Improved voltage‐based protection scheme for an LVDC distribution network interfaced by a solid state smart transformer

Abstract

The increasing electrification of transport and heat will place increasing demand on low voltage (LV) networks with the potential to overload MV/LV transformers and LV cables. Deployment of a solid state transformer (SST) at MV/LV substations and using LV Direct Current (LVDC) distribution systems offer great potential to address such c hallenges. However, the SST deployment in addition to the introduction of LVDC will fundamentally change LV fault behaviour and protection requirements due to the limited short-circuit capabilities of such technologies. The SST will deliver limited fault c urrents, making currentbased protection (widely used in LV networks) less reliable. Therefore, this paper presents an advanced communication-less protection scheme which can effectively detect and locate DC faults even with reduced fault levels. The devel oped protection scheme overcomes the selectivity limitations in LVDC voltage-based protection solutions by using a combination of DC voltage magnitude, voltage concavity (sign of d 2 v/dt 2) and the sign of the rate of change of current (di/dt) regardless of the current magnitudes. The credibility of the developed protection algorithm is tested against different fault scenarios applied on an active LVDC network model built in PSCAD/EMTDC. Noise signals have been included in the simulation to appraise the resilience of the developed scheme.

Coordination of mode switching control and SMES unit for low‐voltage ride‐through fulfillment of power electronic transformer

“…In Ref. [11], the deployment of a PET at MV/LV substations is considered, and an advanced communication-less protection scheme is proposed to detect and locate DC faults to improve the PET's LVRT performance. However, these findings solely depend on additional equipment, such as the additional controller and protection scheme to complete the LVRT procedure, and do not explore the PET's control flexibility to ride through low-voltage gaps.…”

Simulation of a Low-Voltage Direct Current System Using T-SFCL to Enhance Low Voltage Ride through Capability

“…Low-voltage direct-current (LVDC) systems, which comprise DC loads and DC-based distributed energy resources (DER), such as photovoltaics (PV) and wind turbines, have been emphasized to achieve efficient operations [1][2][3][4]. When a fault occurs in the LVDC system, the peak of the fault current is higher and faster than that of the alternating current (AC) system because of the discharge of the DC capacitor within the interconnected system parts between the LVDC and AC [4][5][6][7].…”

Experimental evaluation of an energy storage system for medium voltage distribution grids enabling solid‐state substation functionality

“…Only relatively recently the possibility to use low rated power electronic converters in power systems to increase controllability of power flow and flexibility was formulated [4]. The possibility to fx1fx18embed full solidstate substation was reported in [5][6][7][8][9]. Clare [5] reported the implementation of a 3-port power conversion system interconnected by modules consisting of AC/DC/high-frequency AC converter modules interconnected back-to-back via medium frequency transformers that enabled series connection on one low-frequency AC port, therefore facilitating direct connection to a medium voltage grid, whilst parallel connection of the other low-frequency AC port enables connection to LV distribution grids and therefore implementing solid-state substation functionality.…”

“…Klumpner et al [8] investigated the substation functionality with the integration of energy storage. Wang et al [9] investigated the improvement in the protection scheme for a distribution network powered by a solid-state transformer.…”