent magnet synchronous machines (PMSMs) can generate mechanical vibrations and acoustic noise when excited with non-sinusoidal currents, leading to accelerated aging Therefore, direct integration of windings within a fast charger circuit is only feasible when paired with a carefully designed control algorithm to manage these effects.
Recent trends are focused on developing rare earth-free machines such as Switched Reluctance Machines (SRMs) to enable risk-free, large-scale production in the future SRMs are highly suitable for electric vehicle applications due to their simple structure, high efficiency, robust mechanical design, and excellent temperature endurance resulting from the absence of rotor magnets The most common drive circuits for SRMs include R-dump, C-dump, asymmetric half-bridges (ASHB), and miller converters R-dump converters are cost-effective but limited to low-power applications due to their dissipative operation, while ASHB offers high fault tolerance and redundancy but involves higher manufacturing costs and complex control requirements Miller converters are favored for their simplicity, ease of implementation, and straightforward control, making them a popular choice in SRM drive systems.
This literature review investigates integrated drive topologies across various motor types, including induction motors (IM), permanent magnet synchronous motors (PMSM), and switched reluctance motors (SRM) Section 2.2 discusses two main IM-based techniques: integrated drives utilizing multi-phase IMs and those employing split windings Section 2.3 examines two types of PMSM-based systems, specifically split-phase dual-inverter configurations and multiphase PMSMs, also highlighting an innovative integrated drive solution using two identical PMSMs In Section 2.4, the focus shifts to SRM-based integrated drives, where seven different innovative circuit topologies are analyzed, emphasizing advancements in SRM drive integration.
Fig 2.3 Different types of Integrated Drives using motor windings based on motor type
Integrated drives found in literature can be categorized into the different branches as shown in Fig 2.3 These are reviewed in detail in the following subsections
Permanent Magnet Synchronous Machines (PMSM)
Split-Phase Dual- Inverter PMSM
Integrated Drives with Induction Machines
2.2.1 Integrated Drive using Multiphase Induction Machines
Multiphase machines with five, six, and nine phases are illustrated in Fig 2.4, showcasing their diverse configurations Symmetrical multiphase machines are characterized by equal spatial angles between consecutive phases, as shown in Fig 2.5a, whereas asymmetrical machines have unequal phase angles, depicted in Fig 2.5b and Fig 2.5c These machines may feature one or multiple isolated neutral points; for instance, six-phase machines typically have two neutral points, while nine-phase machines can have three isolated neutral points.
Fig 2.4 Multiphase machine (a) five-phase (b) six-phase (c) nine-phase [10]
Multiphase machines are commonly supplied from multiphase inverters as shown in Fig 2.6 [23]
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Fig 2.5 Integrated charging topologies for multiphase machine (a) nine-phase (b) six-phase (c) five-phase [10]
Fig 2.6 N-phase inverter (n equals to the number of machine phase) and a battery pack with/without dc-dc converter [10]
Three-phase grid currents flow through the motor windings in each topology as shown in Fig 2.5 Since the grid currents are near sinusoidal, the equation below applies [24]:
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Table 2.1 Correlations between machines and grid currents
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In [28] it is shown how an isolated asymmetrical and symmetrical six-phase voltage source can be provided by means of an off-board transformer with dual secondary winding
Fig 2.7 Integrated charging topologies supplied from a multiphase voltage source and based on
Research studies [25], [26], [27] have demonstrated that topologies utilizing three-phase grids and multiphase voltage sources cannot generate torque during the charging process, rendering multiphase machines as passive components like inductors in this context These topologies enable Power Factor Correction (PFC), ensuring a unity power factor without the need for additional hardware between the AC grid and the traction system However, multiphase machines are specialized, less common, and not as widely available as standard three-phase machines.
Ref [29] introduces an innovative integrated charger design that employs a six-phase induction motor functioning as a transformer coupled with a double three-phase inverter During the charging process, the rotor windings are disconnected, ensuring no torque is generated on the motor shaft This novel approach enhances charging efficiency while maintaining system stability.
Fig 2.8 six-phase induction motor with two three-phase drives [29]
2.2.2 Integrated Drive for Induction Machine with Split Windings
The research in [30] introduces a novel topology designed for rapid battery charging in electric vehicles, enhancing charging efficiency and speed As depicted in Fig 2.9, this innovative circuit configuration utilizes split windings instead of a separate inductive element, streamlining the charging process and potentially improving overall system performance.
Fig 2.9 IM integrated drive topology with split windings [30]
During driving mode, the converter utilizes three parallel full bridge converters, one for each phase, combined with a buck-boost converter to regulate the DC-link voltage effectively regardless of the battery pack’s voltage fluctuations The three-phase full bridge converter draws energy from the DC-link capacitor to power the motor, ensuring smooth and reliable operation during driving.
The battery charging connection is established through the midpoint of each motor winding, as shown in Fig 2.9 A three-phase full bridge converter functions as two power factor correction (PFC) converters to ensure unity power factor by synchronizing input AC voltages and currents The circuit includes a two-quadrant buck-boost converter formed by S1, S2, and L, enabling CCCV (constant current, constant voltage) charging The battery pack can be charged in either CC (constant current) or CV (constant voltage) mode, depending on the charging stage Additionally, balanced currents in the half windings of each phase facilitate zero torque production during charging.
Figure 2.10 presents a reformatted circuit that utilizes motor windings as inductive elements during the charging process, allowing significant size reduction The magnetic coupling between the six half windings, inherent to the induction machine's construction, complicates the control algorithm, as controlling one winding’s current influences the others Additionally, the coupling depends on rotor position, adding further complexity to the control strategy While the hardware and control implementation are relatively simple compared to alternative methods, this integrated charger is a non-isolated solution that requires a high number of switches.
Fig 2.10 Equivalent charging circuit consists of an AC/DC converter with double three-phase
Integrated Drives with Permanent Magnet Machines
2.3.1 Integrated Drive with Split-Phase Dual-Inverter Permanent Magnet
A split-phase motor features two identical stator windings shifted in space, sharing the same magnetic circuit, with power evenly distributed via two separate three-phase inverters, enhancing fault tolerance compared to single-winding motors This design allows the system to operate at reduced power mode if one inverter fails PMSM motors are employed in multiphase drive applications using independent inverters, enabling connection to single-phase AC grids through neutral points and allowing the drive system to function as a charger A bidirectional charger with unity power factor is introduced, utilizing the IPMSM with dual inverters, where the single-phase grid connects to neutral points, and motor windings act as energy storage in a single-phase full-bridge step-up rectifier, rated for traction, making it a high-power non-isolated battery charger suitable for demanding applications.
Fig 2.11 Integrated drive and battery charger based on the split-phase IPMSM and dual inverters [34]
Fig 2.12 shows the circuit configuration in charging mode along with its simplified equivalent diagram, highlighting its ability to feed power back to the grid from the battery when needed Both upper and lower switches, such as S11, S13, and S15, operate simultaneously—for simplicity, they are represented as S1 Since the grid supply is connected to the motor's neutral points, the current entering each winding is equal in magnitude but flows in opposite directions, resulting in no torque production during this mode.
Fig 2.12 System configuration in charging mode [34]
2.3.2 Integrated Drive with Multiphase Permanent Magnet Synchronous
Figure 2.13 illustrates the topology of an integrated drive featuring multiphase PMSMs, as introduced in [35], showcasing various motor winding connection options including star with a common neutral, two stars with separate neutrals, or dual delta connections with the same number of contactors [36] The driving mode of this configuration is thoroughly discussed in the literature [37], [38], detailing how a six-phase PMSM employs two sets of windings with 120° phase displacement to achieve optimal performance These phase sets can be configured with 60°, 30°, or 0° phase displacement, depending on whether the machine is symmetrical, asymmetrical, or a dual three-phase system [38].
Fig 2.13 Proposed integrated drive with multiphase PMSM [35]
During charging mode, contactors are energized to connect all circuit components, with each connection directed to one phase of the three-phase power source This configuration ensures that the phase sets are arranged to neutralize each other's produced torque Reconfiguring through the contactors creates a boost converter, where the motor windings function as inductive elements during charging As shown in Figure 2.14, the equivalent charging circuit divides the converter into two phase sets, D1 and another set, facilitating efficient energy transfer.
Phase-set D1 is connected to phase set ABC, while phase-set D2 is connected to DEF, with both sharing a common DC-link established by a capacitor between X1 and X2 The subsequent stage involves a DC-DC converter designed for CCCV battery charging, as illustrated in Fig 2.14, which depicts the Thevenin equivalent with ZDCt and VDCt as functions of the semiconductor device's duty cycle This circuit reconfiguration enables the implementation of an integrated charging system that features a reduced size, minimized weight, and lower cost.
Fig 2.14 The equivalent charging circuit for the topology shown in Fig 2.11 [35]
In this study a torque elimination method has been demonstrated However, the vibration caused by torque oscillation is found to be an issue [39]
2.3.3 Integrated Drives with Two Separated Permanent Magnet
Two three-phase PMSM machines with coupled shafts are employed in high-efficiency electric vehicles (EVs) to enhance modularity and fault tolerance Some drives feature directly coupled shafts that operate at the same speed, synchronized by the rotor, providing improved performance Utilizing multiple motors offers additional degrees of freedom, which helps reduce grid current harmonics through interleaved modulation Additionally, locking the rotor is recommended to mitigate torque issues on the shaft during charging, ensuring smoother operation and improved reliability.
Authors of [44] introduced an integrated EV charger utilizing two symmetrical six-phase IPMSMs powered by a three-phase supply During charging, the motor winding center points are connected to the power source, creating an efficient charging circuit The design also allows seamless switching between charging mode and vehicle-to-grid (V2G) operation, enhancing energy management flexibility.
The authors of [45] proposed a non-isolated three-phase integrated drive featuring two three-phase motor drives, enabling an efficient integrated three-phase battery charger This topology offers key advantages such as eliminating torque on the drive shaft during operation and canceling sinusoidal torque pulsations, resulting in smoother motor performance Additionally, the power converter complies with harmonic distortion standards for both charging and driving interfaces through the use of interleaved modulation, ensuring improved power quality and system efficiency.
The two three-phase PMSMs topology features two coupled shafts, each with its own drive interface, as illustrated in Fig 2.15 Both drives share a common DC-link capacitor and are connected to the same DC-DC converter, enabling efficient CCCV battery charging A changeover contactor allows seamless switching between driving and charging modes, enhancing system versatility and operational flexibility.
Fig 2.15 Integrated drive topology with two PMSM [45]
When contactors short-circuit the terminals, the three-phase motor windings configure into a delta or star connection, effectively disconnecting the power source; this operational state is known as the driving mode A shaft coupler T connects the motors' shafts, enabling torque transfer between motors while allowing them to rotate at the same or different speeds, facilitating efficient drive transmission.
In charging mode, the contactors are energized and connect the motors windings to the three-phase
AC grid source It is important to mention that the grid connection for M2 has an opposite phase sequence This can guarantee zero torque production during the charging process
Each AC grid phase is connected to one leg of converter D1 and D2 which are parallel to each other
D1 and D2 are standard three-phase two-level converters, commonly used in motor control applications Since PMSMs are stationary during certain operations with no back-EMF, they can be modeled as inductors in the charging process Additionally, PMSM inductors are asymmetric, which influences the circuit behavior If the motors are replaced by inductors, the overall circuit configuration remains the same as illustrated in Fig 2.15, facilitating analysis and modeling.
Integrated Drives with Switched Reluctance Machines
2.4.1 SRM Drive with integrated battery charger suitable for PHEV
The authors of [21] present a novel integrated drive system capable of both charging batteries and powering a switched reluctance traction motor This versatile power source can operate using either a battery pack or an internal combustion engine (ICE), enhancing flexibility and efficiency The converter configuration, as depicted in Fig 2.16, illustrates the system's innovative design, combining energy storage and propulsion in a compact setup for improved performance in electric and hybrid vehicles.
Fig 2.16 Three-phase SRM drive with an on-board charger [21]
Various modes of operation can be achieved depending on the states of relays J1, J2, and J The power flow between the internal combustion engine (ICE), switched reluctance motor (SRM), and battery pack during driving, regenerative braking, and charging processes is illustrated in Figure 2.17, highlighting the vehicle's flexible power management system.
Fig 2.17 Power flow for (a), (b), (c), and (d) driving, (e) charging battery through ICE, and (f) charging battery through AC grid [21]
To switch to driving mode, relay J1 must be energized to activate the Miller converter When relay J2 is turned ON and relay J is turned OFF, the battery pack powers the Switched Reluctance Motor (SRM) Conversely, if relay J2 is turned OFF and relay J is turned ON, the Internal Combustion Engine (ICE) serves as the power source for the SRM drive.
On the other hand, in charging mode [48], the relay J 1 is de-energized and the relay J 2 is energized
This mode allows the battery pack to be charged from either the AC grid or the internal combustion engine (ICE), depending on the position of relay J The battery charger is versatile, capable of operating in both buck and boost converter modes to provide variable voltage for efficient charging This design enables the battery to be charged from different AC networks, ensuring flexibility and compatibility across various power sources.
Figure 2.18a illustrates the integrated SRM drive in charging mode, configured as a buck converter When the DC-link voltage—connected to the regulated AC grid or ICE—is higher than the battery pack voltage, the buck converter reduces voltage to facilitate battery charging During this process, switches S1, S2, and S3 remain continuously OFF, while S0 operates in switching mode Figures 2.18b and 2.18c depict these two switching intervals, ensuring efficient voltage regulation for charging.
Fig 2.18 (a) Converter configuration for buck charging mode (b-c) current flow in buck charging mode [21]
If the grid or internal combustion engine (ICE) voltage supplied is lower than the battery pack voltage, the converter switches to boost converter mode to elevate the voltage level During this operation, switch S0 remains always on, while switches S1, S2, and S3 operate in switching mode, as illustrated in Figures 2.19a and 2.19b, which depict two different intervals of the boost converter.
Fig 2.19 Converter configuration for boost charging mode, (a) Inductor charging interval (b)
This converter supports both Power Factor Correction (PFC) and Constant Current, Constant Voltage (CCCV) modes, and can operate with either 1-phase or 3-phase power sources However, it lacks battery voltage equalization capabilities and requires hardware reconfiguration to switch between operational modes, which is a notable drawback The design also has no fault tolerance in case of failures within the motor, battery pack, or semiconductor devices Additionally, the dwell angle must be carefully limited to reduce demagnetization and negative torque effects, primarily due to the use of a common power switch [49].
2.4.2 SRM Drive with Flexible Energy Conversion
In [48], the authors develop an integrated drive constructed by a front-end circuit and a conventional asymmetrical half-bridge converter as shown in Fig 2.20
Fig 2.20 Proposed integrated converter fed by front-end circuit [48]
The input voltage can vary at different levels, as illustrated in Fig 2.21, which displays the resulting output voltages based on the switch states of S01 and S02 To enable rapid demagnetization and achieve the desired speed range during motoring, the return current voltage should always utilize the maximum available voltage As shown in Fig 2.21d, the input voltage remains constant at U1 + U2 regardless of the positions of switches S1 and S2.
Fig 2.21 Different input voltage levels (a) S 01 =ON, S 2 =OFF and I>0 (b) S 01 =OFF S 02 =ON and
Front-end Circuit Asymmetric Half-Bridge Converter
In the initial step, motor windings are energized by the power source as depicted in Fig 2.22a, enabling the storage of energy within the coils This stored energy can then be transferred to the battery bank to facilitate charging Additionally, Fig 2.22b illustrates the energy exchange process between the AC grid or internal combustion engine (ICE) and the battery stack, highlighting the dynamic flow of energy within the system.
2.4.3 Integrated Battery Charger based on Split-Winding SRM
The authors of [50] introduce a new integrated SRM integrated system with potentially reduced the size, weight and cost
Fig 2.23 Proposed integrated SRM drive with battery charger [50]
Figure 2.23 illustrates the circuit topology of the integrated drive, where in driving mode, the relay is energized, and the converter functions as a conventional SRM drive During charging mode, the relay is open-circuited, enabling phase A and B windings along with capacitor C1 to operate as a DC-DC boost converter This configuration facilitates charging the DC-link via the C1 capacitor, which then supplies power to the second circuit segment connected to the AC grid voltage The circuit can be designed as either a DC-DC buck or boost converter to match the battery voltage Figure 2.24 depicts the current commutation process for both positive and negative AC cycles, showing how inductors (motor windings) are charged through switches S Ad for positive currents and S Bd for negative currents when turned on, and how capacitor C1 is subsequently charged when these switches are turned off, ensuring efficient energy transfer during both cycle phases.
Fig 2.24 The operation modes of novel converter front-end in battery charger mode [50]
Phase A and B windings are connected in series with switches S Ab and S Bd to supply the DC-link voltage through capacitor C1, with capacitor charging controlled by the switches' duty cycle The third phase (Phase C) winding, along with switches S Cu and S Cd, can function as either a buck or boost converter depending on their switch states When S Cu and S Cd are turned on or off simultaneously, the circuit operates as a boost converter (Fig 2.25a and 2.25b) Conversely, if S Cd remains off while S Cu switches on and off, the converter operates as a buck converter (Fig 2.25c and 2.25d) This configurable operation allows for a wide range of voltage and current levels.
The battery is connected based on the requirements of the battery stack and control system, enabling efficient management tailored to specific operational needs This configuration facilitates constant current and constant voltage charging, ensuring optimal battery performance and longevity To enhance system flexibility and stability, diode D1 is incorporated at the mid-point of the phase C winding, improving circuit reliability and adaptability.
Fig 2.25 (a) (b) boost converter, (c) (d) buck converter [50]
2.4.4 SRM Integrated Charger using Three-phase Power Module
The authors of [51] have developed an integrated driving and charging SRM drive for electric vehicles, as illustrated in Fig 2.26 This innovative circuit combines a four-phase Miller converter with a step-down and buck-boost power factor correction (PFC) converter, seamlessly bridged with a bidirectional DC-DC converter [52] Designed for on-board installation, this integrated drive system can operate in motoring mode with a boosted DC-link voltage or in PFC battery charging mode, offering versatile functionality for EV applications. -**Sponsor**Looking to optimize your EV article with SEO-friendly content? Highlight the core of your paragraph by mentioning that the integrated driving/charging SRM drive developed by the authors of [51], as shown in Fig 2.26, is key Emphasize the circuit's integration of a four-phase miller converter with buck-boost PFC and a bi-directional DC-DC converter [52], noting its on-board placement for motoring and PFC battery charging modes Need more solutions to enhance your vehicle's functionality? Check out [carlinkit [P]](https://pollinations.ai/redirect-nexad/rKFIu1l5?user_id=983577) for seamless integration and enhanced infotainment in your car!
Fig 2.26 System configuration of the developed SRM drive [51]
Figure 2.27 illustrates the driving mode for a four-phase SRM converter, where relays are set to the D (driving) position In this mode, a boost converter is formed using capacitor Cb, inductor Lb, and switch Sb to adjust the input voltage from the battery pack to the motor drive By controlling switch Sb, the voltage level across the DC-link capacitor Cd can be precisely managed Additionally, switch Sa can be used as a braking system for the SRM, enhancing the motor control and safety features.
Fig 2.27 Driving mode operation of the integrated drive [51]
During charging mode, relays are positioned in the C (Charging) mode to create the circuit shown in Fig 2.28, making the charger suitable for both low-speed and high-speed applications This charger can effectively match source voltage, whether it's lower or higher than the battery pack voltage, ensuring versatile charging capabilities As depicted in Fig 2.28a, the charging circuit operates as a boost converter, with Q3 remaining active during this mode to maintain voltage regulation and efficient power transfer.
Comparison
All topologies presented in literature can be compared based on different criteria Table 2.2 demonstrates comparison between presented configurations
Table 2.2 Comparison between different topologies presented in literature review
1Ph, 3Ph Multiple input power source
Split-winding asymmetric half bridge (SW-ASHB) interconnected converter with
interconnected converter with modular batteries [58]-[59]
This research introduces the split-winding asymmetric half-bridge (SW-ASHB) interconnected converter with modular batteries, an advanced modular asymmetrical half-bridge drive topology that supports a higher number of battery modules connected to a single system The proposed design operates seamlessly in both driving and charging modes without requiring circuit reconfiguration, enhancing operational flexibility It allows battery charging via both DC and AC power sources, making it suitable for integrating renewable energy sources such as photovoltaic (PV) systems Additionally, the topology ensures efficient battery pack voltage equalization during idle and charging states, while high fault tolerance is achieved through separate battery packs and dedicated power circuits for each phase, increasing system reliability.
The split-winding modular asymmetric half-bridge interconnection with modular batteries is depicted in Fig 3.1(a), illustrating a 12/8 Switched Reluctance Motor (SRM) with three phases, each containing four split stator coils connected in series using a central-tapped node, enabling grid charging without additional onboard circuitry This topology uses SRM windings as inductances in the power electronic converter, allowing seamless switching between driving and charging modes without hardware reconfiguration, thanks to the modular asymmetrical half-bridge drive design The circuit features power switches (S₁u–S₆d), freewheeling diodes (D₁u–D₆d), input filter capacitors (C₁–C₆), and winding inductances (L_nm, with n=1–4 and m=a,b,c), where two coils per phase are connected in series and powered by a single half-bridge cell Figure 3.1(b) showcases the actual winding arrangement of the motor, illustrating the practical implementation of this modular, efficient drive topology.
Fig 3.1 (a) Proposed topology with split motor coils - split-winding modular asymmetric half bridge interconnected converter with modular batteries (b) Motor winding arrangement
In driving mode, the AC grid connection remains inactive while the converter functions in motoring mode With only a single connection between the asymmetric half-bridge cells, no current flows through the system.
The L4a flow between the half-bridges is a key feature of this converter, which closely resembles a traditional asymmetrical bridge converter with a modular design Each phase is divided into two separate parts, each powered by a dedicated battery pack, enhancing the system's flexibility This modular structure not only simplifies maintenance but also enables fault-tolerant operation, improving overall system reliability.
3.1.1 Battery Charging Mode with SW-ASHB interconnected converter with modular batteries
The battery packs are charged via a single-phase AC grid, with current paths indicated by different colors during positive and negative voltage cycles During the positive half cycle, switches 𝑆1𝑢 to 𝑆6𝑢 are off, while 𝑆1𝑑, 𝑆2𝑑, and 𝑆3𝑑 remain on, allowing current to gradually increase through the coils during the DC boost converter’s charging phase When any of these switches turn off, the current transfers to the corresponding battery pack, repeating this cycle during the negative half cycle with switches 𝑆4𝑑, 𝑆5𝑑, and 𝑆6𝑑 active Pulse Width Modulation (PWM) controls the duty cycle (D) of switches during both half cycles, enabling charging rates for each battery pack according to the Battery Management System (BMS) requirements, thereby facilitating State of Charge (SoC) equalization across all packs.
Fig 3.2 SW-ASHB interconnected converter with modular batteries charging mode: when the input voltage is in (a) positive (b) negative cycle
Battery State of Charge (SoC) levels can vary due to usage patterns, manufacturing inconsistencies, degradation, rated voltage differences, and motor phase winding variations A voltage balancing procedure is implemented for both standstill and charging modes to ensure uniformity During idle mode, connecting M1 and M2 (as shown in Fig 1) allows the higher SoC batteries to transfer power to those with lower SoC, promoting balanced voltage levels Additionally, Fig 3.3 illustrates the battery pack charging process, emphasizing the importance of voltage equalization for optimal battery performance and longevity.
B6 can be charged using B1 through either step-up or step-down voltage conversion, depending on the specific voltage and current requirements Figures 3.3a and 3.3b illustrate these two modes, demonstrating how B6 is charged by B1 in each respective scenario.
During the charging process, energy transfer to each series-connected cell is controlled by the duration that the cell remains connected to the power source Since the built-in DC converter is a boost type, it allows for regulated output voltage, ensuring efficient charging Cells with lower voltage are positioned at the bottom of the voltage sine wave, enabling them to start charging first and absorb more energy from the source Conversely, higher-voltage cells are placed at the top levels, resulting in later charging and reduced energy intake This arrangement optimizes overall energy utilization while preventing overcharging and over-discharging of the battery cells.
Fig 3.3 SW-ASHB interconnected converter Battery voltage equalization (a) step-down (b) step- up converter mode
3.1.2 Phase Inductance Variation with Rotor Position in an SW-ASHB interconnected SRM
In boost converter operation, maintaining a constant inductance is crucial for high performance Due to the doubly salient structure of the Switched Reluctance Motor (SRM), phase inductances vary with rotor position, affecting overall performance Fig 3.4 illustrates the variation of three-phase inductances and their combined sum However, the series connection of all phase inductances during boosting can impact the converter's efficiency and stability.
L 3c L 4c b in a constant inductance as shown in Fig 3.4 It’s important to mention constant input inductance is critical to ensure the optimum performance of the control system
Fig 3.4 Phase and total inductance as a function of rotor position of an example 60 kW SRM
At any instant of time in the positive half-cycle of the input voltage, the total inductance 𝐿 𝑝𝑜𝑠 in circuit path is given by
Similarly, the negative half-cycle inductance 𝐿 𝑛𝑒𝑔 is given by
At the same time, it is also important to note that for 𝑖 ∈ [𝑎, 𝑏, 𝑐]
Using 3.3, 𝐿 𝑝𝑜𝑠 and 𝐿 𝑛𝑒𝑔 can be written as
3.4 where 𝐿 𝑡𝑜𝑡 is the equivalent inductance of the converter and 𝐿 𝑎𝑏𝑐 is total inductances of switched reluctance motor
3.1.3 Control Strategy for SW-ASHB interconnected converter with modular batteries
Effective battery management in electric vehicles involves equalizing the state of charge (SoC) across multiple battery packs The control system and integrated drive must ensure balanced SoCs to optimize performance and longevity A proposed circuit facilitates voltage equalization by first measuring each battery pack's SoC The controller then charges batteries with differing SoC levels over specific time periods, gradually equalizing their charge states For example, as shown in Figure 3.5a, batteries with SoC B1 < SoC B2 < SoC B3 < SoC B4 undergo charge equalization, enhancing overall battery efficiency and reliability.
This study explores charge equalization between SoC B5 and SoC B6, as shown in Table 3.1, which details the switching states of semiconductor devices with S representing the MOSFET switching mode Figure 3.5b illustrates the battery charging process using the proposed topology, achieving SoC equalization over approximately 5.5 hours Initially, batteries B1, B2, and B3 have SoCs of 25%, 45%, and 60%, respectively, while batteries B4, B5, and B6 start at 10%, 25%, and 40% The results demonstrate that all batteries reach full charge within around five hours, indicating effective charge balancing.
Fig 3.5 (a) Batteries charging placement for voltage equalization (b) voltage equalization process for 5.5 hours
Table 3.1 Switching states of the semiconductor devices in order to utilize voltage equalization in an SW-ASHB interconnected converter
To achieve maximum power quality, a Power Factor Correction (PFC) control technique is employed, utilizing a simplified equivalent circuit of a built-in boost converter This method shapes the input current for both positive and negative cycles of the AC voltage, ensuring proper current synchronization The PFC control system includes a phase extraction via a Phase-Locked Loop (PLL), which captures the phase of the input voltage This phase information is multiplied by a DC reference current to generate a phase-locked AC current reference aligned with the input voltage The hysteresis controller then compares the actual current with the reference, regulating the current waveform to improve power factor and reduce harmonics.
The voltage equalizer circuit activates the appropriate switches of the asymmetrical half-bridge converter based on the battery's SoC and the positive/negative cycle of the input voltage As shown in Fig 3.6c, the converter's input current trajectory highlights the effectiveness of the hysteresis controller in maintaining balanced voltage levels This intelligent control mechanism ensures optimal battery performance by precisely managing charge and discharge cycles.
Fig 3.6 Power factor correction (a) Equivalent circuit in charging mode (b) input current trajectory (c) control system using the SW-ASHB interconnected converter with an SRM
The proposed topology features a single power stage between the AC grid and the battery pack, enabling only Power Factor Correction (PFC) but not Constant Current Constant Voltage (CCCV) charging Achieving both PFC and CCCV requires independent power stages; integrating two separate stages with a DC link interface could enable both functionalities The redesigned circuit incorporates two power stages, allowing it to accomplish both PFC and CCCV charging effectively.
Switched winding circuit integrated multiport converter [61]
This research introduces a novel topology, the switched-winding circuit integrated multiport converter (SWC-IMPC), enhancing EV charging and power conversion capabilities The SWC-IMPC leverages a multiplexed leg to enable integrated EV battery charging with CCCV (constant current/constant voltage) functionality without additional power circuits, ensuring efficient and compact design A key innovation is the switching of the winding circuit to interface directly with the AC grid, which significantly improves grid connectivity and power flow management Overall, this integrated converter combines these advanced concepts to develop a new solution featuring an SRM drive with CCCV charging and power factor correction (PFC), advancing the field of electric vehicle charging and grid integration.
The most commonly used drive circuits for SR machines include R-dump, C-dump, asymmetric half-bridges (ASHB), and Miller converters [19], [20] R-dump converters are cost-effective but suitable only for low-power applications due to their dissipative operation Conversely, ASHB converters are ideal for split converter configurations where high fault tolerance and redundancy are important, though they involve higher manufacturing costs and complex control requirements.
[20] Miller converters are preferred for their simplicity, ease of realization and simple control [19],
A common challenge with these topologies is the need for a large DC capacitor placed in parallel with the input battery source to filter out high-frequency ripple in the drive voltage However, this sizable capacitor occupies significant volume, which negatively impacts the overall power density of the system.
An innovative approach in [63] addresses the high capacitor requirement in power converters by using an integrated multiport converter (IMPC), demonstrating that the dc-link capacitance needs decrease with increasing dc-link voltage Since battery voltage is typically fixed in applications, the authors propose employing a multiplexed switch leg within a miller converter configuration to boost the dc-link voltage This method allows phase powering via a common multiplexed leg, effectively increasing the dc-link voltage while reducing capacitor size The key advantages include lower dc capacitor requirements and improved motor performance, such as faster turn-off transitions, due to the higher available reverse voltage.
In the initial phase of this research, the inductance of the SRM windings is utilized to develop a single-phase bridgeless boost rectifier [65] A cascaded control structure combining PI and model predictive control (MPC) has been designed to ensure unity input power factor and stable dc-link voltage regulation The multiplexed leg facilitates a controlled constant-current constant-voltage (CCCV) charging process for the battery.
3.2.1 Analysis of the SWC-IMPC operation
The IMPC drive structure, first introduced by the authors of [63], is depicted in Fig 3.7 and involves phase inductances L_A, L_B, and L_C for the three-phase 6/4 SRM The circuit includes MOSFET switches (S1 to S5) and power diodes (D1 to D3) that connect each phase of the SRM to the DC link, enabling efficient power control The SRM windings are powered by a battery pack B, which is connected in series with a small inductance L_dc and resistance R to ensure stable operation A DC-link capacitor C is integrated for voltage smoothing, and a relay is incorporated into the system to switch the winding circuit between driving and charging modes, enhancing the motor's overall functionality and control.
Fig 3.7 IMPC for SRM in driving mode
The drive mode is activated by de-energizing the relay, allowing precise control over the motor's operation In this mode, the common terminal of the three phases of the Switched Reluctance Motor (SRM) is connected to a common point of the multiplexed leg, ensuring efficient and synchronized motor performance Utilizing relay de-energization for drive mode selection optimizes motor control and enhances system reliability.
The circuit features a configuration with L C /2, formed by S1 and S2, operating as a conventional Miller converter The multiplexed leg functions as a DC-DC boost converter, regulating the DC-link voltage at a high level through the battery pack via the inductor L_dc Additionally, this multiplexed leg not only maintains the DC-link voltage but also facilitates current commutation for excitation and freewheeling of the SRM phase currents, supporting the SRM controller's requirements.
The IMPC topology offers a significant advantage over conventional asymmetrical half-bridge (ASHB) converters by requiring lower capacitance levels According to calculations in referenced source [63], the minimum necessary capacitance for the DC-link is explicitly determined, highlighting the efficiency benefits of the IMPC design.
3.5 where 𝐿 𝑎𝑙𝑖𝑔 is the SRM phase inductance when the rotor is aligned with the stator pole, and i dc and
The dc-link current (𝑉 𝑑𝑐) and voltage are key parameters influencing system performance Increasing the dc-link voltage reduces the minimum required capacitance (𝐶𝑚𝑖𝑛), allowing for smaller capacitors, as the capacitance is inversely proportional to the square of the dc-link voltage Flexibility in the average and ripple voltages of the dc-link—being higher than those of the battery—further decreases capacitance requirements The operation and analysis of driving modes are detailed in [63] In an IMPC, the ESR of electrolytic capacitors is isolated by power switches, minimizing ESR-related power losses Additionally, higher dc-link voltages facilitate faster demagnetization of SRM windings during phase switching, increasing the conduction angle, enhancing average torque, and expanding the motor's speed range.
This research develops a CCCV charging strategy based on the IMPC drive circuit proposed in [63], ensuring efficient battery charging During the constant current (CC) mode, the system maintains the inductor current at a predefined reference, allowing the voltage to increase gradually for safe charging In the constant voltage (CV) mode, the battery voltage remains steady while the reference current gradually decreases to prevent overcharging [66] The equivalent schematic shown in Fig 3.8 illustrates the charging modes, which are selected by activating a mode-changing relay In charging mode, relay connections are configured so that AC grid terminal-1 connects to phases A and B in parallel, while AC grid terminal-2 connects to phase C, enabling controlled and safe charging operation.
Fig 3.8 Circuit diagram of the proposed CCCV charging scheme with PFC [62]
The charging process for typical batteries involves both constant current (CC) and constant voltage (CV) phases, requiring a converter capable of precisely regulating voltage and current Stable operation of the converter is essential to ensure efficient and safe battery charging.
The IMPC is designed with two distinct power stages to effectively achieve its objectives As illustrated in Fig 3.9, the equivalent charging circuit presents these two power stages as a simplified representation, based on the detailed circuit shown in Fig 3.8 This dual-stage configuration enhances the system's efficiency and performance in the charging process.
Fig 3.9 Simplified equivalent charging circuit [62]
The initial stage is a front-end bridgeless PFC rectifier designed to charge the DC-link capacitor with unity power factor while maintaining the voltage within specified limits This ensures the minimum capacitor voltage remains above the battery voltage, enhancing system stability The motor windings L_A, L_B, and L_C serve as boost inductors for the rectifier, eliminating the need for additional passive components and simplifying the overall design.
Bridgeless PFC Rectifier DC-Link
CCCV Charger DC-Link PFC Rectifier
3.2.2 Phase Inductance Variation with Rotor Position in an SWC-IMPC interconnected SRM
Designing the boost inductor for a PFC rectifier is crucial to optimize converter performance and has been extensively discussed in the literature [67], [68] It is essential for the inductor current to closely follow its reference with minimal total harmonic distortion (THD) In SRM-based EV applications, rotor position uncertainty causes significant fluctuations in effective phase inductances, which directly impact the integrated charger Therefore, mitigating the effects of these inductance variations is vital for maintaining reliable charger operation.
L of the charging circuit is:
Split-rail asymmetric half bridge converter with an extra leg [70]
A novel hybrid power source multiport integrated battery charger is introduced, utilizing a split-rail asymmetric half-bridge (SR-ASHB) converter with an additional leg This innovative circuit topology, detailed in reference [71], enables simultaneous charging of batteries from both AC grid and PV arrays The design involves splitting the DC rail of a standard ASHB converter and integrating an extra half-bridge leg with the battery on the secondary DC-rail, as illustrated in Fig 3.13.
The MPPT algorithm maximizes power extraction from the PV array, ensuring optimal energy harvesting The AC grid supplies additional power to charge the battery with a unity power factor via an AC-DC PFC rectifier, enhancing efficiency This charger employs a CCCV battery charging profile combined with a built-in bidirectional DC-DC converter for reliable and flexible energy management The control system is specifically designed to prioritize the PV array as the primary power source, with the AC grid supplementing only the power deficit, thereby optimizing renewable energy utilization and overall system performance.
3.3.1 Operation analysis of the Split-rail asymmetric half bridge converter with an extra leg
The proposed integrated charger and drive system features a hybrid power source, with a PV array connected to the charger via a diode (DPV) and parallel to the capacitor (C PV), supplying voltage (v PV) and current (i PV) It also includes a single-phase AC grid providing voltage (v ac) and current (i ac) as an additional power source The system utilizes a 6/4 SRM motor, with phase inductances L A, L B, and L C for phases A, B, and C, respectively The circuitry incorporates MOSFET switches (S 1 to S 8) and power diodes (D 1 to D 6) to enable efficient power flow and control within the hybrid setup.
S 1 −S 6 and D 1 −D 6 constitute three ASHB circuits The motor is powered by an on-board battery pack, B which is connected in series with an inductor L dc and a small equivalent resistance R, and
C1 is employed as the dc-link capacitor Furthermore, a relay has been used to toggle between the driving (D) and charging (C) modes
Fig 3.13 Circuit diagram of the proposed topology in charging (C) and driving (D) modes with
CCCV battery charging and PFC
The AC grid connection remains inactive in driving mode due to the PV array voltage consistently staying below the dc-link voltage As a result, the DC power port (DPV) does not conduct, preventing power flow to the grid and ensuring the PV array operates independently under these conditions.
Buck Converter ( S 8 =OFF) dc-Link
Bridgeless PFC Rectifier( S 4 =OFF, S 6 =OFF)
Boost Converter ( S 7 =OFF) dc-Link Asymmetric half-bridge Converter + SRM
The relay disconnects, resulting in a traditional asymmetric half-bridge (ASHB) configuration This setup can operate in various modes, including phase winding magnetization, freewheeling, and demagnetization The winding inductance limits the current rise during a short circuit, as each winding is in series with two switches In this mode, the battery supplies power to the motor through a step-up DC-DC converter, with switch S7 turned OFF and PWM control of S8 enabling the converter to charge the dc-link capacitor C1 The DC-link then supplies the ASHB, providing power to the Switched Reluctance Motor (SRM).
In driving mode, the circuit functions as a simple three-phase half-bridge converter, a configuration widely employed in Switched Reluctance Motor (SRM) drives For comprehensive details on the operation of the driving mode, refer to relevant technical resources and literature.
[20] [72] Integrated charging mode using this topology has not been considered before in a way PFC and CCCV along with an additional power source can be handled
3.3.2 Charging Modes of the Split-rail asymmetric half bridge converter with an extra leg
In charging mode, the relay is de-energized into position C and the battery can be charged by the
PV array and the AC grid simultaneously AC grid is connected to the drain of S 4 and S 6 in charging mode as shown in Fig 3.14
During charging mode, the ASHB related to phase A of SRM functions as a boost DC-DC converter, with its input connected to the PV array and output linked to the dc-link, enabling maximum power extraction from the solar panels The boost converter's power stage uses the motor winding L_A as the inductor, with switch S1 turned on and S2 operating in switching mode to transfer solar energy to the dc-link To charge the battery solely using PV energy, the dc-link capacitor voltage (v_dc) must not drop below the battery voltage (v_B) A simplified equivalent circuit in charging mode is depicted in Fig 3.14.
Fig 3.14 Equivalent circuit in charging mode
Connecting a single-phase AC grid to the drain of switches S4 and S6 creates an AC-DC PFC rectifier, enabling efficient power conversion During the AC grid charging mode, when the alternating current (i_ac) is positive, current flows through the circuit as illustrated in Figure 3.15 At this point, switch S5 is turned on to facilitate the flow of current, ensuring proper operation of the power factor correction system and optimizing energy transfer from the AC source.
In the depicted setup, ON and the inductance L_A + L_B are energized with AC current as shown in Fig 3.15a When switch S_5 is turned OFF, the inductor's stored energy releases, injecting power back into the DC link, as illustrated in Fig 3.15b If the AC current i_ac is less than zero, the current flow becomes symmetrical to the scenario presented in Fig 3.15.
Fig 3.15 Current flow in AC grid charging mode when i ac > 0 (a) Inductor charging cycle (b)
Inductor discharging cycle to the capacitor
Bridgeless PFC Rectifier Boost Converter
Efficient power quality is essential for EV battery chargers, which demand high input currents The strategy of staging power aims to maintain the dc-link voltage higher than the battery voltage while ensuring a unity input power factor This is achieved by modulating switches S3 and S5 so that the input current accurately follows its reference, which is phase-locked to the AC grid voltage Consequently, a unity input power factor is obtained To maximize efficiency, the boost converter must extract the maximum possible power from the PV array to supply the dc-link, with the remaining power supplied by the AC grid, controlled precisely by the system.
Assuming the dc-link voltage consistently exceeds the battery voltage, the DC-DC converter functions as a step-down converter between the battery and the dc-link This converter is capable of regulating either the battery current or voltage through an advanced control system, enabling efficient CC-CV (constant current, constant voltage) battery charging.
3.3.2.3 Control Design of the Split-rail asymmetric half bridge converter with an extra leg
This section discusses a control strategy for an integrated battery charger based on a Split-rail asymmetric half-bridge converter with an extra leg, designed to maximize PV power extraction and implement a CCCV charging profile for batteries The hybrid power source integrated charger comprises three main power stages: a boost DC-DC converter connected to the PV array with an MPPT algorithm for peak power tracking, an AC-DC PFC rectifier to extract real power from the grid while ensuring PV array operation at MPPT, and a bidirectional step-up/down DC-DC converter employing a CCCV charging strategy to enhance battery lifespan The control structures of the PV boost converter and the AC-DC rectifier are illustrated in Fig 3.16, emphasizing their roles in efficient power management within the system.
Fig 3.16 Control mechanism for PV array and AC-DC PFC rectifier
A cascaded control system has been also developed to perform CCCV charging of the battery pack
[73] Fig 3.17 shows the block diagram of the charging control system
Fig 3.17 Cascaded control structure for CCCV charging of the EV battery
Voltage control is managed through an outer control loop that sets the reference charging current When the battery's State of Charge (SoC) is low and the terminal voltage (v_B) is below the set point voltage (v_B*), the reference current (i_B*) is saturated at its maximum value (i_Bmax), initiating constant current charging As the terminal voltage gradually rises and reaches the set point, the reference current begins to decrease, signaling a switch to constant voltage mode, typically around 80% SoC The charging current continues to decline as the SoC increases, approaching full charge.
To create a buck converter using the battery converter section depicted in Fig 3.13, only switch S7 requires active control to regulate the battery charging current Meanwhile, diode S8 functions as the freewheeling diode of the buck converter This configuration ensures efficient energy transfer and stable voltage regulation during the charging process Properly controlling S7 is essential for optimal converter performance and effective battery management.
The following Chapter develops the simulation setup to investigate these three converters proposed in this research in further detail and assess the performance v dc * v dc
MPPT PI D PV i PV v PV i PV * i PV v dc
Conclusion
The modular asymmetrical half-bridge integrated drive is designed for a 12/8 SRM and supports both driving and charging modes without the need for circuit reconfiguration This drive requires the SRM windings to be split and tapped at the center, ensuring seamless mode switching It offers a high degree of fault tolerance and facilitates easy voltage equalization of battery packs during idle and charging modes Additionally, a power factor correction strategy is implemented to shape the grid-side current, enhancing overall system efficiency and reliability.
This thesis introduces a novel multiport integrated drive for an SRM, featuring a strategically placed relay that switches the winding to the AC grid during charging mode The proposed circuit enables CC-CV (constant current-constant voltage) charging of the onboard battery, ensuring efficient energy management Additionally, the design achieves unity power factor on the AC side without requiring any extra circuitry, enhancing overall system performance and energy efficiency.
The proposed third circuit topology features a split-rail asymmetric half-bridge converter designed for SRM drives, enabling seamless hybrid power source integration This charger efficiently supports charging the onboard battery pack using both AC power and a secondary DC source, such as a photovoltaic (PV) array The PV energy is harnessed through a Maximum Power Point Tracking (MPPT) algorithm, ensuring optimal power extraction, while the battery is charged using a constant current-constant voltage (CCCV) strategy The control system prioritizes the PV array as the primary power source, with any power deficit supplied by the AC grid to meet the overall output requirements, ensuring reliable and efficient hybrid charging.