• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.560-564
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM(DPWM) to balance the DC-link voltage of three-level Neutral-Point-Clamped(WPC) inverters at low modulation index. New DPWM methods in multi-level inverter are also introduced. The proposed DPWM method changes the path and duration to flow the neutral point current out of or into neutral point of the DC-link and it makes the overall fluctuation of the DC-link voltage zero during a sampling time of reference voltage vector. Therefore, the voltage of the DC-link can be balanced fairly well and also the voltage ripple of the DC-link is reduced significantly. Moreover, comparing with conventional methods, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by experiment

• Journal of Power Electronics
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• v.9 no.2
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• pp.133-145
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• 2009

In this paper a modular high performance MV-to-LV rectifier based on a cascaded H-bridge rectifier is presented. The proposed rectifier can directly connect to the medium voltage levels and provide a low-voltage and highly-stable DC interface with the consumer applications. The input stage eliminates the necessity for heavy and bulky step-down transformers. It corrects the input power factor and maintains the voltage balance among the individual DC buses. The second stage includes the high frequency parallel-output DC/DC converters which prepares the galvanic isolation, regulates the output voltage, and attenuates the low frequency voltage ripple ($2f_{line}$) generated by the first stage. The parallel-output converters can work in interleaving mode and the active load-current sharing technique is utilized to balance the load power among them. The detailed analysis for modeling and control of the proposed structure is presented. The validity and performance of the proposed topology is verified by simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2004.11a
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• pp.71-75
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• 2004

In this paper, in order to develop a simple and high efficient ballast without an external igniter, a half-bridge type ballast with a coupled inductor and a frequency controlled synchronous rectifier is proposed. The internal LC resonance of the buck converter is used In generate a high voltage pulse for the ignition, and the coupled inductor filter is used for steady state ripple cancellation. Also, a synchronous buck converter is applied for the DC/DC converter stage. In order to improve the efficiency of the ballast, a frequency control method is proposed. This scheme reduces a circulation current and turn off loss of the MOSFET switch on the constant power operation, which results in increase of the efficiency of the ballast system about $4\%$, compared to a fixed frequency control. It consists a 2-stage version ballast with a PFC circuit. The results are verified with hardware experiments.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.384-390
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• 2012

This paper proposes a fault diagnosis method of the line-to-line voltage sensors in 3-phase AC/DC pulse width modulation (PWM) converters. The line-to-line voltage sensors are an essential device to obtain the information of the grid voltages for controlling the 3-phase AC/DC PWM converters. If the line-to-line voltage sensors are mismeasured by various faults, the voltage sensors can obtain wrong information of the grid voltage. It has an adverse effect on the control of the converter. Therefore, the converter causes the unbalance input AC current and the DC-link voltage ripple in the 3-phase AC/DC PWM converter. Hence, fast fault detection and fault tolerant control are needed. In this paper, the fault diagnosis method is proposed and verified through simulations and experiments.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.6 no.2
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• pp.56-61
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• 1992

This paper is reported on the simulation and test results of a constant flux vector control scheme of an induction motor without any speed detecting eqiupment, in which the adaptive current PWM inverter is used. The rotor speed is estimated form stator voltage, current and parameters of motor, and control algorithm in the system is performed with by micro processor. By comparing the waveform of input current of this system with that of the case with taco-generator, good agreement is observed except small ripple component. Experimental results which are acquired at start up and during acceleration/deceleration are quite similar to those of the simulation results.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.198-200
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• 2018

In this paper a single-stage single-phase differential type isolated AC-DC converter is proposed. This converter eliminates the requirement to use bulky electrolytic capacitor from the system and at the same time provides DC charging by employing the AC Power Decoupling waveform control method. All the switches of the converter achieve ZVS turn on during half line cycle and all diodes achieve ZCS turn off during entire line cycle. A conventional controller is implemented for PFC control and output regulation, whereas a power decoupling controller is added to compensate $2^{nd}$ harmonic ripple power. In addition, an interleaving technique is applied to increase the power range of the converter and reduce the input inductor size. In the end simulation verification is performed and results are obtained for 6.6KW.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.4
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• pp.388-396
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• 2005

SRM has not been put into practical applications widely because of its large torque ripple, acoustic noise and low power factor. In addition, a traditional position sensor is needed for the drive control. So we propose an improved sensorless drive method of Switched Reluctance Motors using impressed voltage pulses. Conventional impressed voltage pulse method has a problem of phase delay because of low-pass filter. So in this paper we propose an unproved sensorless driving method based on the impressed voltage pulse using new pulse-shift circuit technique that overcomes the phase delay and start-up problem. Proposed method is implemented in a simple analog circuit instead of using an expensive DSP.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.3
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• pp.276-282
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• 2014

In a single-phase grid-connected power system consisting of a dc-dc converter and a dc-ac converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains double-fundamental frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new double-fundamental current reduction-scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small-signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.24-25
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• 2017

In this paper, a low cost bridgeless interleaved power factor correction topology for electric vehicle charger application is proposed. With the proposed topology the number of switches, inductors, current sensors and associated circuits can be reduced, thereby reducing the cost of the system as compared to the conventional bridgeless PFC circuit. The reduced input current ripple by the proposed interleaved topology makes it suitable for high power applications such as electric vehicle chargers since it can reduce the size of the inductor core and the Electro Magnetic Interference (EMI) problem. In the proposed topology only one current sensor is required. All the boost inductor currents can be reconstructed by sampling the output current and used to control the input current. Therefore the typical problem caused by the unequal current gain of each current sensor inherently does not exist in the proposed topology. In addition the current sharing between converters can be achieved more accurately and the high frequency distortion is decreased. The performance of the proposed converter is verified by the experimental results with a prototype of 6.6kW bridgeless interleaved PFC circuit.

• Journal of Power Electronics
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• v.3 no.4
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• pp.205-214
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM (DPWM) to balance the DC-link voltage of three-level neutral-point-clamped (NPC) inverter at low modulation index. It introduces new DPWM methods in multi-level inverter and one of them is used for balancing the DC-link voltage. The current flowing in the neutral point of the DC-link causes the fluctuation of the DC-link voltage of the NPC inverter. The proposed DPWM method changes the path and duration time of the neutral point current, which makes the overall fluctuation of the DC-link voltage zero during a sampling time of the reference voltage vector. Therefore, by using the proposed strategy, the voltage of the DC-link can be balanced fairly well and the voltage ripple of the DC-link is also reduced significantly. Moreover, comparing with conventional methods which have to perform the complicated calculation, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by the experiment.