Position Sensorless Control Of Permanent Magnet Brushless DC Motor Based On Indirect Inductance Method

Using certain method without position sensors, permanent brushless dc motor (PMBLDCM) can work well in both high-temperature& high-pressure and some place where position sensor can not be installed. So motor space can be saved and those expensive sensors cost can be cut with sensorless method. At the same time, the PMBLDCM has higher reliability. As a result, the study for the sensorless technology has been a hot topic in PMBLDCM.The key points of sensorless technology in PMBLDCM are to study a method which can detect rotor position accurately by simply method in whole speed range. After analyzing current sensorless methods of the PMBLDCM, it is found that those methods are successful at middle and high speed, but they often fail to detect rotor position at low speed when the back electromotive force(back-EMF) is small or zero. Therefore, how to detect rotor position at very low speed is the problem to be solved and the difficulty in sensorless control of PMBLDCM.Interior permanent magnet (IPM) rotor is typical salient structure, which helps to starting performance, over-load capacity. So IPM PMBLDCM is used widely in household and electric vehicle field. The sensorless control for IPM PMBLDCM is studied deeply in this thesis and primary achievements are in the following:First, after benefiting from exist sensorless schemes, such as the inductance method and the back-EMF method, a novel sensorless method, Indirect Inductance Method, is presented to solve the problem that it was very difficult to detect the rotor position at low speed. The method is proved to be independent to rotor velocity in whole speed scope by theoretical derivation and be successful to detect rotor position at very low speeds.Second, Indirect Inductance Method is modified to expand its application scope. For delta-connected PMBLDCM, it is proved that Indirect Inductance Method is also successful. Moreover, for widely used Y-connected PMBLDCM whose neutral point voltage can not be detected directly, the validity of improved new sensorless method is proved by theory inference and experimental results.Third, the inverter loss and torque ripple in PMBLDCM are very serious because H_PWM-L_PWM modulation is used in indirect inductance method. In order to overcome the shortcoming, the indirect inductance method will be switched to the back-EMF method considering armature reaction in which the H_PWM-L_PWM modulation is used when the motor speed is beyond a certain speed. Thus, The PMBLDCM is high efficient in whole speed field.In the end, a new initial rotor position estimation method is presented in the sensorless control. The novel method is based on the salient effect and magnetic saturation effect of the IPM PMBLDCM. The proposed method is successful at the standstill and 30 electrical angle resolution.