Discrete time modeling and control of the voltage source converter for improved disturbance rejection

A new voltage source converter control approach is presented, based on multivariable z-domain control techniques. Using time-averaging theory in the synchronous reference frame, a linear time-varying model of the converter is developed. The new model may be directly employed as an efficient simulation tool and used as a basis for developing discrete time inverter controls. Application of digital control techniques results in current step tracking in one switching period, with zero overshoot. While DC load fluctuations are rapidly compensated through nonlinear feedforward, AC system voltage disturbances are rejected through a positive and negative sequence bias estimation scheme. As a result, the converter may operate at its current limit under even severe AC voltage unbalance and only a balanced AC current will flow, thus ensuring full protection of the semiconductor devices in all three converter legs. Experimental results validate both the time-varying simulation model as well as the proposed control design