Saturday, December 18, 2010
【 Weak current College 】 converter process control 】
Frequency down will cause the input power and output power imbalance between the transmission of power and energy of electromagnetic flux relative increase significantly, motor circuit seriously saturated, and excitation current waveform serious distortion, great peak current. To change the motor speed in the process of mechanical properties of the control. So-called V/F control, by adjusting the frequency inverter output frequency ratio of voltage side (U/f ratio). To change the motor speed in the process of mechanical properties of the control. Asynchronous motor load torque constant; reduces the frequency of the motor speed drops. Will cause the output power is reduced; and motor input power and frequency is no direct contact. The motor of the input power is not because the frequency drop down automatically. Therefore, when the frequency drops will cause the input power and output power imbalance between the transmission of power and energy of electromagnetic flux relative increase significantly, motor circuit seriously saturated, and excitation current waveform serious distortion, great peak current. Therefore, the converter must reduce the frequency, the lower the output voltage, in order to maintain the input power and balance between output power. To run in low frequency while reducing output voltage, and to ensure that this motor can output enough torque to drag the load, this requires that we load characteristics under different appropriately adjusted U/f than to get the required mechanical properties of the motor. A, u/f converter cable
2.U/f line selection based converter can provide multiple U/f line for user selection, or function parameter settings to get the desired U/f line. Applications should be made according to the load of low speed characteristics selection or set the converter to the corresponding line U/f. For constant torque load, that is, whether high or low speed, load resistance torque is not changed, for example of the belt conveyor, it requires motor in low frequency runtime should also have greater torque, as shown in Figure 1. This situation should U/f ratio, such as large a selection in Figure 4 U/f line 1, when the frequency of the voltage reference fx the voltage to the UX1, namely in low frequency runtime for torque compensation and promotion. Some of the load in the high and low speed torque change significantly when resistance, such as the centrifugal casting machines. The torque characteristics as shown in Figure 2. motors in the low-frequency operation does not require too much torque, U/f ratio can choose smaller, as Figure 4 U/f line 2, selection via the function parameter U/f line
Any of U/f line selection, must go through a function parameter is set to true. Following to Fuji G1 * 1S series frequency converter as an example describes the method of setting parameters. Figure 5 is a constant torque characteristics, Figure 6 as the second-party law decline torque characteristics, Figure 7 for the second side of the law of diminishing torque and constant torque characteristics of the ratio between the torque characteristics. From various torque U/f line diagram is visible. The lower part of Figure 7 (low zone) Curve steepness from Figure 5 and Figure 6, i.e. between the corresponding parts than Figure 6 low frequency region more steep, and a gentle low-frequency area in Figure 5. The figure "# 2 O" callout U/f line, the parameter is set to 2.0 F09 curve, other prefix "#" number of figures, meaning the same. The converter parameter name is "F09 torque increase 1", set it to automatic torque for 0.0 enhancing features that automatically adjusts the constant transfer of torque load-torque increase value to # 2.O and 5 # 20.0 U/f line automatically adjust between changes. If the load is centrifugal blower, pump class-two law decrements the torque device, the setting value should be in the F09 0.1 ~ 0.9. Due to the set value is incremented by 0.1 interval, so a total of 9 U/fl lines to choose from. Specific settings should first taken smaller value, if start torque, then gradually increase, avoid excessive magnetic low frequency, or even start a process of trip. If your load has a constant torque characteristics. Not ready to use automatic torque boost function, you can set the parameters of 1709 2.0 ~ a value 20.0 scope, see Figure 5. Here a total of 180 bar U/f cable choice. Sets the principle remains a scale from small gradual, to ensure that meet the starting torque can be. If you are between two laws reducing torque and constant torque characteristics between other load, as shown in Figure 7, the parameter should 1.0 F09 ~ 1.9 choice. This group U/f line total. A converter can U/f line set to polyline forms. intermediate voltage them and intermediate frequency parameters set up after the two parameters in U/f to the corresponding point on the line is the turning point of the curve. Limited to length. will not repeat them, applications may refer to the relevant frequency converter specification.
Editorial: Shin Bo Hun