Siemens 420 manual Reducing the pulse frequency P0290 = 2, Disadvantage

Issue 07/04 3 Functions

When an overload occurs regarding one of these monitoring functions, initially, a warning is output. The warning threshold P0294 (i2t monitoring) and P0292 (heatsink temperature monitoring) can be parameterized relative to the shutdown values.

	Inverter monitoring	Inverter overload reaction
		P0290
r0036	i2t	i_max	A0504
	P0294		A0505
		control
r0037	Heat sink		A0506
	temperature
	P0292	f_pulse	F0004
		control
			F0005

Fig. 3-60 Overload response of the drive inverter (P0290)

Example

The warning threshold P0292 for the temperature monitoring (heatsink temperature) is set to 15 °C in the factory. This means that warning A0504 is output 15 °C below the shutdown threshold.

At the same time that the warning is output, the parameterized responses are initiated via P0290. Possible responses include:

Reducing the pulse frequency (P0290 = 2, 3)

This is an extremely effective method to reduce losses in the power module, as the switching losses represent a very high proportion of the overall losses. In many applications, a temporary reduction of the pulse frequency can be tolerated in favor of maintaining the process.

Disadvantage

The current ripple is increased when the pulse frequency is reduced. This can result in an increase of the torque ripple at the motor shaft (for low moments of inertia) and an increase in the noise level.

Reducing the output frequency (P0290 = 0,2)

This is advantageous if it is not desirable to reduce the pulse frequency or if the pulse frequency is already set to the lowest level. Further, the load should have a characteristic similar to that of a fan, i.e. a square-law torque characteristic for decreasing speed. When the output frequency is reduced, this significantly reduces the drive inverter output current and in turn reduces the losses in the power module.

MICROMASTER 420	Operating Instructions
6SE6400-5AA00-0BP0	141