Research About Static Synchronous Compensator Based On Multilevel AC Converter

With the development of power electronics technology, the multi-level converter has been proposed with the low switch voltage and low output voltage harmonics. A new method to achieve reactive power and harmonic comprehensive compensation with multilevel ac converter was presented in this paper. A novel concept wherein dual virtual quadrature sources are used to synthesis the required additional current. This is seen to result in simple low-cost ac converters, have minimal component count, and can realize harmonic control without requiring multiple sources or energy-storage elements.By improving the method based on instantaneous reactive power theory, it can contemporary achieve the decomposition test for positive and negative-phase-sequence component of high-order harmonic current, finally, the detection of high-order harmonic current is achieved. The concept of dual virtual quadrature sources is presented in this paper for the problem that the traditional control method can not realize phase shift. The control method can be derived by decomposing desired voltage. The impact the control parameters have on the amplitude and phase of the output voltage also been analyzed in this paper.The operating mode of the AC converter has been analyzed and its small signal model has been given. Amplitude and phase frequency curve of the open-loop transfer amplitude were drawn and the compensation network was designed according to the system performance index. The principle of comprehensive compensation was studied. The control section includes reactive current detection, high-order harmonic current detection, PI regulator and logical conversion circuit. The simulation software Saber is used to simulate the AC converter and the simulation waveforms were given.The hardware of the STATCOM based on the multilevel ac converter was designed, including parameter calculation of the input and output filter circuit, selection of MOSFFT and the design of current sampling circuit, synchronous circuit and driven circuit. Reactive power compensation experiments were done based on simulation studies as well as hardware and software design. The experimental results show that the circuit of the system has a good effect on reactive compensation.