CN116470539A

CN116470539A - Micro-grid power supply system and control method thereof

Info

Publication number: CN116470539A
Application number: CN202310334634.XA
Authority: CN
Inventors: 潘羿威; 刘方诚; 辛凯; 修双
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2023-03-24
Filing date: 2023-03-24
Publication date: 2023-07-21

Abstract

The application provides a micro-grid power supply system and a control method thereof, which can be applied to micro-grid off-grid working scenes. The system comprises an energy storage converter and a grid-connected converter, wherein the energy storage converter comprises a controller and a direct current conversion circuit, and the controller is used for controlling the direct current conversion circuit to receive electric energy output by an energy storage unit and supplying power to a micro-grid through a direct current bus after direct current conversion; the grid-connected converter is used for receiving the alternating voltage output by the alternating current power grid, converting the alternating voltage into direct current voltage and supplying power to the micro power grid through the direct current bus. When the micro-grid is switched from the grid-connected working state to the island working state, the energy storage converter is controlled to adjust the output voltage to a value near the rated voltage of the micro-grid, and after the voltage of the direct-current bus is stabilized, the output voltage is adjusted to the rated voltage of the micro-grid, so that the whole switching process is stable and free from impact, and the stability of the power supply network is improved.

Description

Micro-grid power supply system and control method thereof

Technical Field

The present application relates to the field of energy, and more particularly, to a micro-grid power supply system and a control method thereof.

Background

Along with the rapid development of power electronic technology and equipment, a direct current distribution system is widely applied to the fields of renewable energy power generation, building electrification, ship comprehensive power systems and the like, and enters a rapid development period. The direct current micro-grid is one of main realization forms of a direct current power distribution system: when the direct current micro-grid is integrated into an external power grid, the direct current micro-grid can participate in power dispatching of the system to provide voltage support; when the external power grid fails, the micro-grid load can operate in an island mode and independently supply power to the micro-grid load. Therefore, the parallel-off-grid operation of the direct-current micro-grid is important to improve the power supply reliability and the digestion capability of the distributed power supply.

However, the grid-connected and off-grid switching operation of the direct-current micro grid can cause voltage and power fluctuation of the micro grid, and the stable operation of the system is affected; and the damage of the direct current equipment and the misoperation of the protection device can be caused when the direct current equipment is serious, so that secondary faults on the direct current side are caused. Therefore, seamless switching between direct current micro-grid and off-grid modes is important to guaranteeing power supply reliability.

Disclosure of Invention

The utility model provides a micro-grid power supply system and a control method thereof, which are beneficial to improving the stability of a power supply network.

In a first aspect, a micro-grid power supply system is provided, the system comprises an energy storage converter and a grid-connected converter, the energy storage converter comprises a controller and a direct current conversion circuit, the controller is used for controlling the direct current conversion circuit to receive electric energy output by an energy storage unit, and after direct current conversion, the controller supplies power to the micro-grid through a direct current bus; the grid-connected converter is used for receiving the alternating voltage output by the alternating current power grid, converting the alternating voltage into direct current voltage and supplying power to the micro power grid through the direct current bus. The controller is also used for controlling the output voltage of the direct current conversion circuit to the direct current bus to be a first output voltage when the grid-connected converter is disconnected from the direct current bus and the micro-grid is in an island state, supplying power to the micro-grid, and controlling the output voltage of the direct current conversion circuit to the direct current bus to be adjusted from the first output voltage to the rated voltage of the micro-grid after the voltage of the direct current grid is stable, and supplying power to the micro-grid. The difference value between the first output voltage and the rated voltage of the micro-grid is a first threshold value, and the first threshold value is positively related to the load power in the micro-grid.

According to the system disclosed by the application, when the micro-grid is switched from the grid-connected working state to the island working state, the energy storage converter is controlled to firstly adjust the output voltage to a value near the rated voltage of the micro-grid, after the voltage of the direct-current bus is stable, the output voltage is adjusted to the rated voltage of the micro-grid, the whole switching process is stable and free from impact, and the stability of the power supply network is improved.

With reference to the first aspect, in some implementations of the first aspect, the controller is specifically configured to detect a voltage of the dc bus, and determine that the grid-connected converter is disconnected from the dc bus when a duration of the voltage of the dc bus greater than or equal to a first preset value is greater than a first duration, and the micro grid is in an island working state. Or the controller is specifically configured to detect the voltage of the dc bus, and determine that the grid-connected converter is disconnected from the dc bus and the micro-grid is in an island working state when the duration time that the voltage of the dc bus is less than or equal to the second preset value is longer than the second duration time. Or the controller is particularly used for receiving the island signal from the grid-connected converter, determining that the grid-connected converter is disconnected from the direct-current bus according to the island signal, and the micro-grid is in an island working state.

With reference to the first aspect, in some implementations of the first aspect, the dc conversion circuit includes a plurality of switching tubes, and the controller is specifically configured to determine a first driving signal according to a difference between a current voltage of the dc bus and a first output voltage, where the first driving signal is used to control on-off of the plurality of switching tubes, and adjust output power of the dc conversion circuit, so that the output voltage of the dc conversion circuit to the dc bus is the first output voltage; and determining a second driving signal according to the first threshold value, wherein the second driving signal is used for controlling the on-off of the plurality of switching tubes and adjusting the output power of the direct current conversion circuit so that the output voltage of the direct current conversion circuit to the direct current bus is adjusted from the first output voltage to the rated voltage of the micro-grid.

With reference to the first aspect, in certain implementations of the first aspect, the dc conversion circuit includes a first dc conversion circuit and a second dc conversion circuit, and the controller is further configured to control a duty ratio of an output power of the first dc conversion circuit with respect to a rated power of the first dc conversion circuit to be the same as a duty ratio of an output power of the second dc conversion circuit with respect to a rated power of the second dc conversion circuit.

With reference to the first aspect, in some implementations of the first aspect, the controller is further configured to, when it is determined that the grid-connected converter meets the grid-connected condition, control the output voltage of the dc conversion circuit to the dc bus to be adjusted from the rated voltage of the micro-grid to a second output voltage, where the second output voltage is the output voltage of the grid-connected converter, and when it is determined that the dc bus voltage is stable at the second output voltage, send a control signal to the grid-connected converter, where the control signal is used to instruct the grid-connected converter to be connected to the dc bus, and after the grid-connected converter is connected to the dc bus, control the output power of the dc conversion circuit to the dc bus to be the preset power of the dc conversion circuit.

With reference to the first aspect, in certain implementation manners of the first aspect, the controller is specifically configured to receive a grid-connected signal from the grid-connected converter, and determine that the grid-connected converter meets a grid-connected condition according to the grid-connected signal.

With reference to the first aspect, in some implementations of the first aspect, the dc conversion circuit includes a plurality of switching tubes, and the controller is specifically configured to determine a third driving signal according to a rated voltage of the micro-grid and the second output voltage, where the third driving signal is configured to control on-off of the plurality of switching tubes, and adjust output power of the dc conversion circuit, so that a voltage of the dc bus is adjusted from the rated voltage of the micro-grid to the second output voltage.

With reference to the first aspect, in some implementations of the first aspect, the controller is further configured to detect a voltage of the dc bus, and adjust the output power of the dc conversion circuit to adjust the voltage of the dc bus within a preset time after the voltage of the dc bus changes between the first preset value and the second preset value.

With reference to the first aspect, in certain implementations of the first aspect, at least one of a digital signal processor (digital signal processing, DSP), a complex programmable logic device (complex programmable logic device, CPLD), a field programmable gate array (field programmable gate array, FPGA), a central processing unit (central processing unit, CPU), or a micro control unit (microcontroller unit, MCU) is included.

In a second aspect, there is provided a control method of a micro-grid power supply system, the method being performed by the micro-grid power supply system of the first aspect, the method comprising: when the controller determines that the grid-connected converter is disconnected from the direct current bus and the micro-grid is in an island working state, controlling the output voltage of the direct current conversion circuit to the direct current bus to be a first output voltage, supplying power to the micro-grid, wherein the difference value between the first output voltage and the rated voltage of the micro-grid is a first threshold value, the first threshold value is positively related to the power of a load, and at least one intermediate value is included in the process of controlling the output voltage of the direct current conversion circuit to the direct current bus to be the first output voltage. And when the controller determines that the voltage of the direct current bus is stabilized at the first output voltage, controlling the direct current conversion circuit to adjust the output voltage of the direct current bus from the first output voltage to the rated voltage of the micro-grid, and supplying power to the micro-grid.

According to the method disclosed by the application, when the micro-grid is switched from the grid-connected working state to the island working state, the energy storage converter is controlled to firstly adjust the output voltage to a value near the rated voltage of the micro-grid, after the voltage of the direct-current bus is stable, the output voltage is adjusted to the rated voltage of the micro-grid, the whole switching process is stable and free from impact, and the stability of the power supply network is improved.

With reference to the second aspect, in certain implementation manners of the second aspect, the method further includes: when the controller determines that the grid-connected converter meets the grid-connected condition, controlling the output voltage of the direct current conversion circuit to the direct current bus to be adjusted from the rated voltage of the micro-grid to a second output voltage, wherein the second output voltage is the output voltage of the grid-connected converter; when the voltage of the direct current bus is determined to be stable at the second output voltage, a control signal is sent to the grid-connected converter, and the control signal is used for indicating the grid-connected converter to be connected with the direct current bus; after the grid-connected converter is connected with the direct current bus, the output power of the direct current conversion circuit to the direct current bus is controlled to be the preset power of the direct current conversion circuit.

Drawings

Fig. 1 is a schematic view of an application scenario of the present application.

Fig. 2 is a schematic structural diagram of a micro-grid power supply system according to an embodiment of the present application.

Fig. 3 is a specific example of a controller provided in an embodiment of the present application.

Fig. 4 is a flowchart of a control method of a micro-grid power supply system according to an embodiment of the present application.

Fig. 5 is a schematic diagram of an example of simulation results of a control method of a micro-grid power supply system according to an embodiment of the present application.

Fig. 6 is a schematic diagram of another example of simulation results of a control method of a micro-grid power supply system according to an embodiment of the present application.

Fig. 7 is a schematic diagram of a simulation result of another example of a control method of a micro-grid power supply system according to an embodiment of the present application.

Detailed Description

The technical solutions in the present application will be described below with reference to the accompanying drawings.

The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include, for example, "one or more" such forms of expression, unless the context clearly indicates to the contrary. It should also be understood that in the various embodiments herein below, "at least one", "one or more" means one, two or more than two. The term "and/or" is used to describe an association relationship of associated objects, meaning that there may be three relationships; for example, a and/or B may represent: a alone, a and B together, and B alone, wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.

Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.

For ease of understanding, the terminology referred to in this application is first introduced.

1. Island

When the power grid is interrupted due to electric faults, natural factors or misoperation, the power generation systems of the photovoltaic, energy storage and the like of the user terminals do not timely detect the power failure state and are separated from the commercial power grid, the power transmission to the power grid is continuously maintained, meanwhile, an independent self-sufficient power supply island which cannot be controlled by the public power grid is formed with the load, and the system formed at the moment is called an island system.

2. Sagging control

A linear autonomous control method suitable for micro-grid power supply. Depending on the control objective of the micro-grid, a droop curve similar to a conventional generator is used to achieve control of the micro-grid power supply. Voltage active droop control is typically employed in dc microgrid systems. For example, if the power supply load is too large, the output voltage thereof is lowered due to the droop characteristic, thereby automatically lowering the output power of the power supply. In this way, the unbalanced power of the system will be dynamically allocated to the individual power sources for assumption.

The micro-grid is formed by coupling a wind, light and other distributed renewable energy power generation system, an energy storage unit, a load and the like through a direct current bus. As shown in fig. 1, the system 100 includes an energy storage device 110, a grid-tie device 120, a load 130, a dc bus 150, and a micro-grid 160. Optionally, the system 100 may also include a photovoltaic device 140. The grid-connected device 120 is connected to the dc bus 150 through the grid-connected switch 121, and when the grid-connected switch 121 is in a closed state, the micro-grid 160 may be connected to an external power grid (e.g., a three-phase ac power grid or a dc power grid, etc.) through the grid-connected device 120, and after connection, the external power grid may supply power to each device in the system 100, and the system 100 may also supply power to the external power grid. When the grid-connected switch 121 is in a closed state, the micro-grid 160 is connected with an external power grid, and the micro-grid is in a grid-connected working mode at this time; when the grid-connected switch 121 is in the off state, the micro-grid 160 is disconnected from the external grid, and the micro-grid is in the off-grid operation mode, which is also called island operation mode or island state.

When the micro-grid is switched between a grid-connected working mode and an island working mode, voltage and power fluctuation of the micro-grid can be caused, the operation of a system is affected, damage of direct-current equipment and misoperation of a protection device can be caused when the micro-grid is severe, and secondary faults of a direct-current side are caused.

Based on the above, the micro-grid power supply system and the control method thereof can realize seamless switching between the micro-grid off-grid working modes, the whole switching process is stable and impact-free, and the stability of the power supply network is improved.

Fig. 2 shows a schematic structural diagram of a micro-grid power supply system according to an embodiment of the present application. As shown in fig. 2, the system 200 includes an energy storage converter 210, a grid-tied converter 220, a load 230, a dc bus 250, and a micro-grid 260, and optionally, the system 200 may also include a photovoltaic device 240. The energy storage converter 210 includes a controller 212 and a dc conversion circuit 211. The controller 212 is configured to control the dc conversion circuit 211 to receive the electric energy output by the energy storage unit 213, and supply power to the micro grid 260 through the dc bus 250 after performing dc conversion. Grid-tied inverter 220 is configured to receive an ac voltage output from ac grid 222, convert the ac voltage to a dc voltage, and then supply power to micro-grid 260 via dc bus 250. The controller 212 is further configured to control the output voltage of the dc conversion circuit 211 to the dc bus 250 to be the first output voltage to supply power to the micro grid 260 when it is determined that the grid-connected inverter 220 is disconnected from the dc bus 250 (i.e., the grid-connected switch 221 is in an off state) and the micro grid 260 is in an island state. The controller is further configured to control the output voltage of the dc conversion circuit 211 to the dc bus 250 to be adjusted from the first output voltage to the rated voltage of the micro-grid 260 after the dc grid voltage is stabilized at the first output voltage, and supply power to the micro-grid 260. The difference between the first output voltage and the rated voltage of the micro-grid 260 is a first threshold, and the first threshold is positively related to the power of the load 230 in the micro-grid 260.

In the present embodiment, the controller 212 determines that the grid-connected inverter 220 is disconnected from the dc bus 250, so that the micro-grid 260 is in an island state in a variety of ways. For example, the controller 212 may detect the voltage of the dc bus 250, and determine that the grid-connected converter 220 is disconnected from the dc bus 250 and the micro-grid 260 is in the island operation state when the duration of the voltage of the dc bus 250 being greater than or equal to the first preset value is greater than the first duration, that is, the duration of the voltage of the dc bus 250 exceeding the preset voltage upper limit exceeds the prescribed duration. For another example, the controller may detect the voltage of the dc bus 250, and determine that the grid-connected converter 220 is disconnected from the dc bus 250 and the micro-grid 260 is in the island operating state when the duration of the voltage of the dc bus 250 being less than or equal to the second preset value is longer than the second duration, that is, the duration of the voltage of the dc bus being lower than the preset voltage lower limit value exceeds the prescribed duration. For another example, the controller 212 may also receive an island signal from the grid-connected inverter 220, and determine that the grid-connected inverter 220 is disconnected from the dc bus 250 according to the island signal, and the micro-grid 260 is in an island operation state.

Optionally, the dc conversion circuit 211 includes a plurality of switching tubes, and the controller 212 is specifically configured to determine a first driving signal according to a difference between a current voltage of the dc bus 250 and a first output voltage, where the first driving signal is used to control on/off of the plurality of switching tubes, and adjust output power of the dc conversion circuit 211, so that the output voltage of the dc conversion circuit 211 to the dc bus 250 is the first output voltage. After the voltage of the dc bus 250 stabilizes to the first output voltage, the controller 212 determines a second driving signal according to the first threshold, where the second driving signal is used to control the on-off of the plurality of switching tubes, and adjust the output power of the dc conversion circuit 211, so that the output voltage of the dc conversion circuit 211 to the dc bus 250 is adjusted from the first output voltage to the rated voltage of the micro grid 260.

As a possible implementation, the energy storage converter 210 in the system 200 may include a plurality of dc conversion circuits, or the system 200 includes a plurality of energy storage converters, each including at least one dc conversion circuit, and the controller 212 is further configured to control the output power of these dc conversion circuits to have the same duty ratio with respect to the rated power when the micro-grid 260 is in the island operation state. For example, the dc conversion circuit 211 includes a first dc conversion circuit and a second dc conversion circuit, and the controller 212 is further configured to control a duty ratio of an output power of the first dc conversion circuit with respect to a rated power of the first dc conversion circuit to be the same as a duty ratio of an output power of the second dc conversion circuit with respect to a rated power of the second dc conversion circuit.

In this embodiment of the present application, the controller 212 may be further configured to control the output voltage of the dc conversion circuit 211 to adjust from the rated voltage of the micro-grid 260 to a second output voltage when it is determined that the grid-connected converter 220 meets the grid-connected condition, the second output voltage is the output voltage of the grid-connected converter 220, send a control signal to the grid-connected converter 220 after it is determined that the dc bus voltage 250 is stabilized at the second output voltage, and the control signal is used to instruct the grid-connected converter 220 to be connected to the dc bus 250, and control the output power of the dc conversion circuit 211 to the dc bus 250 to be the preset power of the dc conversion circuit 211 after the grid-connected converter 220 is connected to the dc bus 250.

The controller may receive the grid-connected signal from the grid-connected converter 220, and determine that the grid-connected converter 220 meets the grid-connected condition according to the grid-connected signal.

Optionally, the dc conversion circuit 211 includes a plurality of switching tubes, and the controller 212 is specifically configured to determine a third driving signal according to the rated voltage and the second output voltage of the micro-grid 260, where the third driving signal is used to control on/off of the plurality of switching tubes, and adjust the output power of the dc conversion circuit 211, so that the voltage of the dc bus 250 is adjusted from the rated voltage of the micro-grid 260 to the second output voltage.

In this embodiment, when the micro grid 260 is in the grid-connected working state, the controller 212 is further configured to detect the voltage of the dc bus 250, and adjust the output power of the dc conversion circuit 211 in a preset time after the voltage of the dc bus 250 changes between the first preset value and the second preset value, that is, in a short time when the voltage fluctuates between the preset upper voltage limit value and the preset lower voltage limit value, so as to adjust the voltage of the dc bus.

In the embodiment of the present application, the specific form of the controller is not limited, and may be at least one of DSP, CPLD, FPGA, CPU, MCU.

Fig. 3 shows a specific example of a controller provided in an embodiment of the present application. As shown in fig. 3, the controller 300 is a specific example of the controller 212 in fig. 2. The controller 300 includes a detection unit 310, an indirect power controller 330, a first self-resetting controller 340, a droop control unit 350, a voltage loop unit 360, an island voltage secondary regulation controller 370, a second self-resetting controller 380, 4 switches, and a plurality of comparators, and optionally, a ramp control unit 320. Wherein the indirect power controller 330 may also be referred to as an indirect current controller, in the present embodiment, the control power and the control current may be replaced for convenience of description.

Taking the initial operation state of the micro grid 260 as the grid-connected operation state as an example, in this case, the switch 1, the switch 2, the switch 3 and the switch 4 are all located at the M1 node. The island voltage secondary regulation command output by the island voltage secondary regulation controller 370 is negatively fed back to the input end of the island voltage secondary regulation command output by the second self-resetting controller 380, and in steady state, the island voltage secondary regulation command output by the island voltage secondary regulation controller 370 is 0. The indirect power controller 330 generates an indirect power secondary adjustment command according to the difference between the preset power and the actual power, and the sum of the island voltage secondary adjustment command and the indirect power secondary adjustment command is a voltage secondary adjustment command. The droop control unit 350 generates a voltage command according to the voltage secondary adjustment command, and the voltage loop unit 360 generates a driving signal according to the voltage command to control on-off of the plurality of switching tubes in the dc conversion circuit 211, thereby adjusting the output power of the dc conversion circuit 211.

Optionally, when the controller 300 has the ramp control unit 320, the ramp control unit 320 is configured to control the indirect power adjustment command to ramp from the initial value to the target value, so as to avoid voltage oscillation or current impact caused by abrupt change of the command, and improve stability of the power supply system.

Alternatively, the ramp control unit 320 may be other constraint units capable of avoiding abrupt instruction changes, such as a variable ramp control unit, a low-pass filter unit, and the like.

In the embodiment of the present application, when the bandwidth of the indirect power controller 330 is lower than a certain value, even if a direct connection unit is adopted (i.e. no constraint on any change rate of the input command is applied), the abrupt change of the adjustment command is not caused, and the purposes of avoiding voltage oscillation or current impact and improving the stability of the power supply system can be achieved.

Alternatively, the first self-resetting controller 340 and the second self-resetting controller 380 may be set to a unit gain, or may be set to another gain, for example, a low-pass filtering link, a high-pass filtering link, a slope control link, etc., so long as a voltage dynamic process of changing the voltage of the dc bus 250 to a normal level after the micro-grid 260 is in the island operation mode can be achieved, which is not limited in this application.

The process of the controller 212 controlling the power supply system 200 to switch from the grid-connected operation state to the island operation state is as follows:

(1) The detection unit 310 determines that the operation state of the micro-grid 260 is switched from the grid-connected operation state to the island operation state.

Specifically, the detecting unit 310 may determine that the operating state of the micro-grid 260 is switched from the grid-connected operating state to the island operating state by detecting the voltage of the dc bus 250 or by receiving the island signal from the grid-connected converter 220.

As a possible implementation manner, when the detecting unit 310 detects the voltage of the dc bus 250, the detecting unit 310 may obtain the real-time voltage of the dc bus 250, determine that the grid-connected converter 220 is disconnected from the dc bus 250 when the duration of the voltage of the dc bus 250 being greater than or equal to the first preset value is greater than the first duration, that is, the duration of the voltage of the dc bus 250 exceeding the preset voltage upper limit value exceeds the prescribed duration, and the micro-grid 260 is in the island operating state, or determine that the grid-connected converter 220 is disconnected from the dc bus 250 when the duration of the voltage of the dc bus 250 being less than or equal to the second preset value is greater than the second duration, that is, the duration of the voltage of the dc bus being lower than the preset voltage lower limit value exceeds the prescribed duration, and the micro-grid 260 is in the island operating state.

As another possible implementation manner, the detection unit 310 may receive an island signal from the grid-connected converter 220 or other control device, where the island signal is used to indicate that the micro-grid 260 is in an island working state, so as to determine, according to the island signal, that the grid-connected converter 220 is disconnected from the dc bus 250, and that the micro-grid 260 is in the island working state.

(2) The droop control unit 350 controls the output voltage of the dc conversion circuit 211 to the dc bus 250 to be the first output voltage.

Specifically, when the switch 1, the switch 2, and the switch 3 may be virtual switches, the detection unit 310 may adjust the switch 1, the switch 2, and the switch 3 from the M1 node to the M2 node by sending a driving signal, and the indirect power controller 330 and the first self-resetting controller 340 form a negative feedback loop, so that the indirect power secondary adjustment instruction output by the indirect power controller 330 is gradually reduced, and finally is 0, that is, the indirect power controller 330 is disabled, or the indirect power controller 330 is disabled. The droop control unit 350 outputs a first voltage command according to the indirect power secondary regulation command, and the voltage loop unit 360 outputs a first driving signal according to the first voltage command. The first driving signal is used for controlling the on-off of the plurality of switching tubes in the dc conversion circuit 211, and adjusting the output power of the dc conversion circuit 211 so that the output voltage of the dc conversion circuit 211 to the dc bus 250 is the first output voltage. The difference between the first output voltage and the rated voltage of the micro-grid 260 is a first threshold that is positively correlated to the power of the load 230 in the system 200. The first driving signal is a generic term of a type of driving signal, and may include a plurality of driving signals with different magnitudes or duty ratios, where the plurality of driving signals with different magnitudes or duty ratios may make the adjustment of the voltage of the dc bus 250 a progressive process. Specifically, due to the presence of the first self-reset controller 340, the indirect power secondary adjustment command of the indirect power controller 330 is a plurality of continuously decreasing values, which results in the first voltage command output by the droop control unit 350 being a continuously varying value, so that the adjustment of the voltage of the dc bus 250 by the droop control unit 350 is a continuously varying and progressive process, that is, the process of controlling the output voltage of the dc conversion circuit 211 to the dc bus 250 by the droop control unit 350 to adjust from the current voltage to the first output voltage includes at least one intermediate value. Therefore, abrupt change of the voltage of the direct current bus is avoided, and the stability of the power supply system is improved.

(3) The island voltage secondary regulation controller 370 controls the output voltage of the dc conversion circuit 211 to the dc bus 250 to be regulated from the first output voltage to the rated voltage of the micro grid 260.

Specifically, when the switch 4 may be a virtual switch circuit, the detecting unit 310 adjusts the switch 4 from the M1 node to the M2 node after detecting that the voltage of the dc bus 350 is stabilized to the first output voltage, that is, enables the island voltage secondary adjustment controller 370. The island voltage secondary adjustment controller 370 generates an island voltage secondary adjustment command according to the rated voltage of the micro grid 260 and the current voltage (stabilized to the first output voltage) of the dc bus 250, the droop control unit 350 outputs a second voltage command according to the island voltage secondary adjustment command, and the voltage loop unit 360 outputs a second driving signal according to the second voltage command. The second driving signal is used for controlling the on-off of the plurality of switching tubes in the dc conversion circuit 211, and adjusting the output power of the dc conversion circuit 211, so that the output voltage of the dc conversion circuit 211 to the dc bus 250 is adjusted from the first output voltage to the rated voltage of the micro-grid 260.

After the voltage of the dc bus 250 stabilizes to the rated voltage of the micro-grid 260, the power supply system 200 completes the process of switching from the grid-connected operation state to the island operation state.

Alternatively, the energy storage converter 210 in the system 200 may include a plurality of dc conversion circuits, or the air conditioner of the system 200 may include a plurality of energy storage converters, each including at least one dc conversion circuit. The first drive signal and the second drive signal are also used to control the duty ratio of the output power of the dc conversion circuits to the rated power to be the same when the micro grid 260 is in the island operation state. For example, the dc conversion circuit 211 includes a first dc conversion circuit and a second dc conversion circuit, where the first driving signal and the second driving signal are further used to control the duty ratio of the output power of the first dc conversion circuit to the rated power of the first dc conversion circuit to be the same as the duty ratio of the output power of the second dc conversion circuit to the rated power of the second dc conversion circuit. In this way, the output power of the direct current conversion circuit can be distributed according to the respective rated power in proportion, so that the overload of part of direct current conversion circuit and the overload of part of direct current conversion circuit are avoided, and the back and forth switching of part of energy storage converter between an overload constant power mode and a voltage control mode is avoided, and the voltage fluctuation and the power oscillation of the direct current bus are avoided.

When the micro-grid 260 is in the island operation state, the switch 1, the switch 2, the switch 3 and the switch 4 are all located at the M2 node. The indirect power control command output by the indirect power controller 330 is negatively fed back to the input end of the first self-resetter 340, and in steady state, the indirect power control command output by the indirect power controller 330 is 0. The island voltage secondary regulation controller 370 generates an island voltage secondary regulation command according to a difference between the real-time voltage of the dc bus 250 and the rated voltage of the micro grid 260, and the sum of the island voltage secondary regulation command and the indirect power secondary regulation command is the voltage secondary regulation command. The droop control unit 350 generates a voltage command according to the voltage secondary adjustment command, and the voltage loop unit 360 generates a driving signal according to the voltage command to control on-off of the plurality of switching tubes in the dc conversion circuit 211, so as to adjust the output voltage of the dc conversion circuit 211 to the dc bus 250.

The process of the controller 212 controlling the power supply system 200 to switch from the island operation state to the grid-connected operation state is as follows:

(a) The detection unit 310 determines that the system 200 satisfies the grid-tie condition.

Specifically, the detecting unit 310 may receive the grid-connected signal, and determine that the grid-connected converter 220 meets the grid-connected condition according to the grid-connected signal. The grid-connected signal may be from the grid-connected converter 220 or other devices or controllers in the system 200, which is not limited in this application.

(b) Island voltage secondary regulation controller 370 controls the regulation of the output voltage of dc conversion circuit 211 to dc bus 250 from the rated voltage of microgrid 260 to the output voltage of grid-tied inverter 220.

Specifically, the detection unit 310 may detect and obtain an output voltage (may be referred to as a second output voltage) of the grid-connected inverter 220, and the island voltage secondary adjustment controller 370 determines an island voltage secondary adjustment instruction according to a difference between the output voltage of the grid-connected inverter 220 and the rated voltage of the micro-grid 260. The droop control unit 350 determines a third voltage command according to the island voltage secondary adjustment command, and the voltage loop unit 360 outputs a third driving signal according to the third voltage command. The third driving signal is used for controlling the on-off of the plurality of switching tubes in the dc conversion circuit 211, and adjusting the output power of the dc conversion circuit 211, so that the voltage of the dc bus 250 is adjusted from the rated voltage of the micro-grid 260 to the output voltage of the grid-connected inverter 220.

(c) The indirect power controller 330 controls the output power of the dc conversion circuit to the dc bus to be a preset power of the dc conversion circuit.

Specifically, after the voltage of the dc bus 250 stabilizes to the output voltage of the grid-connected inverter 220, the detection unit 310 may send a control signal to the grid-connected switch 221 to control the grid-connected switch 221 to be closed, so that the grid-connected inverter 220 is connected to the dc bus 250. After detecting that the grid-connected converter 220 is connected with the direct current bus 250, the detecting unit 310 adjusts the switch 1, the switch 2, the switch 3 and the switch 4 from the M2 node to the M1 node, and at this time, the island voltage secondary adjusting controller 370 and the second self-resetting controller 380 form a negative feedback loop, so that the island voltage secondary adjusting instruction output by the island voltage secondary adjusting controller 370 is gradually reduced, and finally is 0, namely the island voltage secondary adjusting controller 370 is disabled, or the island voltage secondary adjusting controller 370 is disabled; the indirect power controller 330 generates an indirect power secondary adjustment command according to the difference between the preset power and the current actual power, so as to adjust the output power of the direct current conversion circuit 311, i.e. enable the indirect power controller 330.

Alternatively, the current actual power may be the real-time output power of the dc conversion circuit 211 in the island operation state.

After the output power of the dc conversion circuit 211 is stabilized at the preset power, the power supply system 200 completes the process of switching from the island operation state to the grid-connected operation state.

Optionally, when the power supply system 200 is in the grid-connected operation state, the detecting unit 310 may further continuously detect the voltage of the dc bus 250, and adjust the output power of the dc conversion circuit 211 during a preset time after the voltage of the dc bus 250 changes between the first preset value (the preset upper voltage limit value) and the second preset value (the preset lower voltage limit value), so as to adjust the voltage of the dc bus 250. In this way, when the load in the power supply system generates the jump allowed by the system, the output power of the energy storage converter is controlled to provide transient support for the voltage of the direct current bus, so that the stability of the power supply system is improved. In this process, the portion of the output power of the energy storage converter that does not match the system load power may be borne by the grid-tied converter.

Fig. 4 is a schematic flow chart of a control method of a micro-grid power supply system according to an embodiment of the present application. The method is performed by the power supply system shown in fig. 2, and more particularly, may be performed by the controller shown in fig. 3. Before the method is executed, the micro-grid is in a grid-connected working mode.

S410, determining that the grid-connected converter is disconnected from the direct current bus, and the micro-grid is in an island working state.

Specifically, as a possible implementation manner, the controller may continuously detect the voltage of the dc bus, and determine that the grid-connected converter is disconnected from the dc bus when the duration time that the voltage of the dc bus is greater than or equal to the first preset value is longer than a first duration time, that is, the voltage of the dc bus exceeds a preset voltage upper limit value and the duration time exceeds a specified duration time, and the micro grid is in an island working state; or when the duration that the voltage of the direct current bus is smaller than or equal to the second preset value is longer than the second duration, namely the voltage of the direct current bus is lower than the preset voltage lower limit value, and the duration exceeds the preset duration, the grid-connected converter is determined to be disconnected from the direct current bus, and the micro-grid is in an island working state. As another possible implementation manner, the controller may receive an island signal from the grid-connected converter or other control devices, where the island signal is used to indicate that the micro-grid is in an island working state, so that it is determined that the micro-grid is in the island working state according to the island signal and the dc bus terminal.

If the grid-connected converter is not disconnected from the dc bus, the micro-grid is still in the grid-connected working state, and S410 is continuously executed. And after the grid-connected converter is determined to be disconnected from the direct current bus and the micro-grid is in the island working state, continuing to execute S420.

S420, controlling the output voltage of the direct current conversion circuit to the direct current bus to be the first output voltage.

The difference value between the first output voltage and the rated voltage of the micro-grid is a first threshold value, and the first threshold value is positively related to the load power in the power supply system.

In the embodiment of the application, at least one intermediate value exists in the process of controlling the output voltage of the direct current conversion circuit to change from the initial value to the first output voltage of the direct current bus, so that abrupt change of the voltage of the direct current bus can be avoided, and the stability of a power supply system is improved.

And S430, determining that the voltage of the direct current bus is stabilized at the first output voltage.

Specifically, the controller may continuously detect the voltage of the dc bus, and if the voltage of the dc bus continuously fluctuates or is not stabilized at the first output voltage, continuously perform the detection. After determining that the voltage of the dc bus is stabilized at the first output voltage, S440 is performed.

S440, controlling the output voltage of the direct current conversion circuit to the direct current bus to be adjusted from the first output voltage to the rated voltage of the micro-grid.

After the voltage of the direct current bus is stabilized to be the rated voltage of the micro-grid, the conversion of the power supply system from the grid-connected working mode to the island working mode is completed.

S450, determining that the grid-connected converter meets grid-connected conditions.

Specifically, the controller may receive the grid-connected signal, and determine that the grid-connected converter meets the grid-connected condition according to the grid-connected signal. The grid-connected signal may be from a grid-connected converter or other devices or controllers in the power supply system, which is not limited in this application.

S460, the output voltage of the direct current conversion circuit to the direct current bus is controlled to be adjusted from the rated voltage of the micro-grid to the second output voltage.

The second output voltage is the output voltage of the grid-connected converter.

S470, determining that the voltage of the dc bus is stabilized at the second output voltage.

Specifically, the controller may continuously detect the voltage of the dc bus, and if the voltage of the dc bus continuously fluctuates or is not stabilized at the second output voltage, continuously perform the detection. When it is determined that the voltage of the dc bus is stabilized at the second output voltage, S480 is performed.

And S480, sending a control signal to the grid-connected converter, wherein the control signal is used for indicating the grid-connected converter to be connected with the direct current bus.

S490, the output power of the direct current conversion circuit to the direct current bus is controlled to be the preset power of the direct current conversion circuit.

The beneficial effects of embodiments of the present application are described below in conjunction with fig. 5, 6, and 7. The schematic diagrams shown in fig. 5 and fig. 7 are simulation results that the set value of the output power of the energy storage converter (direct current conversion circuit) is smaller than the load power, and the schematic diagram shown in fig. 6 is a simulation result that the set value of the output power of the energy storage converter (direct current conversion circuit) is larger than the load power. The simulation result comprises a direct-current voltage waveform, a real-time power waveform output by each device, and waveforms of an indirect current regulation command and an island voltage regulation command. In the simulation process of fig. 5 and 6, the rated voltage of the micro-grid is 750V, the bandwidth of the intermediate current-connecting controller of the controller is 1Hz, the bandwidth of the droop control unit is 10Hz, and the droop coefficient is 1.3×10 ^-4 V/W, the first and second self-resetting controllers 340 and 380 each include a unit gain cell.

As shown in fig. 5, before 1s, the micro grid 260 in the power supply system 200 is in a grid-connected working state, and the preset discharge power (i.e., the initial value of the indirect current) of the energy storage converter 210 (more specifically, the direct current conversion circuit 211 in the energy storage converter 210) is 20A (the corresponding power is 15 kW), the current of the load 230 in the system is 100A (the corresponding power is 75 kW), and the remaining 80A (the corresponding power is 60 kW) is provided by the grid-connected converter 220. At 1s, the grid-connected switch 221 is tripped, the output power of the grid-connected converter 220 is 0, and the micro-grid 260 is in an island working state. At this time, since the output current of the energy storage converter 210 is smaller than the current required by the load 230, the dc bus voltage 250 continuously drops to 700V (the second preset voltage, i.e. the preset voltage lower limit value), and then the controller 212 in the energy storage converter 210 is triggered to execute the switching control from the grid-connected operation mode to the island operation mode, and the switch 1, the switch 2 and the switch 3 are adjusted from the M1 node to the M2 node. At this time, the first self-reset controller 340 is started, the indirect power controller 330 is gradually reset, and the output indirect power secondary adjustment command is 0 in the steady state. Specifically, as shown in FIG. 5, the indirect power adjustment command is gradually reset from an initial-40V at 1.09s, reaches-10V at 1.36s, and outputs about 0 at 2s, essentially completing the reset process. Meanwhile, the controller 212 supports the dc bus 250 voltage through the droop control unit 350, the dc bus 350 voltage also slowly recovers, and finally the dc bus 350 voltage is stabilized at 740V (first output voltage). Subsequently, at 3s, the switch 4 is switched from the M1 node to the M2 node, and the dc bus 250 voltage is gradually restored from 740V to 750V (i.e., the rated voltage of the micro grid 260) by the regulation of the island voltage regulation controller 370. In the island operation mode of the micro grid 260, the output current value of the energy storage converter 210 is 100A. Thus, the controller 212 completes the switching control from the grid-connected operation mode to the island operation mode, and the voltage of the direct current bus 250 is stable and has no impact in the switching process.

Between 4s and 5s, the controller 212 receives the grid-connected signal, and meanwhile, the voltage of the direct current bus 250 is stabilized at 750V, and it is determined that the grid-connected condition is met, and switching control from the island operation mode to the grid-connected operation mode can be performed. Subsequently, the island voltage secondary regulation controller 370 regulates the output voltage to the dc bus 250 to the output voltage of the grid-connected inverter 220. Here, the current output voltage of the dc bus 250 is stabilized at 750V, and the output voltage of the grid-connected inverter 220 is also 750V, without additional adjustment. At 5s, the controller 212 sends a control signal to control the grid-tie switch 221 to close and the micro-grid 260 is smoothly connected to an external grid (e.g., ac grid 222). After grid connection, after the voltage of the direct current bus 250 is stable and has no fluctuation, the controller 212 controls the switch 1, the switch 2, the switch 3 and the switch 4 to be switched from the M2 node to the M1 node at 6 s. At this time, the second self-reset controller 380 is activated, and the island voltage secondary regulation controller 330 is gradually reset. Specifically, the island voltage adjustment command output from the island voltage adjustment controller 370 is gradually reset from the initial 10V at 6s, is reduced to 2V at 6.32s, and is output at about 0 at 7s, thereby basically completing the reset process. At the same time, the indirect power controller 330 is re-enabled. The initial value of the indirect power adjustment command is the output current value of the energy storage converter 210 in the island operation mode, namely 100A. The indirect power set point is set to 20A (i.e., the preset power of the direct current conversion circuit 211), and the output power of the direct current conversion circuit 211 is ramped from 75kW (corresponding to a current of 100A) to 15kW (corresponding to a current of 20A). Thus, the controller 212 completes the switching control from the island operation mode to the grid-connected operation mode, and the voltage of the direct current bus 250 is stable and has no impact in the switching process.

In the simulation waveform diagram shown in fig. 6, only the direction of change of the voltage of the dc bus is different from that of fig. 5, and the rest of the structure is the same or similar. As shown in fig. 6, before 1s, the micro grid 260 in the power supply system 200 is in a grid-connected operation state, and the set point of the indirect current of the energy storage converter 210 (more specifically, the direct current conversion circuit 211 in the energy storage converter 210) is 50A (the set point of the corresponding indirect power is 37.5 kW), the current of the load 230 in the system is 20A (the corresponding power is 15 kW), and the additionally generated 22.5kW of power is transmitted to the alternating current grid 222 by the grid-connected converter 220. At 1s, the grid-connected switch 221 is tripped, the output power of the grid-connected converter 220 is 0, and the micro-grid 260 is in an island working state. At this time, since the output current of the energy storage converter 210 is greater than the current required by the load 230, the dc bus voltage 250 continuously increases to 800V (the first preset voltage, i.e., the preset upper voltage limit value), and then the controller 212 in the energy storage converter 210 is triggered to perform the switching control from the grid-connected operation mode to the island operation mode, and the switch 1, the switch 2 and the switch 3 are adjusted from the M1 node to the M2 node. At this time, the first self-reset controller 340 is started, the indirect power controller 330 is gradually reset, and the output indirect power secondary adjustment command is 0 in the steady state. Specifically, referring to fig. 6, the indirect current regulation command output from the indirect power controller 330 is gradually reset from an initial 50V at 1.29s, falls to 10V at 1.62s, and is output at about 0 at 3.3s, essentially completing the reset process. The dc bus 250 voltage slowly drops, and the controller 212 stabilizes the dc bus voltage 250 at 748V (the first output voltage) by droop control in steady state. At 3s, switch 4 is switched from node M1 to node M2, and the dc bus 250 voltage gradually reverts from 748V to 750V (i.e., the rated voltage of the micro-grid 260) by regulation of the island voltage secondary regulator controller 370. In the island operation mode of the micro grid 260, the output current value of the energy storage converter 210 is 20A. Thus, the controller 212 completes the switching control from the grid-connected operation mode to the island operation mode, and the voltage of the direct current bus 250 is stable and has no impact in the switching process.

Between 4s and 5s, the controller 212 receives the grid-connected signal, and meanwhile, the voltage of the direct current bus 250 is stabilized at 750V, and it is determined that the grid-connected condition is met, and switching control from the island operation mode to the grid-connected operation mode can be performed. Subsequently, the island voltage secondary regulation controller 370 regulates the output voltage to the dc bus 250 to the output voltage of the grid-connected inverter 220. Here, the current output voltage of the dc bus 250 is stabilized at 750V, and the output voltage of the grid-connected inverter 220 is also 750V, without additional adjustment. At 5s, the controller 212 sends a control signal to control the grid-tie switch 221 to close and the micro-grid 260 is smoothly connected to an external grid (e.g., ac grid 222). The initial value of the indirect power set point is set to be the output power value of the energy storage converter 210 in off-grid mode, namely 15kW (corresponding to a current value of 20A). At 6s, after the indirect power given value is set to be the target value of 37.5kW (the corresponding current value is 50A), the output power of the energy storage converter 210 is changed from 15kW to 37.5kW, and the output current of the direct current side of the corresponding grid-connected converter 220 is gradually reduced from 0 to-30A. Meanwhile, the island voltage secondary regulation command output by the island voltage secondary regulation controller 370 is gradually reset from the initial 2V at 6s, is reduced to 1V at 6.15s, and is about 0 at 7s, so that the reset is basically completed. Thus, the controller 212 completes the switching control from the island operation mode to the grid-connected operation mode, and the voltage of the direct current bus 250 is stable and has no impact in the switching process.

Fig. 7 shows another example simulation result diagram. In comparison with fig. 5, in the process of obtaining the simulation result shown in fig. 7, the ramp control unit 320 is not present, and the ramp control unit 320 may be replaced by a direct connection unit, and correspondingly, the first self-resetting controller 340 and the second self-resetting controller 380 are set as first-order low-pass filters with a bandwidth of 10 Hz. Since the bandwidth of the indirect power controller 330 is very low (1 Hz), even if the ramp control unit 320 is replaced by a direct connection unit, no abrupt change of the indirect current regulation command is generally caused, and no voltage oscillation or current surge is caused. As shown in fig. 7, compared with the simulation result of the corresponding embodiment in fig. 5, in the corresponding embodiment in fig. 7, after the switching for 6s, the recovery speed of the voltage of the dc bus 250 is faster, and at the same time, the speed of the output current reaching the given value after the energy storage converter 210 enables the indirect current control after the switching is also faster. The embodiment can also realize the off-grid seamless switching of the energy storage converter 210, the switching process is stable and has no impact, the voltage of the direct current bus 250 is recovered at a higher speed after the energy storage converter 210 is switched in the off-grid operation mode, and the power adjustment dynamic response is faster after the off-grid operation mode is switched.

In summary, compared with the existing off-grid operation method, the embodiment of the application adopts a control structure that the current or power control outer ring and the voltage droop control inner ring are connected in series on the control structure, the control command mutation and the current impact problem caused by the control command mutation during switching of different control loops are avoided, and the dynamic stability problem caused by asynchronous off-grid switching of different equipment is avoided, so that smooth switching between the off-grid operation modes can be realized. In addition, voltage sag control in the control structure of the embodiment of the application always acts, so that the energy storage converter has better voltage supporting effect on the direct current bus in a grid-connected mode, and the influence of different energy storage ratios on the operation of a power supply system can be reduced. In addition, in the embodiment of the application, the output of the indirect current or power controller and the output of the direct current bus voltage secondary regulator are subjected to enabling and self-resetting treatment, so that the problem of abrupt change of a voltage reference instruction can be avoided when the energy storage converter is switched in an off-grid operation mode, and the direct current bus oscillation and power fluctuation are avoided.

In the embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. The above-described apparatus embodiments are merely illustrative, for example, the division of the units is merely a logical function division, and there may be additional divisions when actually implemented, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices or units, which may be in electrical, mechanical or other form.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present application may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit.

The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer-readable storage medium. Based on such understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a read-only memory (ROM), a random access memory (random access memory, RAM), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

The foregoing is merely specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present application, and the changes and substitutions are intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A microgrid power supply system, comprising:

the energy storage converter comprises a controller and a direct current conversion circuit, wherein the controller is used for controlling the direct current conversion circuit to receive electric energy output by the energy storage unit and supplying power to the micro-grid through a direct current bus after direct current conversion;

the grid-connected converter is used for receiving alternating voltage output by the alternating current power grid, converting the alternating voltage into direct current voltage and supplying power to the micro power grid through the direct current bus;

the controller is further configured to:

when the grid-connected converter is determined to be disconnected from the direct current bus, and the micro-grid is in an island working state, controlling the output voltage of the direct current conversion circuit to the direct current bus to be a first output voltage, supplying power to the micro-grid, wherein the difference value between the first output voltage and the rated voltage of the micro-grid is a first threshold value, the first threshold value is positively related to the power of the load, and at least one intermediate value is included in the process of controlling the output voltage of the direct current conversion circuit to the direct current bus to be the first output voltage;

And when the voltage of the direct current bus is determined to be stable at the first output voltage, controlling the direct current conversion circuit to adjust the output voltage of the direct current bus from the first output voltage to the rated voltage of the micro-grid, and supplying power to the micro-grid.

2. The system of claim 1, wherein the controller is specifically configured to:

detecting the voltage of the direct current bus, and determining that the grid-connected converter is disconnected from the direct current bus when the duration time of the voltage of the direct current bus being greater than or equal to a first preset value is longer than a first duration time, wherein the micro-grid is in an island working state; or alternatively, the process may be performed,

detecting the voltage of the direct current bus, and determining that the grid-connected converter is disconnected from the direct current bus when the duration time that the voltage of the direct current bus is smaller than or equal to a second preset value is longer than a second duration time, wherein the micro-grid is in an island working state; or alternatively, the process may be performed,

and receiving an island signal from the grid-connected converter, determining that the grid-connected converter is disconnected from the direct current bus according to the island signal, and enabling the micro-grid to be in an island working state.

3. The system according to claim 1 or 2, wherein the dc conversion circuit comprises a plurality of switching tubes, the controller being specifically configured to:

Determining a first driving signal according to the difference value between the current voltage of the direct current bus and the first output voltage, wherein the first driving signal is used for controlling the on-off of the plurality of switching tubes and adjusting the output power of the direct current conversion circuit so that the output voltage of the direct current conversion circuit to the direct current bus is the first output voltage;

and determining a second driving signal according to the first threshold value, wherein the second driving signal is used for controlling the on-off of the plurality of switching tubes and adjusting the output power of the direct current conversion circuit so that the output voltage of the direct current conversion circuit to the direct current bus is adjusted from the first output voltage to the rated voltage of the micro-grid.

4. The system of any one of claims 1 to 3, wherein the DC conversion circuit comprises a first DC conversion circuit and a second DC conversion circuit,

the controller is further configured to control a duty ratio of the output power of the first dc conversion circuit relative to the rated power of the first dc conversion circuit to be the same as a duty ratio of the output power of the second dc conversion circuit relative to the rated power of the second dc conversion circuit.

5. The system of any one of claims 1 to 4, wherein the controller is further configured to:

when the grid-connected converter meets grid-connected conditions, controlling the output voltage of the direct current conversion circuit to the direct current bus to be adjusted from the rated voltage of the micro-grid to a second output voltage, wherein the second output voltage is the output voltage of the grid-connected converter;

when the direct current bus voltage is determined to be stable at the second output voltage, a control signal is sent to the grid-connected converter, and the control signal is used for indicating the grid-connected converter to be connected with the direct current bus;

and after the grid-connected converter is connected with the direct current bus, controlling the output power of the direct current conversion circuit to the direct current bus to be the preset power of the direct current conversion circuit.

6. The system of claim 5, wherein the controller is specifically configured to:

receiving a grid-connected signal from the grid-connected converter, and determining that the grid-connected converter meets grid-connected conditions according to the grid-connected signal.

7. The system according to claim 5 or 6, wherein the dc conversion circuit comprises a plurality of switching tubes, the controller being specifically configured to:

And determining a third driving signal according to the rated voltage of the micro-grid and the second output voltage, wherein the third driving signal is used for controlling the on-off of the switching tubes and adjusting the output power of the direct current conversion circuit so as to adjust the voltage of the direct current bus from the rated voltage of the micro-grid to the second output voltage.

8. The system of any one of claims 5 to 7, wherein the controller is further configured to:

detecting the voltage of the direct current bus, and adjusting the output power of the direct current conversion circuit in a preset time after the voltage of the direct current bus changes between the first preset value and the second preset value so as to adjust the voltage of the direct current bus.

9. The system according to any one of claims 1 to 8, wherein the controller comprises at least one of a digital signal processor DSP, a complex programmable logic device CPLD, a field programmable gate array FPGA, a central processing unit CPU or a micro control unit MCU.

10. A method for controlling a micro-grid power supply system, the system comprising:

the energy storage converter comprises a controller and a direct current conversion circuit, wherein the controller is used for controlling the direct current conversion circuit to receive the electric energy output by the energy storage unit and supplying power to the micro-grid through a direct current bus after direct current conversion,

the method comprises the following steps:

when the controller determines that the grid-connected converter is disconnected from the direct current bus and the micro-grid is in an island working state, controlling the output voltage of the direct current conversion circuit to the direct current bus to be a first output voltage and supplying power to the load, wherein the difference value between the first output voltage and the rated voltage of the micro-grid is a first threshold value, the first threshold value is positively related to the power of the load, and at least one intermediate value is included in the process of controlling the output voltage of the direct current conversion circuit to the direct current bus to be the first output voltage;

and when the controller determines that the voltage of the direct current bus is stable at the first output voltage, controlling the direct current conversion circuit to adjust the output voltage of the direct current bus from the first output voltage to the rated voltage of the micro-grid, and supplying power to the micro-grid.

11. The method according to claim 10, wherein the method further comprises:

When the controller determines that the grid-connected converter meets grid-connected conditions, controlling the output voltage of the direct current conversion circuit to the direct current bus to be adjusted from the rated voltage of the micro-grid to a second output voltage, wherein the second output voltage is the output voltage of the grid-connected converter;

when the controller determines that the voltage of the direct current bus is stable at the second output voltage, a control signal is sent to the grid-connected converter, and the control signal is used for indicating the grid-connected converter to be connected with the direct current bus;

and after the grid-connected converter is connected with the direct current bus, the controller controls the output power of the direct current conversion circuit to the direct current bus to be the preset power of the direct current conversion circuit.