Simulating Microgrids: New Killer Test App?

June 30, 2020
Testing microgrid components can be time consuming. That’s a problem in a world where inverters often don’t play nice. But Powersim says it may have the solution.

Microgrid simulation can help ensure project success, but testing microgrid components can be problematic and time consuming. 

Now, a Maryland-based company says they have an app for that. Powersim says its new DSIM tool is the “killer app” for microgrid simulation, capable of speeds a multiple of previous tools and able to run on a laptop. 

As microgrids continue to proliferate and grow more complex testing could prove to be a major barrier. Without testing, microgrid components, inverters in particular, can interfere with each other and bring down the microgrid or the system to which it is connected. For systems that often are put in place to operate in an emergency and to ensure reliability, that could spell disaster or, at the least, be a setback for further proliferation. 

“One of the problems that pop up with microgrids and power grids in general is that inverters fight each other,” and that can lead to voltage fluctuations that can cause components to trip offline, said Grahame Holmes, an electrical engineer and professor at the Royal Melbourne Institute of Technology (RMIT) in Australia where he researches smart energy systems.

And, as microgrids become more complex, incorporating more components and with them more inverters, the problem only stands to get worse, Holmes said. 

Making inverters play nice

The key is testing components in the lab before they are deployed in the real world. “The big problem in all the literature, and in everyone’s mind, is how to make sure these inverters will play nice with each other,” Holmes said. “The evidence is that they don’t.” 

The goal, he said, is figuring out why they don’t get along and what can be done about it. That requires testing, but one of the major research problems is the time it takes to test components that operate at sub-second speeds. 

The Holy Grail among electronic component testing companies is achieving something like real time simulation, a difficult task when inverter performance is measured in milliseconds. 

Today, it can take hours to simulate a couple seconds of inverter functions. So, testing one inverter’s functioning for 100 milliseconds could take five minutes. If a microgrid has 10 inverters, it could take tens of minutes or hours to test 100 milliseconds of inverter functioning. That can make testing multiple inverters for several seconds untenable. 

“That is a dilemma,” Holmes said. 

One approach to the problem has been to simplify or approximate an inverter’s function, or to test the inverter’s function in principle. That can render the accuracy of the test uncertain. It also fails to test algorithms operators might want to program into an inverter. Those types of simulations can be “relatively inaccurate” and “rigid,” Holmes said. “When we simulate an inverter, we want to be able to program the algorithm,” Brendan McGrath, Associate Professor at RMIT, added. 

Another approach is to run tests using supercomputers, which can quickly become very expensive. But Powersim says DSIM does not need dedicated hardware. It can run on a Windows laptop. 

Powersim achieves speed

Hua Jin, Powersim president, says DSIM also has achieved simulation speeds of 100 times, 1,000 times, and even 10,000 times faster than offline simulation software packages. And, he says, the larger and more complex the system, the greater the time differences become. 

Holmes has tested DSIM and says it runs 50 times faster than other simulations he has tested. “We can run seconds of inverters in about one fifth of the original time and with complete accuracy of the switching system,” he said. “We take 100% of the code of real controller and run in simulation and, when it works, load into real controller without change.” 

“The time taken to perform simulations is significantly shorter compared to any other simulation tools I have used,” Jorge Ramos Ruiz, a PhD student in the power electronics and quality lab at Texas A&M University, said.

Ramos sees the main advantage of DSIM as its ability to enable simulations that could be impossible to do otherwise. “These simulations are closer to reality than less detailed simulations. This, in turn, enables the power electronics engineer to design their experiments with more details. This makes control algorithms testing more affordable, but hardware testing is still required for some applications,” he said. 

While Jin notes that DSIM is not a “real time” simulation, it will handle “very fast.” As microgrids become more complex, the company says simulation times are rising but, “DSIM will allow for these new designs to be fully simulated and for these converters to be simulated working together in ways that have not been possible before now.” 

As welcome as DSIM’s advances in speed and affordability are, Holmes and McGrath say there is still part of the equation missing. A truly robust test, they say, should have the ability to include load from a rotating machine, whether it is a diesel engine or a gas turbine. After all, most microgrids incorporate some form of 24/7 generator. “Without a rotating machine, you only have half a load,” Holmes said. He said Powersim told him they are working on that and expect to add that function soon.

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About the Author

Peter Maloney

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