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

Abstract

The reliability of DC-link capacitors in urban rail transit is considered as a major challenge because of significant maintenance impact. In this paper, 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 DClink capacitor are discussed. The power loss is simulated by the capacitor harmonics of current and equivalent series resistance (ESR) in multi-operating conditions. Considering electro-thermal 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 multi-timescale 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.

Electrothermal Stress Analysis and Lifetime Evaluation of DC-Link Capacitor Banks in the Railway Traction Drive System

“…/ 1000 = (7.75 0.062367 0.00113 ) where mstat and g represent the dynamic mass of trains and the acceleration of gravity, respectively. The motor speed n is proportional to the running speed v, which can be expressed as [22] 60 3.6…”

“…Meanwhile, the solar irradiance at small timescales is handled by the instantaneous electro-thermal method [20]. However, according to the multioperation conditions in the railway, the complex mission profiles need to be dealt with, including the short-term changes in speed and slope as well as the long-term changes in ambient temperature and humidity [21]- [22]. Therefore, the electrothermal stress analysis with the dynamic power losses should be resolved well.…”

A Novel Three-Pulse Equivalent Power Loss Profile for Simplified Thermal Estimation

“…The power losses are a series of rectangular pulses. By the references [25], [26], the corresponding thermal responses are expressed as…”

A Methodology to Determine the Effect of a Novel Modulation in the Reliability of an Automotive DC-Link Capacitor

“…Lifetime models [25], [32]- [34] are important for lifetime estimation, online condition monitoring and benchmark of different capacitor solutions. The estimation of the lifetime of a F-Cap depends on the rate of self-healing events and the energy of each one as the number of operating hours increases [41].…”

“…[32] validates a lifetime model for different capacitor technologies (widely used by industry), which uses the two main stressors to capacitor wear out: the hot-spot temperature and the operational voltage. This model is applied within an interesting damage model for a statistical lifetime prediction in an adjustable speed drive [25], a wind power converter [33] and a metro traction drive system [34]. However, these analyze the electrical and thermal behaviour of the capacitor at various static loading conditions, but not at a dynamic real operation cycle.…”