Research On Switched-autotransformer With Function Of Dynamic Voltage Restorer And Harmonic Elimination

A large number of impact and nonlinear loads used in modern industry and commercemake the power quality more and more serious. However, more and more loads that aresensitive to power quality are used in today’s society.To cope with the voltage sag, voltage swell and voltage harmonics problems, a singlephase circuit structure with function of dynamic voltage restorer and harmonic eliminationutilizing a PWM-switched autotransformer is proposed in this paper. It is connected inseries between grid and load, which can quickly compensate sags, swells and eliminatevoltage harmonic to feed good quality power to load. The circuit topology has no DCenergy storage link improving the system compensation capacity and efficiency greatly,and it also has the same frequency and phase characteristics without PLL reducing thedifficulty of implementation significantly.A fast peak voltage method based on the orthogonal characteristic of sine signal isused in order to detect sags and swells, and the theoretical derivation for its basic principles,transient response and influence of frequency Variation and harmonics on peak detectionare made. Simulation is made using PSIM.In order to eliminate grid low-order harmonic voltage, this paper presents a newPWM harmonic elimination technique that introduces the new modulation function on thebasis of a constant duty cycle control to calculate the real-time PWM duty cycle so as toeliminate the voltage harmonics. The theoretical derivation and Simulation using PSIM aremade.This paper combines sags, swells compensation and harmonic elimination togetherfirstly to implement on PWM-switched autotransformer. Control strategy that combiningthe feed forward control with the output voltage feedback control and detailedimplementation methods are proposed. Design of hardware circuit and control software,made detailed calculation of the parameters of the hardware circuit, and the system controlis completed by32-bit ARM processor stm32. A5KW experimental prototype is built, andexperiment results repeal that the system proposed in this paper can compensate sags,swells in the longest5ms and has good performances for eliminating low-order harmonicvoltage contains in grid.