A predictive control scheme for DC voltage and AC current in grid-connected photovoltaic inverters with minimum DC link capacitance

This paper describes a discrete time control algorithm for regulation of both DC voltage and AC currents in three-phase inverters. It is suitable for application in grid-connected photovoltaic (PV) generation plants due to the intrinsic ability to perform maximum power point tracking (MPPT) of the PV array. Furthermore, the transient response time is of the order of a few PWM sampling periods, therefore the energy storage requirements of the DC capacitor are significantly reduced, and a small non-electrolytic type can be employed. Considering that the DC buffer capacitor of an inverter is often the limiting factor in terms of reliability, the proposed approach can lead to a substantial improvement in the way the entire system is perceived. The technique has similar harmonic performance to regularly sampled PWM, with a fixed switching frequency and low current distortion, and operates at unity power factor. This predictive method avoids problems of stability and loop interactions present in controllers employing cascaded DC voltage and AC current feedback loops. The theory of the algorithm is presented in this paper, together with simulation results.