In-depth research and analysis of servo drive technology principles

At present, mainstream servo drives all use digital signal processors (DSPs) as the control core, which can implement relatively complex control algorithms and realize digitalization, networking and intelligence. Power devices generally use drive circuits designed with intelligent power modules (IPMs) as the core. The IPM integrates the drive circuit internally, and also has fault detection and protection circuits such as overvoltage, overcurrent, overheating, and undervoltage. A soft start circuit is also added to the main circuit to reduce the impact of the start-up process on the drive. The power drive unit first rectifies the input three-phase power or mains power through a three-phase full-bridge rectifier circuit to obtain the corresponding direct current. After the rectified three-phase power or mains power, the three-phase permanent magnet synchronous AC servo motor is driven by a three-phase sinusoidal PWM voltage inverter.

The whole process of the power drive unit can be simply described as an AC-DC-AC process. The main topology circuit of the rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.

With the large-scale application of servo systems, servo drive use, servo drive debugging, and servo drive maintenance are all relatively important technical topics for servo drives today. More and more industrial control technology service providers have conducted in-depth technical research on servo drives.

Servo drives are an important part of modern motion control and are widely used in automation equipment such as industrial robots and CNC machining centers. In particular, servo drives used to control AC permanent magnet synchronous motors have become a research hotspot at home and abroad. The current AC servo drive design generally adopts a three-loop control algorithm based on vector control: current, speed, and position. Whether the speed closed-loop design in this algorithm is reasonable or not plays a key role in the entire servo control system, especially the speed control performance.

Requirements for servo feed systems

1. Wide speed regulation range 2. High positioning accuracy 3. Sufficient transmission rigidity and high speed stability 4. Fast response, no overshoot

In order to ensure productivity and processing quality, in addition to requiring high positioning accuracy, it is also required to have good rapid response characteristics, that is, the response of the tracking command signal must be fast, because when the CNC system starts and brakes, the acceleration and deceleration must be large enough to shorten the transition time of the feed system and reduce the contour transition error.

5. Low speed, high torque, strong overload capacity

Generally speaking, the servo drive has an overload capacity of more than 1.5 times within a few minutes or even half an hour, and can be overloaded 4 to 6 times in a short period of time without damage. 6. High reliability The feed drive system of the CNC machine tool is required to have high reliability and good working stability, strong adaptability to the environment such as temperature, humidity, vibration, and strong anti-interference ability.

Requirements for motors

1. The motor should be able to run smoothly from the lowest speed to the highest speed, with small torque fluctuations, especially at low speeds such as 0.1r/min or lower, there is still a stable speed without creeping. 2. The motor should have a large overload capacity for a long time to meet the requirements of low speed and high torque. Generally, DC servo motors are required to be overloaded 4 to 6 times within a few minutes without damage. 3. In order to meet the requirements of fast response, the motor should have a small moment of inertia and a large stall torque, and have the smallest possible time constant and starting voltage. 4. The motor should be able to withstand frequent starting, braking and reversing.