When natural disasters create power outages anywhere in the world, it has a devastating impact on the local economy and lives. Power restoration can takes weeks to months. In some regions of the world there is no option other than diesel to generate energy.

Microgrids, though, could answer both these challenges, providing a way to sustain power during disasters and allow isolated regions to tap into renewable energy sources in a sustainable way.

Microgrids

The grid as a global entity is fairly reliable. “However, it’s a 95-97% centralised production of power,” Brad Luyster, VP/GM Smart Grid, ABB Inc., says.

“As the director of ABB’s new ten million Smart Grid Center of Excellence in Raleigh, NC, I know that when putting elements like solar and wind into grid transmission, it puts on a mass amount that is subject to very high vacillation.

“ABB saw that microgrids smooth out renewable power generation and also eliminate the power down-time caused by natural disasters. The reliability benefits of microgrids is clear. When the main grid loses power, the microgrid goes into action, and as long as there is an adequate source of power at the local level (diesel generator, wind turbine, fuel cell, PV, etc.), the power continues to flow while the rest of the region is enveloped in darkness.”

“A microgrid adds reliability by adding redundant power. It ensures stability and grid control. Also, there are global regions that cannot be reliably addressed by any existing grid in¬frastructure and need a self-contained power generation method to reduce dependence on diesel power.”

ABB technology

A typical microgrid power system consists of: generators, a power source, distribution feeders, a main grid connection/interconnector switch and energy storage devices for short term storage/stabilisation and long term storage/stabilisation. It also requires demand managed devices for industrial controllable loads, or commercial/residential loads.

“All these individual devices need to be integrated to interact as a strong system. There are two types of interaction between these devices: Electrical connection (existing through the wires that carry the energy to the loads) and communication between the devices,” Luyster says.

ABB has developed distributed controls called RMC600 that handle generation control. For stability, ABB’s PowerStore stabilises the grid. “When going off grid, you have to think about how is that power stabilised and how is it being kept. You can generate power but when you start connecting people and cities, you have to make sure that you have a good, stable system,” he says.

“The RMC600 observes the ups and downs of renewable power generation and in conjunction with our PowerStore stabilization system, can accomplish 100% absorption and 100% discharge in microseconds. This means that in many areas, wind or solar can be used for energy 100% of the time. It can also manage and automate power generation systems that utilize different energy resources such as diesel, HFO, gas, geothermal, hydro, wind, solar, and tidal.

“It enables and maintains the grid integration of renewable and conventional generators in a cost and energy efficient manner. It is designed to allow communication between any electrical device and uses a common hardware platform to run different firmware depending on the type of electrical device attached.

“The RMC600 is manufacturer independent and successful communications have been established with wind turbines, diesel generator controllers, solar and battery inverters as well as with ABB components,” Luyster says.
RCM 600N network control and monitoring system provides information about the status of a Grid/Network connection switch. It synchronizes the microgrid with the main grid and can control power flow across the connection by controlling the power consumption/generation of the electrical devices in the microgrid.

“Rather than battery storage, the RE+ (RMC plus PowerStore) uses a flywheel which is a rotating mass, the ABB PowerStoreTM. It is a three ton flywheel, which is a rotating mass that fits inside of a UM chamber. In our case, the flywheel is low speed rotating at 3600 RPM inside a helium chamber and is extremely low maintenance. When needed, that spinning reserve turns on a generator feeds the system. It acts very fast and only lasts about 20 to 30 seconds. As soon as it’s not needed it, it starts recharging by spinning that mass up higher again,” Luyster says.

“The reason we use this instead of batteries is that batteries typically either completely recharge or discharge. They aren’t designed to do a fast recharge/discharge. The flywheel has a high duty cycle and can recharge and discharge quickly…Two seconds it’s discharging…Two seconds it’s recharging.”

The flywheel coupled to ABB’s PCS100 inverter provides voltage, frequency, and power support, hence, grid stabilization. The full RE+ system can be configured to operate in a grid support mode for use in multimegawatt grids, or as a virtual generator for smaller isolated microgrids.

“A microgrid uses generators; diesel, natural gas, fuel cells, solar, wind. The RMC600 DCS looks at all of those as individual generators and coordinates them to work together and produce a base load of utility grade power. As it sees wind or solar dropping, it knows that it needs to get its generators up and running. For instance, if power is running three gensets at 35% it knows to boost this to 60% because the wind or solar generation is falling off. This is done in real time to prepare for times when renewable power generation does drop to nothing it can bring the generators back up to achieve base load power. The coordination required to make the energy generation smooth at all times is automatic.”

ABB does incorporate batteries for stability in a solar field by charging them up during the day while the sun is strong and then discharging them to the grid when there is no solar being generated. “This compliments the solar system,” Luyster says. “Wind is often the opposite. Wind can tend to be stronger at night, so the batteries will charge up at night and discharge during a wind free day.”

Benefits

Microgrids are a piece of the energy puzzle that make renewable technology more robust. “Instead of installing giant solar fields, we will be able to join it all together using various modes of smaller sets of renewables and control them through a microgrid, making it a big multiplier for renewable energy,” Luyster says.

“The capital outlay required for a microgrid is often much less and payback significantly faster than other initiatives intended to improve the availability and reliability of power. The payback for a microgrid is often measured in years, if not months, whereas the payback for a new utility-scale power generation might be measured in de¬cades and face a barrage of regula¬tory hurdles before it can even begin.”

About: Joyce Laird has an extensive background writing about the electronics industry; semiconductor development, R&D, wafer/foundry/IP and device integration into high density circuit designs.