Control of Power Inverters in Renewable Energy and Smart Grid Integration

23

Sinusoid-locked Loops

Several conventional synchronisation methods are discussed in Chapter 22. Simulation and experimental results have shown that these methods have difficulties in providing the information on the voltage when there are frequency variations and/or harmonics, etc. Moreover, the response is not fast enough. In this chapter, a sinusoid-locked loop (SLL) that is able to quickly track the amplitude, frequency and phase of the fundamental component of a signal is presented. This is based on the idea of mimicking a grid-connected synchronous machine that does not exchange power with the grid because such a machine generates the same instantaneous voltage as the grid voltage. That is, the voltage amplitude, the phase and the frequency of the generated voltage are the same as those of the grid voltage. Following the idea of synchronverters (Zhong and Weiss 2011) discussed in Chapter 18, the mathematical model of a synchronous machine can be adopted as the core of an SLL to lock with the fundamental component of the voltage. The control objective of the SLL is then to zero the real power and reactive power exchanged with the input voltage. Because the dynamics of a tiny machine can be very fast, the SLL is able to provide very fast response. Both simulation and experimental results are presented.

23.1 Single-phase Synchronous Machine (SSM) Connected to the Grid

The simplified model of an SSM connected to the grid is depicted in Figure 23.1, where the grid voltage is ...