Sinusoid-locked loops based on the principles of synchronous machines

Phase-locked loops (PLL), which are widely applied to track the phase of a periodic signal, play an important role in modern electrical engineering. For some applications, it is also necessary to track the amplitude and the frequency of a signal (often sinusoidal), in addition to its phase. A strategy/device that is able to track the amplitude, frequency and phase of the fundamental component of a signal is called a sinusoid-locked loop (SLL). For a synchronous machine connected to the utility grid, the (real and reactive) power exchanged with the grid can be controlled to be zero. In this case, the phase, the frequency and the amplitude of the voltage generated by the machine are the same as those of the grid voltage and the machine is floating on the grid, as an SLL. In this paper, following the recently-proposed synchronverter concept, a virtual synchronous machine is controlled to implement this function so that it is operated as an SLL to provide the phase, frequency and amplitude of the fundamental component of the voltage supplied. Simulation results are provided to demonstrate its excellent performance, with comparison made to some other major approaches.