Resonant control for power converters connected to weak and micro grid systems with variant frequency

Controlled Power Converters are extensively used in industrial applications as they can adapt the electrical energy as required by the application. However, these devices must be properly commutated in order to control voltages and currents. Indeed, power converters are known to be multivariable, coupled, and nonlinear systems; therefore, the control technique needs to be chosen carefully. There are several control techniques reported in the literature for power converters and one of them is the Resonant Control (RC) mainly used on ac based systems. Advantageously, RC guarantees zero steady state error for a sinusoidal reference with a constant frequency and, in addition, it does not need a stationary to rotating reference frame transformation. However, the conventional RC approach requires the exact ac mains frequency value to ensure zero steady state error, being a significant drawback for applications where variable frequency environments are expected. This paper proposes an enhanced RC scheme capable to work under variable frequency scenarios, as in weak and micro grid systems while guaranteeing zero steady state error. The scheme results in a simple algorithm based upon discrete mathematics whose parameters become independent of the ac grid frequency. Results show the feasibility of the proposed approach even under severe ac frequency variations (over 100%) while featuring a stable control loop operation and zero steady state error.