• The Transactions of the Korean Institute of Power Electronics
• /
• v.15 no.6
• /
• pp.451-459
• /
• 2010

This paper describes the performance comparison results for a hybrid back-to-back converter, which is composed of a 3-level 24-pulse converter and a 3-level PWM converter, in order to interconnect a large scale wind farm with the power grid. Also it describes the performance comparison results when the 24-pulse converter operates in only firing-angle control, and both firing-angle and the zero-voltage control. For the purpose of systematic performance comparison, computer simulations with PSCAD/EMTDC software were carried out, and based on simulation results a scaled hardware model with 2 kVA rating was built and tested.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.272-275
• /
• 2000

We investigated a resistive superconducting fault current limiter (SFCL) fabricated using YBCO thin films on 2-inch diameter sapphire substrates. Nearly identical SFCL units were prepared and tested. The units were connected in series and parallel to increase the current and voltage ratings. A serial connection of the units showed significantly unbalanced power dissipation between the units. This imbalance was removed by introducing a shunt resistor to the firstly quenched unit. Parallel connection of the units increased the current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current 25 Ap, was produced and successfully tested at a 220 V circuit. From the resistance increase, we estimated that the film temperature increases to 200 K in 5 msec, and 300 K in 120 msec. Successive quenches revealed that this system is stable without degradation in the current limiting capability under such thermal shocks as quenches at 220 V.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.15 no.5
• /
• pp.411-416
• /
• 2010

A voltage drop characteristics of a transformer-based voltage disturbance generator with series transformers is analysed. It is well known that a voltage disturbance generator with series transformer is cost-effective and reliable compared with other types. The voltage drop depends on the %Z of the transformer, power rating, and output power factor. A wrong design of the transformer results in a severe voltage drop, which can not guarantee the proper performance of the generator. The voltage drop is analysed under the condition of 10kVA output power rating and 4% of %Z with the variation of power factor. It is found through simulations and experiments that the drop increases as the power factor decreases in lagging mode, and the drop is 4% of the rated voltage in case of 0.85 lagging power factor.

• Journal of Power Electronics
• /
• v.18 no.6
• /
• pp.1697-1707
• /
• 2018

In this paper, two large current rectifiers are proposed based on two wye-connected autotransformers. The requirements of the ideal large current rectifier are analyzed, and it is concluded that the large current rectifier has a higher power density and a higher energy conversion efficiency when it is made up of two three-phase half-wave rectifiers and a wye-connected autotransformer. According to theoretical analysis results, the two novel wye-connected autotransformers are designed to feed two three-phase half-wave rectifiers. The two autotransformers can generate two groups of three-phase voltages with a 60o phase shifting, and their kVA ratings account for 95% and 80% of the load power, respectively. These values are less than those of a double star rectifier at 30% and 46%. From the input mains and output side, the power quality of the proposed rectifiers is the same as that of the double star rectifier. Some experiments validate the correctness of the theoretical analysis.

• Journal of Power Electronics
• /
• v.13 no.2
• /
• pp.304-312
• /
• 2013

The most common power quality problems in distribution systems are related to unbalanced voltage sags. Voltage sags must be detected quickly and corrected in a minimum amount of time. One of the most widely used methods for sag detection is based on the d-q transformation. This method has the disadvantage of missing the detection of unbalanced faults, because this method uses a voltage sag level signal obtained from the average of 3 phases for sag detection. In this paper, an adaptive filter sag detection method is proposed for Dynamic Voltage Restorers (DVR) under unbalanced fault conditions. The proposed DVR controller is able to detect balanced, unbalanced and single phase voltage sags. A novel reference voltage generation method is also presented. To validate the proposed control methods, a 3-phase DSP controlling a DVR prototype with a power rating of 1.5-kVA has been developed. Finally, experimental results are presented to verify the performance of the proposed control methods.

• Journal of Power Electronics
• /
• v.10 no.2
• /
• pp.203-209
• /
• 2010

This paper describes the development of a three-phase line-interactive DVR with a new sag detection algorithm. The developed detection algorithm has a hybrid structure composed of an instantaneous detector and RMS-variation detectors. The source voltage passes through the sliding-window DFT and RMS calculator, and the instantaneous sag detector. If an instantaneous sag is detected, the RMS variation detector-1 is selected to calculate the RMS variation. The RMS variation detector-2 is selected when the instantaneous sag occurs under the operation of the RMS variation detector-1. The feasibility of the proposed algorithm is verified through computer simulations and experimental work with a prototype of a line-interactive DVR with a 3kVA rating. The line-interactive DVR with the proposed algorithm can compensate for an input voltage sag or an interruption within a 2ms delay. The developed DVR can effectively compensate for a voltage sag or interruption in sensitive loads, such as computers, communications equipment, and automation equipment.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.11 no.5
• /
• pp.463-470
• /
• 2006

This paper deals with a new 3-phase power quality disturbance generator. The proposed generator can provide phase jump as well as voltage sag, swell, outage, unbalance, and over and under voltage. The operating principle of the generator is described in each mode of disturbance. The magnitude of the phase jump is analysed and it is found that the magnitude is the function of the turn-ratios of the transformers consisting the generator. The scheme has simple structure compared with the conventional one, and the major components of the proposed scheme are SCR thyristor and transformer, which guarantees high reliability and cost-effective implementation of the generator. Furthermore, high efficiency can be obtained because there is no PWM switching of the semiconductor devices, and it is easy to control the system. Simulations are carried out to confirm the operation in each disturbance mode, and experiments has been done with 5kVA power rating. The usefulness of the proposed scheme is verified through simulation and experimental results. It is expected that the scheme can be applied to the performance test of the custom power devices such as UPS, DVR, DSTATCOM, and SSTS with cost-effective system.

• Korean Journal of Acupuncture
• /
• v.37 no.1
• /
• pp.54-62
• /
• 2020

Objectives : Acute low back pain syndrome causes pain and poor quality of life. There are various studies of SBV (Sweet bee venom) pharmacopuncture, but few have identified the therapeutic effects for patients unable to walk due to acute back pain. This case series report three cases of acute low back pain syndrome treated with SBV pharmacopuncture combined with Korean Medicine (KM) treatments. Methods : Three acute low back pain syndrome patients with no other acute abnormalities in the imaging were treated by KM treatments including SBV pharmacopuncture, acupuncture, cupping, herbal medicine and physical therapy. The improvement of symptoms was evaluated using Numerical rating scale (NRS), Oswestry disability Index (ODI), EuroQol-5 dimension index (EQ-5D) and EuroQol-visual analogue scale (EQ-VAS). Results : Patients who were unable to walk due to acute back pain were able to walk. There were significant improvements of NRS, ODI, EQ-5D and EQ-VAS after treatment. The patients experienced an average 90% decrease in low back pain after inpatient KM treatment for about 8 days. NRS decreased by an average of 78.9%, ODI decreased by an average of 49.4%, and EQ-VAS increased by an average of 92.6%. In the case 1, EQ-5D decreased in all categories, but in the case 2, it decreased in all categories except for pain/discomfort and anxiety/depression, but in the case 3, it decreased in all categories except anxiety/depression. There was no serious side effect after treatment of SBV pharmacopuncture. Conclusions : KM treatments including SBV pharmacopuncture may be effective for acute low back pain syndrome patients. However, randomized controlled trials are needed in the future to confirm the clinical effects of these interventions.