Photovoltaic System Research Center of Ministry of Education, Hefei University of Technology, Hefei 230009, China

The establishment of a new power system requires grid-connected inverters to be able to flexibly adapt to complex power grid conditions. The use of traditional dual-mode grid-following/grid-forming control for grid-connected inverters has problems of mode switching and complex control, while there exist problems of multiple control parameters and complicated design when virtual oscillator control is adopted. To this end, by referring to the oscillating voltage self-formation principle of nonlinear oscillators simulated through virtual oscillator control, an oscillator-resembled phase locked loop-less unified power and voltage controller (OR-PLL-less UPVC) for grid-connected inverters is proposed. The OR-PLL-less UPVC consists of power control module, voltage self-formation module, and voltage magnitude regulation module. First, the structure and operation principle of each module in OR-PLL-less UPVC are introduced, and the control law of the inverter output voltage is analyzed. Then, the state-space model of the system is established to analyze its small-signal stability. Finally, through simulation and real-time controller hardware-in-loop experiments, it is verified that the proposed OR-PLL-less UPVC can autonomously adjust the inverter port voltage under variations in parameters such as grid-side line impedance, power grid voltage/frequency, and track the power dispatching instructions, achieving the unified grid-following/grid-forming control under complex operating conditions.