Modulated Model Predictive Current Control of a Three-Phase Photovoltaic Central Inverter

A three-phase two-level voltage source inverter is the most widely adopted configuration for the grid-integration of large-scale photovoltaic energy systems. To obtain high energy conversion during a wide dynamic range and to comply with the stringent grid codes, faster and high-performance nonlinear controllers are required. This paper develops a novel modulated model predictive current control method to control the photovoltaic central inverter for maximum energy yield and reactive power control. The developed control method estimates the future values of stationary-frame grid currents and assesses them by a duty-cycle optimized cost function. Three stationary voltage vectors corresponding to the low cost value are then synthesized by the space vector modulation stage to produce gating signals for the central inverter. The proposed control method ensures constant switching frequency, low steady-state errors and fast transient response simultaneously during rapid environmental changes. To verify the feasibility of the developed control method, simulation studies are conducted on a 1-MVA photovoltaic system, under solar irradiance, temperature and reactive power changes.