An international research team has conceived a dual-component controller for three-phase inverters that can reportedly achieve faster settling times, reduced overshoot and more stable current tracking compared to conventional controllers.
A group of researchers led by the Jouf University in Saudi Arabia has developed a dual-component controller for applications in three-phase two-stage solar inverters.
The dual component controller is based on a cascaded fractional order proportional-integral-tilt (FOPIT) for controlling the DC-link voltage between the two stages of the inverter and a fractional order proportional-integral (FOPI) for controlling the internal active and reactive current loops of the device. The controller also utilizes the bio-inspired marine predator algorithm (MPA) to fine-tune the controller settings, which reportedly minimizes the weighted integral time-squared error (ITSE) of control objectives.
“The primary advantages of the proposed FOPIT-FOPI controller include its simplicity, flexibility, improved tracking performance, and reduction in overshoot amplitude and settling time,” the research group stated, noting that it also provides additional flexibility and degree of freedom compared to conventional PI controllers, as it uses the fractional order differential equations, which are an efficient tool to model various processes arising in science and engineering and are said to minimize steady-state errors, while offering higher flexibility.
The controller generates the direct axis component of the grid current by measuring the difference between the reference and measured DC-link voltage. “This value serves as the reference current for the current control loop, developing the necessary modulation index for injecting active and reactive power into the grid,” the scientists explained, noting that the controller also relies on tilt control terms to provide a “smoother” response under uncertain model parameters and eight different tuning parameters.
For their simulation, the scientists assumed that the inverter is operating in a grid-following mode and its performance is not affected by other grid-connected sources or storage elements. The analysis showed that the proposed controller outperforms conventional PI controllers in several key aspects.
“In the case of a step change in solar irradiance, the proposed controller reduced overshoot to less than 0.33% compared to the 3.33% overshoot seen with the conventional PI-PI controller, with a settling time of approximately 0.05 s versus the conventional controller’s 0.075 s,” the team explained, adding that the controller also achieves faster settling times and more stable current tracking. In electronics, overshoot occurs when a system’s response to a sudden input change exceeds the intended output level.
The novel fractional controller was presented in the study “Optimized grid-connected three-phase photovoltaic inverter system using cascaded FOPIT-FOPI fractional controller,” published in Energy Reports. The research team comprised academics from Universidad San Sebastián in Chile and Aswan University in Egypt.
“Future research may explore real-time implementation and further optimization using advanced metaheuristic algorithms for even better system performance,” the academics said referring to the future direction of their work.