Research on Dynamic Voltage Restorer Based on main

Research on Dynamic Voltage Restorer Based on a single three-phase PWM inverter Li Ke, Li Yandong, Zhu Fang, Li Hongyu, Wang Zhao (Xi'an Jiaotong University 710049) abstract: the principle of dynamic voltage restorer (DVR) is to ensure the customer's power quality with a series voltage source This paper begins with the discussion of the power quality items that DVR copes with, also its’ working principle and control idea are presented. Then analysis and choice of the main circuit connection style are given, and the design of the circuit parameters is proposed. Finally, simulated results obtained with Matlab are also given and analyzed to validate the whole system. Key Words: Dynamic Voltage Restorer, Power quality, Sag. 1 Introduction in the distribution and transmission system, the transient disturbance of electric voltage or the fault of load, such as short circuit, will cause the drop and rise of branch voltage of sensitive load; This change is very fatal to semiconductor manufacturing plants, and tens of thousands of losses are caused by problems such as voltage surges every year. DVR mainly aims to compensate for short-term voltage drop and rise. It adjusts the voltage quality of the user end by inserting a voltage source into the distribution system in series, so as to suppress the impact of the voltage disturbance of the distribution system on the sensitive load since "1025"; Compared with the same type of power quality regulation devices such as UPS, dynamic voltage restorer for the purpose of compensating short-term voltage problems also has the advantages of small capacity and low cost. At present, the research of DVR is receiving more and more attention. There have been considerable research results abroad on DVR. DVR experiments have been reported in Germany, South Korea and Singapore; The megavolt DVR device of Siemens in Germany has been introduced to the market as a product; There are also some experimental research results in China. But compared with foreign countries, there is still a big gap. 2. Power quality problems related to DVR: DVR mainly solves problems such as instantaneous voltage drop and rise; However, according to the choice of control methods, some other power quality problems can also be solved. The definition of power quality in IEC (/4) (International Electric Committee) standard: power quality refers to the physical characteristics of the power supply system provided to the user when the equipment works normally. The most serious power quality problem is voltage sag and complete voltage interruption. Among them, several power quality terms related to DVR and their meanings: voltage sags: the effective value of voltage drops to 10%-90% of the rated value, and the duration is 0 Cycles. Voltage interruptions: in one-phase or multi-phase lines, the manufacturer shall add the corresponding control system to completely lose the voltage (lower than 10% of the rated value) for a period of time. The duration from 0.5 cycles to 3S is instantaneous interruption; The duration of 3S to 60s is temporary interruption; If the duration is more than 60s, the voltage is interrupted. Voltage surges: the effective value of voltage or current rises to more than 110% of the rated value, the typical value is 110% - 180% of the rated value, and the duration is 0 Cycles. Voltage transient: refers to the change of voltage between two steady-state quantities within a certain period of time. The voltage transient can be a unidirectional pulse of arbitrary polarity or a decay with the first peak of arbitrary polarity. Most people use experience to judge the quality of products related to friction, vibration damping and surge. Over voltages: the voltage is 110% - 120% of the rated value, and the duration is about 1min. Under voltages: the voltage is 80% - 90% of the rated value, and the duration is about 1min. Voltage fluctuations (flicker): voltage fluctuations (flicker) refers to the regular or random change of voltage amplitude within a certain range. The variation of its voltage amplitude is usually 90% - 110% of the rated value. This voltage fluctuation is often called voltage flicker. Because DVR is a dynamic regulating device, it can dynamically compensate different degrees of voltage problems within the allowable range of capacity; Among them, according to the compensation capacity set by the device, DVR can compensate voltage fluctuation (flicker), overvoltage, undervoltage, and certain voltage drop and voltage drop to suppress voltage transients. At the same time, under the condition of continuous power supply on the DC side (refer to figure 1), it can have a certain ability to suppress the instantaneous interruption of voltage. Under the condition that the load is not very demanding on the voltage, the DVR can be set to work only after the voltage drop amplitude exceeds a certain limit, which can reduce the design requirements of DVR devices and reduce the design cost. 3 working principle of DVR DVR system is mainly aimed at compensating short-term voltage changes. Generally speaking, the time range of compensating voltage changes is about 0 Voltage cycles. The common structures are three single-phase bridge based split phase compensation structure and a single three-phase bridge based circuit structure. This paper mainly studies the latter case; The specific components include voltage type three-phase bridge converter, DC energy storage capacitor C, energy storage device connected with the capacitor, filter circuit and series transformer, as shown in Figure 1; Control the DVR as a controlled voltage source and output the voltage. When the system S-point voltage changes, in order to ensure that the voltage of the sensitive load is maintained at the normal level, control it to meet the relationship: