Research On Cascaded Multilevel Active Power Filter For Distribution Network

As the nonlinear load of electric power systems increasing, a lot of harmonic current is brought, the power quality is reduced seriously. Active power filter (APF) as the suppression and eliminate harmonic effective method has become the key in research and development of power electronics academic. The purpose of this paper was to study the three-phase cascade multilevel APF with large capacity and high voltage which was suitable for distribution system.The paper pointed out that the inverter used for the distribution system of our country must possess the three conditions: high voltage grade, large power capacity, for three phases connection. Then gave quantitatively the highest voltage grade and the largest power capacity of Three-phase bridge converter,the inverter topology made of three single-phase full-bridge inverters triangle connected and cascade multilevel inverter in accordance with the highest voltage and power capacity level of the semiconductor switch at present. Through studying, it was found that cascade multilevel inverter was the most suitable inverter for the environment in high voltage and large power capacity.In order to choose appropriate modulation method,this paper compared two methods: carrier phase shifting sinusoidal pulse width modulation(CPS-SPWM) and 1 dimension space vector pulse width Modulation (1D–SVPWM) who was applied to cascade multilevel inverter in the output characteristic, Comparison results show that:CPS-SPWM is most suitable for this design, for it can not only improve switch frequency but also shows good ability of resisting dc side voltage fluctuation interference. According to the characteristics of cascade multilevel, the distributed control strategy was adopted, simple PI control is widely applied in current loop, voltage ring, Dc side voltage balance control.At last cascade multilevel inverter topology, the modulation method of CPS-SPWM, the distributed control strategy, simple control method of PI control were selected to be applied to the APF for distribution network developed by this paper.Simulation result demonstrated that APF based on cascaded multilevel topology could trace and compensate the grid harmonics accurately, and good dynamic response and high detection accuracy are approached. Furthermore, DC capacitors voltage of each link could be balanced fast and accurately. The application of APF in high voltage field is expanded.