• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.5
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• pp.349-355
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• 2019

A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at mode change and during clearing time while detecting unintentional islanding. This study proposes a mode transfer method for a grid-connected inverter with critical loads. The proposed method, which integrates the grid-connected and islanded mode control loops into one control block, provides an autonomous and seamless mode transfer from the current control to the voltage control. Therefore, the proposed scheme can supply a stable voltage to critical loads at mode change and during clearing time. Experimental results are provided to validate the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.5
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• pp.334-341
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• 2019

This study proposes the control strategy for the seamless mode transfer of indirect current controlled parallel grid-connected inverters. Under the abnormal grid condition, the grid-connected inverter can convert the operation mode from grid-connected to stand-alone mode to supply power to the local load. For a seamless mode transfer, the time delay problems caused by the accumulated control variable error must be solved, and the indirect current control method has been applied as one of the solutions. In this study, the design of control parameters for the proportional-resonant-based triple-loop indirect current controller and the control strategy for the seamless mode transfer of parallel grid-connected inverters are described and analyzed. The validity of the proposed mode transfer method is verified by the PSiM simulation results.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.6
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• pp.538-548
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• 2014

This study provides a robust control of a grid-connected three-phase two-level photo voltaic inverter. The introduced control method uses the cascade control strategy to regulate AC-side current and DC-link voltage. A robust controller with integration action is used for the inner-loop AC-side current control, which maximizes the convergence rate using a linear matrix inequality-based optimization design method and eliminates the offset error. The robust controller design method considers the parameter uncertainty set to accommodate parameter mismatch and un-modeled components in the inverter model. An outer-loop proportional-integral controller is used to regulate DC-link voltage with linearization of DC/AC relation. The proposed control strategy is applied to a grid-connected 100 kW photo voltaic inverter.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.444-449
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• 2003

This paper presents a vector control method for the parallel-connected motor drive system. In this paper new estimation scheme of rotor flux position is presented to reduce sensitivity due to load difference between the motors. To confirm the validity of the proposed control method, we compare a simulation result of the proposed control method with that of the conventional indirect vector control method. The simulation results show that the proposed control method is effective the step change in load torque.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.2
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• pp.151-158
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• 2000

The growth-strain method was used for shape optimization of multi-connected structures. It was verified that the growth-strain method is very effective for shape optimization of structures with only one free surface to be deformed. But it could not provide reasonable optimized shape for multi-connected structures, when the growth-strain method is applied as it is. The purpose of this study is to improve the growth-strain method for shape optimization of multi-connected two- and three- dimensional structures. In order to improve, the problems that occurred as the growth-strain method was applied to multi-connected structures were examined, and then the improved method was suggested. The effectiveness and practicality of the developed shape optimization system was verified by numerical examples.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.576-585
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• 2016

The current control methods of Y-connected 7 Phase BLDC motor are sine wave current control and square wave control. The sine wave current control method needs dq axis transformation of $7{\times}7$ matrix for current control and very complex. Also this method is not suitable for multi Phase BLDC motor of trapezoidal back emf wave. Therefore, in Y connected multi phase BLDC motor, the square wave current control methods are required. Generally, in the 3Phase BLDC system, Average current control method is used for current control. The average current is obtained that the summation of absolute value of each phase current magnitude is divided by the number of conduction phase. However, if average current control method is applied to multi-phase system, there is a problem that each phase currents are different. This problem affects unbalance of each phase torque and fluctuation of total torque. This paper proposed each phase current control method of Y connected 7Phase BLDC system. Proposed method is used for PI controller of each phase for each phase current control. This method can perfect square wave current control. Also, configuration of the method is easier than DQ axis transformation. Proposed method is verified through simulation and experiments.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1212-1222
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• 2018

This paper presents a model predictive control (MPC) method to reduce the common-mode voltage (CMV) for inverters connected in parallel, which increase the capacity of energy storage systems (ESSs). The proposed method is based on subdivided voltage vectors, and the resulting algorithm can be applied to control the inverters. Furthermore, we use more voltage vectors than the conventional MPC algorithm; consequently, the quality of grid currents is improved. Several methods were proposed in order to reduce the CMV appearing during operation and its adverse effects. However, those methods have shown to increase the total harmonic distortion of the grid currents. Our method, however, aims to both avoid this drawback and effectively reduce the CMV. By employing phase difference in the carrier signals to control each inverter, we successfully reduced the CMV for inverters connected in parallel, thus outperforming similar methods. In fact, the validity of the proposed method was verified by simulations and experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.1
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• pp.57-66
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• 2012

This paper proposes a performance improvement of grid-connected inverter system using sliding-mode based direct power control with a variable gain. The proposed control method determine variable gain of PI controller by using modeling at direct power control (DPC) applied to space vector modulation method. Also, this method use sliding-mode control to maintain excellent dynamic response of character of direct power control (DPC). The validity of the proposed algorithm are verified by simulations and experiments.

• Journal of Power Electronics
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• v.15 no.1
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• pp.116-122
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• 2015

This paper presents a new current sharing control strategy for parallel-connected, synchronised three-phase DC-AC converters employing space vector pulse width modulation (SVPWM) without current sharing reactors. Unlike conventional control methods, the proposed method breaks the paths of the circulating current by dividing the switching cycle evenly between parallel connected equally rated converters. Accordingly, any inter-module reactors or circulating current control will be redundant, leading to reductions in system costs, size, and control algorithm complexity. Each converter in the new scheme employs a synchronous dq current regulator that uses only local information to attain a desired converter current. A stability analysis of the current controller is included together with a simulation of the converter and load current waveforms. Experimental results from a 2.5kVA test rig are included to verify the proposed control method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.5
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• pp.129-135
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• 2010

It is well known that distributed generation(DG) system using renewable energy is an alternative to solve the problems which result from the exhaustion of fossil fuel and the environmental pollution. A PWM inverter is required for a power flow control in the DG systems. This paper proposes a SRF power flow control method considering grid impedance in grid-connected single-phase inverter systems. The proposed SRF power flow control method can provide a voltage-reference for the single-phase inverter even without any grid impedance estimation so that the single-phase inverter system could operate in stand-alone mode and grid-connected mode based on the known nominal value of grid impedance. Also independent controls of active and reactive power are achieved by the proposed control method. The effectiveness and the validity of the proposed control method are demonstrated through simulations. The simulation results show that the proposed control method can control properly power flow in grid-connected single-phase inverter systems.