| Abstract |
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. |
