交流微電網與直流微電網故障保護系統之模擬與實證研究

Simulation and Field Test of AC Microgrid and DC Microgrid Fault Protection Systems

斐明陌(BUI MINH DUONG)

指導教授 ： 陳士麟

中原大學/電機資訊學院/電機工程研究所/博士(2016年)

https://doi.org/10.6840/cycu201600571

摘要

微電網是一種新結構的配電系統，主要是由分散式電源組成，像是可再生能源、分散式發電、儲能系統、負載、能源管理系統和保護裝置等。微電網主要的優點為：(1)提高可再生能源的普及率；(2)改善電力系統的可靠度；(3)具有高效率並對環境有較低的影響。然而，微電網具有以下幾項挑戰：(1)故障保護與協調；(2)分散式電源的電力潮流控制；(3)市電併聯與孤島運轉模式之間的無縫切換；(4)電力品質問題。本文著重於開發交流與直流微電網的故障保護系統。

為了保護多重接地的交流微電網，本論文提出一套快速且高適應性的故障保護系統，此保護系統可解決微電網中多項因素所造成的故障保護問題，包括：因逆變器式的分散式電源與旋轉式的分散式電源之混用所造成的問題、微電網在孤島運轉模式下故障電流因逆變器之限流所造成的問題、雙向的故障電流/電力潮流所造成的問題。換言之，新型的故障保護系統在交流微電網中應該具有自行適應的能力，以期處理隨插即用及非主從之微電網特性。根據卡方分佈統計法、一項簡化的故障電流分析方法以及藉由通訊支援的系統，於本論文提出之快速且高適應性的故障保護系統中，可根據交流微電網的不同電源及負載組合(例如：微電網中電源和負載分路之併網及斷開)來自動調整其相對應的電驛跳脫位準。除此之外，此快速且高適應性的交流微電網保護系統可以準確的偵測、判別，並於1.5週波內定位故障區段，以期未來配合靜態開關防止微電網中逆變器式的分散式電源於微電網故障期間之快速跳脫。於台灣核能研究所中的380V交流微電網試驗平台所做的模擬與試驗結果，可用來驗證本文所提出的快速且高適應性的交流微電網故障保護系統。

本論文亦提出新的直流微電網故障保護系統，使用快速熔絲結合電力電子開關與數位電驛來保護低電壓的直流微電網。尤其是直流微電網的數位電驛包含不同的故障偵測模組，像是：差動電流保護模組、方向性過流/過電流保護模組、低電壓/過電壓保護模組，以及根據直流電流與電壓的時間導數之保護模組來保護於直流微電網的極對極與極對地故障。本文對於直流微電網數位電驛的不同故障保護模組之間、數位電驛之間以及熔絲與數位電驛之間的保護協調策略亦進行分析，以確認此保護系統具有高選擇性。此新的直流微電網保護協調系統之宗旨為縮短故障排除時間且保護系統有好的成本效益同時具有高選擇性，因此，直流電源像是太陽光電、蓄電池和燃料電池系統、電源轉換器等，都應該由快速熔絲來保護以求得其成本效益。直流微電網之數位電驛則用來保護電源/負載分路、幹線和一般的直流匯流排，目的在於讓保護系統具有高選擇性。本文提出之漏電流保護方法是對於高阻抗接地/非接地直流微電網架構(例如：對稱的直流單極微電網或直流雙極微電網)進行保護。依據低電壓直流微電網試驗平台之模擬與試驗結果，本文評估所提出的直流微電網保護系統及其保護協調策略之有效性。

關鍵字

微電網 ； 流微電網的故障保護系統 ； 數位電驛

並列摘要

Microgrid (MG) is an emerging configuration of power distribution systems, which mainly consists of distributed energy resources (DERs) such as renewable energy sources and distributed generators (DGs), energy storage systems (ESS), loads, energy management system (EMS), and protective devices. Main advantages of the microgrid are: (i) facilitating high penetration of renewable energy sources; (ii) improving reliability of the power system, and (iii) having high efficiency and low environment impacts. The microgrid, however, meets with certain challenges in (i) fault protection and coordination, (ii) power-flow control of distributed energy resources, (iii) seamless operation transitions of the microgrid between grid-connected and islanded operation modes, and (iv) power quality issues. This dissertation focuses on the development of fault protection systems for both the AC and DC microgrids.

A fast and adaptable (FA) fault protection system is developed to protect multi-grounded AC microgrids. The proposed fault protection system can solve protection problems caused by the mixed combination of inverter-based DGs and rotating-based DGs in the microgrid, limitation of fault currents by DGs’ inverters under an islanded operation mode of the microgrid, and bi-directional fault currents/power flows. In other words, the novel fault protection system should be self-adaptive, aiming to deal with plug-and-play and peer-to-peer characteristics of the AC microgrid. Based on a Chi-square distribution statistic method, a simplified fault current analysis approach, and the support of communication system, tripping thresholds in the FA fault protection system can be automatically adjusted corresponding with the variational AC-microgrid DG and load combinations (e.g., connection and disconnection of source and load branches to and from the AC-microgrid). Additionally, the fast and adaptable AC-microgrid protection system can accurately detect, identify, and locate the faults within one and half cycles with the future combined with use of solid-state switches, aiming to prevent the fast tripping of inverter-based DGs during the fault period of the AC-microgrid. Simulation and experiment results of a multi-grounded 380V AC-MG test-bed at Institute of Nuclear Energy Research - Taiwan are available to validate the fast and adaptable AC-MG fault protection system proposed.

As regards a novel DC-microgrid fault protection system, fast-acting fuses (FAFs) are combined with power electronic switches and digital relays to protect low-voltage DC microgrids. In particular, a DC-microgrid digital relay contains various fault protection modules such as differential current protection module, directional overcurrent/overcurrent protection modules, under-/over-voltage protection modules, and protection modules based on time derivatives of DC current and voltage to protect DC microgrids against pole-to-pole and pole-to-ground faults. Protection coordination strategies among different fault protection modules in a DC-microgrid digital relay, among the digital relays, and between the fuses and the digital relays are analysed to ensure high selectivity of the protection system. Aims of the novel DC-microgrid protection coordination system are to shorten critical fault clearing time and get cost-effectiveness while still ensuring high selectivity for the protection system. As a result, it is proposed that DC power sources such as PV arrays, battery and fuel-cell systems, and power converters should be protected by fast-acting fuses to get the cost-effectiveness of the protection system. DC-microgrid digital relays are required to protect source/load feeders, trunk lines, and common DC buses to get the high selectivity of the protection system. Leakage-current protection solutions are proposed for high-impedance grounded/ungrounded DC-microgrid configurations (e.g., symmetric DC mono-polar microgrids or DC bi-polar microgrids). Simulation and experiment results from a low-voltage DC microgrid test-bed are available with the effectiveness of the proposed DC-microgrid fault protection system as well as the protection coordination strategies being also evaluated.

並列關鍵字

Microgrid ； AC-Microgrid Fault Protection ； DC-Microgrid Fault Protection ； Digital Relays

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