Modeling and Simulation of MPPT for the Grid-Connected PV System
The grid-connected PV system must be designed to operate at its maximum power point (MPP) at any temperature or solar radiation. Generally if the load is not directly coupled with the PV panel, the operating point and MPP do not coincide. The direct connection of the load to the PV panel may result in the over sizing of the PV panel and thus increases the cost of the entire grid-connected PV system. The solution to this problem is to use the DC/AC converter (inverter) with an automatic trigger angle control which is usually inserted between the PV panel and the load. The current control method is used for modeling and simulating the MPP tracker for regulating the power flow originated from the PV panel-based on the gridconnected DC/AC converter (inverter). Current- based maximum power point tracker (MPPT) is investigated as a means for controlling the trigger angle of the grid-connected inverter. The maximum efficiency is the main issue presented in this article. A strategy for tracking the MPP for several solar radiation intensities has been used in this article. The control loop circuit, the grid-connected DC/AC converter, operating as an inverter, is modeled to verify the proposed control strategy performance. This article shows that the maximum power supplied by the PV panel is reached at any solar radiation intensity when the PV panel current is directly proportional to photocurrent. This important property of the PV panel means that at the MPP the ratio of the output voltage to the output current for the PV panel is a constant, forming an adaptive matching of the panel to the load. Since the current-voltage characteristic of a PV panel depends on the solar cell temperature, the solar radiation, and the load, it is very difficult to achieve an optimum matching at all solar radiation intensities and at all temperature variations. It should be emphasized that this article, in addition to tracking the MPP efficiently, presents analytical solutions of the transcendental equation.