A control system and method for frequency conversion and power frequency cutting of a single series induced draft fan in a thermal power plant

Abstract

The present invention discloses a control system and method for frequency conversion and power frequency switching of a single-series induced draft fan in a thermal power plant. When the induced draft fan inverter trips due to a fault, the method switches the induced draft fan under frequency conversion control to power frequency control. The output of the power frequency control is obtained through the frequency conversion output equivalent curve. Without causing the boiler to extinguish, the method uses the control logic of this technology to smoothly switch the induced draft fan from the frequency conversion operating condition to the power frequency operating condition, providing reliable protection for the stable operation of the thermal power plant and greatly improving the reliability and economy of the generator set.

Description

Technical Field

[0001] The invention belongs to the technical field of induced draft fan control in thermal power plants, and relates to a control system and method for frequency conversion and power frequency switching of a single series induced draft fan in a thermal power plant. Background Art

[0002] Induced draft fans (IDFs) are essential auxiliary equipment in thermal power plants. Because they transport dusty, high-temperature flue gas, they generate large air volumes, high pressures, and significant power consumption. Single-series (i.e., single induced and forced draft fans) consume even greater amounts of power. Therefore, the reliability and economic efficiency of a single IDF fan during production directly impacts the plant's operating costs. Consequently, energy-saving fan upgrades have become a key focus of thermal power plant energy optimization in recent years. A common approach for energy-saving fan upgrades in thermal power plants is to use variable frequency drive (VFD) technology, switching from a throttling control mode to a VFD mode. This reduces throttling power consumption and lowers the power consumption of the IDF fan. However, when operating under load in single-series thermal power units, a VFD failure that causes a fan trip can directly cause the boiler to extinguish and shut down the unit, seriously threatening stable boiler operation. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a control system and method for frequency conversion and power frequency cutting of a single-series induced draft fan in a thermal power plant, so as to solve the problem in the prior art that the fan tripping caused by the inverter failure in the single induced draft fan directly affects the stable operation of the boiler.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A control method for switching from variable frequency to power frequency for a single-series induced draft fan in a thermal power plant, wherein when the induced draft fan inverter trips due to a fault, the induced draft fan under variable frequency control is switched to power frequency control, wherein the power frequency control is to adjust the induced draft fan blades;

[0006] The output value of the induced draft fan blade adjustment is obtained through the variable frequency output equivalent linear function;

[0007] The process of obtaining the variable frequency output equivalent linear function is as follows: collecting the relationship between the output of the induced draft fan inverter and the change of the inverter frequency instruction as the first set of data; collecting the relationship between the output of the induced draft fan under the power frequency control and the change of the induced draft fan rotor blade opening as the second set of data; using the output of the induced draft fan inverter and the output of the induced draft fan under the power frequency control as equivalent values, determining the relationship between the inverter instruction and the rotor blade opening to obtain the variable frequency output equivalent linear function.

[0008] A further improvement of the present invention is:

[0009] Preferably, the process of collecting the relationship between the output of the induced draft fan inverter and the change of the inverter frequency instruction includes the following steps:

[0010] (1) Turn on the supply fan and induced draft fan;

[0011] (2) Set the induced draft fan frequency control to automatic adjustment;

[0012] (3) Manually increase the frequency of the fan inverter in steps of 5 Hz. The induced draft fan inverter automatically adjusts the output. The corresponding induced draft fan output data is recorded in each step.

[0013] (4) When the blower frequency increases to 50 Hz, start the primary blower and open the hot and cold primary blades of the coal mill, gradually adjust the primary air pressure to the rated primary air pressure, and record the corresponding induced draft fan output data;

[0014] (5) Continue to increase the primary fan output and record the corresponding induced draft fan output data. When the primary fan output reaches the upper limit, gradually close the induced draft fan blades. When the induced draft fan inverter is 50Hz, record the induced draft fan output value.

[0015] Preferably, the induced draft fan output data includes induced draft fan current, blower fan current, blower fan frequency conversion instruction, furnace negative pressure, system total air volume, induced draft fan frequency conversion instruction and primary fan adjustment opening.

[0016] Preferably, the process of collecting the relationship between the output of the induced draft fan under power frequency control and the change in the blade opening is as follows:

[0017] (1) The induced draft fan blades are automatically engaged;

[0018] (2) The fan frequency is reduced by 5 Hz or the blade opening is reduced by 5% as one stage, and the induced draft fan output data of each stage is recorded;

[0019] (3) When the air volume of the primary fan is reduced to the minimum, shut down the primary fan; then gradually close the supply fan blades, with the supply fan blade opening reduced by 5% as one stage, and record the output data of the induced draft fan when the induced draft blades are automatically adjusted;

[0020] (4) When the supply fan blades are closed to the minimum, the output data of the induced draft fan when the induced draft fan blades are automatically adjusted are recorded to obtain the relationship between the output of the induced draft fan at the working frequency and the change in the opening of the induced draft fan blades.

[0021] Preferably, the equivalent linear function is obtained by fitting when the total air volume load is greater than 30%.

[0022] A control system for frequency conversion and power frequency cutting of a single series induced draft fan in a thermal power plant, comprising:

[0023] A control conversion module, which is used to switch the induced draft fan from variable frequency control to industrial frequency control when the induced draft fan inverter trips due to a fault. The industrial frequency control is used to adjust the induced draft fan blades.

[0024] The calculation module is used to obtain the adjusted output value of the induced draft fan blades based on the real-time output data of the inverter and the inverter output equivalent curve.

[0025] Preferably, the control conversion module is activated by a frequency conversion fault trigger module, and the frequency conversion fault trigger module is used to obtain a fault signal of the induced draft fan frequency converter.

[0026] Preferably, the calculation module obtains the real-time output data of the inverter through the feedback module.

[0027] Preferably, the calculation module is further connected to a function determination module, and the function determination module is used to determine the variable frequency output equivalent curve.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention discloses a control method and system for switching from variable frequency to industrial frequency for a single-series fan in a thermal power plant. When the induced draft fan inverter trips due to a fault, the method switches the induced draft fan under variable frequency control to industrial frequency control. The output of the industrial frequency control is obtained through the variable frequency output equivalent curve. Without causing the boiler to extinguish, the method uses the control logic of the present technology to smoothly switch the induced draft fan from the variable frequency operating condition to the industrial frequency operating condition, providing reliable protection for the stable operation of the thermal power plant and greatly improving the reliability and economy of the generator set. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the power frequency control diagram of the induced draft fan with variable shear function of the present invention;

[0031] Among them, 1-induced draft fan power frequency output input module; 2-induced draft fan power frequency output module; 3-control conversion module; 4-induced draft fan power frequency output calculation module; 5-induced draft fan inverter output feedback module; 6-inverter fault trigger module; 7-function determination module.

[0032] Figure 2 To adjust the flow chart. DETAILED DESCRIPTION

[0033] The present invention is described in further detail below with reference to the accompanying drawings:

[0034] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] Conventional single-series induced draft fan control systems without variable frequency switching typically have only two modules: induced draft fan power frequency output input module 1 and induced draft fan power frequency output module 2. During variable frequency operation, the rotor blades are fully open. Even after adjusting the frequency converter's fault, the rotor blades fail to activate. This fails to ensure stable operation of the equipment after a single-series induced draft fan frequency converter trips.

[0036] Example 1

[0037] See also Figure 1 To ensure that a single-series induced draft fan can successfully switch to power frequency operation in the event of a variable frequency operation failure, the present invention provides a control system for switching from variable frequency to power frequency in a thermal power plant single-series induced draft fan. The system comprises: an induced draft fan power frequency output input module 1, an induced draft fan power frequency output module 2, a control conversion module 3, a calculation module 4, a feedback module 5, and a variable frequency failure trigger module 6. The control conversion module 3 is disposed between the induced draft fan power frequency output input module 1 and the induced draft fan power frequency output module 2. The control conversion module 3 is connected to both the calculation module 4 and the variable frequency failure trigger module 6. The calculation module 4 is also connected to the feedback module 5.

[0038] See also Figure 1 Under normal working conditions, the control conversion module 3 connects the induced draft fan power frequency output input module 1 and the induced draft fan power frequency output module 2. The induced draft fan power frequency output module 2 outputs the power frequency according to the instructions received from the induced draft fan power frequency output input module; under variable frequency operation, the power frequency moving blades are in a 100% fully open state.

[0039] When a single-series induced draft fan trips due to a frequency converter fault, the frequency converter fault trigger module 6 and control conversion module 3 primarily implement a mechanism to switch the fan's blade control to a stable state without tripping the fan. This switching occurs between the original induced draft fan's power frequency output input module 1 and the induced draft fan's power frequency output module 2.

[0040] Specifically, the frequency conversion fault trigger module 6 is connected to the single-series induced draft fan frequency converter. When it receives a fault signal from the single-series induced draft fan frequency converter, it activates the control-to-control conversion module 3 to complete the control switching, so that the single-series induced draft fan frequency conversion is switched to the industrial frequency moving blade regulation induced draft fan operating condition.

[0041] Control conversion module 3 is used to switch from variable frequency control to power frequency rotor blade adjustment control. Specifically, if the variable frequency mode fails, the control signal for the 100% full-open command input from the induced draft fan power frequency output 1 is blocked. Meanwhile, the rotor blade adjustment command for the equivalent operating condition calculated by calculation module 4 is sent to the fan power frequency output module 2.

[0042] Calculation module 4 is used to calculate the corresponding output for the power frequency rotor blade adjustment condition based on the actual output of the single-series induced draft fan in real time. This command is effectively sent to the fan power frequency output module 2 via the control conversion module 3. This ensures a smooth transition from the single-series induced draft fan's variable frequency operation to the power frequency operation, reducing system failure rates. This module incorporates a linear function equivalent to the variable frequency output, matching the frequency command for the induced draft fan's variable frequency operation with the adjustable rotor blade opening for the induced draft fan's power frequency operation. This ensures that once the frequency command for the variable frequency operation is input, the adjustable rotor blade opening for the power frequency operation is directly output.

[0043] Feedback module 5 is connected to the single-series induced draft fan inverter command. The inverter command output is mainly based on the automatic adjustment of production according to the furnace negative pressure. The command will not change due to inverter failure. Therefore, this module can track the inverter output data in real time and feed the data back to the calculation module 4.

[0044] Example 2

[0045] One embodiment of the present invention discloses a method for controlling frequency conversion and power frequency switching of a single-series induced draft fan in a thermal power plant, the method comprising the following steps:

[0046] Step 1: When the series induced draft fan inverter trips due to fault, the induced draft fan inverter fault module 6 signal is triggered.

[0047] Step 2: The inverter fault module 6 sends a signal to activate the control conversion module 3 in the induced draft fan control loop, which outputs the instruction of the shielding module 1.

[0048] In step 3, the feedback module 5 feeds back the real-time output data of the frequency converter (i.e., the frequency converter instruction) to the calculation module 4. The calculation module 4 determines the corresponding adjustment plate opening under the frequency instruction of the frequency converter working condition at that time through the frequency conversion output equivalent linear function matched with the frequency instruction of the frequency converter working condition of the induced draft fan and the adjustment blade opening of the working frequency working condition of the induced draft fan, and transmits it to the control conversion module 3.

[0049] In step 4, the control conversion module 3 quickly transmits the data in the fan output calculation module 4 to the induced draft fan power frequency output module 2. This allows the induced draft fan power frequency output to quickly reach the equivalent output before the inverter trips, thereby preventing the boiler from extinguishing.

[0050] Example 3

[0051] One embodiment of the present invention discloses a method for determining the power frequency equivalent output based on the output data of the inverter, which specifically includes the following steps:

[0052] Step 1: Collect the output of the induced draft fan inverter

[0053] 1. When the unit is in cold state, start the forced draft and induced draft fan system in variable frequency mode. Slowly open the forced draft and induced draft fan blades to above 90%, and pay attention to stabilizing the furnace negative pressure at a normal value.

[0054] 2. Stabilize the induced draft fan inverter in the 5HZ frequency range, adjust the blower output to stabilize the furnace negative pressure at a normal value, and put the induced draft fan frequency control into automatic adjustment.

[0055] 3. Manually increase the frequency of the blower, slowly changing the frequency converter command by 5 Hz as a stage, and observe the fan output generated by the automatic adjustment of the induced draft fan frequency converter after the output force (i.e., increasing the system air volume) increases, and record the induced draft fan output data of each stage. The induced draft fan output data includes the induced draft fan current, the supply fan current, the supply fan frequency conversion command, the furnace negative pressure, the total system air volume, the induced draft fan frequency conversion command and the primary fan adjustment opening.

[0056] 4. After increasing the fan inverter speed to 50 Hz (i.e., the fan air volume reaches its upper limit), start the two primary fans and open the hot and cold primary rotors of the three coal mills. Maintain stable system ventilation and gradually adjust the primary air pressure to the rated primary air pressure using the primary fan inverter (or adjusting the rotor). Record the induced draft fan output data for each stage and enter it in Table 1.

[0057] 5. Continue to slowly increase the primary fan output (i.e., increase the system air volume) and record the induced draft fan output data at each stage (including induced draft fan current, total system air volume, and furnace negative pressure).

[0058] 6. After the primary fan output is rated (i.e. the primary fan air volume reaches the upper limit), and the induced draft fan inverter has not reached 50HZ, slowly close the induced draft fan blades (this process is to simulate the inverter reaching the maximum output) until the induced draft fan reaches 50HZ. Record the induced draft fan output data for each stage and fill in Table 1.

[0059] Step 2: Collect the power frequency output of the induced draft fan

[0060] 1. Following up on Article 6 above, when the frequency converters of the supply and induced draft fans are at 50 Hz and both primary fans are started, the frequency converters of the induced draft fans are automatically released, the induced draft fan blades are automatically switched on, and the primary fan output is slowly reduced (i.e., the system air volume is reduced). A change of 5% (or a frequency change of 5 Hz) in the primary fan blades is taken as one stage. Observe the output of the induced draft fan when the induced draft fan blades are automatically adjusted, and record the induced draft fan blade adjustment output data for each stage and fill in Table 2. The induced draft fan blade adjustment output data include induced draft fan current, supply fan current, supply fan blade opening, furnace negative pressure, system total air volume, induced draft fan blade opening, and primary fan adjustment opening.

[0061] Table 2 - Output collection table of induced draft fan variable frequency working condition

[0062]

[0063] 2. When the primary fan opening is adjusted to 5% (i.e., the primary fan air volume is reduced to the minimum), stop the primary fan. Slowly close the supply fan blades (i.e., reduce the supply fan air volume). Observe the output of the induced draft fan when the induced draft fan blades are adjusted, with each 5% change in the supply fan blades as one stage. Record the output data of the induced draft fan blade adjustment at each stage and fill in Table 2.

[0064] 3. When the supply fan blades are closed to 5%, that is, the supply fan air volume is reduced to the minimum, observe the output of the induced draft fan when the induced draft fan blades are automatically adjusted, and record the induced draft fan blade adjustment output data of each stage and fill in Table 2. The data collection is completed.

[0065] Step 3: Calculation of equivalent induced draft fan output 3

[0066] Based on the total system air volume and induced draft fan current in the data collection, the frequency control data for the induced draft fan and the blade opening data for the induced draft fan under the same operating conditions were selected. The frequency command for the induced draft fan under variable frequency operating conditions with a total air volume load of more than 30% and the blade opening for the induced draft fan under power frequency operating conditions were fitted into a linear function, forming the data in Table 3. In this linear function, the induced draft fan frequency control command and the equivalent blade opening of the induced draft fan are the X-axis and Y-axis, respectively.

[0067] Step 4: Input equivalent output calculation data 4

[0068] The equivalent output data is input into the induced draft fan control loop 4. When the induced draft fan inverter fails, the system automatically sends the equivalent output data to the moving blade output of the induced draft fan.

[0069] Table 3-Equivalent output table

[0070]

[0071] Example 4

[0072] Function determination module 7, used to implement the calculation method of step 1 to step 3 in embodiment 3, obtain the frequency instruction of the induced draft fan variable frequency working condition and the adjustment blade opening of the induced draft fan working frequency working condition to fit into a linear function

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A control method for frequency conversion and power frequency cutting of a single series induced draft fan in a thermal power plant, characterized in that: When the induced draft fan inverter trips due to a fault, the induced draft fan under variable frequency control is switched to industrial frequency control, where the industrial frequency control is used to adjust the induced draft fan blades; The output value of the induced draft fan blade adjustment is obtained through the variable frequency output equivalent linear function; The process of obtaining the variable frequency output equivalent linear function is as follows: collecting the relationship between the output of the induced draft fan inverter and the change of the inverter frequency command as the first set of data; collecting the relationship between the output of the induced draft fan under power frequency control and the change of the induced draft fan rotor blade opening as the second set of data; using the output of the induced draft fan inverter and the output of the induced draft fan under power frequency control as equivalent values, determining the relationship between the inverter command and the rotor blade opening to obtain the variable frequency output equivalent linear function; The process of collecting the relationship between the output of the induced draft fan inverter and the change of the inverter frequency command includes the following steps: (1) Turn on the supply fan and induced draft fan; (2) Set the induced draft fan frequency control to automatic adjustment; (3) Manually increase the frequency of the fan inverter in stages of 5 Hz. The induced draft fan inverter automatically adjusts the output. The corresponding induced draft fan output data is recorded in each stage. (4) When the fan frequency increases to 50 Hz, start the primary fan and the hot and cold primary rotor blades of the coal mill, gradually adjust the primary air pressure to the rated primary air pressure, and record the corresponding induced draft fan output data; (5) Continue to increase the primary fan output and record the corresponding induced draft fan output data. When the primary fan output reaches the upper limit, gradually close the induced draft fan blades. When the induced draft fan inverter is 50Hz, record the induced draft fan output value; The process of collecting the relationship between the output of the induced draft fan under power frequency control and the change in the blade opening is as follows: (1) The induced draft fan blades are automatically put into operation; (2) Take the frequency of the primary fan reduced by 5 Hz or the blade opening reduced by 5% as one stage, and record the output data of the induced draft fan in each stage; (3) When the air volume of the primary fan is reduced to the minimum, shut down the primary fan; then gradually close the supply fan blades, with the supply fan blade opening reduced by 5% as a stage, and record the output data of the induced draft fan when the induced draft blades are automatically adjusted; (4) When the supply fan blades are closed to the minimum, record the output data of the induced draft fan when the induced draft fan blades are automatically adjusted to obtain the relationship between the output of the induced draft fan at the working frequency and the change in the opening of the induced draft fan blades.

2. A control method for frequency conversion and power frequency cutting of a single series induced draft fan in a thermal power plant according to claim 1, characterized in that: The induced draft fan output data includes the induced draft fan current, the supply fan current, the supply fan frequency conversion instruction, the furnace negative pressure, the total air volume of the system, the induced draft fan frequency conversion instruction and the primary fan adjustment opening.

3. The control method for frequency conversion and power frequency cutting of a single series induced draft fan in a thermal power plant according to claim 1, characterized in that: The equivalent linear function is obtained by fitting when the total air volume load is above 30%.

4. A control system for frequency conversion and power frequency switching of a single series induced draft fan in a thermal power plant for implementing the control method according to claim 1, characterized in that: include: A control conversion module, which is used to switch the induced draft fan from variable frequency control to industrial frequency control when the induced draft fan inverter trips due to a fault. The industrial frequency control is used to adjust the induced draft fan blades. The calculation module is used to obtain the adjusted output value of the induced draft fan blades based on the real-time output data of the inverter and the inverter output equivalent curve.

5. A control system for frequency conversion and power frequency switching of a single series induced draft fan in a thermal power plant according to claim 4, characterized in that: The control conversion module is activated by the frequency conversion fault trigger module, and the frequency conversion fault trigger module is used to obtain the fault signal of the induced draft fan frequency converter.

6. A control system for frequency conversion and power frequency switching of a single series induced draft fan in a thermal power plant according to claim 4, characterized in that: The calculation module obtains the real-time output data of the inverter through the feedback module.

7. A control system for frequency conversion and power frequency switching of a single series induced draft fan in a thermal power plant according to claim 4, characterized in that: The calculation module is further connected to a function determination module, and the function determination module is used to determine a variable frequency output equivalent curve.

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