Virtual oscillator‐based methods for grid‐forming inverter control: A review

Abstract

In inverter‐dominant power systems, grid‐forming (GFM) inverters regulate voltage and frequency. To construct GFM inverters, conventionally, various control methods based on synchronous machine emulation or droop characteristics have been employed. However, recently, inverters are regulated by Virtual Oscillator Control (VOC) to emulate the dynamics of a weakly nonlinear oscillators. In contrast to droop control, VOC is a time‐domain controller that enables interconnected inverters to stabilize arbitrary initial conditions to a synchronized sinusoidal limit cycle rapidly. The fast synchronization, accurate power sharing in grid‐connected and islanded modes, simple and robust implementation make it a promising candidate for inverter‐dominant power systems. Moreover, VOC removes the computational burden within machine emulation‐based methods and provides an approach to measure the frequency without employing phase‐locked loop (PLL). Hence, to leverage the advantages of this method and expand its application in power system control, this paper reviews different VOC implementations. Mainly, this paper focuses on the studies related to the fundamental theory of oscillators and design process. Additionally, there are discussions on the stability analysis of VOC‐based systems, harmonics and pre‐synchronization. Challenges on the compatibility with heterogeneous controllers, fault ride‐through and other limitations of VOC including non‐inertial response and coupled power control are investigated and solutions are outlined.

Virtual oscillator with delayed feedback for transient mitigation in inverter-based islanded microgrids

“…A novel concept of Virtual Oscillator Control (VOC) based on dynamical systems theory is a recent major development in inverter control systems. Herein the inverter and a non-linear oscillator with a stable limit cycle trajectory are coupled to each other, thereby achieving efficiency and additional functionalities with minimal design complexity (Aghdam et al 2022;Costa et al 2021). Synchronisation of coupled oscillators is the key element of the VOC approach that provides sustained oscillations in the inverter output (Joshi et al 2016).…”

Grid-Forming Hybrid Angle Control and Almost Global Stability of the DC-AC Power Converter

“…• Another trend is to model the internal dynamics of the dc-ac converters by oscillator dynamics. This approach is often adopted when studying the stability of interconnected converter-based systems; see [17] for a review and [12], [18] for experimental investigations.…”

“…proposed that synthesize the converter control based on the structural dynamic similarities with the SM [15], [16]. Along a different design direction, the nonlinear oscillators dynamics are recently exploited for a GFM control design [17]- [19]. Finally, the combination of aforementioned techniques has resulted in several hybrid control architectures [20]- [23].…”

Analysis of Grid-Forming Inverter Controls for Grid-Connected and Islanded Microgrid Integration

“…In [28], the author presented inverter-based resources and GFM inverter controllers, which regulate terminal voltage, enable island operation, maintain grid stability, and help with black start capability. A virtual oscillator controller (VOC) is a time-domain control technique that instructs the inverter to simulate the dynamics of a nonlinear electrical oscillator using a digital controller [29]. It can synchronize multiple units, has droop characteristics, and does not require a power filter.…”