Research On A Novel Five-Level Inverter Based On Repetitive Control

In recently years, multilevel converts have received a wide attention and becomes the hot point on power electronics research. Following the distributed generation system such as solar electrical energy generation, the multilevel technology has used in the inverters with medium or low voltage, due to the multilevel inverters have many advantages as: the output voltage of them have low distortion, the inverters can use the smaller filter and hence the level of the electromagnetic interface(EMI). The costs and the volume of the inverter will decrease. A novel single-phase five-level inverter is presented, and then the topology and its derivation, modulation methods and operation states are analyzed. It is the inverter that uses the least power switches in the single-phase five-level inverters, so it is suitable to applications with the medium and the low voltage. Technology of the output waveform is another hot point on power electronics research, it ensures the whole system with the well steady-state and dynamic-state characteristic. To exert the advantages of the novel inverter and study the feasibility of using the multilevel technology and the technology of output waveform, a repetitive controller is added to the system and the results are excellent. The paper reviews the process of the repetitive control, and analyzes the theory of improving the output waveform when a repetitive controller is employed in. The repetitive technology can keep the controlled plant with perfect steady-state characteristic, but its dynamic response is very slow. It can not ensure the qualities of the power supply used alone. The feedback of the capacitor current can quicken the dynamic response and improve the characteristics of the controlled plant. In order to expediently observe the capacitor current and reduce the costs, a digital dimensionality reduction observer is designed to replace the unnecessary sampling circuits. The simulation and experiment results show that the observer can effectively forecast the capacitor current. The paper give a design step of the repetitive controller, considered from the influences to the stability, error convergence speed and harmonic rejection capability of the system. First is the frequency characteristic mensuration of the inverter, second is the filter in the repetitive generator, third is the 2nd order filter, then the phase compensator is ensured and the last one is the design of the repetitive gain. The influence of the stability can be analyzed from the Nyquist curve of the system and the ones of the error convergence speed and harmonic rejection capability can be achieved from the Bode maps. And the influence of the pole assignment to system is analyzed, and the design process of the digital dimensionality reduction observer is also given. A platform based on DSP is constructed to verify the feasibility of the controller and the topology, the experiment results indicate that the system holds an excellent steady-state and dynamic-state characteristics. It is proved that the traditional technology of the output waveform can be transplanted to the multilevel inverters.