• KEPCO Journal on Electric Power and Energy
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• v.6 no.3
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• pp.279-284
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• 2020

This paper presents the conceptual design of a cooperative control with Energy Management System (EMS) and Distribution Management System (DMS). This control enables insufficient reactive power reserve in a power transmission system to be supplemented by surplus reactive power in a power distribution system on the basis of the amount of the needed reactive power reserve calculated by the EMS. This can be achieved, because increased numbers of microgrids with distributed energy resources will be installed in the distribution system. Furthermore, the DMS with smart control strategy by using surplus reactive power in the distribution system of the area has been gradually installed in the system as well. Therefore, a kind of hierarchical voltage control and cooperative control scheme could be considered for the effective use of energy resources. A quantitative index to evaluate the current reactive power reserve of the transmission system is also required. In the paper, the algorithm for the whole cooperative control system, including Area-Q Indicator (AQI) as the index for the current reactive power reserve of a voltage control area, is devised and presented. Finally, the performance of the proposed system is proven by several simulation studies.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.2
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• pp.124-129
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• 2005

This paper presents an advanced method for an initial pole position estimation of a Permanent Magnet Linear Synchronous Motor(PMLSM) that has an accurate incremental encoder for servo applications but does not have Hall sensors as a magnetic pole sensor. By appropriately using the secant method as a numerical method the proposed algorithm finds either of two zero force positions and then the correct d-axis by applying a q-axis test current. It only requires the tuned current controller and the relative position information md so it can be simply applicable to a rotary PMSM. The experimental results show the validity of the proposed method, which has an excellent performance with respect to an accurate pole position estimation under the minimal moving distance(average of about 85㎛) during the estimation process.

• Journal of Power Electronics
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• v.2 no.2
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• pp.146-153
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• 2002

this paper presents an implementation of digital control system of speed sensorless for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The problem of DTC for high-dynamic performance RSM drive is generating a nonlinear torque due to a saturated nonlinear inductance curve with various load currents. The control system consists of stator flux observer, compensating inductance look-up table, rotor position/speed/torque estimator, two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source unverter, and TMS320C31 DSP controller. The stator flux observer is based on the combined voltage and current model with stator flux feedback adapitve control that inputs are the compensated inductances, current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor position is estimated rotor speed is determined by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operation area. It does not requrie the knowledge of any montor paramenters, nor particular care for moter starting, In order to prove the suggested control algorithm, we have simulation and testing at actual experimental system. The developed sensorless control system is showing a good speed control response characterisitic result and high performance features in 20/1500 rpm with 1.0Kw RSM having 2.57 ratio of d/q reluctance.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.1
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• pp.1-8
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• 1996

Recently, much attention has been paid to problems which is concerned with voltage instability phenomena and much works on these phenomena have been made. In this paper, by substituting d $P_{k}$ d $e_{k}$ ( $v^{\rarw}$= e +j f) for $P_{k}$ in conventional load flow, direct method for finging the limit of voltage stability is proposed. Here, by using the fact that taylor se- ries expansion in .DELTA. $P_{k}$ and .DELTA. $Q_{k}$ is terminated at the second-order terms, constraint equation (d $P_{k}$ d $e_{k}$ =0) and power flow equations are formulated with new variables .DSLTA. e and .DELTA.f, so partial differentiations for constraint equation are precisely calculated. The fact that iteratively calculated equations are reformulated with new variables .DELTA.e and .DELTA.f means that limit of voltage stability can be traced precisely through recalculation of jacobian matrix at e+.DELTA.e and f+.DELTA.f state. Then, during iterative process divergence may be avoid. Also, as elements of Hessian mat rix are constant, its computations are required only once during iterative process. Results of application of the proposed method to sample systems are presented. (author). 13 refs., 11 figs., 4 tab.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.247-250
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• 2004

Goldschmidt 알고리즘에 의한 부동소수점 1.f2의 역수는 q=NK1K2....Kn (Ki=1+Aj, j=2i)이다. 본 논문에서는 N과 A 값을 1.f2의 값에 따라서 선정하고 Aj의 값이 유효자리수의 반이하 값을 가지면 연산을 종료하는 개선된 Goldschmidt 부동소수점 역수 알고리즘을 제안한다. 1.f2가 1.01012보다 작으면 N=2-1.f2, A=1.f2-1로 하며, 1.01012보다 크거나 같으면 N=2-0.lf2, A=1-0.lf2로 한다. 한편 Goldschmidt 알고리즘은 곱셈을 반복해서 수행하므로 계산 오류가 누적이 된다. 이러한 누적 오류를 감안하면 배정도실수 역수에서는 2-57, 단정도실수 역수에서는 2-28의 유효자리수까지 연산해야 한다. 따라서 Aj가 배정도실수 역수에서는 2-29, 단정도실수 역수에서는 2-14 보다 작아지면 연산을 종료한다. 본 논문에서 제안한 개선한 Goldschmidt 역수 알고리즘은 N=2-0.1f2, A=1-0.lf2로 계산하는 종래 알고리즘과 비교하여 곱셈 연산 회수가 배정도실수 역수는 22%, 단정도실수 역수는 29% 감소하였다. 본 논문의 연구 결과는 테이블을 사용하는 Goldschmidt 역수 알고리즘에 적용해서 연산 시간을 줄일 수 있다.

• Journal of Power Electronics
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• v.15 no.2
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• pp.411-418
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• 2015

In this paper, a new method for the online estimation of equivalent series resistances (ESR) of the DC-link capacitors in induction machine (IM) drive systems with a front-end diode rectifier is proposed, where the ESR estimation is conducted during the regenerative operating mode of the induction machine. In the first place, a regulated AC current component is injected into the q-axis current component of the induction machine, which induces the current and voltage ripple components in the DC-link. By processing these AC signals through digital filters, the ESR can be estimated by a recursive least squares (RLS) algorithm. To acquire the AC voltage across the ESR, the DC-link voltage needs to be measured at a double sampling frequency. In addition, the ESR current is simply reconstructed from the stator currents and switching states of the inverter. Experimental results have shown that the estimation error of the ESR is about 1.2%, which is quite acceptable for condition monitoring of the capacitor.

• Journal of Power Electronics
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• v.17 no.3
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• pp.744-755
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• 2017

With the high penetration of various sustainable energy sources, the control and protection of Microgrids has become a challenging problem considering the inherent current limitation feature of inverter-based Distributed Generators (DGs) and the bidirectional power flow in Microgrids. In this paper, a hybrid control and protection scheme is proposed, which combines the traditional inverse-time overcurrent protection with the biased differential protection for different feeders with different kinds of loads. It naturally accommodates various control strategies such as P-Q control and V-f control. The parameter settings of the protection scheme are analyzed and calculated through a fast Fourier transform algorithm, and the stability of the control strategy is discussed by building a small signal model in MATLAB. Different operation modes such as the grid-connected mode, the islanding mode, and the transitions between these two modes are ensured. A Microgrid model is established in PSCAD and the analysis results show that a Microgrid system can be effectively protected against different faults such as the single phase to ground and the three phase faults in both the grid-connected and islanded operation modes.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06c
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• pp.105-108
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• 2010

쌍방향으로 질문과 답변을 하는 커뮤니티 기반의 지식검색서비스에서는 질의를 통해 원하는 답변을 얻을 수 있지만, 수많은 사용자들이 참여함에 따라 방대한 문서 속에서 검증된 문서를 찾아내는 것은 점점 더 어려워지고 있다. 지식검색서비스에서 기존 연구는 사용자들이 생성한 데이터 즉 추천수, 조회수 등의 비텍스트 정보를 이용하거나 답변의 길이, 자료첨부, 연결어 등의 텍스트 정보 이용하여 전문가를 식별하거나 문서의 품질을 평가하고, 이를 검색에 반영하여 검색성능을 향상시키는 데 활용했다. 그러나 비텍스트 정보는 질의/응답의 초기에 사용자들에 의해 충분한 정보를 확보할 수 없는 단점이 제기 되며, 텍스트 정보는 전체의 문서를 답변의 길이, 자료 첨부등과 같은 일부요인으로 판단해야하기 때문에 품질평가의 한계가 있다고 볼 수 있겠다. 본 논문에서는 이러한 비텍스트 정보와 텍스트 정보의 문제점을 개선하기 위한 품질평가 알고리즘을 제안한다. 제안된 알고리즘을 통한 품질지수는 텍스트/비텍스트 정보와 소셜 네트워크 사용자 중앙성을 고려하여 질문에 적합하고 신뢰성 있는 답변을 랭킹화 함으로써 지식검색문서를 분별하는 지표가 되며, 이는 지식검색서비스의 성능향상에 기여를 할 수 있을 것으로 기대된다.

• Journal of Drive and Control
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• v.12 no.3
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• pp.11-17
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• 2015

An intelligent deburring control (IDC) device is used to control the constant force for a deburring tool mounted on the end-effector of a robotic arm. This device maintains a constant contact force between the deburring tool and the workpiece in order to provide a good deburring performance. In this paper, we build a mathematical model in Matlab/Simulink to estimate the force control mechanism of the pneumatic system for the IDC device. The Simulink blocks are built for each separate part and are linked into an integrated simulation system. Such a model also relies on the effects of the flow rate through the valve, air compressibility in the cylinder, and time delay in the pressure valve. The results of the simulation are compared to a simple experiment in which convenient math modeling is performed. These results are then used to optimize the mechanical design and to develop a force control algorithm for the pneumatic cylinder.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.18 no.2
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• pp.75-84
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• 2008

Recently, the straightforward CRT-RSA was shown to be broken by fault attacks through many experimental results. In this paper, we analyze the fault attacks against CRT-RSA and their countermeasures, and then propose a new fault infective method resistant to the various fault attacks on CRT-RSA. In our CRT-RSA algorithm, if an error is injected in exponentiation with modulo p or q, then the error is spreaded by fault infective computation in CRT recombination operation. Our countermeasure doesn't have extra error detection procedure based on decision tests and doesn't use public parameter such as e. Also, the computational cost is effective compared to the previous secure countermeasures.