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Enhanced Active Resonant DC Circuit Breakers for HVDC Grids

Time: Wed 2021-05-19 10.00

Location: zoom link for online defense (English)

Subject area: Electrical Engineering

Doctoral student: Tim Augustin , Elkraftteknik, Power Electronics

Opponent: Professor Jürgen Biela, ETH Zürich

Supervisor: Professor Hans-Peter Nee, Elkraftteknik; Associate Professor Marley Becerra, Elektroteknisk teori och konstruktion, ABB Corporate Research, Västerås

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High-voltage DC (HVDC) grids are considered promising for the electricity grid expansion required to integrate renewable energy sources into the existing infrastructure. DC fault currents increase rapidly and lack a current zero crossing. Therefore, HVDC grids require complex DC circuit breakers (DCCBs) capable of interrupting faster than AC circuit breakers to protect against DC faults. Being complex, DCCBs can offer functionality in addition to interruption. Most DCCBs can be categorized as current-injection DCCBs or hybrid DCCBs. Hybrid DCCBs feature more functionality than current-injection DCCBs. Nevertheless, the power semiconductors used in hybrid DCCBs are expensive. The enhanced active resonant (EAR) DCCBs studied in this work are an intermediate solution with the functionality of hybrid DCCBs and the interruption mechanism of current-injection DCCBs. The core of EAR DCCBs are discharge closing switches, which are simple, robust and available for high current and high voltage.

Like all HVDC DCCBs, EAR DCCBs need a fast mechanical switch. A Thomson-coil actuator with active damping is used to open and close the mechanical switch fast. A novel Thomson-coil driver recycling energy during actuation simplifies the Thomson-coil actuator system. Experimental results demonstrate the open-close and open-close-open operation of the Thomson-coil actuator. Extensive experimental studies investigate the DC interruption capability and functionality of a prototype EAR DCCB in a specialized DCCB test circuit. The tests results show that the prototype EAR DCCB can interrupt up to 1.2 kA, abort proactive commutation, and auto-reclose. The studies of the discharge closing switch used find that its minimum voltage is not a serious limitation and that the discharge can become unstable after commutationat low currents. An alternative commutation technique allows EAR DCCBs with less components to operate reliably at all currents.