Unity Power Factor Control In Sensorless Permanent Magnet Synchronous Machine Drive Systems

Among alternating-current electrical machines, permanent magnet synchronous machines (PMSMs) have received much interest in both industry and academia. These machines are preferred because of high power density, high efficiency, high controllability, reliable operation, and good torque-speed response. However, there are still problems in both theory and practice as an emerging technology.The criterion of choosing the appropriate control method usually involves cost, ease of implementation, and waveform quality. In order to reach this, the vector control method using position/speed sensors is usually used for permanent magnet synchronous machine drive systems, which is becoming an industry standard. However, for economic reasons, reducing the cost of the drive system is still under investigation, and one obvious way to achieve this aim is to design the low cost controller. The main objective of this thesis is to develop for an effective and low-cost control method for a permanent magnet synchronous motor drive system based on both the unity power factor control and the sliding mode observer approaches. The unity power factor control approach is based on controlling the d-axis stator current component and the sliding mode observer is designed using a saturation function instead of conventional signum function. The simulation results, hardware implementation, and experimental evualution presented to verify the proposed method is correct and effective. The main research and innovative achievements are as follows:Firstly, the mathematical models of a PMSM in three different coordinates are discussed in detail. The description of the operation principles and control schemes of the two methods have been presented. Two simulation models for the vector control and direct torque control methods have been established and the results of simulation tests have been presented to show the performance of vector control and direct torque control methods in various conditions. The advantages and limitations of the two methods are discussed. A comparative study of these methods is presented. Based on the comparative results, the vector control is considered due to excellent steady state performance.Secondly, normally, an inverter having idealized switches called as ideal inverter is almost universally considered as the simulation study because of its simplicity. However, in practice, the voltage source converter has the nonlinear forward voltage-current characteristic of the power electronic devices (the power diodes and IGBTs). As a results, the performance of the nonlinear forward voltage-current characteristic of the power electronic devices lead to additional distortion of voltage source converter output voltages. Thus, a model of a real two-level three-phase voltage source converter including forward voltage drop of the IGBTs/Diodes is proposed and studied in the MATLAB/Simulink. Space vector PWM techniques applied to both the real and ideal voltage source converters were analyzed and studied. In addition, a model of a current source converter with its space vector PWM technique for high-power medium voltage drives have also presented and studied. A comparative study of the voltage source converter and current source converter is presented.Thirdly, three d-axis stator current control methods, namely, the unity power factor control, constant stator flux-linkage control, and zero d-axis current control methods along with sliding mode observer approach using a saturation function instead of conventional signum function applied to the PMSM drive system have been analyzed and studied. A MATLAB/Simulink model for the sensorless PMSM drive system with the unity power factor control, constant stator flux-linkage control, and zero d-axis current control methods have been developed. Simulation results show that the unity power factor control method can achieve unity power factor. The constant stator flux-linkage control method can achieve near unity power factor. The d-axis current control method achieves lowest unity power factor. Based on the results obtained, an effective and low-cost control method to a PMSM drive system based on both the unity power factor control and the sliding mode observer approaches was proposed. Simulation results show that the proposed method is correct and effective.Finally, the experimental platform of the PMSM drive system was designed and implemented. The hardware circuit, system operation flowchart, and algorithm of the experimental platform have been analyzed in detail. The proposed method was implemented using a digital signal processor TMS320F2808control circuit and successfully tested on the surface mounted PMSM at various speed operating conditions. It is shown that the proposed method provides satisfactory performances and power factor values are close to unity (greater than0.94).