DCS or PLC logic control method for anti-swing power of 380V auxiliary machine of thermal power unit

Abstract

The present application relates to the technical field of thermal power machine control, and particularly relates to a DCS or PLC logic control method for anti-swing power self-starting of 380V auxiliary machines of thermal power units. The method comprises the following steps: S1, collecting in real time a start state signal, a shutdown state signal and an interlocking switching signal of the auxiliary machine; S2, after detecting that the start state signal of the auxiliary machine changes from start to loss, continuously sending a signal for 1 second to generate a start state loss signal; S3, performing AND logic operation on the start state loss signal, the shutdown state signal and the interlocking switching signal; S4, when the state loss signal is valid, the shutdown state signal and the interlocking switching signal are in the input state and are satisfied at the same time, generating a pulse start instruction with a duration of 1 second; and S5, performing OR logic operation on the pulse start instruction and the original DCS / PLC start instruction to combine and jointly access the start control loop of the auxiliary machine.

Description

Technical Field

[0001] This invention relates to the field of thermal power control technology, specifically to a DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations. Background Technology

[0002] In the operation of thermal power plants, critical auxiliary equipment with a voltage level of 380 volts, such as coal feeders, generally adopts a power supply control method using air switches and AC contactors. The AC contactor control power for these auxiliary machines is directly drawn from the bus voltage of the section where the contactor is located, while the start / stop control and interlocking logic of the contactor are implemented by a distributed control system (DCS) or a programmable logic controller (PLC). Operators issue start / stop commands through the DCS / PLC, which drive the contactor coil to be energized or de-energized via intermediate relays, thereby controlling the start and stop of the auxiliary machine motor. When the contactor coil is energized, its auxiliary contacts feed back the equipment operating status to the DCS / PLC, forming a closed-loop control system.

[0003] In actual operation, this control method has a common but significant drawback. When thunderstorms cause grid voltage fluctuations, the plant's auxiliary power system undergoes switching operations, or operators accidentally open a drawer switch within a short period, the 380V busbar experiences a momentary loss of voltage or a short-term voltage drop. Since the contactor's control power is directly drawn from this section of the busbar, once the busbar voltage disappears or drops below the contactor's holding voltage, the contactor coil immediately loses power, the contactor's main contacts open, and the operating auxiliary equipment stops immediately. This type of auxiliary equipment tripping due to a voltage dip is commonly referred to as a voltage drop trip. The busbar voltage usually returns to normal within a very short time, such as a fraction of a second to one or two seconds, or the accidentally opened switch is immediately closed, restoring the voltage supply.

[0004] However, after the voltage is restored, the tripped auxiliary equipment will not restart automatically. This is because the contactor self-holding circuit has been disconnected. Although the DCS / PLC detects the loss of the equipment's operating status signal, the original control logic will not automatically issue a restart command. The equipment will remain in a stopped state until the operator discovers the anomaly through the monitoring screen and manually issues a restart command. During this window of manual intervention, chain reactions such as boiler coal feed interruption, insufficient air volume, and condensate interruption may have already occurred. In severe cases, this can lead to boiler flameout, rapid load reduction of the unit, or even unplanned shutdown, causing significant power generation losses and safety hazards.

[0005] To address this issue, some power plants have attempted hardware upgrades such as installing voltage dip protectors or undervoltage restart devices. These solutions require adding dedicated electronic modules or relays to the electrical control circuits of each auxiliary unit and modifying some wiring to enable automatic output of a start signal after the bus voltage recovers. While these hardware solutions can solve some problems, they also have significant drawbacks. First, adding voltage dip protectors means additional equipment procurement costs and installation work. Second, inserting new electronic components or relay contacts into the existing control circuit adds dozens of wiring points and intermediate links, and each additional contact creates a potential point of failure. When the internal circuitry of the voltage dip protector ages, capacitors fail, or relay contacts stick together, the auxiliary unit may fail to start under normal voltage or fail to start automatically after voltage recovery, reducing the reliability of the entire system. Furthermore, the parameter settings of voltage dip protectors from different manufacturers vary, making debugging and maintenance cumbersome and hindering large-scale deployment across multiple auxiliary units in a power plant. Therefore, it is necessary to find a solution that can achieve automatic restart of auxiliary equipment after power failure without adding hardware or modifying electrical circuits, but only by optimizing control logic. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a DCS or PLC logic control method for the self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations. This method can achieve automatic restart of the auxiliary equipment after the busbar loses power and is restored without adding hardware equipment or modifying the electrical control circuit.

[0007] The basic solution provided by this invention is a DCS or PLC logic control method for self-starting of 380V auxiliary equipment in thermal power units to prevent power fluctuations, comprising the following steps: S1. Real-time acquisition of auxiliary machine start status signals, stop status signals, and interlocking switching signals; S2. When the start status signal of the auxiliary machine is detected to change from started to lost, the signal is continuously sent for 1 second to generate a start status loss signal. S3. Perform AND logic operation on the start-up status loss signal, the shutdown status signal, and the interlocking switching signal; S4. When the status loss signal is valid, and the shutdown status signal and the interlocking switching switch signal are both in the engaged state, a pulse start command with a duration of 1 second is generated. S5. Combine the pulse start command with the original DCS / PLC start command through OR logic operation and connect them together into the start control loop of the auxiliary machine.

[0008] Furthermore, the start status signal, stop status signal, and interlock switching signal of the auxiliary machine are all existing feedback signals and logic switching signals in the DCS / PLC control system.

[0009] Furthermore, the interlocking switch is a software logic switch inside the DCS / PLC control system, used to control whether the automatic restart function of the auxiliary machine is activated in case of undervoltage. When the interlocking switch is in the activated state, S3 and S4 are executed; when the interlocking switch is in the deactivated state, S3 and S4 are not executed.

[0010] Furthermore, the 1-second pulse start command generated in S4 is a single pulse, the width of which is precisely set by the timer module inside the DCS / PLC control system; after the pulse is issued, if the start status signal of the auxiliary machine is detected to have returned to the started state, the trigger condition of this self-start logic is automatically cleared.

[0011] Furthermore, the startup status loss judgment logic used in the startup status loss signal generated in S2 is as follows: when the DCS / PLC control system continuously detects that the startup status feedback signal of the auxiliary machine changes from 1 to 0 and the 0 state is maintained for 1 second, it is determined that the startup status is lost; if the maintenance time is less than 1 second, it is regarded as signal jitter and the startup status loss signal is not generated.

[0012] Furthermore, the start-up status loss signal generated in S2 is implemented through a timer function block in the DCS / PLC control system. This timer function block is configured to a falling edge trigger mode, that is, when the start-up status feedback signal of the auxiliary machine is detected to change from 1 to 0, the timing is triggered, and a valid signal is output after the timing reaches the set 1 second. If the start-up status feedback signal recovers to 1 during the timing period, the timing is reset and no valid signal is output.

[0013] Furthermore, the 380V key auxiliary equipment applied to thermal power units includes a coal feeder.

[0014] The principles and advantages of this invention are as follows: During the operation of thermal power plants, critical 380V auxiliary equipment such as coal feeders uses a circuit breaker and contactor power supply for its electrical circuits, with the contactor's control power drawn from the bus voltage. In the event of lightning strikes, plant power switching, or a brief accidental tripping, the bus voltage will momentarily drop, causing the contactor to trip and the auxiliary equipment to stop operating. Even if the bus voltage recovers quickly or the accidental tripping switch closes immediately, the auxiliary equipment under traditional control methods cannot start automatically and requires manual restart by operators. This process may result in boiler flameout, unit load reduction, or even unplanned shutdown. This solution does not require adding any voltage flicker protectors or other hardware to the auxiliary equipment control circuit, nor does it require any changes to the on-site electrical wiring. It only optimizes the logic configuration of the distributed control system or programmable logic controller. The specific implementation process involves real-time acquisition of the auxiliary equipment's start-up status signal, shutdown status signal, and interlocking switching signal. When the system detects that the auxiliary equipment's start-up status signal has changed from "started" to "lost," it will continuously send a signal for one second, generating a start-up status loss signal. The system then performs a bitwise AND operation on the start-up status loss signal, the shutdown status signal, and the interlocking switch signal. Only when all three conditions are met simultaneously—the start-up status loss signal is valid, the shutdown status signal indicates the auxiliary machine is indeed in a shutdown state, and the interlocking switch is engaged—will the system generate a 1-second pulse start command. Finally, this 1-second pulse start command is combined with the existing distributed control system or programmable logic controller start command via an OR operation, and both are integrated into the auxiliary machine's start control loop. In this way, the auxiliary machine can automatically restart after the bus voltage is restored, without manual intervention.

[0015] This solution has the following advantages compared to existing technologies: 1. Zero hardware investment. Common solutions in existing technologies involve adding power flicker protectors or undervoltage restart devices. These hardware components require purchase costs, with each auxiliary unit costing thousands to tens of thousands of yuan. In contrast, this solution only requires modifying a few lines of logic code in the existing distributed control system or programmable logic controller, without incurring any additional purchase costs.

[0016] 2. No alteration to the main and secondary electrical circuits. Existing hardware modification solutions require power outages, wire disconnection, installation of relays or contactors, and re-crimping of terminals. This not only involves a large amount of construction work but also adds dozens of wiring points and components, with each additional wiring point representing a potential point of failure. This solution completely avoids touching the on-site electrical equipment, preventing potential problems such as wiring errors, loose screws, and stuck relays during construction.

[0017] 3. There is no risk of new hardware failure. Power outage protectors themselves have a probability of failure, such as aging internal capacitors, stuck or burned relay contacts. If the protector fails, auxiliary equipment may fail to start under normal voltage or fail to start automatically after a voltage drop. This solution runs the self-starting logic within the power plant's existing distributed control system or programmable logic controller. These control systems are redundantly configured and have undergone long-term reliability verification; their logic operation failure rate is far lower than that of newly added hardware.

[0018] 4. Debugging and maintenance are extremely simple. Hardware modification solutions require powering off each device, wiring, and testing delay parameters. If the time settings are unreasonable, repeated disassembly and reassembly are necessary. This solution completes the logic configuration in one go on the engineering station and can be verified through simulation testing. All parameters, such as the 1-second delay, can be adjusted at any time in the software without touching any live equipment. Maintenance personnel can check the logic operation status through the operator station.

[0019] 5. This solution addresses the safety hazard of operators not being able to promptly detect tripped equipment. In traditional methods, a momentary loss of bus voltage may only last a fraction of a second, making it difficult for operators to notice auxiliary equipment tripping on the large screen. Often, the tripping is only discovered when abnormal parameters trigger an alarm, by which time the accident has already escalated. This solution enables the auxiliary equipment to automatically restart immediately after voltage restoration, with the entire process taking no more than two or three seconds. Operators may not even be aware that a voltage loss has occurred.

[0020] 6. Extremely low cost of promotion and replication. For the same type of thermal power unit, only the logic configuration file needs to be copied; there is no need to purchase different models of hardware, and it is not limited by supply cycle or inventory. In contrast, hardware solutions require re-purchasing, installing, and commissioning each unit, which is time-consuming and has low standardization. This solution is particularly suitable for the numerous 380V critical auxiliary machines in power plants, such as coal feeders. A single unit may have dozens or even hundreds of such auxiliary machines. This solution can solve the problem of automatic restart of all auxiliary machines under voltage fluctuations at once without adding any hardware costs, while hardware solutions require adding equipment to each machine individually, and the total cost increases linearly with the number of auxiliary machines. In summary, this solution achieves the most reliable anti-voltage fluctuation automatic restart function with the lowest cost and lowest risk. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an embodiment of the DCS or PLC logic control method for the self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations according to the present invention. Detailed Implementation

[0022] The following detailed description illustrates the specific implementation method: The basic implementation examples are as follows: Figure 1 As shown: The DCS or PLC logic control method for self-starting of 380V auxiliary equipment in thermal power units to prevent power fluctuations includes the following steps: S1. Real-time acquisition of auxiliary machine start status signals, stop status signals, and interlocking switching signals; S2. When the start status signal of the auxiliary machine is detected to change from started to lost, the signal is continuously sent for 1 second to generate a start status loss signal. S3. Perform AND logic operation on the start-up status loss signal, the shutdown status signal, and the interlocking switching signal; S4. When the status loss signal is valid, and the shutdown status signal and the interlocking switching switch signal are both in the engaged state, a pulse start command with a duration of 1 second is generated. S5. Combine the pulse start command with the original DCS / PLC start command through OR logic operation and connect them together into the start control loop of the auxiliary machine.

[0023] The start status signal, stop status signal, and interlock switching signal of the auxiliary machine are all existing feedback signals and logic switching signals in the DCS / PLC control system.

[0024] The interlocking switch is a software logic switch inside the DCS / PLC control system, used to control whether the automatic restart function of the auxiliary machine is activated in case of undervoltage. When the interlocking switch is in the activated state, S3 and S4 are executed; when the interlocking switch is in the deactivated state, S3 and S4 are not executed.

[0025] The 1-second pulse start command generated in S4 is a single pulse, and the width of the pulse is precisely set by the timer module inside the DCS / PLC control system. After the pulse is issued, if the start status signal of the auxiliary machine is detected to have returned to the started state, the trigger condition of this self-start logic is automatically cleared.

[0026] The startup status loss judgment logic used in S2 to generate the startup status loss signal is as follows: when the DCS / PLC control system continuously detects that the startup status feedback signal of the auxiliary machine changes from 1 to 0 and the 0 state is maintained for 1 second, it is determined that the startup status is lost; if the maintenance time is less than 1 second, it is regarded as signal jitter and the startup status loss signal is not generated.

[0027] The generation of the start-up status loss signal in S2 is achieved through the timer function block in the DCS / PLC control system. The timer function block is configured to be triggered by a falling edge, that is, when the start-up status feedback signal of the auxiliary machine is detected to change from 1 to 0, the timing is triggered. After the timing reaches the set 1 second, a valid signal is output. If the start-up status feedback signal recovers to 1 during the timing period, the timing is reset and no valid signal is output.

[0028] A key 380V auxiliary machine used in thermal power units, including a coal feeder.

[0029] This embodiment uses a coal feeder as an example for illustration. The electrical circuit of the coal feeder adopts a power supply method of air switch and AC contactor. The control power of the contactor is taken from the bus voltage of the section where the coal feeder is located. The start-stop control and interlocking logic of the contactor are implemented by the DCS system. The DCS system adopts the Emerson Ovation system, but this invention is also applicable to DCS / PLC systems of other brands such as Siemens, Honeywell, ABB, etc.

[0030] In this embodiment, a new function module for anti-power-slip self-starting is first added to the DCS control logic configuration software. This module has three input signals: a start-up status feedback signal for the coal feeder, a stop-operation status feedback signal for the coal feeder, and an interlocking switching signal set by the operator. All three signals originate from existing signal channels in the DCS system, requiring no additional sensors or hardwiring. The start-up status feedback signal comes from the auxiliary contact of the contactor. When the main contacts of the contactor are closed and the motor is running, this auxiliary contact is closed, and the corresponding channel in the DCS displays 1; when the contactor trips and the motor stops, this auxiliary contact is open, and the DCS displays 0. The stop-operation status feedback signal is taken from the logic NOT of the same auxiliary contact, or separately from the normally closed auxiliary contact of the contactor. The interlocking switching soft switch is a software button on the DCS operator station screen, which the operator can click to enable or disable at any time. When the soft switch is enabled, the anti-power-slip self-starting function is activated; when disabled, this function is disabled, and the auxiliary machine operates according to its original logic.

[0031] In actual operation, after the coal feeder starts normally, the DCS detects a start-up status feedback signal of 1, and the coal feeder continuously feeds coal to the boiler. At this time, assume a switching operation in the plant power system causes a momentary loss of voltage on this section of the 380V busbar, lasting approximately 0.8 seconds. Since the contactor control power is drawn from this section of the busbar, after the busbar voltage disappears, the contactor coil is de-energized, the contactor main contacts open, and the coal feeder stops operating. The DCS system detects the start-up status feedback signal change from 1 to 0. At this time, the timer function block inside the DCS is triggered. This timer is configured in falling-edge triggered mode, meaning it starts counting when the signal changes from 1 to 0. The timer's set delay time is 1 second. After 0.8 seconds, the busbar voltage recovers, and the coal feeder contactor coil is re-energized. However, because the contactor's self-holding circuit has been disconnected, the contactor will not automatically engage. At this point, the start signal at its source disappears, but because the delay pulse is 1 second long, the start signal in this path has not actually disappeared.

[0032] Subsequently, the DCS performs a logical AND operation on this lost start status signal, the feeder's shutdown status signal, and the status of the interlocking soft switch. At this point, the lost start status signal is valid, the shutdown status signal is 1 indicating the feeder is in a shutdown state, and the interlocking soft switch is also in the engaged state (1), satisfying all three conditions simultaneously. The AND logic gate outputs a valid signal, which triggers another timer to generate a 1-second pulse start command. This 1-second pulse start command is combined with the start command issued by the operator manually clicking the start button or by sequential control logic in the original DCS system through an OR logic gate. Therefore, when this 1-second pulse command is issued, it is equivalent to simulating an operator's start operation. This pulse signal drives the DCS output relay, which in turn energizes the feeder contactor coil, closes the contactor's main contacts, and restarts the feeder. After the DCS detects that the start status feedback signal has returned to 1, it automatically clears the previous self-starting logic trigger condition to avoid issuing the start command repeatedly. The entire process, from the restoration of the bus voltage to the restart of the coal feeder, took about 1 second, and the operators could hardly detect that the coal feeder had tripped.

[0033] When the power outage lasts longer than 1 second, for example, 1.5 seconds, the DCS will also detect the disappearance of the "started" status, and the start status feedback signal will be 0. The "stopped" status signal will be sent, the shutdown status feedback signal will be 1, and the interlocking switching signal will still be 1. At this time, only two of the three conditions are met, the AND logic output will be 0, the self-starting pulse will not be issued, the auxiliary machine will remain in a shutdown state, and the operator needs to check and confirm before manually starting it.

[0034] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations, characterized in that: Includes the following steps: S1. Real-time acquisition of auxiliary machine start status signals, stop status signals, and interlocking switching signals; S2. When the start status signal of the auxiliary machine is detected to change from started to lost, the signal is continuously sent for 1 second to generate a start status loss signal. S3. Perform AND logic operation on the start-up status loss signal, the shutdown status signal, and the interlocking switching signal; S4. When the status loss signal is valid, and the shutdown status signal and the interlocking switching switch signal are both in the engaged state, a pulse start command with a duration of 1 second is generated. S5. Combine the pulse start command with the original DCS / PLC start command through OR logic operation and connect them together into the start control loop of the auxiliary machine.

2. The DCS or PLC logic control method for anti-power-slip self-starting of 380V auxiliary equipment in thermal power units according to claim 1, characterized in that: The start status signal, stop status signal, and interlock switching signal of the auxiliary machine are all existing feedback signals and logic switching signals in the DCS / PLC control system.

3. The DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations as described in claim 1, characterized in that: The interlocking switch is a software logic switch inside the DCS / PLC control system, used to control whether the automatic restart function of the auxiliary machine is activated in case of undervoltage. When the interlocking switch is in the activated state, S3 and S4 are executed; when the interlocking switch is in the deactivated state, S3 and S4 are not executed.

4. The DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations as described in claim 3, characterized in that: The 1-second pulse start command generated in S4 is a single pulse, and the width of the pulse is precisely set by the timer module inside the DCS / PLC control system. After the pulse is issued, if the start status signal of the auxiliary machine is detected to have returned to the started state, the trigger condition of this self-start logic is automatically cleared.

5. The DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations as described in claim 1, characterized in that: The startup status loss judgment logic used in S2 to generate the startup status loss signal is as follows: when the DCS / PLC control system continuously detects that the startup status feedback signal of the auxiliary machine changes from 1 to 0 and the 0 state is maintained for 1 second, it is determined that the startup status is lost; if the maintenance time is less than 1 second, it is regarded as signal jitter and the startup status loss signal is not generated.

6. The DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations as described in claim 5, characterized in that: The start-up status loss signal generated in S2 is implemented by the timer function block in the DCS / PLC control system. The timer function block is configured to be triggered by a falling edge, that is, when the start-up status feedback signal of the auxiliary machine is detected to change from 1 to 0, the timing is triggered. After the timing reaches the set 1 second, a valid signal is output. If the start-up status feedback signal recovers to 1 during the timing period, the timing is reset and no valid signal is output.

7. The DCS or PLC logic control method for self-starting of 380V auxiliary equipment of thermal power units to prevent power fluctuations as described in claim 6, characterized in that: A key 380V auxiliary machine used in thermal power units, including a coal feeder.

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