Page 411 - Power Electronics Handbook

400 Power semiconductor circuit applications

Figure 14.52 Motor waveforms for a bridge inverter using pulse-width modulation with a sine
wave. fT = 555Hz, fs = 100Hz; (a) motor stalled; (b) motor on no-load; (i) voltage; (ii)
current
rotor, then the quantity (1-S)P is converted into mechanical energy at the
shaft, the remainder (SP) being in the form of electrical energy in the
rotor. If the rotor is closed on itself, or closed through a resistance, this
energy is dissipated as heat, although if it is possible to extract the energy
from the rotor, then the effect on the speed will be the same as if this
energy were dissipated. The extracted energy can now be fed back to the
supply to give a high overall efficiency. It is also possible to feed energy
from an external source into the rotor, the slip now being made negative
(rotor speed exceeding that of the stator field) and energy will flow from
rotor to stator across the gap.