Analysis of power quality control technology
Foreword In recent years, the power quality control technology of power distribution system has made great progress, among which the most representative and most influential are the static reactive power compensation device (DSTATCOM), active power filter (APF), and timely power system data. Monitoring (SCADA), Dynamic Voltage Regulator (DVR). (1) Power system static var compensator (DSTATCOM) There are many fast impact load currents in the power system, such as medium and high frequency electric furnaces. The high-capacity motor has a high-sensitivity anti-load sudden start, which will cause voltage flicker, causing imbalance of current and voltage in the distribution system. Compensator (SVC) to suppress voltage flicker, but SVC's response speed is slow (tens of milliseconds), suppressing flicker rate is difficult to reach more than 50%, compared with PWM-controlled voltage source converter in parallel with power system The static reactive power compensation device (DSTATCOM) of the power distribution system has the advantages of fast dynamic response speed, compensation current independent of system voltage, strong harmonic suppression capability, good suppression of voltage flicker effect, and small active loss. Therefore, the DSTATCOM device is gradually replaced. SVC devices are widely used. (2) Active Power Filter (APF) In power systems, uncontrolled harmonic voltages and harmonic currents are the most important factors affecting power quality. First, measure the instrument and the neutral line with the accurate rms value to measure the harmonics of the circuit and the neutral line. Strengthen the measurement and inspection of the power quality of the transmission lines of users, and regularly test and compare the transmission and distribution systems, especially the medium and low voltage systems, to find out the law of harmonic generation and development. Harmonic pollution suppression and prevention measures are divided into passive filters and active filters composed of power electronic devices according to different working principles of the device. Passive filter devices consist of capacitors, reactors, and sometimes passive components such as resistors to form a low-impedance path for a certain harmonic or higher harmonics to suppress higher harmonics. (iii) Timely monitoring of power system data (SCADA) In the power system, the dynamic power quality problem is exposed in recent years with the development of high-tech. Studying the sensitivity and stress of power users to power quality can provide an important basis for selecting appropriate compensation methods, and also for power quality. The development of standards provides an important reference. The SCADA system for quality monitoring of on-site dynamic data is the research direction of the distribution management system. The field data includes not only measurement data such as power, voltage, and current, but also event data generated by operations such as closing, overcurrent, and quick-break. When an accident occurs and a trip occurs, the fault recording data on the site is also recorded. It can be seen that the amount of data that needs to be communicated is unmatched in general industrial control. Since the on-site data of the power system changes very quickly, an overcurrent may only last for more than ten milliseconds, and the data is fleeting, so the requirements for real-time data and communication speed are very high. The reliable and efficient communication of the underlying data of the monitoring system is the key to system reliability and the focus of designing monitoring software. Some existing softwares use data communication, processing and monitoring in one software. Although it is intuitive and compact, the system upgrade is very inconvenient. A small change must be reorganized for all systems. Therefore, the module is adopted. Structure is a better choice. In the design of a large-scale power monitoring system, the hardware uses a separate way of communication station and monitoring station. The software separates the underlying communication software from the monitoring software and works independently in the communication station. The communication station is responsible for the real-time data of the bottom layer. Acquisition and two-way data communication with the upper monitoring station. Due to the independence of the communication station, the task of the upper monitoring station is greatly reduced, which not only improves the communication speed of the bottom layer, but also speeds up the data refreshing speed of the monitoring interface. If the number of lower-level instruments is large, a multi-channel dual-port RAM intelligent communication card can be used on the communication station, and the serial port can be expanded into multiple serial ports to further improve the underlying communication speed. In this way, the quality of power transmission can be improved in a timely and effective manner. (4) Dynamic Voltage Regulator (DVR) The DVR is equivalent to a dynamically controlled voltage source connected in series in the power distribution system. The appropriate control method can make the voltage source output counteract the adverse effects of the power system disturbance on the load voltage, such as voltage drop, voltage imbalance and harmonics. Wait. When the DC side energy is obtained by rectification from the system, even if a single-phase fault occurs on the system side, the other two phases can still provide power to maintain the normal operation of the DVR, and it is also possible to compensate for the long-term voltage drop. If the battery is connected in parallel at both ends of the DC-side capacitor, or the large-capacity capacitor is used for energy storage, the device can also function as a UPS, that is, it can provide a certain amount of power to the load when a short-term fault occurs on the system side. With appropriate topologies, DVRs can comprehensively address dynamic voltage quality issues such as drops, surges, and steady-state voltage quality issues in power distribution systems (such as harmonics, ripple, and three-phase imbalance), which is a multi-target Voltage quality comprehensive management device. In addition, power distribution system power quality control technology is also uninterruptible power supply (UPS), unified power quality controller (UPQC), solid state switch (SSTS), distributed generation system (DG) and so on. Conclusion With the development of high-tech industries and the application of information technology in various fields of society, the issue of power quality has attracted more and more attention. The realization of intelligent, informational and hierarchical interactive management of power industry, such as power generation, transmission, power supply, electricity consumption, customer sales, grid dispatching, and integrated services, will be the development trend of future power grid quality improvement. Fiber Connector is an important component, using in the fiber optic network. 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