Impact of wind power plant reactive current injection during asymmetrical grid faults

Abstract

As more renewable energy sources, especially more wind turbines (WTs) are installed in the power system; grid codes for wind power integration are being generated to sustain stable power system operation with non-synchronous generation. Common to most of the grid codes, wind power plants (WPPs) are requested to stay connected and inject positive-sequence reactive current in order to boost positive-sequence grid voltage during short-circuit grid faults, irrespective of the fault type; symmetrical or asymmetrical. However, as shown in this study, when WPPs inject pure positive-sequence reactive current in case of asymmetrical faults, as a conventional method (CM) in accordance with the grid code requirement, positive-sequence grid voltage is boosted, but also higher negative sequence voltage in the grid and higher overvoltages at the non-faulty phases occur. In this study, an alternative injection method, where WTs are injecting both positive and negative sequence currents during asymmetrical faults, providing improved grid support, is given and compared with the CM. In addition, effect of coupling between positive, negative and zero sequences when WPPs are injecting currents during asymmetrical faults, is investigated, which was not considered in the wind power impact studies before.

A Review on Grid-Connected Converter Control for Short-Circuit Power Provision Under Grid Unbalanced Faults

“…Therefore, different national and international codes have defined low-voltage fault-ride-though requirements in form of lower limit of a voltage-against-time profile at the PCC [18], [19], whose parameters of voltage and time vary from country to country [20]- [22]. On the other hand, over-voltage problem can occur in non-faulty phases during grid unbalanced faults, which may also lead to power generation disconnection undesirably [23]. As a result, highvoltage fault-ride-through requirements have been imposed in countries such as Australia, Denmark, Spain and Italy.…”

Current Reference Generation Based on Next-Generation Grid Code Requirements of Grid-Tied Converters During Asymmetrical Faults

“…Even though asymmetrical faults account for almost all grid faults, most grid codes do not state any directions and requirements regarding negative-sequence current injection during any type of fault [2], [3]. Consequently, Balanced Positive Sequence Control (BPSC) is a widely used strategy in industrial applications [4].…”

Handling of unbalanced faults in HVDC-connected wind power plants

“…seq. handling by WT converters is treated in [10,11,12,13,14,15,16,17,18] and in the light of VSC-HVDC-interfaced AC grids in [19,20,21,22]. Converter control regarding neg.…”

“…The converter current references during unbalanced (or asymmetrical) faults are either focusing to improve the quality of the power exchange (avoid DC link ripple and constant active power injection) in [11,13,24] or to support the grid (voltage support) in [10,12]. From a power system point of view, it was shown that such voltage support is beneficial for grids with many converter-connected generation and few conventional synchronous generators [10,18]. Ref.…”

“…[11,10,18]) or interaction between the onshore VSC-HVDC and the main grid [12,22]. In [12], unbalanced faults in the onshore grid were investigated and a injection of neg.…”