Compared with DC motors, high-performance Chinese AC motor manufacturers have sufficient advantages in terms of simple structure, easy maintenance, low environmental requirements, energy saving and increased productivity. As a result, AC speed regulation has been widely used in industrial and agricultural production, transportation, In national defense and daily life. With the rapid development of power electronic technology, microelectronic technology, and control theory, AC speed regulation technology has also made great progress. In the field of high-performance AC speed regulation, there are mainly two kinds of vector control and direct torque control.
1. Direct Torque Control Strategy
Direct torque control is based on a stationary coordinate system. As shown in Figure 1, in traditional direct torque control, by detecting the stator two-phase current, DC bus voltage and motor speed (not in the speed sensorless DTC Speed measurement is required) The stator flux linkage observation and torque calculation are performed, so that the two are subtracted from the stator flux linkage reference and torque reference respectively, and the difference is compared by their respective hysteresis, the output torque and flux linkage The increase and decrease signals are input to the optimized vector switch table, and the sector where the stator flux linkage is located is added to obtain a voltage vector that satisfies the flux linkage is circular and the torque output follows the torque given. The hysteresis loop of the flux linkage and torque can be set in multiple stages, and its width is variable. The smaller the width of the hysteresis loop, the higher the switching frequency and the more precise the control.
2. Direct torque control method
Direct torque control has the advantages of simple structure, fast torque response and good parameter robustness, but it is a control method based on the Bang-Bang control of single vector, torque and flux linkage hysteresis. Inevitably, the low-speed switching frequency is low, the switching frequency is not fixed, and the torque ripple is large, which limits the application of direct torque control in the low-speed region. In response to this, many scholars at home and abroad have proposed various methods to increase the switching frequency, fix the switching frequency, and reduce the torque ripple. This section will list and analyze each one.
