By: Louis Lambruschi, Marketing Services and E-Business Manager at Parker Hannifin Corporation
Central inverters are intended for larger applications at higher voltage levels, so they are more likely to be self-contained and field-ready than string and microinverters. They are typically provided in enclosures suitable for direct outdoor installation with integrated switchgear, circuit protection and condition monitoring. In performing basic DC to AC conversion, they are similar to string and micro inverters, but central units are more likely to include advanced features like power factor control, reactive power on demand and revenue metering. Central inverters generally include robust fault ride-through provisions, allowing them not only to continue to operate through a fault, but also to offer grid support. Thanks to their larger size, redundancy can be designed into these inverters to offer continued operation even during a component failure. Users also benefit from the intrinsic lower cost per kilowatt of a larger inverter, which — combined with the right feature set and high efficiency — can result in a lower total cost of ownership.
Some manufacturers are incorporating liquid cooling technology in their central inverter models for a smaller footprint and little or no air filter maintenance. While water/glycol cooling systems are the most widely used, a two-phase evaporative cooling system with pumped refrigerant is emerging as an alternative. This results in a more compact and efficient system that removes a lot of heat with a little liquid. Such a system also minimizes consumable items like filters and coolant additives. This non-conductive system is also much safer than mixing water with high-power electronics.
On the operational side, central inverters are evolving into more than just power conversion devices. Features that make the inverters more grid interactive increase their value to the owner as a dispatchable asset. Many models offer flexibility with dual operating modes, allowing the inverter to work equally well on command in grid-parallel or island mode. Improved monitoring and fault detection with a robust communication interface is another increasingly desirable feature.
Serviceability is also an important concern with central inverters. While a smaller inverter can be literally swapped out on site, central inverters have traditionally had larger and harder to access components. To counter this disadvantage, newer modular designs with lightweight interchangeable phase modules, capacitors, inductors and fans improve field serviceability. With an accessible, modular design, scheduled maintenance or even major repairs can be done in an hour or less — rather than several days. Preferably, all serviceable components can be accessed externally without requiring an operator to enter the inverter enclosure. External access panels also enhance safety and simplify permitting.
Central inverters tend to be most attractive options for ground-mounted installations that are 400 kW and higher, and when 1000-V or higher input capability is required. Central inverters designed and built with environmental sealing and self-contained cooling systems can be sited in desert or coastal conditions without needing housing. Central inverters with “smart” features are also desirable in situations that require energy management. Such central inverters can provide grid support with power factor control or by providing reactive power on demand.
As more renewable sources are deployed, grid power quality will become an increasing concern. There will likely be a corresponding demand for “smart” central inverters that can support the grid. We see a growing demand for devices that will meet both current and proposed industry regulations, and anticipate that this trend will continue.
By: Louis Lambruschi, Marketing Services and E-Business Manager at Parker Hannifin Corporation
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