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19 July, 2024

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Sensor-less salient-pole motors challenge servomotors

03 July, 2024

Mitsubishi Electric has launched a series of salient-pole motors that deliver high-quality speed and position control without encoders. It says that the EM-A motors – which it describes “an industry first” – offer a competitively priced alternative to servomotors.

The motors are designed for applications that that need positioning and/or accurate speed control. They are smaller than most induction motors by one or two frame sizes, and weigh 30-50% less. They achieve IE5 efficiencies, cutting energy losses by almost 50% compared to equivalent IE2 motors, as well as having a smaller footprint.

The motors span the power range 0.1–7.5kW, and unlike induction motors can operate at low speeds without needing a ventilation fan.

The motors’ rotors consist of a patented salient-pole core with surface-mounted permanent magnets. Their inductance changes, depending on their rotational position, and this change is used to achieve sensor-less vector control.

The motors are compatible with Mitsubishi’s FR-A800 and FR-E800 inverters and can carry out point-to-point position control, or accurate speed control, without needing motor-mounted encoders. They therefore need less wiring, while delivering a claimed positioning accuracy of 200 pulses/rev and a command resolution of 4,096 pulses/rev.

Mitsubishi’s salient-pole motors are smaller and lighter than induction machines

The sensor-less vector control capability reduces speed variations during load changes, with a servo-lock function that generates holding torque when the motor stops to prevent movement caused by external forces. With a speed variation range of ±0.05% and a speed control range of 1:1300, the system is said to provide precision speed and positioning control, comparable to that of servomotors. They can deliver 200% torque for up to three seconds.

When used with a variable-speed drive, the motors support all major communications protocols.

Mitsubishi Electric:  LinkedIn  Facebook

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