Research On The Cascaded H-bridge Multilevel Active Power Filter

With the development of power electronics technolo gy and the continuous improvement of the performance of power semiconductor switching devices,many nonlinear converter devices have been widely used in various fields of po wer system,which not only enhance the controllability of power quality,but also b ring harmonic pollution problems.As an efficient and practical filtering tool,active power filter(APF)plays an important role in harmonic management and reactive power compensation.Due to the switching frequency of power semiconductor devices,traditional APFS are generally used in low-voltage and low-power environments.In order to enhance its applicability in high-voltage and high-power situations,this paper takes H-bridge cascaded multilevel active power filter as the research object,mainly studies modulation technology,detection algorithm,control strategy and other aspects,and the results are as follows:(1)The common types of active power filter are discussed,three topological structures under the multi-level technology are reviewed,and the working principle of h-bridge cascade converter is analyzed emphatically.At the same time,the output voltage and harmonic characteristics of single-pole frequency-doubling carrier phase shift modulation are studied,and the effect of cascade number on t he output performance of filter is discussed through simulation experiment.(2)A type ip-iq harmonic current detection algorithm based on instantaneous reactive power theory is studied,and an adaptive filter model is proposed to replace the low-pass filter.In this model,the adaptive variable step size LMS/LMF algorithm based on Sigmiod function is used to estimate the optimal step size by adjusting the weight coefficient of iteration through the feedback of historical errors.Simulation results show that this algorithm can effectively improve the speed and accuracy of harmonic current detection.(3)The control strategy of APF system is studied,and an improved non-differential beat current tracking control algorithm is adopted for current tracking control,and the sampling signal is estimated-corrected by introducing the concept of historical sampling periodic current and combining the(n-1)periodic voltage to reduce the cumulative effect of sampling error;Simulati on results show that the proposed strategy can achieve the expected control objectives,and can ensure the static performance and dynamic performance of the whole system.(4)The system design of H-bridge cascaded active power filter based on DSP+FPGA is analyzed,the parameter selection criteria of the circuit hardware system,the working principle of the module and the programming process of the circuit software system are given,and finally the design of the multi-channel PWM waveform generator based on this is discussed,the correctness of the proposed algorithm is verified by the experimental platform.