Research On The Rotor Position Identification Of Sensorless Control Of PMSM

Permanent Magnet (PM) machine is widely used in both industrial and civilian applications because of the advantages which it inherits, such as high power density, high power factor, high efficiency and high reliability. Also, the maintaining of PM machine is convenient due to the brushless rotor structure. But the risk of irreversible demagnetizing of PM under high temperature is a tough problem. What's more, the expensive position sensor hinders the application of PM machine in some areas. Position senseless control is important for industrial applications because it can reduce price and enhance reliability of the system, especially suitable for the occasions which the position sensors can not be installed, i.e. very high-speed machine, micro machine and under-water machine. Based on the rotor PM structures, the PM machine can be classified to Surface Mounted (SM) machine and Interior Permanent Magnet (IPM) machine. The SM machine has relative wide used because it is cheaper. But the low saliency ratio brings more difficulty in senseless control than IPM machine. In this paper, the senseless control strategy is developed on SM machine, but the method can also be applied to IPM machine.In Chapter 1, the review of PM machine senseless control strategy has been done. Mainly includes the research state of this strategy both at home and abroad; the advantage of senseless control method in SM machine and its prospects in industrial applications. Then, the senseless control technologies of PM machine at zero speed, low speed and high speed has been categorized and compared.In Chapter 2, the mathematic model of PM machine has been derived in detail, based on it, one of the initial position identification methods has been studied. This method includes two steps:firstly, inject immobile sine wave voltage to standstill coordinate, the rotor initial position can be get from an off line look up table; second step is injecting the same voltage to d axis, the positive direction of d axis is obtained by judging the amplitude of current of both positive and negative cycles. This method has high precision which is meaningful in many applications.Chapter 3 introduced a kind of rotor position identification algorithm at low speed. In this method, three-phase high frequency voltage vector has been injected into coordinate; the rotor position is identified by analyzing three-phase current amplitude. This method is based on the presupposition that the current response will change while the rotor position changes because of the variation of flux saturation of three phases. The novelty of this part is a kind of new method of high frequency voltage injection has been proposed. This technology is called carrier wave based high frequency voltage injection. The high frequency voltage vector is got by using 120 degree delayed (not the usual one with 0 degree) three-phase PWM carrier wave. But because of the voltage fundamental wave component is increasing with the rising of speed, the high frequency voltage signal will be hard to detect, so this method is only suitable for low speed operation.In Chapter 4, the technology of senseless control at high speed has been developed. Assuming the d axis voltage component is zero at steady state. A closed loop of position is designed by using a phase-locked loop (PLL) with the input and output are position and speed respectively. On the other hand, a kind of unit power factor control strategy has been studied. This method needs no machine parameters, so the programming can be simplified.In Chapter 5, the PM machine field weakening control method at ultra high speed and its applications in senseless control system has been studied. For getting higher speed than rated speed, the negative d axis current should be applied to PM machine for the controllable terminal voltage based on the inverter. The SVPWM over modulation method has been developed; the needed negative excitation current is analyzed based on the operation time of zero vector. Also, the applicability of proposed field weakening strategy in senseless control is discussed.At last, the experimental platform is introduced. This full digital control system is based on TI TMS320F28335, all of the speed control loop, position loop and position identification algorithm are implemented by software. The programming flow chart is given. The results prove the proposed control strategy can be come to pass by commercial DSP chip.