Study On Control Method Of Static Synchronous Compensator

Static Synchronous Compensator (STATCOM) is an important controller in the flexible AC transmission system (FACTS) which has had some application examples in the power system domestic and overseas. It bases on the inverter technology, and it is equivalent to an adjustable voltage or current source. By controlling the amplitude and phase of the voltage or current source, it can change the size of the reactive power which is transported to the power grid. So far, most of the research is concentrated on the aspects of the structure of the main circuit, the detection method of reactive current, the design of control strategy, and so on. However, most of the current controlling strategies are based on the principle of unequal height and equal interval voltage modulation method, which can only compensate fundamental reactive current in practice.In this dissertation, a new type of voltage modulation method is proposed and applied in STATCOM which can compensate fundamental reactive current and suppress part of harmonic as well.First of all, on the basis of an introduction of the basic principle of STATCOM and Active Power Filter (APF), a new voltage modulation method which has equal height and unequal interval is proposed. The principle of the new STATCOM which includes the new voltage modulation method is explained in detail, and the mathematical model is established. As a result of using new main circuit structure which has the same variable and capacity transformers directly connected, the control of the STATCOM is more flexible and the structure of the STATCOM is more modular. These are favorable to mass production.Then, after a brief introduction of main methods of current detection and kinds of control strategies, a new method of STATCOM detection and control program is proposed according to their characteristics and shortcomings. What is more, the principle of the adopted method is described in detail, and the mathematical model is established as well.At last, several large-capacity main circuit programs are introduced briefly. Afterwards, a new main circuit program is proposed, the calculation formulas of the inductance and capacitance in the main circuit are derived, and the MATLAB simulation model of the new STATCOM is built. The results of simulation reveal the feasibility of the design. The new STATCOM can achieve functions of compensating reactive current and suppressing part of harmonic current.