Robust AC Voltage Controller with Harmonic Elimination for Stand-Alone and Weak-Grid-Connected Operation

This paper presents an ac voltage controller with a high robustness to plant model variations which can operate under a wide range of loads. A robust voltage controller is required in a droop-controlled inverter which operates in island mode with other generators or is connected to a grid. In such modes of operation, the voltage source converter (VSC) can experience a large variation in the load impedance depending on the number of parallel generators or the grid impedance value. The proposal improves the transient performance by selectively minimizing the output impedance of the system at the frequencies which typically contain the largest components of the output current. Complete harmonic control is achieved due to its zero output impedance at a set of design-selected frequencies. The design process only requires, as input parameters, the LC filter values, the sampling frequency, and a set of harmonics where load-current circulation is expected.