Adaptive Virtual Inertia Synthesis via Enhanced Dispatchable Virtual Oscillator Controlled Grid-Tied Inverters
Sima Azizi Aghdam, Mohammed Agamy
Abstract
The frequency instability due to the lack of inertia in the inverter-dominant power system can be alleviated by applying an appropriate virtual inertia (VI) control. A modified dispatchable virtual oscillator control (dVOC), which is a combination of conventional dVOC and an extra loop for providing VI is proposed for frequency stability improvement. This controller, in addition to providing advantages of conventional dVOC such as fast dynamic response and accurate power sharing among inverters, improves the frequency response by adding VI to system. However, a constant VI control is not an efficient approach as it is not able to distinguish various system operating conditions requiring large or small inertia. Thus, in this work an adaptive VI control is proposed in which the control coefficients are dynamically updated in response to different operating conditions. This method reduces the exchanged power during inertial response by accelerating transient response. Also, it does not require frequency measurement using phase-locked loop (PLL) in VI loop. Therefore, this approach not only improves transient response of the system but also removes possible instability due to using PLL. The controller behavior is analyzed and validated for different cases under large transient conditions.