Study On Theory And Technique Of STATCOM Integrated With Distribution Transformer

The technique of Static Synchronous Compensator (STATCOM) is an effective way for reactive power compensation in power system. It performs well in compensation with fast dynamic response and board operating range, which makes it possible to compensate stable or varying reactive power rapidly. Because of its characteristic, STATCOM is now using more and more widely in power system. In order to provide highly effective compensation, it's important to study the topology structure and integrating method of the compensating system, optimize system structure and circuit parameters, and provided feasible control strategy according to the compensating mechanism and the mathematical model of compensating system. This paper focused on the problems above and started relevant researching.This paper proposed the integrating method and technique of STATCOM integrated with distribution transformer (DT-STATCOM) at the high-low voltage crossing point in power system, which realized intensive compensation for distribution load. Study on main circuit topology structure and parameter optimization of DT-STATCOM indicated that the technique of DT-STATCOM was able to lower the integrating voltage effectively, which helps to select the most suitable parameters of power electronic devices and improve main circuit structure design. Using multiple-module coordination and parallel operating method can also solve problems of raising compensating capability and reducing system loss. This paper proposed that the leakage reactance of distribution transformer tapped winding could be used as the second reactance of LCL output filter. In this way it could save an additional filter second reactance, which helped to improve the design of filter. Based on certain principles the range of DT-STATCOM main circuit parameters was decided.According to the special topology structure of DT-STATCOM, this paper stressed on representing DT-STATCOM's working mechanism while it is integrated with distribution transformer tapped windings. System input-output mathematical model was built up under DT-STATCOM's equivalent circuit. The mathematical model raised a current-tracing controlling strategy basing on power balance theory. This controlling strategy calculated compensating current reference with electrical quantity from both low voltage side and high voltage side of transformer. In this way the controlling strategy could be available for different tapping winding integrating method, have board applicability and good dynamic current-tracing ability.In order to start simulating study of the compensating mechanism, steady state characteristics, dynamic state characteristics and main circuit parameters of DT-STATCOM, this paper built up a DT-STATCOM simulating model with Simulink workbox in MATLAB. System simulation proved the effectiveness of compensating structure integrated with distribution transformer and the current-tracing controlling strategy basing on power balance theory. Simulating work also improved optimal design of system structure and circuit parameters.On the foundation of simulating research, a dynamic-simulating experiment system was built with 1.1MVA/10/0.4kV distribution transformer and DT-STATCOM module. DT-STATCOM system no-load loss measuring experiment was perform, the result of which indicated that measured value of no-load loss of DT-STATCOM system was below 1% of distribution transformer's rated capacity.The last part of this paper stated conclusions of research work above, and give out the possible research work in the future.