Frequency Conversion Speed ​​Regulation Control of Paper Machine Sizing System

The paper machine sizing system is responsible for the process of transporting the paper pulp to the headbox of the paper machine wire section through equipment such as slurry pumps, slurry pumps, and multi-stage screens. Among them, the slurry pump and the slurry pump are the most important equipment, because they are related to the forming The quality of paper, especially the weight, must be controlled by frequency conversion to meet the design requirements of the paper machine. Practice has proved that the installation of frequency conversion device can adapt to different vehicle speeds and different types of consumption changes, so that the operation of the slurry pump unit is always in a high-efficiency state. In addition, when the frequency conversion control is adopted, the speed of the motor and the slurry pump decreases, the wear of mechanical parts such as bearings is reduced, the pump end sealing system is not easily damaged, the failure rate of the pump is greatly reduced, and the maintenance workload is also reduced.

The sizing process must meet the following requirements:

1. The amount of slurry conveyed to the wire section of the paper machine must be stable, and the error should not exceed ±5%.

2. The proportion and concentration of the slurry should be stable and uniform.

3. Purify and select the slurry, so the speed control of the slurry pump and the slurry system is the top priority to ensure the realization of items (1) and (2).

The flow of speed control is explained below with a slurry pump as an example: the frequency conversion control adopts the speed control mode of a double closed loop system, the outer loop is a speed closed loop (V-control), and the inner loop is a current or torque closed loop (I-control) . On the one hand, the setting value of the speed of the flushing pump is the V setting obtained by changing the ratio of the pulp speed and the wire speed, and on the other hand, it comes from the pressure controller of the headbox (P-control). The former is the main tune, the latter is the fine tuning. The ratio of pulp speed and wire speed of a paper machine is basically constant. Therefore, when the wire speed of a paper machine changes, the V setting also changes, and the speed of the punching pump also changes; in order to improve the accuracy of the speed regulator And to reflect the actual process of the headbox, it is usually necessary to take the change of ±5% of the PID control output value of the headbox pressure as the additional speed setting value of the flushing pump. The actual value (actual) of the speed is taken from the actual speed sampling of the transmission motor, which can be obtained by a detection device such as a rotating speed motor or a photoelectric rotary encoder. The current setting value (M setting) is taken from the output signal of the speed loop, and the current actual value (M actual) is taken from the measured value of the current transformer at the output end of the AC inverter at each transmission point.

Therefore, for the frequency conversion speed regulation of the pulp pump of a paper machine, PID control is required, and various parameters of the speed feedback mode and PID need to be correctly selected. The setting value of acceleration time 0-100% is generally 60 seconds, and the deceleration time is about 30 seconds. The set input value of the inverter must have two to multiple inputs and be able to perform basic calculations. The feedback signal must have a port for receiving analog signals or pulse signals. Understanding this point is very important for choosing the type of inverter.