Stability enhancement strategy of virtual synchronous generator for cascaded multilevel converter based energy storage system under weak grid conditions

Abstract

Considering that the low-voltage and small capacity ratings of the traditional distributed energy storage system (ESS) cannot meet the increasing capacity of distributed generations, this study describes a cascaded multilevel converter-based ESS. In addition, the virtual synchronous generator (VSG) as a promising solution to enhance the system's inertia is studied. However, some studies indicate that VSG suffers from the inherent resonance near synchronous frequency under weak grid conditions, which may result in power oscillation and even deteriorate the system stability. In this work, the resonance mechanism is investigated with an established wide-band small-signal dynamic model. It is revealed that the resonance poles caused by the small impedance ratio on the AC side introduce a phase lag jump of 180°, which decreases the phase margin of VSG, leading to synchronous power oscillation (SPO). The influence of control parameters on the power oscillation is investigated with the eigenvalue analysis method. Accordingly, a differential feedforward compensation-based SPO suppression strategy is proposed. The stability margins are significantly enhanced with this method. The validity of the SPO analysis and suppression method is verified with simulation and a 10 kW experimental prototype.

Guest Editorial: Challenges in Future Grid‐Interactive Power Converters: ControlStrategies, Optimal Operation, and Corrective Actions

“…Similarly, paper [2] presents a VSM of a PV inverter based on the DC capacitor voltage control which can damp the built-up oscillations in response to the disturbances using a proposed feedforward grid angle. Paper [3] introduces a new resonance mechanism added for VSM to reduce the inherent resonance at synchronous frequency under weak grid conditions.…”

Operation of Unified Power Flow Controller as Virtual Synchronous Generator

“…The emulated operation as VSG demonstrates all the major properties of an SG which include virtual inertia and damping coefficients. Furthermore, these parameters can be flexibly designed according to the specific requirements of the power system or even changed in an adaptive manner [4][5][6][7][8]. Therefore, they can provide functionalities such as oscillation damping and inertia to a modern power system [9,10].…”