Design And Implementation Of Three-phase Four-leg Inverter Based On Repetitive Control

With the rapid development of modern society, inverter technology has become an important part of power electronic technology. Three-phase four-leg inverter is a kind of the new power converter and widely applied in UPS power supply, solar power generation and micro grid systems. The advantages of this inverter are compact structure, high efficiency, flexible control, DC voltage utilization rate is high, and so it is extensively applied to the unbalanced load and nonlinear load. Compared with three-phase three-leg inverters, although a neutral leg is put in the inverter, degree of freedom control system is added comparing to three-phase three-leg, so as to make control system complex. In this paper analyzing some conventional control strategy, a novel control strategy is proposed.The majority of the inverter system in the running process, harmonic, power filter parameters, variation of line parameter, power factor changes, delay of filter and line, delay of control detection circuit, changes in temperature will all cause the voltage waveform distortion and phase changes, thereby causing the output voltage of inverter fundamental component of voltage drop. Accordingly, implicating H00repetitive control theory, collecting the inverter output voltage and current waveform real time, applying H∞repetitive controller to compensate the inverter system, can get the expected performance index.In the control of three-phase four-leg inverter, decoupling control strategy of three-phase four-leg is proposed based on the internal impedance transformation. After equivalent transformation, the impedance of zero-leg is transform into zero and the others are reduced to a lower equivalent impedance value. The three-phase four-leg inverter is decoupled into three independent single-phase inverters which can be controlled by single-phase inverter control method. Then for each inverter designing voltage controller which is basing on repetitive control of a fast tracking ability, and the H∞optimal performance index. The simulation results show that, the three-phase output voltage waveform tracks the given sine wave with highly speed, highly precision, and can obtain good control effect.In the realization of hardware and software of inverter system, developed by DSP2812minimum system and FPGA minimum system as the core of100kW inverter system of experimental platform, write real-time controller algorithm, voltage and current of inverter protection algorithm, and the upper computer of touch screen communication algorithm, and so on. From the experiment data and experimental waveform, the design of inverter control system and its control strategies have achieved the expected results.