• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.535-540
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• 2022

DC-link capacitors are reliability-critical components in a photovoltaic (PV) inverter. Typically, the lifetime of a DC-link capacitor is evaluated by considering the voltage and hot-spot temperature of the capacitor under the specific operating condition of the PV inverter. However, the output of the PV inverter is determined by solar irradiation and ambient temperature, which vary with the seasons; accordingly, the hot-spot temperature of the capacitor also changes. Therefore, the mission profile of the PV system should be considered to effectively evaluate the reliability of the DC-link capacitor. In this study, the reliability of the DC-link capacitor of a three-level NPC inverter is comparatively analyzed with and without considering the mission profiles of the PV system, where two mission profiles recorded in Arizona and Iza are considered. The accumulated damage of the DC-link capacitor is calculated based on the lifetime model by analyzing its thermal loading. Afterward, a reliability evaluation of the DC-link capacitor is performed at the component level and then at the system level by considering all capacitors by means of Monte Carlo analysis. Results reveal the importance of performing a mission-profile-based reliability evaluation during the design of high-reliability PV inverters to achieve the target reliability performance.

• Journal of Power Electronics
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• v.15 no.3
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• pp.763-774
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• 2015

This study investigates the inherent influence of a DC-link voltage controller on both DC-link voltage control and the compensation performance of a three-phase, four-wire shunt active power filter (APF). A nonlinear variable-parameter DC-link voltage controller is proposed to satisfy both the dynamic characteristic of DC-link voltage control and steady-state compensation performance. Unlike in the conventional fixed-parameter controller, the parameters in the proposed controller vary according to the difference between the actual and the reference DC-link voltages. The design procedures for the nonlinear voltage controller with variable parameters are determined and analyzed so that the proposed voltage controller can be designed accordingly. Representative simulation and experimental results for the three-phase, four-wire, center-spilt shunt APF verify the analysis findings, as well as the feasibility and effectiveness of the proposed DC-link voltage controller.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.6
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• pp.615-624
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• 1992

For the operation of the resonant DC link inverters, only limited number of modulation techniques such as the delta modulation and instantaneous current control techniques have been suggested. However, these modulation techniques have some limitations in practical operation. In this paper, the application of conventional inverter modulation techniques is suggested for the control of the resonant DC link inverter. The harmonic analysis results are presented. The results show that these modulation techniques offer good output characteristics similar to conventional inverter PWM techniques for the operation of the resonant DC link inverter. This implies that not only the delta modulation technique and instantaneous current control techniques but also various other modulation techniques can be applied to the operation of the resonant DC link inverter. This also indicates that open loop control as well as closed loop control can be used for the operation of the resonant inverter. The resonant DC link inverter with various modulation strategies is implemented using V-40 microprocessors.

• Journal of Power Electronics
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• v.17 no.4
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• pp.1004-1013
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• 2017

This paper presents an interleaving scheme for parallel-connected power systems to reduce the DC-link current ripple. A paralleled generator system generates current ripple by the Pulse Width Modulation (PWM) of each generator side converter. The current ripple in the DC-link degrades the efficiency of the whole generator system and decreases the lifetime of the DC-link capacitors. To mitigate these issues, the expression of the DC-link current is derived by a double-integral Fourier analysis while considering the modulation schemes. Optimized interleaving angles for the parallel generator system are obtained based on an analysis to minimize the dominant current harmonics component. Finally, the proposed interleaving scheme reduces the RMS value of the DC-link current ripple. Simulation and experimental results verify the effectiveness of the proposed interleaving scheme.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.1
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• pp.72-80
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• 2019

In this paper, we propose a digital DC-Link current control approach for BLDC actuation systems. The proposed approach consists of the following two components: first, DC-Link current measurement with sampling instances synchronized with PWM frequency, and second, current control using single DC-Link current rather than three phases current of a motor. The proposed method proved its performance through experiments and simulation. The results showed that the control performance are increased compared with the BLDC actuation system which does not use current control.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.1
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• pp.47-53
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• 2022

This paper proposes a method for selecting the capacitance of DC-link capacitors of inverters. In general, the DC-link capacitance of the inverter system must be considered for DC-link voltage, ripple current, switching frequency, ripple voltage, and pulse-width modulation techniques. Therefore, the appropriate capacitance can be determined by finding the rms and peak values of the ripple current of the capacitor. In this paper, the process of extracting the ripple current of DC-link capacitor is described in detail. In addition, the simple method for finding DC-link capacitor capacitance using the result value is presented through the simulations.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.169-173
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• 2001

In this paper, dc link ripple currents for three-phase ac/dc/ac PWM converters are ana lysed in a frequency domain. The expression of the harmonic currents is developed by using switching functions and exponential Fourier series expansion. The dc link ripple currents with regard to power factor and modulation index are investigated. In addition, the effect of the displacement angle between the switching periods of line-side converters and load-side inverters on the dc link ripple current is studied. The result of the dc link current analysis is helpful in specifying the dc link capacitor size and its lifetime estimation.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.25-26
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• 2010

본 논문은 전기자동차용 인버터의 DC-Link 전압 가변을 위한 2상 양방향 DC-DC 컨버터의 제어 기법을 제안한다. 제안된 DC-DC 컨버터는 2-스위치 Buck-Boost 컨버터를 병렬구성 하여 전기자동차의 높은 출력에 대응하였으며 출력단 다이오드를 스위치로 교체하여 회생동작을 가능하게 하였다. 이를 시뮬레이션을 통하여 제어알고리즘의 가능성을 확인하였다.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1928-1938
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• 2016

The three-phase four-wire shunt active power filter (APF) is an effective method to solve the harmonic problem in three-phase four-wire power systems. In addition, it has two possible topologies, a four-leg inverter and a three-leg inverter with a split-capacitor. There are some studies investigating DC-link voltage control in three-phase four-wire APFs. However, when compared to the four-leg inverter topology, maintaining the balance between the DC-link upper and lower capacitor voltages becomes a unique problem in the three-leg inverter with a split-capacitor topology, and previous studies seldom pay attention to this fact. In this paper, the influence of the balance between the two DC-link voltages on the compensation performance, and the influence of the voltage balance controller on the compensation performance, are analyzed. To achieve the balance between the two DC-link capacitor voltages, and to avoid the adverse effect the voltage balance controller has on the APF compensation performance, a new DC-link voltage balance control strategy for the three-phase four-wire split-capacitor APF is proposed. Representative simulation and experimental results are presented to verify the analysis and the proposed DC-link voltage balance control strategy.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.223-226
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• 2001

In this paper, dc link ripple currents for three-phase ac/dc/ac PWM converters are analyzed in a frequency domain. The expression of the harmonic currents is developed by using switching functions and exponential Fourier series expansion. The dc link ripple currents with regard to power factor and modulation index are investigated. In addition, the effect of the displacement angle between the switching periods of line-side converters and load-side inverters on the do link ripple current is studied. The result of the do link current analysis is helpful in specifying the dc link capacitor size and its life time estimation.