Three-phase inverters for grid-connected applications typically require some form of grid voltage phase detection in order to properly synchronize to the grid and control real and reactive power. This phase detection is usually based upon some type of grid voltage sensing. However, in the present work a method is proposed whereby the phase angle of the grid can be accurately identified solely via the grid current feedback. In the proposed current control scheme, the only measurement is the output inverter current and no phase locked loop (PLL) exists within the scheme. This phase observer is incorporated into a current controller which can manage the injected power to the grid. The design of this combined observer/controller system is motivated and validated via a Lyapunov stability analysis. The performance of the proposed control scheme has been compared with the conventional PI PLL-based control scheme which needs both a grid voltage and current sensor. Experimental results utilizing a Controller+ Hardware-in-the-Loop test bed have been presented in order to validate the proposed observer/controller scheme under normal operation, weak grid, distorted grid and faulty grid conditions. To summarize, this scheme archives current control for a grid connected inverter using only current feedback. In comparison, traditional methods require voltage and current feedback along with a PLL to synchronize with the grid creating a cascaded closed loop control system.

Three-phase inverters for photovoltaic grid-connected applications typically require some form of grid voltage phase-angle detection in order to properly synchronize to the grid and control real and reactive power generation. Typically, a phase-locked loop scheme is used to determine this real-time phase angle information. However, in the present work, a novel method is proposed whereby the phase angle of the grid can be accurately identified solely via the grid current feedback. This phase-angle observer is incorporated into a current controller which can manage the real and reactive power of the grid-connected PV inverter system. Moreover, the maximum power point of the photovoltaic arrays is achieved without using a DC–DC converter. The proposed method achieves the grid current and DC-link voltage control objectives without the knowledge of the grid information and without the need for a cascaded control scheme. The design of this combined observer/controller scheme is motivated and validated via a Lyapunov stability analysis. The experimental setup is prototyped utilizing a real-time Typhoon HIL 603 and National Instrument cRIO embedded controller in order to validate the proposed observer/controller scheme under different operation scenarios such as irradiation changes, frequency changes, reactive power injection, and operation with a distorted grid. The results show that the DC-link voltage and the active and reactive powers are well regulated from the proposed control scheme without the measurement of the grid phase and frequency.

In this paper, a backstepping nonlinear control scheme has been designed for a single-phase grid-connected inverter system with local load. The main objective of the proposed controller is to simultaneously improve the quality of the local load voltage while injecting clean current to the grid with unity power factor. Furthermore, this control approach ensures the seamless transfer between grid-connected and stand-alone operation modes without adjusting the controller structure. The proposed controller is validated by a Lyapunov stability analysis as well as via instantaneous dynamic circuit simulation in PLECS software.