Research On EMC In The Motor Drive System Based On A Three-Phase Four-Leg Inverter

With the continuous progress of science and technology, power electronics technology is developing rapidly and semiconductor switching device is showing better performance. Power electronic devices become more and more popular as special power supply for industry and daily life.In power drive field, with the development of research in AC drive system, DC drive system is gradually being replaced. AC motor owns many advantages, for example: simple structure, easy maintenance, low failure rate etc .PWM inverter can supply power with adjustable frequency and voltage by PWM technique. Powered by PWM inverter, the AC drive can achieve the same dynamic performance as DC drive.It is a typical application of power electronics technique in energy conservation and environmental protection.The market prospection is also tremendous.PWM inverter is widely used in the power drives and brings many benefits, but its negative effects are also increasingly serious. Three phase PWM inverter output high-frequency PWM pulses which cause the differential mode interference.The three-phase three-bridge unbalance topology produce the common mode voltage on load-neutral point,which is also called motor rotor shaft voltage in PWM inverter-Motor system.Those interference voltage will not only affect the drive control system and danger peripheral equipment, the motor itself may also be damaged by bearing current.In this paper, a three-phase four-bridge topology is analysised and discussed. Based on the SPWM and SVPWM modulation, several improved modulation strategies have been designed and compared.Finally, a 300W three-phase four-leg inverter is designed for AC motor. The simulation and experiments proved that the improved modulation strategies with three-phase four-leg topology can effectively suppress the common mode voltage on the rotor shaft of induction motor.