Discrete-time sliding mode direct power control for grid connected inverter with comparative study

This paper presents a design of a digital direct power control strategy for a three-phase grid-connected inverter combining the discrete-time sliding mode control and the space vector modulation. Using the discrete-time state-space model of the controlled system, a discrete-time sliding mode control system is designed. Its output is a control vector which minimizes the instantaneous active and reactive power displacement from their reference values. The control vector is computed from the samples of voltages and currents and then converted to a switching sequence using space vector modulation. The period of modulated signal is equal to the sample period. A correction of the control vector is defined with aim to eliminate the influence of the system uncertainties using predicted values of the active and reactive powers. In this way a robust control system with a constant switching frequency is designed. Its digital hardware implementation is very simple. This control system is tested on a simulation model and compared with other similar approaches.