Implementing Embedded Speed Control for AC Induction Motors


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Physics of Induction Motors

•Current passing through a conductor creates magnetic field–Direction of magnetic field is determined by the right hand rule•Changing magnetic field produces current in a conductor–Direction of current is determined by right hand rule•Electromagnetic Induction–Changing current induces changing magnetic field around it. –A conductor placed in this field has induced current and induced magnetic field•Interaction between two magnetic fields and two currents in stator and rotors produce the torque•Torque is proportionalto the magnitude and
frequency of the current in stators

Induction Motors

•Motors operate on principle of Induction and hence the name “Induction Motors”is used•Motors also known as AC motors because Alternating Current (AC) is required •All AC motors are “brushless”–No mechanical contacts to wear–Requires AC source–If used, inverter creates desired freq and magnitude of AC•AC induction motors for lower cost applications–Single speed applications: fan, blower, pump, compressor–No control, just start the AC power source–Relays are used for ON/OFF

180°Drive Operation

•Utilizes entire electrical rotation to rotate the motor vs. 120 deg uses only 2/3 rotation
•Requires dead timeregister to make sure two power devices do not conduct at the same time for a given phase
–e.g. Up and Un do not turn on at the same time
•This operation generally can not use the back EMF signal to detect the rotor position
•Allows various modulation strategies including sine wave & pseudo sine wave.