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Posts
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[Motor control] What motor parameters are required for sensorless FOC
Sensorless FOC drives are different from hall-sensor drives or sensorless 6-step drives in that sensorless-FOC drives require accurate motor parameters to perform effectively. We will explore which motor parameters that are important, why controllers require accurate motor parameters, and explain the challenges in calculating motor parameters.
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[Motor control] What is the required PWM frequency for motor controller
All BLDC motor controllers use PWM technique to drive the motor. A PWM signal is characterized by the frequency of the signal. Typical values for the PWM signal vary from about 8kHz to 80kHz. In this blog post we will explore how the PWM frequency affects motor control performance. Based on this understanding, we will determine what should be the minimum and maximum frequency that a drive should operate within.
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[Motor control] space vector modulation explained
Space vector PWM (Pulse width modulation) is common technique used in the control of 3-phase AC motors. The space vector PWM enables smooth and efficient operation of the motor. This post will start with a quick introduction to space vector theory using an example. Then, the concept of voltage space vector PWM will be discussed.
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[Motor control] high frequency injection (HFI) for sensorless zero speed torque
BLDC motor controllers use the back-emf generated in the winding to estimate rotor position. Back emf is created in the winding only while the rotor is rotating. When the rotor is not moving, no back emf is created, therefore the controller cannot determine the rotor position. Rotor position estimation using high-frequency injection (HFI) can be performed even while the rotor is at rest. Another name for this technology is saliency tracking. In this blog article, we will go over some fundamental ideas of HFI.
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[Motor control] startup methods for sensorless motor control
To run a BLDC motor, the rotor position is needed so that the stator field can be set orthogonal to the rotor field. Most sensorless motor controllers rely on the back-emf generated in the stator winding to obtain the rotor position. But a back-emf is generated only when the rotors are moving. So when the rotor is at rest, there is no back-emf generated, and the rotor position cannot be inferred. Thus, sensorless motor controllers implement a startup algorithm. This blog post explores different techniques to start the motor from rest.
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[Motor control] Short introduction to sensorless field oriented control
In hall sensor based 6-step control, rotor position is measured using hall sensors, and the angle between stator and rotor flux varies from 60 to 120 degrees. There are 2 significant improvements in sensorless-FOC drives. First, the rotor position is estimated with better precision. Hall sensors output rotor positions at 60 degrees intervals only. But FOC drives obtain rotor positions at typically 2-5 degree intervals. Second, the 6-step commutation can generate only a fixed set of magnetic fields. FOC drives can generate arbitrary magnetic fields in the motor.
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[Motor control] 6 step commutation using hall sensors
This post describes the operation of 6 step control algorithm also called 6-step commutation. The 6-step algorithm is usually done with the help of hall sensors for rotor position feedback. The hall sensor states and the corresponding commutation table will be developed.