Research On Key Technologies Of Shunt Active Power Filter

With the wide application of power electronic devices,harmonic pollution generated by various types of non-linear electrical equipment has become one of the power quality problems that the society attaches importance to and urgently needs to solve,Active power filter(APF)has gradually developed into one of the main measures to solve the problem of hgrmpnic pollution in power grid because of its advantages of real-time compensatiob,flexible control and high reliability.This paper takes the three-phase three-wire parallel APF as the research object,and studies the key technologies such as main circuit parameter design,harmonic current detection method,phase-locked loop(PLL)design,current tracking and DC-side,voltage control.The article starts from the generation and harm of harmonies,introduces the current harmonic standards and governance methods at home and abroad,and explains the classification of APF and the typical application fields development status.The basic working principle of APF is analyzed,the mathematical model of APF is deduced,the constraint relationship of main eircuit parameters and design selection method are introduced in detail,and the influence of the filter parameters and the DC side voltage on the effect of APF compensation is compared and analyzed.The rationality of the main circuit parameter design method in this paper is verified by simulation and experiment.In addition,the paper studies several common harmonic current detection methods,comparatively analyzes several commonn phase-locked loops,and introduces a phase-locked loop based on complex coefficient-cascade delay signal cancellation method(CCF-CDSC-PLL).The complex coefficient filter is used to supperss the higher harmonic components in the power grid,and shen the caseade delay signal elimination module is used to filter our lower specofoc harmonies and unbalanced negative sequence components.Simulations and experiments have verified that it has good phase-locking performance under complex operating conditions such as grid voltage distortion and imbalance.Then,the common current tracking control methods are briefly introduced,and the advantages and disadvantages of the hysteresis comparison method,the SVPWM modulation method and the SVPWM-based hysteresis current control method are analyzed.An improved SVPWM-based hysteresis current control method for judging the sector of the reference voltage u*by judging the polarity of the three-phase error line current is introduced.The factors that affect the APF DC side voltage fluctuation are briefly analyzed,and the common DC side voltage control and soft start methods are discussed.A DC voltage soft start method of equal voltage and current step-up method is introduced.In this paper,the PI control method is used to control the DC voltage,and the voltage fluctuation under steady state is less than ±2%.Finally,an APF system experimental prototype was built with TMS320F28335 as the core.The experimental results verify the rationality of the APF main circuit parameter design,the effectiveness of the harmonic current detection and current tracking control method,the feasibility of the DC side voltage control method and the necessity of soft start.