• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.31-40
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• 2014

This paper describes an optimal configuration for multi-central inverters in a medium-voltage (MV) grid, which is suitable for large-scale photovoltaic (PV) power plants. We theoretically analyze a proposed common-mode equivalent model for problems associated with multi-central transformerless-type three-phase full bridge(3-FB) PV inverters employing two-winding MV transformers. We propose a synchronized PWM control strategy to effectively reduce the common-mode voltages that may simultaneously occur. In addition, we propose that the existing 3-FB topology may also have the configuration of a multi-central inverter with a two-winding MV transformer by making a simple circuit modification. Simulation and experimental results of three 350kW PV inverters in a multi-central configuration verify the effectiveness of the proposed synchronization control strategy. The modified transformerless-type 3-FB topology for a multi-central PV inverter configuration is verified using an experimental prototype of a 100kW PV inverter.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.427-432
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• 2012

This paper proposes efficient operation method of PV system consisted of multi-central which is suitable for large scale system. The multi-central system used switch at a DC-link and applied proposed algorithm can improve the efficiency and the reliability on the existing system. This algorithm, with advantage of Multi-Central system can minimize the effect of different characteristic of each PV array due to a shadow or damaged PV cell. Each system is analysed and maximum power point tracking control, DC-link voltage control and output current control is used commonly. The validity is verified after comparing of the existing system and proposed system by simulation.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.464-466
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• 2007

H-Bridge Multi-Level (HBML) 고압인버터는 저압의 반도체 소자를 사용하는 단상 H-Bridge 인버터로 구성 된 셀을 직렬로 연결함으로써 정현파에 가까운 고전압을 얻을 수 있고, 입 출력 고조파가 낮아서 필터가 필요 없는 토폴로지로 산업분야에서 사용이 확대되고 있다. 본 논문은 HBML 고압인버터의 마스터 제어기와 셀 제어기의 통신 하드웨어를 병렬로 구성하여서 하나의 전압지령 값과 Angle 값으로 셀에서 PWM을 구현 할 수 있는 분산제어 방식을 제안한다. 이 방식에서 셀 제어기가 전압, 전류, 주파수, 보호기능, 통신감시 정보 등 셀 제어의 대부분을 담당함으로써 마스터 제어기의 부담을 줄이고, 따라서 신호선의 개수를 줄일 수 있다. 또 통신하드웨어의 종단에 마스터 제어기를 연결만 하면 마스터제어기의 2중화가 가능하므로 사용하고 있던 마스터 제어기의 고장 발생 시에 대체하여 사용할 수 있으므로 시스템의 안정성 향상에 도움을 준다. 선간전압 33레벨로 구성된 HBML 고압인버터 시험을 통해 제안된 방식의 타당성과 신뢰성을 검증한다.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.12
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• pp.541-554
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• 1986

This paper presents the results of driving performance analysis of permanent magnet synchronous motor using a microprocessor based control system. The system consists of three phase power transistor inverters, three phase controlled rectifier, three central processing units, and sensors. The three CPUs are, respectively, used to generate PWM control signals for the inverter generating three phase sine wave, to generate the gate control signals for firing the converter, and to supervise other two CPUs. The supervisor is used to compute PI control algtorithm to three phase reference sine wave for the inverter. It is also used to maintain a constant voltage frequency ratio for the converter operating as a constant torque controller. The inverter CPU retrieves precomputed PWM patterns from look up tables because of computation speed limitations found in almost available microprocessors. The converter CPU also retrieves precomputed gate control patterns from another look-up tables. For protecting the control ststem from any damage by extraordinary over currents, the supervisor receives the data from current sensor, CT, and break down the CB to isolate the circuits from source. A resolver has a good performance characteristics of overall speed range, especially on low speed range. Therefor the speed control accuracy is impoved. The microprocessor based PM synchronous motor control system, thus, has many advantages such as constant torque characteristics, improvement of wave, limitation on extraordinary over currents, improvement of speed control accuracy, and fast response speed control using multi-CPU and look-up tables.

• Journal of Power Electronics
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• v.11 no.4
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• pp.449-455
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• 2011

Electric drive vehicles (EDV) have received much attention recently because of their environmental and energy benefits. In an EDV, the motor drive system directly influences the performance of the propulsion system. However, the available DC voltage is limited, which limits the maximum speed of the motors. At high speeds, the inverter voltage increases if the square wave (SW) voltage (six-step operation) is used. Although conventional direct torque control (DTC) has several advantages, it cannot work in the six-step mode required in high-speed applications. In this paper, a single-mode seamless DTC for AC motors is proposed. In this scheme, the trajectory of the reference flux changes continuously between circular and hexagonal paths. Therefore, the armature voltage changes smoothly from a high-frequency switching pattern to a square wave pattern without torque discontinuity. In addition, because multi-mode controllers are not used, implementation is more straightforward. Simulation results show the voltage pattern changes smoothly when the motor speed changes, and consequently, torque control without torque discontinuity is possible in the field weakening area even with a six-step voltage pattern.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.385-386
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• 2010

최근 국내 외의 태양광 발전 시스템은 산업화 대용량화 되어가는 추세이다. 태양광 시스템의 인버터에는 태양전지 모듈의 조합에 따라 MIC(Module-Integrated Converter), 스트링, 멀티 스트링, 센트럴, 멀티 센트럴 인버터로 분류된다. 제한하는 멀티 센트럴 방식의 인버터는 상황에 따른 특정 인버터만 구동하거나, 인버터를 개별적으로 운전하여 태양광 발전설비에 대한 시스템의 효율을 높일 수 있다. 또한 인버터의 가동 시간을 동일하게 운전하여 인버터의 사용 수명을 연장하고, 하나의 인버터 고장이나 유지 보수 시 다른 인버터를 높은 에너지로 발전할 수 있어 에너지 손실을 줄일 수 있다는 장점을 갖는다. 본 논문은 PV 어레이와 인버터를 모델링하였고, 제안하는 멀티 센트럴 인버터의 상황별 동작 모드에 따른 시퀀스 제어 기법을 적용하여 시뮬레이션과 실험을 통하여 그 타당성을 검증하였다.