Page 177 - Electric Drives and Electromechanical Systems

Chapter 6 Brushless motors 171

FIG. 6.5 The switching requirements for an ideal BDCM. (A) The motor to three phase power bridge connections.
The flywheel diodes in the bridge have been omitted for clarity. (B) The switching pattern required to ensure that
the phase currents are in synchronisation with the phase voltages. The voltage for phase A is shown in bold.
Adapted from Miller (1989).

pattern is arranged to give a current flow against the emf; a positive current is defined as
a motoring current. The device switching sequence as shown in Fig. 6.5B is arranged to
produce a balanced three-phase motor supply.
The torque and the speed constants can be determined by considering the balance
between the motor’s mechanical output power and its electrical input power over each
conduction period; that is,
P ¼ u m T e ¼ 2e p I (6.5)