3 Reasons Why 2 Words are Key to an Agile Distribution Grid

by Vince Martinelli

The world of electrical energy delivery is changing. Customer-led disruption is the driver. But technology is also playing a role. One technology, in particular, is core to this evolution and is inexorably migrating from behind the customer meter into the distribution grid itself.

Remember these two words: power electronics.

Solar PV installations in 2016 topped 14.8 GW in the US. The total number of installed sites — including residential, commercial and utility-scale systems — surpassed 1 million during the year. Every solar PV system uses a power electronics-based inverter, or a series of them, to convert the DC power coming from the panels to AC power that can be consumed by appliances or transported via the grid.

Many energy storage systems are based on batteries that also natively produce DC voltage and use the same basic power electronics technology to deliver AC power. These systems recharge using the reverse process, meaning the inverter capability needs to be bi-directional.

The same is true for electric vehicle (EV) systems where the batteries in the car are DC sources or sinks for power and the charger must be able to convert power from AC to DC and vice versa, playing a “brokering” role with the outlet in your home or the grid itself.

It’s not just Tesla building storage systems and EVs. Mercedes-Benz now has an energy storage business and Ford, General Motors and Nissan — in fact, almost all car manufacturers, either produce electric vehicles or have announced plans to do so. Worldwide, more than 2 million electric vehicles, EVs and plug-in hybrids are now on the roads.

Power electronics is important to many products and systems and is key for integrating renewable energy and electrification of transportation, both of which are experiencing significant cost reduction and market growth.

So why is now the time for power electronics in the distribution grid?

Reason #1. New Demands on the Distribution Grid

All these new electric “appliances” connecting to the grid are putting greater demands on the traditional one-way power flow architecture designed for relatively steady state demands. Power flow is increasingly dynamic with distributed variations.

Energy efficiency and demand response programs also are shifting power flow dynamics on the grid, reducing fuel consumption for power plants and lowering peak costs for utilities, but also creating new grid operational challenges in the process.

The substation and distribution feeder circuit may not be the ideal nexus from which to control such a system, since it relies on relatively few control points that react slowly and treat all customers, whether hundreds or a few thousand on a line, as a collective.

Localized power regulation and control, for variable bi-directional power flows, requires a more agile approach; one that recognizes that service demands today increasingly depend on neighborhood-scale solutions to ensure reliable power quality and efficiently manage capacity constraints.

Ironically, power electronics-based devices on the customer side of the meter are creating a need for power electronics solutions on the grid side.

Reason #2. Falling Component Cost Virtuous Cycle

With millions of systems installed, costs for components have dropped dramatically.

A virtuous cycle of market growth and falling costs for PV and EV is fueling markets for power electronics components.

One of the key elements to power electronics systems sized to handle the voltage and current levels for solar inverters, EV chargers and the low-voltage utility grid, are devices known as IGBTs, or Insulated Gate Bipolar Transistors. These transistors are the key to building power processors, much as computer processors rely on microelectronic transistors built into integrated circuits. A well-designed power processor, like its computing cousin, can perform multiple tasks, depending on the software instructions, which are built based on particular application use cases.

And it’s not just the cost points of IGBT modules that have improved. Reliability and performance in elevated-temperature environments are also better, making it possible to design systems that are passively cooled and capable of performing well over a long, maintenance-free life.

The benefit of this virtuous cycle means power electronics solutions for distribution are both capital efficient in the near term and offer a low cost of ownership for utilities over decades. With more than 40 million distribution service transformers in the US alone, these economic trends are essential to achieve deployment at scale.

Reason #3. Inherent Flexibility

Power electronics processor functionality is defined by software, unlike traditional, electro-mechanical grid hardware systems, which are often used in simple on/off control modes. This means the range of functionality is quite broad and can be updated even after the devices have been installed in the field. Another favorable outcome of a software-centric approach is the ability to build distributed operating systems and hosted applications layered onto the hardware platform. This path provides flexibility enabling capabilities that support emerging business and market structures.

Software also enables cross-platform control and coordination, such that a device located near the distribution transformer on the utility side, for example, could play a role in managing behind-the-meter assets, deriving maximum benefits by driving higher utilization of distribution assets. Such systems will help make sure solar owners are allowed to generate and export as much energy as possible from their rooftop systems, EVs will be “fueled” for the morning commute, and storage systems will charge and discharge in synch with owner needs and market signals. All these capabilities contribute to avoiding or deferring broad-based grid capacity expansion programs — saving large sums of money in the process.

Today, utility-scale power electronics systems are appearing in the distribution grid: near service transformers in North America and on low-voltage circuits downstream from secondary substations in Europe. These devices ensure power quality service levels and provide a platform for localized control, which can be applied as part of a coordinated plan for integrating distributed resources.

The underlying technology enabling agile grid modernization boils down to two words: power electronics. Now you know why.

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