This feature enables the MC modules to be reused in other industrial applications, where a high-bandwidth control of torque and 169 FPGA Based Powertrain Control for Electric Vehicles...
Trang 1Electric Vehicles 11
30 15 20 25 250
cycles
2500 cycles
ADC Interface (Currents Acquisiton)
TClarke +TPark
IFOC Start
IFOC Start
PI Rect2Polar SVPWM
30 15 20 25
MC (Left)
MC (Right)
Soft Processor PicoBlaze + SPI + UART + 501 3 85
Table 1 Resource utilization of the main IP cores (Note: the design tool was the ISE WebPack8.2.03i, FPGA family: Spartan 3, Speed Grade: -5)
representing 14% of the 2500 cycles associated with the MC minimum execution rate (20kHz).This minimum rate is the result of the energy dissipation limits in the power semiconductors,which, in hard-switching, high current traction applications, is normally constrained to amaximum of 20kHz switching frequency Albeit the MC modules have been specificallydeveloped for electric traction applications, with the 20 kHz update rate limit, the low value oflatency permits a higher execution rate, up to 147 kHz This feature enables the MC modules
to be reused in other industrial applications, where a high-bandwidth control of torque and
169
FPGA Based Powertrain Control for Electric Vehicles
Trang 212 Will-be-set-by-IN-TECH
(a) Motor controller and SVPWM configuration (b) Debug screen
(c) Telemetry plot for current regulation (d) Telemetry plot for motor position
Fig 6 User interfaces of the software developed to configure and debug the EV controller.speed is necessary Figure 5 also shows the parallel processing capabilities of FPGA, whichallows multiple instantiations of the MC to run simultaneously, independently and withoutcompromising the bandwidth of other modules
A summary of the resource utilization in the IP cores implementation, such as slices, dedicatedmultipliers and Block Ram (BRAM), is presented in Tables 1 and 2 The two Motor Controllersinstantiated in control unit are the most demanding on the FPGA resources, requiring 44% ofthe slices and 92% of the dedicated multipliers available on the chip Although there are aconsiderable number of slices available (39%), the low number of free multipliers prevents theinclusion of additional MC, presenting a restriction for future improvements in this FPGA; inother words, such improvements would need an FPGA with more computational resources,thus more costly In addition to the MC, there are also others modules to perform auxiliaryfunctions (sensor interface, protections, soft processor), described in the previous section, andwhich consume 17% of the FPGA area
Trang 3Electric Vehicles 13
DC Bus Capacitors
Current Sensors
MOSFET Drivers
12x Power MOSFETs
FPGA Control System
DC/AC Power Converters
AC Induction Motor
[2kW @ 1500rpms]
Single-Gear Transmission
a datalogger interface (Fig 6(c)), which enables the real-time acquisition of the EV controllervariables, like the motor currents, voltages and mechanical position, providing an effectivemechanism to inspect the performance of the control loops during fast transients and aid thecontroller tuning process
3.5 Experimental results
In order to evaluate the control system discussed in the previous sections, an EV prototype,named uCar, was built to accommodate the electric powertrain (see Fig 7) The vehicle isbased on a two-seater quadricycle, manufactured by the MicroCar company, and is verypopular among elderly people of southern Europe, mainly due to non-compulsory drivinglicense The original propulsion structure, based on the internal combustion engine, wasreplaced by a new electric powertrain composed by two electric motors (26 Vrms, 2.2 kW
@ 1410 rpm), each one coupled to the front wheels by single gear (7 : 1) transmissions Due to
low cost, lead acid batteries (4x12V@110Ah) were selected as the main energy storage of the
EV, providing a range of 40 km per charge, a sufficient autonomy for urban driving After theconversion, the uCar prototype weights 590 kg and reaches a top speed of 45 km/h
171
FPGA Based Powertrain Control for Electric Vehicles
Trang 4All the powertrain control functions of the EV are concentrated on the Digilent Spartan
3 Start Board, containing, besides the XC3S1000 FPGA, several useful peripherals such asflash memory (2 Mbit) for storing data, serial interface for communications and 4 expansionports for I/O with the FPGA To extend the functionalities of these main peripherals, twoadditional boards were constructed and connected to the main board, containing analog todigital converters (TIADS7818 and TIADS7848) to allow the acquisition of analog variables,and voltage level shifters (3.3↔5.0V) to perform the interface with the external digital I/O.This EV controller interacts with two DC/AC power converters, featuring 120Arms@30Vrmsand 20kHz switching frequency, in order to regulate the current and voltage delivered to theelectric motors, as discussed in the previous sections
To validate the experimental performance of the uCar, several roadtests were conduced insidethe FEUP university campus, characterized by low speed driving cycles, similar to urbanconditions (see Fig 8) From these roadtests, we selected two representative cycles for assessthe influence of the regenerative braking in the energy consumption of the uCar In the firstsituation, with the regenerative braking disabled, the vehicle travels approximately 2.36 kmand shows consumption metrics close to 100 Wh/km (see Table 3) On the other hand, whenthe reg braking is active the EV consumption decreases 13.2%, to 86.8 Wh/km, representing
an important contribute to increase the EV range per charge
Trang 5Electric Vehicles 15
(a) Acceleration + Field Weakening
1806 1808 1810 1812 1814 1816 1818
−40
−20 0 20 40 60 80 100
To further validate the EV control unit performance, Fig 9 show the detailed results of theleft motor controller for tree different operating modes: acceleration, field weakening andregenerative braking The data depicted in these figures was acquired with the controllerinternal datalogger, which enable us to keep track of the most relevant EV variables, suchas: mechanical (motor speed), energy source (voltage, current and power) and the motor
controller ( torque (i q ) and flux (i d ) currents, modulation index (m) and the slip frequency ( f slip)) variables During the acceleration mode (Fig.9(a), 9(c)), performed with the throttle at
100%, the i q and i dcurrents are set at the maximum value in order to extract the maximummotor torque and vehicle acceleration (2.2km/h/s) When the EV reaches 18km/h the motorvoltage saturates at 83% and the flux current is reduced to allow the vehicle to operate inthe field weakening area, with a power consumption of 2.5kW per motor In fact, analyzingthe evolution of the power supplied by the batteries during the experimental driving cycles(Fig 8), it is interesting to note that the electric motors spend most of the time operating inthis field weakening zone Fig 9(b) and 9(d) shows the detailed results of third EV operation
173
FPGA Based Powertrain Control for Electric Vehicles
Trang 616 Will-be-set-by-IN-TECHmode: the regenerative braking In the depicted manoeuvre, the driver is requesting a torquecurrent of -25A to decelerate the vehicle from 30 km/h to 5 km/h in 10s, which enable aconversion of 1kW peak power and emphasizing one of the most promising features in EVs:energy recovering during braking.
4 Conclusion
In this article an FPGA based solution for the advance control of multi-motor EVs wasproposed The design was build around a powertrain IP Core library containing the mostrelevant functions for the EV operation: motor torque and flux regulation, energy lossminimization and vehicle safety Due to the parallel, modularity and reconfigurability features
of FPGAs, this library can be reused in the development of several control architecturesthat best suits the EV powertrain configuration (single or multi-motor) and functionalrequirements As proof of concept, the powertrain library was employed in the design
of minimal control system for a bi-motor EV prototype and implemented in a low costXilinx Spartan 3 FPGA Experimental verification of the control unit was provided, showingreasonable consumption metrics and illustrating the energy benefits from regenerativebraking
In future works, we are planning the inclusion, in the powertrain library, of active torquemethods in order to improve the handling and safety of multi-motor EVs On thetechnological level, we also intent to validate the library on EV prototypes with 4 in-wheelmotors
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Global Design and Optimization of
a Permanent Magnet Synchronous Machine
Used for Light Electric Vehicle
With regard to automobiles, there have been made several attempts to establish a maximum acceptable level of pollution Thus, several car manufacturers have prepared a declaration of
Partnership for a New Generation of Vehicles (PNGV), also called SUPERCAR This concept
provides, for a certain power, the expected performance of a thermal or hybrid car Virtually, every car manufacturer proposes its own version of electric or hybrid car, at
SUPERCAR standard, see Table 1 (Fuhs, 2009)
Of course, at concept level, the investment is not a criterion for the construction of EVs, as in the case of series manufacturing (where profits are severely quantified) For example, nowadays the price of 1 kW of power provided by fuel cell (FC) is around 4,500 €; thus, a FC of
100 kW would cost 450,000 € (those costs are practically prohibitive, for series manufacturing)
By consulting Table 1, it can be noticed the interest of all car manufacturers to get a reduced pollution, with highest autonomy Nowadays, the hybrid vehicles can be seen on streets Although the cost of a hybrid car is not much higher than for the classical engine (about 15-25% higher), however, the first one requires supplementary maintenance costs which cannot
be quantified in this moment
Trang 10Electric Vehicles – Modelling and Simulations
178
AUDI metroproject
quattro turbocharged four-cylinder engine and an electric machine of 30 kW; lithium-ion battery
maximum range on electric-only of
100 km; 0-100 km/h in 7.8 s; maximum speed 200 km/h
BMW x5 hybrid SUV for 1000 rpm, there is a V-8 engine providing 1000 Nm; the electric motor gives 660 Nm fuel economy is improved by an estimated 20%.CHRYSLER eco
voyager FCV propulsion of 200 kW; hydrogen is feed to a PEM fuel cell (FC) range of 482 km and a 0–60 km/h in less than 8 s CITROËN c-cactus
hybrid diesel engine provides 52 kW and the electric motor gives 22 kW fuel consumption is 2.0 L/100 km; maximum speed is 150 km/h FORD hySeries EDGE Li-ion battery has maximum power of 130 kW, and the FC provides 35 kW range of 363 km (limited by the amount of hydrogen for the FC) HONDA FCX electric vehicle with 80 kW propulsion engine, combining ultracapacitors (UC) and PEM FC 55% for overall efficiency, driving range of 430 kmHYUNDAI I-blue
FCV
FC stack produces 100 kW; there is a 100 kW electric machine (front wheels) and 20 kW motor for each rear wheel estimated range is 600 km JEEP renegade diesel–
electric
1.5 L diesel engine provides 86 kW and is teamed with 4 electric motors (4WD) of
85 kW combined power
the diesel provides range extension up
to 645 km beyond the 64 km only range (diesel fuel tank holds 38 L) KIA FCV a 100 kW FC suppliss a 100 kW front wheel electric motor, while the motor driving the
electric-rear wheels is 20 kW range is stated to be 610 km MERCEDES BENZ s-
class direct hybrid
3.5 L (V-6) gasoline engine with motor/generator combined power of 225 kW and combined torque of 388 Nm
acceleration time from 0-100 km/h in 7.5 s
MITSUBISHI pure EV Li-ion battery and wheel-in-motors of 20 kW 150 kg Li-ion battery give a range of 150 km (2010 prospective range of
250 km OPEL flextreme a series hybrid configuration (with diesel engine) with Li-ion battery; the electric motor
has peak power of 120 kW
fuel consumption of 1.5 L/100 km; electric only mode has range of 55 km PEUGEOT 307 hybrid it is diesel/electric hybrid automobile the estimated fuel economy is 82 mpg; this is a hybrid that matches the PNGV
goals SUBARU G4E five passengers EV, using Li-ion batteries driving range is 200 km; the battery can be fully charged at home in 8 h (an 80%
charge is possible in 15 min) TOYOTA 1/X plug-in
hybrid
thermal engine 0.5 L, with a huge reduction
of mass to 420 kg (use of carbon fiber composites, although expensive)
low mass also means low engine power and fuel consumption
VOLKSWAGEN Blue
FC
a 12 kW FC mounted in the front charges
12 Li-ion batteries at the rear; The 40 kW motor is located at the rear
the electric-only range is 108 km; top speed is 125 km/h, and the acceleration time from 0-100 km/h is 13.7 s VOLVO recharge series hybrid with lithium polymer batteries; the engine is of 4-cylinder type with1.6 L; it
has 4 electric wheels motors (AWD)
electric-only range is 100 km; for a
150 km trip, the fuel economy is 1.4 L/100 km
Table 1 Several types of hybrid vehicle concepts
Some predictions on the EV’s were considered by (Fuhs, 2009) In the nearest future the thermal automobiles number will decrease, while the hybrid ones are taking their place By
2037 the fully electric vehicle (called kit car) will replace the engine and then, after a fuzzy
period all vehicles will be powered based on clean energy sources, when a new philosophy
of building and using the cars will be put in place
So, one of the challenges of individual transport refers to finding clean solutions, with enhanced autonomy (Ceraolo et al., 2006; Chenh-Hu & Ming-Yang, 2007; Naidu et al., 2005)
Trang 11Global Design and Optimization of
a Permanent Magnet Synchronous Machine Used for Light Electric Vehicle 179 This is the motivation of this research work For that, an electric scooter will be studied from the motorization, supplying and control point of view The global steps of the design process will be presented here Firstly, the considered load and expected mechanical performances will be introduced The electromagnetic design of the electrical motor, capable
to fulfill the mechanical performances, will be presented too The obtained analytical performances should be validated; for that, the finite element method will be used Also, the machine optimization will fulfill the global designing process of the electrical machine
2 Design of studied electrical machine
The research study presented here concerns the design of a three phase permanent magnet synchronous machine (PMSM) used for the propulsion of an electric scooter It is widely recognized that the common solution, the dc motor, has usually poor performances against
ac motor However, for low small power electrical machines, this advantage is not always obvious Also, a special attention should be paid for the efficiency and power factor of ac machines This will be analyzed here The validation of the obtained results will be made based on finite element method (FEM) analysis The goal is to increase the autonomy of the light electric vehicle, based on a PMSM, with a proper control, and after the optimization of the designed machine
The analytical approach, employed here, can be used for any type of electric vehicle First of all, for a given maximum load, it will be established the necessary power needed for the propulsion of the vehicle Secondly, the main steps in the design process of the studied machine will be given Next, the energetic performances and electro-mechanical characteristics will be presented The validation of the analytical obtained results is made based on finite element method (FEM) By means of numerical computation, it will be demonstrated that a unity power factor control is possible when using ac machines, by employing a field oriented control strategy The optimization of the studied machine will be realized based on gradient type algorithm and the obtained results will show the benefits of using a PMSM for the propulsion of the light electric vehicle
2.1 The needed mechanical performances
The maximum speed and weight of the vehicle are 12 km/h and 158 kg, respectively The considered vehicle has 4 tires of 11 inches in diameter The vehicle dimensions are: 1290 mm
in length, 580 mm in width and 1150 mm in height The vehicle will be supplied from a battery of 24 Vcc
First of all, it is needed to compute the output power of the electric motor which is capable
to run the vehicle Since the mechanical power is the product between the mechanical torque and angular speed, it is possible to establish the speed of the vehicle at the wheel:
where nt is the velocity measured at the vehicle’s wheels (measured in min-1), v is the vehicle
speed (in m/s), Dt is the outer diameter of the wheel (the tire height included, in m) The
resulted velocity is nt=244.4 min -1 From mechanical and controllability considerations, it is desirable to have an electric motor operating at higher speed, so it is considered a gear ratio of
6.1 to 1 Thus the electric motor rated speed is imposed at 1500 min -1
Next, the rated torque has to be established Since the motor torque is proportional to the wheel radius and the force acting on it, one should determine the force involved by the
Trang 12Electric Vehicles – Modelling and Simulations
180
vehicle’s weight and rolling conditions The electric motor has to be capable to produce a mechanical force to balance all other forces which interfere in vehicle’s rolling Thus, the motor force is:
where Facc is the acceleration force, Fh is the climbing force, Fd is the aerodynamic drag force,
Fw is a resistive force due to the wind, and Fr is the rolling force
Since the vehicle studied here is not for racing, and will be controlled to start smoothly, no acceleration constraints are imposed
When the vehicle goes hill climbing, based on angle of incline θ, the climbing force is:
where Mtot, is the total mass of the vehicle (in kg), g is the gravitational constant (9.8 m/s 2) Usually, the degree of incline is given in percentage For this special electric scooter it is considered a maximum 8% degree of incline 1% degree of incline represents the ratio of
1 meter of rise, on a distance of 100 meters Thus, 1%=atan(0.01)=0°34’ (zero degrees and
34 minutes) For an incline of 8%, the angle is 4°34’ (or 4.57 degrees)
The drag force takes into account the aerodynamics of the vehicle This force is proportional with the square of the speed, the frontal area of the vehicle (Afr, here 0.668 m2) and the aerodynamic coefficient, kd, (empirically determined, for each specific vehicle (Vogel, 2009)):
The resistant force due to wind, cannot be precisely computed It depends on various conditions, like (for common automobiles) the fact that windows are entirely or partially open etc Also, the wind will never blow at constant speed However, an expression, determined empirically, which will take into account the speed of wind, vw, can be written
as (Vogel, 2009):
F = 0.98 ∙ (v /v) + 0.63 ∙ (v /v) ∙ k − 0.4 ∙ (v /v) ∙ F (5) where krw is the wind relative coefficient, depending on the vehicle’s aerodynamics, (here is 1.6)
The resistant force due to rolling depends on the hardness of the road’s surface, being proportional with the weight of the vehicle and the angle of incline:
(here, the road surface coefficient, k r, is 0.011)
A more precise computation of the rolling resistant force could take into account also the shape and the width of the tires, but these elements are not critical at low speeds, like in this case
After the computation of the resistant forces, it can be determined the needed torque at the wheel, see Table 2, and finally the rated torque of the electrical machine
For this specific value of the torque at the wheel, a power of 505.1 W is required Nevertheless, for small power electrical traction systems, the efficiency is quite poor Here, the efficiency is estimated at 75% This means that the output power of the electrical motor, capable to operate in the specified road/mechanical conditions, it has to be at least of 673.5 W Thus, rounding the power, it is obtained a 700 W electrical machine
Trang 13Global Design and Optimization of
a Permanent Magnet Synchronous Machine Used for Light Electric Vehicle 181
It is now possible to identify the mechanical characteristics of the electrical machines Two traction motors are considered, with a gear ratio of 6.1 to 1 Thus, the rated mechanical characteristics for one motor are: 350 W, 1500 rpm, 2.2 N.m
123.5 0.026 0.667 16.98 141.2 19.73 Table 2 Computed resistant forces and the torque at the wheel
2.2 Electromagnetic design of the PMSM
The permanent magnet synchronous machine (PMSM) has to provide a maximum power density For that, good quality materials should be used The permanent magnet (PM) material is of Nd-Fe-B type, with 1.25 T remanent flux density The steel used for the construction of PMSM is M530-50A The material characteristics are presented in Fig 1
Fig 1 The PM and steel characteristics used as the active part’s materials of the PMSM
0 0.5 1 1.5
magnetic field intensity (A/m)
magnetic field intensity (A/m)
Trang 14Electric Vehicles – Modelling and Simulations
182
For the PM, the N38SH material was use This rear earth magnet can be irreversible demagnetized starting from 120°C The 1.25 T remanent flux density (at 20°C) is however affected with the temperature increase In order to compute the real value of the PM’ s remanent flux density, for a temperature derivative coefficient of 0.1% and for an increase in temperature of 110 K, the rated operating point of the PM is 1.11 T (based on the mathematical expression X ° = X ° ∙ (1 − α ∙ ΔT))
In order to obtain a smooth torque wave, a fractioned winding type is used Thus, the PMSM has 8 pair of poles and 18 slots The geometry of the PMSM, the winding configuration and the obtained phase resultant vectors are shown in Fig 2
The design approach is based on the scientific literature presented in (Pyrhonen et al., 2008;
Fitzgerald et al., 2003; Huang et al., 1998) The output power (measured in W) of an electric
machine, when the leakage reactance is neglected, is proportional with the number of phases of the machine, nph, the phase current, i(t), and the inducted electromotive force (emf), e(t):
P = η ∙ ∙ e(t) ∙ i(t)dt = η ∙ n ∙ k ∙ E ∙ I (7) where T is the period of one cycle of emf, Emax, and Imax represent the peak values of the emf and phase current, kp is the power coefficient, and η is the estimated efficiency
The peak value of the emf is expressed by introducing the electromotive force coefficient, kE:
gap
2 p PD
All the other geometric parameters will be computed based on this air-gap diameter The designer has to choose only the PMs shape and stator slots
The air-gap flux density is computed based on the next formula:
m rm gap
Trang 15Global Design and Optimization of
a Permanent Magnet Synchronous Machine Used for Light Electric Vehicle 183 where, hm and Brm are the PM length on magnetization direction (in m) and the remanent flux-density (in tesla), respectively, Rsi and Rcr are inner stator radius and rotor core radius, respectively
(a)
(b)
(c) Fig 2 The PMSM: (a) geometry; (b) fractioned type winding configuration; (c) the resultant voltage vectors