Abstract
This paper presents an improved virtual synchronous control (VSynC) for the grid-connected voltage source converter (VSC) so as to continuously operate under the grid voltage with steady unbalance. The improved VSynC introduces the negative sequence power controls on basis of conventional VSynC. The improved VSynC is capable of regulating the negative sequence internal voltage to reduce the negative-sequence injected currents and oscillated powers of the VSC aroused by the negative-sequence grid voltage. Three alternative local control objectives for the VSC itself under steady state unbalanced grid conditions and their corresponding power references are deduced and computed. Simulated and experimental results are presented to validate the correctness and effectiveness of the proposed improved VSynC to enhance the continuous operation performance of VSynC-based VSCs during grid voltage steady-state unbalance.
Highlights
In modern power system, more and more devices, e.g. high voltage direct current (HVDC) transmissions, energy storage systems and renewable energy generations, are integrated into power grid via voltage source converters (VSCs) [1, 2]
Virtual synchronous control (VSynC) is recently developed to feature the inertia characteristics in VSC to satisfy the requirement of inertial supports and frequency stability in power system [3,4,5,6,7,8,9,10]
The control structure and dynamics of direct-VSynC [9, 10] are much different from the best-known vector current control (VC) [11, 12] and direct power control (DPC) [13, 14]
Summary
More and more devices, e.g. high voltage direct current (HVDC) transmissions, energy storage systems and renewable energy generations, are integrated into power grid via voltage source converters (VSCs) [1, 2]. [8] introduces a fault ride through method for the power synchronous controlled VSC, which employs current controllers to reduce the negative sequence currents during the fault in short term It is not suitable for the long-term operation of the VSC under the steady state unbalance. For the natural inertial support for grid frequency and enhancing the continuous operation capability of the VSynC-based VSC attached to voltage-unbalanced network, this paper introduces negative-sequence internal voltage and regulates its dynamics according to the negative sequence active and reactive power components.
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