Online undisturbed switching method for frequency converter of primary air fan

Abstract

The invention relates to a primary fan frequency converter on-line undisturbed switching method which comprises the following steps: when a DCS (Distributed Control System) detects a fault of a frequency converter, the DCS records an instantaneous frequency value of the frequency converter and sends a switching instruction to a local controller; when the local controller controls the primary fan to switch the power frequency, the DCS system adjusts the opening degree of the adjusting baffle to the ideal opening degree according to the frequency of the frequency converter and the equivalent relation function model of the opening degree of the adjusting baffle and the instantaneous frequency value of the frequency converter; and after it is monitored and confirmed that the air volume of the primary air fan is stabilized at the level before switching, the DCS system returns the control right of the adjusting baffle to the local controller. The method has the advantages that the instantaneous frequency value before the frequency converter breaks down is stored through the DCS, the equivalent relation function model of the frequency of the frequency converter and the opening degree of the adjusting baffle is combined, undisturbed switching from the frequency converter fault to the power frequency is achieved, repeated fluctuation of the primary air volume and the hearth pressure is effectively restrained, and the frequency conversion efficiency is improved. And important guarantee is provided for safe and stable operation of the unit.

Description

Technical Field

[0001] This invention belongs to the field of wind turbine emergency technology, and particularly relates to a method for seamless online switching of primary wind turbine frequency converters. Background Technology

[0002] In thermal power plant unit operation, the use of variable frequency drive (VFD) operation for primary air fans has become the mainstream energy-saving solution. This mode, by precisely adjusting the fan speed to match load demand, can significantly reduce plant power consumption and improve unit energy efficiency compared to traditional line frequency operation. However, as a core component of electronic control, the operational stability of the VFD is directly related to the safety of the primary air system: once the VFD fails, the lack of a reliable emergency switching mechanism will lead to interruption or significant fluctuations in primary air supply, directly threatening the stability of furnace combustion and even triggering unit trip protection.

[0003] Under the existing control logic, when a primary wind turbine frequency converter fails, operators often have no choice but to activate the rapid load reduction protection strategy, which forcibly reduces the unit load to below 50% of the rated load to adapt to the unstable state of the wind system by reducing the furnace heat load demand. While this can avoid unplanned outages, it causes a sharp drop in power generation, affecting not only the power plant's economic efficiency but also potentially disrupting grid dispatch plans. Furthermore, the drastic load fluctuations exacerbate temperature differences on the boiler heating surfaces, increasing the risk of equipment fatigue and wear. Frequent triggering of the rapid load reduction protection strategy over a long period will shorten the unit's service life.

[0004] Therefore, developing and applying a set of control logic for rapid and seamless switching between frequency converter failure and power frequency operation has become an urgent technical requirement for thermal power plants to solve the technical problems of sharp drop in power generation, excessive temperature difference of boiler heating surface, and reduced service life of unit. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for seamless online switching of primary air turbine frequency converters.

[0006] This method for seamless online switching of primary air turbine frequency converters includes the following steps:

[0007] Step 1, Fault Response: When the DCS system detects a fault in the frequency converter, the DCS system records the instantaneous frequency value of the frequency converter and sends a switching command to the local controller;

[0008] Step 2, Switching and Adjustment: When the local controller controls the primary air fan to switch to the power frequency, the DCS system adjusts the damper to the ideal opening degree based on the equivalent relationship function model between the inverter frequency and the damper opening degree, combined with the instantaneous frequency value of the inverter.

[0009] Step 3: Handing over control: After monitoring and confirming that the air volume of the primary fan is stable at the level before the switchover, the DCS system hands over the control of the regulating damper to the local controller.

[0010] Preferably, in step one, the DCS system has a T function block, which tracks and outputs the current frequency value of the inverter in real time; when the DCS system detects an inverter fault, the T function block freezes and saves the instantaneous frequency value of the inverter at the last moment before the fault.

[0011] As a preferred option, in step two, the equivalent relationship function model between the inverter frequency and the regulating damper opening is obtained through experiments. During the experiment, when the air volume of the primary fan is the same under both inverter operation and power frequency operation, the corresponding relationship data of adjusting the inverter frequency and the regulating damper opening in the range from no load to full load of the primary fan is recorded. The DCS system has an F(X) function block. Based on the corresponding relationship data, the equivalent relationship function model between the inverter frequency and the regulating damper opening is established in the F(X) function block, and the corresponding relationship data is transformed into continuous calculation logic.

[0012] Preferably, in step two, the F(X) function block interpolates the instantaneous frequency value of the inverter into the equivalent relationship function model between the inverter frequency and the opening degree of the regulating baffle, and outputs the corresponding opening degree value of the regulating baffle. The DCS system adjusts the fully open regulating baffle to the ideal opening degree according to the opening degree value of the regulating baffle.

[0013] Preferably, in step two, when the primary fan is running at the power frequency, it operates at full load at the rated power frequency.

[0014] This online seamless switching system for primary air turbine frequency converters can be applied to any of the methods described above.

[0015] The beneficial effects of this invention are:

[0016] 1) The T function block in the DCS system of the present invention tracks and outputs the current frequency value of the inverter in real time. When the inverter fails, it freezes and saves the instantaneous frequency value at the last moment before the inverter failure. This avoids the technical problem that the original frequency command may be reset or overwritten by the system at the moment the inverter failure signal is triggered under sudden working conditions. It realizes the saving of the instantaneous frequency value before the inverter failure and provides a calculation basis for the adjustment of the damper opening of the primary fan.

[0017] 2) This invention establishes an equivalent functional model of the relationship between the frequency of the inverter and the opening of the regulating baffle. The F(X) function block in the DCS system is used to accurately convert the frequency command before the fault into the opening of the baffle at the power frequency.

[0018] 3) This invention saves the instantaneous frequency value of the frequency converter before the failure by the DCS system, and combines the equivalent relationship function model of the frequency converter frequency and the opening of the regulating baffle to realize the seamless switching from the frequency converter failure to the power frequency, effectively suppressing the repeated fluctuations of the primary air volume and furnace pressure, and providing an important guarantee for the safe and stable operation of the unit.

[0019] 4) Before the inverter fails, the regulating baffle at the outlet of the primary air fan is in a fully open state, eliminating the throttling loss of the baffle and improving the frequency conversion regulation efficiency; when the inverter fails, before the primary air fan is switched to the power frequency, the opening of the regulating baffle at the outlet of the primary air fan is adjusted to the ideal opening, suppressing the sudden increase of the air volume of the fan when the power frequency is started, and avoiding the sudden increase of the primary air pressure impacting the furnace. Attached Figure Description

[0020] Figure 1 This is the logic diagram for achieving the ideal opening degree of the baffle after successful automatic bypass.

[0021] Figure 2 It is a line graph showing the equivalent relationship between the inverter frequency and the opening of the regulating baffle. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0023] Example 1

[0024] As one embodiment, a method for seamless online switching of primary air turbine frequency converters is proposed, such as... Figure 1 and Figure 2 As shown, it includes the following steps:

[0025] Step 1, Fault Response: When the DCS system detects a frequency converter fault, it records the instantaneous frequency value of the frequency converter and sends a switching command to the local controller. Specifically, the DCS system has a T function block, which tracks and outputs the current frequency value of the frequency converter in real time. When the DCS system detects a frequency converter fault, the T function block triggers the hold mode, freezing and saving the instantaneous frequency value of the frequency converter at the last moment before the fault, preventing the parameter from being overwritten by the fault signal. Frequency converter faults are sudden operating conditions. At the moment the fault signal is triggered, the original frequency command may be reset or overwritten by the system. By freezing and saving the instantaneous frequency value of the frequency converter before the fault, the problem of parameter capture is solved, providing a calculation basis for deriving the corresponding baffle opening at the power frequency.

[0026] Furthermore, the DCS system is a distributed control system. The DCS system first identifies the source of the fault, then analyzes whether the boiler load is suitable, and confirms whether the frequency converter has failed. Only when the safety conditions are met will it send a switching command to the local controller to allow the frequency converter to switch, triggering the switch. If the conditions are not met, an alarm will be triggered to activate emergency measures. This approach solves the problem in the existing fan control system where, when the local controller detects a major fault during frequency converter fault handling, it cannot distinguish whether the fault comes from the fan side or itself, nor does it consider the boiler load, and directly switches the fan to the mains frequency. This can easily aggravate the fault, waste energy, or even expand the accident. The DCS system solves the problem of blind switching, making the frequency converter to mains frequency switch more intelligent and reliable, ensuring the safety and stability of the system, and improving energy efficiency.

[0027] Step 2, Switching and Adjustment: When the local controller controls the primary air fan to switch to the power frequency, the DCS system adjusts the damper to the ideal opening degree based on the equivalent relationship function model between the inverter frequency and the damper opening degree, combined with the instantaneous frequency value of the inverter.

[0028] Step 3: Handing over control: After monitoring and confirming that the air volume of the primary fan is stable at the level before the switchover, the DCS system hands over the control of the regulating damper to the local controller.

[0029] Example 2

[0030] As another embodiment, this second embodiment proposes a more specific method for seamless online switching of primary air turbine frequency converters based on the first embodiment, such as... Figure 1 and Figure 2 As shown, it includes the following steps:

[0031] Step 1, Fault Response: When the DCS system detects a fault in the frequency converter, the DCS system records the instantaneous frequency value of the frequency converter and sends a switching command to the local controller;

[0032] Step 2, Switching and Adjustment: When the local controller switches the primary air fan to the mains frequency, the DCS system adjusts the damper to the ideal opening based on the equivalent relationship function model of the inverter frequency and the damper opening, combined with the instantaneous frequency value of the inverter. Specifically, the equivalent relationship function model of the inverter frequency and the damper opening is obtained through experiments. During the experiment, the air volume under both inverter and mains frequency operation of the primary air fan is the same. The corresponding relationship data of adjusting the inverter frequency and the damper opening within the range of 0Hz (no load) to 50Hz (full load) of the primary air fan are recorded. The DCS system is equipped with... The F(X) function block establishes an equivalent relationship function model between the inverter frequency and the damper opening based on the corresponding relationship data, transforming the corresponding relationship data into continuous calculation logic. The F(X) function block interpolates the instantaneous frequency value of the inverter into the equivalent relationship function model between the inverter frequency and the damper opening, and outputs the corresponding damper opening value. The DCS system adjusts the fully open damper to the ideal opening based on the damper opening value. When the primary fan is running at the power frequency, it operates at full load at the rated power frequency, and the air volume is adjusted by adjusting the opening of the damper.

[0033] Furthermore, through field tests, the output at different frequencies during variable frequency operation and the output at different baffle openings during power frequency operation were tested respectively. When the outputs were consistent, the corresponding frequency X and baffle opening Y were recorded. Finally, an equivalent conversion table was formed to obtain the corresponding data on adjusting the inverter frequency and adjusting the baffle opening within the no-load to full-load range of the primary fan:

[0034]

[0035] like Figure 2 As shown, based on the corresponding data of the frequency converter frequency and the damper opening degree in the equivalent conversion table of the primary fan from no load to full load, a piecewise linear function model is established in the F(X) function block of the DCS, that is, the equivalent relationship function model of the frequency converter frequency and the damper opening degree, and the correspondence between the frequency converter frequency and the damper opening degree is transformed into continuous calculation logic.

[0036] This function model covers the full frequency range of 0-50Hz, ensuring that a unique ideal opening can be quickly obtained at different pre-fault frequencies.

[0037] Furthermore, accident tests were conducted to switch the frequency converter to the mains frequency under different load conditions. The focus was on monitoring fluctuations in key parameters such as primary air fan main pipe pressure, furnace negative pressure, steam drum water level, and main reheat steam temperature and pressure before and after the switchover. Taking the switchover test under full load conditions as an example, the core data are as follows:

[0038]

[0039]

[0040] During emergency switching, the regulating damper automatically closes from 100% to 39.3% through ideal opening control, and the furnace pressure fluctuation is controlled within 70Pa, which is far below the allowable fluctuation range for safe operation of the unit. The primary air volume remains basically unchanged before and after the switching, avoiding risks such as unstable furnace combustion and large fluctuations in steam drum water level, thus verifying the effectiveness and stability of the ideal opening technology.

[0041] Step 3: Handing over control: After monitoring and confirming that the air volume of the primary air fan is stable at the level before the switchover, the DCS system returns the control of the regulating damper to the local controller to ensure the normal operation of the unit.

[0042] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 1 can be referred to each other, and will not be repeated in this application.

[0043] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

Claims

1. A method for seamless online switching of a primary air fan frequency converter, characterized in that, Includes the following steps: Step 1, Fault Response: When the DCS system detects a fault in the frequency converter, the DCS system records the instantaneous frequency value of the frequency converter and sends a switching command to the local controller; Step 2, Switching and Adjustment: When the local controller controls the primary air fan to switch to the power frequency, the DCS system adjusts the damper to the ideal opening degree based on the equivalent relationship function model between the inverter frequency and the damper opening degree, combined with the instantaneous frequency value of the inverter. Step 3: Handing over control: After monitoring and confirming that the air volume of the primary fan is stable at the level before the switchover, the DCS system hands over the control of the regulating damper to the local controller.

2. The method for seamless online switching of a primary air fan frequency converter according to claim 1, characterized in that, In step one, the DCS system has a T function block, which tracks and outputs the current frequency value of the frequency converter in real time. When the DCS system detects a frequency converter fault, the T function block freezes and saves the instantaneous frequency value of the frequency converter at the last moment before the fault.

3. The method for seamless online switching of a primary air fan frequency converter according to claim 1, characterized in that, In step two, the equivalent relationship function model between the inverter frequency and the adjustment baffle opening is obtained through experiments. During the experiment, when the air volume of the primary fan is the same under the variable frequency operation and the power frequency operation, the corresponding relationship data of adjusting the inverter frequency and the adjustment baffle opening in the range of no load to full load of the primary fan are recorded. The DCS system has an F(X) function block. Based on the corresponding relationship data, an equivalent relationship function model of the inverter frequency and the opening of the regulating baffle is established in the F(X) function block, and the corresponding relationship data is transformed into continuous calculation logic.

4. The method for seamless online switching of a primary air fan frequency converter according to claim 3, characterized in that, In step two, the F(X) function block interpolates the instantaneous frequency value of the inverter into the equivalent relationship function model between the inverter frequency and the opening degree of the regulating baffle, and outputs the corresponding opening degree value of the regulating baffle. The DCS system adjusts the fully open regulating baffle to the ideal opening degree according to the opening degree value.

5. The method for seamless online switching of a primary air fan frequency converter according to claim 1, characterized in that, In step two, when the primary fan is running at the power frequency, it operates at full load at the rated power frequency.

6. A non-disruptive online switching system for a primary air fan frequency converter, characterized in that, Applied to the method described in any one of claims 1 to 5.

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