A method for grid transformation of distributed power sources based on energy storage inertia compensation

Abstract

The application discloses a distributed power supply network construction type reconstruction method based on energy storage inertia compensation and belongs to the field of distributed power supply reconstruction. The method determines the required damping ratio and inherent oscillation angular frequency of the distributed power supply by analyzing the dynamic response inertia characteristics of a virtual synchronous machine and a power inverter, and obtains expected inertia and damping values. According to the power density and energy density of an energy storage system, the maximum inertia and maximum damping and the oscillation angular frequency margin and damping ratio of the power converter with the energy storage link are calculated, and the optimal damping ratio and inherent oscillation angular frequency are determined by taking the maximum frequency drop and the lowest response speed as constraints. When the energy storage unit of the distributed power supply is insufficient, the energy storage system provides the required inertia and damping under different operating scenarios to generate the power reference value and the frequency compensation value of the power inverter. The application provides inertia characteristics for the distributed power supply, supports the dynamic response of the power inverter, and improves the stability and economy of the overall system.

Description

Technical Field

[0001] This invention belongs to the field of distributed power source transformation, and in particular relates to a method for transforming distributed power source grid configurations based on energy storage inertia compensation. Background Technology

[0002] As distributed generation increasingly integrates into local power grids, the electrical characteristics of distribution networks become more complex and unpredictable, posing new challenges to power quality and grid stability. Traditionally, grid stability relies on the inertia of large synchronous generators to mitigate frequency fluctuations. However, distributed generation connected via inverters lacks the inertia and damping required for effective frequency stability. In grids or microgrids with low short-circuit ratios, this lack of inertia makes the system frequency more susceptible to disturbances, increasing the risk of instability. This patent proposes a distributed generation grid transformation method based on energy storage inertia compensation. Without modifying the system hardware, it simulates the inertia characteristics of the grid-connected inverter by adjusting the output power of the external energy storage device, achieving optimal inertial control of the grid-connected inverter and the virtual synchronous machine, thus improving the dynamic response characteristics of the power inverter. Summary of the Invention

[0003] The purpose of this invention is to overcome the defects existing in the above-mentioned background technology and propose a method for grid-type transformation of distributed power sources based on energy storage inertia compensation. This method is based on the inherent energy storage components of some distributed power sources and achieves the simulation of the inertial characteristics of the grid-connected inverter by adjusting the output power of the external energy storage device without modifying the system hardware.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A method for transforming distributed power grid configurations based on energy storage inertia compensation, the method comprising:

[0006] Step S1: By conducting in-depth analysis of the inertial characteristics of the virtual synchronous machine in the dynamic response process and the characteristics of the power inverter in the dynamic response, the damping ratio required by the distributed power source and the corresponding natural oscillation angular frequency are accurately determined. Based on the above analysis results, the expected inertia and damping value of the distributed power source are further clarified.

[0007] Step S2: Based on the inherent power density and energy density characteristics of the energy storage system, accurately calculate the maximum inertia and maximum damping that the energy storage system can provide. For power converters with energy storage components, calculate in detail their oscillation angular frequency margin and damping ratio, and then determine the optimal damping ratio and the corresponding inherent oscillation angular frequency.

[0008] Step S3: When the energy storage units of the distributed power source are insufficient, the energy storage system is adjusted under different operating scenarios to enable it to provide the required inertia and damping. Through the above adjustment process, the power reference value of the energy storage system and the frequency compensation value of the power inverter are generated.

[0009] Furthermore, step S1 specifically includes:

[0010] Step S1.1: Analyze the frequency dynamic response characteristics of the inverter;

[0011] Step S1.2: Determine the inertia and damping value of the distributed power source itself;

[0012] Step S1.3: Analyze the inertia damping requirements of distributed power sources.

[0013] Further, step S1.1 is as follows: Based on the inverter's frequency dynamic response function under a unit step, calculate its overshoot, rate of frequency change, maximum frequency drop depth, and settling time; the time-domain response of the frequency under a unit step is expressed as:

[0014]

[0015] Where k is the synchronization power coefficient, ω n ξ is the natural oscillation angular frequency, and ξ is the damping ratio;

[0016] The rate of change of frequency is expressed as:

[0017]

[0018] Where RoCoF is the rate of change of frequency;

[0019] When t = 0, the maximum value of RoCoF is expressed as:

[0020]

[0021] The peak frequency deviation Δf peak for:

[0022]

[0023] The overshoot σ can be expressed as:

[0024]

[0025] The settling time is defined as the quasi-steady-state time when the error drops below 2%, and is expressed as:

[0026]

[0027] Furthermore, step S1.2 is as follows:

[0028] Taking lead-acid batteries as an example, the kinetic energy W stored in a fully charged state is... B It can be represented as:

[0029] W B =∫u B i B dt=u B Q N γ SOC

[0030] Among them, the rated capacity is Q N The voltage is u B The discharge current is i B The state of charge (SOC) is γ. SOC ;

[0031] According to the basic definition of synchronous machine inertia, the inertial time constant H represents the ratio of the kinetic energy stored during the rated operation of the synchronous machine to its rated capacity. By extension, the inertia generated by an energy storage device can be related to the ratio of stored energy to its rated capacity. Therefore, the inertial time constant H that the energy storage stage can provide... c It can be represented as:

[0032]

[0033] The damping coefficient D provided by the energy storage stage can be derived from ω n And ξ to determine:

[0034]

[0035] Furthermore, step S1.3 is as follows:

[0036] First, after the frequency deviation occurs, with the maximum RoCof value of 1Hz / s as the target, the minimum inertia requirement can be obtained as follows:

[0037]

[0038] Furthermore, using a damping ratio close to the optimal damping ratio of 0.707 for the second-order system, the optimal matching damping value is determined as follows:

[0039] D=2.828Hω n .

[0040] Furthermore, step S2 specifically includes:

[0041] Step S2.1: Determine the maximum value of the inertial damping provided by the energy storage;

[0042] Step S2.2: Determine the inertial response compensation value provided by the energy storage.

[0043] Furthermore, step S2.1 is as follows:

[0044] In VSG control, the DG can be considered as the prime mover of a single-machine infinite bus system, the energy storage unit and bidirectional converter correspond to the rotational inertia of the prime mover and the SG, and the inverter corresponds to the electromechanical energy conversion process of the SG. The analytical solution of the VSG output during a power step change can be expressed as:

[0045]

[0046] In the formula, ΔP m This is for frequency deviation;

[0047] The real-time dynamic energy absorbed and released by the energy storage unit can be expressed as:

[0048]

[0049] At t=0, the energy storage unit will provide the maximum power required by the system, expressed as:

[0050]

[0051] Furthermore, step S2.2 is as follows:

[0052] The inertia provided by energy storage is given by the following formula:

[0053]

[0054] The total inertia and damping coefficient of the distributed power source are as follows:

[0055]

[0056] Furthermore, step S3 specifically includes:

[0057] Step S3.1: Calculation of energy storage power deviation;

[0058] Step S3.2, Distributed power source inertia damping transfer.

[0059] Furthermore, step S3.1 is as follows:

[0060] The energy storage reference power deviation takes the frequency deviation value Δω as input. Based on the relationship between angular velocity and power angle in the oscillation equation, we can derive:

[0061]

[0062] The power angle is converted into active power using the traditional power equation:

[0063]

[0064] Among them, U i and U L The components are the output voltage of the distributed power source and the grid voltage, Z. i For line impedance, It is the impedance angle of the line;

[0065] Assuming the circuit is purely inductive (X >> R), neglecting circuit resistance, the circuit impedance angle ψ Zi Since it is 90°, it can be simplified to:

[0066]

[0067] Step S3.2 is as follows:

[0068] The frequency compensation is designed as a PI controller, with the frequency deviation value Δω as the input and the output frequency deviation of the power inverter as the feedback. The feedback frequency is shown below.

[0069]

[0070] Where k p It is the proportionality coefficient, k i Δf is the integral coefficient, and Δf is the current frequency deviation of the inverter.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) This invention provides a method for the transformation of distributed power grid based on energy storage inertia compensation, which realizes a distributed generator inertia adaptive compensation control based on energy storage.

[0073] (2) The method described in this invention achieves the simulation of the inertial characteristics of the grid-connected inverter by adjusting the output power of the external energy storage device without modifying the system hardware, thereby realizing the optimal inertial control of the grid-connected inverter and the virtual synchronous machine.

[0074] (3) The method described in this invention provides inertial characteristics for distributed power sources and can effectively support the dynamic response characteristics of power inverters, thereby improving the stability and economy of the overall system. Attached Figure Description

[0075] Figure 1 This is a flowchart of the present invention;

[0076] Figure 2 This is a diagram showing the output results of a distributed power source without energy storage.

[0077] Figure 3 The diagram shows the energy storage output results when a distributed power source without energy storage is retrofitted.

[0078] Figure 4 This is a diagram showing the output results of a distributed power source with energy storage.

[0079] Figure 5 The diagram shows the energy storage output results when a distributed power source with energy storage is retrofitted. Detailed Implementation

[0080] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0081] like Figure 1 As shown, a method for transforming distributed power grids based on energy storage inertia compensation includes the following steps:

[0082] Step S1: Calculation of distributed power source inertia and damping requirements

[0083] Step S1.1, Frequency dynamic response characteristics of the inverter

[0084] Based on the inverter's frequency dynamic response function under a unit step, its overshoot, rate of frequency change, maximum frequency drop depth, and settling time are calculated. The time-domain response of the frequency under a unit step is shown in equation (1):

[0085]

[0086] Where k is the synchronization power coefficient, ω n Let ω be the natural oscillation angular frequency, and ξ be the damping ratio.

[0087] The rate of change of frequency is expressed as:

[0088]

[0089] Where RoCoF is the rate of change of frequency.

[0090] When t = 0, the maximum value of RoCoF is shown in equation (3):

[0091]

[0092] Peak frequency deviation Δf peak for:

[0093]

[0094] The overshoot σ can be expressed as:

[0095]

[0096] The settling time is defined as the quasi-steady-state time when the error drops below 2%, and is expressed as:

[0097]

[0098] Step S1.2: The inertia and damping value inherent in the distributed power source itself.

[0099] Taking lead-acid batteries as an example, the kinetic energy W stored in a fully charged state is... B It can be represented as:

[0100] W B =∫u B i B dt=u B Q N γ SOC (7)

[0101] Among them, the rated capacity is Q N The voltage is u B The discharge current is i B The state of charge (SOC) is γ. SOC .

[0102] According to the basic definition of synchronous machine inertia, the inertial time constant H represents the ratio of the kinetic energy stored during the synchronous machine's rated operation to its rated capacity. By extension, the inertia generated by an energy storage device can be related to the ratio of stored energy to its rated capacity. Therefore, the inertial time constant H that the energy storage element can provide... c It can be represented as:

[0103]

[0104] The damping coefficient D provided by the energy storage stage can be derived from ω n And ξ to determine:

[0105]

[0106] Step S1.3: Distributed power source inertia damping demand analysis

[0107] First, after the frequency deviation occurs, with the maximum RoCof value of 1Hz / s as the target, the minimum inertia requirement can be obtained as follows:

[0108]

[0109] Furthermore, the optimal matching damping value is determined to be as close as possible to the optimal damping ratio of 0.707 for the second-order system, as shown below:

[0110] D=2.828Hω n (11)

[0111] Step S2: Calculation of Energy Storage Inertia Damping Compensation Value

[0112] Step S2.1, Maximum inertial damping provided by energy storage:

[0113] In VSG control, the DG can be considered as the prime mover of a single-machine infinite bus system, the energy storage unit and bidirectional converter correspond to the rotational inertia of the prime mover and the SG, and the inverter corresponds to the electromechanical energy conversion process of the SG. The analytical solution of the VSG output during a power step change can be expressed as:

[0114]

[0115] In the formula, ΔP m This represents the frequency deviation.

[0116] The real-time dynamic energy absorbed and released by the energy storage unit can be expressed as:

[0117]

[0118] At t=0, the energy storage unit will provide the maximum power required by the system, expressed as:

[0119]

[0120] Step S2.2, Inertia Response Compensation Value:

[0121] The inertia provided by energy storage is given by the following formula:

[0122]

[0123] The total inertia and damping coefficient of the distributed power source are as follows:

[0124]

[0125] Step S3: Distributed power grid transformation

[0126] Step S3.1, Calculation of energy storage power deviation:

[0127] The energy storage reference power deviation is input using the frequency deviation value Δω. Based on the relationship between angular velocity and power angle in the oscillation equation, we can derive:

[0128]

[0129] The power angle is converted into active power using the traditional power equation:

[0130]

[0131] Among them, U i and U L The components are the output voltage of the distributed power source and the grid voltage, Z. i For line impedance, It is the impedance angle of the line.

[0132] Assuming the circuit is purely inductive (X >> R), neglecting circuit resistance, the circuit impedance angle ψ Zi It is 90°. Therefore, it can be simplified to:

[0133]

[0134] Step S3.2, Distributed source inertia damping transfer:

[0135] The frequency compensation is designed as a PI controller, with the frequency deviation value Δω as the input and the output frequency deviation of the power inverter as the feedback. The feedback frequency is shown below.

[0136]

[0137] Where k p It is the proportionality coefficient, k i Δf is the integral coefficient, and Δf is the current frequency deviation of the inverter.

[0138] The embodiments described above are merely specific implementations of this application, used to illustrate the technical solutions of this application, and are not intended to limit it. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application. All should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A distributed power supply network construction type renovation method based on energy storage inertia compensation, characterized in that, The method comprises: Step S1, by analyzing the inertia characteristics of the virtual synchronous machine in the dynamic response process and the characteristics of the power inverter in the dynamic response process, the required damping ratio of the distributed power supply and the corresponding inherent oscillation angular frequency are accurately determined, based on the analysis results, the expected inertia and damping value of the distributed power supply are further determined; Step S2, according to the inherent power density and energy density characteristics of the energy storage system, the maximum inertia and maximum damping that the energy storage system can provide are accurately calculated, the oscillation angular frequency margin and the damping ratio of the power converter with the energy storage link are calculated in detail, and the optimal damping ratio and the corresponding inherent oscillation angular frequency are determined; Step S3, in the case that the energy storage unit of the distributed power supply is insufficient, the energy storage system is regulated in different operating scenarios, so that the required inertia and damping can be provided, through the above regulation process, the power reference value of the energy storage system and the frequency compensation value of the power inverter are generated.

2. The distributed power supply network construction type reconstruction method based on energy storage inertia compensation according to claim 1, characterized in that, The step S1 specifically comprises: Step S1.1, analyze the frequency dynamic response characteristics of the inverter; Step S1.2, determine the inertia and damping value of the distributed power supply itself; Step S1.3, analyze the inertia and damping demand of the distributed power supply.

3. The method of claim 2, wherein the method is characterized by: The step S1.1 is specifically as follows: According to the frequency dynamic response function of the inverter under unit step, the overshoot, frequency change rate, maximum frequency drop depth and adjustment time are calculated; the time domain response of frequency under unit step is represented as: ， wherein, k is the synchronous power coefficient, ω n is the natural oscillation angular frequency, ξ is the damping ratio; The frequency change rate is represented as: ， Wherein, RoCoF is the frequency change rate; When t = 0, the maximum value of RoCoF is represented as: ， The maximum frequency drop depth Δ f peak is: ， overshoot σ is represented as: ， The adjustment time is defined as the quasi-steady state time when the error is reduced to 2% or less, which is represented as: 。 4. The distributed power supply network construction type reconstruction method based on energy storage inertia compensation according to claim 3, characterized in that, The step S1.2 is specifically as follows: In the case of a lead-acid battery, the kinetic energy stored by the battery when fully charged W B is represented as: ， wherein the rated capacity is Q N , the voltage is u B , the discharge current is i B , and the state of charge (SOC) is γ SOC ; According to the basic definition of the inertia of a synchronous machine, the inertia time constant H represents the ratio of the kinetic energy stored during the rated operation of the synchronous machine to the rated capacity; by extension, the inertia generated by the energy storage device is associated with the ratio of the stored energy to the rated capacity; thus, the inertia time constant provided by the energy storage link H c is represented as: ， the damping coefficient provided by the energy storage element D determined by ω n and ξ determined by 。 5. The method of claim 4, wherein the method is characterized by: The step S1.3 is specifically as follows: First, after the frequency deviation appears, the minimum inertia demand is as follows, taking the maximum value of RoCof as 1Hz / s as the target: ， Further, the optimal matching damping value is determined close to the optimal damping ratio 0.707 of a second-order system D o As shown below: 。 6. The distributed power supply network construction type reconstruction method based on energy storage inertia compensation according to claim 5, characterized in that, The step S2 specifically comprises: Step S2.1, determine the maximum inertia and damping provided by the energy storage; Step S2.2, determine the inertia response compensation value provided by the energy storage.

7. The method of claim 6, wherein the method is characterized by: The step S2.1 is specifically as follows: In VSG control, the DG is regarded as the prime mover of the single-machine infinite system, the energy storage unit and the bidirectional converter correspond to the rotational inertia of the prime mover and the SG, and the inverter corresponds to the electromechanical energy conversion process of the SG. The analytical solution of VSG output when power step changes is represented as: ， where Δ P m is the frequency deviation; The real-time dynamic energy absorbed and released by the energy storage unit is represented as: ， At t = 0, the energy storage unit will provide the maximum power required by the system, which is represented as: 。 8. The method of claim 7, wherein the method is characterized by: The step S2.2 is specifically as follows: The inertia value provided by the energy storage is given by: ， The total inertia and damping coefficient of the distributed power supply is as follows: 。 9. The method of claim 8, wherein the method is characterized by, The step S3 specifically comprises: Step S3.1, energy storage power deviation calculation; Step S3.2, distributed power supply inertia and damping transmission.

10. The method of claim 9, wherein the method is characterized by: The step S3.1 is specifically as follows: The energy storage reference power deviation takes the angular velocity deviation value ∆ω as the input, and the relationship between the angular velocity and the power angle in the swing equation is obtained: ， The power angle is converted into active power through the traditional power equation: ， wherein, U i and U L Vd is the magnitude of the output voltage of the distributed power supply and Vg is the magnitude of the grid voltage, Z i Z is the line impedance, φ Zi is the impedance angle of the line; Assuming the line is purely inductive, ignoring line resistance, the line impedance angle Ψ Zi is 90°, so this simplifies to: ， The step S3.2 is specifically as follows: The frequency compensation is designed as a PI controller, the angular velocity deviation value Δω as the input, and the output frequency deviation of the power inverter as the feedback. The feedback frequency is as follows ， wherein k p is a proportional coefficient, k i is an integral coefficient, Δ f is the current frequency deviation of the inverter.

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