Improvement of Current Dynamics During Controller Saturation in a STATCOM

This paper presents the dynamic analysis of the currents during controller saturation of a three phase voltage source inverter (VSI), connected to a point of common coupling (PCC). Closed-form solutions of the VSI currents are obtained using a piecewise linear, state-space averaged model of the VSI under the linear and saturated regimes of the current controller. Using these results, a new algorithm is proposed which best improve current dynamics during controller saturation, while simultaneously limiting the reference voltage within the modulation range. This ensures that no lower order harmonics are introduced in the VSI currents, resulting in simplification of the ripple filter design. Experimental results obtained are compared with those from existing algorithms. It is shown that the proposed algorithm results in faster current dynamics.