Research On The Control And Test Methods Of IGBT-based High Power Three-level Inverter

The control of the IGBT-based 750kVA Neutral-Point-Clamped (NPC) three-level inverter is completed in this paper. A virtual instrument and high speed digitizer based on-line test platform of high power converter switching transient is carried out on the NPC converter, and the testability of measuring device currents indirectly is analyzed. The test results of the on-line test are analyzed finally.The three-level Space-Vector-Modulation (SVM) arithmetic is designed on the 750kVA NPC three-level inverter, and the constant V/f control is implemented. Compared with the control the two-level converter, the main differences of the control of NPC three-level converter are about the modulation arithmetic. The SVM control is carried out on the TMS320F2812 DSP, after the control strategy is analyzed. There is a neutral point voltage unbalance problem in the NPC converter, so it is essential to add neutral point voltage balance control. The output currents and the voltages of the DC bus capacitors are measured and feedback to control the neutral point voltage in a closed loop. Finally, the experiments with inductive and motor load are carried out to verify the SVM control.In NPC three-level inverter, dead-time will bring the problem of voltage and current aberrance, and depreciate the control performance. Based on the analysis of the dead-time effects on the fundamental and low order harmonic components of the NPC three-level inverter output voltage, a pulse based dead-time compensation method applied to the NPC three-level inverter is presented. Compared with the error voltage compensation method, the pulse based method eliminates the phase offset between real output waveform and theoretical waveform. The simulation and experimental results are given to demonstrate the validity of this method.The on-line test method of high power converter switching transient is introduced. When the converter is running in normal condition, the switching transient waveforms of all the power devices of the converter during a period can be sampled and recorded, and the work situation of the converter before fault can also be recorded. The on-line test platform based on virtual instrument and high speed digitizer is built. In order to reduce the number of signals to be measured, the testability of measuring device currents indirectly is analyzed.Finally, the experimental results of the on-line test are provided, and the work flow of the on-line test platform is verified, and some analysis conclusions are drawn from the test results.