Research Of Medium-high Voltage Active Power Filter In Industrial Enterprise Distribution Network

The widely using of power electronic device in the distribution network brings powerquality problem. Active power filter (APF) has become an effective solution to harmonicelimination and reactive power compensation because of its good dynamic performance.However, due to the limitation of the voltage capability of the power devices, the traditionalactive power filter cannot be applied to medium-high voltage distribution network directly. Itis necessary to study the active power filter topology, modulation method and its controlstrategy, which applies to medium-high voltage distribution network.Firstly, this paper analyzes various main circuit topology structures, such as shunt activepower filter connected to the low-voltage side of transformer, hybrid active power filter andactive power filter based on multilevel converter. Then, considering the advantages anddisadvantages of these topology structures, this paper provides an analytical study of theactive power filter based on delta-connected cascaded H-bridge.Secondly, the paper presents the modulation strategies of cascaded H-bridge. Then, thepaper provides a detailed mathematical analysis of bipolar SPWM and unipolar SPWM ofsingle H-bridge. The two methods are applied to cascaded H-bridge together with carrierphase-shifted technology. Based on a detailed mathematical analysis of AC side output,voltage gain, distribution of harmonic group and the equivalent switching frequency can beobtained. The simulation verifies the correctness of mathematical analysis. Because ofharmonics performance and more simple output filter, the paper selected unipolardual-frequency CPS-SPWM as the modulation strategies of cascaded H-bridge.Thirdly, the H-bridge cascaded active power filter’s control strategies are further studiedin view of the harmonic detection, the DC side voltage control and the current trackingcontrol. The detection algorithms based on fourier series and instantaneous reactive power areintroduced in this paper. Based on the analysis of H-bridge cascade active power filter’scapacitor voltage unbalance mechanism, the total voltage control and the capacitor voltagebalancing strategy are put forward. The paper focuses the design of the dead-beat control andquasi PR control design. Then, this paper discusses the effects of quasi PR parameters on thetracking performance and steady state performance, finally the quasi PR reasonable controlparameters are put forward. The simulation results show that the quasi PR can realize zerosteady-state error of instruction current tracking, which is better than the deadbeat control intracking performance and harmonic suppression. Finally, the simulation model of the low-voltage single-phase cascaded H-bridge activeis built, and the experimental prototype of power filter is also designed in this paper. Thedetailed design of main circuit, control circuit and software system is put forward. Thesimulation and experimental results show that the correctness and effectiveness of hardwaresystem and control strategy.