Design of optimal controller for photovoltaic maximum power point tracking applications

ABSTRACT

Photovoltaic (PV) maximum power point tracking (MPPT) technology is one of the key technologies that affect the energy utilization of PV power generation systems. How to achieve PV maximum power output quickly, accurately, and simply during the process of changing insolation and temperature conditions is a key problem in current research. At present, the traditional model-free maximum power tracking algorithm suffers from slow response, steady-state oscillations, and large influence of control parameters, whereas the model-based maximum power point tracking algorithm has the advantages of a simple control rate calculation and excellent control performance; however, the nonlinear characteristics of PV cells and power electronic converters lead to difficult controller design and often require a reference value of the maximum power point to be given. In this study, a mathematical model of a PV system was used, and a new PV maximum power tracking algorithm that does not require a reference value to be specified was proposed. The algorithm maps the nonlinear state-space description of the PV power generation system into a linear space through the state feedback linearization design. This solves the problem of difficult controller design for a nonlinear PV power generation system. Starting with the PV maximum power point as the extreme value point of the U-P curve, optimal control theory is applied to derive the PV maximum power tracking control rate, which overcomes the difficulty caused by the model-based control method requiring a reference to be specified. Compared with the traditional method, the proposed maximum power point tracking method improves the response speed by approximately 3–20 times and the tracking accuracy by approximately 3% or less. In addition, the method has a certain amount of immunity to DC bus voltage fluctuations.

KEYWORDS:

• MPPT
• optimal control
• solar energy
• state feedback
• PV module

Highlights

1. Guidelines for designing an optimal controller for MPPT were presented.

2. The guidelines were based on the nonlinear optimal control theory.

3. The energy ratio was improved by approximately 0.5% to 4% compared to other methods.

4. The optimal MPPT method proposed was not affected by DC bus voltage fluctuations.

5. The better performance of the algorithm was confirmed by simulations and experiments.

Nomenclature

Table

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Beijing Natural Science Foundation Project [No. 21JC0026]