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Electronic motor starters and drives
Basics of drives engineering |
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Power Electronics Devices
The power electronics devices provide infinitely variable adjustment of
physical variables – such as speed or torque – to the application process. The power is drawn from the electrical mains, converted in the
power electronics apparatus and fed to the consumer (i.e. the motor).
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Semiconductor contactors
Semiconductor contactor allow fast, silent switching of three-phase
motors and resistive loads. Switching takes place automatically at the ideal point in time and suppresses unwanted current and voltage peaks.
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Soft starters
Soft starters ramp the voltage fed to the motor up to mains voltage, so that the motor starts almost jolt-free. The voltage reduction leads to a
square-law torque reduction in relation to the motor’s normal starting torque. Soft starter are therefore especially well suited to starting
loads with a square-law speed or torque characteristic (such as pumps or fans).
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Frequency inverters
Frequency inverters convert the AC or three-phase system with its constant voltage and frequency into a new, three-phase system with
variable voltage and frequency. This voltage/frequency control enables step less speed control of three-phase motors. The controlled drive can
be operated at rated-load torque even at low speeds.
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Vector frequency inverters
While conventional frequency inverters control three-phase motors using
a charactieristic-controlled U/f (voltage/frequency) relationship, vector frequency inverters work using a sensorless, flow-oriented
control of the motor’s magnetic field. The controlled variable is the motor current. This allows an opimized control of the torque for
demanding applications (mixers and agitators, extruders, transport and conveying installations).
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