Introduction：
Most screw extruders are generally driven by DC motors, but with the rapid development of power electronic devices and microprocessor technology, the proposal of AC control theory and the improvement of AC control software in recent years, AC drive technology is more suitable for many applications. DC drives are more cost-effective. D71 series inverters are used in screw extruders and have better speed control performance and torque response speed than DC drives.
Features：
D71 is a wall-mounted inverter, the power range is 0.75KW-500KW, the voltage level of the incoming line voltage is 380V-480V, and the control method is vector control without speed sensor. D71 has a wealth of control devices, including 8 digital inputs (LI1-LI8), 2 analog inputs (AI), 2 relay outputs (TA), 2 analog outputs (AO), 5V auxiliary power supply for analog power supply The fixed input 24V auxiliary power supply is used for digital input, and all LI/TA, AI/AO can be freely programmed to define functions.
MODBUS interface is standard configuration of D71, no option is required. The QD6600 can be connected to a higher-level automation system through MODBUS.
Advantage：
The vector control theory is advanced, the system computing ability is very strong, the load torque can be quickly detected, controlled and compensated, and the over-torque capability is strong;
High efficiency, about 5% higher than that of the same power DC drive system;
Ensure that the motor output performance is excellent without overheating;
Low frequency large torque, 0.5Hz 150% rated torque;
The response speed of the servo stage, the fluctuation is small when the load torque changes sharply;
Provide screw protection through torque limit function;
It has good overload capacity and environmental adaptability, and has high operational reliability;
The completely independent air duct design can greatly improve the resistance to harsh environments such as oil pollution, dust and humidity;
System Introduction：
In this system, a D71 18.5KW frequency converter drives the 11KW main motor of the screw extruder. The frequency reference of the main motor inverter is given by the PLC through the RS485 interface. During operation, the speed can be arbitrarily modified on the touch screen to realize the accurate speed reference of the main motor; at the same time, the PLC reads the frequency and current of the inverter through MODBUS communication. .
Technical Parameter：
| Inverter technical parameters | Device configuration | |
 Model: D71-X | Output current: 38A | One D71 inverter |
| Input voltage: 3-phase, 380-480V | Frequency range: 0-400Hz | 11kW 1 screw extruder main motor |
| Input frequency: 50/60Hz ±5% | Overload capacity: 150%, 60 seconds | PLC |
| Output power: 118.5KW | Ambient temperature: -10-40°C | touch screen |
| Output voltage: 0-480V (the maximum value is determined by the input voltage) | Protection level: IP20 | |
On Site Usage：
According to the on-site space situation, a D71 series inverter is installed in the control cabinet, and the inverter installation and on-site motor are as shown in the figure
Running Result：
The screw extruder control system using D71 inverter has been put into operation for more than three years, and has achieved good economic and social benefits:
The control device operates reliably, has good environmental adaptability, can resist harsh environments such as oil pollution, dust and damp heat, and has a low failure rate;
Excellent current limiting characteristics, strong overload capacity, can effectively reduce frequency conversion overload, overcurrent protection, and maximize production continuity;
The speed control precision is high, and the production products are more in line with the requirements;
The system has high speed regulation accuracy, which is convenient for on-site personnel to operate.
Customer Benefits：
The inverter and spindle motor run stably, reducing maintenance costs;
The comprehensive protection function of the inverter ensures maximum production continuity;
The production of products is more in line with the requirements, and the defect rate is greatly reduced;
On-site personnel are easier to operate and have high speed regulation accuracy.