• 전기학회논문지
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• 제65권9호
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• pp.1479-1485
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• 2016

This paper presents DC voltage recovery time improvement method in DC link of High Voltage Direct Current (HVDC) with offshore wind farm. The wind farm should be satisfied Low Voltage Ride Through(LVRT) control strategy when grid faults occur. The LVRT control strategy indicates actions which have to be executed according to the voltage dip ratio and the fault duration. However, The LVRT control strategy makes between wind farm and power system through DC Link voltage when grid fault occurs. The de-loading scheme is one of the method to control the DC voltage. But de-loading scheme need to long DC voltage recovery time. Thus, this paper proposes an improved de-loading scheme and we analysis DC voltage and active power reference through a simulation.

• Journal of Power Electronics
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• 제15권4호
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• pp.1119-1130
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• 2015

This study investigates the multi-objective fuzzy optimization of crowbar resistance for the doubly fed induction generator (DFIG) low-voltage ride-through (LVRT). By integrating the crowbar resistance of the crowbar circuit as a decision variable, a multi-objective model for crowbar resistance value optimization has been established to minimize rotor overcurrent and to simultaneously reduce the DFIG reactive power absorbed from the grid during the process of LVRT. A multi-objective genetic algorithm (MOGA) is applied to solve this optimization problem. In the proposed GA, the value of the crowbar resistance is represented by floating-point numbers in the GA population. The MOGA emphasizes the non-dominated solutions and simultaneously maintains diversity in the non-dominated solutions. A fuzzy-set-theory-based is employed to obtain the best solution. The proposed approach has been evaluated on a 3 MW DFIG LVRT. Simulation results show the effectiveness of the proposed approach for solving the crowbar resistance multi-objective optimization problem in the DFIG LVRT.

• 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.

• Journal of Power Electronics
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• 제16권4호
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• pp.1551-1564
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• 2016

The high penetration level of inverter-based distributed generation (DG) power plants is challenging the low-voltage ride-through requirements, especially under unbalanced voltage sags. Recently, a flexible injection of both positive- (PS) and negative-sequence (NS) reactive currents has been suggested for the next generation of grid codes. This can enhance the ancillary services for voltage support at the point of common coupling (PCC). In light of this, considering distant grid faults that occur in a mainly inductive grid, this paper proposes a complete voltage support control scheme for the interface inverters of medium or high-rated DG power plants. The first contribution is the development of a reactive current reference generator combining PS and NS, with a feature to increase the PS voltage and simultaneously decrease the NS voltage, to mitigate voltage imbalance. The second contribution is the design of a voltage support control loop with two flexible PCC voltage set points, which can ensure continuous operation within the limits required in grid codes. In addition, a current saturation strategy is also considered for deep voltage sags to avoid overcurrent protection. Finally, simulation and experimental results are presented to validate the effectiveness of the proposed control scheme.

• Journal of Power Electronics
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• 제13권5호
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• pp.909-918
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• 2013

This paper proposes a coordinated control of the reactive power between the STATCOMs (static synchronous compensators) and the grid-side converters (GSC) of wind farms equipped with PMSGs (permanent-magnet synchronous generators), by which the voltage fluctuations at the PCC (point of common coupling) are mitigated in the steady state. In addition, the level of voltage sags is reduced during grid faults. To do this, the GSC and the STATCOM supply reactive power to the grid coordinately, where the GSCs are fully utilized to provide the reactive power for the grid prior to the STATCOM operation. For this, the GSC capability of delivering active and reactive power under variable wind speed conditions is analyzed in detail. In addition, the PCC voltage regulation of the power systems integrated with large wind farms are analyzed for short-term and long-term operations. With this coordinated control scheme, the low power capacity of STATCOMs can be used to achieve the low-voltage ride-through (LVRT) capability of the wind farms during grid faults. The effectiveness of the proposed strategy has been verified by PSCAD/EMTDC simulation results.

• 전기학회논문지
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• 제64권3호
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• pp.399-404
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• 2015

This paper presents the DC voltage control method in DC link of High Voltage Direct Current(HVDC) for an offshore wind farm in Low Voltage Ride Through(LVRT) situation. Wind generators in an offshore wind farm are connected to onshore network via HVDC transmission. Due to LVRT control of grid side inverter in HVDC, power imbalancing in DC link is generated and this consequentially causes rising of DC voltage. A de-loading scheme is one of the method to protect the wind power system DC link capacitors from over voltage. But the flaw of this method is slow control response time and that it needs long recovery time to pre-fault condition after fault clear. Thus, this paper proposes improved de-loading method and we analyze control performance for DC voltage in LVRT control of HVDC for an offshore wind farm.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.38-40
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• 2019

태양광발전설비 보급확대에 따른 전력계통의 안정도 확보를 위해 태양광인버터 계통안정도 향상을 위한 기능들의 추가가 요구되고 있다. 계통안정도 향상 기능 중 가장 대표적인 것이 LVRT(Low Voltage Ride-Through)이고, 태양광인버터의 계통 연계에서 효과적으로 LVRT 기능을 수행하기 위한 제어기 설계 방법을 제안하고 이를 PSIM 시뮬레이션 및 실험을 통해 검증하였다.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1814-1821
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• 2012

본 논문은 국내에서 설비용량 20MW 이상의 신재생발전기에 대해 계통연계 유지조건을 의무화하는 송배전용 전기설비 이용규정이 2012년부터 적용됨에 따라 이를 모의해석 기반의 풍력발전기 계통연계 검토 시에 고려하기 위한 풍력발전기의 LVRT(Low Voltage Ride Through) 전사모형을 개발하고 이를 풍력발전기가 연계된 전력계통의 성능평가에 적용하여 전사모델의 유용성을 검증한 후 전력계통의 대표적인 상정고장에 적용하여 국내 풍력발전기 계통연계 유지조건의 적용효과를 분석하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.242-244
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• 2011

A wind generator system model includes wind model, rotor dynamics, synchronous generator, power converter, distribution line and infinite bus. This paper investigates the low-Voltage Ride-Through capability of PMSG wind turbine in a variable speed. The drive train of a wind turbine on 2-mass modeling can observe the shaft torsional vibration when the low-voltage occur. To reduce the torsional vibration when the low-voltage occur, this paper designs suppression control algorithm of the torsional vibration and implements simulation. A Matlab/Simulink is used to investigate the response during the transient state.

• 전력전자학회논문지
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• 제10권6호
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• pp.550-559
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• 2005

매트릭스 컨버터는 VS떼 비하여 장수명, 입력역률 직접제어 및 에너지 회생 등의 장점을 갖고 있으나, 제어의 복잡성, ride-through 대책 및 낮은 전압이용률 등은 상용화를 위해 해결해야 할 난제이다. 본 논문에서는 SVM를 적용한 매트릭스 컨버터의 설계 및 구현방법을 제안한다. 입력 고조파를 저감시키기 위한 입력필터와 입출력의 과전압 방지와 free-wheeling을 위한 클램프 회로의 설계기법을 제시하고, 고속 DSP와 CPLD를 사용하여 공간벡터 제어 및 4 단계 전류(commutation) 제어를 구현하며, 매트릭스 컨버터의 양방향 스위치 구동을 위한 전용의 전원회로를 설계하여, 최적 구조의 전력회로를 제안한다. 그리고 구현된 매트릭스 컨버터를 유도전동기에 적용하여 성공적인 운전 결과를 얻을 수 있었다.