Abstract
The extensive connection of distributed generation (DG) with the distribution network (DN) is one of the core features of a smart grid, but in case of a large number, it may result in problems concerning the DN-DG compatibility during fault isolation and service restoration, for which no efficient and economic solutions have been developed. This paper proposes a doubly-fed induction generator (DFIG) adaptive control strategy (ACS) and a coordination technology to be compatible with the typical feeder automation (FA) protection logics in the ring distribution system. First of all, an ACS simulating the inertia/damping characteristics and excitation principles of synchronous generators is developed to achieve seamless switching between DFIG grid-connection/island modes, and make distant synchronization possible. Next, a technology coordinating the DFIG islands controlled by ACS and the remote tie-switches based on local inspection of synchronization conditions for closing is developed to achieve the safety grid-connection of DFIG islands in the absence of DN-DG communication. At the last, a detailed simulation scenario with a ring DN accessed by five DFIGs is used to validate the effectiveness of ACS and coordination technology compatible with FA in various faults scenes.
Highlights
With more distributed generations (DGs) based on renewable energies integrating to the distribution network (DN), traditional DNs are evolving into active ones with more prominent
The reliability of traditional distribution systems are compromised by the installation of DGs as it results in failure of protection coordination
Distant Synchronization Process: when the DFIG1, DFIG2, and DFIG3 enter into the islanding mode with imbalanced power, the amplitude of uT1 remains relatively stable while Ir-DFIG1, Ir-DFIG2 and Ir-DFIG3 close to each other; DFIG1, DFIG2, and DFIG3 automatically distribute Pe-DFIG1, Pe-DFIG2 and Pe-DFIG3 to maintain PC at a relative stable value; fT1 fluctuates around 50.1 Hz to cause the error of voltage phase ∆θL41 between both sides of the tie-switch L41 reducing to 0◦
Summary
With more distributed generations (DGs) based on renewable energies integrating to the distribution network (DN), traditional DNs are evolving into active ones with more prominent. Those improved protection strategies have significantly improved the reliability of protective device whenever the DGs are in grid-connected or island modes They are developed against problems in the active DNs, such as fault identification, location and isolation, and fail to take into consideration the safe operation of DGs when the topology structure of the DN is changing dynamically. Instead of changing the structures and settings of existing DN-side protection system, this strategy further expands the application level of DGs, and directly reduces the costs of DG stopping and restart It is a conservative disconnection strategy essentially that the DGs fail to continuously supply powers to local loads during a fault, and an additional controllable load bank is required.
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