Research On Active Power Filter Based On AC-AC Conversion Technology

In modern AC power systems,active power filters(APF)have become an important device for power quality improvement.The traditional APF adopts an inverter topology,and the DC side needs a DC energy storage device composed of large electrolytic capacitors,which are large in volume,high in cost,short in life,and poor in reliability.To solve this problem,an APF based on AC-AC conversion technology is studied in this paper.Firstly,the VQS theory and EHM technology which can control the odd harmonics of the AC-AC converter are introduced.The compensation mechanism of Buck,Boost and Buck-Boost type AC-AC converter connected with the resistors,inductors and capacitors are separately analyzed.Considering the control difficulty and compensation effect,the Buck-type AC-AC converter with capacitor is selected as the main circuit of the APF.Secondly,the principle,characteristics and implementation methods of the single-phase AC-AC APF are studied in detail.The working mode of the AC-AC type APF is analyzed,and the formula of the compensation current is derived.The small signal model of reactive power compensation is established.The controller design and Matlab simulation verification are carried out.Using the Fourier series method and the data fitting toolbox in Matlab,the frequency and quantity correspondence between each odd harmonic component in the compensation current and each even-modulation wave in the duty cycle are calculated and derived.A single-phase decoupling modulation strategy is proposed.The reactive power and harmonic compensation scheme is designed and verified by Matlab simulation.Then,the principle,characteristics and implementation methods of the three-phase ACAC APF are studied.The system structure is introduced,its mathematical model is deduced,its compensation characteristics are studied,the three-phase EHM coupling problem is analyzed,and a three-phase decoupling modulation strategy is proposed.Based on this,a three-phase compensation control scheme is designed and verified by Matlab simulation.Finally,a prototype of single-phase AC-AC APF was developed.The calculation and selection of main power component parameters are carried out.The design of hardware and software based on DSP chip TMS320F28335 are completed.The experimental results show that the single-phase AC-AC type APF has excellent reactive power and harmonic compensation effects.