Research On Key Technologies Of Active Power Filter Based On Chaotic Frequency Modulation Strategy

Active Power Filter(APF)is widely used in various fields such as industry,civil,and commercial due to its effective suppression of harmonics in power systems and compensation of reactive power to the grid.The Space Vector Pulse Width Modulation(SVPWM)converter is an important part of the APF,which generates compensating currents to counteract harmonics and reactive power components generated by nonlinear loads,thereby maintaining the sinusoidal waveform of the grid current and phase alignment with the grid voltage.However,when SVPWM operates at high frequencies under a fixed switching frequency,it can produce large amplitude high-order harmonics at integer multiples of the carrier frequency,which can cause electromagnetic interference(EMI)due to coupling effects and degrade the performance of the APF in compensating harmonics of nonlinear loads.To suppress the carrier frequency harmonics of the APF,this paper introduces chaotic carrier frequency modulation strategy into the APF system.In the research process,the main innovative work and research results of this paper are:(1)Design of a three-phase parallel APF system.Firstly,the mathematical model of the three-phase parallel APF is established by analyzing the system composition and working principle of the APF,and the principle of SVPWM is explained.Secondly,the parameters of the main circuit of the APF are designed,and the selection of the switching frequency,AC side inductance,DC bus voltage,and DC bus capacitor is determined through theoretical analysis and calculation.The design of the grid-connected filter is completed.(2)Analyze the harmonic detection techniques of the three-phase parallel APF,including the DFT algorithm-based harmonic detection technique,p-q harmonic detection method based on instantaneous reactive power theory,and i_p-i_q harmonic detection method.The principles of the two detection techniques are explained and analyzed.Then,the DFT and p-q and i_p-i_q three detection methods are simulated and compared,and the advantages and disadvantages of the three detection algorithms are analyzed.(3)Analyze the principles and spectral distribution characteristics of periodic frequency modulation and chaotic frequency modulation.Firstly,the spectral quantization calculation of SVPWM with periodic frequency modulation is carried out by using the double Fourier series algorithm,and the theoretical basis for the existence of large harmonic amplitudes at the switching frequency and integer multiples of the carrier frequency is given.Then,the above-mentioned spectral research algorithm is further applied to the spectral quantization calculation of SVPWM with chaotic carrier frequency modulation,and the theoretical basis for suppressing harmonic amplitudes by chaotic carrier frequency modulation is obtained.Finally,simulation analysis verifies the superiority of chaotic frequency modulation compared to periodic frequency modulation.(4)Design and analyze the traditional double-loop PI control strategy and propose improvements to address its drawbacks.Firstly,the proportional coefficient and integral time constant of the current inner loop and voltage outer loop of the traditional PI system are designed,and the correctness of the design is verified by the Bode plot.Secondly,improvements are made in the harmonic suppression aspect of the traditional double-loop PI system,and a double-loop PI control system based on the chaotic control period is proposed.The mathematical model of the improved PI system is established,and parameter design is completed.The tracking accuracy of the waveform of the designed system is verified.Finally,the performance of the traditional double-loop PI control system and the improved double-loop PI control system in harmonic suppression is simulated and compared,and the superior performance of the improved double-loop PI control system in harmonic suppression is verified,demonstrating the correctness of the strategy proposed in this paper.