Research On Single Phase Dynamic Voltage Restorer

Electric power device used in industry and personal living has been increased when new technique is developing. It impacts and charges the capacity and the velocity of the capacity increasing of the grid. Voltage surge and sag, especially voltage sag happens continually, makes some sensitive electric device working abnormally. Dynamic voltage restorer (DVR) is a common device to protect sensitive electric device inflected by voltage sagging or surging.Now, the problems of existed DVR are that the compensation time is limited, can't compensate voltage surge and detect voltage change and compensate the change by real time.This paper discusses a DVR system consists by a series PWM converter and a PWM rectifier. Serried PWM converter uses the concept of current average model. At the restrictions of the transformer's internal magnetic field balance, via controlling the secondary current of series transformer to meet the invariableness of the load current. When load current is meeting, the load voltage is the rated value. As series transformer needs magnetizing current, which make load voltage has state error, this paper designs tow methods of magnetizing current compensation. One of the magnetizing current compensation methods is based on the LMS value feedback of the load current, the other one is transformer magnetizing current complete compensation.This paper uses PWM rectifier to provide the DC voltage for DVR. PWM rectifier can work on unit power factor condition, and could returns energy back to grid. Using PWM rectifier could solve the problem that traditional DVR couldn't compensates the voltage surge. When DVR compensates voltage surge, PWM rectifier returns energy back to grid, while DVR compensates voltage sag, PWM rectifier get energy from grid. This keeps the DC voltage steady.Make DVR working at unit power factor condition to avoid make new pollution to grid. This paper has a parallel Active Power Filter connecting to the load, providing the reactive power current and harmonic current. Only active power current needs to be considered when design the transformer. This cuts the capacity and volume of the transformer efficiently, so as the power level of the power electric device. The compensation result depends on the parallel APF, the velocity and precision of the real-time calculated load current setting value. This paper uses adaptive filter to detect harmonic current. This filter can divide fundamental active power current, fundamental reactive current and harmonic current, then send to DVR and APF as setting signal. This paper introduces the concept, traditional realizing method in analog current and LMS realizing method using digital signal processing of adaptive filter. Based on the cooperation of tow adaptive filter realizing method, this paper designs a new LMS method that converter all signal to unit.The work of this paper is also the preparing work of Unified Power Quality Conditioner (UPQC). Based on DVR discussed in this paper, connects the PWM rectifier to the load form grid. Using the fundamental reactive current and harmonic current from adaptive filter as the setting value, PWM rectifier could work as APF besides keeping the DC voltage by the active power current given by DC voltage loop. The PWM rectifier and series PWM converter make up a Unified Power Quality Conditioner.