
Functions
5.10 Technological functions
Frequency inverter
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Operating Instructions, 08.10. 2008, t.b.d.
5.10
Technological functions
The frequency inverter offers the subsequently listed technological functions.
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Braking functions
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Automatic restart and flying restart
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Basic process control functions
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Positioning deceleration ramp
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Logical and arithmetic functions using function blocks that can be freely interconnected
Please refer to the following sections for detailed descriptions.
5.10.1
Braking functions of the frequency inverter
A differentiation must always be made between electrical braking of a motor and mechanical
braking:
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The motor is electrically braked by the frequency inverter. Electrical braking is completely
wear-free. Generally, a motor is switched off at standstill in order to save energy and so
that the motor temperature is not unnecessarily increased.
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Mechanical brakes are generally motor holding brakes that are closed when the motor is
at a standstill. Mechanical operating brakes, that are closed while the motor is rotating
are subject to a high wear and are therefore often only used as an emergency brake.
Different electrical braking methods for different applications
If an induction motor electrically brakes the connected load and the braking energy that is
released exceeds the mechanical and electrical losses, then it operates as a generator. In
this case, the motor converts mechanical energy to electrical energy. Examples of typical
applications where regenerative operation briefly occurs include:
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Centrifuges
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Grinding disk drives
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Fans
For certain drive applications, the motor can operate in the regenerative mode for longer
periods of time. Examples include:
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Cranes
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Conveyor belts with downward movement of load
Depending on the particular application and the frequency inverter type, there are different
technologies to handle regenerative energy.
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The regenerative energy is converted into heat in the motor (DC and compound brake)
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The frequency inverter stores the regenerative energy in the DC link which means that
the DC link voltage increases.
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The frequency inverter converts the regenerative energy in the voltage DC link using a
braking resistor (dynamic braking).
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The frequency inverter feeds the regenerative energy back to the line supply
(regenerative braking).