The use of AC drives in paper machines is becoming increasingly popular. High-speed paper machines demand more stringent performance from frequency converters, particularly in terms of speed accuracy and dynamic response. As the speed of these machines increases, so does the drive power for each section, which can reach hundreds of kilowatts or more. To reduce wear on the wire mesh or felt, multiple motors are often used to drive smaller sections, thereby reducing tension in these parts. This setup raises concerns about load distribution, and as the total transmission power grows, frequency converters must handle greater power supply fluctuations.
The Danfoss VLT series has earned customer trust thanks to its superior quality and service. The introduction of the VLT5000 FLUX series magnetic flux vector inverter has made it a strong contender in the high-speed papermaking sector. Key features include a 1000:1 speed ratio, speed accuracy under 0.1%, a speed response of less than 3 ms, and full-load torque response under 2 ms. It dynamically adjusts Motor parameters based on temperature changes, supports various fieldbus protocols, and includes a programmable process controller capable of performing PID arithmetic and logic computations. Applications range from load sharing and tension control to retractable volume regulation. The built-in DC reactor minimizes harmonics in the power grid, while the integrated RFI filter prevents interference with other devices. The encoder interface complies with the RS422 standard, allowing cable lengths up to 150 meters, and improves the reliability of real-time monitoring functions.
To address the load distribution issue, our solution involves powering the frequency converters via a common DC bus. Danfoss can provide the rectification/feedback device or users can supply it themselves. Each section's speed can be controlled via fieldbus, and the inverters can establish a speed chain. The inverters operate using speed closed-loop control. The speed reference value is given by the main frequency converter, which also sends the torque signal to the subordinate frequency converters. Based on the difference between their torque and that of the main converter, the speed of the subordinate converters is dynamically adjusted to ensure consistency in output. All processes are executed through a freely programmable process control card.
Additionally, the process control card offers eight programmable I/O ports, enabling field I/O functionality and helping users save costs.
For the load distribution challenge, we propose the following approach: By connecting the frequency converters to a shared DC bus, Danfoss can either supply the rectification/feedback device or it can be sourced by the user. Each section’s speed can be controlled through fieldbus communication, and the inverters can create a speed cascade. Closed-loop speed control is employed, with the main frequency converter providing both the speed reference and torque signals to the secondary converters. Adjustments to the subordinate converters’ speeds occur dynamically, based on the torque discrepancy between them and the main converter, ensuring synchronized outputs. These operations are fully programmable via a dedicated process control card.
In addition, the process control card includes eight programmable I/O ports, facilitating field I/O tasks and reducing user expenses.
The integration of Danfoss VLT inverters into paper machines represents a significant advancement in technology. Their robust design and precision control make them ideal for demanding applications where speed and torque consistency are critical. For instance, the VLT5000 FLUX series ensures exceptional performance, with its ability to maintain a speed ratio of 1000:1, an impressive speed accuracy below 0.1%, and rapid responses within milliseconds. The inverters' capability to adapt to motor temperature changes enhances operational stability, while the inclusion of advanced fieldbus support and programmable controllers makes them highly versatile in industrial settings.
Addressing the load distribution issue, we propose a system where frequency converters are connected to a common DC bus. Danfoss can provide the necessary rectification/feedback device, or this can be sourced externally. Fieldbus communication allows for precise control over each section’s speed, while the inverters work together in a speed cascade. The primary converter provides both the speed reference and torque signal to the secondary converters. Dynamic adjustments to the subordinate converters’ speeds ensure consistent output across all sections. This entire system operates seamlessly through a highly flexible process control card.
Moreover, the process control card comes equipped with eight programmable I/O ports, offering additional functionality at no extra cost to the end-user. These ports can be used for various field I/O tasks, further enhancing the inverters' utility and cost-effectiveness.
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