• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.701-710
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• 2017

This paper presents a five-level PWM inverter using series and parallel connection of voltage sources. The alternative connection is done by an auxiliary circuit consisted of a switch, three diodes, and two batteries. The auxiliary circuit is located between input dc voltage source and H-bridge cell. Thanks to the auxiliary circuit, the proposed inverter synthesizes five-level output voltage in an effective way. Topologically both batteries are charged and discharged in the same rate, so it does not need to apply battery voltage balancing control method. Theoretical analysis of the proposed inverter is verified by computer-aided simulation and experiment based on a prototype of 1kW.

• Journal of Korean Elementary Science Education
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• v.33 no.2
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• pp.335-351
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• 2014

The 96 elementary school teachers' the degrees of understandings about the characteristics of the currents according to the connection methods of batteries in simple electric circuits were investigated. In this study, the concepts on the characteristics of currents according to the connection methods of batteries were divided 'the learned concepts' and 'the differentiated concepts'. The characteristics of the currents in the region of the larger resistance of load than the internal resistance of a battery were called the learned concepts, they are taught in the science curriculum. While the characteristics of the currents in the region of the smaller resistance of load than the internal resistance of a battery were called the differentiated concepts, they are not exposed clearly in the science curriculum. The results obtained in this study are as follows: The average score related to the learned concepts was relatively high, while the degree of the teachers' cognitions of the internal resistance of a battery and the resistance of wires were low. Also the average score related to the differentiated concepts was very low because it seems so new to the elementary school teachers. It strongly suggests that the elementary school teachers did not understand meaningfully the characteristics of the currents related to the connections of batteries on the ground of the cognitions of the internal resistances of batteries and the resistances of loads in simple electric circuits. Hence, they might experience difficulties due to the problems occurred in relation to the connections of batteries in the elementary school science lessons.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.42-44
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• 2018

An integrated charger is used for bi-directional power conversion between an electric vehicle and a power grid. The proposed integrated charger works in a way that motor windings are utilized as filter inductances for charging/discharging of batteries in addition to the original purpose of motor drives. After a mathematical model of the integrated charger based on an dual winding induction machine (DWIM) is discussed, a current control method is designed for grid connection. The effectiveness of the proposed method is examined with simulation results.

• Journal of Power Electronics
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• v.11 no.2
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• pp.120-131
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• 2011

This paper proposes two control strategies for the bidirectional Z-source inverters (BZSI) supplied by batteries for electric vehicle applications. The first control strategy utilizes the indirect field-oriented control (IFOC) method to control the induction motor speed. The proposed speed control strategy is able to control the motor speed from zero to the rated speed with the rated load torque in both motoring and regenerative braking modes. The IFOC is based on PWM voltage modulation with voltage decoupling compensation to insert the shoot-through state into the switching signals using the simple boost shoot-through control method. The parameters of the four PI controllers in the IFOC technique are designed based on the required dynamic specifications. The second control strategy uses a proportional plus resonance (PR) controller in the synchronous reference frame to control the AC current for connecting the BZSI to the grid during the battery charging/discharging mode. In both control strategies, a dual loop controller is proposed to control the capacitor voltage of the BZSI. This controller is designed based on a small signal model of the BZSI using a bode diagram. MATLAB simulations and experimental results verify the validity of the proposed control strategies during motoring, regenerative braking and grid connection operations.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1124-1128
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• 2021

As regulations of emissions from ships become more stringent, electric propulsion systems have been increasingly used to solve this problem in vessels ranging from large merchant ships to small and medium-sized ships. Methods for improving the efficiency of the electric propulsion system include the improvement of power sources; the use of a system linked to environmentally friendly power sources, such as batteries, fuel cells, and solar power; and the development of hardware and control methodology for rectifiers, power conversion devices, and propulsion motors. The method using a phase-shifting transformer with diodes has been widely used for rectification. Power semiconductor devices with grid connection to an environmentally friendly power source using DC distribution, a variable speed power source, and the application of small and medium-sized electric propulsion systems have been developed. Accordingly, the demand for active front-end (AFE) rectifiers is increasing. In this study, a method using a neural network rather than a conventional proportional-integral controller was proposed to control the AFE rectifier. Tested controller data were used to design a neural network controller trained through MATLAB/Simulink. The neural network controller was applied to a rectification system designed using PSIM software. The results indicated the effectiveness of improving the waveform and power factor DC output stage according to the load variation. The proposed system can be applied as a rectification system for small and medium-sized environmentally friendly ships.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.601-610
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• 2020

Recently, damage caused by drought is becoming worse and worse due to the global climate change. To overcome these problems, movable-weir to control the water level has been installed instead of a fixed-weir made from concrete. On the other hand, it is difficult to operate an existing moveable-weir because of the high cost of facility management and manpower consumption. In addition, because most moveable-weirs are installed in power systems, the operating cost and the cost of connection for power systems increase when they are located in remote areas. Therefore, this paper proposes an optimal design algorithm and the evaluation algorithm of the SOC (state of charge) of a lithium-ion battery to replace an existing power supply with eco-friendly movable-power with a power supply system using PV modules and lithium-ion batteries. In addition, this study modeled a 50kW power supply system of a movable-weir using PSCAD/EMTDC S/W. The simulation results confirmed that the proposed algorithm has stable operation characteristics in an independent operation mode and interconnection operation mode and that there is the possibility of commercialization with a benefits evaluation of the eco-friendly power supply system of a movable-weir.