• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1602-1613
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• 2014

The continuous growth of electric vehicles has caused electric power shortages in conventional utilities owing to the charging of electric-vehicle batteries. In order to increase the capacity of these utilities, photovoltaic systems may be an appropriate solution because of their benefits. However, a large amount of loss is generated in a conventional charging structure using photovoltaic sources owing to the many power conversion processes. This paper describes a simple integrated battery charger that utilizes a PV generation system. Moreover, the system control algorithm is deduced by analyzing the operation modes in order to control the proposed integrated system. The proposed system and algorithm are verified by a 3.3-kW prototype, resulting in an increase in the efficiency of approximately 7% to 15% compared with the conventional system. And, to examine the feasibility of the proposed system, the simulation for multi-charger with various conditions are progressed.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.1
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• pp.81-88
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• 2007

In this paper, a new single-phase utility-interactive inverter system for residential power generation with fuel cell is proposed. The proposed inverter system is not only capable of working in both stand-alone and grid-connected mode, but also ensures smooth and automatic transfer between the two modes of operation. The proposed control method has little steady-state error and good transient response characteristic. Also, the control method can be implemented using low-cost, fixed point DSP since it has simpler structure, smaller amount of calculation, and smaller number of sensors. The controller for the proposed utility-interactive inverter system is described, and the validity is verified through simulation and experiment.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1026-1034
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• 2015

In this paper, a unified control strategy using the current space vector modulation (CSVM) technique is proposed and applied to a bidirectional three-phase DC/AC converter. The operation of the converter changes with the direction of the power flow. In the charging mode, it works as a buck type rectifier; and during the discharging mode, it operates as a boost type inverter, which makes it suitable as an interface between high voltage AC grids and low voltage energy storage devices. This topology has the following advantages: high conversion efficiency, high power factor at the grid side, tight control of the charging current and fast transition between the charging and discharging modes. The operating principle of the mode analysis, the gate signal generation, the general control strategy and the transition from a constant current (CC) to a constant voltage (CV) in the charging mode are discussed. The proposed control strategy has been validated by simulations and experimental results obtained with a 1kW laboratory prototype using supercapacitors as an energy storage device.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.4
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• pp.383-390
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• 2014

This paper deals with novel soft-switching method for a bidirectional DC-DC converter in battery charging and discharging system. The proposed soft-switching method provides ZVS and ZCS at turn-on, and ZVS at turn-off of the switch in both charging and discharging operation modes. The soft switching condition can be obtained in wide load range, and provide low switching loss as well as low voltage spike at turn-off of the switch. Proposed method is analyzed in charging and discharging mode. Simulation and experimental results validate the usefulness of the proposed soft-switching method.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.201-202
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• 2012

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. Each mode is operated according to battery states: voltage, current and State of Charging (SOC). The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system. Experiment waveforms confirm the proposed functionality of the charging system.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.235-240
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• 2002

This paper shows the desist concept of an ATS(Antenna Tracking Software) to control the movement of the MSC(Multi-Spectral Camera) antenna. The MSC has a two-axes directional X-band antenna for image transmission to KGS(KOMSAT2 Ground Station). The main objective of the ATS is to drive the APM(Antenna Pointing Mechanism) to the required elevation and the azimuth position according to an appropriate TPF(Tracking Parameter File). The ATS is implemented as one task of the SBC(Single Board Computer) software, which uses VxWorks as a real time OS. The ATS has several operational modes such as STANDBY mode, First EL mode, First AZ mode, Normal Operation mode, and so on. The ATS uses two PI controllers fur the velocity and the position loop respectively, to satisfy the requirements specification. In order to show the feasibility of the described design concept, the various simulations and the experiments are performed under specific test configuration.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.527-532
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• 2005

Among the failure modes which can occur in tube hydroforming such as wrinkling, bursting or buckling, the bursting by local instability under excessive tensile stresses is irrecoverable phenomenon. Thus, the accurate prediction of bursting condition plays an important role in producing the successfully hydroformed part without any defects. As the classical forming limit criteria, strain-based forming limit diagram (FLD) has widely used to predict the failure in sheet metal forming. However, it is known that the FLD is extremely dependant on strain path throughout the forming process. Furthermore, The application of FLD to hydroforming process, where strain path is no longer linear throughout forming process, may lead to misunderstanding for fracture initiation. In this work, stress-based forming limit diagram (FLSD), which is strain path-independent and more general, was applied to prediction of forming limit in tube hydroforming. Combined with the analytical FLSD determined from plastic instability theory, finite element analyses were carried out to find out the state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified by a series of bulge tests in view of bursting pressure and shows a good agreement. Consequently, it is shown that the approach proposed in this paper will provide a feasible method to satisfy the increasing practical demands for judging the forming severity in hydroforming processes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.92-96
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• 2005

Among the failure modes which can be occurred in tube hydroforming such as wrinkling, bursting or buckling, the bursting by local instability under excessive tensile stresses is irrecoverable phenomenon. Thus, the accurate prediction of bursting condition plays an important role in producing the successfully hydroformed part without any defects. As the classical forming limit criteria, strain-based forming limit diagram has widely used to predict the failure in sheet metal forming. However, it is known that the FLD is extremely dependant on strain path throughout the forming process. Furthermore, the path-dependent limitation of FLD makes the application to hydroforming process, where strain path is no longer linear throughout forming process, more careful. In this work, stress-based forming limit diagram (FLSD), which is strain path-independent and more general, was applied to prediction of forming limit in tube hydroforming. Combined with the analytical FLSD determined from plastic instability theory, finite element analyses were carried out to find out Ihe state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified with a series of bulge tests in view of bursting pressure and shows a good agreement. Consequently, it is shown that the approach proposed in this paper will provide a feasible method to satisfy the increasing practical demands for judging the farming severity in hydroforming processes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.36-42
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• 1997

A prototype of 500Wh class flywheel energy storage device was designed and manufactured to check the previously predicted system performance. The system was intentionally designed to show rigid body behavior up to the maximum operating speed of 60000Tpm and to have its 2nd rigid critical mode, of which nodal point lies on the flywheel center of mass, around 4000 to 6000rpm with radial magnetic bearing stiffness of l.e+6 N/m. Numerous experiments an the system behavior showed that the PM axial bearing, designed utilizing a commercial code, acts as resonably as predicted and, most importantly, the system becomes stable after the 2nd critical speed. The EM radial bearing, however, was found out to have orthotropic property with much less radial stiffness values than expected, so that it was observed that the 2nd forward and backward critical modes were excited at 310 and 590rpm respectively with larger vibration amplitudes. Thus, in order to improve the system dynamic behavior, the EM radial bearing is currently being re designed so as to get bigger stiffness and, in turn, smoother operation of the system.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1512-1522
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• 2017

Switched reluctance motor (SRM) is suitable for electric vehicle (EV) applications with the advantages of simple structure, good overload capability, and inherent fault-tolerance performance. The SRM dynamic simulation model is built based on torque, voltage, and flux linkage equations. The EV model is built on the basis of the analysis of forces acting on a vehicle. The entire speed range of the SRM drive is then divided into constant torque and constant power areas. The command torque of the motor drive system is given according to the accelerator pedal coefficient and motor operation areas. A novel adaptive variable angle control is proposed to avoid the switching chattering between the current chopping control and angle position control modes in SRM drives for EV applications. Finally, simulation analysis and experimental results are conducted to verify the accuracy of the proposed simulation model and control strategy.