PLL-Less Nonlinear Current-Limiting Controller for Single-Phase Grid-Tied Inverters: Design, Stability Analysis, and Operation Under Grid Faults

• Published in: IEEE transactions on industrial electronics (1982) Vol. 63; no. 9; pp. 5582 - 5591
• Main Authors: Konstantopoulos, George C., Qing-Chang Zhong, Wen-Long Ming
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Circuit faults; Circuit stability; Controllers; Current-limiting property; Design analysis; Devices; Faults; grid fault; Inverters; nonlinear control; Nonlinearity; Phase locked loops; Power system stability; Reactive power; single-phase inverter; Stability; Stability analysis
• ISSN: 0278-0046; 1557-9948
• DOI: 10.1109/TIE.2016.2564340

A nonlinear controller for single-phase grid-tied inverters, that can operate under both a normal and a faulty grid with guaranteed closed-loop stability, is proposed. The proposed controller acts independently from the system parameters, does not require a phase-locked loop, and can achieve the desired real power regulation and unity power factor operation. Based on nonlinear input-to-state stability theory, it is analytically proven that the inverter current always remains below a given value, even during transients, independently from grid variations or faults (short circuit or voltage sag). The desired performance and stability of the closed-loop system are rigorously proven since the controller has a structure that does not require any switches, additional limiters, or monitoring devices for its implementation. Therefore, nonlinear stability of a grid-tied inverter with a given current-limiting property is proven for both normal and faulty grid conditions. The effectiveness of the proposed approach is experimentally verified under different operating conditions of the grid.