CN115441487A

CN115441487A - SOC (system on chip) balancing method and terminal of common DC bus energy storage system

Info

Publication number: CN115441487A
Application number: CN202210986738.4A
Authority: CN
Inventors: 朱志煌; 马克明; 张新池
Original assignee: Fujian Times Nebula Technology Co Ltd
Current assignee: Fujian Times Nebula Technology Co Ltd
Priority date: 2022-08-17
Filing date: 2022-08-17
Publication date: 2022-12-06

Abstract

The invention provides a method and a terminal for balancing SOC of a common direct current bus energy storage system, wherein the method comprises the following steps of: initializing an upper limit value and a lower limit value of a voltage sampling value of a direct current bus in the energy storage system, and acquiring the working state of the energy storage system and the voltage sampling value of the direct current bus of each subsystem in real time; determining a first charging/discharging subsystem according to the voltage sampling value, acquiring the SOC of an electric cabinet in the first charging/discharging subsystem in real time, and stopping the first charging/discharging subsystem if the SOC of the electric cabinet is charged/discharged to a first charging value/a first discharging value; setting an overvoltage threshold value/undervoltage threshold value of a DC/DC in the first charging/discharging subsystem as a first overvoltage threshold value/first undervoltage threshold value; and repeating the steps for the rest subsystems until the overvoltage threshold value/the undervoltage threshold value of the DC/DC in each subsystem is set as the first overvoltage threshold value/the first undervoltage threshold value. The method can effectively solve the problem that the SOC balance of each subsystem is increasingly poor due to the fact that the energy storage systems cannot be charged and discharged simultaneously.

Description

SOC (system on chip) balancing method and terminal of common DC bus energy storage system

Technical Field

The invention relates to the technical field of energy storage systems, in particular to a SOC (system on chip) balancing method and a terminal of a common direct current bus energy storage system.

Background

The common direct current bus energy storage system is a novel energy storage structure, one common direct current bus energy storage system is generally composed of a plurality of energy storage subsystems connected into a power grid, each subsystem is composed of an electric cabinet, a DC/DC (bidirectional direct current converter), an AC/DC (namely an energy storage converter PCS (power conversion system), an inverter) and an EMS (energy management system), and each EMS system is independent and not communicated with each other. The subsystems are connected in parallel in a mode of sharing one direct current bus, and the direct current bus of the whole energy storage system is established and maintained by the DC/DC of the subsystems.

Ideally, in the process of charging and discharging the common direct current bus energy storage system, each subsystem should be in the same charging and discharging state of sharing power. In practice, the distribution distance of each subsystem is relatively long, so that the length of a direct current bus reaches several kilometers and dozens of kilometers, and the influence of voltage drop exists; and the sampling voltages of the DC/DC direct current buses of the subsystems are not consistent, so that errors exist. Due to the two reasons, sampling results of the DC/DC in the subsystems to the voltage of the same direct current bus are inconsistent, the charging and discharging efficiency of the whole common direct current bus energy storage system is low due to the fact that a certain energy storage subsystem is charged and discharged firstly, and in the past, the balance among the sub energy storage systems of the common direct current bus energy storage system is poorer and poorer.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method and the terminal for balancing the SOC of the common direct current bus energy storage system are provided, and the problem that the SOC balance of each subsystem is increasingly poor due to the fact that the energy storage systems cannot be charged and discharged simultaneously is solved.

In order to solve the technical problems, the invention adopts the technical scheme that:

a SOC balancing method of a common direct current bus energy storage system comprises the following steps:

s1, initializing an upper limit value and a lower limit value of a voltage sampling value of a direct current bus in an energy storage system, and acquiring the working state of the energy storage system and the voltage sampling value of the direct current bus of each subsystem in real time;

s2, determining a first charging/discharging subsystem according to the voltage sampling value, collecting the SOC of an electric cabinet in the first charging/discharging subsystem in real time, and stopping the work of the first charging/discharging subsystem if the SOC of the electric cabinet is charged/discharged to a first charging value/a first discharging value;

s3, setting an overvoltage threshold/an undervoltage threshold of the DC/DC in the initial charging/discharging subsystem as a first overvoltage threshold/a first undervoltage threshold, wherein the first overvoltage threshold is higher than the upper limit value, and the first undervoltage threshold is lower than the lower limit value;

s4, repeating the steps S2-S3 for the rest subsystems until the overvoltage threshold value/the undervoltage threshold value of the DC/DC in each subsystem is set as a first overvoltage threshold value/a first undervoltage threshold value;

and S5, converting the upper limit value and the lower limit value from initial values into the first overvoltage threshold value and the first undervoltage threshold value, and simultaneously charging and discharging the subsystems.

In order to solve the technical problem, the invention adopts another technical scheme as follows:

an SOC equalization terminal of a common dc bus energy storage system comprises a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps in the SOC equalization method of the common dc bus energy storage system as described above when executing the computer program.

The invention has the beneficial effects that: the invention provides a method and a terminal for balancing SOC of a common direct current bus energy storage system, under the condition that subsystems in the common direct current bus energy storage system are unbalanced (for example, SOC is unbalanced due to sampling error of a direct current bus and charging/discharging firstly), the overvoltage threshold/the undervoltage threshold of the subsystem which is charged/discharged firstly to a first charging value/a first discharging value is adjusted to be a first overvoltage threshold/a first undervoltage threshold in sequence, so that the initial upper limit/the lower limit of the direct current bus is smaller/larger than the overvoltage threshold/the undervoltage threshold of the DC/DC of the first charging/discharging subsystem, and belongs to a normal range.

Drawings

Fig. 1 is a system architecture diagram of a common dc bus energy storage system according to an embodiment of the present invention;

fig. 2 is an overall flowchart of an SOC equalization method for a common dc bus energy storage system according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the DC/DC operating principle of maintaining the DC bus by droop control;

fig. 4 is a specific flowchart of an SOC equalization method for a common dc bus energy storage system according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of an SOC equalization terminal of a common dc bus energy storage system according to an embodiment of the present invention.

Description of reference numerals:

10. an SOC balance terminal of a common direct current bus energy storage system; 20. a memory; 30. a processor.

Detailed Description

In order to explain technical contents, achieved objects, and effects of the present invention in detail, the following description is made with reference to the accompanying drawings in combination with the embodiments.

Referring to fig. 1 to 4, an SOC equalization method for a common dc bus energy storage system includes the steps of:

As can be seen from the above description, the beneficial effects of the present invention are: under the condition that all subsystems in a common direct current bus energy storage system are unbalanced (for example, the sampling error of a direct current bus and the SOC of the subsystems are unbalanced due to the prior charging/discharging, the overvoltage threshold/the undervoltage threshold of the subsystem which is charged/discharged firstly to a first charging value/a first discharging value are sequentially adjusted to be a first overvoltage threshold/a first undervoltage threshold, so that the initial upper/lower limit value of the direct current bus is smaller/larger than the overvoltage threshold/the undervoltage threshold of the DC/DC of the primary charging/discharging subsystem, the overvoltage threshold/the undervoltage threshold belongs to a normal range, according to a DC/DC droop strategy, the subsystem which is charged/discharged firstly is in a state of not charging or discharging, so that the power output is stopped, the charging/discharging power needs to be continuously charged/discharged, the charging/discharging power is continuously borne by the rest subsystems, namely the upper/lower limit value of the output of the direct current bus is continuously maintained by the rest subsystems, the upper/lower limit value of the DC/DC in each subsystem is changed into the first overvoltage threshold/undervoltage threshold/the first undervoltage threshold, and the subsequent subsystems in each other subsystems, so that the charging/discharging efficiency of the common direct current bus is improved more and more, and more the common direct current bus energy storage system can be used, and more the like.

Further, the initial values of the upper limit value and the lower limit value are 800V and 750V, respectively;

the first charge value and the first discharge value are 95% and 20% of the electrical cabinet SOC, respectively;

the first over-voltage threshold and the first under-voltage threshold are 805V and 745V, respectively.

It can be known from the above description that the first charge value is 95% of the SOC of the electrical cabinet, that is, 5% of the SOC is reserved to prevent overcharge of the electrical cabinet, and the first discharge value is 20% of the SOC of the electrical cabinet, in consideration of the fact that the electrical cabinet is charged and discharged by a small current due to the small current of the dc bus and the energy flowing, a part of electric quantity is reserved to absorb the small current to prevent overcharge and overdischarge of the electrical cabinet, and all subsystems which do not subsequently reach the value can simultaneously charge and discharge to the maximum and minimum SOC values, and meanwhile, the first overvoltage threshold is slightly higher than the initial upper limit value of the dc bus, and the first undervoltage threshold is slightly lower than the initial lower limit value of the dc bus to avoid the switching between charge-discharge and discharge-discharge.

Further, the step S2 further includes:

and if the charging/discharging voltage of the single battery cell of the electric cabinet reaches the first charging voltage/the first discharging voltage, stopping the operation of the first charging/discharging subsystem.

Further, the first charging voltage and the first discharging voltage are 3.5V and 3.1V, respectively.

As can be seen from the above description, the timing when the first charge/discharge subsystem stops working can be further perfectly determined by whether the voltage of the cell in each subsystem electric cabinet reaches 3.5V of the first charge voltage/3.1V of the first discharge voltage, so as to ensure the timely setting of the first overvoltage threshold/the first undervoltage threshold.

Further, the step S5 specifically includes:

when the energy storage system is in a charging state, the upper limit value is converted into the first overvoltage threshold value from an initial value, and when the energy storage system is subsequently converted into a discharging state from the charging state and the SOC of the electric cabinet in each subsystem reaches a second charging value after each subsystem is discharged simultaneously, the first overvoltage threshold value is reset to be the initial value of the upper limit value;

and when the energy storage system is in a discharging state, the lower limit value is changed into the first under-voltage threshold value from an initial value, and subsequently when the energy storage system is changed into a charging state from the discharging state and the SOC of the electric cabinet in each subsystem is charged to a second discharging value at the same time, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

Further, the second charge value and the second discharge value are 90% and 30% of the electrical cabinet SOC, respectively.

As can be seen from the above description, when the overvoltage threshold or the undervoltage threshold of the DC/DC of the subsystem is set to the first overvoltage threshold or the first undervoltage threshold, the sampling voltage of the DC bus adapts to the working state of the energy storage system and the DC/DC set value of each subsystem, that is, the upper limit = the overvoltage threshold, the lower limit = the undervoltage threshold, but at this time, the SOC of each subsystem has reached 95% in the charging state and is about to be fully charged, in order to form a policy closed loop, the SOC of each electrical cabinet is discharged to 90% and then the overvoltage threshold of each subsystem DC/DC is set as the initial upper limit of the DC bus, and then the upper limit of the DC bus is also restored to the initial value of 800V, that is, the state of the system just charged is restored, and the situation that the sampling voltage of the DC bus is higher and higher until the overvoltage threshold exceeds the initial upper limit after the subsequent outgoing line executes the waiting policy for multiple times to cause the shutdown of the entire system is avoided; similarly, the SOC of each subsystem reaches 20% in a discharging state, in order to form a strategy closed loop, the SOC of each subsystem is charged to 25%, the undervoltage threshold of the DC/DC of each subsystem is set to be the initial lower limit value of the direct current bus, the lower limit value of the direct current bus can be recovered to be the initial value of 750V, namely the state of the system just discharging is recovered, and the condition that the sampling voltage of the direct current bus is lower and lower until the sampling voltage is lower than the limit undervoltage threshold value to cause the shutdown of the whole system after the subsequent outgoing line executes the waiting strategy for multiple times is avoided.

Further, the step S5 further includes:

when the energy storage system is in a charging state, the upper limit value is converted into the first overvoltage threshold value from an initial value, and subsequently when the energy storage system is converted into a discharging state from the charging state, and when the subsystems are simultaneously discharged to the monomer battery cores of the electric cabinet in the subsystems and are all charged to a second charging voltage, the first overvoltage threshold value is reset to be the initial value of the upper limit value;

and when the energy storage system is in a charging state, the lower limit value is changed into the first under-voltage threshold value from an initial value, and subsequently when the energy storage system is changed into the charging state from a discharging state and the single battery cells of the electric cabinet in each subsystem are simultaneously charged to a second discharging voltage, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

Further, the second charging voltage and the second discharging voltage are 3.45V and 3.25V, respectively.

From the above description, it can be known that, similarly, when the charging voltages of the individual battery cells of the electrical cabinets of the subsystems all reach the first charging voltage of 3.5V in the charging state, in order to form a strategy closed loop, the individual battery cells of the electrical cabinets are simultaneously discharged to the voltage of 3.45V of the second charging voltage, and the overvoltage threshold of the DC/DC of each subsystem is set as the initial upper limit of the DC bus, so that the upper limit of the DC bus is also restored to the initial value of 800V, that is, the state of the system just charging is restored, and the problem that the whole system is shut down due to the fact that the sampling voltage of the DC bus is higher and higher until the sampling voltage exceeds the limit overvoltage threshold after the subsequent outgoing line executes the waiting strategy for many times is avoided; and when the single battery cells of the subsystem electric cabinets are discharged until the voltage reaches 3.1V of the first discharge voltage, in order to form a strategy closed loop, the single battery cells of the subsystem electric cabinets are charged again until the voltage reaches 3.25V of the second discharge voltage, and the undervoltage threshold of the DC/DC of each subsystem is set as the initial lower limit value of the DC bus, so that the lower limit value of the DC bus can be recovered to 750V of the initial value, namely the state of the system just discharging is recovered, and the condition that the sampling voltage of the DC bus is lower and lower until the sampling voltage is lower than the limit undervoltage threshold to stop the whole system after the subsequent outgoing line executes the waiting strategy for multiple times is avoided.

Further, the step S1 further includes:

acquiring SOC, short-time unbalanced electric quantity, subsystem periodic load or sampling error of each subsystem;

the steps S1 and S2 further comprise:

and judging whether the unbalance degree among the subsystems reaches an upper limit condition or not according to the SOC difference, the short-time unbalance electric quantity, the subsystem periodic load or the sampling error of the subsystems, if so, judging that the subsystems have the sampling error, and executing a step S2, otherwise, carrying out charging/discharging operation by using the initial values of the upper limit value and the lower limit value as an overvoltage threshold value and an undervoltage threshold value by the DC/DC of the subsystems.

It can be known from the above description that, because differences inevitably exist between subsystems, the differences are not only differences of sampling voltages of DC/DC pairs of common DC buses of the subsystems, but also differences of SOCs of the subsystems themselves and differences caused by short-time unbalanced electric quantities and periodic loads of the subsystems, and finally the degree of imbalance among the subsystems is comprehensively determined by using the SOC differences, the short-time unbalanced electric quantities, the periodic loads of the subsystems or sampling errors, thereby improving accuracy of determining imbalance among the subsystems.

Referring to fig. 5, an SOC equalization terminal of a common dc bus energy storage system includes a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor implements the steps in the SOC equalization method of the common dc bus energy storage system when executing the computer program.

As can be seen from the above description, the beneficial effects of the present invention are: based on the same technical concept, the SOC balancing terminal of the common DC bus energy storage system is provided in cooperation with the SOC balancing method of the common DC bus energy storage system, when there is an imbalance (for example, an imbalance between the SOC due to a sampling error of the DC bus and a previous charging/discharging) in each subsystem in the common DC bus energy storage system, the overvoltage threshold/the undervoltage threshold of the subsystem which is first charged/discharged to a first charging value/a first discharging value is sequentially adjusted to be the first overvoltage threshold/the first undervoltage threshold, so that the initial upper/lower limit value of the DC bus is smaller/larger than the overvoltage threshold/the undervoltage threshold of the DC/DC subsystem which is first charged/discharged, and belongs to a normal range, according to a DC/DC droop strategy, the subsystem which is first charged/discharged is in a state of neither being charged nor being discharged, thereby stopping power output, and the energy storage system needs to continue to be charged/discharged, the charging/discharging power is continuously borne by the remaining subsystems, that the remaining subsystems continue to maintain the output upper/lower limit value of the DC bus, until the overvoltage threshold/DC in each subsystem reaches the first undervoltage threshold/discharging threshold, and the initial value of the first overvoltage threshold/undervoltage of the first charging/discharging subsystem is increased, thereby achieving the maximum use of the common DC bus.

The SOC equalization method and terminal for the common DC bus energy storage system provided by the present invention are suitable for the situation that SOC imbalance exists between subsystems due to errors of the DC/DC in sampling voltages of the DC bus in the subsystems in the common DC bus energy storage system, and the subsystems cannot be charged and discharged simultaneously, and will be specifically described below with reference to the embodiments.

Referring to fig. 1 to fig. 3, a first embodiment of the present invention is:

in this embodiment, as shown in fig. 1, taking a common DC bus energy storage system composed of four energy storage subsystems A, B, C, D as an example, each subsystem is composed of 1 electric cabinet, 1 DC/DC, 1 AC/DC (i.e., energy storage converter PCS, also called inverter) and 1 EMS system, and each EMS system is independent and does not communicate with each other. The subsystems are connected in parallel in a mode of sharing one direct current bus, the direct current bus of the whole energy storage system is subjected to voltage sampling by the DC/DC of the subsystems, the voltage of the direct current bus is established and maintained by the DC/DC of the subsystems, the subsystems A, B, C, D can independently transmit power to the direct current bus and then output the power to respective loads through the AC/DC to a power grid, and energy scheduling in the whole process is controlled by the EMS system.

Before this, the operation principle of DC/DC is explained as follows:

one side of the energy storage subsystem, which is connected with the battery, has a certain voltage working range, the voltage of the battery is matched, and the voltage sampling is positioned at the connection position of the battery and the DC/DC. In the voltage range, the DC/DC can charge or discharge the battery with certain power, and the power and the current can be regulated when the battery works in a constant power or constant current mode.

The side connected with the DC-BUS is also provided with voltage sampling, the control target is to adjust the DC BUS within an allowable voltage range, which can be understood as voltage stabilization, but the voltage stabilization precision is not very high, such as 740V-800V, and is determined by the bearing degree of a load side and the allowable fluctuation of the DC BUS, the range is controlled by a droop mode, namely an automatic feedback function, when the sampling voltage of the DC BUS is lower than 750V, energy is supplemented to the BUS by a battery, and when the sampling voltage of the DC BUS is higher than 750V, the energy is extracted from the BUS to the battery, the power has a proportionality coefficient, and the larger the deviation from the voltage stabilization point of the BUS is, the higher the power is. When the DC/DC collection bus voltage reaches below 745V for example, full power discharge is started, the regulation maximum value is reached, and the reverse is carried out during charging.

Taking discharge as an example: when a direct current bus is formed by a single module (battery + DC/DC), the distance between the load and the DC/DC is relatively short, the fluctuation of the load directly reflects at a bus voltage sampling point of the DC/DC, the regulation is relatively quick, and the direct current bus can be controlled to be relatively small in fluctuation. When a plurality of modules form a direct current bus, a source and a load are distributed at different positions, and the working uncertainty of each load is that the load close to a certain module discharges, the bus voltage sampling of the module is lower than that of other modules far away, and the discharge power is higher than that of other modules far away.

When voltage sampling has errors, extreme conditions are considered, and the sampling of a module at a short distance is low, and the discharge power is relatively maximum. The original scheme is that a mode of dynamically adjusting a lower limit threshold of voltage is adopted to stop full-power discharge of a module with too low SOC, but at the moment, whether the module completely stops working or enters a droop control interval needs to be determined.

The reason for causing the SOC imbalance among the subsystems in the common direct current bus energy storage system is that the DC/DC of a certain module continuously acquires the bus voltage lower than the discharge threshold, and since the position and the power of a load, the voltage sampling error of each DC/DC, the hardware difference of the modules and the like are random, a self-correction positive and negative feedback mechanism needs to be introduced, and the aim is to keep all the modules to work simultaneously, and the imbalance degree is within a certain degree and is not influenced by the random factors.

In this embodiment, as shown in FIG. 3, DC/DC establishes a DC bus voltage U _x DC/DC has two parameters, respectively, the undervoltage threshold V _Uvr And an overvoltage threshold V _Our The two parameters determine the upper and lower limits of the DC bus voltage, namely, the voltage is equivalent to V _Uvr Is the lower limit value, V, of the DC bus _Our The upper limit value of the direct current bus; in addition, the DC/DC also comprises a limit undervoltage value V _Ulimit And a limit overvoltage value U _Qlimit Wherein the extreme under-voltage value V _Ulimit Is less than the under-voltage threshold V _Uvr Extreme overpressure value U _Qlimit Is to be greater than the overvoltage threshold V _Our When the voltage of the DC bus collected by the DC/DC of a certain subsystem is smaller than the limit undervoltage value V of the DC/DC of the subsystem _Ulimit Or greater than the limit overvoltage value U of the DC/DC _Qlimit When the system is charged, the system can be charged or discharged, and even the whole energy storage system is charged or discharged.

DC/DC maintaining DC bus voltage U _x In the process, the DC/DC establishes a bus voltage U _x Then, the DC bus voltage U is maintained through droop control _x . Droop control is understood to mean a DC/DC to DC bus voltage U _x Sampling, e.g. DC bus voltage U _x When the voltage is lower than 750V, the DC/DC can automatically draw power from the electric cabinet, the electric cabinet discharges, and the voltage Ux of the direct-current bus is maintained at 750V; if the voltage of the direct current bus is higher than 800V, the DC/DC automatically transmits power to the electric cabinet, and the electric cabinet is charged to enable the voltage of the direct current bus to be lower than 800V. Under the condition that the direct current bus has no energy input or output, the voltage of the direct current bus is maintained at V _Uvr I.e. 750V. Because the direct current bus has no energy input, the direct current bus voltage is reduced after the direct current bus voltage is established to be 750V by the DC/DC, at the moment, the DC/DC controls the electricity cabinet to discharge through droop control, the direct current bus voltage is maintained to be 750V, the electricity cabinet stops discharging, the electricity cabinet discharges again after the direct current bus voltage is reduced, and the cycle is repeated. ByThe process is dynamic, so the external appearance is that the power cabinet discharges the direct current continuously, and the direct current bus is maintained. The other energy storage subsystems maintain the direct current bus voltage in the same way as the energy storage subsystem A.

And the charging/discharging process of the common direct current bus energy storage system is as follows:

and (3) discharging: taking the energy storage subsystem A as an example, the PCS outputs 50kw of power to the power grid, at the moment, the voltage of the direct current bus is pulled low and is lower than 750V, and the DC/DC detects that the voltage of the direct current bus is lower than V _Uvr And then, drawing 50kw (the discharge power of the electric cabinet is required to be consistent with that of the PCS (power control system) from the electric cabinet, so that power balance is achieved, the discharge power of the electric cabinet is low, the voltage of the direct-current bus is lower than 750V, the discharge power of the electric cabinet is higher than that of the direct-current bus and is larger than 800V), discharging the electric cabinet, and maintaining the voltage of the direct-current bus at 750V.

And (3) charging process: taking the energy storage subsystem A as an example, 50kw of power is pulled from the power grid by the PCS and transmitted to the direct current bus, the voltage of the direct current bus is increased at the moment, the voltage is higher than 800V, and the direct current bus voltage is detected to be higher than V by the DC/DC _Our And then, inputting power 50kw to the electric cabinet (the charging power of the electric cabinet is required to be consistent with the charging power of the PCS to achieve power balance, the charging power of the electric cabinet is low, the voltage of the direct-current bus is higher than 800V, the charging power of the electric cabinet is high, and the voltage of the direct-current bus is less than 750V), and charging the electric cabinet to maintain the voltage of the direct-current bus at 800V.

And the charging and discharging processes of other energy storage subsystems are consistent with that of the energy storage subsystem A. Therefore, if only the PCS of the subsystem A is discharged or charged, the DC/DC of the 4 energy storage subsystems are charged or discharged, because the direct current buses of the 4 energy storage subsystems are connected in parallel, the voltage change of the direct current buses is consistent, and the power is evenly distributed into the electric cabinets of the 4 energy storage subsystems. A plurality of PCS charge or discharge, and the power is still equallyd divide 4 energy storage subsystems's electric cabinet, compares single PCS charge-discharge, and the power of equallyd divide is just big.

Under normal conditions, when the common dc bus energy storage system in the architecture of fig. 1 is charging and discharging, the four energy storage subsystems are simultaneously charged and discharged. But the four energy storage subsystems are distributed at longer distanceThe length of the direct current bus forming line reaches several kilometers and dozens of kilometers, and the influence of voltage drop exists; and the sampling voltages of the four energy storage subsystems DC/DC to the DC bus are not consistent, so that errors exist. For the two reasons, the sampling results of the four DC/DC pairs on the same DC bus voltage are inconsistent, and the lower limit value V of the DC bus is assumed _Uvr Is 750V and the upper limit value V _Uvr At 800V, there may be a sample U of the DC bus voltage from the energy storage subsystem A _xA DC bus voltage sampling value U for 749V subsystem B _xB Sampling value U of voltage of 750V direct current bus of subsystem C _xC 751V, subsystem D and DC bus voltage sampling value U _xD In the case of 752V. The condition can cause the voltage of the direct current bus of the energy storage subsystem A to be always lower than V _Uvr When the common direct-current bus energy storage system discharges, the electric cabinet of the subsystem A preferentially discharges, the other three subsystems do not act, the electric cabinet of the subsystem A discharges electricity, and the whole common direct-current bus energy storage system stops running; similarly, when charging is carried out, a subsystem can be charged preferentially, and the charging of the common direct-current bus energy storage system is stopped after the electric cabinet is fully charged. The low charging and discharging efficiency of the whole common direct current bus energy storage system is caused by the fact that a certain energy storage subsystem is charged and discharged firstly, and the balance among the sub energy storage systems of the common direct current bus energy storage system is poorer and poorer in the past.

In addition, the sampling difference between subsystems can be caused by the difference of short-time unbalanced electric quantity of the common direct current bus energy storage system and the difference of periodic load of the subsystems. The short-time unbalanced electric quantity can filter the power imbalance caused by transient load fluctuation, and can also reflect the practical situations of voltage sampling error, hardware inconsistency among subsystems, position difference, imbalance caused by lead impedance and the like, wherein the imbalance can be a function of the SOC, the charge and discharge power, the capacity of the energy storage subsystem and the time, for example: power integral Wn of subsystem x in a determination period (e.g., 2 minutes); and the subsystem period load is the integral of the subsystem discharge multiplying power in a judgment period and is used for representing the subsystem heating cumulative quantity Qn, and the parameter can allow batteries with different specifications to run in parallel and participate in charging and discharging according to the self load capacity, so that the subsystems which are not limited to the same power are enabled.

In order to solve the above problem that the energy storage systems cannot be charged and discharged simultaneously due to the SOC imbalance among the subsystems, the SOC equalization method for the common dc bus energy storage system provided in this embodiment, as shown in fig. 2, includes the steps of:

s2, determining a first charging/discharging subsystem according to the voltage sampling value, collecting the SOC of an electric cabinet in the first charging/discharging subsystem in real time, and stopping the first charging/discharging subsystem if the SOC of the electric cabinet is charged/discharged to a first charging value/a first discharging value;

s3, setting an overvoltage threshold/undervoltage threshold of a DC/DC in the first charging/discharging subsystem as a first overvoltage threshold/first undervoltage threshold, wherein the first overvoltage threshold is higher than an upper limit value, and the first undervoltage threshold is lower than a lower limit value;

and S5, converting the upper limit value and the lower limit value from the initial values into a first overvoltage threshold value and a first undervoltage threshold value, and simultaneously charging and discharging the subsystems.

In this embodiment, when there is an imbalance (for example, sampling error of the DC bus and SOC imbalance caused by charging/discharging first) among subsystems in the common DC bus energy storage system, the overvoltage threshold/undervoltage threshold of the subsystem that is charged/discharged first to the first charging value/first discharging value is sequentially adjusted to be the first overvoltage threshold/first undervoltage threshold, so that the initial upper/lower limit value of the DC bus is smaller/larger than the overvoltage threshold/undervoltage threshold of the DC/DC of the first charging/discharging subsystem, and belongs to a normal range.

However, as described above, the imbalance of the DC/DC pair DC bus of each subsystem may be caused by various reasons, and therefore, in this embodiment, the step S1 further includes:

the method also comprises the following steps between S1 and S2:

and judging whether the unbalance degree among the subsystems reaches an upper limit condition or not according to the SOC difference, the short-time unbalance electric quantity, the subsystem periodic load or the sampling error of the subsystems, if so, executing a step S2, and otherwise, taking the initial values of the upper limit value and the lower limit value of the DC/DC of the subsystems as an overvoltage threshold value and an undervoltage threshold value to perform charging/discharging operation.

That is, as shown in fig. 4, the SOC difference, the short-time unbalanced electric quantity, the subsystem periodic load, or the sampling error is comprehensively checked to determine the final degree of imbalance between the subsystems, for example, whether the short-time unbalanced electric quantity (Wnmax-Wnmin)/Wnavg is greater than 20%, whether the subsystem periodic load Qn is greater than 1, the SOC difference is greater than 20%, or the sampling error is greater than 0.5%, thereby improving the accuracy of determining the imbalance between the subsystems.

Referring to fig. 4, a second embodiment of the present invention is:

on the basis of the first embodiment, in the embodiment, initial values of an upper limit value and a lower limit value are 800V and 750V respectively; the first charge value and the first discharge value are 95% and 20% of the SOC of the electric cabinet respectively; the first over-voltage threshold and the first under-voltage threshold are 805V and 745V, respectively. In other embodiments, the first overvoltage threshold and the first undervoltage threshold may be set as needed, for example, the upper limit value may be adjusted upward by 0.2% to serve as the first overvoltage threshold, and the lower limit value may be adjusted downward by 0.2% to serve as the first undervoltage threshold.

In this embodiment, the first charge value is set to 95% of the SOC of the electrical cabinet, that is, 5% of the SOC is reserved to prevent overcharge of the electrical cabinet, and the first discharge value is 20% of the SOC of the electrical cabinet, which considers that the electrical cabinet may have low current charge and discharge due to low current of the dc bus, and therefore a part of electricity is reserved to consume the low current to avoid overcharge and overdischarge of the electrical cabinet, and all subsystems which do not subsequently reach the value can simultaneously charge and discharge to the maximum and minimum SOC value, and meanwhile, the first overvoltage threshold is slightly higher than the initial upper limit of the dc bus, and the first undervoltage threshold is slightly lower than the initial lower limit of the dc bus, so as to avoid the switching between charge-discharge and discharge-discharge.

Wherein, step S2 further comprises:

and if the charging/discharging voltage of the single battery cell of the electric cabinet reaches the first charging voltage/first discharging voltage, stopping the operation of the first charging/discharging subsystem. Wherein the first charging voltage and the first discharging voltage are 3.5V and 3.1V, respectively.

That is, in this embodiment, the timing when the first charge/discharge subsystem stops working may be further perfectly determined by whether the voltage of the cell in each subsystem electric cabinet reaches the first charge voltage 3.5V/the first discharge voltage 3.1V, so as to ensure the timely setting of the first overvoltage threshold/the first undervoltage threshold.

Meanwhile, in this embodiment, step S5 specifically is:

when the energy storage system is in a charging state, the upper limit value is converted into a first overvoltage threshold value from the initial value, and subsequently when the energy storage system is converted into a discharging state from the charging state, when the subsystems are discharged simultaneously until the SOC of the electric cabinet in each subsystem reaches a second charging value, the first overvoltage threshold value is reset to be the initial value of the upper limit value;

and when the energy storage system is in a discharging state, the lower limit value is changed into a first under-voltage threshold value from the initial value, and subsequently, when the energy storage system is changed into a charging state from the discharging state, and the SOC of the electric cabinet in each subsystem is charged to reach a second discharging value at the same time, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

Wherein the second charge value and the second discharge value are 90% and 30% of the SOC of the electric cabinet respectively.

Similarly, step S5 may also be:

when the energy storage system is in a charging state, the upper limit value is converted into a first overvoltage threshold value from the initial value, and subsequently when the energy storage system is converted into a discharging state from the charging state, and when the subsystems are simultaneously discharged to the monomer battery cores of the electric cabinets in the subsystems and are uniformly charged to a second charging voltage, the first overvoltage threshold value is reset to be the initial value of the upper limit value;

and when the energy storage system is in a charging state, the lower limit value is changed into a first under-voltage threshold value from the initial value, and subsequently, when the energy storage system is changed into the charging state from a discharging state, and when the subsystems are simultaneously charged to the monomer battery cells of the electric cabinets in the subsystems and are all charged to a second discharging voltage, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

Wherein the second charging voltage and the second discharging voltage are 3.45V and 3.25V, respectively.

In this embodiment, when the charging voltages of the individual battery cells of the electrical cabinets of the subsystems all reach the first charging voltage of 3.5V in the charging state, in order to form a strategy closed loop, the individual battery cells of the electrical cabinets are simultaneously discharged until the voltage is the second charging voltage of 3.45V, and the overvoltage threshold of the DC/DC of each subsystem is set to be the initial upper limit of the DC bus, so that the upper limit of the DC bus is also recovered to be the initial value of 800V, that is, the state of the system when charging is just started is recovered, and the problem that the whole system is shut down due to the fact that the sampling voltage of the DC bus is higher and higher until the sampling voltage exceeds the limit overvoltage threshold after the subsequent outgoing line executes the waiting strategy for many times is avoided; and when the single battery cells of the subsystem electric cabinets are discharged until the voltage reaches 3.1V of the first discharge voltage, in order to form a strategy closed loop, the single battery cells of the subsystem electric cabinets are charged again until the voltage reaches 3.25V of the second discharge voltage, and the undervoltage threshold of the DC/DC of each subsystem is set as the initial lower limit value of the DC bus, so that the lower limit value of the DC bus can be recovered to 750V of the initial value, namely the state of the system just discharging is recovered, and the condition that the sampling voltage of the DC bus is lower and lower until the sampling voltage is lower than the limit undervoltage threshold to stop the whole system after the subsequent outgoing line executes the waiting strategy for multiple times is avoided.

Specifically, in this embodiment, in the discharging process of the energy storage system, due to the problem of the sampling error of the outgoing line, only the subsystem a in the energy storage system shown in fig. 1 is discharging, the other B, C, D three subsystems are not charging and not discharging, the subsystem a is discharging until the SOC of the subsystem a is less than or equal to 20% or the voltage of the single battery cell is less than or equal to 3.1V, and the subsystem a sets the under-voltage threshold V of the DC/DC thereof _Uvr The first undervoltage threshold value is 745V, and the voltage of the DC bus is maintained at an initial value of 750V by the subsystems B, C and D, which means that the DC bus voltage U is _x Is V greater than subsystem A _Uvr (745V), namely in the normal range, according to the droop strategy of DC/DC, the electric cabinet of the subsystem A can be in the state of not charging or discharging, so that the subsystem A stops power output, and the common DC bus energy storage system still discharges outwards, and then the discharge power is borne by the subsystems B, C and D. There are two situations at this time:

the first condition is as follows: the power of the energy storage system discharging outwards is divided evenly by the subsystems B, C and D until the SOC of the three subsystems is less than or equal to 20% or the voltage of the monomer cell is less than or equal to 3.1V, and the discharging action is stopped at the moment;

and a second condition: in the subsystems B, C and D, the subsystem B is discharged only and the subsystems C and D do not operate, again because of the DC/DC sampling error. Similarly, the subsystem B executes the same strategy as the subsystem A, and when the subsystem B discharges until the SOC is less than or equal to 20% or the voltage of the monomer battery cell is less than or equal to 3.1V, the DC/DC undervoltage threshold V of the subsystem B is set _Uvr Also the first undervoltage threshold 745V, so that subsystem B is also in the state of neither charging nor discharging due to the droop strategy of DC/DC, the discharging power of the energy storage system is equally divided by the remaining subsystems C and D or the corresponding individual discharging strategy is still executed like subsystems A or B until each subsystem has V to be set _Uvr Set for the first brown-out threshold 745V. At the moment, the electricity of the direct current busThe pressure requirement is equal to each subsystem, i.e. 750V to 745V. By implementing the strategy, the problems that the lunch charging and discharging of each subsystem are simultaneously carried out and the discharging of the common direct current bus energy storage system is stopped due to the early emptying of a single subsystem caused by DC/DC sampling errors or voltage drop and the like can be avoided. When the SOC of the four subsystems is changed from less than or equal to 20 percent again or the voltage of the single cell is changed from less than or equal to 3.1V, the four subsystems are charged again until the SOC is more than or equal to 30 percent or the voltage of the single cell is more than or equal to 3.25V, the V of each subsystem is reset _Uvr Is an initial under-voltage threshold value of 750V, namely the initial state of the recovery system when just starting to discharge, forms a strategy closed loop, if V is not used _Uvr When the initial value is recovered to 750V, the situation that the voltage of the direct current bus is reduced more and more after the waiting strategy is executed for multiple times can occur until the limit undervoltage value V is exceeded _Ulimit Resulting in shutdown of the entire energy storage system.

Similarly, the energy storage system executes a corresponding strategy in the charging process as in the discharging process, when the overvoltage threshold values of the DC/DC of the subsystems are all set to the first overvoltage threshold values, the sampling voltage of the DC bus can adapt to the working state of the energy storage system and the DC/DC set values of the subsystems, that is, the upper limit value = the overvoltage threshold value, in order to form a strategy closed loop, the SOC of each electric cabinet is discharged to be less than or equal to 90% or the voltage of the single electric core is less than or equal to 3.45V, and then the first overvoltage threshold values V of the DC/DC of each subsystem are set to be the first overvoltage threshold values V _Our The initial upper limit value 800V of the direct current bus is set from 805V, and then the upper limit value of the direct current bus is restored to the initial value 800V, namely, the state of the system when charging is started is restored, namely, the problem that the whole system is shut down because the sampling voltage of the direct current bus is higher and higher until the sampling voltage exceeds the limit overvoltage threshold value after the subsequent outgoing lines execute the waiting strategy for multiple times is solved.

It should be noted that 20%, 30%, 90%, and 95% of the SOC and 3.1V, 3.25V, 3.45V, and 3.5V of the cell voltages set in the subsystems may be equivalent to waiting values of the entire strategy, and may be set according to actual conditions. Namely, a certain subsystem discharges first, executes a waiting strategy after reaching a waiting value, sets an overvoltage threshold or an undervoltage threshold, does not discharge and does not charge during the waiting strategy, and continues to discharge or charge to a protection value when all the subsystems reach the waiting value, namely, synchronous charging and discharging among the subsystems are finally realized, which can be understood as asynchronous synchronous charging and discharging.

Referring to fig. 5, a third embodiment of the present invention is:

an SOC balancing terminal 10 of a common dc bus energy storage system includes a memory 20, a processor 30, and a computer program stored on the memory 20 and executable by the processor 30, where the processor 30 implements the steps in the SOC balancing method of the common dc bus energy storage system in one or two of the above embodiments when executing the computer program.

In summary, the SOC equalization method for the common dc bus energy storage system provided by the present invention has the following beneficial effects:

1. the problem that all subsystems in a common direct-current bus energy storage system cannot be charged and discharged simultaneously due to DC/DC sampling errors and voltage drop caused by overlong direct-current buses is solved;

2. the problem that the SOC imbalance among the subsystems is larger and larger is avoided, and the service efficiency of the common direct current bus energy storage system is greatly improved.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent changes made by using the contents of the present specification and the drawings, or applied directly or indirectly to the related technical fields, are included in the scope of the present invention.

Claims

1. A SOC balancing method of a common direct current bus energy storage system is characterized by comprising the following steps:

2. The SOC balancing method for the common direct current bus energy storage system according to claim 1, wherein the initial values of the upper limit value and the lower limit value are 800V and 750V respectively;

3. The SOC balancing method for the common DC bus energy storage system according to claim 1, wherein the step S2 further comprises:

4. A method for SOC equalization of a common dc bus energy storage system as claimed in claim 3, wherein said first charging voltage and said first discharging voltage are 3.5V and 3.1V, respectively.

5. The SOC balancing method for the common DC bus energy storage system according to claim 1, wherein the step S5 specifically comprises:

and when the energy storage system is in a discharging state, the lower limit value is changed into the first under-voltage threshold value from an initial value, and subsequently, when the energy storage system is changed into a charging state from the discharging state, and the SOC of the electric cabinet in each subsystem which is simultaneously charged reaches a second discharging value, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

6. The method for balancing SOC of the common DC bus energy storage system according to claim 5, wherein the second charging value and the second discharging value are 90% and 30% of the SOC of the electric cabinet, respectively.

7. The SOC balancing method for the common DC bus energy storage system according to claim 5, wherein the step S5 further comprises:

and when the energy storage system is in a charging state, the lower limit value is changed into the first under-voltage threshold value from an initial value, and when the energy storage system is changed into the charging state from a discharging state and all the subsystems are simultaneously charged to the monomer battery cores of the electric cabinet in all the subsystems and are all charged to a second discharging voltage, the first under-voltage threshold value is reset to be the initial value of the lower limit value.

8. A method for balancing SOC of a common DC bus energy storage system according to claim 7, wherein the second charging voltage and the second discharging voltage are 3.45V and 3.25V respectively.

9. The SOC balancing method for the common DC bus energy storage system according to claim 1, wherein the step S1 further includes:

the steps S1 and S2 further comprise:

and judging whether the unbalance degree among the subsystems reaches an upper limit condition or not according to the SOC difference, the short-time unbalance electric quantity, the subsystem periodic load or the sampling error of the subsystems, if so, judging that the subsystems have the sampling error, and executing a step S2, otherwise, carrying out charging/discharging operation by the DC/DC of the subsystems by taking the initial values of the upper limit value and the lower limit value as an overvoltage threshold value and an undervoltage threshold value.

10. An SOC balancing terminal of a common dc bus energy storage system, comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of the SOC balancing method of the common dc bus energy storage system according to any one of claims 1 to 9 when executing the computer program.