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Many of today’s heating/cooling systems are using inverter driven compressors coupled with energy saving control systems for optimal performance. These systems frequently are only available in a 3-phase power configuration. When 3-phase power is not available, a phase converter may be the only solution for this HVAC application.
VFD’s used as a phase converter are not a good solution for this application. When a VFD is connected to a piece of equipment which contains three-phase motors as well as other controls, it is very likely that both the VFD and the equipment would be damaged. If multiple loads are connected to a VFD with individual contactors for each separate load, the VFD
may not be able to handle the current surges which occur when
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individual loads are switched on and off. Also, if
there were any capacitors in the equipment connected directly across
the VFD outputs, the VFD would have to shut down immediately or be
destroyed by the extremely high currents that would flow when the
output voltage pulses were applied to the capacitors.
Rotary phase converters may not be a good solution as well. The widely variable load of modern HVAC equipment exposes the primary weakness of rotary phase converters, namely, the inability to maintain balanced voltage. A rotary phase converter can provide balanced voltage at only one load point and the more variable the load, the worse the voltage balance. Also, standby power consumption of a rotary motor running constantly may be cost prohibitive for the HVAC application.
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A digital phase converter may be a practical and effective solution
for 3-phase HVAC systems where utility 3-phase power is not
available. A true
digital phase converter produces sine wave voltage, making it safe
to power the electronics in the machine.
Digital phase converters are capable of handling multiple
load demands and maintain voltage balance under all load conditions.
A digital converter has no
moving parts, so there is no starting current to cause line
disturbances. Electronic power factor correction allows it to
operate at unity power factor and does not consume reactive power.
In fact, it supplies the reactive power needed by any loads it
operates, making it a very utility friendly converter. The
converter operates at 95-98% efficiency and when energized with no
load consumes very little power.
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