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Abstract

Distributed AC power systems with large percentage of constant power loads (CPL) are susceptible to potential voltage stability problems under abnormal operating conditions. The design of the control system of the CPL can greatly influence the power system stability. In this paper, main focus has been put to use CPLs for transient stability enhancement and fault ride through (FRT) under balanced/unbalanced grid voltage dips instead of employing a dedicated compensating device for such ancillary grid services. The influence of introducing reactive current control by active rectifiers on the CPL instability, and the resulting contribution to the overall voltage stability is investigated and evaluated. A large increase in transient stability margins has been observed under balanced grid voltage sags when CPLs provide the ancillary reactive power during the fault and avoid a possible voltage collapse due to excessive reactive power consumption. Centralized reactive compensation by a STATCOM is used as reference to compare with distributed compensation by the CPLs. Results shows that required distributed injection of reactive current is lower compared to the rating of a centralized STATCOM.

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