PLC control in automatic diesel generating set analysis - the function characteristics and application of design

automatic diesel generating sets with PLC control has many advantages, it is mainly through software control, thus eliminating the hardware development work, few peripheral circuit, greatly improving the system reliability and anti-interference ability; Because of its simple programmable function, do not need to change the external hardware wiring system, can change the system control requirements, the system of 'soft' is greatly increased.

1 main function

automatic diesel generating set as a standby power, should have the following basic functions:

( 1) Automatically start

when the mains failure ( Power cuts, under voltage, over voltage, lack of phase) , the unit can automatically start, automatic speed, automatic switching, supply power to the load.

( 2) Automatic stop

when mains recovery, after judge normal control switch, complete the automatic switching power to the grid, and then control unit speed down, automatic stop idle run 3 minutes.

( 3) Automatic protection

unit in the process of running, if there is a low oil pressure, speed, voltage abnormal failure, emergency stop, send out sound and light alarm signal at the same time, if there is a high temperature, high oil temperature of failure. Send out sound and light alarm signal, after a time delay, the normal downtime.

( 4) Three times start function

unit three times start function, if the first time you start is not successful, after 10 seconds delay time to start again, if the second start-up is not successful, the time delay for the third time after launch. Three times as long as there is a successful start, according to a preset program run down; If three consecutive start is not successful, then as a boot failure, send out sound and light alarm signal, also can control the other units starting at the same time.

( 5) Automatically maintain must start status

unit can automatically maintain must start state. At this point, the unit automatically periodic automatically in the process of the oil supply system, oil and water heating system and battery charging devices to work automatically.

( 6) Function of maintainability boot

when the unit for a long time did not start, maintainability can be switched on, to check the unit performance and status. Boot does not affect the normal power supply mains, maintainability in maintainability boot if mains failure, the system will automatically to normal on and the power supply unit.

( 7) Have two kinds of manual and automatic operation mode. According to the number of input/output points choose PLC models

according to the requirements of the unit automation control, the PLC controller input points to 11, output points to 12. System control quantity is basically a switch quantity, only is analog voltage and rotational speed, and in order to reduce costs, you can through the detection circuit to convert the analog switch quantity, in this way, you can choose not to bring a analog input of the PLC. This system chooses C28P - CDR— D small programmable controller, high reliability, small volume, input points for 16 output points to 12. Power supply, input and output voltage is 24 VDC. 2 input/output

according to the requirements of the automation unit control and electrical schematic diagram, input and output signal distribution list are shown in table 1.

table 1 input/output distribution list

the program design of the control system of 3

when the automatic switch to automatic position of the unit, the unit is in a state must start. PLC to continuous cycle detection of mains, forecast for oil pump periodically to the diesel engine lubricating oil, diesel engine cooling water and the oil temperature can ensure its emergency start at any time. In launching state, once the mains appear lost electricity, undervoltage, overvoltage, and lack of equal fault, and confirmed by the 5 seconds, control unit automatic start, automatic acc to the rated speed, automatic protection. When the unit works normally, the control switch to switch to the state power, close to the load power supply unit. When the mains returned to normal, delay for 5 seconds after confirmation, disconnect the unit output switch, switch control switch to state grid, the unit automatically slow down to the idle state, normal automatically stop after running 3 minutes, the unit is in a state must start.

according to the automation control process of generating unit and the input, output, distribution table, can develop the ladder diagram. Conclusion

4

the FLc control automatic diesel generating sets, simple hardware, good technical and economic indexes, after used on different unit, high reliability, program to modify, can satisfy the requirement of the users of different control.