• Journal of Power Electronics
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• 제19권1호
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• pp.179-189
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• 2019

Four-quadrant converters (4QCs) are widely used as AC-DC power conversion interfaces in many areas. A control delay commonly exists in the digital implementation process of 4QCs, especially for high power 4QCs with a low switching frequency. This usually results in alternating current distortion, increased current harmonic content and system instability. In this paper, the control delay is divided into a computation delay and a PWM delay. The impact of the control delay on the performance of a 4QC is briefly analyzed. To obtain a fundamental value of AC current that is as accurately as possible, a specific sampling method considering the PWM pattern is introduced. Then a current predictive control based on a modified z-transform is proposed, which is effective in reducing the control delay and easy in terms of digital implementation. In addition, it does not depend on object models and parameters. The feasibility and effectiveness of the proposed predictive current control method is verified by simulation and experimental results.

• 전력전자학회논문지
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• 제20권2호
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• pp.130-136
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• 2015

This study describes the structure and operation modes of vertical stabilization (VS) converter for international thermonuclear experimental reactor (ITER) and proposes a protection method. ITER VS converter supplies voltage (${\pm}1000V$)/current (${\pm}22.5kA$) to superconducting magnets for plasma current vertical stabilization. A four-quadrant operation must be achieved without zero-current discontinuous section. The operation mode of the VS converter is separated in 12-pulse mode, 6-pulse mode and circulation current mode according to the magnitude of the load current. Protection measures, such as bypass and discharge, are proposed for abnormal conditions, such as over current, over voltage, short circuit, and voltage sag. VS converter output voltage is controlled to satisfy voltage response time within 20 msec. Bypass operation is completed within 60 msec and discharge operation is performed successfully. The feasibility of the proposed control algorithm and protection measure is verified by assembling a real controller and implementing a power system including the VS converter in RTDS for a hardware-in-loop (HIL) facility.

• 전력전자학회논문지
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• 제19권5호
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• pp.399-406
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• 2014

This study investigates the structure and operation of the ITER VS converter and proposes a sequence control method for six series-connected VS converters to reduce reactive power. The operation and the proposed sequence control method are verified through RTDS simulation. The ITER VS converter must supply voltage/current to the superconducting magnets for plasma current vertical stabilization, and the four-quadrant operation must proceed without a zero-current discontinuous section. The operation mode of the VS converter is separated into a 12- and 6-pulse circulating current and transition modes according to the size of the load current. The output voltage of the unit VS converter is limited because of the rated voltage; however, the superconducting coil must increase the operating output voltage. Thus, the VS converter must be connected in a 6-series to provide the required operating output voltage. The output voltage of the VS converters is controlled continuously; however, reactive power is limited within a minimized value of the grid. In this study, the unit converter is compared with converters connected in a 6-series to determine a suitable sequence control method. The output voltage is the same in all cases, but the maximum reactive power is reduced from 100% to 73%. This sequence control method is verified through RTDS simulation.

• Journal of Power Electronics
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• 제18권3호
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• pp.817-825
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• 2018

In this paper, a current hysteresis control with good decoupling properties for doubly-fed brushless induction machines (BDFIMs) has been proposed based on a generalized vector model. The independent control of the reactive power and speed for BDFIMs has been achieved by controlling the d-axis and the q-axis current of the control windings (CW). The proposed vector control method has been developed for the power winding (PW) flux frame. Experimental verification of a type Y180M-4 BDFIM prototype with 1/4 pole-pairs has been presented. Evidence of its good performance has been shown through experimental results.

• Journal of Power Electronics
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• 제17권4호
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• pp.1048-1057
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• 2017

An indirect matrix converter (IMC) is a modern power generation system that enables a direct ac/ac conversion without the need for any bulky and limited lifetime electrolytic capacitor. This system also allows four-quadrant operation, generation of sinusoidal output voltage waveforms with variable frequency and amplitude, and control of input power factor. This study proposes a pulse-width modulation-based sliding-mode controller to achieve unity input-power factor operation of the IMC independently of the active power exchanged with the grid, as well as a fast dynamic response. The designed equivalent control law determines, at each sampling period, the appropriate q-axis component of the modulated input current to be injected into the grid through the LC input filter. An integral term of the error is included in the expression of the sliding surface to increase the accuracy of the control method. A double space vector modulation method is used to synthesize the direction of the space vector of the input currents as required by the sliding-mode controller and the space vectors of the target output voltages. Simulation and experimental results are provided to show the effectiveness and evaluate the performance of the proposed control method.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.141-142
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• 2013

본 논문에서는 단일 Quasi Z-소스 AC-AC 컨버터에 의한 4상한 출력 AC전압 제어를 제안하였다. 제안된 듀티비 제어방법을 통하여 한 대의 Quasi Z-소스 AC-AC 컨버터로도 동상의 벅-부스트 모드와 역상의 벅-부스트 모드를 모두 출력하는 4상한 출력 AC전압 제어를 하였다. 한 대의 Quasi Z-소스 AC-AC 컨버터만으로 종전의 듀티비 제어에 의해 동상의 부스트 모드와 역상의 벅-부스트 모드의 출력 전압이 발생되며, 제안한 듀티비 제어에 의해 동상의 벅 모드가 출력되는 4상한 출력 AC전압 제어법을 PSIM시뮬레이션에 의하여 입증하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 추계학술대회 논문집
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• pp.225-226
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• 2015

이 논문에서는 ITER 초전도 코일 전원 장치 중 진공 용기내에 형성된 자장의 오차를 보정해주는 CCU/L 컨버터의 4 상한 운전을 위한 제어 알고리즘을 설명하고, 제어 알고리즘을 실제 컨버터에 적용하여 구현하였다. ITER CCU/L 컨버터는 4 상한 제어를 통해 영 전류 불연속 구간 없이 Correction Coil에 전압(${\pm}85V$), 전류(${\pm}10kA$)를 공급해야 하고, 이를 위해선 4 상한 운전을 위한 제어가 매우 중요하다. 4 상한 운전은 다섯 가지 모드에서 동작된다. 본 논문에서, 각 모드에 대해 설명하고, 컨버터가 각 모드에서 정상적으로 제어되는지 시뮬레이션 및 실제 시험을 통해 검증하였다.