Distributed power supply network construction type transformation method based on energy storage inertia compensation

Abstract

The invention discloses a distributed power supply network construction type transformation method based on energy storage inertia compensation, and belongs to the field of distributed power supply transformation. According to the method, the damping ratio and the natural oscillation angular frequency required by the distributed power supply are determined by analyzing the dynamic response inertia characteristics of the virtual synchronous machine and the power inverter, and the expected inertia and the damping value of the distributed power supply are obtained; according to the power density and the energy density of the energy storage system, the maximum inertia and the maximum damping of the energy storage system and the oscillation angular frequency margin and the damping ratio of the power converter with the energy storage link are calculated, and the optimal damping ratio and the natural oscillation angular frequency are determined with the maximum frequency drop and the minimum response speed as constraints; when the energy storage units of the distributed power supply are insufficient, the energy storage system provides required inertia and damping in different operation scenes to generate a power reference value of the energy storage system and a frequency compensation value of a power inverter. The inertia characteristic is provided for the distributed power supply, the dynamic response of the power inverter is supported, and the stability and economical efficiency of the whole system are improved.

Description

Technical Field

[0001] The present invention belongs to the field of distributed power source transformation, and in particular relates to a distributed power source network transformation method based on energy storage inertia compensation. Background Art

[0002] As distributed power sources are increasingly integrated into local power grids, the electrical characteristics of distribution networks have become more complex and unpredictable, posing new challenges to power quality and grid stability. Traditionally, grid stability has relied on the inertia of large synchronous generators to mitigate frequency fluctuations. However, distributed power sources connected through inverters lack the inertia and damping required for effective frequency stabilization. In grids or microgrids with low short-circuit ratios, this lack of inertia makes the system frequency more susceptible to interference, increasing the risk of instability. This patent proposes a distributed power grid configuration transformation method based on energy storage inertia compensation. Without modifying the system hardware, the inertial characteristics of the grid-connected inverter are simulated by adjusting the output power of the external energy storage device, and the optimal inertia control of the grid-connected inverter and the virtual synchronous machine is achieved, which improves the dynamic response characteristics of the power inverter. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects existing in the above-mentioned background technology, and proposes a distributed power supply grid configuration transformation method based on energy storage inertia compensation. This method is based on the inherent energy storage elements of some distributed power sources. Without modifying the system hardware, the inertia characteristics simulation of the grid-connected inverter is realized by adjusting the output power of the external energy storage device.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

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

[0006] Step S1, through in-depth analysis of the inertia characteristics of the virtual synchronous machine in the dynamic response process and the characteristics of the power inverter in the dynamic response, accurately determine the damping ratio required by the distributed power source and the corresponding natural oscillation angular frequency, and further clarify the expected inertia and damping value of the distributed power source based on the above analysis results;

[0007] Step S2: Based on 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. For the power converter with energy storage link, the oscillation angular frequency margin and damping ratio are calculated in detail, so as to determine the optimal damping ratio and the corresponding inherent oscillation angular frequency.

[0008] Step S3: When the energy storage unit of the distributed power source is insufficient, the energy storage system is regulated under different operating scenarios so that it can provide the required inertia and damping. Through the above regulation process, a power reference value of the energy storage system and a frequency compensation value of the power inverter are generated.

[0009] Furthermore, the step S1 specifically includes:

[0010] Step S1.1, analyzing the frequency dynamic response characteristics of the inverter;

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

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

[0013] Further, the step S1.1 is specifically as follows: according to the frequency dynamic response function of the inverter under unit step, its overshoot, frequency change rate, maximum frequency drop depth and adjustment time are calculated; the time domain response of the frequency under unit step is expressed as:

[0014]

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

[0016] The frequency change rate is expressed as:

[0017]

[0018] Wherein, 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 adjustment time is defined as the quasi-steady-state time when the error drops below 2% and is expressed as:

[0026]

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

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

[0029] W B =∫u B i B dt=u B Q N γ SOC

[0030] Among them, the rated capacity is Q N , 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 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 can be related to the ratio of the stored energy to the rated capacity; therefore, the inertia time constant H that the energy storage link can provide c It can be expressed as:

[0032]

[0033] The damping coefficient D provided by the energy storage link can be obtained by ω n and ξ to determine:

[0034]

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

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

[0037]

[0038] Further, the optimal damping ratio close to the second-order system is 0.707, and the optimal matching damping value is determined as follows:

[0039] D=2.828Hω n .

[0040] Furthermore, step S2 specifically includes:

[0041] Step S2.1, determining the maximum inertia damping provided by the energy storage;

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

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

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

[0045]

[0046] In the formula, ΔP m is the 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, the step S2.2 is specifically as follows:

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

[0053]

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

[0055]

[0056] Furthermore, step S3 specifically includes:

[0057] Step S3.1, calculating energy storage power deviation;

[0058] Step S3.2: Distributed power generation inertia damping transfer.

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

[0060] The energy storage reference power deviation takes the frequency deviation value Δω as input. According to the relationship between angular velocity and power angle in the swing equation, it can be obtained that:

[0061]

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

[0063]

[0064] Among them, U i and U L The output voltage of the distributed power supply and the grid voltage are respectively i is the line impedance, is the impedance angle of the line;

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

[0066]

[0067] The step S3.2 is specifically as follows:

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

[0069]

[0070] where k p is the proportionality coefficient, k i 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) The present invention provides a distributed power grid reconstruction method based on energy storage inertia compensation, which realizes an adaptive inertia compensation control of distributed generators based on energy storage.

[0073] (2) The method of the present invention realizes the inertia characteristic simulation of the grid-connected inverter by adjusting the output power of the external energy storage device without modifying the system hardware, thereby achieving the optimal inertia control of the grid-connected inverter and the virtual synchronous machine.

[0074] (3) The method of the present invention provides inertia characteristics for distributed power sources and can effectively support the dynamic response characteristics of the power inverter, thereby improving the stability and economy of the overall system. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 is a flow chart of the present invention;

[0076] Figure 2 This is the output result diagram of the distributed power source without energy storage link;

[0077] Figure 3 This is the energy storage output result diagram for the transformation of distributed power sources without energy storage links;

[0078] Figure 4 This is the output result diagram of the distributed power source with energy storage link;

[0079] Figure 5 This is the energy storage output result diagram for the transformation of distributed power sources with energy storage links. DETAILED DESCRIPTION

[0080] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

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

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

[0084] According to the frequency dynamic response function of the inverter under unit step, its overshoot, frequency change rate, maximum frequency drop depth and adjustment time are calculated. The time domain response of the frequency under unit step is shown in formula (1):

[0085]

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

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

[0088]

[0089] Wherein, RoCoF is the rate of change of frequency.

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

[0091]

[0092] Peak frequency deviation Δf peak for:

[0093]

[0094] The overshoot σ can be expressed as:

[0095]

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

[0097]

[0098] Step S1.2: Inertia and damping value of the distributed power source

[0099] Taking a lead-acid battery as an example, the kinetic energy W stored in a fully charged battery is B It can be expressed 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 , 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 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 can be related to the ratio of the stored energy to the rated capacity. Therefore, the inertia time constant H provided by the energy storage link is c It can be expressed as:

[0103]

[0104] The damping coefficient D provided by the energy storage link can be obtained by ω n and ξ to determine:

[0105]

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

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

[0108]

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

[0110] D=2.828Hω n (11)

[0111] Step S2: Calculation of energy storage inertia damping compensation value

[0112] Step S2.1, the maximum inertia damping provided by energy storage:

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

[0114]

[0115] In the formula, ΔP m is 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 value provided by the energy storage is given by:

[0122]

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

[0124]

[0125] Step S3: Distributed power grid configuration transformation

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

[0127] The energy storage reference power deviation takes the frequency deviation value Δω as input. According to the relationship between angular velocity and power angle in the swing equation, it can be obtained that:

[0128]

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

[0130]

[0131] Among them, U i and U L The output voltage of the distributed power supply and the grid voltage are respectively i is the line impedance, is the impedance angle of the line.

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

[0133]

[0134] Step S3.2, distributed power generation inertia damping transfer:

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

[0136]

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

[0138] The above-described embodiments are only specific implementation methods of the present application, which are used to illustrate the technical solutions of the present application, rather than to limit them. The protection scope of the present application is not limited thereto. Although the present application is described in detail with reference to the aforementioned embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the aforementioned embodiments within the technical scope disclosed in the present application, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. They should all be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A distributed power grid reconstruction method based on energy storage inertia compensation, characterized in that: The method comprises: Step S1, through in-depth analysis of the inertia characteristics of the virtual synchronous machine in the dynamic response process and the characteristics of the power inverter in the dynamic response, accurately determine the damping ratio required by the distributed power source and the corresponding natural oscillation angular frequency, and further clarify the expected inertia and damping value of the distributed power source based on the above analysis results; Step S2: Based on 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. For the power converter with energy storage link, the oscillation angular frequency margin and damping ratio are calculated in detail, so as to determine the optimal damping ratio and the corresponding inherent oscillation angular frequency. Step S3: When the energy storage unit of the distributed power source is insufficient, the energy storage system is regulated under different operating scenarios so that it can provide the required inertia and damping. Through the above regulation process, a power reference value of the energy storage system and a frequency compensation value of the power inverter are generated.

2. A distributed power grid configuration transformation method based on energy storage inertia compensation according to claim 1, characterized in that: The step S1 specifically includes: Step S1.1, analyzing the frequency dynamic response characteristics of the inverter; Step S1.2, determining the inertia and damping value of the distributed power source itself; Step S1.3: Analyze the inertia damping requirements of distributed generation.

3. A distributed power grid configuration transformation method based on energy storage inertia compensation according to claim 2, characterized in that: The step S1.1 is specifically as follows: According to the frequency dynamic response function of the inverter under unit step, its overshoot, frequency change rate, maximum frequency drop depth and adjustment time are calculated; the time domain response of the frequency under unit step is expressed as: Where k is the synchronous power coefficient, ω n is the natural oscillation angular frequency, ξ is the damping ratio; The frequency change rate is expressed as: Wherein, RoCoF is the rate of change of frequency; When t=0, the maximum value of RoCoF is expressed as: The peak frequency deviation Δf peak for: The overshoot σ can be expressed as: The adjustment time is defined as the quasi-steady-state time when the error drops below 2% and is expressed as:

4. A distributed power grid reconstruction method based on energy storage inertia compensation according to claim 2, characterized in that: The step S1.2 is specifically as follows: Taking a lead-acid battery as an example, the kinetic energy W stored in a fully charged battery is B It can be expressed as: W B =∫u B i B dt=u B Q N γ SOC Among them, the rated capacity is Q N , voltage is u B , the discharge current is i B , the state of charge (SOC) is γ SOC ; According to the basic definition of synchronous machine inertia, 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 can be related to the ratio of the stored energy to the rated capacity; therefore, the inertia time constant H that the energy storage link can provide c It can be expressed as: The damping coefficient D provided by the energy storage link can be obtained by ω n and ξ to determine:

5. A distributed power grid configuration transformation method based on energy storage inertia compensation according to claim 2, characterized in that: The step S1.3 is specifically as follows: First, after the frequency deviation occurs, the minimum inertia requirement is obtained with the maximum value of RoCof as 1Hz / s as the target: Further, the optimal damping ratio close to the second-order system is 0.707, and the optimal matching damping value is determined as follows: D=2.828Hω n 。 6. A distributed power grid reconstruction method based on energy storage inertia compensation according to claim 1, characterized in that: The step S2 specifically includes: Step S2.1, determining the maximum inertia damping provided by the energy storage; Step S2.2: Determine the inertia response compensation value provided by the energy storage.

7. A distributed power grid reconstruction method based on energy storage inertia compensation according to claim 6, characterized in that: The step S2.1 is specifically as follows: In VSG control, DG can be regarded as the prime mover of a single-machine infinite system, the energy storage unit and the bidirectional converter correspond to the rotational inertia of the prime mover and SG, and the inverter corresponds to the electromechanical energy conversion process of SG. The analytical solution of the output of VSG during power step change can be expressed as: In the formula, ΔP m is the frequency deviation; The real-time dynamic energy absorbed and released by the energy storage unit can be expressed as: At t = 0, the energy storage unit will provide the maximum power required by the system, expressed as:

8. A distributed power grid reconstruction method based on energy storage inertia compensation according to claim 6, characterized in that: 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 are as follows:

9. A distributed power grid configuration transformation method based on energy storage inertia compensation according to claim 1, characterized in that: The step S3 specifically includes: Step S3.1, calculating energy storage power deviation; Step S3.2: Distributed power generation inertia damping transfer.

10. A distributed power grid configuration transformation method based on energy storage inertia compensation according to claim 9, characterized in that: The step S3.1 is specifically as follows: The energy storage reference power deviation takes the frequency deviation value Δω as input. According to the relationship between angular velocity and power angle in the swing equation, it can be obtained that: The power angle is converted to active power using the traditional power equation: Among them, U i and U L The output voltage of the distributed power supply and the grid voltage are respectively i is the line impedance, is the impedance angle of the line; Assuming the line is purely inductive (X>>R), ignoring the line resistance, the line impedance angle ψ Zi is 90°, so it can be simplified to: The step S3.2 is specifically as follows: The frequency compensation is designed as a PI controller with the frequency deviation value Δω as input and the output frequency deviation of the power inverter as feedback. The feedback frequency is shown below where k p is the proportionality coefficient, k i is the integral coefficient, and Δf is the current frequency deviation of the inverter.

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