Research Of The Low-Voltage Dynamic Voltage Restorer's Capacity Of Compensation

The development of modern technology, different electro-equipments such as exact experimental instruments, spaceflight, semiconductor manufacturing and some produce autocontrol system, commerce, communications, computing center, finance etc. have more and more demands for reliability and quality of power supply. Voltage sags during several ten milliseconds even several milliseconds will influence on facility running. However, according to statistics most of power problems in power system are voltage dynamic sag and swell during the time from several milliseconds to five hundred milliseconds. But it is not voltage complete interruption.According to the frames of distribution system in our country, low-voltage distribution network is the main source of distribution network pollution. It is at the terminal of transmission and distribution network. It is also the power supply of many sensitive users. The paper discusses DVR (Dynamic Voltage Restorer) equipment resolves the high quality requirements of sensitive or hypersensitive loads. This equipment is installed on power network in series. It is used to protect sensitive loads from the influence of voltage fluctuation especially voltage notch. It can compensate voltage sags and makes it rising to normal value in several milliseconds.The prototype main circuit of 380V/100kVA DVR that this topic researched is the structure of three single-phase bridges. The main circuit is composed of DC accumulated energy unit, voltage source type inverter (VSTI), filters and series transformer cutting in unit. So the DVR can be phase splitting controlled, which increases the flexibility of control and functions. The maximum offset voltage of DVR output can reach 0.5p.u by adopting some optimization designs, such as adjusting the phase angle of load voltage according to the property of load, dropping voltage on DC side, changing transformation ratio of series transformer, decreasing capability of accumulated energy unit. At the same time more compensating time can be gained by utilizing capability of accumulated energy effectively under the condition of voltage dip. The prototype of 380V/100kVA DVR can satisfy the design specification by simulating voltage dip when system was fault. This facility can be connected in series with power network to protect sense load from voltage pulsation especially voltage sag. This facility can compensate voltage dip to achieve normal value in milliseconds.