Input-output linearization and stabilization analysis of internal dynamics of three-phase AC/DC voltage-source converters

Based on the input-output linearization method of differential geometry theory, the internal dynamics i.e. remaining dynamics of the nonlinear three-phase AC/DC voltage-source converter system, with output represented by (i_d, u_c) i.e. direct voltage control and (i_d, i_q) i.e. indirect voltage control respectively, are been studied. It is pointed out that the three-phase AC/DC voltage-source converter is actually a nonminimum phase system, and its internal dynamics is unstable when using direct voltage control. But, if the output is represented by (i_d, i_q) i.e. indirect voltage control, the system is a minimum phase system, and its internal dynamics is asymptotically stable. It is reasonable to control the dc voltage indirect through the regulation of (i_d, i_q). If do not add a voltage control loop, the setting time of the output dc voltage is mainly depend on the parameters of the system and too long. So, a simple voltage control method is proposed through ascertain i_Aret to maintain the stabilization of u_c. Thus, a cascade control system is proposed. The inner current loop can maintain the sinusoidal waveform and unity power factor. The outer voltage loop can maintain the DC-bus voltage to the output voltage reference and provides the reference of inner current loop i_d. The control signals are modulated by SVPWM technology. The controlled three-phase AC/DC voltage-source converter has the features of global stability, fast tracking of DC-bus voltage command with zero steady-state error and do not need adding PI controller, asymptotic rejection of load disturbance, robustness against parameter (L,C) variation and decoupled dynamical responses between d and q current loops.