An inrush current mitigation method for the grid-connected converters in the low-voltage ride-through operation

Abstract

With more and more renewable and other distributed energy resources (DERs) being adopted, the utility requires these DERs systems have low voltage ride-through (LVRT) capability, which means the DERs converters must remain grid-connected and to provide reactive or active power for grid support during low voltage situations caused by faults. As such voltage sags occur, the deformed grid voltages often result in magnetic flux deviations in the grid-side transformer of the DERs converter. When the fault clears and the voltages restore to normal level, the flux deviation can easily result in inrush current of the transformer. This paper proposes an inrush current mitigation method for the grid-connected converters in the LVRT operation. The proposed method reduces the risk of inrush current by compensating the magnetic flux deviation during the LVRT operation. A pre-defined ampere constraint is imposed upon the LVRT and flux compensation to avoid burdening the power semiconductor devices. The proposed method can reduce the the stress of the converter and its grid-side transformer while performing the LVRT operation.

Protection of AC and DC microgrids: Challenges, solutions and future trends

“…The contributions of virtual impedance are power flow control [34]- [36], ancillary service i.e. fault ride through, [37]- [40], and harmonic compensations [41]- [43]. One of the proper approaches for limiting the current under the fault current is virtual impedance [37]- [40].…”

“…fault ride through, [37]- [40], and harmonic compensations [41]- [43]. One of the proper approaches for limiting the current under the fault current is virtual impedance [37]- [40]. In this case, virtual impedance reduces the voltage reference to confine the current.…”

“…• Virtual impedance: Although there exists a few papers on limiting the current through virtual impedance [37]- [40], to the authors' knowledge virtual impedance approaches for limiting the current is at its infancy stage in DC microgrids. Thus further models and investigations are still required.…”

Operation of HVDC converters for transformer inrush current reduction

“…Hence, this over flux in the core may provoke that the transformer in the offshore grid is driven into the saturation mode and consequently, it will lead to high non-sinusoidal excitation current occurrence in the high voltage side of transformers in the offshore grid [103,104,106]. The probability of such inrush transients is high during voltage recovery due to the slow decay of magnetic flux deviations [107]. Therefore, transformer inrush currents resulting from voltage recovery after fault occurrence can be introduced as one of the challenges concerning power quality.…”