Abstract
The paper presents the study of a three-phase system coupling a DC power source to a power grid. This study, based on an FPGA, implements a real-time control system and digital models of the power circuit. The proposed proportional–resonant (P+R) controller with a modified structure was part of the system, which can be used as an alternative controller to traditional ones, e.g., in photovoltaic systems. Due to difficulties in implementing resonant controllers, a P+R with a new structure using a PI controller was elaborated. With an appropriate approach to the generation of phase current patterns, it is possible to set the reactive current and, thus, compensate for the reactive power. The operation of the system for typical operating conditions (e.g., system startup, change in preset load) was characterized and compared with a classical solution using a PI controller.
Highlights
Three-phase inverter control systems coupling energy sources to the power grid have traditionally used PI controllers and a natural system transformation to a rotating dq system [1]
The disadvantage of PI controllers is, among others, the distortion of the line current waveform caused by harmonics of the line voltage, inserted through feedback
The P+R controller can be used in systems operating with a constant frequency of output voltage, e.g., in devices coupling renewable energy sources to the power grid [4]
Summary
Three-phase inverter control systems coupling energy sources to the power grid have traditionally used PI controllers and a natural system transformation to a rotating dq system [1] To improve their performance, many variants have been proposed in the literature, including multistate feedback and increasing the proportional gain. The P+R controller can be used in systems operating with a constant frequency of output voltage, e.g., in devices coupling renewable energy sources to the power grid [4] This controller is designed for single-phase systems, but can be applied to three-phase systems, after their transformation to a two-phase orthogonal αβ stationary system [5]. In the literature focused on simulation studies, implementations of structures composed of basic functional blocks are encountered [16,17,18] They mainly concern an ideal regulator with infinite gain for the reference frequency.
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