Abstract
Constant power loads (CPLs), interfaced through active rectifiers can be used for improving the stability of induction generator (IG)-based wind turbines under balanced grid voltage dips by providing the reactive power. Under asymmetrical grid faults, the negative sequence voltage produces additional generator torque oscillations and reduces the lifetime of the installed equipment. This article explores the possibility of using a CPL for mitigation of unbalanced voltage dips in an AC distribution system in addition to consuming a constant active power. Unbalanced fault mitigation as an ancillary service by the load itself could greatly increase the stability and performance of the overall power system. A CPL control structure, capable of controlling the positive and negative sequence of the grid voltage is suggested. The simulation results clearly indicate the effects of compensating the positive and negative sequence of the grid voltage on the performance of IG based wind turbines. The maximum Fault Ride Through (FRT) enhancement has been given priority and is done by the compensation of positive sequence voltage. The remaining CPL current capacity is used to compensate the negative sequence voltage in order to reduce the additional torque ripples in the IG.
Highlights
Distributed energy resources (DERs), based on mainly renewable energy represent only a small part of the present day power infrastructure and have a small impact on the performance and quality of the electrical grid [1]
A simulation analysis is performed for a medium size wind farm to confirm the validity of the proposed Fault Ride Through (FRT) enhancement method discussed in the previous section
This paper explores the possibility of using a Constant power loads (CPLs) to mitigate the asymmetrical grid faults in an induction generator (IG)- based wind turbine instead of using dedicated devices such as a STATCOM or doubly fed induction generator (DFIG) wind turbine
Summary
Distributed energy resources (DERs), based on mainly renewable energy represent only a small part of the present day power infrastructure and have a small impact on the performance and quality of the electrical grid [1]. Power electronic (PE) load interfaces, when tightly regulated, draw a constant active power from the utility and behave like CPL They are adaptive to fluctuations in the grid voltage at its terminal and always keep the input power constant [8,9,10,11,12]. This paper, for the first time, proposes the application of a tightly regulated PE load interface or a CPL that is connected to a squirrel cage IG-based wind turbine and is used for the mitigation of unbalanced grid voltage dips. The main contribution of this work is based on the fact that a dedicated device (STATCOM or DFIG) is not needed for FRT enhancement and an industrial motor drive or any other CPL available in the vicinity of the IG based wind farm can be utilized to provide this additional service. The simulation results indicate that positive sequence voltage compensation by CPL helps to avoid the complete voltage collapse and increases the stability of the wind turbine, while the negative sequence voltage compensation reduces the torque oscillations, thereby increasing the lifetime of the generator drive train
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