The ideal supply voltage should be a pure sinusoidal waveform with nominal amplitude and frequency. However, due to the non-ideality of the supply voltage, the impedance of the line, the various disturbances experienced by the power supply system, the time-varying and nonlinearity of the load, etc., the supply voltage often presents a variety of power quality problems. Voltage-type power quality problems typically manifest as amplitude or waveform anomalies: voltage dips, three-phase imbalances, voltage fluctuations and flicker, harmonics, and frequency variations. Among all these power quality problems, the voltage sag and the short-term interruption of the voltage are particularly harmful to the electrical equipment. The voltage sag in just a few cycles may seriously affect the normal operation of the equipment. In developed countries in Europe and America, the economic loss of voltage sag can reach several million dollars, and the consequences of short-term voltage interruption are more serious. Currently, voltage sag has risen to the most important power quality issue. In many complaints about power quality, user complaints caused by voltage sag accounted for more than 80% of the total complaints, while power quality problems caused by harmonics, switching operation and overvoltage were less than 20%. From another point of view, voltage sag and short-term interruptions are very harmful because they are too sensitive to many electrical equipment. Reducing the device's sensitivity to voltage dips and short-term interruptions and increasing its immunity to disturbances allows users to minimize losses and even avoid losses due to voltage dips and short interruptions.
At present, the solution mainly includes installing UPS power, multi-channel power supply, and installing DVR (dynamic voltage restorer). Among these measures, the cost of high-power UPS is too high, and multi-channel power supply cannot completely avoid the losses caused by voltage sag and short-term interruption. The research of DVR (Dynamic Voltage Restorer) has just started in China. From the perspective of improving the anti-interference ability of the load, different devices can be customized according to the needs of the user, which is called user power technology. User power technology is a new technology developed in the 1990s. It refers to the integration of high-power power electronics technology and distribution automation technology. Based on the user's requirements for power reliability and power quality, the user needs to configure the required power. The main products are solid-state circuit breaker + static compensator (STATCOM), dynamic voltage restorer (DVR, DynamicVoltageRestorer), etc., which can solve various kinds of disturbances caused by power system disturbance such as voltage sag, bump, and instantaneous interruption. problem.
Current technology products for voltage compensation mainly include DVR (Dynamic Voltage Restorer) and UPQC (Unified Power Quality Controller, Dynamic Voltage Restorer (DVR) and Active Filter (APF)). The world's first DVR (Dynamic Voltage Restorer) device was successfully developed by Westinghouse, USA, and was put into operation in August 1997 at Duke Power Company. The APF is connected in parallel to the line, and the DVR is connected in series. The purpose of this is that the APF focuses on the management of current-type power quality problems, while the DVR focuses on voltage-type power quality issues. The two devices share the energy storage unit and the energy interface, and can be operated separately to achieve their own functions.
The current difficulty is that traditional energy storage devices are difficult to respond quickly to transient fluctuations in such electrical energy. By adding a super capacitor bank, the above technical problems can be solved more smoothly. Therefore, as a solution to the problem of power quality of users at the core port of the smart grid system, the device has broad market prospects.
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