The PowerFactory synchronous machine element offers an input signal for the excitation voltage. Usually this signal is connected to a DSL model of an excitation system (AVR or EXC). This modelling approach is widely used and in most cases sufficient enough. The excitation system, consisting of possibly Thyristor bridges, excitation machine and other equipment is in this case not explicitly represented, it exist only as transfer function as part of the DSL model. The attached example shows a way how the hardware equipment of the excitation system can be explicitly modeled, using PowerFactory elements, such as the rectifier (ElmRec, ElmRecmono) and other elements.

Description of the explicit modeling approach

The explicit excitation to the synchronous machine was done via a DC voltage measurement device and a DC current source.

The voltage measurement device measures the explicit DC voltage and applies the measured value to the excitation voltage input signal of the synchronous machine. The DC current source plays back the excitation current from the synchronous machine (signal ie). The load flow initialization is done via a QDSL model. This QDSL model calculates the excitation voltage/current and enforces these values in the rectifier (voltage) and the DC current source. During dynamic simulation the rectifier firing angle (alpha) is controlled by a simple PI control to follow the excitation voltage from the AVR.

The per unit system base for the excitation is in this case explicitly defined by the nominal voltage of the DC nodes and the nominal current of the DC current source (in this example 200V and 10A).

The solution works only in PowerFactory 2023 and later because the QDSL signal for the DC voltage set point of the rectifier was newly introduced in this version.

All explicit control was stored together in one composite model which has the same in- and output signals like the three phase synchronous machine, therefore this composite model can simply be placed in the slot of the standard “Frame Synchronous Generator” (you may have to extend the filter for the type to allow also ElmComp). The QDSL model is stored in the composite model “Plant_Synchronous Machine_explicit”. Please note that you have to link the DC current source, the rectifier and the synchronous generator on the Load Flow page of the QDSL model (if you want to transfer this solution).