Abstract
This paper presents an improved current source equivalent model method to determine the short-circuit current of a distribution system with multiple fixed-speed and variable-speed induction generators (IGs). The correlation coefficients of flux components between stator and rotor under the unsymmetrical fault are analyzed using the positive and negative sequence steady-state equivalent circuits of an IG. The terminal voltage and current responses of fixed-speed and variable-speed IGs with and without the rotor slip changes under different penetration levels are compared to investigate the coupling relation between the short-circuit currents of IGs and the nodal voltages in the distribution network. Then the transient equivalent potential of an IG at the grid fault instant is derived. Sequence components of the short-circuit current in the network can be determined using the proposed technique. The correctness of the proposed method is verified using dynamic simulation.
Highlights
The increased penetration of renewable power has resulted in more distributed generators (DGs) embedded in distribution networks
This paper proposes an improved analytical method to calculate the sequence components of the short-circuit currents of multi-induction generators (IGs) systems
The short-circuit calculation problem is formulated based on the transient response, slip variation of fixed-speed and variable-speed IGs, and parameters of distribution network, and is solved using the iteration technique
Summary
The increased penetration of renewable power has resulted in more distributed generators (DGs) embedded in distribution networks. DGs include synchronous generators, induction generators (IGs), and other power sources with electronic interfaces; of these types, the squirrel-cage IG has received increased attention in distribution networks because of its low cost, small size, and low maintenance requirements [2]. When short-circuit faults occur, IGs are unable to maintain their terminal voltage without an external excitation current, because they have different short-circuit current characteristics compared with synchronous generators [3]. The similar method used for IG cannot calculate the short-circuit currents accurately during the fault process, because it does not consider the electromagnetic transient characteristics of IGs [5,6]. This work aims to study the short-circuit calculation of a multi-IG distribution network
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