#49 🚀 Apple Chargers Power Density
SuperPowers for Electrical Engineers 🦸🏻♂️🦸🏼♀️
👋 Hello friends! Dr. Molina here 👨🔧
Something has happened to me in the last year. In 2014, I spent 5 months in Padova, Italy, I learned a lot about the Italian culture 🇮🇹. Their traditions about coffee, pasta, and pizza.
When you eat pizza, you ONLY eat la pizza. You don´t share it or order anything else.
The coffee is short and intense. One shot. Like drinking tequila. You don´t bring a thermos of coffee.
However, in November 2021, when I started writing this NL, I spent too much time in the USA. Suddenly, I was carrying a thermos of coffee and in my kitchen, I have this new toy 🤷♂️ .
I have moved to the American coffee with my new Moccamaster.
Italians, don´t hold it against me, I still love Italy 😍.
We need a North Star Metric
When you build a startup, the only way to succeed is to have metrics. With metrics, you can track the evolution of your product and understand the impact of your decisions over that metric.
When I tried to analyze the evolution of Frenetic, the variables to track that came to my mind in the first place are related with accuracy. How accurate are the models of temperature, losses…Leakage inductance…We measure the magnetics we are building and we check the prediction.
You can have accurate models and very bad magnetics. Then, I asked myself. Which metric can I use to see how good a design could be? At the power converter level, this parameter is the Power Density (P.D.) for a specific standard.
P.D. is calculated by dividing the Volume over the power ratio of the converter, I like to use kW per dm3 (equivalent to a liter).
We need to consider the impact of safety standards on the size, the values of creepage and clearance can make your system much bigger 🤓, here is an example.
Everything started in Tokyo…
Hiromichi Ohashi is a Japanese researcher in power electronics from the Tokyo Institute of Technology, who published in the year 2003 the next study about power density (P.D.) [1], where we can see that the maximum value in 2003 was around 3 kW/liter but he projected an increase up to 10 to 30 kW/liter due to the coming semiconductor technologies.
He didn´t specify the converter construction (EMI + AC/DC + DC/DC with galvanic isolation).
Three years later, he published the picture below with a more completed study.
In 2008 Johan Kolar from ETH Zurich published a specific paper about the P.D. The picture below shows how he differentiates the P.D. in AC/DC and DC/DC.
In 2008, the average P.D. of the industry for each conversion type was:
0,3 kW/dm3 for 1 phase AC/DC (a regular charger we use at home)
2 kW/dm3 for Isolated DC/DC
4 kW/dm3 for 3 phases AC/DC (>10 kW systems)
20 kW/dm3 for 3 phases AC/AC (High Power systems)
Apple Chargers Power Density
To give some orders of magnitude of devices we are very familiar with, let’s break down Apple chargers. I have taken 4 different chargers, 5W and 20W are for the iPhone, and 96W and 140W are for laptops. The P.D. of these chargers varied between 0,28 and 1,79 kW/liter. Which can be seen as an improvement from the 2008 value (0,3 kW/dm3).
The Magnetics Power Density (MPD)
However, Frenetic doesn´t design the whole power converter, therefore, I choose the Magnetic Power Density (MPD) to be a good technical North Star.
I’m going to start applying this metric only for transformers in DC/DC converters or Flybacks.
I will take a scientific approach and the parameters and considerations will be:
MPD= Power / Volume
Power
I will take the output power ratio of the DC/DC. I will take note of the topology.
Volume
I will calculate the volume calculated as the parallelepiped space defined by the outer limits of the component. Basically, all the space which won´t be used by other components around will be considered part of the magnetic. I will use dm3 or liters as the default unit.
Cooling Systems
I will specify if the system is:
Liquid-cooled
Use Heat Sink
Box with resin
Fan
Natural convection
or a combination
MPD Real cases
To give you some values of the industry and Frenetic, I have taken 4 examples of DC/DC converters in the following table [2]-[5]. As you can see, the Academia publications are from x3 to x15 smaller than the industry products.
This edition is already too long, next week I will share graphs about MPD comparing Industry, Academia, and Frenetic
Next week I will share some current metrics of M.P.D. at Frenetic and I would love to receive designs from you to be included in the graphs as Florent Liffran did. He shared with me the size of their transformers and converter.
Florent Liffran is CEO of BrightLoop Converters.
BrightLoop Converters is a power electronics company, specializing in the highest performance power supplies, from a few kW to a few MW. Thanks to original concepts and mastery in multiple domains, from electronics to real-time software, including electromagnetism, wide Bandgap semiconductors, mechatronics or control algorithms, it designs and manufactures very versatile converters with the best power density on the market, for the most demanding real-life applications.
⚠️ Bad designs Alert
I have seen how you guys are not following a scientific method in Magnetic design. In the medium term, you are losing millions.
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References
[1] H. Ohashi, "Power electronics innovation with next generation advanced power devices," The 25th International Telecommunications Energy Conference, 2003. INTELEC '03., 2003, pp. 9-13.
[2] C. Fei, F. C. Lee and Q. Li, "High-Efficiency High-Power-Density LLC Converter With an Integrated Planar Matrix Transformer for High-Output Current Applications," in IEEE Transactions on Industrial Electronics, vol. 64, no. 11, pp. 9072-9082, Nov. 2017, doi: 10.1109/TIE.2017.2674599.
[3] https://www.pes-publications.ee.ethz.ch/uploads/tx_ethpublications/IEEJ_PowerDensity_Paper_FinalRevised.pdf
Great article!!!!