Research On High-voltage Pulse Generator For Insulation Electrical Aging Test Of Inverter-fed Motor

Inverter-fed motors are extensively used in many fields such as people's livelihood engineering,industrial production and household electrical appliances because of its remarkable advantages of good speed regulation,easy to start and energy efficiency.It adopts pulse width modulation technique,and the output square impulses voltage has a steep rising edges along with high voltage amplitude and high repetition frequency.When the insulation system is subjected to continuous highfrequency and high-amplitude square impulses voltage,there will be a large amount of partial discharge and space charge inside the insulating materials,resulting in premature insulation failure.Therefore,the insulation aging mechanism,the insulation life assessment method and the testing equipment of the previous power frequency AC voltage are not applicable to the condition of pulse electric stress.In order to solve these problems,the methods of accelerating insulation aging by increasing pulse voltage,pulse duration and pulse frequency can be adopted without changing the mechanism of insulation aging failure.The insulation materials can still have a single-value mapping relationship under the real pulse electric stress and the accelerated pulse electrical stress,which can shorten the evaluation time of insulation life.This paper mainly works on developing a bipolar high-frequency and highvoltage square wave pulse generator for insulation electrical aging test of inverter-fed motors,and it is easy to adjust pulse frequency,pulse width,pulse dead time,pulse polarity and pulse voltage.The characteristics and research background of the inverter-fed motor are introduced,and the significance of high-frequency and high-voltage pulse generator and the development of the domestic and foreign countries are illustrated.By analyzing the benefits and drawbacks of several circuit topologies and the various techniques of pulse generator,the starting point of this paper is determined.Then according to the requirements of the technical indexes for electrical aging test of inverter-fed motor,the pulse generator system is divided into rectifying circuit,pulse charging circuit and pulse forming circuit: The primary level adopts three-phase rectifier and filter with stable output;The secondary level adopts the resonant constant current charging circuit,wherein the high-frequency transformer has the electrical isolation function of charging and discharging loop;The final level adopts pulse forming circuit of inverter full-bridge cascade.Based on the simulation analysis of the main circuit topology,and the parameter calculation and selection of the corresponding power devices and drive circuits,the construction and debugging of the prototype are completed.The insulation materials belong to the resistance-capacitive load.After the pulse voltage outputs,the large pulse trailing current will destroy rectangular pulses.Based on the detailed analysis of the pulse tail problem,the paper put forward the chopping method,which is low impedance of the discharge channel,implementation in resistance-capacitive loads can still get good rectangular pulses output characteristic.The phase shift control method is proposed which make the pulse generator be capable of outputting bipolar narrow rectangular pulses.In addition,the pulse voltage can be adjusted accurately by controlling the resonant constant current charging circuit.