Trinamic 11-0011 TMCM-171 BLDC Output For 3-phase BLDC Motors 11-0011 数据表

产品代码

11-0011

TMCM-171 Manual (V0.92 / Nov 7th, 2007)

5.8 Programmable motor current limit

The motor current limiting function is meant as a function for torque limiting, and for protection of
motor, power supply and mechanical load.
Whenever the pre-programmed motor current is exceeded in a chopper cycle, the TMCM-171 calculates
a reduced PWM value for the next chopper cycle. New values are calculated 1000 times a second. The
response time of the current regulation can be set using the parameter “current regulation loop
delay”:
A value of zero means, that in every 1kHz period, the current correction calculation is directly executed
and the resulting PWM value is taken. A higher current loop delay acts like a filter for the current. The
higher the delay value, the slower the current loop response time. A value of 10 (default) leads to a
current regulation response time of about 10 ms for an 1/e response. On the mechanical side, a
higher value simulates a higher dynamic mass of the motor.

The actual current regulation time may differ, depending on the PID settings.

Attention: Please be careful, when programming a high value into the current regulation loop delay

register: The motor current could reach a very high peak value upon mechanical blocking
of the motor. The same goes for the motor current limit value: do not set higher than
16A if you are not sure about this. Please remark, that the current measurement gives
different results in block and in sine commutation mode, due to the different driving
scheme.

The unit has a short circuit protection circuit, which limits coil current to about 40A.
However, this function should not be relied on in normal operating conditions.

There is a number of aspects when using the current limiting function:
• The current measurement is done at a point of the chopper cycle, where just one coil is switched

on. When using sine commutation, the effective motor current is calculated from a measurement
of all three coils.

• The current measurement can not detect currents below about 200-300mA. If the current limit is

set to a too low value, the motor may operate spuriously or become continuously switched off.

• The current limiting function is not meant as a protection against a hard short circuit.
• The performance of the current limiting depends on the motor and on the commutation mode.

The current limit should be programmed to a value high enough, in order to achieve good
positioning and acceleration performance.

• Operation of the current limiter and the PID regulator may result in instable behavior, if the

motor gets into a resonance area. Try adapting the current regulation loop delay parameter.

• If the motor is blocked and the ramp generator is not stopped, the motor will speed up and try

to catch up with the ramp generator position after removal of the blocking. To control this effect,
you can set the parameter “Clear Target Distance” in order to stop the ramp generator, when the
deviation between the positions become to large. The effect of this may look somehow weird if
the user does not expect it.

Please refer to the programming manual for the required current settings.