Allen-Bradley PowerFlex 70 Reference Manual page 58

Bus Regulation
Current Limit Level
Limit
0
SW 1
No Limit
Acc/Dec Rate
Frequency Set Point
Maximum Frequency, Minimum Speed, Maximum Speed, Overspeed Limit
Frequency Reference (to Ramp Control, Speed Ref, etc.)
Speed Control (Slip Comp, Process PI, etc)
Bus Voltage Regulation Point, V
58
Figure 13 Bus Voltage Regulator, Current Limit and Frequency Ramp.
Current Limit
Derivative Gain
PI Gain Block
I Limit,
No Bus Reg
No Limit
Jerk Jerk
Ramp Clamp
SW 2
Bus Reg
reg
PI Gain Block
Bus Voltage Regulator
The derivative term senses a rapid rise in the bus voltage and activates the bus
regulator prior to actually reaching the bus voltage regulation set point Vreg. The
derivative term is important since it minimizes overshoot in the bus voltage when
bus regulation begins thereby attempting to avoid an over-voltage fault. The
integral channel acts as the acceleration or deceleration rate and is fed to the
frequency ramp integrator. The proportional term is added directly to the output
of the frequency ramp integrator to form the output frequency. The output
frequency is then limited to a maximum output frequency.
Bus voltage regulation is the highest priority of the three components of this
controller because minimal drive current will result when limiting the bus voltage
and therefore, current limit will not occur.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Magnitude
Block
Calculator
SW 3
I Limit,
No Bus Reg
Frequency
+
Frequency
Reference
Ramp
(Integrator)
+
+
SW 5
SW 4
Bus Reg On
Derivative
Gain Block
U Phase Motor Current
W Phase Motor Current
Frequency Output Frequency
Limits
+
+
Speed
Control
Mode
Bus Voltage (Vbus)