A Multi-Terminal Current Differential Protection Setting Method for Fully Weak-Infeed Distribution Networks Based on Restricted Enumeration Method

With the high penetration connection of inverter-interfaced distributed generators and the increasing application of large-capacity energy routers, fully weak-infeed distribution networks consisting entirely of power-electronized weak-infeed power sources are set to become one of the fundamental forms of future distribution networks. For fully weak-infeed distribution networks, multi-terminal current differential protection is considered an optional or even preferred line protection scheme. In this paper, a multi-terminal current differential protection setting method for fully weak-infeed distribution networks is proposed based on the restricted enumeration method. To address the impact of data synchronization errors and measurement errors of multi-terminal current on differential current, the problem of determining the maximum differential current superimposed with the multi-terminal current phasor errors is transformed into a high-dimensional non-convex optimization problem. The distribution law of the global optimal solution in the non-convex constraint space is deeply studied and analyzed, and a restricted enumeration method is proposed that can quickly solve the protection setting value, thereby solving the problem of multi-terminal current differential protection setting. The accuracy and rapidity of the proposed method are verified by comparing the calculation accuracy and time consumption of the restricted enumeration method and the exhaustive search. It is shown that the proposed multi-terminal differential protection setting method exhibits sufficient reliability and sensitivity in fully weak-infeed distribution networks, as verified through simulation analysis using a fully weak-infeed distribution network model built in PSCAD/EMTDC.

I. Introduction

Constructing a novel power system predicated on clean and low-carbon energy as its mainstay is a pivotal measure for the effective implementation of the “double carbon” strategy [1]. One of the important forms of new energy grid connection is through large-scale photovoltaic (PV), energy storage (ES), and other inverter-interfaced distributed generators (IIDGs) that are multi-point T-connected to distribution networks (DNs) [2]. To achieve low-voltage ride-through (LVRT), IIDGs limit the magnitude of their output current during the fault ride through, which engenders typical weak-infeed properties [3], [4], [5]. Additionally, the notable benefits of a large-capacity multi-port energy router (ER) in terms of power allocation and voltage regulation render it an exemplary device to replace conventional transformers and serve as a new transmission and distribution interface [6], [7], [8]. To prevent the converter from burning during a fault, the large-capacity ER, with a modular multilevel converter (MMC) as its primary equipment, will adopt the current dependent voltage order limiter to successfully complete the fault ride through, resulting in typical weak-infeed properties [9]. Hence, the high penetration IIDGs multi-point T-connected DNs, empowered by a large-capacity ER as their transmission and distribution interface, can be categorized as fully weak-infeed distribution networks (FWIDNs), which solely rely on power electronic weak-infeed power sources.