• Journal of Power Electronics
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• 제18권3호
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• pp.714-722
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• 2018

This paper presents a wide-range speed control scheme of brushless DC (BLDC) motors based on a hall sensor with separated low- and normal-speed controllers. However, the use of the hall sensor signal is insufficient to detect motor speed in the low-speed region because of low sensor resolution and time delay. In the proposed method, a micro-stepping current control method according to the torque angle variation is presented. In this mode, the motor current frequency and rotating angle are determined by the reference speed without the actual speed fed by the hall sensor. The detected torque angle is used to adjust the current value in a limited band to control the current value in accordance with the load. The torque angle is detected exactly at the changing point of the hall sensor signal. The rotor can follow the rotating flux with the variable torque angle. In a normal speed range, the conventional vector control scheme is used to control the motor current with a PI speed controller using the hall sensor. The torque characteristics are analyzed on the basis of the back EMF and current shape. To adopt the vector control scheme, the continuous rotor position is estimated by the measured speed and hall sensor position. At the mode changing point between low and normal speed range, the proper initial current command and reference rotor position are calculated. The calculated current command can reduce the torque ripple during transient mode. The proposed method is simple but effective in extending the speed control range of a conventional BLDC motor with hall sensor without the need for a high-resolution encoder. The effectiveness of the proposed method is verified by various experiments on a practical BLDC motor.

• Advances in Energy Research
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• 제1권2호
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• pp.97-106
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• 2013

This study designs and tests a photovoltaic system with distributed maximum power point tracking (DMPPT) methodology using a field programmable gate array (FPGA) controller. Each solar panel in the distributed PV system is equipped with a newly designed DC/DC converter and the panel's voltage output is regulated by a FPGA controller using PI control. Power from each solar panel on the system is optimized by another controller where the quadratic maximization MPPT algorithm is used to ensure the panel's output power is always maximized. Experiments are carried out at atmospheric insolation with partial shading conditions using 4 amorphous silicon thin film solar panels of 2 different grades fabricated by Chi-Mei Energy. It is found that distributed MPPT requires only 100ms to find the maximum power point of the system. Compared with the traditional centralized PV (CPV) system, the distributed PV (DPV) system harvests more than 4% of solar energy in atmospheric weather condition, and 22% in average under 19% partial shading of one solar panel in the system. Test results for a 1.84 kW rated system composed by 8 poly-Si PV panels using another DC/DC converter design also confirm that the proposed system can be easily implemented into a larger PV power system. Additionally, the use of NI sbRIO-9642 FPGA-based controller is capable of controlling over 16 sets of PV modules, and a number of controllers can cooperate via the network if needed.

• 한국콘텐츠학회논문지
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• 제21권6호
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• pp.51-61
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• 2021

사물인터넷과 빅데이터 그리고 인공지능으로 상징되는 4차 산업혁명시대에 다양한 임베디드 디바이스가 기하급수적으로 증가하고 있다. 이러한 디바이스는 낮은 사양임에도 통신 기능을 보유하고 있어서 개인 정보유출 가능성이 높아지고 있으며 보안의 위협 또한 증가하고 있다. 임베디드 디바이스는 하드웨어부터 네트워크를 통한 서비스까지 대부분의 단계에서 보안 이슈가 발생 가능하다. 또한 저사양과 저전력 등 자원 제약의 특징을 가지며 관련 기술의 표준화가 이루어지지 않은 상황이므로 일반적인 보안 기법을 적용하기에는 어려움이 따른다. 본 연구에서는 임베디드 디바이스에 SDN 적용 시 취약점과 발생 가능한 문제점과 고려사항을 제시하였다. 하드웨어 관점에서 와이파이 칩과 블루투스의 문제, 오픈플로우 구현상의 문제, SDN 컨트롤러 및 구조적 특성에 따른 사례를 고려하여 제시하였다. SDN은 데이터 플레인과 제어 플레인을 각각 분리하여 둘 사이에 표준화된 인터페이스를 제공하여 통신을 효율적으로 제어할 수 있으며 빠른 변화에 대응하기 어려운 기존 네트워크 기술에서의 보안의 한계에 대응할 수 있다.