A Finite-Control-Set Linear Current Controller With Fast Transient Response and Low Switching Frequency for Grid-Tied Inverters

Abstract

This article presents a linear current controller for a grid-tied inverter with an L or LCL filter that uses a finite-control-set (FCS) operation. Thanks to the FCS operation, the proposed controller provides a very fast transient response, similar to an FCS model-predictive controller (MPC), while needing a low switching frequency and a low computational load. Contrarily to MPC solutions, the proposal uses a linear control structure. Such a linear structure offers a straightforward implementation and stability assessment compared to an MPC, which usually requires complex optimization algorithms and Lyapunov functions that are a field of study in its own right. The proposal does not generate any switching or low-order harmonics. By design, the switching noise is evenly spread at all frequencies instead of it being concentrated at some harmonic frequencies, as in the case of pulsewidth-modulator-based controllers. This reduces the risk of exciting resonances in the utility grid and facilitates the operation of multiple inverters in parallel. In particular, the proposal is shown to achieve compliance with stringent grid harmonic codes using an L filter in a multimegawatt application, where previous proposals required an LCL filter with the same total inductance.