Application of programmable controller (PLC) in automatic parallel diesel generator set
發(fā)布時間：2022-07-02
Programmable controller (PLC for short) is an industrial control device that has developed rapidly and applied widely since the 1960s. It is the first of the three pillars of modern industrial automation. It uses programmable memory to store user instructions. Through digital or analog input / output, it completes certain logic, sequence, timing, counting, operation and some certain functions to control various types of mechanical equipment or production process. Nowadays, PLC absorbs the latest achievements of microelectronics and computer technology, and uses single-chip microcomputer to automate the whole production line and even the whole factory; From flexible manufacturing systems, industrial robots to large-scale distributed control systems, PLC plays an important role.
PLC control of automatic diesel generator set has many advantages. It is mainly controlled by software, which saves the hardware development work, and there are few peripheral circuits, which greatly improves the reliability and anti-interference ability of the system; Because of its simple programmable function, it can change the control requirements of the system without changing the external hardware wiring of the system, so as to greatly improve the "flexibility" of the system; At the same time, because PLC is specially designed for industrial control, multi-level anti-interference and selected component measures are adopted in the process of design and manufacturing, which can work together with strong current equipment in a harsh environment, ensuring the stability and reliability of generator unit operation.
The automatic parallel diesel generator set is based on the automatic diesel generator set and combines PLC with GPC (unit parallel controller), which can realize the automatic startup and parallel operation of multiple units. It has the advantages of reliable operation, high measurement accuracy and convenient operation. It can be widely used in military, civil and other units, as the main power station or standby power station.
1、 Main functions that can be realized
The automatic parallel diesel generator set shall meet the following basic requirements:
1. Auto start
In case of failure (power failure) of normal power supply, the unit can automatically start, speed up and switch on to supply power to emergency loads.
2. Triple start function
The unit has three startup functions. If the first startup is unsuccessful, it will be restarted after delay. If the second startup is unsuccessful, it will be started for the third time after delay, and the delay time can be set. As long as one of the three starts is successful, it will run down according to the preset program; If the startup fails for three consecutive times, it will be regarded as startup failure, and an audible and visual alarm signal will be sent (it can also control the startup of another unit at the same time).
3. Automatic shutdown
When the normal power supply is restored and judged to be normal, control the switch to complete the automatic switching from standby power to normal power, and then control the unit to slow down to idle speed and stop.
4. Automatic protection
During the operation of the unit, if there are faults such as low oil pressure, high water temperature, overspeed, reverse power, abnormal voltage, etc., an audible and visual alarm signal (or emergency shutdown) will be sent to remind the operator to intervene.
5. Automatic paralleling and splitting
When the load reaches the specified value (settable) of single machine power and lasts for the specified time (settable), the standby unit can start automatically and automatically put into parallel operation; When the load is lower than the specified value of single machine power (settable) and continues for the specified time (settable), the standby unit can automatically disconnect and shut down.
6. Automatic frequency modulation and load regulation
7. Automatically maintain the quasi start state
The unit can automatically maintain the quasi start state. At this time, the automatic periodic pre oil supply system of the unit, the automatic heating system of oil and water, and the automatic charging device of the battery are put into operation.
8. It has two operation modes: manual and automatic.
The automatic parallel diesel generator sets controlled by PLC and GPC designed and produced by Yihua power station, such as dpr1000cxz5, dpr500cxz5, CZ150, are widely used in military, petroleum, highway, telecommunications and other departments.
The automatic paralleling function is realized by PLC and GPC, which can complete the manual remote control start, stop, speed increase, speed decrease, closing, opening and automatic paralleling functions of the two units respectively.
In the automatic state, when the mains power is lost, PLC can control two units to start automatically according to the pre selected sequence. After the start is successful, the unit will automatically speed up and automatically switch on to supply power to the load. Each machine can go through three starting cycles. If the three starts are unsuccessful, the corresponding "start failure" signal will be sent. If the main switch fails to close after 10 seconds (settable) after the start is successful and the speed is increased to the rated speed, the corresponding "output failure" alarm signal will be sent and the machine will stop automatically; The other standby machine starts automatically. During the operation of the unit, if the load exceeds 80% of the rated load of a single unit and lasts for 5 seconds, PLC will automatically start the second standby machine, automatically increase the speed, and automatically parallelize the whole step. If the train cannot be paralleled successfully after 2 minutes of paralleling, the signal of failure of paralleling will be sent. After successful paralleling, GPC will automatically adjust frequency and load, so that the difference of active power distribution does not exceed 10%. When the load of parallel operation is less than 20% of the total rated load of the two units and lasts for 10 seconds, PLC and GPC will automatically disconnect and put into parallel units, and automatically stop after idling for 3 minutes. When a diesel engine or generator of a unit fails in parallel operation, its main switch will trip automatically. In case of diesel engine or generator failure during operation, the system will send corresponding audible and visual alarm. Press the "mute" button, and the audible alarm will disappear. After troubleshooting, you must press the "fault reset" button once to restore the system to normal. When the mains power is on, the operating unit will be automatically disconnected and shut down according to the procedure. When the unit idles for 3 minutes, PLC will send a shutdown signal. If the unit fails to stop after 30 seconds, PLC will send an alarm signal of "shutdown failure".
2、 Hardware design
Taking CZ150 shelter power station as an example, the automatic parallel control of diesel generator set is realized by PLC and GPC
1. Composition of control system
The control system consists of three parts: PLC control part; GPC control part, because two units are connected in parallel, there are two sets in total; Two sets of unit monitors. The GPC control part and the unit monitor part adopt ready-made controllers, which will not be introduced in detail here.
The unit monitor can collect and monitor the operating parameters of the unit, send alarm signals for faults such as low oil pressure, high water temperature and overspeed of the diesel engine, and implement shutdown protection.
GPC is the abbreviation of generator paralleling controller, which is designed by Deif company for the realization of unit paralleling function. It has static synchronization, dynamic synchronization, unit fixed load (base load) operation, single machine fixed frequency operation, load distribution, governor relay control output, relay output control main switch opening / closing, adjustable generator load rise / fall vertical line, Standard control functions such as automatic start / stop relay output (high / low load) of standby generator; At the same time, it can realize the reverse power and overcurrent protection in the operation of the unit. The controller is equipped with RS232 display and service interface, which can realize remote monitoring.
According to the functional requirements of CZ150 shelter power station in the previous section, Siemens S7-300 (with input and output modules and equipped with rom-h memory) is selected as the programmable controller. Due to the small capacity of PLC output contact, it can only drive loads below 2A. Large capacity loads must be controlled by solid relays, and important control parts also adopt external interlocking structure.
2. Control system analysis
According to the control requirements and control system diagram, PLC input and output signal distribution
Place the manual / automatic switch of the unit in the automatic position, the input port of PLC 37 receives the automatic operation signal, the PLC program starts to run and scan, and the program status selects the input port (33, 34, 35), which corresponds to different program operation modes respectively: when the main power is lost, unit 1 starts, and unit 2 is the standby; When the main power grid loses power, unit 1 and unit 2 are started at the same time. First, the successful closing and power transmission are started, and the other unit is shut down for standby; When the main power grid loses power, unit 2 starts and unit 1 is standby. In the following, when the main power is lost, unit 1 is started and unit 2 is used as the standby machine for analysis, other similar.
When the main power is lost, the input port of PLC 32 receives the power loss signal, the output port of PLC 2 sends out the start signal of unit 1, the 11K relay coil is powered on, the 11K normally open contact is closed, the input end of monitor 1 is started up, the unit 1 is started, the input port of PLC 2 gets the ignition signal of unit 1, the output port of PLC 6 sends out the high-speed signal of unit 1, the 15K relay coil is powered on, the 15K normally open contact is closed, and the electrical regulator controls the diesel engine to high speed, The input port of PLC 3 receives the high-speed signal of unit 1, gpc1 sends the closing signal, and the main switch 1 closes and sends power.
b. Three starts
If the first start is not successful, the input port of PLC 2 does not receive the ignition signal of unit 1. It is controlled by the timer inside the PLC to start again. Taking 10 seconds as a cycle, the three starts take about 30 seconds, and the alarm is output after 32 seconds. At the same time, the output port of PLC 12 sends the start signal of unit 2, the 21k relay coil is powered on, the 21k normally open contact is closed, the start input end of monitor 2 receives the start signal, and unit 2 is started, The input port of PLC 12 gets the ignition signal of unit 2, the output port of PLC 16 sends the high-speed signal of unit 2, the 25K relay coil is powered on, the 25K normally open contact is closed, the electric regulator controls the diesel engine to high speed, the input port of PLC 13 gets the high-speed signal of unit 2, gpc2 sends the closing signal, and the main switch of unit 2 is closed and powered on.
c. Automatic shutdown
When the main power is powered on, the input port of PLC 32 does not receive the power loss signal, gpc1 sends the opening signal, the diesel engine is opened, the output port of PLC 6 has no signal, the output 15K relay coil loses power, the 15K normally open contact is disconnected, the electrical regulator controls the diesel engine to low speed, the input port of PLC 2 receives the low-speed signal of unit 1, the output port of PLC 3 sends the shutdown signal of unit 1, the 12K relay coil is powered on, the 12K normally open contact is closed, and the 6ka2 relay coil is powered on, 6ka2 normally closed contact is disconnected, 6ka4 relay coil is de energized, 6ka4 normally open contact is disconnected, electric regulator is de energized, and the unit is shut down.
d. Automatic paralleling, frequency modulation and load regulation
During the operation of unit 1, if the load exceeds 80% of the rated load of a single unit and lasts for 5 seconds, gpc2 61 port initiates the standby signal, PLC 16 port receives the standby signal of unit 2, PLC 12 output port sends the start signal of unit 2, 21k relay coil is powered on, 21k normally open contact is closed, the start input end of monitor 2 receives the start signal, unit 2 starts, and PLC 12 input port receives the ignition signal of unit 2, The output port of PLC 16 sends out the high-speed signal of unit 2, the coil of 25K relay is powered on, the 25K normally open contact is closed, the electric regulator controls the diesel engine 2 to high-speed, the input port of PLC 13 gets the high-speed signal of unit 2, the output port of PLC 14 sends out the signal of allowing the parallel operation of unit 2, the coil of 23K relay is powered on, the normally open contact of 23K relay is powered on, and the input port of gpc2 25 gets the signal of allowing the parallel operation through speed regulation The output signal of the voltage regulating port adjusts the unit 2. After gpc2 calculates the synchronization, ports 17 and 18 send synchronous closing signals, and the main switch 2 closes and supplies power in parallel. After the parallel is successful, GPC will automatically adjust frequency and load, so that the difference of active power distribution does not exceed 10%.
When the load of parallel operation is less than 20% of the total rated load of the two units and lasts for 10 seconds, PLC 15 port sends a disconnection signal, 24K relay coil is powered on, 24K normally open contact is closed, gpc2 43 port gets a disconnection signal, gpc2 14 and 15 ports send an opening signal, unit 2 is opened, gpc2 63 port sends a stop standby signal, PLC 17 input port gets a stop standby signal of unit 2, PLC 16 output port has no signal, and the output 25K relay coil loses power, The 25K normally open contact is disconnected, the electric regulator controls the diesel engine to low speed, the input port of PLC 12 receives the low-speed signal of unit 2, the output port of PLC 13 sends the shutdown signal of unit 2, the 22K relay coil is powered on, the 22K normally open contact is closed, the 7ka2 relay coil is powered on, the 7ka2 normally closed contact is disconnected, the 7ka4 relay coil is powered off, the 7ka4 normally open contact is disconnected, the electric regulator is powered off, and the unit 2 is shut down.
e. Automatic fault protection
For fault protection, the unit monitor collects the parameters of the oil engine during the operation of the unit, such as oil pressure, water temperature, speed, etc; GPC monitors the generator voltage, current and other parameters, and finally realizes the automatic protection function of the unit through PLC and monitor. CZ150 shelter power station has the following alarm functions: low oil pressure alarm shutdown, high water temperature alarm shutdown, overspeed alarm shutdown, low battery voltage alarm, GPC fault alarm shutdown, reverse power alarm shutdown, low oil level alarm of oil tank, start failure alarm, voltage fault alarm, shutdown failure alarm, output fault alarm, etc. At the same time, the automatic control panel is equipped with "mute" and "reset" buttons to process the alarm signal. Press the "mute" button, and the alarm sound signal disappears; Press the "reset" button. When the fault is eliminated, the fault memory is eliminated. If the fault is not eliminated, the fault memory is still valid, reminding the user to intervene.
The "emergency stop" button is also set on the automatic control panel. In any case, as long as the "emergency stop" button is pressed, it can automatically stop and handle the fault, so as to effectively protect the unit.
3、 Logic diagram design of control system
PLC adopts a simple language based on standard Boolean expressions (and, or, ont). When the program is not solidified, users can change it according to their own requirements to meet special requirements.
According to the description in the previous section, the program control logic diagram of the automatic parallel diesel generator set is shown in Figure 3. The program design is briefly introduced as follows:
In order to complete automatic control tasks, S7-300 CPU provides two types of basic instructions, and aetp 7-micro/win32, a computer-based programming software, provides different programmer options. These instructions can be used to create unit control programs, and aetp 7-micro/win32 can be used to download the compiled programs to the CPU. S7-300 CPU program is composed of three basic elements, main program, subroutine (optional), and interrupt program (optional), S7-300 continuously executes the user program. The instructions in the main program are executed once in each scan cycle of the CPU in sequence, and different subroutines and interrupt programs can be called.
4、 Conclusion
PLC control of automatic diesel generator set has many advantages. It is mainly controlled by software, which saves the hardware development work, and there are few peripheral circuits, which greatly improves the reliability and anti-interference ability of the system; Because of its simple programmable function, it can change the control requirements of the system without changing the external hardware wiring of the system, so as to greatly improve the "flexibility" of the system; At the same time, because PLC is specially designed for industrial control, multi-level anti-interference and selected component measures are adopted in the process of design and manufacturing, which can work together with strong current equipment in a harsh environment, ensuring the stability and reliability of generator unit operation.
The automatic parallel diesel generator set is based on the automatic diesel generator set and combines PLC with GPC (unit parallel controller), which can realize the automatic startup and parallel operation of multiple units. It has the advantages of reliable operation, high measurement accuracy and convenient operation. It can be widely used in military, civil and other units, as the main power station or standby power station.
1、 Main functions that can be realized
The automatic parallel diesel generator set shall meet the following basic requirements:
1. Auto start
In case of failure (power failure) of normal power supply, the unit can automatically start, speed up and switch on to supply power to emergency loads.
2. Triple start function
The unit has three startup functions. If the first startup is unsuccessful, it will be restarted after delay. If the second startup is unsuccessful, it will be started for the third time after delay, and the delay time can be set. As long as one of the three starts is successful, it will run down according to the preset program; If the startup fails for three consecutive times, it will be regarded as startup failure, and an audible and visual alarm signal will be sent (it can also control the startup of another unit at the same time).
3. Automatic shutdown
When the normal power supply is restored and judged to be normal, control the switch to complete the automatic switching from standby power to normal power, and then control the unit to slow down to idle speed and stop.
4. Automatic protection
During the operation of the unit, if there are faults such as low oil pressure, high water temperature, overspeed, reverse power, abnormal voltage, etc., an audible and visual alarm signal (or emergency shutdown) will be sent to remind the operator to intervene.
5. Automatic paralleling and splitting
When the load reaches the specified value (settable) of single machine power and lasts for the specified time (settable), the standby unit can start automatically and automatically put into parallel operation; When the load is lower than the specified value of single machine power (settable) and continues for the specified time (settable), the standby unit can automatically disconnect and shut down.
6. Automatic frequency modulation and load regulation
7. Automatically maintain the quasi start state
The unit can automatically maintain the quasi start state. At this time, the automatic periodic pre oil supply system of the unit, the automatic heating system of oil and water, and the automatic charging device of the battery are put into operation.
8. It has two operation modes: manual and automatic.
The automatic parallel diesel generator sets controlled by PLC and GPC designed and produced by Yihua power station, such as dpr1000cxz5, dpr500cxz5, CZ150, are widely used in military, petroleum, highway, telecommunications and other departments.
The automatic paralleling function is realized by PLC and GPC, which can complete the manual remote control start, stop, speed increase, speed decrease, closing, opening and automatic paralleling functions of the two units respectively.
In the automatic state, when the mains power is lost, PLC can control two units to start automatically according to the pre selected sequence. After the start is successful, the unit will automatically speed up and automatically switch on to supply power to the load. Each machine can go through three starting cycles. If the three starts are unsuccessful, the corresponding "start failure" signal will be sent. If the main switch fails to close after 10 seconds (settable) after the start is successful and the speed is increased to the rated speed, the corresponding "output failure" alarm signal will be sent and the machine will stop automatically; The other standby machine starts automatically. During the operation of the unit, if the load exceeds 80% of the rated load of a single unit and lasts for 5 seconds, PLC will automatically start the second standby machine, automatically increase the speed, and automatically parallelize the whole step. If the train cannot be paralleled successfully after 2 minutes of paralleling, the signal of failure of paralleling will be sent. After successful paralleling, GPC will automatically adjust frequency and load, so that the difference of active power distribution does not exceed 10%. When the load of parallel operation is less than 20% of the total rated load of the two units and lasts for 10 seconds, PLC and GPC will automatically disconnect and put into parallel units, and automatically stop after idling for 3 minutes. When a diesel engine or generator of a unit fails in parallel operation, its main switch will trip automatically. In case of diesel engine or generator failure during operation, the system will send corresponding audible and visual alarm. Press the "mute" button, and the audible alarm will disappear. After troubleshooting, you must press the "fault reset" button once to restore the system to normal. When the mains power is on, the operating unit will be automatically disconnected and shut down according to the procedure. When the unit idles for 3 minutes, PLC will send a shutdown signal. If the unit fails to stop after 30 seconds, PLC will send an alarm signal of "shutdown failure".
2、 Hardware design
Taking CZ150 shelter power station as an example, the automatic parallel control of diesel generator set is realized by PLC and GPC
1. Composition of control system
The control system consists of three parts: PLC control part; GPC control part, because two units are connected in parallel, there are two sets in total; Two sets of unit monitors. The GPC control part and the unit monitor part adopt ready-made controllers, which will not be introduced in detail here.
The unit monitor can collect and monitor the operating parameters of the unit, send alarm signals for faults such as low oil pressure, high water temperature and overspeed of the diesel engine, and implement shutdown protection.
GPC is the abbreviation of generator paralleling controller, which is designed by Deif company for the realization of unit paralleling function. It has static synchronization, dynamic synchronization, unit fixed load (base load) operation, single machine fixed frequency operation, load distribution, governor relay control output, relay output control main switch opening / closing, adjustable generator load rise / fall vertical line, Standard control functions such as automatic start / stop relay output (high / low load) of standby generator; At the same time, it can realize the reverse power and overcurrent protection in the operation of the unit. The controller is equipped with RS232 display and service interface, which can realize remote monitoring.
According to the functional requirements of CZ150 shelter power station in the previous section, Siemens S7-300 (with input and output modules and equipped with rom-h memory) is selected as the programmable controller. Due to the small capacity of PLC output contact, it can only drive loads below 2A. Large capacity loads must be controlled by solid relays, and important control parts also adopt external interlocking structure.
2. Control system analysis
According to the control requirements and control system diagram, PLC input and output signal distribution
The nit has automatic and manual functions. Manual functions are not introduced here. The automatic control circuit is introduced below.
Place the manual / automatic switch of the unit in the automatic position, the input port of PLC 37 receives the automatic operation signal, the PLC program starts to run and scan, and the program status selects the input port (33, 34, 35), which corresponds to different program operation modes respectively: when the main power is lost, unit 1 starts, and unit 2 is the standby; When the main power grid loses power, unit 1 and unit 2 are started at the same time. First, the successful closing and power transmission are started, and the other unit is shut down for standby; When the main power grid loses power, unit 2 starts and unit 1 is standby. In the following, when the main power is lost, unit 1 is started and unit 2 is used as the standby machine for analysis, other similar.
When the main power is lost, the input port of PLC 32 receives the power loss signal, the output port of PLC 2 sends out the start signal of unit 1, the 11K relay coil is powered on, the 11K normally open contact is closed, the input end of monitor 1 is started up, the unit 1 is started, the input port of PLC 2 gets the ignition signal of unit 1, the output port of PLC 6 sends out the high-speed signal of unit 1, the 15K relay coil is powered on, the 15K normally open contact is closed, and the electrical regulator controls the diesel engine to high speed, The input port of PLC 3 receives the high-speed signal of unit 1, gpc1 sends the closing signal, and the main switch 1 closes and sends power.
b. Three starts
If the first start is not successful, the input port of PLC 2 does not receive the ignition signal of unit 1. It is controlled by the timer inside the PLC to start again. Taking 10 seconds as a cycle, the three starts take about 30 seconds, and the alarm is output after 32 seconds. At the same time, the output port of PLC 12 sends the start signal of unit 2, the 21k relay coil is powered on, the 21k normally open contact is closed, the start input end of monitor 2 receives the start signal, and unit 2 is started, The input port of PLC 12 gets the ignition signal of unit 2, the output port of PLC 16 sends the high-speed signal of unit 2, the 25K relay coil is powered on, the 25K normally open contact is closed, the electric regulator controls the diesel engine to high speed, the input port of PLC 13 gets the high-speed signal of unit 2, gpc2 sends the closing signal, and the main switch of unit 2 is closed and powered on.
c. Automatic shutdown
When the main power is powered on, the input port of PLC 32 does not receive the power loss signal, gpc1 sends the opening signal, the diesel engine is opened, the output port of PLC 6 has no signal, the output 15K relay coil loses power, the 15K normally open contact is disconnected, the electrical regulator controls the diesel engine to low speed, the input port of PLC 2 receives the low-speed signal of unit 1, the output port of PLC 3 sends the shutdown signal of unit 1, the 12K relay coil is powered on, the 12K normally open contact is closed, and the 6ka2 relay coil is powered on, 6ka2 normally closed contact is disconnected, 6ka4 relay coil is de energized, 6ka4 normally open contact is disconnected, electric regulator is de energized, and the unit is shut down.
d. Automatic paralleling, frequency modulation and load regulation
During the operation of unit 1, if the load exceeds 80% of the rated load of a single unit and lasts for 5 seconds, gpc2 61 port initiates the standby signal, PLC 16 port receives the standby signal of unit 2, PLC 12 output port sends the start signal of unit 2, 21k relay coil is powered on, 21k normally open contact is closed, the start input end of monitor 2 receives the start signal, unit 2 starts, and PLC 12 input port receives the ignition signal of unit 2, The output port of PLC 16 sends out the high-speed signal of unit 2, the coil of 25K relay is powered on, the 25K normally open contact is closed, the electric regulator controls the diesel engine 2 to high-speed, the input port of PLC 13 gets the high-speed signal of unit 2, the output port of PLC 14 sends out the signal of allowing the parallel operation of unit 2, the coil of 23K relay is powered on, the normally open contact of 23K relay is powered on, and the input port of gpc2 25 gets the signal of allowing the parallel operation through speed regulation The output signal of the voltage regulating port adjusts the unit 2. After gpc2 calculates the synchronization, ports 17 and 18 send synchronous closing signals, and the main switch 2 closes and supplies power in parallel. After the parallel is successful, GPC will automatically adjust frequency and load, so that the difference of active power distribution does not exceed 10%.
When the load of parallel operation is less than 20% of the total rated load of the two units and lasts for 10 seconds, PLC 15 port sends a disconnection signal, 24K relay coil is powered on, 24K normally open contact is closed, gpc2 43 port gets a disconnection signal, gpc2 14 and 15 ports send an opening signal, unit 2 is opened, gpc2 63 port sends a stop standby signal, PLC 17 input port gets a stop standby signal of unit 2, PLC 16 output port has no signal, and the output 25K relay coil loses power, The 25K normally open contact is disconnected, the electric regulator controls the diesel engine to low speed, the input port of PLC 12 receives the low-speed signal of unit 2, the output port of PLC 13 sends the shutdown signal of unit 2, the 22K relay coil is powered on, the 22K normally open contact is closed, the 7ka2 relay coil is powered on, the 7ka2 normally closed contact is disconnected, the 7ka4 relay coil is powered off, the 7ka4 normally open contact is disconnected, the electric regulator is powered off, and the unit 2 is shut down.
e. Automatic fault protection
For fault protection, the unit monitor collects the parameters of the oil engine during the operation of the unit, such as oil pressure, water temperature, speed, etc; GPC monitors the generator voltage, current and other parameters, and finally realizes the automatic protection function of the unit through PLC and monitor. CZ150 shelter power station has the following alarm functions: low oil pressure alarm shutdown, high water temperature alarm shutdown, overspeed alarm shutdown, low battery voltage alarm, GPC fault alarm shutdown, reverse power alarm shutdown, low oil level alarm of oil tank, start failure alarm, voltage fault alarm, shutdown failure alarm, output fault alarm, etc. At the same time, the automatic control panel is equipped with "mute" and "reset" buttons to process the alarm signal. Press the "mute" button, and the alarm sound signal disappears; Press the "reset" button. When the fault is eliminated, the fault memory is eliminated. If the fault is not eliminated, the fault memory is still valid, reminding the user to intervene.
The "emergency stop" button is also set on the automatic control panel. In any case, as long as the "emergency stop" button is pressed, it can automatically stop and handle the fault, so as to effectively protect the unit.
3、 Logic diagram design of control system
PLC adopts a simple language based on standard Boolean expressions (and, or, ont). When the program is not solidified, users can change it according to their own requirements to meet special requirements.
According to the description in the previous section, the program control logic diagram of the automatic parallel diesel generator set is shown in Figure 3. The program design is briefly introduced as follows:
In order to complete automatic control tasks, S7-300 CPU provides two types of basic instructions, and aetp 7-micro/win32, a computer-based programming software, provides different programmer options. These instructions can be used to create unit control programs, and aetp 7-micro/win32 can be used to download the compiled programs to the CPU. S7-300 CPU program is composed of three basic elements, main program, subroutine (optional), and interrupt program (optional), S7-300 continuously executes the user program. The instructions in the main program are executed once in each scan cycle of the CPU in sequence, and different subroutines and interrupt programs can be called.
4、 Conclusion
The automatic parallel diesel generator set controlled by PLC has simple hardware, good technical and economic indicators and high reliability. With a little modification of the program, it can meet the different control requirements of users.
