What is a servo driver?
Servo drives, also known as servo controllers or servo amplifiers, are controllers used to control servo motors. Their function is similar to that of a frequency converter for a regular AC motor. They are part of a servo system and are primarily used in high-precision positioning systems. Generally, they control the servo motor through position, speed, and torque to achieve high-precision positioning of the transmission system. Currently, they represent a high-end product in transmission technology.
Servo drives are an important component of modern motion control and are widely used in automated equipment such as industrial robots and CNC machining centers. Servo drives for controlling AC permanent magnet synchronous motors, in particular, have become a research hotspot both domestically and internationally. Current AC servo drive designs commonly employ a three-loop control algorithm based on vector control, encompassing current, speed, and position. The rationality of the speed closed-loop design within this algorithm plays a crucial role in the overall performance of the servo control system, especially in terms of speed control performance.
In the speed closed loop of a servo drive, the real-time speed measurement accuracy of the motor rotor is crucial for improving the dynamic and static characteristics of the speed loop's speed control. To achieve a balance between measurement accuracy and system cost, incremental photoelectric encoders are generally used as speed sensors, and the commonly used speed measurement method is the M/T (Mean Transmission/Turning) method. While the M/T method offers a certain level of measurement accuracy and a wide measurement range, it has inherent drawbacks, primarily: 1) at least one complete encoder pulse must be detected within the measurement cycle, limiting the minimum measurable speed; 2) the two timer switches used for speed measurement are difficult to keep strictly synchronized, making it impossible to guarantee measurement accuracy in situations with large speed variations. Therefore, traditional speed loop designs using this method struggle to improve the speed tracking and control performance of servo drives.
Servo driver working principle
Currently, most mainstream servo drives use digital signal processors (DSPs) as their control core, enabling complex control algorithms and achieving digitalization, networking, and intelligence. Power devices generally employ drive circuits designed around intelligent power modules (IPMs). The IPM integrates the drive circuitry and includes fault detection and protection circuits for overvoltage, overcurrent, overheating, and undervoltage. A soft-start circuit is also added to the main circuit to reduce the impact on the driver during startup. 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 DC power. The rectified three-phase power or mains power is then frequency-converted by a three-phase sinusoidal PWM voltage-type inverter to drive the three-phase permanent magnet synchronous AC servo motor. The entire process of the power drive unit can be simply described as an AC-DC-AC process. The main topology of the rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.
The role of servo drivers
A servo drive is used to power servo motors and enable equipment to operate normally. Its functions are diverse, and the specific features vary depending on the brand. For example, servo motors from companies like Kefeng Automation offer a relatively wide range of functions, which can be summarized as follows:
1. Parameter grouping settings and control modes can be switched arbitrarily online;
2. Control power supply AC input, configurable wide voltage input;
3. Instantaneous power failure and rapid shutdown protection function;
4. Regenerative braking and dynamic braking functions;
5. Absolute value system voltage monitoring and low voltage warning function;
6. The debugging software supports parameter management, monitoring, and oscilloscope functions.
