First, the basic situation
The sewage treatment plant uses three horizontal screw discharge sedimentation centrifuge (LW520W) for sludge dewatering, dewatered sludge to maintain a certain degree of humidity. Each decanter centrifuge using four inverters: 75KW, 22KW, 15KW and 1.5KW, 75KW inverter control 55KW main motor and 15KW inverter control 15KW inverter motor as a secondary motor, 15KW inverter control feed pump, 1.5KW Inverter control dosing pump.
This debugging is mainly aimed at the control of the main machine and the auxiliary machine. The main machine and the auxiliary machine share the DC bus. The inverter models used are VT2-4T-075 and VT2-4T-015 Before I arrived, our company had carried out the initial debugging. The AO1 and AO2 analog output terminals of the host were output frequency and output current respectively (output and input signals are 0 ~ 20mA), as the monitoring signals P7.03 = 50, P7 .04 = 48, acceleration / deceleration time P0.08 = 360.0, P0.09 = 360.0; Slave AO1 and O2 analog output terminals are output frequency and output torque respectively. Slave AI2 terminal receives PLC output control signal, P0 .03 = 4, P0.04 = 2, P7.03 = 52, P7.04 = 48, P0.08 = 126, P0.09 = 126. PLC control strategy using differential control and torque control are problems. The torque control can not be stable, gradually increasing, the use of torque control steady over-current. Sketch map of slip control and torque control are shown in the figure below.
Application of a Centrifuge in a Sewage Treatment Plant in Jiangsu Province
Figure 1 slip control and torque control diagram
Second, the matching test results
At the beginning of the auxiliary machine torque control out of control, after the use of torque control program, followed by a test machine. First remove the belt on the secondary motor, the rotation of self-learning. PLC controls the slave output torque (38% at steady state), Pd.00 = 1, P6.21 = 2, Pd.06 = 50.00, Pd.07 = 10.00, Pd.08 = 40.00, Pd.09 = 40.00 , Pd.12 = 1.0, Pd.13 = 1.0. At this moment, the running frequency of the slave reaches 50.00Hz quickly, but the frequency is still 50.00Hz after changing the output torque, and the frequency is reduced to 0 after changing Pd.21 to 21 finally.
Torque control program of PLC control inverter speed, the effect is recognized. On the morning of November 30, it decided to try out the torque control scheme of PLC control sub-inverter speed to find out the problem. In this case, the acceleration / deceleration time is changed to 6 seconds, P0.08 = 6.0, P0.09 = 6.0, P0.03 = 0, and the motor parameters adopt the results of the previous night's rotation self-learning. Afternoon debugging no problem, I feel better; repeated tests at night, contrast, the customer approved the program. The difference between this time and the day before debugging only in acceleration and deceleration time, vector control and motor rotation self-learning three aspects.
Third, the summary
1. Vector control mode 1 is preferred, and control strategies may be considered for further optimization.
2. The field proved that vector control 2 and torque control is also a viable control method.
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