Regional power grid heterogeneous frequency modulation resource inertia evaluation method

Abstract

The invention relates to the technical field of power systems, in particular to a regional power grid heterogeneous frequency modulation resource inertia evaluation method, which comprises the following steps: establishing an aggregation model of system frequency response under disturbance input for a synchronous generator system; aiming at the synchronous generator system, obtaining the critical inertia of the synchronous generator; for a power electronic power supply system, obtaining the critical inertia of a power electronic power supply; for the synchronous generator system, obtaining the actual response inertia of the synchronous generator; for a power electronic power supply system, obtaining the actual response inertia of a power electronic power supply; and evaluating the stability of the power system through the inertia release depth evaluation index. According to the method, aiming at the inertia level of a regional power grid, system frequency responses containing various heterogeneous resources are established, inertia capabilities of different adjustment resources are researched, and factors such as equipment configuration, control strategies and operation conditions of a power system under different control modes are considered, so that the virtual inertia contribution capability when a new energy field station accesses the power grid is comprehensively evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid. Background Art

[0002] The risk of low-inertia operation is a major issue in the process of low-carbon transformation of electricity, and has become a pain point and key bottleneck restricting the transformation and development of new power systems towards power electronics. New energy power generation represented by photovoltaic and wind power has gradually replaced synchronous units, resulting in a continuous decrease in the system inertia level, weakening the system's inertia support and frequency regulation capabilities under active power impacts, and facing severe challenges in stable operation. The frequency support capability of the new power system directly affects the power quality, safety and stability of the power grid. Inertia assessment is the basis for realizing the perception and control of low-inertia risks in the system. However, the current concepts related to inertia demand are still unclear, and the impact of the power grid frequency safety line has not been fully considered, resulting in unreasonable assessment results.

[0003] As the proportion of new energy increases, the power grid needs to rely more on heterogeneous frequency regulation resources. In view of the reduction of inertia under the trend of power electronics in the power system and the weakening of frequency support capacity caused by it, it is necessary to design an inertia evaluation method for heterogeneous frequency regulation resources in the regional power grid, so as to evaluate its contribution to the frequency stability of the power grid through inertia calculation and ensure that the power grid can recover quickly when disturbed. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a method for evaluating the inertia of heterogeneous frequency regulation resources in a regional power grid.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: a method for evaluating the inertia of heterogeneous frequency modulation resources in a regional power grid, comprising the following steps:

[0006] Step 1: for the synchronous generator system, an aggregation model of the system frequency response under disturbance input is established, and a time domain expression of the synchronous machine disturbance response power after the disturbance is obtained according to the aggregation model;

[0007] Step 2, for the synchronous generator system, obtain the critical inertia of the synchronous generator; for the power electronic power supply system, obtain the critical inertia of the power electronic power supply;

[0008] Step 3, for the synchronous generator system, obtain the actual response inertia of the synchronous generator; for the power electronic power supply system, obtain the actual response inertia of the power electronic power supply;

[0009] Step 4: Define the ratio of the actual response inertia of the synchronous generator to the critical inertia of the synchronous generator, and the ratio of the actual response inertia of the power electronic power supply to the critical inertia of the power electronic power supply as inertia release depth evaluation indicators, so as to evaluate the stability of the power system through the inertia release depth evaluation indicators.

[0010] Furthermore, in the step 1, it specifically includes:

[0011] In a synchronous generator system, the dynamic process of the generator frequency under disturbance can be described by the rotor motion balance equation:

[0012]

[0013] In formula (1), ω is the rotor angular frequency, H is the inertia time constant of the synchronous generator, D is the damping coefficient, ΔP m is the rotor power change, ΔP d is the load power change, ΔP m With ΔP d The signs are opposite;

[0014] Synchronous generator installed capacity S sys The equivalent inertia time constant H of the synchronous generator as a whole is calculated by formula (2): sys Calculated by formula (3);

[0015]

[0016] In formula (2) and formula (3), H m,i and S m,i are the inertia time constant and rated capacity of the i-th synchronous generator in the region, and Ω is the set of synchronous generators;

[0017] The equivalent damping coefficient D of the whole system sys for:

[0018]

[0019] In formula (4), D i and are the damping coefficients of the i-th synchronous generator in the region;

[0020] In a system with multiple synchronous generator sets, the key parameters of the system are calculated by weighted average method, as follows:

[0021]

[0022] In formula (5) and formula (6), F H is the high pressure turbine coefficient, T R is the time constant of the intermediate reheating process, K mis the mechanical power gain coefficient, R is the speed regulator adjustment coefficient, F Hi , T Ri , K mi , R i are respectively the high pressure turbine coefficient, the time constant of the intermediate reheating process, the mechanical power gain coefficient, and the speed governor adjustment coefficient of the i-th synchronous generator;

[0023] In a power system consisting of multiple synchronous generators, the frequency of the power system is defined as the frequency center of the inertial system ω COI , specifically:

[0024]

[0025] Aggregate the parameters of multiple synchronous generators to obtain the frequency center of an equivalent inertial system, simplify the entire power system into a single-machine system, and establish an aggregate model of the system frequency response under disturbance input;

[0026] After the power system is disturbed, the frequency change of the system is:

[0027]

[0028] Among them, ω n satisfy:

[0029]

[0030] The active power disturbance is represented by a step function, namely:

[0031] ΔP d (t) = ΔP step ·u(t) (11)

[0032] In formula (11), ΔP step is the active power disturbance amplitude, in units of per-unit value; u(t) is the unit step function; Formula (11) is expressed in the frequency domain:

[0033]

[0034] Substituting equation (12) for equation (8), the frequency change of the synchronous generator can be expressed as:

[0035]

[0036] At a given power P ref Under the condition of constant, the change of synchronous generator rotor output power ΔP m (s) is:

[0037]

[0038] Substituting formula (13) into formula (14) and simplifying it, we get:

[0039]

[0040] Using the inverse Laplace transform, the time domain expression of the synchronous machine disturbance response power after the disturbance is obtained:

[0041]

[0042] Furthermore, in step 2, the critical inertia of the synchronous generator is obtained, which specifically includes:

[0043] For synchronous generators, the inertia level refers to the kinetic energy stored in the rotor when running at rated angular speed, expressed in MW·s, and is expressed as:

[0044]

[0045] In formula (17), E GEN , J m ,ω n are the rotor kinetic energy, moment of inertia and rated angular velocity of the generator respectively; H m , S m are the generator inertia time constant and capacity respectively;

[0046] The theoretical value of the synchronous generator response inertia is:

[0047]

[0048] In formula (18), ω t represents the speed of the generator rotor at time t, f t is the mechanical frequency at time t, f n is the system rated frequency;

[0049] According to formula (18), the critical inertia of the synchronous generator in the power system is measured:

[0050]

[0051] In formula (19), f min is the lowest acceptable frequency of the power system in the dynamic process, f min The value is 49.25Hz.

[0052] Furthermore, in step 2, the deriving of the critical inertia of the power electronic power supply specifically includes:

[0053] The power electronic power supply at the station level includes power reserve for station load shedding and energy reserve mainly based on capacitors and electrochemical. Its critical inertia E IBR It is expressed as:

[0054]

[0055] In formula (20), P MPPT and P e are the maximum power generation and actual output active power of the power generation unit in the station under the current resource conditions, T H is the duration of inertia response; C, U c and U c,min are the capacitor capacitance, voltage and minimum voltage limit respectively; E B The energy stored in electrochemical OC and S OC，min They are the energy storage state of charge and the minimum state of charge limit respectively.

[0056] Furthermore, in step 3, obtaining the actual response inertia of the synchronous generator specifically includes:

[0057] For synchronous generators, according to the law of conservation of energy, the actual response inertia E m Equal to the change in energy output ΔE on the grid-connected side of the power generation unit out The energy injection change ΔE of the power generation unit source side in Difference:

[0058] E m =ΔE in -ΔE out (twenty one)

[0059] Energy change ΔE on the source side of the power generation unit after the disturbance in The input power P in Solve the time integral:

[0060]

[0061] In formula (22), t0 is the time when the disturbance starts, t nadir is the moment when the synchronous machine output power reaches the extreme value, P in (t) is the source side input power of the power generation unit at time t, P in0 (t) is the source-side input power of the power generation unit before the disturbance occurs;

[0062] If a primary frequency modulation dead zone is set, the source-end frequency modulation device starts to operate when the frequency is lower than the dead zone, and the energy change at the source end is:

[0063]

[0064] In formula (23), t DB The frequency of the power generation unit is lower than the dead zone of the primary frequency regulation action. If t nadir ≤tDB When t nadir >t DB , then the input power change is t nadir Input power P at the moment in (t) and the input power P before disturbance in0 (t) difference;

[0065] From the perspective of energy output, the energy change ΔE on the grid-connected side of the power generation unit out Through its grid-connected output power P out The integral of the change of with respect to time is solved:

[0066]

[0067] In formula (24), P out (t) is the output power of the synchronous machine on the grid side at time t, P out0 is the power output of the synchronous machine on the grid side before the disturbance;

[0068] In summary, the actual response inertia of the synchronous machine itself is E m It can be calculated by the following formula:

[0069]

[0070] In formula (25), during the inertia response period, the inertia provided by the synchronous generator can be calculated by calculating the source side input power change ΔP in (t) and the output power change on the grid side ΔP out (t) Determined by integrating the deviation over time;

[0071] At a given power P ref Under the condition that the source side input power of the generator remains unchanged, the change in ΔP in (t) = 0, at this time, ΔP out (t) = ΔP m (t), according to equations (25) and (16), the actual response inertia of the synchronous generator E m for:

[0072]

[0073] Furthermore, in step 3, obtaining the actual response inertia of the power electronic power supply specifically includes:

[0074] In the power electronic power supply system, the output active power ΔP e The expression is:

[0075]

[0076] In formula (28), K D represents the droop coefficient, J represents the moment of inertia, K p It represents the gain coefficient between the virtual power angle small signal and the active power small signal, w o Indicates the angular frequency when the system is running stably, Δω g Indicates the grid angular frequency difference, ΔP eref Indicates active reference difference;

[0077] From the above formula, it can be concluded that the output power of the interface converter is affected by ΔP eref With Δω g Influence; It can be seen that the dynamic response of the virtual synchronous machine output is given by the second-order characteristic equation Jω0s 2 +K D ω0s+K p Decide;

[0078] For a step input signal, the system output power is calculated according to Jω0s 2 +K D ω0s+K p The over-damped, critically damped or under-damped output characteristics are shown. The power changes are analyzed by the system response process after the changes.

[0079] The change of converter output power over time and the power reference change ΔP eref The transfer function between them is:

[0080]

[0081] In formula (29), ω n is the natural frequency of the system, ξ is the system damping;

[0082] The energy released or stored by DC energy storage needs to be discussed separately according to different situations:

[0083] When ξ>1, the overdamped condition is:

[0084] At this time G ref (s) has two negative real characteristic roots:

[0085]

[0086] Two negative real characteristic roots s1 = -1 / T1, s2 = -1 / T2, due to ξ 2 > 2 -1, then T1>T2; when the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is:

[0087]

[0088] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0089]

[0090] When ξ=1, that is, the critical damping situation is:

[0091] At this time G ref (s) has two identical negative characteristic roots:

[0092] s 1,2 =-ω n (33)

[0093] When the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is:

[0094]

[0095] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0096]

[0097] When 0<ξ<1, the underdamped case is:

[0098] At this time G ref (s) has conjugate characteristic roots:

[0099]

[0100] When the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is:

[0101]

[0102] In formula (37), ω d is the system damped oscillation frequency, β is the damping angle, these two parameters determine the output power oscillation characteristics and output stability of the system after being disturbed, and:

[0103]

[0104] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0105]

[0106] It can be concluded from formula (39) that the energy change of the energy storage unit under virtual synchronous control is affected by two main parameters: the inertia time constant J and the droop coefficient K D .

[0107] Furthermore, in step 4, it specifically includes:

[0108] Define the inertia release depth evaluation index K rls , K rls It is equal to the ratio of the actual response inertia of each heterogeneous frequency modulation resource to the critical inertia during the system disturbance, that is:

[0109]

[0110] For the power generation unit, K rls The indicator intuitively shows the inertia level provided by different types of frequency modulation resources under the current disturbance, K rls It intuitively reflects the state of energy storage on the source side and its impact on system stability;

[0111] If K rls Close to 1, which indicates that under the current disturbance, the energy storage on the source side is insufficient, and it is necessary to increase the energy storage capacity or optimize the frequency regulation strategy to ensure the stable operation of the system; if K rls Close to 0, it indicates excess energy storage or poor configuration of control parameters.

[0112] It can be seen from the above description of the present invention that, compared with the prior art, the method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid of the present invention includes at least one of the following beneficial effects:

[0113] 1. The present invention aims at the inertia level of the regional power grid, establishes a system frequency response including various heterogeneous resources, studies the inertia capacity of different regulating resources, considers factors such as equipment configuration, control strategy and operating conditions of the power system under different control modes, so as to comprehensively evaluate the virtual inertia contribution capacity of new energy sites when they are connected to the power grid, which has important theoretical and practical significance for guiding the design and operation of future power grids.

[0114] 2. The present invention adopts transfer function to describe the complex dynamic relationship between active power and frequency of the power system containing new energy, and derives the time domain expression of the output power of the equivalent synchronous unit after disturbance, and proposes a calculation method for the actual response inertia and an indicator of the inertia release depth. By accurately calculating the inertia of different frequency modulation resources, the power grid can be better dispatched, the use of resources can be optimized, and the operation efficiency and reliability of the power grid can be improved.

[0115] 3. The inertia calculation and evaluation of the present invention can ensure that the power grid still maintains a high level of stability and reliability during this transformation process.

[0116] 4. Inertia is an important indicator for the power grid to cope with frequency deviation. The present invention calculates and evaluates the inertia of frequency regulation resources, which helps to understand their contribution to frequency response in the short term, thereby formulating more effective frequency control strategies.

[0117] 5. Heterogeneous frequency regulation resources mainly include renewable energy power generation equipment. Through the inertia evaluation of the present invention, its frequency regulation capability can be quantified, which can enhance the trust in renewable energy power generation and promote its larger-scale access to the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Figure 1 This is a flowchart of the steps of a method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to an embodiment of the present invention;

[0119] Figure 2 Schematic diagram of the topological structure of the node system model in an embodiment of the present invention. DETAILED DESCRIPTION

[0120] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0121] Reference Figure 1-Figure 2 As shown, an embodiment of the present invention provides a method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid, comprising the following steps:

[0122] Step 1: for the synchronous generator system, an aggregation model of the system frequency response under disturbance input is established, and a time domain expression of the synchronous machine disturbance response power after the disturbance is obtained according to the aggregation model;

[0123] Step 2, for the synchronous generator system, obtain the critical inertia of the synchronous generator; for the power electronic power supply system, obtain the critical inertia of the power electronic power supply;

[0124] Step 3, for the synchronous generator system, obtain the actual response inertia of the synchronous generator; for the power electronic power supply system, obtain the actual response inertia of the power electronic power supply;

[0125] Step 4: Define the ratio of the actual response inertia of the synchronous generator to the critical inertia of the synchronous generator, and the ratio of the actual response inertia of the power electronic power supply to the critical inertia of the power electronic power supply as inertia release depth evaluation indicators, so as to evaluate the stability of the power system through the inertia release depth evaluation indicators.

[0126] As a preferred embodiment of the present invention, it may also have the following additional technical features:

[0127] In this embodiment, step 1 specifically includes:

[0128] In a synchronous generator system, the dynamic process of the generator frequency under disturbance can be described by the rotor motion balance equation:

[0129]

[0130] In formula (1), ω is the rotor angular frequency, H is the inertia time constant of the synchronous generator, D is the damping coefficient, ΔP m is the rotor power change, ΔP d is the load power change, ΔP m With ΔP d The signs are opposite;

[0131] Synchronous generator installed capacity S sys The equivalent inertia time constant H of the synchronous generator as a whole is calculated by formula (2): sys Calculated by formula (3);

[0132]

[0133] In formula (2) and formula (3), H m,i and S m,i are the inertia time constant and rated capacity of the i-th synchronous generator in the region, and Ω is the set of synchronous generators;

[0134] The equivalent damping coefficient D of the whole system sys for:

[0135]

[0136] In formula (4), D i and are the damping coefficients of the i-th synchronous generator in the region;

[0137] In a system with multiple synchronous generator sets, the key parameters of the system are calculated by weighted average method, as follows:

[0138]

[0139] In formula (5) and formula (6), F H is the high pressure turbine coefficient, T R is the time constant of the intermediate reheating process, K m is the mechanical power gain coefficient, R is the speed regulator adjustment coefficient, F Hi , T Ri , K mi , R i are respectively the high pressure turbine coefficient, the time constant of the intermediate reheating process, the mechanical power gain coefficient, and the speed governor adjustment coefficient of the i-th synchronous generator;

[0140] In a power system consisting of multiple synchronous generators, the frequency of the power system is defined as the frequency center of the inertial system ω COI , specifically:

[0141]

[0142] Aggregate the parameters of multiple synchronous generators to obtain the frequency center of an equivalent inertial system, simplify the entire power system into a single-machine system, and establish an aggregate model of the system frequency response under disturbance input;

[0143] After the power system is disturbed, the frequency change of the system is:

[0144]

[0145] Among them, ω n satisfy:

[0146]

[0147] The active power disturbance is represented by a step function, namely:

[0148] ΔP d (t) = ΔP step ·u(t) (11)

[0149] In formula (11), ΔP step is the active power disturbance amplitude, in per-unit value; u(t) is the unit step function;

[0150] Express equation (11) in the frequency domain:

[0151]

[0152] Substituting equation (12) for equation (8), the frequency change of the synchronous generator can be expressed as:

[0153]

[0154] At a given power P ref Under the condition of constant, the change of synchronous generator rotor output power ΔP m (s) is:

[0155]

[0156] Substituting formula (13) into formula (14) and simplifying it, we get:

[0157]

[0158] Using the inverse Laplace transform, the time domain expression of the synchronous machine disturbance response power after the disturbance is obtained:

[0159]

[0160] In this embodiment, in step 2, the critical inertia of the synchronous generator is obtained, which specifically includes:

[0161] For synchronous generators, the inertia level refers to the kinetic energy stored in the rotor when running at rated angular speed, expressed in MW·s, and is expressed as:

[0162]

[0163] In formula (17), E GEN , J m ,ω n are the rotor kinetic energy, moment of inertia and rated angular velocity of the generator respectively; H m , S m are the generator inertia time constant and capacity respectively;

[0164] The theoretical value of the synchronous generator response inertia is:

[0165]

[0166] In formula (18), ω t represents the speed of the generator rotor at time t, f t is the mechanical frequency at time t, f n is the system rated frequency;

[0167] According to formula (18), the critical inertia of the synchronous generator in the power system is measured:

[0168]

[0169] In formula (19), f min is the lowest acceptable frequency of the power system in the dynamic process, f minThe value is 49.25Hz.

[0170] In this embodiment, in step 2, the step of obtaining the critical inertia of the power electronic power supply specifically includes:

[0171] The power electronic power supply at the station level includes power reserve for station load shedding and energy reserve mainly based on capacitors and electrochemical. Its critical inertia E IBR It is expressed as:

[0172]

[0173] In formula (20), P MPPT and P e are the maximum power generation and actual output active power of the power generation unit in the station under the current resource conditions, T H is the duration of inertia response; C, U c and U c,min are the capacitor capacitance, voltage and minimum voltage limit respectively; E B The energy stored in electrochemical OC and S OC，min They are the energy storage state of charge and the minimum state of charge limit respectively.

[0174] In this embodiment, in step 3, obtaining the actual response inertia of the synchronous generator specifically includes:

[0175] For synchronous generators, according to the law of conservation of energy, the actual response inertia E m Equal to the change in energy output ΔE on the grid-connected side of the power generation unit out The energy injection change ΔE of the power generation unit source side in Difference:

[0176] E m =ΔE in -ΔE out (twenty one)

[0177] Energy change ΔE on the source side of the power generation unit after the disturbance in The input power P in Solve the time integral:

[0178]

[0179] In formula (22), t0 is the time when the disturbance starts, t nadir is the moment when the synchronous machine output power reaches the extreme value, P in (t) is the source side input power of the power generation unit at time t, P in0 (t) is the source-side input power of the power generation unit before the disturbance occurs;

[0180] If a primary frequency modulation dead zone is set, the source-end frequency modulation device starts to operate when the frequency is lower than the dead zone, and the energy change at the source end is:

[0181]

[0182] In formula (23), t DB The frequency of the power generation unit is lower than the dead zone of the primary frequency regulation action. If t nadir ≤t DB When t nadir >t DB , then the input power change is t nadir Input power P at the moment in (t) and the input power P before disturbance in0 (t) difference;

[0183] From the perspective of energy output, the energy change ΔE on the grid-connected side of the power generation unit out Through its grid-connected output power P out The integral of the change of with respect to time is solved:

[0184]

[0185] In formula (24), P out (t) is the output power of the synchronous machine on the grid side at time t, P out0 is the power output of the synchronous machine on the grid side before the disturbance;

[0186] In summary, the actual response inertia of the synchronous machine itself is E m It can be calculated by the following formula:

[0187]

[0188] In formula (25), during the inertia response period, the inertia provided by the synchronous generator can be calculated by calculating the source side input power change ΔP in (t) and the output power change on the grid side ΔP out (t) Determined by integrating the deviation over time;

[0189] At a given power P ref Under the condition that the source side input power of the generator remains unchanged, the change in ΔP in (t) = 0, at this time, ΔP out (t) = ΔP m (t), according to equations (25) and (16), the actual response inertia of the synchronous generator E m for:

[0190]

[0191] In this embodiment, in step 3, obtaining the actual response inertia of the power electronic power supply specifically includes:

[0192] In the power electronic power supply system, the output active power ΔP e The expression is:

[0193]

[0194] In formula (28), K D represents the droop coefficient, J represents the moment of inertia, K p It represents the gain coefficient between the virtual power angle small signal and the active power small signal, w o Indicates the angular frequency when the system is running stably, Δω g Indicates the grid angular frequency difference, ΔP eref Indicates active reference difference;

[0195] From the above formula, it can be concluded that the output power of the interface converter is affected by ΔP eref With Δω g Influence; It can be seen that the dynamic response of the virtual synchronous machine output is given by the second-order characteristic equation Jω0s 2 +K D ω0s+K p Decide;

[0196] For a step input signal, the system output power is calculated according to Jω0s 2 +K D ω0s+K p The over-damped, critically damped or under-damped output characteristics are shown. The power changes are analyzed by the system response process after the changes.

[0197] The change of converter output power over time and the power reference change ΔP eref The transfer function between them is:

[0198]

[0199] In formula (29), ω n is the natural frequency of the system, ξ is the system damping;

[0200] The energy released or stored by DC energy storage needs to be discussed separately according to different situations:

[0201] When ξ>1, the overdamped condition is:

[0202] At this time G ref (s) has two negative real characteristic roots:

[0203]

[0204] Two negative real characteristic roots s1 = -1 / T1, s2 = -1 / T2, due to ξ 2 > 2 -1, then T1>T2; when the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is:

[0205]

[0206] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0207]

[0208] When ξ=1, that is, the critical damping situation is:

[0209] At this time G ref (s) has two identical negative characteristic roots:

[0210] s 1,2 =-ω n (33)

[0211] When the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is:

[0212]

[0213] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0214]

[0215] When 0<ξ<1, the underdamped case is:

[0216] At this time G ref (s) has conjugate characteristic roots:

[0217]

[0218] When the power given value ΔP eref A step change occurs, and its output power ΔP eThe time domain expression of is:

[0219]

[0220] In formula (37), ω d is the system damped oscillation frequency, β is the damping angle, these two parameters determine the output power oscillation characteristics and output stability of the system after being disturbed, and:

[0221]

[0222] Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞):

[0223]

[0224] It can be concluded from formula (39) that the energy change of the energy storage unit under virtual synchronous control is affected by two main parameters: the inertia time constant J and the droop coefficient K D .

[0225] In this embodiment, step 4 specifically includes:

[0226] Define the inertia release depth evaluation index K rls , K rls It is equal to the ratio of the actual response inertia of each heterogeneous frequency modulation resource to the critical inertia during the system disturbance, that is:

[0227]

[0228] For the power generation unit, K rls The indicator intuitively shows the inertia level provided by different types of frequency modulation resources under the current disturbance, K rls It intuitively reflects the state of energy storage on the source side and its impact on system stability;

[0229] If K rls Close to 1, which indicates that under the current disturbance, the energy storage on the source side is insufficient, and it is necessary to increase the energy storage capacity or optimize the frequency regulation strategy to ensure the stable operation of the system; if K rls Close to 0, it indicates excess energy storage or poor configuration of control parameters.

[0230] A specific operation example is provided below to better understand the present invention:

[0231] A 10-machine 39-bus system model based on the improved New England standard is constructed. First, the unit parameters are aggregated according to the parameters of each synchronous generator in the region; then, based on the time domain expression of the synchronous machine output power after the disturbance, the output power function of the equivalent synchronous unit in the regional power grid is derived; finally, the actual released inertia of the system is calculated, and the error analysis between the actual value and the theoretical value of the inertia is carried out, and the performance of each frequency regulation resource in inertia release is evaluated, so as to comprehensively analyze the inertia level of the system. The topology of the system is as follows: Figure 2 shown.

[0232] In my country, the provincial regional power grid mainly adopts 220kV AC transmission system, which connects the power supply centers of each province with the power supply centers of each city to form the transmission backbone grid in the region. In order to more accurately simulate the behavior of such power grid, we made the following improvements and settings to the 10-machine 39-node system:

[0233] Setting 1: The base voltage of the system is set to 220 kV and the rated frequency is set to 50 Hz to meet the standards of the domestic power grid;

[0234] Setting 2: The parameters of the 10 synchronous generators included in the system are detailed in Table 1;

[0235] Setting 3: In the system, the generator G1 connected to node 39 is used to simulate the adjacent power grid. The capacity and inertia of the generator are treated as equivalent to ensure the authenticity of the regional power grid model.

[0236] Setting 4: At 3 seconds into the simulation, a power disturbance occurs on bus 10, and the load suddenly changes to 300· (7% of the system capacity), that is, ΔP d =-300MW; this disturbance is usually represented by a step function, and the amplitude of the active power disturbance is ΔP step =-300M, unit is per unit value.

[0237] Table 1 Improved 39-bus system synchronous generator parameters

[0238] No. <![CDATA[S i ]]> <![CDATA[H i ]]> <![CDATA[1 / R i ]]> <![CDATA[T CHi ]]> <![CDATA[T Ri ]]> <![CDATA[F Hi ]]> <![CDATA[λ i ]]> G1 600 5.0 20 0.27 6 0.19 0.15 G2 350 4.329 20 0.27 6 0.19 0.09 G3 400 4.475 25 0.23 7.5 0.17 0.12 G4 400 3.575 25 0.23 7.5 0.17 0.12 G5 300 4.333 15 0.22 6.5 0.22 0.05 G6 400 4.35 15 0.22 6.5 0.22 0.07 G7 350 3.771 18 0.42 12 0.39 0.08 G8 350 3.471 18 0.42 12 0.39 0.08 G9 500 4.6 20 0.49 14 0.36 0.12 G10 500 4.5 20 0.49 14 0.36 0.12

[0239] When analyzing the 10 synchronous generators in the regional power grid, we performed parameter aggregation according to equations (5) and (6). The aggregation results are shown in Table 2. These data reflect the comprehensive parameters of each generator after integration, providing a basis for subsequent storage inertia calculation and system analysis.

[0240] Table 2 Aggregation results of regional power grid synchronous generator parameters

[0241] <![CDATA[S sys ]]> <![CDATA[H sys ]]> 1 / R <![CDATA[D sys ]]> <![CDATA[K m ]]> <![CDATA[T CH ]]> <![CDATA[T R ]]> <![CDATA[F H ]]> 4150 4.30 20 2 1 0.33 9.3 0.257

[0242] Next, the active power, rated capacity, and stored inertia of each synchronous generator set are listed in detail, as shown in Table 3:

[0243] Table 3 Calculation of storage inertia of system generator sets

[0244] No. G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 system <![CDATA[P i / MW]]> 500 192 325 316 254 325 280 270 415 125 3002 <![CDATA[S i / MVA]]> 600 350 400 400 300 400 350 350 500 500 4150 <![CDATA[H mi / s]]> 5.00 4.329 4.475 3.575 4.333 4.35 3.771 3.471 4.60 4.50 4.3 <![CDATA[E GEN / MJ]]> 3000 1515.1 1790 1430 1299.9 1740 1319.8 1214.8 2300 2250 17860

[0245] According to the expression of synchronous machine disturbance response power described by equation (16) and the regional synchronous machine parameters after aggregation in Table 2, the equivalent synchronous machine output power function of the regional power grid after the disturbance is constructed. This function accurately simulates the power output change of the synchronous machine after the disturbance occurs. The calculation results are as follows:

[0246]

[0247]

[0248] Furthermore, based on the output power expression, the disturbance response power curve of the equivalent synchronous machine after the regional power grid is disturbed is drawn. This curve shows the power response process of the synchronous machine after the disturbance occurs. As shown in the figure, the time domain expression of the output power change is an important reference for understanding and analyzing the response process of the power grid to the disturbance in actual operation. The transient frequency response curve recorded in the system simulation of the frequency change time domain expression is compared and analyzed.

[0249] By calculating the actual value of the theoretical value of the synchronous generator response inertia, the error between the theoretical value and the actual value can be compared.

[0250] According to formula (18), the theoretical value of the synchronous generator response inertia is calculated as:

[0251]

[0252] According to formula (26), the actual value of the synchronous generator response inertia is calculated as:

[0253]

[0254] The error between the theoretical and actual values ​​of the system response inertia is calculated, and the critical inertia and inertia release depth are calculated, and these results are summarized in Table 4.

[0255] Table 4 Theoretical and actual values ​​of synchronous machine response inertia and release depth in the region

[0256]

[0257]

[0258] From the data in Table 4, we can observe the comparison between the theoretical value and the actual value of the inertia of the overall response of the system from the occurrence of the disturbance to the lowest point of the system frequency. It can be seen that the error of the overall inertia of the released system calculated by the two calculation methods is 4%. min When the critical inertia of each synchronous generator in the system remains unchanged, the overall inertia release depth of the system is 77%. Through calculation and analysis, not only can the dynamic response capability of the power system be accurately evaluated, but also scientific data support and decision-making basis can be provided for power grid design and operation.

[0259] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and improved concepts of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A method for evaluating the inertia of heterogeneous frequency modulation resources in a regional power grid, characterized in that: The following steps are involved: Step 1: for the synchronous generator system, an aggregation model of the system frequency response under disturbance input is established, and a time domain expression of the synchronous machine disturbance response power after the disturbance is obtained according to the aggregation model; Step 2, for the synchronous generator system, obtain the critical inertia of the synchronous generator; for the power electronic power supply system, obtain the critical inertia of the power electronic power supply; Step 3, for the synchronous generator system, obtain the actual response inertia of the synchronous generator; for the power electronic power supply system, obtain the actual response inertia of the power electronic power supply; Step 4: Define the ratio of the actual response inertia of the synchronous generator to the critical inertia of the synchronous generator, and the ratio of the actual response inertia of the power electronic power supply to the critical inertia of the power electronic power supply as inertia release depth evaluation indicators, so as to evaluate the stability of the power system through the inertia release depth evaluation indicators.

2. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 1, characterized in that: In the step 1, it specifically includes: In a synchronous generator system, the dynamic process of the generator frequency under disturbance can be described by the rotor motion balance equation: In formula (1), ω is the rotor angular frequency, H is the inertia time constant of the synchronous generator, D is the damping coefficient, ΔP m is the rotor power change, ΔP d is the load power change, ΔP m With ΔP d The signs are opposite; Synchronous generator installed capacity S sys The equivalent inertia time constant H of the synchronous generator as a whole is calculated by formula (2): sys Calculated by formula (3); In formula (2) and formula (3), H m,i and S m,i are the inertia time constant and rated capacity of the i-th synchronous generator in the region, and Ω is the set of synchronous generators; The equivalent damping coefficient D of the whole system sys for: In formula (4), D i and are the damping coefficients of the i-th synchronous generator in the region; In a system with multiple synchronous generator sets, the key parameters of the system are calculated by weighted average method, as follows: In formula (5) and formula (6), F H is the high pressure turbine coefficient, T R is the time constant of the intermediate reheating process, K m is the mechanical power gain coefficient, R is the speed regulator adjustment coefficient, F Hi , T Ri , K mi , R i are respectively the high pressure turbine coefficient, the time constant of the intermediate reheating process, the mechanical power gain coefficient, and the speed governor adjustment coefficient of the i-th synchronous generator; In a power system consisting of multiple synchronous generators, the frequency of the power system is defined as the frequency center of the inertial system ω COI , specifically: Aggregate the parameters of multiple synchronous generators to obtain the frequency center of an equivalent inertial system, simplify the entire power system into a single-machine system, and establish an aggregate model of the system frequency response under disturbance input; After the power system is disturbed, the frequency change of the system is: Among them, ω n satisfy: The active power disturbance is represented by a step function, namely: ΔP d (t)=ΔP step ·u(t) (11) In formula (11), ΔP step is the active power disturbance amplitude, in per-unit value; u(t) is the unit step function; Express equation (11) in the frequency domain: Substituting equation (12) for equation (8), the frequency change of the synchronous generator can be expressed as: At a given power P ref Under the condition of constant, the change of synchronous generator rotor output power ΔP m (s) is: Substituting formula (13) into formula (14) and simplifying it, we get: Using the inverse Laplace transform, the time domain expression of the synchronous machine disturbance response power after the disturbance is obtained:

3. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 2, characterized in that: In step 2, the critical inertia of the synchronous generator is obtained, which specifically includes: For synchronous generators, the inertia level refers to the kinetic energy stored in the rotor when running at rated angular speed, expressed in MW·s, and is expressed as: In formula (17), E GEN , J m ,ω n are the rotor kinetic energy, moment of inertia and rated angular velocity of the generator respectively; H m , S m are the generator inertia time constant and capacity respectively; The theoretical value of the synchronous generator response inertia is: In formula (18), ω t represents the speed of the generator rotor at time t, f t is the mechanical frequency at time t, f n is the system rated frequency; According to formula (18), the critical inertia of the synchronous generator in the power system is measured: In formula (19), f min is the lowest acceptable frequency of the power system in the dynamic process, f min The value is 49.25Hz.

4. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 3, characterized in that: In step 2, the step of obtaining the critical inertia of the power electronic power supply specifically includes: The power electronic power supply at the station level includes power reserve for station load shedding and energy reserve mainly based on capacitors and electrochemical. Its critical inertia E IBR It is expressed as: In formula (20), P MPPT and P e are the maximum power generation power and actual output active power of the power generation unit in the station under the current resource conditions, T H is the duration of inertia response; C, U c and U c,min are the capacitor capacitance, voltage and minimum voltage limit respectively; E B The energy stored in electrochemical OC and S OC，min They are the energy storage state of charge and the minimum state of charge limit respectively.

5. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 4, characterized in that: In step 3, obtaining the actual response inertia of the synchronous generator specifically includes: For synchronous generators, according to the law of conservation of energy, the actual response inertia E m Equal to the change in energy output ΔE on the grid-connected side of the power generation unit out The energy injection change ΔE of the power generation unit source side in Difference: E m =ΔE in -ΔE out (21) Energy change ΔE on the source side of the power generation unit after the disturbance in The input power P in Solve the time integral: In formula (22), t0 is the time when the disturbance starts, t nadir is the moment when the synchronous machine output power reaches the extreme value, P in (t) is the source side input power of the power generation unit at time t, P in0 (t) is the source-side input power of the power generation unit before the disturbance occurs; If a primary frequency modulation dead zone is set, the source-end frequency modulation device starts to operate when the frequency is lower than the dead zone, and the energy change at the source end is: In formula (23), t DB The frequency of the power generation unit is lower than the dead zone of the primary frequency regulation action. If t nadir ≤t DB When t nadir >t DB , then the input power change is t nadir Input power P at the moment in (t) and the input power P before disturbance in0 (t) difference; From the perspective of energy output, the energy change ΔE on the grid-connected side of the power generation unit out Through its grid-connected output power P out The integral of the change of with respect to time is solved: In formula (24), P out (t) is the output power of the synchronous machine on the grid side at time t, P out0 is the power output of the synchronous machine on the grid side before the disturbance; In summary, the actual response inertia of the synchronous machine itself is E m It can be calculated by the following formula: In formula (25), during the inertia response period, the inertia provided by the synchronous generator can be calculated by calculating the source side input power change ΔP in (t) and the output power change ΔP on the grid side out (t) Determined by integrating the deviation over time; At a given power P ref Under the condition that the source side input power of the generator remains unchanged, the change in ΔP in (t) = 0, at this time, ΔP out (t) = ΔP m (t), according to equations (25) and (16), the actual response inertia of the synchronous generator E m for:

6. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 5, characterized in that: In step 3, obtaining the actual response inertia of the power electronic power supply specifically includes: In the power electronic power supply system, the output active power ΔP e The expression is: In formula (28), K D represents the droop coefficient, J represents the moment of inertia, K p It represents the gain coefficient between the virtual power angle small signal and the active power small signal, w o Indicates the angular frequency when the system is running stably, Δω g Indicates the grid angular frequency difference, ΔP eref Indicates active reference difference; From the above formula, it can be concluded that the output power of the interface converter is affected by ΔP eref With Δω g Influence; It can be seen that the dynamic response of the virtual synchronous machine output is given by the second-order characteristic equation Jω0s 2 +K D ω0s+K p Decide; For a step input signal, the system output power is calculated according to Jω0s 2 +K D ω0s+K p The over-damped, critically damped or under-damped output characteristics are shown. The power changes are analyzed by the system response process after the changes. The change of converter output power over time and the power reference change ΔP eref The transfer function between them is: In formula (29), ω n is the natural frequency of the system, ξ is the system damping; The energy released or stored by DC energy storage needs to be discussed separately according to different situations: When ξ>1, the overdamped condition is: At this time G ref (s) has two negative real characteristic roots: Two negative real characteristic roots s1 = -1 / T1, s2 = -1 / T2, due to ξ 2 > 2 -1, then T1>T2; when the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is: Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞): When ξ=1, that is, the critical damping situation is: At this time G ref (s) has two identical negative characteristic roots: s 1,2 =-ω n (33) When the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is: Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞): When 0<ξ<1, the underdamped case is: At this time G ref (s) has conjugate characteristic roots: When the power given value ΔP eref A step change occurs, and its output power ΔP e The time domain expression of is: In formula (37), ω d is the system damped oscillation frequency, β is the damping angle, these two parameters determine the output power oscillation characteristics and output stability of the system after being disturbed, and: Virtual response inertia E of power electronic power supply vi (t) The relationship between the time and E dc (t) and E dc (+∞) are the dynamic energy of DC side energy storage and the retained energy of DC side energy storage (t→+∞): It can be concluded from formula (39) that the energy change of the energy storage unit under virtual synchronous control is affected by two main parameters: the inertia time constant J and the droop coefficient K D .

7. A method for evaluating inertia of heterogeneous frequency modulation resources in a regional power grid according to claim 6, characterized in that: In the step 4, it specifically includes: Define the inertia release depth evaluation index K rls , K rls It is equal to the ratio of the actual response inertia of each heterogeneous frequency modulation resource to the critical inertia during the system disturbance, that is: For the power generation unit, K rls The indicator intuitively shows the inertia level provided by different types of frequency modulation resources under the current disturbance, K rls It intuitively reflects the state of energy storage on the source side and its impact on system stability; If K rls Close to 1, which indicates that under the current disturbance, the energy storage on the source side is insufficient, and it is necessary to increase the energy storage capacity or optimize the frequency regulation strategy to ensure the stable operation of the system; if K rls Close to 0, it indicates excess energy storage or poor configuration of control parameters.

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