Research On Phase-locked Technology For Static Synchronous Reactive Power Compensator

An important index of the power supply is power quality. At present, reactive static synchronous compensator(STATCOM) is the development direction of reactive power compensation device. The basic requirement of static synchronous reactive power compensator is synchronization, which is common problem for all topology type of STATCOM. "Synchronous" is defined as the frequency of converter between power grid output voltage and input voltage has always been consistent. Real-time detecting and locking phase of power grid voltage, and high precision accuracy locking the frequency of the power grid voltage is premise that STATCOM has good performance.This paper provides the phase locking technology research foundation for STATCOM. It starts from the synchronous technology research status and the principle of the traditional phase-locked loop, in different development stages with different basic methods to improve the phase locked time, and improves the basic methods in the inaccurate phase locking situation under the influence of the harmonic. When researching single link control part, it adopts the method of zero phase lock, considering the influence of harmonic, added low-pass filter in the form of analog circuit to ensure precision phase lock. When in the study of the central control part, it adopts the closed loop dq transformation method to realize precision phase lock in the three-phase steady-state, considering the influence of the harmonic will cause unbalanced for three-phase, improved algorithm on the basis of closed loop dq transformation method, designed a double synchronous coordinate decoupling method to realize precise phase lock in the unbalanced state. Through the process of the research and development of complete sets of equipment, comparing different phase locking method in different lock time on the basis of precision lock capability.According to the working principle, this paper establishes the mathematical model and makes simple analysis on it. And then sets up a simulation model respectively, obtains the simulation result. Comparative analysis of simulation result show that, the designed low pass filter can effectively filter out harmonic, and implement precision phase locked with zero phase locking method under the influence of harmonic; Double synchronous coordinate decoupling method can realize precision phase locked under the unbalanced three-phase but the closed loop dq transformation method cannot; It is with high locked time for closed loop dq transformation method belonged to carrier adjustment method than the zero phase lock method belonged to fundamental wave adjustment method.