Hydroelectric generating set inertia estimation method considering water hammer effect

Abstract

The invention discloses a hydroelectric generating set inertia estimation method considering a water hammer effect, and the method comprises the steps: calculating the active power at an evaluation moment on the basis of obtaining the electric quantity data of a grid-connected point of a hydroelectric generating set, and solving the active power variation of the grid-connected point of the hydroelectric generating set in a frequency modulation time period; meanwhile, according to the frequency change of the grid-connected point and the known hydroelectric generating set water starting time, the permanent descent rate and the electro-hydraulic speed regulator parameters, the mechanical power change of the water turbine is deduced, then the inertia power released by a hydroelectric generating set rotor is decoupled, finally the hydroelectric generating set inertia time constant is evaluated based on average window integration, and when the calculation result converges, the hydroelectric generating set inertia time constant is calculated. And outputting a result. According to the hydroelectric generating set inertia estimation method considering the water hammer effect, the inertia power is decoupled on the basis of considering the water hammer effect, the inertia time constant can be accurately calculated and obtained, the actual frequency supporting capacity is reflected, and the method has important guiding significance on evaluation of the actual frequency supporting capacity of a new energy station.

Description

Technical Field

[0001] The present invention relates to the technical field of hydropower unit inertia evaluation, and in particular to a method for estimating the inertia of a hydropower unit considering water hammer effect. Background Art

[0002] The development of renewable energy, represented by wind and solar power, will accelerate further. The power system is gradually transitioning from a traditional AC system dominated by thermal and hydropower synchronous generators to a power electronic AC / DC hybrid system dominated by renewable energy sources such as wind and solar power. The inertia and primary frequency regulation capabilities of the power system are gradually weakening, resulting in a significant deterioration in the frequency index after disturbances. Accurately measuring the inertia of generator sets and systems contributes to the safe and stable operation of power systems with a high proportion of renewable energy.

[0003] Generally speaking, the moment of inertia of a hydropower unit is measured at the factory through no-load self-deceleration tests or load rejection acceleration tests, eliminating the need for additional evaluation. However, for hydropower units with a long history, the situation may be different: on the one hand, as time passes, the unit will experience equipment aging and rotor deformation, which may have a certain impact on the unit's inertia support performance; on the other hand, the replacement of old rotating exciters will also change the inertia time constant of the synchronous generator to a certain extent. Therefore, using measured data to evaluate the inertia of a hydropower unit not only verifies the data provided by the manufacturer, but also derives the actual inertia support capacity of the hydropower unit after long-term operation.

[0004] The increasing proportion of renewable energy has accelerated the frequency change rate of the system, which has greatly shortened the time it takes for the generator frequency to cross the frequency regulation dead zone after a disturbance occurs, making primary frequency regulation actions more frequent. In actual measurement, relying solely on power changes when the frequency does not cross the dead zone to evaluate inertia has the problems of limited data volume and low accuracy. Therefore, it is necessary to use measurement data over a longer period of time to estimate inertia. However, the unique water hammer effect of hydropower units makes the dynamic process of primary frequency regulation power complex in the early stages of disturbances. How to separate the primary frequency regulation power of hydropower units from the inertia support power is the key to accurately estimating the inertia of hydropower units. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for estimating the inertia of a hydropower unit considering the water hammer effect, which solves the problem of inertia power decoupling under the water hammer effect. By using PMU data and known parameters, through normalization, decoupling and integral calculation, the inertia time constant of the hydropower unit is accurately evaluated, providing a basis for the frequency support capability evaluation of new energy stations.

[0006] To achieve the above object, the present invention provides a method for estimating the inertia of a hydropower unit taking into account the water hammer effect, comprising the following steps:

[0007] S1. Obtain the frequency, frequency change rate and active power data of the hydropower unit based on the PMU and standardize them;

[0008] S2. Obtain the time when the inertia time constant is entered into the evaluation according to the frequency deviation value, and take the average active power value 1 second before the start of the disturbance as the active power reference value for the frequency modulation evaluation;

[0009] S3. Calculate the frequency-regulated active power change of the hydropower unit during the evaluation period based on the active power reference value at the time of entering the evaluation inertia time constant;

[0010] S4. Reversely calculate the mechanical power output based on the frequency change at the grid connection point, the water start-up time of the hydropower unit, the permanent state descent rate, and the parameters of the electro-hydraulic speed governor, and decouple the inertia power of the hydropower unit;

[0011] S5. According to the decoupled inertia power and the time scale of starting frequency modulation, the inertia time constant of the hydropower unit is evaluated based on the average window integral. When the calculation result converges, the result is output.

[0012] Preferably, in S1, electrical quantity data including the frequency, frequency change rate and active power data of the hydropower unit are obtained based on the PMU configured at the grid connection point of the hydropower unit and normalized as shown in the following formula:

[0013]

[0014] In the formula, f*, df* / dt, and P* are the per-unit hydropower unit frequency, frequency change rate, and active power data respectively; N is the standard frequency of the power grid; f is the frequency data measured by PMU; df / dt is the frequency change rate data measured by PMU; N is the rated power of the hydropower unit, which is determined based on the rated power of the unit; P is the active power data measured by the PMU; and t is a certain moment.

[0015] Preferably, in S2, the frequency deviation value is the deviation value of the grid connection point frequency relative to the nominal frequency, and the calculation formula is as follows:

[0016] |Δf(t0)|=|f(t0)-f0|=Δf dead ;

[0017] Where Δf(t0) is the deviation of the grid connection point frequency relative to the nominal frequency f0. When the frequency deviation is equal to the primary frequency modulation control dead zone, the time is recorded as t0, and the frequency value at this time is f(t0); Δf dead It is the dead zone of primary frequency modulation control;

[0018] The formula for calculating the average active power is as follows:

[0019]

[0020] Where P0 is the average active power 1s before the disturbance, T s is the power sampling time interval, and i is the sequence number of the power sampling sequence.

[0021] Preferably, in S3, the calculation formula for the frequency regulation active power change of the hydropower unit is as follows:

[0022] ΔP(t)=P(t)-P0;

[0023] Where ΔP(t) is the change in frequency-regulated active power at the grid-connected point of the hydropower unit at time t; P(t) is the active power at the grid-connected point of the hydropower unit at time t; and P0 is the average active power 1 second before the disturbance, i.e., the active power reference value.

[0024] Preferably, in S4, the mechanical power output is inferred based on the frequency change of the grid connection point and the water start-up time, permanent state decline rate and electro-hydraulic speed governor parameters to decouple the inertia power of the hydropower unit, that is:

[0025]

[0026] Where ΔP m* is the per-unit value of the mechanical power variation of the hydropower unit; Δf* is the per-unit value of the grid-connected frequency of the hydropower unit; K is the permanent slip rate b of the hydropower unit p The reciprocal of K p is the proportional coefficient of the electro-hydraulic speed regulator; K i is the integral coefficient of the electro-hydraulic speed regulator; T G is the time constant of the guide vane servo motor; T w is the water start-up time of the hydropower unit; s is the Laplace operator; P N is the rated power of the hydropower unit; ΔP*(t) is the per-unit inertia power decoupled from the hydropower unit.

[0027] Preferably, in S5, the inertia time constant of the hydropower unit is evaluated based on the average window integral according to the decoupled inertia power and the time scale of starting frequency modulation. When the calculation result converges, the result is output:

[0028]

[0029] Where: H P is the estimated value of the inertia time constant of the hydropower unit, ΔP*(t) is the per-unit inertia power value decoupled from the hydropower unit; ΔP m* (t) is the per-unit value of the mechanical power change of the hydropower unit; f*(t) is the per-unit value of the frequency at the grid connection point of the hydropower unit, t0 is the time when the disturbance occurs, and t1 is the duration of the evaluation function.

[0030] Therefore, the present invention adopts the above-mentioned method for estimating the inertia of a hydropower unit considering the water hammer effect, and the beneficial effects are as follows:

[0031] (1) The present invention is based on the frequency, frequency change rate and active power data obtained by the PMU at the grid connection point of the hydropower unit and normalized. In combination with the known water start-up time, permanent descent rate and electro-hydraulic speed regulator parameters of the hydropower unit, the inertia time constant of the hydropower unit can be accurately evaluated by reversely deducing the inertia power of the mechanical power output, providing a new and effective method for unit inertia evaluation.

[0032] (2) The present invention fully considers the complexity of the primary frequency modulation power dynamic process caused by the water hammer effect, adopts measurement data of a longer time period, solves the problem of limited data volume and low accuracy in inertia evaluation based solely on power changes when the frequency does not cross the dead zone, and improves the accuracy and reliability of inertia estimation.

[0033] (3) The present invention calculates the inertia time constant of the hydropower unit through average window integration and outputs the result when it converges. It can determine the size of the inertia time constant of the hydropower unit based on the post-disturbance data, which has important guiding significance for the evaluation of the real frequency support capability of the new energy station and contributes to the safe and stable operation of the high-proportion new energy power system.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is an overall flow chart of an embodiment of a method for estimating the inertia of a hydropower unit considering the water hammer effect of the present invention;

[0036] Figure 2 This is an active power diagram of a hydropower unit grid connection point according to an embodiment of a method for estimating the inertia of a hydropower unit considering the water hammer effect of the present invention;

[0037] Figure 3 This is a comparison diagram between the calculated value and the actual value of the primary frequency modulation power of a hydropower unit according to an embodiment of the method for estimating the inertia of a hydropower unit considering the water hammer effect of the present invention;

[0038] Figure 4 This is a diagram of the evaluation results of the inertia time constant of a hydropower unit according to an embodiment of the present invention, a method for estimating the inertia of a hydropower unit considering the water hammer effect. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0040] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0041] like Figure 1 As shown, a method for estimating the inertia of a hydropower unit considering the water hammer effect includes the following steps:

[0042] S1. Based on the PMU configured at the hydropower unit grid connection point, electrical quantity data is obtained, including the frequency, frequency change rate, and active power data of the hydropower unit, and normalized as shown in the following formula:

[0043]

[0044] In the formula, f*, df* / dt, and P* are the per-unit hydropower unit frequency, frequency change rate, and active power data respectively; N is the standard frequency of the power grid, which is 50Hz; f is the frequency data measured by the PMU; df / dt is the frequency change rate data measured by the PMU; P N is the rated power of the hydropower unit, which is determined based on the rated power of the unit; P is the active power data measured by the PMU; and t is a certain moment.

[0045] S2. Obtain the time when the inertia time constant for evaluation begins based on the frequency deviation value, and take the average active power value 1 second before the start of the disturbance as the active power reference value for the frequency modulation evaluation.

[0046] The frequency deviation value is the deviation value of the grid connection point frequency relative to the nominal frequency, and the calculation formula is as follows:

[0047] |Δf(t0)|=|f(t0)-f0|=Δf dead ;

[0048] Where Δf(t0) is the deviation of the grid connection point frequency relative to the nominal frequency f0. When the frequency deviation is equal to the primary frequency modulation control dead zone, the time is recorded as t0, and the frequency value at this time is f(t0); Δf dead It is the dead zone of primary frequency modulation control.

[0049] The formula for calculating the average active power is as follows:

[0050]

[0051] Where P0 is the average active power 1s before the disturbance, T s is the power sampling time interval, and i is the sequence number of the power sampling sequence.

[0052] S3. Based on the active power reference value at the time of entering the inertia time constant evaluation, the frequency regulation active power change of the hydropower unit during the evaluation period t is calculated using the following formula:

[0053] ΔP(t)=P(t)-P0;

[0054] Where ΔP(t) is the change in frequency-regulated active power at the grid-connected point of the hydropower unit at time t; P(t) is the active power at the grid-connected point of the hydropower unit at time t; and P0 is the average active power value 1 second before the disturbance obtained in S2, i.e., the active power reference value.

[0055] S4. According to the frequency change of the grid connection point and the known water start-up time, permanent state decline rate and electro-hydraulic speed governor parameters of the hydropower unit, the mechanical power output is reversed and the inertia power of the hydropower unit is decoupled, that is:

[0056]

[0057] Where ΔP m* is the per-unit value of the mechanical power variation of the hydropower unit; Δf* is the per-unit value of the grid-connected frequency of the hydropower unit; K is the permanent slip rate b of the hydropower unit p The reciprocal of K p is the proportional coefficient of the electro-hydraulic speed regulator; K i is the integral coefficient of the electro-hydraulic speed regulator; T G is the time constant of the guide vane servo motor; T w is the water start-up time of the hydropower unit; s is the Laplace operator; P N is the rated power of the hydropower unit; ΔP*(t) is the per-unit inertia power decoupled from the hydropower unit.

[0058] S5. According to the decoupled inertia power and the time scale of starting frequency modulation, the inertia time constant of the hydropower unit is evaluated based on the average window integral. When the calculation result converges, the result is output.

[0059] Among them, the relationship between the inertia power and frequency change rate of the hydropower unit is expressed as follows:

[0060]

[0061] Where ΔP* is the per-unit inertia power of the hydropower generator set, H is the inertia time constant of the hydropower generator set, and df* / dt is the per-unit frequency change rate of the hydropower generator set at the grid connection point.

[0062] The relationship between the estimated value of the inertia time constant of the hydropower unit and the inertia power of the hydropower unit is:

[0063]

[0064] Where: H P is the estimated value of the inertia time constant of the hydropower unit, ΔP*(t) is the per-unit inertia power value decoupled from the hydropower unit; ΔP m* (t) is the per-unit value of the mechanical power change of the hydropower unit; f*(t) is the per-unit value of the frequency at the grid connection point of the hydropower unit, t0 is the time when the disturbance occurs, and t1 is the duration of the evaluation function.

[0065] The following uses simulated hydroelectric generator operating data to illustrate the method described in the present invention. Using the grid connection point frequency, frequency change rate, active power, and known hydroelectric generator water start-up time, permanent state droop rate, and electro-hydraulic speed regulator parameters, the steps for evaluating the hydroelectric generator inertia time constant are as follows:

[0066] 1. Obtain the active power value and frequency value at the time of evaluation from the frequency change rate and frequency deviation value, and perform evaluation data preprocessing.

[0067] 2. Based on the frequency change at the grid connection point, the active power increment, and the known water start-up time, permanent droop rate, and electro-hydraulic speed regulator parameters of the hydropower unit, the mechanical output power increment of the hydropower unit is reversed to decouple the inertia power of the hydropower unit.

[0068] 3. Based on the decoupled inertia power of the hydropower unit and the time scale of starting frequency modulation, the inertia time constant of the hydropower unit is evaluated based on the average window integral. When the calculation result converges, the result is output.

[0069] Depend on Figure 2 It can be seen that at 100s, the active power of the hydropower unit grid connection point showed an obvious jump, rapidly increasing from a low value to around 6000MW, and then began to decline. During the period of 102s-110s, the active power gradually stabilized and maintained at a level slightly above 5500MW.

[0070] like Figure 3 As shown in the figure, the blue broken line represents the calculated value of the primary frequency regulation power of the hydropower unit. During the period from 95s to 100s, the calculated value remains at 0; at 100s, there is a downward mutation, reaching about -100MW; then it begins to rise and continues to grow during the period from 105s to 110s.

[0071] The red broken line represents the theoretical value of the primary frequency regulation power of the hydropower unit. During the period of 95s-100s, the theoretical value also remains at 0; it begins to decline at 100s, reaches the lowest point, and then gradually rises. The overall upward trend is relatively smooth, and it is close to 400MW at 110s. Figure 3 It can be seen that when the present invention decouples the primary frequency modulation power by taking the water hammer effect into consideration, the primary frequency modulation power increase can be calculated more accurately.

[0072] like Figure 4 As shown in the figure, the red solid line represents the estimated inertia time constant Hp of the hydropower unit. During the period of 95s-100s, the value of Hp is 0. At 100s, the value of Hp suddenly jumps to nearly 8, then drops slightly and rises slowly during the period of 100s-110s, finally approaching 8. The blue dotted line represents the actual inertia time constant H of the hydropower unit. During the entire period of 95s-110s, the value of H remains constant at approximately 8.

[0073] Depend on Figure 4 It can be seen that, by using the method proposed in the present invention, the frequency, frequency change rate and active power of the hydropower unit can be analyzed, and the inertia time constant of the hydropower unit can be extracted using the measured data and known data.

[0074] As demonstrated in the examples, the proposed method can accurately assess the inertia time constant of a hydroelectric generator. Based on frequency, frequency change rate, and active power data collected at the generator's grid connection point, along with known generator water start-up time, permanent droop rate, and electro-hydraulic speed regulator parameters, the proposed method decouples the primary frequency modulation power to estimate the generator's inertia time constant.

[0075] Therefore, the present invention adopts the above-mentioned method for estimating the inertia of a hydropower unit considering the water hammer effect. Based on the active power and frequency data measured by the PMU at the grid connection point of the hydropower unit, and on the basis of the known water start-up time, permanent descent rate and electro-hydraulic speed regulator parameters of the hydropower unit, the inertia time constant of the hydropower unit can be theoretically evaluated using the post-disturbance data.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for estimating the inertia of a hydropower unit considering the water hammer effect, characterized by: The following steps are involved: S1. Obtain the frequency, frequency change rate and active power data of the hydropower unit based on the PMU and standardize them; S2. Obtain the time when the inertia time constant is entered into the evaluation according to the frequency deviation value, and take the average active power value 1 second before the start of the disturbance as the active power reference value for the frequency modulation evaluation; S3. Calculate the frequency-regulated active power change of the hydropower unit during the evaluation period based on the active power reference value at the time of entering the evaluation inertia time constant; S4. Reversely calculate the mechanical power output based on the frequency change at the grid connection point, the water start-up time of the hydropower unit, the permanent state descent rate, and the parameters of the electro-hydraulic speed governor, and decouple the inertia power of the hydropower unit; S5. According to the decoupled inertia power and the time scale of starting frequency modulation, the inertia time constant of the hydropower unit is evaluated based on the average window integral. When the calculation result converges, the result is output.

2. The method for estimating the inertia of a hydropower unit considering the water hammer effect according to claim 1 is characterized in that: In S1, the PMU configured at the hydropower unit grid connection point obtains electrical quantity data, including the frequency, frequency change rate, and active power data of the hydropower unit, and normalizes them into units, as shown in the following formula: In the formula, f*, df* / dt, and P* are the per-unit hydropower unit frequency, frequency change rate, and active power data respectively; N is the standard frequency of the power grid; f is the frequency data measured by PMU; df / dt is the frequency change rate data measured by PMU; N is the rated power of the hydropower unit, which is determined based on the rated power of the unit; P is the active power data measured by the PMU; and t is a certain moment.

3. The method for estimating the inertia of a hydropower unit considering the water hammer effect according to claim 2 is characterized in that: In S2, the frequency deviation value is the deviation value of the grid connection point frequency relative to the nominal frequency. The calculation formula is as follows: |Δf(t0)|=|f(t0)-f0|=Δf dead ; Where Δf(t0) is the deviation of the grid connection point frequency relative to the nominal frequency f0. When the frequency deviation is equal to the primary frequency modulation control dead zone, the time is recorded as t0, and the frequency value at this time is f(t0); Δf dead It is the dead zone of primary frequency modulation control; The formula for calculating the average active power is as follows: Where P0 is the average active power 1s before the disturbance, T s is the power sampling time interval, and i is the sequence number of the power sampling sequence.

4. The method for estimating the inertia of a hydropower unit considering the water hammer effect according to claim 3 is characterized in that: In S3, the calculation formula for the frequency regulation active power change of the hydropower unit is as follows: ΔP(t)=P(t)-P0; Where ΔP(t) is the change in frequency-regulated active power at the grid-connected point of the hydropower unit at time t; P(t) is the active power at the grid-connected point of the hydropower unit at time t; and P0 is the average active power 1 second before the disturbance, i.e., the active power reference value.

5. The method for estimating the inertia of a hydropower unit considering the water hammer effect according to claim 4 is characterized in that: In S4, the mechanical power output is inversely calculated based on the frequency change at the grid connection point, the water start-up time of the hydropower unit, the permanent state descent rate, and the parameters of the electro-hydraulic speed governor, and the inertia power of the hydropower unit is decoupled, that is: Where, ΔP m* is the per-unit value of the mechanical power variation of the hydropower unit; Δf* is the per-unit value of the grid-connected frequency of the hydropower unit; K is the permanent slip rate b of the hydropower unit p The reciprocal of K p is the proportional coefficient of the electro-hydraulic speed regulator; K i is the integral coefficient of the electro-hydraulic speed regulator; T G is the time constant of the guide vane servo motor; T w is the water start-up time of the hydropower unit, s is the Laplace operator; P N is the rated power of the hydropower unit; ΔP*(t) is the per-unit inertia power decoupled from the hydropower unit.

6. A method for estimating the inertia of a hydropower unit considering the water hammer effect according to claim 5, characterized in that: In S5, based on the decoupled inertia power and the time scale for starting frequency modulation, the inertia time constant of the hydropower unit is evaluated based on the average window integral. When the calculation results converge, the output results are: Where: H P is the estimated value of the inertia time constant of the hydropower unit, ΔP*(t) is the per-unit inertia power value decoupled from the hydropower unit; ΔP m* (t) is the per unit value of the mechanical power variation of the hydropower unit; f*(t) is the per-unit frequency of the hydropower unit grid connection point, t0 is the time when the disturbance occurs, and t1 is the duration of the evaluation function.

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