Study On Dynamic Var Compensation For Fluctuating Load

Fluctuating loads in the power system, such as the impact loads in the industrial production, will cause voltage fluctuation, reduce power factor, and shorten the service life of electrical equipment. Grid-connected wind farm needs to absorb lots of reactive power from the grid, therefore, on the view of reactive power, wind farm can also be considered as a kind of fluctuating load. Dynamic var compenstors such as SVC and STATCOM have an encouraging application prospect due to its excellent performance. This paper focuses on the ultra-short-time load forecasting algorithm for fluctuating loads, STATCOM reactive current control method and wind farm dynamic var compensation.Considering the special characteristics of fluctuating load, an improved Sage-Husa adaptive filtering algorithm is proposed in this paper. The new algorithm is based on Kalman filtering algorithm, and can correctly estimate input noise variance Q and measurement noise variance R. The calculation method of weighted coefficient is also given in the new algorithm, which effectively improve forecasting accuracy. The reactive current forecasting results of some substation buses in an iron and steel enterprise show that the improved algorithm has a high forecasting accuracy, and inherits the advantages of the original algorithm whose computing speed is rapid and storage capacity is small, and is perfectly suitable for online applications.The indirect and direct reactive current control method of STATCOM based on the improved Sage-Husa adaptive filtering algorithm is studied in this paper. In the direct current control method, the improved algorithm and other common ultra-short-time load forecasting algorithms are introduced to compute the STATCOM output current and reference current. Simulation results show that using the improved algorithm can make a better control of the reactive current produced by STATCOM, meanwhile, the average tracking error and maximum tracking error are both smaller than other common forecasting algorithms. In the indirect current control, the improved algorithm is used to forecast the reactive current produced by STATCOM. Considering the highly inherent nonlinearity of STATCOM, grey PID control method is presented to estimate the uncertain and time-varying parameters and modify the PI control. Simulation results show that grey estimator can reduce the reactive current tracking error, and has much stronger controllability and robustness against external disturbances. The ultra-short-time load forecasting method is also intrduced to the control strategy of hybrid var compensator based on TSC and D-STATCOM. The simulation results show that the new coordinate control method can decrease the response time of TSC, and improve the hybrid var compensator’s performance.A simple wind farm connected to infinite bus is modeled. Influences of different wind disturbances, network voltage fluctuating and short-circuit faults on wind farms with SVC and STATCOM are simulated respectively. The simulation results show that SVC and STATCOM can both provide reactive power quickly and smoothly, improve the voltage stability of power grid, and keep the wind farm connecting to the power grid. Compared to SVC, STATCOM has a faster response speed, and the reactive power produced by STATCOM has nothing to do with the voltage of the installation site.