Operating DC Circuit Breakers With MMC

Cwikowski, Oliver; Wood, Alan; Miller, Allan; Barnes, Mike; Shuttleworth, R.

doi:10.1109/tpwrd.2017.2658540

Cited by 82 publications

(52 citation statements)

References 18 publications

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“…This paper has shown, for the first time that the HB-MMC is capable of limiting the prospective dc fault current level and capable of supporting the dc CB during opening, using a Modified blocking scheme. This modified blocking scheme can be used to prevent pseudo-rectifier operation, just as the double bypass thyristors can [17] [16]. The modified blocking scheme may allow this to be achieved with no additional hardware and may also allow for a faster recovery.…”

Section: Discussionmentioning

confidence: 99%

“…The fault limitation effect may provide sufficient time for the dc circuit breaker to open before the current limits are reached. The dc current in the modified case slowly decays due to the natural RL circuit formed when the ac terminals of the converter are short circuited [17]. This decay is very slow due to the large inductance and low resistance of the circuit.…”

Section: Blocking Strategymentioning

confidence: 99%

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Modular Multilevel Converter DC Fault Protection

Cwikowski

Wickramasinghe

Konstantinou

et al. 2018

IEEE Trans. Power Delivery

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-High voltage direct current grids will require the development of dc protections that provide fast fault isolation and minimize the disturbance caused to the existing ac power networks. This paper investigates how the dc fault recovery performance of a half-bridge modular multilevel converter (HB-MMC) is impacted by different dc protection design choices. A HB-MMC point-to-point HVDC system that is protected with dc circuit breakers (CBs) is simulated on a real time digital simulator (RTDS) using detailed switch models of the converters and switch gear. A dc CB controller has been developed and implemented in a software-in-the-loop fashion, and has been made available free for download. A novel blocking scheme for the HB-MMC is proposed, which limits the prospective dc-side fault current, benefiting dc switch gear. A comparison of circulating current controllers shows that the standard dq controller is likely to be unsuitable for fault studies. Finally, benchmarking shows that a 48% reduction in power flow recovery time and a 90% reduction in the energy dissipated in the circuit breaker can be achieved, along with other benefits, depending on the protection design.Index Terms -HVDC, RTDS, protection, dc circuit breaker voltage-source converter, modular multilevel, ac grid impact.

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Section: Discussionmentioning

confidence: 99%

Section: Blocking Strategymentioning

confidence: 99%

Modular Multilevel Converter DC Fault Protection

Cwikowski

Wickramasinghe

Konstantinou

et al. 2018

IEEE Trans. Power Delivery

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“…This is proven by (18) resulting from (14) with k 3 = 0.5, where k AC measures the ac voltage magnitude's relative variation to its nominal value (10). This results in a voltage rating increase of the stacks of SMs by ±2.5% for an ac voltage magnitude variation of ±15%…”

Section: Ac Voltage Magnitude Variationmentioning

confidence: 95%

“…The half-bridge SM version of the MMC is the most power efficient variant but requires large arm inductors [8] to limit di/dt and prospective fault current arising from dc-side faults. On pointto-point HVDC links, we may also require bypass thyristors in the SMs in order to protect the freewheel diodes from excessive fault currents before the ac circuit breakers open, preventing any further rectification of ac-side fault current [9], and on multiterminal schemes, dc circuit breakers [10]- [14] are needed in order to prevent the entire dc grid from being blacked out as a result of a single dc-side fault. Recent design innovations have helped the MMC to cope with these fault situations either by using hybrid stacks consisting of both full-and half-bridge SMs [15]- [20] or new SM circuits such as the double clamped submodule [21]- [24] and other designs [17], [25]- [27].…”

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confidence: 99%

The Extended Overlap Alternate Arm Converter: A Voltage-Source Converter With DC Fault Ride-Through Capability and a Compact Design

Merlin

Soto

Judge

et al. 2018

IEEE Trans. Power Electron.

121

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Abstract-The alternate arm converter (AAC) was one of the first modular converter topologies to feature dc-side fault ridethrough capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with an additional short overlap period) resulted in 1) substantial sixpulse ripples in the dc current waveform, 2) large dc-side filter requirements, and 3) limited operating area close to an energy sweet spot. This paper presents a new mode of operation called extended overlap (EO) based on the extension of the overlap period to 60• , which facilitates a fundamental redefinition of the working principles of the AAC. The EO-AAC has its dc current path decoupled from the ac current paths, a fact allowing 1) smooth dc current waveforms, 2) elimination of dc filters, and 3) restriction lifting on the feasible operating point. Analysis of this new mode and EO-AAC design criteria are presented and subsequently verified with tests on an experimental prototype. Finally, a comparison with other modular converters demonstrates that the EO-AAC is at least as power efficient as a hybrid modular multilevel converter (MMC) (i.e., a dc fault ride-through-capable MMC), while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume.Index Terms-AC-DC power conversion, active filters, capacitive energy storage, HVDC transmission, power system faults, power transmission protection.

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“…Fast fault isolation is only possible using DC breaker (DCCB)s [5] or converters with fault blocking capability [6]. Additionally, selective and fast detection of faults is difficult for the protection algorithm, because it must be done in less than 5 milliseconds in order to have minimum damage in HVDC converter switches [7] and correctly detect the faulty section of the transmission grid. According to the mentioned challenges in the protection of VSC-MTDC grids, designing fast, accurate and selective fault detection algorithms is one of the important topics in the field of HVDC protection and is investigated in this study.…”

Section: Introductionmentioning

confidence: 99%

A Harmonic Based Pilot Protection Scheme for VSC-MTDC Grids with PWM Converters

2019

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This paper presents a selective harmonic-based pilot protection scheme for detecting faults happened in the DC transmission section of VSC-MTDC grids with pulse width modulation (PWM) voltage source converters (VSCs). When a DC fault occurs in VSC-MTDC grids with PWM converters, first carrier frequency harmonic (FCFH) currents will be generated by all VSCs through the grid. FCFH currents have different flowing directions depending on the characteristics and the location of the fault. According to the characteristics of the existing FCFH in the fault currents, a selective pilot protection algorithm is designed for VSC-MTDC grids. Considering the internal and external DC transmission faults for specific zones, and the circulating flow of FCFH current in the DC link capacitors, the relays cannot detect FCFH currents for external faults, while for the internal faults, FCFH currents are clearly detected. To design the selective protection algorithm, Hilbert-Huang transform (HHT) is used to detect the instantaneous frequency and the instantaneous amplitude of the high frequency intrinsic mode function (IMF)s, which are extracted from the fault current waves. Multiple faults with different characteristics are applied to CIGRE DCS-2 VSC-MTDC grid with two-level and three-level VSCs modeled in PSCAD, and the HHT-based selective protection scheme is designed in MATLAB. According to the results, the proposed algorithm can truly discriminate between internal and external faults.

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Operating DC Circuit Breakers With MMC

Cited by 82 publications

References 18 publications

Modular Multilevel Converter DC Fault Protection

Modular Multilevel Converter DC Fault Protection

The Extended Overlap Alternate Arm Converter: A Voltage-Source Converter With DC Fault Ride-Through Capability and a Compact Design

A Harmonic Based Pilot Protection Scheme for VSC-MTDC Grids with PWM Converters

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