CN115776130A

CN115776130A - Grid-connected and off-grid switching method, energy storage converter, energy storage system and power system

Info

Publication number: CN115776130A
Application number: CN202211717147.3A
Authority: CN
Inventors: 欧阳超; 王仕城; 胡磊; 范科
Original assignee: Beijing Suoying Electric Technology Co ltd
Current assignee: Beijing Suoying Electric Technology Co ltd
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2023-03-10
Anticipated expiration: 2042-12-29
Also published as: CN115776130B

Abstract

The application discloses grid-connected and off-grid switching method, energy storage converter, energy storage system and power system, the method comprises the following steps: receiving a switching instruction; judging whether the SOC value of the energy storage system is larger than a set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval and whether the first apparent power is in a first apparent power preset interval; if so, controlling the energy storage converter to enter a soft grid-connected and off-grid switching SVF mode; judging whether the switch state of the public connection point is in a switching-off state, whether the voltage of the second power grid side exceeds a second preset voltage interval, whether the frequency of the second power grid side exceeds a second preset frequency interval, or whether the second apparent power exceeds a second apparent power preset interval; and if so, controlling the energy storage converter to be switched from the SVF mode to the off-grid mode. The application realizes the grid-connection and off-grid seamless switching of the load, and improves the power consumption feeling of the load side user.

Description

Grid-connected and off-grid switching method, energy storage converter, energy storage system and power system

Technical Field

The application relates to the technical field of power systems, in particular to a grid-connected and grid-disconnected switching method, an energy storage converter, an energy storage system and a power system.

Background

At present, under some micro-grid or important load power-protection scenes, when a power grid loses power, an energy storage system runs off the grid and serves as a voltage source to supply power to a load through an energy storage converter, when the power grid is powered on, the energy storage system runs in a grid-connected mode to charge a battery through the energy storage converter, and meanwhile, the load is connected to the power grid and is supplied with power to the load through the power grid.

The prior art requires that when a power grid is powered off, the energy storage system is switched from grid-connected operation to off-grid operation, so that the switching time of switching power supply of the power grid to load supply and switching off-grid of the energy storage system to load supply is not more than 20 milliseconds, otherwise, the load and equipment in a corresponding circuit are shut down or are in fault shutdown. And when the grid-connected and grid-disconnected switching time is from hundreds of microseconds to a few milliseconds, the load is not influenced by grid-connected and grid-disconnected switching and can continue to operate stably and reliably.

With the function of the energy storage system becoming more and more abundant, how to implement load and off-grid seamless switching becomes a technical problem that needs to be solved urgently by those skilled in the art in order to improve the power consumption experience of the load terminal.

Disclosure of Invention

In view of this, the application discloses a grid-connected and grid-disconnected switching method, an energy storage converter, an energy storage system and an electric power system, so as to implement load-unaware grid-connected and grid-disconnected seamless switching, and greatly improve the power consumption experience of a load-side user.

In a first aspect, the present application provides a grid-connected and grid-disconnected switching method, which is applied to an energy storage converter in an energy storage system, and the method includes:

receiving a switching instruction;

acquiring an energy storage system SOC value, a first power grid side voltage and a first power grid side frequency of a public connection point switch lower port of an energy storage converter and a load, and a first apparent power based on a switching instruction;

judging whether the SOC value of the energy storage system is larger than a set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval and whether the first apparent power is in a first apparent power preset interval;

if so, controlling the energy storage converter to enter a soft grid-connected and off-grid Switching (SVF) mode, and when the energy storage converter is in the SVF mode, determining a driving signal of an Insulated Gate Bipolar Transistor (IGBT) in the energy storage converter by the three-phase voltage of the grid side of the energy storage converter;

acquiring a public connection point switch state, a second power grid side voltage, a second power grid side frequency and a second apparent power of a lower port of a public connection point switch after the energy storage converter enters an SVF mode;

judging whether the switch state of the public connection point is in a switching-off state, whether the voltage of the second power grid side exceeds a second preset voltage interval, whether the frequency of the second power grid side exceeds a second preset frequency interval, or whether the second apparent power exceeds a second apparent power preset interval;

if the voltage of the load is higher than the preset voltage, the energy storage converter is controlled to be switched from the SVF mode to the off-grid mode, and the load is switched from the power supply loop of the power grid to the power supply loop of the energy storage converter.

In some possible embodiments, the controlling the energy storage converter to enter the SVF mode includes:

acquiring three-phase voltage of a power grid side of the energy storage converter;

performing Clark transformation on the three-phase voltage of the power grid side to obtain a d-axis voltage component and a q-axis voltage component in a rectangular coordinate system;

processing the d-axis voltage component to obtain a d-axis voltage;

processing the q-axis voltage component to obtain a q-axis voltage;

performing Clark reverse transformation on the d-axis voltage and the q-axis voltage, and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) AC side pin of the energy storage converter based on a Clark reverse transformation result and a three-phase voltage phase-locked frequency value of a power grid side of the energy storage current device;

and inputting the three-phase voltage driving signal into an IGBT driver for IGBT modulation, so that the energy storage converter enters an SVF mode.

In some possible embodiments, processing the d-axis voltage component to obtain a d-axis voltage includes:

obtaining d-axis voltage correction by subtracting the d-axis voltage component and a voltage compensation quantity, wherein the voltage compensation quantity is the product of a d-axis current variation quantity and a compensation coefficient of the alternating-current side inductive current of the energy storage converter;

inputting the result of the difference between the d-axis voltage correction quantity and the d-axis voltage component into a first PI regulator to obtain a d-axis voltage regulating quantity;

and adding the d-axis voltage adjustment quantity and the d-axis voltage correction quantity to obtain a d-axis voltage.

In some possible embodiments, processing the q-axis voltage component to obtain a q-axis voltage includes:

and inputting a difference result between the q-axis voltage component and the q-axis voltage given quantity into a second PI regulator to obtain a q-axis voltage, wherein the q-axis voltage given quantity takes a value of 0.

In some possible embodiments, after controlling the energy storage converter to switch from the SVF mode to the off-grid mode, so that the load is switched from the grid supply circuit to the energy storage converter supply circuit, the method further includes:

acquiring third power grid side voltage and third power grid side frequency of an upper port of a switch of a public connection point after the energy storage converter enters an off-grid mode;

judging whether the voltage of the third power grid side is in a third preset voltage interval or not and whether the frequency of the third power grid side is in a third preset frequency interval or not;

if so, determining that the energy storage converter completes the following of the voltage frequency and the phase of the power grid;

controlling a common connection point switch of the energy storage converter and the load to be switched on, so that the load is switched to a power supply loop of a power grid;

and controlling the energy storage converter to exit the SVF mode.

In a second aspect, the present application provides an energy storage converter comprising:

an instruction receiving unit for receiving a switching instruction;

the first acquisition unit is used for acquiring the SOC value of the energy storage system, and the first power grid side voltage, the first power grid side frequency and the first apparent power of the lower port of the public connection point switch of the energy storage converter and the load based on the switching instruction;

the first judging unit is used for judging whether the SOC value of the energy storage system is larger than the set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval and whether the first apparent power is in a first apparent power preset interval;

the first mode switching unit is used for controlling the energy storage converter to enter a soft grid-connected and off-grid Switching (SVF) mode under the condition that the first judgment unit judges that the voltage of the energy storage converter is positive, and when the energy storage converter is in the SVF mode, a driving signal of an Insulated Gate Bipolar Transistor (IGBT) in the energy storage converter is determined by the three-phase voltage of the power grid side of the energy storage converter;

the second acquisition unit is used for acquiring the switching state of the public connection point after the energy storage converter enters the SVF mode, and the second power grid side voltage, the second power grid side frequency and the second apparent power of the lower port of the public connection point switch;

the second judging unit is used for judging whether the switch state of the public connection point is a switching-off state or not, whether the voltage of the second power grid side exceeds a second preset voltage interval or not, whether the frequency of the second power grid side exceeds a second preset frequency interval or not, or whether the second apparent power exceeds a second apparent power preset interval or not;

and the second mode switching unit is used for controlling the energy storage converter to be switched from the SVF mode to the off-grid mode under the condition that the second judging unit judges that the voltage is positive, so that the load is switched to the power supply loop of the energy storage converter.

In some possible embodiments, the first mode switching unit includes:

the voltage acquisition subunit is used for acquiring the three-phase voltage of the power grid side of the energy storage converter;

the transformation subunit is used for carrying out Clark transformation on the three-phase voltage at the power grid side to obtain a d-axis voltage component and a q-axis voltage component in a rectangular coordinate system;

the first correction subunit is used for processing the d-axis voltage component to obtain a d-axis voltage;

the second correction subunit is used for processing the q-axis voltage component to obtain a q-axis voltage;

the inverse transformation subunit is used for carrying out Clark inverse transformation on the d-axis voltage and the q-axis voltage and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) alternating-current side pin of the energy storage converter based on a Clark inverse transformation result and a three-phase voltage phase-locked frequency value of a power grid side of the energy storage current device;

and the adjusting subunit is used for inputting the three-phase voltage driving signal to the IGBT driver for IGBT modulation, so that the energy storage converter enters an SVF mode.

In a third aspect, the present application provides an energy storage system comprising: the energy storage converter is provided.

In a fourth aspect, the present application provides a power system comprising: a power grid, a power generation system, a load, a common ac bus, a master controller, a grid switch, a load switch, an energy storage ac side switch and the energy storage system of claim 8;

the power grid is connected to the public alternating current bus through a power grid switch;

the load is connected to the public alternating current bus through the load switch;

the energy storage system includes: the energy storage device is connected to the public alternating current bus through the energy storage converter, the transformer and the energy storage alternating current side switch in sequence;

the power generation system includes: at least one power generation device and a corresponding power generation AC side switch, each power generation device being connected to a common AC bus through one power generation AC side switch;

the total controller is connected with load, energy memory, energy storage converter, each power generation facility, grid switch, load switch, energy storage AC side switch and each electricity generation AC side switch respectively, and wherein, power generation facility includes: any one or more of a wind power generation apparatus, a photovoltaic power generation apparatus, and a fuel oil power generation apparatus.

In some possible embodiments, the power generation apparatus comprises: during wind power generation set, photovoltaic power generation set and fuel power generation set, total controller is used for:

acquiring a first switching instruction for switching from grid connection to grid disconnection;

based on the first switching instruction, adjusting the generating power of the wind driven generator set, the generating power of the photovoltaic equipment and the operating power of the energy storage system, and combining the total power of the load, adjusting the lower port power of a common connection point switch of the energy storage converter and the load to the power of the common connection point switch, and adjusting the SOC value of the electric quantity of the energy storage system within a preset SOC range;

sending a mode switching instruction to the energy storage converter, and enabling the energy storage converter to enter an SVF mode under the condition that a first mode switching condition is met, wherein the first mode switching condition is as follows: the voltage of the lower port of the public connection point switch is in a fourth preset voltage interval, the frequency of the power grid side of the public connection point switch is in a fourth preset frequency interval, and the power of the lower port of the public connection point switch is in a preset power interval;

acquiring feedback information sent by the energy storage converter after the energy storage converter enters an SVF mode;

controlling the switch of the public connection point to be switched off according to the feedback information;

adjusting the SOC value of the energy storage system to a preset SOC range, controlling the energy storage converter to be switched into an off-grid mode by the SVF mode when meeting a second mode switching condition, and switching the load to an energy storage converter power supply loop, wherein the second mode switching condition is as follows: and the lower port voltage exceeds a fifth preset voltage interval, or the frequency of the power grid side exceeds a fifth preset frequency interval, or the range of the lower port power is in a sixth preset power interval, or a switching-off feedback signal of the switch of the public connection point is received.

In some possible embodiments, after controlling the energy storage converter to switch from the SVF mode to the off-grid mode, the method further includes:

judging whether a power protection mode of a priority power supply load is started or not;

if so, judging whether the SOC value of the energy storage battery is not greater than a first preset warning value or not;

and if so, disconnecting a load switch connected between the non-priority power supply load and the public alternating current bus, wherein the load in the power system comprises: a priority power supply load and a non-priority power supply load;

judging whether the SOC value of the latest energy storage battery is not greater than a second preset alarm value or not;

and if so, disconnecting the connection paths between the wind power generation device and the photovoltaic power generation device and the public alternating current bus.

In some possible embodiments, after the step of disconnecting the connection path between the wind power generation device and the photovoltaic power generation device and the common ac bus, the method further includes:

conducting a power generation branch where the fuel power generation device is located;

judging whether the voltage range of the fuel oil power generation side is in a preset voltage range or not and whether the frequency range of the fuel oil power generation side is in a preset frequency range or not;

if so, controlling the energy storage converter to follow the frequency and the phase of the fuel oil power generation side;

acquiring a following result fed back by the energy storage converter at any time, and conducting a connecting passage between the fuel power generation device and a public alternating current bus to switch a load to a fuel power supply loop;

and controlling the energy storage converter to exit the VF mode.

In some possible embodiments, the power generation apparatus comprises: during wind power generation set, photovoltaic power generation set and fuel power generation set, total controller still is used for:

acquiring a second switching instruction from the off-grid to the on-grid;

calculating the power sum of the generated power of the wind generating set and the generated power of the photovoltaic equipment;

calculating the absolute value of the difference between the power sum and the total power consumption value of the load;

judging whether the absolute value of the difference value is not greater than the absolute value of the first preset apparent power;

if the current is the grid-connected state, the energy storage converter is controlled to start to be switched from the grid to the grid, and the frequency and the phase of an upper port power grid of the public connection point switch are followed when the energy storage converter confirms that a preset following condition is met, wherein the preset following condition is as follows: the public connection point switch is in a switching-off state, the voltage range of an upper port of the public connection point switch is in a preset voltage range, the frequency of the upper port of the public connection point switch is in a preset frequency range, and the apparent power of the energy storage converter is not larger than the absolute value of a first preset apparent power;

and acquiring a following result fed back by the energy storage converter after the following is finished, and controlling the power grid switch to be switched on to switch the load to a power grid power supply loop.

In some possible embodiments, after the master controller controls the grid switch to be turned on, so that the load is switched to the grid power supply loop, the energy storage converter is further configured to:

judging whether the latest apparent power of the energy storage converter is not less than a second preset apparent power or not, and whether the instantaneous current detected by the energy storage converter is not less than a preset instantaneous current threshold or not, or acquiring a closing feedback signal of a switch of a public connection point;

and if so, controlling the energy storage controller to exit the off-grid mode.

From the technical scheme, the application discloses a grid-connected and off-grid switching method, an energy storage converter, an energy storage system and a power system, and the method comprises the following steps: receiving a switching instruction; acquiring an SOC value of an energy storage system, a first power grid side voltage and a first power grid side frequency of a public connection point switch lower port of an energy storage converter and a load and a first apparent power based on a switching instruction; judging whether the SOC value of the energy storage system is larger than a set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval and whether the first apparent power is in a first apparent power preset interval; if so, controlling the energy storage converter to enter a soft grid-connected and off-grid Switching (SVF) mode, and when the energy storage converter is in the SVF mode, determining a driving signal of an Insulated Gate Bipolar Transistor (IGBT) in the energy storage converter by the three-phase voltage of the grid side of the energy storage converter; acquiring a public connection point switch state, a second power grid side voltage, a second power grid side frequency and a second apparent power of a lower port of a public connection point switch after the energy storage converter enters an SVF mode; judging whether the switch state of the public connection point is in a switching-off state, whether the voltage of the second power grid side exceeds a second preset voltage interval, whether the frequency of the second power grid side exceeds a second preset frequency interval, or whether the second apparent power exceeds a second apparent power preset interval; if so, controlling the energy storage converter to be switched from the SVF mode to the off-grid mode, and switching the load from the power grid power supply loop to the energy storage converter power supply loop.

Therefore, the switching time of the load from grid connection to grid disconnection is shortened under the condition that extra hardware is not needed. In some examples, because the switching frequency of an IGBT module in the energy storage converter is generally several KHz to several tens of KHz, the switching time of a load from grid connection to grid disconnection can be shortened to several hundred microseconds to several milliseconds, so that the load is completely unaware and can continuously and stably and reliably operate, the grid-connected and off-grid seamless switching of the load is realized, the problem of the grid-connected and off-grid seamless switching of the load under the application scenes of energy storage systems such as isolated micro-grids, remote micro-grids, important load power conservation and the like is solved, and the power consumption feeling of users at the load side is greatly improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the disclosed drawings without creative efforts.

Fig. 1 is a flowchart of a grid-connected and off-grid handover method disclosed in an embodiment of the present application;

fig. 2 is a schematic diagram of an energy storage system architecture according to an embodiment of the present disclosure;

fig. 3 is a schematic diagram illustrating an energy storage converter entering into an SVF mode according to an embodiment of the present disclosure;

fig. 4 is a flowchart of another grid-connected and off-grid handover method disclosed in the embodiment of the present application;

fig. 5 is a schematic structural diagram of an energy storage converter disclosed in an embodiment of the present application;

fig. 6 is a schematic structural diagram of an electrical power system disclosed in an embodiment of the present application;

fig. 7 is a communication framework diagram in an electrical power system according to an embodiment of the present disclosure.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The application discloses grid-connected and grid-disconnected switching method, an energy storage converter, an energy storage system and a power system, wherein the energy storage converter receives a switching instruction for starting a grid-connected to grid-disconnected seamless switching function, acquires an energy storage system SOC value and a first grid side voltage, a first grid side frequency and a first apparent power of a lower port of a public connection point switch of the energy storage converter and a load based on the switching instruction, and controls the energy storage converter to enter an SVF mode when the energy storage system SOC value is determined to be larger than a set value of battery health electric quantity, the first grid side voltage is in a first preset voltage interval, the first grid side frequency is in a first preset frequency interval, and the first apparent power is in the first apparent power preset interval, wherein the SVF mode is a soft grid-connected and grid-disconnected seamless switching mode. When the state of the public connection point switch is determined to be a switching-off state after the energy storage converter enters the SVF mode, the voltage of the second power grid side of the lower port of the public connection point switch exceeds a second preset voltage interval, the frequency of the second power grid side of the lower port of the public connection point switch exceeds a second preset frequency interval, or the second apparent power of the lower port of the public connection point switch exceeds a second apparent power preset interval, the energy storage converter is controlled to be switched from the SVF mode to the off-grid mode, and the load is seamlessly switched from the power grid power supply loop to the energy storage converter power supply loop.

Therefore, under the condition that extra hardware is not needed to be added, the switching frequency of an IGBT module in the energy storage converter is generally from several KHz to dozens of KHz, the switching time from grid connection to grid disconnection of a load can be shortened to several hundred microseconds to several milliseconds, so that the load is completely unaware and can continue to operate stably and reliably, and therefore the grid-connected and off-grid seamless switching of the load is realized, the problems of no sensing and off-grid seamless switching of the load under the application scenes of energy storage systems such as island micro-grids, remote micro-grids, important load power conservation and the like are solved, and the power consumption experience of users on the load side is greatly improved.

Referring to fig. 1, a flow chart of a grid-connected and grid-disconnected switching method disclosed in an embodiment of the present application is applied to an energy storage converter in an energy storage system, and particularly to a controller of the energy storage converter, and the method includes:

and S101, receiving a switching instruction for starting a grid-connected to off-grid seamless switching function.

It should be noted that, the process of the grid-connected and grid-disconnected switching method executed by the energy storage converter is actually executed by the controller in the energy storage converter.

Referring to fig. 2, an energy storage system architecture schematic diagram disclosed in the embodiment of the present application includes: an energy storage device (battery cluster), an energy storage converter PCS (converting DC to AC), a transformer T1 and respective loads (three loads are shown in fig. 2, load 1, load 2 and load 3 respectively).

The energy storage device is connected with an energy storage converter PCS through a switch F4, the energy storage converter PCS is connected with a common end of a switch F2 and a common end of a switch F5 through a switch F3, the other end of the switch F5 is connected with a load 1 through a switch F6, connected with the load 2 through a switch F7 and connected with the load 3 through a switch F8, and the switch F2 is connected with a Grid through a transformer T1 and the switch F1.

In this embodiment, a controller inside the energy storage converter PCS receives an externally sent switching instruction for switching from grid connection to grid disconnection.

Step S102, acquiring an SOC value of an energy storage system and a first power grid side voltage, a first power grid side frequency and a first apparent power of a public connection point switch lower port of an energy storage converter and a load based on a switching instruction.

Referring to fig. 2, the switch F2 is a Point of Common Coupling (PCC) switch of the energy storage converter and the load.

As shown in fig. 2, the upper port of the public connection point switch includes a point P2, and the lower port of the public connection point switch includes a point P1. The first grid side voltage of the lower port of the public connection point switch is the voltage of a point P1 and is represented by U _ PCC1, the first grid side frequency of the lower port of the public connection point switch is the frequency of the point P1 and is represented by F _ PCC1, and the first apparent power of the lower port of the public connection point switch is the apparent power of the point P1 and is represented by P _ PCC 1.

Step S103, judging whether the SOC value of the energy storage system is larger than the set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval, and whether the first apparent power is in a first apparent power preset interval, if so, executing step S104.

It should be noted that, when the SOC value of the energy storage system is greater than the set value of the healthy electric quantity of the battery, it indicates that the electric quantity of the energy storage system is sufficient at this time, and the energy storage system can supply power to the load; when the SOC value of the energy storage system is smaller than the set value of the healthy electric quantity of the battery, the electric quantity of the energy storage system is low, and the energy storage system is not suitable for supplying power to a load. When the first power grid side voltage is in a first preset voltage interval and the first power grid side frequency is in a first preset frequency interval, the fact that the power grid runs normally is indicated, and grid-connection and grid-disconnection switching can be conducted on the load. When the first power grid side voltage is not in the first preset voltage interval and the first power grid side frequency is not in the first preset frequency interval, it indicates that the power grid is abnormal in operation, and at the moment, grid-connection and grid-disconnection switching is not suitable for the load. When the first apparent power is in the first apparent power preset interval, the load power of the lower port of the switch of the public connection point is close to balance, and at the moment, when the switch of the public connection point between the load and the power grid is turned off, the switch of the public connection point can be turned off normally. If the first apparent power is not in the first apparent power preset interval, the common point connection point switch between the load and the power grid is turned off, and the common point connection point switch may not be normally turned off.

Assuming that the set value of the health electric quantity of the battery is represented by H _ set, the first preset voltage interval is [ U1, U2], the first preset frequency interval is [ F1, F2], the first apparent power preset interval is [ P1, P2], and when the SOC value of the energy storage system is greater than H _ set, U _ PCC1 belongs to [ U1, U2], F _ PCC1 belongs to [ F1, F2], and P _ PCC1 belongs to [ P1, P2], the energy storage system is controlled to enter the SVF mode.

And step S104, controlling the energy storage converter to enter an SVF mode.

The SVF mode is a self-defined mode of the application and represents a soft grid-connected and off-grid seamless switching mode, and when the energy storage converter is in the SVF mode, a driving signal of an IGBT in the energy storage converter is determined by a three-phase voltage at the power grid side of the energy storage converter.

And S105, acquiring the switching state of the public connection point after the energy storage converter enters the SVF mode, and the second grid side voltage, the second grid side frequency and the second apparent power of the lower port of the public connection point switch.

In this embodiment, after the energy storage converter enters the SVF mode, the switching state of the common connection point may be determined according to the switching-on/off feedback signal of the switch on the side of the public power grid of the load and the energy storage system.

Step S106, judging whether the switch state of the public connection point is in a switching-off state, whether the voltage of the second power grid side exceeds a second preset voltage interval, whether the frequency of the second power grid side exceeds a second preset frequency interval, or whether the second apparent power exceeds a second apparent power preset interval, and if so, executing step S107.

It should be noted that, in order to ensure safe operation of the load and the grid, the load must be disconnected from the grid power supply circuit before being connected to the storage converter power supply circuit. When the public connection point switch state is the opening state, the load is disconnected with the power grid at the moment, namely the load is disconnected from the power grid power supply loop. The feedback of the public connection point switch state is generally slow, the acquisition speed of the grid side voltage, the grid side frequency and the apparent power is generally fast, especially when the load and the grid public connection point switch are switched off, the voltage, the frequency and the power of a switch lower port can be disturbed, and in practical application, whether the load is disconnected from a grid power supply loop can be judged through the grid side voltage, the grid side frequency and the apparent power. Specifically, if the second grid-side voltage exceeds a second preset voltage interval, or the second grid-side frequency exceeds a second preset frequency interval, or the second apparent power exceeds the second apparent power preset interval, any one condition is met, it can be determined that the load is disconnected from the grid power supply loop.

In this embodiment, when it is determined that the switch state of the common connection point is the open-circuit state, or U _ PCC2 exceeds a second preset voltage interval [ U3, U4], or F _ PCC2 exceeds a second preset frequency interval [ F3, F4], or P _ PCC2 exceeds a second preset apparent power interval [ P1, P2], the energy storage converter is controlled to be switched from the SVF mode to the off-network mode.

And S107, controlling the energy storage converter to be switched from the SVF mode to the off-grid mode, and enabling the load to be seamlessly switched from the power grid power supply loop to the energy storage converter power supply loop.

Among them, the off-grid mode is also the VF mode. When the load is disconnected from the power grid power supply loop, the load can be connected to the energy storage converter power supply loop, and the load is seamlessly switched to the energy storage converter power supply loop from the power grid power supply loop.

In this embodiment, the time for switching the energy storage converter from the SVF mode to the off-grid mode is the time for switching the load from the power grid power supply circuit to the energy storage converter power supply circuit, and the switching frequency of the IGBT module in the energy storage converter is generally several KHz to several tens KHz, and the switching time can be shortened to several hundreds microseconds to several milliseconds.

In summary, the application discloses a grid-connected and off-grid switching method, an energy storage converter receives a switching instruction for starting a grid-connected to off-grid seamless switching function, obtains an energy storage system SOC value and a first grid side voltage, a first grid side frequency and a first apparent power of a lower port of a public connection point switch of the energy storage converter and a load based on the switching instruction, and controls the energy storage converter to enter an SVF mode when the SOC value of the energy storage system is determined to be greater than a set value of a healthy electric quantity of a battery, the first grid side voltage is in a first preset voltage interval, the first grid side frequency is in a first preset frequency interval, and the first apparent power is in the first apparent power preset interval, wherein the SVF mode is a soft grid-connected to off-grid seamless switching mode. When the state of the public connection point switch is determined to be a switching-off state after the energy storage converter enters the SVF mode, the voltage of the second power grid side of the lower port of the public connection point switch exceeds a second preset voltage interval, the frequency of the second power grid side of the lower port of the public connection point switch exceeds a second preset frequency interval, or the second apparent power of the lower port of the public connection point switch exceeds a second apparent power preset interval, the energy storage converter is controlled to be switched from the SVF mode to the off-grid mode, and the load is seamlessly switched from the power grid power supply loop to the energy storage converter power supply loop.

For further optimizing the above embodiment, referring to fig. 3, a schematic diagram of the energy storage converter entering into the SVF mode disclosed in the embodiment of the present application is as follows:

(1) And the controller of the energy storage converter (hereinafter referred to as PCS) acquires three-phase voltages UA, UB and UC on the power grid side of the PCS.

(2) And (3) carrying out Clark conversion on three-phase voltages UA, UB and UC at the power grid side of the PCS to obtain a d-axis voltage component Ud _ PCS and a q-axis voltage component Uq _ PCS in a rectangular coordinate system.

In this embodiment, the clark converter is implemented on the PCS controller.

(3) And processing the d-axis voltage component Ud _ pcs to obtain a d-axis voltage Ud.

Specifically, the d-axis voltage component Ud _ PCS is subtracted from a voltage compensation quantity Ud _ Current to obtain a d-axis voltage correction quantity Ud _ Current _ Ref, wherein the voltage compensation quantity Ud _ Current is a product of a d-axis Current variation quantity Id _ Current of an alternating-Current side inductance Current of the energy storage converter and a compensation coefficient K, three-phase currents IA, IB and IC on a PCS alternating-Current side inductance are changed, corresponding Id and Iq are also changed, and the d-axis Current variation quantity is represented by Id _ Current.

And inputting the result of the difference between the d-axis voltage correction quantity Ud _ Current _ Ref and the d-axis voltage component Ud _ pcs into a first PI regulator to obtain a d-axis voltage regulating quantity Ud' (the voltage regulating quantity of Ud _ pcs).

And adding the d-axis voltage adjustment quantity Ud' and the d-axis voltage correction quantity Ud _ Current _ Ref to obtain the d-axis voltage Ud.

The voltage compensation quantity Ud _ Current is described as follows:

the three-phase Current change of an alternating-Current side inductor (a component inside a power supply system (PCS)) of the energy storage converter (PCS) can be caused by voltage fluctuation of a power grid side, inductive currents Id and Iq are obtained by subjecting the three-phase Current to Clark conversion, and a compensation coefficient K of a d-axis Current change quantity Id _ Current of the alternating-Current side inductive Current of the energy storage converter is obtained as Ud _ Current. The Ud _ Current is used for compensation adjustment during the SVF mode of PCS operation and grid coexistence, so that coexistence is more stable.

(4) And processing the q-axis voltage component Uq _ pcs to obtain a q-axis voltage Uq.

Specifically, the result of the difference between the q-axis voltage component Uq _ pcs and the q-axis voltage given quantity Uq _ Current _ Ref (the value of Uq _ Current _ Ref is set to 0) is input to the second PI regulator, and the q-axis voltage Uq is obtained.

(5) And performing Clark reverse transformation on the d-axis voltage Ud and the q-axis voltage Uq, and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) AC side pin of the energy storage converter based on a Clark reverse transformation result and the three-phase voltage phase-locked frequency value F _ PLF _ Current of the grid side of the energy storage Current device.

Wherein, it is the clarke inverse transformer that carries out clarke inverse transformation, lie in PCS controller.

(6) And inputting the three-phase voltage driving signal into an IGBT driver for IGBT modulation, so that the energy storage converter enters the SVF mode.

It should be noted that the schematic diagram of the SVF mode shown in fig. 3 is executed at any time, so that the PCS and the power grid can coexist when the power grid is not powered down. It should be clear that if the PCS is in the VF mode (i.e. off-grid mode), in the VF mode, the system formed by the PCS + the energy storage device is equivalent to a voltage source, and the power grid is also a voltage source, and the two voltage sources have no way of long-time reliable coexistence. Therefore, if only the PCS operating VF mode is used as the voltage source to supply power to the loads, if the grid tie switch is turned off or the grid side loses power, then the PCS operating VF mode supplies power to the loads, or if the PCS and the loads form a microgrid which has no grid, then the PCS may operate VF mode and then supply power to the loads. Therefore, the direct VF mode cannot be switched seamlessly from grid to grid.

In the application, the PCS determines whether the power grid is coming through by judging whether the power grid side voltage and the power grid side frequency of the upper port of the switch of the public connection point of the PCS and the load change after the PCS enters the off-grid mode.

Therefore, in order to further optimize the above embodiment, referring to fig. 4, a flowchart of another grid-connected and off-grid switching method disclosed in the embodiment of the present application, which is applied to an energy storage converter in an energy storage system, on the basis of the embodiment shown in fig. 1, after step S107, the method may further include:

step S108, acquiring third power grid side voltage and third power grid side frequency of a public connection point switch upper port (P2 point) after the energy storage converter enters an off-grid mode;

step S109, judging whether the voltage of the third power grid side is in a third preset voltage interval or not, and whether the frequency of the third power grid side is in a third preset frequency interval or not, if so, executing step S110;

step S110, determining that the energy storage converter completes power grid voltage frequency and phase following;

s111, controlling a common connection point switch of the energy storage converter and a load to be switched on, and enabling the load to be seamlessly switched to a power supply loop of a power grid;

and step S112, controlling the energy storage converter to exit the VF mode.

After the energy storage converter is controlled to exit from the VF mode, the energy storage converter may enter a PQ mode (i.e., a grid-connected mode) or a standby mode or a shutdown mode, and the energy storage converter specifically enters which mode, which mode is determined according to actual needs, and the application is not limited herein.

Corresponding to the method embodiment, the application also discloses an energy storage converter.

Referring to fig. 5, a schematic structural diagram of an energy storage converter disclosed in an embodiment of the present application, the energy storage converter includes:

the instruction receiving unit 201 is configured to receive a switching instruction for starting a function of seamless switching from a grid-connected mode to a grid-disconnected mode.

The first obtaining unit 202 is configured to obtain, based on the switching instruction, an SOC value of the energy storage system, and a first grid-side voltage, a first grid-side frequency, and a first apparent power of a lower port of a switch of a point of common connection between the energy storage converter and a load.

The first judging unit 203 is configured to judge whether the SOC value of the energy storage system is greater than a set value of the healthy electric quantity of the battery, and whether the voltage of the first grid side is within a first preset voltage interval, and whether the frequency of the first grid side is within a preset frequency interval, and whether the first apparent power is within a first apparent power preset interval.

The first mode switching unit 204 is configured to control the energy storage converter to enter an SVF mode when the first determining unit 203 determines that the mode is yes, where the SVF mode is a soft grid-connected and off-grid seamless switching mode.

The SVF mode is a self-defined mode of the application and represents a soft grid-connected and off-grid seamless switching mode.

A second obtaining unit 205, configured to obtain a state of a switch of a public connection point after the energy storage converter enters the SVF mode, and a second grid-side voltage, a second grid-side frequency, and a second apparent power of a lower port of the switch of the public connection point.

A second determining unit 206, configured to determine whether the switch state of the common node is an open-circuit state, or whether the voltage on the second grid side exceeds a second preset voltage interval, or whether the frequency on the second grid side exceeds a second preset frequency interval, or whether the second apparent power exceeds a second apparent power preset interval.

And a second switching-off mode switching unit 207, configured to control the energy storage converter to switch from the SVF mode to the off-grid mode when the second determining unit 206 determines that the load is switched to the power supply loop of the energy storage converter seamlessly.

The off-grid mode is also called VF mode.

In this embodiment, the energy storage converter is switched from the SVF mode to the off-grid mode at the completion time, that is, the time when the load has a power grid power supply circuit switched to the energy storage converter power supply circuit, because the switching frequency of the IGBT module in the energy storage converter is generally several KHz to several tens KHz, the switching time can be shortened to several hundreds microseconds to several milliseconds, and therefore, the switching time when the energy storage converter is switched from the SVF mode to the off-grid mode is between several tens microseconds to several hundreds microseconds, the load is completely unaware, and the operation can be continued stably and reliably, thereby realizing the grid-connected and off-grid seamless switching of the load.

In summary, the application discloses an energy storage converter, which is used for controlling the energy storage converter to enter an SVF mode, wherein the SVF mode is a soft grid-connected and off-grid seamless switching mode, and switching off controls the energy storage converter to be switched from the SVF mode to the off-grid mode, so that a load is seamlessly switched from a power supply loop of a power grid to a power supply loop of the energy storage converter. This application need not additionally to increase under the condition of hardware, because of the switching frequency of IGBT module generally is several KHz to tens KHz among the energy storage converter, the switchover time can shorten to several hundred microseconds to several milliseconds, so the load is complete does not have the perception, can continue stably, the reliable operation, thereby the seamless switching of load and off-grid has been realized, island microgrid has been solved, remote landing microgrid, the problem of the seamless switching of load does not have the perception and off-grid under the energy storage system application scenes such as important load guarantor, user's power consumption impression has greatly been promoted.

To further optimize the above embodiment, the first mode switching unit 204 includes:

the inverse transformation subunit is used for carrying out Clark inverse transformation on the d-axis voltage and the q-axis voltage and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) AC side pin of the energy storage converter based on a Clark inverse transformation result and a three-phase voltage phase-locked frequency value of the grid side of the energy storage current device;

and the adjusting subunit is used for inputting the three-phase voltage driving signal to an IGBT driver for IGBT modulation, so that the energy storage converter enters the SVF mode.

In this embodiment, the first modification subunit is specifically configured to:

and subtracting the d-axis voltage component Ud _ PCS from a voltage compensation quantity Ud _ Current to obtain a d-axis voltage correction quantity Ud _ Current _ Ref, wherein the voltage compensation quantity Ud _ Current is the product of a d-axis Current variation quantity Id _ Current of the alternating-Current side inductance Current of the energy storage converter and a compensation coefficient K, three-phase currents IA, IB and IC on the alternating-Current side inductance of the PCS change, and corresponding Id and Iq also change.

The second correction subunit is specifically configured to:

and inputting a difference result between the q-axis voltage component Uq _ pcs and a q-axis voltage given quantity Uq _ Current _ Ref (the value of Uq _ Current _ Ref is set to be 0) into a second PI regulator to obtain the q-axis voltage Uq.

It should be noted that, for the specific working principle of each component in the first mode switching unit 204, please refer to the corresponding part of the method embodiment, which is not described herein again.

The present application also discloses an energy storage system, detailed in fig. 2, comprising: the energy storage converter in the above embodiment.

Corresponding to the embodiment, the application also discloses an electric power system.

Referring to fig. 6, a schematic structural diagram of an electrical power system disclosed in an embodiment of the present application, the electrical power system includes: grid, power generation system 11, load, ac bus 12, general controller (not shown in fig. 6), grid switch F1, load switch, ac side switch F4, and energy storage system 13 in the above embodiments.

The Grid is connected to the ac bus 12 via the Grid switch F1.

The load is connected to the ac bus 12 through the load switch.

In practical applications, loads can be divided into priority power supply loads (i.e. important loads) and non-priority power supply loads (i.e. general loads) according to different power supply requirements of the loads, the priority power supply loads can be represented by the load 1 in fig. 6, the corresponding load switch is F5, and the load 1 is connected to the common alternating current bus 12 through the switch F10, the transformer T2 and the load switch F5. The non-priority power supply load may be represented by load 2 in fig. 6, with the corresponding load switch F6, and load 2 connected to common ac bus 12 through switch F9, transformer T3, and load switch F6.

The energy storage system 13 includes: the energy storage device (which can be a battery cluster), the energy storage converter PCS and the transformer T1 are sequentially connected to the public alternating current bus 12 through the energy storage converter PCS, the transformer T1 and the energy storage alternating current side switch F4.

In practical application, a switch F12 is connected between the energy storage device and the energy storage converter PCS, and a switch F11 is connected between the energy storage converter PCS and the transformer T1.

The power generation system 11 includes: at least one power generation device and a corresponding power generation AC side switch, each of the power generation devices being connected to the common AC bus through one of the power generation AC side switches.

In this embodiment, the power generation device includes, but is not limited to, any one or more of a wind power generation device, a photovoltaic power generation device, and a fuel power generation device, the fuel power generation device may be a diesel power generation device or a gasoline power generation device, and the power generation system may further include other power generation devices, which is determined according to actual needs, and the application is not limited herein.

As shown in fig. 6, the wind power generation device is connected to the ac bus 12 through an ac-side switch F2, the photovoltaic power generation device is connected to the ac bus 12 through an ac-side switch F3, the fuel power generation device is connected to the ac bus 12 through an ac-side switch F7, and the other power generation devices are connected to the ac bus 12 through an ac-side switch F8.

The master controller is respectively connected with the load, the energy storage device, the energy storage converter, each power generation device, the power grid switch, the load switch, the energy storage AC side switch and each power generation AC side switch and is used for controlling each device connected with the master controller.

For convenience of explanation, referring to fig. 7, an embodiment of the present application discloses a communication framework diagram in an electric power system, and the present application defines all switches controlled by a master controller 21 as a switch subsystem 22. The other devices which are communicated with the master controller are all provided with controllers with communication functions, and the other devices are respectively defined as follows: the system comprises an energy storage converter communication subsystem 23, a battery management subsystem 24, a wind generating set subsystem 25, a photovoltaic power generation subsystem 26, a load monitoring subsystem 27 and a fuel power generation subsystem 28, wherein the master controller 21 calls each subsystem, and each subsystem calls corresponding equipment.

Specifically, the main controller 21: the system is responsible for the total control of the whole system, interacts with each subsystem and controls each subsystem by sending instructions.

The switching subsystem 22: the switch is in charge of controlling all the switches of the system, can be communicated with the energy storage converter communication system besides being communicated with the master control communication system, and aims to realize quick interaction with the energy storage converter communication system by the opening and closing instructions of part of important switches so as to better complete the planned and off-grid switching function.

Battery management subsystem 24: the battery system on the direct current side of the energy storage converter is mainly responsible for the management of the battery, is communicated with the energy storage converter communication system besides the master control communication system, is mainly used for the hard node feedback of a battery emergency stop signal, and improves the protection speed of the energy storage converter on the battery.

Wind turbine subsystem 25: the system is responsible for controlling the wind generating set, interacts with a master control communication system, receives a master control instruction and executes the master control instruction.

Photovoltaic power generation subsystem 26: the system is responsible for the control of the photovoltaic power generation equipment, interacts with a master control communication system, receives a master control instruction and executes the master control instruction.

The load monitoring subsystem 27: the system is responsible for monitoring the load power utilization load in real time, and sends data to a master control communication system for the comprehensive control of fan power generation, photovoltaic power generation, energy storage charging and discharging and diesel/gas power generation of the master control.

The fuel power generation subsystem 28: the system is responsible for controlling the diesel/gas power generation equipment, interacts with a master control communication system, receives a master control instruction and executes the master control instruction.

The combination form of the power system is as follows:

the combination 1, the power grid, the energy storage system and the load are combined, when the power grid is powered off or a fault triggers a breaker on the power grid side to open, the energy storage converter has a grid-connected and off-grid seamless switching function, power supply of the power grid is switched into power supply of the energy storage system, and the load is not sensed. And simultaneously, the method supports the function of planned on-grid and off-grid switching, namely on-grid and off-grid switching according to a plan. The planned grid connection and disconnection mainly actively initiates grid connection and disconnection switching when needed according to an operation strategy, for example, power failure is needed in power grid side line repair, the power consumption price is high in the prime period, passive grid connection and disconnection switching is mainly used for guaranteeing load power consumption and important load uninterrupted power consumption at the moment of power grid failure. The control method provided by the application can enable a user at the load side to have no perception, greatly improves the power utilization experience, and is friendly to system strategies.

The combination 2, the power grid, the wind turbine system, the photovoltaic power generation system, the energy storage system and the load can save power grid energy, the load is powered by wind and photovoltaic energy or the energy storage system is charged at the same time, and the wind and photovoltaic energy storage system has an economical and selectable function.

The combination 3, the power grid + the energy storage system + the load + the fuel power generation system can increase the endurance capacity of supplying power to the load at a special moment, and when the wind turbine generator and the photovoltaic power generation system do not have power generation conditions, the power grid energy or the fuel/gas system can be used for charging the energy storage, so that the wind turbine generator and the photovoltaic power generation system have an economical optional function.

The combination 4, the wind turbine generator system, the photovoltaic power generation system, the energy storage system, the load and the fuel oil power generation system can be started when wind power generation and photovoltaic power generation cannot continue to output power in a PCS off-grid mode, the SOC (state of charge) of a battery on a direct current side of the PCS is exhausted and cannot supply power to the load for a long time, the diesel/gas power supply system can be started, the PCS performs off-grid to on-grid switching, the load is switched to a diesel/gas power supply circuit (after the diesel/gas equipment is started, the PCS is also a voltage source, and a VF mode of the PCS cannot coexist with the diesel/gas, so that the PCS needs a VF to be switched to a PQ mode (namely the on-grid mode), the load is switched to the diesel/gas power supply circuit), the off-grid mode is rich and friendly, the off-grid of the whole system is gradually switched to the off-grid of the energy storage and the load, and then the off-grid seamless switching of the fuel oil and the load is realized, and the whole process does not have a gradual execution control strategy along with the conditions of the power generation equipment.

1. Execution logic for grid-connected to off-grid of power system

In the present application, a power generation device includes: during wind power generation set, photovoltaic power generation set and fuel power generation set, total controller is used for:

(1) And acquiring a first switching instruction for switching from grid connection to grid disconnection.

(2) Based on the first switching instruction, adjusting the generating power of the wind driven generator set, the generating power of the photovoltaic equipment and the operating power of the energy storage system, and combining the total power of the load, adjusting the lower port power of a PCC switch at a common connection point of the energy storage converter and the load to be the power P _ PCC at the switch at the common connection point, and adjusting the SOC value of the energy storage system to be within a preset SOC range [ SOC1, SOC2]. Wherein P _ PCC refers to power at PCC.

The voltage and frequency of the lower port of the PCC switch can be the voltage of any point of the public alternating current bus (the parallel voltage is equal) at the lower port of the PCC switch, and can also be the low-voltage side of a PCS alternating current side transformer; the common ac bus is typically high voltage, and the corresponding [ p1, p2] is the range of high voltage values; the AC side of the PCS is low voltage, and the corresponding [ p1, p2] is a range of low voltage values.

(3) Sending a mode switching instruction to the energy storage converter, so that the energy storage converter enters an SVF mode under the condition that a first mode switching condition is determined to be met, wherein the first mode switching condition is as follows: the lower port voltage of the public connection point switch is in a fourth preset voltage interval, the power grid side frequency of the public connection point switch is in a fourth preset frequency interval, and the lower port power of the public connection point switch is in a preset power interval.

The master controller sends a mode switching instruction to the energy storage converter, the energy storage converter determines that the voltage of a lower port of the PCC switch is [ u1, u2], the power grid side frequency F _ PCC range of the switch of the public connection point is [ F1, F2], the power of the lower port of the switch of the public connection point is [ p1, p2], and the energy storage converter enters an SVF mode and sends feedback information to the master controller.

(4) And acquiring feedback information sent by the energy storage converter after the energy storage converter enters the SVF mode.

(5) And controlling the switch of the public connection point to be switched off according to the feedback information.

(6) Executing maximum load balancing control to enable the SOC value of the energy storage system to be in the preset SOC range, and controlling the energy storage converter to be switched into an off-grid mode from an SVF mode when a second mode switching condition is met, so that the load is seamlessly switched to a power supply loop of the energy storage converter, wherein the second mode switching condition is as follows: the lower port voltage exceeds a fifth preset voltage interval, or the grid side frequency exceeds a fifth preset frequency interval, and the range of the lower port power P _ PCC is within a sixth preset power interval, or a switching-off feedback signal of the public connection point switch is received.

The switching-on and switching-off feedback signal of the switch at the public connection point comprises the following feedback paths: the two ways can be designed in a redundant manner, and the PCS performs corresponding actions by firstly acquiring the switching-on and switching-off feedback of the switch of the common connection point.

To further optimize the above embodiment, after step (6), the overall controller may be further configured to:

(7) And judging whether to start the power-maintaining mode of the priority power supply load.

(8) If so, judging whether the SOC value of the energy storage battery is not larger than a first preset warning value or not.

The first preset warning value can be represented by H _ import, which is a preset parameter, below which it represents that the power generation equipment cannot meet the load power requirement, and when the PCS supplies power to the load, the SOC (battery level) of the battery continuously decreases to a limit, and a non-priority power supply load needs to be switched off, so as to ensure that the priority power supply load has a longer power consumption time.

(9) If so, disconnecting the load switch connected between a non-priority power supply load and the AC utility bus, wherein the load in the power system comprises: the priority power supply load and the non-priority power supply load.

(10) And judging whether the SOC value of the latest energy storage battery is not greater than a second preset alarm value.

The second preset alarm value can be represented by H _ alarm, and the battery SOC less than or equal to H _ alarm means that the battery power is lower than an alarm value, which indicates that the PCS energy storage system is about to be unable to continue to supply power to the load. (thus it is necessary to start the diesel/gas power generation system for endurance, the PCS needs to complete the switch of the load to the diesel/gas supply circuit, similarly to the switch of the load to the grid circuit, the grid is a voltage source, the PCS operates in VF mode as a voltage source, and the diesel/gas supply system is a voltage source)

(11) And if so, disconnecting the connection paths between the wind power generation device and the photovoltaic power generation device and the public alternating current bus.

To further optimize the above embodiment, after step (11), the overall controller may be further configured to:

(12) And conducting the power generation branch where the fuel power generation device is located.

The master controller controls the conduction of the AC side switch F7 to conduct the power generation branch where the fuel power generation device is located.

(13) And judging whether the voltage range of the fuel oil power generation side is in a preset voltage range [ u1, u2] or not, and whether the frequency range of the fuel oil power generation side is in a preset frequency range [ f1, f2] or not.

(14) And if so, controlling the frequency and the phase of the energy storage converter following the fuel oil power generation side.

(15) And acquiring a following result fed back by the energy storage converter at any time, and conducting a connecting passage between the fuel power generation device and the public alternating current bus to enable the load to be seamlessly switched to a fuel power supply loop.

(16) And controlling the energy storage converter to exit the VF mode.

After exiting the VF mode, the energy storage converter may be switched to a PQ mode (grid-connected mode) or shut down or standby, which is specifically determined according to actual needs, and the application is not limited herein.

2. Execution logic for converting off-grid into on-grid of power system

In the present application, a power generation device includes: during wind power generation set, photovoltaic power generation set and fuel power generation set, total controller still can be used to:

(21) And acquiring a second switching instruction from the off-grid to the on-grid.

(22) And calculating the power sum of the generated power of the wind generating set and the generated power of the photovoltaic equipment.

(23) And calculating the absolute value of the difference between the power sum and the total power consumption value of the load.

(24) And judging whether the absolute value of the difference value is not greater than the absolute value of the first preset apparent power.

The expression of the absolute value of the difference value between the total power sum of the generated power of the wind generating set and the generated power of the photovoltaic equipment and the total power consumption value of the load is as follows: the absolute value of the first preset apparent power is | P _ pcs _ va _ flag1|, the specific value is determined according to the actual requirement, and the application is not limited herein.

In this embodiment, whether | P _ balance | ≦ P _ pcs _ va _ flag | is determined, and if not, the process returns to step (22).

(25) If yes, controlling the energy storage converter to start off-grid to grid connection, and following the upper power grid frequency and the phase of the public connection point switch when the energy storage converter determines that a preset following condition is met, wherein the preset following condition is as follows: the public connection point switch is in a switching-off state, the voltage range of an upper port of the public connection point switch is in a preset voltage range, the frequency of the upper port of the public connection point switch is in a preset frequency range, and the apparent power of the energy storage converter is not larger than the absolute value of first preset apparent power.

Assuming that the apparent power of the energy storage converter is represented by P _ PCS _ va, P _ PCS _ va ≦ P _ PCS _ va _ flag1| refers to the condition that the apparent power of the PCS is less than or equal to | P _ PCS _ va _ flag1|. If the master control starts to switch from the off-network to the on-network, the system is in the off-network operation mode at present, namely the PCS executes a VF mode (the off-network operation mode), namely the energy storage system is used as a voltage source, the PCS cannot control power per se, the power is determined by a load, the load power is increased, the power of the PCS is increased, the load power is reduced, the power of the PCS is reduced, in order to ensure that the master control system adjusts the power summation value of other power generation equipment to be close to the load power, the power generation equipment is matched with the load power as far as possible, and the PCS is only used as the voltage source, so a reasonable apparent power preset parameter of the PCS is set, and P _ PCS _ va is less than or equal to | P _ PCS _ va _ flag1|.

(26) And obtaining a following result fed back by the energy storage converter after the following is finished, and controlling the power grid switch to be switched on to enable the load to be seamlessly switched to a power grid power supply loop.

To further optimize the above embodiment, after step (26), the overall controller may be further configured to:

(27) And judging whether the latest apparent power of the energy storage converter is not less than a second preset apparent power or not, and whether the instantaneous current detected by the energy storage converter is not less than a preset instantaneous current threshold or not, or acquiring a closing feedback signal of the switch of the public connection point.

If the latest apparent power of the energy storage converter is still represented by P _ PCS _ va and the second preset apparent power is represented by P _ PCS _ va _ flag2, the condition that the apparent power of the PCS is greater than or equal to the second preset apparent power is that a user with the second preset apparent power is different from a user with the first preset apparent power, and the condition that the P _ PCS _ va is greater than or equal to the second preset apparent power is assumed to be higher than or equal to the second preset apparent power. After the switch at the public connection point is switched on, a switching-on feedback signal may be switched off, but switching-on may cause apparent power jitter and instantaneous current increase of the PCS, so that the power jitter and the sudden current rise may also be used as judgment conditions. The second predetermined apparent power is typically several times greater than the first predetermined apparent power.

The I _ PCS _ current is larger than or equal to I _ PCS _ flag1, which means that instantaneous current detected by the PCS is larger than or equal to a preset instantaneous current threshold.

(28) And if so, controlling the energy storage controller to exit the off-grid mode.

After exiting the off-grid mode, the energy storage controller is switched to a PQ mode (grid-connected mode), or is shut down or standby, which is determined according to actual needs.

The existing energy storage system needs to realize the grid-connected and off-grid switching function through switching devices such as STS switches and thyristors, the switching time is generally dozens of milliseconds, the grid-connected and off-grid switching cost is increased, the problem of high equipment failure rate caused by long switching time is also increased, and the user experience on the load side is not friendly. The energy storage converter has a soft grid-connection and grid-disconnection seamless switching function, a system framework is not changed under the existing energy storage system, grid-connection and grid-disconnection seamless switching can be achieved through the control method provided by the application by utilizing the potential property of the energy storage converter, the switching time is shortened from dozens of milliseconds to hundreds of milliseconds, the load is not sensed, and the power consumption feeling of a user on the load side is greatly improved.

After the energy storage system is designed, the battery capacity is quantitative, the endurance time is fixed, and the energy storage system cannot supply power for a load for a long time or cannot preserve power for an important load for a long time. The utility model provides an electric power system combines the energy storage converter who has soft and off-grid seamless switching function that this application provided to apply to the system, conventional wind-powered electricity generation had both been kept, photovoltaic power generation system's original function, the function of load and off-grid seamless switching has been provided again, make the system can be economic for the load power supply under the little electric wire netting, can save unnecessary electricity to energy storage system under the economic scene, can break away from the electric wire netting and preserve electricity for the load, and wind generating set, can further seamlessly switch to diesel oil/gas power generation system under the energy storage system battery power exhausts and continue to be important load continuation of journey when photovoltaic power generation equipment can't provide energy, the ability of preserving electricity has been improved, the very big promotion load side user power consumption of gradual electricity-preserving strategy is experienced.

Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another identical element in a process, method, article, or apparatus that comprises the element.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A grid-connected and off-grid switching method is applied to an energy storage converter in an energy storage system, and comprises the following steps:

receiving a switching instruction;

acquiring an energy storage system SOC value, a first power grid side voltage and a first power grid side frequency of a public connection point switch lower port of the energy storage converter and a load and a first apparent power based on the switching instruction;

judging whether the SOC value of the energy storage system is larger than a set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval, and whether the first apparent power is in a first apparent power preset interval;

acquiring a public connection point switch state, a second power grid side voltage, a second power grid side frequency and a second apparent power of a lower port of the public connection point switch after the energy storage converter enters an SVF mode;

judging whether the switch state of the public connection point is a switching-off state or not, whether the voltage of the second power grid side exceeds a second preset voltage interval or not, whether the frequency of the second power grid side exceeds a second preset frequency interval or not, or whether the second apparent power exceeds a second apparent power preset interval or not;

if so, controlling the energy storage converter to be switched from the SVF mode to the off-grid mode, and switching the load from a power grid power supply loop to an energy storage converter power supply loop.

2. The method of claim 1, wherein said controlling said energy storage converter into SVF mode comprises:

acquiring the three-phase voltage of the power grid side of the energy storage converter;

performing Clark transformation on the three-phase voltage at the power grid side to obtain a d-axis voltage component and a q-axis voltage component in a rectangular coordinate system;

processing the d-axis voltage component to obtain a d-axis voltage;

processing the q-axis voltage component to obtain a q-axis voltage;

performing Clark reverse transformation on the d-axis voltage and the q-axis voltage, and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) alternating-current side pin of the energy storage converter based on a Clark reverse transformation result and a three-phase voltage phase-locked frequency value of the grid side of the energy storage current device;

and inputting the three-phase voltage driving signal into an IGBT driver for IGBT modulation, so that the energy storage converter enters the SVF mode.

3. The method of claim 2, wherein the processing the d-axis voltage component to obtain a d-axis voltage comprises:

obtaining a d-axis voltage correction quantity by making a difference between the d-axis voltage component and a voltage compensation quantity, wherein the voltage compensation quantity is a product of a d-axis current variation quantity and a compensation coefficient of the alternating-current side inductive current of the energy storage converter;

and adding the d-axis voltage regulating quantity and the d-axis voltage correction quantity to obtain the d-axis voltage.

4. The method of claim 2, wherein processing the q-axis voltage component to obtain a q-axis voltage comprises:

and inputting a difference result between the q-axis voltage component and the q-axis voltage given quantity into a second PI regulator to obtain the q-axis voltage, wherein the q-axis voltage given quantity takes a value of 0.

5. The method according to claim 1, after controlling the energy storage converter to switch from the SVF mode to the off-grid mode, so that the load is switched from the grid supply circuit to the energy storage converter supply circuit, further comprising:

acquiring a third power grid side voltage and a third power grid side frequency of the upper port of the public connection point switch after the energy storage converter enters the off-grid mode;

judging whether the voltage of the third power grid side is in a third preset voltage interval or not, and whether the frequency of the third power grid side is in a third preset frequency interval or not;

controlling a switch of a common connection point of the energy storage converter and a load to be switched on, so that the load is switched to a power supply loop of a power grid;

and controlling the energy storage converter to exit the SVF mode.

6. An energy storage converter, comprising:

an instruction receiving unit for receiving a switching instruction;

the first obtaining unit is used for obtaining an energy storage system SOC value, and a first power grid side voltage, a first power grid side frequency and a first apparent power of a public connection point switch lower port of the energy storage converter and a load based on the switching instruction;

the first judging unit is used for judging whether the SOC value of the energy storage system is larger than a set value of the healthy electric quantity of the battery, whether the voltage of the first power grid side is in a first preset voltage interval, whether the frequency of the first power grid side is in a first preset frequency interval and whether the first apparent power is in a first apparent power preset interval;

the first mode switching unit is used for controlling the energy storage converter to enter a soft grid-connected and off-grid switching SVF mode under the condition that the first judgment unit judges that the voltage of the energy storage converter is positive, and when the energy storage converter is in the SVF mode, a driving signal of an IGBT (insulated gate bipolar transistor) in the energy storage converter is determined by the three-phase voltage of the power grid side of the energy storage converter;

the second obtaining unit is used for obtaining the switching state of a public connection point after the energy storage converter enters an SVF mode, and the second power grid side voltage, the second power grid side frequency and the second apparent power of a lower port of the public connection point switch;

and the second mode switching unit is used for controlling the energy storage converter to be switched from the SVF mode to the off-grid mode under the condition that the second judging unit judges that the voltage of the energy storage converter is positive, so that the load is switched to a power supply loop of the energy storage converter.

7. The energy storage converter according to claim 6, wherein the first mode switching unit comprises:

the inverse transformation subunit is used for carrying out Clark inverse transformation on the d-axis voltage and the q-axis voltage and obtaining a three-phase voltage driving signal of an IGBT (insulated gate bipolar translator) AC side pin of the energy storage converter based on a Clark inverse transformation result and a grid side three-phase voltage phase-locked frequency value of the energy storage current device;

and the adjusting subunit is used for inputting the three-phase voltage driving signal into an IGBT driver for IGBT modulation, so that the energy storage converter enters the SVF mode.

8. An energy storage system, comprising: a power converter as claimed in claim 6 or 7.

9. An electrical power system, comprising: a power grid, a power generation system, a load, a common ac bus, a master controller, a grid switch, a load switch, an energy storage ac side switch, and the energy storage system of claim 8;

the power grid is connected to the public alternating current bus through the power grid switch;

the power generation system includes: at least one power generation device and a corresponding power generation AC-side switch, each power generation device being connected to the common AC bus through one power generation AC-side switch;

the master controller is respectively connected with the load, the energy storage device, the energy storage converter, each power generation device, the power grid switch, the load switch, the energy storage AC side switch and each power generation AC side switch, wherein the power generation device comprises: any one or more of a wind power generation apparatus, a photovoltaic power generation apparatus, and a fuel oil power generation apparatus.

10. The power system of claim 9, wherein the power generation device comprises: when the wind power generation device, the photovoltaic power generation device and the fuel oil power generation device are used, the master controller is used for:

sending a mode switching instruction to the energy storage converter, so that the energy storage converter enters an SVF mode under the condition that a first mode switching condition is met, wherein the first mode switching condition is as follows: the voltage of the lower port of the public connection point switch is in a fourth preset voltage interval, the frequency of the power grid side of the public connection point switch is in a fourth preset frequency interval, and the power of the lower port of the public connection point switch is in a preset power interval;

acquiring feedback information sent by the energy storage converter after the energy storage converter enters the SVF mode;

adjusting the SOC value of the energy storage system to the preset SOC range, and controlling the energy storage converter to be switched to an off-grid mode from an SVF mode when a second mode switching condition is met, so that the load is switched to an energy storage converter power supply loop, wherein the second mode switching condition is as follows: and the lower port voltage exceeds a fifth preset voltage interval, or the power grid side frequency exceeds a fifth preset frequency interval, or the range of the lower port power is in a sixth preset power interval, or a switching-off feedback signal of the switch at the common connection point is received.

11. The power system of claim 10, further comprising, after controlling the energy storage converter to switch from the SVF mode to the off-grid mode:

if so, disconnecting the load switch connected between a non-priority power supply load and the AC utility bus, wherein the load in the power system comprises: the priority power supply load and the non-priority power supply load;

12. The power system of claim 11, further comprising, after the step of disconnecting the connection between the wind power plant and the photovoltaic plant and the common ac bus:

if so, controlling the frequency and the phase of the energy storage converter following the fuel oil power generation side;

acquiring a following result fed back by the energy storage converter at any time, and conducting a connecting passage between the fuel power generation device and the public alternating current bus to switch the load to a fuel power supply loop;

and controlling the energy storage converter to exit the VF mode.

13. The power system of claim 9, wherein the power generation device comprises: when the wind power generation device, the photovoltaic power generation device and the fuel oil power generation device are used, the master controller is also used for:

acquiring a second switching instruction from the off-grid to the on-grid;

judging whether the absolute value of the difference value is not greater than the absolute value of a first preset apparent power;

if yes, controlling the energy storage converter to start off-grid to grid connection, and following the upper power grid frequency and the phase of the public connection point switch when the energy storage converter determines that a preset following condition is met, wherein the preset following condition is as follows: the public connection point switch is in a switching-off state, the voltage range of an upper port of the public connection point switch is in a preset voltage range, the frequency of the upper port of the public connection point switch is in a preset frequency range, and the apparent power of the energy storage converter is not larger than the absolute value of the first preset apparent power;

14. The power system of claim 13, wherein after the master controller controls the grid switch to conduct to switch the load to the grid supply loop, the energy storage converter is further configured to:

judging whether the latest apparent power of the energy storage converter is not less than a second preset apparent power or not, and whether the instantaneous current detected by the energy storage converter is not less than a preset instantaneous current threshold or not, or acquiring a closing feedback signal of the switch of the public connection point;

and if so, controlling the energy storage controller to exit the off-grid mode.