Dynamic properties of PCM-controlled current-fed boost converter in photovoltaic system interfacing

The interfacing of photovoltaic (PV) energy source is known to be problematic due to the highly varying terminal characteristics of the energy harvesting unit, generally a PV generator. Therefore, its power flow needs to be regulated and a certain maximum power point (MPP) traced. The switched-mode dc-dc converters are conventionally used to interface energy sources possessing constant-voltage nature. These voltage-fed (VF) converters have been used as a basis for the MPP-tracking devices as well. It is observed, however, that the performance of such converter is not optimal in this purpose, because the PV generator possesses a current-source nature. Therefore, an additional capacitor is usually added between the source and the converter to enhance the constant-voltage properties of the source. The PV regulation is also performed by controlling the input voltage. These modifications change, however, the VF converter into a current-fed (CF) converter, which has totally different static and dynamic behavior than the original converter. This implicit duality transformation also causes a situation, where the usage of conventional inner-loop control, such as peak-current-mode (PCM) control, may lose its beneficial nature or the converter may even cease to operate in a stable manner. This paper analyses the static and dynamic properties of the buck-derived PV converter known as a dual or CF boost converter under the input-voltage and PCM controls. Investigations show that the conventional PCM control is not recommended to be used in the CF converters due to its inherent VF properties.