• 전력전자학회논문지
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• 제22권4호
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• pp.369-372
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• 2017

This paper presents a control scheme for three-level NPC inverters using small DC-link capacitors. To reduce the inverter system volume, the film capacitor with small capacitance is a promising candidate for the DC-link. When small capacitors are applied in a three level inverter, however, the AC ripple component increases in the DC-link NPV (neutral point voltage). In addition, the three-phase input grid currents are distorted when the DC-link capacitors are fed by diode rectifier. In this paper, the additional circuit is applied to compensate for small capacitor systems defect, and the offset voltage injection method is presented for the stabilization in NPV. These two proposed processes evidently ensure the quality improvement of the input grid currents and output load currents. The feasibility of the proposed method is verified by experimental results.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제2B권3호
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• pp.133-139
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• 2002

In this paper, a prototype of an active auxiliary quasi-resonant DC link (QRDCL) snubber assisted voltage source bidirectional power converter (AC to DC and DC to AC) operating at zero voltage soft-switching (BVS) PWM nlode is presented for a Battery Energy Storage System (BESS). The operating principle of this QRDCL circuit and multifunctional control-based converter system, including PWM inverter mode in which energy flows from the battery bank to the three-phase utility-grid in addition to an active PWM converter mode in which energy flows from the utility-grid to the battery banks are described respectively by the control implementation on the basis of d-q coordinate plane transformation. The multifunctional operation characteristics of this three-phase ZVS PWM bi-directional converter with QRDCL is demonstrated fer a BESS under the power conditioning and processing schemes of energy supply mode and energy storage mode, and compared with a conventional three-phase hard switching PWM bi-directional converter for a BESS. The effectiveness of the three-phase ZVS PWM hi-directional converter with QRDCL is proven via the simulation analysis.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권3호
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• pp.384-390
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• 2012

This paper proposes a fault diagnosis method of the line-to-line voltage sensors in 3-phase AC/DC pulse width modulation (PWM) converters. The line-to-line voltage sensors are an essential device to obtain the information of the grid voltages for controlling the 3-phase AC/DC PWM converters. If the line-to-line voltage sensors are mismeasured by various faults, the voltage sensors can obtain wrong information of the grid voltage. It has an adverse effect on the control of the converter. Therefore, the converter causes the unbalance input AC current and the DC-link voltage ripple in the 3-phase AC/DC PWM converter. Hence, fast fault detection and fault tolerant control are needed. In this paper, the fault diagnosis method is proposed and verified through simulations and experiments.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 하계학술대회 논문집
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• pp.530-532
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• 2007

This paper presents the design, development and performance of a power conditioning system (PCS) for application to a 250kW Molten Carbonate Fuel Cell (MCFC) generation system. A DSP controller was used to control the dc-dc and dc-ac converter operation for grid connection and power injection to the grid. The controller must also supervise the total PCS operation while communicating with the fuel cell system controller. A control method for parallel operation of dc-dc converters was proposed and verified. A 250kW prototype was successfully built and tested. Experimental performances are compared to minimum target requirements of the PCS for MCFC.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.1119-1124
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• 2014

High temperature superconducting magnetic energy storage (HTS SMES) is known as an effective solution to significantly decrease the voltage and power fluctuations of grid connected wind power generation system (WPGS). This paper implements an effective control scheme of a back-toback converter with shunt-connected HTS SMES for the frequency regulation of an islanded microgrid. The back-to-back converter is used to connect the WPGS to the grid. A large-scale HTS SMES is linked to the DC side of the back-to-back converter through a two-quadrant DC/DC chopper. An adaptive control strategy is implemented for the back-to-back converter and the two-quadrant DC/DC chopper to improve the efficiency of the whole system. The performance of the proposed control system was evaluated in a test power system using PSCAD/EMTDC. The simulation results clearly show that the back-to-back converter with shunt-connected HTS SMES operates effectively with the proposed control strategy for stabilizing the power system frequency fluctuations.

• 전력전자학회논문지
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• 제26권5호
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• pp.372-375
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• 2021

A three-leg inverter-type isolated DC-DC Converter that can use 220 and 440 V grid input voltages is introduced. The secondary circuit structure of the proposed topology is center-tap, which is the same as the conventional phase-shifted full-bridge converter. However, the primary circuit structure is composed of a three-leg inverter structure and a transformer, in which two primary windings are connected in series. The proposed circuit structure has a wider input voltage range than the conventional phase-shifted full-bridge converter, and the circulating-current on the primary-side is reduced. In addition, the voltage stress at the secondary rectifier is greatly improved, and high efficiency can be achieved at a high input voltage by removing the snubber circuit added to the conventional converter. Prototype converters with input DC of 311 V, output of 622 V, and 50 V and 6 kW class specifications were designed and manufactured to verify the validity of the proposed topology; the experimental results are presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.83-86
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• 2006

A grid-connected distributed generation system which consists of engine generator, dc link with multiple energy sources and inverter is proposed. All six of the stator leads of the generator, which is a surface mount permanent magnet machine, are brought out to the terminal of the generator. Three leads are connected to the inverter and the others are connected to the utility grid. In this proposed system the power from the engine-generator and the power from dc link can be controlled simultaneously by only one three-phase power converter. A control algorithm for the system is developed and verified by experiment results.

• Journal of Power Electronics
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• 제16권3호
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• pp.960-969
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• 2016

High-power three-level voltage-source converters are widely utilized in high-performance AC drive systems. In several ultra-power instances, the harmonics on the grid side should be reduced through multiple rectifications. A combined harmonic elimination method that includes a dual primary-side series-connected winding transformer and selective harmonic elimination pulse-width modulation is proposed to eliminate low-order current harmonics on the primary and secondary sides of transformers. Through an analysis of the harmonic influence caused by dead time and DC magnetic bias, a synthetic compensation control strategy is presented to minimize the grid-side harmonics in the dual primary side series-connected winding transformer application. Both simulation and experimental results demonstrate that the proposed control strategy can significantly reduce the converter input current harmonics and eliminates the DC magnetic bias in the transformer.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.130-131
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• 2013

In this paper, it suggests offset compensation method of output current in single phase PV-BES system which is connected with grid. The algorithm applied removes grid's frequency ingredient using a notch filter and it extracts only DC offset current. It can reduce problems as saturation of power transformer cause by DC current when it is indoctrinated to grid.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권8호
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• pp.413-419
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• 2003

The paper presents a simulation model and analysis of a grid-connected variable speed wind energy conversion scheme (VSWECS) using the PSCAD/EMTDC software. The modeled system uses a variable speed drive, a fixed pitch angle, a synchronous generator as a wind generator and an AC-DC-AC conversion scheme, which facilitates the wind generation to efficiently operate under varying wind speed while connected to the distribution network. The power output of the WECS is controlled by the AC-DC-AC conversion scheme, the objective of which is to capture the maximum active power under varying wind conditions and to keep the voltage magnitude of the terminal bus at a specific level. Aerodynamic models are applied for a wind turbine model. An simulation analysis of the scheme in terms of its responding to wind variations is also presented.