Drive System For Electric Vehicles-1.pdf

Drive System for Electric Vehicles Presented by

K Krishna Murthy, DGM – Power Electronics Ramesh Perla, Sr. Manager – Automation and Controls 2/21/2019

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Contents • Why electric vehicles (EV) • EV system and control • Motor control • Power Electronic Drive design • Summary

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Why Electric vehicles

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Electric Vehicles: Benefits & challenges Benefits

Opportunities

Zero pollution

Range

Fuel Cost

Charging time

Silent / low noise

Capital cost

Low maintenance

Charging infra

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Transport Sector Pollution

Ref: Electric mobility paradigm shift capturing the opportunities- TERI 2/21/2019

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Energy cost: IC Engine vs Electric motor

Fuel consumption (Min): 235g/Kwh Diesel density: 832 g/L KWh/L = 832/235 = 3.54 Diesel price: 72/L Energy cost / KWh: 72/3.6 = Rs. 20.33 (much higher compared to Electrical energy cost / KWh)

Mitsubishi S4S – DT 53Kw ICE 2/21/2019

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Electric vehicle System

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Battery Electric Vehicle: Types

Battery Electric Vehicle(BEV)

Series Hybrid Electric Vehicle 2/21/2019

Mild hybrid Electric Vehicle

Parallel Hybrid Electric Vehicle 8

Electric Vehicle Control System

Battery Charging

Driver Display Unit

Datalogging & Diagnostics

Battery

Vehicle control

Accelerator Brake Clutch

Regenerative Braking

Motor Drive

Auxiliary Loads

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Vehicle Control Logic: A,B,C # 1

Released

Released

Released

2

Pressed

Released

Released

3

Pressed

Released

Pressed

Action to be taken ¨¨¨¨¨¨¨¨¨ ¨¨¨¨¨¨¨¨¨ ¨¨¨¨¨¨¨¨¨

4

Change from Pressed to Released Released Change from Pressed to Pressed Released

Released

¨¨¨¨¨¨¨¨¨

Released

¨¨¨¨¨¨¨¨¨

Change from Pressed to Released Released

Pressed

¨¨¨¨¨¨¨¨¨

5 6

Accelerator

Brake

Clutch

¨¨

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Driver Display Unit (DDU)

Real-time updation at 500ms Data over serial port / CAN bus 2/21/2019

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Motor Control System

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Permanent Magnet Synchronous Motor (PMSM)

Pros

Cons

 Flat torque production till rated

 Availability of magnets

speed

 Cost

 Higher efficiency  Compact size

Motor rating: 10hp, RPM

Ref: http://empoweringpumps.com/ac-induction-motors-versuspermanent-magnet-synchronous-motors-fuji/

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HBL’s 50KW motor 13

PMSM winding type: Star vs Independent

For pure sine backEMF

 Back EMF(Ph-N): 120V / 1000 RPM  Vdc = 600V  Load current assumed to be zero

Nmax

Nmax 73.2% higher speed 2/21/2019

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PMSM winding topology: Star vs Independent Bemf wave 170 120 70 20 -30 0

50

100

150

200

250

300

350

-80 -130 -180 Phase U

Phase V

Phase W

UV

Pune sine BackEMF

VW

WU

15% third harmonic in backEMF  Vfund –max = 100V

 Vph –max = 100V

 Vph –max = 86.8 V

 Vrms = 70.7 V

 Vrms = 71.5 V

 RMS is 70.7% of peak

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16.5% higher RMS

 RMS is 82.4 % of peak

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PMSM Control: Utilizing 3rd harmonic

 Vdc = 600V  Back EMF(Ph-N): 120V / 1000 RPM Pune sine BackEMF

15% third harmonic in backEMF

Nmax

Nmax ~ 2 times

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PMSM Independent phase control • Better utilization of DC bus voltage • Current Imbalance need to taken care • More hardware

Ref: Control Strategies for Open-End Winding Drives Operating in the Flux-Weakening Region IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 9, SEPTEMBER 2014 2/21/2019

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Motor Control: Speed control system

dq0 to abc Transf ormati on

PI Controller

I0* i0

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Resolver

0

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Motor Control: Torque control system

Ref: Control Strategies for Open-End Winding Drives Operating in the Flux-Weakening Region, IEEE TRANSACTIONS ON POWER ELECTRONICS

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Motor Control: Unipolar modulation MOSFET is used as switch, the gate signal is ON for + Vdc and OFF for 0V S1

Switch pairs (S1, S4) and (S2, S3) are complementary (when one switch in a pair is closed, the other is opened)

S3

S4

S1

S2

S1 is on when Vsine > Vtri S4 is on when Vsine < Vtri S3 is on when -Vsine > Vtri S2 is on when -Vsine < Vtri 2/21/2019

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Motor Control: Rotor position sensing Stator

 Wide operating temperature range  withstands higher vibrations and shock loads  better suited for extremely harsh applications

Rotor Brushless frameless resolver

Open-loop position calculation: Excitation signal: Vr = V sin (ωt) Rotor Position: θ = Tan-1 (Vs/Vc)

 Not accurate with noisy signals

(Use excitation to identify quadrant of θ) 2/21/2019

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Motor Control: Rotor position sensing Resolver-to-Digital Converter (RDC) ICs:

Ref: PGA411-Q1 Resolver Sensor Interface by Texas Instruments

Ref: Design considerations for resolver-to-digital converters in electric vehicles by TI

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Motor Control: Finding Zero position

Alignment with d axis - schematic

Alignment with q axis - schematic

Finding zero position in independent phase control https://www.researchgate.net/publication/273944807

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Motor Control: Safety aspects • Dead-band time to avoid shoot through • Acceleration & deceleration limits • PI control output limits • Overload monitoring • Stator temperature • Drive temperature • DC bus Voltage

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Motor Control: Hardware implementation

Resolver

NI GPIC

NI 9607 NI 9683

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GPIC: General Purpose Inverter Control 25

Prototype hardware: sbRIO-9607

• 667 MHz Dual-Core CPU, 512 MB DRAM, 512 MB Storage,

sbRIO: Single-Board RIO

• Zynq-7020 FPGA for custom I/O timing, control, and processing programmable with LabVIEW FPGA (Field Programmable Gate Array • NI Linux Real-Time OS programmable with LabVIEW RealTime or C/C++ • 96 3.3 V DIO lines; Gigabit Ethernet, RS232 serial, CAN, and USB ports; 9 VDC to 30 VDC supply input • -40 °C to 85 °C local ambient operating temperature range

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NI 9683 - Mezzanine Card for NI sbRIO High-speed, high-bandwidth connector that provides direct access to the processor and digital I/O FPGA lines

IO details DI: 28 sourcing DI, 0~24V DC, 5 μs LV TTL DIO - 32, 3.3V DIO DO: 14 Half-bridge -source/sink 24 sinking DO, 0~24V DC, 50 μs 4-relay DO 0~30V sinking AI: 16ch, 12bit simultaneous,±5 V, 100KS/s 8ch, 12-bit scan type, 0~5, 1KS/s AO: 8ch, 12 bit, 0~5V, 1KS/s

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Motor controller validation

Drive commander

Dyno controller

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Voltage transducers

cRIO based DAQ

Current Transducers

COTS Drive

PMSM

Dynamometer

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Power Electronic Drive for Motor Control

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Motor Controller 1. Intermediate device between battery and motor 2. Performs two functions - Motor driving or Regenerative braking (battery charging) 3. It works as motor controller during normal operation 4. It charges the battery during brake operation

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EV Power flow - Electrical Schematic

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Motor controller Functional Flow sequence 1. Receives 24 VDC when ignition key is ON 2. Checks for 24 VDC health, i.e. it is with in specified range or not. 3. Checks for battery leakage fault signals, which are coming from leakage monitoring circuit (leakage to chassis). 4. Checks clutch, brake, throttle signals, all shall at normal position. 5. Checks resolver signals, motor and controller temperature, they shall be normal. 6. Checks input current, phase current, phase voltage, faults signals.

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Motor controller Function Flow sequence 1. Enables inrush current protection circuit. 2. Energizes DC path contactors if input is reached to specified level and disable inrush current protection 3. Sends ready to start status to ‘Driver Display Unit’ if observed no error. 4. Send fault/error status if observed during initial (power ON) health checks.

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Main components of the Motor controller 1. DC link capacitor 2. Switching devices 3. Controller 4. Driver for switching devices 5. Current sensors 6. Sensing circuits 7. Snubber capacitor

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DC link capacitor 1. The DC link capacitor is used at input of motor controller to decouple the effects of the inductance from the DC voltage source to the power bridge. 2. The bus link capacitor provides a low impedance path for the ripple currents associated with a hard switched inverter. 3. The ripple currents are a result of the output inductance of the load, the bus voltage and the PWM frequency of the inverter. 4. Capacitor value depends on bus voltage, winding inductance, PWM frequency

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Types of DC Link Capacitors 1. Aluminum Electrolytic Capacitor 2. Film Capacitor (Polypropylene)

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Electrolytic vs Film capacitors Description

Electrolytic

Film

Ripple current

Low

High

ESR

High

Low

Life expectancy (at 85 0C)

20,000 Hours (approx)

2,00,000 Hours (approx)

Dissipated watts as heating High losses

Low

Volume

Low

High

Conclusion: Film capacitor will be the best choice for DC link applications

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DC Link Capacitor Calculations

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DC Link Capacitor Ripple Current Calculations • When the switch is turned on, the voltage is applied across • The inductor L is defined as VL . The current in the • inductor L will integrate up at a rate that is determined by the • voltage and inductance as defined in the following; • VL = L (dI/dt)

(1)

• dI = VL/L dt

(2)

• Integrating with respect to t; • ∫ dI = ∫ VL/L dt

(3)

• ΔI = VL/L ∫ dt

(4)

• ΔI = (VL) (Δt) /L

(8)

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DC Link Capacitor Ripple Current Calculations • Where L is the winding inductance and Δt is the switch • on time. • When the top switch is turned on (and corresponding • bottom switch also); • VL = Vbus - Vout

(9)

• Substituting in equation (9) into (8) yields; • ΔI = (Vbus - Vout ) (Δt) /L

(10)

• Vout = d X Vbus, Substituting in equation (10); • ΔI = (Vbus – (d Vbus )) (Δt) /L 2/21/2019

(11) 40

DC Link Capacitor Ripple Current Calculations • The switch on time can be defined as; • Δ t = d PWM period

(12) or

• Δ t = d 1/PWM Frequency

(13)

• Let’s define the PWM frequency as f. so therefore; • Δ t = d 1/f

(14)

• Substituting in equation (14) into (11) yields; • ΔI = (Vbus – (d X Vbus )) X (d )/(f X L)

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(15)

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DC Link Capacitor Ripple Current Calculations • Simplifying equation (15); • ΔI = d X (1– d) X Vbus / (f X L)

(16)

• As per above equation, Maximum ΔI will occur when d is equal to 0.5 or 50% duty cycle. • Substituting in 0.5 for d in equation (16); • ΔI 0.5t = 0.5 X (1– 0.5) X Vbus / (f X L) • ΔI 0.5t = (0.25 X Vbus ) / (f X L)

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(17) (18)

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DC link Capacitor value Calculation • • • • • • • • • • •

Now that the ripple current in the bus link capacitor is known, it is now simple to calculate the resulting bus link capacitor ripple voltage. A capacitor’s current (iC) is expressed as; iC = C (dV/dt) (19) Where C is the input capacitance, and dV/ dt is the rate of change in voltage with respect to time. Rearranging the equation and solving for dV yields; dV = (iC / C) dt (20) Since iC = ΔI 0.5t iC = ΔI 0.5t = 0.25 Vbus / (f L) (21)

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DC link Capacitor value Calculation • dV = [0.25 Vbus / (f L C)] dt

(22)

• ∫ dV = ∫ [0.25 Vbus / (f L C)] dt

(23)

• ΔV0.5t = [0.25 Vbus / (L C)] ∫ (1/f ) dt

(24)

• Since 1/f = t; • ΔV0.5t = [0.25 Vbus / (L C)] ∫ (t ) dt

(25)

• ΔV0.5t = [0.25 Vbus / (L C)] (Δt2 / 2 )

(26)

• ΔV0.5t = [(Vbus / (8 L C )] (Δt2 )

(27)

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DC link Capacitor value Calculation  Using the Δt for a 50% duty cycle;  Δt = 0.5 t = 1 / (2 f )  ΔV0.5t = Vbus / (32 L C f 2 )

(28) (29)

 Where ΔV0.5t is the maximum peak to peak ripple voltage across the bus link capacitor at a 50% PWM duty cycle, Vbus is the bus voltage, L is the phase inductance in Henries, C is the bus link capacitance in Farads, and f is the PWM frequency in Hertz.  C = Vbus / (32 L ΔV0.5t f 2 )

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Switching devices Types of devices 1. SI MOSFET 2. IGBT 3. SIC MOSFET

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Comparison between different Devices Parameter

IGBT

SI MOSFET

SIC MOSFET

Cost

Low

High

Very High

Voltage rating

Available up to 1700 V

Available up to 900 V

Available up to 1200 V

Current rating

Available up to 1000 Amps

Available up to 90 Amps

Available up to 400 Amps

Switching losses High

Medium

Low

Conduction losses

Depending on Vce sat

Depending on Rdson

Depending on Rdson

Lead time

Low

High

Very high

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Switching Device selection • SI MOSFET will be better device for motor controllers operating with below 300 VDC or below 10 KW power. • IGBT will be better device for motor controllers operating with above 300 VDC or above 10 KW power. • SIC MOSFET will be suitable for motor controllers for input operating voltage up to 700 VDC or power up to 100 KW, but device cost will be 10 times higher than IGBT and lead times are 25- 30 weeks. • IGBT will be the better device for motor controller application (< 10 KW)

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Parameters for Switching device selection • Voltage rating • Current rating (collector) • Turn ON & Turn OFF Energy losses • Pulse current rating • Collector - emitter saturation voltage (vcesat) • Freewheeling diode forward voltage drop • Freewheeling diode recovery time. • Operating junction temperature. • Switching times (ton, toff). • Input capacitance, gate voltage, gate charge 2/21/2019

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Power losses Device losses can be broken down into: • Switching device (IGBT) 1. Switching losses (Turn On and turn OFF) 2. Conduction losses • Free wheeling diode 1. Conduction losses 2. Reverse recovery losses 2/21/2019

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Device losses calculation IGBT losses • IGBT conduction losses = 0.5 ((Vceo x (Ipk/4)) + Ro x (Ipk2/4)) + m x Cosθ (Vceo x (Ipk/8) + Ro (Ipk2/(3Xπ)))

• IGBT switching losses ((Eon+Eoff)x Ipk x Fsw x Vdc)/(π x Vnom x inom)

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Device loss calculation • Free wheeling diode losses • Conduction losses 0.5 ((Vdo x (Ipk/4)) + Rd x (Ipk2/4)) + m x Cosθ (Vdo x (Ipk/8) + Rd (Ipk2/(3Xπ)))

• Reverse recovery losses (Erec x Ipk x Fsw x Vdc)/(π x Vnom x inom)

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Device loss calculation • Total losses per device = IGBT conduction + IGBT switching + Diode conduction + Diode reverse recovery

• Power losses/controller = Total device losses X number of devices

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Thermal Design • Junction temperature of the device will increase due to Power dissipation (posses). • To operate IGBT safely, It is necessary not to allow the junction temperature to exceeds specified junction temperature. • Proper thermal engineering/Cooling method shall be provide to maintain junction temperature at below specified limit. • Cooling method - Heat sink with natural or forced cooling (air/liquid).

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Thermal Design • Heat sink thermal resistance can be calculated by: Rθja= (Tj – Ta)/total power losses Rθja = Rθjc+ Rθcs+ Rθsa Where: Tj = Junction temperature Ta = operating ambient temperature Rθja = Junction to ambient thermal resistance Rθjc = Junction to case thermal resistance Rθcs = Case to heat sink thermal resistance Rθsa = Heat sink to ambient thermal resistance 2/21/2019

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Thermal Design • Example: Tj = 100◦ C Ta = 50◦ C Rθjc = 0.1◦C/W Rθcs = 0.1◦C/W Power losses = 150 W Rθsa = ((100 – 50)/150) – 0.1 – 0.1 = 0.13◦C/W

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Thermal Design • Heat sink thermal resistance can be calculated by: • Natural cooling: Rθsa = 1/(heat sink surface area x 0.008 x sqrt (heat sink length))

• Forced cooling: Rθsa = 1/(heat sink surface area x 0.011 x sqrt (heat sink length x (LFM/100)))

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IGBT driver • It receives PWM signals (3.3 V) from NI/DSP board. • Generates isolated 15 V PWM signals with increasing driving capability. • It also monitors Collector –emitter saturation voltage, generates error signal and shut down the PWM signals if voltage is above the specified limit. It protects the IGBT from shoot through/over currents.

• Gate drive current can be calculated by: • I drive = Qg/Tr 2/21/2019

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Snubber circuit • It can protect the device (IGBT) from high voltage surges, generated during turn-off time. • Film capacitor, which is connected as close as to IGBT, works to bypass the high frequency surges. • Snubber capacitor value can be calculated by: •

C = (L x Io2)/(Vsurge – Vbus)

•

L = Circuit wiring parasitic inductance

•

Io = Collector current.

•

Vsurge = Snubber capacitor peak voltage

•

Vbus = input bus voltage.

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Validation of DC link & Snubber capacitors • Performance of the selected devices can be validated by Double pulse test

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Double pulse Test method 1.Connect the switching device and motor winding as shown in the diagram 2.Turn ON (from 10 us to 90 % of the PWM signal time period) – Turn OFF (10 us) - Turn ON (10 us) – Turn OFF the switching device. 3.For ex: if switching frequency is 12 KHz, T = 1/f = 83 us. 4. Initial Turn ON time shall vary from 10 to 75 us (0.9 X 83) with 10 us per step. 5. Collector to emitter voltage and collector current shall be monitored. 6. Voltage and current shall not above the device safe operating limits.

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Double pulse test Results. Without snubber capacitor

With snubber capacitor

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DSP/NI Controller • It is the major component of the motor controller. • It generates PWM signals to drive the motor as per information received from throttle. • It also generates PWM signals to charge the battery during brake operation. • It communicates with driver display unit with speed, RPM, battery health, sub-components/modules health information. • It continuously monitors the sub-module/components health, turn off the motor driving if observed any error.

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Sensing circuits • Input voltage: for input power calculations, turn OFF the controller if voltage is beyond the specified limit. • Input current: for input power calculations, turn OFF the controller if current is beyond the specified level. • Switch current: to disable the controller if current is above the specified level. • Throttle : for speed and phase current (Iq) • Clutch: to disable the controller when clutch is operated,

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Sensing circuits • Brake: to disable the controller and enable the regenerative braking system when brake is pressed. • Resolver signals: to generate motor drive signals as per position. • Motor winding temperature: to disable the controller if temperature is above the specified limit. • Controller temperature: to disable the controller if temperature is above the specified limit.

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Sensing circuits • Pressure: to disable the drive if pressure in the brake cycler is below the specified limit. • Phase currents: for torque control • Cooling system: to disable the controller if cooling system is not working.

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Regenerative braking System • Regenerative braking system will enable when brake is pressed. • During regenerative braking: •

- Controller disables the motor driving signals.

•

- Power circuit will act as active frond end rectifier (boost)

•

- Motor will act as alternator

•

- Controller will enable the regenerative braking only

• •

when speed of the motor is above the specified level - It will control the charging current by control the turn

•

ON time of the switching device.

•

- Controls the charging current as per motor speed.

•

- Regeneration will stop if speed is below the specified limit.

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Regenerative braking system Block diagram

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Motor controller assembly

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Summary • Electric vehicles has far better energy costs • PMSM has flat torque characteristics and well suited for EV application • PMSM has better efficiency than Induction Motor • Independent phase control of PMSM increases the speed range of vehicle. • DC link capacitor and snubber capacitor are critical for switching device protection • Regenerative braking system harnesses energy and increases mileage 2/21/2019

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Thank you

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