Cross-Forming Control: "Our algorithm could be a key enabler for integrating more renewable energy"
Maitraya Desai is a doctoral student in the Power Systems Laboratory, researching at the intersection of power systems, power electronics and control. In this interview, he explains a novel control approach for grid-forming converters that could enhance the stability of future power grids, especially with high penetration of renewable energy sources.
Maitraya Desai, could you briefly outline your current research for us?
Sure. My research focuses on stability issues in power systems with high penetration of converter-interfaced distributed energy resources. I conduct dynamic power system studies using detailed models to analyse stability and explore modifications to control schemes to ensure stable and reliable operation of present and future power systems.
One of your recent discoveries could significantly contribute to the energy transition. Can you describe this invention and how it came about?
Today’s power systems operate on alternating current (AC), synchronized at a frequency of 50 Hz (e.g. in Europe) or 60 Hz (e.g. in the United States). Traditionally, this synchronization was maintained by physically rotating synchronous generators. However, as these generators (from powerhouses) are being phased out in favour of environmentally friendly, distributed renewable energy sources like solar and wind, we face a challenge. These sources don’t naturally produce electricity at a fixed frequency – solar generates direct current (DC), and wind can produce variable-frequency AC. So, we use converters to interface them with the grid. The problem is that today’s converters latch onto the grid frequency and behave like current sources. Now if there is no frequency to latch on to, one needs to reprogram the control of the converter to exhibit voltage source behaviour and generate its own frequency. There has been extensive research in this space and this control is given the name of ‘grid-forming’. But during grid faults – say, a tree touching an uninsulated transmission line – a large surge in current is demanded. Unlike synchronous generators, semiconductor-based converters can’t handle such surges and must limit their output current, which leads to instability due to loss of synchronization even for these grid-forming converters. Together with Dr. Xiuqiang He, Dr. Linbin Huang – both former postdoctoral researchers and senior scientists at the Automatic Control Laboratory –, and Prof. Florian Dörfler, we developed a control strategy that, even under grid faults, preserves grid-forming voltage-source behaviour to the greatest extent possible. We call it Cross-Forming Control.
Could you explain how this control method works?
In essence, we realized that to maintain stability, we need to independently manage two things: the voltage angle, which handles synchronization, and the current magnitude, which ensures the converter isn’t overloaded. This decoupled control structure allows the converter to behave like a voltage source (to the greatest extent possible) even during faults, maintaining stability and supplying as much current as safely possible.
What makes your solution particularly effective?
Our approach builds on years of existing research and is designed to be backward-compatible with present grid-forming solutions. It requires only software modifications – almost no new hardware. That makes it easy to implement and integrate into existing systems.
Is your solution specific to the European grid, or could it be adapted for global use?
It can definitely be adapted. The control strategy is flexible and can be tuned to different grid frequencies. It’s applicable worldwide with minor adjustments.
Could this solution accelerate the energy transition?
I’m very hopeful it can. We’ve already validated it mathematically and in small-scale experiments. We’re now working with industry partners to test it on a larger scale. If successful, it could be a key enabler for integrating more renewables into the grid.
“We developed a control strategy that, even under grid faults, preserves grid-forming voltage-source behaviour to the greatest extent possible.”Maitraya Desai
Has the patent already been filed?
Yes, the patent was filed in April 2024. Since then, we’ve published a couple of papers and are in discussions with industry partners for potential collaborations, including Master’s theses and larger-scale validations.
To what extent does this algorithm contribute to your overall doctoral research?
I am focusing on various topics for my doctoral research ranging from revisiting the modelling of present and future power systems to their stable and optimal operation. This algorithm fits right into this doctoral research scope. For instance, I am currently performing comparative performance analyses of different control approaches – including ours – in terms of grid services.
Would your algorithm work with all types of renewable energy?
Yes, it’s designed to be compatible with various renewable sources – solar, wind, etc. – as long as they’re interfaced through converters. The control logic applies regardless of the specific energy source.
What’s the next step for your work?
We’re aiming to validate the algorithm in a large-scale setup by the end of this year. If successful, it could pave the way for technology transfer and broader deployment.
Finally, what drew you to Electrical Engineering and ETH Zurich?
I’ve always enjoyed math and problem-solving. During my bachelor’s in Mumbai, I became interested in the control of power systems and came across research papers from various labs across the world. It was one such paper by Professors Florian Dörfler and Gabriela Hug that inspired me to apply to ETH Zurich for my Master’s, and now I’m pursuing my doctoral studies here.
About Maitraya Desai
Maitraya Desai's research highlights the importance of innovative control concepts for the integration of renewable energy sources. His solution could be a crucial component for a stable and sustainable power grid in the future.
Before beginning his doctorate at the Power Systems Laboratory (PSL), headed by Prof. Gabriela Hug, Maitraya Desai completed a Bachelor's degree in Electrical Engineering at Veermata Jijabai Technological Institute in Mumbai. He then pursued a Master's degree in Electrical Engineering and Information Technology at ETH Zurich. During his Master's studies, he worked on a semester project at the Automatic Control Laboratory under the guidance of Prof. Florian Dörfler, Dr. Xiuqiang He, and Dr. Linbin Huang. He is currently conducting his doctoral research under the supervision of Prof. Hug, with Prof. Dörfler serving as his second supervisor.