Research On Instantaneous Tracking Control Of Three-phase Four-leg Inverter

During the running process of inverter system, many factors can cause a non-sinusoidal output of voltage waveforms, such as the nonlinear load, the change of circuit parameters, dead zone of control signal, temperature change and so on. Tend to pursue the amplitude and phase between output signal and given signal are the same, it is unable to control the instantaneous waveform in traditional scheme, thus the output waveform distortion rate is high when the loads are nonlinear loads and asymmetric loads.In order to overcome the problems existing in the traditional control scheme, this dissertation comes up with the virtual impedance estimator based on the traditional amplitude and phase control scheme, it generates a correction signal to correct the output signal of amplitude phase controller. The corrected modulating signal is compared with the triangle wave, so the design of the virtual impedance estimator is equivalent to the instantaneous compensation channel for the original system, and it can improve the control precision of the instantaneous value as well as improve the system response speed. This dissertation is mainly about the instantaneous control scheme about output voltage waveform of inverter in independent operation mode.During the design of three-phase inverter main circuit, three-phase four-leg topological structure is used in this system, after the decouple control, the three-phase four-leg inverter can be converted to the single phase inverter which can be controlled by single phase inverter control method, thus this scheme can greatly improve the output characteristics with nonlinear and unbalanced loads. Then for each inverter designing instantaneous voltage controller which is basing on virtual estimator and the control principles of amplitude phase are intorduced. This system can get the perfect performance like three phase four wire public power system through the instantaneous amplitude phase voltage controller, so this system is especially suitable for large scale photovoltaic power generation system. At the same time, single-phase and three-phase simulation models are set up then simulation results with different loads are given, at last the ideal control effects are obtained.Finally, the hardware and software implementation schemes of system as well as some important program flow charts are discussed. At the same time, the waveforms are given; so the validity of the system can be verified through waveform analysis. All of this can prove that the inverter control system has good amplitude phase tracking control and compensation abilities.