Research On The Key Technology Of High Power AC-DC-AC Inverter Used IGCT

In this paper,a series of problems of high power AC-DC-AC inverter based IGCT are further researched,such as the switching characteristic of power device,commutation process,electromagnetic energy transfer,topological structure combination and so on.A set of 10MVA/3.3kV NPC three-level inverter and a set of 20MVA/6.6kV NPC/H-bridge five-level inverter have been developed.High power experiments and engineering application have been completed.A precise functional simulation model of IGCT and diode are proposed.This paper has researched the turn-on transient process of IGCT and switching transient processes of power device when three different types of snubber circuit are applied.On the basis of loss characteristic analyses,the design principle based RLCD+RCD snubber circuit has been put forward.The proposed snubber circuit can increase the maximum output capacity of inverter in the condition that the total loss of system didn't increase too much.The commutation process of NPC three-level inverter based IGCT has been completely analyzed and the commutation path is clearly pointed out.The influences of stray inductance,diode characteristic,dead-time and clamped resistance to commutation process are researched.This paper has derived the voltage charateristic,current characteristic and loss distribution characteristic in the running process of inverter.This paper has investigated the electromagnetic energy conversion process of PWM AC-DC-AC inverter.According to the different time constant,the electromagnetic energy conversion process can be divided into three parts:the switching transient process of power device,the electromagnetic energy conversion process between AC and DC energy storage and active power energy transfer process of AC-DC-AC inverter.The design principles and theoretical calculation formulae of dc energy storage capacitance are respectively derived in different topologies.On the basis of IGCT-based NPC three-level power module,several topological structure combination schemes have been put forward.This paper has researched the topologies of three-level inverter based open-end winding machine,NPC/H-bridge five-level inverter and NPC+NPC/H-bridge seven-level inverter.The SPWM modulation strategies based carrier disposition and the output harmonic spectrum characteristics are derived.Futher more,the topological structure combination scheme of super-high power AC-DC-AC inverter has been proposed.The scheme is convenient to implement the capacity expansion and production-manufacturing.Based on the above research content,NPC three-level inverter and NPC/H-bridge five-level inverter used IGCT are developed.A series of experiments have been successfully completed,such as the switching transient test of power semi-conductor device,the high power load test and so on.The experimental results validate the correctness of the research content in this paper.