Alternating current and direct current hybrid micro-grid system suitable for stacked three-dimensional caged chicken coop and control method of alternating current and direct current hybrid micro-grid system

Abstract

The invention provides an AC-DC hybrid micro-grid system suitable for a stacked three-dimensional caged chicken coop and a control method, and the system comprises three-dimensional chicken coop electrical loads which comprise an AC-side load and a DC-side load; a photovoltaic power generation system in the direct current subnet comprises a photovoltaic array considering shadow shielding power optimization and a Boost circuit; the lithium battery energy storage system in the direct current subnet comprises a lithium battery pack and a bidirectional buck-boost circuit; a wind power generation system in the AC subgrid; the bidirectional AC / DC converter is responsible for energy exchange between the direct current subnet and the alternating current subnet; the harmonic wave processing unit is responsible for processing various harmonic waves from a photovoltaic system, an energy storage system, a wind power generation system and a nonlinear load of a chicken house; the energy management and control method comprises a grid-connected and off-grid smooth switching strategy, a pre-synchronization control strategy, a grid-connected energy management strategy based on time-of-use electricity price and a nonlinear MPPT optimization strategy considering multiple peaks of photovoltaic array power.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply control for stacked three-dimensional cage chicken houses, and in particular to an AC / DC hybrid microgrid power supply system and a control method suitable for stacked three-dimensional cage chicken houses. Background Art

[0002] With the rapid development of the economic level, the demand for chicken products among the Chinese people is increasing. The breeding equipment of chicken farming enterprises is gradually developing in the direction of scale, intensiveness and automation. In the "National Modern Facility Agriculture Construction Plan (2023-2030)" document published by the Ministry of Agriculture and Rural Affairs in June 2023, it is pointed out that the country should build a modern facility animal husbandry based on high efficiency and intensiveness. Adhere to the stability of pig and poultry production capacity, transform and upgrade facility animal husbandry, promote facility breeding standards and technical models for different regions and different livestock species, and accelerate the upgrading of animal husbandry facility breeding to efficient and intensive types. In areas where land resources are relatively scarce, develop three-dimensional facility farms for pigs and poultry on the premise of saving and intensive land use. Build three-dimensional multi-layer breeding pens, promote pig farming in high-rise buildings according to local conditions, equip with full-process efficient production equipment and intelligent management systems, and realize closed breeding from basic sows to fattening pigs. We will further call for the promotion of stacked cage farming, build closed laying hen and broiler pens, and equip them with equipment for precise feeding management, brooding and hatching, disease prevention and control, environmental control, resource utilization of manure and sewage, egg collection and grading and packaging, so as to achieve efficient output of laying hens and broiler chickens.

[0003] In response to national policies, in order to make more rational use of land resources and reduce labor costs, the stacked cage model has gradually been widely recognized by the majority of chicken farms, and its development prospects are widely optimistic. This model has a high degree of intensiveness, which can well solve the contradiction between the increasing tension of land resources and human resources in my country and the urgent need to expand the scale of breeding. It can effectively reduce the dual pressure of land and labor, and effectively control the problem of breeding environmental pollution caused by chicken manure. At the same time, the stacked cage model is equipped with a digital and intelligent chicken house environmental control equipment system, which can improve the breeding environment and living conditions of the chickens. Compared with the traditional flat breeding model, the breeding capacity of a single chicken house in this three-dimensional and efficient breeding model can be increased from 10,000 to 20,000 to 30,000 to 60,000, and the breeding capacity of a single person can be increased from 5,000 to a maximum of 100,000.

[0004] Therefore, the three-dimensional breeding house containing multiple rows of stacked chicken cages has indeed solved the problem of scarce land resources. Through large-scale breeding, it has efficiently increased the output of chicken, eggs and other products, meeting the needs of consumers.

[0005] However, in the existing technology, this breeding model also has some problems in the process of promotion:

[0006] 1. The number of fan equipment in a single-story stacked chicken house increases and is concentrated, which causes the harmonic components of a single house to be concentrated and exceed the standard. High-order harmonics will affect the reliability of a single chicken house and the entire electrical system and control system.

[0007] 2. If there is a power outage due to various reasons during the breeding period, the current model is to manually activate the backup diesel generator, which will more easily cause hypoxia in the chickens during the power supply replacement process.

[0008] 3. Currently, all electricity consumption of three-dimensional chicken houses comes from external traditional energy generation, which has high carbon emissions and cannot meet the new development needs of emission reduction and carbon reduction in the future. Summary of the invention

[0009] The present invention is made to solve the above-mentioned problems, and aims to provide an AC / DC hybrid microgrid power supply system and control method suitable for stacked three-dimensional cage chicken houses.

[0010] The present invention provides an AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses, which has the following characteristics, including: a three-dimensional chicken house electrical load, including an AC electrical load and a DC electrical load, wherein the AC electrical load is divided into a critical AC load and a non-critical AC load, and the DC electrical load is divided into a critical DC load and a non-critical DC load, wherein the non-critical AC load is arranged outside the AC subnet and separated by a switch, so that when there is a power outage or other fault in the external power grid of the system, the system can directly cut off the connection with the non-critical AC load through the switch, and only retain the critical load, thereby ensuring the power supply demand in a single three-dimensional chicken house; a photovoltaic power generation system in the DC subnet, including a photovoltaic array and a Boost circuit that take into account a shadow shielding power optimization algorithm, wherein the photovoltaic power generation system in the DC subnet is connected to a DC bus through the Boost circuit; a lithium battery energy storage system in the DC subnet, including a lithium battery pack and a bidirectional buck-boost circuit, wherein the bidirectional buck-boost circuit is a combination of a Boost boost circuit and a Buck buck circuit, wherein the circuit is in a discharge state when operating in a Boost mode, and can The energy flows from the low voltage side to the high voltage side; when the circuit works in Buck mode, it is in charging state, and the energy flows from the high voltage side to the low voltage side; the wind power generation system in the AC subgrid includes a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectification circuit, a boost chopper circuit, a grid-side converter and an output filter circuit. The wind power generation system is a direct-drive wind power generation system, which adopts uncontrolled rectification, Boost boost and PWM inverter topology. The machine-side converter is composed of diodes, and the grid-side converter is composed of fully controlled IGBTs; the bidirectional AC / DC converter is responsible for the DC subgrid and the AC For energy exchange between sub-grids, a three-phase voltage source bridge topology is adopted, and an LC filter is adopted on the output side; the harmonic processing unit is responsible for processing various harmonics from the photovoltaic system, energy storage system, wind power generation system and the non-linear load of the chicken farm itself, and the harmonic processing unit adopts a parallel APF active power filter; the energy management unit is responsible for coordinating the energy flow between the subsystems as a whole; among them, the photovoltaic power generation system, energy storage system, and all DC loads constitute the DC sub-grid, and the wind power generation system and key AC loads constitute the AC sub-grid.

[0011] In the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: the three-dimensional chicken house is a three-dimensional breeding house containing multiple rows of stacked chicken cages, the three-dimensional chicken house is 108.9 meters long, 21.2 meters wide, and 11.6 meters high, with 6 rows of 10-layer cages built in, and the total electrical load of a single three-dimensional laying hen house is 203.55kW, of which the critical load is 112.8kW and the non-critical load is 90.75kW. According to engineering experience, the required coefficient for the operation of farm equipment is 0.65, then the normal load demand of a single three-dimensional chicken house is 132.3kW, and considering 150kW, the rated output power of the photovoltaic system is 100kWp, and the rated output power of wind power generation is 50kW; the electrical load in the three-dimensional chicken house is divided into AC side load and DC side load. The AC side load includes a single-phase or three-phase ventilation fan, a feeding device, a small window water curtain device, an egg collection and conveying device, and a manure conveying device. The DC side load includes an LED lighting system and an electric observation vehicle in the house. The lithium battery pack uses a lithium iron phosphate battery cell with a minimum unit of 3.2V and 37Ah. Each battery module of the lithium battery pack is formed by 10 battery cells in series. The parameters of a single module are 32V, 37Ah, and 1.184kWh. 13 battery modules are connected in series to form a battery pack. The lithium battery energy storage system includes three working modes: charging, discharging, and shutdown mode. The lithium battery energy storage system converts the charging and discharging mode of the battery through a Buck-Boost circuit. The normal working range of the SOC of the battery module is 0.2-0.9. The charging and discharging process is as follows: the DC side voltage U dc With reference value U dcref The current reference value is obtained after PI adjustment and compared with the battery output current I b The difference is then adjusted by PI to output the control signal, and the driving signal is obtained through pulse width modulation to control the charging and discharging of the Buck-Boost circuit; the grid-side converter of the wind power generation system adopts a vector control strategy of double closed-loop control, and the control process is as follows: first, the grid voltage and current are changed from the three-phase stationary coordinate system to the synchronous rotating coordinate system, and θ is the electrical angle of the grid voltage; then the DC bus voltage actually measured is compared with the given bus voltage, and the difference is obtained after the PI regulator outputs the given value i of the d-axis current dref , and then compare the given value with the actual d-axis current and add the feedforward compensation term to get the reference voltage U d * Similarly, for the q-axis current, the given value of the q-axis current is 0, which is different from the actual i q The value obtained by comparison passes through the PI regulator and adds the feedforward compensation term to obtain the reference voltage U q * ; Finally, the obtained reference voltage U d* , U q * The two-phase synchronous rotating coordinate system is transformed into a two-phase stationary coordinate system, and then the SVPWM method is used to generate a PWM waveform to control the grid-side inverter.

[0012] The AC / DC hybrid microgrid system for stacked three-dimensional cage chicken houses provided by the present invention may also have the following features: the output of the photovoltaic power generation system and the lithium battery energy storage system is direct current, and energy is transferred and converted through rectification and inversion devices. In engineering, a combination of photovoltaic cells connected in series or in parallel is called a photovoltaic array. In the photovoltaic array, a single photovoltaic cell generates electricity by absorbing light and generating current using the photovoltaic principle. Among the existing photovoltaic cell models, the single diode model is the most commonly used mathematical model, which can accurately fit the battery output characteristics. Its mathematical model is shown in formula (1):

[0013] (1)

[0014] In formula (1), I ph is the photocurrent, I0 is the reverse saturation current inside the diode, which is not affected by the light intensity, V pv is the output voltage of the photovoltaic cell, R se is the equivalent series resistance, R sh is the equivalent parallel resistance, Q = 1.6 × 10 -19 is the charge, K = 1.38 × 10 -18 J / K is the Boltzmann constant, A is the diode quality factor, T is the absolute temperature,

[0015] The engineering model of photovoltaic cells is shown in formula (2):

[0016] (2)

[0017] Among them, the expressions of coefficients C1 and C2 are:

[0018]

[0019] Using the standard parameter I SC , U OC ,I m and U m Substitute into the modified equation to obtain I under non-standard conditions SC '、U OC '、I m 'and U m ', the correction equation is shown in formula (5):

[0020] (5)

[0021] In formula (5), ΔS is the light intensity difference, that is, ΔS = (S / S ref )-1, ΔT is the temperature difference, that is, ΔT=TT ref , a, b and c are correction compensation coefficients, the values ​​are a = 0.0025 / ℃, b = 0.5 / (W / m 2 ), c = 0.00288 / °C, e is the base of the natural logarithm.

[0022] In the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, the following features may also be provided: the bidirectional DC / DC converter parameter design is specifically as follows:

[0023] The bidirectional DC / DC converter combines the Boost circuit and the Buck circuit together. It is a power electronic conversion device in which energy can flow in both directions. Udc represents the high voltage side and Ub represents the low voltage side. When the circuit works in the Boost mode, VT1 is the main control switch. By controlling the duty cycle of VT1, energy flows from the low voltage side to the high voltage side (discharge state); when the circuit works in the Buck mode, VT2 is the main control switch. By controlling the duty cycle of VT2, energy flows from the high voltage side to the low voltage side (charge state).

[0024] The selection of inductance parameters in bidirectional DC / DC converters is relatively important, which determines the size of current ripple and the dynamic response speed of the system. When the inductance parameter value is large, the current ripple is small, but the system response speed is relatively slow; when the inductance value is small, the current ripple coefficient is large, but the system response speed is fast. The voltage on the high-voltage side of the energy storage system is DC750V, and the voltage on the low-voltage side is DC416V. The switching frequency is set to f=20000Hz, the output voltage ripple ≦1%, and the input current ripple ≦5%. Then the voltage ripple ΔU≦750×1%=7.5V, and the current ripple ΔI≦111×5%=5.55A,

[0025] The formula for calculating inductance is:

[0026] (8)

[0027] In the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: the wind power generation system is composed of a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectifier, a boost chopper, a grid-side converter, and an output filter. The function of the wind turbine is to convert the captured wind energy into mechanical energy, and its power and torque can be expressed as:

[0028] (9)

[0029] In formula (9), P wis the mechanical power output of the wind turbine (W), T w is the mechanical torque, ρ is the air density (kg / m 3 ), C p (λ, β) is the wind turbine utilization coefficient, which is a nonlinear function of the tip speed ratio λ (λ = ωR / V) and the blade pitch angle β. When the pitch angle is constant, there is a λ that makes C p The value is the largest, the output power is the largest, which is called the optimal tip speed ratio; R is the radius of the fan blade (m); V w is the tip wind speed (m / s); ω is the mechanical angular velocity of the generator,

[0030] The stator voltage and flux equations of the permanent magnet synchronous generator are both nonlinear differential equations. In order to simplify the equations and facilitate analysis and calculation, the analysis is carried out in a rotating coordinate system (dq coordinate system), see formula (10),

[0031] (10)

[0032] In formula (10), V d 、V q is the dq-axis component of the stator voltage; R s is the stator resistance; i d 、i q is the dq axis component of the stator current; L d , L q is the dq axis component of inductance; Ψ d ,Ψ q is the magnetic flux of dq axis; ω e is the synchronous electrical angular velocity, n p is the number of permanent magnet generator pole pairs, ω m is the mechanical angular velocity of the synchronous motor rotor; pm is the rotor permanent magnet flux,

[0033] It can be seen from formula (10) that the electromagnetic torque of the permanent magnet generator is controlled by controlling the stator q-axis current, and then the generator speed is controlled so that the system can achieve maximum power output or limited power output. These functions are achieved by the generator side converter control strategy.

[0034] In the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: the capacitance value of the DC side of the bidirectional AC / DC converter is 6.0mF, so as to avoid the slowdown of the voltage returning to a stable value due to excessive capacitance value, and the interconnected converter adopts a three-phase voltage source bridge topology structure, U dc is the DC bus voltage, i dc is the DC side current, C dc is the DC side filter capacitor, S a1 , Sa2 , S b1 , S b2 , S c1 , S c2 IGBT turn-on and turn-off signals, U a , U b , U c are the three-phase voltages on the AC side of the converter, i La 、i Lb 、i Lc are the three-phase currents on the AC side of the converter, U oa , U ob , U oc are the three-phase voltages on the AC side, R, L, and C are the AC side filtering devices of the interconnected converter,

[0035] In the converter, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 The switching function is defined as expression (16):

[0036] (16)

[0037] According to Kirchhoff's law, the dynamic equation of the AC side voltage is expressed as equation (17):

[0038] (17)

[0039] Equation (17) shows the relationship between the parameters. The three-phase sinusoidal components are converted into DC components. The three-phase stationary coordinate system can be converted into a two-phase synchronous rotating dq coordinate system through the three-dimensional transformation method. After Clark and Park transformation, the mathematical model (18) can be obtained:

[0040] (18)

[0041] It can be seen from equation (18) that in the two-phase synchronous rotating dq coordinate system, there are coupling components between the d-axis and q-axis components, and decoupling control is required subsequently.

[0042] In the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: the whole-field harmonic current evaluation method of the laying hen farm is as follows: the transformer capacity used in the laying hen farm is 3000KVA, and the maximum allowable value of the total harmonic current of the whole laying hen farm is 563.4A. For a single three-dimensional laying hen house, the maximum allowable value of the total harmonic current is <31.3A, so in the subsequent calculation, the value is taken as 30A as the calculation basis of the APF main capacity, inductance and capacitance.

[0043] Voltage V dc Adjust to 10% higher than the maximum input voltage of the inverter, the DC bus voltage V dc The expression is as follows:

[0044] (26)

[0045] V dc The value is 700V, and the value of the DC side capacitor is:

[0046] (27)

[0047] The DC side capacitance is 2200μF.

[0048] The general inductance is estimated by the empirical formula (28):

[0049] (28)

[0050] Among them, Δi max The maximum allowable error between the APF command current and the actual output current is 10A. The system sampling period T s =80μs, inductance is 4mH.

[0051] The present invention also provides a control method for an AC / DC hybrid microgrid system suitable for a stacked three-dimensional cage chicken house, which has the following characteristics: the photovoltaic array adopts a hybrid optimization algorithm of gray wolf optimization and disturbance observation method to realize nonlinear MPPT control of multi-peak power, and the photovoltaic power generation system has three control modes: MPPT, shutdown and power-limited operation; the energy storage system has three control modes: charging, discharging and shutdown mode, and the system charging and discharging are controlled by the outer loop voltage and inner loop current, and the main task is to be responsible for the stability of the bus voltage in the DC subnet; the wind power generation system has three modes of MPPT, shutdown and power-limited operation on the machine side; the bidirectional AC / DC converter adopts the PQ control mode when it is connected to the grid, and the values ​​of active power P and reactive power Q are derived from the time-sharing power grid. The power management strategy of the price is adopted. In the grid-connected mode, the voltage / frequency of the AC bus is supported by the large power grid, and the voltage stability of the DC bus is the responsibility of the energy storage system. When off-grid, V / f control is adopted, and the voltage / frequency support is provided by the interconnected converter, and the voltage stability of the DC bus is still the responsibility of the energy storage system. Harmonic detection adopts the ip-iq detection method based on instantaneous reactive power theory, and adopts voltage outer loop + current inner loop dual closed-loop control to realize harmonic suppression and reactive power compensation functions. Among them, the voltage outer loop and the APF DC side voltage adopt PI control; the current inner loop and the APF current regulation adopt hysteresis control; the internal strategies of the energy management unit include on-grid and off-grid smooth switching strategy, pre-synchronization control strategy, on-grid energy management strategy based on time-of-use electricity price, and off-grid energy management strategy.

[0052] In the control method of the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: when the microgrid is in a grid-connected state, the system as a whole adopts an energy management strategy based on time-of-use electricity prices, the AC / DC bidirectional converter is in PQ control mode, the frequency and voltage of the AC subgrid are supported by the large power grid, the bus voltage of the DC subgrid is kept stable by the energy storage system, the PV system and the WT system are power generation sources, and the AC load and the DC load are power consumption terminals. The specific working modes are introduced as follows: Mode 1&2: When there is surplus energy on the DC subgrid side and there is surplus energy on the AC subgrid side When there is surplus electricity and the amount of energy storage system is within the appropriate range, if the electricity price of the electricity generated by the new energy is high, the AC / DC bidirectional converter will be in the inverter state, guiding the excess electricity in the DC subnet to flow to the large power grid to obtain better economic returns. The energy storage system will not charge or discharge. If the selling price of the electricity generated by the new energy is low, the AC / DC bidirectional converter will be in the rectification state, guiding the excess electricity in the AC subnet to move to the DC subnet and charge the energy storage system to ensure energy reserve; Mode 3, 4, and 5: When the power generation of the new energy in the AC / DC subnet is far less than the respective load consumption, and the energy storage system When the energy system has a large amount of electricity, when the price of purchasing electricity from the external grid is high, the energy storage system will be responsible for the energy gap of the AC and DC loads, and the system will not purchase electricity from the large grid to save costs. When the price of purchasing electricity from the external grid is low, the energy storage system will only be responsible for the energy gap on the DC subgrid side, and the large grid will be responsible for the energy gap on the AC subgrid side. When the amount of electricity in the energy storage system is low, the energy storage system will shut down, and the large grid will be responsible for all the energy gaps in the AC and DC subgrids. Mode 6: When the WT power generation in the AC subgrid is less than the AC load consumption, the PV system power generation in the DC subgrid is greater than the DC load, and the excess energy in the DC subgrid is greater than the energy in the AC subgrid. When there is a power gap and the energy storage system has sufficient power, if the price of electricity sold to the external grid is low, the AC / DC bidirectional converter will be in a shutdown state, forcing the excess energy on the DC side to be charged into the energy storage system, and the power gap of the AC subgrid will be supplemented by the external grid; Mode 7: When the WT power generation in the AC subgrid is less than the AC load consumption, the PV system power generation in the DC subgrid is greater than the DC load, the excess energy in the DC subgrid is less than the energy gap in the AC subgrid and the energy storage system has sufficient power, the energy storage system will be shut down, and the AC / DC bidirectional converter will guide the excess power of the DC subgrid to flow to the AC subgrid, and the insufficient power on the AC side will be supplemented by the large grid;Mode 8&9: When the WT power generation in the AC subgrid is greater than the AC load consumption, the PV system power generation in the DC subgrid is less than the DC load, the excess energy in the AC subgrid is greater than the energy gap in the DC subgrid and the energy storage system has sufficient power, when the price of purchasing electricity from the external grid is high, the energy gap of the DC subgrid will be provided by the energy storage system, and the excess power of the AC subgrid will flow into the large power grid in exchange for economic benefits. When the power of the energy storage system is not enough to make up for the energy gap in the DC subgrid, the excess power in the AC subgrid will be rectified by the AC / DC bidirectional converter and enter the DC subgrid. ;

[0053] In the control method of the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses provided by the present invention, it can also have the following characteristics: when the microgrid is off-grid, the AC / DC bidirectional converter is in V / f control mode, the frequency and voltage of the AC subgrid are supported by the AC / DC bidirectional converter, and the bus voltage of the DC subgrid is still kept stable by the energy storage system. The PV system and the WT system are power generation sources, and the AC load and the DC load are power consumption terminals. The specific working modes are introduced as follows: Mode 1 & 2: When there is surplus energy on both the AC and DC subgrid sides, and the energy storage system is very sufficient, the WT and PV systems will be adjusted to power tracking power generation LPT In C mode, the energy storage system neither charges nor discharges, and each subgrid maintains energy balance. When the energy storage system is within the range allowed for charging, in order to make full use of renewable energy generation, the system will control the WT and PV systems to operate at full power in MPPT mode, and the energy storage system will be in charging mode to absorb excess electricity, and each subgrid maintains energy balance. Mode 3 & 4: When there is a gap in energy on both the AC and DC subgrid sides, and the energy storage system has a large amount of power, the energy missing from the system will be compensated by the energy storage system to ensure the operation of AC loads and part of the DC loads. When the energy storage system has little power, the system will only retain the more important part of the AC load and cut off all DC loads and non-critical loads. Key AC load; Mode 5&6: When there is surplus energy on the DC subgrid side, but there is a shortage of energy on the AC subgrid side, and the surplus energy on the DC side is greater than the missing energy on the AC side, according to the principle of energy balance, part of the surplus energy on the DC side will flow to the AC side to make up for its energy gap, and the remaining part will flow into the energy storage system for charging. When the energy storage system is fully charged, the system will control the PV system to operate in LPTC mode; Mode 7&8: When there is surplus energy on the DC subgrid side and there is a shortage of energy on the AC subgrid side, but the surplus energy on the DC side is less than the missing energy on the AC side, this part of the missing energy will be made up by the energy storage system when the energy storage system is fully charged. When the system power is low, the non-critical loads on the AC subgrid side must be cut off; Mode 9: When there is surplus energy on the AC subgrid side, there is a gap in energy on the DC subgrid side, and the excess energy on the AC side is greater than the missing energy on the DC side, when the energy storage system has sufficient power, the system will control the WT system to operate in LPTC mode; Modes 10&11: When there is surplus energy on the AC subgrid side, there is a gap in energy on the DC subgrid side, and the excess energy on the AC side is less than the missing energy on the DC side, when the energy storage system has sufficient power, the energy still missing on the DC side is supplemented by the energy storage system. When the energy storage system is low, the energy storage system shuts down, and the DC side cuts off non-critical loads to ensure system energy balance.

[0054] Functions and Effects of the Invention

[0055] According to the AC / DC hybrid microgrid power supply system and control method suitable for stacked three-dimensional cage chicken houses involved in the present invention, the AC / DC topological structure designed for the three-dimensional chicken house is conducive to the direct utilization of AC and DC loads in the chicken house, reducing the loss in energy conversion. At the same time, through the photovoltaic power generation system, wind power generation system and lithium battery energy storage system, the external traditional energy consumption is reduced, carbon emissions are reduced, and it is beneficial to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is the AC / DC hybrid microgrid topology of the stacked three-dimensional cage chicken house in the embodiment of the present invention;

[0057] Figure 2 is a plan view of the entire laying hen farm in an embodiment of the present invention;

[0058] Figure 3 is the whole-field load statistics of the laying hen farm in the embodiment of the present invention;

[0059] Figure 4 It is a cage elevation view of a single three-dimensional chicken house in an embodiment of the present invention;

[0060] Figure 5 is a vertical view of the fan arrangement of a single three-dimensional chicken house in an embodiment of the present invention;

[0061] Figure 6 It is the hardware composition of the photovoltaic power generation system in the embodiment of the present invention;

[0062] Figure 7 It is the hardware composition of the energy storage system in the embodiment of the present invention;

[0063] Figure 8 It is the internal composition of the battery module in the embodiment of the present invention;

[0064] Fig. 9 is the internal composition of the battery pack in the embodiment of the present invention;

[0065] Fig.10 It is the hardware composition of the wind power generation system in the embodiment of the present invention;

[0066] Fig.11 It is the hardware composition of the bidirectional AC / DC converter in the embodiment of the present invention;

[0067] Fig.12 It is the hardware composition of the APF unit in the embodiment of the present invention;

[0068] Fig.13 It is the whole field harmonic current evaluation of the laying hen farm in the embodiment of the present invention;

[0069] Fig.14is a photovoltaic system control strategy in an embodiment of the present invention;

[0070] Fig.15 is a wind power system control strategy in an embodiment of the present invention;

[0071] Fig.16 is the energy storage system control strategy in the embodiment of the present invention;

[0072] Fig.17 is a bidirectional AC / DC converter control strategy in an embodiment of the present invention;

[0073] Fig.18 is the harmonic processing unit control strategy in the embodiment of the present invention;

[0074] Fig.19 The AC / DC hybrid microgrid in the embodiment of the present invention is modeled by Matlab Simulink;

[0075] Fig. 20 It is a simulink simulation of the power flow of each module of the system in the embodiment of the present invention. DETAILED DESCRIPTION

[0076] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0077] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically describe the AC / DC hybrid microgrid power supply system and control method applicable to stacked three-dimensional cage chicken houses of the present invention.

[0078] Figure 1 This is an AC / DC hybrid microgrid topology for a stacked three-dimensional cage chicken house in an embodiment of the present invention.

[0079] like Figure 1 As shown in the figure, in the system of the stacked three-dimensional cage chicken house AC / DC hybrid microgrid 100 designed by the present invention, a single chicken farm can include N small three-dimensional chicken houses. The whole farm is connected by a 10KV cable input line through a transformer and a complete set of power distribution cabinets to output multiple AC380V branch power supplies to each three-dimensional chicken house. The AC / DC hybrid microgrid system inside each chicken house is as follows Figure 1As shown, from the electrical topology, it is divided into a DC subgrid 50, an AC subgrid 60, an AC / DC interconnection conversion unit and an energy management unit, which specifically include: a photovoltaic power generation system, a wind power generation system, a battery energy storage system, an energy management system 40, a bidirectional AC / DC interconnection converter 30 and AC and DC loads in a three-dimensional chicken house.

[0080] The AC / DC hybrid microgrid of a single three-dimensional chicken house, as a single integrated distributed "source-storage-load" unit, can achieve on-grid / off-grid coordination with the external power grid. The various hybrid microgrids can also share emergency power in the event of a fault through the bus tie switch to ensure the production safety of the chicken flock.

[0081] The AC / DC hybrid microgrid system of a single three-dimensional cage chicken house is internally divided into an AC subnet 60 and a DC subnet 50.

[0082] The working principle of the AC / DC hybrid microgrid 100 system for three-dimensional cage chicken house is:

[0083] In the DC subgrid 50, the photovoltaic array is an electric energy generating unit, which is connected to the DC bus through a unidirectional DC / DC converter and can operate in three states: MPPT (Maximum Power Point Tracking) control, LPTC (Load Power Tracking Control) control and shutdown.

[0084] The energy storage battery group 20 is a storage unit for electric energy, which is connected to the DC bus through a bidirectional AC / DC converter 30. It is mainly responsible for stabilizing the voltage of the DC bus, and timely smoothing power fluctuations and maintaining the balance between supply and demand. When the microgrid is in grid-connected mode, the energy storage battery group 20 is in a charging or discharging state according to the set time-of-use electricity price power adjustment algorithm; when the microgrid is in off-grid mode, the battery is in a charging or discharging state according to the principle of energy balance. The charging and discharging power always depends on the energy balance relationship. It is variable but will not exceed the limited power, and the discharge will not exceed the minimum value of SOC (State of Charge). The DC load is the LED lighting system in the cage, the inspection and observation vehicle in the chicken house, etc., which are directly connected to the DC bus.

[0085] In the AC subgrid 60, the wind turbine is connected to the AC bus through an uncontrolled rectifier circuit, a boost circuit, and a grid-side converter. By controlling the power of the machine-side converter, it can be put into MPPT, LPTC or shutdown mode. The AC bus of the microgrid is connected to the large power grid through a common connection point PCC (Point of Common Connection). The ventilation equipment, feed line equipment, egg collection equipment and other loads in the three-dimensional chicken house are the main consumption units of electric energy, and are directly connected to the AC bus as AC loads. When the microgrid is short of electric energy, the load can be cut off according to the priority level of the load.

[0086] The interconnected converter ILC (Interlinked Converter), also known as the bidirectional AC / DC converter 30, serves as a connecting bridge between the DC bus and the AC bus. Its main function is to enable bidirectional power flow. The steady-state working modes of the microgrid include grid-connected and islanded modes. When connected to the grid, the interconnected converter adopts PQ (constant power) control to achieve power balance and power exchange of the load in the grid. The value of PQ is obtained according to the set time-of-use electricity price power adjustment method. Photovoltaic and wind power generation are in MPPT control or shutdown mode. When the distribution network fails or the microgrid actively operates alone, the microgrid receives an off-grid signal, disconnects the static switch at the common connection point (PCC), and the interconnected converter switches to V / f (constant voltage and frequency) control to provide the AC bus voltage and frequency support required for the normal operation of the microgrid. Photovoltaic and wind power generation use MPPT or LPTC control according to the operating status of the microgrid; when the off-grid microgrid meets the conditions for reconnection to the grid and receives a grid connection signal, the pre-synchronization controller starts working. When the microgrid enters the grid-connected mode, the interconnected converter switches back to PQ control, and the pre-synchronization controller exits. The microgrid can smoothly switch between the grid-connected and island modes according to demand.

[0087] Figure 2 It is a whole plan view of a laying hen farm in an embodiment of the present invention.

[0088] like Figure 2 As shown, the stacked three-dimensional cage chicken house is divided into a three-dimensional cage broiler house and a three-dimensional cage laying hen house. The load equipment in the laying hen house in the present invention generally includes single-phase or three-phase ventilation fans, feed conveying equipment, small window water curtain equipment, egg collecting and conveying equipment, manure conveying equipment, etc. Among them, environmental control equipment and ventilation equipment (such as fans and tunnel door motors) are relatively important loads. They are related to the air volume supply for the daily growth of the chickens and the ventilation of animals in emergencies. They are called critical loads. Therefore, the AC / DC hybrid microgrid of the three-dimensional cage chicken house of the present invention mainly considers whether the coordinated power supply strategy between modules and the switching logic are reasonable when powering such equipment loads in the future, and whether the hardware configurations of the system are reasonable.

[0089] Figure 3 It is the whole load statistics of the laying hen farm in the embodiment of the present invention.

[0090] like Figure 3 As shown, the egg-laying chicken farm selected by the present invention has 18 three-dimensional chicken houses, and the entire farm also includes 6 outdoor egg belts, office buildings, restaurants, egg packaging workshops, power distribution rooms, sewage treatment and other functional areas.

[0091] Figure 4 It is a cage elevation view of a single three-dimensional chicken house in an embodiment of the present invention. Figure 5 It is a vertical view of the fan arrangement of a single three-dimensional chicken house in an embodiment of the present invention.

[0092] like Figure 4-5 As shown, a single three-dimensional chicken house is 108.9 meters long, 21.2 meters wide, and 11.6 meters high, with 6 rows of 10 layers of cages built in.

[0093] Table 1 Equipment data of single-building three-dimensional cage laying hen house

[0094]

[0095] Table 1 shows the equipment data of a single three-dimensional laying hen house.

[0096] As shown in Table 1, the total electrical load of a single three-dimensional laying hen house is 203.55kW, of which the critical load is 112.8kW and the non-critical load is 90.75kW. From engineering experience, it can be seen that the required coefficient for the operation of farm equipment is 0.65, so the normal load demand of a single three-dimensional chicken house is 132.3kW, and 150kW is considered in the present invention. Therefore, in the present invention, the rated output power of the photovoltaic system is 100kWp, and the rated output power of the wind power generation is 50kW.

[0097] The AC / DC hybrid microgrid suitable for stacked three-dimensional cage chicken houses includes six subsystems, specifically including: three-dimensional chicken house load, photovoltaic power generation system in DC subnet 50, lithium battery energy storage system in DC subnet 50, wind power generation system in AC subnet 60, bidirectional AC / DC converter 30 and harmonic processing unit.

[0098] Among them, the load of the three-dimensional chicken house includes AC side load and DC side load. The AC side load includes single-phase or three-phase ventilation fans, feeding equipment, small window water curtain equipment, egg collection and transportation, and manure transfer equipment. The DC side load includes LED lighting system and electric observation vehicle in the house.

[0099] Figure 6 It is the hardware composition of the photovoltaic power generation system in the embodiment of the present invention.

[0100] like Figure 6As shown, the photovoltaic power generation system in the DC subnet 50 includes a photovoltaic array and a Boost circuit, and the entire photovoltaic array is connected to the DC bus through the Boost circuit.

[0101] In engineering, a combination of several photovoltaic cells connected in series or in parallel is called a photovoltaic array. In a photovoltaic array, a single photovoltaic cell generates electricity by absorbing light and generating current based on the photovoltaic principle. Among the existing photovoltaic cell models, the single diode model is the most commonly used mathematical model, which can accurately fit the battery output characteristics. Its mathematical model is shown in formula (1):

[0102] (1)

[0103] In formula (1), I ph is the photocurrent, I0 is the reverse saturation current inside the diode, which is not affected by the light intensity, V pv is the output voltage of the photovoltaic cell, R se is the equivalent series resistance, R sh is the equivalent parallel resistance, Q = 1.6 × 10 -19 is the charge, K = 1.38 × 10 -18 J / K is the Boltzmann constant, A is the diode quality factor, and T is the absolute temperature.

[0104] But in reality, photovoltaic manufacturers do not provide I ph ,I0,R se and R sh Instead of providing the following parameters to the user: SC (short-circuit current), U OC (open circuit voltage), I m (maximum power point current), U m (maximum power point voltage). Therefore, the engineering model of photovoltaic cells is shown in formula (2):

[0105] (2)

[0106] Among them, the expressions of coefficients C1 and C2 are:

[0107]

[0108] In actual laying hen farms, the photovoltaic panels will be blocked by the material tower, outdoor egg belt, clouds or office buildings, and shadows will appear. The light intensity S and temperature T will change. At this time, the parameters I under standard conditions need to be used. SC , U OC ,I m and U m Substitute into the modified equation to obtain I under non-standard conditions SC '、UOC '、I m 'and U m '. The correction equation is shown in formula (5):

[0109] (5)

[0110] In formula (5), ΔS is the light intensity difference, that is, ΔS = (S / S ref )-1. ΔT is the temperature difference, that is, ΔT=TT ref a, b and c are correction compensation coefficients, and their values ​​are a=0.0025 / ℃, b=0.5 / (W / m 2 ), c = 0.00288 / °C. e is the base of the natural logarithm.

[0111] Table 2 TSM-250PC05A photovoltaic module parameters (reference size 1640mm×992mm)

[0112] parameter Numeric <![CDATA[Peak power (P max )]]> 250Wp <![CDATA[Open-circuit voltage (V oc )]]> 38.0V <![CDATA[Short-circuit current (I sc )]]> 8.79A <![CDATA[Peak voltage (V mp )]]> 30.3V <![CDATA[Peak current (I mp )]]> 8.27A

[0113] Table 2 shows the main parameters of TSM-250PC05A under standard test conditions (air temperature 25℃, irradiance 1000W / m2).

[0114] In the three-dimensional photovoltaic array of the laying hen farm of the present invention, the factors such as economy, power of single module, practicality of the site, market price, supply reliability and performance stability and reliability of actual commercial application are comprehensively considered. The present invention intends to use a single crystal photovoltaic module 10 with a single power of 250Wp (Note: photovoltaic modules of other specifications can also be used, as long as the key parameters are the same as those of the present invention), and use leading brands such as LONGi, JA Solar, and JinkoSolar. The present invention selects the photovoltaic module 10 of model TSM-250PC05A provided by Trina Solar when calculating, and the standard test conditions (air temperature 25°C, irradiance 1000W / m 2 )The main parameters of TSM-250PC05A are shown in Table 2.

[0115] Combined with the analysis of the load in the previous article, the proposed design capacity of the photovoltaic array in the present invention is 100kWp, and the low-voltage side voltage of the Boost circuit is DC400V, and the high-voltage side output voltage is DC750V. Therefore, the total number of solar cell modules required is initially calculated to be N=100kW / 250W=400, and the number of modules in series is N s =400V / 30.3V=13.20, take N s =14; Number of components connected in parallel N p =400 / 14=28.57, take N p =30. (The total floor area is less than the roof area of ​​the laying hen house)

[0116] Therefore, the photovoltaic array on the roof of a single three-dimensional egg-laying chicken house consists of 14 250W modules connected in series, with a total of 30 lines, and the total power of the photovoltaic array is P pv =250×14×30=105kWp, peak voltage U m =424.2V, peak current I m =248.1A, open circuit voltage U oc =532V, short circuit current I sc =263.7A. The photovoltaic array is composed of multiple photovoltaic cells. Each cell is easily in different conditions, such as the influence of material towers, outdoor egg belts, clouds or office buildings, the aging degree of the cells themselves is inconsistent, and the thickness of dust on the surface of the solar panels is uneven. These will cause local shading of the photovoltaic array cells and reduce the total output power of the photovoltaic power generation system.

[0117] Boost circuit parameter design:

[0118] Figure 6 It is the hardware composition of the photovoltaic power generation system in the embodiment of the present invention.

[0119] like Figure 6 As shown in the figure, after the voltage output by the photovoltaic array is stabilized, a Boost circuit is used to increase the voltage of the photovoltaic system from DC400V to DC750V and connect it to the DC bus. Set the switching frequency f = 20000Hz, the Boost output voltage is 750V, the output voltage ripple ≤ 1%, the input current ripple ≤ 5%, then the voltage ripple ΔU ≤ 750 × 1% = 7.5V, and the current ripple ΔI ≤ 248.1 × 5% = 12.42A.

[0120] The formula for calculating inductance is:

[0121] (6)

[0122] The capacitance calculation formula is:

[0123] (7)

[0124] Figure 7 It is the hardware composition of the energy storage system in the embodiment of the present invention.

[0125] like Figure 7 As shown, the lithium battery energy storage system in the DC subnet 50 includes a lithium battery pack and a bidirectional buck-boost circuit. The bidirectional buck-boost circuit is a combination of a Boost circuit and a Buck circuit. When the circuit works in the Boost mode, it is in a discharging state, and energy flows from the low-voltage side to the high-voltage side; when the circuit works in the Buck mode, it is in a charging state, and energy flows from the high-voltage side to the low-voltage side.

[0126] Lithium battery pack capacity design:

[0127] When the energy storage system is connected to the grid or off the grid, its only function is to maintain the voltage of the DC bus stable. Therefore, the capacity does not need to be designed to be very large, which also meets the cost-saving requirements of the laying hen farm.

[0128] Table 3 Lithium iron phosphate battery parameters

[0129] parameter Numeric Rated voltage / V 3.2 Rated capacity / Ah 37 Length × width × thickness / mm 148×97×27 Weight / g 800 AC internal resistance / mΩ <0.7 Maximum continuous discharge current / A 111 10s peak discharge current / A 148 Cycle life / times >6000

[0130] Table 3 shows the parameters of lithium iron phosphate battery cells.

[0131] As shown in Table 3, in the present invention, the battery pack uses a lithium iron phosphate battery cell with a minimum unit of 3.2V and 37Ah, and the parameters are shown in Table 3.

[0132] Figure 8 It is the internal composition of the battery module in the embodiment of the present invention.

[0133] like Figure 8 As shown, 10 lithium iron phosphate cells 72 are connected in series to form a battery module 71, and the parameters of a single module are 32V, 37Ah, and 1.184kWh.

[0134] Fig. 9 It is the internal composition of the battery pack in the embodiment of the present invention.

[0135] like Fig. 9 As shown, 13 battery modules 71 are connected in series to form a battery pack 70, with a total output voltage of 416V and a total system energy of 15.4kWh, 37Ah.

[0136] Bidirectional DC / DC converter parameter design:

[0137] like Figure 7 As shown in Figure 1, one of the important components of the energy storage system is the bidirectional DC / DC converter, which can be regarded as a combination of the Boost circuit and the Buck circuit. It is a power electronic conversion device that can flow energy in both directions. dc Indicates the high voltage side, U b Indicates the low voltage side. When the circuit works in Boost mode, VT1 is the main control switch tube. By controlling the duty cycle of VT1, energy flows from the low voltage side to the high voltage side (discharge state); when the circuit works in Buck mode, VT2 is the main control switch tube. By controlling the duty cycle of VT2, energy flows from the high voltage side to the low voltage side (charge state).

[0138] The selection of inductance parameters in bidirectional DC / DC converters is relatively important, which determines the size of current ripple and the dynamic response speed of the system. When the inductance parameter value is large, the current ripple is small, but the system response speed is relatively slow; when the inductance value is small, the current ripple coefficient is large, but the system response speed is fast. The voltage on the high-voltage side of the energy storage system is DC750V, the voltage on the low-voltage side is DC416V, the switching frequency is set to f=20000Hz, the output voltage ripple ≦1%, the input current ripple ≦5%, then the voltage ripple ΔU≦750×1%=7.5V, the current ripple ΔI≦111×5%=5.55A.

[0139] The formula for calculating inductance is:

[0140] (8)

[0141] The wind power generation system in the AC subgrid 60 includes a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectification circuit, a boost chopper circuit, a grid-side converter and an output filter circuit. The wind power generation system is a direct-drive wind power generation system, which adopts uncontrolled rectification, Boost and PWM inverter topology. The machine-side converter is composed of diodes, and the grid-side converter is composed of fully controlled IGBTs.

[0142] The small direct-drive wind power generation system configured on the AC bus side of the present invention adopts an uncontrolled rectification + Boost boost + PWM inverter topology, the machine side converter is composed of diodes, and the grid side converter is composed of fully controlled IGBTs, so a PWM inverter is adopted. The three-phase voltage is converted into a DC voltage by a diode, and the Boost boost link is used to control the bus voltage, thereby avoiding the problem of low bus voltage of the generator at a low speed. Compared with the back-to-back converter topology, the topology of the converter on the generator side is composed of only six uncontrolled diodes and an uncontrolled rectification converter, thereby eliminating multiple power switch tubes and their driving circuits, greatly simplifying the design difficulty of the converter and improving the reliability of the system. Since this type of converter topology has only one controllable power switch tube, the maximum power tracking strategy and power factor correction of the fan can be realized by controlling this switch tube, and the control on the generator side does not need to adopt a vector control strategy, thereby greatly simplifying the modulation algorithm of the machine side converter.

[0143] Fig.10 It is the hardware composition of the wind power generation system in the embodiment of the present invention.

[0144] like Fig.10 As shown in Figure 1, the wind power generation system consists of a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectifier circuit, a boost chopper circuit, a grid-side converter, and an output filter circuit. The function of the wind turbine is to convert the captured wind energy into mechanical energy. Its power and torque can be expressed as:

[0145] (9)

[0146] In formula (9), P w is the mechanical power output of the wind turbine (W), T w is the mechanical torque, ρ is the air density (kg / m 3 ), C p (λ, β) is the wind turbine utilization factor, which is a nonlinear function of the tip speed ratio λ (λ = ωR / V) and the blade pitch angle β. When the pitch angle is constant, there is a λ that makes C p The value is the largest, the output power is the largest, which is called the optimal tip speed ratio; R is the radius of the fan blade (m); V w is the tip wind speed (m / s); ω is the mechanical angular velocity of the generator.

[0147] The stator voltage and flux equations of the permanent magnet synchronous generator are both nonlinear differential equations. In order to simplify the equations and facilitate analysis and calculation, the analysis is carried out in a rotating coordinate system (dq coordinate system), see formula (10).

[0148] (10)

[0149] In formula (10), V d 、V q is the dq-axis component of the stator voltage; R s is the stator resistance; i d 、i q is the dq axis component of the stator current; L d , L q is the dq axis component of inductance; Ψ d ,Ψ q is the magnetic flux of dq axis; ω e is the synchronous electrical angular velocity, n p is the number of permanent magnet generator pole pairs, ω m is the mechanical angular velocity of the synchronous motor rotor; pm is the magnetic flux of the rotor permanent magnet.

[0150] It can be seen from formula (10) that when the demagnetization effect is not considered, the pole pair number and the permanent magnet flux are both constants. If the stator d-axis current is set to 0, the generator electromagnetic torque is only proportional to the stator q-axis current. Therefore, the electromagnetic torque of the permanent magnet generator can be controlled by controlling the stator q-axis current, and then the generator speed can be controlled to enable the system to achieve maximum power output or limited power output. These functions are achieved by the generator side converter control strategy.

[0151] Machine-side busbar capacitor and LC filter parameter design:

[0152] Machine side converter capacitor C dc The main function of the capacitor is to stabilize the DC bus voltage. It is necessary to reasonably select the capacitor C dc The size of the DC side voltage ripple is limited to a certain range to ensure the quality of the output power. If the DC side capacitor voltage fluctuation is required to not exceed 5%, the rated capacity of the wind turbine is 50kW, and the capacitor value must satisfy equation (11):

[0153] (11)

[0154] The essence of the grid-side converter is a three-phase full-bridge DC / AC inverter, whose main function is to achieve grid-connected output of active power and reactive power of the wind turbine by controlling the converter. However, the output voltage of the DC side after being inverted by the DC / AC converter contains a large number of high-order harmonics, which need to be filtered to output a more ideal sine wave. Because the LCL filter will introduce a resonant peak and the control strategy is relatively complex, the present invention adopts a relatively simple LC filtering method to filter out high-order harmonics so that the output voltage and current are approximately sine waves.

[0155] In order to meet the current instantaneous tracking performance, the inductor L should satisfy formula (12):

[0156] (12)

[0157] For voltage-source inverters, the designed inductor L should meet the DC / AC converter output active power and reactive power indicators. Under unity power factor, it should satisfy formula (13):

[0158] (13)

[0159] In addition, the inductor L parameter also needs to consider the maximum ripple index of the inductor current and should satisfy formula (14):

[0160] (14)

[0161] Where P is the converter capacity, Δi max It is the maximum pulsation of the inductor current, which is generally 5% of the maximum current.

[0162] Resonance frequency f c Formula (15) should be satisfied:

[0163] (15)

[0164] In the formula, f s is the PWM carrier signal frequency, which is 8kHz; f n is the voltage fundamental frequency; L, C are the filter inductance and capacitance values ​​respectively.

[0165] The grid-side converter capacity is designed to be 50kW. Substituting various parameters, it is calculated that the inductance value range is: 2.74mH≦L≦6.22mH, taking L=5mH. By formula (15), it is calculated that: 7.92μF≦C≦20.28μF, taking C=15μF.

[0166] The bidirectional AC / DC converter 30 includes a voltage-type DC energy storage element and a current-type DC energy storage element, and adopts a three-phase voltage source bridge topology structure.

[0167] The essence of the interconnected converter is a bidirectional AC / DC converter, which is a key component for energy exchange between the DC subnet 50 and the AC subnet 60. The bidirectional AC / DC converter can be divided into two types: voltage type and current type according to the properties of the DC energy storage element. When the interconnected converter adopts the voltage source type, the current injected into the AC subnet 60 contains not only the fundamental component but also the harmonics of the switching frequency and its multiples. The effect of the traditional L-type filter is not ideal. In the present invention, we adopt the more conventional LC filtering.

[0168] Fig.11 It is the hardware composition of the bidirectional AC / DC converter in the embodiment of the present invention.

[0169] like Fig.11 As shown in FIG. 1 , the interconnected converter in the present invention adopts a three-phase voltage source bridge topology. dc is the DC bus voltage, i dc is the DC side current, C dc is the DC side filter capacitor, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 IGBT turn-on and turn-off signals, U a , U b , U c are the three-phase voltages on the AC side of the converter, i La 、i Lb 、i Lc are the three-phase currents on the AC side of the converter, U oa , U ob , U oc They are the three-phase voltages on the AC side, and R, L, and C are the filtering devices on the AC side of the interconnected converter.

[0170] In the converter, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 The switching function is defined as expression (16):

[0171] (16)

[0172] According to Kirchhoff's law, the dynamic equation of the AC side voltage is expressed as equation (17):

[0173] (17)

[0174] Equation (17) shows the relationship between various parameters, but the voltage and current on the AC side are time-varying variables, which are not conducive to calculation. Therefore, the three-phase sinusoidal components are converted into DC components. The three-phase stationary coordinate system can be converted into a two-phase synchronous rotating dq coordinate system through the three-dimensional transformation method. After Clark and Park transformation, the mathematical model (18) can be obtained:

[0175] (18)

[0176] It can be seen from equation (18) that in the two-phase synchronous rotating dq coordinate system, there are coupling components between the d-axis and q-axis components, and decoupling control is required subsequently.

[0177] The harmonic processing unit is responsible for processing various harmonics from the photovoltaic system, energy storage system, wind power generation system and the chicken farm’s own nonlinear load.

[0178] Generally speaking, there are many sources of harmonics generated in AC / DC hybrid distribution networks. In the AC / DC microgrid designed by the present invention, the sources of harmonics specifically include photovoltaic and energy storage systems, wind power generation systems, and nonlinear loads in chicken farms.

[0179] Photovoltaic and energy storage systems: The output of photovoltaic power generation systems and energy storage systems is direct current. When generating electricity and connecting to the grid, energy transfer and conversion are required. In this process, rectifiers and inverters are used. The devices contain a large number of power electronic devices. Nonlinear power electronic devices are applied to sinusoidal voltage and are the main source of harmonics.

[0180] Wind power generation system: Similar to photovoltaic power generation system, harmonic problem is also a key factor affecting the power quality of wind power generation equipment. In addition to the harmonics generated by AC / DC and DC / AC equipment in the wind power system, which will affect the stability of the power grid, the randomness of the output side of the wind turbine will also have an overlapping effect on the stability of the microgrid. In the wind power generation system, there are no third and even harmonics. The main harmonics in the wind power generation system are 5th, 7th, 11th, 13th and 17th. In addition, the rotating magnetic field of the wind turbine is generated by the rotor current. This rotating magnetic field causes electromagnetic induction on the stator side and generates induced current. The harmonic current is the same principle. When there is a harmonic current in the rotor voltage, a harmonic current will be induced on the stator side, and the AC excitation system of the generator will generate a large number of harmonics, which will flow into the large power grid after being amplified on the stator side. This is also the main source of harmonics in the wind power system.

[0181] Non-linear loads in chicken farms: The loads of the electrical system of egg-laying chicken farms are usually non-linear resistive and inductive loads (such as various motors), LED lighting fixtures, inverters, etc. The relationship between the voltage across these devices and the current passing through them is usually non-linear, which means that during the switching and operation of the equipment, the resistance will change and generate harmonics. In particular, the ventilators centrally arranged in each egg-laying chicken house are numerous and have high power, and are the main source of harmonics on the load side of a single three-dimensional egg-laying chicken house.

[0182] In summary, the various distributed power sources in the AC / DC hybrid microgrid of the laying hen farm are connected to the hybrid microgrid through power electronic devices. The harmonics generated by different converters have different spectrum characteristics, and there are a large number of nonlinear loads on the load side. Therefore, in addition to the characteristics of harmonics in ordinary power grids, the harmonics in the AC / DC hybrid microgrid of the laying hen farm also have their own unique characteristics:

[0183] A. Rich harmonic frequencies. When various DG (Distributed Generation) are connected to the AC bus of the microgrid, the frequency of the switch tube IGBT in the present invention is generally 8KHz to 20KHz, and the harmonic components generated are high-order harmonics. When multiple units are connected in parallel, higher-frequency harmonics will be generated due to the interaction of harmonics. Therefore, the harmonics of the AC / DC hybrid microgrid have a wider frequency band.

[0184] B. The harmonic suppression method is complex. Because the harmonics of the microgrid have a very high bandwidth, this determines that the use of a single PPF (Passive Power Filter) or a single APF (Active Power Filter) to suppress harmonics will have great limitations.

[0185] C. Resonance problems are prone to occur. Generally, multiple DGs are connected to the grid in parallel. As the number of parallel DGs increases, the system's external output impedance increases accordingly. This causes the system's resonant frequency to continuously move toward high frequencies, causing resonance near high frequencies, amplifying the higher harmonics of the AC bus and exacerbating the waveform distortion of the AC bus.

[0186] The commonly used filter structures on the market are mainly divided into two categories: passive filters and active filters. Passive filters have incomparable advantages in eliminating given harmonics. However, in the AC / DC hybrid microgrid established by the present invention, the harmonic sources of the system are variable, the harmonic content is rich, and the number of the dominant harmonics of the system during operation changes dynamically, so a simple passive filter is not suitable for suppressing harmonics in an AC / DC hybrid microgrid. According to the above summary of the harmonic characteristics in the AC / DC hybrid microgrid, the harmonics in the AC / DC hybrid microgrid include both current-type harmonics and voltage-type harmonics, but the dominant harmonics are still current-type harmonics. Therefore, the use of a series structure cannot completely eliminate the harmonics on the AC bus, and the parallel filter is equivalent to a harmonic current source, which mainly injects current into the AC bus, quickly tracks the harmonic current of the AC bus and compensates for it, and is suitable for eliminating current-type harmonics.

[0187] Combining the above filter structures and the characteristics of harmonics in the AC / DC hybrid microgrid in laying hen farms.

[0188] Fig.12 It is the hardware composition of the APF unit in the embodiment of the present invention.

[0189] like Fig.12 As shown, the present invention adopts a parallel APF and is applied to harmonic suppression of an AC / DC hybrid microgrid.

[0190] The working principle of the parallel APF is: first, a suitable harmonic current detection algorithm is adopted, and its output obtains the harmonic current value in the system. At this time, the APF can be regarded as a special inverter structure. The inverter outputs a compensation current with the same magnitude and opposite phase as the load harmonic current. Finally, the switch tube sends the compensation current signal to the power grid. The compensation current and the harmonic components in the load current offset each other. In this way, the current at the common confluence point of the power grid no longer contains harmonic components, thereby achieving harmonic suppression.

[0191] The present invention adopts a three-phase three-wire parallel harmonic suppression system, which can not only suppress harmonic current, but also perform reactive power compensation and balance the three-phase current. The structure of the main circuit is shown in Figure 11, where e a 、e b 、e c and i a 、i b 、i care the grid side voltage and current respectively; i la 、i lb 、i lc and i ca 、i cb 、i cc They are the current and harmonic compensation current of the nonlinear electrical device of the laying hen house; S1~S6 are fully controlled switches; L, C0 and C represent the output inductance and capacitance of the AC side and the energy storage capacitor of the DC side respectively; V dc Indicates the voltage across capacitor C; U a , U b , U c is the three-phase voltage of abc; 0 point is the zero voltage reference point, and the voltage reference point voltage is U N To facilitate the analysis, the switching loss of the power device and the influence of the dead time are ignored. The switching function S k as follows:

[0192]

[0193] According to the parallel APF topology diagram and KCL, KVL, the APF three-phase circuit equation is:

[0194]

[0195] Where: u ck =S k U dc +u n , k = a, b, c. In a three-phase three-wire system, the voltage and current satisfy the vector sum of zero. The simultaneous equation (23) yields:

[0196]

[0197] Substituting equation (24) into equation (23), we can get the state equation of APF as follows:

[0198]

[0199] Parameter design:

[0200] Fig.13 It is the whole field harmonic current evaluation of the laying hen farm in the embodiment of the present invention;

[0201] As mentioned above Figure 2 As shown, the transformer capacity used in the entire laying hen farm is 3000KVA. Substitute Fig.12 In the formula shown, the maximum allowable value of the total harmonic current of the entire laying hen farm is 563.4 A. For a single three-dimensional laying hen house, the maximum allowable value of the total harmonic current is <31.3A, so in the subsequent calculations, the value is taken as 30A as the basis for calculating the main capacity, inductance and capacitance of the APF.

[0202] Due to the high switching frequency of the APF, the actual value of the inductor is very small. In order to make the inverter voltage approximately equal to the power supply voltage U s , and considering a certain margin, the voltage V dc Adjust to 10% higher than the maximum input voltage of the inverter, the DC bus voltage V dc The expression is as follows:

[0203]

[0204] Through the analysis of the mathematical model of APF, it can be seen that when APF is working normally, if the DC side voltage V dc The larger the value, the greater the rate of change of the compensation current, and the faster the current tracking compensation speed; however, V dc Setting it too large will make the system less stable and put higher requirements on the voltage withstand level of the switching devices, resulting in increased system costs. dc When selecting, it is necessary to consider both the tracking compensation speed of the system and the stability and cost of the system. dc The value of is 700V. The value of the DC side capacitor can be expressed as:

[0205] In the present invention, the DC side capacitance is 2200 μF.

[0206] The selection of the AC side inductor needs to take into account the harmonic compensation effect and the current ripple size. The smaller the inductance L, the faster the tracking compensation speed, but the current ripple is larger; the larger the L value, the smaller the output current ripple, but it will affect the tracking compensation speed. The general inductance can be estimated by the empirical formula (28):

[0207]

[0208] Among them, Δi max is the maximum allowable error between the APF command current and the actual output current, which is set to 10A in the present invention. The system sampling period T s =80μs, leaving a certain margin, the final value of the inductor is selected as 4mH.

[0209] The coordinated control strategy of the AC / DC hybrid microgrid 100 of the three-dimensional cage chicken house mainly includes energy management strategy, photovoltaic power generation system control strategy, wind power generation system control strategy, energy storage system control strategy, bidirectional AC / DC converter 30 on-grid and off-grid control strategy and harmonic processing unit control strategy.

[0210] The overall logic of AC / DC hybrid microgrid energy management:

[0211] Table 4 AC / DC hybrid system mode switching table - grid-connected mode

[0212]

[0213]

[0214] Table 4 is the switching table of the AC / DC hybrid system mode and the grid-connected mode.

[0215] As shown in Table 4, when the microgrid is in the grid-connected state, the AC / DC bidirectional converter is in the PQ control mode, the frequency and voltage of the AC subgrid 60 are supported by the large power grid, the bus voltage of the DC subgrid 50 is kept stable by the energy storage system, the PV system and the WT system are the power generation sources, and the AC load and the DC load are the power consumption terminals. The specific working modes are described as follows:

[0216] Mode 1 & 2: When there is surplus energy on the DC subgrid 50 side, there is surplus energy on the AC subgrid 60 side, and the amount of energy storage system is within the appropriate range, if the electricity price of the electricity generated by the new energy to the external grid is high at this time, the AC / DC bidirectional converter will be in the inverter state, guiding the excess electricity in the DC subgrid 50 to flow to the large power grid to obtain better economic returns. The energy storage system does not charge or discharge. If the price of the electricity generated by the new energy is low at this time, the AC / DC bidirectional converter will be in the rectification state, guiding the excess electricity in the AC subgrid 60 to move to the DC subgrid 50 side and charge the energy storage system to ensure energy reserve.

[0217] Mode 3, 4, and 5: When the amount of renewable energy power generation in the AC / DC subgrid is far less than the respective load consumption, and the energy storage system has a large amount of power, when the price of purchasing electricity from the external grid is high, the energy storage system will be responsible for the energy gap of the AC and DC loads, and the system will not purchase electricity from the large grid to save costs. When the price of purchasing electricity from the external grid is low, the energy storage system will only be responsible for the energy gap on the DC subgrid 50 side, and the large grid will be responsible for the energy gap on the AC subgrid 60 side. When the power in the energy storage system is low, the energy storage system will shut down, and the large grid will be responsible for all the energy gaps in the AC and DC subgrids 50.

[0218] Mode 6: When the WT power generation in the AC subgrid 60 is less than the AC load consumption, the PV system power generation in the DC subgrid 50 is greater than the DC load, the excess energy in the DC subgrid 50 is greater than the energy gap in the AC subgrid 60, and the energy storage system has sufficient power, if the price of electricity sold to the external grid is low, the AC / DC bidirectional converter will be in a shutdown state, forcing the excess energy on the DC side to be charged into the energy storage system, and the power gap of the AC subgrid 60 will be supplemented by the external grid.

[0219] Mode 7: When the WT power generation in the AC subgrid 60 is less than the AC load consumption, the PV system power generation in the DC subgrid 50 is greater than the DC load, the excess energy in the DC subgrid 50 is less than the energy gap in the AC subgrid 60, and the energy storage system has sufficient power, the energy storage system shuts down. The AC / DC bidirectional converter guides the excess power of the DC subgrid 50 to flow to the AC subgrid 60, and the insufficient power on the AC side is supplemented by the large power grid.

[0220] Mode 8 & 9: When the WT power generation in the AC subgrid 60 is greater than the AC load consumption, the PV system power generation in the DC subgrid 50 is less than the DC load, the excess energy in the AC subgrid 60 is greater than the energy gap in the DC subgrid 50 and the energy storage system has sufficient power, when the price of purchasing electricity from the external grid is high, the power gap of the DC subgrid 50 will be provided by the energy storage system. The excess power of the AC subgrid 60 flows into the large power grid in exchange for economic benefits. When the power of the energy storage system is not enough to make up for the power gap in the DC subgrid 50, the excess power in the AC subgrid 60 is rectified by the AC / DC bidirectional converter and enters the DC subgrid 50.

[0221] Table 5 AC / DC hybrid system mode switching table - off-grid mode

[0222]

[0223]

[0224] Table 5 is the switching table of the off-grid mode of the AC / DC hybrid system mode.

[0225] As shown in Table 5, when the microgrid is off-grid, the AC / DC bidirectional converter is in V / f control mode, the frequency and voltage of the AC subgrid 60 are supported by the AC / DC bidirectional converter, the bus voltage of the DC subgrid 50 is still kept stable by the energy storage system, the PV system and the WT system are the power generation sources, and the AC load and the DC load are the power consumption terminals. The specific working modes are described as follows:

[0226] Mode 1&2: When there is surplus energy on both the AC and DC subgrid 50 sides, and the energy storage system is fully charged, the WT and PV systems will be adjusted to the power tracking generation LPTC mode. At this time, the energy storage system will neither charge nor discharge, and each subgrid will maintain energy balance. When the energy storage system is within the range allowed for charging, in order to make full use of renewable energy generation, the system will control the WT and PV systems to operate at full power in MPPT mode, and the energy storage system will be in charging mode to absorb excess electricity, and each subgrid will maintain energy balance.

[0227] Mode 3 & 4: When there is a gap in energy on both the AC and DC subgrids 50, and the energy storage system has a large amount of power, the energy missing from the system will be compensated by the energy storage system to ensure the operation of the AC load and part of the DC load. When the energy storage system has little power, the system will only retain the more important part of the AC load and cut off all DC loads and non-critical AC loads.

[0228] Mode 5&6: When there is surplus energy on the DC subgrid 50 side, but there is a shortage of energy on the AC subgrid 60 side, and the surplus energy on the DC side is greater than the missing energy on the AC side, according to the principle of energy balance, part of the surplus energy on the DC side will flow to the AC side to make up for its energy gap, and the remaining part will flow into the energy storage system for charging. When the energy storage system is fully charged, the system will control the PV system to operate in LPTC mode.

[0229] Mode 7 & 8: When there is surplus energy on the DC subgrid 50 side and a shortage of energy on the AC subgrid 60 side, but the surplus energy on the DC side is less than the missing energy on the AC side, the energy storage system will make up for the shortage when the energy storage system is fully charged. When the energy storage system is low in power, non-critical loads on the AC subgrid 60 side must be cut off.

[0230] Mode 9: When there is surplus energy on the AC subgrid 60 side and a shortage of energy on the DC subgrid 50 side, and the excess energy on the AC side is greater than the missing energy on the DC side, when the energy storage system is fully charged, the system will control the WT system to operate in LPTC mode.

[0231] Mode 10&11: When there is surplus energy on the AC subgrid 60 side and a shortage of energy on the DC subgrid 50 side, and the surplus energy on the AC side is less than the missing energy on the DC side, when the energy storage system is fully charged, the energy still missing on the DC side is supplemented by the energy storage system. When the energy storage system is low in power, the energy storage system shuts down, and the DC side cuts off non-critical loads to ensure system energy balance.

[0232] Photovoltaic power generation system control strategy:

[0233] Fig.14 is a photovoltaic system control strategy in an embodiment of the present invention;

[0234] like Fig.14 As shown, the photovoltaic power generation system has three modes: MPPT, shutdown and power limiting operation.

[0235] In actual laying hen farms, photovoltaic arrays laid over large areas of rooftops will inevitably be obscured by shadows from various surrounding objects, such as clouds in the sky, material towers, office buildings, etc. This will cause a multi-peak phenomenon in the output power of the photovoltaic array. The number of peaks is closely related to the type of shadow obstruction. The most commonly used maximum power point tracking method at this stage will no longer be applicable.

[0236] P&O (Perturbation & Observation Method) is currently the most widely used maximum power tracking algorithm, but it is easy to fall into a local optimal state in a complex shading environment. The P&O algorithm first calculates the power by measuring the voltage and current of the photovoltaic array, tracks the peak power according to the perturbation point, and then observes the change in power before and after the perturbation. However, when the output power of the photovoltaic array presents multiple peaks, finding the global maximum power point of the photovoltaic array under multiple peaks becomes a nonlinear optimization problem. Therefore, many intelligent algorithms are applied to the maximum power point tracking of photovoltaic systems. The gray wolf optimization algorithm is a biologically inspired algorithm. It is a new group intelligent optimization algorithm that imitates the hierarchy and prey capture behavior of the gray wolf society in nature. Because the gray wolf optimization algorithm has the advantages of few system parameters, not easy to fall into the local optimal solution during the search process, and fast solution speed, it has begun to attract attention in recent years and has been applied to the maximum power point tracking of photovoltaic power generation. In the present invention, we use the gray wolf optimization + perturbation observation hybrid algorithm to realize the MPPT control of multi-peak photovoltaic arrays. In MPPT control, the wolf pack is the duty cycle. In LPTC mode, the PV array only needs to generate enough power to meet the DC load consumption. Therefore, the reference current is calculated using the difference between the actual power of the PV array and the DC load, and then the duty cycle at this power is calculated to adjust the overall power generation of the PV system.

[0237] Wind power generation system control strategy:

[0238] Fig.15 is a wind power system control strategy in an embodiment of the present invention;

[0239] like Fig.15 As shown, there are three operation modes on the machine side of the wind power generation system: MPPT, shutdown and power limiting operation.

[0240] In the present invention, the MPPT algorithm on the wind turbine side adopts a power duty cycle algorithm. First, the voltage and current on the rectifier output side are collected in real time, and the PWM switch command is obtained through the algorithm, and then the mechanical torque of the wind turbine is adjusted to make its wind energy utilization efficiency always close to the optimal, and finally the maximum power is output. When the WT system is in LPTC mode, it only needs to send out power that meets the AC load consumption. Therefore, the reference current is calculated using the difference between the actual power of the WT system and the AC load, and then the duty cycle under this power is calculated, and then the overall power generation of the WT system is adjusted.

[0241] In the vector control strategy of the grid-side converter, the present invention adopts dual closed-loop control, namely voltage outer loop and current inner loop control. The purpose to be achieved is: the voltage outer loop control keeps the DC bus voltage stable, while the current inner loop control adjusts the power factor to the target value. The control process is: first, the grid voltage and current are changed from the three-phase stationary coordinate system to the synchronous rotating coordinate system, and θ is the electrical angle of the grid voltage. Then the actual measured DC bus voltage is compared with the given bus voltage, and the difference is passed through the PI regulator to output the given value i of the d-axis current. dref , and then compare the given value with the actual d-axis current and add the feedforward compensation term to get the reference voltage U d * Similarly, for the q-axis current, the given value of the q-axis current is 0, which is different from the actual i q The value obtained by comparison passes through the PI regulator and adds the feedforward compensation term to obtain the reference voltage U q * Finally, the obtained reference voltage U d * , U q * The two-phase synchronous rotating coordinate system is transformed into a two-phase stationary coordinate system, and then the SVPWM method is used to generate a PWM waveform to control the grid-side inverter, thereby achieving the purpose of ensuring the constant DC bus voltage and adjusting the power factor on the grid side.

[0242] Energy storage system control strategy:

[0243] Fig.16 It is the energy storage system control strategy in the embodiment of the present invention.

[0244] like Fig.16 As shown, the energy storage system has three working modes: charging, discharging and shutdown mode. The energy storage system converts the charging and discharging mode of the battery through the Buck-Boost circuit. In the present invention, we set the normal working range of the SOC of the energy storage battery group 20 to 0.2-0.9. The system charging and discharging is controlled by the outer loop voltage and inner loop current. The main task is to be responsible for the voltage stability of the busbar in the DC subnet 50. The charging and discharging process is: the DC side voltage U dc With reference value U dcref The current reference value is obtained after PI adjustment and compared with the battery output current I b The difference is then made, and the output control signal is adjusted through PI. After pulse width modulation (PWM), the drive signal is obtained to control the charging and discharging of the Buck-Boost circuit.

[0245] Fig.17 This is a bidirectional AC / DC converter control strategy in an embodiment of the present invention.

[0246] like Fig.17 As shown in the figure, the PQ control mode is adopted when the interconnected converter is connected to the grid. The values ​​of active power P and reactive power Q come from the power management strategy based on time-of-use electricity price. In the grid-connected mode, the voltage / frequency of the AC bus is supported by the large power grid, and the voltage stability of the DC bus is the responsibility of the energy storage system; when off-grid, V / f control is adopted, and the voltage / frequency support is provided by the interconnected converter, and the voltage stability of the DC bus is still the responsibility of the energy storage system. The specific strategies are as follows:

[0247] A. Smooth switching strategy for on-grid and off-grid:

[0248] According to the power reference value and the grid-side voltage dq component, the current reference value can be calculated as i dref =2P ref / 3u d with i qref =-2Q ref / 3u d , where P ref , Q ref are the reference values ​​of active power and reactive power output by the interconnected converter, which are calculated by the time-of-use electricity price energy management strategy. dref and i qref are the reference values ​​of the dq axis current components output by the interconnected converter, u d 、u q They are respectively the dq axis components of the grid-side voltage. Before the interconnected converter switches between the grid and off-grid, the output of the current inner loop in the PQ control has reached a steady state. After switching to V / f control, the reference value of the current inner loop is inconsistent, which will generate an impact current and affect the system stability. In order to solve this problem, we propose a current reference value compensation control strategy for interconnected converters based on the initial value of the integral. When the switching signal = 1, the microgrid is in the grid-connected mode; when the switching signal = 0, it is in the off-grid mode. The current reference value of the PQ controller of the interconnected converter before switching is i dref1 、i qref1 , after switching, the current reference value of the V / f controller is i dref2 、i qref2 After the on-grid switching, the current reference value of the voltage outer loop output of the V / f controller needs to be gradually adjusted to a steady state, and there will be a sudden change compared to the steady-state current reference value before the switching. In order to solve this problem, the PI controller of the V / f controller is improved. In the on-grid mode, the initial value of the integral link in the PI controller of the V / f controller always follows i d , when switching to off-grid mode, i d Assign a value to the initial value of the integral so that it changes from i d Point starts to change, that is, i dref2 =idref1 、i qref2 =i qref1 , so that the output of the outer loop controller remains unchanged at the switching moment, achieving a smooth transition between on-grid and off-grid, and reducing the current impact on the microgrid and the large grid.

[0249] B. Pre-synchronization control strategy:

[0250] When the microgrid switches between on-grid and off-grid, the voltage amplitude and phase of the microgrid need to be consistent with those of the large grid. When the microgrid detects the grid-connected signal, the amplitude pre-synchronization starts to work, so that the voltage of the microgrid gradually becomes consistent with the voltage of the large grid. At the same time, the phase pre-synchronization also starts to work. Since the magnitude of the frequency determines the phase, the phases of the two can be made consistent by changing the frequency. The phase difference between the two can be compared and then PI-regulated to generate a frequency regulation signal. The regulated frequency is calculated and integrated to obtain the reference phase of the main controller. When the voltage amplitude and phase meet the grid-connected conditions, the pre-synchronization stops working and the switching signal is set to 1. Conversely, when the microgrid detects the off-grid signal from the grid-connected state, the pre-synchronization controller also needs to act accordingly. The switching process can reduce the impact current caused by the difference in phase and amplitude, so it can effectively ensure the smooth switching of the microgrid from on-grid to off-grid.

[0251] Harmonic processing unit control strategy:

[0252] Fig.18 It is the harmonic processing unit control strategy in the embodiment of the present invention.

[0253] like Fig.18 As shown, the harmonic processing unit adopts a parallel APF active power filter. Harmonic detection adopts the ip-iq detection method based on instantaneous reactive power theory, and adopts voltage outer loop + current inner loop double closed loop control to achieve harmonic suppression and reactive power compensation functions. Among them, the voltage outer loop: APF DC side voltage adopts PI control; the current inner loop: APF current regulation adopts hysteresis control.

[0254] Fig.19 and Fig. 20 It is the simulation modeling and output result of the AC / DC hybrid microgrid in the embodiment of the present invention on Matlab software.

[0255] The simulation parameters set on the simulink platform are: the total simulation time is set to 2.2s. 0.0s-0.5s system is off-grid, 0.5s-1.5s system is on-grid, 1.5s-2.0s system is off-grid, and 2.0s-2.2s system is on-grid. In the initial state, the DC load in the DC subnet is 7KW (to simulate the LED load), and the DC load suddenly increases by 50KW at 0.15s (to simulate the charging of the electric observation car); in the initial state, the critical AC load in the AC subnet is 35KW, and it increases by 80KW after 0.65s to 115KW (to simulate the change of critical AC load during operation). The non-critical AC load is 85KW and is always connected. The PV system is set to 100KW and the WT system is 50KW.

[0256] The time-of-use electricity price is set as follows:

[0257] Time period: [0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.51.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4]

[0258] Electricity price: [0.2 0.3 0.3 0.4 0.6 0.3 0.4 0.5 0.55 0.58 0.8 0.8 0.7 0.7 0.70.9 0.9 0.95 0.5 0.5 0.2 0.2 0.2 0.2 0.2]

[0259] The meaning is: during the period of 0.6s-0.7s, the electricity price is 0.4 yuan. The same applies to other periods. In the simulink model, the action threshold of the electricity price is set to 0.4 yuan.

[0260] The simulation results are as follows Fig. 20 As shown: No. 1 is the output power of the PV system, No. 2 is the power of the energy storage system, No. 3 is the power of the DC load in the DC subnet, No. 4 is the power of the AC load in the AC subnet, and No. 5 is the power output of the WT system.

[0261] At 0.13s, the system is off-grid. The PV system output is 96.52KW, the DC load in the DC subnet is 7.07KW, and the DC subnet has 89.45KW of remaining energy; the AC load in the AC subnet is 34.96KW, the WT system generates 28.83KW of energy, and the AC subnet has a deficit of 6.13KW. At this time, the system is off-grid and will operate according to Mode 5 in Table 5, that is, the AC / DC bidirectional converter will pass 6.13KW of energy in an inverting manner, and the excess 83.3KW of energy will be stored in the energy storage system in a charging manner.

[0262] At 0.58s, the system is in grid-connected state. The PV system output is 97.08KW, the DC load in the DC subnet is 56.70KW, and the DC subnet has 40.38KW of remaining energy; the AC load in the AC subnet is 34.98KW, the WT system generates 28.82KW of energy, and the AC subnet has a deficit of 6.15KW of energy. At this time, the system is in grid-connected state and the current electricity price is 0.3 yuan. The system will operate according to mode 6 in Table 4, that is, no energy will flow through the AC / DC bidirectional converter, and the remaining 40.38KW of energy will be stored in the energy storage system in the form of charging. The 6.15KW of energy deficit on the AC side is supplemented by the external power grid.

[0263] At 0.62s, the system is still connected to the grid. The conditions of PV, WT, AC and DC loads are similar to those at 0.58s, but the electricity price becomes 0.4 yuan, reaching the threshold for energy sale. Therefore, the system will operate according to Mode 1 in Table 4, that is, the AC / DC bidirectional converter will pass all the 40.38KW of surplus energy in an inverter mode, and the energy storage system will neither charge nor discharge. After the 40.38KW of surplus energy supplements the 6.15KW of energy owed on the AC side, the excess 34.23KW of energy will be sold to the external grid in exchange for revenue.

[0264] At 1.2s, the system is still in the grid-connected state. The PV system output is 96.68KW, the DC load in the DC subnet is 56.92KW, and the DC subnet has 39.76KW of remaining energy; at this time, the AC load in the AC subnet becomes 115.08KW, the WT system generates 28.95KW of energy, and the AC subnet has a deficit of 86.13KW. At this time, the system is in the grid-connected state and the current electricity price is 0.7 yuan. The system will operate according to Mode 3 in Table 4, that is, the AC / DC bidirectional converter will flow all the 39.76KW of remaining energy in an inverting manner, and the energy storage system needs to supplement 46.37KW of energy through discharge.

[0265] At 1.8s, the system is off-grid. The PV system output is 97.82KW, the DC load in the DC subnet is 57.02KW, and the DC subnet has 40.8KW of remaining energy; the AC load in the AC subnet is 115.02KW, the WT system generates 28.85KW of energy, and the AC subnet has a deficit of 86.17KW. The system will operate according to mode 7 in Table 5, that is, the AC / DC bidirectional converter will invert all the 40.8KW of remaining energy, and the energy storage system needs to supplement 45.37KW of energy by discharging.

[0266] At 2.1s, the system is in grid-connected state. The PV system output is 96.88KW, the DC load in the DC subnet is 56.62KW, and the DC subnet has 40.26KW of remaining energy; at this time, the AC load in the AC subnet is 114.98KW, the WT system generates 28.95KW of energy, and the AC subnet has a deficit of 86.03KW of energy. At this time, the system is in grid-connected state and the current electricity price is 0.2 yuan. The system will operate according to mode 6 in Table 4, that is, no energy will flow through the AC / DC bidirectional converter, and the remaining 40.26KW of energy will be stored in the energy storage system in the form of charging. The 86.03KW of energy deficit on the AC side is supplemented by the external power grid.

[0267] Through Fig. 20 From the simulation analysis, it can be seen that for the AC / DC microgrid described in the present invention, when the load changes during actual operation, the microgrid system can smoothly and freely achieve seamless control in the processes of mode conversion, grid-connected and off-grid switching, etc. The energy flow strategy based on time-of-use electricity prices proposed in the present invention can effectively guide the rational flow of energy and achieve effective control of the wind, solar, energy storage, AC / DC microgrid, which further verifies the effectiveness of the various control strategies described in the above text of the present invention.

[0268] Functions and Effects of the Embodiments

[0269] According to the AC / DC hybrid microgrid power supply system and control method suitable for stacked three-dimensional cage chicken houses involved in the present invention, the AC / DC topological structure designed for the three-dimensional chicken house is conducive to the direct utilization of AC and DC loads in the chicken house, reducing the loss in energy conversion. At the same time, through the photovoltaic power generation system, wind power generation system and lithium battery energy storage system, the external traditional energy consumption is reduced, carbon emissions are reduced, and it is beneficial to environmental protection.

[0270] The AC / DC hybrid microgrid suitable for stacked three-dimensional cage chicken houses involved in the present invention is designed with a smooth on-grid and off-grid switching strategy, ensuring that the voltage and frequency on the AC and DC sides of the three-dimensional chicken house always meet the standards and remain stable during the on-grid-off-grid switching during power outages and the off-grid-on-grid switching during power restoration.

[0271] The AC / DC hybrid microgrid suitable for stacked three-dimensional cage chicken houses involved in the present invention is designed to ensure the local consumption of renewable energy, and an energy management strategy based on automatic control of time-of-use electricity prices is designed, which promotes the self-generation and self-use of clean energy power generation in a single chicken house and the access to the grid of surplus electricity.

[0272] The AC / DC hybrid microgrid applicable to the stacked three-dimensional cage chicken house involved in the present invention takes into account the harmonic conditions of a single three-dimensional chicken house, and the microgrid system is designed with a harmonic control function based on active filtering.

[0273] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses, characterized in that: include: The electrical load of the three-dimensional chicken house includes an AC electrical load and a DC electrical load. The AC electrical load is divided into a critical AC load and a non-critical AC load. The DC electrical load is divided into a critical DC load and a non-critical DC load. The non-critical AC load is arranged outside the AC subnet and separated by a switch, so that when there is a power outage or other fault in the external power grid of the system, the system can directly cut off the connection with the non-critical AC load through the switch, and only retain the critical load, thereby ensuring the power supply demand in a single three-dimensional chicken house; The photovoltaic power generation system in the DC subnet includes a photovoltaic array and a Boost circuit that takes into account a shadow-shielding power optimization algorithm, and the photovoltaic power generation system in the DC subnet is connected to the DC bus through the Boost circuit; The lithium battery energy storage system in the DC subgrid includes a lithium battery pack and a bidirectional buck-boost circuit, wherein the bidirectional buck-boost circuit is a combination of a Boost circuit and a Buck circuit, wherein the circuit is in a discharging state when working in the Boost mode, and energy flows from the low-voltage side to the high-voltage side; and the circuit is in a charging state when working in the Buck mode, and energy flows from the high-voltage side to the low-voltage side; The wind power generation system in the AC subgrid includes a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectifier circuit, a boost chopper circuit, a grid-side converter and an output filter circuit. The wind power generation system is a direct-drive wind power generation system, which adopts uncontrolled rectifier, Boost boost and PWM inverter topology. The machine-side converter is composed of diodes, and the grid-side converter is composed of fully controlled IGBTs. The bidirectional AC / DC converter is responsible for the energy exchange between the DC subnet and the AC subnet. It adopts a three-phase voltage source bridge topology and an LC filter on the output side. The harmonic processing unit is responsible for processing various harmonics from the photovoltaic system, energy storage system, wind power generation system and the nonlinear load of the chicken farm itself. The harmonic processing unit adopts a parallel APF active power filter; The energy management unit is responsible for overall coordination of energy flows between various subsystems; Among them, the photovoltaic power generation system, energy storage system, and all DC loads constitute the DC subgrid, and the wind power generation system and key AC loads constitute the AC subgrid.

2. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1 is characterized in that: in, The three-dimensional chicken house is a three-dimensional breeding house containing multiple rows of stacked chicken cages. The three-dimensional chicken house is 108.9 meters long, 21.2 meters wide, and 11.6 meters high, with 6 rows of 10-layer cages built in. The total electrical load of a single three-dimensional laying hen house is 203.55kW, of which the critical load is 112.8kW and the non-critical load is 90.75kW. From engineering experience, it is known that the required coefficient for the operation of farm equipment is 0.65, then the normal load demand of a single three-dimensional chicken house is 132.3kW, and considering 150kW, the rated output power of the photovoltaic system is 100kWp, and the rated output power of wind power generation is 50kW; the electrical load in the three-dimensional chicken house is divided into AC side load and DC side load, and the AC side load includes single-phase or three-phase The DC side load includes an LED lighting system and an electric observation vehicle in the house. The lithium battery pack uses a lithium iron phosphate battery cell with a minimum unit of 3.2V and 37Ah. Each battery module of the lithium battery pack is formed by 10 batteries connected in series. The parameters of a single module are 32V, 37Ah, and 1.184kWh. 13 battery modules are connected in series to form a battery pack. The lithium battery energy storage system includes three working modes: charging, discharging and shutdown mode. The lithium battery energy storage system converts the charging and discharging mode of the battery through a Buck-Boost circuit. The normal working range of the SOC of the battery module is 0.2-0.

9. The charging and discharging process is as follows: the DC side voltage U dc With reference value U dcref The current reference value is obtained after PI adjustment and compared with the battery output current I b The difference is then adjusted by PI to output the control signal, and the driving signal is obtained through pulse width modulation to control the charging and discharging of the Buck-Boost circuit; the grid-side converter of the wind power generation system adopts a vector control strategy of double closed-loop control, and the control process is as follows: first, the grid voltage and current are changed from the three-phase stationary coordinate system to the synchronous rotating coordinate system, and θ is the electrical angle of the grid voltage; then the DC bus voltage actually measured is compared with the given bus voltage, and the difference is obtained after the PI regulator outputs the given value i of the d-axis current dref , and then compare the given value with the actual d-axis current and add the feedforward compensation term to get the reference voltage U d * Similarly, for the q-axis current, the given value of the q-axis current is 0, which is different from the actual i q The value obtained by comparison passes through the PI regulator and adds the feedforward compensation term to obtain the reference voltage U q * ; Finally, the obtained reference voltage U d * , U q * The two-phase synchronous rotating coordinate system is transformed into a two-phase stationary coordinate system, and then the SVPWM method is used to generate a PWM waveform to control the grid-side inverter.

3. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1 is characterized in that: in, The output of the photovoltaic power generation system and the lithium battery energy storage system is direct current, and energy is transferred and converted through rectification and inversion devices. In engineering, a combination of photovoltaic cells connected in series or in parallel is called a photovoltaic array. In the photovoltaic array, a single photovoltaic cell generates electricity by absorbing light and generating current based on the photovoltaic principle. Among the existing photovoltaic cell models, the single diode model is the most commonly used mathematical model, which can accurately fit the battery output characteristics. Its mathematical model is shown in formula (1): (1) In formula (1), I ph is the photocurrent, I0 is the reverse saturation current inside the diode, which is not affected by the light intensity, V pv is the output voltage of the photovoltaic cell, R se is the equivalent series resistance, R sh is the equivalent parallel resistance, Q = 1.6 × 10 -19 is the charge, K = 1.38 × 10 -18 J / K is the Boltzmann constant, A is the diode quality factor, T is the absolute temperature, The engineering model of photovoltaic cells is shown in formula (2): (2) Among them, the expressions of coefficients C1 and C2 are: (3) (4) Using the standard parameter I SC , U OC ,I m and U m Substitute into the modified equation to obtain I under non-standard conditions SC ’ , U OC ’ ,I m ’ and U m ’ , the correction equation is shown in formula (5): (5) In formula (5), ΔS is the light intensity difference, that is, ΔS = (S / S ref )-1, ΔT is the temperature difference, that is, ΔT=TT ref , a, b and c are correction compensation coefficients, the values ​​are a = 0.0025 / ℃, b = 0.5 / (W / m 2 ), c = 0.00288 / °C, e is the base of the natural logarithm.

4. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1 is characterized in that: in, The bidirectional DC / DC converter parameter design is as follows: The bidirectional DC / DC converter combines the Boost circuit and the Buck circuit together. It is a power electronic conversion device in which energy can flow in both directions. Udc represents the high voltage side and Ub represents the low voltage side. When the circuit works in the Boost mode, VT1 is the main control switch. By controlling the duty cycle of VT1, energy flows from the low voltage side to the high voltage side (discharge state); when the circuit works in the Buck mode, VT2 is the main control switch. By controlling the duty cycle of VT2, energy flows from the high voltage side to the low voltage side (charge state). The selection of inductance parameters in bidirectional DC / DC converters is relatively important, which determines the size of current ripple and the dynamic response speed of the system. When the inductance parameter value is large, the current ripple is small, but the system response speed is relatively slow; when the inductance value is small, the current ripple coefficient is large, but the system response speed is fast. The voltage on the high-voltage side of the energy storage system is DC750V, and the voltage on the low-voltage side is DC416V. The switching frequency is set to f=20000Hz, the output voltage ripple ≦1%, and the input current ripple ≦5%. Then the voltage ripple ΔU≦750×1%=7.5V, and the current ripple ΔI≦111×5%=5.55A, The formula for calculating inductance is: (8) 5. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1 is characterized in that in, The wind power generation system is composed of a wind turbine, a permanent magnet synchronous generator, an uncontrolled rectifier, a boost chopper, a grid-side converter, and an output filter. The function of the wind turbine is to convert the captured wind energy into mechanical energy. Its power and torque can be expressed as: (9) In formula (9), P w is the mechanical power output of the wind turbine (W), T w is the mechanical torque, ρ is the air density (kg / m 3 ), C p (λ, β) is the wind turbine utilization coefficient, which is a nonlinear function of the tip speed ratio λ (λ = ωR / V) and the blade pitch angle β. When the pitch angle is constant, there is a λ that makes C p The value is the largest, the output power is the largest, which is called the optimal tip speed ratio; R is the radius of the fan blade (m); V w is the tip wind speed (m / s); ω is the mechanical angular velocity of the generator, The stator voltage and flux equations of the permanent magnet synchronous generator are both nonlinear differential equations. In order to simplify the equations and facilitate analysis and calculation, the analysis is carried out in a rotating coordinate system (dq coordinate system), see formula (10), (10) In formula (10), V d 、V q is the dq-axis component of the stator voltage; R s is the stator resistance; i d 、i q is the dq axis component of the stator current; L d , L q is the dq axis component of inductance; Ψ d ,Ψ q is the magnetic flux of dq axis; ω e is the synchronous electrical angular velocity, n p is the number of permanent magnet generator pole pairs, ω m is the mechanical angular velocity of the synchronous motor rotor; pm is the rotor permanent magnet flux, It can be seen from formula (10) that the electromagnetic torque of the permanent magnet generator is controlled by controlling the stator q-axis current, and then the generator speed is controlled so that the system can achieve maximum power output or limited power output. These functions are realized by the generator side converter control strategy.

6. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1, characterized in that: in, The capacitance value of the DC side of the bidirectional AC / DC converter is 6.0mF, so as to avoid the voltage returning to a stable value slowed down due to excessive capacitance. The interconnected converter adopts a three-phase voltage source bridge topology structure. dc is the DC bus voltage, i dc is the DC side current, C dc is the DC side filter capacitor, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 IGBT turn-on and turn-off signals, U a , U b , U c are the three-phase voltages on the AC side of the converter, i La 、i Lb 、i Lc are the three-phase currents on the AC side of the converter, U oa , U ob , U oc are the three-phase voltages on the AC side, R, L, and C are the AC side filtering devices of the interconnected converter, In the converter, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 The switching function is defined as expression (16): (16) According to Kirchhoff's law, the dynamic equation of the AC side voltage is expressed as equation (17): (17) Equation (17) shows the relationship between the parameters. The three-phase sinusoidal components are converted into DC components. The three-phase stationary coordinate system can be converted into a two-phase synchronous rotating dq coordinate system through the three-dimensional transformation method. After Clark and Park transformation, the mathematical model (18) can be obtained: (18) It can be seen from equation (18) that in the two-phase synchronous rotating dq coordinate system, there are coupling components between the d-axis and q-axis components, and decoupling control is required subsequently.

7. The AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 1, characterized in that: in, The method for evaluating the harmonic current of the entire laying hen farm is as follows: the transformer capacity used in the laying hen farm is 3000KVA, and the maximum allowable value of the total harmonic current of the entire laying hen farm is 563.4A. For a single three-dimensional laying hen house, the maximum allowable value of the total harmonic current is <31.3A, so in the subsequent calculation, the value is taken as 30A as the basis for calculating the main capacity, inductance and capacitance of the APF. Voltage V dc Adjust to 10% higher than the maximum input voltage of the inverter, the DC bus voltage V dc The expression is as follows: (26) V dc The value is 700V, and the value of the DC side capacitor is: (27) The DC side capacitance is 2200μF. The general inductance is estimated by the empirical formula (28): (28) Among them, Δi max The maximum allowable error between the APF command current and the actual output current is 10A. The system sampling period T s =80μs, inductance is 4mH.

8. A control method for an AC / DC hybrid microgrid system suitable for a stacked three-dimensional cage chicken house as claimed in any one of claims 1 to 7, characterized in that: The photovoltaic array adopts a hybrid optimization algorithm of grey wolf optimization and perturbation observation method to realize nonlinear MPPT control of multi-peak power. The photovoltaic power generation system has three control modes: MPPT, shutdown and power-limited operation. The energy storage system has three control modes: charging, discharging and shutdown mode. The system charging and discharging are controlled by the outer loop voltage and inner loop current. Its main task is to stabilize the bus voltage in the DC subnet. The wind power generation system has three modes of operation: MPPT, shutdown and power limit; The bidirectional AC / DC converter adopts the PQ control mode when connected to the grid. The values ​​of active power P and reactive power Q come from the power management strategy based on time-of-use electricity price. In the grid-connected mode, the voltage / frequency of the AC bus is supported by the large power grid, and the voltage stability of the DC bus is the responsibility of the energy storage system. When off-grid, V / f control is adopted, and the voltage / frequency support is provided by the interconnected converter, while the voltage stability of the DC bus is still the responsibility of the energy storage system. Harmonic detection adopts the ip-iq detection method based on instantaneous reactive power theory, and adopts voltage outer loop + current inner loop dual closed-loop control to achieve harmonic suppression and reactive power compensation functions. In the voltage outer loop, the APF DC side voltage adopts PI control; the current inner loop, the APF current regulation adopts hysteresis control; The internal strategies of the energy management unit include on-grid and off-grid smooth switching strategy, pre-synchronization control strategy, on-grid energy management strategy based on time-of-use electricity price, and off-grid energy management strategy.

9. The control method of the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 8, characterized in that: When the microgrid is in the grid-connected state, the system as a whole adopts an energy management strategy based on time-of-use electricity prices. The AC / DC bidirectional converter is in PQ control mode. The frequency and voltage of the AC subgrid are supported by the large power grid. The bus voltage of the DC subgrid is kept stable by the energy storage system. The PV system and WT system are the power generation sources, and the AC load and DC load are the power consumption terminals. The specific working modes are described as follows: Mode 1&2: When there is surplus energy on the DC subgrid side, there is surplus energy on the AC subgrid side, and the amount of energy in the energy storage system is within an appropriate range, if the price of electricity generated by renewable energy to the external grid is high at this time, the AC / DC bidirectional converter will be in the inverter state, guiding the excess energy in the DC subgrid to flow to the large grid to obtain better economic returns. The energy storage system will neither charge nor discharge. If the price of renewable energy power generation is low at this time, the AC / DC bidirectional converter will be in the rectification state, guiding the excess energy in the AC subgrid to move to the DC subgrid side and charge the energy storage system to ensure energy reserves; Modes 3, 4, and 5: When the amount of renewable energy power generation in the AC / DC subgrid is far less than the respective load consumption, and the energy storage system has a large amount of power, when the price of purchasing electricity from the external grid is high, the energy storage system will be responsible for the energy gap of the AC and DC loads, and the system will not purchase electricity from the large grid to save costs. When the price of purchasing electricity from the external grid is low, the energy storage system will only be responsible for the energy gap on the DC subgrid side, and the large grid will be responsible for the energy gap on the AC subgrid side. When the power in the energy storage system is low, the energy storage system will shut down, and the large grid will be responsible for all the energy gaps in the AC and DC subgrids. Mode 6: When the WT power generation in the AC subgrid is less than the AC load consumption, the PV system power generation in the DC subgrid is greater than the DC load, the excess energy in the DC subgrid is greater than the energy gap in the AC subgrid, and the energy storage system has sufficient power, if the price of electricity sold to the external grid is low, the AC / DC bidirectional converter will be in a shutdown state, forcing the excess energy on the DC side to be charged into the energy storage system, and the power gap of the AC subgrid will be supplemented by the external grid; Mode 7: When the WT power generation in the AC subgrid is less than the AC load consumption, the PV system power generation in the DC subgrid is greater than the DC load, the excess energy in the DC subgrid is less than the energy gap in the AC subgrid, and the energy storage system has sufficient power, the energy storage system shuts down, and the AC / DC bidirectional converter guides the excess power of the DC subgrid to flow to the AC subgrid, and the insufficient power on the AC side is supplemented by the large power grid; Mode 8&9: When the WT power generation in the AC subgrid is greater than the AC load consumption, the PV system power generation in the DC subgrid is less than the DC load, the excess energy in the AC subgrid is greater than the energy gap in the DC subgrid and the energy storage system has sufficient power, when the price of purchasing electricity from the external grid is high, the energy gap of the DC subgrid will be provided by the energy storage system, and the excess power of the AC subgrid will flow into the large grid in exchange for economic benefits. When the power of the energy storage system is not enough to make up for the energy gap in the DC subgrid, the excess power in the AC subgrid will be rectified by the AC / DC bidirectional converter and enter the DC subgrid.

10. The control method of the AC / DC hybrid microgrid system suitable for stacked three-dimensional cage chicken houses according to claim 8, characterized in that: When the microgrid is off-grid, the AC / DC bidirectional converter is in V / f control mode. The frequency and voltage of the AC subgrid are supported by the AC / DC bidirectional converter, and the bus voltage of the DC subgrid is still kept stable by the energy storage system. The PV system and WT system are power generation sources, and the AC load and DC load are power consumption terminals. The specific working modes are described as follows: Mode 1&2: When there is surplus energy on both the AC and DC subgrid sides, and the energy storage system has sufficient power, the WT and PV systems will be adjusted to the power tracking generation LPTC mode. At this time, the energy storage system will neither charge nor discharge, and each subgrid will maintain energy balance. When the energy storage system power is within the allowable charging range, in order to make full use of renewable energy power generation, the system will control the WT and PV systems to operate at full power in MPPT mode, and the energy storage system will be in charging mode to absorb excess power, and each subgrid will maintain energy balance; Mode 3 & 4: When there is a gap in energy on both the AC and DC subgrid sides, and the energy storage system has a large amount of power, the energy missing from the system will be compensated by the energy storage system to ensure the operation of the AC load and part of the DC load. When the energy storage system has little power, the system will only retain the more important part of the AC load and cut off all DC loads and non-critical AC loads. Mode 5&6: When there is surplus energy on the DC subgrid side but there is a shortage of energy on the AC subgrid side, and the surplus energy on the DC side is greater than the missing energy on the AC side, according to the principle of energy balance, part of the surplus energy on the DC side will flow to the AC side to make up for its energy gap, and the remaining part will flow into the energy storage system for charging. When the energy storage system is fully charged, the system will control the PV system to operate in LPTC mode. Mode 7 & 8: When there is surplus energy on the DC subgrid side and a shortage of energy on the AC subgrid side, but the surplus energy on the DC side is less than the missing energy on the AC side, the energy storage system will make up for the shortage when the energy storage system is fully charged. When the energy storage system is low in charge, the AC subgrid side must cut off non-critical loads. Mode 9: When there is surplus energy on the AC subgrid side and a shortage of energy on the DC subgrid side, and the excess energy on the AC side is greater than the missing energy on the DC side, and the energy storage system is fully charged, the system will control the WT system to operate in LPTC mode; Mode 10&11: When there is surplus energy on the AC subgrid side and there is a shortage of energy on the DC subgrid side, and the excess energy on the AC side is less than the missing energy on the DC side, when the energy storage system has sufficient power, the energy still missing on the DC side is supplemented by the energy storage system. When the energy storage system is low in power, the energy storage system shuts down and the DC side cuts off non-critical loads to ensure system energy balance.

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