IN Brief:
- Toray and Nagoya University demonstrated inverter operation at 150°C using a prototype film capacitor.
- Thermal modelling suggests a possible 50% reduction in the size of a cooling structure, not a verified product improvement.
- Further reliability, manufacturing and commercial evaluation of the dielectric is planned.
Toray Industries has demonstrated operation of a prototype inverter at 150°C using a film capacitor manufactured with its proprietary heat-resistant dielectric material. The Japanese materials company conducted research with Nagoya University, combining a physical inverter demonstration with thermal simulation indicating the potential to reduce the size of a heat dissipation structure in an electric mobility power control unit by approximately 50%.
Film capacitors can constrain inverter thermal design when their permitted dielectric temperature is lower than the temperatures tolerated by nearby switching devices. An inverter converts direct current into alternating current to control an electric motor, using semiconductor switches to regulate frequency and electrical characteristics of the output. Film capacitors are used in these circuits to stabilise DC link voltage and manage electrical energy during switching and changes in motor loading.
A film capacitor consists of conductive electrodes separated by a thin polymer dielectric, which stores electrical energy through the electric field established between them. The material must withstand applied voltage while maintaining acceptable insulation resistance, capacitance stability and electrical losses during operation. Temperature affects these properties and can accelerate dielectric ageing, meaning thermal limits are important when establishing permitted operating conditions of a power conversion assembly.
As inverter designers increase power density, capacitors may be positioned close to semiconductor switching modules and other components generating substantial heat. Silicon carbide power devices can operate in demanding thermal environments, but surrounding passive components may require additional cooling, physical separation or protective structures. Increasing temperature capability of the dielectric provides another engineering option, although a completed capacitor must still satisfy electrical and lifetime requirements.
Toray has developed a film intended for capacitor operation at 150°C and incorporated it into a prototype device evaluated with Professor Masayoshi Yamamoto of Nagoya University’s Institute of Materials and Systems for Sustainability. The researchers demonstrated stable capacitor operation within a model inverter under high-temperature conditions. The result provides experimental evidence that the material can function in the circuit environment, although full long-term endurance data and commercial qualification results have not been published.
In parallel with inverter tests, Toray used thermal simulation to examine the potential effect on a power control unit designed for electric mobility. Its calculations indicate that adopting a higher-temperature capacitor could allow the relevant heat dissipation structure to be reduced in size by approximately half. The figure is an estimated design benefit derived from modelling as of September 2026, rather than a measured reduction in dimensions or mass of a completed production inverter.
Greater dielectric temperature tolerance may allow a capacitor to operate closer to surrounding semiconductor switching devices, reducing the cooling or isolation needed in some inverter configurations. The final thermal design still depends on switching losses, heat transfer paths, ambient conditions and temperature limits of other components.
Temperature is only one constraint on a DC link capacitor because ripple current and switching transients also affect internal heating. Equivalent series resistance, dielectric thickness and electrode construction influence both electrical behaviour and the trade-off between capacitance, package volume and voltage withstand capability.
Toray is extending earlier polymer film work on withstand voltage and dielectric performance into a representative inverter operating environment. The demonstration advances that work from material testing into operation within an inverter, providing a more representative assessment alongside switching and control functions. Further evaluation will determine manufacturing consistency, lifetime and suitability for individual voltage and current requirements.
NEDO supports the research into heat-resistant capacitor film for electric mobility systems, including electric vehicles and electrically powered aircraft. Air-cooled power control units are among the objectives because reducing cooling equipment can constrain mass and physical volume of an electric drive system.
In electrically powered aircraft, the mass and occupied volume of cooling equipment affect packaging options for the entire drive system. Yet potential benefits depend on the complete electrical architecture and do not amount to verified improvements in vehicle weight, energy consumption or range. The current results establish high-temperature operation of a prototype capacitor and a modelled cooling structure reduction under specified conditions.
Toray plans to continue developing and evaluating the film with Nagoya University before commercialisation. The company is also presenting the technology through NEDO at CEATEC 2026 in Japan from 13 to 16 October. Later engineering work must establish whether the dielectric meets reliability, manufacturing and electrical requirements for commercial high-temperature inverter capacitors.
