Synchronization method for limiting grid-connected reactive impact of water-turbine generator set

Abstract

The invention discloses a synchronization method for limiting grid-connected reactive power impact of a water-turbine generator set, and the method comprises the steps: calculating an additional allowable voltage difference required for limiting the reactive power impact through building a quantitative relation model between a generator grid-connected reactive power impact amplitude and a generator end-system voltage difference. In specific implementation, the maximum allowable pressure difference, the frequency difference, the phase angle difference and the reactive impact amplitude are set firstly; calculating an additional allowable voltage difference according to the latter; collecting and comparing voltage at a machine side and voltage at a system side in real time; when the five conditions that the phase sequence is the same, the voltage difference is smaller than a traditional and additional allowable value, and the phase angle difference and the frequency difference are both in an allowable range are met at the same time, switching-on grid connection is triggered. According to the method, quantitative limitation and active suppression of grid-connected reactive power impact are realized, reactive power disturbance and electrical mechanical stress during grid connection are effectively reduced, and the stability of unit grid connection and the safe and stable operation level of a power system are improved. Actual operation data verification shows that the method is high in calculation accuracy and remarkable in control effect.

Description

Technical Field

[0001] This invention belongs to the field of hydro-generator grid connection technology, and in particular relates to a synchronization method for limiting reactive power impact during grid connection of hydro-generator units. Background Technology

[0002] Before a generator is put into operation in the power system, its state variables are often not equal to those of the grid's parallel bus. Appropriate operations must be performed on the generator set to ensure it meets the paralleling conditions before the circuit breaker can be closed for grid connection. The process of connecting a synchronous generator to the grid is called synchronization or grid connection. During paralleling, it is necessary to avoid generating large electromagnetic and mechanical shocks to prevent damage to the synchronous generator and interference to the grid. For the generator stator current and electromagnetic torque to be zero at the instant the circuit breaker closes, the instantaneous values ​​of the electromotive force of each phase of the generator must be completely consistent with the instantaneous values ​​of the corresponding phase voltages at the grid terminals. That is, the ideal generator grid connection conditions include: the generator frequency is the same as the system frequency; the generator output voltage amplitude is the same as the system voltage amplitude and has the same waveform; the generator phase sequence is the same as the system phase sequence; and the generator output voltage phase is consistent with the system voltage phase.

[0003] The process of adjusting a generator to fully meet grid connection conditions before closing it is called the quasi-synchronous method. Using this method minimizes inrush current and reactive power disturbance to the grid, making it the primary grid connection method in power system operation. During the adjustment process, synchronization indicators are commonly used to determine the fulfillment of conditions. Quasi-synchronous grid connection requires that, before closing, the generator to be connected be accelerated to near synchronous speed, energized, and its terminal voltage adjusted to match the grid voltage. Once the voltage amplitude and frequency conditions are met, based on the "constant lead time principle," the quasi-synchronous controller automatically selects an appropriate time to issue a closing command, and the unit is quickly pulled into synchronization after being connected to the power system.

[0004] Existing quasi-synchronous grid connection methods automatically monitor the frequency difference, voltage amplitude difference, and phase angle difference between the generator-side voltage and the system-side voltage by collecting data from both sides. When the phase sequence of the generator-side and system-side voltages is the same, and their frequency difference, amplitude difference, and phase angle difference are all within the maximum allowable range, a suitable synchronization time is calculated, and a closing command is issued one lead time in advance. After synchronization verification and blocking relay, the command is sent to the circuit breaker to complete grid connection. Generally, the maximum allowable frequency difference, maximum allowable voltage difference, and maximum allowable phase angle difference are all set empirically. Existing technology has the following drawbacks: First, there is currently a lack of methods for calculating the reactive power surge amplitude during generator grid connection reactive power regulation; second, existing methods for synchronizing hydro-generator units with the grid only set allowable voltage difference conditions, which cannot accurately limit the reactive power surge amplitude within the ideal range, potentially leading to excessive reactive power surge amplitude and affecting the safe and stable operation of the power system.

[0005] Therefore, a synchronization method is needed to limit the reactive power impact of hydro-generator units connected to the grid to solve the above problems. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a synchronization method for limiting the reactive power impact of hydro-generator units during grid connection. It aims to solve the problem that the existing synchronization methods only set the voltage difference allowable condition and cannot accurately limit the reactive power impact amplitude within the ideal range. It has the characteristics of effectively limiting the reactive power impact amplitude during the grid connection of hydro-generator units, improving the service life of circuit breakers, reducing the reactive power disturbance of the units, and improving the safety and stability of the power system.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit includes the following steps: S1, Set the maximum allowable differential pressure for simultaneous grid connection. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; S2, based on the maximum permissible grid-connected reactive power impact amplitude The additional allowable voltage difference was calculated. ; S3, collects and monitors the voltage on the machine side and the system side; S4. Determine whether the following five conditions are met simultaneously: Condition 1: The phase sequence of the voltage on the machine side and the system side is the same; Condition 2: The magnitude difference between the voltage at the machine terminal and the system side Less than or equal to the maximum permissible pressure difference And less than or equal to the additional permissible voltage difference. ; Condition 3: Phase angle difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible phase angle difference ; Condition 4: Frequency difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible frequency difference ; Condition 5: Lead time signal generation; S5. If the above five conditions are met simultaneously, calculate the appropriate synchronization time and issue a closing command one lead time in advance. After synchronization identification and blocking relay, the command is sent to the circuit breaker to complete grid connection.

[0008] Preferably, in step S2, the additional permissible voltage difference Calculated in the following way: ; Where K is the coefficient relating reactive power surge amplitude to grid voltage difference, in units of... .

[0009] Preferably, the relationship coefficient K is calculated using the following formula: ; in, This indicates the rated capacity of the transformer. This indicates the rated voltage of the transformer. This indicates the percentage of the transformer's impedance voltage drop. Indicates the voltage amplitude on the high-voltage side of the busbar. This indicates the rated voltage on the high-voltage side of the main transformer. This indicates the rated voltage on the low-voltage side of the main transformer.

[0010] Preferably, the difference between the generator terminal line voltage and the converted bus voltage is set to... When the reactive power is adjusted to its maximum value, the generator terminal voltage reaches the instantaneous grid connection voltage under the action of AVR regulation. At this time, the active power is stable, the power angle is considered to be 0, and all current is considered as reactive current. The corresponding single-phase reactive current is: ; The reactive power is: ; That is, the reactive power impact amplitude during the generator grid connection regulation process is: ; in, The impedance of the transformer has a nominal value; This is the low-voltage side equivalent value of the bus voltage.

[0011] Preferably, based on the transformer parameters, the rated capacity of the transformer is used. and rated voltage As the reference value, the corresponding reference value for impedance is: ; The calculated impedance of the transformer is: ; In the formula This is the voltage drop across the transformer impedance.

[0012] Preferably, the relationship coefficient K is calculated based on the following approximate formula: ; in, This indicates the maximum reactive power surge amplitude during the generator grid connection adjustment process. This represents the low-voltage side converted values ​​of the terminal line voltage and the bus voltage. The difference between them.

[0013] Preferably, the low-voltage side converted value of the bus voltage Calculated using the following formula: ; in, Indicates the voltage amplitude on the high-voltage side of the busbar. The transformer ratio between the low-voltage side and the high-voltage side of the main transformer.

[0014] Furthermore, the maximum permissible grid-connected reactive power surge amplitude The maximum allowable pressure difference is set based on the electrical parameters of the hydro-generator unit and transformer, as well as the requirements for safe and stable system operation; Maximum permissible frequency difference Maximum permissible phase angle difference Adjustments are made based on experience.

[0015] Furthermore, the range of values ​​for the relationship coefficient K is as follows: to .

[0016] Furthermore, the method is automatically executed by the quasi-synchronous controller of the hydro-generator unit, including automatically acquiring voltage, automatically judging five conditions, automatically calculating the grid connection time, and automatically issuing a closing command.

[0017] Preferably, a synchronizing device for limiting the reactive power impact of a hydro-generator unit connected to the grid is used to perform the aforementioned synchronizing method for limiting the reactive power impact of a hydro-generator unit connected to the grid. The device includes: The voltage acquisition module is used to acquire and monitor the terminal-side voltage and the system-side voltage; The parameter setting module is used to set the maximum allowable differential pressure. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; The calculation module is used to calculate the maximum allowable grid-connected reactive power surge amplitude. Calculate the additional allowable voltage difference ; The judgment module is used to determine, based on the signal acquired by the voltage acquisition module, whether the voltage phase sequence on the machine side and the system side are the same and the voltage amplitude difference is the same. Less than or equal to and less than or equal to Phase angle difference Less than or equal to Frequency difference Less than or equal to These five conditions; The control module is used to calculate a suitable synchronization time and issue a closing command one lead time in advance when the judgment module determines that the five conditions are met simultaneously, so as to control the circuit breaker to complete grid connection.

[0018] Preferably, a computer device includes a memory and a processor, which are communicatively connected to each other. The memory stores computer instructions, and the processor executes the computer instructions to perform the aforementioned synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit.

[0019] Preferably, a computer-readable storage medium stores computer instructions for causing a computer to execute the aforementioned synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit.

[0020] The beneficial effects of this invention are as follows: Based on the synchronous conditions of frequency difference, amplitude difference, phase sequence, and phase angle difference between the generator terminal voltage and the system voltage, this method, based on the reactive power regulation mechanism of generator grid connection, and combined with the electrical parameters of generator and transformer, converts the reactive power impact amplitude limit condition into an additional voltage difference condition, using five conditions as the judgment basis for the grid connection of hydro-generator units. This method effectively limits the reactive power impact amplitude during the grid connection of hydro-generator units, extends the service life of circuit breakers, reduces the reactive power disturbance of the units, and improves the safety and stability of the power system. Attached Figure Description

[0021] Figure 1 This is a flowchart of the synchronization condition judgment for limiting the reactive power impact of hydro-generator units connected to the grid in an embodiment of the present invention; Figure 2 This is a synchronous logic condition diagram for limiting the reactive power impact of the hydro-generator unit when it is connected to the grid in an embodiment of the present invention; Figure 3 This is a schematic diagram of the reactive power regulation process of the hydro-generator unit connected to the grid in an embodiment of the present invention; Figure 4 This is a schematic diagram showing the relationship between the reactive power impact amplitude and the grid voltage difference of a hydropower station unit during 20 grid connection events in an embodiment of the present invention. Detailed Implementation

[0022] Example 1: like Figure 1 As shown, a synchronization method for limiting the reactive power impact of a hydro-generator unit connected to the grid includes the following steps: S1, Set the maximum allowable differential pressure for simultaneous grid connection. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; S2, based on the maximum permissible grid-connected reactive power impact amplitude The additional allowable voltage difference was calculated. ; S3, collects and monitors the voltage on the machine side and the system side; S4, determine whether the following five conditions are met simultaneously, such as Figure 2 As shown: Condition 1: The phase sequence of the voltage on the machine side and the system side is the same; Condition 2: The magnitude difference between the voltage at the machine terminal and the system side Less than or equal to the maximum permissible pressure difference And less than or equal to the additional permissible voltage difference. ; Condition 3: Phase angle difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible phase angle difference ; Condition 4: Frequency difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible frequency difference ; Condition 5: Lead time signal generation; S5. If the above five conditions are met simultaneously, calculate the appropriate synchronization time and issue a closing command one lead time in advance. After synchronization identification and blocking relay, the command is sent to the circuit breaker to complete grid connection.

[0023] Preferably, in step S2, the additional permissible voltage difference Calculated in the following way: ; Where K is the coefficient relating reactive power surge amplitude to grid voltage difference, in units of... .

[0024] Preferably, the relationship coefficient K is calculated using the following formula: ; in, This indicates the rated capacity of the transformer. This indicates the rated voltage of the transformer. This indicates the percentage of the transformer's impedance voltage drop. Indicates the voltage amplitude on the high-voltage side of the busbar. This indicates the rated voltage on the high-voltage side of the main transformer. This indicates the rated voltage on the low-voltage side of the main transformer.

[0025] Preferably, the difference between the generator terminal line voltage and the converted bus voltage is set to... When the reactive power is adjusted to its maximum value, the generator terminal voltage reaches the instantaneous grid connection voltage under the action of AVR regulation. At this time, the active power is stable, the power angle is considered to be 0, and all current is considered as reactive current. The corresponding single-phase reactive current is: ; The reactive power is: ; That is, the reactive power impact amplitude during the generator grid connection regulation process is: ; in, The impedance of the transformer has a nominal value; This is the low-voltage side equivalent value of the bus voltage.

[0026] Preferably, based on the transformer parameters, the rated capacity of the transformer is used. and rated voltage As the reference value, the corresponding reference value for impedance is: ; The calculated impedance of the transformer is: ; In the formula This is the voltage drop across the transformer impedance.

[0027] Preferably, the relationship coefficient K is calculated based on the following approximate formula: ; in, This indicates the maximum reactive power surge amplitude during the generator grid connection adjustment process. This represents the low-voltage side converted values ​​of the terminal line voltage and the bus voltage. The difference between them.

[0028] Preferably, the low-voltage side converted value of the bus voltage Calculated using the following formula: ; in, Indicates the voltage amplitude on the high-voltage side of the busbar. The transformer ratio between the low-voltage side and the high-voltage side of the main transformer.

[0029] Furthermore, the maximum permissible grid-connected reactive power surge amplitude The maximum allowable pressure difference is set based on the electrical parameters of the hydro-generator unit and transformer, as well as the requirements for safe and stable system operation; Maximum permissible frequency difference Maximum permissible phase angle difference Adjustments are made based on experience.

[0030] Furthermore, the range of values ​​for the relationship coefficient K is as follows: to .

[0031] Furthermore, the method is automatically executed by the quasi-synchronous controller of the hydro-generator unit, including automatically acquiring voltage, automatically judging five conditions, automatically calculating the grid connection time, and automatically issuing a closing command.

[0032] Preferably, a synchronizing device for limiting the reactive power impact of a hydro-generator unit connected to the grid is used to perform the aforementioned synchronizing method for limiting the reactive power impact of a hydro-generator unit connected to the grid. The device includes: The voltage acquisition module is used to acquire and monitor the terminal-side voltage and the system-side voltage; The parameter setting module is used to set the maximum allowable differential pressure. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; The calculation module is used to calculate the maximum allowable grid-connected reactive power surge amplitude. Calculate the additional allowable voltage difference ; The judgment module is used to determine, based on the signal acquired by the voltage acquisition module, whether the voltage phase sequence on the machine side and the system side are the same and the voltage amplitude difference is the same. Less than or equal to and less than or equal to Phase angle difference Less than or equal to Frequency difference Less than or equal to These five conditions; The control module is used to calculate a suitable synchronization time and issue a closing command one lead time in advance when the judgment module determines that the five conditions are met simultaneously, so as to control the circuit breaker to complete grid connection.

[0033] Preferably, a computer device includes a memory and a processor, which are communicatively connected to each other. The memory stores computer instructions, and the processor executes the computer instructions to perform the aforementioned synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit.

[0034] Preferably, a computer-readable storage medium stores computer instructions for causing a computer to execute the aforementioned synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit.

[0035] Example 2: This embodiment provides a practical process for applying this method to a large hydropower station unit, and the results are as follows: Figure 3 and Figure 4 As shown.

[0036] Figure 3 The figure shows a typical waveform of reactive power change over time during grid connection of a hydro-generator unit. As can be seen from the figure, at the instant of grid connection, if there is a difference between the generator terminal voltage and the system voltage... This will cause a significant reactive power inrush current, leading to drastic fluctuations in reactive power, as shown by the dotted line in the figure, with peak values ​​reaching [missing information]. This will impact the generating units and the power grid.

[0037] This invention calculates and limits the additional allowable voltage difference. This limits the voltage difference between the terminal and the system during grid connection to a smaller range, thereby effectively limiting the reactive power surge amplitude to a preset value. As shown by the solid line in the figure below, it significantly smooths out reactive power fluctuations during grid connection, which is conducive to the unit quickly and smoothly entering synchronous operation and reduces the electrical and mechanical stress on the circuit breaker and the power grid.

[0038] Figure 4 The statistical analysis results based on actual grid connection data from a hydropower station are presented. The scatter points in the graph represent the measured grid connection voltage differences during 20 grid connection events. With the corresponding reactive power impact amplitude The solid line represents the theoretical relationship curve obtained by the calculation method proposed in this invention.

[0039] like Figure 4 As shown, the measured data points are closely distributed on both sides of the theoretical curve, indicating a high goodness of fit. The theoretical value of the coefficient of relationship between the two was calculated. Compared with measured statistical values The relative error is less than 3%, and the accuracy rate is over 90%. This result verifies the correctness and reliability of the linear relationship model between reactive power impact amplitude and voltage difference established in this invention, and shows that the additional voltage difference condition calculated and set by the method of this invention can accurately and effectively control the reactive power impact of grid connection within the expected range, thereby improving the predictability and safety of the grid connection process.

[0040] Combination Figure 3 and Figure 4 It can be seen that by introducing the reactive power impact-voltage difference relationship based on electrical parameters and adding corresponding additional voltage difference conditions in the synchronization judgment, the present invention achieves quantitative limitation and active suppression of the reactive power impact amplitude of grid connection, which helps to improve the grid connection stability of hydro-generator units and the operation stability of the power system.

Claims

1. A synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit, characterized in that, Includes the following steps: S1, Set the maximum allowable differential pressure for simultaneous grid connection. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; S2, based on the maximum permissible grid-connected reactive power impact amplitude The additional allowable voltage difference was calculated. ; S3, collects and monitors the voltage on the machine side and the system side; S4. Determine whether the following five conditions are met simultaneously: Condition 1: The phase sequence of the voltage on the machine side and the system side is the same; Condition 2: The magnitude difference between the voltage at the machine terminal and the system side Less than or equal to the maximum permissible pressure difference And less than or equal to the additional permissible voltage difference. ; Condition 3: Phase angle difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible phase angle difference ; Condition 4: Frequency difference between the voltage on the machine side and the system side Less than or equal to the maximum permissible frequency difference ; Condition 5: Lead time signal generation; S5. If the above five conditions are met simultaneously, calculate the appropriate synchronization time and issue a closing command one lead time in advance. After synchronization identification and blocking relay, the command is sent to the circuit breaker to complete grid connection.

2. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 1, characterized in that, In step S2, the additional permissible voltage difference Calculated in the following way: ； Where K is the coefficient relating reactive power surge amplitude to grid voltage difference, in units of... .

3. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 2, characterized in that, The relationship coefficient K is calculated using the following formula: ； in, This indicates the rated capacity of the transformer. This indicates the rated voltage of the transformer. This indicates the percentage of the transformer's impedance voltage drop. Indicates the voltage amplitude on the high-voltage side of the busbar. This indicates the rated voltage on the high-voltage side of the main transformer. This indicates the rated voltage on the low-voltage side of the main transformer.

4. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 3, characterized in that, The difference between the terminal line voltage and the converted bus voltage is When the reactive power is adjusted to its maximum value, the generator terminal voltage reaches the instantaneous grid connection voltage under the action of AVR regulation. At this time, the active power is stable, the power angle is considered to be 0, and all current is considered as reactive current. The corresponding single-phase reactive current is: ； The reactive power is: ； That is, the reactive power impact amplitude during the generator grid connection regulation process is: ； in, The impedance of the transformer has a nominal value; This is the low-voltage side equivalent value of the bus voltage.

5. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 4, characterized in that, Based on the transformer parameters, using the transformer's rated capacity and rated voltage As the reference value, the corresponding reference value for impedance is: ； The calculated impedance of the transformer is: ； In the formula This is the voltage drop across the transformer impedance.

6. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 3, characterized in that, The relationship coefficient K is calculated based on the following approximate formula: ； in, This indicates the maximum reactive power surge amplitude during the generator grid connection adjustment process. This represents the low-voltage side converted values ​​of the terminal line voltage and the bus voltage. The difference between them.

7. The synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit according to claim 6, characterized in that, The low-voltage side equivalent value of the bus voltage Calculated using the following formula: ； in, Indicates the voltage amplitude on the high-voltage side of the busbar. The transformer ratio between the low-voltage side and the high-voltage side of the main transformer.

8. A synchronizing device for limiting reactive power impact during grid connection of a hydro-generator unit, characterized in that, The apparatus for performing the synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit as described in any one of claims 1-7 includes: The voltage acquisition module is used to acquire and monitor the terminal-side voltage and the system-side voltage; The parameter setting module is used to set the maximum allowable differential pressure. Maximum permissible frequency difference Maximum permissible phase angle difference and maximum permissible grid-connected reactive power surge amplitude ; The calculation module is used to calculate the maximum allowable grid-connected reactive power surge amplitude. Calculate the additional allowable voltage difference ; The judgment module is used to determine, based on the signal acquired by the voltage acquisition module, whether the voltage phase sequence on the machine side and the system side are the same and the voltage amplitude difference is the same. Less than or equal to and less than or equal to Phase angle difference Less than or equal to Frequency difference Less than or equal to These five conditions; The control module is used to calculate a suitable synchronization time and issue a closing command one lead time in advance when the judgment module determines that the five conditions are met simultaneously, so as to control the circuit breaker to complete grid connection.

9. A computer device, characterized in that, It includes a memory and a processor, which are interconnected and communicate with each other. The memory stores computer instructions, and the processor executes the computer instructions to perform the synchronization method for limiting the reactive power impact of a hydro-generator unit connected to the grid, as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to perform a synchronization method for limiting reactive power impact during grid connection of a hydro-generator unit, as described in any one of claims 1 to 7.

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