Improved limited power tracking of a photovoltaic plant connected across voltage-controlled DC bus

The objective of this paper is to improve the performance of limited power point tracking (LPPT) of photovoltaic plants. The limited power point tracking refers to controlling the power output of a photovoltaic array at a level below the maximum power point. The limited power point tracking exhibits advantages over maximum power point tracking (MPPT) both in terms of economy and system security. The previously reported LPPT methods, however, exhibit more oscillations at low power levels or require additional mode changing action under power scarcity and may malfunction under the rapidly varying environmental conditions. To avoid those difficulties, two novel LPPT control schemes are proposed. Both the schemes are carefully designed with minimum deviation from the traditional MPPT control so as to ensure easy implementation. Each of the controllers proposed has its own merit. The LPPT control under the proposed schemes can be implemented without the support of any local energy storage. Detailed case studies are performed to verify the effectiveness of proposed LPPT controllers.