Disruptive Capacitor Technology to Improve Efficiency of Inverters Used in Hybrid and Electric Vehicles
Chief Executive Officer
PolyCharge America, Inc.
Interview conducted by:
Lynn Fosse, Senior Editor
Published – February 3, 2020
CEOCFO: Dr. Yializis, what is PolyCharge America, Inc?
Dr. Yializis: PolyCharge is a spin-off of Sigma Technologies International, in collaboration with Delphi Automotive. The focus of the company is to manufacture DC-link capacitors for inverters used in electric drives.
CEOCFO: What is it about your capacitors that makes them different, better, faster, cheaper; any or all of the above?
Dr. Yializis: We have developed a disruptive capacitor technology that will have a major impact in the energy and power density of inverters used in hybrid and electric vehicles. The metallized polypropylene capacitor technology used today to manufacture DC-link capacitors is more than forty years old. In fact, while working at the General Electric company in the 1970s I myself made major contributions to the development of the polypropylene film capacitor technology. Since then, there have not been any major changes to the technology other than the manufacture of thinner polypropylene films. DC-link capacitors have to operate in conjunction with power semiconductors that “chop” the DC battery voltage and eventually convert it into three-phase AC that drives the electric motors. The power semiconductors range from traditional silicon based IGBT (Insulated Gate Bipolar Transistor) components to newer and more efficient silicon carbide and gallium nitride MOSFETs (Metal–Oxide–Semiconductor Field-Effect Transistor) that operate at higher voltages and frequencies and can operate at higher temperatures. Polypropylene capacitors have severe temperature limitations which are exacerbated as the operating frequency increases. Higher frequency translates to higher current that causes the capacitor temperature to increase. The maximum temperature limit of polypropylene capacitors is typically 115oC.
It should be noted that in addition to the temperature and size limitations of the current technology, thin capacitor grade polypropylene films are produced by a handful of film OEMs worldwide. The film is then processed by metallizing OEMs that deposit the metal electrodes and slit the film into bobbins of different widths as specified by the capacitor manufacturers. Capacitor OEMs process the metallized film bobbins into wound capacitors. Therefore, the whole metallized capacitor film industry uses the same polymer dielectric, living little room for innovation and improvements in capacitor performance.
CEOCFO: Is this your PolyCharge NanoLam™ technology?
Dr. Yializis: The Polycharge Nanolam technology is a radical departure in the way metallized capacitors are produced. The film production, metallization process and capacitor winding, are replaced with a “black box” that is fed with two materials to produce the capacitors. Aluminum wire and a liquid monomer are converted into a large area nanolaminate composite material which is segmented into individual capacitors. Therefore, the three steps required to produce a conventional metallized film capacitor by three different OEMs, which also translates into three different profit margins, are reduced to a single process performed by the capacitor OEM, who now has control of the polymer dielectric chemistry, the metallization process and the dielectric thickness.
Our capacitors comprise a highly cross linked, self-healing, polymer dielectric, which allows the capacitors to be processed at temperatures as high as 250oC. In addition to the high temperature properties, Nanolam capacitors typically have two or more times higher energy density than conventional metallized polypropylene film capacitors. The high energy density is due to several factors that include the polymer dielectric thickness and a higher dielectric constant. Conventional polypropylene film dielectrics have a thickness of the order of two or more microns. Some years ago, we discovered that as the thickness of the dielectric is decreased to submicron levels, the breakdown strength increases. Therefore, all Nanolam capacitors are produced with a dielectric thickness is <1.0 micrometers and as low as 0.1 micrometer. Also, the dielectric constant of the Nanolam polymer is 3.2, in contrast with 2.2 for the polypropylene film, which translates to 45% higher energy storage. This in combination with the higher breakdown strength of nanothick dielectrics, is responsible for the increase in capacitor energy density. The higher temperature polymer dielectric results in capacitors that have stable capacitance and dissipation factor up to 200oC.
As we transition from silicone IGBTs to silicon carbide MOSFETs, what we are finding from discussions with major automotive Tier-1 suppliers and automotive OMEs, is that polypropylene capacitors become larger than they need to be in order to handle the higher current and their projected life is shortened. There are no simple solutions to improve a capacitor technology that is more than 40 years old. Instead, alternative technologies are required to service new applications that combine high current and high temperature requirements. The Nanolam capacitor technology which results in monolithic, self-healing capacitors with 1000s of nanothic capacitor layers, is such an alternative and truly disruptive technology. The Nanolam one step manufacturing process utilizes components such as monomer flash evaporators, plasma reactors and electron beam curtains, which combine to advance the state of the art in metallized film capacitors.
CEOCFO: It would seem hard to resist!
Dr. Yializis: It is hard to resist! Our biggest problem right now is also the advantage that we have over the current technology. Although we have a superior product and we have attracted the attention of many major players in the industry, the problem that we are facing is that the Nanolam capacitors are smaller than the current capacitors and can take higher temperature. Therefore, the challenge for a major inverter OEM that is introducing a new inverter model with say a volume of one or two hundred thousand units per year, is to trust that Polycharge who at this stage has limited resources, will be able to supply this quantity without interruption, from a single manufacturing facility. If they design a smaller inverter to take advantage of our capacitor properties and there is disruption in the supply, they will not be able to fit a conventional capacitor in the allocated space that will meet the size and temperature requirements.
CEOCFO: How are you addressing that challenge?
Dr. Yializis: We are basically addressing that in two ways. We are planning to put a second manufacturing facility in a different location and we are negotiating a license with a major multinational capacitor OEM to create a second source.
CEOCFO: Are you seeking additional investment, funding and partnerships?
Dr. Yializis: Yes. We are in the process of another round of financing.
CEOCFO: Is there much innovation in batteries today? Competition for PolyCharge?
Dr. Yializis: It is very interesting that you are asking this question, because if you look at batteries, there are at least one hundred companies around the planet that are looking to develop and manufacture advanced lithium batteries. In parallel there is also a significant level of development in low voltage battery-like electrochemical capacitors. However, there is relatively little development in the area of self-healing high voltage electrostatic capacitors, thus little or no competition for Polycharge. This is the reason why metallized polypropylene capacitors are still a leading technology, in spite of the low melting temperature of the polymer. There has been some development in the area of extruded high temperature polymer films but this technology has stalled. The films are relatively thick, to service most DC-link inverter capacitors, the resin cost is prohibitively high and unlike polypropylene and the Nanolam polymer dielectrics, most such film chemistries are not self-healing. That is, if there is a breakdown in the capacitor dielectric the capacitor will not be able to self-heal and continue to function. Looking at the Nanolam innovation strictly from a cost perspective, the two materials that are fed into the “black box” (aluminum wire and monomer) to produce the capacitor material, have relatively low cost. The monomer chemistry is no different than monomers used in the UV printing industry and various other protective coatings, including linoleum floors, wood panels, etc.
I should also note that in addition to developing the Nanolam capacitors, Sigma Technologies utilized the same high-speed submicron polymer deposition technology for multiple other commercial applications. For example, Sigma manufactures radiant barrier materials for attic insulation and window coverings using multilayer polymer/metal coatings on large web-based substrates, as well as a nanoflake aluminum pigment that is used in inks and paints. Sigma has also licensed the Nanolam technology to major OEMs for applications that include security devices for currency applications in the form of multilayer pigments and films and heat management for commercial and residantial housing applications. Sigma Technologies also co-founded with Battelle-PNL, Vitex Systems, a company that used the Nanolam technology to produce multilayer ultrahigh moisture barrier coatings for protecting OLED (organic light-emitting diode) devices. The Vitex Systems technology was sold some years ago to Samsung who used it on the backplane of OLED displays on their cellular phones. Therefore, one could say that the Nanolam Capacitor process for depositing submicron polymer coatings is somewhat mature and has been demonstrated using similar large-scale equipment in other applications.
CEOCFO: Are you confident that it is just a matter of time?
Dr. Yializis: Absolutely. There is no question in my mind! This technology is here to stay. We have had Nanolam capacitors with a very flat shape operating in an inverter of a Formula-e car for the last couple of years, that have functioned extremely well. It allowed the inverter to have high power density in a relatively small package. Conventional metallized polypropylene capacitors could not fit in the allocated space and survive in the high ambient operating temperature. It is just a matter of scaling-up the technology and producing adequate quantities to satisfy the needs of different inverter OEMs and the need is rapidly growing.
CEOCFO: When did you know you had a solution?
Dr. Yializis: We knew we had a solution when the DOE, (Department Of Energy), put out a solicitation for the development of a high energy density and high temperature DC-link capacitor. The DOE has a vehicle technology group that is looking to advance new vehicle technologies. At the time, it almost felt that they were looking for something that very difficult to achieve. We partnered with Delphi Automotive and we were awarded a three-year development contract. During this period, we developed the Nanolam capacitor that met and exceeded all of the DOE’s requirements. At that point, we knew we had a solution to the size and temperature limitations of the current polymer film technology.
CEOCFO: Why pay attention right now to PolyCharge? Why is the company important?
Dr. Yializis: The company is important because there are not too many innovations in this area of technology. Addressing parameters such as cost, size and temperature in a capacitor which is a key component of inverters used in hybrid and electric vehicles can be a huge deal. We believe that we are going to grow along with the growth of the electric drive vehicle market. The numbers for projected capacitor sales for the next five to ten years, translate to billions of dollars. Beyond the automotive applications, there are other markets and applications that we are starting to address, where the qualification requirements are more relaxed and the profit margins can be significantly higher.