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Power Electronic Handbook P14

Step motors are used in many low-lost positioning applications due to their inherent ability to stop at discrete positions and follow position vs. time profiles while being controlled open loop. A step motor is a synchronous machine, but historically has been used almost exclusively in positioning and position tracking applications. Recently, however, some types of step motors have been applied in variable speed drives applications. | 14 Step Motor Drives Ronald H. Brown Marquette University 14.1 14.2 14.3 14.4 Introduction Types and Operation of Step Motors Variable Reluctance Step Motor Drive Circuits for Variable Reluctance Step Motors Permanent Magnet Can-Stack Step Motor Hybrid Step Motor Drive Circuitry for Permanent Magnet and Hybrid Step Motors Step Motor Models Variable Reluctance Step Motor Model Bifilar-Wound Hybrid Step Motor Model Drive Circuit Modeling Control of Step Motors Excitation of Step Motors Open-Loop Control 14.1 Introduction Step motors are used in many low-lost positioning applications due to their inherent ability to stop at discrete positions and follow position vs. time profiles while being controlled open loop. A step motor is a synchronous machine but historically has been used almost exclusively in positioning and position tracking applications. Recently however some types of step motors have been applied in variable speed drives applications. Step motors can be driven without feedback to stop at discrete angular positions known as detent positions. The number of detent positions can be as low as 12 steps or detent positions per revolution to 400 or 500 or more steps per revolution. The location accuracy of the detent positions varies typically within 5 of the step size. The repeatability of the motor is also high in that the rotor can start on one position move away to other positions and then return to within typically 3 of step size of the original position. The motors with relatively few steps are typically used in higher-speed applications where the motors with many steps per revolution are often used in high-torque low-speed direct drive applications or applications where many repeatable discrete positions are required. Step motors have been successfully applied in many applications such as computer peripherals e.g. disk drives pen plotters and printers office machines e.g. copiers scanners automotive e.g. seat positioning speed control aerospace e.g. flap .