Fixed-frequency sliding mode control of a single-phase voltage source inverter with input filter

This paper describes a sliding mode controller for a single-phase voltage source inverter. The work is motivated by power converter systems including two input filters with well separated corner frequencies. Since the inverter input current contains a low frequency component at twice the output voltage frequency, the high frequency input filter is designed to have low damping (no supplementary ohmic resistance). The stability of the closed-loop system is ensured by the control scheme resulting in stable large-signal behaviour while maintaining fast dynamic response to external disturbances. The analytical study provides general tools to design variable and fixed-frequency control implementations. It is shown that for the voltage source inverter, the simplest way to realise the proposed variable structure control law consists of adding a three level disturbance signal to the switching function. As a result, the power converter operates at constant switching frequency in the steady-state. The steady-state error is determined and a method is proposed to reduce the resulting harmonic distortion of the output voltage. The static and dynamic performances of the sliding mode controller are verified by an experimental 5 kVA inverter.