Toshiba TOSVERT VF-S11 Instruction Manual page 29

Low loads and low inertia loads
The motor may demonstrate instability such as abnormal vibrations or overcurrent trips at light loads of
50 % or under of the load percentage, or when the load's inertia moment is extremely small. If that hap-
pens reduce the carrier frequency.
Occurrence of instability
Unstable phenomena may occur under the load and motor combinations shown below.
Combined with a motor that exceeds applicable motor ratings recommended for the inverter
Combined with special motors
To deal with the above lower the settings of inverter carrier frequency.
Combined with couplings between load devices and motors with high backlash
When using the inverter in the above combination, use the S-pattern acceleration/deceleration function,
or when vector control is selected, adjust the speed control response/stability factor or switch to V/f
control mode.
Combined with loads that have sharp fluctuations in rotation such as piston movements
In this case, adjust the response time (inertial moment setting) during vector control or switch to V/f
control.
Braking a motor when cutting off power supply
A motor with its power cut off goes into free-run, and does not stop immediately. To stop the motor
quickly as soon as the power is cut off install an auxiliary brake. There are different kinds of brake de-
vices, both electrical and mechanical. Select the brake that is best for the system.
Load that produces regenerative torque
When combined with a load that produces regenerative torque, the overvoltage or overcurrent protec-
tion function may be activated to trip the inverter. For this kind of situation, you must install a dynamic
braking resistor, etc. that complies with the load conditions.
Motor with brake
If a motor with brake is connected directly to the output side of the inverter, the brake will not release
because voltage at startup is low. Wire the brake circuit separately from the motor's main circuits.
MC1
FLB FLC
Three-phase
power
supply
MC1
MC3
Circuit Configuration 1
MC2
B
IM
ST CC
MC3
MC3
MC2
A-17
MC2
MC1
RC
Three-phase
RY
power supply
MC2
Circuit Configuration 2
E6581158
1
B
IM