Dynamic modeling of DC-DC converters with peak current control in double-stage photovoltaic grid-connected inverters

In photovoltaic (PV) double-stage grid-connected inverters a high-frequency DCDC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DCDC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DCDC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DCDC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230?W experimental inverter working from a single PV panel. The inverter is based on a Flyback DCDC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DCDC + inverter) is also shown to validate the concept. Copyright (c) 2011 John Wiley & Sons, Ltd.