• Journal of Power Electronics
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• v.17 no.2
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• pp.542-550
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• 2017

Aiming at the deficiencies of power sharing control performances when a traditional droop control is adopted for microgrid inverters, this paper proposes a microgrid inverter power sharing control strategy based on a virtual synchronous generator. This control method simulates the electromechanical transient characteristics of a synchronous generator in a power system by an ontology algorithm and the control laws of a synchronous generator by control over the speed governor and excitation regulator. As a result, that the microgrid system is able to effectively retain the stability of the voltage and frequency, and the power sharing precision of the microgrid inverter is improved. Based on an analysis of stability of a microgrid system controlled by a virtual synchronous generator, design thoughts are provided for further improvement of the power sharing precision of inverters. The simulation results shows that when the virtual synchronous generator based control strategy was adopted, the power sharing performances of microgrid inverters are improved more obviously than those using the droop control strategy.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.6
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• pp.42-48
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• 2015

DC distribution system is difficult to compose the single-system because of the capacity restriction of power semiconductors. Therefore, DC Distribution system needs parallel operation of AC/DC converters for increase to system capacity. However, this system generates the circulating current. This paper is reducing the circulating current and safely sharing the load using the proposed DC current droop control method when each other 3-phase AC/DC converter connected. This system confirms through the simulation and experiment. Also, when each other converter of parallel operate. it is compared the response characteristics

• Journal of Power Electronics
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• v.15 no.6
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• pp.1628-1639
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• 2015

Line-interactive uninterruptible power supply (UPS) systems are good candidates for providing energy storage within a microgrid. In this paper, a control scheme for a line-interactive UPS system applied in a low-voltage microgrid is presented. It is based on the Q-w and P-E droop control to achieve a seamless transition between grid-connected and stand-alone operation modes. Moreover, a new model for designing the controllers is built in the dq-frame based on the instantaneous power definition. The new-built model takes into account the dynamic performance of the output impedance of the inverter in the dq-frame and can be evaluated in the time domain. Compared to the traditional model based on the instantaneous power definition, the new-built model is more accurate to describe the dynamic performance of the system. Simulation and experimental results obtained with a microgrid consisting of two 40-kW line-interactive UPS systems are given to validate the control strategy of the line-active UPS system and the accuracy of the new-built model.

• Journal of Power Electronics
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• v.10 no.1
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• pp.97-105
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• 2010

This paper presents the modeling, control and simulation of an interconnection system (ICS) of cascaded distributed generation (DG) modules for both grid-tied and stand-alone operations. The overall configuration of the interconnection system is given. The interconnection system consists of a cascaded DC/DC boost converters and a DC/AC inverter. Detailed modeling of the interconnection system incorporating a cascaded architecture has not been considered in previous research. In this paper, suitable control systems for the cascaded architecture of power electronic converters in an interconnection system have been studied and modeled in detail. A novel control system for DC/DC boost converters is presented based on a droop voltage controller. Also, a novel control strategy for DC/AC inverters based on the average large signal model to control the aggregated DG modules under both grid-tied and stand-alone modes is demonstrated. Simulation results indicate the effectiveness of the proposed control systems.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.1
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• pp.44-51
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• 2003

The module UPS can flexibly implement expansion of power system capacities. Further-more, it can be used to build up the parallel redundant system to improve the reliability of power system operation. To realize the module UPS, load sharing without interconnection among parallel connecting modules as well as a small scale and lightweight topology is necessary. In this paper, the three-arm converter/inverter is compared with the general full-bridge and half-bridge topology from a practical point of view and chosen as the module UPS topology. The switching control approaches based on a pulse width modulation of the converter and inverter of the system are presented independently. The frequency and voltage droop method is applied to parallel operation control to achieve load sharing. Two prototype 3㎸A modules are designed and implemented to confirm the effectiveness of the pro-posed approaches. Experimental results show that the three-arm UPS system has a high power factor, a low distortion of output voltage and input current, and good load sharing characteristics.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.123-127
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• 2020

KEPCO has installed Frequency Regulation ESS (FR ESS) of 376 MW since 2015. Frequency Regulation is ancillary service to support stabilizing system frequency, which is divided into governor free and automatic generation control. KEPCO operates FR ESS as governor free application and leads FR ESS market with capability of diverse demonstration and operation experiences. To expand FR ESS role during transient states of power system, KEPCO has extended operating time of charging and discharging. KEPCO has also changed speed droop lower than before to improve contribution on frequency compensation, and acquired much experiences of differentiating bad cells from others. Based on these technologies and know-hows, KEPCO Research Institutes received request of feasibility study and technical cooperation for overseas FR ESS business. This paper suggests the simple and practical method for making technological feasibility study of FR ESS.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2315-2326
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• 2016

This paper discusses the elimination of DC voltage deviation and the enhancement of load current sharing accuracy in multi-terminal high voltage direct current (MT-HVDC) systems. In order to minimize the power line losses in different parallel network topologies and to insure the stable operation of systems, a decentralized control method based on a modified droop control is presented in this paper. Averaging the DC output voltage and averaging the output current of two neighboring converters are employed to reduce the congestion of the communication network in a control system, and the decentralized control method is implemented. By minimizing the power loss of the cable, the optimal load current sharing proportion is derived in order to achieve rational current sharing among different converters. The validity of the proposed method using a low bandwidth communication (LBC) network for different topologies is verified. The influence of the parameters of the power cable on the control system stability is analyzed in detail. Finally, transient response simulations and experiments are performed to demonstrate the feasibility of the proposed control strategy for a MT-HVDC system.

• Journal of KIEE
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• v.10 no.1
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• pp.35-42
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• 2000

An equivalent load sharing control based on the frequency and voltage droop concept for parallel operation of two three-phase Uninterruptible Power Supply (UPS) systems with no control interconnection lines is presented in this paper. First of all, due to the use of active power and reactive power as control variables, the characteristics of output powers according to amplitude and phase differences between output voltages of two UPS systems are analyzed. Secondly, simulation results under different line impedance demonstrate the feasibility of the wireless parallel operation control. Finally, experiments are presented to verify the theoretical discussion with two three-phase 20kVA UPS systems employed TMS320C32, a kind of real time digital signal processor (DSP).

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.153-158
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• 2005

In this paper, a filter is proposed to compensate droop of the CIC filter for SDR. The proposed compensation filter has almost linear-phase characteristic, requires low operational complexity, and is cost-effective due to its second-order characteristic and lowest operational rate in the baseband.. Especially, it compensates droop in the passband with little performance degradation in the stopband. It is shown, by a design example and its performance analysis, that the proposed compensation method gives performance enhancement in communication systems. It is also shown that the proposed method is superior to conventional ones in view of memory usage and computational load.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.274-277
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• 2016

Effects of interlayer insertion between multi-quantum well and electron blocking layer of green light emitting diode on diode performances were studied by device simulation. Dependence of Mg doping depth on characteristics of current-voltage, emitting wavelength, leakage current, and external quantum efficiency was investigated, and the optimum diode structure was presented. Device structures with interlayers doped in entire region and up to 30 nm showed remarkable reduced leakage current and effectively relieved efficiency droop which is one of the biggest challenges in green light emitting diode. Furthermore, the most improved characteristics in current-voltage and electroluminescence was obtained by the latter structure.