Research On Control Strategy And Fault Diagnosis Of Three-phase T-type Active Power Filter

With the continuous development of power system,the degree of power electronization of electrical equipment is getting higher and higher,and the power quality is getting worse.Active power filter(APF)can dynamically compensate harmonic current.As a new type of power management equipment,it has attracted much attention.This thesis takes the three-level T-type topology APF as the research object,and mainly studies the harmonic current detection,model predictive control(MPC),fault diagnosis and fault tolerant control of APF.The performance of the phase-locked loop during APF current detection will seriously affect the accuracy of the d-q detection method.The DC offset in the voltage signal will cause the phase-locked loop to fail to accurately extract the phase information.Therefore,this thesis proposes a phase-locked loop based on dual improved adaptive notch filter and moving average filter.The traditional adaptive notch filter is improved,and the positive and negative sequence separation module is combined to form an outer loop filter,which can effectively suppress the DC offset and the fundamental negative sequence component;A moving average filter is added to the inner loop of the phase-locked loop to attenuate higher harmonics,and a faster response speed is obtained by reducing its window length.Aiming at the problem that there are few optional voltage vectors and the weight factor of value function is difficult to be adjusted in MPC strategy,a model predictive control strategy without weight factor based on virtual vector is proposed.Multiple virtual vectors are synthesized by real vectors to increase the number of optional voltage vectors;The large sector is further divided into three small sectors,which are directly located to the small sector based on the voltage error to reduce the vector set involved in the optimization;The constraints of vector selection are increased,and the main control objectives are optimized and the threshold is set to eliminate the weight factor.Aiming at the open circuit fault of Insulated Gate Bipolar Transistor(IGBT)and current sensor fault in T-type APF,a comprehensive fault diagnosis method based on reconstructed current is proposed.The fault characteristics are analyzed to distinguish the two faults.The phase A output current is reconstructed according to the positive electrode output current on the DC side.The voltage residual and reconstruction deviation are used to judge whether the APF is faulty.After a short delay,the fault type is determined and the fault element position is accurately located according to the variable criterion.In order to make APF continue to operate with better compensation performance after current sensor failure,a fault tolerant control strategy based on model prediction is proposed.In the reconfigurable state,the fault phase current is reconstructed and replaced according to the normal phase current.In the non-reconfigurable state,the MPC predictive current is used to replace the feedback signal of the fault sensor,and two candidate vector sets are set according to the different replacement methods;Aiming at the prediction error,the unreconfigurable voltage vector is reduced by synthesizing virtual vectors,and two vector sets are used alternately to prevent error accumulation.The fault tolerant control strategy enables APF to maintain good current tracking ability after sensor failure.The simulation model of the research content of this thesis is built in MATLAB /Simulink and the simulation results are analyzed.Based on RT-LAB,a semi-physical experimental platform is built to verify the feasibility and effectiveness of the research results.The thesis has 75 figures,7 tables,and 84 references.