SOC balancing method of isolated island DC micro-grid and related equipment

Abstract

The invention relates to the technical field of isolated island direct current micro-grids, and provides an SOC balancing method of an isolated island direct current micro-grid and related equipment. The method comprises the following steps: acquiring current charge state values of multiple groups of energy storage units of a target isolated island DC micro-grid; determining a droop coefficient of each group of energy storage units by using an arc tangent function based on the charge state value of each group of energy storage units; determining the secondary compensation amount of each group of energy storage units; and for each group of energy storage units, constructing an adaptive droop control model based on the droop coefficient and the secondary compensation amount of the energy storage unit, calculating the output voltage of the energy storage unit according to the adaptive droop control model, and carrying out charge balance control on the energy storage unit according to the output voltage. According to the method, the stability of SOC equalization can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of isolated DC microgrids, and in particular to a SOC balancing method and related equipment for an isolated DC microgrid. Background Art

[0002] Considering the actual application of isolated DC microgrid system, the energy storage unit capacity may be different, the line resistance is not matched, which seriously affects the balancing effect of the state of charge (SOC). At the same time, the traditional droop control will cause the DC bus voltage to drop. Existing research on SOC balancing, such as the load power dynamic allocation method with bus voltage drop compensation function in DC microgrid energy storage system, sets the droop coefficient to be equal to SOC. n The power function is inversely proportional to n, where n can adjust the SOC balancing speed. This method does not require communication, but it can only achieve SOC balancing when the circuit impedance and capacity are the same. When the energy storage unit is discharged for a period of time, the SOC is low, and its droop coefficient is too large, which will cause the bus voltage to drop beyond the allowable range (±5%), thereby affecting the stability of the system. Considering the multi-energy storage SOC stable balancing control strategy with time-varying line resistance, it is proposed to calculate the line impedance by adopting the impedance detection method based on the fundamental frequency component of the pulse width modulation carrier, and compensate the line impedance value in real time to the droop control. However, this method is easily affected by external environmental factors when calculating the line impedance value. The interference of the elements leads to large measurement errors, and the influence of line impedance cannot be effectively eliminated. In addition, SOC balancing and reasonable power distribution cannot be achieved when considering the difference in energy storage unit capacity. Considering the SOC balancing and power distribution strategies of energy storage with different capacities, the initial droop coefficient is linked to the capacity of the energy storage unit, and the concept of relative capacity (maximum capacity in the energy storage unit / capacity of this unit) is proposed. Multiple secondary compensation controls are designed to realize the functions of power distribution according to capacity and voltage regulation. However, the coupling effect between multiple compensation control loops is difficult to meet the stability requirements of the energy storage system, and in order to avoid excessive bus voltage drop due to excessive droop coefficient, it is not easy to select parameters. It can be seen that there is currently a problem of low SOC balancing stability in isolated DC microgrids. Summary of the invention

[0003] The present application provides a SOC balancing method and related equipment for an isolated DC microgrid, which can solve the problem of low SOC balancing stability of the isolated DC microgrid.

[0004] In a first aspect, an embodiment of the present application provides a SOC balancing method for an island DC microgrid, the SOC balancing method comprising:

[0005] Obtain current state of charge values ​​of multiple groups of energy storage units of the target island DC microgrid;

[0006] Based on the state of charge value of each energy storage unit group, use the arctangent function to determine the droop coefficient of each energy storage unit group;

[0007] Determine the secondary compensation amount of each energy storage unit group;

[0008] For each energy storage unit group respectively, construct an adaptive droop control model based on the droop coefficient and secondary compensation amount of the energy storage unit, calculate the output voltage of the energy storage unit according to the adaptive droop control model, and perform charge equalization control on the energy storage unit according to the output voltage.

[0009] Optionally, based on the state of charge value of each energy storage unit group, using the arctangent function to determine the droop coefficient of each energy storage unit group includes:

[0010] Through the formula:

[0011]

[0012] Calculate the droop coefficient \(R_i\) of the \(i\)-th energy storage unit group vi ;

[0013] where \(R_i\) oi represents the initial droop coefficient of the \(i\)-th energy storage unit group, \(m\) represents the acceleration factor, \(n\) represents the convergence factor, \(S\) ave represents the average state of charge, \(SOC_i\) i represents the current state of charge value of the \(i\)-th energy storage unit group, \(I_i\) dc represents the output current of the \(i\)-th energy storage unit group, \(i = 1, 2, \cdots, I\), and \(I\) represents the number of energy storage unit groups in the target islanded DC microgrid.

[0014] Optionally, determining the secondary compensation amount of each energy storage unit group includes:

[0015] For each energy storage unit group respectively, perform the following steps:

[0016] Calculate the power distribution variable of the energy storage unit, and calculate the information exchange amount of the energy storage unit based on the power distribution variable;

[0017] Calculate the secondary compensation amount of the energy storage unit according to the information exchange amount and the power distribution variable.

[0018] Optionally, calculating the power distribution variable of the energy storage unit includes:

[0019] Through the formula:

[0020]

[0021] Calculate the power distribution variable \(x_i\) of the \(i\)-th energy storage unit group;

[0022] where \(C_i\) min represents the minimum capacity, \(C_i\)bati represents the capacity of the i-th energy storage unit, U viri represents the virtual voltage drop, ΔU dc_max represents the maximum allowable deviation of the bus voltage.

[0023] Optionally, calculate the information exchange amount of the energy storage unit based on the power distribution variable, including:

[0024] Through the formula:

[0025] ξ i =γ i U bus

[0026] Calculate the information exchange amount ξ of the i-th energy storage unit i ;

[0027] where, U bus represents the bus voltage.

[0028] Optionally, calculate the secondary compensation amount of the energy storage unit according to the information exchange amount and the power distribution variable, including:

[0029] Through the formula:

[0030]

[0031] Calculate the secondary compensation amount δv of the i-th energy storage unit i ;

[0032] where, k represents the integral coefficient, U ref represents the bus voltage reference value, ξ ave represents the average value of the information exchange amounts of all energy storage units, i = 1, 2,..., I, and I represents the number of groups of energy storage units in the target islanded DC microgrid.

[0033] Optionally, the adaptive droop control model is:

[0034] U dci =U ref -R vi I dci +δν i

[0035] where, U dci represents the output voltage of the i-th energy storage unit, U ref represents the bus voltage reference value, R vi represents the droop coefficient of the i-th energy storage unit, I dci represents the output current of the i-th energy storage unit, δv i represents the secondary compensation amount of the i-th energy storage unit, i = 1, 2,..., I, and I represents the number of groups of energy storage units in the target islanded DC microgrid.

[0036] In a second aspect, an SOC balancing device for an islanded DC microgrid provided by an embodiment of the present application includes:

[0037] An acquisition module, configured to acquire the current state of charge values of multiple groups of energy storage units in a target islanded DC microgrid;

[0038] A first determination module, configured to determine the droop coefficient of each group of energy storage units by using the arctangent function based on the state of charge value of each group of energy storage units;

[0039] A second determination module, configured to determine the secondary compensation amount of each group of energy storage units;

[0040] A construction module, configured to respectively for each group of energy storage units, construct an adaptive droop control model based on the droop coefficient and the secondary compensation amount of the energy storage unit, calculate the output voltage of the energy storage unit according to the adaptive droop control model, and perform charge equalization control on the energy storage unit according to the output voltage.

[0041] In a third aspect, an embodiment of the present application provides a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the SOC balancing method for the islanded DC microgrid described above is implemented.

[0042] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the SOC balancing method for the islanded DC microgrid described above is implemented.

[0043] The above solution of the present application has the following beneficial effects:

[0044] In the embodiment of the present application, by acquiring the current state of charge values of multiple groups of energy storage units in a target islanded DC microgrid, then determining the droop coefficient of each group of energy storage units by using the arctangent function based on the state of charge value of each group of energy storage units, then determining the secondary compensation amount of each group of energy storage units, and finally respectively for each group of energy storage units, constructing an adaptive droop control model based on the droop coefficient and the secondary compensation amount of the energy storage unit, calculating the output voltage of the energy storage unit according to the adaptive droop control model, and performing charge equalization control on the energy storage unit according to the output voltage. Among them, by combining the arctangent function with the state of charge value, using the characteristics of the arctangent function to limit the range of the droop coefficient, determining the secondary compensation amount and constructing an adaptive droop control model based on the secondary compensation amount and the droop coefficient, the influence of the line impedance can be eliminated. Calculating the output voltage of the energy storage unit based on the adaptive droop control model and performing charge equalization control according to the output voltage can effectively improve the stability of charge equalization.

[0045] Other beneficial effects of the present application will be described in detail in the following specific implementation section. Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 It is a flowchart of the SOC balancing method for an islanded DC microgrid provided by an embodiment of the present application;

[0048] Figure 2 It is a schematic diagram of an equivalent circuit provided by an embodiment of the present application;

[0049] Figure 3 It is a curve graph of the droop coefficient variation under different parameter values provided by an embodiment of the present application;

[0050] Figure 4 It is a schematic diagram of the simulation result of Example 1 provided by an embodiment of the present application;

[0051] Figure 5 It is a schematic diagram of the bus voltage of Example 1 provided by an embodiment of the present application;

[0052] Figure 6 It is a schematic diagram of the simulation result of Example 2 provided by an embodiment of the present application;

[0053] Figure 7 It is a schematic diagram of the simulation result of Example 3 provided by an embodiment of the present application;

[0054] Figure 8 It is a schematic diagram of the structure of the SOC balancing device for an islanded DC microgrid provided by an embodiment of the present application;

[0055] Figure 9 It is a schematic diagram of the structure of a terminal device provided by an embodiment of the present application. Specific Embodiments

[0056] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented in order to thoroughly understand the embodiments of the present application. However, those skilled in the art should clearly understand that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present application.

[0057] It should be understood that, as used in the specification of this application and the appended claims, the term "comprising" indicates the presence of the described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups.

[0058] It should also be understood that the term "and / or" as used in the specification of this application and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0059] As used in the specification of this application and the appended claims, the term "if" can be interpreted, depending on the context, as "when" or "once" or "in response to determining" or "in response to detecting". Similarly, the phrase "if determined" or "if [the described condition or event] is detected" can be interpreted, depending on the context, as meaning "once determined" or "in response to determining" or "once [the described condition or event] is detected" or "in response to detecting [the described condition or event]".

[0060] In addition, in the description of the specification of this application and the appended claims, the terms "first", "second", "third", etc. are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0061] Reference to "one embodiment" or "some embodiments" or the like described in the specification of this application means that a particular feature, structure or characteristic described in connection with that embodiment is included in one or more embodiments of this application. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "comprising", "including", "having" and their variants all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0062] In view of the problem of low SOC balancing stability in existing isolated DC microgrids, the embodiments of the present application provide a method for SOC balancing in an isolated DC microgrid. The SOC balancing method obtains the current state of charge values of multiple energy storage units in the target isolated DC microgrid, and then based on the state of charge values of each group of energy storage units, uses the arctangent function to determine the droop coefficient of each group of energy storage units, then determines the secondary compensation amount of each group of energy storage units, and finally for each group of energy storage units, constructs an adaptive droop control model based on the droop coefficient and the secondary compensation amount of the energy storage unit, calculates the output voltage of the energy storage unit according to the adaptive droop control model, and performs charge equalization control on the energy storage unit according to the output voltage. Among them, by combining the arctangent function with the state of charge value, using the characteristics of the arctangent function to limit the range of the droop coefficient, determining the secondary compensation amount and constructing an adaptive droop control model based on the secondary compensation amount and the droop coefficient, the influence of line impedance can be eliminated. Calculating the output voltage of the energy storage unit based on the adaptive droop control model and performing charge equalization control according to the output voltage can effectively improve the stability of charge equalization.

[0063] Next, an exemplary description is given of the SOC balancing method for an isolated DC microgrid provided by the present application.

[0064] As Figure 1 shown, the SOC balancing method for an isolated DC microgrid provided by the present application includes the following steps:

[0065] Step 11, obtain the current state of charge values of multiple energy storage units in the target isolated DC microgrid.

[0066] The above-mentioned target isolated DC microgrid is an isolated DC microgrid that needs to perform SOC balancing.

[0067] In some embodiments of the present application, the current state of charge value of the energy storage unit can be obtained through the battery management system of the target isolated DC microgrid.

[0068] Exemplarily, the equivalent circuit of a DC microgrid with two energy storage units of equal capacity is as Figure 2 shown, BESS 1 and BESS 2 represent two groups of energy storage units, U ref is the voltage value of the power supply in the energy storage unit, R v1 represents the droop coefficient of BESS 1 , R v2 represents the droop coefficient of BESS 2 , I dc1 represents the output current of BESS 1 , U dc1 represents the output voltage of BESS 1 , I dc2Denote the BESS 2 's output current, U dc2 Denote the BESS 2 's output voltage, R line1 Denote the BESS 1 's line impedance, R line2 Denote the BESS 2 's line impedance, R load Denote the load equivalent resistance, U bus is the bus voltage.

[0069] In the DC microgrid, the expression of the traditional droop control is:

[0070] U dci = U ref - R vi I dci

[0071] From the Figure 2 equivalent circuit, the voltage-current characteristic expression of the traditional droop control can be obtained as:

[0072]

[0073] Select the ampere-hour integration method as the main means to estimate the SOC, and take the derivative of its expression, we can get:

[0074]

[0075] Among them, C bati represents the capacity of the energy storage unit.

[0076] Combining the above expressions, we have:

[0077]

[0078] It can be seen from the above formula that the charge and discharge rate of the energy storage unit is related to the droop coefficient, line impedance and capacity.

[0079] Step 12, based on the state of charge value of each group of energy storage units, use the arctangent function to determine the droop coefficient of each group of energy storage units.

[0080] Specifically, through the formula:

[0081]

[0082] Calculate the droop coefficient R of the i-th group of energy storage units vi .

[0083] Among them, R oi represents the initial droop coefficient of the i-th group of energy storage units, m represents the acceleration factor, n represents the convergence factor, S ave represents the average state of charge, SOCi represents the current state of charge value of the i-th energy storage unit group, i dc represents the output current of the i-th energy storage unit group, i = 1, 2,..., I, where I represents the number of energy storage unit groups in the target islanded DC microgrid.

[0084] Exemplarily, taking Figure 2 the equivalent circuit shown as an example, assuming SOC 1 > SOC 2 , since the arctangent function is a monotonically increasing function, for the energy storage unit with a larger SOC, the value of its virtual impedance is lower, while for the energy storage unit with a higher SOC, its virtual impedance is lower, so R v1 < R v2 . Also, from the above formula for calculating the droop coefficient, when the influence of line impedance and battery capacity is ignored, the energy storage unit with a larger SOC has a faster discharge rate, while the energy storage unit with a larger SOC has a slower discharge rate, which results in the SOC 1 decreasing at a faster rate than SOC 2 . Eventually, as the number of iterations increases, the droop coefficient gradually approaches The SOCs of the two energy storage unit groups gradually converge to their average values, achieving SOC balance among the energy storage units. Considering that the variation range of the arctangent function is (-π / 2, π / 2), from the above formula, when the energy storage unit is in the charging state or the discharging state, the range of its droop coefficient R vi is (0, R oi ), effectively avoiding the influence of too large droop coefficient on system stability.

[0085] Among them, by introducing m and n, the difference between the droop coefficients can be increased, so as to obtain a faster equalization speed and a higher convergence accuracy when the SOC deviation is small. Considering that the variation range of the SOC of the energy storage unit during normal operation is usually (0.2, 1), the variation range of S ave / SOC i can be obtained as (1 / 4, 5), and the variation range of SOC i / S ave is (1 / 5, 4). The curves of R vi under different variable values during discharge are as shown in Figure 3 . Figure 3 In the figure, the horizontal axis represents the value of SOC, SOC i * , and the vertical axis represents the value of R vi . R oi represents the initial droop coefficient. Figure 3 (a) is the variation curve of R vi when m takes different values. m = 1, n = 1 means that when m takes 1 and n takes 1, R viThe variation curve, where m = 2 and n = 1 indicates R when m takes 2 and n takes 1 vi The variation curve, where m = 5 and n = 1 indicates R when m takes 5 and n takes 1 vi The variation curve, where m = 10 and n = 1 indicates R when m takes 10 and n takes 1 vi The variation curve Figure 3 (b) is the variation curve of R for different values of n vi The variation curve, and the four curves are respectively: when m = 1 and n = 1, it indicates R when m takes 1 and n takes 1 vi The variation curve, where m = 1 and n = 2 indicates R when m takes 1 and n takes 2 vi The variation curve, where m = 1 and n = 5 indicates R when m takes 1 and n takes 5 vi The variation curve, where m = 1 and n = 10 indicates R when m takes 1 and n takes 10 vi The variation curve Indicates Figure 3 R in (b) vi The value taken

[0086] From Figure 3 (a), it can be seen that the R vi Curve is smooth and continuous. When the parameter n remains unchanged, for the energy storage unit with a large SOC, its The larger the value of m, the smaller R vi becomes. And for the energy storage unit with a small SOC, its The larger the value of m, the larger R vi becomes. From Figure 3 (b), it can be seen that when m is fixed, the larger the value of n, for the energy storage unit with a large SOC, 1 / 4 < SOC i * < 1, The larger the value of n, the smaller R vi becomes. And for the energy storage unit with a small SOC, 1 < SOC i * < 4, The larger the value of n, the larger R vi becomes. Therefore, increasing the values of the parameters m and n can make the difference in the droop coefficient near SOC i * = 1 increase, thereby accelerating the SOC balancing speed. Since the droop coefficient R vi is monotonically increasing in the range of 1 / 4 < SOC i * < 4, therefore, R vi has a minimum value R i * at SOC minFurthermore, when m is fixed and n gradually increases to make (1 / 4)^n << 1, the minimum value R of the droop coefficient can be obtained min , and its expression is:

[0087]

[0088] To ensure the stable operation of the system, the bus voltage is generally required to operate at 0.95U ref ~1.05U ref . To avoid excessive voltage drop of the bus, the droop coefficient R vi needs to satisfy:

[0089]

[0090] where ΔU dc_max is the maximum deviation of the bus voltage, I dc_max is the maximum output current of the energy storage unit, and P max is the maximum output power of the energy storage unit.

[0091] The arctangent function limits the change range of the droop coefficient R vi to 0~R oi . Taking the normal discharge of two energy storage units with the same capacity as an example and ignoring the influence of line impedance and capacity, we can get:

[0092]

[0093] where P out1 , P out2 are the output powers of energy storage unit 1 and energy storage unit 2 respectively. When the value of parameter n satisfies (1 / 4)^n << 1, the calculation shows that:

[0094]

[0095] Set the total output power of the energy storage unit to P sum . When P sum is constant, the calculation shows that:

[0096]

[0097] Combining the above formulas, the value range of parameter m can be obtained as:

[0098]

[0099] Considering that only when the parameter m > 0 can the SOC balance be ensured, from the above formula, we can get:

[0100]

[0101] Therefore, when the maximum output power P of the energy storage unitmax When it is greater than 4 / 3 times the output power at the SOC balance of each unit, the power distribution can be restricted by adjusting the design parameter m, and the SOC balance speed can be accelerated by increasing the value of n. However, if it is impossible to limit the output power of the energy storage unit to P while ensuring a relatively fast SOC balance speed max or less.

[0102] Step 13: Determine the secondary compensation amount of each group of energy storage units.

[0103] In some embodiments of the present application, the above step of determining the secondary compensation amount of each group of energy storage units includes:

[0104] For each group of energy storage units respectively, perform the following steps:

[0105] The first step: Calculate the power distribution variable of the energy storage unit, and calculate the information exchange amount of the energy storage unit based on the power distribution variable.

[0106] Specifically, through the formula:

[0107]

[0108] Calculate the power distribution variable of the i-th group of energy storage units.

[0109] Among them, C min represents the minimum capacity, C bati represents the capacity of the i-th group of energy storage units, U viri represents the virtual voltage drop, and ΔU dc_max represents the maximum allowable deviation of the bus voltage.

[0110] Through the formula:

[0111] ξ i =γ i U bus

[0112] Calculate the information exchange amount ξ of the i-th group of energy storage units i .

[0113] Among them, U bus represents the bus voltage.

[0114] The second step: Calculate the secondary compensation amount of the energy storage unit according to the information exchange amount and the power distribution variable.

[0115] Specifically, through the formula:

[0116]

[0117] Calculate the secondary compensation amount δv of the i-th group of energy storage units i .

[0118] Among them, k represents the integral coefficient, and U ref represents the reference value of the bus voltage, and ξ ave represents the average value of the information exchange volume of all energy storage units, where i = 1, 2,..., I, and I represents the number of energy storage unit groups in the target islanded DC microgrid.

[0119] Exemplarily, assuming that the calculation formula of the secondary compensation amount converges, the calculation formula of the power distribution variable, the expression obtained by analyzing the example in step 11 Figure 2 and the expression of the virtual impedance are combined to obtain:

[0120]

[0121] U bus = U ref

[0122] When the above formula holds, the DC bus voltage will be stabilized near the reference value of the bus voltage, and the change rate of the SOC of the energy storage unit is only related to the magnitude of its droop coefficient, eliminating the influence of the line impedance and the capacity of the energy storage unit.

[0123] Step 14: For each group of energy storage units, an adaptive droop control model is constructed based on the droop coefficient and secondary compensation amount of the energy storage unit, and the output voltage of the energy storage unit is calculated according to the adaptive droop control model, and the charge equalization control of the energy storage unit is performed according to the output voltage.

[0124] Specifically, the above adaptive droop control model is:

[0125] U dci = U ref - R vi I dci + δν i

[0126] Among them, U dci represents the output voltage of the i-th group of energy storage units, U ref represents the reference value of the bus voltage, R vi represents the droop coefficient of the i-th group of energy storage units, I dci represents the output current of the i-th group of energy storage units, and δv i represents the secondary compensation amount of the i-th group of energy storage units, where i = 1, 2,..., I, and I represents the number of energy storage unit groups in the target islanded DC microgrid.

[0127] It should be noted that the droop coefficient and secondary compensation amount of the energy storage unit calculated above are substituted into the adaptive droop control model, the output voltage of the energy storage unit is calculated, and the output voltage of the energy storage unit is controlled to be the output voltage calculated above to achieve charge equalization control.

[0128] It is worth mentioning that by combining the arctangent function with the state of charge value, using the characteristics of the arctangent function to limit the range of the droop coefficient, determining the secondary compensation amount, and constructing an adaptive droop control model based on the secondary compensation amount and the droop coefficient, the influence of line impedance can be eliminated. By calculating the output voltage of the energy storage unit based on the adaptive droop control model and performing charge equalization control according to the output voltage, the stability of charge equalization can be effectively improved.

[0129] The method of the present application will be exemplarily described below with a specific example.

[0130] To verify the effectiveness and correctness of the strategy proposed by the method of the present application, a DC microgrid model composed of 3 energy storage units, 1 photovoltaic unit, and 1 load was built based on the simulation software PSIM. The specific system parameters are shown in Table 1.

[0131] Parameter Value Bus reference voltage Uref / V 48 Maximum bus voltage deviation ΔUdc_max / V 2.4 Capacity Cbat1 / Cbat2 / Cbat3 / Ah 0.1 / 0.2 / 0.3 Line impedance r1 / r2 / r3 / Ω 1 / 0.5 / 0.3 Bus load RLoad / Ω 10 Initial droop coefficient Roi / Ω 0.6 Integration coefficient k 10 Voltage PI control loop kp / ki 0.8 / 100 Current PI control loop kp / ki 0.08 / 160

[0132] Table 1

[0133] The simulation verified that the proposed control strategy can achieve rapid SOC equalization, bus voltage recovery, and eliminate the influence of capacity and line impedance.

[0134] Example 1

[0135] To verify that the method of the present application can overcome the influence of capacity on the power distribution of energy storage units. The initial SOCs of the three groups of energy storage units were set to 85%, 80%, and 75% respectively. The capacity parameters are shown in Table 2. Ignoring the influence of line impedance, the simulation time was t = 40 s, and the simulation results are as Figure 4 shown. Figure 4 (a) represents the change curve of SOC. The horizontal axis represents time, and the vertical axis represents the value of SOC. SOC 1 is the change curve of the SOC of the first group of energy storage units, SOC 2 is the change curve of the SOC of the second group of energy storage units, SOC 3 is the change curve of the SOC of the third group of energy storage units. Figure 4 (b) represents the change curve of the output power. The horizontal axis represents time, and the vertical axis represents the output power, with the unit of watt (W). P out1 is the change curve of the output power of the first group of energy storage units, P out2 is the change curve of the output power of the second group of energy storage units, P out3 is the change curve of the output power of the third group of energy storage units. The bus voltage is as Figure 5 shown. Figure 5 The horizontal axis represents time, and the vertical axis represents the bus voltage U bus , with the unit of volt (V).

[0136] From Figure 4 Figure 5 It can be seen that under the method of this application, the SOC of the energy storage unit reaches the balanced state at t = 16 s, with a relatively high balancing accuracy. The bus voltage is stabilized at the reference value of 48 V. Therefore, the method of this application can eliminate the influence of capacity on SOC balancing.

[0137] Example 2

[0138] To verify that the method of this application can eliminate the influence of line impedance on power distribution, assume that the capacities of three groups of energy storage units are all 0.1 Ah, and at t = 20 s, the line impedance r3 increases from 0.3 Ω to 0.6 Ω, and the simulation time is t = 40 s. The specific simulation results are as Figure 6 shown. Figure 6 (a) represents the change curve of SOC. The horizontal axis represents time, and the vertical axis represents the value of SOC. SOC 1 is the change curve of the SOC of the first group of energy storage units, SOC 2 is the change curve of the SOC of the second group of energy storage units, SOC 3 is the change curve of the SOC of the third group of energy storage units. Figure 6 (b) represents the change curve of the output power. The horizontal axis represents time, and the vertical axis represents the output power, with the unit of watt (W). P out1 is the change curve of the output power of the first group of energy storage units, P ou t 2 is the change curve of the output power of the second group of energy storage units, P out3 is the change curve of the output power of the third group of energy storage units.

[0139] By using the method of this application, when the line impedance is different, SOC balancing can be achieved in about 12.6 s with a relatively high balancing accuracy, and when the line impedance undergoes a sudden change, the SOC between the energy storage units still remains in the balanced state. When the line impedance suddenly changes, the output power of the converter can quickly recover to the state where the power is distributed according to the capacity. Therefore, the method of this application can eliminate the influence of line impedance on power distribution.

[0140] Example 3

[0141] To verify that the strategy proposed in this paper can maintain SOC balancing, bus voltage stability, and accurate distribution of output power under the condition of fluctuating output power of the photovoltaic unit. The initial SOCs are 35%, 40%, and 45% respectively. Initially, the output power of the photovoltaic unit Ppv = 600 W, and MPPT is used for control. At t = 15 s, the light intensity is changed so that Ppv = 300 W; and at t = 30 s, the photovoltaic unit is cut out from the DC microgrid, and the simulation time is t = 40 s. The specific simulation results are as Figure 7 shown.Figure 7 (a) represents the SOC change curve. The horizontal axis represents time, and the vertical axis represents the value of SOC. SOC 1 is the SOC change curve of the first group of energy storage units. SOC 2 is the SOC change curve of the second group of energy storage units. SOC 3 is the SOC change curve of the third group of energy storage units. Figure 7 (b) represents the output power change curve. The horizontal axis represents time, and the vertical axis represents the output power, with the unit of watt (W). P out1 is the output power change curve of the first group of energy storage units. P out2 is the output power change curve of the second group of energy storage units. P out3 is the output power change curve of the third group of energy storage units. Figure 7 (c) shows the fluctuation of the bus voltage. The horizontal axis represents time, and the vertical axis represents the bus voltage U bus , with the unit of volt (V). Figure 7 (d) shows the change of the secondary compensation amount. The horizontal axis represents time, and the vertical axis represents the secondary compensation amount, δV d1 is the secondary compensation amount change curve of the first group of energy storage units. δV d2 is the secondary compensation amount change curve of the second group of energy storage units. δV d3 is the secondary compensation amount change curve of the third group of energy storage units.

[0142] It can be seen from Figure 7 that when the photovoltaic output power fluctuates, the system can maintain good stability. The SOCs between the energy storage units still remain in an equilibrium state, and have a high equilibrium accuracy. The secondary compensation amount can also respond quickly when the photovoltaic output power fluctuates, and adjust the reference voltage of the droop coefficient, so as to realize the capacity-based distribution of the output power of the energy storage units and the rapid recovery of the bus voltage.

[0143] Next, an exemplary description is given to the SOC equalization device of the islanded DC microgrid provided in this application.

[0144] As Figure 8 shown, an embodiment of this application provides an SOC equalization device for an islanded DC microgrid. The SOC equalization device 800 of the islanded DC microgrid includes:

[0145] An acquisition module 801, configured to acquire the current state-of-charge values of multiple groups of energy storage units of a target islanded DC microgrid;

[0146] A first determination module 802, configured to determine the droop coefficient of each group of energy storage units based on the state-of-charge value of each group of energy storage units by using the arctangent function;

[0147] The second determination module 803 is configured to determine the secondary compensation amount of each group of energy storage units;

[0148] The construction module 804 is configured to, for each group of energy storage units, construct an adaptive droop control model based on the droop coefficient and the secondary compensation amount of the energy storage units, calculate the output voltage of the energy storage units according to the adaptive droop control model, and perform charge equalization control on the energy storage units according to the output voltage.

[0149] It should be noted that, for the information interaction, execution process, etc. between the above-mentioned devices / units, since they are based on the same concept as the method embodiments of the present application, their specific functions and the technical effects brought thereby can be specifically referred to the method embodiment part, and will not be elaborated here.

[0150] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the above-mentioned division of each functional unit and module is used for illustration. In actual applications, the above-mentioned functions can be allocated to different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of the present application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiments and will not be elaborated here.

[0151] As Figure 9 shown, an embodiment of the present application provides a terminal device. The terminal device D10 in this embodiment includes: at least one processor D100 ( Figure 9 only one processor is shown in the figure), a memory D101, and a computer program D102 stored in the memory D101 and executable on the at least one processor D100. When the processor D100 executes the computer program D102, the steps in any of the above method embodiments are implemented.

[0152] Specifically, when the processor D100 executes the computer program D102, it obtains the current state-of-charge values of multiple energy storage units in the target island DC microgrid, then determines the droop coefficient of each group of energy storage units using the arctangent function based on the state-of-charge value of each group of energy storage units, then determines the secondary compensation amount of each group of energy storage units, and finally constructs an adaptive droop control model for each group of energy storage units based on the droop coefficient and secondary compensation amount of the energy storage unit, calculates the output voltage of the energy storage unit according to the adaptive droop control model, and performs charge equalization control on the energy storage unit according to the output voltage. Among them, by combining the arctangent function with the state-of-charge value, using the characteristics of the arctangent function to limit the range of the droop coefficient, determining the secondary compensation amount and constructing an adaptive droop control model based on the secondary compensation amount and the droop coefficient, the influence of the line impedance can be eliminated. Calculating the output voltage of the energy storage unit based on the adaptive droop control model and performing charge equalization control according to the output voltage can effectively improve the stability of charge equalization.

[0153] The so-called processor D100 may be a central processing unit (CPU, Central Processing Unit), and this processor D100 may also be other general-purpose processors, digital signal processors (DSP, Digital Signal Processor), application specific integrated circuits (ASIC, Application Specific Integrated Circuit), field-programmable gate arrays (FPGA, Field-Programmable Gate Array), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or this processor may also be any conventional processor, etc.

[0154] In some embodiments, the memory D101 may be an internal storage unit of the terminal device D10, such as the hard disk or memory of the terminal device D10. In some other embodiments, the memory D101 may also be an external storage device of the terminal device D10, such as a plug-in hard disk equipped on the terminal device D10, a smart media card (SMC, Smart Media Card), a secure digital (SD, Secure Digital) card, a flash card (Flash Card), etc. Further, the memory D101 may also include both the internal storage unit of the terminal device D10 and the external storage device. The memory D101 is used to store an operating system, application programs, a boot loader (BootLoader), data, and other programs, such as the program code of the computer program, etc. The memory D101 may also be used to temporarily store data that has been output or will be output.

[0155] An embodiment of the present application also provides a computer-readable storage medium storing a computer program, which when executed by a processor, can implement the steps in the above-mentioned method embodiments.

[0156] An embodiment of the present application provides a computer program product, which when running on a terminal device, enables the terminal device to implement the steps in the above-mentioned method embodiments.

[0157] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, to implement all or part of the processes in the above-mentioned method embodiments of the present application, a computer program can be used to instruct relevant hardware to complete. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments can be implemented. Among them, the computer program includes computer program code, which can be in the form of source code, object code, executable file or some intermediate form, etc. The computer-readable medium can at least include: any entity or device that can carry the computer program code to the SOC balancing method device / terminal device of the isolated DC microgrid, recording medium, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium. For example, a USB flash drive, a mobile hard disk, a magnetic disk or an optical disc, etc. In some jurisdictions, according to legislation and patent practice, the computer-readable medium cannot be an electrical carrier signal and a telecommunication signal.

[0158] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0159] Those of ordinary skill in the art can realize that the units and algorithm steps of the examples described in combination with the embodiments disclosed herein can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present application.

[0160] The above are the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A SOC balancing method for an isolated DC microgrid, characterized in that: include: Obtain current state of charge values ​​of multiple groups of energy storage units of the target island DC microgrid; Based on the state of charge value of each group of energy storage units, the droop coefficient of each group of energy storage units is determined by using an inverse tangent function; Determining a secondary compensation amount for each group of energy storage units; For each group of the energy storage units, an adaptive droop control model is constructed based on the droop coefficient and the secondary compensation amount of the energy storage unit, and the output voltage of the energy storage unit is calculated according to the adaptive droop control model, and the energy storage unit is subjected to charge balancing control according to the output voltage.

2. The SOC balancing method according to claim 1, characterized in that: The method of determining the droop coefficient of each group of energy storage units by using an inverse tangent function based on the state of charge value of each group of energy storage units includes: By formula: Calculate the droop coefficient R of the i-th group of energy storage units vi ; Among them, R oi represents the initial droop coefficient of the i-th group of energy storage units, m represents the acceleration factor, n represents the convergence factor, S ave Indicates the average state of charge, SOC i represents the current state of charge value of the i-th group of energy storage units, I dc represents the output current of the i-th group of energy storage units, i=1,2,...,I, and I represents the number of energy storage units in the target island DC microgrid.

3. The SOC balancing method according to claim 1, characterized in that: Determining the secondary compensation amount of each group of energy storage units includes: For each group of energy storage units, perform the following steps: Calculating a power allocation variable of the energy storage unit, and calculating an information exchange amount of the energy storage unit based on the power allocation variable; The secondary compensation amount of the energy storage unit is calculated according to the information exchange amount and the power allocation variable.

4. The SOC balancing method according to claim 3, characterized in that: The calculating the power allocation variable of the energy storage unit includes: By formula: Calculate the power allocation variable of the i-th group of energy storage units; Among them, C min Indicates the minimum capacity, C bati represents the capacity of the i-th group of energy storage units, U viri Indicates the virtual voltage drop, ΔU dc_max Indicates the maximum allowable deviation of the bus voltage.

5. The SOC balancing method according to claim 4, characterized in that: The calculating the information exchange amount of the energy storage unit based on the power allocation variable includes: By formula: x i =c i U bus Calculate the information exchange amount ξ of the i-th group of energy storage units i ; Among them, U bus Indicates the bus voltage.

6. The SOC balancing method according to claim 5, characterized in that: The calculating the secondary compensation amount of the energy storage unit according to the information exchange amount and the power allocation variable includes: By formula: Calculate the secondary compensation δv of the i-th group of energy storage units i ; Where k represents the integral coefficient, U ref represents the bus voltage reference value, ξ ave represents the mean value of information exchange of all energy storage units, i=1,2,...,I, and I represents the number of energy storage units in the target island DC microgrid.

7. The SOC balancing method according to claim 1, characterized in that: The adaptive droop control model is: THE dci =U ref -R vi I dci +δν i Among them, U dci represents the output voltage of the i-th group of energy storage units, U ref Indicates the bus voltage reference value, R vi represents the droop coefficient of the i-th group of energy storage units, I dci represents the output current of the i-th group of energy storage units, δv i represents the secondary compensation amount of the i-th group of energy storage units, i=1, 2, ..., I, and I represents the number of energy storage units in the target island DC microgrid.

8. A SOC balancing device for an isolated DC microgrid, characterized in that: include: An acquisition module, used to obtain current state of charge values ​​of multiple groups of energy storage units of a target isolated DC microgrid; A first determination module, configured to determine a droop coefficient of each group of energy storage units by using an inverse tangent function based on the state of charge value of each group of energy storage units; A second determination module is used to determine the secondary compensation amount of each group of energy storage units; A construction module is used to construct an adaptive droop control model for each group of energy storage units based on the droop coefficient and the secondary compensation amount of the energy storage unit, calculate the output voltage of the energy storage unit according to the adaptive droop control model, and perform charge balancing control on the energy storage unit according to the output voltage.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the SOC balancing method for the isolated island DC microgrid is implemented as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the SOC balancing method for an island DC microgrid is implemented as described in any one of claims 1 to 7.

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