Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 21)

Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014 21
Overview of Drive Chapter 1
Motor Compatibility The PowerFlex 7000L achieves near sinusoidal current and voltage waveforms to
the motor, resulting in no significant additional heating or insulation stress.
Temperature rise in the motor connected to the VFD is typically 3°C (5.5°F)
higher compared to across the line operation. Dv/dt in the voltage waveform is
less than 10 volts / microsecond. The peak voltage that the motor insulation will
see is the rated motor RMS voltage divided by 0.707. Reflected wave and dv/dt
issues often associated with VSI (voltage source inverter) drives are a non-issue
with the PowerFlex 7000L. Typical motor waveforms are shown in
Figure 4 .
These motor friendly waveforms are achieved by utilizing a selective harmonic
elimination (SHE) pattern in the inverter to eliminate major order harmonics, in
conjunction with a small output capacitor (integral to the drive) to eliminate
harmonics at higher speeds.
Standard motors are compatible without derating, even on retrofit applications.
Motor cable distance is virtually unlimited. This technology has been tested,
controlling motors up to 15 km (9.3 miles) away from the drive.
Figure 4 - Motor waveforms @ full load, full speed
300.00
200.00
100.00
0.00
-100.00
-200.00
-300.00
10.00K
7.50K
5.00K
2.50K
0.00K
-2.50K
-5.00K
-7.50K
-10.00K
100.00 110.00 120.00 130.00
TIME (ms)
140.00 150.00
Arms
Vrms
Motor
Current
Motor
Voltage