A control method for primary frequency modulation in a power dead zone range of a hydroelectric generating set

Abstract

The application discloses a control method for primary frequency modulation in a power dead zone range of a hydroelectric generating set, and belongs to the technical field of hydroelectric generating set regulation. The method comprises the following steps: S1, calculating H1 and H2 of a water diversion system according to the water flow inertia time constant of the water diversion system and the mechanical inertia time constant of the generating set; S2, calculating a dynamic analytical expression of the generating set power when a frequency unit step disturbance occurs; S3, calculating a first-order differential link coefficient decomposed by a second-order correction link based on the dynamic analytical expression of the generating set power; and S4, calculating the output of a PID speed regulator in a current sampling period. The scheme calculates the oscillation link transfer function parameters in a dynamic process, and a second-order system correction transfer function of a frequency given value is designed on the basis, so that the oscillation phenomenon of the generating set power does not occur when the frequency given value of the generating set changes, the problem that the power exceeds the power dead zone in the dynamic process is prevented, and a limiting link is arranged at the frequency deviation value to ensure that the power steady-state value exceeds the power dead zone range.

Description

Technical Field

[0001] This invention belongs to the field of hydropower generator set regulation technology, specifically relating to a control method for primary frequency regulation within the power dead zone of a hydropower generator set. Background Technology

[0002] Hydropower units are the primary regulating power source for grid frequency regulation. Primary frequency regulation balances random load fluctuations on the grid, while secondary frequency regulation maintains the grid frequency stable within permissible ranges. Currently, in hydropower unit control, the speed governor performs secondary frequency regulation control based on the grid load setpoint and power dead zone, while the unit performs primary frequency regulation control based on grid frequency fluctuations. However, during primary and secondary frequency regulation, the primary frequency regulation amplitude often becomes too large, causing the power to exceed the secondary frequency regulation dead zone. This triggers reverse operation of the primary and secondary frequency regulation, leading to power oscillations during the unit's regulation process, and even serious accidents such as unit instability.

[0003] Currently, the method of disengaging from secondary frequency regulation during primary frequency regulation and re-engaging in secondary frequency regulation after the primary frequency regulation ends greatly reduces the unit's ability to regulate the power grid. Summary of the Invention

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

[0005] To solve the above-mentioned technical problems, the present invention provides a control method for primary frequency regulation within the power dead zone of a hydropower unit, comprising the following steps:

[0006] S1. Calculate H1 to H4 of the water diversion system based on the water flow inertia time constant and the unit mechanical inertia time constant;

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

[0008] S3. Based on H1, H2 and the feature analysis results, calculate the coefficients of the first-order differential element decomposed by the second-order correction element;

[0009] S4. Based on the coefficients of the first-order differential element, calculate the output of the PID speed controller in the current sampling period.

[0010] Preferably, S1 includes:

[0011] S11. Within the power dead zone of the hydropower unit, without considering the change in power input, obtain the transfer function of the hydropower unit's output power with respect to the frequency input.

[0012] S12. Under the conditions of S11, the characteristic equation of the transfer function of the hydropower unit's output power with respect to a given frequency is obtained.

[0013] S13. Considering the general range of values ​​for the water flow inertia time constant and the unit mechanical inertia time constant, according to relevant standards, the matching of the water flow inertia time constant and the unit mechanical inertia time constant is constrained, and the PID parameters are formulated using the Krivchenko recommended formula to obtain the PID parameter expression.

[0014] S14. Calculate 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 a quartic equation in one variable, and then the H1 to H4 of the water diversion system are calculated.

[0016] Preferably, the transfer function of the hydropower unit's output power with respect to a given frequency is specifically expressed as follows:

[0017]

[0018] The transfer function parameters A0, A1, A2, A3, A4, B0, B1, B2, and B3 satisfy the following:

[0019]

[0020] In the formula, x r P is the frequency setpoint for the generator set. e Where is the generator power, x is the instantaneous speed of the unit during actual operation, and K is the generator speed. P K is the proportional gain of the speed controller. I K is the integral gain of the speed controller. D T is the differential gain of the speed controller. w e is the inertial time constant of the water flow in the water diversion system. y Let be the transmission coefficient of turbine torque to guide vane opening, and e be the turbine coefficient. qh T is the transfer coefficient of turbine flow rate to head. a P is the mechanical inertia time constant of the hydroelectric generator unit. r For the power setpoint, e p is the power slip coefficient of the speed governor, and s is the Laplace operator.

[0021] As a preferred option, the specific expressions for H1 to H4 are as follows:

[0022]

[0023] Among them, the parameters satisfy:

[0024]

[0025] Where D0, D1, D2, and D3 are the standardized coefficients of the characteristic equation, and p, q, and k are the correlation coefficients in solving a quartic equation using the Ferrari method.

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

[0027] P e (s)=P1(s)+P2(s)+P3(s);

[0028]

[0029] In the formula, E1, E2, F1, F2, and F3 satisfy:

[0030]

[0031] In the formula, t is time, P1 is the monotonically decaying component corresponding to the real root of the system, P2 is the oscillatory decaying component corresponding to the conjugate complex root of the system, P3 is the constant component after the system stabilizes, 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 coefficients of the equivalent second-order transfer function, F3 is the steady-state component coefficient, P1 is the oscillatory decaying component corresponding to the conjugate complex root of the system, P2 is the monotonically decaying component corresponding to the real root of the system, and P3 is the constant component after the system stabilizes.

[0032] As a preferred option, the feature analysis results include: since P1 is the oscillation decay component corresponding to the system's conjugate complex root, H1 and H2 in the transfer function corresponding to P1 are possible factors that cause the system power to oscillate dynamically with the frequency setpoint, resulting in power peak 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] As a preferred option, in S3, the second-order correction element is decomposed into the sum of the first-order derivative and the first-order inertial element, and the actual derivative element is used instead of the ideal derivative element in the PID control strategy.

[0034] As a preferred embodiment, in S3, the analytical expression for the coefficients of the first-order differential element is specifically expressed as follows:

[0035]

[0036] Where a and b are the coefficients of the first-order differential element.

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

[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, the parameters satisfy:

[0044]

[0045] In the formula, m is the number of samplings, ΔT is the sampling period, x1, x2, and x3 are the outputs of the first-order differential element obtained from the decomposition of the second-order correction element, and x4 is the output of the first-order inertial element obtained from the decomposition of the second-order correction element. I For the integral term input, T d Let y be the response time constant of the differential element. P Output as the proportional term, y I Output the integral term, y D The output is the differential term, where Δx is the unit frequency deviation, and x is the differential term output. in K is the input to the PID controller. P K is the proportional gain of the speed controller. I K is the integral gain of the speed controller. D x is the differential gain of the speed controller. r P is the frequency setpoint for the generator set. e Let x be the generator power, x be the instantaneous speed of the unit during actual operation, and Δx be the generator speed. max The upper limit of the unit frequency deviation; Δx min P is the lower limit of the unit frequency deviation limit. r For the power setpoint, e p This is the power slip coefficient of the speed governor.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] This scheme derives and analyzes the power transfer function of the unit's regulation system to the frequency setpoint, calculates the transfer function parameters of the oscillation element during dynamic processes, and designs a second-order system correction transfer function for the frequency setpoint. This ensures that the unit's power does not oscillate when the unit's frequency setpoint changes, preventing the power from exceeding the power dead zone during dynamic processes. Simultaneously, a limiting element is set at the frequency deviation value to ensure that the steady-state power value does not exceed the power dead zone range. Thus, it achieves the effect of primary frequency regulation within the secondary frequency regulation dead zone range of the hydropower unit, avoiding the problem of power oscillation caused by primary frequency regulation triggering secondary frequency regulation, thereby improving the stability of the hydropower unit's regulation process. Attached Figure Description

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

[0049] Figure 2 This is a frequency response characteristic diagram of a conventional hydroelectric generator set regulating system in the method of this invention;

[0050] Figure 3 This is a block diagram of the control strategy of the improved speed governor in the method of the present invention. Detailed Implementation

[0051] Example 1: A control method for primary frequency regulation within the power dead zone of a hydropower unit, based on... Figure 1 The typical block diagram of a traditional hydroelectric generator set regulation system shown illustrates that the power setpoint remains unchanged within the unit's power dead zone. Therefore, neglecting changes in the power setpoint, the transfer function of the unit's output power with respect to the frequency setpoint is:

[0052]

[0053] The transfer function parameters A0, A1, A2, A3, A4, B0, B1, B2, and B3 satisfy the following:

[0054]

[0055] Where, x r P is the frequency setpoint for the generator set. e Where is the generator power, x is the instantaneous speed of the unit during actual operation, and K is the generator speed. P K is the proportional gain of the speed controller. I K is the integral gain of the speed controller. D T is the differential gain of the speed controller. w e is the inertial time constant of the water flow in the water diversion system. y Let be the transmission coefficient of turbine torque to guide vane opening, e be the turbine coefficient, eqh be the transmission coefficient of turbine flow rate to head, and T be the transmission coefficient of turbine flow rate to head.a P is the mechanical inertia time constant of the hydroelectric generator unit. r ε is the power setpoint, ep is the power slip coefficient of the speed governor, and s is the Laplace operator.

[0056] The characteristic equation of the system at this time is:

[0057] A4s 4 +A3s 3 +A2s 2 +A1s+A0=0 (3)

[0058] For T in the project w With T a The general range of values ​​for T is... w Within the range [0.5, 4], T a Within the range [2.5, 15], and simultaneously according to the standard GB9652.1-2019 Technical Conditions for Speed ​​Regulation Systems of Hydropower Turbines, T... w / T a <1.2 to T w With T a The matching constraints are applied, and the PID parameters are determined using the Krivchenko recommended formula, which is as follows:

[0059]

[0060] Wherein, KP0 is the initial value of the proportional gain of the speed governor, KI0 is the initial value of the integral gain of the speed governor, and KD0 is the initial value of the derivative gain of the speed governor.

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

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

[0063]

[0064] Since the characteristic equation is a quartic equation in one variable, and its characteristic roots are a pair of conjugate complex roots and two distinct real roots, according to Ferrari's method for quartic equations, the characteristic equation shares the same roots as the following two quadratic equations in one variable:

[0065]

[0066] H1, H2, H3, and H4 are the coefficients of the equivalent second-order characteristic equation.

[0067] Among them, the parameters satisfy:

[0068]

[0069] Where D0, D1, D2, and D3 are the standardized coefficients of the characteristic equation, and p, q, and k are the correlation coefficients in solving a 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)=P1(s)+P2(s)+P3(s) (7)

[0072]

[0073] In the formula, E1, E2, F1, F2, and F3 satisfy:

[0074]

[0075] The expressions for each parameter are as follows:

[0076]

[0077] Where C0, C1, C2, and C3 are the standardized coefficients of the transfer function, E1, E2, F1, and F2 are the coefficients of the equivalent second-order transfer function, F3 is the steady-state component coefficient, P1 is the oscillatory decay component corresponding to the conjugate complex root of the system, P2 is the monotonic decay component corresponding to the real root of the system, and P3 is the constant component after the system stabilizes.

[0078] We can obtain:

[0079]

[0080] Since P1 is the oscillation decay component corresponding to the system's conjugate complex root, the system power may oscillate dynamically as the frequency setpoint changes, which may cause 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 will cause the unit power to exceed the power dead zone limit during the primary frequency regulation process.

[0081] To prevent power from exceeding the power dead zone during the unit's primary frequency regulation, a second-order correction is applied to the frequency disturbance to eliminate power fluctuations caused by system oscillations. Simultaneously, to prevent excessive frequency setpoint disturbances from causing the steady-state value to exceed the power dead zone, frequency deviation is limited. Therefore, the improved system transfer function is as follows: Figure 2 As shown, the input x of the PID controller in It can be represented as:

[0082]

[0083] Where Δx is the unit frequency deviation; T1 and T2 are the response time constants of the second-order system; Δx max The upper limit of the unit frequency deviation; Δx min This is the lower limit of the unit frequency deviation limit.

[0084] The purpose of limiting the unit's frequency deviation is to prevent the unit from exceeding its power dead zone under steady-state operating conditions; therefore, Δx max With Δx min Should meet

[0085]

[0086] Where, ΔP max ΔP is the upper limit of the unit's power dead zone; min This is the lower limit of the unit's power dead zone.

[0087] The second-order correction element can be decomposed into the sum of the first-order derivative and the first-order inertial element. Simultaneously, the actual derivative element is used instead of the ideal derivative element in the PID control strategy. The control strategy block diagram of the speed controller is as follows: Figure 3 As shown, x1 and x2 are the outputs of the first-order differential elements obtained from the decomposition of the second-order correction element, and x3 is the output of the first-order inertial element obtained from the decomposition of the second-order correction element. I For the integral term input, T d Let y be the response time constant of the differential element. P Output as the proportional term, y I Output the integral term, y D This is the output of the differential term. At this point, the unit frequency deviation Δx can be expressed as:

[0088]

[0089] Where a and b are coefficients of a differential element, they can be expressed as:

[0090]

[0091] Since the currently widely used microcomputer speed controllers can only process discrete data after the system has been sampled, it is necessary to implement... Figure 3 The speed controller control strategy shown needs to be... Figure 3 Discretize, Figure 3 After discretization, the calculation process of the control strategy within the microcomputer speed controller can be obtained as follows:

[0092]

[0093] In the formula, m is the number of samples; ΔT is the sampling period.

[0094] This scheme derives and analyzes the power transfer function of the unit's regulation system to the frequency setpoint, calculates the transfer function parameters of the oscillation element during dynamic processes, and designs a second-order system correction transfer function for the frequency setpoint. This ensures that the unit's power does not oscillate when the unit's frequency setpoint changes, preventing the power from exceeding the power dead zone during dynamic processes. Simultaneously, a limiting element is set at the frequency deviation value to ensure that the steady-state power value does not exceed the power dead zone range. Thus, it achieves the effect of primary frequency regulation within the secondary frequency regulation dead zone range of the hydropower unit, avoiding the problem of power oscillation caused by primary frequency regulation triggering secondary frequency regulation, thereby improving the stability of the hydropower unit's regulation process.

Claims

1. A control method for primary frequency regulation within the power dead zone of a hydropower unit, characterized in that, Includes the following steps: S1. Calculate the water diversion system based on the water flow inertia time constant and the unit mechanical inertia time constant. to ; S1 includes: S11, within the power dead zone of the hydropower unit, without considering the change in power input, obtaining the transfer function of the output power of the hydropower unit with respect to the frequency input; S12. Under the conditions of S11, the characteristic equation of the transfer function of the hydropower unit's output power with respect to a given frequency is obtained. S13. Considering the range of values ​​for the water flow inertia time constant and the unit mechanical inertia time constant, the matching between the water flow inertia time constant and the unit mechanical inertia time constant is constrained, and the PID parameters are determined using the Krivchenko recommended formula to obtain the PID parameter expression. S14. Calculate 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 using the Ferrari method for quartic equations in one variable, and then the water diversion system is calculated. to ; S2. Calculate the dynamic analytical expression of unit power under unit frequency step disturbance, perform characteristic analysis on the expression, and obtain the characteristic analysis results; In S2, the dynamic analytical expression for unit power during a unit frequency step disturbance is specifically expressed as follows: ； ； ； ； In the formula, Where t is the generator power, and t is time. , , , These are the standardized coefficients of the transfer function. , , , These are the coefficients of the equivalent second-order transfer function. These are the steady-state component coefficients. This represents the oscillatory decay component corresponding to the system's conjugate complex root. This represents the monotonically decaying component corresponding to the real root of the system. These are the constant components after the system stabilizes. , , , These are the coefficients of the equivalent second-order characteristic equation; S3, based on the above , Based on the feature analysis results, the coefficients of the first-order differential element, decomposed from the second-order correction element, are calculated; in step S3, the second-order correction element is decomposed into the sum of the first-order differential and the first-order inertial element, and the actual differential element is used to replace the ideal differential element in the PID control strategy; at this time, the unit frequency deviation... Represented as: ； The analytical expression for the coefficients of the first-order differential element is as follows: ； Where a and b are the coefficients of the first-order differential element; is the generator frequency setpoint; x is the instantaneous speed of the generator during actual operation; s is the Laplace operator; , These are the coefficients of the equivalent second-order characteristic equation; This refers to the unit's frequency deviation. , Let be the response time constant of the second-order system; , The output is the first-order differential element obtained from the decomposition of the second-order correction element. The output of the first-order inertial element is obtained from the decomposition of the second-order correction element; S4. Based on the coefficients of the first-order differential element, calculate the output of the PID speed controller in the current sampling period.

2. The control method for primary frequency regulation within the power dead zone of a hydropower unit according to claim 1, characterized in that, The transfer function of the hydropower unit's output power with respect to a given frequency is specifically expressed as follows: ； Among them, the pass function parameters , , , , , , , , satisfy: ； In the formula, The setpoint for the generator frequency. Where is the generator power, and x is the instantaneous speed of the unit during actual operation. The proportional gain of the speed controller, The integral gain of the speed controller. The differential gain of the speed controller, The inertial time constant of the water flow in the water diversion system, Let be the transmission coefficient of turbine torque to guide vane opening, and e be the turbine coefficient. The transfer coefficient of water head from turbine flow rate is denoted as . The mechanical inertia time constant of the hydroelectric generator set. For the power setpoint, is the power slip coefficient of the speed governor, and s is the Laplace operator.

3. The control method for primary frequency regulation within the power dead zone of a hydropower unit according to claim 2, characterized in that, The to The specific expression is: ； Among them, the parameters satisfy: ； in, , , , denoted as the standardized coefficients of the characteristic equation, and p, q, and k are the correlation coefficients in solving a quartic equation using the Ferrari method. , , , These are the coefficients of the equivalent second-order characteristic equation.

4. The control method for primary frequency regulation within the power dead zone of a hydropower unit according to claim 1, characterized in that, The feature analysis results include: due to This is the oscillatory decay component corresponding to the system's conjugate complex root, therefore In the corresponding transfer function and It is a dynamic process that causes the system power to oscillate with the frequency setpoint, resulting in 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.

5. The control method for primary frequency regulation within the power dead zone of a hydropower unit according to claim 1, characterized in that, In S4, the PID speed controller output for the current sampling period is specifically represented as follows: ； in, , , ,satisfy: ； Among them, the parameters satisfy: ； In the formula, m is the number of samples. The sampling period is , , is the output of the first-order differential element obtained from the decomposition of the second-order correction element. The output of the first-order inertial element is obtained from the decomposition of the second-order correction element. Input for the integral term. Let be the response time constant of the differential element. Output as a proportional term. Output the integral term. Output the differential term. For unit frequency deviation, For the input of the PID controller, The proportional gain of the speed controller, The integral gain of the speed controller. The differential gain of the speed controller, The setpoint for the generator frequency. Where is the generator power, and x is the instantaneous speed of the unit during actual operation. This is the upper limit of the unit's frequency deviation. This is the lower limit of the unit frequency deviation limit. For the power setpoint, This is the power slip coefficient of the speed governor.

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