Currently, mainstream servo drives utilize a Digital Signal Processor (DSP) as their core control unit, enabling the implementation of complex control algorithms and facilitating digitalization, networking, and intelligent operation. For power switching, drive circuits designed around Intelligent Power Modules (IPMs) are widely adopted; these IPMs feature integrated internal drive circuitry and incorporate fault detection and protection circuits-covering conditions such as overvoltage, overcurrent, overheating, and undervoltage. Furthermore, a soft-start circuit is incorporated into the main power loop to mitigate the impact on the drive unit during the startup process.
The power drive unit first rectifies the incoming three-phase power-or utility mains-via a three-phase full-bridge rectification circuit to obtain the corresponding DC power. This rectified power is then processed by a three-phase sinusoidal PWM voltage-source inverter to drive a three-phase permanent magnet synchronous AC servo motor. The entire operation of the power drive unit can be simply described as an AC-DC-AC conversion process. The primary circuit topology of the rectification unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.
With the widespread adoption of servo systems, the operation, commissioning, and maintenance of servo drives have emerged as critical technical subjects in the modern landscape; consequently, an increasing number of industrial control technology service providers are conducting in-depth technical research into servo drives.
Servo drives constitute a vital component of modern motion control systems and are widely deployed in automated equipment, such as industrial robots and CNC machining centers. In particular, servo drives designed to control AC permanent magnet synchronous motors have emerged as a focal point of research both domestically and internationally. Current AC servo drive designs commonly employ a triple-loop control algorithm-encompassing current, velocity, and position loops-based on vector control principles. Within this framework, the proper design of the velocity control loop plays a pivotal role in the overall performance of the servo control system, and specifically in optimizing its velocity control capabilities.
Requirements for Servo Feed Systems
1. Wide speed regulation range
2. High positioning accuracy
3. Sufficient transmission rigidity and high speed stability
4. Rapid response with no overshoot
To ensure both productivity and machining quality, in addition to requiring high positioning accuracy, excellent rapid-response characteristics are also essential-specifically, the ability to track command signals with speed. This is because, during the startup and braking phases of a CNC system, sufficiently high acceleration and deceleration rates are required to shorten the transient response time of the feed system and minimize contour transition errors.
5. High Torque at Low Speeds; Strong Overload Capability
Generally speaking, servo drives possess an overload capacity of more than 1.5 times their rated load, sustained for periods ranging from several minutes up to half an hour; furthermore, they can withstand overload levels of 4 to 6 times their rated capacity for short durations without sustaining damage.
6. High Reliability
The feed drive systems of CNC machine tools are required to exhibit high reliability and excellent operational stability. They must possess robust adaptability to environmental conditions-such as variations in temperature, humidity, and vibration-as well as strong resistance to external interference.
Motor Requirements
1. The motor must operate smoothly across its entire speed range-from the lowest to the highest speeds-with minimal torque fluctuation. In particular, at very low speeds (such as 0.1 r/min or lower), it must maintain smooth velocity without exhibiting any "crawling" phenomena.
2. The motor must possess substantial, sustained overload capacity to satisfy the requirements for high torque at low speeds. Typically, DC servo motors are required to withstand an overload of 4 to 6 times their rated capacity for several minutes without sustaining damage.
3. To ensure rapid response capabilities, the motor should feature low rotational inertia and high stall torque, while also exhibiting the smallest possible time constant and starting voltage.
4. The motor must be capable of withstanding frequent starting, braking, and reversal operations.