Lifetime Estimation of DC-Link Capacitors in Adjustable Speed Drives Under Grid Voltage Unbalances

Abstract

Electrolytic capacitor with a DC-side inductor is a typical DC-link filtering configuration in grid-connected diode rectified Adjustable Speed Drives (ASDs). The criteria to size the DC-link filter are mainly from the aspects of stability and power quality. Nevertheless, the reliability of the DC-link filter is also an essential performance factor to be considered, which depends on both the component inherent capability and the operational conditions (e.g., electro-thermal stresses) in the field operation. Nowadays, unbalanced voltage has the most frequent occurrence in many distribution networks. It brings more electrical-thermal stress to the component, affecting the reliability of the capacitors. In order to study the reliability performance of the LC filter in an ASD system quantitatively, this paper proposes a mission profile based reliability evaluation method for capacitors. Different from the conventional lifetime estimation, a nonlinear accumulated damage model is proposed for the long-term estimation, considering the nonlinear process of ESR growth and capacitance reduction during the degradation. Based on the proposed lifetime estimation procedure, four case studies are investigated: 1) Lifetime benchmarking of capacitors in LC filtering and slim capacitor filtering configurations; 2) Scalability analysis for the lifetime of capacitors in terms of system power rating and grid-unbalanced levels; 3) Lifetime estimation of capacitors in DC-link filter with long-term mission profile, and 4) The impact of the capacitor sizing on the lifetime of DC-link capacitor under grid-balanced and grid-unbalanced conditions. The results serve as a guideline for proper selection of DC-link configurations and parameters to fulfill a specification in adjustable speed drives.

An Overview of Condition Monitoring Techniques for Capacitors in DC-Link Applications

“…C-LINK capacitors are an important part in the majority of electronic converters, which contribute to suppressing dc-link voltage ripple, absorbing harmonics, and balance the instantaneous power difference between the front-end and rear-end of converter systems [1], [2]. In some applications, they are also served to provide sufficient energy for transient and abnormal operations [3], [4]. However, capacitors are sensitive to thermal and electrical stresses and have the main disadvantage of finite lifespan and high degradation failure rate [6]− [8].…”

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

“…As mentioned (see Fig. 1), the lifetime of a capacitor is very important and necessary to be considered in the design of the complete system, and thermal stress caused by current is a critical stressor to capacitor wear out [25].…”

“…[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.…”

Applications of Power Electronics

“…The main aim of this Special Issue was to seek high-quality submissions that highlight and address recent breakthroughs over the whole range of emerging applications of power electronics, the harmonic and electromagnetic interference (EMI) issues of the devices and system levels, as also discussed in [1][2][3][4], robust and reliable power electronics technologies, including fault prognosis and diagnosis techniques [5][6][7], the stability of grid-connected converters [8,9], and the smart control of power electronics for devices, microgrids and at system levels [10][11][12][13].…”