Abstract
A device securing undisturbed operation of a variable frequency electric drive is developed and investigated. By its purpose, the developed device is an uninterrupted power supply source of a frequency converter (FC UPS) and is intended for being used in the electric drives of hoisting mechanisms due to its ability to improve their power efficiency by using the descended cargo's braking energy for charging the backup power supply source. The power part of the considered electric drive comprises a frequency converter and an induction motor with the former made according to a standard arrangement involving an uncontrolled rectifier, a self-excited voltage inverter, and a direct current link between them. A storage battery and a switching control unit are the basic functional elements of the FC UPS. During operation, the brake unit is involved (which is used together with all frequency converters that have the considered standard structure) for control of braking energy. This module serves for charging the FC UPS storage battery during the electric drive's brake modes in descending the cargo. The FC UPS operation logic performs control of the main function, namely, automatically switching over the frequency converter's DC link for taking power from the storage battery when power supply from the network is lost. In addition, the FC UPS control unit can support the operation mode in which the fully charged storage battery supplies its stored energy to the electric drive when it lifts up the cargo. This mode of operation from the backup power source can continue until reaching the preset storage battery discharge limit. On reaching the storage battery discharge limit, the FC UPS is switched over to the mode of charging the backup power supply source, which is activated in performing the cargo descending operations. Although such discharging/ charging cycles are repeated many times, but with such cyclic operation the total energy consumed by the mechanism becomes smaller because the potential energy released in descending the cargo is used by the electric drive in the motor mode for lifting up the cargoes. Thus, by applying the proposed FC UPS in the electric drive of the considered type and purpose it becomes possible not only to ensure uninterrupted operation of the hoisting mechanism when power supply from the network is lost, but also to improve its power efficiency. The article presents a description of the laboratory installation and the results of experimental investigations confirming the serviceability of the proposed device, the novelty of which is fixed by a patent of the Russian Federation.
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