Abstract: Servo motors are widely used in high-precision control systems. They offer diverse and intelligent control methods and incorporate feedback systems to achieve closed-loop control. In dynamometers, servo motors can be used for reverse dragging, further amplifying their control advantages.
A dynamometer mainly consists of two parts: a cabinet and a test bench. The test bench primarily contains the motor under test, torque and speed sensors, and a mechanical load. Currently, servo motors are often chosen as the load. Servo motors convert electrical signals into torque and speed to drive the controlled object. The rotor speed of a servo motor is controlled by the input signal and can respond quickly. In automatic control systems, it is used as an actuator and has characteristics such as a small electromechanical time constant, high linearity, and low starting voltage.
Figure 1
Servo motors can drive each other. The common DC bus uses a separate rectifier/feedback device to provide power to the system. The speed control inverter is directly connected to the DC bus. When the system is in motor mode, the inverter obtains power from the bus. When the load is driven in reverse by the tested motor, the servo motor will become a generator, and the energy will be directly fed back to the grid through the bus and feedback device to achieve energy saving and improve the reliability of equipment operation.
Figure 2
So here's the question: can't a variable frequency motor achieve the same energy feedback effect without a servo motor ? Actually, the key to variable frequency motors is frequency control. A variable frequency motor can adjust its speed by changing the motor's frequency according to the work requirements. However, it doesn't have better torque characteristics; it only overcomes the need for ordinary motors to adapt to PWM (Pulse Width Modulation) to simulate sinusoidal AC power.
Figure 3
When testing the load characteristics of a motor, national standards require that the test be conducted as quickly as possible to minimize temperature changes in the motor during the test. In this context, the superiority of servo motors becomes highly apparent. Load changes require the load motor to respond quickly to a given waveform; servo motors not only possess high control precision and fast control speed, but also have built-in PID control functions, and can simulate continuous load changes in the tested motor. Servo motors are recommended as test loads when the speed or torque is not particularly high or low.
Servo motors, as drag loads, overcome the limitations of traditional dynamometers that can only apply loads one load point at a time. ZLG Zhiyuan Electronics' MPT motor testing platform boasts a unique "free loading engine" technology, enabling arbitrary load curve loading and waveform measurement during motor testing. This meets the transient measurement needs of motors and drivers, taking motor testing to a new level.
