The Research On Control Strategy Of Three-Phase Inverter Under Unbalanced Output Voltage

The same to the rectifier, inverter which is one of important electronic devices has a very important role in power converters. Along with the exploit of new energy resources, researchers have carried out an extensive research on distributed power generation system. In order to parallel into the power grid or supply for the user directly, a large amount of power electronics are needed in power generation system, in which inverters have a critical role. However, with the development of technology, the kinds of loads are increased greatly. So the requirement of ability for the power system to take the unbalance loads and nonlinear loads is more and more strict. So this thesis is mainly about the research on the three-phase inverter with unbalance loads.The thesis has researched the three-wire three-phase inverter, based on the analysis the output characteristic of inverter with unbalance loads, the method of restrain the unbalance output voltage was introduced, then the models of inverter in dq0-frame andαβ0-frame were established. Based on the model in dq0-frame, the dual-loop control of inverter was designed, and based on the model inαβ0-frame; the repetitive controller of inverter was designed. According to the symmetrical component theory, the unbalanced output voltage is composed of three balanced parts:Positive sequence voltage,Negative sequence voltage and Zero sequence voltage. In the dq0-frame, the positive sequence voltage is the DC signal, and the negative sequence voltage is the harmonic component whose frequence is 100Hz. The PI controller with a good dynamic response can not eliminate the periodic disturbance; and the repetitive controller can eliminate the periodic disturbance, but the dynamic response is not very good. Consider the cases above, the thesis was promoted a multiple control stratge in which the dual-loop controller and repetitive controller were designed respectively in dq0-frame andαβ0-frame.In order to verify the control strategy, the simulation model of inverter control system was established in MATLAB. The thesis has compared the control effect of dual-loop control, repetitive control and the composited control method promoted in this thesis. On the basis of simulation, the experiment platform was designed and constructed in which the DSP-TMS320F28335 was used for the control chip, the control strategies were realized by programming in DSP. The results of simulate and experiment has proved the correctness and availability of control strategy promoted in this thesis.