Motor Control Algorithms

Brushed DC (BDC) motors can be operated with a simple on/off control or a variable-speed control with optional feedback mechanism. The control system also depends on the drive type, which can be a unidirectional low-side drive, unidirectional high-side drive or bidirectional drive.

Stepper motors have various drive techniques depending on the application and phase configuration of the motor. The drive can be either unipolar or bipolar and the step mode can be wave drive, full-step drive, half-step drive or microstep drive.

Brushless DC (BLDC) motors are Permanent Magnet Synchronous Motors (PMSMs) that are designed to use six-step trapezoidal control. This can be implemented by using Hall sensors for sensored control or by measuring the motor’s back EMF for a sensorless implementation.

Closed-loop Field-Oriented Control (FOC) is essential for getting the best performance from Permanent Magnet Synchronous Motors (PMSMs). Our complete ecosystem for developing FOC control algorithm includes these resources:

The Zero-Speed/Maximum-Torque (ZS/MT) control algorithm is a new variation of the sensorless Field-Oriented Control (FOC) algorithm that enables the adoption of sensorless control techniques in high-torque or low-speed motor control applications. These types of applications typically require three Hall effect position sensors. ZS/MT eliminates the need for Hall effect sensors, connectors and cables by using a reliable Initial Position Detection (IPD) method based on High-Frequency Injection (HFI) to determine the exact rotor position at zero and low speeds. This enables the control algorithm to deliver maximum torque to a variety of applications including drilling machines, garage door openers, automotive starters and e-bikes. The ZS/MT algorithm runs on dsPIC33 Motor Control Digital Signal Controllers and SAM C2x, SAM D/E5x, SAM E7x and PIC32MK MCUs and can be used with salient motors, especially Interior Permanent Magnet (IPM) motors.

Advantages:

• Reduces overall system cost in applications requiring high torque at zero (standstill) or low motor speeds
• Offers improved reliability by eliminating potential issues due to faulty cables and ESD-sensitive Hall effect sensors

Versions 2.45 and later of motorBench^® Development Suite provide the ZS/MT algorithm for dsPIC33 DSCs. To access the algorithm, please download MPLAB^® X IDE, install the MPLAB Code Configurator (Melody) plug-in then download and run the motorBench Development Suite library.

To help you overcome the challenges of implementing FOC and improve the performance of your PMSM application, we offer a number of application notes and a variety of algorithms within our motor control software library such as:

• Flux weakening
• Initial Position Detection (IPD)
• Soft stop
• Stall detection
• Windmilling
• Torque compensation

Our technical brief discusses some algorithms that can improve the Field-Oriented Control of your PMSM.

Air conditioners and refrigerators: To enable heat exchange, motor-driven compressors are major components in air conditioning and refrigeration systems. Due to pressure variations during a compression cycle, the compressor loads the motor unevenly, causing vibrations in the motor, compressor and pipes. These vibrations, especially at low speeds, can cause fatigue in pipes and can lead to premature failure of the unit. At high speeds, the motor, compressor and pipes react less due to their typical mechanical responses. The Torque Compensation algorithm can be used to minimize vibrations in compressors.

Washing machines: With the combination of a high-inertia load and a motor running at a very high speed, an abrupt stop can suddenly transfer the energy back to the electrical system. The Soft Stop algorithm provides a controlled reduction to the motor speed to prevent a surge in the DC bus voltage when a washing machine is running in spin-dry mode and is suddenly stopped.

AC Induction Motors (ACIMs) are the most popular motors for Variable Frequency Drives (VFDs). Speed control of ACIMs can be implemented using either the Scalar Control Algorithm (V/f Control) or Field-Oriented Control (FOC).