Elmo HARSFEN0602, HARmonica software manual 117, Peak/Continuous current limit selection

HARSFEN0602ElmoHARmonicaSoftwareManual PRELIMINARYDRAFT

adapt to the specific amplifier model you bought. Units".

Program PL[1] smaller then MC if you don't want to utilize the full power of the amplifier – because the amplifier is oversized with respect to the application, or because the line voltage

is not enough to drive MC amperes into the motor. Do not specify PL[1] > VB R M , where

VB is the DC motor supply voltage and where R M is the motor resistance. We advise to choose PL[1] small enough so that at peak current there is enough voltage to drive current changes. Otherwise, at large currents the amplifier speed of response will be limited by voltage saturation.

The continuous current limit for your application is programmed by CL[1]. The parameter CL[1] cannot exceed MC/2, since greater continuous currents will risk amplifier overheating.

You may set CL[1] < MC/2 to avoid motor overheating.

We advice to select PL[1] and CL[1] as large as the amplifier and the application permit. This will extend the linear range of the amplifier to maximum and will thus optimize the servo performance.

The parameters PL[1] and CL[1] specify limits for the current demand. At transients, the motor current may exceed PL[1] and CL[1] due to overshooting.

117

The decision if to limit the motor current demand to CL[1] or to PL[1] is made by the amplifier in real-time. The LC flag reports the current limiting status. The decision mechanism is depicted below.

Ia

Low Pass filter

					RMS
Ib		RMS
I	2	I	2	I	2
	a		b		c
Ic
					Filtered RMS current
			If RMS > THOLD, then			LIMIT (CL[1] or PL[1])
					LIMIT=CL[1]
					THOLD=0.9CL[1]
					LC=1	LC

	else
	LIMIT=PL[1]
THOLD	THOLD=CL[1]
	LC=0

Figure 11: Peak/Continuous current limit selection

When the current limit switches, the comparison threshold (named THOLD in the figure above) is slightly changed. This hysteresis prevents to frequent switching of the current limit.

Slower time constants in the low pass filter will permit a peak current demand for longer times, but will also take more time to recover from a limiting to CL[1]. The time constant

τof the low pass filter is selected by PL[2] as follows: