What Is a Variable-Frequency Drive?

Servo drives (servo drives), also known as "servo controllers" and "servo amplifiers", are a type of controller used to control servo motors. Their functions are similar to those of inverters on ordinary AC motors, and they are part of the servo system. Mainly used in high-precision positioning systems. Generally, the servo motor is controlled by three methods of position, speed and torque to achieve high-precision positioning of the transmission system. It is currently a high-end product of transmission technology.

Servo drives are an important part of modern motion control and are widely used in industrial robots and CNC machining centers and other automation equipment. Especially the servo driver used to control the AC permanent magnet synchronous motor has become a research hotspot at home and abroad. Current AC servo drive design generally adopts vector control based current, speed, and position 3 closed-loop control algorithms. Whether the speed closed-loop design in this algorithm is reasonable or not plays a key role in the performance of the entire servo control system, especially the speed control performance ^[1]

At present, all mainstream servo drives use

Requirements for servo feed systems

1.Wide speed range

At present, there are the following test platforms for servo drives: a test platform that uses servo drive-motor mutual feedback and drag, a test platform that uses adjustable analog loads, a test platform that uses an executive motor but no load, and an executive motor tow Test platform for dynamic inherent load and test platform using online test method ^[2]

Position proportional gain

1. Set the proportional gain of the position loop regulator;

2. The larger the setting value, the higher the gain and the greater the stiffness. Under the same frequency command pulse condition, the position lag is smaller. However, too large a value may cause oscillation or overshoot;

3. The parameter value is determined by the specific servo system model and load situation.

Position feedforward gain

1. Set the feedforward gain of the position loop;

2. The larger the setting value is, the smaller the position lag is under the command pulse of any frequency;

3. The feedforward gain of the position loop is large, and the high-speed response characteristics of the control system are improved, but the position of the system is unstable and it is easy to generate oscillation;

4. When high response characteristics are not required, this parameter is usually set to 0 to indicate the range: 0 ~ 100%.

Speed proportional gain

1. Set the proportional gain of the speed regulator;

2. The larger the setting value, the higher the gain and the greater the stiffness. The parameter value is determined according to the specific servo drive system model and load value. In general, the larger the load inertia, the larger the setting value;

3. Under the condition that the system does not oscillate, set a larger value as much as possible.

Velocity integral time constant

1. Set the integral time constant of the speed regulator;

2. The smaller the setting value, the faster the integration speed. The parameter value is determined according to the specific servo drive system model and load situation. In general, the larger the load inertia, the larger the setting value;

3. Under the condition that the system does not oscillate, try to set a smaller value.

Speed feedback filter factor

1. Set the speed feedback low-pass filter characteristics;

2. The larger the value, the lower the cut-off frequency and the smaller the noise generated by the motor. If the load inertia is large, the set value can be appropriately reduced. If the value is too large, the response will be slow and oscillation may be caused;

3. The smaller the value, the higher the cut-off frequency and the faster the speed feedback response. If a higher speed response is required, the set value can be appropriately reduced.

Maximum output torque setting

1. Set the internal torque limit value of the servo motor;

2. The setting value is a percentage of the rated torque;

3. At any time, this limitation effectively locates the completion range;

4. Set the positioning completion pulse range under the position control mode;

5. This parameter provides the basis for the driver to judge whether the positioning is completed under the position control mode. When the number of remaining pulses in the position deviation counter is less than or equal to the value set in this parameter, the driver considers that the positioning is completed and the in-position switch signal is ON, otherwise OFF

6. In position control mode, output position positioning completion signal, acceleration and deceleration time constant;

7. The setting value indicates the acceleration time of the motor from 0 ~ 2000r / min or the deceleration time from 2000 ~ 0r / min;

8. The acceleration / deceleration characteristic is a linear range of arrival speed;

9. Set the arrival speed;

10. In non-position control mode, if the motor speed exceeds this set value, the speed arrival switch signal is ON, otherwise it is OFF;

11. In position control mode, this parameter is not used.

12. It has nothing to do with the direction of rotation.

Servo drives are widely used in the fields of injection molding machines, textile machinery, packaging machinery, and CNC machine tools.

Speed ratio 1: 5000
Speed ratio 0.3: 1500
With position control and zero speed lock overload capacity 200 [%]-300 [%]
Large starting torque and high speed

1. The servo controller can easily convert the operation module and fieldbus module through the automation interface. At the same time, different fieldbus modules are used to implement different control modes (RS232, RS485, optical fiber, InterBus, ProfiBus), and the universal inverter The control method is relatively single.
2. The servo controller is directly connected to the resolver or encoder to form a closed loop of speed and displacement control. The universal inverter can only form an open loop control system.
3The various control indicators (such as steady-state accuracy and dynamic performance) of the servo controller are superior to general-purpose inverters.