An ac-dc hybrid microgrid power control method and system

Abstract

A kind of AC-DC hybrid microgrid power control method and system, at the k th sampling moment of current control cycle, the operating state quantity of system is measured, the mathematical model of AC side of interconnection converter is established according to operating state quantity;According to the operating state quantity of interconnection converter, the power transmission direction of interconnection converter is judged;Establish power prediction model, solve the active power and reactive power prediction value of k+1 moment in combination with different switch states;Power reference trajectory is calculated, and the cost function value corresponding to each switch state is calculated in combination with the prediction value of active power and reactive power;The cost function value under all switch states is obtained, and the switch state corresponding to the smallest cost function value is selected from it, which is applied to the interconnection converter bridge arm switch control;Enter next control cycle, repeat the above steps.The present application can realize bidirectional power mutual aid between AC-DC hybrid power grid in flexible interconnection hybrid power grid multiple scenarios, and improve voltage stability capability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of AC-DC hybrid micro-grid power control, and particularly relates to an AC-DC hybrid micro-grid power control method and system. BACKGROUND

[0002] The penetration rate of flexible power resources dominated by renewable energy is increasing, which has a great impact on the safe and stable operation of distribution networks. The topology structure of AC-DC interconnected hybrid power grid can efficiently accommodate large-scale flexible power resources through the coordinated operation of AC and DC sides. Therefore, the AC-DC interconnected hybrid power grid will become the main form of flexible power resources accessing the distribution network in the future.

[0003] The flexible interconnection converter (FIC) of the AC-DC hybrid power grid is the core equipment for balancing the power of the two sides of the micro-grid, and can coordinate and control the AC-DC micro-grid, playing a key role in maintaining the stability of system frequency and voltage. The existing power control strategy of the interconnection converter mostly adopts double closed-loop tracking in the dq coordinate system to realize decoupling control of active and reactive power. Independent control loops are designed for voltage and current, and are connected in series to realize control tracking. In the double closed-loop control, there are a total of 5 PI regulation parameters (voltage inner loop, current inner loop, and phase-locked loop) that need to be adjusted, and the parameter adjustment is very complex, with slow response speed. Moreover, the coupling effect of the flexible interconnection converter on the AC and DC sides will expand the disturbance influence range, and especially in off-grid operation, the flexible interconnection converter will have an impact on the stable operation of the entire system.

[0004] The flexible interconnection converter of AC-DC hybrid power grid needs to regulate AC frequency and DC voltage at the same time, and the traditional voltage source converter (VSC) only considers the method of single side quantity, which is no longer applicable. In the prior art, the document ("New control strategy of AC / DC bidirectional power converter in AC-DC hybrid microgrid", Power System Protection and Control, Tang Lei et al., 2013), the document ("Cooperative control strategy of AC-DC hybrid microgrid", Electric Power Automation Equipment, Zhou Wen et al., 2015), the document ("Review of control of bidirectional interface converter in AC-DC hybrid microgrid", Transactions of China Electrotechnical Society, Wang Xiaosheng et al., 2016) and the document ("Research on control strategy of bidirectional AC / DC power converter in AC-DC hybrid microgrid", Taiyuan University of Technology, Liu Jiayi et al., 2014) improve the traditional droop control equation or study the coupling relationship between AC frequency and DC voltage, and a bidirectional power control strategy capable of regulating AC frequency and DC voltage at the same time is proposed. For example, the document ("Virtual synchronous machine control strategy of AC-DC bus interface converter in hybrid microgrid", Proceedings of the Chinese Society for Electrical Engineering, Li Feng et al., 2019) and the document ("A dual-adaptivity inertia control strategy for virtual synchronous generator", IEEE Transactions on Power Systems, Li M et al., 2020) link AC frequency and DC voltage for unified droop control based on the normalization method or from the energy balance angle when controlling the microgrid interconnection converter, and realize the bidirectional control of power between AC-DC microgrids.

[0005] In the power regulation process of the hybrid microgrid in island operation, the existing method is limited by the power regulation ability of the adjustable flexible resource, and there is often a contradiction between AC frequency optimization and DC voltage optimization. How to solve the contradiction between the control objectives of the AC side and the DC side within the regulation ability constraint range is the key to improving the control performance of the flexible interconnection converter. SUMMARY

[0006] To address the shortcomings of existing technologies, this invention provides a bidirectional power model predictive control for flexible interconnected converters with flexible resource access. This invention is applicable to AC / DC hybrid power grids to ensure the stability of AC grid frequency and DC grid voltage. Addressing the limitations of traditional interconnected converter control strategies, such as difficult parameter tuning, slow response speed, difficulty in achieving multi-objective optimization, and limited applicability, this invention establishes a discretized mathematical model of the flexible interconnected converter and optimizes the cost function, which includes active and reactive power tracking and switching frequency, to achieve direct power control of the flexible interconnected converter. This invention predicts power over a single long period and uses a finite set solution for the cost function, resulting in lower computational resource requirements. It combines the advantages of strong robustness to parameter changes in PI control and good dynamic characteristics of model predictive control. Furthermore, this invention can adaptively adjust the power flow direction according to operating conditions, effectively achieving bidirectional power mutual assistance between AC and DC hybrid power grids in various scenarios of flexible interconnected hybrid power grids, improving the frequency and voltage stability of the hybrid power grid, and exhibiting smooth control effects and good dynamic performance.

[0007] The present invention adopts the following technical solution.

[0008] This invention proposes a power control method for AC / DC hybrid microgrids, comprising:

[0009] S1, in the current control cycle... At each sampling time, the operating state variables of the system are measured, and a mathematical model of the AC side of the interconnected converter is established based on the operating state variables; the AC side mathematical model is then converted to... In coordinate system, we obtain The operating state variables of the interconnected converter in the coordinate system are Components in the coordinate system;

[0010] S2, utilizing runtime state variables in Calculate the AC frequency deviation and DC voltage deviation, and the AC voltage deviation and DC voltage deviation in the coordinate system to determine the power transmission direction of the interconnected converter;

[0011] S3, different switching states For different interconnected converter AC side voltages, combined with Mathematical model of AC side and power transmission direction in coordinate system, as well as switching state. Based on the corresponding AC side voltage, a power prediction model is established to obtain the active power at time k+1. and reactive power The predicted value;

[0012] S4, Calculate the active power reference trajectory and reactive power reference trajectory and combined with active power and reactive power of the prediction; in combination with the prediction of active power and reactive power , the cost function value of each switching state is calculated , the cost function value is taken as the evaluation of the control effect under this switching state;

[0013] S5, the cost function values under all switching states are obtained, from which the minimum cost function value corresponding to the switching state is selected, denoted as , which is applied to the switching control of the interconnection converter bridge arm;

[0014] S6, enter the next control period, repeat S1-S5.

[0015] Further, in S1, the measured operating state quantities include three-phase voltage and current at the AC side output of the converter at the moment , , three-phase voltage at the AC bus at the moment , AC frequency at the moment , DC bus voltage at the moment .

[0016] Further, in S2, the AC frequency deviation, AC voltage deviation and DC voltage deviation in the operating state quantities are normalized; for multiple scenarios, the description is as follows:

[0017] If the normalized AC frequency deviation is equal to the DC voltage deviation, and the AC voltage deviation is equal to the DC voltage deviation, the interconnection converter does not need to transmit power, which belongs to the normal operation condition;

[0018] If the normalized AC frequency deviation is greater than the DC voltage deviation, and the AC voltage deviation is greater than the DC voltage deviation, the interconnection converter transmits active power and reactive power to the AC side, which belongs to the condition that the AC side has a fault;

[0019] If the normalized AC frequency deviation is less than the DC voltage deviation, and the AC voltage deviation is less than the DC voltage deviation, the interconnection converter transmits active power to the DC side, which belongs to the condition that the DC side has a fault.

[0020] Further, in S3, the AC side mathematical model of the interconnection converter in the coordinate system is discretized to obtain the discrete mathematical model of the interconnection converter, as shown in the following formula:

[0021] ;

[0022] wherein: denotes two components of the three-phase current outputted by the converter at time k+1 in the coordinate system; is the sampling period; is the DC voltage at time k of the converter; denotes two components of the three-phase voltage of the AC bus at time k in the coordinate system; denotes two components of the switching state of the three-phase bridge arm of the interconnection converter at time k in the coordinate system; is the total inductance of the filter and line between the AC side of the converter and the AC bus.

[0023] Further, in S3, the predicted value of the power of the interconnection converter is obtained in combination with the judgment result of the power transmission direction of the interconnection converter, and the power prediction model is as shown in the following formula:

[0024]

[0025]

[0026] wherein: , denote the predicted value of the active power and the reactive power of the interconnection converter at time k+1 respectively; and denote two components of the three-phase current outputted by the converter at time k+1 in the coordinate system respectively; and denote two components of the three-phase voltage of the AC bus at time k+1 in the coordinate system respectively.

[0027] Further, in S4, the active power reference trajectory of the interconnection converter is set in the form of the following formula:

[0028]

[0029] wherein, is the normalized AC frequency deviation; is the normalized DC voltage deviation; is the proportional control coefficient, is the integral control coefficient.

[0030] Further, in S4, the cost function as shown in the following formula is constructed:

[0031] ​​​​​​

[0032] In the formula, For active power reference trajectory, , These represent the predicted active and reactive power values ​​of the interconnected converter at time k+1, respectively. For reactive power reference trajectory, , , These are the weighting coefficients for active power, reactive power, and the number of switching operations, respectively. This represents the sum of the number of switching actions from the previous control moment to the current control moment.

[0033] This invention also proposes an AC / DC hybrid microgrid power control system, including an AC-side mathematical model construction module, a power transmission direction determination module, a power prediction module, a cost function value calculation module, and an action module:

[0034] The mathematical model construction module on the communication side, in the current control cycle, At each sampling time, the operating state variables of the system are measured, and a mathematical model of the AC side of the interconnected converter is established based on the operating state variables.

[0035] The power transmission direction determination module determines the power transmission direction of the interconnected converter based on the operating status parameters of the interconnected converter.

[0036] The power prediction module establishes a power prediction model, taking into account different switching states. Solve for the active power at time k+1. and reactive power The predicted value;

[0037] The cost function value calculation module calculates the power reference trajectory. and combined with active power and reactive power The predicted value is used to calculate each switching state. The corresponding cost function value ;

[0038] The action module obtains the cost function values ​​for all on / off states and selects the minimum cost function value from them. The corresponding switch state is denoted as This is applied to the control of bridge arm switches in interconnected converters.

[0039] Furthermore, the power prediction module also includes a discrete mathematical model building unit for interconnected converters and a power prediction model building unit;

[0040] In the discrete mathematical model construction unit, the mathematical model construction module for the AC side... The mathematical model of the communication side in the coordinate system is discretized.

[0041] Further, the AC / DC hybrid micro-grid power control system is run in each control cycle, and repeated iteration is implemented to realize optimal control.

[0042] The application further provides a terminal comprising a processor and a storage medium:

[0043] The storage medium is used for storing instructions;

[0044] The processor is used for operating according to the instructions to perform the steps of the method according to any one of the above.

[0045] Compared with the prior art, the application has the beneficial effects that:

[0046] 1. The application can realize flexible interconnected hybrid power grid multi-scene stable operation, such as AC side fault, DC side fault, normal operation, etc., and the running condition is judged according to the deviation value of the corresponding quantity of the AC side and the DC side, and the power flow is adaptively adjusted.

[0047] 2. The application establishes a discrete mathematical model of the interconnected converter through principle derivation, designs a multi-objective cost function considering AC side frequency optimization and DC side voltage optimization, realizes AC / DC bilateral coordinated control through rolling optimization, and improves the dynamic response capability of the interconnected converter.

[0048] 3. The application optimizes the cost function in each sampling period, adopts finite set solution, obtains the switch input of the flexible interconnected converter, has lower demand for computing resources, does not need complex parameter setting, and has the advantages of strong parameter change robustness of PI control and good dynamic characteristic of model predictive control. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a flexible interconnected hybrid power grid topology of the application;

[0050] Figure 2 is a model predictive control flowchart of the application;

[0051] Figure 3 is a flexible interconnected converter topology structure of the application;

[0052] Figure 4 is a simulation result of the application. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0054] Example 1

[0055] This invention proposes a power control method for AC / DC hybrid microgrids. For example... Figure 1 The diagram shows a flexible interconnected hybrid power grid topology. The AC microgrid and DC microgrid are flexibly interconnected through a flexible interconnection converter (FIC). Power can flow bidirectionally on both the AC and DC sides. The operation mode of the hybrid power grid, whether it is connected to the grid or off-grid, is determined by the closing and opening of the switches.

[0056] AC microgrids contain two Adjustable power supplies DG1, DG2 and one with droop control The controlled, non-adjustable power supply DG3, the DC microgrid contains two Adjustable power supplies with droop control DG4, DG5 and one The uncontrolled power supply DG6.

[0057] Flexible interconnected converter topology such as Figure 2 The diagram shows a voltage source converter (VSC), where: , ( These represent the three-phase voltage and current output from the AC side of the converter, respectively. ( () represents the three-phase voltage of the AC bus. The total inductance of the filters and lines between the AC side of the converter and the AC bus. For DC filter capacitors, Let be the DC-side voltage of the converter; let be the DC-side current of the converter. The active power exchanged between AC and DC microgrids is denoted as .

[0058] The flowchart of model predictive control is as follows: Figure 2 As shown, model predictive control iteratively solves for the predicted power value for the next cycle based on the current operating state of the system and the control command in each control cycle. The switching state that minimizes the cost function is then used as the control output to act on the interconnected converter, achieving optimal bidirectional power control.

[0059] S1, in the current control cycle... At each sampling time, the operating state variables of the system are measured, and a mathematical model of the AC side of the interconnected converter is established based on the operating state variables; the AC side mathematical model is then converted to... In coordinate system, we obtain The operating state variables of the interconnected converter in the coordinate system are Components in the coordinate system;

[0060] The system's operational state variables include The three-phase voltage output from the AC side of the converter at any time and current , AC bus three-phase voltage , Frequency of communication at any moment , DC bus voltage at time .

[0061] by Figure 3 The inverter direction shown is the positive power direction. Taking the positive power direction as the reference direction, the AC side mathematical model of the hybrid power grid flexible interconnection converter is established as shown in the following formula.

[0062] ;

[0063] In the formula: The switching status of the three-phase bridge arm of the interconnected converter ( = a, b, c), = 1 indicates the first The upper bridge arm is conducting, and the lower bridge arm is turning off; = 0 indicates the first The upper bridge arm is turned off, and the lower bridge arm is turned on.

[0064] To facilitate decoupled control of the active and reactive power of the interconnected converter, a Clark transformation is applied to the AC side mathematical model of the hybrid power grid flexible interconnected converter to convert the three-phase current and voltage data to... In coordinate system:

[0065] ;

[0066] get The interconnected converter model in the coordinate system is shown in the following equation.

[0067] ;

[0068] In the formula: , These represent the three-phase output voltage and current of the converter on the AC side, respectively. Two components in the coordinate system; represents two components of three-phase voltage of AC bus in coordinate system; represents two components of switching state of three-phase bridge arm of interconnection converter in coordinate system; is total inductance of filter and line between AC side of converter and AC bus.

[0069] S2, calculates AC frequency deviation and DC voltage deviation, AC voltage deviation and DC voltage deviation using components in coordinate system, and judges power transmission direction of interconnection converter.

[0070] To realize global power distribution of AC / DC hybrid microgrid, flexible interconnection converter should adjust bidirectional power between AC / DC microgrid, balance and compensate AC frequency deviation and DC voltage deviation, AC voltage deviation and DC voltage deviation, so that normalized AC frequency deviation and DC voltage deviation, AC voltage deviation and DC voltage deviation are equal, that is, the following conditions are met:

[0071] ;

[0072] In the formula, is normalized AC frequency deviation; is normalized DC voltage deviation; is normalized AC voltage deviation; represents difference between normalized AC frequency deviation and DC voltage deviation; represents difference between normalized AC voltage deviation and DC voltage deviation.

[0073] When operating normally, AC frequency, voltage and DC voltage are at rated values, two sets of change rate difference of model predicted power distribution are 0; when AC side fails, AC frequency and voltage rapidly decrease, DC voltage is unchanged for a short time, at this time >0, >0, and and need to be reduced as much as possible to tend to 0, so that flexible interconnection converter needs to transmit active power and reactive power to AC side to stabilize AC frequency and voltage. When DC side fails, DC voltage rapidly decreases, AC frequency is unchanged for a short time, at this time <0, <0, to tend to 0, flexible interconnection converter needs to transmit active power to DC side to stabilize DC voltage.

[0074] By normalizing the AC frequency deviation, AC voltage deviation and DC voltage deviation, the relative changes of each parameter can be better compared to determine the direction of power transmission. This method can effectively reduce the error under different operating conditions, so that the system can quickly respond under different fault scenarios. After normalization, the deviation can be reasonably controlled to improve the robustness of the system, ensure the coordination between AC and DC grids in multiple scenarios, and ensure the stability of the grid.

[0075] S3, different switch states Corresponding to different interconnection converter AC side voltages, combined with the AC side mathematical model in the coordinate system and the power transmission direction, and the switch state corresponding to the AC side voltage, a power prediction model is established to obtain the predicted values of active power and reactive power at time k+1.

[0076] Three-phase switch state There are 8 different combinations, respectively corresponding to 8 different interconnection converter AC side voltages. If the voltage vector is represented by the following formula, the correspondence between the switch state and the voltage vector is shown in Table 1.

[0077] ;

[0078] In the formula, the voltage vector is represented by , respectively, the components of the voltage vector in the coordinate system.

[0079] Table 1 Switch state and voltage vector

[0080]

[0081] The interconnection converter model in the coordinate system is discretized using the first-order forward difference method to obtain the discrete mathematical model of the interconnection converter, as shown in the following formula:

[0082] ;

[0083] In the formula: the two components of the three-phase current output by the converter on the AC side at time k+1 in the coordinate system are represented by is the sampling period; is the DC side voltage of the converter at time k; the two components of the three-phase voltage of the AC bus at time k in the coordinate system are represented by This indicates the switching state of the three-phase bridge arm of the interconnected converter at time k. Two components in the coordinate system; This refers to the total inductance of the filters and lines between the AC side of the converter and the AC bus.

[0084] Interconnected converters regulate the power interaction between AC and DC microgrids by controlling their own power direction and magnitude. Based on instantaneous power theory, the predicted power of the interconnected converter can be obtained. The power prediction model is shown in the following equation:

[0085] ;

[0086] ;

[0087] In the formula: , These represent the predicted active and reactive power values ​​of the interconnected converter at time k+1, respectively. and These represent the three-phase output currents on the AC side of the converter at time k+1. Two components in the coordinate system; and These represent the three-phase voltages of the AC bus at time k+1. The two components in the coordinate system can be obtained using the quadratic Lagrange interpolation formula:

[0088] ;

[0089] In the formula, , Representing the three-phase voltages of the AC bus at times k-1 and k-2 respectively. Quantity, , Representing the three-phase voltages of the AC bus at times k-1 and k-2 respectively. Quantity.

[0090] By discretizing the AC-side mathematical model of the interconnected converter, its dynamic behavior can be accurately described, resulting in more precise power prediction. Discretization enables the system to calculate more accurate power values ​​in each sampling period, thereby improving the precision of power control. This method makes real-time control more feasible, optimizes power flow, and enhances the grid's response speed and control accuracy in various scenarios.

[0091] S4, Calculate the active power reference trajectory and reactive power reference trajectory and combined with active power and reactive power The predicted value; combined with active power and reactive power for each switching state corresponding cost function value the cost function value as an evaluation of the control effect under this switching state.

[0092] Active power reference trajectory of flexible interconnection converter which can be set in the form of:

[0093] ;

[0094] wherein, is the normalized AC frequency deviation; is the normalized DC voltage deviation; is the proportional control coefficient, is the integral control coefficient.

[0095] To achieve the tracking control of active and reactive power reference values by the flexible interconnection converter, a cost function is constructed as shown in the following formula :

[0096] ;

[0097] wherein, , respectively represent the active and reactive power prediction values of the interconnection converter at k+1 time, is the reactive power reference trajectory, and its calculation method is the same as that of the active power reference trajectory , , , are the weight coefficients of active power, reactive power, and switching frequency, respectively; represents the sum of switching actions from the previous control time to the current control time.

[0098] By calculating the reference trajectories of active and reactive power and combining the prediction values for optimized control, a more accurate power control strategy can be achieved. This method can dynamically adjust the power reference trajectory according to the actual operating conditions, so that the power grid can maintain efficient and stable operation under changing load conditions. Real-time adjustment and accurate calculation of the reference trajectory make the power regulation more reasonable, avoiding energy waste caused by excessive adjustment and improving the energy efficiency and stability of the system.

[0099] S5, get the cost function values under all switching states, and select the minimum cost function value corresponding to the switching state, denoted as Apply it to the interconnection converter bridge arm switching control.

[0100] Optimized control can be achieved by calculating the cost function values ​​under different switching states and selecting the switching state corresponding to the minimum value. This process effectively reduces energy loss during control and improves the system's dynamic response capability. By evaluating the cost function of different switching states, it can be ensured that the system always adopts the optimal control strategy in each control cycle, thereby achieving more efficient and smooth power control and improving the stability and reliability of the power grid.

[0101] S6, in the next control cycle Repeat S1~S5.

[0102] Example 2

[0103] The purpose of this embodiment is to experimentally verify the AC / DC hybrid microgrid power control method described in Embodiment 1. A system was built in MATLAB / Simulink as follows: Figure 1 The simulation model of the hybrid microgrid shown is illustrated. The simulation system parameters are shown in Table 2.

[0104] Table 2 System Parameters

[0105]

[0106] The effectiveness of the proposed control strategy was verified through simulation under load changes on both sides of the AC / DC microgrid. The verification scenario was set as follows: at the start of the simulation, the load in both the AC and DC microgrids was 0.3MW, and DG1 and DG2 each output 0.3MW. At this time, the source and load in the AC / DC microgrid were balanced, and the AC frequency and DC voltage were controlled at their rated values. A fault occurred on the AC side at 2 seconds, a fault occurred on the DC side at 4 seconds, and the AC side fault was resolved at 6 seconds. The simulation results are as follows. Figure 4 As shown.

[0107] Example 3

[0108] This invention also provides a power control system for an AC / DC hybrid microgrid, comprising an AC-side mathematical model construction module, a power transmission direction determination module, a power prediction module, a cost function value calculation module, and an action module:

[0109] The mathematical model construction module on the communication side, in the current control cycle, At each sampling time, the operating state variables of the system are measured, and a mathematical model of the AC side of the interconnected converter is established based on the operating state variables.

[0110] The power transmission direction determination module determines the power transmission direction of the interconnected converter based on the operating status parameters of the interconnected converter.

[0111] The power prediction module establishes a power prediction model, taking into account different switching states. Solve for the active and reactive power at time k+1. and predicted values of

[0112] a cost function value calculation module, which calculates a power reference trajectory in combination with active power and reactive power and predicted values of corresponding cost function values ;

[0113] an action module, which obtains cost function values for all switching states, selects the smallest cost function value corresponding switching state, denoted as and applies it to the interconnection converter bridge arm switching control.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the present application can still be modified or replaced equivalently without departing from the spirit and scope of the present application. Any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered within the protection scope of the claims of the present application.

Claims

1. A power control method for an AC / DC hybrid microgrid, characterized in that, Comprise: S1, in the current control cycle... The system's operating state variables are measured at each sampling time, and a mathematical model of the AC side of the interconnected converter is established based on these variables. The AC side mathematical model is then converted to... In coordinate system, we obtain Operating state variables in coordinate system Components in the coordinate system; S2, utilizing runtime state variables in The components in the coordinate system are used to determine the power transmission direction of the interconnected converter; S3, bind The AC side mathematical model under the coordinate system, the power transmission direction, and the different AC side voltages corresponding to different switching states are used to establish a power prediction model to obtain the predicted values of the active power and the reactive power at the k+1 time. The power prediction model is shown in the following formula: ； ； In the formula: , respectively represent the active and reactive power prediction values of the interconnected converter at time k+1; and respectively represent two components of the three-phase current output by the converter on the AC side at time k+1 in the coordinate system; and respectively represent two components of the three-phase voltage of the AC bus at time k+1 in the coordinate system; wherein, and the calculation formulae of and are as follows: ； wherein: represents two components of the three-phase current outputted by the converter at the k+1th moment in the coordinate system; is the sampling period; is the DC voltage of the converter at the kth moment; represents two components of the three-phase voltage of the AC bus at the kth moment in the coordinate system; represents two components of the switching state of the three-phase bridge arm of the interconnection converter at the kth moment in the coordinate system; is the total inductance of the filter and line between the AC side of the converter and the AC bus; and The calculation formula is: ； In the formula, , , respectively, represent the k-1 and k-2 time instant three-phase voltage of the AC bus component, , , respectively, represent the k-1 and k-2 time instant three-phase voltage of the AC bus component; S4, calculate the active power reference trajectory and reactive power reference trajectory, calculate the cost function value corresponding to each switching state; S5, obtaining the cost function value in all switching states, selecting the switching state corresponding to the minimum cost function value, and applying it to the interconnection converter bridge arm switching control; wherein the cost function As follows: ； In the formula, is the active power reference trajectory, , respectively represent the active power and reactive power prediction values of the interconnected converter at k+1 time, is the reactive power reference trajectory, , , respectively are the weight coefficients of active power, reactive power and switching frequency; represents the sum of switching actions from the previous control time to the current control time. S6, enter the next control cycle, repeat S1-S5.

2. The power control method of the AC-DC hybrid microgrid according to claim 1, characterized in that: In S1 the measured operating state quantities comprise the three-phase voltage outputted by the time-varying transformer on the AC side and the current , the three-phase voltage of the AC bus at the time , the AC frequency at the time , the DC bus voltage at the time .

3. The power control method of the AC-DC hybrid microgrid according to claim 1, characterized in that: In S2, the AC frequency deviation, AC voltage deviation and DC voltage deviation in the operating state quantity are normalized; the multiple scenarios are described: If the normalized AC frequency deviation is equal to the DC voltage deviation, and the AC voltage deviation is equal to the DC voltage deviation, the interconnection converter does not need to transmit power, which belongs to the normal operation condition; If the normalized AC frequency deviation is greater than the DC voltage deviation, and the AC voltage deviation is greater than the DC voltage deviation, the interconnection converter transmits active power and reactive power to the AC side, which belongs to the condition that the AC side has a fault; If the normalized AC frequency deviation is less than the DC voltage deviation, and the AC voltage deviation is less than the DC voltage deviation, the interconnection converter transmits active power to the DC side, which belongs to the condition that the DC side has a fault.

4. The power control method of the AC-DC hybrid microgrid according to claim 1, characterized in that: In S4, the active power reference trajectory of the interconnecting converter is set in the form of: ； wherein is the normalized AC frequency deviation; is the normalized DC voltage deviation; is the proportional control coefficient, is the integral control coefficient.

5. A power control system of an AC-DC hybrid microgrid using the method of any one of claims 1-4, comprising an AC side mathematical model construction module, a power transmission direction judgment module, a power prediction module, a cost function value calculation module and an action module, characterized in that: The AC side mathematical model construction module measures the operating state quantity of the system at the first sampling moment of the current control period, and establishes the AC side mathematical model of the interconnected converter according to the operating state quantity. ​ The power transmission direction judgment module judges the power transmission direction of the interconnection converter according to the operating state quantity of the interconnection converter; A power prediction module establishes a power prediction model, combining different switch states Solves the predicted values of active power and reactive power at k+1 time ​​ a cost function value calculation module calculates a power reference trajectory in combination with predicted values of active power and reactive power calculates a cost function value corresponding to each switching state ; An action module obtains the cost function values for all switching states and selects the minimum cost function value The corresponding switching state is denoted as It is applied to the control of the interconnection converter bridge arm switches.

6. The power control system of the AC-DC hybrid microgrid according to claim 5, characterized in that: The power prediction module further comprises an interconnection converter discrete mathematical model construction unit and a power prediction model construction unit; In the discrete mathematical model construction unit, the mathematical model construction module for the AC side... The mathematical model of the communication side in the coordinate system is discretized.

7. The power control system of the AC-DC hybrid microgrid according to claim 5, characterized in that: The power control system of the AC-DC hybrid microgrid is operated in each control cycle, repeatedly iterated, and optimal control is achieved.

8. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is used to operate according to the instructions to perform the steps of the method according to any one of claims 1-4.

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