| Microgrid integrates energy storage devices, micro-sources, load,protection relays and control together to form a single controlleddistribution network unit. Microgrid can achieve high penetration oflarge-scale distributed and renewable generators, improve power supplyreliability, and make efficient utilization of all kinds of energy. Theinterfaces of micro-sources are commonly electronic inverter. When failureoccurs within the network, the micro-source output short-circuit current willbe limited by the over-current saturation module in inverter. Meanwhile, asthe access location of micro-sources is flexibility, power flows within thenetwork can start in this double-ended power flow situation when Microgridconnected to power system. These factors result in that the traditionaldistribution network protection with amplitude criterion is no longersuitable for fault diagnosis. Thus, it’s very necessary to have a deep researchon fault characteristics and protection scheme for the microgrid.Micro-grids have different operating modes and distributed energysources have various control strategies and switch frequently. Consideringthese characteristics, this article proposed a new method of pilot protectionscheme for lines main protection based on fault component direction and abackup protection which consists of distance protection in zone III andzero-sequence over-current protection. This main protection can operateaccurately and quickly at different fault condition by using reasonablecriteria、compensating voltage and protection logic on the side of weeksource. Simulationed results show that this method can operate correctlywith different operating modes、control strategies、transition resistances、fault types and DG switching. This backup protection combined the characteristics of distance protection in zone III and zero-sequenceover-current protection. Simulationed results show that this method canadapt to change of operating modes、 control strategies and transitionresistances. |
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