LEON Partner

The hybrid stepper motor is an attractive substitute for an asynchronous motor (AM) with a gearbox thanks to its high torque. It is a unipolar motor with a strong axial magnet in the rotor. The magnetic flux in the stator therefore also has a significant axial component, but the stator lamination is designed for radial magnetic flux. This causes eddy currents and heating of the motor, commonly above 100 °C. These motors also suffer from resonances and noise.

We have developed a unipolar PMSM with magnets in the stator, which brings low cost and high efficiency. The robust rotor without magnets and the significantly improved air cooling allow the design to be used for high-speed motors as well.

A NEMA 34 (86 mm) hybrid stepper motor with a 65 mm stator stack has a torque of 4 Nm. Our motor of the same size has the same torque.

Dead times when switching the output bridge have a major impact on the quality of motor control, especially at low frequencies, and can cause motor oscillations.

We have used various methods to eliminate the uncertainty in measuring the polarity of the output currents near the zero crossing caused by noise or measurement offset (analog integration of the phase voltages, or measuring them just before the transistor switches on).

Our own solution proved to be the most robust and at the same time the simplest: digital integration of the output voltages using comparators with a DAC reference, ADC measurement of the DC link voltage and fast counters, all contained in the uP STM32F303.

High-quality measurement of the motor phase currents with a single shunt resistor requires, in addition to a fast ADC with an OPAMP, an adapted modulation that does not adversely affect the operation or noise of the motor.

Our solution using the uP STM32F303 meets these requirements, simplifies the design and enables vector control of the motor.

Short-range radio communication (NFC) is becoming a standard in mobile phones and tablets, as well as in electrical appliances and equipment. Besides user comfort and the low price of dual EEPROMs, it also allows reading parameters and fault history even when the device is not powered. We have developed an NFC package including software modules for the inverter and for PC / tablet / mobile, with emphasis on functional safety.

We have developed a method for FEM modeling and calculation of a motor with a monolithic multipole ferrite ring.

This design is becoming increasingly popular because it significantly reduces the number of components and the manufacturing cost of the motor.

The method replaces the continuous change of the magnetization direction in the magnet with a large number of segments (Halbach array).