#68🚀 An Optimal Frequency for Power Converters?
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👋 Hello, friends! Dr. Molina here 👨🔧
Welcome to Dr.Molina Newsletter, where I break down Magnetic design for you every week, in
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Today I bring you an article from my new colleague and Product Director at Frenetic Online, Jonathan Church. He was a Frenetic customer and now he is working here…amazing. Enjoy his article!!
An Optimal Frequency for Power Converters?
By Jonathan Church
All too often, I find myself thinking about the design processes that we take as engineers to make power converters (what a revelation!!! Hardly surprising considering my job). Especially as our experience grows over time, do we ever stop experimenting? Or do we become set in our ways, use the topologies and the boundaries we know best and take less risks just to bring the money home?
Two things that play on my mind weekly are the processes that we take to choose the correct topologies and the processes we take to choose the optimal operating frequencies for our designs. I could talk about both at length, but today I want to talk about optimal switching frequencies, perhaps another time I can talk about the former.
I want to refer back to Chema´s recent article: #65 Where is the Problem with the Magnetics? He reflects upon the idea that magnetics are the bottleneck of power converter designs and discusses how industry perceptions have lead this to become a common belief. I would like you to bear this in mind throughout.
A cardinal virtue of every proud and prudent power electronics engineer is an understanding of their priorities. And YES, there must be a priority. A pursuit for the smallest, cheapest, most efficient power supply that arrives tomorrow is only going to end in disappointment. A good engineer understands the brief, and knows how to strike the right balance between size and efficiency for each and every project they undertake. Lurking somewhere amidst size and efficiency is the greatest power density you can achieve for your design, we can play with operating frequencies to effectively achieve our goals here, but it requires a well-rounded understanding of our system.
Increasing the operating frequency will reduce converter size, but eventually the gains will be eroded by the need for additional heatsinking or other forms of more advanced and costly cooling. Alas, another plate to spin. Let’s take a holistic look at the effect that the changing of frequency has on our power system components below.
Intuitively, your switching losses and gate-drive losses are going to proportionally increase. Many great innovations are reducing the gradient to which these losses increase but despite this and despite any type of soft-switching resonant converter you may be using, this is still going to happen so keep an eye on them.
The reactive components in the system will reduce in size as you increase the frequency, notably your input and output filtering. This is a quick win for your power density providing you have well in hand (sorry Luke) the knowledge required to design an effective filter, plus you understand the control and stability aspects of your design.
Now let’s talk about the “bottleneck”, or perhaps a better term I think would be the “pacemaker”. When we increase the operating frequency from the magnetics’ perspective it isn’t as straight forward. If we increase the frequency we want a Return On Investment (ROI), we want to see a reduction in core size ideally. This can be achieved, and you may or may not be able to maintain your core losses I would hate to say… Bear in mind however, the same losses in a smaller object will result in a greater temperature rise and that must be managed somehow.
Finally, as we increase the frequency and cash in by reducing our core size, our winding window gets smaller, the current density increases and so will the effect of AC losses in our wires. Needless to say, magnetics are the most complex part of a power converter design, especially as we push the boundaries.
Now this is my opinion (but it’s hardly original), and I would like to hear your response. I think that often the greatest bottlenecks of a power converter project are actually TIME and MONEY. These two priorities easily stifle any engineers ability to experiment and hone their craft, they’ll be busy battling timelines and budgets.
Luckily the Frenetic online platform will save on both time and money by simplifying the design process. It will also allow you to experiment and learn along the way. Things are changing daily in the world of power electronics, don’t lose your curiosity. Come and join us to make sure you don’t get left behind.