Switching Losses Minimization Method for EV Inverter with Individual Sequential Gating of Parallel-Connected Switches

Im Seong-Hwan,Park Gwangmin,Kim Jae-Heon,Gu Bon-Gwan 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.6

To achieve high output currents at a low cost, semiconductor switch modules are frequently operated in parallel. The simplest way to drive the parallel switching module is to synchronize all on and off gate signals of each switch. Individual control is used in this article to reduce switching losses by applying a short delay time to each switching signal based on current level. Experiments are performed to compare the individual control method and the synchronization control method, and the optimal switching combination with the lowest switching loss is proposed. This proposed switching method is simulated by applying to the Urban Dynamometer Driving Schedule and the Highway Fuel Economy Test, both of which are energy effi ciency calculation standards in electric vehicles. The results of the analysis demonstrate the feasibility and practicality of the proposed individual switching method.

솔리드 스테이트 스위치를 이용한 AC/AC 전압 변환기 설계

엄기홍 한국지식정보기술학회 2012 한국지식정보기술학회 논문지 Vol.7 No.1

Conventional power transformer adopted AC/DC and DC/AC converters in order to transform an AC voltage signal to another AC voltage signal. Recently, a few studies have been done on the direct conversion of an AC voltage to another AC voltage. In this paper, we present a digital controller system which can be applied to intelligent AC to AC voltage conversion to be used for an automatic voltage control by using only few transistors, replacing conventional electrical power transformers with solid state switches. We have designed an AC to AC voltage converter by adopting solid state switches in order to obtain an AC output power. It was possible to obtain highly efficient AC to AC converter by adopting AC power switches for pulse-width modulator(PWM). By introducing only few solid-state switches, high power solid state devices and networks of power distribution. The P-spice simulation showed the effective output of our converter we designed.

PL 판정을 위한 저압용 스위치의 소손 패턴 해석기법

최충석 한국화재소방학회 2010 한국화재소방학회논문지 Vol.24 No.5

The purpose of this study is to examine the structure and heat generation mechanism of low voltage switches used to turn on or off the power supply to an indoor lighting system and investigate how the fixtures and movable contacts of the switches are damaged depending on the types of energy sources in order to secure the judgment base for expected PL disputes. Based on the Korean Standard (KS) testing method for incombustibility, this study applied a general flame to the switch. In addition,current was supplied to the switch using the PCITS (Primary Current Injection Test System). The ambient temperature and humidity were maintained at 22 ± 2oC and 40~60% respectively while performing the test. It is thought that the switch generated heat due to a defective connection of the wire and clip, insulation deterioration and defective contact of the movable contact, etc. The surface of the switch damaged by the general flame was uniformly carbonized. When the flame source was removed,the fire on the switch was extinguished naturally. From the result obtained by disassembling the switch carbonized by the general flame, it could be seen that fixtures and movable contacts remained in comparatively good shape but the enclosure, clip support, movable contact, indicating lamp, etc. showed carbonization and discoloration. In the case of the switch damaged by overcurrent, the clip connecting the wires, clip support, etc. showed almost no trace of damage, but the fixtures, movable contact, indicating lamp, etc. were severely carbonized. That is, the sections with high contact resistance were intensively damaged and showed a damage pattern indicating that carbonization progressed from the inside to the outside. Therefore, it is possible to judge the initial energy source by analyzing the characteristics of the carbonization pattern and the metal fixtures of damaged switches. 본 연구에서는 옥내 조명 설비의 전원을 ON/OFF 하기 위해 사용되는 저압용 스위치의 구조 및 발열메커니즘을 제시하고, 에너지원의 종류에 따라 스위치의 고정금구 및 가동 접점 등의 소손패턴을 제시함으로써 향후 예상되는 PL 분쟁의 판단 근거를 확보하는데 있다. 스위치에 인가된 일반 화염은 한국산업규격(KS)의 난연성 시험 방법을 적용하였다. 또한 스위치에 공급된 전류는 대전류공급장치(PCITS)를 이용하였다. 실험이 진행될 때 주위의 온도는 22 ± 2oC, 습도는 40~60%를 유지시켰다. 스위치의 발열은 배선과 클립의 접속 불량, 가동 접점의 절연 열화 및 접촉 불량 등에 의해서 생성되는 것으로 판단된다. 일반 화염에 의해 소손된 스위치는 표면이 균일하게 탄화되었으며, 화원을 제거하면 자연 소화되었다. 일반화염에 의해 탄화된 스위치를 분해한 결과 고정금구 및 가동 접점 등은 비교적 양호한 형태를 보였으나외함, 클립 지지대, 가동 접점, 표시램프 등에서 탄화 및 변색을 확인할 수 있었다. 과전류에 의해 소손된스위치는 배선을 연결하는 클립 및 클립 지지대 등은 소손의 흔적이 거의 없으나 고정금구, 가동 접점,표시 램프 등은 심하게 탄화되었다. 즉 접촉 저항이 큰 부분에서 집중적으로 소손되었고 내부에서 외부로탄화가 진행되는 패턴을 나타냈다. 따라서 소손된 스위치의 탄화 패턴 및 금속 금구류의 특성을 분석하면최초의 에너지원 판정이 가능하다.

초도감사의 감사보수 할인 현상에 대한 실증연구

이상철,박재완,정갑수 韓國公認會計士會 2011 회계·세무와 감사 연구 Vol.53 No.2

본 연구에서는 한국의 상장기업을 대상으로 초도감사의 경우 감사보수 할인 현상이 존재하는지와 감사인 교체 유형별로 초도감사보수 할인에 차이가 있는지 검증하였다. 2000년부터 2006년까지 한국증권선물거래소 유가증권시장에 상장된 12월 결산 비금융기업 가운데 감사보수자료를 입수할 수 있는 1,436개 기업-연 자료를 최종 분석대상으로 선정하였다. 주요 연구결과는 다음과 같다. 전체기업과 회계법인을 교체한 기업을 대상으로 실시한 분석 모두에서 감사보수 변화에 영향을 미치는 요인을 통제한 후에도, 계속감사기업보다 초도감사기업에서 감사보수변화율이 낮게 나타났다. 따라서 초도감사의 경우 감사보수 할인 현상이 존재한다는 사실을 알 수 있다. BIG4에서 BIG4 또는 non-BIG4에서 non-BIG4와 같이 동일한 등급으로 감사인을 교체한 기업(수평교체집단)에 대한 분석에서는 초도감사여부가 감사보수변화율에 유의적인 음의 영향을 미치는 것으로 나타났다. BIG4에서 non-BIG4로 감사인을 교체한 기업(하향교체집단)에 대한 분석에서, 초도감사여부는 감사보수변화율에 유의적인 음의 영향을 미치며, 그 영향의 크기가 수평교체집단의 경우보다 큰 것으로 조사되었다. non-BIG4에서 BIG4로 감사인을 교체한 기업(상향교체집단)을 대상으로 분석한 결과, 초도감사여부는 감사보수변화율에 유의적인 영향을 미치지 않는 것으로 나타났다. 이러한 분석결과는 감사인 교체로 발생하는 감사보수의 차이를 통제한 후에도, 초도감사보수 할인 현상이 존재한다는 사실을 지지하는 것으로 볼 수 있다. Initial audit fee discounting, frequently termed “low-balling”, means that auditors lowball the fees for initial-year audits. The practice of setting audit fees below costs on initial audit engagements has been the subject of a number of studies because of its potential impact on auditor independence. The Korean Institute of Certified Public Accountants(KICPA) Code of Professional Conduct says that the practice of setting initial audit fees significantly less than predecessor or other auditors' fees might be considered impairment of auditor independence. The investigation of initial-year audit fee cutting not only can be quite helpful for facilitating future studies on the effects of low-balling, but also can provide regulatory agencies with validating the regulations on audit fees. However, because most of Korean prior studies examined the initial audit fee discounting using the level variable model, they didn't get around the omitted variable bias. In this respect, using the difference variable model in order to resolve the problem of correlated omitted variable bias, we need to investigate whether initial audit fees are discounted by audit firms. Furthermore, after controlling the effect of auditor change on audit quality, we can afford to examine the fee cutting on initial audit engagements. To address our research questions, we empirically test whether there exists a significant reduction in audit fees on initial audit engagements in Korean audit market, and then examine whether the extent of discounting initial audit fees varies with types of auditor switches. In addition, we investigate the effect of initial audit contracts on audit time and managers' earnings management. Our final data consist of 1,436 Korean listed firm-year observations from the year 2000 to 2006 which are identified using sample selection criteria such as non-financing firms, fiscal year and data availability. We identify 159 firm-year observations which represent those switching auditors during the sampling period. Using the difference variable regression model, we investigate the fee cutting on initial audit engagements. In our model, the dependent variable is defined as the difference in audit fees between current audit fees and previous year's audit fees divided by the prior year's audit fees. The independent variable is a dummy variable indicating whether each observation is on the initial audit engagement or not; 1 for the firms if observation is on the initial audit engagements, 0 otherwise. In order to control the effects of variables that may affect the change in audit fees, we regard the changes of total assets, account receivables, inventory, foreign sales, return on investment and debt ratio as control variables. We also introduce industry and year dummy variables to control the difference in audit fees due to the type of industry in which firms are listed and the year in which observations are. We empirically test our first hypothesis and find that a significant reduction in audit fees for initial audit engagements exists, compared with audit fees of continuing audit engagements. Using a subgroup sample of clients switching their auditors, we classify types of auditor switches into the following four categories: auditor switches from Big to Big, from Big to non-Big, from non-Big to Big, and from non-Big to non-Big auditors. For firms switching between auditors of the same type such as auditor switches from Big to Big and from non-Big to non-Big auditors, we find that there is a significant fee discount on initial audit contracts. For firms switching from Big to non-Big auditors, we find that there exist significant fee discounts on initial audit engagements and the extent of fee discounts is significantly larger than that of firms switching between auditors of the same type. However, we cannot find a significant fee reduction on initial audit contracts for firms switching from non-Big to Big auditors. As robustness tests, we use the audit fees per hour and change in audit time as dependent variables instead of the difference in audit fees. The dummy variable which represents initial audit engagements has a significant negative association with audit fees per hour but a significant positive relationship with the difference in audit time. These results imply that although auditors increase audit time, auditors lowball the fees for initial-year audits. As additional robustness check, we find that the dummy variable which represents initial audit contracts has no significant associations with managers' earnings management. These robustness checks confirm our hypotheses and test results that there exists a significant reduction in fees on initial audit engagements in Korean audit market and the extent of discounting initial audit fees varies with types of auditor switches. While previous Korean literatures investigated the initial audit fee discounting using the level variable model, this study examines low-balling using the difference variable model, in result our study expands previous literatures investigating initial-year audit fee cutting in Korean audit market. Our findings also can help regulatory agencies validate the audit fee regulations.

Optimal Service Restoration and Adaptive Switching of Tie Switches Method of Distributed Self-healing Control in Distribution Systems

Chen Chun,Liu ShengPeng,Cao Yijia,Tang Liangxing,Li Yong 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.5

Because the distribution networks distribute electric energy to customers, has many equipment, a wide range and complex network structure, various failures are prone to occur. Rapid failure self-healing is the key means to improve the reliability of power supply in distribution network. This paper proposes a method for fast service restoration of out-of-service areas without failures based on peer-to-peer (P2P) communication of intelligent terminals. It uses distributed intelligent terminal units as the algorithm carrier and a P2P communication network composed of loop Ethernet. It can accurately distinguish the normal state and the failure state based on the generalized Kirchhoff Current Law setting and realize the failure location and isolation without the delay setting problem of the three-stage current protection. In order to verify its effectiveness, a 0.4 kV dynamic simulation model was developed, and scenarios including different types of switches and different topologies are established. The experimental results show that, unlike other algorithms, such as building a convex model, then, using various intelligent algorithms to solve it, the proposed method can complete the load transfer more quickly, whether switches are all circuit breakers, or partly circuit breakers and partly load switches. In the former case, service restoration can be completed within 2.4 s, faster than other centralized or distributed methods, even when the failure occurs in the worst point, as is shown in the results of test scenario 1. In addition, in the latter case, service restoration can be achieved at least within 4.2 s.

New Three-Phase Multilevel Inverter with Shared Power Switches

Hew Wooi Ping,Nasrudin Abd. Rahim,Jafferi Jamaludin 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5

Despite the advantages offered by multilevel inverters, one of the main drawbacks that prevents their widespread use is their circuit complexity as the number of power switches employed is usually high. This paper presents a new multilevel inverter topology with a considerable reduction in the number of power switches used through the switch-sharing approach. The fact that the proposed inverter applies two bidirectional power switches for sharing among the three phases does not prevent it from producing seven levels in the line-to-line output voltage waveforms. A modified scheme of space vector modulation via the application of virtual voltage vectors is developed to generate the PWM signals of the power switches. The performance of the proposed inverter is investigated through MATLAB/SIMULINK simulations and is practically tested using a laboratory prototype with a DSP-based modulator. The results demonstrate the satisfactory performance of the inverter and verify the effectiveness of the modulation method.

포화자심을 이용한 하프브릿지 컨버터의 소프트스위칭에 관한 연구

Kang , Chan-Ho,Kim , Hee-Jun,Harada, Koosuke,Sakamoto, Hiroshi 대한전자공학회 2002 電子工學會論文誌-SC (System and control) Vol.39 No.6

본 논문은 하프브릿지 컨버터와 포화자심으로 구성되는 간단한 회로에 의하여 소프트스위칭이 가능한 새로운 회로방식을 제안한다. 본 방식에서는 컨버터의 출력단자와 병렬로 각형의 자화특성을 갖는 포화인덕터를 결합하여 컨버터의 온시간과 인덕터의 불포화기간을 일치시킨다. 2개의 MOSFET 스위치에는 짧은 데드타임을 설정하여 그 기간에 자심의 포화인덕턴스와 스위치의 기생용량 성분에 의한 공진을 일으켜 소프트스위칭을 실현시킨다. 또한 전원 전압의 변동에 대처하기 위해 반도체와 선형인덕터를 가지고 자심의 동작을 모의한 새로운 실용회로를 제안한다. 본 논문에서는 포화자심의 모델링의 방법을 통하여 소프트스위칭의 원리를 해석하고 1.25kW의 컨버터에 대한 실험에 의해 그 타당성을 확인하였다. A method of soft switching in the half bridge converter using a small saturable core is presented. For the soft switching, a small dead time of both switch off is made in a pair of MOSFET switch. The saturable core is of rectangular magnetization characteristics and the core flux swings from the minus to the plus saturation during ON time of the switch. The soft switching is realized in dead time by a resonance between the saturating inductance of the core and the stray capacitance of MOSFET. As an extension of this concept, instead of the saturable core, we propose a new soft switching circuit using a linear inductance and two switches, which is especially suitable for regulating the output and also for high frequency switching. A theoretical principle of soft switching presented here was confirmed by experiments on a half bridge converter of 1.25 KW.

New Three-Phase Multilevel Inverter with Shared Power Switches

Ping, Hew Wooi,Rahim, Nasrudin Abd.,Jamaludin, Jafferi The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5

Despite the advantages offered by multilevel inverters, one of the main drawbacks that prevents their widespread use is their circuit complexity as the number of power switches employed is usually high. This paper presents a new multilevel inverter topology with a considerable reduction in the number of power switches used through the switch-sharing approach. The fact that the proposed inverter applies two bidirectional power switches for sharing among the three phases does not prevent it from producing seven levels in the line-to-line output voltage waveforms. A modified scheme of space vector modulation via the application of virtual voltage vectors is developed to generate the PWM signals of the power switches. The performance of the proposed inverter is investigated through MATLAB/SIMULINK simulations and is practically tested using a laboratory prototype with a DSP-based modulator. The results demonstrate the satisfactory performance of the inverter and verify the effectiveness of the modulation method.

높은 격리도와 고속 스위칭의 PIN 다이오드 스위치

주인권,염인복,박종흥,Ju Inkwon,Yom In-Bok,Park Jong-Heung 한국전자파학회 2005 한국전자파학회논문지 Vol.16 No.2

직렬 PIN 다이오드 스위치의 격리도는 PIN 다이오드의 병렬 커패시턴스에 의해 제한을 받으며, 스위치 구동회로는 PIN 다이오드 스위치의 스위칭 속도를 제한한다. 이런 문제를 극복하기 위해, 병렬 공진 인턱턴스와 TTL 호환의 스위치 구동회로가 적용된 높은 격리도와 고속 스위칭의 PIN 다이오드 스위치를 제안하였다. 3 GHz PIN 다이오드 스위치의 측정 결과, 1 GHz의 주파수 대역폭, 1.5 dB 이내의 삽입 손실, 65 dB의 격리도, 15 dB 이상의 반사 손실 그리고 30 ns 이내의 스위칭 속도를 나타내었다. 특히, 병렬 공진 인덕턴스를 사용한 3 GHz스위치는 15 dB의 격리도 향상을 나타내었다. The isolation of the series PIN diode switch is restricted by the parallel capacitance of PIN diode and the switch driver circuit limits switching speed of PIN diode switch. To overcome these problems, a high isolation and high switching speed Pin diode switch is proposed adapting the parallel resonant inductance and TTL compatible switch driver circuit. The measurement results of the 3 GHz PM diode switch show 1 GHz frequency band, less than 1.5 dB insertion loss, 65 dB isolation, more than 15 dB return loss and less than 30 ns switching speed. In particular the 3 GHz PIN diode switch using the parallel resonant inductance exhibits the improvement of isolation by 15 dB.

Investigation on Switching Structure Material Selection for RF-MEMS Shunt Capacitive Switches Using Ashby, TOPSIS and VIKOR

Deepankar Deshmukh,Mahesh Angira 한국전기전자재료학회 2019 Transactions on Electrical and Electronic Material Vol.20 No.2

This paper utilizes three material selection methodologies to select the most promising material for switching structure of RF-MEMS shunt capacitive switches. The material should be selected such that RF-MEMS capacitive switches should have low pull-in voltage, low RF loss, high thermal conductivity and maximum displacement of the beam. For this purpose, the concerned material indices are as follows: low value of Young’s modulus, low electrical resistivity, high thermal conductivity and high fracture strength. Following Ashby, TOPSIS and VIKOR method were used to select the best material. The results obtained from these methods show good correlation. The end results suggest that gold and copper are the most suitable materials for RF-MEMS switches.