Island AC-DC hybrid microgrid power sharing method and device in master-slave mode

Abstract

The invention relates to a power sharing method and device for an island AC / DC hybrid micro-grid in a master-slave mode. The method comprises the following steps: an AC micro-grid adopts a double-loop control system to control a converter in the AC micro-grid; the DC micro-grid adopts a boost / buck bidirectional converter to control a converter in the DC micro-grid; after stored energy of the micro-grids on the alternating current side and the direct current side stabilizes power fluctuation of the micro-grids where the micro-grids are located, all the controllable distributed power sources share stored energy output according to capacity proportions of the controllable distributed power sources, the micro-grid on one side transmits power to the micro-grid on the other side through the bidirectional interconnection converter, and global power mutual aid of the micro-grids on the alternating current side and the direct current side is achieved. Compared with the prior art, the method has the advantages that global effective sharing and balancing of power are achieved, the available capacity and fluctuation suppression capacity of the main control unit are improved, and the system stability is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid power control, and in particular to a power sharing method and device for an island AC / DC hybrid microgrid in a master-slave mode. Background Art

[0002] Nowadays, as the energy crisis and environmental pollution caused by the use of fossil energy become increasingly prominent, the scale of development and utilization of renewable energy such as solar energy, wind energy and hydropower is growing rapidly. Countries around the world have paid much attention to and conducted a lot of research on microgrid technology that can integrate distributed power sources based on renewable energy. Compared with traditional DC and AC microgrids, AC / DC hybrid microgrids have many advantages such as flexible connection of various types of distributed power sources and loads, power mutual assistance and mutual support, and will be one of the most promising architectures in the future smart grid.

[0003] Depending on the connection between the busbar in the microgrid and the large grid, the AC / DC hybrid microgrid can operate in an island or grid-connected mode. When operating in grid-connected mode, if the AC busbar is connected to the large grid, the voltage and frequency of the AC microgrid will be supported by the grid, and only the impact of voltage fluctuations on the DC microgrid side needs to be considered. When operating in an island mode, system stability faces greater challenges and the control strategy is more complex.

[0004] The AC / DC hybrid microgrid in island operation is mainly divided into master slave mode (MSM) and peer-to-peer mode (PPM). (1) If the peer-to-peer operation control mode is adopted, the controllable distributed generators (DPDGs) and energy storage in the AC microgrid adopt power-frequency (Pf) or power-voltage (PU) droop control, and finally realize the sharing and sharing of AC load. The controllable distributed generators and energy storage in the DC microgrid adopt PU droop control to achieve reasonable sharing of DC load. On this basis, the relevant technical research uses the characteristics of voltage U and frequency f deviation generated by droop control to control the bidirectional interlinking converter (BIC) to balance the power of the microgrids on both sides of the microgrid, perform bidirectional power mutual assistance, and ensure stable and reliable operation of the system; (2) If the master-slave control mode is adopted, the main control unit of each microgrid is responsible for stabilizing the voltage and frequency of the bus, and the slave control unit outputs power according to the actual situation and the instruction. At present, most of the micro-power sources in the microgrid use power electronic interfaces, so when the microgrid is operated in an isolated island, the equivalent inertia of the microgrid is very small. When the output power and load of the intermittent slave control unit fluctuate, the voltage and frequency of the main control unit of the microgrid will also fluctuate. If improperly controlled, it may even cause the voltage and frequency fluctuations to exceed the allowable range, resulting in the problem that the microgrid cannot operate normally.

[0005] After searching, the Chinese invention patent application publication number CN118174380B discloses a hierarchical coordinated control method and system for an isolated AC / DC hybrid microgrid group, which is used to effectively suppress the steady-state and dynamic over-limit risks of frequency and voltage in the AC / DC hybrid microgrid group. The method includes: constructing an AC / DC hybrid microgrid group model, based on the microgrid group control layer, constructing a microgrid group interconnected converter power allocation strategy based on the AC / DC sub-microgrid limit power point clamping, and controlling the AC / DC hybrid microgrid group model through the microgrid group interconnected converter power allocation strategy; based on the sub-microgrid control layer, constructing a sub-microgrid instantaneous power control strategy based on frequency and voltage differential feedforward compensation, and controlling the AC / DC hybrid microgrid group model through the sub-microgrid instantaneous power control strategy. This existing patent application has the problem of coordination between controllable distributed power sources and energy storage systems. Different types of controllable distributed power sources have different intermittency and uncertainty, and energy storage systems are required to perform power balance regulation. However, the capacity of the energy storage system is limited, and the coordination of its charging and discharging strategy with the power output characteristics of the distributed power source and load demand is a difficult problem. If the coordination is not good, excessive charging and discharging of energy storage and excessive power fluctuations may occur, affecting the stable operation of the system.

[0006] How to achieve power sharing control of isolated AC / DC hybrid microgrid in master-slave mode has become a technical problem that needs to be solved. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a power sharing method and device for an island AC / DC hybrid microgrid in a master-slave mode.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] According to one aspect of the present invention, a power sharing method for an isolated AC / DC hybrid microgrid in a master-slave mode is provided, wherein each micro-source model of the AC / DC hybrid microgrid includes a converter located at a DC microgrid, an AC microgrid, each interface, and a bidirectional interconnected converter connected to an AC / DC bus; the DC microgrid and the AC microgrid both include energy storage and a plurality of controllable distributed power supplies, the energy storage and each of the controllable distributed power supplies are connected to the AC / DC bus through a converter corresponding to the interface, the energy storage serves as a master control unit, and the plurality of controllable distributed power supplies serve as slave control units, wherein the method comprises:

[0010] The AC microgrid uses a dual-loop control system to control the converters therein;

[0011] The DC microgrid uses a step-up / step-down bidirectional converter to control the converter therein;

[0012] After the energy storage smoothes the power fluctuations of their respective microgrids, all controllable distributed power sources share the energy storage output according to their respective capacity ratios. The microgrid on one side transfers power to the microgrid on the other side through a bidirectional interconnected converter, achieving global power mutual assistance between the microgrids on both sides of the AC and DC.

[0013] Preferably, the method also includes: if all controllable distributed power sources reach rated power, they will not be able to share the power of energy storage to smooth fluctuations, and the energy storage capacity of the microgrids on both sides is balanced according to the energy storage output efficiency, and power sharing is achieved.

[0014] Preferably, the AC microgrid adopts a dual-loop control system to control the converter therein, including: the energy storage as the main control unit adopts constant voltage and frequency control, and the controllable distributed power supply as the slave control unit adopts constant active and reactive power control;

[0015] The dual-loop control system is specifically: the outer loop controller adopts a voltage control loop, and the inner loop controller adopts current control, wherein the inner loop controller generates a control signal.

[0016] Preferably, the DC microgrid uses a step-up / step-down bidirectional converter to control the converter therein, including: the energy storage in the DC microgrid is connected to the DC bus through a step-up / step-down bidirectional converter, and constant voltage control is used to stabilize the DC bus voltage of the DC microgrid in the master-slave mode; the controllable distributed power supply of the DC microgrid adopts constant power control.

[0017] Preferably, the bidirectional interconnected converter only considers bidirectional transmission and distribution of active power and operates at unity power factor.

[0018] Preferably, all controllable distributed power sources share the energy storage output according to their respective capacity ratios, including: the deviation between the actual output power of the energy storage and the reference power is obtained by a PI controller to obtain the reference power of each controllable distributed power source in the AC / DC microgrid, and the reference power of each controllable distributed power source is added to obtain the total reference power P of the system. ref ;

[0019] Active power output reference value P of each controllable distributed power source in AC / DC microgrid dcref,i and P dcref,j They are:

[0020] P dcref,i =k dc,i *P ref ,i∈[1,n]

[0021] P acref,j =k ac,j *P ref ,j∈[1,m]

[0022] In the formula, k dc,i is the power allocation factor of the ith controllable distributed generation in the DC microgrid; k ac,i is the power allocation factor of the jth controllable distributed generation in the AC microgrid; n and m represent the number of controllable distributed generation in the DC and AC microgrids, respectively; P ref is the total reference power of the hybrid microgrid system; P dcref,i and P acref,j are the active power output reference values ​​of controllable distributed power sources in DC microgrid and AC microgrid respectively;

[0023] k dc,i and k ac,i The calculation formula is:

[0024]

[0025] In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid, P dcn,iis the power of the ith controllable distributed power source among the n controllable distributed power sources in the DC microgrid, P acn,j is the power of the jth controllable distributed power source among the n controllable distributed power sources in the AC microgrid.

[0026] Preferably, the global power mutual assistance of the microgrids on both sides of the AC and DC is achieved through the bidirectional interconnected converter, including: when the AC microgrid has power fluctuations, the DC microgrid is regarded as a DC equivalent power source, and the equivalent power source is the same as the other controllable distributed power sources connected in parallel to the AC bus, and the size of its active power is determined by the bidirectional interconnected converter according to the power allocated by the controllable distributed power source of the DC microgrid;

[0027] When power fluctuation occurs in the DC microgrid, the AC microgrid regards it as an AC equivalent power supply. The equivalent power supply, like the other controllable distributed power supplies connected in parallel to the DC bus, determines the size of its active power according to the power allocated by the controllable distributed power supplies of the AC microgrid through a bidirectional interconnected converter.

[0028] Preferably, when the power fluctuations in the microgrids on both sides coincide, the bidirectional interconnected converter transmits a power reference value P ref,BIC It is expressed as:

[0029] P ref,BIC =P acref,DG k dc -P dcref,DG k ac

[0030] In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid respectively; P acref,DG and P dcref,DG are the reference powers of the controllable distributed power sources of the AC and DC microgrids respectively; P ac,ES and P dc,ES They are the power emitted or absorbed by the AC and DC microgrid energy storage, respectively. They are positive when the energy storage emits power and negative when it absorbs power.

[0031] More preferably, when the controllable distributed power source reaches the rated value, the bidirectional interconnected converter transmits a power reference value P ref,BIC It is expressed as:

[0032]

[0033] In the formula, k p and k i are the proportional and integral control parameters of the PI controller, η ac and η dc are the energy storage output efficiencies of the AC microgrid and the DC microgrid respectively, and S is a complex variable.

[0034] According to another aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the method described above is implemented when the processor executes the program.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1) The invention utilizes the fast charging and discharging characteristics of energy storage on both sides of the AC / DC microgrid as the main control unit to instantly smooth the power fluctuation of the system, and then distributes it to all controllable distributed power sources in the system as slave control units according to the capacity ratio. Through the bidirectional interconnected converter, global power sharing of the microgrids on both sides of the isolated AC / DC in the master-slave mode is realized, which improves the available capacity of the energy storage of the main control unit and the ability to suppress system fluctuations, thereby enhancing the stability of the system.

[0037] 2) The present invention uses the energy storage system as the main control unit to suppress system power fluctuations through rapid charging and discharging to maintain the stability of the bus voltage and frequency. It then adjusts the active power setting value of the slave control unit based on the system global information, and shares all or part of its own power with the controllable distributed power sources in the system, giving full play to the advantages of mutual support and mutual assistance between the microgrids on both sides, and achieving long-term stable operation of the microgrid system.

[0038] 3) The simulation analysis results show that the power sharing research method can ensure the power balance of the system, achieve zero-difference control of voltage and frequency, and increase the available capacity of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a power sharing control flow chart of an isolated AC / DC hybrid microgrid in the present invention;

[0040] Figure 2 Schematic diagram of the topological structure of the AC / DC hybrid microgrid in the present invention;

[0041] Figure 3 It is a schematic diagram of inverter control in the AC microgrid of the present invention;

[0042] Figure 4 It is a schematic diagram of the principle of the inverter outer loop controller in the present invention;

[0043] Figure 5 It is a control schematic diagram of a step-up / step-down bidirectional converter in the present invention;

[0044] Figure 6 Schematic diagram of the global power sharing control model in the present invention;

[0045] Figure 7 It is a schematic diagram of the principle of a DC equivalent power supply in the present invention;

[0046] Figure 8 A schematic diagram of the current dual-loop control principle of the bidirectional interconnected converter in the present invention;

[0047] FIG9( a ) is a schematic diagram of simulation results of active power of AC and DC microgrid loads in the present invention;

[0048] FIG9( b ) is a schematic diagram of simulation results of active power transmission of bidirectionally interconnected converters in the present invention;

[0049] FIG9( c ) is a schematic diagram of simulation results of DC microgrid energy storage and controllable distributed power source active power in the present invention;

[0050] FIG9( d ) is a schematic diagram of simulation results of AC microgrid energy storage and controllable distributed power source active power in the present invention. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0052] In order to solve the problem of difficult power exchange between microgrids when an isolated AC / DC hybrid microgrid adopts a master-slave mode, the present invention utilizes the fast charging and discharging characteristics of energy storage on both sides of the AC / DC microgrid to instantly smooth the power fluctuation of the system, and then distributes it to all controllable distributed power sources in the system according to their respective capacity ratios, thereby improving the available capacity of energy storage and the ability to suppress system fluctuations.

[0053] This embodiment relates to a power sharing method for an island AC / DC hybrid microgrid in slave mode, comprising the following steps:

[0054] Step a. Establish each micro-source model of the AC / DC hybrid microgrid in master-slave mode, wherein each micro-source model of the AC / DC hybrid microgrid includes a DC microgrid, an AC microgrid, and a bidirectional interconnected converter connected to the AC / DC bus, and each controllable distributed power source of the DC microgrid and the AC microgrid is connected to the AC / DC bus through a corresponding interface converter.

[0055] Controllable distributed power sources include micro gas turbines, diesel generators, hydrogen fuel cells, etc.

[0056] A DC microgrid, an AC microgrid and a bidirectional interconnected converter (BIC) connected to the AC / DC bus are set up, wherein each controllable distributed power source (DPDG) in the AC and DC microgrids is connected to the AC and DC buses through direct current to direct current (DC / DC), direct current to alternating current (DC / AC) and alternating current to alternating current (AC / AC) interface converters, respectively.

[0057] Step b. In order to successfully connect the controllable distributed power source to the AC microgrid, the AC microgrid inverter needs to be reasonably controlled;

[0058] Step c. The energy storage in the DC subgrid is connected to the DC bus through a buck-boost bidirectional converter, which serves as the main control unit to stabilize the DC bus voltage in the master-slave control (MSM). Therefore, it is necessary to perform constant power control on the controllable distributed power supply in the DC microgrid, and adopt a voltage outer loop-current inner loop dual closed-loop control system. The AC and DC microgrids are respectively operated in the master-slave mode to achieve power balance within the microgrid;

[0059] Step d. In order to smooth the power fluctuation of the system, global output power allocation is required. Regardless of whether the microgrid on one side or both sides fluctuates simultaneously, the bidirectional interconnected converter (BIC) can perform global power sharing and precise transmission.

[0060] Step e. As an important part of realizing power mutual assistance between microgrids in AC / DC hybrid microgrid, the bidirectional interconnected converter has the characteristic of bidirectional energy flow. Therefore, it is necessary to control the bidirectional interconnected converter to maximize the power mutual assistance between the two sides.

[0061] Step f. In order to verify the correctness and effectiveness of the control strategy, an island AC / DC hybrid microgrid model is established, and simulation analysis is performed using the Matlab / Simulink simulation platform.

[0062] like Figure 1 As shown in FIG. 1 , the specific process of the power sharing method of the isolated AC / DC hybrid microgrid in the master-slave mode includes:

[0063] Step 301, build each micro-source model of the AC / DC hybrid microgrid in master-slave mode, such as Figure 2 As shown in the figure, renewable energy (RES) in AC / DC microgrids are generally controlled by maximum power point tracking (MPPT). Due to the volatility, randomness and intermittency of renewable energy, it is also called uncontrollable micro energy. In most cases, energy storage can be used to smooth the power fluctuation of renewable energy. Figure 2The microgrid central control (MGCC) uses the detection system to collect information such as energy storage, load and power from the controllable distributed generation (DPDG) and bidirectional interconnected converter (BIC) units in the AC / DC microgrid through communication lines, and sends control signals to the local controllers of each interface converter. Interface converters include DC to DC (DC / DC), DC to AC (DC / AC) and AC to AC (AC / AC).

[0064] The DC microgrid includes energy storage, controllable distributed power supply, load and photovoltaic power generation; the AC microgrid includes energy storage, controllable distributed power supply, load and wind power generation.

[0065] The active power balance of the AC / DC hybrid microgrid system can be expressed as:

[0066] P ac,ES +P ac,DG +P BIC =P ac,load -P WT (1)

[0067] P dc,ES +P dc,DG -P BIC =P dc,load -P PV (2)

[0068] Where P ac,ES and P dc,ES are the power emitted or absorbed by the AC and DC microgrid energy storage, respectively. The value is positive when the energy storage emits power and negative when it absorbs power; P ac,DG and P dc,DG are the total power generated by the controllable distributed power sources of the AC and DC microgrids respectively; P WT is the wind power generation power; P PV is the photovoltaic power generation power; P BIC is the power transmitted by the bidirectional interconnected converter, and the direction of power transmission from the DC microgrid to the AC microgrid is defined as the positive direction of the power of the bidirectional interconnected converter; P ac,load and P dc,load are the load powers of the AC and DC side microgrids respectively.

[0069] Step 302: Build an AC microgrid converter control model (inverter dual-loop control), mainly for the DC / AC and AC / AC interface converters in the AC microgrid. Figure 3As shown in the figure, in the AC microgrid, accurate and reasonable control of the converter of the AC microgrid is the key to realize the controllable distributed power supply access to the microgrid. A dual-loop control system is used to control the AC microgrid converter. In order to achieve different control purposes and functions, the outer loop controller uses a voltage control loop to generate control signals for the inner loop controller at the same time. In order to achieve precise control of the injected current and improve the dynamic response speed of the system, current control is used for the inner loop controller.

[0070] Build a constant voltage and frequency control (V / f) model for the energy storage main control unit. Figure 4 As shown in the figure, in the master-slave mode, in order to maintain the constant voltage and frequency of the system, the energy storage as the master control unit can adopt constant voltage frequency control (V / f). V / f controls the d-axis and q-axis components of the output voltage (U d ,U q ) with the given voltage d-axis and q-axis components (U dref ,U qref ) and obtain the reference values ​​of the current d-axis and q-axis components (i dref and i qref ) and is controlled by a current controller.

[0071] Build a controllable distributed power source slave control unit constant active and reactive power control (PQ) model. Figure 4 As shown in the figure, in order to maintain the constant power output of the system in the master-slave mode, controllable distributed power sources such as micro gas turbines and diesel generators are used as slave control units using PQ control. PQ control requires the d-axis and q-axis components (U d , U q ,i d ,i q ) after power calculation and the given active and reactive output power reference value (P ref and Q ref ) and obtain the reference values ​​of the current d-axis and q-axis components (i dref and i qref ), then the voltage control signal (Um,d and Um,q) is output through the current control loop, and finally realized through Park inverse transformation and space vector pulse width modulator.

[0072] Step 303, build a DC microgrid converter control model (boost / buck bidirectional converter control), mainly for the DC / DC interface converter in the DC microgrid, such as Figure 5 As shown, the energy storage in the DC microgrid is connected to the DC bus through a buck-boost bidirectional converter (Buck-Boost).

[0073] Energy storage is used as the main control unit in a DC microgrid, and a constant voltage control model is established to stabilize the bus voltage of the DC microgrid in the master-slave mode (MSM).

[0074] In order to maintain constant power operation, the controllable distributed power source is used as the slave control unit in the DC microgrid, and constant power control is adopted.

[0075] Step 304: Build a global shared control model for the isolated AC / DC hybrid microgrid system. Figure 6 As shown, regarding the power ratio distribution, considering the limited capacity of the energy storage system on both sides of the AC / DC microgrid, continuous charging and discharging will reduce the service life of the internal battery. At the same time, if the remaining energy storage capacity is insufficient, it is difficult to support the system voltage and frequency when the system power fluctuates again. Therefore, the rapid charging and discharging characteristics of the energy storage are used to instantly smooth the power fluctuations of each microgrid, and then all controllable distributed power sources are allowed to share the energy storage output, so that the energy storage output gradually returns to the set value to better cope with the next power fluctuation of the system. Therefore, the focus of the present invention is to do a good job in the global output power distribution, and whether there is a fluctuation in the single-sided microgrid or the two-sided microgrid at the same time, the bidirectional interconnected converter (BIC) can perform global power sharing and precise transmission. Since there is no reactive power in the DC microgrid, the bidirectional interconnected converter does not participate in reactive management during rectification. In order to reduce the power burden of the bidirectional interconnected converter, the mutual assistance strategy of the present invention only considers the bidirectional transmission and distribution of active power, and the bidirectional interconnected converter always operates at a unit power factor.

[0076] Figure 6 Medium dc,ES and P ac,ES is the actual power of energy storage on the DC and AC sides, P dcref,ES and P acref,ES P is the reference power of energy storage on the DC and AC sides. If the controllable distributed generation shares all the power, P dcref,ES =0,P aref,ES = 0. The deviation between the actual output power of the energy storage and the reference power is obtained by the PI controller to obtain the reference power P of the controllable distributed power supply of the microgrid on both sides of the AC and DC dcref,DG and P acref,DG In order to achieve global power sharing, the reference power of each controllable distributed power source on both sides of the AC and DC microgrid is added to obtain the total reference power of the system P ref .

[0077] In order to make the output of the controllable distributed power source proportional to its capacity, the active power output reference value P of each controllable distributed power source in the AC / DC microgrid is dcref,i and P dcref,j They are:

[0078] P dcref,i =k dc,i *Pref , i∈[1,n] (3)

[0079] P acref,j =k ac,j *P ref , j∈[1,m] (4)

[0080] In the formula, k dc,i is the power allocation factor of the ith controllable distributed generation in the DC microgrid; k ac,i is the power allocation factor of the jth controllable distributed generation in the AC microgrid; n and m represent the number of controllable distributed generation in the DC and AC microgrids, respectively; P ref is the total reference power of the hybrid microgrid system.

[0081] k dc,i and k ac,i It is derived as:

[0082]

[0083] In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid, P dcn,i is the power of the ith controllable distributed power source among the n controllable distributed power sources in the DC microgrid, P acn,j is the power of the jth controllable distributed power source among the n controllable distributed power sources in the AC microgrid.

[0084] Combined with the above formula, the total system controllable distributed power reference power P ref It can be described as:

[0085]

[0086] Step 305: Build a bidirectional interconnected converter control model. Figure 8 As shown in the figure, regarding the control of the bidirectional interconnected converter, the bidirectional interconnected converter BIC is the core device for realizing power mutual assistance between microgrids in the AC / DC hybrid microgrid, and has the characteristics of bidirectional energy flow. When the power of the AC microgrid fluctuates, for the DC microgrid connected to the AC bus through the bidirectional interconnected converter, it can be regarded as Figure 7 The "DC equivalent power supply" shown is the same as the other controllable distributed power supply units connected in parallel to the AC bus. This power supply determines the size of its active power (inflow or outflow) according to the power allocated by the DC microgrid controllable distributed power supply through a bidirectional interconnected converter. Similarly, when the DC microgrid experiences power fluctuations, the AC microgrid can be regarded as an "AC equivalent power supply".

[0087] In addition to the power fluctuations in a single microgrid, considering that the power fluctuations in the two-side microgrids can overlap, the bidirectional interconnected converter transmission power reference value P ref,BIC It can be expressed as:

[0088] P ref,BIC =P acref,DG k dc -P dcref,DG k ac (9)

[0089] In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid, P acref,DG and P dcref,DG are the reference power of the controllable distributed power source of the AC / DC microgrid, P ac,ES and P dc,ES They are the power emitted or absorbed by the AC and DC microgrid energy storage, respectively. They are positive when the energy storage emits power and negative when it absorbs power.

[0090] Step 306, check whether the controllable distributed power sources in the system have reached the rated value. If all the controllable distributed power sources DPDGs in the system have reached the rated power, they will not be able to share the power storage to smooth the fluctuations, and execute step 307; otherwise, if they have all reached the rated power, the process ends.

[0091] Step 307, after the controllable distributed power source in the system reaches the rated value, referring to equations (9) and (10), the capacity of the energy storage units on both sides can be balanced to maximize the power mutual assistance. The output efficiency of the main control units on both sides is:

[0092]

[0093] In the formula, η ac and η dc are the energy storage output efficiency of AC microgrid and DC microgrid respectively, P acn,ES and P dcn,ES are the energy storage ratings on the AC side and the DC side, respectively, P dc,ES and P ac,ES is the actual power of energy storage on the DC and AC sides.

[0094] P ref,BIC It can be expressed as:

[0095]

[0096] In the formula, k p and k i are the proportional and integral control parameters of the PI controller respectively.

[0097] Figure 8Figure 2 is a current dual-loop control diagram of a bidirectional interconnected converter. When a bidirectional interconnected converter is used for power transmission, a power current dual-loop control is often used. Since the bidirectional interconnected converter always operates at unity power factor, the reactive power reference value Q is ref,BIC = 0. According to the following formula, active power control is only related to the d-axis active current, i qref,BIC = 0, then the inner loop controller reference signal i dref,BIC can be simplified to:

[0098]

[0099] In the formula, P is the active power, U is d , U q ,i d ,i q are the d-axis and q-axis components of the output voltage and current, respectively, P ref,BIC is the reference value of the bidirectionally interconnected converter transmission power, i dref,BIC is the d-axis reference value of the output current of the bidirectionally interconnected converter, u d,BIC is the d-axis component of the output voltage of the bidirectionally interconnected converter.

[0100] The AC / DC hybrid microgrid power sharing research method proposed in this invention and the isolated AC / DC hybrid microgrid model established are simulated and analyzed through the Matlab / Simulink simulation platform. The specific data is shown in Table 1. The simulation platform consists of 2 energy storage modules and 4 controllable distributed power sources DPDGs.

[0101] Table 1

[0102]

[0103] According to equations (5), (6) and the active power capacity of AC / DC subgrid energy storage and controllable distributed generation in Table 1, k can be obtained: dc,1 =4 / 15, k dc,2 =7 / 30, k ac,1 =1 / 6, k dc,2 =1 / 3, k dc =k ac =1 / 2.

[0104] In the initial state, at t = 1s, the loads on both sides of the AC / DC microgrid are 90kw, P dc,load =P ac,load =90kW, BIC does not transmit power P BIC = 0. Referring to formulas (3), (4) and (8), we can obtain P dc,1 =48kW, P dc,2 =42kW, P ac,1 =30kW, Pac,2 =60kW. Under this strategy, a load mutation point is set for verification. The simulation results when the load fluctuates are shown in FIG9 . The present invention sets the controllable distributed power source to share the entire power of the energy storage, P dcref,ES =0,P acref,ES =0.

[0105] When t = 3s, as shown in Figure 9(a), the active load of the DC microgrid increases by 30kW, and as shown in Figure 9(c), the active power output of the energy storage of the DC microgrid master control unit increases by 30kW instantaneously to maintain the power balance in the microgrid. Subsequently, under the proposed global power sharing strategy, all controllable distributed power sources in the system bear the energy storage output power, that is, increase the output power ΔP dc,1 =8kW, ΔP dc,2 =7kW, ΔP ac,1 =5kW, ΔP ac,2 =10kW. At this time, since there is no power fluctuation in the AC microgrid, it is equivalent to the AC equivalent source. As shown in Figure 9(b), the 15kW added by the controllable distributed power source DGPGs at the AC microgrid end is supplied to the DC microgrid through BIC mutual assistance, and the main control unit gradually recovers to 0.

[0106] Similarly, when t = 5s, as shown in Figure 9(a), the active load of the AC microgrid increases by 48kW, and as shown in Figure 9(d), the active power output of the AC microgrid main control unit energy storage increases by 48kW instantaneously. Subsequently, all controllable distributed power sources increase their output power ΔP dc,1 =12.8kW, ΔP dc,2 =11.2kW, ΔP ac,1 =8kW, ΔP ac,2 =16kW. At this time, since the DC microgrid has no power fluctuation, it is equivalent to a "DC equivalent power supply". The BIC reduces power transmission by 24kW, and the main control unit gradually returns to 0.

[0107] When t=7s, the AC and DC microgrids experience power fluctuations at the same time, and the active power of the AC and DC loads decreases by 20kW and 40kW respectively. The energy storage on both sides is quickly charged to maintain system stability. Subsequently, all controllable distributed power sources DPDGs reduce their output power, ΔP dc,1 =-16kW, ΔP dc,2 =-14kW, ΔP ac,1 =-10kW, ΔP ac,2 =-20kW. According to formula (9), the power transmitted by BIC is 10kW. In summary, the control strategy of the present invention can maintain system stability and improve the mutual support capability of micro-grids.

[0108] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0109] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0110] The processing unit performs the various methods and processes described above. For example, in some embodiments, the method can be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program can be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the method described above can be performed. Alternatively, in other embodiments, the CPU can be configured to perform the method in any other appropriate manner (e.g., by means of firmware).

[0111] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), complex programmable logic devices (CPLDs), and the like.

[0112] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0113] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0114] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A power sharing method for an isolated AC / DC hybrid microgrid in a master-slave mode, wherein each micro-source model of the AC / DC hybrid microgrid includes a converter located at a DC microgrid, an AC microgrid, each interface, and a bidirectional interconnected converter connected to an AC / DC bus; the DC microgrid and the AC microgrid both include energy storage and a plurality of controllable distributed power supplies, the energy storage and each of the controllable distributed power supplies are connected to the AC / DC bus through converters of corresponding interfaces, the energy storage serves as a master control unit, and the plurality of controllable distributed power supplies serve as slave control units, characterized in that: The method includes: The AC microgrid uses a dual-loop control system to control the converters therein; The DC microgrid uses a step-up / step-down bidirectional converter to control the converter therein; After the energy storage smoothes the power fluctuations of their respective microgrids, all controllable distributed power sources share the energy storage output according to their respective capacity ratios. The microgrid on one side transfers power to the microgrid on the other side through a bidirectional interconnected converter, achieving global power mutual assistance between the microgrids on both sides of the AC and DC.

2. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: The method also includes: if all controllable distributed power sources reach rated power, they will not be able to share the power of energy storage to smooth the fluctuations, and the energy storage capacity of the microgrids on both sides is balanced according to the energy storage output efficiency, and power sharing is achieved.

3. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: The AC microgrid adopts a dual-loop control system to control the converter therein, including: the energy storage as the main control unit adopts constant voltage and frequency control, and the controllable distributed power supply as the slave control unit adopts constant active and reactive power control; The dual-loop control system is specifically: the outer loop controller adopts a voltage control loop, and the inner loop controller adopts current control, wherein the inner loop controller generates a control signal.

4. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: The DC microgrid uses a step-up / step-down bidirectional converter to control the converter therein, including: the energy storage in the DC microgrid is connected to the DC bus through the step-up / step-down bidirectional converter, and constant voltage control is used to stabilize the DC bus voltage of the DC microgrid in the master-slave mode; the controllable distributed power supply of the DC microgrid adopts constant power control.

5. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: The bidirectional interconnected converter only considers the bidirectional transmission and distribution of active power and operates at unity power factor.

6. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: All controllable distributed power sources share the energy storage output according to their respective capacity ratios, including: the deviation between the actual output power of the energy storage and the reference power is obtained through the PI controller to obtain the reference power of each controllable distributed power source in the AC / DC microgrid, and the reference power of each controllable distributed power source is added to obtain the total reference power P of the system ref ; Active power output reference value P of each controllable distributed power source in AC / DC microgrid dcref,i and P dcref,j They are: P dcref,i =k dc,i *P ref ,i∈[1,n] P acref,j =k ac,j *P ref ,j∈[1,m] In the formula, k dc,i is the power allocation factor of the ith controllable distributed generation in the DC microgrid; k ac,i is the power allocation factor of the jth controllable distributed generation in the AC microgrid; n and m represent the number of controllable distributed generation in the DC and AC microgrids, respectively; P ref is the total reference power of the hybrid microgrid system; P dcref,i and P acref,j are the active power output reference values ​​of controllable distributed power sources in DC microgrid and AC microgrid respectively; k dc,i and k ac,i The calculation formula is: In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid, P dcn,i is the power of the ith controllable distributed power source among the n controllable distributed power sources in the DC microgrid, P acn,j is the power of the jth controllable distributed power source among the n controllable distributed power sources in the AC microgrid.

7. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: The global power mutual assistance of the microgrids on both sides of the AC and DC is achieved by the bidirectional interconnected converter, including: when the AC microgrid has power fluctuations, the DC microgrid is regarded as a DC equivalent power supply, and the equivalent power supply is the same as the other controllable distributed power supplies connected in parallel to the AC bus, and the size of its active power is determined by the bidirectional interconnected converter according to the power allocated by the controllable distributed power supply of the DC microgrid; When power fluctuation occurs in the DC microgrid, the AC microgrid regards it as an AC equivalent power supply. The equivalent power supply, like the other controllable distributed power supplies connected in parallel to the DC bus, determines the size of its active power according to the power allocated by the controllable distributed power supplies of the AC microgrid through a bidirectional interconnected converter.

8. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 1 is characterized in that: When the power fluctuations in the microgrids on both sides coincide, the bidirectional interconnected converter transmission power reference value P ref,BIC It is expressed as: P ref,BIC =P acref,DG k dc -P dcref,DG k ac In the formula, k dc and k ac are the power allocation coefficients of the DC microgrid and the AC microgrid respectively; P acref,DG and P dcref,DG are the reference powers of the controllable distributed power sources of the AC and DC microgrids respectively; P ac,ES and P dc,ES They are the power emitted or absorbed by the AC and DC microgrid energy storage, respectively. They are positive when the energy storage emits power and negative when it absorbs power.

9. The power sharing method of an isolated AC / DC hybrid microgrid in a master-slave mode according to claim 2 is characterized in that: When the controllable distributed power source reaches the rated value, the bidirectional interconnected converter transmission power reference value P ref,BIC It is expressed as: In the formula, k p and k i are the proportional and integral control parameters of the PI controller, η ac and η dc are the energy storage output efficiencies of the AC microgrid and the DC microgrid respectively, and S is a complex variable.

10. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 9 is implemented.

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