Conventional Synchronisation Techniques
One of the most important problems in renewable energy and smart grid integration is how to synchronise the inverters with the grid. There are two different scenarios: one is before connecting an inverter to the grid and the other is during the operation. If the inverter is not synchronised with the grid or another power source it is to be connected to, then large transient currents may appear at the time of connection, which may damage the equipment. During the normal operation, the inverter needs to be synchronised with the source it is connected to so that the system can work properly. In both cases, the grid information is needed accurately and in a timely manner. Depending on the control strategies adopted, the grid information needed can be any combination of the phase, the frequency and the voltage amplitude.
In this chapter, some synchronisation methods widely available in the literature are discussed. Simulation and experimental results are provided for two widely adopted methods, SOGI-PLL and STA.
There are two categories of methods for the purpose of synchronisation: open-loop methods and close-loop methods. Typical open-loop methods include detecting the zero crossing of the grid voltage and directly filtering the grid voltage, etc. An example of the filtering method is the one used in Chapters 3, 15 and 16, where a phase-lead low-pass filter is adopted to provide the information of the grid voltage. Other ...