Uninterruptible motor drives and systems.
Solution that supply power to variable frequency drive through standard UPS may have some limitations from the UPS power, voltage, size and price. In addition, the variable frequency drive harmonics may bring negative effect to the UPS and cause malfunction or bad conditions.
Starting from 100 kW uninterruptible motor drives (UMD) could be optimal choice for critical applications that require nonstop operation of pumps, funs, hoist or conveyor. When connected to variable frequency drives the UMD could provide instant back-up power supply directly to its DC bus.
Engineering Center ART suggests using standard inverter with output reactors and specially developed software as the interface DC/DC converter between the battery and LV VFD.
Usually the nominal voltage of the battery bank is lower that the VFD DC bus voltage. During normal operation, a small current form the DC bus of variable frequency drive is going through DC/DC converter to keep the battery charged. To keep the battery in normal condition DC/DC converter may perform special care cycles of higher voltage charge (care cycle).
If the main power interrupts or the power voltage drops then the DC/DC converter starts to use buster gate to inject power from the battery bank to the VFD.
Such modular solution allows to fir the power supply with battery or super capacitor bank to drives systems with different topology and voltage. Possible connection diagrams could be as follows.
Simple connection of one battery bank with one UMD and with one LV VFD.
Connection of one battery bank with one UMD and several LV inverters with common DC bus.
Connection of one battery bank with several UMD and several LV VFD and inverters.
Connection of UMD with medium voltage VFD system with "step down step up" topology.
In July 2015 Engineering Center ART turned on the complex UMD system for two 200 kW blowing fans and for two 400 kW exhaust fans for power boiler. Those fans are equipped with 6 kV motors and the applied frequency drives use step down step up topology. The designed UMD system allow the power boiler to operate continuously ever when power supply interrupts up to 10 sec.
