Primary frequency control method

Abstract

The application is suitable for supercritical technical field, and provides a primary frequency modulation control method, which comprises the following steps: designing a low-pass high filter and a high-pass low filter, decomposing a frequency signal, and obtaining low-frequency components and high-frequency components of the frequency signal respectively; sending the low-frequency components into a condensate water flow bypass valve controller, adjusting the bypass valve opening degree according to the low-frequency components; sending the low-frequency components into a low-level feedwater heater water level adjustment logic as a feedforward signal, and pre-judging and adjusting the low-level feedwater heater water level; sending the high-frequency components into a feedwater flow bypass valve controller, and adjusting the feedwater bypass valve opening degree according to the high-frequency components; and sending the high-frequency components into a high-level feedwater heater water level adjustment logic as a feedforward signal, and pre-judging and adjusting the high-level feedwater heater water level. By adjusting the water quantity on the high-level feedwater heater side, the steam side extraction quantity is changed, the temperature change is stable, and the stable operation of the unit is beneficial; the primary frequency modulation of the power grid is provided with an effective auxiliary means, and the frequency modulation precision and the frequency modulation response speed are improved.

Description

Technical Field

[0001] This invention belongs to the field of supercritical technology, and particularly relates to a primary frequency modulation control method. Background Technology

[0002] Due to the limited heat storage capacity of supercritical once-through boilers, the unit's load-changing capacity is insufficient within the required range of variations. There is an inherent difference in response speed between the turbine and the boiler; the turbine has a fast response time on the order of seconds, while the boiler system involves combustion, heat transfer, and heat exchange processes. This lag is particularly exacerbated in direct-fired pulverized coal systems, resulting in a response time on the order of minutes. Therefore, methods using air-coal feedforward at the boiler side are too time-consuming, and research must focus on the turbine side. To address this situation, scholars both domestically and internationally have proposed several solutions.

[0003] A certain ultra-supercritical unit abroad used condensate throttling during primary frequency regulation to instantaneously reduce the extraction steam from the low-pressure cylinders of the unit to increase the unit load. However, for safe operation, the condensate throttling flow rate and the instantaneous extraction steam flow rate are limited and cannot meet the load changes.

[0004] A domestic ultra-supercritical unit has added an inlet steam regulating valve to the high-pressure heater extraction steam pipeline. During low-frequency operation of the primary frequency regulation, the high-pressure heater extraction valve is partially closed to reduce the extraction steam flow, increase the turbine's work capacity, and increase the load variation. However, a sudden reduction in high-pressure heater extraction will cause a drastic drop in water-side temperature, potentially leading to high-pressure heater disconnection and affecting the safe operation of the unit. Summary of the Invention

[0005] The purpose of this invention is to provide a primary frequency modulation control method, aiming to solve the problems existing in the background art.

[0006] The present invention is implemented as follows: a primary frequency modulation control method, which includes the following steps:

[0007] Step 1: Design low-pass high-filter and high-pass low-filter filters to decompose the frequency signal and obtain its low-frequency and high-frequency components respectively.

[0008] Step 2: Send the low-frequency component to the condensate flow bypass valve controller. Adjust the bypass valve opening according to the low-frequency component. Reduce the low-pressure cylinder air extraction by throttling the condensate and adjust the load to meet the low-frequency component of the frequency difference signal.

[0009] Step 3: Send the low-frequency component as a feedforward signal into the low-level water supply adjustment logic to predict and adjust the low-level water supply in advance;

[0010] Step 4: Send the high-frequency component to the feedwater flow bypass valve controller, and adjust the opening of the feedwater bypass valve according to the high-frequency component. Reduce the high-pressure cylinder air extraction by throttling the feedwater, and adjust the load to meet the high-frequency component of the frequency difference signal.

[0011] Step 5: Send the high-frequency component as a feedforward signal into the high-pressure water level adjustment logic to predict and adjust the high-pressure water level in advance.

[0012] As a further embodiment of the present invention, in step 1, the filtering rule of the low-pass filter is that low-frequency signals can pass normally, while high-frequency signals exceeding a set threshold are blocked or weakened. The magnitude of the blocking or weakening varies depending on the frequency and the filtering procedure, and the transfer function is as follows:

[0013]

[0014] Filter out frequencies greater than ω c High-frequency components, with frequencies less than ω. c The low-frequency components.

[0015] As a further embodiment of the present invention, in step 1, the high-pass filtering rule is to allow frequencies above a certain cutoff frequency to pass through while attenuating lower frequencies, thus removing low-frequency interference from the signal. The transfer function form is:

[0016]

[0017] Filter out frequencies less than ω c The low-frequency components retain frequencies higher than ω. c The high-frequency components.

[0018] As a further embodiment of the present invention, in step 1, the high-pass filter allows high-frequency or AC components in the signal to pass through, while the filter that suppresses low-frequency or DC components is used to retain signals with frequencies greater than the cutoff frequency.

[0019] A low-pass filter is a filter that allows low-frequency or DC components in a signal to pass through while suppressing high-frequency components or interference and noise. It is used to retain signals below the cutoff frequency.

[0020] The primary frequency modulation control method provided in this embodiment of the invention has the following beneficial effects:

[0021] After adopting the new feedwater primary frequency regulation technology, the ultra-supercritical units in power plants can adjust the water volume on the high-pressure heater feedwater side and thus change the steam extraction volume on the steam side, resulting in stable temperature changes, which is conducive to the stable operation of the unit.

[0022] This new water supply frequency regulation technology provides an effective auxiliary means for primary frequency regulation of the power grid, improves the accuracy and speed of frequency regulation response, and better meets the frequency regulation requirements of the power grid for generating units. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the water supply frequency regulation system.

[0024] Figure 2 Diagram of a frequency modulation system;

[0025] Figure 3 Layout diagram of frequency regulation bypass for water supply lines 1 and 2;

[0026] Figure 4 This is a layout diagram of the frequency regulation bypass for water supply lines 3 and 4. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] like Figure 1 As shown, in this embodiment of the invention, it includes:

[0030] Step 1: Design low-pass high-filter and high-pass low-filter to decompose the frequency signal and obtain its low-frequency and high-frequency components respectively.

[0031] Low-pass filtering is a filtering method that allows low-frequency signals to pass through normally, while blocking or attenuating high-frequency signals exceeding a set threshold. However, the extent of blocking or attenuation varies depending on the frequency and the specific filtering procedure (purpose). A common transfer function form is...

[0032]

[0033] Filter out frequencies greater than ω c High-frequency components, with frequencies less than ω. c The low-frequency components.

[0034] A high-pass filter, also known as a low-cutoff filter or low-impedance filter, is a filter that allows frequencies above a certain cutoff frequency to pass through while significantly attenuating lower frequencies. It removes unwanted low-frequency components or low-frequency interference from the signal. A common transfer function form is...

[0035]

[0036] Filter out frequencies less than ω c The low-frequency components retain frequencies higher than ω. c The high-frequency components.

[0037] The difference between a high-pass filter and a low-pass filter is that a high-pass filter allows high-frequency or AC components of a signal to pass through while suppressing low-frequency or DC components. A low-pass filter, on the other hand, allows low-frequency or DC components of a signal to pass through while suppressing high-frequency components, interference, and noise. In general, a low-pass filter preserves signals with frequencies below the cutoff frequency, while a high-pass filter preserves signals with frequencies above the cutoff frequency.

[0038] Step 2: Send the low-frequency component to the condensate flow bypass valve controller. Adjust the bypass valve opening according to the low-frequency component to reduce the low-pressure cylinder pumping by condensate throttling, thereby adjusting the load to meet the low-frequency component of the frequency difference signal. The purpose is that the low-frequency component has a relatively small amplitude change and a slow frequency, while condensate throttling has a small impact on load adjustment, thus meeting the adjustment requirements of the low-frequency component.

[0039] Step 3: Send the low-frequency component as a feedforward signal into the low water level adjustment logic to realize the early prediction and adjustment of the low water level.

[0040] Step 4: Send the high-frequency component to the feedwater flow bypass valve controller. Based on the high-frequency component, adjust the opening of the feedwater bypass valve to reduce high-pressure cylinder air extraction through feedwater throttling, thereby quickly adjusting the load to meet the high-frequency component of the frequency difference signal. The function is that the high-frequency component has a relatively large amplitude variation and a fast frequency, while feedwater throttling has a significant impact on load adjustment, thus meeting the adjustment requirements of the high-frequency component.

[0041] Step 5: Send the high-frequency component as a feedforward signal into the high-pressure water level adjustment logic to realize the advance prediction and adjustment of the high-pressure water level.

[0042] Example 1:

[0043] 1. New technology for primary frequency regulation of water supply

[0044] By adjusting the feedwater flow rate into the high-pressure heater of the power plant, the steam extraction rate is changed, which in turn changes the steam inlet rate to the turbine, thus achieving primary frequency regulation. A schematic diagram of the feedwater frequency regulation system is shown below. Figure 1 As shown.

[0045] 2. Application effect of primary frequency regulation in water supply

[0046] After adopting the new technology of primary frequency regulation of feedwater in ultra-supercritical power plants, the steam extraction volume on the steam side can be changed by adjusting the water volume on the high-pressure heater feedwater side, resulting in stable temperature changes and facilitating the stable operation of the unit.

[0047] Tests have shown that, provided the quality of the high-pressure heater water level control meets the requirements, it is technically feasible to achieve primary frequency regulation of the unit using primary frequency regulation of the feedwater.

[0048] This new water supply frequency regulation technology provides an effective auxiliary means for primary frequency regulation of the power grid, improves the accuracy and speed of frequency regulation response, and better meets the frequency regulation requirements of the power grid for generating units.

[0049] 3. Condensate primary frequency regulation scheme

[0050] The load regulation effect of condensate throttling is characterized by fast rate, small amplitude, and temporary nature, which conforms to the regulation characteristics of primary frequency regulation.

[0051] The principle of condensate throttling can be summarized as adjusting the condensate flow rate by increasing the low-pressure heater bypass, with a capacity selection of 25% of the condensate flow rate. This affects the heat balance of the low-pressure heater, thereby changing the steam extraction rate from the low-pressure cylinder and ultimately altering the unit load. For ease of description of the energy storage in the condensate throttling system, referencing the concept of volumetric heat storage coefficient, the throttling energy storage coefficient is defined as follows: the portion of heat carried by the change in condensate flow rate affected by adjusting the low-pressure heater bypass that can be converted into electrical energy, expressed in kJ / kg.

[0052] The calculation process for the "power increment - throttling flow" gain coefficient is as follows: Changes in the unit's condensate flow rate will alter the power contribution of the deaerator and the extraction steam of each stage of low-pressure heaters, specifically the power contribution of heaters 4 through 8. Based on operational data analysis, the change in the extraction steam power of the No. 5 low-pressure heater caused by condensate throttling can be used as a characterizing quantity of the unit's power change caused by throttling. After performing soft-sensor calculations on parameters without measurement points, such as extraction steam flow rate, a nonlinear calculation model for the condensate throttling power is obtained.

[0053] The throttling energy storage coefficient was verified using experimental data on condensate throttling disturbance. At 100% rated load, the throttling flow rate was 350 t / h, resulting in a 6.7 MW increase in the power of the computer unit.

[0054] 4. Frequency Modulation Scheme

[0055] like Figure 2 As shown, it is proposed to add a primary frequency regulation bypass for condensate at the outlet of No. 7 low-pressure heater and a primary frequency regulation bypass for feedwater at the outlet of No. 3 high-pressure heater.

[0056] 5. Scheme Design

[0057] A feedwater frequency regulation bypass is added to the feedwater outlet of Unit 1 and Unit 2 at the No. 3 high-pressure heater outlet, connected to the feedwater gate valve outlet of Unit 1, with a capacity of 25% of the feedwater flow rate and a pipe diameter of Φ273×30.

[0058] The frequency modulation bypass is equipped with a hydraulic regulating valve with an opening time of 2-3 seconds, and electric gate valves are installed before and after it. The frequency modulation bypass layout is relatively easy to implement; the layout of the No. 1 and No. 2 water supply frequency modulation bypasses is shown below. Figure 3 The layout of the frequency regulation bypass for water supply lines 3 and 4 is shown in the attached diagram. Figure 4 .

[0059] During operation, the hydraulic regulating valve is quickly opened according to the frequency regulation command to reduce the feedwater flow of the high-pressure heater, thereby reducing the amount of steam extracted and increasing the turbine output to achieve the purpose of rapid load increase.

[0060] 6. Verification of frequency modulation bypass capacity

[0061] The frequency regulation capability of Unit 3 was initially determined by verifying its frequency regulation bypass capacity. The feedwater frequency regulation bypass is set to 25% of the feedwater capacity, i.e., a flow rate of 503.5 t / h, with a pipe diameter of Φ273×30. When the bypass is open, the steam flow rate of the first extraction stage is reduced by approximately 28.6 t / h, the second extraction stage by approximately 40.6 t / h, and the third extraction stage by approximately 18.9 t / h. The turbine's steam intake increases accordingly by approximately 88.1 t / h, increasing the unit's output by approximately 12.2 MW. The hydraulic regulating valve opens in 2–3 seconds, allowing the unit to increase its output by 12.2 MW within 3 seconds, meeting the primary frequency regulation requirements of the power grid.

[0062] TMCR before frequency modulation FM bypass After frequency modulation enthalpy extraction kJ / kg 3063.4 3063.4 Second enthalpy kJ / kg 2984.5 2984.5 Triple enthalpy kJ / kg 3415.5 3415.5 Low-pressure cylinder exhaust enthalpy kJ / kg 2449.5 2449.5 One draw t / h 114.5 25％ 28.6 Two pumps t / h 162.5 25％ 40.6 Three-pump volume t / h 75.4 25％ 18.9 High-pressure cylinder efficiency 0.85 0.85 Low-pressure cylinder efficiency 0.9 0.9 One pump power generation MW 14.9 3.7 Secondary pumping power generation MW 18.5 4.6 Three pumps generate electricity MW 15.5 3.9 Total power generation MW 48.9 12.2 Water supply t / h 2014 25％ 503.5

[0063] 7. Frequency Modulation Control Strategy

[0064] Control strategy

[0065] The primary frequency regulation operation is relatively short, requiring an instantaneous increase in the unit's power output. Improving the primary frequency regulation capability mainly relies on changes in turbine-side control. This project employs a "condensate primary frequency regulation bypass" and a "feedwater primary frequency regulation bypass" scheme. When increased unit output is required, the condensate flow regulating bypass valve is opened. By adjusting the condensate flow rate entering the low-pressure heater and the feedwater flow rate entering the high-pressure heater, a portion of the condensate is diverted through the bypass pipeline, reducing the condensate flow rate into the heater. This causes the heater pressure to rise, reducing the extraction steam volume and increasing the flow rate through the turbine's flow path, resulting in an instantaneous increase in power, thus achieving the purpose of primary frequency regulation.

[0066] Control strategy

[0067] The process of multi-scale signal decomposition based on rate of change can be viewed as follows: First, a signal is decomposed into a part that passes the rate limit (slow-changing part) and the remaining part (fast-changing part). Then, the fast-changing part is further decomposed, and this process is repeated n times to decompose the signal into components with different rates of change. Each rate-limiting element corresponds to the variable load regulation rate capability of the controlled object: the slow-changing, continuous first-level signal is suitable for fuel energy, and the fast-changing, temporary second-level signal is suitable for condensate and feedwater combined frequency regulation. The feedwater frequency regulation range is large, while the condensate frequency regulation range is small.

[0068] To meet the load increase rate requirements of the "Regulations on the Operation and Management of Primary Frequency Regulation of Generating Units in North China Power Grid" (hereinafter referred to as the "Regulations"), the following action logic for the frequency regulation bypass of condensate and feedwater is added: When the power grid requests a rapid load increase, the feedwater and condensate frequency regulation bypass isolation valves are opened respectively, and the frequency regulation bypass is activated. The opening of the regulating valve in the frequency regulation bypass is adjusted according to the load increase rate requirement requested by the power grid. Based on the process expert's information, taking Unit #3 of Dingzhou Power Plant as an example, under the maximum load increase rate required by the "Regulations", both bypass valves are fully open, the feedwater bypass flow is controlled at 503.5 t / h, and the condensate bypass flow is controlled at 350 t / h. If the central dispatch reduces the load increase rate requirement, the regulating valve opening is reduced by a certain proportion. The valve opening command is calculated and given by the DCS based on the load increase rate parameters. When the power grid cancels the rapid load increase requirement or the unit has completed the power grid's load increase requirement, the frequency regulation bypass isolation valve is closed, and the frequency regulation bypass is disconnected.

[0069] After the automatic adjustment of the heater water level and the frequency modulation action, the water inlet to the heater suddenly drops, the heater pressure rises rapidly, the steam extraction rate decreases, and the liquid level drops rapidly. In order to stabilize the heater water level, a feedforward command signal needs to be added to the corresponding heater water level adjustment loop to improve the control response speed of the heater water level, so as to achieve a step action. At the same time, the automatic adjustment parameters are optimized to make the recovery of the feedforward quantity smooth and ensure the stability of the heater liquid level.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of controlling frequency modulation, characterized in that, The primary frequency modulation control method includes the following steps: Step 1: Design low-pass high-filter and high-pass low-filter filters to decompose the frequency signal and obtain its low-frequency and high-frequency components respectively. Step 2: Send the low-frequency component to the condensate flow bypass valve controller. Adjust the bypass valve opening according to the low-frequency component. Reduce the low-pressure cylinder air extraction by throttling the condensate and adjust the load to meet the low-frequency component of the frequency difference signal. Step 3: Send the low-frequency component as a feedforward signal into the low-level water supply adjustment logic to predict and adjust the low-level water supply in advance; Step 4: Send the high-frequency component to the feedwater flow bypass valve controller, and adjust the opening of the feedwater bypass valve according to the high-frequency component. Reduce the high-pressure cylinder air extraction by throttling the feedwater, and adjust the load to meet the high-frequency component of the frequency difference signal. Step 5: Send the high-frequency component as a feedforward signal into the high-pressure water level adjustment logic to predict and adjust the high-pressure water level in advance.

2. The method of claim 1, wherein, In step 1, the high-pass low-pass filter allows high-frequency or AC components in the signal to pass through while suppressing low-frequency or DC components, thus retaining signals above the cutoff frequency.

3. The method of claim 1, wherein, In step 1, the low-pass high-filter allows low-frequency or DC components in the signal to pass through while suppressing high-frequency components or interference and noise, thus preserving signals below the cutoff frequency.

4. The method of claim 1, wherein, By adjusting the feedwater flow rate into the high-pressure heater of the power plant, the steam extraction rate is changed, which in turn changes the steam inlet rate of the steam turbine.

5. The method of claim 1, wherein, The function of this primary frequency regulation control method is evaluated using a throttling energy storage coefficient, which is the portion of the heat carried by the change in the steam extraction volume on the low-pressure cylinder side of the turbine caused by the change in condensate flow rate due to the adjustment of the low-pressure bypass that can be converted into electrical energy.

6. The method of claim 5, wherein, The unit for calculating the throttling energy storage coefficient is kJ / kg.

Images