Research On Key Technical Issues Of High Power Multiphase Motor Drive System

Energy is both the material base of supporting development in human civiliza-tion and basic condition of modern society. With the development of human econo-my and society, people use more enery, especially fossil fuel, and are more restrict in energy consuming. Also, environment polution and global warming are serious problems today. Energy saving and environment protection are two issues in modern society.High power adjustable drive system (HP ASD) is very important in motor sav-ing system. The dessertation proposed some schemes in HD ASD key technical area, these schemes are descrbied briefly below.Based on multiphase technology, motor drive system can reach high power class by using power electronic device with present power rate, and the performance and fault tolerance of the drive system can be improved. Based on the vector space decomposition method, the dessertation decomposed the motor phase variables and inverter switch states into three subspace by using decomposition matrix, the motor model and inverter space vector are obtained. According to the sector of the refer-ence voltage falling in, two largest space vectors in d-q subspace are selected to synthesize the referce voltage. This PWM modulation method is identical to the combination function of the two identical inverters, which use two different sectors of the traditional three-phase modulation method. This simplifies the PWM modula-tion process and saving calculation time.It is difficult to start permenent magnet motor (PM motor) when it is still. In the dessertation, the dq model of PM motor at standstill was analyzed, and the starting method based on space vector reference voltage was proposed. The amplitude and position of reference voltage were setup by the control system. Keeping the ampli-tude of reference voltage constant, the control system rotated the reference volage. When reference voltage arrived some position, the PM motor can started. If the mo-tor cannot start, the control system increased the amplitudue of reference voltage and rotated it again. Repeating the same procedure, the control system can start the PM motor. Besideds, the dessertation also proposed another PM motor starting method which based on PM motor’s static starting torque. Both starting method proposed in the dessertation didn’t estatmate the rotor initial postion and started the PM motor with no load or full load.Based on classical M/T measuring speed method, the dessertation presented the synthesis measuring method of motor speed and rotor position (synthesis M/T method). Because of the counter numbers of code wheel are less compared to the encoder’s, the rising (fall) edges of code wheel’s output pulse may not align with the measuring time, the pulse counting is wrong, so there are errors in motor speed mearing and calculation. Synthesis M/T method pre-processed the pulse of encode output, dividing the pulse counting number in two parts, in which one part was inte-ger number, the same as the counting number of M/T method, another part was decimal fraction number. The decimal fraction number standed for misalign of the rising (fall) edge in code wheel’s output pulse and measuring time, and was used in motor speed calculation, hence, the errors in motor speed mearing and calculation were corrected. Meanwhile, with the decimal fraction number in pulse counting, the rotor postion also was measured.