An improved method for frequency regulation of a hydro-generator set under no-load condition

Abstract

The application discloses an improved method for frequency regulation of a hydroelectric generator set under no-load working condition, which comprises the following steps: limiting the input frequency difference in the proportional, integral and differential links; adding a preset no-load opening degree to the total output link of the PID to regulate the frequency PID, wherein the no-load opening degree is the corresponding guide vane opening degree when the unit is under no-load working condition and maintains at the rated frequency; finding the no-load opening degree by using the interpolation method according to the preset array of the water head and the no-load opening degree, inversely calculating the maximum value of the integral output limitation by using the no-load opening degree, and limiting the integral output; and when the unit is under no-load working condition, temporarily locking the PID calculation and keeping the current comprehensive guide vane opening degree unchanged if the unit temporarily has no demand for synchronous grid connection, so that the stability of the frequency is controlled. The application realizes the speediness and stability control requirements of the frequency control of the hydroelectric generator set.

Description

Technical Field

[0001] This invention relates to an improved method for frequency regulation of a hydro-generator unit under no-load conditions, belonging to the field of hydro-generator technology. Background Technology

[0002] Currently in China, most hydropower unit speed governors use digital speed governors, with frequency control employing classic PID regulation. When the unit operates under no-load conditions, the requirement is to quickly and accurately stabilize the unit's frequency near the rated frequency to provide the technical conditions for rapid grid connection. Conventional control methods suffer from slow frequency rise, large overshoot, and poor accuracy. Figure 1 This is a common block diagram of the frequency regulation principle of a speed controller.

[0003] Figure 1 As can be seen, the difference between the frequency setpoint and the frequency feedback is used to obtain Δf, which is then sent to the PID module for calculation to obtain the PID output. This output is then applied to the actuator to control the frequency of the hydro-generator unit.

[0004] During the process of the unit accelerating from standstill to rated speed, due to the inherent inertia of the unit (the magnitude of inertia varies depending on the type and mass of the unit), if the unit needs to start up to rated speed quickly, the PID parameters cannot be set too high (setting them too high will lead to instability in small frequency difference regulation). Therefore, it can only be started with small parameters and slow adjustment, otherwise overshoot will occur.

[0005] Secondly, in the classic PID control, the integral component is calculated very quickly during dynamic control. When the frequency deviates significantly from the setpoint, it can easily calculate a large value in a short time. When frequency overshoot occurs, certain limitations and nonlinear processing of the integral are needed to prevent integral saturation and excessive overshoot.

[0006] Therefore, the classic PID parameter settings and control strategies are difficult to meet the requirements for precise and rapid frequency adjustment. Improvements to the control methods are needed to achieve precise frequency control of hydropower units. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide an improved method for frequency regulation of hydro-generator units under no-load conditions, so as to achieve the speed and stability control requirements of frequency control of hydro-generator units.

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0009] This invention provides an improved method for frequency regulation of a hydro-generator unit under no-load conditions, comprising:

[0010] In the input stage of frequency difference, the frequency difference of the input is restricted in the proportional, integral and derivative stages respectively;

[0011] A preset no-load opening is added to the output stage of the PID controller to adjust the frequency. The no-load opening is the guide vane opening when the unit is in no-load condition and maintains the rated frequency.

[0012] Based on the preset array of head and no-load opening, the no-load opening is found by interpolation, and the maximum value of the integral output limit is calculated by using the no-load opening, and the integral output is limited.

[0013] When the unit is unloaded, if there is no need for synchronous grid connection, the PID calculation is temporarily locked, the current integrated guide vane opening is kept unchanged, and the frequency stability is controlled.

[0014] Furthermore, in the input stage of the frequency difference, the input frequency difference is limited in the proportional, integral and derivative stages respectively, wherein the proportional stage is limited to ±5Hz, the integral stage is limited to ±1Hz, and the derivative stage is limited to ±1Hz.

[0015] Furthermore, the addition of a preset no-load opening to the overall output stage of the PID controller to adjust the frequency PID includes:

[0016] A preset no-load opening degree Ynld is added to the PID output stage, wherein the no-load opening degree and the power station head are in a corresponding relationship.

[0017] When the unit starts up, the PID output is temporarily locked, and the overall guide vane opening is directly set to 0.9*Ynld. When the frequency is close to 95% of the target value, the PID is then engaged to calculate the frequency. At this time, the overall guide vane opening is set to Ypid + Ynld, where Ypid is the PID output.

[0018] Furthermore, the correspondence between the no-load opening degree and the power station head is obtained based on years of power station operation data.

[0019] Furthermore, the maximum value of the integral output limit is calculated using the no-load opening degree, as shown in the following formula:

[0020] Yi_Max = 0.8 * Ynld - Yp - Yd

[0021] Where Yi_Max is the maximum limit of the integral output; Ynld is the no-load opening degree; Yp is the proportional output; and Yd is the derivative output.

[0022] Furthermore, the step of keeping the current integrated guide vane opening constant and controlling the stability of the frequency includes:

[0023] When no synchronization signal is received, Ypid is assigned to the preset intermediate value Ypid_Temp of the PID output only once, then Ypid = 0, and then the combined guide vane opening setpoint = Ypid_Temp + Ynld;

[0024] When a synchronization signal is received, the combined guide vane opening is given by Ypid + Ynld.

[0025] Furthermore, it also includes: filtering the frequency sample values ​​based on the square root property of the numerical values, specifically as follows:

[0026] The process involves taking the square root of the current sample value and the sample value from the previous period, and then multiplying the two values. The formula is as follows: Where p is the processed sampled value, p (t-1) p is the current sampled value. (t) This is the sampled value from the previous period.

[0027] If the burrs are dense, use a longer processing cycle, as shown in the following formula: Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0028] 1. This invention provides an improved method for frequency regulation of a hydro-generator unit under no-load conditions. To achieve the speed and stability control requirements of frequency control of the hydro-generator unit, it proposes to add a limit at the PID input and superimpose the no-load opening degree on the PID integral output and the total PID output; thus improving the classic frequency PID regulation control method of the governor.

[0029] 2. This invention provides an improved method for frequency regulation of a hydro-generator unit under no-load conditions. It proposes a method to find the no-load opening degree based on the head using interpolation, and then use the no-load opening degree to back-calculate the maximum value of the integral output limit, thereby preventing the PID calculation from being too fast and the integral output from being too excessive.

[0030] 3. This invention provides an improved method for frequency regulation of a hydro-generator unit under no-load conditions. It proposes that when the unit is under no-load, if there is no need for synchronous grid connection, the PID calculation is temporarily locked, and the current comprehensive guide vane opening (comprehensive output) is kept unchanged to achieve stable system operation.

[0031] 4. This invention provides an improved method for frequency regulation of a hydro-generator unit under no-load conditions. Addressing the adverse effects of frequency fluctuations (caused by the unit's own inertia, hydraulic factors, or electromagnetic interference) on frequency regulation, a novel frequency sampling value filtering method is proposed based on the square root characteristic (nonlinear bending). This method effectively weakens sampling spikes without compromising accuracy and response speed, thereby improving the stability of frequency regulation. Attached Figure Description

[0032] Figure 1 This is a block diagram illustrating the frequency regulation principle of the speed controller under no-load conditions in the background art of this invention.

[0033] Figure 2 This is a block diagram of the frequency regulation principle of the improved speed governor under no-load conditions provided in the embodiments of the present invention;

[0034] Figure 3 This is a schematic diagram of a comprehensive processing method provided in an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of unit frequency sampling provided in an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the unit frequency PID regulation module provided in an embodiment of the present invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment introduces an improved method for frequency regulation of a hydro-generator unit under no-load conditions, including:

[0040] In the input stage of frequency difference, the frequency difference of the input is restricted in the proportional, integral and derivative stages respectively;

[0041] A preset no-load opening is added to the output of the PID controller to regulate the frequency using PID control. The no-load opening is the guide vane opening when the unit is operating under no-load conditions and maintaining the rated frequency.

[0042] Based on the preset array of head and no-load opening, the no-load opening is found by interpolation, and the maximum value of the integral output limit is calculated by using the no-load opening, and the integral output is limited.

[0043] When the unit is unloaded, if there is no need for synchronous grid connection, the PID calculation is temporarily locked, the current integrated guide vane opening is kept unchanged, and the frequency stability is controlled.

[0044] The improved method for frequency regulation of a hydro-generator unit under no-load conditions provided in this embodiment involves the following steps in its application:

[0045] (1) Control methods for fast start-up and suppression of overshoot in high-frequency regulation

[0046] The improved principle block diagram of the speed controller frequency regulation is as follows: Figure 2 As shown in the software control block diagram, the input frequency difference is limited in the proportional, integral, and derivative stages. The proportional limit is ±5Hz, the derivative limit is ±1Hz, and the differential limit is ±1Hz. Limiting the frequency difference in the input stage restricts the PID calculation speed within a certain range, effectively suppressing overshoot problems caused by large frequency differences. Simultaneously, to prevent excessive integral saturation, there is also a maximum limit on the output; the value of this limit is based on empirical data.

[0047] At the same time, a preset "no-load opening" is added to the PID output stage (the guide vane opening that the unit can maintain at the rated speed when the unit is in no-load condition; symbol: Ynld).

[0048] There is a corresponding relationship between the no-load opening degree and the power station head. This relationship can be obtained from years of power station operation data, as shown in Table 1, where the data relationship is for illustrative purposes only. Since the water head of the hydropower station changes continuously, in order to obtain the no-load opening degree under each water head, the program uses interpolation to perform linear processing or fits it into an equation for calculation.

[0049] Table 1. Correspondence between 9 water heads and no-load opening degree

[0050]

[0051] Since the no-load opening corresponding to the rated speed is known in advance, the Ypid output is temporarily locked during unit startup, and the overall guide vane opening setpoint is directly set to 0.9*Ynld. When the frequency approaches 95% of the target value, the PID controller is then engaged for frequency calculation, at which point the overall guide vane opening setpoint = Ypid + Ynld. This method effectively suppresses start-up overshoot and enables rapid start-up.

[0052] The maximum value of the integral output limit, Yi_Max, is calculated as follows:

[0053] Yi_Max = 0.8 * Ynld - Yp - Yd

[0054] In the formula, Yi_Max is the maximum limit of the integral output; Ynld is the no-load opening degree; Yp is the proportional output; and Yd is the differential output.

[0055] (2) Frequency stability control.

[0056] When the generator unit is under no-load operation, the governor maintains the unit frequency near the setpoint (target value), with the ultimate goal of enabling the unit to track the grid frequency and achieve grid connection. However, due to power plant operation requirements, the unit may need to operate under no-load for a period of time without immediate grid connection. If the governor continuously performs PID control during this time, it will lead to frequent adjustments of the governor's mechanical actuator and relay, causing oil pressure losses and frequent pump start-ups and shutdowns. To reduce unnecessary sensitive control and enhance the stability of the governor and mechanical hydraulic actuator, the overall guide vane opening setpoint can be kept constant, as follows:

[0057] When no synchronization signal is received, Ypid is assigned to Ypid_Temp (defined as the intermediate value of the PID output) only once, then Ypid = 0, and then the combined guide vane opening setpoint = Ypid_Temp + Ynld.

[0058] When a synchronization signal is received, the combined guide vane opening setting is calculated as Ypid + Ynld. The entire logic process can be used... Figure 3 express.

[0059] (3) Frequency feedback filtering module

[0060] Figure 4 This diagram illustrates the frequency sampling and recording of a generator set. The frequency signal is typically input as a 5-12V high-frequency pulse signal to the high-speed counting module of the speed governor. After analog-to-digital conversion, it is converted into the corresponding code value. Generally, 1Hz corresponds to 4000, and 50Hz corresponds to 200000.

[0061] Assume the frequency signal at point A is 50.3Hz, corresponding to a code value of 201200; the analog frequency signal at point B (the sampling point of the next cycle) is 51.5Hz, corresponding to a code value of 206000; if mean filtering is used, the processing method is (A+B) / 2 = 203600. This invention uses a method of taking the square root of the current sample value and the sample value of the previous cycle, and then multiplying the two values, i.e.: Using the square root method, based on the characteristics of the square root data curve (non-linear bending), it is known that instantaneous distortion peaks can be effectively weakened. If the spikes are dense, this method can be used... That is, to increase the period. Taking the above values ​​as an example, the sampled values ​​after processing points A and B should be: This value is closer to the actual value than the result calculated by the mean method.

[0062] This filtering function can be activated or deactivated during large frequency fluctuations in the generator set without substantially affecting power regulation. When frequency regulation enters the convergence phase and steady state, such as within a 5% deviation, activating it is beneficial for precise and stable frequency control.

[0063] (4) Overall design of frequency adjustment module

[0064] If the method proposed in this project is considered as a dedicated control module, it can be used... Figure 5 The input signals are represented as follows: external switch signals are power-on command and synchronization command; analog input is water head; and frequency measurement pulse input is unit frequency feedback.

[0065] The regulating module receives the input signal, performs calculations and switching, and finally outputs the "comprehensive guide vane opening setpoint". The comprehensive guide vane opening setpoint drives the unit's water guiding mechanism (actuator), thereby controlling the unit's speed.

[0066] The entire regulation process, from unit startup to grid connection, can be briefly described as follows:

[0067] 1) When the speed controller receives the start-up command from the external (monitoring system), the speed controller enters the "start-up process" and retrieves the start-up curve. Based on the start-up pattern, it directly changes the guide vane opening setpoint (also known as: opening setpoint, guide vane setpoint, i.e. the target value of the actuator), thereby driving the actuator to start the unit.

[0068] This process is called the "power-on process," the control mode is "open mode," and the frequency is set to 50 Hz.

[0069] 2) When the unit operates at more than 95% capacity, the governor switches to "no-load" mode and enters frequency mode, where the primary task of regulation is the target frequency. At this time, frequency PID calculation is activated, and the unit frequency is filtered by the program to form negative feedback.

[0070] At this point, the frequency is given, and the control target is 50Hz.

[0071] 3) Enter frequency mode, and the sum of the guide vane setpoint = PID calculation output (Ypid) + no-load opening (Ynld).

[0072] The relationship between the no-load opening and the head is shown in Table 9, and can be automatically calculated based on the head.

[0073] 4) The integrated guide vane setting is amplified by hydraulics to drive the actuator, which in turn drives the guide vane to control the water flow rate and thus the unit speed.

[0074] 5) However, when an external synchronization and grid connection order is issued, the frequency setting is changed from 50Hz to: grid frequency + 0.05Hz, which is the target value of the unit frequency (speed). This ensures that the unit frequency (speed) tracks the grid frequency, allowing the unit to meet the frequency accuracy requirements for grid connection.

[0075] Since the specific details of PID regulation have been explained above, only the entire control conversion process is briefly described here.

[0076] The beneficial effects of this invention are as follows:

[0077] The speed governor is the core equipment for frequency control of hydropower units. The industry practice is to use a conventional PID model for frequency regulation and control. However, due to the instability of the unit's frequency caused by hydraulic factors, and the change in operating conditions from standstill to start-up to no-load, conventional PID control cannot meet the control requirements for speed and stability during such startup processes.

[0078] Therefore, for large fluctuations (large frequency differences) in regulation, based on the known no-load opening degree, during unit startup, the comprehensive guide vane opening setpoint is changed only according to the no-load opening degree, and the PID controller is not involved in the calculation. Once the frequency approaches the target value, the PID controller is then engaged in calculation. This effectively reduces start-up overshoot problems.

[0079] Meanwhile, to prevent the PID calculation from being too fast and the integral output from being too excessive (excessive integral calculation can easily lead to saturation and is not conducive to reverse callback), frequency difference limits are set at the inputs of proportional, integral and derivative, and these limits are empirical values; a limit is also added to the integral output, and this limit is calculated based on the no-load opening degree, and the calculation method is described above.

[0080] Secondly, this invention also proposes a new filtering method based on the square root characteristic for unit frequency sampling, which effectively weakens sampling spikes without compromising accuracy and response speed, thereby improving the stability of frequency regulation.

[0081] This invention is a pure software control strategy with a simple control structure and easy programming; the filtering method is simple to calculate, effective and feasible.

[0082] Among them: Guide vanes (movable guide vanes) and guide vane opening: These are movable blades installed in front of the runner of a reaction turbine, evenly distributed along the circumference, and adjustable by rotation. They are used to guide and cut off water flow and regulate the flow rate through the turbine. Guide vanes are part of the water intake system of a hydroelectric power station, and their function is similar to a sluice gate controlling the water flow. Guide vane opening is the size of the opening when the guide vane is open or closed.

[0083] Hydro-generator set: includes a turbine, a generator, and the connecting shaft. The turbine is the prime mover, absorbing water energy, and the generator generates active power when connected to the grid.

[0084] No-load opening: When the unit is in no-load condition and maintains the rated frequency, the corresponding guide vane opening is the no-load opening.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An improved method for frequency regulation of a hydro-generator unit under no-load conditions, characterized in that, include: In the input stage of frequency difference, the frequency difference of the input is restricted in the proportional, integral and derivative stages respectively; A preset no-load opening is added to the output stage of the PID controller to adjust the frequency. The no-load opening is the guide vane opening when the unit is in no-load condition and maintains the rated frequency. Based on the preset array of head and no-load opening, the no-load opening is found by interpolation, and the maximum value of the integral output limit is calculated by using the no-load opening, and the integral output is limited. When the unit is unloaded, if there is no need for synchronous grid connection, the PID calculation is temporarily locked, the current comprehensive guide vane opening is kept unchanged, and the frequency stability is controlled. The method of adding a preset no-load opening to the overall output stage of the PID controller to adjust the frequency PID includes: A preset no-load opening degree Ynld is added to the PID output stage, wherein the no-load opening degree and the power station head are in a corresponding relationship. When the unit starts up, the PID output is temporarily locked, and the overall guide vane opening is directly set to 0.9*Ynld. When the frequency is close to 95% of the target value, the PID is then engaged to calculate the frequency. At this time, the overall guide vane opening is set to Ypid + Ynld, where Ypid is the PID output. The maximum value of the integral output limit is calculated by back-calculating the no-load opening degree, using the following formula: Yi_Max = 0.8 * Ynld - Yp - Yd; Where Yi_Max is the maximum limit of the integral output; Ynld is the no-load opening degree; Yp is the proportional output; and Yd is the derivative output. The method of keeping the current integrated guide vane opening constant and controlling the stability of the frequency includes: When no synchronization signal is received, Ypid is assigned to the pre-set intermediate value Ypid_Temp of the PID output. This assignment is done only once, and then Ypid = 0. The overall guide vane opening setpoint is then set to Ypid_Temp + Ynld. When a synchronization signal is received, the overall guide vane opening is given by Ypid + Ynld.

2. The improved method for frequency regulation of a hydro-generator unit under no-load conditions according to claim 1, characterized in that: In the input stage of frequency difference, the input frequency difference is limited in the proportional, integral and derivative stages respectively. The proportional stage is limited to ±5Hz, the integral stage is limited to ±1Hz, and the derivative stage is limited to ±1Hz.

3. The improved method for frequency regulation of a hydro-generator unit under no-load conditions according to claim 1, characterized in that: The correspondence between the no-load opening degree and the power station head is obtained based on years of power station operation data.

4. The improved method for frequency regulation of a hydro-generator unit under no-load conditions according to claim 1, characterized in that, Also includes: Based on the square root property of the numerical values, the frequency sample values ​​are filtered. The specific method is as follows: The process involves taking the square root of the current sample value and the sample value from the previous period, and then multiplying the two values. The formula is as follows: ,in The processed sampled values, This is the current sampled value. This is the sampled value from the previous period; If the burrs are dense, use a longer processing cycle, as shown in the following formula: .

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