Control And Implementation Of Three Phase-Four Legs Inverter Based On DSP

With the rapid development of industrial automation and modern science technology, the load on the power quality requirements are increasing, inverter as an important part in power electronics field, plays a key role in a variety of energy transformation. In modern production and life, because of the diversity and unbalance characteristics of the load, inverter has to be a strong ability to adapt it. While deepening the study of modern control theory and power electronics technology provide development of the inverter a strong guarantee.This thesis presents an in-depth and meticulous research for the three-phase inverter under unbalanced load conditions. In order to ensure the symmetry of three-phase output voltage, power electronics, mainly from the main circuit topology, the closed-loop control algorithm and the modulation of these three strategies aspects were improved. The traditional three-phase three-leg inverter topology can be output when the load balancing symmetrical three-phase voltage,but when the load is unbalanced or non-linear, the three-phase output will have a serious imbalance or harmonic distortion. Through the study, three-phase four-wire inverter topology has a strong ability to adapt to unbalanced load. Increasing fourth lines can provide a path for load imbalance arising from the zero-sequence current, thereby the three-phase the output voltage of symmetry can be ensured. Based on this, some scholars have proposed a three-phase four-leg inverter main circuit topology. The topology is simple,flexible control, high DC voltage efficiency and power density, as a way of dealing with unbalanced load topology has been widely applications.This paper is based on three-phase four-leg inverter, its control strategy with unbalanced load on the system when conducted in-depth research. Through the establishment of a three-phase four-leg inverter system mathematical model analysis and three-phase voltage output waveform asymmetry mechanism works under its research and unbalanced load conditions, the paper proposes effective closed-loop control algorithms and modulation strategy. For the structure and principles of hysteretic current control and SVPWM control,combined with the advantages of both proposed a Hysteresis SVPWM control strategy and application of Matlab simulation software to build the model and simulation analysis to verify the correctness of the policy and feasibility. Meanwhile, the widely used PI voltage and current double closed loop control and repetitive control methods are studied and analyzed.And then composite control strategy combining PI dual loop control and repetitive control is compared with PI dual loop control, and repetitive control by the way of simulation.Simulation results show that this method can effectively reduce the imbalance degree of the inverter output voltage, and ensure the symmetry.On the basis of theoretical analysis,experiments about three-phase four-leg inverter are taken on a DSP control platform. Debug the circuit,analyze the experiment results based on the composite control strategy combining dual-loop PI control with repetitive control, and finally verify the inverter system can achieve the ideal control effect when using the compound control strategy.