• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.508-513
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• 2014

Heavy load start but light load operation is a common case in practical drive applications. When an induction motor is employed for such applications, its rated power is usually chosen according to the heavy load start. Then, during light load operation, its efficiency and power factor are low. To solve this problem, it is proposed to adjust the motor windings from the startup to the normal operation conditions. In this paper, arrangement of the adjustable windings is introduced, air gap field with different windings is investigated, and steady state operation performance under various loads is examined. It can be seen that by using proper winding arrangement both startup and operation performances are satisfactory.

• 전자공학회논문지
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• 제52권3호
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• pp.59-66
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• 2015

본 논문에서는 4bit SAR-ADC(Successive Approximation ADC) 기반의 LDO(Low Drop-Out Regulator)와 파워 트랜지스터의 사이즈 선택을 통하여 DC-DC 벅 컨버터의 효율을 개선하는 방법을 제안한다. 제안하는 회로는 부하 전류에 따라서 파워 트랜지스터 사이즈를 선택하여 DC-DC 벅 컨버터의 효율을 개선한다. 이를 위해, 우리는 스위칭 손실과 전도 손실이 교차하는 지점을 파워 트랜지스터의 적절한 사이즈로 선택하였다. 또한, standby mode 또는 sleep mode로 동작 시에는 효율을 개선하기 위해 LDO로 동작하도록 하였다. 제안하는 회로는 4bit로 파워 트랜지스터 사이즈(X1, X2, X4, X8)를 선택하였고, 저부하에서 단일 사이즈를 이용한 기존의 방식보다 최대 25%의 효율 개선을 얻을 수 있었다. 입력 전압은 5V, 출력 전압은 3.3V, 최대 부하 전류는 500mA이다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.601-602
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• 2008

This paper presents pulse-frequency modulation(PFM) to improve the light-load efficiency. The proposed circuit is designed by using the device parameter of standard $0.13{\mu}m$ CMOS process. The performance of proposed circuit is evaluated by HSPICE simulation Measured efficiency in a light-load is measured 78-90 % for 0.1 to 100mA output current.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권4호
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• pp.493-500
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• 2015

A flyback converter operates with either pulse width modulation (PWM) or pulse frequency modulation (PFM) control scheme depending on the load current. At light load condition, PFM control is employed to reduce the switching frequency and thereby minimize the switching power loss. For heavier load, PWM control is used to regulate the output voltage of the flyback converter. The flyback controller has been implemented in a $0.35{\mu}m$ BCDMOS process and applied to a 40-W flyback converter. The light-load power efficiency of the flyback converter is improved up to 5.7-% comparing with the one operating with a fixed switching frequency.

• Journal of Electrical Engineering and Technology
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• 제11권5호
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• pp.1274-1281
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• 2016

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.249-255
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• 2017

Efficient operation of induction motor at light loads has been getting wide attention recently because the operating of induction motor at light loads occupies big portion of its operating regions in many applications such as environment friendly vehicle. As one of approaches to improve efficiency, Adaptive Maximum Torque Per Amp (Adaptive MTPA) control for induction motor drives has been proposed to achieve a desired torque with the minimum possible stator current. However, the Adaptive MTPA control was validated only at heavy load where, in general, control scheme tends to perform better than at light loads since the error in measurement of sensors is lower and signal to noise is better. Thus, although the performance of a control scheme is good at rated operating point, its performance at light load is somewhat in doubt in practice. This has led to considerable interest in efficiency of Adaptive MTPA control at light loads. This work experimentally demonstrates performance of Adaptive MTPA control at light loads regardless of rotor resistance variation, thus showing its good performance over all operating conditions.

• 전력전자학회논문지
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• 제21권6호
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• pp.506-513
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• 2016

In general, LLC converters show great promise in applications that require high efficiency, especially under light load conditions. In particular, LLC converters feature wide gain capability with pulse-frequency modulation and zero voltage switching over entire load conditions. However, output voltage increases in light load conditions. In this study, Bode plot and impedance asymptotes analyses were conducted to obtain insights into the regulation characteristics of LLC converters under light load conditions. To improve the regulation characteristic of LLC converters, a new resonant tank with an additional capacitor is proposed. The design guideline for the proposed LLC converter is determined by the Bode plot and impedance asymptotes analyses. Therefore, the proposed LLC converter achieves the light load regulation while maintaining the advantages of typical LLC converters.

• Journal of Power Electronics
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• 제18권4호
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• pp.975-984
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• 2018

This work presents a high efficiency phase shifted full bridge (PSFB) DC-DC converter for use in the second stage of a battery charger for neighborhood electrical vehicle (EV) applications. In the design of the converter, Lithium-ion battery cells are preferred due to their high voltage and current rates, which provide a high power density. This requires wide range output voltage regulation for PSFB converter operation. In addition, the battery charger works with a light load when the battery charge voltage reaches its maximum value. The soft switching of the PSFB converter depends on the dead time optimization and load condition. As a result, the converter has to work with soft switching at a wide range output voltage and under light conditions to reach high efficiency. The operation principles of the PSFB converter for the continuous current mode (CCM) and the discontinuous current mode (DCM) are defined. The performance of the PSFB converter is analyzed in detail based on wide range output voltage and load conditions in terms of high efficiency. In order to validate performance analysis, a prototype is built with 42-54 V / 15 A output values at a 200 kHz switching frequency. The measured maximum efficiency values are obtained as 94.4% and 76.6% at full and at 2% load conditions, respectively.

• Journal of Power Electronics
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• 제16권6호
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• pp.2024-2034
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• 2016

This paper presents a DC-DC buck converter with a Phase-Locked Loop (PLL) that can compensates for power efficiency degradation over a wide input range. Its switching frequency is kept at 2 MHz and the delay difference between the High side driver and the Low side driver can be minimized with respect to Process, Voltage and Temperature (PVT) variations by adopting the PLL. The operation mode of the proposed DC-DC buck converter is automatically changed to Pulse Width Modulation (PWM) or PWM frequency modes according to the load condition (heavy load or light load) while supporting a maximum load current of up to 1.2 A. The PWM frequency mode is used to extend the CCM region under the light load condition for the PWM operation. As a result, high efficiency can be achieved under the light load condition by the PWM frequency mode and the delay compensation with the PLL. The proposed DC-DC buck converter is fabricated with a $0.18{\mu}m$ BCD process, and the die area is $3.96mm^2$. It is implemented to have over a 90 % efficiency at an output voltage of 5 V when the input range is between 8 V and 20 V. As a result, the variation in the power efficiency is less than 1 % and the maximum efficiency of the proposed DC-DC buck converter with the PLL is 95.4 %.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.391-392
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• 2016

A phase shedding control algorithm to increase efficiency of 3-Phase interleaved boost converter is proposed. Conventional interleaved converter has low efficiency under the light load condition. In this paper, the number of phase is controlled in accordance with the load condition to increase the light load efficiency. The validity of proposed phase control algorithm is verified by simulation results based on measured efficiency.