Research On Control Strategy Of Cascaded H Bridge Multilevel Active Power Filter

With the rapid development of power industry in modern society,power quality problems are getting more and more attention,especially in industrial production,so the performance requirements of filter equipment are stricter.In the existing devices for harmonic filtering and reactive power compensation,Active Power Filter(APF)has better harmonic elimination and reactive compensation effect than passive filter,so APF has been rapidly development of.Due to the continuous improvement of the voltage level and the limitation of the withstand voltage of the switch,the traditional two-level APF,diode-clamped and flying capacitor APF have complicated control,low capacity and difficult to expand,which can not meet the requirements of working conditions.H-bridge cascade structure consists of a number of the same converter unit cascaded to increase the converter power capacity,reducing the voltage of a single switching device withstand voltage and easy modular and package.So in the field of high-power power quality control has considerable prospects.This paper first analyzes the basic principle of carrier phase shift SPWM technology.Based on the organic combination of cascaded H-bridge topology and SPWM technology,this paper analyzes the principle of dead-band effect when the SPWM driving signal triggers the switching device in practice,and studies an algorithm that can effectively restrain the dead-zone effect while compensating.The purpose of compensating dead time is achieved by making a feed forward compensation to the equivalent voltage disturbance value.Verification of SPWM transmission performance studies confirmed the ability to achieve higher efficiency switching frequencies.Secondly,based on instantaneous reactive power theory,the algorithm is used to detect the harmonic current in real time.Triangle wave with a fixed switching frequency control method for current tracking control.Based on the balanced control of the capacitor voltage of cascaded H-bridge DC side,an algorithm is designed to ensure the capacitor voltage and bus voltage balance.It is divided into two parts: module average voltage control and DC bus voltage control.Finally,cascade Multilevel APF simulation model is set up to validate the proposed algorithm.The simulation results show that the proposed scheme has high real-time performance,strong robustness and good harmonic compensation performance.It proves that the proposed algorithm The feasibility and complete design of hardware and software system.