I. Parameter setting table for constant-pressure water supply tests
Function code | Name | Set value | Function code | Name | Set value |
b2.01 | Numerically set frequency | 5 (PID) | E5.05 | Engineering unit | 1 (pressure) |
C0.01 | Function of Terminal X1 | 48 (1# interlock input) | E5.06 | Min. setting of engineering unit | 0 MPa |
C0.02 | Function of Terminal X2 | 49 (2# interlock input) | E5.07 | Max. setting of engineering unit | 0.60 MPa (set according to the measurement range of the actual pressure ) |
C0.03 | Function of Terminal X3 | 50 (3# interlock input) | E5.08 | Decimals digits for engineering unit | 2 (2-digit decimal) |
C0.04 | Function of Terminal X4 | 51 (4# interlock input) | E5.26 | PID deviation limit | 0.01% |
C1.04 | Function of Terminal T1 | 41 (1# control) | E5.29 | PID shutdown computation | 1 (shutdown computation) |
C1.05 | Function of Terminal T2 | 42 (2# control) | E6.00 | Multi-pump control modes | 4 (variable-frequency pump circulating; automatic switching available) |
C1.06 | Function of Terminal T3 | 43 (3# control) | E6.01 | Amount of motors for multi-pump control | 4 pcs |
C1.07 | Function of Terminal T4 | 44 (4# control) | E6.05 | Motor interlocking enabling | 11 (interlocking enabling, determined by E6.06) |
C2.08 | Min. input of AI2 | 2V | E6.06 | Numerical setting of motor interlocking | 1111 (four pumps connected with the system) |
C2.09 | Settings corresponding to the min. input of AI2 | 0% | E6.07 | Time of automatic switching | 24 h (adjustable as required) |
C2.10 | Max. input of AI2 | 10V | E6.08 | Frequency limit of automatic switching | 40 Hz (adjustable as required) |
C2.11 | Settings corresponding to the max. input of AI2 | 100% | E6.10 | Starting frequency 1 | 48 Hz (adjustable as required) |
E5.01 | Numerical given by PID | 0.23 (adjusted as required by the water pressure) | E6.12 | Starting frequency 2 | 48 Hz (adjustable as required) |
E5.03 | PID feedback source | 1 (AI2) | E6.14 | Starting frequency 3 | 48 Hz (adjustable as required) |
II. Logic of adding and reducing pumps
1) Set E5.01 (PID giving) = 0.30 (greater than the sum of running pressure of four pumps) and E6.01 (quantity of motors) = 4, then run the VFD and observe the pump adding conditions of the system as follows:
![Parameter settings for CDE500&CDE350 one-driving-four constant-pressure water supply]( "Parameter settings for CDE500&CDE350 one-driving-four constant-pressure water supply")
2) Set PID giving > PID feedback. When all water pumps are connected into the system, reset the parameters so that PID giving < PID feedback. Observe the pump reduction conditions of the system as follows:
![Parameter settings for CDE500&CDE350 one-driving-four constant-pressure water supply]( "Parameter settings for CDE500&CDE350 one-driving-four constant-pressure water supply")
III. Automatic switching
In case that E6.00 (multi-pump control mode) = 4 (variable-frequency pump circulating; automatic switching available), set E6.07 (interval of automatic switching) = 0.3 (18 s) and E6.08 (frequency limit of automatic switching) = 40 Hz. Through regulation, make sure that only the variable-frequency pump 1 and power-frequency pump 2 are connected into the system and the output frequency of the VFD is lower than E6.08. The conditions are observed as follows:
Switching sequence and conditions | Running status of pumps after automatic switching |
Switching sequence | Running status of pumps | 1# | 2# | 3# | 4# |
Before switching | Running at lower than 40 Hz. | Running at power frequency. | Running at variable frequency. | Shutdown | Shutdown |
First switching | Running at lower than 40 Hz for over 18 s, hence the logic is triggered to start the automatic switching. | Shutdown | Pump 2# is switched from variable-frequency running to power-frequency running. | Pump 3# is started in variable-frequency soft start mode. | Shutdown |
Second switching | Running at lower than 40 Hz for over 18 s, hence the logic is triggered to start the automatic switching. | Shutdown | Shutdown | Pump 3# is switched from variable-frequency running to power-frequency running. | Pump 4# is started in variable-frequency soft start mode. |
Third switching | Running at lower than 40 Hz for over 18 s, hence the logic is triggered to start the automatic switching. | Pump 1# is started in variable-frequency soft start mode. | Shutdown | Shutdown | Pump 4# is switched from variable-frequency running to power-frequency running. |
IV. Cautions during operation of constant-pressure water supply
S/N | Problem description | Analysis | Solutions |
1 | During the test of control mode 4, the variable-frequency pump 2 and power-frequency pump 1 are made the only pumps connected with the system through PID regulation, which fulfills the conditions of automatic switching. However, after the automatic switching, it is found that the running frequency of the variable-frequency pump 3, which is newly connected into the system, is 0 Hz. | After the variable-frequency pump 2 shuts down naturally, the PID stops running as well. When the variable-frequency pump 3 is connected, PID will re-perform computation. In this case, the given is equal to the feedback, which gives rise to running frequency of 0 Hz of the VFD. | Set E5.29 (PID shutdown computation) = 1 and the problem is solved. |
2 | During the test of control mode 3, the given pressure is set to 0.22 MPa, and the system will input a variable-frequency pump and a power-frequency pump. However, the latter will be trapped in the endless loop of pump adding and reducing. | After the variable-frequency pump reaches 50 Hz, the feedback pressure of the system will become 0.18 MPa (i.e. the upper limit of pressure that can be provided by a single variable-frequency pump). In this case, a pump adding act will be performed, after which the system pressure turns to 0.25 MPa (i.e. the upper limit of pressure that can be provided by a single power-frequency pump). And then, when the VFD frequency is reduced by 0 Hz, the feedback pressure still remains at 0.25 MPa, where the act of reducing pumps is performed once more, leading to the endless loop. | To complement the pressure difference of water supply by the pumps due to the deviation between the grid voltage and the VFD output voltage, adjust the maximum frequency and the upper limit of frequency of the VFD to 60 Hz so that the water supply pressure of the variable-frequency pump is the same as the power-frequency pump, and the problem is solved. |
3 | During the test of control mode 3, the given pressure is set to 0.25 MPa. When the feedback pressure is 0.25 MPa as well, the frequency will keep increasing. Only after setting the E5.26 (PID deviation limit) = 0.01 will the VFD stay at fixed frequency. | In case that no deviation limit is set, the given value for PID computation is not equal to the feedback value. | Set E5.26 (PID deviation limit) and the problem is solved. |