A simple PV constrained production control strategy

Photovoltaic (PV) panels usually work with a Maximum Power Point Tracking (MPPT) algorithm to produce as much power as possible. Their output power changes mainly according to the solar irradiation, so they are unpredictable power sources. For grid-connected PV systems, the PV MPPT production could be strongly fluctuating due to possible significant variations of solar irradiation, which could be an issue for grid power quality with consideration of future PV penetration level. On the other hand, for stand-alone PV systems, which usually work with energy storage, the MPPT production would cause extra problems in power balancing when the storage reaches its upper state of charge limit. In these cases, the PV production should be constrained. This paper proposes a simple PV constrained production control strategy, which leads to control the PV power at any level within the MPPT production ability. If the solar irradiation decreases and PV MPPT power is not able to output the desired constrained power, the control strategy continues to operate PV system with MPPT algorithm. The transition between MPPT and constrained mode is continuous and seamless; the two modes operate separately. Experimental results validate the proposed control strategy.