Volume 118 No. 16 2018, 815-829 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu ijpam.eu Simulation and Implementation of FPGA based three phase BLDC drive for Electric Vehicles A.Bharathi sankar 1 and Dr.R.Seyezhai 2 1 Research scholar, Renewable Energy Conversion Laboratory, Department of Electrical & Electronics Engineering, SSN college of Engineering Chennai, Tamilnadu, INDIA. bharathisankar.1987@gmail.com, 2 Associate Professor, Renewable Energy Conversion Laboratory, Department of Electrical & Electronics Engineering, SSN college of Engineering Chennai, Tamilnadu, INDIA. seyezhair@ssn.edu.in. December 30, 2017 Abstract Objective : This paper describes about the FPGA control of Brushless DC (BLDC) machines for electric vehicle applications. Methods : BLDC motors are generally powered by a three-phase voltage source inverter which is controlled based on the rotor position feedback. In this work, the electronic commutation is implemented on FPGA as it provides greater flexibility and higher resources for implementing 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 in MATLAB environment. 1 815
Novelty : A prototype of three-phase inverter along with the FPGA control is implemented for BLDC motor and the results are verified. Keywords: Brushless Direct Current Motor, Field Programmable Gate Array, Voltage Source Inverter. 1 INTRODUCTION The block diagram of the control system for the BLDC motor drive system is shown in Figure 1. The three-phase inverter is usually responsible for the electronic commutation and current regulation. For the six-step commutation current control with star connected BLDC motor winding and no neutral connection, the inverter current flow is restricted to two of the three phases. This leads to the DC link and phase current to be equal in magnitude 1,2. Figure 1: BLDC Motor Control System The inverter consists of two switches one in upper leg and the other in lower leg, which conducts based on the rotor position information. Pulse width modulation current controllers are typically used to regulate the actual machine currents in order to match the rectangular current reference waveforms as shown in Figure 2. 2 816
Figure 2: Back EMF and current waveform of BLDC motor drive system. Each of the upper side switches is always chopped for one 120 degree interval and the corresponding lower switch is always turned on per interval. The freewheeling diodes provide the necessary paths for the current to circulate when the switches are turned off during the commutation intervals 3,4. There are two types of sensors for the BLDC drive system: a current sensor and a hall position sensor. In six-step commutation current control, the dc link current is measured instead of the phase current as they are equal. For current sensor, shunt resistor in series with the inverter, is used. The Hall-effect position sensors typically provide the rotor position information needed to synchronize the stator excitation with rotor position in order to produce a constant torque. The rotor magnets are used as triggers for the hall sensor. A transistor logic-compatible pulse with sharp edges and high noise immunity is produced by signal conditioning circuit for connection to the controller 5,6. 2 SENSORED CONTROL OF BRUSH- LESS DC MOTOR Brushless DC motor consists of a permanent magnet rotor and a wound field stator which is connected to a power electronic switching circuit. This drive system is based on the rotor position, and it 3 817
is obtained at fixed points typically every 60 electrical degrees for six-step commutations of the phase currents. Moreover, the permanent magnets produce an air gap flux density distribution that is of trapezoidal in shape and results in trapezoidal back-emf waveforms. Brushless DC motors use electric switches to realize current commutation, and thus continuously rotate the motor 7,8. These switches are usually connected in a three-phase bridge structure for a three-phase BLDC motor and the block diagram is shown in Figure 3. Figure 3: Sensored control of three-phase brushless DC motor. Figure 4: BLDC motor drive along with typical phase current and hall signal. A three-phase BLDC motor requires three Hall sensors to detect the rotors position. These hall sensors are placed 120 degree 4 818
interval from each other and it provides the required digital signals (high/low signal) for the controller to determine the rotor position in intervals of 60 electrical degrees 9,10. Figure 4 shows the Brushless DC motor drive along with typical phase stator current and hall signal. Three Hall sensors A, B, and C are mounted on the stator at 120 degree intervals, while the three phase windings are in a star formation. For every 60 degree rotation, one of the Hall sensors changes its state; it takes six steps to complete a whole electrical cycle as shown in Table: 1.In synchronous mode, the phase current switching updates every 60degree. However, every one signal cycle may not correspond to a complete full mechanical revolution. The number of signal cycles to complete a one mechanical rotation is determined by the number of each rotor pole pairs. Every rotor pole pair requires one signal full cycle in one mechanical rotation. So, the number of signal cycles is equal to the rotor pole pairs 11 15. Conduction table of commutation sequence of BLDC is shown in Table1. Based on the rotor position, the conduction table of VSI is shown in Table: 2. Table 1: Conduction table of commutation sequence of BLDC Hall Sensors Motor Phase HA HB HC PH A PH B PH C 1 1 0 OFF + - 0 1 0 - + OFF 0 1 1 - OFF + 0 0 1 OFF - + 1 0 1 + - OFF 1 0 0 + OFF - 5 819
Table 2: Conduction table of VSI based on rotor position of BLDC HALL HALL HALL PWM PWM PWM PWM PWM PWM A B C 1 2 3 4 5 6 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 shown in Figure 5. Table 3 shows simulation parameter for three-phase BLDC drive. Figure 5: Simulink model of the sensored control of BLDC drive Table 3: Simulation parameters Three-phase BLDC drive Simulation parameters Values Three phase voltage source inverter Vin = 24 V BLDC P= 1KW, V= 36V, N= 3000 rpm, Pole = 16 6 820
The simulated results (rotor speed, electromagnetic torque, stator 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. 7 821
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 3000 rpm and torque is about 4 Nm. Figures 8 & 9 show that the BLDC motor stator current and back emf voltage. Figure 10 shows that the 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 drive is developed using IGBTs as the power device, along with isolation and driver circuit. The gating pulses were obtained from a Xilinx- FPGA SPARTAN 6 whose input is supplied from the hall sensors. 8 822
International Journal of Pure and Applied Mathematics 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 SPARTAN 6 is shown in Figures 12.Table 4 shows motor specification for three phase BLDC drive. Figure 12: FPGA SPARTAN 6 and Three phase BLDC drive. The hardware prototype presents the development of XilinxFPGA 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. VHDL language is used to model the PWM switching strategies and Xilinx ISE 14.1 software is used as a simulation and compiler tool. Generation of PWM pulses is obtained with Xilinx-FPGA SPARTAN 6 board is shown in Figure 14. The VHDL code successfully embedded in FPGA. 9 823
International Journal of Pure and Applied Mathematics 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. 10 824
Figures 15 shows that output voltage of three-phase BLDC with the following testing conditions: starting voltage: 4.6 V, minimum speed: 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 speed of BLDC. Figure 17: Experimental values of motor speed and stator current Vs duty cycle for BLDC drive. Figure 16 shows that with the prototype developed using FPGA control, a motor speed measured was 1672 rpm which is verified experimentally. Figure 17 shows experimental values of actual speed and stator current with respect to duty cycle for BLDC drive. From the results, it is found that FPGA based sensored control of BLDC employing voltage source inverter provides a better performance in 11 825
terms of fast response and good speed regulation compared to the classical controller system. 5 CONCLUSION This paper has presented the sensored control of BLDC motor using FPGA. By suitably developing the electronic commutation in FPGA, appropriate line to line voltage output was obtained for the three-phase voltage source inverter. Therefore, implementing the control using Field Programmable Gate Array for a Brushless DC motor gives a better output and improved flexibility in design. The performance of the BLDC drive can be further improved by employing multilevel inverters. 6 Acknowledgement The authors wish to thank the management of SSN College of Engineering for funding this research work. References [1] Jiancheng Fang, Haitao Li, and Bangcheng Han, Torque Ripple Reduction in BLDC Torque Motor With Non ideal Back EMF, IEEETransactions on power Electronics,Vol,27,NO,11,NOVEMBER 2012. [2] R.Goutham GovindRaju, S.JohnPowl, A.Sathishkumar and P.Sivaprakasam,Mitigation of Torque for Brushless DC Motor: Modeling and Control, International Journal of Scientific & Engineering Research Volume 3, Issue 5, May- 2012. [3] S.B.Ozturk,W. C. Alexander, and H. A. Toliyat, Direct torque control of four-switch brushless DC motor with non-sinusoidal back EMF, IEEE Trans. Power Electronics volume no. 2, pp. 263271, Feb. 2010. [4] T.N.Shi,Y.T.Guo, P.Song, and C.L.Xia, A new approach of minimizing commutation torque ripple for brushless DC motor 12 826
based on DC-DC converter, IEEE Trans. Ind. Electron., vol. PP, no. 99, pp. 19, 2010. [5] Bhim Singh, B P Singh, K Jain, Implementation of DSP Based Digital Speed Controller for Permanent Magnet Brushless dc Motor, IE(I) Journal-EL, Volume 84, pp. 16-21, June 2003 [6] Alecsa, B.; Onea, A.;, Design, validation and FPGA implementation of a brushless DC motor speed controller, Electronics, Circuits, and Systems (ICECS), 2010 17th IEEE International Conference on, vol., no., pp.1112-1115, 12-15 Dec. 2010. [7] Nikola Milivojevic, Mahesh Krishnamurthy, Yusuf Gurkaynak, Anand Sathyan, Young-Joo Lee and Ali Emadi,Stability Analysis of FPGA-Based Control of Brushless DC Motors and Generators Using Digital PWM Technique. IEEE Trans. Ind. Electron., vol. 56, no. 8, pp.3040-3049, Aug.2011. [8] Dagbagi, M.; Idkhajine, L.; Monmasson, E.; Charaabi, L.; Slama-Belkhodja, I.;, FPGA implementation of a synchronous motor real-time emulator based on delta operator, Industrial Electronics (ISIE), 2011 IEEE International Symposium on, vol., no., pp.1581-1586, 27-30 June 2011. [9] Ming-Fa Tsai; Tran Phu Quy; Bo-Feng Wu; Chung-Shi Tseng,Model construction and verification of a BLDC motor using MATLAB/SIMULINK and FPGA control, Industrial Electronics and Applications (ICIEA), 2011 6th IEEE Conference on, vol., n.,pp.1797-1802, 21-23 June 2011doi: 10.1109/ICIEA.2011.5975884. [10] H.S.Chuang and Y.-L.Ke, Analysis of commutation torque ripple using different PWM modes in BLDC motors, in Conf. Rec. IEEE Ind. Commercial Power Syst. Tech. Conf., 2009, pp. 16. [11] D.Chen and J.C.Fang, Commutation torque ripple reduction in PM brushless DC motor with non ideal trapezoidal back EMF, in Proc. CSEE, Oct. 2008, vol. 28, no. 30, pp. 7983. [12] W. Chen, C. L. Xia, and M. Xue, A torque ripple suppression circuit for brushless DC motors based on power DC/DC converters, in Proc. IEEE Ind. Electron. Appl. Conf., 2006, pp. 14. 13 827
[13] K. Wei, C. S. Hu, and Z. C. Zhang, A novel commutation torque ripple suppression scheme in BLDCM by sensing the DC current, in 36th IEEE Power Electron. Spec. Conf., 2005, pp. 12591263. [14] H. Lu, L. Zhang, and W. Qu, A new torque control method for torque ripple minimization of BLDC motors with un-ideal back EMF, IEEE Trans. Power Electron., vol. 23, no. 2, pp. 950958, Mar. 2008. [15] WaelA Salah, Dahaman Ishak, Khaleel and J. Hammadi PWM switching strategy for torque ripple minimization in BLDC motor Journal of Electrical Engineering, VOL. 62, NO. 3, 2011, 141146. 14 828
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