In addition to Field-Oriented Control (FOC), other motor control algorithms are used depending on the motor type, application requirements, and desired performance level. These algorithms range from simple and low-cost to complex and high-performance.

1. Scalar Control (V/Hz)

This is a simple, open-loop control method, primarily used for AC induction motors in low-performance applications like fans and pumps.

• How It Works: Scalar control operates by keeping the ratio of the motor’s voltage to its frequency (V/Hz) constant. By controlling the frequency, you control the motor’s speed. To maintain a constant magnetic flux and prevent the motor from overheating, the voltage is adjusted proportionally.
• Pros: It’s very simple, easy to implement, and inexpensive. It doesn’t require complex mathematical transformations or a position sensor.
• Cons: It provides poor dynamic performance and a lack of precise torque control. Because it’s an open-loop system, it’s not suitable for applications that require high-precision speed or position control, such as robotics or electric vehicles.

2. Direct Torque Control (DTC)

Direct Torque Control is a high-performance vector control method that, like FOC, can provide precise and rapid control of a motor’s torque and speed. However, it achieves this in a different way.

• How It Works: Instead of using PI controllers and transformations to control currents, DTC directly controls the motor’s magnetic flux and torque. It estimates these values from the motor’s measured voltage and current and then uses a simple lookup table (a switching table) to select the optimal inverter state that will correct any error in the flux and torque values.
• Pros: DTC provides a very fast and dynamic torque response, often faster than FOC. It’s also simpler to implement because it doesn’t require a position sensor or complex transformations.
• Cons: A major drawback of DTC is that it leads to higher current and torque ripple and a variable switching frequency, which can cause more motor noise and stress on the power electronics. Modern DTC implementations often use more advanced techniques like Space Vector Modulation (SVM) to address this.

3. Pulse Width Modulation (PWM) and Space Vector Modulation (SVM)

While not a full control algorithm on their own, these are crucial techniques used by most advanced motor control algorithms, including FOC and DTC, to create the necessary AC waveforms.

• Pulse Width Modulation (PWM): PWM is a technique that creates an analog signal from a digital source by rapidly switching a voltage on and off. The “width” of the pulses determines the output voltage. It’s a fundamental technique used in motor controllers to convert the DC battery voltage into a variable AC voltage for the motor.
• Space Vector Modulation (SVM): SVM is a more advanced and efficient form of PWM. It’s a complex algorithm that calculates the optimal switching pattern for the inverter’s transistors to produce a smoother, more sinusoidal output voltage.
• SVM vs. PWM: SVM is generally preferred over basic PWM because it provides a higher DC bus voltage utilization (meaning more power is delivered to the motor) and reduces harmonic distortion, which results in a smoother, quieter, and more efficient motor operation. Many modern FOC and DTC systems use SVM as their primary modulation technique.