• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.325-334
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• 2015

This paper deals with a control method for a hybrid energy storage system (ESS) with a battery and super capacitor for grid-connected operation. To improve the grid regulation and to minimize the depth of discharge of the battery, control algorithms for the hybrid ESS are proposed. A p-q control with predictive current control is used for the inverters for the super-capacitor and the battery. To verify the effectiveness of the proposed control method, simulation studies using the PSIM and RTDS are carried out for the actual grid model.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.4
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• pp.296-308
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• 2010

This paper proposes a design of the three-parallel converter system and grid-connection technique for a PMSG based wind turbine systems. The back-to-back converter of the PMSG based wind turbine system is directly connected to the grid so that both the power devices and the filters are needed to have large power ratings. The three-parallel converter configuration can reduce the required power ratings of the devices and filters. However, the three-parallel converter can cause circulating currents. These circulating currents can be suppressed by sellecting proper inner inductance at each leg. An LCL filter design is used to meet the THD regulations. The latent resonance caused by the LCL filter is compensated by an active damping method without additional loss. The decline of the power quality caused by the unbalanced and distorted grid voltages is also compensated with an additional compensation algorithm. The simulation and experimental results show that the proposed system and compensation methods are effective for the wind turbine systems.

• Journal of Power Electronics
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• v.13 no.3
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• pp.437-446
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• 2013

This paper proposes a design scheme for an LCL-filter used for the three-parallel operation of the power converters in high-capacity wind turbines. The designs of the power devices and grid connected filter are difficult due to the high level voltages and currents in huge-capacity wind turbines. To solve these problem, this paper presents three-parallel operation and LCL-filter design techniques optimized by parallel operation. Furthermore, the design of an inverter side inductance of the LCL-filter is discussed in detail considering the switching modulation method. Simulation and experimental results demonstrate the validity of the designed filter and wind turbines.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.2
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• pp.107-114
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• 2007

Islanding of PV systems occurs when the utility grid is removed but the PV systems continue to operate and provide power to local loads. Islanding is one of the serious problems in an electric power system connected with dispersed power sources. This can present safety hazards and the possibility of damage to other electric equipments. In the passive method, the voltage and frequency of PCC are measured and it determines islanding phenomena if their values excess the allowed limits. If the real and reactive power of RLC load and those of the PV system are closely matched, islanding phenomena can't be detected by the passive methods. Several active methods were proposed to detect islanding operation in the region where the passive method can not detect it. The most effective method is SFS method which was suggested by Sandia National Laboratory. In this paper, a new islanding detection method using automatic phase-shift is proposed and its validity is verified through the simulation and experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1112-1121
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• 2011

A microgrid is an aggregation of multiple distributed generators (DGs) such as renewable energy sources, conventional generators, and energy storage systems that provide both electric power and thermal energy. Generally, a microgrid operates in parallel with the main grid. However, there are cases in which a microgrid operates in islanded mode, or in a disconnected state. Islanded microgrid can change its operational mode to grid-connected operation by reconnection to the grid, which is referred to as synchronization. Generally, a single machine simply synchronizes with the grid using a synchronizer. However, the synchronization of microgrid that operate with multiple DGs and loads cannot be controlled by a traditional synchronizer, but needs to control multiple generators and energy storage systems in a coordinated way. This is not a simple job, considering that a microgrid consists of various power electronics-based DGs as well as alternator-based generators that produce power together. This paper introduces the results of research examining an active synchronizing control system that consists of the network-based coordinated control of multiple DGs. Consequently, it provides the microgrid with a deterministic and reliable reconnection to the grid. The proposed method is verified by using the test cases with the experimental setup of a microgrid pilot plant.

• New & Renewable Energy
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• v.2 no.3
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• pp.15-22
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• 2006

As the distributed generation becomes more reliable and economically feasible, it is expected that a higher application of the distributed generation units would be interconnected to the existing grids. This new market penetration using the distributed generation technology is linked to a large number of factors like economics and performance, safety and reliability, market regulations, environmental issues, or grid connection standards. KEPCO, a government company in Korea, has performed the project to identify and evaluate the performance of Micro Gas Turbine(MGT) technologies focused on 30, 60kW-class grid-connected optimization and combined Heat & Power performance. This paper describes the results for the mechanical, electrical, and environmental tests of MGT on actual grid-connection under Korean regulations. As one of the achievements, the simulation model of Exhaust-gas Absorption Chiller was developed, so that it will be able to analyze or propose new distributed generation system using MGT. In addition, KEPCO carried out the field testing of the MGT Cogeneration system at the R&D Center Building, KEPCO. The field test was conducted in order to respond to a wide variety of needs for heat recovery and utilization. The suggested method and experience for the evaluation of the distributed generation will be used for the introduction of other distributed generation technologies into the grid in the future.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.18-20
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• 2008

An electrical balance of plant(EBOP) of a 600kW molten carbonate fuelcell (MCFC) has to transit from grid-connected(GC) mode to grid-independent(GI) mode when a grid is in a fault conditions. A minimum transition time is limited by four cycle for a 600kW MCFC to ride through a grid fault. In this paper, we propose a control algorithm of a 600kW EBOP for a MCFC system. The EBOP has three operation modes, i.e., GC mode, GI mode, and grid-synchronized(GS) mode. The EBOP controls output currents in a GC mode and regulates output voltages in GI or GS mode. GS mode is defined as an interface between GC mode and GI mode to make a mode transition smooth, i.e., limitation of inrush currents, regulation of output voltages within ANSI standard. Simulations and experiments carried out to verify the effectiveness of the proposed control algorithm.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.330-331
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• 2011

The interleaving method is usually used to reduce the ripple of output current of filter inductor in parallel operation of PWM DC/DC converter. Although the current ripple of filter inductor decreases, each current ripple of filter inductor is not decreased. In this study, the operation of interleaved buck converter with coupled inductor is analyzed in each operation mode. It is verified through experiment. The possibility of application to grid connected inverter with parallel operation is identified.

• Fire Science and Engineering
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• v.29 no.1
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• pp.73-79
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• 2015

There are three kinds of design method of the fire sprinkler systems. Grid type is connected all branch as a trapezoid. Loop type is connected cross-mains like circle. The last one is a tree type most commonly used. Grid type needs computer program to calculate the friction loss and flow rate apart from very simple form. In loop type, manual calculation is possible. Design engineer can draw up and calculate the demands without computer program. Because water supplies two direction in loop type, friction loss is smaller than tree type. Water distribution in operation area is uniform because of the small differences of sprinklers discharge pressure. Loop type is superior to tree type in respect of total pressure and flow rate. Using the small diameter pipe, the labor and construction cost will be decreased in the end. Loop type sprinkler design is rarely laid out because design engineers don't know the method. This paper is intended to inform that the loop type is better than the tree type in performance and economic point of view. And also this paper intend to use the loop type easily and widely.

• New & Renewable Energy
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• v.10 no.3
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• pp.39-46
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• 2014

The performances of three different types of photovoltaic (PV) module technologies namely, copper-indium-diselenide (CIGS), mono-crystalline silicon (mo-Si) and amorphous silicon (a-Si) have been comparatively studied in the grid-connected system for more than a year under the tropical monsoon climate of Thailand. The yields, performance ratios and system efficiencies for the respective PV module technologies have been calculated and a comparison is presented here. The performance ratios of the initial operation year for CIGS showed highest among the compared technologies under Thailand climate conditions by marking 97.0% while 89.6% for a-Si and 81.5% for mo-Si. Although mo-Si has shown highest efficiencies all over the period, under the testing conditions, the operating efficiency of mo-Si was down-graded from its reference value mainly due to high operating temperature and the efficiency of the tested CIGS module was also found as high as that of mo-Si in the study. Accordingly, outdoor assessment shows that CIGS modules have demonstrated high performance in terms of yields and performance ratios in Thailand climate conditions.