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Appendix A - Power Supply Design
03/2006
Danaher Motion Kollmorgen
An adequately sized bus capacitor helps provide the high peak bus current needed for
rapid motor acceleration with minimum bus voltage sag. If the bus voltage sags
excessively during acceleration, inverter voltage saturation occurs with loss of motor
torque.
4. Bus capacitance lowers peak current requirements in the silicon of the power
supply.
Sizing the power supply for average power, rather than peak power, lowers power
supply cost and size.
5. In most cases, a bus capacitor does not need to be mounted close to the drive.
The inductance of the bus and ground wiring is not critical because the internal drive
bus capacitance generally handles all the PWM current of the drive. A local capacitor is
not needed in the following cases:
3/9 ARMS DC S200
6/18 ARMS DC S200 with HSTemp less than 65° C
6/18 ARMS DC S200 mounted adjacent to other S200 drives with main bus
supplies tied locally together. The internal bus capacitors of the adjacent drives
should provide the needed capacitance.
The exception is a single, isolated 6/18 ARMS DC S200 drive running hot
(HSTemp > 65° C). In this case, connect across the bus within 1 ft of the drive,
using twisted wire, a 470 µf (min), 100 V, low ESR, and an aluminum bus
capacitor.
6. Bus capacitor for multiple drives
A conservative rule is to scale up the recommended output capacitance for one drive
by the number of drives. If this value is too large, the capacitor can be calculated from
Bus Energy & Power Numerical Examples.
energy flows. See the A.4
NOTE
NOTE
Bus capacitance can be tweaked experimentally. Increase bus
capacitance if there are overvoltage trips. In general, there is
sufficient bus capacitance if the bus voltage variation is ± 5 V (from
75 VDC) during the machine cycle. Check the bus voltage with an
oscilloscope. Scope ground on J1-2 (Bus/Ctrl Gnd) and probe on J13 (+bus), Hor: 5 ms / div.
Some bus voltage variation is normal and required for the output
bus capacitor to supply or absorb energy.
7. Bus over-voltage fault (non-latching)
If regeneration is too high while bus capacitance is too low, the bus voltage rises to the
bus over-voltage fault threshold and disables the drive transistors. It typically takes 1 to
2 ms for the motor current and torque to go to zero. After it has reached zero, there is
no further rise in the bus voltage. When the bus capacitors discharge to below the overvoltage threshold by a hysteresis value, the over-voltage fault is cleared and normal
operation resumes. While this protects the drive by limiting the bus voltage rise, it may
not be desirable because it interrupts normal motor torque.
8. Unregulated power supply
External bus capacitance requirements are usually met by the output capacitor in an
unregulated power supply, as long as there is no diode between the drives and bus
capacitor. The same capacitor that filters the 120 Hz or 360 Hz line ripple also provides
energy leveling and regeneration absorption capability.
106
M-SM-200-01
S200 Reference Manual