Research On The Cascaded H-Bridge Type DSTATCOM

As a kind of important user power device, DSTATCOM can solve the powerquality problems of power distribution network such as voltage fluctuation and flicker,current distortion and three-phase voltage unbalance. With the increasing of the powerload, there is higher requirement on the capacity of DSTATCOM. As H-bridgecascaded DSTATCOM is easy to modular design and expand in High voltage field, ithas become the research hotspot in the power field at home and abroad. TakingH-bridge cascaded DSTATCOM control system as the research object, PWMmodulation algorithm, the compensation current control and dc side capacitor voltagebalance control system are researched in-depth in this paper.In this paper, the working principle and main circuit topology of DSTATCOMare analyzed, and on these bases, the mathematical model is established in ABC、 and dq coordinate system. And carrier phase shift PWM technology (CPS-PWM) wasintroduced in detail, including the dual polarity CPS-PWM and unipolar doublefrequency CPS-PWM mainly. Research the structure of H-bridge cascaded topology.Using the advantage CPS-PWM and SVPWM technology for reference put forwardPhase space vector pulse width modulation (PS-SVM) that is suitable for H-bridgecascaded DSTATCOM control. Simulation verifies correct of this method.On the basis of further analysis for mathematical model of DSTATCOM,establishe system model, and introduce linear PI controller to decouple the reactivecurrent and active current to put forward power decoupling control strategy. Inaddition, use virtual flux to orientate power grid voltage, and research the integrationinitial value problem of virtual flux observation, achieve control without theelectromotive force sensor grid side. On the basis of analysis of the capacitor voltageimbalance of dc side, hierarchical control strategy is used for capacitor voltage.Simulation verifies the effectiveness of these methods.Finally, device selection method for main circuit of H-bridge cascadedDSTATCOM is introduced. And the platform experiment has set up to verify thetheory proposed in this paper, whose results showed correct and effective of relevanttheory.