• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.06a
• /
• pp.355-356
• /
• 2009

In this paper, we investigated the fault current limiting characteristics according to the increase of voltage in the separates three-phase flux-lock type high-Tc superconducting fault current limiter using YBCO CC. The separated three-phase flux-lock type SFCL consists of single-phase flux-phase type SFCL in each phase. Superconductor was using the YBCO CC. To analyze the current limiting characteristics of a three-phase flux-lock type SFCL, the short circuit experiments were carded out fault such as the triple line-to-ground fault. The experimental result shows that fault current limiting characteristics was improved on the high voltage level.

• Journal of Power Electronics
• /
• v.17 no.2
• /
• pp.422-431
• /
• 2017

The equivalent circuit of a three-leg, four-wire voltage source converter (VSC) is derived using switching functions. Simulations and experiments are conducted (i) to investigate the effects of the zero sequence on VSCs when a three-phase imbalance exists and (ii) to use the consistency of simulations and laboratory experiments to validate the equivalent circuit. The impact of a three-phase imbalance on the VSC has yet to be fully investigated because of the lack of an equivalent circuit to show rigorously how the zero sequence currents flow through the VSC.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.55 no.1
• /
• pp.47-53
• /
• 2006

In this paper, a simple scheme compensating for the effect of dc-link ripple voltages on output voltage of two-leg and three-phase PWM inverters is proposed, where single-phase half-bridge PWM convertor and two-leg inverter are used. The voltage at neutral point of the dc-link is controlled so that the upper-half of do-link voltage is equal to the lower-half voltage in average concept. However, the effect of the do-link ripple voltage results in the inverter output voltage and current distortion. This effect can be eliminated by introducing a compensation voltage in switching time calculation. Also, the inverter dead time should be compensated for sinusoidal output waveform. The proposed scheme has been verified by experimental results which were obtained from the V/F constant operation of the induction motor fed by two-leg inverter.

• Proceedings of the KIPE Conference
• /
• 2011.11a
• /
• pp.63-64
• /
• 2011

The inevitable calculation time delay of digital controller especially degrades the voltage control performance of three-phase UPS systems. This paper proposes time delay compensators based on the Smith-predictor for both voltage and current controllers of three-level NPC inverters. The PSIM-based simulation results show that the proposed controller with delay compensator gives improved voltage control performance with respect to time delay.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.56 no.3
• /
• pp.123-128
• /
• 2007

Hydro power supplies no pollution energy, mainly induction generator has been applied at the small capacity power station. The generating power of small hydro-electric power station connects on the 22.9kV distribution system or low voltage system in the case of three-phase four-wire supply system. There are side effects of various kinds in the 3-three phase 4-wire distribution system mixing 1-phase load and 3-phase load. This system generates the voltage unbalance by unbalanced load operating condition. They have various serious effects on generator and connection system. In this paper, we analyzed what kind of operation characteristic are happened in the induction generator by customer load variation at the 3-three phase 4-wire distribution system.

• Journal of Power Electronics
• /
• v.12 no.4
• /
• pp.559-566
• /
• 2012

A new design method for the LCL filters of three-phase voltage source PWM rectifiers is presented in this paper. Based on the single-phase harmonic equivalent model, the harmonic voltage of the rectifier side is calculated to design the LCL filter parameters by an iterative algorithm, in which the resonance frequency $f_{res}$ and the ratio r between the grid-side inductance and the rectifier-side inductance are selected as known constants. The design criteria and process are introduced and the influence on the design result by the value of the resonance frequency $f_{res}$, ratio r is analyzed. Finally an example (600V, 500kW) is tested by simulation and experiment to verify the validity of the new design method.

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

• Journal of Power Electronics
• /
• v.14 no.3
• /
• pp.531-540
• /
• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

• Proceedings of the KIPE Conference
• /
• 1999.07a
• /
• pp.489-492
• /
• 1999

This paper proposes a control method for three-phase voltage-source PWM converters using only a single current sensor in the DC link. A predictive current controller for the voltage-source PWM converter is used so that all phase currents can be reconstructed in a switching period although one or two of active vectors are applied only for a short time. Compensation of the 2 step delays is also included. In this paper single sensor current control using predictive state observer will be discussed, and investigated experimentally.

• Journal of Electrical Engineering and Technology
• /
• v.4 no.2
• /
• pp.266-271
• /
• 2009

In this paper, improved direct torque control(DTC) of five-phase induction motor(IM) is proposed. Due to the additional degrees of freedom, five-phase IM drives present unique characteristics. One of them is the ability of enhancing the torque producing capability of the motor. Also five-phase motor drives possess many others advantage compared with the traditional three-phase motor drives. Such as, reducing the amplitude and increasing of frequency of torque pulsation, reducing amplitude of current per phase without increasing the voltage per phase and increasing the reliability. The direct torque control method is advantageous when it is applied to the five-phase IM. Because the five-phase inverter provides 32 space vectors in comparison to 8 space voltage vectors by the three-phase inverter. The 32 space voltage vectors are divided into three groups according to their magnitudes. The characteristics and dynamic performance of traditional five-phase DTC are analyzed and new DTC for five-phase IM is proposed. Therefore, a more precise flux and torque control algorithm for the five-phase IM drives can be suggested and explained. For presenting the superior performance of the pro-posed direct torque control, experimental results is presented using a 32 bit fixed point TMS320F2812 digital signal processor