• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.1
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• pp.36-40
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• 2008

Most of the low-voltage feeder are designed with approximately balanced and connected at the three phase four wire systems. However, Most of the power distribution systems' load which is composed of single or three phase are unbalanced by generating load unbalance. Unbalanced current will draw a highly unbalanced voltage. The power factor of an induction motor at rated operation is between 25 and 90%, depending on the size and speed of the motor. However, many induction motors operate below the nominal rating, resulting in poor power factor. This condition needs power factor improvement. Addition of power capacitor at the motor terminal may draw to stress due to voltage unbalance. This paper presents operation characteristics on steady states of a three-phase induction motor under unbalanced voltages with power capacitor. The existence of voltage unbalance have an effect on stress of power capacitor.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.286-288
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• 2005

Conventional phase shift full bridge (PSFB) converter has serious voltage oscillation problem across the secondary rectifier diodes, which would require the dissipate snubber circuit, thus degrades the overall efficiency. To overcome this problem, a new voltage oscillation reduction technique (VORT) which effectively reduce the voltage oscillation of the secondary rectifier diodes for phase shift 1011 bridge converter is proposed. Therefore, no dissipate snubber for rectifier diodes is needed. In addition, since it has wide zero voltage switching (ZVS) range, high efficiency can be achieved. Operational principle, analysis of voltage oscillation, and design consideration are presented compare with that of the conventional PSFB converter. To confirm the validity of the proposed VORT, experimental results from a 420W, 385Vdc/210Vdc prototype are presented.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.12-15
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• 2002

This propose a simple DC voltage sensor less single phase PFC(Power Factor Correction Circuit) converter by detecting a AC current sensors are not required to construct the control system. The DC voltage is directly controlled by the command input signal Kd($V_o/V_a$)for the boost chopper circuit. The DC voltage regulation is small because of the feed forward control for the AC line voltage VS and no dependence of the circuit parameters. The sinusoidal current waveform in phase with the AC input voltage can be obtained. These characteristics are confirmed by some experiment results.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.4
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• pp.566-574
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• 2013

In this paper, direct power control system for three-phase PFC AC/DC converter without the source voltage sensors is proposed. The sinusoidal input current and unity effective power factor are realised based on the estimated flux in the observer. Both active and reactive power calculated using estimated flux. The estimation of flux is performed based on the reduced-order virtual flux observer using the actual currents and the command control voltage. Moreover, source voltage sensors are replaced by a estimated flux. DC output voltage has been compensated by DC output ripple voltage estimation algorithm. The active and reactive powers estimation are performed based on the estimated flux and Phase angle. The proposed algorithm is verified through simulation and experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.4
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• pp.322-331
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• 2002

In this paper, a single-phase to three-phase PWM converter topology using a single-phase half-bridge PWM rectifier and a 2-leg inverter for low cost three-phase induction motor drives is proposed. In addition, the source voltage sensor is eliminated with a state observer which controls the deviation between the model current and the system current to be zero. The converter topology is of lower cost than the conventional one, which gives sinusoidal input current, unity power factor, dc output voltage control, bidirectional power flow and VVVF output voltage. The experimental results for V/F control of 3Hp induction motor drives have been shown.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.2
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• pp.128-136
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• 2003

This paper investigates the application of the anti-windup scheme to control U voltage of the three-phase four-wire active power filter, installed in a three-phase four-wire power system. In order to reduce efficiently the harmonic currents caused by the switching loads and to improve the whole performance of the flower system, the DC voltage of the three-phase four-wire active power filter should be properly controlled. PI controller can be applied to the U voltage controller of the three-phase four-wire active power filter. However, a large error input to PI controller leads to a windup phenomenon which deteriorate the dynamic characteristics of the U voltage controller Therefore, the application of the anti-windup scheme for the DC voltage controller is proposed and the improved performances of the anti-windup U voltage controller are proved through the computer simulation study.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.684-687
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• 1999

In this paper, a method for controlling a single phase PWM AC/DC converter without any voltage sensors is proposed. In this method, the source voltage is estimated by sliding mode observer and input current is synchronized with the estimated source voltage. The source voltage is estimated by current error between the actul and the estimated current. The experimental results confirm the validity of the proposed control method.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.158-161
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• 1998

A precision high voltage generator for ion injection is implemented on HFZVS-PSCI (High Frequency Zero-Voltage-Switching Phase-Shift-Controlled Inverter). Some practical aspects of implementing precision high voltage generator with HFZVS-PSCI, such as a HFHV transformer, multiflier, and precision CR divider are discussed. The results show that the generator under the Phase-Shift-Controller has a fast dynamic response, low ripple voltage, and high accuracy.

• Journal of Power Electronics
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• v.3 no.1
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• pp.1-9
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• 2003

This paper presents a performance analysis of typical Auxiliary Resonant Commutation Snubber-assisted three phase voltage source soft switching inverter which can operate under a condition of Zero Voltage Switching (ZVS) using a digital control scheme which is suitable for high power applications compared with resonant DC link snubber assisted soft switching inverter. The system performances of this inverter are illustrated and evaluated on the basis of experimental results.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.318-320
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• 2007

Single-phase cycloconverters are widely used for ac-ac power conversion especially for speed control of ac drives. In this paper, a new single-phase to single-phase Z-source cycloconverter topology is proposed. The proposed single-phase Z-source cycloconverter can boost to a desired voltage with various frequency. Thus, it is called a frequency step-down and amplitude voltage step-up converter. The operating principle of the proposed topology is presented. Analysis and simulation for this single-phase Z-source cycloconverter are also presented.