simulation and implementation of fpga based three phase ...signal. three hall sensors a, b, and c...

Simulation and Implementation ofFPGA based three phase BLDC drive

for Electric Vehicles

A.Bharathi sankar1 and Dr.R.Seyezhai21Research scholar,

Renewable Energy Conversion Laboratory,Department of Electrical & Electronics Engineering,

SSN college of Engineering Chennai, Tamilnadu, [email protected],

2Associate Professor,Renewable Energy Conversion Laboratory,

Department of Electrical & Electronics Engineering,SSN college of Engineering Chennai, Tamilnadu, INDIA.

[email protected].

December 30, 2017

Abstract

Objective : This paper describes about the FPGA con-trol of Brushless DC (BLDC) machines for electric vehicleapplications.

Methods : BLDC motors are generally powered bya three-phase voltage source inverter which is controlledbased on the rotor position feedback. In this work, theelectronic commutation is implemented on FPGA as it pro-vides greater flexibility and higher resources for implement-ing control algorithms compared to other digital controllers.

Findings : A model of the BLDC motor is simulated,and its controller is implemented on a FPGA system inMATLAB environment.

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 815-829ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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Novelty : A prototype of three-phase inverter alongwith the FPGA control is implemented for BLDC motorand the results are verified.

Keywords: Brushless Direct Current Motor, Field Pro-grammable Gate Array, Voltage Source Inverter.

1 INTRODUCTION

The block diagram of the control system for the BLDC motor drivesystem is shown in Figure 1. The three-phase inverter is usuallyresponsible for the electronic commutation and current regulation.For the six-step commutation current control with star connectedBLDC motor winding and no neutral connection, the inverter cur-rent flow is restricted to two of the three phases. This leads to theDC link and phase current to be equal in magnitude1,2.

Figure 1: BLDC Motor Control System

The inverter consists of two switches one in upper leg and theother in lower leg, which conducts based on the rotor position infor-mation. Pulse width modulation current controllers are typicallyused to regulate the actual machine currents in order to match therectangular current reference waveforms as shown in Figure 2.

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International Journal of Pure and Applied Mathematics Special Issue

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Figure 2: Back EMF and current waveform of BLDC motor drivesystem.

Each of the upper side switches is always chopped for one 120◦

degree interval and the corresponding lower switch is always turnedon per interval. The freewheeling diodes provide the necessarypaths for the current to circulate when the switches are turnedoff during the commutation intervals 3,4.

There are two types of sensors for the BLDC drive system: acurrent sensor and a hall position sensor. In six-step commutationcurrent control, the dc link current is measured instead of the phasecurrent as they are equal. For current sensor, shunt resistor in serieswith the inverter, is used. The Hall-effect position sensors typicallyprovide the rotor position information needed to synchronize thestator excitation with rotor position in order to produce a constanttorque. The rotor magnets are used as triggers for the hall sensor.A transistor logic-compatible pulse with sharp edges and high noiseimmunity is produced by signal conditioning circuit for connectionto the controller 5,6.

2 SENSORED CONTROL OF BRUSH-

LESS DC MOTOR

Brushless DC motor consists of a permanent magnet rotor and awound field stator which is connected to a power electronic switch-ing circuit. This drive system is based on the rotor position, and it

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is obtained at fixed points typically every 60 electrical degrees forsix-step commutations of the phase currents. Moreover, the perma-nent magnets produce an air gap flux density distribution that isof trapezoidal in shape and results in trapezoidal back-EMF wave-forms. Brushless DC motors use electric switches to realize currentcommutation, and thus continuously rotate the motor 7,8. Theseswitches are usually connected in a three-phase bridge structure fora three-phase BLDC motor and the block diagram is shown in Fig-ure 3.

Figure 3: Sensored control of three-phase brushless DC motor.

Figure 4: BLDC motor drive along with typical phase current andhall signal.

A three-phase BLDC motor requires three Hall sensors to de-tect the rotors position. These hall sensors are placed 120 degree

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interval from each other and it provides the required digital signals(high/low signal) for the controller to determine the rotor positionin intervals of 60 electrical degrees 9,10. Figure 4 shows the Brush-less DC motor drive along with typical phase stator current and hallsignal. Three Hall sensors A, B, and C are mounted on the stator at120◦ degree intervals, while the three phase windings are in a starformation. For every 60◦ degree rotation, one of the Hall sensorschanges its state; it takes six steps to complete a whole electricalcycle as shown in Table: 1.In synchronous mode, the phase currentswitching updates every 60degree. However, every one signal cyclemay not correspond to a complete full mechanical revolution. Thenumber of signal cycles to complete a one mechanical rotation isdetermined by the number of each rotor pole pairs. Every rotorpole pair requires one signal full cycle in one mechanical rotation.So, the number of signal cycles is equal to the rotor pole pairs11−15.Conduction table of commutation sequence of BLDC is shown inTable1. Based on the rotor position, the conduction table of VSI isshown in Table: 2.

Table 1: Conduction table of commutation sequence of BLDCHall Sensors Motor Phase

HA HB HC PH A PH B PH C1 1 0 OFF + -0 1 0 - + OFF0 1 1 - OFF +0 0 1 OFF - +1 0 1 + - OFF1 0 0 + OFF -

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Table 2: Conduction table of VSI based on rotor position of BLDCHALL

AHALL

BHALL

CPWM

1PWM

2PWM

3PWM

4PWM

5PWM

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0 0 1 0 0 0 1 1 0

0 1 0 1 0 0 0 0 1

0 1 1 1 0 0 1 0 0

1 0 0 0 1 1 0 0 0

1 0 1 0 1 0 0 1 0

1 1 0 0 0 1 0 0 1

3 SIMULATION RESULTS

The simulink model of the sensored control of BLDC motor is shownin Figure 5. Table 3 shows simulation parameter for three-phaseBLDC drive.

Figure 5: Simulink model of the sensored control of BLDC drive

Table 3: Simulation parameters Three-phase BLDC driveSimulation parameters ValuesThree phase voltage

source inverterVin = 24 V

BLDCP= 1KW, V= 36V,

N= 3000 rpm, Pole = 16

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The simulated results (rotor speed, electromagnetic torque, sta-tor current and back EMF) of BLDC motor are shown in Figures[6-9] respectively.

Figure 6: Rotor speed for BLDC drive.

Figure 7: Motor torque for BLDC drive.

Figure 8: Stator current for BLDC drive.

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Figure 9: Back EMF for BLDC drive.

Figure 10: Stator current T.H.D for three-phase BLDC drive.

Figures 6 & 7 show that the BLDC motor speed is settled 3000rpm and torque is about 4 Nm. Figures 8 & 9 show that the BLDCmotor stator current and back emf voltage. Figure 10 shows thatthe stator current T.H.D which is about 18.21%.

4 HARDWARE IMPLEMENTATION

OF BLDC DRIVE

The hardware prototype of the proposed three-phase BLDC driveis developed using IGBTs as the power device, along with isolationand driver circuit. The gating pulses were obtained from a Xilinx-FPGA SPARTAN 6 whose input is supplied from the hall sensors.

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The block diagram of the hardware setup is shown in Figure 11.

Figure 11: Block diagram of the hardware setup for BLDC Drive.

The hardware set-up for three BLDC drive with FPGA SPAR-TAN 6 is shown in Figures 12.Table 4 shows motor specification forthree phase BLDC drive.

Figure 12: FPGA SPARTAN 6 and Three phase BLDC drive.

The hardware prototype presents the development of Xilinx-FPGA SPARTAN 6 as a control circuit for VSI is shown in fig 13.Six I/O lines of SPARTAN 6 are used as PWM output lines. VHDLlanguage is used to model the PWM switching strategies and Xil-inx ISE 14.1 software is used as a simulation and compiler tool.Generation of PWM pulses is obtained with Xilinx-FPGA SPAR-TAN 6 board is shown in Figure 14. The VHDL code successfullyembedded in FPGA.

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Figure 13: FPGA Commutation logic for BLDC.

Figure 14: Gating pattern of VSI for each phase (RYB).

Figure 15: Output voltage of three-phase BLDC drive.

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Figures 15 shows that output voltage of three-phase BLDC withthe following testing conditions: starting voltage: 4.6 V, minimumspeed: 50 rpm, maximum voltage: 36 V,2500 rpm, high frequency- 10 KHz and low frequency-50 Hz

Figure 16: Experimental verification of a duty cycle & motor speedof BLDC.

Figure 17: Experimental values of motor speed and stator currentVs duty cycle for BLDC drive.

Figure 16 shows that with the prototype developed using FPGAcontrol, a motor speed measured was 1672 rpm which is verified ex-perimentally. Figure 17 shows experimental values of actual speedand stator current with respect to duty cycle for BLDC drive. Fromthe results, it is found that FPGA based sensored control of BLDCemploying voltage source inverter provides a better performance in

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terms of fast response and good speed regulation compared to theclassical controller system.

5 CONCLUSION

This paper has presented the sensored control of BLDC motor us-ing FPGA. By suitably developing the electronic commutation inFPGA, appropriate line to line voltage output was obtained forthe three-phase voltage source inverter. Therefore, implementingthe control using Field Programmable Gate Array for a BrushlessDC motor gives a better output and improved flexibility in design.The performance of the BLDC drive can be further improved byemploying multilevel inverters.

6 Acknowledgement

The authors wish to thank the management of SSN College of En-gineering for funding this research work.

References

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simulation and implementation of fpga based three phase ...signal. three hall sensors a, b, and c...

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