Flexible Voltage Support Control with Imbalance Mitigation Capability for Inverter-Based Distributed Generation Power Plants under Grid Faults

Abstract

The high penetration level of inverter-based distributed generation (DG) power plants is challenging the low-voltage ride-through requirements, especially under unbalanced voltage sags. Recently, a flexible injection of both positive-(PS) and negative-sequence (NS) reactive currents has been suggested for the next generation of grid codes. This can enhance the ancillary services for voltage support at the point of common coupling (PCC). In light of this, considering distant grid faults that occur in a mainly inductive grid, this paper proposes a complete voltage support control scheme for the interface inverters of medium or high-rated DG power plants. The first contribution is the development of a reactive current reference generator combining PS and NS, with a feature to increase the PS voltage and simultaneously decrease the NS voltage, to mitigate voltage imbalance. The second contribution is the design of a voltage support control loop with two flexible PCC voltage set points, which can ensure continuous operation within the limits required in grid codes. In addition, a current saturation strategy is also considered for deep voltage sags to avoid overcurrent protection. Finally, simulation and experimental results are presented to validate the effectiveness of the proposed control scheme.

Review of distributed generation (DG) system planning and optimisation techniques: Comparison of numerical and mathematical modelling methods

“…In particular, standard requirements i.e. low voltage ride [110], frequency limit [111] and unintentional islanding control [112] make it highly inflexible for DG technology incorporation. Moreover, these standards are often obsolete and not instantaneously updated in response to the latest development in DG best practice developments.…”

A Comprehensive Review of Control Strategies to Overcome Challenges During LVRT in PV Systems

“…In [89], the injection of reactive current by using a three-level T-type inverter for medium switching frequency and lowvoltage applications, has been considered. The proposed strategy employed DDSRF-PLL to extract the positive and negative sequence current components at PCC.…”

Voltage support control strategy of grid‐connected inverter system under unbalanced grid faults to meet fault ride through requirements

“…In the literature, while most of the control strategies have been applied in inductive grids, some studies proposed in [20,22] have examined the control strategy in resistive-inductive grid impedance. While active and reactive powers are delivered from inverter to grid and loads in [2,22,24,25], reducing active and reactive oscillations are not considered. Guo et al [29] have only focused on reactive power control in the resistive grid.…”

“…In [24], a reactive current injection control strategy is reported to avoid overvoltage. In [25], a flexible VSS is proposed based on reactive current reference generation to mitigate voltage imbalance. Khoshooei et al [26] have presented a VSS for the static synchronous compensator, where there is no active power delivery.…”