A method and system for establishing an index system for evaluating power grid inertia demand

Abstract

A method and system for establishing an index system for evaluating power grid inertia demand, comprising: obtaining power grid inertia, including synchronous machine inertia, asynchronous machine inertia, voltage source type virtual inertia, current source type virtual inertia and static load voltage equivalent inertia; calculating the minimum value of power grid inertia under the constraint of frequency change rate; calculating the minimum value of power grid inertia under the constraint of frequency deviation; correcting the minimum value of power grid inertia under the constraint of frequency deviation using system energy storage device constraint; taking the maximum value of the two as the minimum inertia of the power grid; calculating the inertia safety domain within the evaluation period T according to the minimum inertia of the power grid; and evaluating the power grid inertia demand based on the inertia safety domain. The present application solves the problem of calculating the minimum inertia value for maintaining stable operation of the power grid under different constraint conditions according to known parameters of the power grid, comparing the calculation results obtained under different constraint conditions, and giving the inertia domain for safe operation of the power grid.

Description

Technical Field

[0001] This invention belongs to the field of power system safety technology, specifically relating to a method and system for establishing a power grid inertia demand assessment index system. Background Technology

[0002] With the continuous development of renewable energy, its proportion in the power system is increasing. However, since wind power, photovoltaic, and other new energy units are generally connected to the grid via power electronic devices, they cannot provide rotational inertia support for the power system under conventional control. When the system is subjected to disturbances that cause frequency deviations, the power system lacking inertia support will find it more difficult to counteract these deviations, leading to a series of stability problems, such as triggering low-frequency load shedding and high-frequency tripping of safety automatic devices, affecting reliable power supply. According to the Energy Transition 2030 / 2050 plans, the proportion of renewable energy generation in many countries around the world will increase significantly. Therefore, in the foreseeable future, the dominant position of converters will become increasingly apparent, which will further exacerbate the trend of system inertia deterioration.

[0003] In existing technologies, domestic and international scholars have achieved significant research results in areas such as the static voltage safety domain and the distribution network safety domain, and have also conducted some research on inertia demand assessment under different scenarios. However, the concept and method of the overall system inertia demand assessment index system are still unclear. While the existing technology "Minimum Inertia Demand Assessment of Microgrids in Islanded and Grid-connected Modes" introduces the concept of minimum inertia demand for microgrids, it only proposes methods for assessing minimum inertia demand under islanded and grid-connected modes. Considering that the power grid is a continuously operating system, a complete inertia demand assessment system should be continuous and closed along the time axis. Therefore, it is necessary to calculate the system inertia under multiple constraints and simultaneously consider the time scale to obtain a complete inertia demand assessment index system, as well as a method that comprehensively considers the influencing factors related to inertia demand, for evaluating the safety margin of system inertia and clarifying its adjustable space. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for establishing a power grid inertia demand assessment index system. This system solves the problem of calculating the minimum inertia value required to maintain stable operation of the power grid under different constraints based on known power grid parameters, comparing the calculation results obtained under different constraints, and providing the inertia domain for safe operation of the power grid.

[0005] The present invention adopts the following technical solution. A method for establishing a power grid inertia demand assessment index system, comprising:

[0006] Step 1: Obtain the grid inertia, including synchronous machine inertia, asynchronous machine inertia, voltage source virtual inertia, current source virtual inertia, and static load voltage equivalent inertia;

[0007] Step 2: Calculate the minimum power grid inertia considering the frequency change rate constraint;

[0008] Step 3: Calculate the minimum power grid inertia considering frequency deviation constraints;

[0009] Step 4: Correct the minimum grid inertia value calculated in Step 3 considering frequency deviation constraints using system energy storage device constraints;

[0010] Step 5: Compare the minimum inertia of the power grid calculated in Step 2 and Step 4, and take the maximum value of the two as the minimum inertia of the power grid.

[0011] Step 6: Calculate the inertia safety domain within the evaluation period T based on the minimum inertia of the power grid obtained in Step 5.

[0012] Step 7: Assess the grid inertia requirement based on the inertia safety domain.

[0013] In step 1, the voltage source type virtual inertia is realized through a virtual synchronous machine; the current source type virtual inertia is realized by feeding back the system frequency change rate signal to the active power control loop of the converter to change the active power reference value.

[0014] The grid inertia E expressed in terms of energy in step 1 sys The following relationship must be satisfied:

[0015] E sys =E SG +E IM +E V(VS) +E V(CS) +E load-U

[0016] In the formula,

[0017] E SG For the inertia of the synchronous machine,

[0018] E IM For asynchronous machine inertia,

[0019] E V(VS) It is a voltage source type virtual inertia.

[0020] E V(CS) It is a current source type virtual inertia.

[0021] E load-U This is the equivalent inertia of the static load voltage.

[0022] The inertial constant of a power grid system is determined by both the grid's inertia and the system's capacity. The inertial constant H sys The following relationship must be satisfied:

[0023]

[0024] In the formula, S sys This refers to the system capacity.

[0025] In step 2, under the condition of maximum disturbance power in the power grid system, the minimum value of the power grid inertia under the constraint of the frequency change rate is calculated so as to ensure that the frequency change rate does not exceed a set threshold value, and the following relationship is satisfied:

[0026]

[0027] In the formula,

[0028] This represents the minimum value of the power grid inertia under the constraint of the rate of change of frequency.

[0029] ΔP max For the maximum disturbance power,

[0030] RoCoF max Set a threshold value for the rate of change of frequency.

[0031] The set threshold value for the frequency change rate meets the following requirements: when the grid capacity is 3 million kilowatts or above, the set threshold value for the frequency change rate shall not exceed ±0.2Hz; when the grid capacity is below 3 million kilowatts, the set threshold value for the frequency change rate shall not exceed ±0.5Hz.

[0032] The rate of change of frequency, RoCoF, depends only on the grid inertia and the magnitude of the disturbance power, and satisfies the following relationship:

[0033] 2H sys RoCoF=ΔP d

[0034] In the formula, ΔP d For the disturbance power, H sys It is the inertial constant.

[0035] In step 3, the factors affecting frequency deviation include: inertia constant, generator primary frequency regulation, load frequency regulation, and load voltage characteristics;

[0036] Frequency deviation constraints include: frequency deviation constraints for systems without speed regulation and frequency deviation constraints for systems with speed regulation.

[0037] The frequency deviation constraint Δf of the speed-regulating system satisfies the following relationship:

[0038]

[0039] In the formula,

[0040] D sys This is the load frequency adjustment coefficient;

[0041] For systems with frequency deviation constraints, considering the equivalent droop coefficient and response time constant of the generator primary frequency regulation, as well as the influence of power electronic power supply on grid inertia and droop coefficient, the penetration rate K of power electronic power supply is introduced on the basis of systems without frequency deviation constraints.

[0042] In step 4, based on the calculation results of step 3, the power electronic power supply penetration rate K under the frequency deviation constraint is corrected using the system energy storage device constraint, satisfying the following relationship:

[0043] K = 1 - K SG +K re +K store

[0044] In the formula,

[0045] K SG The percentage of traditional synchronous machines replaced after new energy sources are integrated into the system.

[0046] K re The proportion of inertia provided by a virtual synchronous machine composed of power electronic devices to the system.

[0047] K store The proportion of inertia provided to the system's energy storage device.

[0048] In step 5, the minimum inertia H of the power grid min The maximum value among the minimum values ​​of the power grid inertia under different constraints satisfies the following relationship:

[0049]

[0050] In the formula,

[0051] This represents the minimum grid inertia under the RoCoF constraint of the rate of change of frequency.

[0052] This represents the minimum grid inertia under the constraints of frequency deviation and system energy storage devices.

[0053] In step 6, the inertia safety region is obtained by integral calculation within the set evaluation period T, which satisfies the following relationship:

[0054]

[0055] In the formula,

[0056] S ISR Indicates the inertia safety region.

[0057] H MIL (t) represents the total available inertia of the system at time t.

[0058] Hmin (t) represents the minimum inertia of the power grid at time t.

[0059] T represents the length of the evaluation period.

[0060] In step 7, from the perspective of safety and stability, when the actual inertia of the power grid or the predicted value of the power grid inertia is within the inertia safety domain, the power grid inertia should slow down the rate of frequency change regardless of the disturbance event that occurs in the system.

[0061] In step 7, from the perspective of operational scheduling feasibility, the grid inertia within the inertia safety domain is less than the total available inertia of the system. Therefore, any operating point within the inertia safety domain is taken as the target value for adjusting the grid inertia.

[0062] A system for establishing an index system for assessing power grid inertia demand is provided, which is used to implement a method for establishing an index system for assessing power grid inertia demand.

[0063] The beneficial effects of this invention are that, compared with the prior art,

[0064] 1. The minimum grid inertia calculated by the method proposed in this invention is jointly determined by RoCoF constraints, frequency deviation constraints, and system energy storage device constraints. Based on the calculated minimum grid inertia, the actual inertia requirement can be accurately evaluated, and the frequency stability requirements of the system under different disturbance scenarios can be met.

[0065] 2. The method proposed in this invention takes into account the continuous operation of the power grid system, obtains the inertia safety domain based on the time scale, and uses the inertia safety domain as a complete inertia demand assessment index system. It can not only evaluate the safety margin of the system inertia, but also clearly give the adjustable space of the inertia, which helps dispatching and operation personnel to evaluate the sufficiency and safety of the system inertia. Attached Figure Description

[0066] Figure 1 This is a flowchart of a method for establishing a power grid inertia demand assessment index system proposed in this invention.

[0067] Figure 2 This is a schematic diagram of the frequency response of the speed-regulating system in an embodiment of the present invention;

[0068] Figure 3 This is a schematic diagram of the frequency response of the speed regulation system in an embodiment of the present invention;

[0069] Figure 4 This is a schematic diagram of frequency deviations at different permeability rates in an embodiment of the present invention. Detailed Implementation

[0070] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0071] This invention proposes a method for establishing a power grid inertia demand assessment index system, such as... Figure 1 As shown, it includes:

[0072] Step 1: Obtain the grid inertia, including synchronous machine inertia, asynchronous machine inertia, voltage source virtual inertia, current source virtual inertia, and static load voltage equivalent inertia.

[0073] Power system inertia manifests as resistance to frequency changes caused by external disturbances; slowing down the rate of frequency change is crucial for system frequency stability. The components of a complete power system that provide inertial support include synchronous machines, asynchronous machines, virtual synchronous machines, and loads. The grid inertia E, expressed as energy in step 1, is... sys The following relationship must be satisfied:

[0074] E sys =E SG +E IM +E V(VS) +E V(CS) +E load-U ……(1)

[0075] In the formula,

[0076] E SG As the inertia of the synchronous machine, it can achieve inertia support without delay;

[0077] E IM For asynchronous machine inertia;

[0078] E V(VS) It is a voltage source type virtual inertia, implemented through a virtual synchronous machine, which can achieve inertia support without delay;

[0079] E V(CS) As a current-source type virtual inertia, the system RoCoF (Rate of Change of Frequency) signal is fed back to the active power control loop of the converter to change the active power reference value to achieve inertia support, which has a time delay;

[0080] E load-U It is the equivalent inertia of static load voltage, which is essentially a power response.

[0081] The inertial constant of a power grid system is determined by both the grid's inertia and the system's capacity. The inertial constant H sys The following relationship must be satisfied:

[0082]

[0083] In the formula, S sys This refers to the system capacity.

[0084] Step 2: Calculate the minimum grid inertia considering RoCoF constraints.

[0085] RoCoF is an indicator of frequency variation. The grid inertia is at its minimum and RoCoF is at its maximum at the instant the system is subjected to a disturbance. With RoCoF not exceeding a set threshold value as a constraint, under the condition that the grid system experiences maximum disturbance power, RoCoF is kept below the set threshold value. The boundary value of the grid inertia calculated is the minimum grid inertia under the constraint of RoCoF.

[0086] Specifically, in step 2, RoCoF represents the rate of change of the power grid system frequency, which satisfies the following relationship:

[0087]

[0088] In the formula, Δf is the frequency change.

[0089] For systems with a small proportion of voltage-sensitive loads, RoCoF depends only on the grid inertia and the magnitude of the disturbance power, i.e., it satisfies the following relationship:

[0090] 2H sys RoCoF=ΔP d ……(4)

[0091]

[0092] In the formula,

[0093] ΔP d The disturbance power;

[0094] This represents the minimum grid inertia under RoCoF constraints.

[0095] ΔP max This represents the maximum disturbance power.

[0096] RoCoF max Set a threshold value for the rate of change of frequency.

[0097] From equations (4) and (5), it can be seen that when the system experiences its maximum disturbance power ΔP max In this case, to ensure that RoCoF does not exceed the set threshold value RoCoF max The power grid inertia is not less than H. min Maximum disturbance power ΔP max The larger the RoCoF max The smaller the value, the minimum inertia H of the power grid. minThe larger the value, the lower the minimum value of the power grid inertia H. min The smaller.

[0098] Step 3: Calculate the minimum inertia considering the frequency deviation constraint.

[0099] Specifically, the system frequency dynamic response in step 3 satisfies the following relationship:

[0100]

[0101] In the formula,

[0102] f(t) represents the primary frequency regulation of the generator at time t;

[0103] f0 is the system's rated frequency;

[0104] P m (t) represents the equivalent mechanical power of the generator at time t.

[0105] P e (t) represents the equivalent electromagnetic power of the generator at time t.

[0106] D sys This is the load frequency adjustment coefficient.

[0107] Factors affecting frequency deviation include inertia constant, generator primary frequency regulation, load frequency regulation coefficient, and load voltage characteristics. For frequency deviation constraints, analysis is performed separately for systems with and without speed regulation. The grid inertia is calculated based on the given maximum frequency deviation value to obtain the minimum grid inertia considering the frequency deviation constraint.

[0108] Figure 2 This is a schematic diagram of the frequency response of a speed-regulating system in an embodiment of the present invention; for a speed-regulating system, the frequency deviation constraint satisfies the following relationship:

[0109]

[0110] According to equation (7) and the frequency dynamic response model, the minimum grid inertia can be obtained as the grid inertia corresponding to the maximum disturbance and the maximum frequency deviation.

[0111] Figure 3 This is a schematic diagram of the frequency response of a speed-regulating system in an embodiment of the present invention. For a speed-regulating system, considering the equivalent droop coefficient and response time constant of the system's primary frequency regulation, as well as the influence of the power electronic power supply on the grid inertia and droop coefficient, the processing method is similar to that of a speed-unregulating system.

[0112] Step 4: Based on the calculation results of Step 3, the minimum inertia value under the frequency deviation constraint is corrected using the system energy storage device constraint.

[0113] The expression for the influence coefficient (power electronic power supply penetration rate) K of the power electronic power supply on the system droop coefficient and inertia without considering the constraints of the system energy storage device is as follows:

[0114] K = 1 - K SG +K re ……(8)

[0115] In the formula, K SG K represents the percentage of traditional synchronous machines replaced after new energy sources are integrated into the system. re The proportion of inertia provided by a virtual synchronous machine composed of power electronic devices to the system.

[0116] Figure 2 Chinese R sys and T sys Here, represents the equivalent droop coefficient and response time constant for primary frequency regulation, respectively, and K describes the influence of the power electronic power supply on the system inertia and droop coefficient. With the power electronic power supply not participating in frequency regulation and other system parameters remaining constant, gradually increasing the penetration rate of the power electronic power supply results in the system frequency curve shown below. Figure 4 As shown, it can be seen that as the permeability increases, the frequency curve shifts downward as a whole, increasing the maximum frequency deviation and steady-state deviation, but the time to reach the lowest frequency point remains unchanged.

[0117] The droop coefficient and inertia influence coefficient τ, considering the constraints of the system's energy storage device, can be expressed as follows:

[0118] K = 1 - K SG +K re +K store ……(9)

[0119] In the formula, K store The proportion of inertia provided to the system's energy storage device.

[0120] Step 5: Compare the minimum inertia of the power grid calculated in Step 2 and Step 4, and take the maximum value as the minimum inertia of the power grid.

[0121] Specifically, in step 5, the minimum inertia H of the power grid min This represents the maximum value among the minimum values ​​of the power grid inertia under different constraints, i.e.:

[0122]

[0123] In the formula, This represents the minimum grid inertia under RoCoF constraints. This represents the minimum grid inertia under the constraints of frequency deviation and system energy storage devices.

[0124] Step 6: Calculate the inertia safety domain within the evaluation period T based on the minimum inertia of the power grid obtained in Step 5.

[0125] Specifically, in step 6, the inertia safety region is obtained by integral calculation within the set evaluation period T, and the expression is:

[0126] S ISR =∫0 T H MIL (t)-H min (t)dt……(11)

[0127] In the formula, S ISR H represents the inertia safety region. MIL H(t) represents the total available inertia of the system at time t. min (t) represents the minimum inertia of the power grid at time t, and T represents the length of the evaluation period.

[0128] Step 7: Assess the grid inertia requirement based on the inertia safety domain.

[0129] From a safety and stability perspective, when the actual overall inertia of the system or its predicted value is within the ISR (Inertia Security Region), regardless of any potential disturbance events occurring in the system, the system inertia should reliably mitigate rapid frequency changes, thus gaining sufficient time for subsequent frequency regulation intervention. From an operational scheduling feasibility perspective, the inertia values ​​within the ISR are all less than the total usable inertia of the system, allowing the system inertia level to be adjusted to any operating point within the inertia security region.

[0130] In another aspect, this invention proposes a system for establishing an evaluation index system for power grid inertia demand, which is used to realize the method for establishing an evaluation index system for power grid inertia demand.

[0131] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for establishing a power grid inertia demand assessment index system, characterized in that, The establishment method includes: Step 1: Obtain grid inertia, including synchronous machine inertia, asynchronous machine inertia, voltage source virtual inertia, current source virtual inertia, and static load voltage equivalent inertia; voltage source virtual inertia is achieved through a virtual synchronous machine; current source virtual inertia is achieved by feeding back the system frequency change rate signal to the converter active power control loop to change the active power reference value. Step 2: Under the condition of maximum disturbance power in the power grid system, ensure that the frequency change rate does not exceed a set threshold value, and calculate the minimum power grid inertia under the constraint of frequency change rate; the set threshold value of frequency change rate satisfies the following: when the power grid capacity is 3 million kilowatts or above, the set threshold value of frequency change rate does not exceed ±0.2Hz; when the power grid capacity is below 3 million kilowatts, the set threshold value of frequency change rate does not exceed ±0.5Hz. Step 3: Calculate the minimum power grid inertia considering frequency deviation constraints; In step 3, the factors affecting frequency deviation include: inertia constant, generator primary frequency regulation, load frequency regulation, and load voltage characteristics; Frequency deviation constraint for speed control system The following relationship must be satisfied: In the formula, For disturbance power, This is the load frequency regulation coefficient. Let t be the inertia constant and t be the time interval. For systems with frequency deviation constraints, considering the equivalent droop coefficient and response time constant of the generator's primary frequency regulation, as well as the influence of power electronic power supplies on the grid inertia and droop coefficient, the penetration rate of power electronic power supplies is introduced on the basis of systems without frequency deviation constraints. ; Step 4: Correct the minimum grid inertia calculated in Step 3, considering frequency deviation constraints, using system energy storage device constraints. Frequency deviation constraints include: frequency deviation constraints for systems without speed regulation and frequency deviation constraints for systems with speed regulation. Based on the calculation results in Step 3, use system energy storage device constraints to adjust the power electronic power supply penetration rate considering frequency deviation constraints. After modification, the following relationship is satisfied: In the formula, The percentage of traditional synchronous machines replaced after new energy sources are integrated into the system. The proportion of inertia provided by a virtual synchronous machine composed of power electronic devices to the system. The proportion of inertia provided to the system's energy storage devices; Step 5: Compare the minimum inertia of the power grid calculated in Step 2 and Step 4, and take the maximum value of the two as the minimum inertia of the power grid. Step 6: Within the set evaluation period, based on the minimum inertia of the power grid obtained in Step 5, calculate the inertia safety region using integration, satisfying the following relationship: In the formula, Indicates the inertia safety region. This represents the total available inertia of the system at time t. Let t represent the minimum inertia of the power grid at time t, and T represent the length of the evaluation period; Step 7: Assess the grid inertia requirement based on the inertia safety domain.

2. The method for establishing the power grid inertia demand assessment index system according to claim 1, characterized in that, The grid inertia expressed in terms of energy in step 1 The following relationship must be satisfied: In the formula, For the inertia of the synchronous machine, For asynchronous machine inertia, It is a voltage source type virtual inertia. It is a current source type virtual inertia. This is the equivalent inertia of the static load voltage.

3. The method for establishing the power grid inertia demand assessment index system according to claim 2, characterized in that, The inertial constant of a power grid system is determined by both the grid's inertia and the system's capacity. The following relationship must be satisfied: In the formula, This refers to the system capacity.

4. The method for establishing the power grid inertia demand assessment index system according to claim 1, characterized in that, In step 2, the minimum value of the power grid inertia satisfies the following relationship: In the formula, This represents the minimum value of the power grid inertia under the constraint of the rate of change of frequency. For the maximum disturbance power, Set a threshold value for the rate of change of frequency.

5. The method for establishing the power grid inertia demand assessment index system according to claim 4, characterized in that, Rate of change of frequency Depends solely on the grid inertia and the magnitude of the disturbance power, satisfying the following relationship: In the formula, For disturbance power, It is the inertial constant.

6. The method for establishing the power grid inertia demand assessment index system according to claim 1, characterized in that, Minimum inertia of the power grid in step 5 The maximum value among the minimum values ​​of the power grid inertia under different constraints satisfies the following relationship: In the formula, Rate of change of frequency Minimum inertia of the power grid under constraints This represents the minimum grid inertia under the constraints of frequency deviation and system energy storage devices.

7. The method for establishing the power grid inertia demand assessment index system according to claim 1, characterized in that, In step 7, from the perspective of safety and stability, when the actual inertia of the power grid or the predicted value of the power grid inertia is within the inertia safety domain, the power grid inertia should slow down the rate of frequency change regardless of the disturbance event that occurs in the system.

8. The method for establishing the power grid inertia demand assessment index system according to claim 1, characterized in that, In step 7, from the perspective of operational scheduling feasibility, the grid inertia within the inertia safety domain is less than the total available inertia of the system. Therefore, any operating point within the inertia safety domain is taken as the target value for adjusting the grid inertia.

9. A system for establishing an index system for evaluating the inertia demand of a power grid, characterized in that, A method for establishing a power grid inertia demand assessment index system as described in any one of claims 1 to 8.

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