Copley Controls Xenus R10 Manual page 41

OUTPUT VOLTAGE LIMITS
The R11 rectifies the AC mains power to produce an internal DC
supply (HV). The rectified mains power is stored temporarily in a
capacitor. As the load power increases, energy is drawn from the
capacitor, discharging it until re-charged by the next cycle of the
mains. Because the capacitor is only charged for a brief time at
2X the line frequency, the voltage will decrease between these
charges producing "ripple" on the DC supply. As the motor voltage
increases (a combination of BEMF (Back ElectroMotive Force) and
voltage-drop across the motor's resistance) it eventually hits the
bottom of the ripple voltage waveform on the DC supply.
DC SUPPLY VOLTAGE AT LOW OUTPUT CURRENT
AND POWER
Clipping Voltage
EXAMPLE
Assume 8 Adc is required to accelerate a linear motor to 2.5 m/s. Motor
resistance is 12 Ω and BEMF constant is 36 V/m/s. The motor is brushless
driven with sinusoidal commutation:
1) Find I*R voltage drop:
8 Adc * 12 Ω * 0.75 = 72 Vdc.
The 0.75 factor converts the line-line resistance of the motor to the
effective resistance when commutating sinusoidally.
2) Find BEMF at 2.5 m/s: 36 V/m/s * 2.5 m/s = 90 Vdc
3) Find motor terminal voltage:
I*R + BEMF = 72 + 90 = 162 Vdc
4) The dotted lines on the graph to the right show the clipping voltages at
8 Adc. Operation at 240 Vac would give about 28 V of headroom. But, at
200 Vac, either the motor velocity or accelerating current would have to be
reduced to avoid clipping.
Finally, note that the motor resistance will increase 29% if it heats from 25C
to 100C. That would change the required terminal voltage to 183 Vdc. In
general, allow 20~30% headroom between motor terminal voltage demand
and the clipping voltage. Using the oscilloscope in CME 2 software, the bus
voltage and motor terminal voltage can be displayed for a final determination
of the headroom in the working machine.
Copley Controls, 20 Dan Road, Canton, MA 02021, USA
Tech Support: E-mail: sales@copleycontrols.com, Internet: http://www.copleycontrols.com
Xenus R11 RUGGEDIZED DIGITAL
SERVO DRIVE FOR
BRUSHLESS/BRUSH MOTORS
This is called "clipping" as the output voltage can no longer increase
to control motor current. The graph below shows the clipping
voltages for the R11 when operated at some common mains
voltages over the range of output currents.
In order to avoid clipping, select a motor winding to provide some
headroom between the clipping voltage and the expected terminal
voltage to allow for low-line conditions on the mains, resistance
changes in the motor due to heating, etc.
DC SUPPLY VOLTAGE AT HIGH OUTPUT CURRENT
AND POWER
Clipping Voltage
CLIPPING VOLTAGE VS. OUTPUT CURRENT
Clipping Voltage (Vdc)
350
300
240 Vac
250
200 Vac
200
150
120 Vac
100
50 100 Vac
0
1 2 3 4
Output Current (Adc)
Tel: 781-828-8090
R11
5 6 7 8 9 10
Fax: 781-828-6547
Page 11 of 24
RoHS
350
300
250
200
150
100
50
0