Research Of Dynamic Voltage Restorer And Its Detection Method

With the extensive application and development of power electronic technology,because of power quality problem, the grid has a higher demand for power quality.Research showed that voltage sag happened most frequently, leading the biggest economic loss and the most serious impact. Therefore, it is urgent to take effective measures to improve the voltage sag and ensure the voltage quality and power supply reliability. Owing to good compensation effect and high performance price, dynamic voltage restorer is one of necessary means for voltage sag compensation. Once the voltage sag occurs, rapid detection of voltage sag compensation is a prerequisite for the effectiveness and rapidity of DVR compensation. Therefore, the research on voltage sag detection method has important theoretical and practical significance.Working principle of DVR is introduced in this paper and the components of DVR, the forms of its main circuit topological structure are analyzed in detail. Based on the selected main circuit and its parameters, compensation method and control method of the DVR device, the voltage sag detection module of DVR are explored and optimized in depth.In order to solve the problem of excessive energy consumption and detection delay in continuous operation of the detection module, an interactive detection method based on improved generalized S transform and RMS algorithm is proposed.The generalized S transform method is improved by using the time-frequency resolution characteristic criterion to obtain the high time-frequency resolution,locating the point of abrupt change. For denoising and filtering, the generalized S inverse transform is performed on the processed module time-frequency matrixes.Once detecting voltage sag, RMS detection module starts and calculates the value of voltage sag. If the voltage sag is not detected, the generalized S transform module is operated separately.Due to the limited scope use of interactive detection method, and the defect that is hard to realize in the experiment, an improved dq transform algorithm based on adaptive least mean square(LMS) filter and software phase-locked loop isproposed.The adaptive LMS algorithm with time delayed feedback is applied to the digital filter, which is applied to the control process of software phase-locked loop.The filtering process is conducted in advance, where instead of the traditional low pass filter, derivative method is used to isolate the DC component under dq coordinate system instantaneously.Simulation models is built in EMTDC /PSCAD to validate the effectiveness of proposed methods, improved detection methods and the effect on DVR compensation are analyzed and compared. Results show that the interactive detection method with small delay is more suitable for the occasion of low accuracy and low frequency occurrence; the improved dq transformation detection method is easy to achieve and used widely, both meeting the accurate, fast and real-time requirement of DVR. A single phase DVR prototype system is constructed, and the power conversion circuit,signal conditioning circuit and synchronous circuit are designed, STM32 series of main control chip is used for software programming of DVR prototype system, the feasibility and effectiveness of improved dq transformation detection method are verified by experimental results.