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## Publications

Publications (77)

Thyristor based multilevel current reinjection (MLCR) current source converter (CSC) provides self-commutation capability to thyristors. It also has high quality line current waveform by accurately shaping the DC bus current using an auxiliary reinjection bridge. However the theoretical and PSCAD/ETDC simulation analysis do not take into account th...

SUMMARY This paper presents the first experimental validation of a Harmonic State-Space (HSS) model. The HSS framework is capable of capturing the transient evolution of harmonics as well as their steady-state, and the frequency cross-coupling nature of power electronic circuits is fully represented. The HSS requires non-linear power electronic cir...

This article presents a comprehensive analysis of the thyristor based seven-level multi-level current reinjection current source converter. The seven-level multi-level current reinjection current source converter increases the pulse number from 12 to 72, thereby producing high-quality AC current and DC voltage waveforms, thus lowering harmonics on...

The high-power self-commutated voltage-source converter (VSC) and current-source converter (CSC) are the key control devices in high-voltage direct current, flexible ac transmission systems, and distribution flexible ac transmission systems. To achieve the expected control objectives, suitable control strategies must be implemented based on the ava...

The high-power self-commutated voltage-source converter (VSC) and current source converter (CSC) are the key control devices in HVDC, flexible ac transmission systems (FACTS) and distribution FACTS systems. To achieve the expected control objectives, suitable control strategies must be implemented based on the available devices, system, and control...

The mechanism of harmonic current injection from single-phase grid-connected converters is comprehensively investigated. The measurable impacts from grid voltage, converter commutation, power factor, PWM modulation and control strategy are demonstrated on the harmonic current injection. According to the mechanism, a tailor-made control solution whi...

Multi-level Current Reinjection (MLCR) concept adds self commutation capability to thyristors, and produces a high quality line current waveforms and provides reactive power compensation in current source converters (CSC). Multi-level conversion is applied to generate the required optimum linear multilevel injection current which, when reinjected t...

The multi-level current reinjection (MLCR) concept produces high quality line current waveforms in current source converters (CSC) by injecting an reinjection current. Two rein-jected waveforms: Symmetrical waveform and Linear waveform are known. In this paper the influence of varying the zero width period (ZWP) of symmetrical waveform on line curr...

In this paper a comparative evaluation study is carried out for a 3-level, 5-level, 7-level thyristor based multi-level current reinjection (MLCR) current source converters (CSC) in terms of line current total harmonic distortion (THD) obtained, reinjection transformer requirements, reinjection switch ratings, reinjection control circuitry complexi...

The objective of this paper is to compare and assess the performance of the conventional and hybrid high voltage direct current (HVDC) rectifiers based on the CIGRE benchmark model for both static and dynamic conditions with the phase lock loop (PLL) control replaced by PLL-less control. Traditional HVDC rectifier uses a 12-pulse thyristor bridge w...

This paper presents a comparative simulation study between the DQO gate firing unit (GFU) and a proposed GFU for high voltage direct current (HVDC) system, using the CIGRE benchmark model in the Matlab/Simulink environment. The proposed GFU does not use traditional phase lock loop (PLL) and offers structural simplicity, fast response and immunity t...

The 6-pulse controlled rectifier circuit is very well known. For proper operation of the 6-pulse rectifier, it is necessary to synchronise the firing signals with the mains voltage, else the operation of the rectifier is affected. A firing angle controller, without using any phase lock loop (PLL), is described here. This scheme employs the dq-refer...

In accordance with the randomness and intermittent characteristics of wind power, the static synchronous compensator (STATCOM) is more competent and competitive for reactive power compensation in large scale wind farm. An average state model for the VSC-STATCOM is derived, according to the wind farm reactive power compensation characteristics, a no...

The high power self-commutated VSC are the key control devices in HVDC, FACTS and DFACTS systems. The self-commutated voltage source converter back to back (VSCBTB) link connects two ac power systems asynchronously, can control the active power exchanged between the two ac system and the reactive powers at the both terminals independently. To achie...

Grid connected power electronic converters must be synchronized to the mains voltage by using suitable converter control circuit and gate signals, in order to function correctly. Without proper synchronization, the operation of the converter is adversely affected. This paper proposes a method to synchronize power converters to the mains voltage wit...

Phase-Lock-Loops (PLL) are critical components for control of power electronic converters that interface to the electrical power system and are also used in variety of other applications such as communication etc. This paper presents a phase-lock-loop based mains frequency counter with resolution up to three decimal places. Phase lock loop design e...

A quadrature phase shifter for sinusoidal signal is proposed in this paper based on a voltage controlled 2-pole Butter worth low pass filter. The cut off frequency of the filter is maintained approximately equal to the input frequency using an OTA based scale changer thereby maintaining unity gain and 90° phase shift.

This paper presents a comprehensive review of power quality improvements made by applying the concept of DC ripple reinjection in current source series connected AC-DC rectifier for HVDC transmission. Recent advances in applying the reinjection concept, their suitability and selection is discussed. The main aim is to present a state of the art on t...

A simulation study between the DQO gate firing unit (GFU) and a proposed GFU for high voltage direct current (HVDC) rectifier based on the CIGRE benchmark model in Matlab/Simulink is carried out. The proposed GFU does not use traditional phase lock loop (PLL) and offers structural simplicity, fast response and immunity to ac system voltage unbalanc...

This paper presents an electronically tunable Proportional Integral (PI) controller employing Operational Transconductance Amplifiers (OTA) for use in a Phase Lock Loop (PLL). Bandwidth, time constants, phase margin, cross-over frequency, damping factor can all be electronically tuned by the use of OTA based PI controller. Parameter design equation...

In recent years Operational Transconductance Amplifier based high frequency integrated circuits, filters and systems have been widely investigated. The usefulness of OTAs over conventional OP-Amps in the design of both first order and second order active filters are well documented. This paper proposes two first order voltage controlled all pass fi...

In recent years Operational Transconductance Amplifier (OTA) based integrated circuits, filters and analog circuits have been widely investigated. The usefulness of OTAs over conventional OP-Amps in the design of active circuits are well documented. This paper presents a new sinusoidal frequency-to-voltage converter which can linearly convert low v...

A new tunable all pass filter is presented. It is based on the simple op-amp based filter with a programmable floating capacitor and a programmable resistor. The proposed floating capacitor value can be widely varied by adjusting the transconductance parameter which depends on bias current. The floating capacitor consists of only five OTAs. Using s...

Large-current, low-voltage applications such as aluminium smelters use diodesaturable reactors or thyristor-based rectification to control the DC current. Transformer on-load tap-changers are also used to minimise the steady-state reactive power requirements. This paper describes a new double-group, two-quadrant thyristor-based concept suitable for...

IntroductionProvision of independent reactive power controlMLCR back-to-back linkControl system designDynamic performanceWaveform qualitySummaryReferences

For very high voltage or very high current applications, the power industry still relies on thyristor-based Line Commutated Conversion (LCC), which limits the power controllability to two quadrant operation. However, the ratings of self-commutating switches such as the Insulated-Gate Bipolar Transistor (IGBT) and Integrated Gate-Commutated Thyristo...

IntroductionSMES technologyPower conditioningThe SMES coilMLCR current source converter based SMES power conditioning systemSimulation verificationDiscussion - the future of SMESReferences

IntroductionMLCR-HVDC transmissionSimulated performance under normal operationSimulated performance following disturbancesProvision of independent reactive power controlSummaryReferences

IntroductionPresent high current rectification technologyHybrid double-group configurationCentre-tapped rectifier optionTwo-quadrant MLCR rectificationParallel thyristor/MLCR rectificationMulticell rectification with PWM controlSummaryReferences

IntroductionThe reinjection concept in line-commutated current source conversionApplication of the reinjection concept to self-commutating conversionMultilevel reinjection (MLR) - the waveformsMLR implementation - the combination conceptMLR implementation - the distribution conceptSummaryReferences

Early developmentsState of the large power semiconductor technologyVoltage and current source conversionThe pulse and level number conceptsLine-commutated conversion (LCC)Self-commutating conversion (SCC)Concluding statementReferences

IntroductionState of the DC cable technologyBasic self-commutating DC link structureThree-level PWM structurePWM–VSC control strategiesDC link support during AC system disturbancesSummaryReferences

IntroductionControl system levelsNon-linearity of the power converter systemModelling the voltage source converter systemModelling grouped voltage source converters operating with fundamental frequency switchingModelling the current source converter systemModelling grouped current source converters with fundamental frequency switchingNon-linear con...

IntroductionModular multilevel conversionMultilevel H-bridge voltage reinjectionSummaryReferences

IntroductionBasic VSC operationMain converter componentsThree-phase voltage source conversionGate driving signal generationSpace-vector PWM patternBasic current source conversion operationSummaryReferences

Although the multilevel current reinjection concept has been presented as a possible self-commutating alternative to line-commutated conversion for large power HVDC transmission, in its present form, the lack of independent reactive power control at the two converter terminals constitutes a severe limitation to its eventual acceptability. For very...

The main purpose of this paper is to describe advances in high current source converter (CSC) and control for use in superconductive magnetic energy storage (SMES) schemes instead of the conventional PWM-chopper based VSC configurations. The multi-level current reinjection (MLCR) CSC provides the simplest structure, as well as switching at zero cur...

A three-phase converter configuration, with each phase consisting of a series chain of H-bridges has become a popular multilevel solution for STATCOM application. Such a configuration, however, is not suitable for HVDC transmission. A new concept, where the series chain of H-bridge cells is used to derive a multilevel voltage reinjection waveform,...

A new multilevel configuration is proposed for use in voltage source conversion of large power and voltage ratings; it consists of the standard double bridge converter and a series chain of H-bridges, each connected to a capacitor. The H-bridge chain is connected between the middle node of the dc capacitors and the neutral point of the two main bri...

A new concept referred to as reinjection AC/DC conversion is described, applicable to both self- commutating voltage source and current source conversions. It combines all the benefits of the multi-level, soft switching and ripple reinjection concepts. The aim is to achieve high-quality waveforms, simplify the structural configuration and the inter...

In self-commutating multi-level voltage source conversion (VSC) transmission, the reactive power contributions of the two converter terminals are interdependent. To overcome this problem, a new control scheme is proposed, applicable to high voltage direct current (HVDC) interconnections of large power ratings with more than one 12-pulse group per c...

The development of power semiconductors with greater ratings and improved characteristics has meant that the power industry has become more willing to develop new converter configurations. These new configurations take advantage of the higher controllability and switching frequencies of the new devices. The next few years will decide which of the p...

IntroductionSemiconductor PrinciplesPower Semiconductor ElementsDynamic Stresses on Power SwitchesOther Switching IssuesThyristor-Type Power SwitchesInsulated Gate Bipolar TransistorDiodesPrognostic AssessmentReferences

IntroductionCapacitor Commutated ConversionContinuously Tuned AC FiltersActive DC Side FiltersSTATCOM-Aided DC TransmissionAC Transmission Lines Converted for Use with HVDCHVDC Transmission at Voltages above 600 kVConcluding StatementsReferences

IntroductionMulti-Level VSC TransmissionMulti-Level CSC TransmissionSummaryReferences

IntroductionPower Transfer CharacteristicsStructure of the VSC LinkVSC DC System ControlHVDC Light TechnologyOther VSC ProjectsPotential for Multi-Terminal Sub-Transmission SystemsDiscussionReferences

IntroductionDiode ClampingFlying Capacitor ConfigurationCascaded H-Bridge ConfigurationCombined PWM/Multi-Level ConversionRelative Merits of the Multi-Level AlternativesReferences

IntroductionSoft Switching in Multi-Level Reinjection ConvertersClamp-Controlled MLVRTransformer-Coupled MLVRCascaded H-Bridge MLVRSummary of Main Characteristics of MLVR AlternativesMulti-Level Current Reinjection (MLCR)MLCR-CSC Versus MLVR-VSCReferences

IntroductionPWM Operating PrinciplesSelective Harmonic CancellationSinusoidal (Carrier-Based) PWMPWM Carrier-Based ImplementationModulation in Multi-Bridge ConvertersSummaryReferences

IntroductionThree-Phase AC–DC ConversionThe Commutation ProcessRectifier OperationInverter OperationPower Factor and Reactive PowerCharacteristic HarmonicsMulti-Pulse ConversionUncharacteristic Harmonics and InterharmonicsHarmonic Reduction by FiltersFrequency Cross-Modulation Across the LCCSummaryReferences

IntroductionThe Line-Commutated HVDC ConverterHVDC Converter DisturbancesStructure of the HVDC LinkDC System ConfigurationsDC System Control and OperationAC–DC System InteractionAC–DC–AC Frequency InteractionsDC Link Response to External DisturbancesReliability of LCC TransmissionConcluding StatementsReferences

IntroductionVoltage Source ConversionComparison of LCC and VSCCurrent Source ConversionThe Reinjection Concept with Self-CommutationDiscussionReferences

The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reacti...

A multi-level current reinjection concept, already shown to provide acceptable harmonic reduction with fewer switching components than the conventional multi-level schemes, is described in this paper with reference to its performance when operated as a STATCOM. PSCAD/EMTDC is used to illustrate the steady state and fast dynamic response to system c...

An old concept proposed to double the pulse number of a line commutated converter and designated "dc-ripple reinjection," is made more effective by the use of self-commutating reinjection switches, such as GTO or IGCT. It is shown that the self-commutating reinjection switches can be controlled to force the thyristor valve currents to commutate ind...

This paper presents a method which incorporates self-commutated CSC transmission directly in a fast decoupled Newton-Raphson a.c. load flow. The d.c. equations are presented in a per unit form that is compatible with the per unit a.c. equations. A sequential method of solution is adopted in solving the load flow equations. The a.c. system equations...

A new self-commutated AC-DC converter is proposed based on the reinjection of multilevel DC pulses via the mid-point of the series double-bridge converter using a GTO-switched multitapped single-phase transformer. The ideal reinjection waveform for complete elimination of the harmonic content of the AC-side current is derived and a practical approx...

A new self-commutated current source converter is proposed, based on the reinjection of multi-level dc current pulses via a GTO-switched multi-tapped interphase reactor. The ideal reinjection waveform for complete elimination of the harmonic content of the ac system side current is derived and a practical approximation proposed to increase the puls...

In common with conventional multi-level conversion configurations, the multi-level voltage reinjection scheme uses multi-level clamping and dc series connected capacitors. The operation conditions that lead to capacitor voltage unbalance are analyzed and the use of adaptive adjustment of the clamping switches conducting periods is investigated. It...

A new multi-level VSC is proposed with highly reduced voltage and current harmonic distortion, without the need for filters or PWM. The multi-pulse waveform is achieved by means of two auxiliary reinjection bridges, which produce voltage pulses at six times the fundamental frequency. The proposed scheme simplifies the switching circuitry of present...

A multi-level voltage reinjection concept, already shown to provide acceptable harmonic reduction with fewer switching components than the conventional multi-level schemes, is described in this paper with reference to its performance when operated as a STATCOM. EMTDC-PSCAD is used to illustrate the steady state and fast dynamic response to system c...

In the past two decades, the development of the FACTS technology has produced high power forced-commutated converters of high reliability and control flexibility. These developments have now permeated the DC transmission area with the acceptance of the HVDC Light technology and new converter concepts are continually being proposed. This paper provi...

A multi-level dc voltage reinjection concept is described that multiplies the pulse number of the twelve-pulse dual parallel converter. The ideal reinjection waveform for complete elimination of the harmonic content is first derived, and a practical approximation is proposed which converts the standard dual converter into a sixty-pulse scheme, thus...

A DC-ripple reinjection concept, described in the literature with reference to the line-commutated current source converter, is applied in this paper to the self-commutated current source converter. This is achieved by means of a reinjection converter fed, via a single-phase transformer, from the triple frequency ripple signal. It is shown that the...

A new double bridge parallel, voltage source converter is proposed, based on reinjection of dc voltage via the neutral point of the standard 12-pulse converter. The ideal reinjection waveform for complete elimination of harmonic content is derived and a practical approximation is proposed, which converts standard 12-pulse into a 60-pulse configurat...

A new STATCOM configuration is described in this paper that combines the advantages of the diode clamped, d.c. voltage reinjection VSC and soft switching concepts. The new scheme uses asymmetrical switches instead of diodes in a common clamping switching circuit for the three-phases of the converter bridges. Detailed analysis is provided of the ste...

Only the use of power electronic control, either in the form of HVDC or FACTS, can meet the requirement of an unregulated network interconnections. The degree of flexibility provided by these two alternative technologies is discussed in this paper, as well as recent developments that make the asynchronous interconnection the most effective solution...

A multi-level dc voltage reinjection concept is described that multiplies the pulse number of the twelve-pulse dual parallel converter. The ideal reinjection waveform for complete elimination of the harmonic content is first derived, and a practical approximation is proposed which converts the standard dual converter into a sixty-pulse scheme, thus...

A dc-ripple reinjection scheme is described that doubles the number of pulses of the forcecommutated
current source converter. The reinjection circuit includes a feedback converter in series
with the dc output which provides automatic adjustment of the reinjected current as the dc side current
changes. The reinjection concept is also generalised to...

A voltage source converter is proposed, in which the multi-step output voltage waveform is achieved by the reinjection of different DC voltage levels via the common neutral point of the converter bridges. The number of clamping switches are substantially reduced, permitting the use of higher level numbers to achieve very low distortion without the...

A new voltage source converter is proposed, based on the reinjection of the dc voltage via the neutral point of the double bridge converter. It differs from the conventional in that the voltage applied to the bridges varies, even though the dc voltage remains constant. To this effect a periodically varying waveform is supplied to the bridge and use...

The proposed converter is based on the reinjection of a series of DC voltage pulses, at a frequency multiple of the fundamental, that shape the output voltage waveforms into a multilevel scheme. The reinjection ratio and frequency are chosen to convert the standard 12-pulse into 36-pulse configuration without the assistance of filters or PWM. Thus,...

The configuration consists of a series connected dual voltage source converter with an auxilliary circuit that reinjects voltage pulses at six times the funda-mental frequency, derived from the dc capacitor terminals and a reinjection transformer, into the output voltage waveform. The result is a 36-step output voltage waveform that complies with p...

The proposed converter is based on the reinjection of a series of dc voltage pulses, at a frequency multiple of the fundamental, that shape the output voltage waveforms into a multilevel scheme. The reinjection ratio and frequency are chosen to convert the standard 12-pulse into 36-pulse configuration without the assistance of filters or PWM. Thus...

The proposed four quadrant back-to-back HVDC link uses a DC voltage pulse reinjection concept, that shapes the voltage and current waveforms into a multi-level scheme, thus controlling their harmonic content without the assistance of harmonic filters or pulse width modulation. The switching rate is considerably reduced and results in lower switchin...

A new multi-level VSC is proposed with highly reduced voltage and current harmonic distortion, without the need for filters or pulse-width modulation. The multi-pulse waveform is achieved by means of an auxiliary reinjection bridge that produces voltage pulses at six times the fundamental frequency. The proposed scheme requires fewer switches than...

The proposed multilevel voltage-sourced converter is based on the
reinjection of DC voltage pulses at six times the fundamental frequency.
The extra (reinjection) components required are justified by a
substantial reduction in the capacitor size. It is shown that the
resulting voltage and current harmonics are well within the present
standards with...