Field Oriented Control of PMSM Using SVPWM Technique

Transcription

1 Field Oriented Control of PMSM Using SVPWM Technique E.PRASAD 1 B.SURESH 2, K.RAGHUVEER 3 Abstract: The principle of space vector pulse width modulation (SVPWM) was introduced and implementing for PMSM. Applying SVPWM technique to the PMSM and obtaining the speed, torque, current responses when load was increased. The mathematical model of PMSM is analyzed by neglecting the saturation of the electric motor ferrite core, turbulent flow and hysteresis loss in electric motor. Assuming that the current in the electric motor is symmetrical three phase sinusoidal current and the system model of FOC vector control has-been established. The control system has been simulated by MATLAB/SIMULINK. Simulation results show that the model is effective, and the method provides a frame of reference for software and hardware designs Index Terms:-Modeling and simulation, permanent magnet synchronous motor (PMSM), space vector pulse width modulation (SVPWM). NOMENCLATURES L d - d-axis self inductance L q - q-axis self inductance i d - d-axis current V d - d-axis voltage i q - q-axis current V q - q-axis voltage J - Inertia B - Friction L - Self inductance Ψ s - Stator flux linkage Ψ f - Field flux linkage Τ - Output Torque hysteresis Ф - Output flux hysteresis δ - Load angle Va,Vb,Vc - Three Phase Voltage R s - Rotor resistance P - Pair of poles T e - Developed torque ω r - rotor electrical speed V dc - DC Voltage S A,S B,S C - Switching states 1. Introduction Some different types of techniques used for speed control of PMSM as shown in the figure 1. Digital control techniques of AC motors, such as the space vector pulse width modulation (SVPWM), have been developed with wide range industrial applications. The SVPWM was brought forward in the 1980 s, specifically for the frequency varying and speed regulation of AC motors. It controls the motor based on the switching of space voltage vectors, by which an approximate circular rotary magnetic field is obtained. In other words, the inverter is controlled to output an appropriate voltage waveform. This forms the basis of the magnetic flux linkage tracking pulse width modulation The basis of SVPWM is different from that of sine pulse width modulation (SPWM). SPWM aims to achieve symmetrical 3-phase sine voltage waveforms of adjustable voltage and frequency, while SVPWM takes the inverter and motor as a whole, using the eight fundamental voltage vectors to realize variable frequency of voltage and speed adjustment. If the voltage drop across stator resistance is ignored, when the stator windings are supplied with perfect sine waveform voltages, a rotating voltage space vector is formed with constant magnitude and hence the air gap flux density rotates with constant speed and circular track SVPWM is achieving by implementing the zero voltage space vectors in the phase modulation wave of sine pulse width modulation SPWM. Sine pulse width modulation is easy for hardware implementation but it is not easy for digital implementation. Low utilization ratio of the voltage. Chances of short circuit at DC bus of the inverter. Page 39

2 Global Journal of Advanced Engineering Technologies, Vol1, Issue ISSN: Scalar Baced Voltz/Hertz Direct variable frequency control Rotor Flux Oriented Vector Baced field oriented control Direct torque Control Stator Flux Oriented Indirect Closed loop Flux and Torque control Figure 1: Some Common Control Techniques Uses for PMSM 2. Field Oriented Control Field Oriented Control was invented in the beginning of 1970 s and it demonstrates that an induction motor or synchronous motor could be controlled like a separately excited dc motor by the orientation of the stator mmf or current vector in relation to the rotor flux to achieve a desired objective. Field Oriented Control usually refers to controllers which maintain a 90 0 electrical angle between rotor and stator field components. Systems which depart from the 90 0 orientation are referred to as field angle control or angle control. The performance of FOC is comparable to DC Machine. It produces less ripples but the system is more complex and less robust compares to DTC. The Field Orientated Control (FOC) consists of controlling the stator currents represented by a vector. This control is based on projections which transform a three phase time and speed dependent system into a two co-ordinate (d and q co-ordinates) time invariant system. These projections lead to a structure similar to that of a DC machine control. Field orientated controlled machines need two constants as input references: the torque component (aligned with the q co-ordinate) and the flux component (aligned with d co-ordinate). As Field Orientated Control is simply based on projections the control structure handles instantaneous electrical quantities. This makes the control accurate in every working operation (steady state and transient) and independent of the limited bandwidth mathematical model. The FOC thus solves the classic scheme problems, in the following ways the ease of reaching constant reference (torque component and flux component of the stator current) the ease of applying direct torque control becausee in the (d,q) reference frame the expression of the torque is: By maintaining the amplitude of the rotor flux at a fixed value we have a linear relationship between torque and torque component (i Sq ). We can then control the torque by controlling the torque component of stator current vector. Page 40

3 3. Principle of SVPWM SVPWM aims to generate a voltage vector that is close to the reference circle through the various switching modes of inverter. Fig. 2 is the typical diagram of a three-phase voltage source inverter model. For the on-off state of the three-phase inverter circuit, every phase can be considered as a switch S. Here, S A (t), S B (t) and S C (t) are used as the switching functions for the three phases, respectively. one, it is composed of V4, V6, V0 and V7 and can be obtained by Vout = T4V4/ T+T6V6/T (3) The eight on-off states of inverter are listed in Table.1 Table 1: Eight on-off states of the inverter Inver ter state /3-1/3 2/ /3 2/3-1/ /3 1/3 1/ /3-1/3-1/ /3-2/3 1/ /3 1/3-2/ Figure.2: Typical diagram of a three-phase inverter. The space vector of output voltage of inverter can be expressed as,, Where V dc is the DC bus voltage of inverter and α=ej120. If we express the on state of the upper-arm with 1 and the off state with 0, the on-off states of three phases have eight combinations, correspondingly forming eight voltage space vectors, as shown in Fig. 3. T refers to the operation times of two adjacent non-zero voltage space vectors in the same zone. Both V0(000) and V7(111) are called the zero voltage space vector, and the other six vectors are called the effective vector with a magnitude of 2Vdc/3. For example, when the output voltage vector V is within zone Figure 3 Diagram of voltage space vector. 4. SIMULINK Simulation of SVPWM Based on the principle of SVPWM, the simulation models for generating SVPWM waveforms mainly include the sector judgment model, calculation model of operation, time of fundamental vectors, Page 41

4 Figure.4 FOC system structure diagram of the PMSM based on SVPW Calculation model of switching time, and generation model of SVPWM waveforms. 4.1 Sector Judgment For applying the technology of SVPWM, firstly it is requested to determine the sector which the voltage vector is within. Considering that the expression of vector in the α-β coordinate is suitable for controlling implementation, the following procedure is used for determining the sector. When Vβ > 0, A = 1; when 3Vα Vβ > 0, B=1; when 3Vα+Vβ < 0, C = 1. Then, the sector containing the voltage vector can be decided according to N = A+2B+4C, listed in Table 2. Table 2: The sector containing the voltage vector versus N Sector Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ N Fig.5 shows the corresponding model. 4.2 Calculation of Operation Times of Fundamental Vectors Table 3 lists the operation times of fundamental vectors against N, where t 1 and t 2 refer to the operation times of two adjacent non-zero voltage space vectors in the same zone. Fig.7 shows the calculation model of XYZ, Figure 6 Simulation model of XYZ Where Z=T( 3Vα+Vβ)/(2Vdc), Y=T(3Vα+Vβ)/(2Vdc), X=2T [Vβ/(2Vdc)] The sum of t 1 and t 2 must be smaller than or equal to T (PWM modulation period). The over saturation state must be judged: Table 3 calculation of t 1 t 2 Sector N I II III IV V VI t 1 Z Y -Z -X X -Y t 2 Y -X X Z -Y -Z Fig.5. Model of sector judgment. Page 42

5 if t 1 + t 2 > T, take T 1 = t 1 [T/( t 1 + t 2 )], T 2 = t 2 [T/( t 1 + t 2 )].figure 6 shows the simulation model of acting time of basic voltage vector. Table 4 calculation of t aon t bon t con Sector number I II III IV V VI t aon T b T a T a T c T c T b t bon T a T c T b T b T a T c t con T c T b T c T a T b T a 4.4 The production of PWM signal Figure.7 Illustrates the SIMULINKbased model. The PMSM simulation model of closed loop system can be built by connecting the above-mentioned submodels. Because the measured rotor angle and speed are in mechanic degrees, but in the actual coordinate transform in the electrical angle is adopted, the measured angle and speed are multiplied by the number of pole-pairs of the motor. Figure.8 The simulation model of the inverter at the switch time 4.3 Generation of SVPWM Waveform The relation between N and switch operation times is shown in Table 4 and realized in Fig. 8, where Ta=(T T1 Tm)/4, Tb=Ta+T1/2, and Tc=Tb+Tm/2, Tcm1, Tcm2 and Tcm3 are the operation times of the three phases respectively. Figure 9 the simulation model of the inverter at the switch time Figure.9 Generation model of SVPWM waveforms Table 5: Major parameter of a PMSM Magnetic flux linkage d-axis inductance q-axis inductance Armature resistance 0.3Wb 8.5mH 8.5mH 0.5ohms Page 43

6 B. THE MODULE OF SVPWM PRODUCTION 5. Simulation Results Set the motor speed at 500 rad/s, PWM cycle T=0.001S. At time 0s, the electrical motor no-load start up, at time 0.03s, the load increases to 3 Nm. Simulation time is 0.06s, and then the simulation waveform shows as follows: Simulation results are in accord with the performance characteristic of PMSM, which proves the accuracy of the SVPWM algorithm and the control model, and provides theory basis for actual design of the control system. Figure 10 SVPWM simulation model Figure.12 The speed response when load is increased Figure.11 The current response when load is increased Figure.13 The torque response when load is increased Page 44

7 REFERENCES [1] XU Jun-Feng, FENG Jiang-Hua, XU Jian-Hua. Control policy of permanent magnetism synchronous motor summery. The electrical trasimissionof Locomotive, 2005, pp [2] CHENG Min-Jun. Research of high performance magnetism synchronous motor vector velocity modulation system.the master s degree paper in Zhe Jiang Industrial university, 2006, pp [3] Li Chuan-Fang, Li Feng, QU Ji-Sheng and so on. Thechnology characteristic and optional method of the space vector polse-duration modulation(svpwm).shan Dong university Journal, 2005, pp [4] SUN Ye-Shu, ZHOU Xin-Yun, LI Zheng-Ming. SIMULINK simulation of space vector PWM.Farm machinery reseach, 2003, pp [5] TEAXS INSTRUMENTS, Space-Vector PWM with TMS320C24x Using Hardware & Software Determined Switching Patternts, 2000, pp [6] Ke Song, Wei guo Liu. Permanent Magnet Synchronous Motor Field Oriented Control and HIL Simulation. IEEE Vehicle Power and Propulsion Conference, Harbin, 2008, pp.4-6. E.prasad 1 was born in He received Diploma in EEE from S.B.T.E.T., Hyderabad in the year He graduated from SRI VENKATESWARA UNIVERSITY,TIRUPATI in the year in Presently he is persuing his M.Tech with Power And Industrial Drives Specialization in J.N.T.U. ANANTAPUR. A.P., INDIA. He is working in the area of PMSM. His area of interest is machines, power electronics and Power Semiconductor Drives. B.Suresh 2 was born in He graduated from ANNA UNIVERSITY,CHENNAI in the year in Presently he is persuing his M.Tech with Power electronics Specialization in J.N.T.U. HYDERABAD. A.P., INDIA. He is working in the area of PMSM. His area of interest is machines, power electronics and Power Semiconductor Drives. K.Raghuveer 3 was born in 1987.He received B.Tech in Electrical and Electronics Engineering from JNTU, Anantapur, A.P.in 2008.He is pursuing M.Tech in Power Electronics and Electrical Drives in JNTU, Anantapur,A.P His research interests include Power Electronics and Drives. Page 45