Configuration of the frequency inverter
For work on the frequency inverter (FI):
DANGER
Life-threatening voltages inside the FI housing!
Contact can lead to serious injuries or death.
Never open the FI housing in operation!
Switch off the main switch and secure it against being switched on again.
Wait for at least 5 minutes until all capacitors have been discharged!
Before switching on again, close the FI housing.
CAUTION
In operation, the heat sink of the frequency inverter will get hot.
Risk of burns upon contact!
Prior to performing work on the frequency inverter, disconnect the power supply and wait for at least 15 minutes until the heat sink has cooled down.
Risk of frequency inverter failure caused by over-voltage!
Always disconnect the frequency inverter from the circuit to be tested before any high potential tests or an isolation test on lines in operation!
Risk of motor damage!
Check the switching frequency of the converter in the frequency inverter and set it, if necessary! Recommended value: 2 .. 6 kHz
- Set the minimum and maximum frequency (or speed)
- Set the nominal motor data (see name plate)
- current
- voltage
- frequency
- number of motor poles
- (motor speed)
- (power)
- (cos φ)
- control logic: U/f (proportional)
- switching frequency of the converter in the frequency inverter: use approx. 3 kHz as standard
- Low switching frequencies reduce the strain on the isolation of the motor windings, in summary this results in higher efficiency.
- Higher switching frequencies may cause less motor sound, slightly reduced motor losses and motor heat-up. On the other hand, they lead to higher losses and thus a higher temperature in the frequency inverter (possibly consider degrading, i.e. the output load decreases with rising ambient temperature).
- Activate the "Autotune" function of the frequency inverter, if available.
- Define the ascending ramp (start sequence) and descending ramp (stop sequence), see below.
- Define the speed ramps during operation (between min. and max. frequency). Here, the frequency change should be much slower than during start and stop, which is advantageous for the compressor and the entire system. The optimal ramp times also depend on the type of system (compound system, single compressor in liquid chiller, etc.). Especially for liquid chillers and heat pumps, the capacity should change over several minutes rather than within seconds. Typically the ramp up should be much slower than the ramp down – with Bitzer products it is usually only half as fast. The VARIPACK has e.g. the following factory settings:
- Ramp up: 10s/50Hz
- Ramp down: 5s/50Hz
With Bitzer Varipack frequency inverters, not all of these steps are necessary, since they are pre-configured and may be adapted to system requirements via the Best Software, see:
Vibrations
Danger of material fatigue and damage caused by vibrations in the system due to FI speed drive!
Check the whole system carefully at all possible operating frequencies for vibrations and resonances.
Blend out frequencies which cause resonances by appropriate parameter setting at the inverter!
If a vibration problem is identified at a certain speed or combination of speeds, it may be possible to modify or reinforce the piping design to correct it. After any such changes, the system should be retested across the entire speed range to make sure that solving the problem at one speed does not create a problem at another.
Alternatively, most inverters have the ability to program "gap" speed ranges (frequency bypass ranges): While the compressor will be permitted to pass through the gap speed range, it will not be permitted to dwell within that range. Any frequency ranges where vibration or sound problems are identified can be "excluded" in this manner.
For further questions, please contact Bitzer.