access icon free Robust optimal current control for grid-connected three-phase pulse-width modulated converters

This study deals with the current control of three-phase inverters connected to the grid by means of LCL filters. The control action is given by the feedback of the filter states, in coordinates αβ0, and of the internal states of resonant controllers. The control gains are computed by means of an optimal linear quadratic regulator that is robust to uncertain and time-varying parameters related to the grid impedance at the point of common coupling. As contributions, one has the detailed proof of a robust discrete linear quadratic control, showing its applicability also for the time-varying case, the experimental validation of the results in terms of the total harmonic distortion and harmonic limits for the grid injected current, according to the IEEE 1547 standard, and the analysis of the ℋ norm of the closed-loop system for several values of grid inductance, indicating a value of grid inductance for which one has best performance for the time-invariant case. For comparison, a conventional state feedback controller is designed and implemented, showing the limitation of the non-robust strategy.

Inspec keywords: optimal control; resonant power convertors; electric current control; control system synthesis; power harmonic filters; harmonic distortion; linear quadratic control; power system control; discrete systems; linear systems; time-varying systems; PWM power convertors; robust control; LC circuits

Other keywords: grid-connected three-phase pulse-width modulated converter; total harmonic distortion; time-varying parameter; optimal linear quadratic regulator; state feedback controller; grid inductance; robust discrete linear quadratic control; point of common coupling; closed-loop system; LCL filter; grid injected current; robust optimal current control; IEEE 1547 standard; resonant controller; three-phase inverter

Subjects: Power supply quality and harmonics; Current control; Power convertors and power supplies to apparatus; Optimal control; Stability in control theory; Discrete control systems; Time-varying control systems; Control of electric power systems; Power system control

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