Micro-grid stability control method and device considering reactive power

Abstract

The invention relates to a microgrid stability control method and device considering reactive power. The method comprises the following steps: establishing a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid; through abc-dq coordinate transformation, converting into an equivalent nonlinear model of a micro-grid system based on a d axis and a q axis; based on the equivalent nonlinear model of the micro-grid system, establishing a large signal model of the micro-grid system according to a mixed potential function method; and according to a stability theorem, generating a quantitative constraint relationship among the capacitance, the inductance, the dynamic load power, and the active power and the reactive power of the photovoltaic micro-source, and completing stable control of the AC / DC hybrid micro-grid. According to the invention, the reactive power effect of the AC-DC hybrid micro-grid can be suppressed through the large signal stability criterion, and the stability of the micro-grid system is enhanced.

Description

Technical Field

[0001] The present disclosure relates to the field of microgrids, and in particular to a microgrid stability control method and device taking reactive power into consideration. Background Art

[0002] Since the 21st century, the world energy crisis has become increasingly serious. Renewable energy has gradually replaced traditional fossil energy due to its advantages of low carbon, environmental protection, and economy. The Chinese government also strongly supports the development of renewable energy technologies such as solar energy and wind power to accelerate the goal of replacing traditional fossil energy with renewable energy. However, renewable energy itself has the characteristics of uneven output and large fluctuations, which will seriously affect the stability of the power system. Therefore, how to ensure the smooth access of a large number of renewable energy to the power grid is a problem worthy of in-depth study. Microgrids have the advantages of small scale, easy development, and strong compatibility. They can meet the grid connection needs of renewable energy and maximize the advantages of renewable energy. Most microgrid systems are composed of distributed generation units, energy storage units, and load units. At present, they are mainly divided into three types: DC microgrids, AC microgrids, and AC / DC hybrid microgrids. Among them, DC microgrids are easy to control, simple in structure, and do not need to consider power angle stability and frequency stability; AC microgrids can be directly connected to the grid, compatible with large power grids, and have good stability. However, AC microgrids and DC microgrids can only access micro sources and loads of the same type, and cannot be compatible with different types of new energy and multiple loads. On the other hand, the AC-DC hybrid microgrid has the characteristics of both AC microgrid and DC microgrid, including AC system, DC system and bidirectional AC-DC converter, which can integrate different types of distributed power generation units, and can also supply power to AC and DC loads at the same time, reducing intermediate links, reducing energy loss, and achieving the advantages of power balance within the microgrid and power flow between AC and DC microgrids. Therefore, the AC-DC hybrid microgrid system is widely used.

[0003] The AC-DC hybrid microgrid has both an AC bus and a DC bus. The bidirectional AC-DC converter coordinates the control of the AC subsystem and the DC subsystem. When the system is subject to a large disturbance, the bidirectional converter needs to control the charge and discharge of the energy storage unit to achieve power balance and enhance the system stability. Therefore, it is very important to study the control strategy of the bidirectional converter. In the prior art, the AC-DC microgrid bidirectional converter modeling mainly uses the microgrid nonlinear model obtained by the abc-dq coordinate transformation to convert the AC system to the DC system for analysis, and realizes the transmission of active power on the DC side. Since the reactive current is given as zero, the analysis only considers the situation where the microgrid system works at a unit power factor, and does not consider the transient process of the system disturbance, resulting in inaccurate control of the AC-DC hybrid microgrid. Therefore, it is necessary to quantitatively analyze the impact of reactive power on the stability of the microgrid system during the transient process. Therefore, it is necessary to establish a nonlinear model that considers reactive power during the transient process, so as to analyze the impact of transient reactive power on the large signal stability of the microgrid system.

[0004] Therefore, one or more methods are needed to solve the above problems.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present disclosure is to provide a microgrid stability control method and device taking reactive power into consideration, thereby overcoming one or more problems caused by limitations and defects of related technologies at least to a certain extent.

[0007] According to one aspect of the present disclosure, a microgrid stability control method considering reactive power is provided, comprising:

[0008] Based on the topological circuit of AC-DC hybrid microgrid, a nonlinear model of bidirectional AC-DC converter is established;

[0009] Under the condition of considering reactive power in transient process, the nonlinear model of the bidirectional AC / DC converter is converted into an equivalent nonlinear model of the microgrid system based on d-axis and q-axis through abc-dq coordinate transformation;

[0010] Based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system is established according to a mixed potential function method;

[0011] Based on the large signal model of the microgrid system, according to the stability theorem, a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of the photovoltaic micro-source and reactive power is generated;

[0012] Based on the quantitative constraint relationship, stable control of the AC / DC hybrid microgrid is completed.

[0013] In an exemplary embodiment of the present disclosure, the method further includes:

[0014] Based on the topological circuit of AC / DC hybrid microgrid, the models of energy storage unit, photovoltaic distributed generation unit and dynamic load are established respectively;

[0015] Based on the models of the energy storage unit, the photovoltaic distributed power generation unit and the dynamic load, a nonlinear model of the bidirectional AC-DC converter is established.

[0016] In an exemplary embodiment of the present disclosure, the method further includes:

[0017] Under the condition of considering reactive power in transient process, the projections of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis are calculated respectively through abc-dq coordinate transformation;

[0018] An equivalent nonlinear model of a microgrid system based on the d-axis and the q-axis is generated according to the projection of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis.

[0019] In an exemplary embodiment of the present disclosure, the method further includes:

[0020] Based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system without considering the influence of reactive power is established according to the mixed potential function method;

[0021] Based on the large signal model of the microgrid system that does not consider the influence of reactive power, according to the reactive current in the transient process, a large signal model of the microgrid system that considers the influence of reactive power is established according to the hybrid potential function method.

[0022] In an exemplary embodiment of the present disclosure, the method further includes:

[0023] Based on the large signal model of the microgrid system considering the influence of reactive power, a large signal stability criterion between capacitance, inductance, dynamic load power, active power of photovoltaic micro-sources and reactive power is generated according to the stability theorem.

[0024] In one aspect of the present disclosure, there is provided a microgrid stability control device considering reactive power, comprising:

[0025] The first modeling module is used to establish a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid;

[0026] A model conversion module, used for converting the nonlinear model of the bidirectional AC-DC converter into an equivalent nonlinear model of the microgrid system based on the d-axis and the q-axis by abc-dq coordinate transformation while considering reactive power in a transient process;

[0027] A second modeling module is used to establish a large signal model of the microgrid system according to a mixed potential function method based on an equivalent nonlinear model of the microgrid system;

[0028] A stability criterion generation module is used to generate a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power and reactive power of a photovoltaic micro-source based on a large signal model of the microgrid system and according to the stability theorem;

[0029] A control module is used to complete the stable control of the AC / DC hybrid microgrid based on the quantitative constraint relationship.

[0030] A microgrid stability control method considering reactive power in an exemplary embodiment of the present disclosure, wherein the method includes: establishing a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid; converting to an equivalent nonlinear model of a microgrid system based on the d-axis and q-axis through abc-dq coordinate transformation; establishing a large signal model of the microgrid system based on the equivalent nonlinear model of the microgrid system according to a hybrid potential function method; generating a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of a photovoltaic microsource, and reactive power according to the stability theorem, and completing the stable control of the AC-DC hybrid microgrid. The present disclosure can suppress the reactive power effect of the AC-DC hybrid microgrid through a large signal stability criterion, thereby enhancing the stability of the microgrid system.

[0031] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other features and advantages of the present disclosure will become more apparent by describing in detail example embodiments thereof with reference to the attached drawings.

[0033] Figure 1 A flow chart of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0034] Figure 2 A typical AC / DC hybrid microgrid system topology diagram of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0035] Figure 3 A block diagram of AC / DC converter droop control of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0036] Figure 4 A double PI closed-loop control block diagram of an AC / DC converter of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0037] Figures 5A-5C A schematic diagram of equivalent models of various parts of an AC / DC hybrid power grid of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0038] Figure 6 A typical topological structure diagram of an AC-DC converter of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0039] Figure 7 An equivalent model diagram of an AC-DC converter in a dq rotating coordinate system of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0040] Figures 8A-8B A schematic diagram of a nonlinear model of an AC / DC hybrid microgrid system of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0041] Fig. 9 A schematic diagram of a main circuit simulation model of an AC / DC hybrid microgrid according to a microgrid stability control method taking reactive power into consideration according to an exemplary embodiment of the present disclosure is shown;

[0042] Fig.10 A dynamic load main circuit diagram of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0043] Fig.11 An AC dynamic load closed-loop control diagram of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0044] Fig.12 A DC / AC converter main circuit model diagram of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0045] Fig.13 A DC / AC converter closed-loop control diagram of a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0046] Figures 14A-14B A waveform diagram of three-phase current of an AC bus after a large signal disturbance is shown according to a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure;

[0047] Fig.15 A waveform diagram of three-phase current of an AC bus after a resistive load is removed 1 second later according to a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure is shown;

[0048] Figures 16A-16B A waveform diagram of three-phase current of an AC bus after a large signal disturbance is shown according to a microgrid stability control method considering reactive power according to an exemplary embodiment of the present disclosure;

[0049] Fig.17 A schematic block diagram of a microgrid stability control device considering reactive power according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0050] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0051] In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of the specific details, or other methods, components, materials, devices, steps, etc. may be adopted. In other cases, known structures, methods, devices, implementations, materials or operations are not shown or described in detail to avoid blurring the various aspects of the present disclosure.

[0052] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or these functional entities or parts of functional entities may be implemented in one or more software hardened modules, or these functional entities may be implemented in different networks and / or processor devices and / or microcontroller devices.

[0053] In this exemplary embodiment, a microgrid stability control method considering reactive power is first provided; Figure 1 As shown in , the microgrid stability control method considering reactive power may include the following steps:

[0054] Step S110, establishing a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid;

[0055] Step S120, in the case of considering reactive power in a transient process, converting the nonlinear model of the bidirectional AC / DC converter into an equivalent nonlinear model of a microgrid system based on a d-axis and a q-axis through abc-dq coordinate transformation;

[0056] Step S130, based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system is established according to a mixed potential function method;

[0057] Step S140, based on the large signal model of the microgrid system and according to the stability theorem, generating a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of the photovoltaic micro-source, and reactive power;

[0058] Step S150: completing stability control of the AC / DC hybrid microgrid based on the quantitative constraint relationship.

[0059] A microgrid stability control method considering reactive power in an exemplary embodiment of the present disclosure, wherein the method includes: establishing a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid; converting to an equivalent nonlinear model of a microgrid system based on the d-axis and q-axis through abc-dq coordinate transformation; establishing a large signal model of the microgrid system based on the equivalent nonlinear model of the microgrid system according to a hybrid potential function method; generating a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of a photovoltaic microsource, and reactive power according to the stability theorem, and completing the stable control of the AC-DC hybrid microgrid. The present disclosure can suppress the reactive power effect of the AC-DC hybrid microgrid through a large signal stability criterion, thereby enhancing the stability of the microgrid system.

[0060] Next, a microgrid stability control method considering reactive power in this example embodiment will be further described.

[0061] Embodiment 1:

[0062] In step S110, a nonlinear model of a bidirectional AC-DC converter may be established based on a topological circuit of an AC-DC hybrid microgrid.

[0063] In the embodiment of this example, the method further includes:

[0064] Based on the topological circuit of AC / DC hybrid microgrid, the models of energy storage unit, photovoltaic distributed generation unit and dynamic load are established respectively;

[0065] Based on the models of the energy storage unit, the photovoltaic distributed power generation unit and the dynamic load, a nonlinear model of the bidirectional AC-DC converter is established.

[0066] In step S120, the nonlinear model of the bidirectional AC / DC converter can be converted into an equivalent nonlinear model of the microgrid system based on the d-axis and the q-axis by abc-dq coordinate transformation while considering reactive power in the transient process.

[0067] In the embodiment of this example, the method further includes:

[0068] Under the condition of considering reactive power in transient process, the projections of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis are calculated respectively through abc-dq coordinate transformation;

[0069] An equivalent nonlinear model of a microgrid system based on the d-axis and the q-axis is generated according to the projection of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis.

[0070] In step S130, a large signal model of the microgrid system may be established based on the equivalent nonlinear model of the microgrid system and according to a mixed potential function method.

[0071] In the embodiment of this example, the method further includes:

[0072] Based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system without considering the influence of reactive power is established according to the mixed potential function method;

[0073] Based on the large signal model of the microgrid system that does not consider the influence of reactive power, according to the reactive current in the transient process, a large signal model of the microgrid system that considers the influence of reactive power is established according to the hybrid potential function method.

[0074] In step S140, based on the large signal model of the microgrid system and according to the stability theorem, a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of the photovoltaic micro-source and reactive power may be generated.

[0075] In the embodiment of this example, the method further includes:

[0076] Based on the large signal model of the microgrid system considering the influence of reactive power, a large signal stability criterion between capacitance, inductance, dynamic load power, active power of photovoltaic micro-sources and reactive power is generated according to the stability theorem.

[0077] In step S150, stable control of the AC / DC hybrid microgrid may be completed based on the quantitative constraint relationship.

[0078] In the embodiment of this example, the present disclosure first establishes a nonlinear model of a bidirectional AC-DC converter through abc-dq coordinate transformation, and then obtains models of energy storage unit, photovoltaic distributed power generation unit and dynamic load, and then obtains equivalent nonlinear models of microgrid systems of d and q axes respectively under the condition of reactive power in transient process; based on the model, a large signal model of the microgrid system is established by applying the hybrid potential function method, and according to the stability theorem, a quantitative constraint relationship between line capacitance, inductance, dynamic load power, active power of photovoltaic micro-source and reactive power is given, which provides a theoretical basis for the stable design of AC / DC hybrid microgrid system.

[0079] Embodiment 2:

[0080] In the embodiment of this example, the nonlinear model of the microgrid system considering reactive power includes:

[0081] The topology of AC / DC hybrid microgrid is as follows: Figure 2 As shown in Figure 1. A typical AC / DC hybrid microgrid consists of an energy storage unit, a dynamic load connected to the AC bus, a bidirectional AC-DC converter, and a photovoltaic distributed generation unit. The energy storage unit consists of a battery and a bidirectional DC-DC converter. The battery is connected to the DC bus through a bidirectional DC-DC converter and can work in a charging and discharging mode.

[0082] In the AC-DC hybrid microgrid, the bidirectional AC-DC converter uses droop control to maintain the AC bus voltage. The control block diagram is shown in Figure 3 The PWM drive signal of the AC-DC converter is obtained through double PI closed-loop control. The block diagram of the AC / DC converter double PI closed-loop control is shown in Figure 4 As shown. Among them, v abc is the AC bus voltage, i abc is the AC bus current, ω is the AC bus angular frequency, p is the instantaneous active power, q is the instantaneous reactive power, is the average active power, is the average reactive power, v abcref is the reference voltage given value in the abc coordinate system, v dref and v qref are the voltage given values ​​of the d-axis and q-axis in the dq rotating coordinate system, respectively, v d and v q are the actual voltages on the d-axis and q-axis respectively.

[0083] In an AC / DC hybrid microgrid, the distributed generation units are connected to the AC bus through converters and can be modeled as active power sources P G And the equivalent resistor R1 in series, the reactive power source Q G And the equivalent resistor R1 in series, such as Figure 5A shown.

[0084] Typical structure of energy storage unit Figure 5B As shown, the battery power is P b When the battery is charging, P b is positive, when the battery is discharged b is negative.

[0085] In AC / DC microgrids, the modeling of bidirectional AC-DC converters is very complex, and the abc-dq coordinate transformation is used to simplify the model. Figure 6 As shown. k(t) (k=a,b,c) is the instantaneous value of the three-phase electromotive force, L is the inductance on the AC side, C S is the AC side capacitor, R is the equivalent resistance of the AC side inductance and power switch loss, C dcis the DC filter capacitor. dc is the DC voltage, R L is the DC side load. L is the DC side electromotive force, and N is the reference ground.

[0086] When e L = 0, the bidirectional DC-AC converter works in rectification mode. Kirchhoff's voltage law and current law give:

[0087]

[0088]

[0089] In formula (1), v NO is the voltage between N and ground.

[0090] The upper and lower switch devices of each bridge arm are in a complementary state. When the upper switch of the same bridge arm is turned on, the lower switch is turned off. Conversely, when the upper switch is turned off, the lower switch is turned on. Therefore, the single-pole binary logic switching function s k Defined as:

[0091]

[0092] When a Open, a ′ is closed, the switch function s a =1,v aN =v dc ,i aN =i a When s a Close, a ′ is turned on, the switch function s a =0,v aN =0,i aN = 0. Since v aN =s a v dc ,i aN =s a i a Similarly, the three-phase equations of a, b, and c can be obtained:

[0093]

[0094]

[0095] From the three-phase symmetrical system, we can know that:

[0096]

[0097] Substituting into equations (4), (5), and (6), we can see that v NOfor:

[0098]

[0099] From the mathematical model, we know that the DC side current i dc , when the switch function s a,b,c =1, the upper bridge arm of the three phases is turned on, and the corresponding phase current flows through the capacitor on the DC side, and we can get:

[0100]

[0101] Therefore, the mathematical model of AC-DC converter can be established in the abc coordinate system, such as Figure 6 As shown. Since many three-phase AC parameters are involved, it is very difficult to analyze the AC model. Therefore, the abc-dq coordinate transformation is used to simplify the AC model. Under the condition of complying with the power conservation principle, the three-phase AC parameters in the abc coordinate system are converted into DC quantities in the dq synchronous rotating coordinate system. The transformation matrix from the abc coordinate system to the dq rotating coordinate system is

[0102]

[0103] According to equation (9), equations (4) to (8) are simplified to transform the AC-DC converter model into a dq synchronous rotating coordinate system, as follows: Figure 7 As shown, it is expressed as:

[0104]

[0105] In formula (10), e d 、e q They are the d-axis and q-axis projections of the grid-side electromotive force vector E, respectively. ed 、i eq are the d-axis and q-axis projections of the grid-side current vector I, respectively. d 、i q is the d-axis and q-axis projection of the AC side inductor current. d and q They are the switching components of the DC-AC converter on the d-axis and q-axis respectively.

[0106] Take v d =v dc s d , v q =v dc s q , then the bidirectional AC-DC converter in the dq synchronous rotating coordinate system can be regarded as a two-port electrical network. The current of the controlled current source is i dc , which can be expressed as:

[0107]

[0108] Model the distributed generation as an active power source P G and reactive power source Q G , where P = V for dynamic load RMS ×I RMS = constant. The battery and the connected DC-DC converter are equivalent to the energy storage unit, and the charging and discharging power of the energy storage unit is P b The bidirectional DC-AC converter in the dq synchronous rotating coordinate system is regarded as a two-port electrical network.

[0109] The nonlinear model of AC / DC hybrid microgrid in dq rotating coordinate system is as follows: Figure 7 As shown. R1 and L1 are the equivalent circuit resistance and inductance respectively, R S and L S are the filter inductance and equivalent resistance respectively, i1 and i2 are P G and Q G The line inductance current, R is the resistive load, and P is the dynamic load. d is the d-axis projection of the AC voltage, v q is the q-axis projection of the AC voltage. dc is the current of the controlled current source. C dc is the DC side voltage regulating capacitor. dc is the capacitance C dc The voltage, C s is the AC side filter capacitor. v1 and v2 are the capacitors C s The d-axis and q-axis components of the voltage.

[0110] In the embodiment of this example, the large signal modeling of the microgrid system includes:

[0111] (1) Microgrid large signal model without considering the effect of reactive power

[0112] based on Fig. 8A The microgrid system topology shown in the figure does not consider the fluctuation of reactive current in transient process, and the system works at unity power factor, that is, i q = 0, the line equivalent inductance current i2 and q-axis filter inductance current i corresponding to the q-axis equivalent model q The equivalent voltage source v2 on the q-axis grid side is a constant. The equivalent inductance current i1 on the d-axis line and the filter inductance current i on the d-axis are selected. d , DC bus voltage v dc , the equivalent voltage source v1 on the d-axis grid side is the state variable, and the nonlinear energy function model is listed:

[0113]

[0114] Based on formula (12), the current potential function A(i) and voltage potential function B(v) of the system under unity power factor are obtained as follows:

[0115]

[0116] According to the stability theorem of current potential function, voltage potential function and mixed potential function, the second-order partial derivatives of current potential function and voltage potential function with respect to current and voltage state variables can be obtained as shown in formula (13):

[0117]

[0118] Based on the stability theorem of mixed potential function, we know that The minimum eigenvalues ​​of the current potential function and the voltage potential function are defined respectively. Based on formula (14), we can get:

[0119]

[0120] Satisfying the criterion μ1+μ2>0, the stability criterion is

[0121]

[0122] Without considering the influence of reactive power, formula (16) can ensure that the AC / DC hybrid microgrid system can resume stable operation after a large disturbance. Formula (16) gives the maximum value range of the dynamic load of the microgrid, which is related to the photovoltaic micro-source power P G , Battery charging and discharging power P b , filter inductance parameter L s And capacitance parameter C dc The parameters are relevant.

[0123] (2) Large signal model of microgrid system considering the influence of reactive power

[0124] based on Figure 8B The microgrid system topology shown in the figure considers the reactive current in the transient process, that is, when i q ≠0, select the d-axis and q-axis line equivalent inductance currents i1 and i2, and the d-axis and q-axis filter inductance currents i d 、i q , DC bus voltage v dc , the equivalent voltage sources v1 and v2 on the d and q axis grid sides are state variables, which are determined by the voltage v at the output port of the grid-connected converter on the AC side. d 、v q , resistive load R, resistor R s +R1, energy storage unit, dynamic load and capacitor list nonlinear energy function model:

[0125]

[0126] The large signal mixed potential function model is related to linear resistance, nonlinear dynamic load, energy storage unit, capacitor, inductor and structure. Based on formula (17), the system current potential function A(i) and voltage potential function B(v) can be obtained:

[0127]

[0128] According to the current potential function and voltage potential function and the stability theorem shown in formula (18), the second-order partial derivatives of the current potential function and voltage potential function with respect to the current and voltage state variables can be obtained:

[0129]

[0130] Based on the stability theorem of mixed potential function, the minimum eigenvalues ​​of the current potential function and the voltage potential function are obtained as

[0131]

[0132] Since the criterion μ1+μ2>0 is satisfied, the large signal stability criterion can be derived as

[0133]

[0134] Formula (21) can ensure that the AC / DC hybrid microgrid system can resume stable operation after a large disturbance, taking into account the reactive power impact of the transient process. At the same time, Formula (21) also gives the maximum value range of the microgrid dynamic load, which is related to the photovoltaic micro-source power P G and Q G , Battery charging and discharging power P b , filter inductance parameter L s And capacitance parameter C dc The parameters are all related, which provides an important basis for the design of AC / DC microgrid systems.

[0135] when i q = 0, the stability criterion formula (16) is actually a special form of formula (21).

[0136] Embodiment three:

[0137] In the embodiment of this example, an AC / DC hybrid microgrid system simulation platform was built using MATLAB / Simulink software to verify the correctness of the stability control strategy shown in equation (21). Fig. 9 It is the main circuit simulation model of the microgrid system. Fig.10 It is the main circuit model of AC dynamic load, which is composed of a closed-loop controlled rectifier connected to a resistor. Fig.11 is the dynamic load control circuit model, Fig.12 is the main circuit model of AC / DC converter, Fig.13The model of the current loop control circuit of the AC-DC converter is shown in Figure 1. The large disturbance signal is simulated by dynamic load power step, resistive load switching and photovoltaic micro-source power step.

[0138] The parameters of the AC / DC hybrid microgrid model are shown in Table 1.

[0139] Table 1 Simulation parameters of AC / DC hybrid microgrid

[0140]

[0141]

[0142] Substituting the simulation model parameters shown in Table 1 into equation (21), we can obtain:

[0143]

[0144] It can be seen from formula (22) that in order to ensure the stability of the AC / DC hybrid microgrid system under large disturbance conditions, the AC dynamic load power must meet the following requirements:

[0145] P<10.6kW (23)

[0146] Different dynamic load power fluctuation ranges are selected. Group a is to step the power of the AC dynamic load from 1kW to 10kW, which meets the large signal stability criterion shown in formula (22). Group b is to step the power of the AC dynamic load from 1kW to 22.5kW, which does not meet the large signal stability criterion.

[0147] Table 2 Power of AC dynamic load

[0148]

[0149] When t=1s, the AC dynamic load power jumps from 1kw to 10kw. The three-phase current waveform on the AC bus side is shown in Figure 14-a. It can be observed that the AC / DC hybrid microgrid can operate stably before and after the disturbance. On the contrary, under the same conditions, when the AC dynamic load power jumps from 1kw to 22.5kw, the three-phase current waveform on the AC bus side is shown in Figure 14-b. After the disturbance occurs, the three-phase current of the microgrid system oscillates and cannot operate stably.

[0150] It can be seen from the simulation results in Figure 14 that when the AC dynamic load power step meets the criteria (22) and (23), the AC / DC hybrid microgrid can operate stably under large signal disturbances. When the AC dynamic load power step does not meet the criteria, the AC / DC hybrid microgrid cannot operate stably under large signal disturbances.

[0151] In order to ensure the large signal stability of the AC / DC hybrid microgrid system, the resistive load is removed after 1s, that is, R = 0, satisfying the obtained criterion formula (22). The three-phase current waveform on the AC bus side is as follows: Fig.15 As shown, it can be observed that after the disturbance occurs, the current fluctuates slightly and then quickly returns to stability, and the microgrid system can operate stably.

[0152] Depend on Fig.15 The simulation results show that when the resistive load power is switched on and off, the criterion (22) is met, the microgrid system can operate stably under large disturbance conditions, and the resistive load has little impact on the AC / DC hybrid microgrid.

[0153] From formula (22), in order to ensure the large signal stability of the AC / DC hybrid microgrid system, when the dynamic load power remains unchanged, the photovoltaic micro-source power must meet the following conditions:

[0154] P G >15.8kW (24)

[0155] The large signal disturbances of photovoltaic micro-sources under different conditions are selected. Group C is to reduce the power of the AC dynamic load from 30kW to 20kW, which meets the large signal stability criterion shown in formula (22). Group D is to reduce the power of the AC dynamic load from 30kW to 0W, which does not meet the large signal stability criterion.

[0156] Table 3 Photovoltaic micro-source power step

[0157]

[0158] When t=1s, the AC bus current waveforms of the photovoltaic micro-source under conditions of group c and group d are shown in Figure 16-a. Under group c, the AC / DC hybrid microgrid can operate stably before and after the disturbance. Under group d, after the disturbance occurs, the three-phase current waveforms on the AC bus side are shown in Figure 16-b. The three-phase current of the AC / DC hybrid microgrid is distorted and cannot operate normally.

[0159] It can be seen from the simulation results in Figure 16 that when the photovoltaic micro-source power step meets the criteria (22) and (24), the AC / DC hybrid microgrid can operate stably under large signal disturbances. When the AC dynamic load power step does not meet the criteria, the AC / DC hybrid microgrid cannot operate stably under large signal disturbances.

[0160] It should be noted that, although the steps of the method in the present disclosure are described in a specific order in the drawings, this does not require or imply that the steps must be performed in this specific order, or that all the steps shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps, etc.

[0161] In addition, in this exemplary embodiment, a microgrid stability control device considering reactive power is also provided. Fig.17 As shown, the microgrid stability control device 200 considering reactive power may include: a first modeling module 210, a model conversion module 220, a second modeling module 230, a stability criterion generation module 240 and a control module 250. Among them:

[0162] A first modeling module 210 is used to establish a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid;

[0163] A model conversion module 220 is used to convert the nonlinear model of the bidirectional AC-DC converter into an equivalent nonlinear model of the microgrid system based on the d-axis and the q-axis by abc-dq coordinate transformation while considering reactive power in a transient process;

[0164] A second modeling module 230 is used to establish a large signal model of the microgrid system according to a mixed potential function method based on an equivalent nonlinear model of the microgrid system;

[0165] A stability criterion generation module 240 is used to generate a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power and reactive power of a photovoltaic micro-source based on a large signal model of the microgrid system and according to the stability theorem;

[0166] The control module 250 is used to complete the stability control of the AC / DC hybrid microgrid based on the quantitative constraint relationship.

[0167] The specific details of each of the above-mentioned microgrid stability control device modules considering reactive power have been described in detail in a corresponding microgrid stability control method considering reactive power, so they will not be repeated here.

[0168] It should be noted that, although several modules or units of a microgrid stabilization control device 200 considering reactive power are mentioned in the above detailed description, such division is not mandatory. In fact, according to an embodiment of the present disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided into multiple modules or units to be embodied.

[0169] In addition, the above-mentioned figures are only schematic illustrations of the processes included in the method according to an exemplary embodiment of the present invention, and are not intended to be limiting. It is easy to understand that the processes shown in the above-mentioned figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0170] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary technical means in the art that are not disclosed in the present disclosure. The specification and examples are to be considered as exemplary only, and the true scope and spirit of the present disclosure are indicated by the claims.

[0171] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A microgrid stability control method considering reactive power, It is characterized in that The method comprises: Based on the topological circuit of AC-DC hybrid microgrid, a nonlinear model of bidirectional AC-DC converter is established; Under the condition of considering reactive power in transient process, the nonlinear model of the bidirectional AC / DC converter is converted into an equivalent nonlinear model of the microgrid system based on d-axis and q-axis through abc-dq coordinate transformation; Based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system is established according to a mixed potential function method; Based on the large signal model of the microgrid system, according to the stability theorem, a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power of the photovoltaic micro-source and reactive power is generated; Based on the quantitative constraint relationship, stable control of the AC / DC hybrid microgrid is completed.

2. The method according to claim 1, It is characterized in that The method further comprises: Based on the topological circuit of AC / DC hybrid microgrid, the models of energy storage unit, photovoltaic distributed generation unit and dynamic load are established respectively; Based on the models of the energy storage unit, the photovoltaic distributed power generation unit and the dynamic load, a nonlinear model of the bidirectional AC-DC converter is established.

3. The method according to claim 1, It is characterized in that The method further comprises: Under the condition of considering reactive power in transient process, the projections of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis are calculated respectively through abc-dq coordinate transformation; An equivalent nonlinear model of a microgrid system based on the d-axis and the q-axis is generated according to the projection of the nonlinear model of the bidirectional AC-DC converter on the d-axis and the q-axis.

4. The method according to claim 1, It is characterized in that The method further comprises: Based on the equivalent nonlinear model of the microgrid system, a large signal model of the microgrid system without considering the influence of reactive power is established according to the mixed potential function method; Based on the large signal model of the microgrid system that does not consider the influence of reactive power, according to the reactive current in the transient process, a large signal model of the microgrid system that considers the influence of reactive power is established according to the hybrid potential function method.

5. The method according to claim 4, It is characterized in that The method further comprises: Based on the large signal model of the microgrid system considering the influence of reactive power, a large signal stability criterion between capacitance, inductance, dynamic load power, active power of photovoltaic micro-sources and reactive power is generated according to the stability theorem.

6. A microgrid stability control device considering reactive power, It is characterized in that The device comprises: The first modeling module is used to establish a nonlinear model of a bidirectional AC-DC converter based on a topological circuit of an AC-DC hybrid microgrid; A model conversion module, used for converting the nonlinear model of the bidirectional AC-DC converter into an equivalent nonlinear model of the microgrid system based on the d-axis and the q-axis by abc-dq coordinate transformation while considering reactive power in a transient process; A second modeling module is used to establish a large signal model of the microgrid system according to a mixed potential function method based on an equivalent nonlinear model of the microgrid system; A stability criterion generation module is used to generate a quantitative constraint relationship between capacitance, inductance, dynamic load power, active power and reactive power of a photovoltaic micro-source based on a large signal model of the microgrid system and according to the stability theorem; A control module is used to complete the stable control of the AC / DC hybrid microgrid based on the quantitative constraint relationship.

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