Toshiba VF-A7 Braking of a motor after power shutoff, Load producing negative torque

･A load, e.g., a reciprocating load, which requires a frequent change in the rotating speed

In this case, if the inverter is in vector control mode, adjust the response time (setting of moment of inertia) or switch to V/f control mode to stabilize the operation.

If it is operated in vector control mode, only a motor whose capacity is same as inverter standard or 1 rank lower is applied.

If it is operated in V/F (other than vector control), the rotating of motor can be unstable in combination with 3 or more ranks smaller motor.

<Stabilizing operation>

①Lower the setting value of F300(PWM carrier frequency). (It causes much magnetic noise of motor, but it is not abnormal.)

②In the case that it is still unstable even if the carrier frequency is lowered to 2.2kHz at (①), set the setting value of F489(Dead time compensation) to 1 (Disabled) .

Braking of a motor after power shutoff

If the power is shut off while the motor is still rotating, the motor keeps rotating (or coasting) for a while before it comes to a complete stop. If you wish to stop it soon after turning off the power, equip the motor with an auxiliary braking system. There are several types of braking systems available, for example, mechanical and electrical types. Select a braking system which matches your system.

Load producing negative torque

When the inverter is combined with a load producing negative torque, the over-voltage or over-current protective function of the inverter sometimes works and causes the motor to trip. In this case, it is necessary to install a dynamic braking resistor, etc., suitable for the load.

Motor with a braking system

When a brake-equipped motor is connected directly with the inverter, the brake cannot be released at start-up because of an insufficient voltage. To avoid this, connect the brake cables separately from the motor main cables.

			(Non-exciting brake)			(Non-exciting brake)
		MC2			MC2
			B			B
MC1				MC1		IM
	FLB	FLC ST	IM	Three-phase	OUT1
Three-phase			CC			P24
				power supply
power supply			MC3
						LOW
	MC1		MC3		LOW	MC3
	MC3		MC2		MC3	MC2
	Circuit configuration 1				Circuit configuration 2

In circuit configuration 1, the brake is turned on and off by means of MC2 and MC3. If the circuit is configured differently, the motor can trip because of a locked rotor current produced during braking.

In circuit configuration 2, the brake is turned on and off by means of a low-speed signal OUT1. However, for certain applications, e.g., elevator applications, it is recommended to use a low-speed detection signal (function of terminal OUT1) to turn on and off the motor. Contact your Toshiba dealer before designing a system.

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