• 한국산업융합학회 논문집
• /
• 제24권4_1호
• /
• pp.377-385
• /
• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• Wind and Structures
• /
• 제32권1호
• /
• pp.71-80
• /
• 2021

In steel cable bridges, the use of magnetorheological (MR) dampers between butt cables is constantly increasing to dampen vibrations caused by rain and wind. The biggest problem in the actual applications of those devices is to launch a kind of appropriate algorithm that can effectively and efficiently suppress the perturbation of the tie through basic calculations and optimal solutions. This article discusses the optimal evolutionary design based on a linear and quadratic regulator (hereafter LQR) to lessen the perturbation of the bridges with cables. The control numerical algorithms are expected to effectively and efficiently decrease the possible risks of the structural response in amplification owing to the feedback force in the direction of the MR attenuator. In addition, these numerical algorithms approximate those optimal linear quadratic regulator control forces through the corresponding damping and stiffness, which significantly lessens the work of calculating the significant and optimal control forces. Therefore, it has been shown that it plays an important and significant role in the practical application design of semiactive MR control power systems. In the present proposed novel evolutionary parallel distributed compensator scheme, the vibrational control problem with a simulated demonstration is used to evaluate the numerical algorithmic performance and effectiveness. The results show that these semiactive MR control numerical algorithms which are present proposed in the present paper has better performance than the optimal and the passive control, which is almost reaching the levels of linear quadratic regulator controls with minimal feedback requirements.

• Smart Structures and Systems
• /
• 제29권4호
• /
• pp.617-624
• /
• 2022

A new intelligent adaptive control scheme was proposed that combines the control based on interference observer and fuzzy adaptive s-curve for flight path tracking control of unmanned aerial vehicle (UAV). The most important contribution is that the control configurations don't need to know the uncertainty limit of the vehicle and the influence of interference is removed. The proposed control law is an integration of fuzzy control estimator and adaptive proportional integral (PI) compensator with input. The rated feedback drive specifies the desired dynamic properties of the closed control loop based on the known properties of the preferred acceleration vector. At the same time, the adaptive PI control compensate for the unknown of perturbation. Additional terms such as s-surface control can ensure rapid convergence due to the non-linear representation on the surface and also improve the stability. In addition, the observer improves the robustness of the adaptive fuzzy system. It has been proven that the stability of the regulatory system can be ensured according to linear matrix equality based Lyapunov's theory. In summary, the numerical simulation results show the efficiency and the feasibility by the use of the robust control methodology.

• 한국기계가공학회지
• /
• 제20권11호
• /
• pp.43-51
• /
• 2021

A robust tracking controller design was developed for a rotary motion control system. The friction force versus the angular velocity was measured and modeled as a combination of linear and nonlinear components. By adding a model-based friction compensator to a nominal proportional-integral-derivative controller, it was possible to build a simulated control system model that agreed well with the experimental results. A zero-phase error tracking controller was selected as the feedforward tracking controller and implemented based on the estimated closed-loop transfer function. To provide robustness against external disturbances and modeling uncertainties, a disturbance observer was added in the position feedback loop. The performance improvement of the overall tracking controller structure was verified through simulations and experiments.

• Nuclear Engineering and Technology
• /
• 제55권8호
• /
• pp.2952-2965
• /
• 2023

Advanced reactors, such as Small Modular Reactors or existing Nuclear Power Plants, often use Field Programmable Gate Array (FPGA) based controllers in new Instrumentation and Control (I&C) system architectures or as an alternative to existing analog-based I&C systems. Compared to CPU-based Programmable Logic Controllers (PLCs), FPGAs offer better overall performance. However, programming functions on FPGAs can be challenging due to the requirement for a hardware description language that does not explicitly support the operation of real numbers. This study aims to implement the Reactor Trip (RT) functions of the existing analog-based Reactor Protection System (RPS) using FPGAs. The RT equations for Overtemperature delta Temperature and Overpower delta Temperature involve dynamic compensators expressed with the Laplace transform variable, 's', which is not directly supported by FPGAs. To address this issue, the trip equations with the Laplace variable in the continuous-time domain are transformed to the discrete-time domain using the Z-transform. Additionally, a new operation based on a relative value for the equation range is introduced for the handling of real numbers in the RT functions. The proposed approach can be utilized for upgrading the existing analog-based RPS as well as digitalizing control systems in advanced reactor systems.

• 대한방사선치료학회지
• /
• 제30권1_2호
• /
• pp.191-199
• /
• 2018

목 적 : 본 연구는 colloid gel(slime)을 자체 제작하여, 방사선치료에서 불규칙한 환자 체표면에 대한 보상체로 적용하기 위하여 유용성을 평가하고자 한다. 대상 및 방법 : 본 연구를 위하여 치료에 적합한 colloid gel을 자체적으로 제작하였고, 방사선 치료 적용 가능성 평가를 위해 네 가지 실험을 하였다. 치료 장비 및 CT 장비로는 Trilogy(Varian)와 CT(SOMATOM, Siemens)를 이용하였다. 첫 번째로 colloid gel의 조성에 따른 균질도를 EBT3 Film(RIT)을 이용하여 측정하였다. 두 번째는 colloid gel의 Hounsfield Unit(HU)값을 CRIS phantom과 Eclipse RTP(Eclipse 13.1, Varian) 및 CT 촬영을 이용하여 선량 측정 및 확인을 하였다. 세 번째로 colloid gel의 치료 기간 내 변형 및 변질을 검사하기 위하여 ion chamber(PTW-30013, PTW)를 이용하여 매일 3회씩, 2주간 측정하였다. 네 번째 실험은 자체 제작한 아크릴 팬텀을 이용하여 실제 치료와 유사한 환경에서 bolus, rice, colloid gel을 이용한 치료계획 및 측정된 선량 분포 비교하였고, 추가적으로 dose profile도 확인하였다. 결 과 : 첫 번째 실험에서 조성된 colloid gel case 1, 2, 3의 밀도는 각각 평균 $1.02g/cm^3$, $0.99g/cm^3$, $0.96g/cm^3$이었으며, 6 MV 및 9 MeV에서 측정된 균질도를 판단하였을 때 case 1이 표준편차 1.55, 1.98로 다른 case들에 비해 더 균질한 것으로 확인되었다. 두 번째 실험에서는 HU값은 case 1, 2, 3 평균 15 HU로 확인되었으며, 치료계획과 측정된 선량을 비교하였을 때 9, 12 MeV 모든 측정 위치에서 1 % 이내 차이를 보였으며, 6 MV는 두 측정 위치에서 -1.53 %, -1.56 % 차이로 전체 2 % 내의 오차를 보였다. 세 번째 실험에서는 2주 동안 측정하였을 때 colloid gel의 선량변화가 1 % 내외로 측정되었다. 네 번째 실험에서는 치료계획과 EBT3 film으로 측정된 결과를 비교하였을 때 6 MV에서는 bolus, rice 모두 비슷한 선량 차이를 보였으며, 9 MeV에서는 photon과 달리 colloid gel이 bolus, rice와 비교하여 선량 차이가 적게 나는 것을 확인하였다. Dose profile 면에서도 colloid gel이 bolus, rice보다 균일한 dose 분포를 보였다. 결 론 : 본 연구에서 방사선치료를 위해 제작된 colloid gel의 밀도는 $1.02g/cm^3$로 물의 밀도와 비슷하며, 방사선치료 과정 동안 변질 및 변형이 확인되지 않았다. Colloid gel 제작 시 밀도에 유의를 해야 하지만, bolus, rice보다 환자의 체표면에 대한 충분한 보상을 통해 선량을 균일하게 전달할 수 있고, 저가에 제작을 할 수 있다는 점에서도 충분한 장점이 있다. 앞으로 임상적용을 위한 추가적인 실험 및 연구를 통해 방사선치료에 적용할 수 있을 것으로 사료된다.

• 한국통신학회논문지
• /
• 제32권9C호
• /
• pp.905-912
• /
• 2007

본 논문에서는 OFDM 기반 무선 LAN 시스템에서 긴 훈련심볼을 이용하는, 시간동기 오차의 영향이 고려된 IQ imbalance 추정 및 보상 기법을 제안한다. 기존의 긴 훈련심볼을 이용한 IQ imbalance 보상 기법은 시간동기 오차에 민감한 구조를 갖기 때문에 시간동기 오차가 필연적인 실제 시스템에서는 심각한 성능 저하를 보인다. 본 논문에서는 시간동기 오차로 인해 발생하는 위상회전을 상쇄시킬 수 있는 새로운 criterion을 정의하고, 이에 따른 IQ imbalance 추정 및 보상 기법을 제안한다. 제안된 기법은 시간동기 오차가 존재할 경우에도 IQ imbalance 의 영향을 이상적인 경우 대비 최대 0.2dB 이하로 보상할 수 있으며, IEEE 802.11a 시스템의 54Mbps 전송모드에 적용하였을 경우 기존 기법에 비해 약 4.3dB의 성능 이득을 보인다. 제안된 기법을 이용한 IQ imbalance 추정 및 보상단은 Verilog HDL을 이용하여 하드웨어 설계 및 검증 되었으며, 0.18um CMOS 공정을 이용하여 합성한 결과, 약 75K gates 와 6K bits의 메모리로 구현되었다.

• 한국태양에너지학회 논문집
• /
• 제32권spc3호
• /
• pp.235-244
• /
• 2012

This paper presents a design and simulation of bi-directional DC/DC boost converter for a fuel cell system. In this paper, we analyze the equivalent model of both a boost converter and a buck converter. Also we propose the controller of bi-directional DC-DC converter, which has buck mode of charging a capacitor and boost mode of discharging a capacitor. In order to design a controller, we draw bode plots of the control-to-output transfer function using specific parameters and incorporate proper compensator in a closed loop. As a result, it has increased PM(Phase Margin) for better dynamic performance. The proposed bi-directional DC-DC converter's 3pole-2zero compensation method has been verified with computer simulation and simulation results obtained demonstrates the validity of the proposed control scheme.

• 한국철도학회논문집
• /
• 제15권4호
• /
• pp.357-363
• /
• 2012

본 논문에서는 단상PWM컨버터 차량의 새로운 운전방식에 대해 기술하였다. 최근의 전기차량은 PWM 컨버터를 채택함으로써 그 이전의 차량들에 비하여 역률을 1.0에 가깝도록 유지할 수 있게 되었다. 그러나 이들 차량은 컨버터 제어방식의 비교적 간단한 수정을 통하여 진상 역률 영역에서의 운전이 가능한데, 이러한 특징은 차량 자체만으로는 큰 의미가 없을지 모르나 급전계통과 연계하여 검토하는 경우 선로의 무효전력 손실을 보상함으로써 급전선로의 유효전력 손실을 감소시키고 전압 분포를 개선하는 효과를 나타내게 된다. 이동형 보상장치가 될 수 있다는 특징으로 무효전력 보상을 위해 일반적으로 검토되는 SVC와 비교해도 장점을 가지게 된다. PWM컨버터차량의 진상운전 조건 및 관련식의 유도와 함께 이러한 방식을 적용하기 위한 새로운 역률 제어 알고리즘을 제시하였다. SIMULINK 모델을 사용한 모의를 통하여 제시된 방법의 실 적용 가능성을 검토하였으며 만족할 만한 결과를 얻을 수 있었다.

• 전력전자학회논문지
• /
• 제18권3호
• /
• pp.232-239
• /
• 2013

This paper proposes an improved stator flux estimator through ensuring conventional PLPF to act as a pure integrator for sensorless control of induction motors. Conventional PLPF uses the estimated synchronous speed as a cut-off frequency and has the gain and phase compensators. The gain and phase compensators are determined on the assumption that the estimated synchronous angular speed is coincident with the real speed. Therefore, if the synchronous angular speed is not same as the real speed, the gain and phase compensation will not be appropriate. To overcome the problem of conventional PLPF, this paper analyzes the relationship between the synchronous speed error and the phase lag error of the stator flux. Based on the analysis, this paper proposes the synchronous speed error compensation scheme. To achieve a start-up without speed sensor, the current model is used as the stator flux estimator at the standstill. When the motor starts up, the current model should be switched into the voltage model. So a stable transition between the voltage model and the current model is required. This paper proposes the simple transition method which determines the initial values of the voltage model and the current model at the transition moment. The validity of the proposed schemes is proved through the simulation results and the experimental results.