Page 169 - Electric Drives and Electromechanical Systems

162 Electric Drives and Electromechanical Systems

If the limiting values shown in Fig. 5.19 are calculated, the maximum energy that can be
returned from the motor is -12.34 J, and no energy will be returned when the regenerative
current equals -94.25A.
Given these conditions determine the value of capacitor or shunt resistance required to
maintain the bus voltage at less than 110 V. The nominal rating of the d.c. bus is 100 V. The
cycle time of the drive is 10 s.
The minimum values of the supply capacitance required to prevent over-voltages is
2E r
C 5460 mF
2
2
V mav V norm
If a shunt voltage regulator, Fig. 5.20 is to be used, the maximum value of the resistor required
will be
V max 110
R ¼ ¼ ¼ 3:7U
I R 30
The average power dissipation of the resistor will be approximately 1W, given a pulse of power
of with a value of 3.3 kW for 2.97 ms, every 10 s.
nnn

FIG. 5.21 Energy flow in a drive system. Following the power supply, energy storage is provided, this can be
either a large capacitance primary to smooth the supply to the drive or a battery to recover the lost energy in a
vehicle application. The drive is capable of bi-directional energy flow, allowing the return of energy during
regeneration. Finally the motor and transmission system provide the required energy to the load.