Motor control systems

Different kinds of motor control solution are compared in the following tables.

Fig. N75 – Comparison of different motor control solutions

Type	Is/In	Ts/Tn	Speed control	Torque control	Pros	Cons
Direct on line	5-10	5-10	No	No	Reduced cost, high starting torque	High in-rush current
Star – Delta	2-3	1-2	No	No	Reduced in-rush current	Reduced starting torque
Auto-transformer	2-3	1-2	No	No	Reduced in-rush current	High weight
Soft starter	3-5	1.5-2.5	No	Yes	Reduced in-rush current, controlled start and stop	Reduced starting torque
Variable speed drive	1.5	1.5-2	Yes	Yes	Controlled speed, Energy saving at reduced speed	Higher cost