Alternative Energy (Solar, Wind, Grid Stabilization)
In Alternative Energy systems, Power Ring Film Capacitors™ are the DC Link Capacitors used in inverters and power conversion systems. The Power Ring Film Capacitor greatly reduces the total system cost and component complexity requirements, while not sacrificing the long-term reliability required in today’s demanding environments of energy grids using alternative energy. Typical voltages range from 200V – 2500Vdc and ripple currents range from 20 – 1000 Arms at 10 – 100khz switching frequencies.
In inverters, the DC link capacitor is used to filter unwanted ripple current components from the output AC waveform. The DC link capacitor is a key component from a cost point of view, as it represents 30% of the volume, weight and cost of the inverter. It also requires extensive cooling for a longer, reliable operation, as all of the currents produced by the windmill/solar array must pass over the capacitor. For those reasons, selecting a DC Link capacitor with higher performance for a given size, resulting in lower temperature rise has a significant impact on cost. 
In power conversion systems, the DC link capacitor functions as a short-term current source and sink to limit transient voltages seen by power conversion semiconductor switches and the input DC bus.
High Performance, Less Cooling Requirement and Better Space Utilization
SBE Power Ring Film Capacitor™ allows the total system cost and packing requirements to be greatly reduced and not sacrifice the long-term reliability required in today’s demanding environments of energy grids using alternative energy.
Power Ring Film Capacitor
The ability of the Power Ring to handle significant current with lower temperature rise allows the designer to choose the smallest capacitance value that the system can accept often greatly reducing cost.
Due to its thin profile and patented features, Power Ring Film Capacitor offers high power density and delivers the lowest available Effective Series Resistance [ESR], Effective Series Inductance [ESL], and low temperature rise [Trise]. This resulting much shorter path of current between the electrodes allows the Power Ring to produce the lowest ESR among film capacitors in the industry. These low losses under heavy current loads allow for a number of greatly improved designs especially in ripple current applications.
Traditional Capacitors
ESR ratings of 0.25milliohms are typical and constant over time, and low ESL in the 3nH to 5nH range. Consequently, in situations where the typical DC link capacitor under full load conditions would normally see a 40-50°C temperature rise, the Power Ring Film Capacitor can deliver less than 10°C temperature rise, under the same conditions, or it can handle much more current with similar temperature rise as the traditional capacitor bank. For the usual Alternative Energy cooling parameters this can mean 2 or 3 times the safe current rating per mF.
The example below shows the Power Ring temperature rise in a DC Link application when compared with the typical DC link film capacitor parallel array. Due to lower energy losses than a conventional array, the Power Ring can provide for a significantly greater ripple current filtering in less space, for less money and with less required cooling. The volume of the capacitor can be reduced by up to 75% versus the traditional DC Link Capacitor implementation, when used with the traditional cooling methods.
- Temperature Rise Power Ring vs Conventional Capacitor
Cutting the size of the capacitor and the related materials used greatly reduces costs. For the first time, a capacitor has been designed for increased current under long-term exposure rather than the typical approach of adding more and more capacitors until a reliable current rating is achieved.
The Power Ring bus terminal structure offers loop inductance as low as 3nH on a properly configured laminated bus which allows for less stress on IGBT turnoff giving the designer previously unavailable choices:
- run a higher bus voltage for a given IGBT rating,
- specify lower voltage, less costly IGBTs,
- enjoy the increased safety margin and resulting MTBF by banking the lower temperature rise and inductance into longer MTBF for the capacitors AND the IGBT as currently designed.
The result is a cost-effective total system solution operating at a lower temperature resulting in a long lifetime.
Integrating the Power Ring into Your Design
Customers often use the Power Ring Film Capacitor as a drop-in replacement for a bank of aluminum electrolytic or conventional film capacitors. However, our application engineers can work with you on a custom design to fully integrate the capacitor for maximum performance. Contact our application engineering team by phone or email to discuss your requirements.
Additional Readings:
- Our technical team has presented numerous papers on the use of the Power Ring Film Capacitor in the DC Link Application including optimum ways of connecting the capacitor to the switch bus. Please check them out on our technical papers/presentations page.
- DoE Research of DC Link Film Capacitors using 105°C Coolant
SBE Inc. has been the recipient of a Phase I and Phase II grant from the Department of Energy (DoE). See here for details on initial results and progress. - Examples of alternative energy applications: Click here for detailed specifications.
- High Energy Storage Controller
- Inverter DC Link
- High Voltage Utility Grade
- Power Conversion
- Corona Free