Research And Implementation On Modulation Strategies Of Cascaded Multi-Level Inverter

Multi-level converter which uses special circuit structure can achieve high voltage and large power output, at the same time it has excellent output quality. It is widely used in High-voltage Inverter, Flexible AC Transmission(FACTS), Active power filter (APF) and other high-voltage and large-power fields. In common of multi-level topology, cascaded topology has such advantages:easy to realize modular, do not need equalizing control, easy to realize soft-switching technology, which makes it attracted much attention. The paper researches the PWM modulation methods and high performance control strategies which are based on the cascade inverter.Firstly, this paper overviews the current status of development and application of high voltage inverter, and introduces the carrier disposition SPWM and carrier phase-shifted SPWM. Based on the carrier phase-shifted SPWM, a novel carrier phase shifted PWM modulation method is introduced, of which the three harmonic injection method and unipolar SPWM technology is introduced. This method has the advantage of high utilization of DC voltage, less required of PWM plus generator and can reduce the switching loss of the device effectively, etc. Through simulation studies and comparative analysis, the paper verifies the correctness of the novel carrier phase shifted PWM.Based on the two-level SVPWM, phase-shifted SVPWM technology of cascaded inverter are taken out by using phase-shifting principle, and applied to vector control, of which the performance is superior. By using MATLAB simulation software, the simulation research and analysis of cascaded inverter’s vector control system which is based on phase shifted SVPWM technology is taken out.Through theoretical analysis and system requirements analysis, the paper builds experimental platform of which the main circuit uses three units cascaded inverter and the control system uses DSP+FPGA architecture. In the control circuit, the main task of DSP is to generate the initial control signal, monitor and manage the entire system. FPGA accepts and decodes the data from DSP, and then generates relevant signal, finally generates36PWM pulses which contain dead time.Finally, the paper verifies relevant modulation algorithm of the cascaded inverter, and gives out the waveforms and results analysis of the experimental which is based on the experimental platform.