Equivalent modeling method and device for isomerized direct-current micro-grid

Abstract

The invention provides an equivalent modeling method and device for an isomerized direct-current micro-grid, and belongs to the field of direct-current micro-grids. The method comprises the following steps: for each loop of the interleaved parallel three-level converter, combining an upper branch and a lower branch of the loop according to a control strategy of the loop to obtain a branch equivalent model of the loop; based on the branch equivalent model of each loop, obtaining a loop equivalent model of the interleaved parallel three-level converter, and determining a loop control strategy of the loop equivalent model; according to the loop control strategy, combining two loops in the loop equivalent model to obtain an equivalent two-level converter model of the interleaved parallel three-level converter, and determining a model control strategy of the equivalent two-level converter model; and based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter, establishing an isomerization DC micro-grid equivalent model. According to the invention, the equivalent reduced-order model can be established for the isomerized DC micro-grid.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current microgrids, and in particular to an equivalent modeling method and device for a heterogeneous direct current microgrid. Background Art

[0002] DC microgrids have the advantages of high energy efficiency and simple control structure. They can more efficiently accept DC sources and loads such as distributed power sources, energy storage, and electric vehicles, and play an important role in promoting the realization of the "dual carbon" goal. DC microgrids are usually composed of different types of converters. The interaction between different types of converters and the negative resistance of constant power loads may cause oscillation instability, resulting in DC microgrids with heterogeneity and weak damping.

[0003] The reduced-order model can facilitate the small-disturbance stability analysis of DC microgrids. The related art mainly provides corresponding small-disturbance reduced-order modeling solutions for isomorphic DC microgrids composed of multiple converters of the same type. However, there are large differences in the circuit structure and control links between different types of converters. It is difficult for the existing solutions to clearly explain the inherent mechanism similarities between the differential mathematical models of different types of converters. The inventors found that the related art lacks a small-disturbance reduced-order model for heterogeneous DC microgrids formed by staggered parallel three-level DC / DC converters and conventional two-level DC / DC converters, making it difficult to accurately perform stability analysis on such heterogeneous DC microgrids. Summary of the invention

[0004] The embodiments of the present invention provide an equivalent method and device for a heterogeneous DC microgrid, so as to establish a small disturbance reduced-order model for a heterogeneous DC microgrid formed by staggered parallel three-level DC / DC converters and conventional two-level DC / DC converters, so as to accurately analyze such a heterogeneous DC microgrid.

[0005] In a first aspect, an embodiment of the present invention provides an equivalent method for a heterogeneous DC microgrid, wherein the heterogeneous DC microgrid includes a staggered parallel three-level converter and a two-level converter, wherein the staggered parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the staggered parallel three-level converter includes two loops, each loop including an upper branch and a lower branch; the method includes:

[0006] For each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop;

[0007] Based on the branch equivalent model of each loop, a loop equivalent model of the interleaved parallel three-level converter is obtained, and a loop control strategy of the loop equivalent model is determined;

[0008] According to the loop control strategy, two loops in the loop equivalent model are merged to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and a model control strategy of the equivalent two-level converter model is determined;

[0009] Based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter, an equivalent model of a heterogeneous DC microgrid is established.

[0010] In a possible implementation, for each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain a branch equivalent model of the loop, including:

[0011] For each loop, determining a loop current closed-loop transfer function of the loop according to a control strategy of the loop;

[0012] Determining the branch equivalence relationship between the upper branch and the lower branch of the loop according to the loop current closed-loop transfer function;

[0013] Based on the branch equivalent relationship, the upper branch and the lower branch of the loop are merged to obtain a branch equivalent model of the loop.

[0014] In a possible implementation, according to the loop control strategy, two loops in the loop equivalent model are merged to obtain an equivalent two-level converter model of the interleaved parallel three-level converter, including:

[0015] Determining an open-loop transfer function of the loop equivalent model according to the loop control strategy;

[0016] Determining, according to the open-loop transfer function, an equivalent relationship between filter capacitors and an equivalent relationship between filter inductors of two loops in the loop equivalent model;

[0017] Based on the filter capacitor equivalent relationship and the filter inductor equivalent relationship, two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the interleaved parallel three-level converter.

[0018] In a possible implementation manner, determining a model control strategy of the equivalent two-level converter model includes:

[0019] Determining a model current closed-loop transfer function of the loop equivalent model according to the loop control strategy;

[0020] Determining an equivalent relationship between current control parameters of two loops in the loop equivalent model according to the model current closed-loop transfer function;

[0021] Determining a voltage closed-loop transfer function of the loop equivalent model according to the loop control strategy;

[0022] Determining, according to the voltage closed-loop transfer function, an equivalent relationship between voltage control parameters and an equivalent relationship between droop coefficients of two loops in the loop equivalent model;

[0023] Based on the current control parameter equivalent relationship, the voltage control parameter equivalent relationship and the droop coefficient equivalent relationship, a model control strategy of the equivalent two-level converter model is determined.

[0024] In a possible implementation, based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter, an equivalent model of a heterogeneous DC microgrid is established, including:

[0025] Performing equivalent merging on the equivalent two-level converter model and the two-level converter to obtain a reduced-order equivalent model;

[0026] Determining the filter inductance, filter capacitance, current control parameters, voltage control parameters and droop coefficient of the reduced-order equivalent model according to the model control strategy and the control strategy of the two-level converter;

[0027] Based on the reduced-order equivalent model, and the filter inductance, filter capacitance, current control parameter, voltage control parameter and droop coefficient of the reduced-order equivalent model, an equivalent model of a heterogeneous DC microgrid is obtained.

[0028] In a possible implementation, the expression of the open-loop transfer function is:

[0029]

[0030] In the formula, G T_vd (s) represents the open-loop transfer function, s represents the Laplace operator, x represents the xth loop, L T_fx represents the equivalent filter inductance of the xth loop of the loop equivalent model, C T_fx represents the equivalent filter capacitor of the xth loop of the loop equivalent model, D T_x represents the duty cycle of the xth loop of the loop equivalent model, V represents the DC bus voltage, and P represents the power value of the constant power load.

[0031] In a possible implementation, the expression of the model current closed-loop transfer function is:

[0032]

[0033] In the formula, G T_iisys (s) represents the current closed-loop transfer function of the model, R0 Indicates the equivalent resistance of the constant power load, k T_pix represents the current proportionality coefficient of the xth loop of the loop equivalent model, k T_iix represents the current integral coefficient of the xth loop of the loop equivalent model.

[0034] In a second aspect, an embodiment of the present invention provides an equivalent device of a heterogeneous DC microgrid, an equivalent method of a heterogeneous DC microgrid, wherein the heterogeneous DC microgrid includes a staggered parallel three-level converter and a two-level converter, wherein the staggered parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the staggered parallel three-level converter includes two loops, each loop includes an upper branch and a lower branch; the device includes:

[0035] A branch module, for merging the upper branch and the lower branch of each loop according to the control strategy of the loop to obtain a branch equivalent model of the loop; based on the branch equivalent model of each loop, obtaining a loop equivalent model of the staggered parallel three-level converter, and determining a loop control strategy of the loop equivalent model;

[0036] A loop module, configured to merge two loops in the loop equivalent model according to the loop control strategy, obtain an equivalent two-level converter model of the staggered parallel three-level converter, and determine a model control strategy of the equivalent two-level converter model;

[0037] An equivalent module is used to establish an equivalent model of a heterogeneous DC microgrid based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter.

[0038] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0039] The embodiment of the present invention combines the upper branch and the lower branch of each loop in the staggered parallel three-level converter to obtain a branch equivalent model of each loop, and then obtains a loop equivalent model of the staggered parallel three-level converter, which can reduce the order of the staggered parallel three-level converter; then, the two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and the loop equivalent model can be reduced again, so that the staggered parallel three-level converter can be equivalent to a two-level converter model; finally, the equivalent two-level converter model and the two-level converter in the heterogeneous DC microgrid can be directly combined and reduced to achieve the reduction of the heterogeneous DC microgrid, so that the reduced-order equivalent model can be used to accurately analyze the stability of such heterogeneous DC microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 is a structural schematic diagram of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0042] Figure 2 is a flow chart of an implementation of an equivalent method for a heterogeneous DC microgrid provided in an embodiment of the present invention;

[0043] Figure 3 It is a schematic structural diagram of branch equivalents of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0044] Figure 4 It is a schematic diagram of the equivalent structure of the loop of the heterogeneous DC microgrid provided by an embodiment of the present invention;

[0045] Figure 5 is a flow chart for implementing a model control strategy according to an embodiment of the present invention;

[0046] Figure 6 is an equivalent schematic diagram of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0047] Figure 7 This is a diagram of the oscillation instability simulation result of the heterogeneous DC microgrid provided by an embodiment of the present invention;

[0048] Figure 8 This is a diagram of oscillation instability simulation results of an equivalent model of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0049] Fig. 9 is a diagram of dynamic stability simulation results of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0050] Fig.10 is a diagram of dynamic stability simulation results of an equivalent model of a heterogeneous DC microgrid provided by an embodiment of the present invention;

[0051] Fig.11 It is a structural schematic diagram of an equivalent device of a heterogeneous DC microgrid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may 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 prevent unnecessary details from obstructing the description of the present invention.

[0053] The inventors found that in order to analyze the stability of small disturbances of DC microgrids, some technologies aggregate and equate multiple constant power loads from the perspective of small disturbance modeling, and evaluate the small disturbance stability of DC microgrids at different numbers of constant power loads through the proposed reduced-order model, but the applicability of this method in voltage source converters needs to be further verified. Some technologies use the participation factor analysis method to select the converter circuit / control state variables that are strongly related to the DC bus voltage stability, and establish a small disturbance reduced-order model of the converter. On this basis, combined with the system topology, a small disturbance reduced-order model of the DC distribution system containing three converters is established. Some technologies treat the voltage proportion / integral coefficient into the form of virtual resistance / inductance under the premise of ignoring the current control parameters, and establish a DC microgrid reduced-order circuit model suitable for analyzing the low-frequency time scale range. There is also a technology that treats the converter voltage and current control link into a virtual impedance, combined with the negative resistance of the constant power load, and establishes a second-order analytical model of the DC microgrid, revealing the high-frequency oscillation instability mechanism caused by unreasonable selection of voltage and current control parameters. However, this reduced-order model is difficult to apply to the analysis of small disturbance stability of DC microgrids within the low-frequency / medium-frequency time scale range.

[0054] Due to the large differences in circuit structure and control links between different types of converters, it is difficult for existing schemes to clearly explain the inherent mechanism similarities between the different mathematical models of different types of converters. Therefore, it is necessary to consider a method to perform equivalent work on heterogeneous DC microgrids.

[0055] Based on the idea of ​​equivalence of heterogeneous DC microgrid, in the implementation of the present application, the upper branch and the lower branch of each loop in the staggered parallel three-level converter in the heterogeneous DC microgrid are merged to obtain the branch equivalent model of each loop, and then the loop equivalent model of the staggered parallel three-level converter is obtained; then the two loops in the loop equivalent model are merged to obtain the equivalent two-level converter model of the staggered parallel three-level converter; finally, the equivalent two-level converter model and the two-level converter in the heterogeneous DC microgrid are merged and reduced in order. Among them, the reduction of the heterogeneous DC microgrid is achieved by merging and reducing the order of the staggered parallel three-level converter and the two-level converter in the heterogeneous DC microgrid layer by layer, so that the stability analysis of such heterogeneous DC microgrid can be accurately performed using the equivalent model after the reduction in order.

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0057] Figure 1 The schematic diagram of the structure of the heterogeneous DC microgrid provided by the embodiment of the present invention. Figure 1 As shown, the heterogeneous DC microgrid includes an interleaved parallel three-level converter and a two-level converter, and the interleaved parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the interleaved parallel three-level converter includes two loops, each loop includes an upper branch and a lower branch. The interleaved parallel three-level converter can be an interleaved parallel three-level DC / DC converter, and the two-level converter can be a two-level DC / DC converter.

[0058] Here, the upper branch of the first loop of the interleaved parallel three-level converter includes the filter inductor L T_fu1 、Filter capacitor C T_fu1 and two modulation signals g 1_1 and g 1_2 ; The lower branch includes the filter inductor L T_fd1 、Filter capacitor C T_fd1 and two modulation signals g 1_1 and g 1_2 The upper branch of the second loop includes the filter inductor L T_fu2 、Filter capacitor C T_fu2 and two modulation signals g 2_1 and g 2_2 ; The lower branch includes the filter inductor L T_fd2 、Filter capacitor C T_fd2 and two modulation signals g 2_1 and g 2_2 In the interleaved parallel three-level converter, the power supply voltage U s The two-level converter includes a filter inductor L C_f 、Filter capacitor CC_f and two modulation signals g 3 and g 4 , and the two-level converter also includes a supply voltage U s A constant power load is also set on the DC bus. The DC bus voltage is V and the current value of the constant power load is I o , the power value of the constant power load is P. Figure 1 It also includes the filter inductor current I of the upper branch in the first loop T_su1 , the filter inductor current I of the lower branch in the first loop T_sd1 , the filter inductor current I in the upper branch of the second loop T_su2 , the filter inductor current I in the lower branch of the second loop T_sd2 , the filter inductor current I of the two-level converter C_s .

[0059] In addition, in the heterogeneous DC microgrid, each loop of the staggered parallel three-level converter corresponds to a control strategy, and each two-level converter corresponds to a control strategy. The above three control strategies constitute the overall control strategy of the heterogeneous DC microgrid. The specific control block diagram is shown in Figure 1 as shown on the left side of the diagram.

[0060] Here, in the control strategy of the first loop of the interleaved parallel three-level converter, its input is the output current I of the interleaved parallel three-level converter T_o , DC bus voltage V and filter inductor current I in the upper branch of the first loop T_su1 The output current I of the interleaved three-level converter T_o Enter the droop control loop of the first loop, through the droop coefficient k of the first loop T_d1 Perform droop control to obtain the feedback of the droop control loop, and add the feedback to the DC bus voltage V and the voltage reference value V of the first loop. T_r1 Then input the voltage control loop of the first loop, and then use the voltage proportional coefficient k of the first loop T_pv1 and voltage integration coefficient k T_iv1 , get the filter inductor current reference value I of the first loop T_r1 , the filter inductor current reference value I of the first loop T_r1 The filter inductor current I T_su1 Superimpose and input the current control loop of the first loop, and pass the current proportional coefficient k of the first loop T_pi1 and current integration coefficient k T_ii1 , determine the duty cycle D of the first loop T_1 , thus obtaining the modulation signal g of the first loop 1_1 and g 1_2.

[0061] Correspondingly, in the control strategy of the second loop of the interleaved parallel three-level converter, its input is the output current I T_o and the filter inductor current I in the upper branch of the second loop T_su2 The output current I of the interleaved three-level converter T_o Enter the droop control loop of the second loop, through the droop coefficient k of the second loop T_d2 Perform droop control to obtain the feedback of the droop control loop, and add the feedback to the DC bus voltage V and the voltage reference value V of the second loop. T_r2 Then, the voltage control loop of the second loop is input, and the voltage proportional coefficient k of the second loop is T_pv2 and voltage integration coefficient k T_iv2 , get the filter inductor current reference value I of the second loop T_r2 , the second loop filter inductor current reference value I T_r2 The filter inductor current I T_su2 The current proportionality coefficient k of the second loop is calculated by superimposing the current control loop of the second loop. T_pi2 and current integration coefficient k T_ii2 , determine the duty cycle D of the second loop T_2 , thus obtaining the modulation signal g of the second loop 2_1 and g 2_2 .

[0062] In the control strategy of the two-level converter, the input is the output current I of the two-level converter C_o and the filter inductor current I C_s The output current I of the two-level converter C_o Input the droop control loop of the two-level converter, through the droop coefficient k of the two-level converter C_d Perform droop control to obtain the feedback of the droop control loop, and add the feedback to the DC bus voltage V and the voltage reference value V of the two-level converter. C_r Then, it is input into the voltage control loop of the two-level converter, and the voltage proportional coefficient k of the two-level converter is C_pv and voltage integration coefficient k C_iv , and obtain the filter inductor current reference value I of the two-level converter C_r , the filter inductor current reference value I C_r The filter inductor current I C_s The current proportionality coefficient k of the two-level converter is used to calculate the current control loop of the two-level converter. C_pi and current integration coefficient kC_ii , determine the duty cycle D of the two-level converter C , thus obtaining the modulation signal g of the two-level converter 3 and g 4 .

[0063] Figure 2 The implementation flow chart of the equivalent method of the heterogeneous DC microgrid provided by the embodiment of the present invention is detailed as follows:

[0064] Step S201 : for each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain a branch equivalent model of the loop.

[0065] In this embodiment, considering that the interleaved parallel three-level converter includes multiple loops, each loop also includes multiple branches, that is, the smallest unit in the interleaved parallel three-level converter is a branch, therefore, the upper branch and the lower branch in each loop are first merged, and the order of each loop is reduced.

[0066] Step S202: obtaining a loop equivalent model of the interleaved parallel three-level converter based on the branch equivalent model of each loop, and determining a loop control strategy of the loop equivalent model.

[0067] In this embodiment, see Figure 3 The schematic diagram of the branch equivalent structure of the heterogeneous DC microgrid shown in FIG, wherein the loop equivalent model of the staggered parallel three-level converter and the corresponding loop control strategy are shown. Here, since the upper branch and the lower branch in each loop use the same droop control loop, voltage control loop and current control loop to generate the PWM modulation signal, the droop control loop, voltage control loop and current control loop of each loop can remain unchanged, that is, the loop control strategy of the loop equivalent model is the same as the control strategy of the staggered parallel three-level converter.

[0068] Step S203 , according to the loop control strategy, two loops in the loop equivalent model are merged to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and a model control strategy of the equivalent two-level converter model is determined.

[0069] In this embodiment, after the branches are merged, the smallest unit in the loop equivalent model is the loop. Therefore, the upper branch and the lower branch in each loop are merged, and the loop equivalent model is reduced in order, so that the staggered parallel three-level converter can be equivalent to an equivalent two-level converter model.

[0070] Step S204: establishing an equivalent model of a heterogeneous DC microgrid based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter.

[0071] In this embodiment, the staggered parallel three-level converter has been reduced to an equivalent two-level converter model, and the heterogeneous DC microgrid also includes a two-level converter. Therefore, the equivalent two-level converter model and the two-level converter can be equivalently merged to construct an equivalent model of the heterogeneous DC microgrid.

[0072] The embodiment of the present invention combines the upper branch and the lower branch of each loop in the staggered parallel three-level converter to obtain a branch equivalent model of each loop, and then obtains a loop equivalent model of the staggered parallel three-level converter, which can reduce the order of the staggered parallel three-level converter; then, the two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and the loop equivalent model can be reduced again, so that the staggered parallel three-level converter can be equivalent to a two-level converter model; finally, the equivalent two-level converter model and the two-level converter in the heterogeneous DC microgrid can be directly combined and reduced to achieve the reduction of the heterogeneous DC microgrid, so that the reduced-order equivalent model can be used to accurately analyze the stability of such heterogeneous DC microgrid.

[0073] In some embodiments, see Figure 3 The structural schematic diagram of the branch equivalence of the heterogeneous DC microgrid shown in the figure, for each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop, for each loop, according to the control strategy of the loop, the loop current closed-loop transfer function of the loop can be determined; according to the loop current closed-loop transfer function, the branch equivalent relationship between the upper branch and the lower branch of the loop is determined; based on the branch equivalent relationship, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop.

[0074] In this embodiment, when the upper branch and the lower branch of each loop are equivalently merged, the loop current closed-loop transfer function of the loop can be determined first, and the loop current closed-loop transfer function can be used to determine the equivalent relationship between the filter capacitor of the upper branch and the filter capacitor of the lower branch, as well as the equivalent relationship between the filter inductor of the upper branch and the filter inductor of the lower branch, so that the filter capacitor of the upper branch and the filter capacitor of the lower branch are equivalently merged, and the filter inductor of the upper branch and the filter inductor of the lower branch are equivalently merged, and finally the upper branch and the lower branch of the loop are merged.

[0075] Here, for each loop, the filter inductance reference value and the filter inductance current of the loop are used as the input signal and the output signal respectively, and the corresponding loop current closed-loop transfer function can be obtained.

[0076] Optionally, the closed-loop transfer function of the loop current is expressed as:

[0077]

[0078] In the formula, G T_iisysx (s) represents the closed-loop transfer function of the loop current of the x-th loop, s represents the Laplace operator, x represents the x-th loop, U s Indicates the power supply voltage, L T_fux represents the filter inductance of the upper branch of the xth loop of the interleaved parallel three-level converter, L T_fdx represents the filter inductance of the lower branch of the xth loop of the interleaved parallel three-level converter, C T_fux represents the filter capacitor of the upper branch of the xth loop of the interleaved parallel three-level converter, C T_fdx represents the filter capacitor of the lower branch of the xth loop of the interleaved parallel three-level converter, k T_pix represents the current proportionality coefficient of the xth loop of the interleaved parallel three-level converter, k T_iix It represents the current integral coefficient of the xth loop of the interleaved parallel three-level converter.

[0079] Based on the above loop current closed-loop transfer function, it can be known that the equivalent relationship between the filter capacitor of the upper branch and the filter capacitor of the lower branch, as well as the equivalent relationship between the filter inductor of the upper branch and the filter inductor of the lower branch are as follows:

[0080]

[0081] In the formula, C T_fx It represents the equivalent filter capacitor in the branch equivalent model corresponding to the x-th loop, that is, the equivalent filter capacitor of the x-th loop in the loop equivalent model, L T_fx It represents the equivalent filter inductance in the branch equivalent model corresponding to the x-th loop, that is, the equivalent filter inductance of the x-th loop in the loop equivalent model, where the value of x can be 1 or 2.

[0082] Here, the number of zero poles of the loop current closed-loop transfer function is consistent with the number of zero poles of the current closed-loop transfer function of the two-level converter. Therefore, after the upper branch and the lower branch of each loop of the interleaved parallel three-level converter are equivalent, the current control loops of the first loop and the second loop also remain unchanged.

[0083] Correspondingly, for each loop, the voltage reference value of the loop and the DC bus voltage are used as the input signal and the output signal respectively, and the corresponding loop voltage closed-loop transfer function can be obtained, and its expression is:

[0084]

[0085] In the formula, G T_uisysx (s) represents the closed-loop transfer function of the loop voltage of the xth loop, kT_pvx represents the voltage proportionality factor of the xth loop of the interleaved parallel three-level converter, k T_ivx It represents the voltage integral coefficient of the xth loop of the interleaved parallel three-level converter.

[0086] Here, the number of zero poles of the loop voltage closed-loop transfer function is consistent with the number of zero poles of the voltage closed-loop transfer function of the two-level converter. Therefore, after the upper branch and the lower branch of each loop of the staggered parallel three-level converter are equivalent, the voltage control loop of the first loop and the second loop also remain unchanged. Correspondingly, the droop control loop of the first loop and the second loop also remains unchanged.

[0087] Based on this, the loop control strategy of the loop equivalent model can be determined according to the control strategy of each loop in the staggered parallel three-level converter and the control strategy of the two-level converter.

[0088] In addition, if Figure 3 As shown in the loop equivalent model, the equivalent filter inductor current in the first loop is I T_s1 , the equivalent filter inductor current in the second loop is I T_s2 .

[0089] In some embodiments, see Figure 4 As shown in the structural schematic diagram of the loop equivalent of the heterogeneous DC microgrid, according to the loop control strategy, the two loops in the loop equivalent model are merged to obtain the equivalent two-level converter model of the staggered parallel three-level converter. The open-loop transfer function of the loop equivalent model can be determined according to the loop control strategy; then, according to the open-loop transfer function, the filter capacitor equivalent relationship and the filter inductor equivalent relationship of the two loops in the loop equivalent model are determined; finally, based on the filter capacitor equivalent relationship and the filter inductor equivalent relationship, the two loops in the loop equivalent model are merged to obtain the equivalent two-level converter model of the staggered parallel three-level converter.

[0090] In this embodiment, when two loops are equivalently merged, the open-loop transfer function of the loop equivalent model can be first determined, and the open-loop transfer function can be used to determine the equivalent relationship between the filter capacitors and the filter inductors of the two loops in the loop equivalent model, so that the filter capacitors in the two loops are equivalently merged, and the filter inductors in the two loops are equivalently merged to achieve the merger of the two loops, thereby reducing the order of the staggered parallel three-level converter to an equivalent two-level converter model.

[0091] Here, the effect of duty cycle on DC bus voltage in the first loop and the second loop is considered as a whole, thereby obtaining an open-loop transfer function.

[0092] Optionally, the expression for the open-loop transfer function is:

[0093]

[0094] In the formula, G T_vd (s) represents the open-loop transfer function, s represents the Laplace operator, x represents the xth loop, L T_fx Represents the equivalent filter inductance of the xth loop of the loop equivalent model, C T_fx Denotes the equivalent filter capacitor of the xth loop of the loop equivalent model, D T_x represents the duty cycle of the xth loop of the loop equivalent model, V represents the DC bus voltage, and P represents the power value of the constant power load.

[0095] Rewriting the above open-loop transfer function, we can get the following expression:

[0096]

[0097] Based on the above open-loop transfer function, it can be known that the equivalent relationship between the filter capacitor of the first loop and the filter capacitor of the first loop, as well as the equivalent relationship between the filter inductor of the first loop and the filter inductor of the first loop are as follows:

[0098]

[0099] In the formula, C T_f represents the model equivalent filter capacitor in the equivalent two-level converter model, L T_f Represents the model equivalent filter inductance in the equivalent two-level converter model.

[0100] After equivalent treatment of the filter capacitors and filter inductors in the first loop and the second loop, an equivalent two-level converter model of the interleaved parallel three-level converter can be established. Figure 4 As shown. Figure 4 The equivalent two-level converter model includes the model equivalent filter inductor L T_f , Model equivalent filter capacitor C T_f and two model equivalent modulation signals g 1 and g 2 .

[0101] In some embodiments, see Figure 5 The implementation flow chart of determining the model control strategy shown in FIG. 1 can be described in detail as follows:

[0102] Step S501: determining a model current closed-loop transfer function of a loop equivalent model according to a loop control strategy.

[0103] In this embodiment, since the circuit parameters and control parameters of the first loop and the second loop are the same, the following expression is established: Among them, I T_s represents the model equivalent filter inductor current in the equivalent two-level converter model, I T_r represents the reference value of the model equivalent filter inductance in the equivalent two-level converter model, and the value of x is 1 or 2.

[0104] Based on the current control parameters of the first and second loops, the model equivalent filter inductor current reference value I T_r And the model equivalent filter inductor current I T_s As input signal and output signal respectively, the expression of model current closed-loop transfer function can be obtained.

[0105] Optionally, the expression of the model current closed-loop transfer function is:

[0106]

[0107] In the formula, G T_iisys (s) represents the model current closed-loop transfer function, R 0 Indicates the equivalent resistance of the constant power load, k T_pix represents the current proportionality coefficient of the xth loop of the loop equivalent model, k T_iix Indicates the current integral coefficient of the x-th loop of the loop equivalent model.

[0108] Step S502: determining the equivalent relationship between current control parameters of two loops in the loop equivalent model according to the model current closed-loop transfer function.

[0109] In this embodiment, the current control parameters in the model current closed-loop transfer function are combined to obtain an equivalent relationship of the current control parameters.

[0110] Optionally, the expression of the equivalent relationship of the current control parameters can be: In the formula, k T_pi The model equivalent current proportionality coefficient of the equivalent two-level converter model, k T_ii The model equivalent current integral coefficient of the equivalent two-level converter model, k T_pix Indicates the current proportionality coefficient of the xth loop, k T_iix Represents the current integral coefficient of the xth loop.

[0111] Step S503: determining a voltage closed-loop transfer function of the loop equivalent model according to the loop control strategy.

[0112] Based on the consideration of the voltage control parameters and droop coefficients of the first and second loops, the model equivalent voltage reference value V T_rand the DC bus voltage V as the input signal and output signal respectively, the expression of the model voltage closed-loop transfer function can be obtained.

[0113] Optionally, the expression of the voltage closed-loop transfer function is:

[0114]

[0115] In the formula, G T_uisys (s) represents the voltage closed-loop transfer function, D T It means that k T_pvx represents the voltage proportionality coefficient of the xth loop of the loop equivalent model, k T_ivx represents the voltage integral coefficient of the xth loop of the loop equivalent model, k T_dx Indicates the droop coefficient of the x-th loop of the loop equivalent model.

[0116] Step S504: determining the voltage control parameter equivalent relationship and the droop coefficient equivalent relationship of the two loops in the loop equivalent model according to the voltage closed-loop transfer function.

[0117] In this embodiment, the voltage control parameters in the model voltage closed-loop transfer function are combined to obtain the voltage control parameter equivalent relationship. Similarly, the droop coefficients in the model voltage closed-loop transfer function are combined to obtain the droop coefficient equivalent relationship.

[0118] Optionally, the expression of the voltage control parameter equivalent relationship can be: In the formula, k T_pv The model equivalent voltage proportionality coefficient of the equivalent two-level converter model, k T_iv The model equivalent voltage integral coefficient of the equivalent two-level converter model, k T_pvx Indicates the voltage proportionality coefficient of the xth loop, k T_ivx Represents the voltage integral coefficient of the xth loop.

[0119] Optionally, the expression of the droop coefficient equivalent relation can be: In the formula, k T_d represents the model equivalent droop coefficient of the equivalent two-level converter model, k T_dx represents the droop coefficient of the x-th loop.

[0120] Step S505 , determining a model control strategy of the equivalent two-level converter model based on the current control parameter equivalent relationship, the voltage control parameter equivalent relationship and the droop coefficient equivalent relationship.

[0121] In this embodiment, the model equivalent current proportional coefficient, model equivalent current integral coefficient, model equivalent voltage proportional coefficient, model equivalent voltage integral coefficient and model equivalent droop coefficient in the model control strategy of the equivalent two-level converter model are determined through the above-mentioned current control parameter equivalent relationship, voltage control parameter equivalent relationship and droop coefficient equivalent relationship; the corresponding droop control loop is determined through the model equivalent droop coefficient, the corresponding voltage control loop is determined through the model equivalent voltage proportional coefficient and the model equivalent voltage integral coefficient, and the corresponding current control loop is determined through the model equivalent current proportional coefficient and the model equivalent current integral coefficient, thereby determining the model control strategy of the equivalent two-level converter model.

[0122] In the model control strategy of the equivalent two-level converter model, the input is the output current I of the equivalent two-level converter model. T_o And the model equivalent filter inductor current I T_s The output current I of the equivalent two-level converter model is T_o Input the corresponding droop control loop, through the model equivalent droop coefficient k T_d Perform droop control to obtain the feedback of the droop control loop, and add the feedback to the DC bus voltage V and the model equivalent voltage reference value V T_r Then input the corresponding voltage control loop, and use the model equivalent voltage proportional coefficient k T_pv And the model equivalent voltage integral coefficient k T_iv , get the model equivalent filter inductor current reference value I T_r , the model equivalent filter inductor current reference value I T_r The equivalent filter inductor current I T_s Superimpose and input the corresponding current control loop, and use the model equivalent current proportional coefficient k T_pi And the model equivalent current integral coefficient k T_ii , determine the duty cycle D of the equivalent two-level converter model T , thus obtaining the modulation signal g of the equivalent two-level converter model 1 and g 2 .

[0123] In some embodiments, see Figure 6The equivalent schematic diagram of the heterogeneous DC microgrid shown in the figure establishes an equivalent model of the heterogeneous DC microgrid based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter. The equivalent two-level converter model and the two-level converter are firstly equivalently merged to obtain a reduced-order equivalent model; and then the filter inductor, filter capacitor, current control parameter, voltage control parameter and droop coefficient of the reduced-order equivalent model are determined according to the model control strategy and the control strategy of the two-level converter; finally, the equivalent model of the heterogeneous DC microgrid is obtained based on the reduced-order equivalent model and the filter inductor, filter capacitor, current control parameter, voltage control parameter and droop coefficient of the reduced-order equivalent model.

[0124] In this embodiment, Figure 4 The equivalent two-level converter model shown in the figure and the two-level converter are further processed to obtain Figure 6 The equivalent model of the heterogeneous DC microgrid is shown.

[0125] Here, the reduced-order equivalent model refers to a model obtained by equivalently merging the equivalent two-level converter model and the two-level converter. The heterogeneous DC microgrid equivalent model refers to a model including the above reduced-order equivalent model and the corresponding control strategy.

[0126] By comparison Figure 4 and Figure 6 It can be seen that the equivalent relationship between the corresponding filter inductor and filter capacitor is:

[0127]

[0128] In the formula, C f represents the filter capacitor in the reduced-order equivalent model, that is, the filter capacitor of the heterogeneous DC microgrid equivalent model, L f It represents the filter inductance in the reduced-order equivalent model, that is, the filter inductance of the heterogeneous DC microgrid equivalent model.

[0129] By comparison Figure 4 and Figure 6 It can be seen that the equivalent relationship of the corresponding current control parameters is:

[0130]

[0131] In the formula, k pi represents the reduced-order equivalent current proportionality coefficient in the reduced-order equivalent model, that is, the reduced-order equivalent current proportionality coefficient of the heterogeneous DC microgrid equivalent model, k ii represents the reduced-order equivalent current integral coefficient in the reduced-order equivalent model, that is, the reduced-order equivalent current integral coefficient of the heterogeneous DC microgrid equivalent model, h T represents the first power sharing factor of the interleaved parallel three-level converter, hC represents the second power sharing coefficient of the two-level converter. T and the second power sharing coefficient h C The sum is 1.

[0132] Here, the reduced-order equivalent current proportionality coefficient k in the reduced-order equivalent model is pi and the reduced-order equivalent current integral coefficient k in the reduced-order equivalent model ii Current control parameters that constitute the reduced-order equivalent model.

[0133] By comparison Figure 4 and Figure 6 It can also be known that the equivalent relationship of the corresponding voltage control parameters is:

[0134]

[0135] In the formula, k pv represents the reduced-order equivalent voltage proportionality coefficient in the reduced-order equivalent model, that is, the reduced-order equivalent voltage proportionality coefficient of the heterogeneous DC microgrid equivalent model, k iv It represents the reduced-order equivalent voltage integral coefficient in the reduced-order equivalent model, that is, the reduced-order equivalent voltage integral coefficient of the heterogeneous DC microgrid equivalent model.

[0136] Here, the reduced-order equivalent voltage proportionality coefficient k in the reduced-order equivalent model is pv and the reduced-order equivalent voltage integral coefficient k in the reduced-order equivalent model iv Voltage control parameters that constitute the reduced-order equivalent model.

[0137] Similarly, the equivalent relationship of the droop coefficient is:

[0138]

[0139] In the formula, k d It represents the droop coefficient in the reduced-order equivalent model, that is, the droop coefficient of the equivalent model of the heterogeneous DC microgrid.

[0140] In the control strategy of the reduced-order equivalent model, the input is the output current I of the reduced-order equivalent model. o And the model equivalent filter inductor current I s The output current I of the reduced-order equivalent model o Input the corresponding droop control loop, through which the droop coefficient k d Perform droop control to obtain the feedback of the droop control loop, and add the feedback to the DC bus voltage V and the voltage reference value V of the reduced-order equivalent model. r Then, the corresponding voltage control loop is input, and the equivalent voltage proportional coefficient k is reduced. pv And the reduced-order equivalent voltage integral coefficient kiv , and obtain the filter inductor current reference value I of the reduced-order equivalent model r , the filter inductor current reference value I of the model equivalent model r The filter inductor current I of the reduced-order equivalent model s Superimpose and input the corresponding current control loop, and reduce the equivalent current proportional coefficient k pi And the reduced-order equivalent current integral coefficient k ii , determine the duty cycle D of the reduced-order equivalent model T , thus obtaining the modulation signal g of the reduced-order equivalent model 1 and g 2 .

[0141] Based on this, the heterogeneous DC microgrid can be equivalent to obtain the equivalent model of the heterogeneous DC microgrid, and the stability of the heterogeneous DC microgrid can be analyzed using the equivalent model of the heterogeneous DC microgrid.

[0142] Optionally, when all poles of the loop voltage closed-loop transfer function of the heterogeneous DC microgrid equivalent model are located on the left side of the imaginary axis of the s-plane, that is, when the heterogeneous DC microgrid equivalent model meets the stability criterion, the heterogeneous DC microgrid equivalent model is stable, and accordingly, it can be determined that the heterogeneous DC microgrid is also stable; when the heterogeneous DC microgrid equivalent model does not meet the stability criterion, the heterogeneous DC microgrid equivalent model oscillates, and accordingly, it can be determined that the heterogeneous DC microgrid is also oscillating.

[0143] In a feasible embodiment, in order to verify the effectiveness of the equivalent method of the heterogeneous DC microgrid proposed in the present invention, the Figure 1 The structure and application of heterogeneous DC microgrid in Figure 6 The structure of the heterogeneous DC microgrid equivalent model in the simulation is verified. Here, the structure can be built on the PLECS software.

[0144] The simulation is carried out with the current proportional coefficient of the interleaved parallel three-level converter being 0.02, the current integral coefficient being 40, the voltage proportional coefficient being 0.029, the voltage integral coefficient being 481, and the droop coefficient being 0.3, and the current proportional coefficient of the two-level converter being 0.02, the current integral coefficient being 40, the voltage proportional coefficient being 0.029, the voltage integral coefficient being 481, and the droop coefficient being 0.15 as the first group of control parameters.

[0145] The current proportional coefficient of the interleaved parallel three-level converter is 0.0213, the current integral coefficient is 93.7903, the voltage proportional coefficient is 2.2063, the voltage integral coefficient is 349.3399, and the droop coefficient is 0.3, and the current proportional coefficient of the two-level converter is 0.0213, the current integral coefficient is 93.7903, the voltage proportional coefficient is 2.2063, the voltage integral coefficient is 349.3399, and the droop coefficient is 0.15, which are used as the second group of control parameters for simulation.

[0146] During the simulation, the power of the constant power load steps from 20kW to 26kW at 1 second. The time domain simulation results of the DC bus voltage of the heterogeneous DC microgrid at the first group of control parameters are shown in Figure 2. Figure 7 As shown in the figure, the time domain simulation results of the DC bus voltage of the equivalent model of the heterogeneous DC microgrid at the first group of control parameters are as follows: Figure 8 As shown. Figure 7 and Figure 8 It can be seen that the time-domain simulation results of the DC bus voltage of the heterogeneous DC microgrid and the equivalent model of the heterogeneous DC microgrid are almost the same, and both have oscillation and instability phenomena.

[0147] Under the same power disturbance conditions, the time domain simulation results of the DC bus voltage of the heterogeneous DC microgrid at the second set of control parameters are shown in Fig. 9 As shown in the figure, the time domain simulation results of the DC bus voltage of the heterogeneous DC microgrid equivalent model at the second group of control parameters are as follows: Fig.10 As shown. Fig. 9 and Fig.10 It can be seen that the time-domain simulation results of the DC bus voltage of the heterogeneous DC microgrid and its equivalent model are almost the same, and both show dynamic stability.

[0148] Here, in Figure 7 , Figure 8 , Fig. 9 and Fig.10 In the figure, the horizontal axis is time (s) and the vertical axis is DC bus voltage (V).

[0149] It can be seen from this that the equivalent method of the heterogeneous DC microgrid proposed in the present invention is effective. The equivalent method of the heterogeneous DC microgrid can be used to perform equivalent modeling on the heterogeneous DC microgrid, and an equivalent model of the heterogeneous DC microgrid can be obtained. The stability analysis of the heterogeneous DC microgrid can be performed through the equivalent model.

[0150] The embodiment of the present invention combines the upper branch and the lower branch of each loop in the staggered parallel three-level converter to obtain a branch equivalent model of each loop, and then obtains a loop equivalent model of the staggered parallel three-level converter, which can reduce the order of the staggered parallel three-level converter; then, the two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and the loop equivalent model can be reduced again, so that the staggered parallel three-level converter can be equivalent to a two-level converter model; finally, the equivalent two-level converter model and the two-level converter in the heterogeneous DC microgrid can be directly combined and reduced to achieve the reduction of the heterogeneous DC microgrid, so that the reduced-order equivalent model can be used to accurately analyze the stability of such heterogeneous DC microgrid. Among them, when performing reduced-order merging, the current closed-loop transfer function is determined by taking the filter inductor current reference value and the filter inductor current as the input signal and the output signal respectively, and the voltage closed-loop transfer function is determined by taking the voltage reference value and the DC bus voltage as the input signal and the output signal respectively. The equivalent relationship between the current control loop, the voltage control loop and the droop control loop can be determined respectively, and then the control strategy of the equivalent model can be obtained, so as to accurately establish the equivalent model of the heterogeneous DC microgrid and clarify the control strategy of the equivalent model.

[0151] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0152] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0153] Fig.11 The structural schematic diagram of the equivalent device of the heterogeneous DC microgrid provided by the embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0154] An equivalent method for a heterogeneous DC microgrid, wherein the heterogeneous DC microgrid includes an interleaved parallel three-level converter and a two-level converter, wherein the interleaved parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the interleaved parallel three-level converter includes two loops, and each loop includes an upper branch and a lower branch. Fig.11 As shown, the equivalent device 110 of the heterogeneous DC microgrid includes:

[0155] The branch module 111 is used for merging the upper branch and the lower branch of each loop according to the control strategy of the loop to obtain a branch equivalent model of the loop; based on the branch equivalent model of each loop, obtaining a loop equivalent model of the staggered parallel three-level converter, and determining the loop control strategy of the loop equivalent model;

[0156] A loop module 112 is used to merge two loops in the loop equivalent model according to the loop control strategy to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and determine a model control strategy of the equivalent two-level converter model;

[0157] The equivalent module 113 is used to establish an equivalent model of a heterogeneous DC microgrid based on an equivalent two-level converter model, a two-level converter, a model control strategy and a control strategy of the two-level converter.

[0158] In a possible implementation, the branch module 111 is specifically configured to:

[0159] For each loop, determining a loop current closed-loop transfer function of the loop according to a control strategy of the loop;

[0160] According to the closed-loop transfer function of the loop current, the branch equivalent relationship between the upper branch and the lower branch of the loop is determined;

[0161] Based on the branch equivalent relationship, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop.

[0162] In a possible implementation, the loop module 112 is specifically configured to:

[0163] According to the loop control strategy, determine the open-loop transfer function of the loop equivalent model;

[0164] According to the open-loop transfer function, determine the equivalent relationship between the filter capacitors and the filter inductors of the two loops in the loop equivalent model;

[0165] Based on the equivalent relationship of filter capacitors and filter inductors, the two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the interleaved parallel three-level converter.

[0166] In a possible implementation, the loop module 112 is specifically configured to:

[0167] According to the loop control strategy, a model current closed-loop transfer function of the loop equivalent model is determined;

[0168] According to the model current closed-loop transfer function, the equivalent relationship between the current control parameters of the two loops in the loop equivalent model is determined;

[0169] According to the loop control strategy, determine the voltage closed-loop transfer function of the loop equivalent model;

[0170] According to the voltage closed-loop transfer function, the equivalent relationship between the voltage control parameters and the equivalent relationship between the droop coefficients of the two loops in the loop equivalent model is determined;

[0171] Based on the equivalent relationship of current control parameters, the equivalent relationship of voltage control parameters and the equivalent relationship of droop coefficient, a model control strategy of the equivalent two-level converter model is determined.

[0172] In a possible implementation, the equivalent module 113 is specifically used for:

[0173] An equivalent two-level converter model and a two-level converter are equivalently merged to obtain a reduced-order equivalent model;

[0174] According to the model control strategy and the control strategy of the two-level converter, the filter inductor, filter capacitor, current control parameter, voltage control parameter and droop coefficient of the reduced-order equivalent model are determined;

[0175] Based on the reduced-order equivalent model, as well as the filter inductance, filter capacitance, current control parameters, voltage control parameters and droop coefficient of the reduced-order equivalent model, an equivalent model of the heterogeneous DC microgrid is obtained.

[0176] In one possible implementation, the closed-loop transfer function of the loop current is expressed as:

[0177]

[0178] In the formula, G T_iisysx (s) represents the closed-loop transfer function of the loop current, s represents the Laplace operator, x represents the xth loop, U s Indicates the power supply voltage, L T_fux represents the filter inductance of the upper branch of the xth loop of the interleaved parallel three-level converter, L T_fdx represents the filter inductance of the lower branch of the xth loop of the interleaved parallel three-level converter, C T_fux represents the filter capacitor of the upper branch of the xth loop of the interleaved parallel three-level converter, C T_fdx represents the filter capacitor of the lower branch of the xth loop of the interleaved parallel three-level converter, k T_pix represents the current proportionality coefficient of the xth loop of the interleaved parallel three-level converter, k T_iix It represents the current integral coefficient of the xth loop of the interleaved parallel three-level converter.

[0179] In one possible implementation, the expression of the open-loop transfer function is:

[0180]

[0181] In the formula, G T_vd (s) represents the open-loop transfer function, s represents the Laplace operator, x represents the xth loop, L T_fx Represents the equivalent filter inductance of the xth loop of the loop equivalent model, C T_fx Denotes the equivalent filter capacitor of the xth loop of the loop equivalent model, D T_x represents the duty cycle of the xth loop of the loop equivalent model, V represents the DC bus voltage, and P represents the power value of the constant power load.

[0182] In one possible implementation, the expression of the model current closed-loop transfer function is:

[0183]

[0184] In the formula, G T_iisys (s) represents the model current closed-loop transfer function, R 0 Indicates the equivalent resistance of the constant power load, k T_pix represents the current proportionality coefficient of the xth loop of the loop equivalent model, k T_iix Indicates the current integral coefficient of the x-th loop of the loop equivalent model.

[0185] In one possible implementation, the voltage closed-loop transfer function is expressed as:

[0186]

[0187] In the formula, G T_uisys (s) represents the voltage closed-loop transfer function, D T It means that k T_pvx represents the voltage proportionality coefficient of the xth loop of the loop equivalent model, k T_ivx represents the voltage integral coefficient of the xth loop of the loop equivalent model, k T_dx Indicates the droop coefficient of the x-th loop of the loop equivalent model.

[0188] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0189] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0190] If the module / 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, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable media may include: any entity or device that can carry computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium, etc.

[0191] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. An equivalent modeling method for a heterogeneous DC microgrid, characterized in that: The heterogeneous DC microgrid includes a staggered parallel three-level converter and a two-level converter, wherein the staggered parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the staggered parallel three-level converter includes two loops, each loop includes an upper branch and a lower branch; and the method includes: For each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop; Based on the branch equivalent model of each loop, a loop equivalent model of the interleaved parallel three-level converter is obtained, and a loop control strategy of the loop equivalent model is determined; According to the loop control strategy, two loops in the loop equivalent model are merged to obtain an equivalent two-level converter model of the staggered parallel three-level converter, and a model control strategy of the equivalent two-level converter model is determined; Based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter, an equivalent model of a heterogeneous DC microgrid is established.

2. The equivalent modeling method of the heterogeneous DC microgrid according to claim 1 is characterized in that: For each loop, according to the control strategy of the loop, the upper branch and the lower branch of the loop are merged to obtain the branch equivalent model of the loop, including: For each loop, determining a loop current closed-loop transfer function of the loop according to a control strategy of the loop; Determining the branch equivalence relationship between the upper branch and the lower branch of the loop according to the loop current closed-loop transfer function; Based on the branch equivalent relationship, the upper branch and the lower branch of the loop are merged to obtain a branch equivalent model of the loop.

3. The equivalent modeling method of the heterogeneous DC microgrid according to claim 1 is characterized in that: According to the loop control strategy, two loops in the loop equivalent model are merged to obtain an equivalent two-level converter model of the staggered parallel three-level converter, including: Determining an open-loop transfer function of the loop equivalent model according to the loop control strategy; Determining, according to the open-loop transfer function, an equivalent relationship between filter capacitors and an equivalent relationship between filter inductors of two loops in the loop equivalent model; Based on the filter capacitor equivalent relationship and the filter inductor equivalent relationship, two loops in the loop equivalent model are combined to obtain an equivalent two-level converter model of the interleaved parallel three-level converter.

4. The equivalent modeling method of the heterogeneous DC microgrid according to claim 3 is characterized in that: Determining a model control strategy of the equivalent two-level converter model includes: Determining a model current closed-loop transfer function of the loop equivalent model according to the loop control strategy; Determining an equivalent relationship between current control parameters of two loops in the loop equivalent model according to the model current closed-loop transfer function; Determining a voltage closed-loop transfer function of the loop equivalent model according to the loop control strategy; Determining, according to the voltage closed-loop transfer function, an equivalent relationship between voltage control parameters and an equivalent relationship between droop coefficients of two loops in the loop equivalent model; Based on the current control parameter equivalent relationship, the voltage control parameter equivalent relationship and the droop coefficient equivalent relationship, a model control strategy of the equivalent two-level converter model is determined.

5. The equivalent modeling method of a heterogeneous DC microgrid according to any one of claims 1 to 4, characterized in that: Based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter, an equivalent model of a heterogeneous DC microgrid is established, including: Performing equivalent merging on the equivalent two-level converter model and the two-level converter to obtain a reduced-order equivalent model; Determining the filter inductance, filter capacitance, current control parameters, voltage control parameters and droop coefficient of the reduced-order equivalent model according to the model control strategy and the control strategy of the two-level converter; Based on the reduced-order equivalent model, and the filter inductance, filter capacitance, current control parameter, voltage control parameter and droop coefficient of the reduced-order equivalent model, an equivalent model of a heterogeneous DC microgrid is obtained.

6. The equivalent modeling method of the heterogeneous DC microgrid according to claim 2 is characterized in that: The expression of the closed-loop transfer function of the loop current is: In the formula, G T_iisysx (s) represents the closed-loop transfer function of the loop current, s represents the Laplace operator, x represents the xth loop, U s Indicates the power supply voltage, L T_fux represents the filter inductance of the upper branch of the xth loop of the interleaved parallel three-level converter, L T_fdx represents the filter inductance of the lower branch of the xth loop of the interleaved parallel three-level converter, C T_fux represents the filter capacitor of the upper branch of the xth loop of the interleaved parallel three-level converter, C T_fdx represents the filter capacitor of the lower branch of the xth loop of the interleaved parallel three-level converter, k T_pix represents the current proportionality coefficient of the xth loop of the interleaved parallel three-level converter, k T_iix represents the current integral coefficient of the xth loop of the interleaved parallel three-level converter.

7. The equivalent modeling method of the heterogeneous DC microgrid according to claim 4 is characterized in that: The expression of the open-loop transfer function is: In the formula, G T_vd (s) represents the open-loop transfer function, s represents the Laplace operator, x represents the xth loop, L T_fx represents the equivalent filter inductance of the xth loop of the loop equivalent model, C T_fx represents the equivalent filter capacitor of the xth loop of the loop equivalent model, D T_x represents the duty cycle of the xth loop of the loop equivalent model, V represents the DC bus voltage, and P represents the power value of the constant power load.

8. The equivalent modeling method of the heterogeneous DC microgrid according to claim 7 is characterized in that: The expression of the model current closed-loop transfer function is: In the formula, G T_iisys (s) represents the current closed-loop transfer function of the model, R0 represents the equivalent resistance of the constant power load, k T_pix represents the current proportionality coefficient of the xth loop of the loop equivalent model, k T_iix represents the current integral coefficient of the xth loop of the loop equivalent model.

9. The equivalent modeling method of the heterogeneous DC microgrid according to claim 8 is characterized in that: The expression of the voltage closed-loop transfer function is: In the formula, G T_uisys (s) represents the voltage closed-loop transfer function, D T It means that k T_pvx represents the voltage proportionality coefficient of the xth loop of the loop equivalent model, k T_ivx represents the voltage integral coefficient of the xth loop of the loop equivalent model, k T_dx represents the droop coefficient of the x-th loop of the loop equivalent model.

10. An equivalent modeling device for a heterogeneous DC microgrid, characterized in that: An equivalent method for a heterogeneous DC microgrid, wherein the heterogeneous DC microgrid comprises an interleaved parallel three-level converter and a two-level converter, wherein the interleaved parallel three-level converter and the two-level converter are connected in parallel on a DC bus, wherein the interleaved parallel three-level converter comprises two loops, each loop comprising an upper branch and a lower branch; and the device comprises: A branch module, for merging the upper branch and the lower branch of each loop according to the control strategy of the loop to obtain a branch equivalent model of the loop; based on the branch equivalent model of each loop, obtaining a loop equivalent model of the staggered parallel three-level converter, and determining a loop control strategy of the loop equivalent model; A loop module, configured to merge two loops in the loop equivalent model according to the loop control strategy, obtain an equivalent two-level converter model of the staggered parallel three-level converter, and determine a model control strategy of the equivalent two-level converter model; An equivalent module is used to establish an equivalent model of a heterogeneous DC microgrid based on the equivalent two-level converter model, the two-level converter, the model control strategy and the control strategy of the two-level converter.

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