IMPROVING INDUCTION MOTOR’S SPEED AND TORQUE IN ELECTRIC MOTORBIKES

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING GRADUATION PROJECT IMPROVING INDUCTION MOTOR’S SPEED AND TORQUE IN ELECTRIC MOTORBIKES Student NGUYỄN HỮU TUẤN KIỆT Student ID 16145026 Student NGUYỄN TRUNG ĐỨC Student ID 16145010 Major AUTOMOTIVE ENGINEERING Advisor LÊ THANH PHÚC, Ph D Ho Chi Minh City, August 2020 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING GRADUATION PROJECT IMPROVING INDUCTION MOTOR’S SPEED.

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND

EDUCATION FACULTY FOR HIGH QUALITY TRAINING

THE SOCIALIST REPUBLIC OFVIETNAM

Independence – Freedom– Happiness

-Ho Chi Minh City, August 14, 2020

GRADUATION PROJECT ASSIGNMENT

Student name: Nguyễn Hữu Tuấn Kiệt Student ID: 16145026

Student name: Nguyễn Trung Đức Student ID: 16145010

Major: Automotive Engineering Class: 16145CLA

Advisor: Lê Thanh Phúc, Ph.D Phone number: 0938518256

Date of assignment: 19/2/2020 Date of submission: 12/8/2020

1 Project title: Improving induction motor’s speed and torque in electric motorbikes

2 Initial materials provided by the advisor: Text books + Model + Soft file

3 Content of the project: Build block diagrams

Calculate and design system

Build circuit, experiment

4 Final product: Demonstration report + Model + Soft file

CHAIR OF THE PROGRAM

(Sign with full name)

ADVISOR

(Sign with full name)

THE SOCIALIST REPUBLIC OFVIETNAM

Independence – Freedom– Happiness

-Ho Chi Minh City, August 14, 2020

ADVISOR’S EVALUATION SHEET

Student name: Nguyễn Hữu Tuấn Kiệt Student ID: 16145026

Student name: Nguyễn Trung Đức Student ID: 16145010

Major: Automotive Enginerring

Project title: Improving induction motor’s speed and torque in electric motorbike

Advisor: Lê Thanh Phúc, PhD

EVALUATION

1 Content of the project:

2 Strengths:

3 Weaknesses:

4 Approval for oral defense? (Approved or denied)

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom– Happiness

-Ho Chi Minh City, August 14, 2020 PRE-DEFENSE EVALUATION SHEET Student name: Nguyễn Hữu Tuấn Kiệt Student ID: 16145026 Student name: Nguyễn Trung Đức Student ID: 16145010 Major: Automotive Enginerring Project title: Improving induction motor’s speed and torque in electric motorbike Name of Reviewer: Nguyễn Trung Hiếu, M.S EVALUATION 1 Content and workload of the project

2 Strengths:

3 Weaknesses:

4 Approval for oral defense? (Approved or denied)

5 Overall evaluation: (Excellent, Good, Fair, Poor)

6 Mark:……….(in words: )

Ho Chi Minh City, August 14, 2020

REVIEWER

(Sign with full name)

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom– Happiness Independence – Freedom–

-Ho Chi Minh City, August 14, 2020 EVALUATION SHEET OF DEFENSE COMMITTEE MEMBER Student name: Nguyễn Hữu Tuấn Kiệt Student ID: 16145026 Student name: Nguyễn Trung Đức Student ID: 16145010 Major: Automotive Enginerring Project title: Improving induction motor’s speed and torque in electric motorbike Name of Defense Committee Member: EVALUATION 1 Content and workload of the project

2 Strengths:

3 Weaknesses:

4 Overall evaluation: (Excellent, Good, Fair, Poor)

5 Mark:……….(in words: )

Ho Chi Minh City, August 14, 2020

COMMITTEE MEMBER

(Sign with full name)

I hereby declare that this thesis is a record of our work undertaken by ourselves, that ithas not been submitted anywhere, and other sources of information, papers, documentsused in this work have been duty acknowledged

We would like to express my special appreciation and thanks to our advisor PhD Phuc

Le Thanh, you have been a tremendous mentor for us We would like to thank you forencouraging our research and for allowing us to grow as research scientists Your advice

on both research as well as on our career have been invaluable We would also like tothank Engineer Tri Dinh Cao and other members of Viet Duc laboratory for supportingeven at hardship We also want to thank all of you for letting our defense be an enjoyablemoment, and for your brilliant comments and suggestions, thanks to you

Finally, a special thanks to our family Words cannot express how grateful we are to ourmothers, fathers for all the sacrifices that they have made on our behalf Their prayer for

us was what sustained us thus far Thank you for supporting us for everything, andespecially we cannot thank you enough for encouraging us throughout this experience

Table of Contents

C HAPTER 2: LITERATURE REVIEW 3

2.14 Induction motor’s speed-torque characteristics and Volt/Hertz (V/f) method

2.14.1 Induction motor’s speed-torque characteristic 39

2.14.3 Limitations imposed by the inverter-constant power and constant torque regions 42

2.14.4 Determination of voltage boost region in V/f control 44

C HAPTER 3: BUILDING SYSTEM 45

3.1 Requirements of the system 45

C HAPTER 4: DESIGN AND ASSEMBLY CONCEPTS 53

4.3 Aluminum heatsink case design for circuits 70

6.2 Recommendations 76

List of Figures

Figure 2.7 IR2103 wave form output and input signal [6] 10

Figure 2.11 Non-polarized and polarized capacitor [8] 14

Figure 2.14 Forward bias and reverse bias [10] 16

Figure 2.27 Squirrel cage rotor [19] 33

Figure 2.28 Traditional three-phase sine PWM signal 34

Figure 2.29 Triangle wave and sine wave signal 35

Figure 2.30 The Sine PWM is generated by comparing the carrier amplitude value and

Figure 2.31 Three-phase voltage source inverter using six IGBTs [20] 37

Figure 2.35 Fast PWM Mode- timing diagram [22] 39

Figure 2.37 The pure speed and torque for each frequency [23] 41

Figure 2.38 Typical torque-speed curves for inverter-fed induction motor [23] 42

Figure 2.39 Constant torque, constant power and high-speed motoring regions [23] 43

Figure 2.40 Voltage boost of VVVF drive at low speed [23] 44

Figure 3.3 Moment levels are equivalent to each frequency [23] 47

Figure 3.4 V/f control for induction motor [23] 48

Figure 3.5 Diagram of generating 3-phase current from PWM [24] 49

Figure 3.6 Diagram of 3-phase motor and 3-phase voltage [24] 49

Figure 3.7 Connection diagram of central control block [6] 50

Figure 3.8 Algorithm flowchart of central control block 51

Figure 4.5 Check the output pins of the control circuit 55

Figure 4.6 Graph of voltage at the pin of Lin when controlled at 5 Hz 56

Figure 4.7 Graph of voltage at the pin of Lin when controlled at 10 Hz 57

Figure 4.8 Graph of voltage at the pin of Lin when controlled at 20 Hz 57

Figure 4.9 Graph of voltage at the pin of Lin when controlled at 30 Hz 58

Figure 4.12 Block diagram of Integrated Circuits 61

Figure 4.17 Signal from shunt resistor at low voltage 64

Figure 4.18 Signal from shunt resistor rate voltage 65

Figure 4.19 Signal from shunt resistor boost voltage 65

Figure 4.22 Average of ADC and instantaneous ADC 67

Figure 4.27 Making a heat sink by milling method 71

Figure 4.30 Attach the controller to the frame 74

List of Table

Table 6.1 System test result 75

ABSTRACT

Motorbike basically is a form of popular transportation method that can be use by people

to move from one place to another in Vietnam In conventional way, motorbikes useinternal combustion engine and fossil fuels to operate So, an invention has been createdand it was electric motorbike, basically using an electric motor and battery powered Themain aim of this graduation project is to research and test semi-closed, low cost PWM-VSI controlled AC machines using one DC – link current sensor to improve inductionmotor’s speed and torque in electric motorbikes The performance is especially improved

at low speed where nonlinearities like blanking-time and voltage drop are dominant Anoften-used modulation technique is described, and basic compensation techniques arepresented Only one current sensor in the DC-link is used for reconstruction of all threephase currents and the currents are used for compensation Different limitations arediscussed The compensation techniques are tested in an 8 – bit microcontroller-basedinverter Tests show that the phase currents can be reconstructed by measurement of theDC-link current both at low and high speed They also show that a highly improvedtorque speed characteristic can be obtained by using the compensation techniques and analmost ideal inverter is obtained

Keywords:

V/f: Voltage/frequency

IGBT: Insulated Gate Bipolar Transistor

IC: Integrated Circuit

PCB: Printed Circuit Board

SMD: Surface-Mount Device

PWM: Pulse Width Modulation

VVVF: Variable Voltage Variable Frequency

ADC: Analog to Digital Converter

VSI: Voltage Source Inverter

CAN: Controller Area Network

RMS: Root Mean Square

VCM: Common-Mode Rejection

SPI: Serial Periphera Interface

Chapter 1: INTRODUCTION

1.1 Background

Environmental pollution, especially air pollution, is a worldwide problem in general andVietnam in particular It is an inevitable consequence of industrialization andmodernization However, we can reduce these consequences by using new energy sourcesinstead of fossil fuels Transportation is a major source of air pollution and it is alsoimperative to gradually switch to new energy use

In the world, many electric car manufacturers have appeared, as well as traditionalautomakers have started to produce their first electric cars as a step to reduceenvironmental pollution save natural resources

In Vietnam, vehicles are mainly motorcycling, so the electric vehicle market is mainlyelectric motorcycles, and most of them are originated from foreign countries Vinfast isthe car manufacturer that launched their first product that resonates with the Vinfast Klaraelectric motorbike However, the cost is still high compared to the income of manypeople

Desiring to produce a line of electric motorbikes, both to protect the environment and toserve the travel needs of the people, and to be able to produce locally, using manycomponents and devices The research team chose the topic " Improving inductionmotor’s speed and torque in electric motorbikes "

1.2 Research purpose

● Replace the traditional internal combustion engine in a motorbike with anasynchronous 3-phase AC electric motor

● Increase moment for motorbike’s motor for a road performance

● Control the motor according to the user needs

● Operate the system stably and safely for users

1.3 Research scope

The project “Improving induction motor’s speed and torque in electric motorbikes”concentrates on following subjects:

● Atmega328P

● The inverter using IGBT

● AVR programing with C-language

● Design printed board with Proteus

● Design a battery source by Invertor

● Design a heatsink

1.4 Research limitation

Due to the limited time, just over six months, the team focused on improving what wasavailable The research team concentrated on increasing motor moment and find newdirections to make the bike perform better

1.5 Research method

The team researched from the Internet sources, performed research based on basicelectronic textbooks, power electronics, micro-controllers, coupled with learning how touse the necessary software regarding to simulation, mechanical design

1.6 The graduation project content

● Build block diagrams

● Calculate and design system

● Printed board circuit

● Build circuit, experiment

1.7 The graduation project platform

Chapter 1: Introduction

Chapter 2: Literature review

Chapter 3: Theoretical basis

Chapter 4: Building system

Chapter 5: Design and build system

Chapter 6: Experiment

Chapter 7: Conclusions and recommendations

Chapter 2: LITERATURE REVIEW

2.1 Atemega328p

ATmega328P is a high performance yet low power consumption 8-bit AVRmicrocontroller that can achieve the most single clock cycle execution of 131 powerfulinstructions thanks to its advanced RISC architecture It can commonly be found as aprocessor in Arduino boards such as Arduino Fio and Arduino Uno [1]

Features: [1]

● High performance, low power AVR® 8-bit microcontroller

● Advanced RISC architecture

- 131 powerful instructions – most single clock cycle execution

- Fully static operation

- Up to 16MIPS throughput at 16MHz

- On-chip 2-cycle multiplier

● High endurance non-volatile memory segments

● 32K bytes of in-system self-programmable flash program memory

- 1 Kbytes EEPROM

- 2 Kbytes internal SRAM

- Write/erase cycles: 10,000 flash/100,000 EEPROM

- Optional boot code section with independent lock bits

- In-system programming by on-chip boot program

- True read-while-write operation

- Programming lock for software security

● Peripheral features

- Two 8-bit Timer/Counters with separate prescaler and compare mode

- One 16-bit Timer/Counter with separate prescaler, compare mode, and capturemode

- Real time counter with separate oscillator

- Six PWM channels

- 8-channel 10-bit ADC in TQFP and QFN/MLF package

- Temperature measurement

- Programmable serial USART

- Master/slave SPI serial interface

- Byte-oriented 2-wire serial interface (Phillips I2C compatible)

- Programmable watchdog timer with separate on-chip oscillator

- On-chip analog comparator

- Interrupt and wake-up on pin change

● Special microcontroller features

- Power-on reset and programmable brown-out detection

- Internal calibrated oscillator

- External and internal interrupt sources

- Six sleep modes: Idle, ADC noise reduction, power-save, power-down,standby, and extended standby

● I/O and packages

- 23 programmable I/O lines

- 32-lead TQFP, and 32-pad QFN/MLF

● Operating voltage:

- 2.7V to 5.5V for ATmega328P

● Temperature range:

- Automotive temperature range: –40°C to +125°C

● Speed grade:

- 0 to 8MHz at 2.7 to 5.5V (automotive temperature range: –40°C to +125°C)

- 0 to 16MHz at 4.5 to 5.5V (automotive temperature range: –40°C to +125°C)

● Low power consumption

- Active mode: 1.5mA at 3V - 4MHz

- Power-down mode: 1µA at 3V

2.2 IGBT technology and IGBT H20R1203

An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductordevice primarily used as an electronic switch which, as it was developed, came tocombine high efficiency and fast switching It consists of four alternating layers (P-N-P-N) that are controlled by a metal–oxide–semiconductor (MOS) gate structure withoutregenerative action Although the structure of the IGBT is topologically the same as athyristor with a 'MOS' gate (MOS gate thyristor), the thyristor action is completelysuppressed and only the transistor action is permitted in the entire device operation range

It is used in switching power supplies in high-power applications: variable-frequencydrives (VFDs), electric cars, trains, variable speed refrigerators, lamp ballasts, arc-welding machines, and air conditioners [2]

Since it is designed to turn on and off rapidly, the IGBT can synthesize complexwaveforms with pulse-width modulation and low-pass filters, so it is also used inswitching amplifiers in sound systems and industrial control systems In switchingapplications modern devices feature pulse repetition rates well into the ultrasonic range—frequencies which are at least ten times the highest audio frequency handled by thedevice when used as an analog audio amplifier As of 2010, the IGBT is the second mostwidely used power transistor, after the power MOSFET [3]

2.2.1 IGBT H20R1203

2.2.1.1 Definition

H20R1202 is a type of IGBT manufactured and developed for high efficiency and quickswitching, so IGBT H20R1202 is often used to switch electrical power in many moderndevices: induction cookers, inverters, control 3-phase motors, electric cars, airconditioners and even amplifiers in the audio system Because IGBT has a heat-resistantback cover with a middle leg (D), it is necessary to design a proper heat sink, avoidingcontact with water, causing short-circuiting and IGBT failure [4]

2.2.1.2 Structure and operating principles of IGBT H20R1203

● G: Gate

The equivalent circuit of an IGBT is shown below When both the gate-emitter (G-E) andcollector-emitter (C-E) paths are positively biased, the N-channel MOSFET conducts,causing drain current to flow This drain current also flows to the base of QPNP andcauses the IGBT to turn on Since the DC current gain (α) of QPNP is exceedingly small,almost the entire emitter current (IE (pnp)) flows as base current (IB (pnp)) However,part of IE (pnp) flows as collector current (IC (pnp)) The IC (pnp) does not turn onQNPN because it bypasses the RBE inserted between the base and emitter of the QNPN.Therefore, almost the entire collector current of the IGBT flows as the drain current ofthe N-channel MOSFET via the emitter-base paths of QPNP At this time, holes areinjected into the high-resistance drift region of the N-channel MOSFET from the emitter

of QPNP This causes the resistivity of the drift region (Rd (MOS)) to decrease

considerably, reducing the on-resistance during a conduction period This phenomenon iscalled conductivity modulation.

Turning off the gate (G) signal causes the N-channel MOSFET to turn off and therefore

causes the IGBT to turn on

● Check for shorted IGBT

Using a digital ohmmeter on the diode scale:

- Measure resistance between C2/E1 and E2

- Measure resistance between C2/E1 and C1

- If you measure a short (0 ohms) in step 1a or 1b., the IGBT is not usable

● TURN ON Q1, Q2

Using a digital ohmmeter on the diode scale:

- Touch the + (red) meter lead to G1 and the - (black) to E1

- Touch the + (red) meter lead to G2 and the - (black) to E2

- Measure resistance between C1 and C2/E1 Should read a low resistance (about a diode drop) Reverse meter leads, reading should be the same

- Measure resistance between E2 and C2/E1 Should read a low resistance(about a diode drop) Reverse meter leads, reading should be the same

● TURN OFF Q1, Q2

Using an ohmmeter on the diode scale:

- Touch the + (red) meter lead to E1 and the - (black) to G1

- Touch the + (red) meter lead to E2 and the - (black) to G2

- Measure resistance between C2/E1 (+) and C1 (-) Should read a lowresistance (same as in step 2c.) Reverse meter leads Read infinite resistance

- Measure resistance between C2/E1 (-) and E2 (+) Should read a lowresistance (same as in step 2d.) Reverse meter leads Read infinite resistance.Note: Some digital ohmmeters do not have enough power to turn on an IGBT A 9-voltbattery may be used instead

2.3 IR2103

The IR2103(S) are high voltage, high speed power MOSFET and IGBT drivers withdependent high and low side referenced output channels Proprietary HVIC and latchimmune CMOS technologies enable ruggedized monolithic construction The logic input

is compatible with standard CMOS or LSTTL output, down to 3.3V logic The outputdrivers feature a high pulse current buffer stage designed for minimum driver crossconduction The floating channel can be used to drive an N-channel power MOSFET orIGBT in the high side configuration which operates up to 600 volts.[6]

Typical connection diagram:

Voltage sources in a circuit may have fluctuations resulting in not providing fixed voltageoutputs A voltage regulator IC maintains the output voltage at a constant value 7805 IC,

a member of 78xx series of fixed linear voltage regulators used to maintain suchfluctuations, is a popular voltage regulator integrated circuit (IC) The xx in 78xxindicates the output voltage it provides 7805 IC provides +5 volts regulated powersupply with provisions to add a heat sink [7]

An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of

a metal that forms an insulating oxide layer through anodization This oxide layer acts asthe dielectric of the capacitor A solid, liquid, or gel electrolyte covers the surface of thisoxide layer, serving as the cathode or negative plate of the capacitor Due to their verythin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a

much higher capacitance-voltage (CV) product per unit volume than ceramiccapacitors or film capacitors, and so can have large capacitance values [8]

Table 2.1 Capacitor parameters

Breakdown voltage (V/μm)

Electric layer thicknes

The non-polarized capacitors applied in pure AC circuits, and because of its smallcapacitance, it can also be applied to high-frequency filtering [8]

● The difference between Non – polarized Capacitor and Polarized Capacitors:Both polarity and non-polarized capacitors have same principles, that is, storing andreleasing charges; the voltage on the plate (here the electromotive force of chargeaccumulation is called voltage) cannot change suddenly

The different media, different performance, different capacity and different structureresults in different using environment and usage Conversely, more excellent anddiversified capacitors will emerge with the development of science and technology andthe discovery of new materials

- Different dielectric:

In other words, it is the substance between two capacitor plates Most of the

polarity capacitors use electrolytes as dielectric, which makes polarity capacitor haslarger capacitance compared to other capacitors that has same volume

In addition, polarity capacitors produced by different electrolyte materials andprocesses will have different capacitance Meanwhile, voltage withstand is related mostly

to the dielectric material And there are also many non-polarized materials, including themost used metal oxide film and polyester, the use of polarity and non-polarized capacitors is determined by whether the nature of the dielectric is reversible

- Different performance:

Performance and the demand maximization are the requirement of use If the powersupply of the TV use metal oxide film capacitor as filter, and if the capacitance andvoltage withstand are required to meet the filter, I'm afraid only a power supply can beinstalled inside the shell Therefore, filter can only use polarity capacitor, and polaritycapacitance is irreversible

Generally, the electrolytic capacitor is above 1 MF, which participates in coupling,decoupling, power supply filtering and so on The non-polar capacitor is mostly below 1

MF, which is involved in resonance, coupling, frequency selection, current limiting and

so on Of course, there are also non-polar capacitors with large capacity and high voltage,mostly used in reactive power compensation, motor phase shifting, frequency conversionpower phase shifting and other purposes There are many kinds of non-polarized capacitors

- Different capacity:

As mentioned before, capacitors of the same volume have different capacitance underdifferent dielectric.

- Different structure:

In principle, it is possible to use a capacitor of any shape in the environment withoutconsidering the point discharge The most using electrolytic capacitors are circular, andthe square type is rare The shape of capacitors is varied, such as tubular, deformedrectangular, sheet, square, circular, combined square or circular and so on, depending onwhere they are used Of course, there is also invisible ones called distributedcapacitor, which must not be ignored in high frequency and intermediate frequencydevices

2.6 Diode

A diode is a semiconductor device that essentially acts as a one-way switch for current Itallows current to flow easily in one direction, but severely restricts current from flowing

in the opposite direction

Diodes are also known as rectifiers because they change alternating current (AC) intopulsating direct current (DC) Diodes are rated according to their type, voltage, andcurrent capacity.[10]

Diodes have polarity, determined by an Anode (positive lead) and Cathode (negative

lead) Most diodes allow current to flow only when positive voltage is applied to theanode A variety of diode configurations are displayed in this graphic:

When a diode allows current flow, it is forward-biased When a diode is reverse-biased, itacts as an insulator and does not permit current to flow.

Strange but true: The diode symbol's arrow points against the direction of electron flow.Reason: Engineers conceived the symbol, and their schematics show current flowingfrom the positive (+) side of the voltage source to the negative (-) It is the same

convention used for semiconductor symbols that include arrows—the arrow points in thepermitted direction of "conventional" flow, and against the permitted direction of electronflow

A digital multimeter's diode test diode produces a small voltage between the test leadsenough to forward-bias a diode junction Normal voltage drop is 0.5 V to 0.8 V Theforward-biased resistance of a good diode should range from 1000 ohms to 10 ohms.When reverse-biased, a digital multimeter's display will read OL (which indicates veryhigh resistance).[10]

Diodes are assigned current ratings If the rating is exceeded and the diode fails, it mayshort and either a) allow current to flow in both directions and b) halt current fromflowing in either direction

2.7 Resistance

Definition:

Resistance is an electrical quantity that measures how the device or material reducesthe electric current flow through it.

The resistance is measured in units of ohms (Ω)

If we make an analogy to water flow in pipes, the resistance is bigger when the pipe isthinner, so the water flow is decrease

● Calculation:

The resistance of a conductor is resistivity of the conductor's material times theconductor's length divided by the conductor's cross-sectional area [11]

Where: R is the resistance in ohms (Ω).

ρ is the resistivity in ohms-meter (Ω × m)

l is the length of the conductor in meter (m)

A is the cross-sectional area of the conductor in square meters (m2)

Calculation with Ohm’s Law

Where: R is the resistance of the resistor in ohms (Ω).

V is the voltage drop on the resistor in volts (V).

I is the current of the resistor in amperes (A).

Temperature effects of resistance

The resistance of a resistor increases when temperature of the resistor increases

R2 is the resistance at temperature T2 in ohms (Ω).

R1 is the resistance at temperature T1 in ohms (Ω)

α is the temperature coefficient.

Series/ Parallel Circuit

In fact, in order to read the value of a resistor, in addition to the manufacturer printing itsvalue on the component, a common convention is used to read the resistance value andother necessary parameters The value is calculated in units of Ohm

2.8 Shunt resistor

A shunt is an electrical device that generates a low-resistance path for an electricalcurrent This enables the current to flow to an alternative point in the circuit Shunts mayalso be referred to as ammeter shunts or current shunt resistors

Shunt resistors are commonly used to measure high currents, with the low levels ofassociated resistance Shunting literally translates as diverting or following a force along

a set path

There are several instances in which the measurement of current will be required.Common applications include over-current protection, 4-20mA systems, battery charging,and H-bridge motor control The application of the Ohm’s law equation allows the level

of voltage and current flow to be measured in amperes This requires the positioning of aresistor in parallel with the ammeter There is a resulting division of current, enabling themeasurement of the amperage level

Figure 2.17 Shunt resistor [12]

2.8.1 Electrical shunts in circuit

There are various ways of measuring the electrical current flowing through a circuit.However, the most common method is to make an indirect measurement, identifying thelevel of voltage across a precision resistor with reference to Ohm’s law The resultingvoltage drop will correspond directly with the current which passes through the circuit.The correct identification of this voltage drop will enable you to gauge the magnitude ofthe current flow [13]

A high level of care should be taken over the positioning of the shunt within the circuit It

is usual to place the shunt as close to the ground as possible when there is shared groundbetween the circuit and the measurement device This allows for the protection of theammeter against the common mode voltage, which might otherwise cause damage andmisleading results It will be necessary to isolate the shunt from the ground or incorporate

a voltage divider for protection inside the ungrounded leg

See the diagram below for help identifying the different components of a shunt:

2.8.2 Shunt working principle

The electrical shunt is a device that enables the current to pass through or be diverted past

a set point in the circuit through the creation of a low-resistance path Some metersfeature in-built precision current shunts and allow measurements to be taken in terms of

DC current and Watts There are also electrical shunts that measure the flow of DCcurrent

The Ohm’s law formula is applied as follows:

This equation is specific to the voltage (V) across the resistance (R in ohms) beinggenerated as a result of the resistance and current (I in amps) circulating through theresistance As an example, a current shunt with resistance of 0.002 ohms and current of

30 Amps will result in the generation of 0.002 x 30 = 0.06 volts or 60 mV (millivolts).You can assess the voltage drop across the shunt by integrating a current shunt within acircuit set up for measurement The assessment of the current shunt resistance will allowfor the calculation of current measurement in accordance with the Ohm’s law calculation.Ohm’s law can also be used in calibration of the current shunt resistance

Common applications of the shunt resistor include:

● Measurement of current circulating through a battery and monitoring of powergeneration

● Redirection of high frequency noise (this requires a shunt featuring a capacitator)before the signal reaches circuit elements

● Installation within a DC connect enclosure featuring a negative conductor betweenthe batteries and inverter

● Overload protection in control devices including battery chargers and powersupplies

You might use the types of shunts highlighted in this table:

Table 2.2 Shunt resistor types

200 mV

Converting digitalpanel meters with199.9mV full-scaledeflection intoammeters

Gilgen Muller &

Chauvin Arnoux

Plate Shunt 100 mV10 A to a rating of 10A withMeasuring currents up

a high level ofaccuracy

There is a difference between the technical limitations of the shunt resistor and standardresistor Shunt resistors allow for high levels of precision, offset against a minimal ohmicvalue Kelvin connection is recommended to achieve such high precision Thisconnection avoids issues such as lead resistance and sensitivity

There are a variety of reversible and irreversible factors that may have a bearing on thevalue of a shunt resistor The associated mechanical, electrical, and thermal loads meanthat there is long term stability and irreversible change in resistance The TemperatureCoefficient of Resistance (TCR) is expressed in ppm/oC and corresponds with the driftresulting from the cooling or heating of the transistor due to the fluctuation in ambienttemperature The level of power that the resistor must dissipate is expressed in terms ofthe Power Coefficient of Resistance (PCR) or ppm/W

Electrical shunts are typically used to protect the speed controller from a load that draws

an excess current or limits the speed of the attached motor It is possible to increase the

speed of the controller by disconnecting the shunt from the sense line The sense line willthen have to be connected to the ground There will not be any voltage drop, so the speedcontroller will generate as much power as possible However, this could be dangerous ifthe load placed upon the controller transistors is too great.

A high precision current shunt may also be used in the bench testing of equipment Thistype of current shunt can be used in combination with a voltmeter for assessment of thecurrent level flowing through the circuit The use of a sensitive voltmeter will mean thatthere is a good degree of safety assured in the measurement of larger currents than may

be achieved with a standard multimeter

2.9 IC A7840

The HCPL-7840 isolation amplifier family was designed for current sensing in electronicmotor drives In a typical implementation, motor current flow through an external resistorand the resulting analog voltage drop is sensed by the HCPL-7840 A differential outputvoltage is created on the other side of the HCPL-7840 optical isolation barrier Thisdifferential output voltage is proportional to the motor current and can be converted to asingle-ended signal by using an Op-Amp as shown in the recommended applicationcircuit

Since common-mode voltage swings of several hundred volts in tens of nanoseconds arecommon in modern switching inverter motor drives, the HCPL-7840 was designed toignore extremely high common-mode transient slew rates The high CMR capability ofthe HCPL-7840 isolation amplifier provides the precision and stability needed toaccurately monitor motor current in high noise motor control environments, providing forsmoother control (less "torque ripple") in various types of motor control applications

The product can also be used for general analog signal isolation applications requiringhigh accuracy, stability, and linearity under similarly severe noise conditions For generalapplications, we recommend the HCPL-7840 (gain tolerance of /- 5%) The HCPL7840utilizes sigma delta (S-D) analog-to-digital converter technology, chopper stabilizedamplifiers, and a fully differential circuit topology fabricated using Avago Technologies’0.8 mm CMOS IC process Together, these features deliver unequaled isolation modenoise rejection, as well as excellent offset and gain accuracy and stability over time andtemperature This performance is delivered in a compact, auto insertable, industrystandard 8-pin DIP package that meets worldwide regulatory safety standards (Agullwing surface mount option #300 is also available)

2.9.1 Feature [14]

● 15 kV/ms Common-Mode Rejection at VCM = 1000 V

● Compact, Auto-Insertable Standard 8-pin DIP Package

● 0.00025 V/V/ degrees C Gain Drift vs Temperature

● 0.3 mV Input Offset Voltage

● 100 kHz Bandwidth

● 0.004% Nonlinearity

● Worldwide Safety Approval: UL 1577 (3750 Vrms/1 min.) and CSA (pending),IEC/EN/DIN EN 60747-5-2 (option 060 only)

● Advanced Sigma-Delta (S-D) A/D Converter Technology

● Fully Differential Circuit Topology

● 0.8 mm CMOS IC Technology

2.9.2 Applications

● Motor Phase and Rail Current Sensing

● Inverter Current Sensing

● Switched Mode Power Supply Signal Isolation

● General Purpose Current Sensing and Monitoring