TECHNOLOGYINVERTERS
A shift in attitudes toward inverters and requirements is extremely likely as penetration grows, as evidenced by the ride through requirements that have emerged for grid connected wind replacing the interconnection requirements that still apply to other renewable and distributed resources
The role of the inverter has two facets: first, it is tasked with managing and extracting the maximum power from the input source; and second, it is tasked with conditioning the power—putting clean and compliant AC power on the grid. Because of the electronic nature of the inverter and the switching frequency (which is many orders of magnitude higher than the line frequency), the quality of the output power can be exceptional. Inverters have the speed and the intelligence to be a powerful resource on the grid.
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They also have the communications capabilities needed to be aggregated and controlled in unison, so they can effectively act as a large power plant or an active power network device. High speed, aggregated, distributed power generation has proved to be extremely valuable in the modern power grid, even replacing spinning reserve requirements in certain locations. In this context, grid connected inverters offer the ultimate in speed of response and controllability.
An important trend to acknowledge is the move toward large, multi megawatt, renewable energy distributed generation systems. These large systems achieve economies of scale in terms of installed cost, enhanced efficiencies from large scale interconnection and inverters, and more efficient grid integration through direct medium voltage interconnection. Because electronics are capable of acting much faster than traditional grid connected devices, there is understandable concern about the effect of grid connected
Dr Leo Casey
Dr. Leo Casey is vice president and chief technology officer of Satcon Technology Corporation, a leading provider of utility scale, grid connected renewable energy solutions for distributed power markets, enabling the industry’s most advanced, reliable, and proven clean energy alternatives. Dr. Casey has driven continuous innovation in the field of renewable power conversion over the past 10 years, with specialized focus on conventional and alternative sources of primary energy, associated energy storage mechanisms, and grid interconnection techniques. Dr. Casey has long promoted the use of inverters and advanced control techniques to enable a stable, efficient, highly distributed, rugged,
microgridable electrical grid as the key to our energy future. He was recently appointed chairman of the High Megawatt Inverter Program organized with DOE and NIST and focused on developing “fast grid” capabilities enabled by large inverters with advanced utility features.
Dr. Casey received a BE degree at the University of Auckland in New Zealand and MSc, EE, and ScD degrees at MIT, coming to the United States as a Fulbright Scholar. He has more than 25 years of experience in the renewable energy conversion industry and is an editor of the Energy Conversion Transactions of the Power Engineering Society of the IEEE.
inverters on the stability of the grid. Strong interconnection regulations such as UL1741 and IEEEP1547 have been developed to specify and control this interconnection.
The high speed nature of the inverter has acted as an encumbrance in terms of the majority of the interconnection requirements, which are orders of magnitude tighter than for thermal power plants. A shift in attitudes toward inverters and requirements is extremely likely as penetration grows, as evidenced by the ride through requirements that have emerged for grid connected wind replacing the interconnection requirements that still apply to other renewable and distributed resources. The role of advanced inverters will become increasingly important, since they enable renewable energy resources to ride through grid disturbances rather than trip off, operate in islanded conditions under utility control, and operate in microgrid mode with the addition of complementary generation, storage, or real time load control.
The next generation inverter will be the glue that ties renewable or alternative energy sources such as PV or fuel cells to the utility grid. The inverter will become the interconnect that supplies distributed intelligence to a power system. It will be high speed and large scale, offer additional active filter features, and be remotely controlled. The ingredients are in place; grid integration and integration into utility SCADA systems are the logical next steps to make inverters and renewable energy sources a true utility asset.
www.solar-pv-management.com Issue V 2010
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