PV Voltage Control in Spite of Disturbances on MCB Boost Output Voltage in Parallel Association

Abstract

We present a specific control law designed to Magnetically Coupled Boost (MCB) converters used as photovoltaic (PV) optimizers in parallel association. In the case of inappropriate control algorithms, conflicts appear between boosts, preventing energy injection on output power bus for some of them. In this work, we highlight that an important disturbance on output bus induces consequent perturbation of PV module operating point, when controlling in open loop. In a second time we show how to implement a formula designed to compute duty cycle in pulse width modulation control (PWM), in spite of not perfect MCB model and no linear PV module behavior. Indeed, challenge is to adjust duty cycle according to actual power bus voltage when PV module voltage has to be constant, especially when Maximum Power Point is reached. A closed loop with elementary correction law is implemented in sampled control to ensure PV voltage as reference, preventing any variation of PV operating point. In a third time, experiments with different settings in sampled controller are analyzed, and comparisons between responses allow to conclude on robustness of such control, in the case of only one MCB converter disturbed by output voltage. Further studies of converter behavior in parallel association are also mentioned at the end of this paper, with objectives, for example, to characterize impact of possible shading on photovoltaic module and even to allow coupling of storage units to power bus.