Research On Digital Control Technique Of Three-phase PWM Inverter

With the rapid development of semiconductor power devices and various controlmethods, the inverter had been promoted a lot. Digital control is well satisfied with thetrend of modularization and high reliability of the power supplies for its advantages ofexcellent control ability and easily to be manufactured standard. This paper is mainly aboutthe digital control for the inverter.The first chapter introduces some basic knowledge of digital control and some featuresof the inverter, including the advantage compared with analog control and some of itsproblems, such as the quantization error and one-step-delay. The second chapter introducesthe abc frame and dq frame mathematical model of three-phase inverter, and analyzed thecharacter of load in the dq frame. In the third chapter, the discrete model of the inverter isdeduced from the principal of how the circuit works, a comparison between themathematical model and circuit simulation is done to verify the accuracy of themathematical model, and a dual loop control system is built on the inductor current andoutput voltage with the mathematical model, the impact to the stability of the inverter isanalyzed when the DC power fluctuates through the pole-zero map, and the system is stillstable when the DC power rises+25%. Then the output impedance is deduced in thediscrete domain when the inductor current or capacitor current is feedback. In the last partof this chapter the simulation and experiment is done to verify the validity of the controllerand the poor waveform when the inverter is with a rectifier load is found. In the fourthchapter a resonant controller is introduced into the control of inverter, by comparing theinfluence of different discretization methods, the zero-order hold discrete method withone-step lead is used, the resonant frequency is confirmed through the analysis of thesystem harmonic content, the gain of the resonant controller is confirmed by comparing theopen loop bode diagram with dual-loop PI controller, then the resonant controller is complete, the stability of system is validated through the pole-zero map, simulation andexperiment results is given in the last, good harmonic suppression can be found from theresult, so the validity of the resonant controller and controller design method.