Overvoltage Protection And Control Of High Voltage Motor Drives

The advantages of Neutral Point Clamped (NPC) three-level high voltage motor drives are more and more outstanding for the improvement of power electronics towards high voltage and high power. There are a lot of researches and applications of NPC motor drives. But the withstand voltage of power electronic device is still finite, which not only limits the overvoltage tolerant capability, but also presents challenges on overvoltage protection. To solve the problem, this dissertation researches on overvoltage protection and control of high voltage motor drives.For the different causes of overvoltage, the effects and behaviors are also different in the high voltage motor drives. Detailed analysis of each causes of overvoltage can make the effects more clearly and give strong theoretical support for overvoltage protection design of high voltage motor drives. Considering the characteristics of ZnO varistor which is widely used in power system overvoltage protection, this dissertation chooses it as the overvoltage protection device for NPC three-level high voltage motor drives.To solve the problem of low withstand voltage of single power electronic device and high residual voltage of ZnO varistor, this paper presents a method by protecting the inverter part of high voltage motor drives based on analysis of each kind of overvoltage. If the inverter part is not overvoltage, the whole system is not overvoltage either. The withstand voltage is detailed analysis based on switch states of three-level motor drives. Calculations of how to choose the ZnO varistors is given based on practical project parameters. Experimental results show that the designed ZnO varistors meet the theoretical analysis quite well. Simulation results proved that the designed ZnO varistors can protect NPC three-level high voltage motor drives from overvoltage effectively.Motor drives are ideal starting device for motors. The calculation of motor drives starting frequency is given to satisfy the starting requirement of motors and reduce the starting current. Simulation results based on practical motor parameters proved that the calculation of starting frequency is correct.Multiphase motors have a lot of advantages include low voltage input and high power output. This paper presents a novel topology of multiphase motor drives. It is not need the phase-shifting transformer, which reduces the system volume. In addition, the withstand voltage and power requirements of power electronic device is significantly reduced. Moreover, comparing with the traditional multiphase motor drives, it is easy to implement modularization and redundancy, and enhance system transplant. Simulation results and low voltage nine-phase motor drives experimental results are both proved that the novel topology of multiphase motor drives is correct and feasibility.Detailed calculation of harmonic magnetomotive force based on nine-phase motor is given. Furthermore, considering space harmonic magnetomotive force effects, harmonic electromagnetic torque has been analyzed. The detailed expression of harmonic electromagnetic torque has been give. It can be the theoretical support for multiphase motor design and multiphase motor drives control strategy optimization.