| Power quality problem obtains more and more attention in recent forty years. Reactive power, harmonic and unbalance is always the focal point which people pays attention. This dissertation works to study the power quality problem, including following contents:This dissertation presents a dynamic voltage restorer (DVR) based on asymmetry cascade multilevel inverter(ACMI) and its control strategy. The asymmetry cascade multilevel inverter is used in this DVR, so the capacity of the DVR can be made very large. The control strategy is based on a combination of pre-sag phase compensation and post-sag phase compensation. Once a sag event occurs, the phase will therefore slowly shift from the pre-sag phase to the post-sag phase, so the voltage as seen by the load will be smooth without any sudden jump. This gives the benefit of the load which is sensitive to the voltage phase. The effect of the DVR is close to the pre-sag phase compensation, but the consumption of energy is close to the post-sag phase compensation. The practicability and validity of the structure and control strategy are confirmed by MATLAB simulation.This dissertation establishes the universal electric model and investigates the structure and principle of several typical series hybrid active power filters (SHAPF). In addition, this paper analyzes the characteristic of several basic control strategies. The effects of control strategies under different conditions are investigated. The conclusion can help us to make the best choice under complex operating modes.This dissertation works to design and realize APF experimental prototype, the mainly work include as following: 1. Gives the main circuit scheme of the prototype. 2. Designs the control system based on industrial control computer, motor control board and data collection board. 3. Develops the software for the control system, providing opening data and program interfaces. 4. Validates the parameter and the control method of the device by MATLAB simulation.
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