Abstract
This paper analyses, the effect of the phase locked loop (PLL) controller in the stability of the voltage source converter(VSC) in a microgrid or when connected to a weak AC grid. While designing the controller for PLL, it may not be possible to consider the effect of the load and line impedance as they are not readily known. In a microgrid or in a weak grid, the dynamics of the PLL are affected due to the high impedance nature of the network. A small signal model is built to show how the PLL controller affects the stability of the VSC. A comparison is made between proportional (P) and proportional-integral (PI) controller, using detailed time domain simulation in PSCAD/EMTDC to demonstrate this problem.
Highlights
With the increase in power demand all over the world, distributed generations (DG) plays a key role in the electrical power distribution system
To verify the performance of phase locked loop (PLL), a detailed time domain model given in Fig. 6 is developed in PSCAD/EMTDC
The following two cases were simulated with different Gc(s) to analyse their dynamic performance
Summary
With the increase in power demand all over the world, distributed generations (DG) plays a key role in the electrical power distribution system. While designing the PLL in vector control, the strength of the grid (effect of grid impedance) is generally not considered. In [5]–[9], the effect of the weak grid on the stability of vector control is discussed in detail. Several methods have been reported in the literature in order to avoid the stability issue caused due to PLL in VSC when connected to a weak grid. Reshaping the impedance of the VSC has been proposed in [13], [14] to overcome the stability issue of PLL in a weak grid All these methods requires either the information of the grid impedance which may not be readily available or uses complex control structure. A simplified small signal model is built to analyse the effect of the PLL controller on the stability of the overall VSC control system.
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