Photovoltaic-based multi-load hybrid energy storage system and method

Abstract

The invention provides a photovoltaic-based multi-load hybrid energy storage system. The photovoltaic-based multi-load hybrid energy storage system comprises a photovoltaic array, a capacitor C1, a capacitor C2, a capacitor C6, a first DC-DC converter, a second DC-DC converter, a third DC-DC converter, a fourth DC-DC converter, a DC bus, a supercapacitor bank, a storage battery pack, a first DC-AC converter, a second DC-AC converter, a filter LCL, a DC load and an AC load. The first DC-DC converter connected with the photovoltaic array is controlled by adopting an MPPT control method based on a conductance increment method, the second DC-DC converter and the third DC-DC converter which are connected with the super capacitor bank and the storage battery pack adopt a control method of voltage outer loop and current inner loop, and the first DC-AC converter connected with the power grid adopts three-phase current decoupling control. The control method of the fourth DC-DC converter connected with the direct-current load and the second DC-AC converter connected with the alternating-current load can be changed according to load requirements, the advantages can be reasonably exerted according to different application scenes, and the clean energy, namely light energy, can be better utilized.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a photovoltaic-based multi-load hybrid energy storage system and method. Background Art

[0002] As the global demand for clean energy continues to rise, renewable energy sources such as photovoltaics and wind power are increasingly attracting widespread attention due to their unique advantages. The penetration rate of photovoltaic power generation and solar power generation in the power grid has increased year by year, which not only realizes the ability of large-scale centralized power generation to be connected to the grid, but also demonstrates the flexibility of distributed power generation to supply power to loads. However, solar and wind power generation still faces a series of challenges, including relatively low power density, discontinuous energy input, conversion efficiency needs to be improved, susceptibility to climate and environmental fluctuations, high system construction and operation and maintenance costs, and unpredictable power generation.

[0003] In order to effectively respond to these challenges, we urgently need to continue to explore and innovate, and develop a more efficient and intelligent multi-port power conversion system. This system can efficiently convert the electricity generated by photovoltaic power generation into stable and reliable DC power. On this basis, the system can flexibly respond to various practical needs: on the one hand, it can safely and efficiently feed the converted DC power into the power grid to achieve grid-connected power transmission; on the other hand, it can also convert and store clean energy power generation in energy storage devices for emergency use. In addition, the system can also flexibly transform clean energy power generation according to the actual needs of the load, ensuring that the converted power can be stably and reliably connected and meet the load requirements.

[0004] Based on the above analysis, the present invention proposes a photovoltaic-based multi-load hybrid energy storage system and analyzes the working method of the system to promote the widespread application and sustainable development of clean energy. Summary of the invention

[0005] The object of the present invention is to provide a photovoltaic-based multi-load hybrid energy storage system and method to solve the problems raised in the above background technology.

[0006] The present invention is achieved through the following technical solutions:

[0007] On the one hand, the present invention provides a photovoltaic-based multi-load hybrid energy storage system, including a photovoltaic array, a capacitor C1, a capacitor C2, a capacitor C6, a first DC-DC converter, a second DC-DC converter, a third DC-DC converter, a fourth DC-DC converter, a DC bus, a supercapacitor group, a battery group, a first DC-AC converter, a second DC-AC converter, a filter LCL, a DC load and an AC load;

[0008] The DC output side of the photovoltaic array is connected in parallel with a capacitor C1 and connected to one side of the first DC-DC converter, the other side of the first DC-DC converter is connected in parallel with a capacitor C2 and connected to the DC bus, the supercapacitor group is connected to one side of the second DC-DC converter, and the other side of the second DC-DC converter is connected in parallel to the DC bus; the battery group is connected to one side of the third DC-DC converter, and the other side of the third DC-DC converter is connected in parallel to the DC bus, the DC side of the first DC-AC converter is connected in parallel to the DC bus, the AC side is connected to one side of the filter LCL, and the other side of the filter LCL is connected to the power grid, the DC load is connected in parallel with a capacitor C6 and then connected to one side of the fourth DC-DC converter, and the other side of the fourth DC-DC converter is connected in parallel to the DC bus, the AC load is connected to the AC side of the second DC-AC converter, and the DC side of the second DC-AC converter is connected in parallel to the DC bus.

[0009] Specifically, the filter LCL includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C3, a capacitor C4, and a capacitor C5. One side of the inductor L1, the inductor L2, and the inductor L3 is respectively connected to one side of the capacitor C3, the capacitor C4, and the capacitor C5 and is connected to one side of the inductor L4, the inductor L5, and the inductor L6. The other sides of the inductor L4, the inductor L5, and the inductor L6 are respectively connected to the power grid, and the other sides of the capacitor C3, the capacitor C4, and the capacitor C5 are connected to each other.

[0010] Specifically, the first DC-DC converter connected to the photovoltaic array is controlled by an MPPT control method based on a conductance increment method, the second DC-DC converter connected to the supercapacitor group and the third DC-DC converter connected to the battery group are both controlled by a voltage outer loop and current inner loop control method, the first DC-AC converter connected to the power grid is controlled by a three-phase current decoupling control method, and the control methods of the fourth DC-DC converter connected to the DC load and the second DC-AC converter connected to the AC load vary according to load requirements.

[0011] Specifically, the power of the first DC-DC converter connecting the photovoltaic array and the DC bus can only flow in single phase, and the specific power flow direction is from the photovoltaic array side to the DC bus side. The power of the fourth DC-DC converter connecting the DC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the DC load side. The power of the second DC-AC converter connecting the AC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the AC load side. The power of the second DC-DC converter connecting the DC bus and the supercapacitor group, the third DC-DC converter connecting the battery group, and the first DC-AC converter connecting the power grid and the DC bus can all flow in both directions.

[0012] Specifically, the first DC-DC converter, the second DC-DC converter, the third DC-DC converter, the fourth DC-DC converter, the first DC-AC converter and the second DC-AC converter connected to the DC bus all have fast-isolating switching devices for quickly disconnecting from the DC bus under abnormal conditions.

[0013] Specifically, the first DC-AC converter connecting the grid and the DC bus has two modes: island operation and grid-connected operation. In island operation, it can provide power for the AC load. In grid-connected operation, it can feed DC bus power into the grid, and can also distribute grid power to the DC bus.

[0014] On the other hand, the present invention also provides a photovoltaic-based multi-load hybrid energy storage system method, which is applied to the system and includes control methods in different scenarios, and the steps are as follows:

[0015] S1: Specific implementation steps under lighting scenarios:

[0016] The first DC-DC converter converts the electric energy of the photovoltaic array to the DC bus, the second DC-DC converter and the third DC-DC converter convert the electric energy of the DC bus and store it in the supercapacitor group and the battery group, the first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the power grid, the fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load, and the second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load;

[0017] S2: Specific implementation steps in the scenario where there is no sunlight and the supercapacitor bank and battery bank have sufficient power:

[0018] The output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, the capacitor C2 remains connected in parallel to the DC bus, and the second DC-DC converter, the third DC-DC converter, the first DC-AC converter, the fourth DC-DC converter, and one side of the second DC-AC converter are all connected to the DC bus;

[0019] The second DC-DC converter and the third DC-DC converter convert the electric energy stored in the supercapacitor group and the battery group and feed it back to the DC bus. The first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the grid. The fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load. The second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load.

[0020] S3: Specific implementation steps in the scenario of no sunlight and insufficient power of supercapacitor bank and battery bank:

[0021] The output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, and the capacitor C2 remains connected in parallel to the DC bus. The switch devices of the second DC-DC converter and the third DC-DC converter are operated to disconnect the supercapacitor group and the battery group from the DC bus, and one side of the first DC-AC converter, the fourth DC-DC converter, and the second DC-AC converter are all connected to the DC bus;

[0022] The first DC-AC converter operates in a grid-connected rectification mode to convert the grid power and connect it to the DC bus. The fourth DC-DC converter converts the DC bus power according to the DC load demand and provides power to the DC load. The second DC-AC converter converts the DC bus power according to the AC load demand and provides power to the AC load.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The MPPT control method based on the conductance increment method is used to convert the photovoltaic power generation and connect it to the DC bus, which is convenient for the use of loads, grid-connected converters, energy storage capacitors and batteries, and more efficiently converts the photovoltaic power generation.

[0025] (2) The system has a variety of power conversion functions and can achieve grid connection, energy storage and power supply, which more reasonably solves the shortcoming of distributed photovoltaic power generation.

[0026] (3) The system has energy storage function, which makes up for the shortcoming of intermittent operation of photovoltaic power generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only preferred embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A structural diagram of a photovoltaic-based multi-load hybrid energy storage system provided by the present invention.

[0029] Figure 2 The control block diagram of the first DC-DC converter controlled by the MPPT control method based on the conductance increment method.

[0030] Figure 3 The present invention is a control block diagram of a second DC-DC converter and a third DC-DC converter which are controlled by a voltage outer loop and current inner loop control method and in which a super capacitor bank or a battery bank operates in a charging mode.

[0031] Figure 4 The present invention is a control block diagram of a first DC-AC converter using three-phase current decoupling control working in a grid-connected inverter mode.

[0032] Figure 5 This is a control block diagram of a fourth DC-DC converter controlled by a voltage outer loop and current inner loop control method.

[0033] Figure 6 The present invention is a control block diagram of a second DC-DC converter and a third DC-DC converter which are controlled by a voltage outer loop and current inner loop control method and in which a super capacitor group or a battery group operates in a discharge mode.

[0034] Figure 7 The present invention is a control block diagram of a first DC-AC converter using three-phase current decoupling control working in a grid-connected rectification mode. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention more obvious, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the protection scope of the present invention.

[0036] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0037] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0038] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0039] In order to fully understand the present invention, a detailed structure will be proposed in the following description to illustrate the technical solution proposed by the present invention. The optional embodiments of the present invention are described in detail as follows, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0040] See also Figure 1 , On the one hand, the present invention provides a photovoltaic-based multi-load hybrid energy storage system, including a photovoltaic array, a capacitor C1, a capacitor C2, a capacitor C6, a first DC-DC converter, a second DC-DC converter, a third DC-DC converter, a fourth DC-DC converter, a DC bus, a supercapacitor group, a battery group, a first DC-AC converter, a second DC-AC converter, a filter LCL, a DC load and an AC load;

[0041] The DC output side of the photovoltaic array is connected in parallel with a capacitor C1 and connected to one side of the first DC-DC converter, the other side of the first DC-DC converter is connected in parallel with a capacitor C2 and connected to the DC bus, the supercapacitor group is connected to one side of the second DC-DC converter, and the other side of the second DC-DC converter is connected in parallel to the DC bus; the battery group is connected to one side of the third DC-DC converter, and the other side of the third DC-DC converter is connected in parallel to the DC bus, the DC side of the first DC-AC converter is connected in parallel to the DC bus, the AC side is connected to one side of the filter LCL, and the other side of the filter LCL is connected to the power grid, the DC load is connected in parallel with a capacitor C6 and then connected to one side of the fourth DC-DC converter, and the other side of the fourth DC-DC converter is connected in parallel to the DC bus, the AC load is connected to the AC side of the second DC-AC converter, and the DC side of the second DC-AC converter is connected in parallel to the DC bus.

[0042] Specifically, the filter LCL includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C3, a capacitor C4, and a capacitor C5. One side of the inductor L1, the inductor L2, and the inductor L3 is respectively connected to one side of the capacitor C3, the capacitor C4, and the capacitor C5 and is connected to one side of the inductor L4, the inductor L5, and the inductor L6. The other sides of the inductor L4, the inductor L5, and the inductor L6 are respectively connected to the power grid, and the other sides of the capacitor C3, the capacitor C4, and the capacitor C5 are connected to each other.

[0043] Specifically, the first DC-DC converter connected to the photovoltaic array is controlled by an MPPT control method based on a conductance increment method, the second DC-DC converter connected to the supercapacitor group and the third DC-DC converter connected to the battery group are both controlled by a voltage outer loop and current inner loop control method, the first DC-AC converter connected to the power grid is controlled by a three-phase current decoupling control method, and the control methods of the fourth DC-DC converter connected to the DC load and the second DC-AC converter connected to the AC load vary according to load requirements.

[0044] Specifically, the power of the first DC-DC converter connecting the photovoltaic array and the DC bus can only flow in single phase, and the specific power flow direction is from the photovoltaic array side to the DC bus side. The power of the fourth DC-DC converter connecting the DC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the DC load side. The power of the second DC-AC converter connecting the AC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the AC load side. The power of the second DC-DC converter connecting the DC bus and the supercapacitor group, the third DC-DC converter connecting the battery group, and the first DC-AC converter connecting the power grid and the DC bus can all flow in both directions.

[0045] Specifically, the first DC-DC converter, the second DC-DC converter, the third DC-DC converter, the fourth DC-DC converter, the first DC-AC converter and the second DC-AC converter connected to the DC bus all have fast-isolating switching devices for quickly disconnecting from the DC bus under abnormal conditions.

[0046] Specifically, the first DC-AC converter connecting the grid and the DC bus has two modes: island operation and grid-connected operation. In island operation, it can provide power for the AC load. In grid-connected operation, it can feed DC bus power into the grid, and can also distribute grid power to the DC bus.

[0047] On the other hand, the present invention also provides a photovoltaic-based multi-load hybrid energy storage system method, which is applied to the system and includes control methods in different scenarios, and the steps are as follows:

[0048] S1: Specific implementation steps under lighting scenarios:

[0049] Exemplarily, the first DC-DC converter converts the electric energy of the photovoltaic array to the DC bus, the second DC-DC converter and the third DC-DC converter convert the electric energy of the DC bus and store it in the supercapacitor group and the battery group, the first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the grid, the fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load, and the second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load;

[0050] Among them, the first DC-DC converter connected to the photovoltaic array is controlled by the MPPT control method based on the conductance increment method, and the theoretical derivation of the control method is as follows:

[0051] The real-time output power of the photovoltaic array is:

[0052] P=UPV I PV (1)

[0053] Where P is the real-time output power of the photovoltaic array, U PV is the real-time output voltage, I PV It is the real-time output current.

[0054] If the system DC bus power comes entirely from the photovoltaic array, the following relationship holds:

[0055]

[0056] Where U DC and I DC are the voltage of the DC bus and the current flowing from the photovoltaic array to the DC bus, respectively. m and n represent the conversion factors of the converter's electric energy change.

[0057] Furthermore, the real-time output power of the photovoltaic array can be expressed as:

[0058]

[0059] For the real-time output power of the photovoltaic array, the voltage derivative can be expressed as:

[0060]

[0061] When equation (4) is equal to 0, the photovoltaic array operates at the maximum power point, and the following relationship exists:

[0062]

[0063] Furthermore, formula (5) can be written as:

[0064]

[0065] The criteria for using the conductance increment method to complete the maximum power tracking of the photovoltaic array output are as follows:

[0066]

[0067] In the MPPT control mode, the specific control process of the first DC-DC converter connected to the photovoltaic array is as follows: Figure 2 As shown, the DC voltage reference U ref_DC It is calculated by the conductivity increment method, U ref_DC and U DC As the reference value and feedback value of the PI voltage control loop, the PI voltage control loop outputs I ref_DC and I DCAs the reference value and feedback value of the PI current control loop, the D output of the PI current control loop is DC The duty cycle is given to the PWM modulation module to generate a switch device drive signal PWM of the first DC-DC converter. DC , driving signal PWM DC The switch tube of the first DC-DC converter is controlled to be turned on or off, the electric energy generated by the photovoltaic array is converted and fed into the DC bus, and the MPPT control method based on the conductance increment method is used to ensure the voltage stability of the DC bus.

[0068] The second DC-DC converter and the third DC-DC converter connected to the supercapacitor group and the battery group adopt a dual-loop control method of voltage outer loop and current inner loop, and the control method is implemented as follows:

[0069] First, the photovoltaic array generates electricity to achieve energy storage, which is stored in the supercapacitor group and the battery group. The control process of the second DC-DC converter and the third DC-DC converter is as follows: Figure 3 shown.

[0070] The smaller of the voltage outer loop output value and the current reference value is used as the reference value of the current inner loop. This new dual-loop control method of voltage outer loop and current inner loop can realize fast charging of supercapacitor group or battery group in constant current working mode when the stored energy is low, and floating charging in constant voltage working mode when the stored energy is high or close to the rated value until it is fully charged; this charging method can greatly protect the battery and extend the battery life. Rated voltage U of supercapacitor group or battery group ref_B and the actual U B As the reference value and feedback value of the PI voltage outer loop, it is given to the voltage outer loop. The I ref_B and the rated charging current I of the supercapacitor bank or battery bank ref Take the minimum value, and the minimum value and I B As the reference value and feedback value of the PI current inner loop, the duty cycle D of the current inner loop output is B After being sent to the PWM modulation module, a switch device driving signal PWM of the second DC-DC converter or the third DC-DC converter is generated. B , driving signal PWM B The switch device of the second DC-DC converter or the third DC-DC converter is controlled to be turned on or off, so as to convert the electric energy generated by the photovoltaic array and store it in the super capacitor group or the battery group.

[0071] Among them, the DC-AC converter #1 connected to the grid adopts three-phase current decoupling control, and the control method is theoretically derived as follows:

[0072] The electric energy generated by the photovoltaic array is fed into the power grid. The control process of the first DC-AC converter is as follows Figure 4 As shown. Assuming that the power factor of a certain time-state power grid is 1, the expressions of three-phase voltage and current are:

[0073]

[0074] Where U F and I F are the maximum values ​​of voltage and current.

[0075] The abc / dq0 transformation matrix is:

[0076]

[0077] After the abc / dq0 transformation of the abc three-phase AC voltage, we can get:

[0078]

[0079] Similarly, after the abc / dq0 transformation of the abc three-phase alternating current, we can get:

[0080]

[0081] i ref_d and i d They are used as the reference value and feedback value of the PI current loop respectively, and the output i after passing through the PI loop refd ,i ref_q and i q They are used as the reference value and feedback value of the PI current loop respectively, and the output i after passing through the PI loop refq .

[0082] The decoupling control of current has the following relationship:

[0083]

[0084] Where ω is the grid angular frequency and L is the filter inductance.

[0085] E d and e q Performing the inverse park transform yields the following expression:

[0086]

[0087] The inverse transformation of e a 、e b and e c After being sent to the PWM modulation module, a switching device driving signal PWM of the first DC-AC converter is generated. G , driving signal PWM GThe switch tube of the first DC-AC converter is controlled to be turned on or off to feed electric energy into the power grid.

[0088] The control process of the dual-loop control method of the voltage outer loop and the current inner loop of the fourth DC-DC converter is as follows: Figure 5 As shown, according to the load power demand, the electric energy of the DC bus is converted into the electric energy required by the load, including the conversion of the voltage level and the supply of the current. The control method is implemented as follows:

[0089] Supply voltage level U according to load requirements ref_DC1 , U ref_DC1 And the actual voltage value U DC1 As the reference value and feedback value of the PI voltage control loop, it is given to the voltage control loop. The reference value I of the PI voltage control loop output ef_DC1 and the actual current value I DC1 As the reference value and feedback value of the PI current control loop, the duty cycle D of the PI current control loop output is DC1 It is sent to the PWM modulation module, which generates a switch drive signal PWM DC1 , driving signal PWM DC1 The switch device of the fourth DC-DC converter is controlled to be turned on or off to realize power conversion to supply power to the DC load.

[0090] The second DC-AC converter can generate corresponding AC power according to load demand to supply power to the corresponding AC load.

[0091] S2: Specific implementation steps in the scenario where there is no sunlight and the supercapacitor bank and battery bank have sufficient power:

[0092] Exemplarily, the output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, the capacitor C2 remains connected in parallel to the DC bus, and the second DC-DC converter, the third DC-DC converter, the first DC-AC converter, the fourth DC-DC converter, and one side of the second DC-AC converter are all connected to the DC bus;

[0093] The second DC-DC converter and the third DC-DC converter convert the electric energy stored in the supercapacitor group and the battery group and feed it back to the DC bus. The first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the grid. The fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load. The second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load.

[0094] In this scenario, the control flow of the second DC-DC converter and the third DC-DC converter connecting the supercapacitor group and the battery group is as follows: Figure 6 shown.

[0095] To ensure the voltage stability of the DC bus, the supercapacitor group and the battery group feed back power to the DC bus. The rated voltage of the DC bus is U ref_DC2 And the actual DC bus voltage value U DC2 As the reference value and feedback value of the PI voltage control loop, it is given to the voltage control loop. The I ref_DC2 and the actual current value I flowing to the DC bus DC2 As the reference value and feedback value of the PI current control loop, the D output of the current control loop is given to the current control loop. DC2 It is sent to the PWM modulation module, which generates a switch drive signal PWM DC2 , driving signal PWM DC2 The switch devices of the second DC-DC converter and the third DC-DC converter are controlled to be turned on or off to realize power conversion and supply power to the DC bus.

[0096] The working modes of the fourth DC-DC converter, the first DC-AC converter and the second DC-AC converter are consistent with the working modes in the illumination scene, and are not described in detail here.

[0097] S3: Specific implementation steps in the scenario of no sunlight and insufficient power of supercapacitor bank and battery bank:

[0098] The output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, and the capacitor C2 remains connected in parallel to the DC bus. The switch devices of the second DC-DC converter and the third DC-DC converter are operated to disconnect the supercapacitor group and the battery group from the DC bus, and one side of the first DC-AC converter, the fourth DC-DC converter, and the second DC-AC converter are all connected to the DC bus;

[0099] The first DC-AC converter operates in a grid-connected rectification mode to convert the grid power and connect it to the DC bus. The fourth DC-DC converter converts the DC bus power according to the DC load demand and provides power to the DC load. The second DC-AC converter converts the DC bus power according to the AC load demand and provides power to the AC load.

[0100] In this scenario, the switching devices of the first DC-DC converter, the second DC-DC converter and the third DC-DC converter are actuated to disconnect the photovoltaic array, the supercapacitor bank and the battery bank from the DC bus. At this time, the first DC-AC converter works in the grid-connected rectification mode to feed the power of the grid back to the DC bus. The control process of the first DC-AC converter is as follows: Figure 7 shown.

[0101] Assuming that the power factor of a certain time-state power grid is 1, the expressions of three-phase voltage and current are:

[0102]

[0103] Where U F and I F are the maximum values ​​of voltage and current.

[0104] The abc / dq0 transformation matrix is:

[0105]

[0106] Then the three-phase AC voltage of the power grid abc is transformed into abc / dq0:

[0107]

[0108] Similarly, after the abc / dq0 transformation of the three-phase AC current of the power grid abc, we can get:

[0109]

[0110] DC bus rated voltage U DC_ref And the actual DC bus voltage U DC As the reference value and feedback value of the PI voltage control loop, it is given to the voltage control loop. The voltage control loop outputs i ref_d1 and i d1 They are respectively used as the reference value and feedback value of the PI current control loop and are given to the current control loop. After the PI current control loop, the output i refd1 ,i ref_q1 and i q1 They are used as the reference value and feedback value of the PI current loop and are given to the current control loop respectively. After passing through the PI current control loop, the output i refq1 .

[0111] The decoupling control of three-phase current has the following relationship:

[0112]

[0113] Where ω is the grid angular frequency and L is the filter inductance.

[0114] E d1 and eq1 Performing the inverse park transform yields the following expression:

[0115]

[0116] The inverse transformation of e a1 、e b1 and e c1 After being sent to the PWM modulation module, a switching device driving signal PWM of the first DC-AC converter is generated. G1 , driving signal PWM G1 The switch device of the first DC-AC converter is controlled to be turned on or off to realize the feedback of grid power to the DC bus.

[0117] The working modes of the fourth DC-DC converter and the second DC-AC converter are consistent with the working modes in the illumination scene, and are not described in detail here.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic-based multi-load hybrid energy storage system, characterized in that: It includes a photovoltaic array, a capacitor C1, a capacitor C2, a capacitor C6, a first DC-DC converter, a second DC-DC converter, a third DC-DC converter, a fourth DC-DC converter, a DC bus, a supercapacitor group, a battery group, a first DC-AC converter, a second DC-AC converter, a filter LCL, a DC load and an AC load; The DC output side of the photovoltaic array is connected in parallel with a capacitor C1 and connected to one side of the first DC-DC converter, and the other side of the first DC-DC converter is connected in parallel with a capacitor C2 and connected to the DC bus. The supercapacitor group is connected to one side of the second DC-DC converter, and the other side of the second DC-DC converter is connected in parallel to the DC bus. The battery group is connected to one side of the third DC-DC converter, and the other side of the third DC-DC converter is connected in parallel to the DC bus. The DC side of the first DC-AC converter is connected in parallel to the DC bus, and the AC side is connected to one side of the filter LCL, and the other side of the filter LCL is connected to the power grid. The DC load is connected in parallel with a capacitor C6 and then connected to one side of the fourth DC-DC converter, and the other side of the fourth DC-DC converter is connected in parallel to the DC bus. The AC load is connected to the AC side of the second DC-AC converter, and the DC side of the second DC-AC converter is connected in parallel to the DC bus.

2. A photovoltaic-based multi-load hybrid energy storage system according to claim 1, characterized in that: The filter LCL includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C3, a capacitor C4, and a capacitor C5. One side of the inductor L1, the inductor L2, and the inductor L3 is respectively connected to one side of the capacitor C3, the capacitor C4, and the capacitor C5 and is connected to one side of the inductor L4, the inductor L5, and the inductor L6. The other sides of the inductor L4, the inductor L5, and the inductor L6 are respectively connected to the power grid, and the other sides of the capacitor C3, the capacitor C4, and the capacitor C5 are connected to each other.

3. A photovoltaic-based multi-load hybrid energy storage system according to claim 2, characterized in that: The first DC-DC converter connected to the photovoltaic array is controlled by an MPPT control method based on a conductance increment method, the second DC-DC converter connected to the supercapacitor group and the third DC-DC converter connected to the battery group are both controlled by a voltage outer loop and current inner loop control method, the first DC-AC converter connected to the power grid is controlled by a three-phase current decoupling control method, and the control methods of the fourth DC-DC converter connected to the DC load and the second DC-AC converter connected to the AC load vary according to load requirements.

4. A photovoltaic-based multi-load hybrid energy storage system according to claim 3, characterized in that: The power of the first DC-DC converter connecting the photovoltaic array and the DC bus can only flow in single phase, and the specific power flow direction is from the photovoltaic array side to the DC bus side. The power of the fourth DC-DC converter connecting the DC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the DC load side. The power of the second DC-AC converter connecting the AC load and the DC bus can only flow in single phase, and the specific power flow direction is from the DC bus side to the AC load side. The power of the second DC-DC converter connecting the DC bus and the supercapacitor group, the third DC-DC converter connecting the battery group, and the first DC-AC converter connecting the power grid and the DC bus can all flow in both directions.

5. A photovoltaic-based multi-load hybrid energy storage system according to claim 4, characterized in that: The first DC-DC converter, the second DC-DC converter, the third DC-DC converter, the fourth DC-DC converter, the first DC-AC converter and the second DC-AC converter connected to the DC bus all have fast-isolating switching devices for quickly disconnecting from the DC bus under abnormal conditions.

6. A photovoltaic-based multi-load hybrid energy storage system according to claim 5, characterized in that: The first DC-AC converter connecting the grid and the DC bus has two modes: island operation and grid-connected operation. In island operation, it can provide power to the AC load. In grid-connected operation, it can feed DC bus power into the grid, and can also distribute grid power to the DC bus.

7. A photovoltaic-based multi-load hybrid energy storage system method, the method being applied to the system according to any one of claims 1 to 6, characterized in that: Including control methods in different scenarios, the steps are as follows: S1: Specific implementation steps under lighting scenarios: The first DC-DC converter converts the electric energy of the photovoltaic array to the DC bus, the second DC-DC converter and the third DC-DC converter convert the electric energy of the DC bus and store it in the supercapacitor group and the battery group, the first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the power grid, the fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load, and the second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load; S2: Specific implementation steps in the scenario where there is no sunlight and the supercapacitor bank and battery bank have sufficient power: The output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, the capacitor C2 remains connected in parallel to the DC bus, and the second DC-DC converter, the third DC-DC converter, the first DC-AC converter, the fourth DC-DC converter, and one side of the second DC-AC converter are all connected to the DC bus; The second DC-DC converter and the third DC-DC converter convert the electric energy stored in the supercapacitor group and the battery group and feed it back to the DC bus. The first DC-AC converter works in the grid-connected inverter mode to convert the DC bus electric energy and feed it into the grid. The fourth DC-DC converter converts the DC bus electric energy according to the DC load demand and provides electric energy to the DC load. The second DC-AC converter converts the DC bus electric energy according to the AC load demand and provides electric energy to the AC load. S3: Specific implementation steps in the scenario of no sunlight and insufficient power of supercapacitor bank and battery bank: The output side of the photovoltaic array and the capacitor C1 are disconnected from the DC bus by the action of the switch device of the first DC-DC converter, and the capacitor C2 remains connected in parallel to the DC bus. The switch devices of the second DC-DC converter and the third DC-DC converter are operated to disconnect the supercapacitor group and the battery group from the DC bus, and one side of the first DC-AC converter, the fourth DC-DC converter, and the second DC-AC converter are all connected to the DC bus; The first DC-AC converter operates in a grid-connected rectification mode to convert the grid power and connect it to the DC bus. The fourth DC-DC converter converts the DC bus power according to the DC load demand and provides power to the DC load. The second DC-AC converter converts the DC bus power according to the AC load demand and provides power to the AC load.

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