Gyu-Ha Choe

Step-up/down AC voltage regulator using transformer with tap changer and PWM AC chopper

A step-up/down AC voltage regulator is proposed, in which a tap-changing transformer and a pulsewidth modulation (PWM) AC chopper are combined. The proposed regulator can step up or down the output voltage to input voltage. Also, the proposed regulator restrains more harmonics of output voltage compared to the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional PWM regulator. Through digital simulation, several characteristics are investigated theoretically and then compared with those of conventional schemes. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed regulator.

Design of current controller for 3-phase PWM converter with unbalanced input voltage

Generally current controllers of three-phase PWM power converters have been implemented in the synchronous frame because the synchronous frame controller can eliminate steady state error and has fast transient response by decoupling control. However most of such controllers have been designed under balanced input voltage. Therefore such designed current controllers showed undesirable current control characteristics under unbalanced conditions because the current reference is distorted by the second order harmonic voltage due to negative sequence. In this paper, a current controller for a PWM power converter, considering unbalanced input voltage, is designed and verified by both simulation and experiment.

Analysis of torque ripple in BLDC motor with commutation time

Torque ripple generated in the commutation period is the main drawback of the brushless DC (BLDC) motor, which deteriorates its precision. Many methods to solve this problem have been studied. In many control methods, torque ripple reduction was considered at the point of current control, which means that if current can be controlled properly, the BLDC motor does not produce any torque ripple. In this paper, the authors propose that torque ripple in the commutation period of a BLDC motor is inevitable, even if the current control is successful. A torque model, considered with decaying phase back EMF, is introduced and the causes of commutation torque are analyzed. The influence of commutation time on torque ripple and the relationship between commutation time and speed are introduced. This paper deals with torque ripple reduction of a BLDC motor from the viewpoint of commutation time and gives a theoretical background to reduce it.

Improvement of input power factor in AC choppers using asymmetrical PWM technique

An asymmetrical pulse width modulated (APWM) control technique for AC choppers is proposed to improve the input power factor. The switching function for the proposed technique is derived and hence converted into the asymmetrical PWM waveform for practical implementation of an AC chopper. Through digital simulation several characteristics are investigated theoretically and then compared with those of the conventional PWM control technique. The proposed strategy is simplified to an approximate APWM which can be realized by the analog circuit. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed technique. >

A new instantaneous output current control method for inverter arc welding machine

According to the adoption of inverter circuit topology for welding machine area, the improvement of welding performance con be achieved. However conventional CO/sub 2/ inverter arc welding machine uses the constant voltage characteristics. So the metal transfer is performed under nonoptimum conditions in view of spatter generation. In this paper the new control algorithm is proposed for welding machine, which is the instantaneous output current control method using single chip microprocessor. But the optimum waveform of welding current is still uncertain, as a first step for figuring out the optimized waveforms, this study was performed, and as a result of performance test of the proposed system, it was demonstrated that all of the waveform variation parameters could be set individually and the generated spatter is reduced compared to conventional inverter arc welding machine.

Asymmetrical PWM technique with harmonic elimination and power factor control in AC choppers

This paper describes the asymmetrical pulse width modulated (APWM) control technique for single phase AC choppers, which improves the input power factor and eliminates the harmonics of the output voltage up to a specified order. This technique also enables linear control of the fundamental component of the output voltage. The APWM switching patterns at the specified phase angle are obtained by the Newton-Raphson method and can be implemented by a one-chip microprocessor. Theoretical comparisons are made with conventional PWM technique and the computed performance indicates the superiority of the proposed APWM technique. Practical verification of the theoretical predictions is presented to conform the capabilities of the new technique. >

Analysis and control of PWM converter with V-I output characteristics of solar cell

In this paper, the virtual implementation of a solar cell (VISC) was proposed to solve problems such as the reappearance and repetition of situations in photovoltaic power system experiments, and to achieve reliable experimental results on PV power systems. VISC emulates the solar cell output characteristics, and can substitute for solar cells in laboratory experiment systems. To realize the VISC, a mathematical model of solar cell for the driving power converter was studied and the buck and buck-boost power converters were compared from the viewpoint of the tracking error of the characteristic curve of solar cells using computer simulation.

Asymmetrical PWM technique for AC choppers

An asymmetrical pulse-width modulated (APWM) control technique for an AC chopper which can improve the input power factor and suppress the harmonic contents of currents at both its input and its load sides is proposed. The ideal switching function for the proposed technique is derived and converted into the APWM pattern for practical implementation of an AC voltage regulator. By digital simulation several characteristics are investigated theoretically and then compared with those of the phase angle control and conventional PWM technique. The experimental results show good agreement with calculated ones, indicating the feasibility of the proposed technique.<<ETX>>

Analysis and control of active power filter with optimized injection

The active power filter is the harmonic filter which suppresses the ac harmonics by injecting PWM compensating current into the ac side. The novel model of PWM compensating current Is derived from the optimized injection method. By injecting the derived PWM current, the ac harmonics up to the order of the modulation number are eliminated. With no external source it is possible to build up the inductor current to the desired value, which is limited within the upper and lower limits. The value can be controlled by adjusting the fundamental current flowing Into the filter. Hence the power flow becomes bidirectional In the filter with the optimized injection. The overall characteristics of the proposed method are analyzed theoretically and its validity is proved with the experimental results using microcomputer.

Design of Leakage Inductance in Resonant DC-DC Converter for Electric Vehicle Charger

In this paper, the electric charger with single phase PWM converter and a bidirectional half-bridge converter is proposed. A transformer leakage inductance is used for making resonance at the resonant converter, which can make switched current to be sinusoidal without extra inductive component. Both operating principle and design guideline are described in detail. The feasibility for the proposed design is verified through hardware implementation and the experimental results. Detailed results have been obtained to show several advantages such as the compact design and reduced switching losses for different values and conditions of leakage inductance and resonance cases.