Control method for performing primary frequency modulation in power dead zone range of hydroelectric generating set

Abstract

The invention discloses a control method for performing primary frequency modulation in a power dead zone range of a hydroelectric generating set, and belongs to the technical field of hydroelectric generating set adjustment. Comprising the following steps: S1, calculating H1 and H2 of a water diversion system according to a water flow inertia time constant and a unit mechanical inertia time constant of the water diversion system; s2, calculating a unit power dynamic analytical expression during frequency unit step disturbance; s3, calculating a first-order differential link coefficient decomposed by a second-order correction link based on the unit power dynamic analytical expression; and S4, calculating the output quantity of the PID speed regulator in the current sampling period. According to the scheme, the oscillation link transfer function parameters in the dynamic process are calculated, the second-order system correction transfer function with the given frequency value is designed on the basis, it is guaranteed that the unit power does not oscillate when the unit frequency is given to change, the problem that the power exceeds a power dead zone in the dynamic process is prevented, and the power efficiency is improved. And meanwhile, an amplitude limiting link is arranged at the frequency deviation value so as to ensure that the power steady-state value exceeds the power dead zone range.

Description

Technical Field

[0001] The invention belongs to the technical field of hydroelectric generator set regulation, and in particular relates to a control method for performing primary frequency regulation within a power dead zone of a hydroelectric generator set. Background Art

[0002] Hydropower units are the main regulating power source for grid frequency regulation. They balance random load changes on the grid through primary frequency regulation, and maintain grid frequency stability within the allowable range through secondary frequency regulation. In the current control of hydropower units, the speed regulator performs secondary frequency regulation control based on the grid load set value and the power dead zone range, and the unit performs primary frequency regulation control based on grid frequency fluctuations. However, when the unit performs primary and secondary frequency regulation, the primary frequency regulation amplitude is often too large, causing the power to exceed the secondary frequency regulation dead zone range, causing the unit's secondary frequency regulation and primary frequency regulation to act in the opposite direction, causing power oscillation during the unit regulation process, and even serious accidents of unit regulation instability.

[0003] Currently, the unit exits the secondary frequency regulation during the primary frequency regulation, and re-enters the secondary frequency regulation after the primary frequency regulation is completed. This method greatly reduces the unit's ability to regulate the power grid. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of power oscillation in the unit regulation process caused by the power exceeding the secondary frequency regulation dead zone when the unit performs primary frequency regulation and secondary frequency regulation in the prior art.

[0005] In order to solve the above technical problems, the present invention provides a control method for performing primary frequency modulation within the power dead zone of a hydropower unit, comprising the following steps:

[0006] S1. Calculate the H of the water diversion system based on the water flow inertia time constant of the water diversion system and the mechanical inertia time constant of the unit. 1 To H 4 ;

[0007] S2. Calculate the dynamic analytical expression of the unit power when the frequency unit step disturbance occurs, perform characteristic analysis on the expression, and obtain the characteristic analysis result;

[0008] S3, based on the H 1 , H 2 and characteristic analysis results, calculate the coefficients of the first-order differential link decomposed by the second-order correction link;

[0009] S4. Calculate the output of the PID speed regulator in the current sampling period based on the first-order differential link coefficient.

[0010] Preferably, S1 comprises:

[0011] S11. Within the dead zone of the hydropower unit power, without considering the change of the power setting, the transfer function of the output power of the hydropower unit to the frequency setting is obtained;

[0012] S12. Under the condition of S11, obtain the characteristic equation of the transfer function of the output power of the hydropower unit to the given frequency;

[0013] S13, considering the general value range of the water flow inertia time constant and the unit mechanical inertia time constant, according to relevant standards, constraining the matching of the water flow inertia time constant and the unit mechanical inertia time constant and adopting the Krivchenko recommended formula to formulate the PID parameters, and obtaining the PID parameter expression;

[0014] S14, calculating the root of the characteristic equation based on the characteristic equation and S13;

[0015] S15. Based on the form of the characteristic equation, the characteristic equation is transformed by the Ferrari method of the quartic equation to calculate the H of the water diversion system. 1 To H 4 .

[0016] As a preferred embodiment, the transfer function of the output power of the hydropower unit to a given frequency is specifically expressed as:

[0017]

[0018] Among them, the transfer function parameter A 0 , A 1 , A 2 , A 3 , A 4 , B 0 , B 1 , B 2 , B 3 satisfy:

[0019]

[0020] In the formula, x r is the unit frequency given value, P e is the generator power, x is the instantaneous speed value when the unit is actually running, K P is the proportional gain of the speed regulator, K I is the integral gain of the speed regulator, K D is the differential gain of the speed regulator, T w is the water flow inertia time constant of the water diversion system, e y is the transfer coefficient of turbine torque to guide vane opening, e is the turbine coefficient, e qh is the transfer coefficient of turbine flow to water head, T a is the mechanical inertia time constant of the hydroelectric generator set, P ris the power given value, e p is the power slip coefficient of the speed regulator, and s is the Laplace operator.

[0021] Preferably, H 1 To H 4 The specific expression is:

[0022]

[0023] Among them, each parameter satisfies:

[0024]

[0025] Among them, D 0 , D 1 , D 2 , D 3 is the standardized coefficient of the characteristic equation, and p, q, k are the correlation coefficients in solving the quartic equation using the Ferrari method.

[0026] As a preferred embodiment, in S2, the dynamic analytical expression of the unit power during the frequency unit step disturbance is specifically expressed as:

[0027] P e (s) = P 1 (s)+P 2 (s)+P 3 (s);

[0028]

[0029] Where E 1 、E 2 、F 1 、F 2 、F 3 satisfy:

[0030]

[0031] Where t is time, P 1 is the monotonically decaying component corresponding to the real root of the system, P 2 is the oscillation attenuation component corresponding to the conjugate complex root of the system, P 3 is the constant component after the system stabilizes, K 1 , K 2 , K 3 、F 3 ,δ,ω,ψ are the coefficients in the system expression; C 0 , C 1 , C 2 , C 3 is the transfer function normalization coefficient, E 1 、E 2 、F 1、F 2 is the equivalent second-order transfer function coefficient, F 3 is the steady-state component coefficient, P 1 is the oscillation attenuation component corresponding to the conjugate complex root of the system, P 2 is the monotonically decaying component corresponding to the real root of the system, P 3 is the constant component after the system stabilizes.

[0032] As a preferred feature analysis result, the characteristic analysis result includes: 1 is the oscillation attenuation component corresponding to the conjugate complex root of the system, so P 1 Corresponding to the transfer function H 1 and H 2 It is a possible factor that causes the system power to oscillate dynamically with the disturbance of the given frequency value, causing the power peak to overshoot. When the unit frequency disturbance causes the unit power change to approach the power dead zone limit, the power overshoot causes the unit power to exceed the power dead zone limit during the primary frequency regulation process.

[0033] Preferably, in S3, the second-order correction link is decomposed into the sum of the first-order differential link and the first-order inertia link, and the actual differential link is used to replace the ideal differential link in the PID control strategy.

[0034] Preferably, in S3, the analytical expression of the first-order differential link coefficient is specifically expressed as:

[0035]

[0036] Among them, a and b are the coefficients of the first-order differential link.

[0037] Preferably, in S4, the output of the PID speed regulator in the current sampling period is specifically expressed as:

[0038] y(m)=y P (m)+y I (m)+y D (m).

[0039] Among them, y P (m), y I (m), y D (m), satisfying:

[0040] y P (m) = K P x in (m)

[0041]

[0042] y I (m) = y I (m-1)+x I(m)K I ΔT;

[0043] Among them, each parameter satisfies:

[0044]

[0045] In the formula, m is the number of sampling times, ΔT is the sampling period, and x 1 、x 2 , is the output of the first-order differential link decomposed from the second-order correction link, x 3 is the first-order inertia link output obtained by decomposing the second-order correction link, x I is the integral term input, T d is the differential link response time constant, y P is the proportional output, y I is the integral output, y D is the differential output, Δx is the unit frequency deviation, x in is the input of the PID controller, K P is the proportional gain of the speed regulator, K I is the integral gain of the speed regulator, K D is the differential gain of the speed regulator, x r is the unit frequency given value, P e is the generator power, x is the instantaneous speed value when the unit is actually running, Δx max Δx is the upper limit of the unit frequency deviation limit; min is the lower limit of the unit frequency deviation, P r is the power given value, e p is the power slip coefficient of the speed regulator.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] This scheme derives and analyzes the power-to-frequency transfer function of the unit regulation system, calculates the transfer function parameters of the oscillation link in the dynamic process, and designs a second-order system correction transfer function based on the frequency value, ensuring that the unit power does not oscillate when the unit frequency setting changes, preventing the problem of power exceeding the power dead zone in the dynamic process, and setting a limit link at the frequency deviation value to ensure that the steady-state power value exceeds the power dead zone. This achieves the effect of performing a primary frequency regulation within the dead zone of the secondary frequency regulation of the hydropower unit, avoiding the problem of power oscillation in the regulation process caused by the primary frequency regulation of the unit, and improving the stability of the regulation process of the hydropower unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a typical structural block diagram of a conventional hydroelectric generator set regulating system in the method of the present invention;

[0049] Figure 2 It is a frequency response characteristic diagram of a conventional hydroelectric generator set regulation system in the method of the present invention;

[0050] Figure 3 It is a control strategy block diagram of the improved speed regulator in the method of the present invention. DETAILED DESCRIPTION

[0051] Embodiment 1: A control method for performing a primary frequency modulation within a power dead zone of a hydropower unit, according to Figure 1 The typical structural block diagram of the regulation system of a traditional hydroelectric generator set is shown in FIG. 1 . In the dead zone of the unit power, the power setting value does not change. Therefore, without considering the change of the power setting, the transfer function of the unit output power to the frequency setting can be obtained as follows:

[0052]

[0053] Among them, the transfer function parameter A 0 , A 1 , A 2 , A 3 , A 4 , B 0 , B 1 , B 2 , B 3 satisfy:

[0054]

[0055] Among them, x r is the unit frequency given value, P e is the generator power, x is the instantaneous speed value when the unit is actually running, K P is the proportional gain of the speed regulator, K I is the integral gain of the speed regulator, K D is the differential gain of the speed regulator, T w is the water flow inertia time constant of the water diversion system, e y is the transfer coefficient of turbine torque to guide vane opening, e is the turbine coefficient, eqh is the transfer coefficient of turbine flow to water head, T a is the mechanical inertia time constant of the hydroelectric generator set, P r is the power given value, ep is the power slip coefficient of the speed regulator, and s is the Lagrangian operator.

[0056] At this time, the characteristic equation of the system is:

[0057] A 4 s 4 +A 3 s 3 +A 2 s 2 +A1 s+A 0 =0 (3)

[0058] For engineering w With T a The general value range of T w In the range [0.5, 4], T a In the range [2.5, 15], according to the standard "GB9652.1-2019 Technical Conditions for Hydro-Turbine Speed ​​Control System" T w / T a <1.2 to T w With T a The matching of is constrained, and the Krivchenko recommended formula is used to formulate the PID parameters. The recommended formula is as follows:

[0059]

[0060] Among them, KP 0 is the initial value of the proportional gain of the speed regulator, KI 0 KD is the initial value of the speed regulator integral gain. 0 is the initial value of the speed regulator differential gain.

[0061] Thus, the roots of the characteristic equation (3) are calculated. The roots of the characteristic equation calculated under different Tw and Ta matching are shown in Table 1. It can be seen from Table 1 that when the system parameters change within the common engineering range, the characteristic equation (3) always has a pair of conjugate complex roots and two unequal real roots.

[0062] Table 1 Distribution of roots of system characteristic equation

[0063]

[0064] Since the characteristic equation is a quartic equation, and the characteristic roots are a pair of conjugate complex roots and two unequal real roots, according to the Ferrari method for quartic equations, the characteristic equation has the same roots as the following two quadratic equations:

[0065]

[0066] Among them, H 1 , H 2 , H 3 , H 4 are the coefficients of the equivalent second-order characteristic equation.

[0067] Among them, each parameter satisfies:

[0068]

[0069] Among them, D 0 , D1 , D 2 , D 3 is the standardized coefficient of the characteristic equation, and p, q, k are the correlation coefficients in solving the quartic equation using the Ferrari method.

[0070] For a unit step disturbance in the grid frequency, the unit power can be expressed as:

[0071] P e (s) = P 1 (s)+P 2 (s)+P 3 (s) (7)

[0072]

[0073] Where E 1 、E 2 、F 1 、F 2 、F 3 satisfy:

[0074]

[0075] The expressions of each parameter are:

[0076]

[0077] Among them, C 0 , C 1 , C 2 , C 3 is the transfer function normalization coefficient, E 1 、E 2 、F 1 、F 2 is the equivalent second-order transfer function coefficient, F 3 is the steady-state component coefficient, P 1 is the oscillation attenuation component corresponding to the conjugate complex root of the system, P 2 is the monotonically decaying component corresponding to the real root of the system, P 3 is the constant component after the system stabilizes.

[0078] We can get:

[0079]

[0080] Because P 1 It is the oscillation attenuation component corresponding to the conjugate complex root of the system, which causes the dynamic process in which the system power may oscillate with the disturbance of the given frequency value, and causes the possibility of overshoot of the power peak. When the unit frequency disturbance causes the unit power change to approach the power dead zone limit, the power overshoot causes the unit power to exceed the power dead zone limit during the primary frequency regulation process.

[0081] In order to avoid the power exceeding the power dead zone during the dynamic process of the unit's primary frequency regulation, the frequency disturbance is corrected by the second order to eliminate the power fluctuation caused by the system oscillation link. At the same time, in order to prevent the frequency given value from being disturbed too much and causing the steady-state value to exceed the power dead zone, the frequency deviation is limited. Therefore, the improved system transfer function is as follows: Figure 2 As shown, the input x of the PID controller is in It can be expressed as:

[0082]

[0083] Where Δx is the unit frequency deviation; T 1 、T 2 is the response time constant of the second-order system; Δx max Δx is the upper limit of the unit frequency deviation limit; min It is the lower limit of the unit frequency deviation.

[0084] The purpose of the unit frequency deviation limit is to prevent the unit steady-state operating condition from exceeding the unit power dead zone, so Δx max With Δx min Should meet

[0085]

[0086] Among them, ΔP max ΔP is the upper limit of the unit power dead zone; min It is the lower limit of the unit power dead zone.

[0087] The second-order correction link can be decomposed into the sum of the first-order differential link and the first-order inertia link. At the same time, the actual differential link is used to replace the ideal differential link in the PID control strategy. The control strategy block diagram of the speed regulator is as follows: Figure 3 As shown, where x 1 , x 2 is the output of the first-order differential link decomposed from the second-order correction link, x 3 is the first-order inertia link output obtained by decomposing the second-order correction link, x I is the integral term input, T d is the differential link response time constant, y P is the proportional output, y I is the integral output, y D is the differential output. At this time, the unit frequency deviation Δx can be expressed as:

[0088]

[0089] Among them, a and b are the coefficients of a differential link, which can be expressed as:

[0090]

[0091] Since the currently commonly used microcomputer speed regulator can only process discrete data after system sampling, it is difficult to implement Figure 3 The speed regulator control strategy shown requires Figure 3 To discretize, Figure 3 After discretization, the control strategy calculation process in the microcomputer speed regulator is:

[0092]

[0093] Where m is the number of sampling times; ΔT is the sampling period.

[0094] This scheme derives and analyzes the power-to-frequency transfer function of the unit regulation system, calculates the transfer function parameters of the oscillation link in the dynamic process, and designs a second-order system correction transfer function based on the frequency value, ensuring that the unit power does not oscillate when the unit frequency setting changes, preventing the problem of power exceeding the power dead zone in the dynamic process, and setting a limit link at the frequency deviation value to ensure that the steady-state power value exceeds the power dead zone. This achieves the effect of performing a primary frequency regulation within the dead zone of the secondary frequency regulation of the hydropower unit, avoiding the problem of power oscillation in the regulation process caused by the primary frequency regulation of the unit, and improving the stability of the regulation process of the hydropower unit.

Claims

1. A control method for primary frequency modulation within the power dead zone of a hydropower unit, characterized in that: The steps include: S1. Calculate H1 to H4 of the water diversion system based on the water flow inertia time constant of the water diversion system and the mechanical inertia time constant of the unit; S2. Calculate the dynamic analytical expression of the unit power when the frequency unit step disturbance occurs, perform characteristic analysis on the expression, and obtain the characteristic analysis result; S3, based on the H1, H2 and characteristic analysis results, calculate the first-order differential link coefficient decomposed by the second-order correction link; S4. Calculate the output of the PID speed regulator in the current sampling period based on the first-order differential link coefficient.

2. A control method for primary frequency modulation within the power dead zone of a hydropower unit according to claim 1, characterized in that: The S1 includes: S11. Within the dead zone of the hydropower unit power, without considering the change of the power setting, the transfer function of the output power of the hydropower unit to the frequency setting is obtained; S12. Under the condition of S11, obtain the characteristic equation of the transfer function of the output power of the hydropower unit to the given frequency; S13, considering the general value range of the water flow inertia time constant and the unit mechanical inertia time constant, according to relevant standards, constraining the matching of the water flow inertia time constant and the unit mechanical inertia time constant and adopting the Krivchenko recommended formula to formulate the PID parameters, and obtaining the PID parameter expression; S14, calculating the root of the characteristic equation based on the characteristic equation and S13; S15. Based on the form of the characteristic equation, the characteristic equation is transformed by the Ferrari method of a quartic equation to calculate H1 to H4 of the water diversion system.

3. A control method for primary frequency modulation within the power dead zone of a hydropower unit according to claim 2, characterized in that: The transfer function of the output power of the hydropower unit to a given frequency is specifically expressed as: Among them, the transfer function parameters A0, A1, A2, A3, A4, B0, B1, B2, B3 satisfy: In the formula, x r is the unit frequency given value, P e is the generator power, x is the instantaneous speed value when the unit is actually running, K P is the proportional gain of the speed regulator, K I is the integral gain of the speed regulator, K D is the differential gain of the speed regulator, T w is the water flow inertia time constant of the water diversion system, e y is the transfer coefficient of turbine torque to guide vane opening, e is the turbine coefficient, e qh is the transfer coefficient of turbine flow to water head, T a is the mechanical inertia time constant of the hydroelectric generator set, P r is the power given value, e p is the power slip coefficient of the speed regulator, and s is the Laplace operator.

4. A control method for primary frequency modulation within the power dead zone of a hydroelectric unit according to claim 3, characterized in that: The specific expressions of H1 to H4 are: Among them, each parameter satisfies: Among them, D0, D1, D2, and D3 are the standardized coefficients of the characteristic equation, and p, q, and k are the correlation coefficients in solving the quartic equation using the Ferrari method.

5. The control method for primary frequency modulation within the power dead zone of a hydropower unit according to claim 1, characterized in that: In S2, the dynamic analytical expression of the unit power during the frequency unit step disturbance is specifically expressed as: P e (s)=P1(s)+P2(s)+P3(s); Where E1, E2, F1, F2, and F3 satisfy: Wherein, t is time, P1 is the monotonic attenuation component corresponding to the real root of the system, P2 is the oscillatory attenuation component corresponding to the conjugate complex root of the system, P3 is the constant component after the system is stabilized, K1, K2, K3, F3, δ, ω, ψ are coefficients in the system expression; C0, C1, C2, C3 are the standardized coefficients of the transfer function, E1, E2, F1, F2 are the equivalent second-order transfer function coefficients, F3 is the steady-state component coefficient, P1 is the oscillatory attenuation component corresponding to the conjugate complex root of the system, P2 is the monotonic attenuation component corresponding to the real root of the system, and P3 is the constant component after the system is stabilized.

6. A control method for primary frequency modulation within the power dead zone of a hydroelectric unit according to claim 5, characterized in that: The characteristic analysis results include: since P1 is the oscillation attenuation component corresponding to the conjugate complex root of the system, H1 and H2 in the transfer function corresponding to P1 are possible factors that cause the system power to oscillate dynamically with the disturbance of the given frequency value, causing the power peak to overshoot. When the unit frequency disturbance causes the unit power change to approach the power dead zone limit, the power overshoot causes the unit power to exceed the power dead zone limit during the primary frequency modulation process.

7. A control method for primary frequency modulation within the power dead zone of a hydroelectric unit according to claim 1, characterized in that: In S3, the second-order correction link is decomposed into the sum of the first-order differential link and the first-order inertia link, and the actual differential link is used to replace the ideal differential link in the PID control strategy.

8. A control method for primary frequency modulation within the power dead zone of a hydroelectric generator set according to claim 7, characterized in that: In S3, the analytical expression of the first-order differential link coefficient is specifically expressed as: Among them, a and b are the coefficients of the first-order differential link.

9. A control method for primary frequency modulation within the power dead zone of a hydroelectric unit according to claim 1, characterized in that: In S4, the output of the PID speed regulator in the current sampling period is specifically expressed as: y(m)=y P (m)+y I (m)+y D (m); Among them, y P (m), y I (m), y D (m), satisfying: y p (m)=K P x in (m) y I (m)=y I (m-1)+x I (m)K I ΔT; Among them, each parameter satisfies: Where m is the number of sampling times, ΔT is the sampling period, x1 and x2 are the first-order differential link outputs obtained by decomposing the second-order correction link, x3 is the first-order inertia link output obtained by decomposing the second-order correction link, and x I is the integral term input, T d is the differential link response time constant, y P is the proportional output, y I is the integral output, y D is the differential output, Δx is the unit frequency deviation, x in is the input of the PID controller, K P is the proportional gain of the speed regulator, K I is the integral gain of the speed regulator, K D is the differential gain of the speed regulator, x r is the unit frequency given value, P e is the generator power, x is the instantaneous speed value when the unit is actually running, Δx max Δx is the upper limit of the unit frequency deviation limit; min is the lower limit of the unit frequency deviation, P r is the power given value, e p is the power slip coefficient of the speed regulator.

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