Power Ring Technology

The Power Ring Film Capacitor™ provides:

  • Extremely low internal losses (ESR) and low inductive properties (ESL)
  • Industry-leading ESR/ESL characteristics
  • Extreme current pulse survival
  • Significant volumetric capacitor density
  • Inverter topology design for optimized current rating and reduced coolant need
  • High temperature polypropylene film capacitor designs

SBE has developed the Power Ring Film Capacitor™ after years of research and experimentation on the optimum use of Polyester and Polypropylene film capacitor dielectrics.

The ring shape (annular form factor) provides extremely low internal losses (ESR) within the film and also provides for the purest form of interconnect symmetry which can dramatically lower the inductive properties (ESL). These properties drive the leading-edge electrical characteristics that the designing engineer can take advantage of.

While the dimensional changes to the traditional film capacitor form factor are straightforward on the surface, there are many things which emerge as challenges to the ultimate success in a customer application. SBE has developed manufacturing processes which have solved these issues to produce a robust product under extreme operating conditions.

Lowest Losses – Industry-leading ESR
The much shorter path of current between the electrodes produces the lowest ESR for film capacitors in the industry. The reasons are described in the technical paper “An Extremely Low ESR and ESL Annular Film Capacitor” (pdf link). These low losses allow for a number of greatly improved designs especially in ripple current applications.

SBE’s Power Ring film capacitors demonstrate ESR values as low as 0.15 mOhm for a 1000µF – 600V DC Link. This is the industry’s lowest ESR value.

This example shows the very low temperature rise in an automotive hybrid inverter DC link application when compared with the typical capacitor implementation and design.
graph temperature rise power ring vs conventional capacitor
Much more information is available in the Technical Papers page and the Applications pages.

capacitance ripple current graph capacitor
The features of SBE’s optimized Power Ring film capacitors result in a highly efficient use of microfarads in the ripple current application. These features give the power electronics designers a new ability to optimize their design for current handling capability while being only mindful of schematical needs of microfarads (such as ripple voltage at a given switching frequency). Previously, they had to “bulk up” on capacitance solely for the purpose of current handling survival and lifetime requirements. With SBE Power Ring film capacitor technology, this expensive and space consuming practice is no longer required.

Lowest Inductance – Industry-leading ESL
The circular shape and short distance connection paths to the terminal pairs, which can be orientated symmetrically around a large current carrying area, are ideal to provide for the lowest system ESL. Additionally, the Power Ring can be optimized with the bus connection structure providing the lowest possible ESL presentation to the switch die. The result is extremely low voltage overshoot and the potential for greatly increased power efficiency of the switch module.
With an optimized integrated module design, the ESL as seen at the switch module will be in the range of 10 – 15nH.

See Technical papers for more information on extremely low ESR/ESL.

Are Snubbers the Right Choice for High Performance Inverters?
The SBE Power Ring with integrated bus bar can offer very similar inductances to the system as would a snubber capacitor (3 – 8nH is typical and is mostly dependent on the connection topology of the IGBT module). For this reason, there is usually no improvement of the overshoot of the typical snubber application vs. using the SBE integrated Power Ring capacitor solution. In fact, often, the snubber cannot equal the measured overshoot improvement provided by the SBE solution.
Snubbers get very hot since they are connected to the IGBT pins (often the hottest point other than under the die itself) and are almost never direct cooled due to the difficult of connecting cooling plates to this spot on the device. While they only see a fraction of the total power, their small physical size and poor cooling environment mean they are THE weak link in the reliability chain for an inverter and  are always desired to be eliminated.
As the desire to increase usable operating voltage intensifies, there can be a tendency to add a snubber to get every bit of safe operating voltage out of a system. The SBE integrated Power Ring is a much better way to achieve the same improvement (reduced overshoot resulting in increased safe operating voltage) without any concern of an added element being the weak link in the reliability chain. Please see our Presentation on various snubber, DC Link, and switch module package combinations as frequencies increase in next generation systems.

High Temperature Polypropylene Film Capacitor Designs
SBE is leading the capacitor industry on discovering the reliable high temperature boundaries of polypropylene film used in ripple current applications for the electric drivetrain automotive and wind and solar markets. As a result, we have produced the world’s first cost-effective DC link capacitor utilizing polypropylene film which can operate reliably for over 20,000 hours utilizing only 105°C engine temperature coolant and at 100kW power level utilizing a 1,000µF capacitor.

No matter what your need is for extremely low ESR and ESL or for increased temperature performance, the Power Ring film capacitor is an industry leader in this regard. The circular shape and short distance connection paths provide the highest performance characteristics available and at prices competitive with traditional film capacitor products.

For additional information, please contact SBE Application Engineering at [email protected].