TABLE OF CONTENTS
DRIVES ARE MORE EFFICIENT BUT MORE EXPENSIVE
HIGHER POWER DENSITY AND LOWER ROTOR INERTIA, PARTICULARLY WITH HIGH-ENERGY PERMANENT MAGNET
TRUE SPEED TRACKING IN PARALLEL MULTIPLE-MACHINE DRIVE
POWER FACTOR CAN BE PROGRAMMABLE LEADING, LAGGING, OR UNITY WITH FIELD CONTROL
CONVERTER WILL BE LESS EXPENSIVE WITH UNITY POWER FACTOR
EXCITATION CONTROL NEEDS SEPARATE CONVERTER
ABSOLUTE POSITION SENSOR IS MANDATORY IN ANY CLOSED-LOOP CONTROL
CAN REPRESENT TRUE BRUSHLESS COMMUTATORLESS DC MOTOR (BLDM)
CONVERTER FAULT CAN CAUSE DANGEROUS PULSATING TORQUE DUE TO MACHINE CEMF
Although synchronous motors, in general, are more expensive, synchronous machines have higher efficiency (with less cooling needs), particularly PM machines, which can make the life-cycle cost of the drives less depending on electricity costs. Again, the converter rating is lower with a near-unity power factor. With the present trend toward decreasing costs for NdFeB magnets, the cost of PM machines is expected to decrease substantially in the future. With the leading power factor control of WFSMs, a low-cost thyristor load-commutated inverter is even more economical than a traditional PWM inverter. Of course, an additional converter is needed for field current control of WFSM drives. For true speed tracking in multiple-motor textile mill drives, for example, PM synchronous motors (or SyRM) are essential. Another disadvantage is that an absolute position sensor is essential in most of the drives. Both induction (cage) and PM synchronous machines are brushless (also commutatorless). With vector control, the drives behave like separately excited dc motor...
