New energy primary frequency modulation method considering amplitude limiting link of speed regulator of synchronous unit

Abstract

The invention provides a new energy primary frequency modulation method considering an amplitude limiting link of a synchronous unit speed regulator. The new energy primary frequency modulation method comprises the following steps: constructing a first system frequency response model before the synchronous unit speed regulator reaches amplitude limiting; and constructing a second system frequency response model after the synchronous unit speed regulator reaches the amplitude limit, wherein a state variable initial value of the second system frequency response model is calculated by the first system frequency response model when the synchronous unit speed regulator reaches the amplitude limit. A synchronous unit speed regulator amplitude limiting link is introduced into a system frequency response model, system dynamic frequency characteristics of the new energy unit participating in primary frequency modulation are corrected, the method can be used for assisting setting of primary frequency modulation control parameters of the new energy unit, the system can be effectively prevented from triggering low-frequency load shedding, and the frequency stability of a power system is maintained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power systems, and in particular relates to a new energy primary frequency modulation method considering a synchronous unit governor limiter. BACKGROUND

[0002] Frequency is one of the important indicators to measure power quality. The frequency variation of a power system will have adverse effects on users, power plants and the power system itself. In recent years, new energy units are connected to the grid in large scale through power electronic devices, which leads to a decrease in the equivalent inertia of the power system and a weakening of the system primary frequency modulation capability, and the frequency stability of the system is threatened. Therefore, in order to alleviate the deterioration of the frequency stability of the system caused by the large-scale connection of new energy units to the grid, new energy units need to have active primary frequency modulation capability.

[0003] At present, most of the researches on new energy participating in primary frequency modulation are based on the system SFR (system frequency response) model. Since this model is difficult to handle complex nonlinear operations, the current research generally does not consider the limiter of the synchronous unit governor, which leads to an optimistic result and even a large deviation, which will have a negative impact on the selection of new energy frequency modulation control parameters, and even trigger low-frequency load shedding, affecting the frequency stability of the power system. In view of such problems, the limiter of the synchronous unit governor needs to be included in the research scope of primary frequency modulation, the actual influence of the limiter on primary frequency modulation is solved from the mechanism level, the dynamic frequency characteristics of the system are corrected, and the frequency instability problem caused by improper setting of new energy frequency modulation control parameters is avoided. SUMMARY

[0004] The technical problem solved by the present application is how to consider the limiter of the synchronous unit governor when performing new energy primary frequency modulation.

[0005] The present application provides a new energy primary frequency modulation method considering a limiter of a synchronous unit governor, which comprises:

[0006] A first system frequency response model before the synchronous unit governor reaches the limiter is constructed.

[0007] A second system frequency response model after the synchronous unit governor reaches the limiter is constructed, wherein the initial value of the state variable of the second system frequency response model is calculated by the first system frequency response model when the synchronous unit governor reaches the limiter.

[0008] Optionally, the method for constructing the first system frequency response model before the synchronous unit governor reaches the limiter comprises:

[0009] A disturbance power P d is set, and the disturbance power P is a step function with a step amount of Pstep The system frequency variation is calculated as follows:

[0010]

[0011] Wherein:

[0012]

[0013] In the formula, H is the inertia time constant of the traditional unit, D is the damping coefficient, K m is the mechanical power gain coefficient, R is the governor adjustment coefficient, F H is the reheating constant of the steam turbine, T R is the reheating time constant of the steam turbine, K df is the droop control coefficient, in the per-unit calculation, the system frequency variation Δf is equal to the traditional unit angular velocity variation Δω;

[0014] The time domain expression of the system frequency variation Δf is solved from the formula (1) as follows:

[0015]

[0016] Wherein:

[0017] Optionally, the method for constructing the second system frequency response model of the synchronous unit governor after the amplitude limiting comprises:

[0018] The equivalent disturbance power P d2 of the system after the governor reaches the amplitude limiting value is set as:

[0019]

[0020] In the formula, P step2 is the step quantity of P d2 , ΔP mmax is the mechanical power variation of the synchronous unit when the governor reaches the amplitude limiting;

[0021] The system state space corresponding to the state variable x is constructed as follows:

[0022]

[0023] Wherein:

[0024] The initial value of the state variable is set as x(0), and the formula (6) is solved as follows:

[0025] y(s)=C sc (sI-A sc ) -1 [x(0)+B sc u(s)] (8)

[0026] Wherein:

[0027] Simplifying to obtain the system frequency variation Δf after the amplitude limiting sc is:

[0028]

[0029] Obtain the time-domain expression of the system frequency variation Δf sc is:

[0030]

[0031] Optionally, the calculation method of the initial value of the state variable of the second system frequency response model is as follows:

[0032] When the governor does not reach the amplitude limiting value, the variation ΔP of the output power of the synchronous unit m is:

[0033]

[0034] The time-domain expression is:

[0035]

[0036] Wherein:

[0037] Solve the equation: ΔP m (t) = ΔP mmax (15)

[0038] The moment t when the governor reaches the amplitude limiting value can be obtained max , the moment t is substituted into formula (3) to obtain the initial value of the state variable: max

[0039] x(0) = Δf(t max ).

[0040] Optionally, the new energy primary frequency modulation method further comprises:

[0041] Substitute the calculated initial value of the state variable into formula (11) to obtain the expression of the system frequency variation of the second system frequency response model.

[0042] The new energy primary frequency modulation method provided by the application has the following technical effects:

[0043] ​The amplitude limiting link of the synchronous unit governor is introduced into the system frequency response model, the system dynamic frequency characteristic under the participation of the new energy unit in primary frequency modulation is corrected, which can be used for assisting the setting of the primary frequency modulation control parameter of the new energy unit, and can more effectively avoid the triggering of the low frequency load shedding of the system and maintain the frequency stability of the power system. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A flowchart of a new energy primary frequency modulation method considering the amplitude limiting link of a synchronous unit governor according to one or more embodiments;

[0045] Figure 2 A schematic diagram of a first system frequency response model according to one or more embodiments;

[0046] Figure 3 A schematic diagram of a second system frequency response model according to one or more embodiments;

[0047] Figure 4 A schematic diagram of an equivalent second system frequency response model according to one or more embodiments;

[0048] Figure 5 A decomposition schematic diagram of an equivalent second system frequency response model according to one or more embodiments;

[0049] Figure 6 A comparison diagram of the system dynamic frequency curves before and after correction according to one or more embodiments. DETAILED DESCRIPTION

[0050] In order to make the purposes, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0051] Before describing the various embodiments of the present application in detail, first, the technical concept of the present application is simply described: the current new energy primary frequency modulation process is based on the SFR model, and usually does not consider the amplitude limiting problem of the synchronous unit governor, which is easy to cause inaccurate frequency modulation. Therefore, the new energy primary frequency modulation method considering the amplitude limiting link of the synchronous unit governor provided by the present application respectively constructs a first system frequency response model and a second system frequency response model before and after the synchronous unit governor reaches the amplitude limiting, wherein the second system frequency response model considers the amplitude limiting link, the initial value of the state variable thereof is calculated according to the first system frequency response model when the synchronous unit governor reaches the amplitude limiting, and a segmented function is used to describe the primary frequency modulation process in different stages, which is conducive to improving the frequency modulation accuracy. The specific principle of the new energy primary frequency modulation method considering the amplitude limiting link of the synchronous unit governor of the present application will be described in combination with more embodiments.

[0052] Specifically, as shown in the figure, the new energy primary frequency modulation method provided by the embodiment one considering the governor limiter of the synchronous unit comprises the following steps: Figure 1

[0053] Step S10: constructing a first system frequency response model before the governor of the synchronous unit reaches the limiter;

[0054] Step S20: constructing a second system frequency response model after the governor of the synchronous unit reaches the limiter, wherein the initial value of the state variable of the second system frequency response model is calculated by the first system frequency response model when the governor of the synchronous unit reaches the limiter.

[0055] In one or more embodiments, in step S10, Figure 2 the first system frequency response model is shown, and the method for constructing the first system frequency response model before the governor of the synchronous unit reaches the limiter comprises:

[0056] Set the disturbance power P d is a step function, and the step amount is P step , and the system frequency change amount is calculated as follows:

[0057]

[0058] wherein:

[0059]

[0060] In the formula, H is the inertia time constant of the conventional unit, D is the damping coefficient, K m is the mechanical power gain coefficient, R is the governor adjustment coefficient, F H is the reheating constant of the steam turbine, T R is the reheating time constant of the steam turbine, K df is the droop control coefficient, and in the per-unit calculation, the system frequency change amount Δf is equal to the conventional unit angular velocity change amount Δω.

[0061] The time domain expression of the system frequency change amount Δf is solved from the formula (1) as follows:

[0062]

[0063] wherein:

[0064] In one or more embodiments, in step S20, Figure 3 the second system frequency response model is shown, and at this time, the nonlinear part therein needs to be solved by a segmented function, and when the governor reaches the limit value, ΔP m reaches the maximum value ΔP mmax ​And remain unchanged, at this time the frequency response model diagram of the second system can be equivalent to: Figure 4 Δw sc This refers to the change in system frequency after the governor reaches its limit. For example, a method for constructing a second system frequency response model after the synchronous generator governor reaches its limit includes:

[0065] The equivalent disturbance power P of the system after the speed governor reaches the limit value is set. d2 for:

[0066]

[0067] In the formula, P step2 For P d2 The step quantity, ΔP mmax This refers to the change in mechanical power of the synchronous generator unit when the speed governor reaches its limit.

[0068] right Figure 4 The model is decomposed, such as Figure 5 As shown, the decomposed model has a state variable x. Construct the system state space corresponding to state variable x:

[0069]

[0070] in:

[0071] Let the initial value of the state variable be x(0), and solve equation (6) to get:

[0072] y(s)=C sc (sI-A sc ) -1 [x(0)+B sc u(s)] (8)

[0073] in:

[0074] Simplifying, we obtain the system frequency change Δf after reaching the amplitude limit. sc for:

[0075]

[0076] The system frequency change Δf is obtained. sc The time-domain expression is:

[0077]

[0078] For example, in step S20, the initial values ​​of the state variables of the second system frequency response model are calculated as follows:

[0079] When the speed governor does not reach the limit value, the change in output power ΔP of the synchronous generator unitm for

[0080]

[0081] Its time-domain expression is:

[0082]

[0083] in:

[0084] Solve the equation: ΔP m (t)=ΔP mmax (15)

[0085] The instant t when the speed controller reaches the limit value can be obtained. max , will be the instantaneous moment t max Substituting into equation (3), we obtain the initial values ​​of the state variables:

[0086] x(0)=Δf(t max ).

[0087] Next, the calculated initial values ​​of the state variables are substituted into equation (11) to obtain the expression for the system frequency change of the second system frequency response model, so as to correct the system dynamic frequency curve.

[0088] For example, to verify the correction effect, this embodiment uses a power reference value of 100MVA, a frequency reference value of 50Hz, an output power of 1p.u. during normal operation of the synchronous generator, a value of R of 0.05, a value of H of 4s, and K... m The value is 0.95, F H The value is 0.3, T R The value is 4s, D is 1, and K... df The value is set to 4. The system initially generates a power deficit of -0.1 pu, and the synchronous generator speed governor's limit value is -0.06 pu. The correction result is as follows: Figure 6 As shown, the results indicate that the minimum and steady-state frequency values ​​of the corrected system are both lower than those before the correction, which can more accurately represent the actual dynamic frequency characteristics of the system and assist new energy units in setting more reasonable primary frequency control parameters.

[0089] The specific embodiments of this application have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that modifications and improvements can be made to these embodiments without departing from the principles and spirit of this application as defined by the claims and their equivalents, and such modifications and improvements should also be within the protection scope of this application.

Claims

1. A method for primary frequency regulation of new energy sources that takes into account the limiting element of the synchronous generator speed governor, characterized in that, The primary frequency regulation method for new energy sources includes: Construct a first-system frequency response model for the synchronous generator unit before the speed governor reaches its limit. A second system frequency response model is constructed after the synchronous generator speed governor reaches its limit, wherein the initial values ​​of the state variables of the second system frequency response model are calculated by the first system frequency response model when the synchronous generator speed governor reaches its limit.

2. The method for primary frequency regulation of new energy sources considering the limiting link of the synchronous generator speed governor according to claim 1, characterized in that, The method for constructing the first system frequency response model before the synchronous generator speed governor reaches its limit includes: Set disturbance power P d Let P be a step function. step The change in system frequency is calculated as follows: in: In the formula: H is the inertial time constant of the traditional unit, D is the damping coefficient, and K is the damping coefficient. m R is the mechanical power gain coefficient, and F is the speed governor droop coefficient. H T is the reheat constant of the steam turbine. R K is the reheat time constant of the steam turbine. df As the droop control coefficient, in the per-unit value calculation, the system frequency change Δf is equal to the angular velocity change Δω of a traditional unit; The time-domain expression for the system frequency change Δf, obtained from equation (1), is: in:

3. The method for primary frequency regulation of new energy sources considering the limiting link of the synchronous generator speed governor according to claim 2, characterized in that, The method for constructing the second system frequency response model after the synchronous generator speed governor reaches its limit includes: The equivalent disturbance power P of the system after the speed governor reaches the limit value is set. d2 for: In the formula, P step2 For P d2 The step quantity, ΔP mmax This refers to the change in mechanical power of the synchronous generator unit when the speed governor reaches its limit. Construct the system state space corresponding to state variable x: in: Let the initial value of the state variable be x(0), and solve equation (6) to get: y(s)=C sc (sI-A sc ) -1 [x(0)+B sc u(s)] (8) in: Simplifying, we obtain the system frequency change Δf after reaching the amplitude limit. sc for: The system frequency change Δf is obtained. sc The time-domain expression is:

4. The method for primary frequency regulation of new energy sources considering the limiting link of the synchronous generator speed governor according to claim 3, characterized in that, The method for calculating the initial values ​​of the state variables in the frequency response model of the second system is as follows: When the speed governor does not reach the limit value, the change in output power ΔP of the synchronous generator unit m for Its time-domain expression is: in: Solve the equation: ΔP m (t)=ΔP mmax (15) The instant t when the speed controller reaches the limit value can be obtained. max , will be the instantaneous moment t max Substituting into equation (3), we obtain the initial values ​​of the state variables: x(0)=Δf(t max )。 5. The method for primary frequency regulation of new energy sources considering the limiting element of the synchronous generator speed governor according to claim 4, characterized in that, The primary frequency regulation method for new energy sources also includes: Substituting the calculated initial values ​​of the state variables into equation (11), we obtain the expression for the system frequency change of the second system frequency response model.

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