Propose a MPPT Algorithm Based on Thevenin Equivalent Circuit for Improving Photovoltaic System Operation

Abstract

Smart grids are considered as key solutions to solve current power security issues. Among these suggestions, microgrid is proposed to integrate distributed generations (DGs) such as photovoltaic (PV) system into the network and the control of DGs output power is getting more attention. The output power of PV arrays with nonlinear characteristics is affected by temperature, solar irradiation and load. Various maximum power point tracking (MPPT) methods for photovoltaic (PV) power systems have been considered and developed to maximize the delivered possible power. In this paper, a modelized photovoltaic source is introduced, based on the Thevenin equivalent circuit. An ordinarily employed solar system model is linearized into simple Thevenin source-resistance representation. Next, a control algorithm associated with the relationship between controller's PWM duty cycle of the MPPT boost converter and solar array output power, namely proposed MPPT algorithm, is introduced. This proposed method is compared with an existing popular MPPT algorithm to confirm its superior performance by using the MATLAB/SIMULINK ® simulation. The results show an improvement in the power generation from a PV array in any weather condition, and also help to reduce the impact of rapid change of solar irradiation on the output power variation within the time duration of change. Therefore, the proposed algorithm reduces the effect on grid frequency and motivate the PV generation penetration into the microgrids. Finally, a 50W DC-DC boost converter prototype is implemented and tested to verify the feasibility of the proposed control scheme.

A Proposal for an MPPT Algorithm Based on the Fluctuations of the PV Output Power, Output Voltage, and Control Duty Cycle for Improving the Performance of PV Systems in Microgrid

“…The control parameter of the power electronics stage is the switching duty cycle of the PWM signal of the MPPT controller. Therefore, another approach to maximize the output power of the PV system is based on the relationship curve between the PV system output power and the PWM duty cycle [21,22]. Figure 6 shows a typical hill-shaped PV array output power curve with respect to the PWM duty cycle, where P PV is the PV array output power and D represents the PWM duty cycle of a DC/DC boost converter [21].…”

“…The advantage of the HC MPPT algorithm is its simplicity. Furthermore, the MPP can be tracked accurately when the solar irradiance increases rapidly [21]. However, it is only effective in the case of using a small value of the duty cycle steps.…”

“…At this moment, the MPPT controller will increase the duty cycle D according to the HC algorithm as ∆P PV > 0 and ∆D > 0. From [21], when the solar irradiation increases, the duty cycle at the MPP (D MPP ) is also widened. Hence, the MPP moves to the right of the power and duty cycle plane.…”

“…The duty cycle D should be increased in the following cycle. This adjustment of D is also applied in the case of stable irradiation [21]. Path 1 in Figure 13 presents the adaptiveness of the proposed method in this case.…”

“…Hence, MPPT techniques can improve the PV system's performance and reduce the total system cost. Multiple MPPT techniques have been developed and improved in the literature and widely used in practice, such as Perturb and Observe (P&O), Incremental Conductance (INC), and Hill Climbing (HC) [20][21][22][23][24][25]. In general, they aim to quickly track the MPP operation point under such continuously changing conditions and generate small output power fluctuation.…”