Abstract
DC-bus capacitors take up substantial space in an electric vehicle (EV) traction inverter, limiting the traction drive’s volumetric power density. Film capacitors are typically used, but other capacitor technologies with higher energy densities can help reduce the overall size. In this article, several commercial capacitor technologies are considered for use as dc-bus capacitors for EV traction inverters. They are characterized, evaluated, and compared for optimized design for volume reduction. This article also proposes a novel capacitor packaging technique that utilizes symmetrically distant parallel capacitor branches from termination, which improves electrical and thermal performance compared to a traditional flat-printed circuit board-based design. The proposed design was prototyped for a 100-kW traction inverter, and then, the thermal and electrical characteristics were evaluated under various operating conditions. Results show that the proposed symmetrical design has 40% lower layout inductance and 80% lower temperature difference than a traditional package among the parallel capacitor branches.
Highlights
T HE purpose of the DC bus capacitor within a voltage source inverter is to decouple the load from the DC supply unit
The equivalent series resistance (ESR) value of PLZT decreases with higher operating temperatures, and the value for all three capacitors becomes similar at 100◦C, suggesting that the PLZT capacitor will
It is clear from previous discussions that PLZT-based capacitors can be utilized to optimize DC bus capacitor volume for traction inverters due to their higher energy density, highcurrent conduction capability, and high-temperature operation
Summary
T HE purpose of the DC bus capacitor within a voltage source inverter is to decouple the load from the DC supply unit. In [2] and [8], the process of identifying the RMS current stress on the DC link capacitor, along with the required capacitance for a three-phase inverter, is presented for the optimal selection of the capacitor bank. In [10], an additional current source inverter is used to control the DC link voltage in the low-speed region, reducing the RMS current stress of the DC link capacitor This method will increase the capacitor lifetime by reducing capacitor losses but will adversely affect the overall inverter volume. The low-inductance windings introduce high-current distortion, which increases motor and inverter losses One way this challenge can be eliminated without introducing a large sine filter at the output of the inverter is to increase switching frequency, which increases the fundamental frequency of the DC-link capacitor current. The proposed package performance is validated with experimental results
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