VSG virtual inertia and damping coefficient feasible region analysis, design and application method and equipment

Abstract

The invention discloses a VSG virtual inertia and damping coefficient feasible region analysis, design and application method and device, and relates to the field of power system analysis processing, and the method comprises the steps: employing a VSG frequency stability analysis model to determine a frequency stability index, a virtual synchronous generator power constraint and an energy index constraint based on physical parameters, depicting a basic feasible region, and determining a frequency dynamic damping ratio and a time constraint; depicting a feasible region based on the basic feasible region in combination with a frequency dynamic damping ratio and a time constraint; and based on the customized dynamic performance requirement, determining whether the feasible region meets the feasible region existence condition, if so, taking the feasible region as a finally designed feasible region, and if not, adjusting the physical parameters, and carrying out feasible region analysis and design again. According to the invention, the problem that the fixed inverter parameters cannot meet the dynamic requirements of the system can be solved, and the problem that the system stability is poor after the static power generation unit is connected to the power grid can be effectively solved.

Description

Technical Field

[0001] The present application relates to the field of power system analysis and processing, and in particular to a feasible domain analysis, design and application method and equipment for VSG virtual inertia and damping coefficient. Background Art

[0002] In recent years, renewable energy power generation has maintained its growth potential due to its continuous cost reduction and has shown competitive advantages. Therefore, its penetration rate in the power system has gradually increased, and energy storage devices are usually configured to weaken power fluctuations and reduce the impact on the safe operation of the power grid. However, unlike conventional generators, these grid-connected units based on inverter interfaces have fast dynamic response speeds and almost no inertia. Therefore, their access to the power grid will also face new problems such as the loss of a large amount of rotational kinetic energy, reduced energy reserves, and threats to the transient stability of the system. Based on this, how to ensure the dynamic stability of the system frequency will become the first problem that needs to be solved when renewable energy is connected to the power grid.

[0003] In view of the excellent inertia and damping characteristics of synchronous generators in traditional power grids, and the ability to operate autonomously and participate in the regulation of grid voltage and frequency. Therefore, if the new energy grid-connected unit can be virtualized as a synchronous generator, many new problems and challenges faced by active distribution networks can be solved to a large extent. Based on this idea, in recent years, the virtual synchronous generator (VSG) technology, which introduces an appropriate amount of energy storage units on the DC side of traditional new energy grid-connected inverters and integrates the synchronous generator control model, has received widespread attention. Because it realizes the physical and mathematical equivalence of new energy grid-connected units and synchronous generators, it can effectively reduce the impact of large-scale renewable energy grid connection on the grid. The existing VSG virtual inertia and damping coefficient are mainly determined by the parameters of the inverter, which cannot meet the dynamic needs of the system at all. Moreover, after the power generation unit is connected to the grid, it will also face the problem of poor system stability. Summary of the invention

[0004] The purpose of this application is to provide a feasible domain analysis, design and application method and equipment for VSG virtual inertia and damping coefficient, which can solve the problem that fixed inverter parameters cannot meet the dynamic requirements of the system, and thus effectively solve the problem of poor system stability faced by static power generation units after being connected to the power grid.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a feasible domain analysis and design method for VSG virtual inertia and damping coefficient, including:

[0007] Ignoring the electromagnetic transient process of the inductance inside the AC network in the photovoltaic power generation system and the first-order lag link of the diesel generator speed regulator, a VSG frequency stability analysis model is constructed.

[0008] The VSG frequency stability analysis model is used to determine the frequency stability index, virtual synchronous generator power constraint and energy index constraint based on the physical parameters of the photovoltaic power generation system; the physical parameters include: inertia and damping of the distributed power generation system, speed regulator parameters, maximum power disturbance, and VSG power limit and energy limit;

[0009] Describing the basic feasible domain of the VSG virtual inertia and damping coefficient based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint;

[0010] Determine the frequency dynamic damping ratio and the time constraint based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint; the time constraint includes the power dynamic adjustment time constraint and the virtual synchronous generator equivalent power smoothing time constraint;

[0011] On the basis of the basic feasible domain, the feasible domain of the VSG virtual inertia and damping coefficient is characterized in combination with the frequency dynamic damping ratio and time constraint;

[0012] Based on the customized dynamic performance requirements, determining whether the feasible domain satisfies the feasible domain existence condition;

[0013] When the feasible domain satisfies the feasible domain existence condition, taking the feasible domain as the feasible domain of the final design;

[0014] When the feasible domain does not satisfy the feasible domain existence condition, the physical parameters are adjusted, and the execution returns to the method of using the VSG frequency stability analysis model to determine the frequency stability index, the virtual synchronous generator power constraint, and the energy index constraint based on the physical parameters of the photovoltaic power generation system.

[0015] Optionally, determining a frequency dynamic damping ratio and a time constraint based on the frequency stability index, the virtual synchronous generator power constraint, and the energy index constraint includes:

[0016] Based on the frequency stability index, determining a first frequency dynamic damping ratio and a time constraint;

[0017] A second frequency dynamic damping ratio and a time constraint are determined based on the virtual synchronous generator power constraint and the energy index constraint.

[0018] Optionally, the first frequency dynamic damping ratio and time constraint are expressed as:

[0019]

[0020] In the formula, ρ represents the intermediate variable, D eq represents the comprehensive damping coefficient of the photovoltaic power generation system, H eqRepresents the comprehensive inertia of the photovoltaic power generation system, ΔP max represents the maximum power disturbance of the photovoltaic power generation system, t nadir represents the time corresponding to the maximum frequency deviation of the distributed generation system, |Δf nadir | max Represents the maximum frequency deviation limit, where e is the natural logarithm.

[0021] Optionally, the second frequency dynamic damping ratio and time constraint are expressed as:

[0022] T smooth ΔP max ≤E max ;

[0023] In the formula, E max represents the energy limit of the converter under the maximum power disturbance of the photovoltaic power generation system, T smooth Indicates the equivalent power smoothing time of the virtual synchronous generator.

[0024] Optionally, based on the customized dynamic performance requirement, determining whether the feasible domain satisfies the feasible domain existence condition includes:

[0025] Setting the customized dynamic performance requirements; the customized dynamic performance requirements include: the damping ratio of the AC microgrid frequency dynamics, the adjustment time of the AC microgrid frequency dynamics, and the VSG equivalent power smoothing time;

[0026] The conditions for the existence of a feasible domain are determined based on the customized dynamic performance requirements set; the conditions for the existence of a feasible domain include: a first virtual damping and virtual inertia constraint, a second virtual damping and virtual inertia constraint, and a third virtual damping and virtual inertia constraint.

[0027] Optionally, the first virtual damping and virtual inertia constraint are expressed as:

[0028] ξ(H vsg ,D vsg )≥ξ min ;

[0029] Where ξ represents the frequency dynamic damping ratio of the AC microgrid, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator, ξ min It represents the minimum limit of the frequency dynamic damping ratio of the AC microgrid.

[0030] Optionally, the second virtual damping and virtual inertia constraint are expressed as:

[0031] t s (H vsg ,D vsg )≤ts,max ;

[0032] Where, t s represents the adjustment time of the dynamic recovery of the AC microgrid frequency, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator, t s,max Indicates the maximum limit of the adjustment time for dynamic recovery of the AC microgrid frequency.

[0033] Optionally, the third virtual damping and virtual inertia constraint is expressed as:

[0034] T smooth (H vsg ,D vsg )≥T smooth,min ;

[0035] Where, T smooth represents the equivalent power smoothing time of the virtual synchronous generator, T smooth,min The minimum limit of the equivalent power smoothing time of the virtual synchronous generator, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator.

[0036] In a second aspect, the present application provides a feasible domain application method of VSG virtual inertia and damping coefficient, including:

[0037] The feasible domain of the VSG virtual inertia and damping coefficient is obtained by using the feasible domain analysis and design method of the VSG virtual inertia and damping coefficient provided above;

[0038] Based on the designed feasible domain, the virtual inertia and damping coefficient parameters of a single or multiple virtual synchronous generators are adjusted and optimized online.

[0039] In a third aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the feasible domain analysis and design method of VSG virtual inertia and damping coefficient or the feasible domain application method of VSG virtual inertia and damping coefficient provided above.

[0040] According to the specific embodiments provided in this application, this application has the following technical effects:

[0041] This application provides a feasible domain analysis, design and application method and equipment for VSG virtual inertia and damping coefficient. By obtaining the corresponding feasible domain of virtual inertia and damping coefficient according to frequency stability index, photovoltaic storage generator power and energy constraints, and customized dynamic performance requirements, it provides a basis for the design of photovoltaic storage generator control parameters to solve the problem that fixed inverter parameters cannot meet the dynamic requirements of the system. In addition, in view of the special dynamic performance requirements of AC microgrids, different constraints are considered when describing the feasible domain of virtual damping and virtual inertia, and the dynamic performance of the system can be customized, thereby effectively solving the problem of poor system stability faced by static power generation units after connecting to the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 A flowchart of a feasible domain analysis and design method for VSG virtual inertia and damping coefficient provided in one embodiment of the present application;

[0044] Figure 2 A schematic diagram of a basic grid structure of a power system provided in one embodiment of the present application;

[0045] Figure 3 A schematic diagram of a VSG frequency stability analysis model provided by another embodiment of the present application;

[0046] Figure 4 A schematic diagram of the change trend of the maximum frequency change rate and the maximum frequency deviation of a diesel generator provided in one embodiment of the present application;

[0047] Figure 5 A schematic diagram of the power dynamic response of each power generation unit of the system after the AC microgrid provided in one embodiment of the present application is disturbed;

[0048] Figure 6 A schematic diagram of a feasible domain I of virtual damping and virtual inertia taking into account basic constraints provided in an embodiment of the present application;

[0049] Figure 7 A schematic diagram of a feasible region of virtual damping and virtual inertia taking into account frequency dynamic damping ratio and time constraints provided in an embodiment of the present application;

[0050] Figure 8 A schematic diagram of the adjustment and optimization process of virtual damping and virtual inertia provided in an embodiment of the present application;

[0051] Fig. 9 A schematic diagram of the structure of a photovoltaic power generation system including multiple virtual synchronous generators provided in one embodiment of the present application;

[0052] Fig.10 The system comprehensive inertia H provided in one embodiment of the present application is eq and the damping coefficient D eq Schematic diagram of the feasible domain;

[0053] Fig.11 A schematic diagram of the feasible domain of virtual inertia and damping parameters of two VSGs (ie, VSG1 and VSG2) in a system provided in an embodiment of the present application;

[0054] Fig.12 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0056] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0057] In an exemplary embodiment, the present application provides a feasible domain analysis and design method for VSG virtual inertia and damping coefficient, which is executed by a computer device, specifically, it can be executed by a computer device such as a terminal or a server alone, or it can be executed by a terminal and a server together. In the embodiment of the present application, the method is applied to a processor or a controller as an example for explanation. Figure 1 As shown, the feasible domain analysis and design method of VSG virtual inertia and damping coefficient provided in this application includes:

[0058] Step 100: Ignoring the electromagnetic transient process of the inductance inside the AC network in the photovoltaic power generation system and the first-order lag link of the diesel generator speed regulator, a VSG frequency stability analysis model is constructed.

[0059] Step 101: The VSG frequency stability analysis model is used to determine the frequency stability index, the virtual synchronous generator power constraint, and the energy index constraint based on the physical parameters of the photovoltaic power generation system. The physical parameters include: the inertia and damping of the distributed generation system (DGS), the speed regulator parameters, the maximum power disturbance, and the VSG power limit and energy limit.

[0060] Step 102: Describe the basic feasible domain of the VSG virtual inertia and damping coefficient based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint.

[0061] Step 103: Determine the frequency dynamic damping ratio and time constraint based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint. The time constraint includes the power dynamic adjustment time constraint and the virtual synchronous generator equivalent power smoothing time constraint.

[0062] Step 104: Based on the basic feasible domain, the feasible domain of the VSG virtual inertia and damping coefficient is characterized in combination with the frequency dynamic damping ratio and the time constraint.

[0063] Step 105: Based on the customized dynamic performance requirements, determine whether the feasible domain meets the feasible domain existence condition.

[0064] Step 106: When the feasible domain meets the feasible domain existence condition, the feasible domain is used as the feasible domain of the final design.

[0065] Step 107: When the feasible region does not satisfy the feasible region existence condition, adjust the physical parameters and return to step 101.

[0066] In another exemplary embodiment of the present application, Figure 2 The power system shown in the figure is taken as an example to illustrate the implementation process of the feasible domain analysis and design method of the VSG virtual inertia and damping coefficient provided in this application. Among them, an appropriate amount of energy storage unit is introduced on the DC side of the grid-connected inverter of the photovoltaic power generation unit, and a virtual synchronous generator (VSG) of the synchronous generator control model is integrated to construct a design method for the feasible domain of the VSG virtual inertia and damping coefficient. The power system includes a diesel generator, a virtual synchronous generator based on virtual synchronous control, a new energy power generation unit and a load. The system structure of the diesel generator mainly includes a prime mover and its speed regulator, a synchronous generator and an excitation control system. L g and R g Respectively represent the equivalent inductance and resistance (including transformer and line impedance) of the diesel generator connected to the AC bus. Based on this structure, this embodiment focuses on the active power-frequency control characteristics of the photovoltaic power generation system, so the influence of the excitation system is ignored in subsequent modeling and analysis.

[0067] The rotor motion equation of a diesel generator can be described as:

[0068]

[0069] In the formula, ω g is the rotor angular frequency of the diesel generator (abbreviated as diesel generator). g and Dg are the moment of inertia and mechanical damping coefficient of the diesel generator respectively. m and P g are the input power and electromagnetic output power of the diesel generator respectively. t is the time.

[0070] The speed governor of the diesel generator uses a proportional-integral (PI) controller to achieve error-free frequency regulation. At the same time, a first-order lag link is used to approximate the dynamic response characteristics of the diesel generator prime mover and the speed governor. Therefore, the mechanical input power characteristics of the diesel generator can be expressed as:

[0071]

[0072] Where ω0 is the rated rotor angular frequency of the diesel generator. p and k i are the proportional coefficient and integral coefficient of the speed regulator, τ is the time constant of the first-order lag link, and s is the Laplace operator.

[0073] The energy storage converter topology adopts a typical three-phase two-level structure. Each phase consists of two groups of anti-parallel diodes that can be turned off. The AC side is an LCL filter structure. f , C f and R f They are filter inductance, filter capacitance and filter resistance respectively. VSG and R VSG are the line inductance and resistance of the VSG outlet respectively. dc is the DC side voltage. The energy storage converter adopts voltage source type virtual synchronous control technology. The converter reactive outer loop adopts conventional QV droop control, Q ref With Q VSG are the reactive power reference value and actual output value of the converter, k q is the reactive droop coefficient, and V0 is the rated voltage value. The active outer loop control adopts VSG, and the relationship between the output frequency and the output active power of the energy storage converter can be described as:

[0074]

[0075] In the formula, ω VSG is the VSG output frequency. ref With P VSG Respectively represent the VSG active power reference value and actual output value. VSG With D VSG The virtual inertia and damping coefficient of VSG respectively.

[0076] After obtaining the frequency and voltage amplitude references through the outer loop VSG control, the inner loop of the energy storage converter can adopt voltage / current dual closed-loop control based on the dq coordinate system or the αβ coordinate system to track the converter voltage and current references and finally generate a modulated voltage signal. Figure 2 In, v dref is the d-axis component of the voltage reference value, and the q-axis component of the voltage reference value is usually set to 0. dref ′ and v qref ′ are the d-axis and q-axis components of the voltage reference value after adding the virtual impedance. dref and i td 、i qref and i tq They are the d-axis current reference value and actual value, and the q-axis current reference value and actual value respectively. t is the d-axis voltage reference value of the grid-connected point, and the q-axis voltage reference value of the grid-connected point is usually set to 0. invd and v invq They are the d-axis and q-axis components of the controller output modulation voltage reference value respectively. v and R v They are the virtual inductance and virtual resistance added in VSG control respectively.

[0077] Based on the above-mentioned power system structure, the following simplifications are made when establishing the frequency stability analysis model:

[0078] (1) Consider that the output frequency of VSG is ω VSG Approximately the output frequency of the diesel generator ω g equal.

[0079] (2) The rotor motion equation of the diesel generator and the active-frequency outer loop control characteristics of the VSG are taken into account. In addition, since the electromagnetic transient of the AC network is an influencing factor of the high-frequency dynamics of the system and has little impact on the low-frequency dynamics of the system, the electromagnetic transient process of the inductance inside the AC network is ignored during modeling to simplify the analysis.

[0080] (3) Since the time constant of the first-order lag link of an actual diesel generator speed regulator is usually small and has little impact on the low-frequency dynamics of the system, this link is ignored during modeling.

[0081] Based on the above simplified conditions, the VSG frequency stability analysis model constructed in the above step 100 of the present application is as follows: Figure 3 shown.

[0082] based on Figure 3 Given the structure, the load disturbance ΔP can be calculated load To diesel generator output frequency Δω g and the active power output of the i-th VSG ΔP VSGi The transfer functions are:

[0083]

[0084] In the formula, G ω (s) and G Pvsgi (s) represents the load disturbance ΔP load To diesel generator output frequency Δω g and the active power output of the i-th VSG ΔP VSGi The transfer function value of H eq and D eq are the comprehensive inertia and comprehensive damping coefficient of the system respectively, and the specific expressions are:

[0085]

[0086] In the formula, H vsgi (i=1,2,...,n) is the virtual inertia of the i-th VSG, D vsgi (i=1,2,...,n) is the damping coefficient of the i-th VSG.

[0087] The transfer function obtained above can be used as a basic mathematical model, which represents the relationship between the two quantities of inertia and comprehensive damping coefficient and load disturbance and frequency change. Load disturbance will affect the change of grid frequency, and the amount of frequency change is determined by the transfer function, which is determined by inertia and damping coefficient.

[0088] In another exemplary embodiment of the present application, the above step 101 is to obtain system performance indicator constraints.

[0089] Based on the above given Figure 3 The VSG frequency stability analysis model shown in the figure generally considers the lowest frequency point f of the diesel generator in the transient process. nadir and the maximum frequency change rate RoCoF max As the basic frequency stability indicators of AC microgrid, the two are defined as follows:

[0090]

[0091] Considering the load power disturbance ΔP in the AC microgrid load Increase from zero to the maximum allowable capacity ΔP max When the energy storage converter adopts the conventional control strategy, it is assumed that the maximum frequency change rate and the maximum frequency deviation of the diesel generator have the following changing trends: Figure 4 The basic control goal that VSG should achieve is: even if the maximum power disturbance ΔP max When the AC microgrid has the maximum frequency change rate RoCoF max and maximum frequency deviation |Δf nadir| still does not exceed its limit (respectively Figure 4 China|RoCoF max | max and |Δf nadir | max shown).

[0092] In order to meet the above basic goals, the selection of VSG virtual inertia and damping coefficient is crucial. Based on this, the process of determining the frequency dynamic damping ratio and time constraint based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint in the above step 101 of the present application includes:

[0093] (1) Based on the frequency stability index (also called the basic frequency stability index), the first frequency dynamic damping ratio and time constraint are determined.

[0094] For example, the load disturbance ΔP load To diesel generator output frequency Δω g The transfer function of can be used to find the time domain analytical expression of DGS angular frequency:

[0095]

[0096] In the formula, the intermediate variable ρ = D eq 2 -8H eq k i .

[0097] Furthermore, based on the time-domain analytical expression of the DGS angular frequency given above, through mathematical derivation, the maximum frequency change rate corresponding to the initial moment of the disturbance can be obtained as:

[0098]

[0099] Based on the above analytical expression of the maximum frequency change rate, considering the system maximum power disturbance ΔP max and maximum frequency change rate specification limit |RoCoF max | max , it can be obtained that the virtual inertia of VSG must satisfy its minimum inertia H VSG,min Restrictions include:

[0100]

[0101] Similarly, the maximum frequency deviation of DGS |Δf can be obtained by the above time domain analytical expression of DGS angular frequency: nadir | and its corresponding time t nadir They are:

[0102]

[0103] Based on the maximum frequency deviation |Δf nadir |, considering the maximum frequency deviation limit |Δf nadir | max , then the first frequency dynamic damping ratio and time constraint can be obtained as:

[0104]

[0105] (2) Determine the second frequency dynamic damping ratio and time constraint based on the virtual synchronous generator power constraint and energy index constraint.

[0106] Since the maximum power that a VSG can output is limited by its capacity, the energy it can release also has an upper limit, especially when the energy storage system (ESS) uses power-type energy storage such as supercapacitors. In addition, in an AC microgrid system that includes an energy storage system and renewable energy generation, different operating conditions may also lead to different power and energy constraints of the converter. Therefore, in H VSG and D VSG In constructing the feasible domain, the actual power and energy limitations must also be considered.

[0107] After the energy storage system adopts voltage source type virtual synchronous control, its maximum power for frequency response and transient support generally appears at the initial moment of disturbance. The output active power ΔP of the i-th virtual synchronous generator is VSGi By applying the initial value theorem to the transfer function, the active power ΔP output by the virtual synchronous generator at the moment of load disturbance can be calculated. VSG (0 + ),for:

[0108]

[0109] Consider the power constraint limit ΔP of VSG VSG (0 + ) max , then we can get the following virtual inertia H VSG The maximum limit of:

[0110]

[0111] Active power ΔP is output through the i-th VSG 光VSGi The transfer function of VSG transient power response can be obtained by the time domain expression ΔP VSG (t), and by integrating it, we can obtain the energy ΔE absorbed or released by VSG during the transient support process, which is:

[0112]

[0113] Among them, a, b, c and d are coefficients b=2D VSG Heq -H VSG D eq , d=4H eq Variable T smooth Defined as the equivalent power smoothing time of VSG, this parameter is related to H VSG , D VSG Related.

[0114] The energy limit E of the converter under the maximum power disturbance of the system is considered max , then the second frequency dynamic damping ratio and time constraint can be obtained as:

[0115] T smooth ΔP max ≤E max .

[0116] In the formula, E max represents the energy limit of the converter under the maximum power disturbance of the photovoltaic power generation system, T smooth Indicates the equivalent power smoothing time of the virtual synchronous generator.

[0117] In another exemplary embodiment of the present application, in addition to meeting the basic frequency stability index and the physical constraints of the converter itself such as power and energy, different types of AC microgrids may have special requirements for dynamic performance or transient support effects. In order to better meet actual needs, this embodiment focuses on special customized dynamic performance indicators such as the dynamic damping ratio of the frequency of the AC microgrid, the dynamic frequency adjustment time, and the equivalent power smoothing time of the VSG. Based on this, the implementation process of the above step 105 of the present application may include:

[0118] (1) Set customized dynamic performance requirements. The customized dynamic performance requirements include: the damping ratio of the AC microgrid frequency dynamics, the adjustment time of the AC microgrid frequency dynamics, and the VSG equivalent power smoothing time.

[0119] Among them, (1.1) is the customization process of the damping ratio of the AC microgrid frequency dynamics.

[0120] The active power ΔP output by the i-th VSG VSGi The transfer function of the AC microgrid frequency dynamic damping ratio ξ can be obtained as follows:

[0121]

[0122] (1.2) Customization process of the dynamic adjustment time of AC microgrid frequency.

[0123] Adjustment time t s It can reflect the speed at which the system returns to a stable state. The calculation formula is:

[0124]

[0125] (1.3) Customization process of VSG equivalent power smoothing time.

[0126] When the DGS capacity in the AC microgrid is small, its ramp rate has certain limitations. In addition, when a large load power disturbance occurs in the system, in order to ensure that the system has sufficient time for emergency coordinated control, requirements are usually put forward for the transient support effect or power smoothing effect of the VSG. To this end, this paper defines the equivalent power smoothing time index of the VSG to quantitatively analyze and evaluate its transient power support or smoothing performance, that is, the variable T smooth .

[0127] If the AC microgrid is set to overdamping, the power dynamic response of each power generation unit in the system after being disturbed is as follows: Figure 5 shown. Figure 5 The shaded area represents the energy ΔE. smooth The larger the value, the more energy VSG releases in the transient process, which means that the frequency and power of the diesel generator can transition to a new stable state more smoothly. VSG can bear the unbalanced power for a longer period of time, providing sufficient response time for subsequent emergency coordinated control and power distribution.

[0128] (2) Determine the conditions for the existence of a feasible domain based on the customized dynamic performance requirements. The conditions for the existence of a feasible domain include: a first virtual damping and virtual inertia constraint, a second virtual damping and virtual inertia constraint, and a third virtual damping and virtual inertia constraint.

[0129] In order to ensure the frequency stability in the transient process, the minimum limit of the dynamic damping ratio of the AC microgrid frequency is generally set. min , then the virtual damping and virtual inertia constraints (i.e., the first virtual damping and virtual inertia constraints) that meet this requirement are as follows:

[0130] ξ(H vsg ,D vsg )≥ξ min .

[0131] From the perspective of optimal control, ξ min It can be set to 0.707. If you want to avoid low-frequency power oscillation in the transient support process of VSG to reduce energy loss, ξ min It can also be set to 1, making the AC microgrid in an overdamped state on the frequency dynamic time scale.

[0132] Furthermore, considering the maximum limit of the adjustment time of the AC microgrid frequency dynamic recovery t s,max , then the virtual damping and virtual inertia constraints that meet this requirement (i.e., the second virtual damping and virtual inertia constraints) are:

[0133] t s (H vsg ,D vsg )≤t s,max .

[0134] Furthermore, the equivalent power smoothing time of VSG usually considers the minimum limit T smooth,min , then the damping and inertia constraints that meet this requirement (i.e., the third virtual damping and virtual inertia constraints) are:

[0135] T smooth (H vsg ,D vsg )≥T smooth,min .

[0136] Since the equivalent power smoothing time T smooth It is related to the energy ΔE released by VSG, and there is a coupling relationship between the two. Therefore, when setting the limits of the two, it is necessary to consider these two indicators comprehensively so that VSG can achieve better power smoothing effect while meeting the energy constraints.

[0137] The present application also provides a feasible domain application method of VSG virtual inertia and damping coefficient, including:

[0138] Step 200: Obtain the feasible domain of the VSG virtual inertia and damping coefficient by using the feasible domain analysis and design method of the VSG virtual inertia and damping coefficient provided above.

[0139] Step 201: Based on the designed feasible region, online adjustment and optimization are performed on the virtual inertia and damping coefficient parameters of a single or multiple virtual synchronous generators.

[0140] In an exemplary embodiment, based on the designed feasible domain, the process of online adjustment and optimization of the virtual inertia and damping coefficient of a single VSG can be described as follows:

[0141] Based on the basic frequency stability index of the system and the power and energy index constraints of the VSG, the feasible domain I (i.e., the basic feasible domain) of virtual damping and virtual inertia that meets the above constraints can be characterized. The feasible domain I is Figure 6 Middle shaded area R abcd , that is, the area enclosed by the intersection points a, b, c and d.

[0142] assumed Figure 6 D at the midpoints a, b, c and d VSG The values ​​are represented by D VSG,a , D VSG,b , D VSG,c and D VSG,d It is easy to get the feasible region R abcd The conditions for existence are:

[0143]

[0144] Based on the basic frequency stability index of the system, VSG power and energy index constraints, taking into account the frequency dynamic damping ratio constraint and the frequency dynamic adjustment time constraint, the following can be obtained: Figure 7 Part (a) shows the feasible domain II of virtual damping and virtual inertia. The feasible domain II corresponds to Figure 7 The area enclosed by the intersection points a, b, f, e and d in part (a). It should be noted that the shape of the feasible region actually formed in the application varies due to different system parameters, constraints, etc. Figure 7 From part (a), we can see that the feasible region R abfed The condition for existence is: to ensure that when taking into account ξ and t s The new intersection points e and f after constraints are in the original feasible region R abcd within the range.

[0145] Based on the basic frequency stability index of the system and the VSG power and energy index constraints, taking into account the frequency dynamic damping ratio constraint and the VSG equivalent power smoothing time constraint, it can be obtained Figure 7 Part (b) shows the feasible domain III of virtual damping and virtual inertia. The feasible domain III corresponds to Figure 7 (b) The area enclosed by the intersection points a, b, f, h, and g. Figure 7 From part (b) of the paper, we can see that the feasible region R abfhg The condition for existence is: to ensure that ξ and T are taken into account smooth The new intersection points f, g, h after constraints are in the original feasible region R abcd within the range.

[0146] Based on the above analysis, this application proposes the following AC microgrids with different operation requirements: Figure 8 The adjustment and optimization process of the VSG virtual inertia and damping parameters in the photovoltaic power generation system shown includes:

[0147] 1. Input known conditions.

[0148] 1.1 Physical parameters of diesel-storage microgrid.

[0149] 1.2 Frequency stability indicators and constraints.

[0150] 2.H vsg and D vsg Characterization of basic feasible domain.

[0151] 3. Have you considered special customized dynamic performance requirements?

[0152] 3.1 Considering ξ and t s Constrained H vsg and Dvsg Characterization of feasible domain.

[0153] 3.2 Considering ξ and t smooth Constrained H vsg and D vsg Characterization of feasible domain.

[0154] 4. Determine whether the conditions for the existence of the feasible domain are met.

[0155] 5. When the conditions for the existence of the feasible domain are not met, adjust the indicators or constraints.

[0156] 6. When the feasible region existence condition is met, H vsg and D vsg Feasible domain output.

[0157] In an exemplary embodiment, Fig. 9 Taking the structure of the photovoltaic power generation system including two VSGs as an example, the process of online adjustment and optimization of the virtual inertia and damping coefficient parameters of multiple virtual synchronous generators is explained.

[0158] When designing the virtual inertia and damping coefficient of the two VSGs in the system, a similar analysis and construction method is used. First, according to the system RoCoF max Constraints, f nadir Constraints, VSG total power constraints and total energy constraints are used to construct the system comprehensive inertia and damping coefficient H eq and D eq The feasible domain of Fig.10 shown.

[0159] From the transfer function of the active power output of the i-th VSG, it can be obtained that in a photovoltaic power generation system including multiple VSGs, the expression of the active power output of the i-th VSG at the moment of load disturbance is:

[0160]

[0161] From the expression of the active power output by the i-th VSG at the moment of load disturbance, it can be seen that the active power output by the VSG at the transient moment is proportional to its own virtual inertia, and has nothing to do with the virtual damping coefficient. That is, when the power constraints of each VSG are different, the comprehensive inertia H can be obtained in proportion. eq The inertia range of each VSG is obtained by allocating it within the range.

[0162] From the energy ΔE absorbed or released by the VSG during the transient support process, it can be obtained that in a multi-machine system, the energy ΔE absorbed or released by the i-th VSG during the transient support process is i for:

[0163]

[0164] The energy absorbed or released by the i-th VSG during the transient support process is ΔE i From the expression, we can know that during the transient support process, the energy ΔE absorbed or released by the i-th VSG i It is proportional to its own virtual damping coefficient and has nothing to do with the virtual inertia. That is, when the energy constraints of each VSG are different, the system comprehensive damping coefficient D can be obtained in proportion. eq The range of virtual damping coefficient is allocated to obtain the range of virtual damping coefficient of each VSG.

[0165] Based on the above analysis, the feasible domain of the virtual inertia and damping parameters of the two VSGs in the system can be obtained as follows: Fig.11 Part (a) and Fig.11 As shown in part (b) of .

[0166] Based on the above description, the construction idea of ​​the feasible domain of virtual inertia and damping coefficient of each VSG unit in the photovoltaic storage power generation system containing multiple VSGs is as follows:

[0167] First, according to the total power constraints and total energy constraints of each VSG unit, the feasible domain of the system's comprehensive inertia and comprehensive damping coefficient is constructed. Then, according to the constraints and requirements of each energy storage converter, the parameters of the comprehensive inertia and comprehensive damping coefficient are assigned to obtain the feasible domain of each VSG's virtual inertia and virtual damping coefficient. Finally, within the feasible domain, the virtual inertia and damping coefficient parameters of the VSG are adjusted and optimized online according to the actual optimization objectives of the system.

[0168] In summary, compared with the known technology, the feasible domain analysis and design method of VSG virtual inertia and damping coefficient provided by this application also has the following advantages:

[0169] 1. Based on the frequency stability index, power and energy constraints of the photovoltaic power generator, and customized dynamic performance requirements, this application can obtain the corresponding virtual damping and virtual inertia feasible domain, providing a basis for the control parameter design of the photovoltaic power generator.

[0170] 2. In addition to meeting the basic frequency stability index and the physical constraints of the converter itself, such as power and energy, different types of AC microgrids may have special requirements for dynamic performance or transient support effects. Based on this, this application considers different constraints when describing the feasible domain of virtual damping and virtual inertia to customize the dynamic performance of the system in response to the special dynamic performance requirements of AC microgrids.

[0171] In addition, the following applications can also be performed based on the feasible domain determined in this application:

[0172] 1) Optimize the design of virtual damping and virtual inertia parameters based on a certain optimization goal (such as minimizing transient support energy consumption, etc.);

[0173] 2) According to the dynamic performance requirements of the specified frequency, the inverse is applied to the power and energy optimization configuration of the energy storage converter.

[0174] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Fig.12 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store feasible domain analysis and design data of VSG virtual inertia and damping coefficient. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a feasible domain analysis and design method of VSG virtual inertia and damping coefficient is implemented.

[0175] Those skilled in the art will understand that Fig.12 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0176] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0177] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0178] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0179] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0180] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0181] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0182] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A feasible domain analysis and design method for VSG virtual inertia and damping coefficient, characterized in that: The feasible domain analysis and design method of the VSG virtual inertia and damping coefficient includes: Ignoring the electromagnetic transient process of the inductance inside the AC network in the photovoltaic power generation system and the first-order lag link of the diesel generator speed regulator, a VSG frequency stability analysis model is constructed. The VSG frequency stability analysis model is used to determine the frequency stability index, virtual synchronous generator power constraint and energy index constraint based on the physical parameters of the photovoltaic power generation system; the physical parameters include: inertia and damping of the distributed power generation system, speed regulator parameters, maximum power disturbance, and VSG power limit and energy limit; Describing the basic feasible domain of the VSG virtual inertia and damping coefficient based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint; Determine the frequency dynamic damping ratio and the time constraint based on the frequency stability index, the virtual synchronous generator power constraint and the energy index constraint; the time constraint includes the power dynamic adjustment time constraint and the virtual synchronous generator equivalent power smoothing time constraint; On the basis of the basic feasible domain, the feasible domain of the VSG virtual inertia and damping coefficient is characterized in combination with the frequency dynamic damping ratio and time constraint; Based on the customized dynamic performance requirements, determining whether the feasible domain satisfies the feasible domain existence condition; When the feasible domain satisfies the feasible domain existence condition, taking the feasible domain as the feasible domain of the final design; When the feasible domain does not satisfy the feasible domain existence condition, the physical parameters are adjusted, and the execution returns to the method of using the VSG frequency stability analysis model to determine the frequency stability index, the virtual synchronous generator power constraint, and the energy index constraint based on the physical parameters of the photovoltaic power generation system.

2. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 1 is characterized in that: Determining a frequency dynamic damping ratio and a time constraint based on the frequency stability index, the virtual synchronous generator power constraint, and the energy index constraint includes: Based on the frequency stability index, determining a first frequency dynamic damping ratio and a time constraint; A second frequency dynamic damping ratio and a time constraint are determined based on the virtual synchronous generator power constraint and the energy index constraint.

3. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 2 is characterized in that: The first frequency dynamic damping ratio and time constraint are expressed as: In the formula, ρ represents the intermediate variable, D eq represents the comprehensive damping coefficient of the photovoltaic power generation system, H eq Represents the comprehensive inertia of the photovoltaic power generation system, ΔP max represents the maximum power disturbance of the photovoltaic power generation system, t nadir represents the time corresponding to the maximum frequency deviation of the distributed generation system, |Δf nadir | max Represents the maximum frequency deviation limit, where e is the natural logarithm.

4. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 2 is characterized in that: The second frequency dynamic damping ratio and time constraint are expressed as: T smooth ΔP max ≤E max ; In the formula, E max represents the energy limit of the converter under the maximum power disturbance of the photovoltaic power generation system, T smooth Indicates the equivalent power smoothing time of the virtual synchronous generator.

5. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 1 is characterized in that: Based on the customized dynamic performance requirements, determine whether the feasible domain meets the feasible domain existence conditions, including: Setting the customized dynamic performance requirements; the customized dynamic performance requirements include: the damping ratio of the AC microgrid frequency dynamics, the adjustment time of the AC microgrid frequency dynamics, and the VSG equivalent power smoothing time; The conditions for the existence of a feasible domain are determined based on the customized dynamic performance requirements set; the conditions for the existence of a feasible domain include: a first virtual damping and virtual inertia constraint, a second virtual damping and virtual inertia constraint, and a third virtual damping and virtual inertia constraint.

6. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 5 is characterized in that: The first virtual damping and virtual inertia constraints are expressed as: ξ(H vsg ,D vsg )≥ξ min ; Where ξ represents the frequency dynamic damping ratio of the AC microgrid, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator, ξ min It represents the minimum limit of the frequency dynamic damping ratio of the AC microgrid.

7. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 5 is characterized in that: The second virtual damping and virtual inertia constraint are expressed as: t s (H vsg ,D vsg )≤t s,max ; Where, t s represents the adjustment time of the dynamic recovery of the AC microgrid frequency, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator, t s,max Indicates the maximum limit of the adjustment time for dynamic recovery of the AC microgrid frequency.

8. The feasible domain analysis and design method of VSG virtual inertia and damping coefficient according to claim 5 is characterized in that: The third virtual damping and virtual inertia constraint is expressed as: T smooth (H vsg ,D vsg )≥T smooth,min ; Where, T smooth represents the equivalent power smoothing time of the virtual synchronous generator, T smooth,min The minimum limit of the equivalent power smoothing time of the virtual synchronous generator, H VSG represents the virtual inertia of the virtual synchronous generator, D VSG represents the damping coefficient of the virtual synchronous generator.

9. A feasible domain application method for VSG virtual inertia and damping coefficient, characterized in that: The feasible domain application method of the VSG virtual inertia and damping coefficient includes: The feasible domain of the VSG virtual inertia and damping coefficient is obtained by adopting the feasible domain analysis and design method of the VSG virtual inertia and damping coefficient as described in any one of claims 1 to 8; Based on the designed feasible domain, the virtual inertia and damping coefficient parameters of a single or multiple virtual synchronous generators are adjusted and optimized online.

10. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the feasible domain analysis and design method of the VSG virtual inertia and damping coefficient described in any one of claims 1 to 8, or to implement the feasible domain application method of the VSG virtual inertia and damping coefficient described in claim 9.

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