• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.5
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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.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.54-60
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• 2006

A power limiting algorithm is proposed for stable operation of grid-connected inverter in case of grid voltage unbalance considering the operation limit of inverter. During the voltage unbalance the control performance of Inverter. is degraded and the output power contains 120Hz ripple due to the negative sequence of voltage. In this paper, conventional dual sequence current controller is implemented to solve these problems using separated control of positive and negative sequence. Especially the maximum power limit which guarantees the maximum rated current of the inverter is automatically calculated as the instant grid voltage changes. As soon as the voltage recovers the proposed algorithm can return to the normal power control mode accomplishing low voltage ride through. Proposed algorithm is verifed using PSCAD/EMTDC simulations and tested experimentally at 4.4kW wind turbine simulator set-up.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.2
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• pp.92-99
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• 2014

The paper is related to smart maximum power system based on program logic. Especially, this system compares the total demand power with the target power by using the signal from the digital kilo watt meter. Based on the power information by the maximum power control equipment the consumed future power is anticipated. In addition, through consumed future power the controllable target power is set, and it applies on the maximum power control equipment. User or manager would control the load efficiently through the simple programming which could control load based on the control sequence and relay. To begin with the conventional maximum power control algorithm is surveyed, and the smart maximum power control system based on program logic is used, and the new algorithm from full load to proportion shut down is proposed by using PLC program. the validity of the proposed control scheme is investigated by both simulation results.

• Journal of Industrial Technology
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• v.19
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• pp.217-226
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• 1999

A single phase to three phase power converter with cost effective and simple structure is proposed. The converter consists of rectifier and inverter. The rectifier is composed of a half wave rectifier, a dc link capacitor, and a current limiting inductor, and the inverter is of only two switches with PWM control. For negative sequence operation the inverter output voltage leads the line input by $60^{\circ}$, and for positive sequence operation the inverter output voltage leads by $60^{\circ}$. We can see that positive sequence operation shows higher output voltage, slight harmonic distortion(2%), and better performances such as high efficiency and high power factor. A mathematical model for system analysis is provided, and specifications for selection and control scheme both for start-up and for steady state are analyzed. comparison and operational limits of positive and negative sequence operation are performed, and simulations and experiments are executed to verify the proposed.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.273-274
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• 2012

This paper investigates control algorithms for a doubly fed induction generator(DFIG) with a back-to-back three-level neutral-point clamped voltage source converter in medium voltage wind power system under unbalanced grid conditions. Two different control algorithms to compensate for unbalanced conditions are proposed. Evaluation factors of control algorithm are fault ride-through(FRT) capability, efficiency, harmonic distortions and torque pulsation. Zero regulated negative sequence stator current control algorithm has the most effective performance concerning FRT capability and efficiency. Ripple-free control algorithm nullifies oscillation component of active power and reactive power. Ripple-free control algorithm shows the least harmonic distortions and torque pulsation. Combination of zero regulated negative sequence stator current and ripple-free control algorithm control algorithm depending on the operating requirements and depth of grid unbalance presents the most optimized performance factors under the generalized unbalanced operating conditions leading to high performance DFIG wind turbine system.

• Journal of Power Electronics
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• v.12 no.3
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• pp.495-502
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• 2012

This paper presents an improved grid voltage control strategy for wind farms with doubly-fed induction generators (DFIGs) connected to distribution networks based on an analysis of the operation limits of DFIG systems. A modified reactive power limit calculation method in different operation states is proposed and a reactive power control strategy during grid voltage dips/rises is further discussed. A control strategy for compensating unbalanced grid voltage, based on DFIG systems, by injecting negative sequence current into the grid through the grid side converter (GSC) is proposed. In addition, the negative current limit of the GSC is discussed. The distribution principle of the negative sequence current among the different DFIG systems in a wind farm is also introduced. The validity of the proposed voltage control strategy is demonstrated by Matlab/Simulink simulations. It is shown that the stability of a wind farm and the power grid can be improved with the proposed strategy.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1637-1649
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• 2017

This paper describes an intensive analysis of a harmonic identification algorithm in non-ideal voltages source systems. The dq-axis Fourier with a positive sequence voltage detector (DQFP) is a novel harmonic identification algorithm for active power filters. A compensating current control system based on repetitive control is presented. A design and stability analysis of the proposed current control are also given. The aim of the paper is to achieve a robustness of the harmonic identification in a distorted and unbalanced voltage source. The proposed ideas are supported by a hardware in the loop technique based on a $eZdsp^{TM}$ F28335 and the Simulink program. The obtained results are presented to demonstrate the performance of the harmonic identification and the control strategy for the active power filter in non-ideal systems.

• Journal of Power Electronics
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• v.13 no.3
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• pp.487-496
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• 2013

The three-phase synchronous reference frame phase-locked loop (SRF-PLL) is widely used for synchronization applications in power systems. In this paper, a new control strategy for three-phase grid-connected LCL inverters without a PLL is presented. According to the new strategy, a current reference can be generated by using the instantaneous power control scheme and the proposed positive-sequence voltage detector. Through theoretical analysis, it is indicated that a high-quality grid current can be produced by introducing the new control strategy. In addition, a kind of independent control for reactive power can be achieved under unbalanced and distorted grid conditions. Finally, the excellent performance of the proposed control strategy is validated by means of simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.622-625
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• 2001

Photovoltaic generation systems need MPPT (Maximum Power Point Tracking) control because the output power depends on the operating voltage and current. Therefore, many researchers propose various types of MPPT control methods. A new MPPT control scheme is proposed in this paper in order to realize higher efficiency with simple calculation. The line search algorithm with fibonacci sequence which is one of the optimizing method is employed for the MPPT. The line search method is modified for real-time operation. The method is verified by simulations and experiments. It is concluded that the scheme can respond fast variation of irradiance.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.932_933
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• 2009

A technology based on thyristors will be used to manufacture the super-conducting coil AC/DC converters because of the low ratio of cost over installed power compared to a design based on GTO or similar technology. But phase-controlled converter suffers from fundamental disadvantage. They inject current harmonics into the input ac mains due to their nonlinear characteristics, thereby distort the supply voltage waveform, and demand reactive power from the associated ac power system at retarded angles. To overcome this disadvantage, in the case of two series converters at the DC side, connected to the same step-down transformer, apply for the sequence control. It is the most simple and efficient way to reduce the reactive power consumption at low cost. Analytical sequence control algorithm is suggested, the validity of the proposed scheme has been verified by experimental results with the small-scaled International Thermonuclear Experimental Reactor (ITER) Power Supply to minimize reactive power consumption.