Publications
424 results found
Bell N, Hutchinson CL, Green TC, et al., 2015, Randomised control trial of humidified high flow nasal cannulae <i>versus</i> standard oxygen in the emergency department, EMERGENCY MEDICINE AUSTRALASIA, Vol: 27, Pages: 537-541, ISSN: 1742-6731
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- Citations: 65
Zhao Z, Yang P, Cai Z, et al., 2015, Analysis and improvement of steady-state voltage stability for isolated medium-voltage microgrid with wind power, Dianli Zidonghua Shebei/Electric Power Automation Equipment, Vol: 35, Pages: 13-19, ISSN: 1006-6047
The power-voltage characteristics of DFIG (Doubly-Fed Induction Generator) with wind turbine in the isolated microgrid are analyzed and a strategy based on the local energy-storage stability control and fast pitch-angle control is proposed according to the constraints of different operating modes of microgrid with DFIG to enhance its steady-state voltage stability control. A model of microgrid system with stability control strategy is built based on PSCAD /EMTDC and the results of research indicate that, the proposed strategy enhances effectively the steady-state voltage stability of microgrid under the wind disturbances in different operating modes to guarantee its safe and stable operation.
Zhao Z, Yang P, Guerrero JM, et al., 2015, Multiple-time-scales hierarchical frequency stability control strategy of medium-voltage isolated microgrid, IEEE Transactions on Power Electronics, Vol: 31, Pages: 5974-5991, ISSN: 1941-0107
Chaffey G, Green TC, 2015, Directional current breaking capacity requirements for HVDC circuit breakers, 2015 IEEE Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, Pages: 5371-5377, ISSN: 2329-3721
Circuit breakers are expected to be a vital element within any high capacity HVDC network. This paper examines the directional current breaking capacity requirements that might be seen on a typical HVDC grid, as required for the specification of backup protection. It is shown that there is a significant difference between the peak prospective fault currents observed when the current direction is analysed. Several meshed network topologies are examined in order to evaluate and quantify the characteristics of the directional breaker requirement. Results are presented determining that both the current breaking magnitude duty and the time constraint typically associated with the DC fault are both significantly different when comparing the current direction through the breaker, which may influence future breaker design.
Sheridan CE, Merlin MMC, Green TC, 2015, Benefits of Operating a Four Terminal HVDC Network with a Normally Open Point, International High Voltage Direct Current Conference 2015
It is likely that any HVDC grids will evolve over time and will likely be multi-vendor and use several different technologies. This paper studies a four terminal network where the interconnecting link is operated as a normally open point. This allows the network to be reconfigured in the event of DC side fault, without the need for DC circuit breakers. The network uses the popular Modular Multi-level converter at one terminal and a fault tolerant converter at the other terminal. A simple cost benefit shows the economic advantage of the interconnecting link. The operation of this network is then verified through simulation for a normal operating scenario and a DC fault scenario.
Pipelzadeh Y, Chaudhuri B, Green T, 2015, Modelling and Dynamic Operation of the Zhoushan DC Grid: Worlds First Five-Terminal VSC-HVDC Project, International High Voltage Direct Current 2015 Conference, Publisher: IET, Pages: 87-95
This paper highlights the world’s first operational MTDC grid, namely the 5-terminal Zhoushan DC grid. The scheme went under operation in 2014. The topology and operation of the Zhoushan DC grid are demonstrated with recorded measurements obtained from the converter station, after being subjected to system disturbances. A generic modeling framework for the Zhoushan DC grid is developed inPSCAD/EMTDC. One particular concern is how the Zhoushan DC grid would react to DC side faults and the resulting power imbalance. Despite the completion of the Zhoushan MTDC grid, technological barriers such as the unavailability of fast protection systems, DC circuit breakers and highly efficient VSCs with DC side fault-clearing capabilities have all been bottlenecks at the time of commissioning, but are now under extensive research and development. The challenges and importance of DC grid protection are highlighted through case studies performed on the DC grid model in PSCAD/EMTDC.
Zhao Z, Yang P, Cai Z, et al., 2015, Cooperative control of transient voltage stability for islanded medium-voltage microgrid with wind power, Dianli Zidonghua Shebei/Electric Power Automation Equipment, Vol: 35, Pages: 1-9, ISSN: 1006-6047
The transient operating characteristics of DFIG(Doubly-Fed Induction Generator) and dynamic loads are analyzed for islanded medium-voltage microgrid. A locally coordinative control strategy based on the energy storage stability control, fast wind turbine pitch angle control and dynamic load shedding is proposed to improve the transient voltage stability of microgrid with DFIG. The medium-voltage microgrid system of Dongao Island and the corresponding stability control strategy model are established based on PSCAD/EMTDC. Research results indicate that, the transient voltage stability of microgrid is closely related to the penetration rate of wind power and the load characteristic;the proposed control strategy can effectively enhance the voltage stability of microgrid under serious disturbance.
Zhang X, Green TC, 2015, The modular multilevel converter for high step-up ratio DC-DC conversion, IEEE Transactions on Industrial Electronics, Vol: 62, Pages: 4925-4936, ISSN: 0278-0046
High step-up ratio dc-dc converters with megawatt ratings are of interest in wind turbine interfaces and high-voltage direct-current systems. This paper presents a modular multilevel dc-dc converter based on the standard boost converter topology but with the normal single switches replaced by a number of capacitor-clamped submodules. The converter is operated in resonant mode with resonance between submodule capacitors and the arm inductor. A phase-shifted switching arrangement is applied such that there is a constant number, i.e., N, of submodules supporting the high voltage at a time. In this operation mode, the step-up ratio is dependent on the number of submodules and the inductor charging ratio. The converter exhibits scalability without using a transformer and is capable of bidirectional power flow. An application example of a wind turbine interface with a 10 : 1 conversion ratio is demonstrated in simulation. The experimental verification of the concept using a lab-scale prototype is provided.
Dinh MM, Kastelein C, Bein KJ, et al., 2015, Use of a syndromic surveillance system to describe the trend in cycling-related presentations to emergency departments in Sydney, EMERGENCY MEDICINE AUSTRALASIA, Vol: 27, Pages: 343-347, ISSN: 1742-6731
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- Citations: 2
Dinh MM, Green TC, Bein KJ, et al., 2015, Emergency department clinical redesign, team-based care and improvements in hospital performance: A time series analysis, EMERGENCY MEDICINE AUSTRALASIA, Vol: 27, Pages: 317-322, ISSN: 1742-6731
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- Citations: 12
Judge PD, Chaffey G, Clemow P, et al., 2015, Hardware testing of the alternate arm converter operating in its extended overlap mode, International High Voltage Direct Current 2015 Conference (HVDC2015)
Junyent-Ferre A, Pipelzadeh Y, Green TC, 2015, Blending HVDC-link energy storage and offshore wind turbine inertia for fast frequency response, IEEE Transactions on Sustainable Energy, Vol: 6, Pages: 1059-1066, ISSN: 1949-3029
This paper explores the benefits of combining the dc-link energy storage of a voltage source converter-based high-voltage dc (VSC-HVDC) link and the kinetic energy storage from wind turbines to facilitate in fast primary frequency control and system inertia to an ac network. Alongside physical and analytical justifications, a method is proposed which blends the energy stored in the HVDC link with the power control capabilities of the wind turbines to provide frequency response that is fast while not requiring excessive volume of capacitance nor demanding performance requirements on the wind turbines.
Judge PD, Green TC, 2015, Dynamic thermal rating of a Modular Multilevel Converter HVDC link with overload capacity, PowerTech Eindhoven 2015, Publisher: IEEE
The power rating of Modular Multilevel Converter based HVDC has increased rapidly over the past decade, with individual links in the gigawatt power range now technically feasible and further power increases on the horizon. Such large links may be required to provide ancillary services such as fast frequency response or emergency power re-routing in the event of a system disturbance. Providing such services may require converters to be designed with overload capacity. This paper examines how the thermal aspects of semiconductor devices may impact the operation of such converters and how the exploitation of short-term thermal dynamics may lead to dynamic overload rating.
Chaffey G, Green TC, 2015, Reduced DC circuit breaker requirement on mixed converter HVDC networks, PowerTech Eindhoven 2015, Publisher: IEEE
Recently proposed meshed HVDC networks include both converters and DC circuit breakers, and the fault currents experienced and therefore the capacity requirement of circuit breakers are dependent on the topology of converters used on the network. This paper analyses the difference in fault currents seen in various network configurations utilising fault-feeding and fault-blocking converters. Results are presented showing the reduced fault currents seen in the regions of the DC network where fault current limiting converters have been implemented, which could have an impact on the topology, current rating and therefore size and cost of the circuit breaker.
Pipelzadeh Y, Moreno Vieyra R, Chaudhuri B, et al., 2015, Role of Smart Grid Technology and Corrective Control in Enhancing Network Capacity Utilisation in Great Britain with HVDC links, CIGRE SYMPOSIUM, Publisher: CIGRE
A range of advanced, technically effective and economically efficient corrective (or postfault) actions has been proposed to release latent transmission network capacity of the existing system and thus reduce network congestion and accommodate increased connection of low-carbon generation. Although the increased use of corrective control that can manage post-fault transmission overloads has proven to be clearly beneficial from an economic perspective, there are concerns related to the consequent stability (angular and voltage) of transmission systems. In this context, this paper demonstrates various corrective control measures (that can be undertaken by Special Protection Schemes –SPS–) including rapid response of generation and demand against double line outages (N-2) under extremely high power transfer conditions. To demonstrate these benefits, case studies are carried out on a detailed (full) dynamic system model of the Great Britain (GB) transmission network in DIgSILENT, which includes the Western Line-Commutated Converter based High Voltage Direct Current (LCC-HVDC). The value of corrective control measures, based on generationand demand response accompanied by Transient Assistive Measures (TAM) such as rapid changes in DC power order to improve system stability is demonstrated. It is shown that such measures can significantly increase the power transfers through the England-Scotland inter-connector while maintaining N-2 security. Moreover, it is demonstrated that although a generation ramp up/down response is naturally slower than a step-change tripping action over generation and demand (tripping actions are preferred in SPS) and therefore more prone to transient instability problems, generation-only operational measures can be deployed to deal with double circuit (N-2) outages under extremely high power transfers, given that the right portfolio of TAM is deployed. Thus TAM can effectively enhance the set of correctivecontrol measures considered b
Zhang X, Green TC, 2015, The new family of high step ratio modular multilevel DC-DC converters, 2015 IEEE Applied Power Electronics Conference and Exposition (APEC), Publisher: IEEE, Pages: 1743-1750
This paper presents a family of modular multilevel converters (MMCs) for high step ratio dc-dc conversion. The modular multilevel unidirectional step-down dc-dc converter topologies are presented. The high step-up ratio bidirectional modular multilevel dc-dc converter is also provided. Operation principle and analysis of the bidirectional dc-dc converter are shown, and verified by experimental results with a conversion ratio of 1 : 10. The proposed converters achieve high voltage step ratio depending on the number of sub-modules and the charging ratio.
Merlin MMC, Green TC, 2015, Cell capacitor sizing in multilevel converters: cases of the modular multilevel converter and alternate arm converter, IET Power Electronics, Vol: 8, Pages: 350-360, ISSN: 1755-4535
Multilevel converters, such as the modular multilevel converter (MMC) or the alternate arm converter (AAC), rely on charged capacitors in their cells to generate their AC voltage waveform. Since the cell capacitors are physically large and occupy approximately half the cell volume, their capacitance must be kept minimal while limiting the voltage fluctuation caused by the current passing periodically through these capacitors. This study proposes a mathematical model which estimates the energy deviation for the stacks of both the MMC and the AAC during steady‐state operation under any power factor and for AC voltage magnitude fluctuation of up to ±10%. The analysis is then used to calculate the minimum size for the cell capacitors in order to keep their voltage fluctuation within set boundaries for both topologies. The results show that the MMC requires 39 kJ/MVA of capacitive energy storage under sinusoidal modulation but this reduces with triplen injection modulation. The AAC has a lower requirement for storage in its cells of 11 kJ/MVA but the AAC has a six‐pulse DC current ripple which requires a filter estimated to have a further 33% capacitive storage.
Moreno FJ, Merlin MMC, Trainer DR, et al., 2015, Zero phase sequence voltage injection for the alternate arm converter, 11th IET International Conference on AC and DC Power Transmission, Publisher: IET
The Alternate Arm Converter (AAC) is a voltage source converter being developed as an alternative to the Modular Multilevel Converter (MMC) for HVDC power transmission and reactive power compensation. Each Arm of the converter contains high voltage series IGBT Director Switches and full-bridge cells, which enables the VSC to ride through AC and DC network faults. This paper describes how the AAC can be optimised by modulating the converter terminal voltages with zerophase sequence triplen harmonic components. The optimisation reduces the ratio of the number of the full-bridge cells compared to the simpler Director Switches which offers a valuable improvement in footprint and efficiency.
Husain N, Bein KJ, Green TC, et al., 2015, Real time shift reporting by emergency physicians predicts overall ED performance, EMERGENCY MEDICINE JOURNAL, Vol: 32, Pages: 130-133, ISSN: 1472-0205
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- Citations: 2
Zhao Z, Yang P, Xu Z, et al., 2015, Control Strategy of Energy Storage System for Frequency Support of Autonomous Microgrid, 18th International Conference on Electrical Machines and Systems (ICEMS), Publisher: IEEE, Pages: 422-426
Zhao Z, Yang P, Green TC, et al., 2015, Steady-State Voltage Stability Analysis and Improvement Strategies of Microgrid With Double Fed Induction Wind Generator, 18th International Conference on Electrical Machines and Systems (ICEMS), Publisher: IEEE, Pages: 1063-1068
Zhang X, Green TC, Junyent-Ferre A, 2015, A New Resonant Modular Multilevel Step-Down DC-DC Converter with Inherent-Balancing, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 78-88, ISSN: 0885-8993
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- Citations: 71
Zhao Z, Yang P, Guerrero JM, et al., 2015, Dynamic Stability Analysis of Autonomous Medium-Voltage Mixed-Source Microgrid, 41st Annual Conference of the IEEE-Industrial-Electronics-Society (IECON), Publisher: IEEE, Pages: 1801-1806, ISSN: 1553-572X
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- Citations: 1
Zhao Z, Yang P, Xu Z, et al., 2015, Control Strategy of Energy Storage System for Frequency Support of Autonomous Microgrid, 18th International Conference on Electrical Machines and Systems (ICEMS), Publisher: IEEE, Pages: 422-426
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- Citations: 4
Zhao Z, Yang P, Green TC, et al., 2015, Steady-State Voltage Stability Analysis and Improvement Strategies of Microgrid With Double Fed Induction Wind Generator, 18th International Conference on Electrical Machines and Systems (ICEMS), Publisher: IEEE, Pages: 1063-1068
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- Citations: 1
Pipelzadch Y, Chaudhuri B, Green TC, et al., 2015, Role of Western HVDC Link in Stability of Future Great Britain (GB) Transmission System, General Meeting of the IEEE-Power-and-Energy-Society, Publisher: IEEE, ISSN: 1944-9925
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- Citations: 1
Frost T, Mitcheson PD, Green TC, 2015, Power Electronic Voltage Regulation In LV Distribution Networks, IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), Publisher: IEEE, Pages: 127-133, ISSN: 2329-5759
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- Citations: 2
Bottrell N, Green TC, 2015, Investigation into the Post-Fault Recovery Time of a Droop Controlled Inverter-Interfaced Microgrid, IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), Publisher: IEEE, Pages: 223-229, ISSN: 2329-5759
Spallarossa CE, Merlin MMC, Pipelzadeh Y, et al., 2015, Reduced Dynamic Model of a Modular Multilevel Converter in PowerFactory, IEEE 16th Workshop on Control and Modeling for Power Electronics (COMPEL), Publisher: IEEE, ISSN: 2151-0997
Lueth T, Merlin MMC, Green TC, et al., 2014, High-frequency operation of a DC/AC/DC system for HVDC applications, IEEE Transactions on Power Electronics, Vol: 29, Pages: 4107-4115, ISSN: 0885-8993
Voltage ratings for HVdc point-to-point connections are not standardized and tend to depend on the latest available cable technology. DC/DC conversion at HV is required for interconnection of such HVdc schemes as well as to interface dc wind farms. Modular multilevel voltage source converters (VSCs), such as the modular multilevel converter (MMC) or the alternate arm converter (AAC), have been shown to incur significantly lower switching losses than previous two- or three-level VSCs. This paper presents a dc/ac/dc system using a transformer coupling two modular multilevel VSCs. In such a system, the capacitors occupy a large fraction of the volume of the cells but a significant reduction in volume can be achieved by raising the ac frequency. Using high frequency can also bring benefits to other passive components such as the transformer but also results in higher switching losses due to the higher number of waveform steps per second. This leads to a tradeoff between volume and losses which has been explored in this study and verified by simulation results with a transistor level model of 30-MW case study. The outcome of the study shows that a frequency of 350 Hz provides a significant improvement in volume but also a penalty in losses compared to 50 Hz.
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