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Bench Talk for Design Engineers

Bench Talk

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Going Off-Grid Efficiently With MicroGrids Paul Lee

Microgrids in Focus

(Source: Mouser Electronics)

I’m no survivalist and my efforts to save the planet are pretty puny in the grand scheme of things. Still, it seems increasingly attractive to go off-grid—be independent of national grid energy from potentially unsustainable sources. This is the altruistic reason, but there are some possible cost savings—as well as environmental benefits—and then reassurance that I can continue writing blogs on a keyboard rather than with a pen if the power goes down. The term in vogue is a microgrid—it could just be a universal power supply (UPS) or a miniature version of the national grid, with its own local energy source, such as solar, wind, hydro, or an old car alternator strapped to an exercise bike, and local loads such as lighting, HVAC, or blog-enabling laptops. I’d be particularly pleased if I could get fit, lose weight, and write with the energy expended.

The terminology is a marketer’s playground—although a nano-grid of a backpack-mounted solar panel, topping up a cellphone is an amusing idea—microgrids are something much more serious and becoming a big market: $47 billion (USD) globally by 2025, according to some analysis. Most installations are domestic, with typically solar power just feeding into the local alternating current (AC) mains and reducing utility bills a little. More complex arrangements include a battery that can store cheap utility overnight energy or excess solar during the day, and even pass energy back to the main grid with a feed-in tariff (FIT) giving some cash back. The battery could also supply all nighttime needs after sunset and, of course, provide emergency backup.

The potential environmental benefits, cost savings, ability to sustain operations in the event of a power outage are key drivers fueling the interest in microgrid installations. However, adoption is dependent on efficient power conversion electronics enabled by the increasing use of wide bandgap semiconductors. Here we will explore how wide bandgap semiconductors using silicon carbide or gallium nitride provide a solution to making microgrids power-efficient.

Optimizing Power Usage and Savings with Microgrids

EV Installations

Many of us with EVs have to think about the charging regime—the whole point is to save energy, so power from local renewables in a microgrid is definitely in the spirit of things. The EV battery is a big load to charge, so a carefully designed system will use excess local energy first and utility power as second-best, at the cheapest rate time. But then if you really have gone off-grid and don’t travel far, the car might sit idle for long periods. Utility companies will pay you to return some of the energy to the main grid for load balancing at times of peak demand. Keep in mind that you will need a bidirectional charger for this.

Neighborhood Microgrid Installations

Microgrids can also apply to neighborhoods with an independent power source that shares and meters electricity between households. These might already be grid-connected, but could also be fully ‘islanded’ when utility power is distant or just not available, such as in developing countries.

Larger Microgrid Installations

Larger installations can benefit from microgrids as well. Hospitals, data centers, factories, and military sites realize the advantages of resilience against power outages, cheaper local power sources, and increasingly, security against cyber-attacks through the network. In these microgrid implementations, making the system smart is essential to get the quickest return from the capital investment. The installation achieves the best outcome when the operation of the microgrid integrates with site-wide efficiency initiatives, such as the Industrial Internet of Things (IIoT) in factories. With everything optimized, interconnected, and able to ride-through outages, productivity improves, as well as energy and costs.

Microgrids Must Be Efficient

If there is a downside to microgrids, it might be the necessity for various power conversion stages, as seen in solar DC-AC inverters and maximum power point-tracking controllers, bidirectional battery chargers, and wind turbine AC-AC converters. As the aim is to save energy—and money—these conversion stages should be as efficient as possible. There is a historical trade-off, though. Old technology IGBT-based power conversion uses switch-mode techniques that operate at relatively low frequency. This keeps efficiency up, but the low frequencies dictate large associated components, particularly transformers and filter inductors, which are expensive. Switching faster makes magnetics smaller, and suitable components do it efficiently in the form of MOSFETs, but only at relatively low power. This is fine for a domestic UPS, but in the larger installations, MOSFET converters run out of steam.

SiC and GaN Wide Bandgap Semiconductors

The solution is a new class of wide bandgap semiconductors using silicon carbide or gallium nitride as the base material. These switch phenomenally fast, so frequencies can be pushed up, making magnetics small and cheap. Even so, losses remain exceptionally low, so cooling arrangements are smaller, lighter, and of course, cheaper. SiC and GaN devices can be easily paralleled and stacked in cascode arrangements for hundreds of amps and kV ratings to compete with IGBTs at almost any power level.

Decentralization

Decentralizing power generation is a definite trend. It makes best use of local renewable energy sources, increases resilience, and lowers overall costs to consumers. And with more people working at home, keeping those laptops powered and productive is also a priority. Wide bandgap semiconductor switch technology is key to making it practical.

Conclusion

 The promises of maximizing local renewable energy, cost-savings, independence, resilience, and security, have led many to adopt microgrids and the expectation that the microgrid market will reach around $47.4 billion (USD) by 2025.  However, microgrids might not prove to be power efficient or cost-effective, depending on the components used in their design. Wide bandgap semiconductors offer a solution. SiC and GaN wide bandgap semiconductors offer extremely fast switching, low losses, and can be paralleled and stacked to compete with IGBTs at almost any power level.



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Pauil LeePaul Lee is the author of over 200 articles and blogs on power subjects as well as a book on power supply design techniques: ‘Power Supplies Explained’. As a Chartered Engineer and with a degree in electronics, Lee has worked as a Director of Engineering for Murata Power Solutions and manages the European Power Supplies Manufacturers’ Association.


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