Study On Current Detection Method And Control Technology Of STATCOM Based On Instantaneous Reactive Power Theory

Power quality issues are attracting more and more attention with the wide application of non-linear and jerky loads in power system, and thereby reactive compensation and harmonics contamination have been a research hotpot. As one of key technology of FACTS. STATCOM is becoming the development trend of reactive compensation equipment because of its effective compensation performance. This paper systematically studies STATCOM detecting method and control methodology of reactive power currents through theoretical analysis and simulation modeling.Firstly, the paper analyzes the traditional p-q and ip-iq methods based on the instantaneous reactive power theory. And then a modified method based on current average value is proposed by improving the circuit structure and low-pass filtering link in its physical realization. The new method simplifies the detection circuit as well as improves response speed of the detection algorithm for it does not require phase-locked loop circuit. Simulation results demonstrate the effectiveness and correctness of the new method under both normal and distorted voltage conditions.The advantages of the direct current control method of STATCOM compared with the indirect control method are summarized and two specific methods of the direct method based on PWM tracking techniques, which are hysteresis control and triangular wave control, are emphatically discussed. Meanwhile, the setting of hysteresis width and the design of PI regulator parameters are analyzed particularly. Simulation results of the two control methods shows that the switching frequency of hysteresis control is varying with the change of hysteresis width. In details, the switching frequency and loss increases as the hysteresis width grows. However, with the higher switching frequency, the tracking effect of compensation current is better and the harmonic content is lower. Besides, the simulation results also show that although the switching frequency of triangular wave control is fixed, distortion components with the same frequency as triangular carrier will be introduced in the compensation current. The STATCOM system models are established with Matlab/Simulink. According to the simulation with linear load, nonlinear load and impact load, the detection results between traditional and improved detection methods are compared and the response characteristics between hysteresis and triangle wave control methods are studied. The results not only indicate that both the traditional ip-iq method and the improved method can accurately detect the referenced reactive current for STATCOM but also prove that the improved method can produce a faster dynamic response. Additionally, both of the control strategies of STATCOM can rapidly track the reference current, realize effective compensation of harmonic and reactive power, and improve the operation performance of the system, whereas, the harmonic contents of system current after compensation have differences due to the different switching frequencies.Finally, the paper briefly describes the characteristics of wind power generation, the impact of wind power integration on power grid and the importance of dynamic reactive compensation to the wind power system. On this basis, by constructing the wind farm model, which is connected with an infinite system, simulations are carried out to study the dynamic running characteristics of the system according to whether STATCOM is installed or not in the gradual wind. The results show that STATCOM can compensate for the reactive power fluctuations caused by the wind change and maintain the voltage stability of the power grid.