Improving the Damping Properties of a Virtual Synchronous Generator by Using a Feedforward Controller

In modern power systems, a continuous growth in the number of generating facilities based on grid inverters is observed, which leads to a significant change in the dynamic properties of power systems. This is primarily expressed in the reduction of the inertial response provided by conventional synchronous generators. In this regard, a new control strategy for grid inverters based on the virtual synchronous generator (VSG), which simulates the properties and capabilities of synchronous generation, is becoming a key technology for modern hybrid power systems. However, the conventional VSG control algorithms are characterized by a number of fundamental problems, such as the mutual influence of active and reactive power control loops. The article proposes an alternative VSG structure controlled by a reference current signal (CC-VSG). However, this structure is complex and is characterized by an insufficient damping torque when the grid strength changes. To overcome this drawback, an approach is proposed to enhance the damping properties of the CC-VSG by using a feedforward controller consisting of a simple proportional section. The analysis of the closed-loop transfer function presented in the article has demonstrated the reduction of the model order to the second one due to the proposed controller, which made it possible to derive simple dependencies for tuning the model. By considering the state-space model as well as the sensitivity and participation coefficients, the predominant influence of the developed controller's gain on the low-frequency roots has been proven, which leads to a significant improvement in the CC-VSG damping properties. The results of dynamic simulation in the time domain have confirmed the indicated properties and capabilities of the modified CC-VSG structure with the feedforward controller. It has also been demonstrated that the damping effect has no influence on the inertial response of the modified CC-VSG structure, which is expressed in the constant frequency variation rate with increasing the damping coefficient. Accordingly, it is concluded that the modified CC-VSG structure is efficient, stable and can be flexibly tuned to obtain any desired dynamic response under conditions of different grid strength and the grid inverter power load.