Imperial College London

ProfessorTimothyGreen

Faculty of Engineering

Director of the Energy Futures Laboratory (EFL)
 
 
 
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Contact

 

+44 (0)20 7594 6171t.green Website CV

 
 
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Assistant

 

Ms Beata Cypcar +44 (0)20 7594 5865

 
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Location

 

Energy Futures Lab, Electrical Eng BuildingElectrical EngineeringSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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326 results found

Gu Y, Bottrell N, Green TC, 2018, Reduced-Order Models for Representing Converters in Power System Studies, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 33, Pages: 3644-3654, ISSN: 0885-8993

JOURNAL ARTICLE

Judge PD, Merlin MMC, Green TC, Trainer DR, Vershinin Ket al., 2018, Thyristor-Bypassed Submodule Power-Groups for Achieving High-Efficiency, DC Fault Tolerant Multilevel VSCs, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 33, Pages: 349-359, ISSN: 0885-8977

JOURNAL ARTICLE

Wang B, Wang X, Wang X, Shao C, Judge PD, Green TCet al., 2018, An Analytical Approach to Evaluate the Reliability of Offshore Wind Power Plants Considering Environmental Impact, IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, Vol: 9, Pages: 249-260, ISSN: 1949-3029

JOURNAL ARTICLE

Xiang X, Zhang X, Chaffey GP, Green TCet al., 2018, An Isolated Resonant Mode Modular Converter With Flexible Modulation and Variety of Configurations for MVDC Application, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 33, Pages: 508-519, ISSN: 0885-8977

JOURNAL ARTICLE

Xiang X, Zhang X, Luth T, Merlin MMC, Green Tet al., 2018, A Compact Modular Multilevel DC-DC Converter for High Step-ratio MV and HV Use, IEEE Transactions on Industrial Electronics, ISSN: 0278-0046

CCBY In multi-terminal dc networks or future dc grids, there is an important role for high step-ratio dc-dc conversion to interface a high voltage network to lower voltage infeeds or offtakes. The efficiency and controllability of dc-dc conversion will be expected to be similar to modular multi-level ac-dc converters. This paper presents a modular multilevel dc-dc converter with a high step-ratio for medium voltage and high voltage applications. Its topology on high-voltage side is derived from the half-bridge single-phase inverter with stacks of sub-modules replacing each of the switch positions. A near-square-wave current operation is proposed which achieves near-constant instantaneous power for single-phase conversion, leading to reduced stack capacitor and filter volume and also increased the power device utilization. A controller for energy balancing and current tracking is designed. The soft-switching operation on the low-voltage side is demonstrated. The high step-ratio is accomplished by combination of inherent half-bridge ratio, sub-module stack modulation and transformer turns-ratio, which also offers flexibility to satisfy wide-range conversion requirement. The theoretical analysis of this converter is verified by simulation of a full-scale 40MW, 200 kV converter with 146 sub-modules and also through experimental testing of a down-scaled prototype at 4.5 kW, 1.5 kV with 18 sub-modules.

JOURNAL ARTICLE

Chaffey G, Green TC, 2017, Low speed protection methodology for a symmetrical monopolar HVDC network

Protecting a future HVDC network from short circuit DC faults is presently expected to require extensive implementation of fast HVDC circuit breakers, allowing for rapid fault isolation. The requirement for circuit breakers may, however, be reduced or removed depending on the protection methodology, resulting in a slower post-fault recovery. The expected fault response and the subsequent network recovery is dependent on the circuit breaker, network, and converter configurations. This paper examines a low speed protection methodology for a symmetrical monopolar HVDC system, a configuration which requires pole to pole balancing following a pole to ground fault. The fault clearance and network recovery timings are therefore evaluated for both pole to pole and pole to ground faults on several case study networks.

CONFERENCE PAPER

Gu Y, Bottrell, Green, 2017, Reduced-Order Models for Representing Converters in Power System Studies

Matlab codes of reduced-order models for representing power electronic converters in power system analyses.

SOFTWARE

Guo J, Liang J, Zhang X, Judge PD, Wang X, Green TCet al., 2017, Reliability Analysis of MMCs Considering Submodule Designs with Individual or Series-Operated IGBTs, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 32, Pages: 666-677, ISSN: 0885-8977

JOURNAL ARTICLE

Judge PD, Chaffey G, Merlin MMC, Clemow PR, Green TCet al., 2017, Dimensioning and Modulation Index Selection for the Hybrid Modular Multilevel Converter, IEEE Transactions on Power Electronics, ISSN: 0885-8993

CCBY The Hybrid MMC, comprising a mixture of full-bridge and half-bridge sub-modules, provides tolerance to DC faults within compromising the efficiency of the converter to a large extent. The inclusion of full-bridges creates a new freedom over the choice of ratio of AC to DC voltage at which the converter is operated, with resulting impact on the converter's internal voltage, current and energy deviation waveforms, all of which impact the design of the converter. A design method accounting for this, and allowing the required level of de-rating of nominal sub-module voltage and up-rating of stack voltage capability to ensure correct operation at the extremes of the operating envelope is presented. A mechanism is identified for balancing the peak voltage that the full-bridge and half-bridge sub-modules experience over a cycle. Comparisons are made between converters designed to block DC side faults and converters that also add STATCOM capability. Results indicate that operating at a modulation index of 1.2 gives a good compromise between reduced power losses and additional required sub-modules and semi-conductor devices in the converter. The design method is verified against simulation results and the operation of the converter at the proposed modulation index is demonstrated at laboratory-scale.

JOURNAL ARTICLE

Merlin MMC, Judge PD, Chaffey G, Wylie J, Green TCet al., 2017, Soft-switching of the director switch in the alternate arm converter using blocked sub-modules, 2017 IEEE 18th Workshop on Control and Modeling for Power Electronics, COMPEL 2017

© 2017 IEEE. The presence of Director Switches (DS) in its arms enables the Alternate Arm Converter (AAC) to generate smooth current waveforms while using a reduced number of Sub-Modules (SMs) when compared to the Modular Multilevel Converter. To maximise the power efficiency of the AAC and simplify the DS design, it is highly beneficial to soft-switch the DS. This paper presents a method which reliably ensures their soft-switching operation using the blocked state of SMs during the non-conducting part of the cycle of an arm. Experimental results demonstrate the effectiveness of the proposed method over a wide range of operating conditions.

CONFERENCE PAPER

Merlin MMC, Soto Sanchez D, Judge PD, Chaffey G, Clemow P, Green TC, Trainer DR, Dyke KJet al., 2017, The Extended Overlap Alternate Arm Converter: A Voltage Source Converter with DC Fault Ride-Through Capability and a Compact Design, IEEE Transactions on Power Electronics, ISSN: 0885-8993

CCBY The Alternate Arm Converter (AAC) was one of the first modular converter topologies to feature DC-side fault ride-through capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with a short overlap period) resulted in (i) substantial 6-pulse ripples in the DC current waveform, (ii) large DC-side filter requirements, and (iii) 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 & #x00B0; which facilitates a fundamental redefinition of the AAC working principles. The EO-AAC has its DC current path decoupled from the AC current paths, a fact allowing (i) smooth DC currents, (ii) elimination of DC filters, and (iii) restriction lifting on the feasible operating. 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 MMC (with DC fault ride-through capability) while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume.

JOURNAL ARTICLE

Pipelzadeh Y, Chaudhuri NR, Chaudhuri B, Green TCet al., 2017, Coordinated Control of Offshore Wind Farm and Onshore HVDC Converter for Effective Power Oscillation Damping, IEEE TRANSACTIONS ON POWER SYSTEMS, Vol: 32, Pages: 1860-1872, ISSN: 0885-8950

JOURNAL ARTICLE

Pipelzadeh Y, Moreno R, Chaudhuri B, Strbac G, Green TCet al., 2017, Corrective Control With Transient Assistive Measures: Value Assessment for Great Britain Transmission System, IEEE TRANSACTIONS ON POWER SYSTEMS, Vol: 32, Pages: 1638-1650, ISSN: 0885-8950

JOURNAL ARTICLE

Sang Y, Junyent-Ferre A, Green TC, 2017, Transformer Design in a Medium Voltage DC/DC Converter for a DC Collection Network, 19th European Conference on Power Electronics and Applications (EPE ECCE Europe), Publisher: IEEE, ISSN: 2325-0313

CONFERENCE PAPER

Sanz IM, Judge PD, Spallarossa CE, Chaudhuri B, Green TCet al., 2017, Dynamic Overload Capability of VSC HVDC Interconnections for Frequency Support, IEEE TRANSACTIONS ON ENERGY CONVERSION, Vol: 32, Pages: 1544-1553, ISSN: 0885-8969

JOURNAL ARTICLE

Wang B, Wang X, Bie Z, Judge PD, Wang X, Green TCet al., 2017, Reliability Model of MMC Considering Periodic Preventive Maintenance, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 32, Pages: 1535-1544, ISSN: 0885-8977

JOURNAL ARTICLE

Wylie J, Merlin MC, Green TC, 2017, Analysis of the Effects from Constant Random and Wear-out Failures of Sub-modules within a Modular Multi-level Converter with Varying Maintenance Periods, 19th European Conference on Power Electronics and Applications (EPE ECCE Europe), Publisher: IEEE, ISSN: 2325-0313

CONFERENCE PAPER

Xiang X, Zhang X, Chaffey GP, Gu Y, Green TCet al., 2017, The isolated resonant modular multilevel converters with large step-ratio for MVDC applications

© 2017 IEEE. The DC-DC conversion will play an important role in multi-Terminal dc networks and dc grids. This paper presents two isolated resonant modular multilevel converters (IRMMCs) to fulfill the large step-ratio conversion for medium voltage dc (MVDC) networks. The conventional resonant modular multilevel converters (RMMCs) suffer the common problems of non-isolation and high current stress, which are solved in the proposed IRMMCs. They not only inherit the beneficial features of inherent sub-module (SM) voltage-balancing and soft-switching operation from RMMCs, but also develop multi-module configurations to neutralize the current ripples on both sides of the dc-links. The theoretical analysis is verified by a set of full-scaled simulations for different application examples in MVDC collection and distribution. The results demonstrate the proposed IRMMCs and its derived configurations have good potential for operation as large step-ratio MVDC transformers.

CONFERENCE PAPER

Zhang X, Xiang X, Green TC, Yang Xet al., 2017, Operation and Performance of Resonant Modular Multilevel Converter With Flexible Step Ratio, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, Vol: 64, Pages: 6276-6286, ISSN: 0278-0046

JOURNAL ARTICLE

Beddard A, Sheridan CE, Barnes M, Green TCet al., 2016, Improved Accuracy Average Value Models of Modular Multilevel Converters, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 31, Pages: 2260-2269, ISSN: 0885-8977

JOURNAL ARTICLE

Beddard A, Wang W, Barnes M, Green PR, Beddard A, Green TCet al., 2016, Impact of Parameter Uncertainty on Power Flow Accuracy in Multi-terminal Systems, IEEE-Power-and-Energy-Society General Meeting (PESGM), Publisher: IEEE, ISSN: 1944-9925

CONFERENCE PAPER

Bloemink JM, Green TC, 2016, Required VSC Efficiency for Zero Net-Loss Distribution Network Active Compensation, 7th IEEE International Symposium On Power Electronics for Distributed Generation Systems (PEDG), Publisher: IEEE, ISSN: 2329-5759

CONFERENCE PAPER

Cao W, Wu J, Jenkins N, Wang C, Green Tet al., 2016, Operating principle of Soft Open Points for electrical distribution network operation, APPLIED ENERGY, Vol: 164, Pages: 245-257, ISSN: 0306-2619

JOURNAL ARTICLE

Cao W, Wu J, Jenkins N, Wang C, Green Tet al., 2016, Benefits analysis of Soft Open Points for electrical distribution network operation, APPLIED ENERGY, Vol: 165, Pages: 36-47, ISSN: 0306-2619

JOURNAL ARTICLE

Chaffey G, Judge PD, Merlin MMC, Clemow PR, Green TCet al., 2016, DC Fault Ride Through of Multilevel Converters, IEEE Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, ISSN: 2329-3721

CONFERENCE PAPER

Judge PD, Merlin MMC, Green TC, Trainer DR, Vershinin Ket al., 2016, The augmented trapezoidal alternate arm converter: a power-group augmented DC fault tolerant voltage source converter, 2nd International Conference on High Voltage Direct Current

Achieving DC fault tolerance in modularmultilevel converters requires the use of a significantnumber sub-modules which are capable of generatinga negative voltage. This results in an increase in thenumber of IGBT devices in the current path, resultingin an increase in conduction losses within the converter.This paper introduces a thyristor augmented multilevelstructure called a Power-Group, offering both negativevoltage capability as well as a low conduction loss state,which can be used to construct high efficiency DC faulttolerant converters. When combined with the AlternateArm Converter topology the power-group concept hasbeen found to result in a converter topology that exhibitsvery low power-losses, high quality AC and DC currentwaveforms, while also achieving DC fault tolerance.

CONFERENCE PAPER

Pereda J, Green TC, 2016, Direct Modular Multilevel Converter With Six Branches for Flexible Distribution Networks, IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 31, Pages: 1728-1737, ISSN: 0885-8977

JOURNAL ARTICLE

Spallarossa CE, Merlin MMC, Green TC, 2016, Augmented Inertial Response of Multi-level Converters using Internal Energy Storage, IEEE International Energy Conference (ENERGYCON), Publisher: IEEE, ISSN: 2164-4322

CONFERENCE PAPER

Xiang X, Merlin MMC, Green TC, 2016, Cost analysis and comparison of HVAC, LFAC and HVDC for offshore wind power connection

Low frequency AC (LFAC) has been proposed as a means to avoid some of the large converter station costs of high voltage DC (HVDC) while delivering some of the benefits in terms of better cable utilization and its technical feasibility has been established. It is said to offer lower costs than HVDC or conventional high voltage AC (HVAC) for a range of intermediate distances, with HVDC becoming cheaper over long distances. However, the basis for identifying the distance range and extent of cost saving has not been established. Here, cost estimate methodologies are extended for LFAC. A difficulty is the absence of commercial schemes that can provide practical examples of costs. In this paper, costs are broken down into constituent terms and estimates are made from the most similar equipment from other schemes. The capacity limits and power losses associated with subsea cables are analyzed for low frequency cases. For a given power transfer and for each distance, a choice of operating voltage, cable size and number of parallel circuits is made in order to find the lowest route cost. This yields cost as a function of distance that is a non-linear and discontinuous function. The cost curves for LFAC are compared with HVDC and HVAC options. The results for current cost estimates show that LFAC has a range of route length over which it is the lowest cost option and but this range narrows and eventually ceases to exist for higher power transfer ratings.

CONFERENCE PAPER

Zhao Z, Yang P, Guerrero JM, Xu Z, Green TCet al., 2016, Multiple-Time-Scales Hierarchical Frequency Stability Control Strategy of Medium-Voltage Isolated Microgrid, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 31, Pages: 5974-5991, ISSN: 0885-8993

JOURNAL ARTICLE

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