An improved sliding mode controller for a multifunctional photovoltaic grid tied inverter

This paper proposes a robust control algorithm for a photovoltaic (PV) multifunctional grid tied inverter (MFGTI). The MFGTI is used to simultaneously inject the active power of a PV panel and enhance the power quality of a microgrid. The proposed algorithm will estimate the positive fundamental component of the source current even under strongly disturbed main voltage and load conditions. First, a Sliding Mode Controller is used to estimate the magnitude of the source current. Then, a positive fundamental component estimator is used to estimate the unity vector of the main voltage. By multiplying the output of the two blocks, we obtain a pure sinusoidal source current in phase with the main voltage. Using this algorithm, the MFGTI will inject the active power, compensate the reactive power, and enhance the power quality of the microgrid. Thus, the main grid will only supply some amount of active power with a unity power factor. The proposed algorithm is compared with the conventional method to verify its effectiveness. Several loads and main voltage scenarios are simulated and then experimentally tested. The results prove the superiority and effectiveness of the proposed algorithm.