Reliability Of DC-link Capacitors Research Articles

Reliability of DC-link capacitor in pulsed power supply for accelerator magnet

Reliability of DC-link capacitor in pulsed power supply for accelerator magnet

A Digital Twin System of Capacitive DC Bank Using Rogowski Coil to Monitor Individual Capacitors

The reliability of dc link capacitors is closely related to the operational safety of the whole power electronic system. To meet the application requirements, it is usually necessary to use a series or parallel structure of multiple capacitors to increase the capacity and withstand voltage, which also makes it difficult to monitor the individual capacitors in the capacitor bank. This article proposed a digital twin system for dc-link capacitor banks with PCB integrated Rogowski coils as sensors. The system uses highly integrated Rogowski coils to obtain the operating currents of individual capacitors in order to realize parameter correction of the digital twin system and ensure that the digital twin system can accurately reflect the electrothermal behavior of the dc-link capacitor bank. In addition, the effect of operating temperature on capacitor parameters is also considered, and the capacitor parameters and the operating temperature monitored by the digital twin system simultaneously are used to standardize the parameters. The standardized parameters are used as indicators to realize the health status assessment of each capacitor in the capacitor bank, which further provide an important basis for operation and maintenance.

불연속 전압 변조 방법 적용 범위에 따른 태양광 NPC 인버터의 DC-link 커패시터 신뢰성 분석

The voltage modulation method has a significant effect on the performance of 3-level neutral-point clamped (NPC) inverters such as efficiency and output quality. Discontinuous pulse width modulation (DPWM) has been proposed to improve efficiency by reducing the switching loss of power devices. In previous research, the output quality, power loss, and reliability of the power device were considered when the DPWM method was applied. However, the influence of the DPWM on the reliability of DC-link capacitors, one of the reliability-critical components, has not been investigated. In this paper, the effect of DPWM on the reliability of DC-link capacitors is studied in the NPC inverter. Considering the mission profile of the photovoltaic (PV) system, the accumulated damage of DC-link capacitors is analyzed at the component level first under different applied angles of DPWM. The reliability of DC-link capacitors is then evaluated at the system level by considering all capacitors of the NPC inverter. In addition, the current of the DC-link capacitor is analyzed through the experiment to validate the negative effect of the DPWM on the reliability of the DC-link capacitor.

Reliability-Oriented Optimal DPWM Strategy for Single-Phase Five-Level T-Type Inverter in PV Systems

Many efforts have been devoted to improving the reliability of PV inverters with a focus on reliability-critical components such as power devices and capacitors. Discontinuous pulsewidth modulation (DPWM) methods are representative of improving the reliability of power devices by decreasing their thermal loadings. However, although the DPWM method affects the ripple current of the DC-link capacitor, prior-art research is only focusing on the power devices. There is a lack of study on the effect of applying the DPWM method on the reliability of the DC-link capacitor. It may have a negative effect on the reliability of the DC-link capacitor and thus affects the reliability of overall PV inverters. In this article, the influence of the DPWM method with different clamping periods on the reliability of power devices and DC-link capacitors of the single-phase five-level T-type inverter is investigated, where a 7-kW PV system and annual mission profile of PV system are considered as a case study. Then, a reliability-oriented optimal DPWM strategy is presented for the target lifetime of the T-type inverter by considering system-level reliability, including the lifetimes of both power devices and DC-link capacitors.

An event-oriented reliability assessment for DC link capacitors in grid connected inverter with low voltage ride through operation

Low voltage ride-through (LVRT) capability has been standard into the operating specifications of grid-connected inverters in many countries. Due to the mismatch of the time scale and lack of stress description model under the LVRT operation, the traditional mission profile reliability analysis tools are difficult to be applied for capacitors under LVRT operation. To overcome the above issue, this paper analysis the electrical and thermal stress of the DC link capacitors under LVRT operation, and established a lifetime model for the LVRT operation by the accelerated aging test. An extended mission profile and a nonlinear damage accumulation model have been proposed to evaluate the impact of the LVRT event on the reliability of DC link capacitors. A reliability assessment has been conducted for a 7.5 kW inverter which experienced one LVRT incident as an analytical example.

Multitimescale Reliability Evaluation of DC-Link Capacitor Banks in Metro Traction Drive System

The reliability of DC-link capacitors in urban rail transit is considered as a major challenge because of significant maintenance impact. In this article, the DC-link capacitor reliability is researched in metro traction drive system. In the small timescale of control level, the current harmonics of multiple operating conditions and different control methods in the DC-link capacitor are discussed. The power loss is simulated by the capacitor harmonics of current and equivalent series resistance (ESR) in multioperating conditions. Considering electrothermal coupling, the time-ordered and continuity of thermal stress are analyzed to evaluate the hot spot temperature dynamic conformed to the reality. Combining with the analysis of electrical stress and thermal stress, a multitimescale capacitor reliability evaluation method is proposed. It is divided into four steps: the discrete small timescale, the single route timescale, the daily operation timescale, and the whole lifetime cycle. In the different timescales, the lifetime distribution changes with the dynamics of the complex mission profiles, so as to estimate the lifetime bottleneck of the DC-link capacitor banks with different control methods by the Weibull distribution. In addition, experimental validation is provided to verify the accuracy of the proposed method.

Artificial Neural Network Algorithm for Condition Monitoring of DC-link Capacitors Based on Capacitance Estimation

In power electronic converters, reliability of DC-link capacitors is one of the critical issues. The estimation of their health status as an application of condition monitoring have been an attractive subject for industrial field and hence for the academic research filed as well. More reliable solutions are required to be adopted by the industry applications in which usage of extra hardware, increased cost, and low estimation accuracy are the main challenges. Therefore, development of new condition monitoring methods based on software solutions could be the new era that covers the aforementioned challenges. A capacitance estimation method based on Artificial Neural Network (ANN) algorithm is therefore proposed in this paper. The implemented ANN estimated the capacitance of the DC-link capacitor in a back-toback converter. Analysis of the error of the capacitance estimation is also given. The presented method enables a pure software based approach with high parameter estimation accuracy.