• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.33-34
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• 2017

This paper presents a linear droop control scheme based on the generation costs of DGs in an autonomous DC microgrid. Unlike the proportional power sharing of the conventional droop control, in the proposed control algorithm, the minimum output voltage range is adjusted and the droop coefficients are regulated according to the generation costs of DGs. As a result, the DGs with lower costs supplies more power in comparison with those with higher costs. Therefore, total generation cost of the system is reduced significantly. The proposed method is simple to implement and it does not require the centralized controller and communication links.

• Proceedings of the KIPE Conference
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• 2019.11a
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• pp.148-149
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• 2019

Voltage unbalance can be occured in AC-DC microgrid systems when AC loads or AC systems are connected. To solve this problem, 3-phase 4-wire interlinking converter is used. This paper proposes in PLL method that can detect accurate phase and voltage magnitude.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.371-372
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• 2015

Dc microgrid has the advantage of high efficiency as compared to the ac system. Droop method has been realized to suppress the current mismatching among the distributed sources. However, this method involves distribution loss due to the line impedance. In this paper, a novel droop method is proposed to minimize the distribution loss as well as the voltage deviation by adjusting the droop coefficient. The proposed droop method is verified by using the simulation based on PSCAD/EMTDC.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.4
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• pp.474-481
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• 2013

It is anticipated that AC distribution system can be replaced by DC distribution system in the near future because of the operation of various distributed source or microgrid system. However DC distribution system replacing 22.9kV AC distribution line is not sufficiently studied still. This paper describes lightning overvoltage analysis among many research fields should be studied to realize DC overhead distribution systems. DC distribution system is modeled using EMTP and overvoltage is analyzed according to interval of arrestor location, earth interval of overhead grounding wire and grounding resistance. It is evaluated that analysis results can be effectively used to design of future DC distribution system.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1595-1607
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• 2018

In this paper, a hierarchical control strategy is introduced to control a new three-port multidirectional DC-DC converter for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the states of charge (SoC) of the ESS. Previous studies tend to balance the voltage of the BPDCMG buses with active sources or by transferring power from one bus to another. Furthermore, the batteries available in BPDCMGs were charged equally by both buses. However, this power sharing method does not guarantee efficient operation of the whole system. In order to achieve a higher efficiency and lower energy losses, a triple-layer hierarchical control strategy, including a primary droop controller, a secondary voltage restoration controller and a tertiary optimization controller are proposed. Thanks to the multi-functional operation of the proposed converter, its conversion stages are reduced. Furthermore, the efficiency and weight of the system are both improved. Therefore, this converter has a significant capability to be used in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter are extracted. Comprehensive simulation studies are carried out and a BPDCMG laboratory setup is implemented in order to validate the effectiveness of the proposed converter and its hierarchical control strategy. Simulation and experimental results show that using the proposed converter mitigates voltage imbalances. As a result, the system efficiency is improved by using the hierarchical optimal power flow control.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.2
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• pp.86-93
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• 2018

In this work, control methods and operating modes are proposed to manage standalone microgrid. A standalone microgrid generally consists of two sources, namely, battery energy storage system (BESS) and diesel generator (DG). BESS is the main source that supplies active and reactive power regardless of load conditions, whereas DG functions as an auxiliary power source. BESS operates in a constant voltage constant frequency (CVCF) control, which includes proportional-integral + resonant controller in a parallel structure. In CVCF control, the concept of fundamental positive and negative transformation is utilized to generate a three-phase sinusoidal voltage under imbalanced load condition. Operation modes of a standalone microgrid are divided into three modes, namely, normal, charge, and manual modes. To verify the standalone microgrid along with the proposed control methods, a demonstration site is constructed, which contains 115 kWh lead-acid battery bank, 50 kVA three-phase DC - AC inverter, and 50 kVA DG and controllable loads. In the CVCF control, the total harmonic distortion of output voltage is improved to 1.1% under imbalanced load. This work verifies that the standalone microgrid provides high-quality voltage, and three operation modes are performed from the experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.10
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• pp.42-48
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• 2010

The Microsource has to supply high quality Power that has high reliability and high energy efficiency to Load according to operating type of Microgrid. The energy sources of microsource type have various dynamic characteristic and transient response corresponding to classes and application skill. This paper shows dynamic characteristic of Microgrid according to Energy Source of microsource type. This research has been carried out by detailed modelling of Microturbine system and Fuelcell system. All models are realized by EMTP/RV and simulated change of operating type and load increase within Microgrid of DC constant voltage inverter model and Microturbine, Fuelcell based Microsource.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.817-825
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• 2017

The AC-common bus microgrid system can overcome several weaknesses of the DC microgrid system by interconnecting the DC/AC inverters used for renewable energy with an AC network. Nevertheless, the unbalanced loads inherent in the electric power systems of island and small communities can deteriorate the performance of the AC microgrid system. This is because of the limited voltage regulation capability and mixed power flow in the voltage source inverter. In order to overcome the unbalanced load condition, this paper proposes a voltage and current control algorithm for the 4-leg inverter based on the single phase d-q control method, as well as the modeling of the voltage controller using Matlab/Simulink S/W. From the S/W simulation and experiment of the 250KW proto-type inverter, it is confirmed that the proposed algorithm is a useful tool for the design and operation of the AC microgrid system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.8
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• pp.70-81
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• 2011

In this paper, a multi-agent control system for DC-coupled photovoltaic (PV), fuel cell (FC), ultracapacitor(UC) and battery hybrid power system is studied for commercial buildings & apartment buildings microgrid. In this proposed system, the PV system provides electric energy to the electrolyzer to produce hydrogen for future use and transfer to the load side, if possible. Whenever the PV system cannot completely meet load demands, the FC system provides power to meet the remaining load. A multi-agent system based-power management and control algorithm is proposed for the hybrid power system by taking into account the characteristics of each power source. The main works of this paper are hybridization of alternate energy sources with FC systems using long and short storage strategies to build the multi-agent control system with pragmatic design, and a dynamic model proposed for a PV/FC/UC/battery bank hybrid power generation system. A dynamic simulation model for the hybrid power system has been developed using Matlab/Simulink, SimPowerSystems and Stateflow. Simulation results are also presented to demonstrate the effectiveness of the proposed multi-agent control and management system for building microgrid.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6419-6424
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• 2015

Recently, high-cost energy storage systems are applying to hybrid generation systems with wind turbine and diesel generator in island areas for stable operation. But, this paper proposes an operating algorithm and modeling method of an islanding microgrid that is composed of PMSG(Permanent Magnet Synchronous Generator) and Diesel Generator applied in island areas without such energy storage system. Initially, the operating algorithm was proposed for frequency and voltage to be maintained within the proper ranges for the load and weather change. And then the modeling method were proposed for PMSG, WT-side AC/DC converter and Grid-side DC/AC converter. The proposed operating algorithm and modeling method were applied to a typical islanded microgrid with PMSG wind turbine and diesel generator. The frequency and voltage was kept within the permissible ranges and the proposed method was proven to be appropriate through simulations.