Discrete-time sliding mode control system of the grid-connected doubly fed induction generator at the low sampling frequency
A new design of a digital control system for the grid-connected doubly fed induction generator is described in this paper. A discrete-time state-space model of the controlled system is obtained in the stator stationary reference frame. Using this model, a discrete-time sliding mode based control system is designed. Its tasks are the grid synchronization and the direct power control. The discrete-time equivalent control method is applied, and the control vector is calculated from the samples of voltages and currents. The control vector is converted to a switching sequence in a power converter using the space vector modulation. The modulation period is equal to the sampling period. A disturbance compensator is designed to eliminate the influence of the discretization effect and model uncertainties. In this way, a robust control system with a constant switching frequency is designed. Its digital hardware implementation is simple. The performance of the designed control system is tested on a simulation model.