Conventional combined heat and power (CHP) systems have typically used externally excited synchronous generators or squirrel cage induction generators to produce electrical power. However, this era of using induction generators in CHP systems is ending, as the systems cannot provide electricity during outages and the so-called “black start” feature is missing. Also, while synchronous generators are efficient at the nominal operation point, their excitation unit requires regular maintenance.
Introducing permanent magnet generators as the next generation technology
The permanent magnet generator (PMG) is similar to the conventional synchronous generator, yet it eliminates the need for an external excitation unit and is very efficient throughout the operational area. When combined with a converter, a PMG-converter package offer clear benefits for engine-driven CHP system grid interconnection.
Benefits of a converter for engine-driven CHP system grid interconnection
Grid friendliness
Because fault currents are not controllable with grid overcurrent protectors, many US utilities like ConEd will not allow new synchronous generators to be connected to grid without a CHP converter, especially in some areas in Manhattan, NY. These utilities require that the building power generation does not contribute the grid fault current under any circumstance. Unlike the directly grid-connected synchronous or induction AC generator, the CHP converter is designed to limit any short circuit current to the grid, The Switch CHP converters fulfill all utility requirements and have the ability to disconnect within milliseconds when needed.
Black-start capability
New NYSERDA (New York State Energy Research and Development Authority) incentives require that systems provide electricity during power outages. The CHP converter features island mode “micro grid” functionality that allows a power grid to be created inside the building in case of an outage.
Fuel savings and energy efficiency, LCOE
The CHP converter operates in variable speed mode. When building or site loads are lower than the generator’s nominal power, the CHP converter allows the engine speed to be reduced. This variable speed ability lowers fuel usage and emissions. This system becomes even more efficient when the generator is a PMG instead of an externally excited synchronous generator. PMGs are very efficient over the entire speed area. To illustrate, The Switch PMG 2200 kW – 1500 rpm efficiency starts at 96.4% with a 50% load and approaches 97.5% with a 100% load.
NYSERDA’s current incentive programs, the Combined Heat and Power Performance program (PON2701) and Acceleration Program (PON2568), help building owners develop CHP systems with funding of up to 100 million dollars available for applicants.
The Switch has suitable products available for both programs. Our CHP system achieves better overall efficiency with an almost maintenance-free PMG and power converter package, which ultimately lowers the levelized cost of energy (LCOE).
Risto Ahvo
GM, The Switch Controls and Converters