Abstract
As more and more inverter interfaced distributed generators (IIDGs) such as PV are connected to the distribution network (DN), the existing relay protection system may malfunction due to the impact of the IIDGs. In order to evaluate that impact, the fault analysis of the DN with IIDGs is needed and the fault modelling of IIDG is of great significant for the fault analysis and the protection system validation and improvement. This paper proposes a new fault modelling method of IIDG that could consider the detailed characteristics of the inverter in different situations including the limitation of the modulation. The symmetrical fault model of PQ controlled IIDG is deduced by the proposed method, based on which the symmetrical fault analysis of the DN with IIDGs is carried out. The proposed model depicts IIDG as a voltage-controlled current source or a voltage-controlled voltage source according to whether the modulation is limited, therefore covers the full characteristics of the inverter under different conditions, improving the modelling accuracy. The case study based on the modified IEEE 13 nodes system shows that the fault analysis results obtained from the proposed model are more consistent with electromagnetic transient simulation than that of the state-of-art fault model, verifying its effectiveness.
Highlights
Nowadays, more and more distributed generators utilizing renewable energy resources are connected to the medium and low voltage distribution network (DN) due to the promotion of the energy reform characterized by clean, renewable and sustainable [1]
In order to improve the fault model’s accuracy under different conditions, we propose a new fault modelling method of interfaced distributed generators (IIDGs) that considers the detailed characteristics of the inverter in different situations including the modulation limitation
As more and more IIDGs integrated into the distribution network, the fault characteristics of IIDG and its impact should be evaluated properly
Summary
More and more distributed generators utilizing renewable energy resources are connected to the medium and low voltage distribution network (DN) due to the promotion of the energy reform characterized by clean, renewable and sustainable [1]. The fault models given above mainly focus on the formulation of FRT control strategy of IIDGs and assume the current of IIDG tracks the reference exactly These models may lose accuracy due to the behavior variation of the inverter, which is a complex nonlinear system with many strong nonlinear links such as current limiter and modulation limiter. The IIDG should try to generate the same active power as pre-fault [9], the active and reactive current order idref and iqref given by FRT control strategy to inverter control system could be calculated as follows [9], [11], [ 16].
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