Dynamic Modeling and Nonlinear Decoupled Control of Back-to-back Voltage Source Converter

A dynamic model of back-to-back voltage source converter under synchronous rotating d-q coordinate system is developed. The system is transformed to a new equivalent nonlinear system which consists of a linear decoupled subsystem, and a nonlinear subsystem characterizing the dynamics of the dc-link voltage in terms of the state variables in the linear subsystem via the feedback linearization technique. Then a decoupled controller which consists of an outer loop for determination of d- and q-axis components of reference currents and an inner loop for tracking the reference currents is designed for active and reactive power exchange control between the VSC and the two ac systems. The validity of the proposed controller is demonstrated by the simulation results under electromagnetic software PSCAD/EMTDC and experimental results on a 30kVA/380V prototype system, respectively.