Control Method And PWM Modulation Strategy Of Cascade STATCOM On Tansmission Line

With the development of China’s power grid, people pay more and more attention toFlexible AC Transmission technology, as an important member of the family FACTS, largecapacity chain STATCOM has been widely concerned owing to the benefits like fastresponse, the compensation current which is not affected by the effect of system voltageand so on. For this new reactive power compensation device, following works are mainlydid:A discussion about the significance of reactive power compensation, the demand andprospect of the chain STATCOM has been done, and the development of control methodsare briefly described；In this paper, it establishes an external characteristic of low-frequencydynamic model of the chain STATCOM in the three-phase static equilibrium coordinatesystem, the theory of coordinate transformation is discussed in detail, and the method ofinstantaneous reactive power is used to analyze the problem of the STATCOM exchangewith the system power； The PWM modulation strategy for the chain STATCOM isresearched, and the level of carrier phase shifting method and specific method of harmonicelimination are mainly described. The main work of eliminating harmonic method issolving the nonlinear equations, the carrier phase shifting method is based on singlepolarity double frequency, which output harmonic characteristics is excellent, it can beadjusted continuously, so the level of the carrier phase shift method is chosen as theunderlying device and control method；The internal model of chain STATCOM is analyzedcomprehensively, the unbalance cause of DC capacitor voltage is verified, so solutionsbased on hierarchical control is proposed, and it builds the foundation for the use ofexternal characteristic model to solve practical problems；This paper focus on the controlmethod of the main circuit of STATCOM, the traditional PI control method, input-outputfeedback linearization method, and ADRC based on extended state observer (ESO) areintroduced through comparing the feasibility of the simulation method；For multi-objectivecontrol of transmission line chain STATCOM, stable voltage and reactive power to designsystem level controller are selected, as a result, control objectives are completed well.