There are several ways of modelling an SVC system:

1. Using the SVS Interface in PowerFactory: A number of standard controls for SVS are available in the global library. There, you can also find composite model frames (refer to \Library\Dynamic Models\FACTS). The SVS interface is a PowerFactory element of the class ElmSvsctrl that controls the number of switched capacitors of the tyhristor switched capacitor (TSC) and the firing angle of the thyristor controled reactor (TCR). It also initialises the controller output to zero. This should be used with care since the consideration of the SVS control limits will be then offset by the initial SVC admittance. The interface has the advantage that operates the parallel capacitors when required. As an example, the file SVCExampleWithInterface.pfd is given below.
2. It is also possible to control the SVS element without an interface. In this case, the limits of the control must be properly considered for any initial condition. The parallel capacitors have to be modelled separately and explicitly controlled. Examples can be found in the corresponding WECC SVS templates available in the global library (DIgSILENT Library\Templates FACTS).
3. There is also a third possibility available. This could be used if the switching nature of the TSC (thyristor switched capacitors is not important). One could use in this case the input signal 'bsvs', this signal corresponds to the admittance of the whole SVS. A positive input is interpreted as capacitive reactive power while a negative value is interpreted as reactive power consumed by the TCR (thyristor controlled reactor). This implementation is shown in the example project SVCExampleContinuous.pfd.

For more information refer to the technical reference of the ElmSvs.