ABB 3BHB003023P104 Sequence control module

If maximum motor speed is not too high, a drive typically will not need regen, because the rotational energy can be handled by the drive caps and motor resistance. The following example uses a PC804 with a simple inertia.

If the deceleration time from very high

 speed to zero speed at full torque takes 100 msec, then the peak shaft power at the beginning of the deceleration can be estimated at about 6kW. The shape of the power pulse is triangular, so the rotational energy to be absorbed is 300 joules (=0.5 x 6,000 watts x 100 msec). The caps in the PC804 are rated to absorb ≅ 40 joules. The copper loss of a medium size motor operating at the drive continuous rating of 10A (0 to pk) is often in the 100 watt range, so at x3 pk current the motor copper loss will be in the 900 watt range. Therefore, in 100 msec, the motor copper for a full current deceleration will absorb about 90 joules (=900 watts x 100 msec). The balance of 170 joules (= 300 joules - 40 joules - 90 joules) will be dissipated in the regen resistor.

Now reduce the max speed in half.

 The rotational energy is reduced by four to 75 joules. The deceleration time is reduced by two, so motor copper energy loss is reduced by two to 45 joules. The bus cap absorption energy remains at 40 joules. As a result, the 75 joules of rotational energy is handled by the copper loss and bus caps without the need of a regen resistor. If the max speed had been reduced to about one third, then the copper loss or cap alone could handle the rotational energy.

                                                                        

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