• Journal of Power Electronics
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• v.14 no.4
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• pp.796-805
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• 2014

A digital controller with a low-power approach for point-of-load synchronous buck converters is discussed and compared with its analog counterpart to confirm its feasibility for system integration. The tri-mode digital controller IC in $0.35{\mu}m$ CMOS process is presented to demonstrate solutions that include a PID, quarter PID, and robust RST compensators. These compensators address the steady-state, stand-by, and transient modes according to the system operating point. An idle-tone free condition for ${\Sigma}-{\Delta}$ DPWM reduces the inherent tone noise under DC-excitation. Compared with that of the traditional approach, this condition generates a quasi-pure modulation signal. Experimental results verify the closed-loop performances and confirm the power-saving mechanism of the proposed controller.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1551-1561
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• 2014

Design, Simulation and experimental analysis of closed loop time domain based Discrete PWM buck-boost converter are described. To improve the transient response and dynamic stability of the proposed converter, Discrete PID controller is the most preferable one. Discrete controller does not require any precise analytical model of the system to be controlled. The control system of the converter is designed using digital PWM technique. The proposed controller improves the dynamic performance of the buck-boost converter by achieving a robust output voltage against load disturbances, input voltage variations and changes in circuit components. The converter is designed through simulation using MATLAB/Simulink and performance parameters are also measured. The discrete controller is implemented, and design goal is achieved and the same is verified against theoretical calculation using LabVIEW.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.295-296
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• 2015

본 논문에서는 LCL-필터가 사용된 계통연계 인버터의 공진 전류를 저감하기 위한 개선된 불연속 전압 변조 방식을 제안한다. 기존의 불연속 전압 변조 방식은 전압변조신호가 60도마다 불연속적으로 변하기 때문에 많은 고조파가 발생하며, 이 고조파와 LCL-필터를 사용하는 계통연계 시스템의 공진주파수 대역이 겹치면 계통전류가 공진하는 문제가 발생한다. 제안하는 불연속 전압 변조 방식은 3상 지령 전압의 최대, 최소값을 이용한 오프셋을 전압 변조 신호에 주입하여 불연속적인 부분에 의해 발생하는 고조파를 저감하여, 공진주파수 대역이 겹치게 되었을 경우 발생하는 문제를 방지한다. PSIM 시뮬레이션을 통해 제안하는 불연속 전압 변조 방식의 타당성을 검증한다.

• Journal of Power Electronics
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• v.13 no.2
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• pp.232-242
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• 2013

To obtain phase currents information in AC drives, shunt sensing technology is known to show great performance in cost-effectiveness and therefore it is widely used in low cost applications. However, shunt sensing methods are unable to acquire phase currents in certain operation conditions. This paper deals with the derivation of the boundary conditions for phase current reconstruction in three-shunt sensing inverters and proposes a voltage injection method to expand the measurable areas. As the boundary conditions are deeply dependent on the switching patterns, they are typically analyzed on the voltage vector plane for space vector pulse width modulation (SVPWM) and discontinuous pulse width modulation (DPWM). In the proposed method, the voltage injection and its compensation are conducted within one sampling period. This guarantees fast current reconstruction and the injected voltage is decided so as to minimize the current ripple. In addition to the voltage injection method, a sampling point shifting method is also introduced to improve the boundary conditions. Simulation and experimental results are presented to verify the boundary condition derivation and the effectiveness of the proposed voltage injection method.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.221-227
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• 2022

The reliability improvement of PV systems is an important factor in reducing the cost of PV energy because it is closely related to the annual energy production as well as the maintenance cost of PV systems. The reliability of PV inverters plays a key role in the reliability of PV systems because it is regarded as one of the most reliable critical parts of PV systems. The lifetime evaluation of PV inverters considering the mission profile in the design phase plays an important role in reliability design to ensure the required lifetime of PV inverters. In this paper, the lifetime of representative single-phase T-type and I-type NPC inverters are comparatively evaluated by considering the mission profile of a PV system recorded at Iza, Spain. Furthermore, the effect of the pulse width modulation methods on the lifetime is also discussed. The lifetime evaluation of PV inverters is performed at the component-level first and then the system level by considering all power devices.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.1
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• pp.56-62
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• 2022

In this paper, the effect of pulse width modulation methods on thermal loadings and power losses of single-phase five-level NPC inverters for photovoltaic systems are analyzed. The pulse width modulation methods affect the power losses of the NPC inverters and thus lead to different thermal loadings of NPC inverters. To identify the reliability-critical power device with respect to thermal stress, the thermal loadings of I- and T-type NPC inverters are analyzed by applying the unipolar pulse modulation method. Then, the effect of the discontinuous pulse width modulation method on power losses and thermal loadings of power devices of I- and T-type NPC inverters are analyzed. Finally, the operation of NPC inverters applying the discontinuous pulse modulation method is confirmed by experiments. The results show that the discontinuous pulse modulation method is able to improve the reliability of NPC inverters by reducing thermal loadings of reliability-critical power devices and it is more effective for T-type NPC inverters than I-type NPC inverters.

• Archives of Pharmacal Research
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• v.20 no.6
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• pp.560-565
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• 1997

The physicochemical properties of melatonin (MT) in propylene glycol (PG) and 2-hydroxypropyl-.betha.-cyclodextrin $(2-HP{\beta}CD)$ vehicles were characterized. MT was endothermally decomposed as determined by differential scanning calorimetry (DSC). Melting point and heat of fusion obtained were $116.9{\pm}0.24^{\circ}C $.and $7249{\pm}217 cal/mol$., respectively. MT as received from a manufacture was very pure, at least 99.9%. The solubility of MT in PG solution increased slowly until reaching 40% PG and then steeply increased. Solubility of MT increased linearly as concentration of $2-HP{\beta}CD$ without PG INCREASED$(R^2=0.993)$. MT solubility in the mixtures of pg and $2-HP{\beta}CD$ also increased linearly but was less than the sum of its solubility in $2-HP{\beta}CD$ and PG individually. The MT solubility was low in water, simulated gastric or intestinal fluid but the highest in the mixture of PG(40v/v%) and $2-HP{\beta}CD$ (30w/v%) although efficiency of MT solubilization in $2-HP{\beta}CD$ decreased as the concentration of PG increased. MT was degraded in a fashion of the first order kinetics $(r^2>0.90)$. MT was unstable in strong acidic solution (HCl-NaCl buffer, pH 1.4) but relatively stable in other pH values of 4-10 at $70^{\circ}C$. In HCl-NaCl buffer, MT in 10% PG was more quickly degraded and then slowed dpwm at a higher concentration. However, the degradation rate constant of MT in 2-HP.betha.CD was not changed significantly when compared to the water. The current studies can be applied to the dosage formulations for the purpose of enhancing percutaneous absorption or bioavailability of MT.

• Journal of IKEEE
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• v.24 no.4
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• pp.1074-1080
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• 2020

This paper proposes a digitally controlled buck converter insensitive to process, voltage and temperature and capable of three modes of operation depending on the state of the output voltage. Conventional digital-controlled buck converters utilized A/D converters, counters and delay line circuits for accurate output voltage control, resulting in increasing the number of counter and delay line bits. This problem can be resolved by employing the 8-bit and 16-bit bidirectional shift registers, and this design technique leads a buck converter to be able to control duty ratio up to 128-bit resolution. The proposed buck converter was designed and fabricated with a CMOS 180 nano-meter 1-poly 6-metal process, generating an output voltage of 0.9 to 1.8V with the input voltage range of 2.7V to 3.6V, a ripple voltage of 30mV, and a power efficiency of up to 92.3%. The transient response speed of the proposed circuit was measured to be 4us.