Application of the GD350 VFD on the
rolling machine for electrode material
of Lithium batteries.

Device Principle:

During the operation of the battery electrode sheet rolling mill, crucial for lithium battery manufacturing, the start and stop operations require continuous and precise stepless speed control of both rolls according to technological requirements. Simultaneously, it is essential to ensure uniform linear speed between these rolls. The rolling process of the battery electrode sheet involves generating friction forces between the rolls and the electrode material, which is then drawn into the rotating rolls where it undergoes deformation. This rolling mill consists of two rolls: the upper roll serving as a fixed element and the lower roll, which is adjustable. Hydraulic mechanisms regulate the gap and pressure settings between these rolls. The incoming material consists of aluminum foils coated with polar materials and has approximately 820 mm spacing between the uncoated polar materials. The initial coating thickness of the incoming material is about 210 μm. After rolling, it is carefully maintained at approximately 164-165 μm. It is important to emphasize that the uniformity of the initial material thickness significantly influences whether the rolling thickness meets the required standards. The motor is connected to the rolls via universal joints to complete this crucial process in lithium battery manufacturing.

Customer Requirements:

Due to deficiencies in the current AB frequency division control strategy, such as insufficient power balance between the main and auxiliary units, different linear speeds of the moving and fixed rolls, and issues during startup when the fixed and moving rolls meet at the transition of the aluminum foil coating, the customer has the following requirements for an updated control strategy:

1. The frequency inverter must maintain the rolling speed with minimal fluctuations and ensure robust starting torque.
2. The linear speeds of both the moving and fixed rolls must be uniform and synchronized throughout the speed spectrum.
3. The frequency inverter must allow acceleration and deceleration adjustments throughout the rolling mill system, with acceleration and deceleration times controlled by the PLC.

System Solution:

In response to the customer’s requirements, we propose the following system solution: (1) Motor setup with encoders. By using vector control and encoders, the frequency inverter precisely regulates the rolling speed and ensures robust starting torque. (2) Integration of a frequency inverter with a CAN communication card. This card is essential for controlling the speed of both rolls and achieving uniform linear speed and a balanced power ratio between the upper and lower rolls. (3) Implementation of a brake module. The frequency inverter is equipped with a brake module to meet the rapid stopping requirements of the entire rolling mill.

Benefits of this Solution:

Through the implementation of the Invt Master-Slave control strategy:

• Simplified device control:The frequency inverter master seamlessly responds to a start signal from the PLC and sets acceleration and deceleration times to zero. These time intervals are now precisely controlled by the analog speed signaling of the PLC. The slave unit seamlessly follows the speed changes of the master.
• Simplified synchronization of device master-slave setup:The process now requires fewer steps for synchronization error troubleshooting. A minimal set of parameters is required for troubleshooting, and these parameters exhibit remarkable consistency and easy reproducibility.
• Increased production stability:The system ensures significant torque availability, especially at low frequencies, effectively preventing torque instabilities during the starting phase between the two electrode sheets. Low-frequency control contributes to overall stability and facilitates precise thickness measurement of electrode sheets at low speeds, reducing the production of substandard electrode sheets.
• Significant increase in production efficiency:The linear speeds of the moving and fixed rolls are continuously synchronized throughout the speed spectrum. This synchronization gives the rolling mill flexibility to make speed adjustments within the specified speed range, leading to a significant increase in production efficiency.

Summary:

The implementation of the Invt GD350 CAN Master-Slave control solution in the rolling machine for lithium battery electrode foils has proven to be extremely successful. By using the frequency inverter to control the rolls using CAN Master-Slave control technology, various performance aspects have been significantly improved. In particular, the stability of low-frequency control has been enhanced, and the uniform linear speeds of both the moving and fixed rolls have been ensured across the entire frequency spectrum. This solution effectively allows the rolling mill to operate at variable speeds, strengthening its key role in the comprehensive production of lithium batteries.