• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권10호
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• pp.521-529
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• 2001

This paper deals with the commutation failures of HVCD system. Commutation failures are caused by AC voltage distrotions at inverter side and cause the HVDC system oscillations. In this paper, in order to know a correct incidence and onset of the failures, theoretical analysis, the simulation and the investigation at actual system are carried out and the dynamic performace simulations are performed by PSCAD/EMTDC. Finally, the condition that the failure could be generated and how to reduce the failures are analyzed.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권9호
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• pp.490-497
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• 1999

This paper presents a novel current control method to reduce the current ripple due to commutation in brushless DC motor fed with unipolar PWM voltage source inverter. The proposed current control method can reduce the current ripple due to commutation in high speed range where the DC link voltage of the inverter is less than four times of the phase back-emf. The effectiveness of the proposed current control method is verified with digital simulations and experiments on the 250W brushless DC motor drive systems.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.1365-1366
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• 2011

• Journal of Power Electronics
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• 제15권5호
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• pp.1367-1379
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• 2015

A hybrid HVDC system that is composed of line commutated converter (LCC) at the rectifier side and voltage source converter (VSC) in series with LCC at the inverter side is studied in this paper. The start-up strategy, DC fault ride-through capability, and fault recovery strategy for the hybrid HVDC system are proposed. The steady state and dynamic performances under start-up, AC fault, and DC fault scenarios are analyzed based on a bipolar hybrid HVDC system. Furthermore, the immunity of the LCC inverter in hybrid HVDC to commutation failure is investigated. The simulation results in PSCAD/EMTDC show that the hybrid HVDC system exhibits favorable steady state and dynamic performances, in particular, low susceptibility to commutation failure, excellent DC fault ride-through, and fast fault recovery capability. Results also indicate that the hybrid HVDC system can be a good alternative for large-capacity power transmission over a long distance byoverhead line.

• 전력전자학회논문지
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• 제9권3호
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• pp.195-202
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• 2004

본 연구에서는 Brushless DC Motor의 전환구간에서 토크리플 저감을 위한 전류제어 기법을 제안하였다. 전환구간에서 토크리플은 증가하는 전류의 변화율과 감소하는 전류의 변화율이 같지 않음에 주원인이 있고, 실제 역기전력의 모양에 의해서도 영향을 받는다. 이에 제안된 제어기법은 전환하는 전류들의 변화율을 같게 하는 실제 역기전력이 고려된 보상전압을 추하고, 전환구간동안에만 보상전압을 인가함으로써 토크리플을 줄이는 것이다. 시뮬레이션과 실험 결과는 제안된 방법이 토크와 전류의 리플을 현저히 줄일 수 있음을 보여준다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 추계학술대회 논문집
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• pp.148-150
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• 2007

A novel torque sharing function (TSF) is presented. To improve efficiency and to reduce torque ripple in commutation region, only a phase torque under commutation is regulated to produce a uniform torque. And the torque developed by the other phase remains with the previous state under a current limit of the motor and drive. If the minimum change of a phase torque reference can not satisfy the total reference torque, two-phase changing mode is used. Since a phase torque is constant and the other phase torque is changed at each rotor position, total torque error can be reduced within a phase torque error limit. And the total torque error is dependent on the change of phase torque. To consider non-linear torque characteristics and to suppress a tail current at the end of commutation region, the incoming phase current is changed to torque increasing direction, but the outgoing phase current is changed to torque decreasing direction. So, the torque sharing of the outgoing phase and incoming phase can be smoothly changed with a minimum current cross over. The proposed control scheme is verified by some computer simulations and experimental results.

• 전력전자학회논문지
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• 제3권3호
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• pp.191-198
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• 1998

본 논문에서는 브러시리스 직류 전동기의 상 전류 제어를 위해 유니폴라 PWM 방식이 적용될 때 상 전환에 의한 토크 맥동을 저감시키기 위한 새로운 전류 제어 방식을 제안한다. 상 전환은 통전된 상의 평균 전압의 순간적인 변동을 야기시켜 전류에 맥동을 발생시키고, 이 맥동 전류는 토크 맥동을 발생시킨다. 본 논문에서는 PWM 패턴에 따를 전환 구간에서의 통전된 상의 평균 전압 변화를 분석하고 평균 전압 변동을 보상하기 위한 전류 제어기를 설계한다. 그리고 실험 결과를 통하여 제안된 방식의 효용성을 입증한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1015-1019
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• 2001

This paper presents a novel three-phase current-fed Pulse Width Modulation converter with switched capacitor type resonant DC link commutation circuit operating PWM pattern strategy under a design consideration of low-pass filter, which can operate on the basis of the principle of zero current soft switching commutation. In the first place, the steady state operating principle of this converter with a new resonant DC link snubber circuit is described in connection with the equivalent operation circuit, together with the practical design procedure of the switched-capacitor type resonant DC link circuit is discussed from a theoretical viewpoint on the basis of a design example for high-power applications. The actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open loop control scheme so as to acquire the new optimum PWM pattern. Finally, the experiment of set-up in laboratory system of this converter is concretely demonstrated herein to confirm a zero current soft-switching commutation of this converter. The comparative evaluations between current-fed hard switching PWM and soft-switching PWM converters are carried out from a viewpoint of their PWM converter characteristics.

• 전기의세계
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• 제31권1호
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• pp.50-58
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• 1982

As a method for improving the power factor and the waveform of ac line current drawn by ac to dc converters, converters of pulse-width control type with forced commutation circuits have been developed in recent years. However, these converters have rather complex commutation circuits which contain auxiliary thyristors in addition to the main thyristors, and their performance is not satisfactory. This paper proposes a new pulse-width controlled ac to dc converter, and analyses its commutation mechanism and its input and output characteristics. The proposed converter circuit consists of a usual thyristor bridge circuit with series diodes to which reactors and diodes are added. This circuit dose not contain auxiliary thyristors, and in this sense it is simpler than the previous converter circuits of pulse-width control type. Since the main thyristors of the converter can be forcedly turned off several times in a half cycle of source voltage, a pulse-width modulation control is possible in order to improve the current waveform as well as the power factor on ac line side. As to dc output side it is shown that the adjustable range of output voltage is wide and the voltage regulation is good due to a rapid reversal of voltage across the commutating capacitors by LC resonance during commutation period. It is also shown that the regenerative operation of the converter is possible.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.201-210
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• 2018

This paper proposes a new start-up method for a load commutated inverter (LCI) in a large synchronous gas-turbine generator. The initial rotor position for start-up torque is detected by the proposed initial angle detector, which consists of an integrator and a phase-locked loop. The initial rotor position is accurately detected within 150ms, and the angle difference between the real position and the detected position is less than 1%. The LCI system operates in two modes (forced commutation mode and natural commutation mode) according to operating speed range. The proposed controllers include a forced commutation controller for the low-speed range, a PI speed controller and a PI current controller, where the forced commutation controller is connected to the current controller in parallel. The current controller is modeled by Matlab/Simulink, where a six-pulse delay of the thyristor and a processing delay are considered by using a zero-order hold. The performance of the proposed start-up method is evaluated in Matlab/Psim at standstill and at low speed. To verify the feasibility of the method, a 5kVA LCI system prototype is implemented, and the proposed initial angle detector and the system performance are confirmed by experimental results from standstill to 900rpm.