APF Research Of Cascaded H Bridge Based On Deadbeat And Repetitive Control

With the wide application of all kinds of new power electronic equipment,a large number of harmonics are introduced into the power system,they cause a very bad impact on the power quality.Therefore,harmonic suppression is an urgent problem to be solved.Active Power filter(APF)can accurately and quickly detect the harmonic components in the power grid current,and then generate the same amplitude and inverse phase signal with each harmonic,and send it back to the power grid,so that the two cancel each other,so as to eliminate each harmonic in the power grid and improve the power quality.Therefore,active power filter has become one of the most effective measures to improve power supply quality.In this paper,active power filter is studied from the following aspects: multilevel topology,carrier phase shift modulation,harmonic detection technology,harmonic current tracking technology and DC side voltage equalization technology.Firstly,in view of the limitation of voltage withstand level and switching frequency of power electronic switching devices,APF based on cascaded H bridge multilevel technology is studied.Through the cascaded H bridge module,the number of output levels and overall voltage withstand level of APF are improved,so that it has a good application prospect in high voltage and high power occasions.The basic working principle of APF of cascade H bridge is introduced in detail and its mathematical model is deduced.The cascade H-bridge APF studied in this paper adopts carrier phase shift modulation(CPS-SPWM)technology.Simulation experiments verify that when the switching frequency of the device is low,the equivalent switching frequency can be obtained by using this modulation strategy.Secondly,a voltage stratified control strategy is proposed to solve the capacitor voltage balance problem of APF DC side of cascade H bridge.Firstly,the power equation of H-bridge module is used to analyze the factors leading to capacitor voltage imbalance on the DC side.Then,the hierarchical control strategy of overall voltage control,phase-to-phase voltage control and interphase voltage control is adopted to control the capacitor voltage on the DC side of nine h-bridge modules to be consistent,so as to achieve voltage balance.Finally,in order to improve the current tracking control effect of the cascaded H-bridge APF,the traditional Deadbeat control has low steady-state accuracy and good dynamic characteristics.The repetitive control has the problem of high steady-state accuracy and poor dynamic characteristics.This paper proposes a compound control strategy which integrates the Deadbeat control and repetitive control,carries on the detailed theoretical analysis,deduces and establishes the mathematical model,formulates the implementation method,and realizes the complementary advantages of the two.The simulation model of 10 k V system was built in Matlab/Simulink,and the experimental comparison of Deadbeat control,repeat control and compound control in this paper are carried out.The simulation results verify the effectiveness of the compound control strategy proposed in this paper.It has good dynamic characteristics and stable characteristics,and can effectively compensate harmonic and improve the power quality of power grid.