High-voltage frequency converters are widely used in various industries. For frontline equipment users and maintenance personnel, a basic understanding of the converter's control mechanisms, input and output contact circuits is sufficient; in-depth knowledge of the internal control technology is not necessary. However, it's beneficial to learn more about the technical approaches to frequency converter control to lay a foundation for future learning and improvement. A brief explanation is provided here.
frequency converter
1. PWM Control. This technology uses the switching on and off of semiconductor devices to convert DC voltage into a voltage pulse sequence of a specific shape to achieve frequency and voltage control and eliminate harmonics. Most variable frequency speed control devices use this technology. PWM technology used in inverter control can significantly improve the output waveform, reduce motor harmonic losses, reduce torque ripple, simplify inverter structure, accelerate adjustment speed, and improve system dynamic response performance.
2. Vector Control. This method simulates an AC motor as a DC motor, using the rotor magnetic field for orientation. Vector transformation is employed to achieve complete coupling between the AC motor's speed and flux linkage control. It offers high speed control accuracy and excellent characteristics such as constant power control and proportional torque control. It also features fast dynamic response, enabling rapid four-quadrant operation, controllable stall torque, and high starting torque. At low speeds, measures to reduce torque ripple can expand the speed range. The disadvantage is that the control characteristics are highly dependent on motor parameters, requiring accurate input; otherwise, torque control will be inaccurate.
3. Direct Torque Control (DTC) analyzes the motor's mathematical model directly in the stator coordinate system, using stator field orientation without decoupling current, and directly controls the motor's flux linkage and torque. It is unaffected by motor parameters, exhibits good dynamic response, and can achieve rapid torque response during dynamic processes such as motor acceleration, deceleration, or sudden load changes. The control algorithm and system structure are simple, and the switching frequency is low. Disadvantages include torque ripple, slightly poor low-speed performance, and a limited speed range.
