Linear Current Controller With Fast Transient Response and Low Switching Frequency

This article presents a finite control set (FCS) linear current controller for grid-tied inverters with L filter that provides a very fast transient response with low switching frequency, similarly to an FCS model predictive controller (MPC). The presented solution uses a state-space linear controller structure (with low computational complexity) that incorporates integral action so as to achieve zero steady-state error at the fundamental grid frequency. Thus, this solution offers a simpler design process and an easier method to assess the stability and performance of the system compared to an MPC, which usually requires complex optimization algorithms that are a field of study in its own right. Moreover, thanks to the FCS operation, the presented controller achieves a faster transient response compared to a solution based on a pulse width modulator with an equivalent switching frequency. In addition, the proposal does not generate any switching or low-order harmonics. The switching noise is evenly spread at all frequencies instead of it being concentrated at some harmonic frequencies. This reduces the risk of exciting resonances in the utility grid and facilitates the operation of multiple inverters in parallel.