Real Time Speed Control of Induction Motor Using New Generation DSP Controller

Transcription

1 Real Time Speed Control of Induction Motor Using New Generation DSP Controller Gopal L.Jat 1, Kartar Singh 2, Abhay Mahajan 3, Ms. Shimi S.L. 4 1,2,3 Research Scholar, Department of Electrical Engineering, NITTTR Chandigarh 4 Assistant Professor, Department of Electrical Engineering, NITTTR Chandigarh Abstract This paper is concerned with real time implementation of voltage/frequency (V/F) speed control method with the help of digital signal processor (DSP). This method is helpful in controlling the speed of induction motor drive which is fed via voltage source inverter. The speed control technique is implemented using a new generation digital signal processor TMS32F28335 with a high sampling rate to make it possible that it achieve good dynamics. The algorithm is designed using MATLAB/SIMULINK and converted into C language using Code Composer Studio (CCS) environment. The sine pulse width modulation (SPWM) control algorithm is proposed for 3 phase 3- leg IGBT voltage source inverter. effortless in implementation, with lesser harmonics contents in the output. II. DSP BASED INDUCTION MOTOR CONTROL Digital Signal Processors (DSP) provides high speed, high resolution and more accurate control of induction motor in various load conditions. Keywords Digital Signal Processor (DSP), Induction Motor with Loader, Intlegant Power Module (IPM) and FLUKE Power Quality Analyzer. I. INTRODUCTION In the past few years the combination of high performance digital signal processors (DSP) and power electronics devices have provided a superior control in the field of electrical machines. High performance electric motor drives are viewed as a major part of advanced control and operation. Controlling of ac drives is a tedious job so mostly ac motors are generally controlled by complex algorithms which can be achieved by microprocessors or high speed controllers with the help of fast switching power converters. DSP based method is found to be most satisfactory and also possess the ability to perform the associated signal calculations easily and quickly. Control of voltage, frequency and current is required in variable speed applications for ac machines drives. Speed of induction motor can be determined with the help of frequency of supply system. Some applications require variable speed and this kind of control is obtained with the help of variable speed drive (VSD). The VSD system comprises of power converter, the electrical machine and the control system. Voltage source inverter (VSI) is also used for speed control induction motor in modern drive applications. The output terminal voltage of inverter can be controlled if we control the input terminal voltage of inverter and that is done by voltage control inside the inverter PWM (Pulse width modulation). The PWM approach is useful in controlling voltage and it also optimizes the harmonics by manipulating switching control in inverter. The various PWM techniques are voltage or current control, carrier or non carrier based control method, feed forward or feedback methods so on. The efficiency of induction motor can also be increased by using a better PWM technique. Induction motor drive with SPWM technique will gives high efficiency. SPWM is preferred for IGBT inverter as it is Fig.1 Block Diagram of DSP based induction motor control Setup The DSP based induction motor drive system consist hardware devices for instance induction motor, rectifier, inverter, eddy current load setup, torque indicator and DSP board with sensing unit. The PWM signal is generate by comparison of modulated signal and carrier signal as shown by Fig. 2. Amplitude (High) (Low) Modulated Signal Carrier Signal PWM.1.2 Time (Sec) Fig.2 PWM Generation by Comparison of Modulation signal with Carrier Signal For the generation of desired SPWM pulses the sinusoidal signal with frequency F m and voltage V m is compared with high frequency triangular carrier with frequency F c and voltage V c to operate gate drive for voltage source inverter. The variation in output voltage amplitude and frequency of inverter is totally depends on sinusoidal (modulated) signal /16/$ IEEE

2 Real Time Speed Control of Induction Motor Using New Generation DSP Controller 91 because the triangular (carrier) signal has fix amplitude and constant frequency. The carrier signal frequency is used to decide the switching frequency of PWM signal. The power quality parameter (RMS voltage-current, harmonics, transients, active and reactive power) of output voltage of inverter is depends on switching frequency of PWM signal. In other word we can say that the modulated signal is used to control motor speed and torque whereas the carrier signal is concern on switching frequency and power quality issues. From Fig.2, it is clear that the pulse width is varies according to modulated signal and frequency is varies according to carrier signal. For realistic safety concern, dead bands have been injected to the ideal PWM waveform. The dead-band is given to protect the IGBTs at the instant of commutation by averting conduction overlap. The PWM signals are generated according to the speed feedback and control algorithm. The actual speed of motor is sensed by quadrature encoder pulse (QEP) speed detector. In this proposed plan the V/Hz control is utilized, so speed of induction motor is controlled by the stator voltage and frequency in such a manner that the air gap flux is constantly kept up at the desired value at the steady state. III. SYSTEM DESIGN AND SIMULATION The simulation is designed according to hardware specification and control algorithm. The V/F-SPWM model is executed progressively equipment setup utilizing DSP- MATLAB interface. The MATLAB target support package (TSP) instrument tool has many modules for easy programming or user friendly design. The descriptions of some use full module are given below in Table 1. The real time speed of motor is sense by QEP sensor which gives pulses of 12.8 KHz at 15 RPM speed. The QEP sensor gives two quadrature signals, i.e. QEPA and QEPB. The real time QEP encoder output has been shown in Figure 4. Fig. 4 Output Obtain from QEP Sensor at 14 RPM Fig.4 shows that the phase angle between QEPA and QEPB is approx 9 and signal frequency is approx 12.2 KHz, which indicate 14 RPM speed. The frequency of QEPA signal is capture by ecap module as capture count. The frequency of QEP sensor and DSP clock must be synchronising for speed measurement so the given formula is evaluated for accurate speed measurement. Speed of motor (RPM) = (1) TABLE 1. TI C28X3X DSP CHIP SUPPORTED LIBRARY MODULE DESCRIPTION Module C28x epwm C28x ecap C28x GPIO DI C28x GPIO DO C28x SCI Description Configure one or more pairs of pulse width modulators (PWMs) (for 6 PWM signal) Configure with a rotary incremental encoder to get position, direction, and speed information (for capture digital signal) Configure general purpose input-output as digital input Configure general purpose input-output as digital outputs Transfer data from target via serial communications interface (SCI) to host Fig.5 MATLAB/SIMULINK Model of ecap Module The error between set and actual speed is given to the speed proportional integral (PI) controller. The PI controller is tune by trial and check method. The MATLAB/SIMULINK model of speed PI controller/regulator is shown in Figure 6. Fig.3 MATLAB/SIMULINK Model for DSP Based Speed Control of Induction Motor Using V\Hz Techniques Fig. 6 MATLAB/SIMULINK Model of PI-Controller The output of PI controller (pi_out) is used to generate desired sinusoidal signal. The control model is design in MATLAB/SIMULINK for generation of desired modulated (sinusoidal) signal. The all possible sample of sinusoidal

3 92 Innovative Applications of Computational Intelligence on Power, Energy and Controls with their Impact on Humanity (CIPECH-16) signal is store in memory as look up table. The frequency and amplitude of sinusoidal signal is control by frequency and amplitude modulation index (MI) respectively. The frequency modulation index of sinusoidal signal is derived by given derivation. Specified frequency of carrier signal (F c) = 1 KHz Rated frequency of sinusoidal signal (F m) = 5 Hz Required number of sample (n) = = = 2 (2) Available sample by DSP = 2 16 = Sample step count = Frequency step count = = = 327 (3) = =.218 So Frequency Modulation Index (MI f) =.218 The amplitude modulation index of sinusoidal signal is derived by given derivation. Available Maximum Amplitude of Sinusoidal signal = 375 Required Maximum Amplitude of Sinusoidal signal = 9% of Available Maximum Amplitude of Sinusoidal signal Required Maximum Amplitude of Sinusoidal signal = Required Maximum Amplitude of Sinusoidal signal = 3375 Amplitude step count = = = 2.25 So Amplitude Modulation Index (MI A) = 2.25 (4) (5) modulation index (MI f). So according to pi_out value sin variable is varies from to and generates variable frequency sinusoidal signal from lookup table. The desired amplitude of sinusoidal signal is acquired by pi_out and amplitude modulation index. Fig.8 shows that three sinusoidal signals each shifted by 12 o phase is generated by above model. Now this signal is use to generate desire PWM sequence. Amplitude Sin A Sin B Sin C Time (Sec.) Fig.8. Generated Sinusoidal Signal The high frequency (1 KHz) triangular carrier signal is generated by epwm module by up-down count mode. The nature of carrier signal is unidirectional and sinusoidal signal is bidirectional so they are not intersects in negative half cycle of sinusoidal signal. The problem is solved by biasing the sinusoidal signal with half of TBPRD value i.e. 375 for symmetrical complimentary PWM generation as shown in Fig.2. The MATLAB/SIMULINK model for PWM signal generation is shown in Fig.9. The MATLAB/SIMULINK model of sinusoidal signal generation is shown in Figure 7. Fig.9 MATLAB/SIMULINK Model of epwm Module for SPWM Signal Generation Fig.7. MATLAB/SIMULINK Model for Sinusoidal Signal Generation According to above derivation all available (65536) sample of one cycle of sin wave with zero phase and 12 o phase are store in lookup table A and lookup table B respectively. The output value of lookup table is depends on predefined sin variable. The sin variable is depends on pi_out and frequency In the practical implementation of the system, the PWM waveform creation is accomplished by the comparison between a time-base counter (TBCTR) value (the carrier signal) and instantaneous value of sinusoidal signal. The instantaneous value of sinusoidal signal is store in a countercompare register (CMPA). When time-base counter (TBCTR) is equal to CMPA in up count mode then it set the epwma register and clear in down count mode. To obtain the required PWM frequency, time-base period register (TBPRD) is needed to be determined. PWM frequency (f PWM) can be written as. TBPRD = As per the design requirement of the project and the DSP configuration, the specified PWM frequency (f PWM) is 1 KHz (6)

4 Real Time Speed Control of Induction Motor Using New Generation DSP Controller 93 and the clock frequency of system (fsysclkout) of the DSP F28335 is 15MHz. For convenience, CLKDIV and HSPCLKDIV is chosen to be 1. Based on equation (6), the value set in the time-base period register (TBPRD) can be obtained directly. TBPRD = TBPRD = = D The high frequency complimentary PWM drive signal epwma and epwmb are observed using Agilent DSO as shown in Fig.1. Fig.12. Hardware Setup of DSP Based IM Drives System TABLE II. SPECIFICATIONS OF THE INDUCTION MOTOR Fig.1. Complementary PWM Pulses Generated by epwma and epwmb Module The amplitude of drive signal was found to be 4.45 Volt with a frequency 1 khz. Motor Parameter Specification Power Type 1HP(.75kw) 4-Pole, Squirrel Cage Supply 3-ϕ, 415V ac, 5 Hz input Rated Current 1.8 Amp ( star connection ) Rated Speed and Torque 141 RPM and 5 Nm V. EXPERIMENTAL RESULT The experimental results for the proposed speed control schemes were successfully carried out in this paper. The dc link voltage of inverter is first set at 3 V by auto transformer for protection and safety purpose and then PWM is given to IGBTs. Table 3 shows the V/F ratio of proposed control method at various speeds. TABLE III. EVALUTION OF V/F AT VARIOUS SPEEDS Speed (RPM) Voltage (Volt) Frequency (Hz) V/F Ratio Fig.11. PWM Generation with Dead Band (2.6 µs) by epwm Module IV. HARDWARE IMPLEMENTATION The induction motor has been loaded by eddy current loader which is controlled by dc regulator. The strain gauge based torque sensor is sense accurate torque on motor shaft. The practical implementation is done on DSP based induction motor drive setup. The DSP TMS32F28335 board is connected to PC using JTAG emulator. The SCI transmit module transfer real time speed, torque and current values of motor to PC. The real time data are acquired from SCI receive module with the help of RS232 cable and plots in MATLAB/SIMULINK environment. Fig.13. Real Time Line Parameter Measurement of Motor at 14 RPM Using FLUKE Power Analyzer

5 94 Innovative Applications of Computational Intelligence on Power, Energy and Controls with their Impact on Humanity (CIPECH-16) TABLE IV. TIME RESPONSE ANALYSIS OF SPEED STEP RESPONSE No Load Full Load Delay Time Td Rise Time Tr Peak Time Tp Settling Time Overshoot (Sec) (Sec) (Sec) Ts(Sec) Mp(%) Fig.14. Real Time Line Voltage Trace of Motor at 14RPM using FLUKE Power Analyzer Table 3 shows that the V/F ratio is almost constant over large range of motor speed. The voltage and frequency has been measured by FLUKE power quality analyzer. The real time step and ramp response of motor speed at no load and full load are shown in Fig.15. The Step and ramp set commend is given by GPIO switch on DSP board. The real time current of motor is sense by hall-effect sensor and measured by DSP (using ADC module). All acquired data of DSP has been transmits to PC (MATLAB) using SCI module. The real time data are trace by MATLAB/SIMULINK and shown in given figure. Speed (RPM) Current (Amp) Set Speed Actual speed (No Load) Actual speed (Full Load) Time (Sec.) Fig.15. Real Time Step Response (14 RPM) of Motor Phase A Phase B Phase C Time (Sec) Fig.16. Real Time Three Phase Current of Motor The time response analysis of above results is carried out by Table 4. The result shows that the step response of motor at no load and full load has good dynamic response. The real time speed ramp response of motor at no load and full load are shown in Fig.17. The slop of ramp input is preadjusted by programming. Here the slop of ramp signal is set by 1 rpm/sec. The ramp speed output of motor increase linearly as input with constant drift called steady state error. The steady state error at no load and full load are 4.4% and 5.% respectively. 14 Set Speed Actual Speed (NO Load) 12 Actual Speed (Full Load) Speed (RPM) Time (Sec) Fig.17. Real Time Ramp Response of Motor The main drawback of V/Hz control technique is that it does not tracks the input at a range (-3 RPM). So this control technique is suitable for an application where the speed is required above 3 % of rated speed. VI. CONCLUSION This paper proposes DSP based real time speed control of induction motor. The design and implementation process of DSP based MATLAB/SIMULINK model for speed control of induction motor has been explained very clearly. The sinusoidal PWM (SPWM) signals are generated using the DSP processor (TMS32F28335) dead band is precisely programmed for three phase operation and the signals are given to inverter module. The DSP based system is found to be compact, user friendly and reduces complexity. The experimental results show that DSP based control schemes have good performance, higher control processor made the speed control of the motor most effective compared to other conventional techniques. Hardware implementation was validated with utilization of ongoing workshop module of MATLAB/SIMULINK and CCS environment. REFERENCES [1] Joachim Bocker and Shashidhar Mathapati, State of the Art of Induction Motor- Control, IEEE Conference on Electric Machines & Drives, Antalya, Vol. 2, pp , May 27. [2] L. ling and S. Mekhilef DSP Based Implementation of Adaptive Speed Controller for Three-phase Induction Motor, IEEE international conference, Vol 2, 29.

6 Real Time Speed Control of Induction Motor Using New Generation DSP Controller 95 [3] M Harsha Vardhan Reddy and V. Jegathesan, Open loop V/f Control of Induction Motor based on hybrid PWM with Reduced Torque Ripple, ICETECT 211, Karunya University. [4] Mi Ching and Jeng Hu Chen, A Practical Implementation of a Linear Induction Motor Drive Using New Generation DSP Controller, IEEE International Conference on Control Applications, Kohala Coast-bland of Hawai, Hawei, USA August 22-27, pp , [5] The MathWorks, Inc, Simulink- Dynamic System Simulation for Matlab (Natick, M A, USA, The MathWorks, Inc, 2). [6] Texas Instrument TMS32x28xx, 28xxx DSP Peripheral Reference Guide (SPRU566E), October 27 [7] Joachim Bocker and Shashidhar Mathapati, State of the Art of Induction Motor- Control, IEEE Conference on Electric Machines & Drives, Antalya, Vol. 2, pp , May 27. [8] L.ling and S. Mekhilef DSP Based Implementation of Adaptive Speed Controller for Three-phase Induction Motor, IEEE Confernce Vol.2,29 [9] M Harsha Vardhan Reddy and V. Jegathesan, Open loop V/f Control of Induction Motor based on hybrid PWM with Reduced Torque Ripple, ICETECT 211, Karunya University. [1] Mi Ching and Jeng Hu Chen, A Practical Implementation of a Linear Induction Motor Drive Using New Generation DSP Controller, IEEE International Conference on Control Applications, Kohala Coast-bland of Hawai, Hawei, USA August 22-27, pp , [11] The MathWorks, Inc, Simulink- Dynamic System Simulation for Matlab (Natick, M A, USA, The MathWorks, Inc, 2). [12] Texas Instrument TMS32x28xx, 28xxx DSP Peripheral Reference Guide (SPRU566E), October 27. [13] Jaswant Singh, Bindeshwar Singh, S. P. Singh, Ravi Chaurasia,Sulabh Sachan Performance Investigation Of Permanent Magnet Synchronous Motor Drive Using Vector Controlled Technique" 2nd International Conference on Power, Control and Embedded Systems,212. [14] Hong-Ming Chen, Jyh-Chyang Renn, Juhng-Perng S Electro-hydraulic position servo system Sliding mode controlvarying boundary layer International Journal of Advanced Manufacturing Technology Vol.26, pp [15] V. M. Yashasvi and B. Amarapur, Digital Signal Processing Based Speed Control of Induction Motor Drive System, No. 1, pp , 212. [16] H. A. Shah, DSP based Pulse Generation for Induction Motor Speed Control, Vol. 122, No. 14, pp. 1 5, 215.