A high-frequency circulating current calculation method for a cascade-coupled parallel structure of a motor simulator

Abstract

The application provides a high-frequency circulating current calculation method for a motor simulator cascaded coupling parallel structure, comprising the following steps: establishing an equivalent decoupling circuit model of each branch in the cascaded coupling parallel structure based on the voltage relationship of each branch in the motor simulator cascaded coupling parallel structure, wherein the equivalent decoupling circuit of each branch comprises an equivalent voltage source and an equivalent leakage inductance connected in series, and the equivalent leakage inductance is determined based on the self-inductance and mutual inductance of each branch choke; dividing a plurality of duty cycle intervals between 0 and 1, and the number of duty cycle intervals is equal to the number of branches in the cascaded coupling parallel structure; and using the equivalent decoupling circuit model to calculate the high-frequency circulating current of each branch when the duty cycle of the modulation signal of the motor simulator is in each duty cycle interval. The method provided by the application can accurately calculate the high-frequency circulating current of the motor simulator cascaded coupling parallel structure, and provides effective support for the targeted design of a high-frequency circulating current suppression scheme.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of motor simulator control, and particularly relates to a high-frequency circulating current calculation method for a cascade-coupled parallel structure of a motor simulator. BACKGROUND

[0002] The motor simulator (EME) is a test equipment for electric drive systems of new energy vehicles. Since the EME can test the drive system without an actual motor, simulate various working conditions, and perform extreme performance tests such as high-temperature and low-temperature tests, the EME can significantly shorten the development cycle of the electric drive system.

[0003] Existing motor simulators mostly adopt a parallel topology structure to improve the redundancy and reliability of the system. By increasing the number of branches, the maximum single-phase port current can be expanded, and the equivalent switching frequency can be increased. Meanwhile, a carrier phase-shifted algorithm is used to generate a multi-level, improve the control frequency, and reduce the output current harmonics. However, this will cause the switching states of the branches to be inconsistent, and a high-frequency differential-mode circulating current close to the switching frequency will be generated.

[0004] The high-frequency circulating current will have many adverse effects on the EME system, such as increasing the output current harmonics, increasing the load of the switching devices, reducing the service life of the switching devices and increasing the energy loss, and reducing the system efficiency. In order to suppress the high-frequency circulating current between the branches, the EME mostly adopts a cascade-coupled parallel structure, and uses a common-mode choke to suppress the differential-mode circulating current while almost not affecting the common-mode current. However, simulation and experimental results show that in the cascade-coupled parallel structure, the high-frequency circulating current will still increase with the increase in the number of branches. Excessive high-frequency circulating current will saturate the choke and lose the suppression ability, which will limit the expansion of the number of branches in the cascade-coupled parallel structure and limit the improvement of the performance of the EME. Therefore, it is necessary to further explore the changes of the high-frequency circulating current with the modulation signal under different numbers of branches, and design a high-frequency circulating current suppression scheme according to the characteristics. However, there is no report on related research work at present. SUMMARY

[0005] The application aims to provide a high-frequency circulating current calculation method for a cascade-coupled parallel structure of a motor simulator, which is used to obtain the quantitative characteristics of the high-frequency circulating current in the cascade-coupled parallel structure of the motor simulator under different numbers of branches and different duty cycles of the modulation signal. The high-frequency circulating current calculation method comprises the following steps:

[0006] S1, an equivalent decoupling circuit model of each branch in the cascade-coupled parallel structure is established based on the voltage relationship of each branch in the cascade-coupled parallel structure of the motor simulator, wherein the equivalent decoupling circuit of each branch comprises an equivalent voltage source and an equivalent leakage inductance connected in series, and the equivalent leakage inductance is determined based on the self-inductance and mutual inductance of the choke of each branch;

[0007] S2, dividing a plurality of duty cycle intervals between 0 and 1, wherein the number of duty cycle intervals is equal to the number of branches in the cascade coupled parallel structure;

[0008] S3, using the equivalent decoupling circuit model to calculate the high-frequency circulating current of each corresponding branch when the duty cycle of the modulation signal of the motor simulator is in each duty cycle interval.

[0009] Furthermore, step S1 includes the following steps:

[0010] S11, establishing a voltage equation for each branch in the cascade coupled parallel structure;

[0011] S12, jointly calculating and combining the voltage equations of each branch in the cascade coupled parallel structure to obtain an equivalent voltage source-leakage inductance relationship equation for each branch, wherein the equivalent voltage source-leakage inductance relationship equation has a polynomial including a coupling factor as a coefficient term, and the coupling factor is determined based on the self-inductance and mutual inductance of the choke corresponding to each branch;

[0012] S13, establishing the equivalent decoupling circuit model based on the equivalent voltage source-leakage inductance relationship, wherein the equivalent voltage source and the equivalent leakage inductance in the equivalent decoupling circuit model are connected in series between the midpoint of each branch and the voltage output end of the cascade coupled parallel structure;

[0013] S14, determining an expression for a current flowing through the equivalent leakage inductance and an expression for a voltage at a virtual node based on the equivalent decoupling circuit model, wherein the virtual node is a node between the equivalent voltage source and the equivalent leakage inductance.

[0014] Furthermore, step S3 is specifically as follows: using the current expression flowing through the equivalent leakage inductance and the voltage expression at the virtual node, the high-frequency circulating current of each branch corresponding to the duty cycle of the modulation signal of the motor simulator is calculated in turn when the duty cycle is in each duty cycle interval.

[0015] Preferably, the high-frequency circulating current calculation method further includes the following steps:

[0016] Based on the high-frequency circulating current calculation result, the variation of the amplitude of the high-frequency circulating current with the variation of the duty cycle of the modulation signal and the duty cycle of the modulation signal corresponding to the maximum amplitude of the high-frequency circulating current are determined.

[0017] Preferably, the number of branches of the cascade coupled parallel structure of the motor simulator is 2 to 6.

[0018] Preferably, the self-inductances of the chokes corresponding to the branches are equal, and the mutual inductances of the chokes corresponding to the branches are equal; the coupling factor is the ratio of the mutual inductance to the self-inductance.

[0019] Preferably, when the number of branches of the motor simulator cascaded coupling parallel structure is odd, the amplitude of the high-frequency circulating current increases with the increase of the duty cycle D of the modulation signal of the motor simulator when D is in the interval [0, (N-1) / 2N], remains unchanged when D is in the interval [(N-1) / 2N, (N+1) / 2N], and decreases with the increase of D when D is in the interval [(N+1) / 2N, 1], wherein N is the number of branches of the motor simulator cascaded coupling parallel structure; when the number of branches of the motor simulator cascaded coupling parallel structure is even, the amplitude of the high-frequency circulating current increases with the increase of D when D is in the interval [0, 1 / 2], and decreases with the increase of D when D is in the interval [1 / 2, 1].

[0020] Preferably, when the duty cycle of the modulation signal of the motor simulator is 0.5, the amplitude of the high-frequency circulating current of each branch has a maximum value.

[0021] Further, when the number of branches of the motor simulator cascaded coupling parallel structure is 2, the maximum value of the amplitude of the high-frequency circulating current of each branch is:

[0022]

[0023] wherein T is the period of the modulation signal, V in is the bus voltage, k=M / L is the coupling factor, M and L are the mutual inductance and self-inductance of the choke coil corresponding to each branch, respectively;

[0024] When the number of branches of the motor simulator cascaded coupling parallel structure is 3, the maximum value of the amplitude of the high-frequency circulating current of each branch is:

[0025]

[0026] When the number of branches of the motor simulator cascaded coupling parallel structure is 4, the maximum value of the amplitude of the high-frequency circulating current of each branch is:

[0027]

[0028] When the number of branches of the motor simulator cascaded coupling parallel structure is 5, the maximum value of the amplitude of the high-frequency circulating current of each branch is:

[0029]

[0030] When the number of branches of the motor simulator cascaded coupling parallel structure is 6, the maximum value of the amplitude of the high-frequency circulating current of each branch is:

[0031]

[0032] Further, the high-frequency circulating current increases with the increase of the number of branches, increases with the increase of the bus voltage, increases with the increase of the switching period, and decreases with the increase of the self-inductance of the choke coil.

[0033] The embodiment of the application provides a high-frequency circulating current calculation method for a cascade coupling parallel structure of a motor simulator, an equivalent decoupling circuit model of each branch is established based on a voltage equation of each branch, different duty cycle intervals are divided according to the number of branches, and then quantitative expressions of a modulation signal in different duty cycle intervals are obtained through the equivalent decoupling circuit model. Through the method provided by the application, the factors influencing the high-frequency circulating current in the cascade coupling parallel structure of the motor simulator and the variation law of the high-frequency circulating current amplitude can be quantitatively analyzed, and a theoretical basis is provided for subsequent high-frequency circulating current suppression research. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a schematic diagram of the architecture of a cascade coupling parallel structure of a motor simulator;

[0035] Figure 2a It is a schematic diagram of the high-frequency circulating current of each branch of a two-branch cascade coupling parallel structure;

[0036] Figure 2b It is a schematic diagram of the high-frequency circulating current of each branch of a three-branch cascade coupling parallel structure;

[0037] Figure 2c It is a schematic diagram of the high-frequency circulating current of each branch of a four-branch cascade coupling parallel structure;

[0038] Figure 2d It is a schematic diagram of the high-frequency circulating current of each branch of a five-branch cascade coupling parallel structure;

[0039] Figure 2e It is a schematic diagram of the high-frequency circulating current of each branch of a six-branch cascade coupling parallel structure;

[0040] Figure 3 It is a flowchart of the high-frequency circulating current calculation method for the cascade coupling parallel structure of the motor simulator provided by the embodiment of the application;

[0041] Figure 4 It is a schematic diagram of the architecture of the equivalent decoupling circuit model of three branches provided by the embodiment of the application;

[0042] Figure 5 It is a schematic diagram of the variation of the voltage of each branch of the equivalent decoupling circuit model of three branches when the duty cycle is in the interval (0, 1 / 3];

[0043] Figure 6 It is a schematic diagram of the variation of the voltage of each branch of the equivalent decoupling circuit model of three branches when the duty cycle is in the interval (1 / 3, 2 / 3);

[0044] Figure 7 A schematic diagram of the variation of the voltage of each branch of the equivalent decoupling circuit model of three branches when the duty ratio is in the interval [2 / 3, 1);

[0045] Figure 8 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of two branches when the duty ratio is equal to 0.5;

[0046] Figure 9 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.1;

[0047] Figure 10 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.2;

[0048] Figure 11 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.3;

[0049] Figure 12 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.4;

[0050] Figure 13 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.5;

[0051] Figure 14 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.6;

[0052] Figure 15 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.7;

[0053] Figure 16 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.8;

[0054] Figure 17 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of three branches when the duty ratio is equal to 0.9;

[0055] Figure 18 A schematic diagram of the variation of the high-frequency circulation of the first branch of the equivalent decoupling circuit model of four branches when the duty ratio is equal to 0.5;

[0056] Figure 19Fig. 2 is a schematic diagram of the variation of the high-frequency circulating current of the first branch of the equivalent decoupling circuit model with five branches at a duty ratio of 0.5;

[0057] Figure 20 Fig. 3 is a schematic diagram of the variation of the high-frequency circulating current of the first branch of the equivalent decoupling circuit model with six branches at a duty ratio of 0.5;

[0058] Figure 21 Fig. 4 is a schematic diagram of the influence of the coupling factor on the high-frequency circulating current amplitude of different branches. DETAILED DESCRIPTION

[0059] Hereinafter, the present application will be further described based on the preferred embodiments and with reference to the accompanying drawings.

[0060] In the description in the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the embodiments of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, in the description of the present application, in order to distinguish different units, the first, second and the like are used in the description, but these are not limited by the order of manufacture, and cannot be understood as indicating or implying relative importance, and the names may be different in the detailed description and the claims of the present application.

[0061] The words in the specification are used to illustrate the embodiments of the present application, but are not intended to limit the present application. It should be noted that, unless otherwise explicitly specified and limited, if the terms "provided", "connected", "connected" appear, they should be understood in a broad sense, for example, they can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be specifically understood.

[0062] Figure 1 A schematic diagram of a cascaded coupling parallel structure of an electric motor emulator (EME) known to those skilled in the art is shown as Figure 1 As shown, for any phase of the electric motor emulator, a plurality of branches (such as Figure 1 A three-branch parallel topology is used, and a common-mode choke is used to suppress differential-mode circulating current.

[0063] Figures 2a to 2eThe high-frequency circulation in the cascade coupling topology structure of EME is respectively shown when two branches, three branches, four branches, five branches and six branches are adopted. As shown in the figures, the high-frequency circulation increases with the increase of the number of branches. Excessive circulation can saturate the choke coil and lose the inhibition ability, which limits the expansion of the number of branches in the cascade coupling parallel structure and limits the performance improvement of EME.

[0064] At present, there is no research on the mechanism of high-frequency circulation between branches in the cascade coupling parallel structure of the motor simulator, and there is no accurate calculation method for high-frequency circulation between branches. The influencing factors of high-frequency circulation cannot be quantitatively analyzed, and the circulation cannot be specifically reduced.

[0065] To solve the above problems, the application provides a high-frequency circulation calculation method for a cascade coupling parallel structure of a motor simulator, as shown in the method, the method comprises the following steps: Figure 3

[0066] S1, an equivalent decoupling circuit model of each branch in the cascade coupling parallel structure is established based on the voltage relationship of each branch in the cascade coupling parallel structure, wherein the equivalent decoupling circuit of each branch comprises an equivalent voltage source and an equivalent leakage inductance connected in series, and the equivalent leakage inductance is determined based on the self-inductance and mutual inductance of the choke coil of each branch;

[0067] S2, a plurality of duty cycle intervals are divided between 0 and 1, wherein the number of duty cycle intervals is equal to the number of branches in the cascade coupling parallel structure;

[0068] S3, the high-frequency circulation of each branch when the duty cycle of the modulation signal of the motor simulator is in each duty cycle interval is calculated using the equivalent decoupling circuit model.

[0069] The implementation mode of each step is described in detail below in combination with specific drawings and specific embodiments.

[0070] <Establishing an equivalent decoupling circuit model>

[0071] Step S1 establishes an equivalent decoupling circuit model of each branch according to the voltage relationship of each branch in the cascade coupling parallel structure of the motor simulator, which is used as the basis for quantitative calculation of the high-frequency circulation of each branch under the control of the modulation signal at different duty cycles.

[0072] In some specific embodiments, step S1 further comprises the following steps:

[0073] S11, the voltage equation of each branch in the cascade coupling parallel structure is established.

[0074] The establishment process of the voltage equation of each branch is described below, taking the cascade coupling parallel structure of each phase of the motor simulator as an example, which comprises three branches.​

[0075] Reference Figure 1 For the three-branch cascade-coupled parallel structure, when the self-inductance L of each branch choke coil is equal, and the mutual inductance M of each branch choke coil is equal, the voltage equation of the three-branch parallel can be established as shown in equation (1):

[0076]

[0077] wherein V L1 , V L2 , and V L3 are the voltages between the midpoints of the first, second, and third branches and the output terminal, and i1, i2, and i3 are the currents of the first, second, and third branches, respectively.

[0078] S12, the voltage equations of each branch in the cascade-coupled parallel structure are solved simultaneously and combined to obtain an equivalent voltage source-inductance relationship of each branch, wherein the equivalent voltage source-inductance relationship has a polynomial containing a coupling factor as a coefficient term, and the coupling factor is determined based on the self-inductance and mutual inductance of the choke coil corresponding to each branch.

[0079] Still taking three branches as an example, according to equation (1), the sum of the voltage equations of the second and third branches can obtain equation (2):

[0080]

[0081] Substituting equation (2) into the voltage equation of the first branch, and defining the coupling factor k as , a voltage equation of the first branch containing the coupling factor k as shown in equation (3) can be obtained:

[0082]

[0083] For the second and third branches, a voltage equation containing the coupling factor k as shown in equation (3) can also be established.

[0084] As can be seen from equation (3), V L1 can be regarded as being composed of two parts: one part is caused by the change of the current i1 passing through the self-inductance L, and the coefficient is a polynomial containing k The other part is caused by the voltages (V L2 + V L3 ) of the second and third branches, and the coefficient is a polynomial containing k In this application, V is regarded as an equivalent inductance L k , and V is regarded as an equivalent voltage source, so the voltage equation of each branch in the form of equation (3) is also called an equivalent voltage source-inductance relationship of each branch.

[0085] S13, establishing the equivalent decoupling circuit model based on the equivalent voltage source-inductive relationship of each branch, wherein the equivalent voltage source and the equivalent inductance in series in the equivalent decoupling circuit model are connected between the midpoint of each branch and the voltage output end of the cascade coupling-parallel structure.

[0086] Still taking the three-branch as an example, the equivalent decoupling circuit model of three branches as shown in (4) can be established by using the equivalent voltage source-inductive relationship of each branch as shown in (3), wherein each branch includes an equivalent voltage source and an equivalent inductance in series connected between the midpoint of each branch and the voltage output end of the entire cascade coupling-parallel structure. Figure 4 o

[0087] S14, determining the current expression flowing through the equivalent inductance and the voltage expression at the virtual node based on the equivalent decoupling circuit model, wherein the virtual node is the node between the equivalent voltage source and the equivalent inductance.

[0088] As shown in the equivalent decoupling circuit model of (4), the current expressions flowing through the equivalent inductances of each branch are as shown in (5): Figure 4

[0089]

[0090] wherein V x1 , V x2 , V x3 are the voltages at the virtual nodes between the equivalent voltage source and the equivalent inductance in the first, second and third branches respectively, and V o is the voltage at the output end, which can be further expressed as (6):

[0091]

[0092] wherein V1, V2 and V3 are the voltages at the midpoints of the three branches respectively.

[0093]

[0094] As shown in (5) and (6), in the decoupling equivalent circuit model of each branch, the interaction between the choke coils is decoupled into the equivalent voltage source and the equivalent inductance, wherein the voltage and current changes at the virtual node of each branch are simultaneously affected by the voltage changes of the branch and other branches, and therefore, when the modulation signals of the power device switches of the motor simulator are in different duty cycle intervals, the mutual influence of the voltages of the branches is different, and it is necessary to discuss them in different intervals.

[0095] ​​​​Specifically, in step S2, according to the number of branches in the cascade coupling parallel structure, equal number of duty cycle intervals between 0~1 are divided, for example, when three branches are used, 0<D≤1 / 3, 1 / 3<D<2 / 3, 2 / 3≤D<1 three duty cycle intervals are divided, wherein D is the duty cycle of the modulation signal, and for example, when two branches are used, two duty cycle intervals are divided as 0<D≤1 / 2, 1 / 2<D<1, and when other number of branches are used, similar way is used to divide the same number of duty cycle intervals as the number of branches.

[0096] Specifically, in step S3, using (5) and (6) respectively, the high frequency circulating current of each branch when the duty cycle of the motor simulator modulation signal is in each duty cycle interval is calculated in turn.

[0097] The following still takes three branches as an example to describe the calculation method of high frequency circulating current in each duty cycle interval.

[0098] 1) 0<D≤1 / 3

[0099] When the duty cycle D is in the interval (0, 1 / 3], the branch voltage changes as shown in the following table: Figure 5 wherein, V in represents the bus voltage (i.e. U DC ), T is the switching period. It can be seen from Figure 5 that the voltages of each branch do not coincide with each other, and the voltages and currents of each branch change in turn in the six stages divided by 0, DT, T.

[0100] For stage ①, V1, V2, V3 and V o satisfy the following equations:

[0101]

[0102] For the first branch, the current change amount of this stage can be expressed as:

[0103]

[0104] For stage ②, V1, V2, V3 and V o satisfy the following equations:

[0105]

[0106] The current change amount of this stage can be expressed as: Δi2=0.

[0107] For stage ③, V1, V2, V3 and V o satisfy the following equations:

[0108]

[0109] The current variation of this stage can be expressed as:

[0110]

[0111] For stage IV, V1, V2, V3 and V o The following equation is satisfied:

[0112]

[0113] The current variation of this stage can be expressed as: Δi4=0.

[0114] For stage V, V1, V2, V3 and V o The following equation is satisfied:

[0115]

[0116] The current variation of this stage can be expressed as:

[0117]

[0118] For stage VI, V1, V2, V3 and V o The following equation is satisfied:

[0119]

[0120] The current variation of this stage can be expressed as: Δi6=0.

[0121] 2) 1 / 3 < D < 2 / 3

[0122] When the duty ratio D is in the interval (1 / 3, 2 / 3), the voltage variation of each branch is as shown in Figure 6 It can be seen that the voltages of each branch overlap with each other, and the voltages and currents of each branch change in the interval (0, Figure 6 DT, T divided into six stages in turn.

[0123] For stage I, V1, V2, V3 and V o The following equation is satisfied:

[0124]

[0125] The current variation of this stage can be expressed as:

[0126]

[0127] For stage II, V1, V2, V3 and V o ​The following equation is satisfied:

[0128]

[0129] The current change in this stage can be expressed as:

[0130]

[0131] For stage ③, V1, V2, V3 and V o The following equation is satisfied:

[0132]

[0133] The current change in this stage can be expressed as:

[0134]

[0135] For stage ④, V1, V2, V3 and V o The following equation is satisfied:

[0136]

[0137] The current change in this stage can be expressed as:

[0138]

[0139] For stage ⑤, V1, V2, V3 and V o The following equation is satisfied:

[0140]

[0141] The current change in this stage can be expressed as:

[0142]

[0143] For stage ⑥, V1, V2, V3 and V o The following equation is satisfied:

[0144]

[0145] The current change in this stage can be expressed as:

[0146]

[0147] 3) 2 / 3≤D<1

[0148] When the duty cycle D is in the range of [2 / 3,1), the voltage changes of each branch are as follows: Figure 7 As shown, through Figure 7 It can be seen that the voltages of each branch overlap with each other, and the voltage and current of each branch are 0. DT, T

[0149] The changes occur in the divided 6 stages in turn.

[0150] For stage ①, V1, V2, V3 and V o The following equation is satisfied:

[0151]

[0152] The current change amount of this stage can be expressed as:

[0153] Δi1= 0.

[0154] For stage ②, V1, V2, V3 and V o The following equation is satisfied:

[0155]

[0156] The current change amount of this stage can be expressed as:

[0157]

[0158] For stage ③, V1, V2, V3 and V o The following equation is satisfied:

[0159]

[0160] The current change amount of this stage can be expressed as:

[0161] Δi3= 0.

[0162] For stage ④, V1, V2, V3 and V o The following equation is satisfied:

[0163]

[0164] The current change amount of this stage can be expressed as:

[0165]

[0166] For stage ⑤, V1, V2, V3 and V o The following equation is satisfied:

[0167]

[0168] The current change amount of this stage can be expressed as:

[0169] Δi5= 0.

[0170] For stage ⑥, V1, V2, V3 and V oThe following equation is satisfied:

[0171]

[0172] The current change amount of this stage can be expressed as:

[0173]

[0174] <Analysis of the relationship between high-frequency circulating current and duty cycle>

[0175] After obtaining the expression of the high-frequency circulating current when the duty cycle of the modulation signal is in different intervals through the above steps, the change of the amplitude of the high-frequency circulating current with the change of the duty cycle of the modulation signal can be determined based on the calculation result of the high-frequency circulating current, and the duty cycle of the modulation signal corresponding to the maximum value of the amplitude of the high-frequency circulating current.

[0176] The specific analysis steps are still described by taking three branches as an example:

[0177] 1) 0 < D ≤ 1 / 3

[0178] When the duty cycle D of the modulation signal is in the interval (0, 1 / 3], it can be known from equations (7)-(9) that the high-frequency circulating current rises in stage ①, decreases in stages ③ and ⑤, and remains unchanged in stages ②, ④ and ⑥, and the rising amplitude of stage ① is equal to the sum of the decreasing amplitudes of stages ③ and ⑤. Therefore, when D is in the interval (0, 1 / 3], the amplitude of the high-frequency circulating current is equal to the rising amplitude of stage ①, that is:

[0179]

[0180] It can be observed from equation (19) that when D is in the interval (0, 1 / 3], the amplitude of the high-frequency circulating current increases with the increase of D, until D = 1 / 3, and the amplitude reaches the maximum value

[0181] 2) 1 / 3 < D < 2 / 3

[0182] When D is in the interval (1 / 3, 2 / 3), it can be known from equations (10)-(15) that the high-frequency circulating current rises in stages ①, ② and ③, and decreases in stages ④, ⑤ and ⑥, and the sum of the rising amplitudes is equal to the sum of the decreasing amplitudes. Therefore, when D is in the interval (1 / 3, 2 / 3), the amplitude of the high-frequency circulating current is equal to the sum of the rising amplitudes of stages ①, ② and ③, that is:

[0183]

[0184] After combining like terms, the term containing D is eliminated, and finally the following equation is obtained:

[0185] ​​​

[0186] From equation (20), it can be seen that when D is in the interval (1 / 3, 2 / 3), the amplitude of the high-frequency circulating current remains unchanged and is equal to the maximum value when D is in the interval (0, 1 / 3).

[0187] 3) 2 / 3≤D<1

[0188] When D is in the interval [2 / 3, 1), it can be seen from equations (16) to (18) that the high-frequency circulating current rises in stages ② and ④, decreases in stage ⑥, and remains unchanged in stages ①, ③, and ⑤, and the sum of the rising amplitudes in stages ② and ④ is equal to the decreasing amplitude in stage ⑥. Therefore, when D is in the interval [2 / 3, 1), the amplitude of the high-frequency circulating current is equal to the sum of the rising amplitudes in stages ② and ④, i.e.,

[0189]

[0190] From equation (21), it can be seen that when D is in the interval [2 / 3, 1), the amplitude of the high-frequency circulating current decreases with the increase of D, and when D = 2 / 3, the amplitude is the maximum value. Based on the same method, the equivalent decoupling circuit models corresponding to two branches, four branches, five branches, and six branches are established, and the high-frequency circulating currents and their amplitude changes of each branch when D is in different duty cycle intervals are calculated and analyzed. The conclusions are shown in Table 1:

[0191] Table 1. Calculation results of high-frequency circulating currents of cascade coupling-parallel structure for two to six branches

[0192]

[0193]

[0194] From Table 1, it can be seen that when the number of branches of the motor simulator in the cascade coupling-parallel structure is odd, the amplitude of the high-frequency circulating current increases with the increase of D when the duty cycle D of the modulation signal of the motor simulator is in the interval [0, (N-1) / 2N], remains unchanged when D is in the interval [(N-1) / 2N, (N+1) / 2N], and decreases with the increase of D when D is in the interval [(N+1) / 2N, 1], where N is 3 or 5.

[0195]

[0196] ​​​When the number of branches in the cascade coupled parallel structure of the motor simulator is even, the amplitude of the high-frequency circulating current increases with the increase of D when D is in the interval [0,1 / 2], and decreases with the increase of D when D is in the interval [1 / 2,1].

[0197] At the same time, it can be seen that no matter whether the number of branches is odd or even, when the duty cycle of the modulation signal of the motor simulator is 0.5, the amplitude of the high-frequency circulating current of each branch reaches the maximum value.

[0198] <Specific embodiment 1>

[0199] This embodiment uses the above-mentioned high-frequency circulating current calculation method to simulate different duty cycles of a single-phase multi-branch cascade coupled parallel structure. The simulation parameters are as follows: bus voltage 500V, simulation step size 0.1us, control period 20us, dead time 2us, coupled inductor self-inductance 15mH, mutual inductance 14.9985mH.

[0200] Figure 8 The figure shows the high-frequency circulating current when the duty cycle is 0.5 under the two-branch topology. Figures 9 to 17 The high-frequency circulating current conditions when the duty cycle is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 under the three-branch topology are shown respectively. Figures 18 to 20 The high-frequency circulation conditions of the four-branch, five-branch, and six-branch topologies are shown respectively when the duty cycle is 0.5.

[0201] Table 2 below shows the comparison results between the calculated and simulated values ​​of the high-frequency circulating currents in different branches.

[0202] Table 2 Calculated and simulated values ​​of high-frequency circulating currents in different branches

[0203] Branch number duty cycle Calculated value (mA) Simulated value (mA) Two branch duty cycle 0.5 41.669 43.42 Three branch duty cycle 0.1 14.815 13.27 Three branch duty cycle 0.2 29.631 29.26 Three branch duty cycle 0.3 44.446 44.26 Three branch duty cycle 0.4 49.384 48.89 Three branch duty cycle 0.5 49.384 48.89 Three branch duty cycle 0.6 49.384 48.89 Three branch duty cycle 0.7 44.446 44.26 Three branch duty cycle 0.8 29.631 29.45 Three branch duty cycle 0.9 14.815 13.29 Four branch duty cycle 0.5 83.333 82.50 Five branch duty cycle 0.5 106.662 106.0 Six branch duty cycle 0.5 152.763 151.2

[0204] By attaching Figure 8 To the attached Figure 20 Table 2 can verify the validity of the high-frequency circulating current calculation method provided by this application. In addition, according to the derived cascade coupled parallel multi-branch high-frequency circulating current expression, it can be obtained that the maximum amplitude of the high-frequency circulating current between branches increases with the increase of the number of branches and increases with the bus voltage V in It increases with the increase of , increases with the increase of switching period T, and decreases with the increase of choke coil self-inductance L.

[0205] According to the calculation formula of the maximum amplitude of high-frequency circulating current in each branch, we can get the following: Figure 21 The relationship curve between the maximum amplitude of the high-frequency circulating current of each branch and the coupling factor k is shown. Figure 21It can be seen that for two branches to six branches, when the branch number is less than four, the high-frequency circulating current amplitude decreases with the increase of k; when the branch number is equal to four, the high-frequency circulating current amplitude does not change with the change of k; when the branch number is greater than four, the high-frequency circulating current amplitude increases with the increase of k.

[0206] The specific implementation of the present application is described in detail above, and those skilled in the art can make some improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also belong to the protection scope of the claims of the present application.

Claims

1. A method for calculating high-frequency circulating current in a cascade coupled parallel structure of a motor simulator, characterized in that: The following steps are involved: S1, establishing an equivalent decoupling circuit model of each branch in the cascade coupled parallel structure based on the voltage relationship of each branch in the cascade coupled parallel structure of the motor simulator, wherein the equivalent decoupling circuit of each branch includes an equivalent voltage source and an equivalent leakage inductance connected in series, and the equivalent leakage inductance is determined based on the self-inductance and mutual inductance of each branch choke; S2, dividing a plurality of duty cycle intervals between 0 and 1, wherein the number of duty cycle intervals is equal to the number of branches in the cascade coupled parallel structure; S3, using the equivalent decoupling circuit model to calculate the high-frequency circulating current of each branch corresponding to the duty cycle of the modulation signal of the motor simulator in each duty cycle interval; Step S1 further includes the following steps: S11, establishing a voltage equation for each branch in the cascade coupled parallel structure; S12, jointly calculating and combining the voltage equations of each branch in the cascade coupled parallel structure to obtain an equivalent voltage source-leakage inductance relationship equation for each branch, wherein the equivalent voltage source-leakage inductance relationship equation has a polynomial including a coupling factor as a coefficient term, and the coupling factor is determined based on the self-inductance and mutual inductance of the choke corresponding to each branch; S13, establishing the equivalent decoupling circuit model based on the equivalent voltage source-leakage inductance relationship, wherein the equivalent voltage source and the equivalent leakage inductance in the equivalent decoupling circuit model are connected in series between the midpoint of each branch and the voltage output end of the cascade coupled parallel structure; S14, determining an expression for a current flowing through the equivalent leakage inductance and an expression for a voltage at a virtual node based on the equivalent decoupling circuit model, wherein the virtual node is a node between the equivalent voltage source and the equivalent leakage inductance.

2. The high-frequency circulating current calculation method according to claim 1, characterized in that: Step S3 is specifically: using the current expression flowing through the equivalent leakage inductance and the voltage expression at the virtual node, sequentially calculating the high-frequency circulating current of each branch corresponding to when the duty cycle of the modulation signal of the motor simulator is in each duty cycle interval.

3. The high-frequency circulating current calculation method according to claim 2, characterized in that: The following steps are also included: Based on the high-frequency circulating current calculation result, the variation of the amplitude of the high-frequency circulating current with the variation of the duty cycle of the modulation signal and the duty cycle of the modulation signal corresponding to the maximum amplitude of the high-frequency circulating current are determined.

4. The high-frequency circulating current calculation method according to any one of claims 1 to 3, characterized in that: The number of branches of the motor simulator cascade coupled parallel structure is 2 to 6.

5. The high-frequency circulating current calculation method according to claim 4, characterized in that: The self-inductance of the choke coils corresponding to each branch is equal, and the mutual inductance of the choke coils corresponding to each branch is equal; The coupling factor is the ratio of the mutual inductance to the self-inductance.

6. The high-frequency circulating current calculation method according to claim 5, characterized in that: When the number of branches of the cascade coupled parallel structure of the motor simulator is an odd number, the amplitude of the high-frequency circulating current is equal to the duty cycle of the modulation signal of the motor simulator. In the range When, increases with the increase of In the range remains unchanged, In the range When, decreases with the increase of is the number of branches of the cascade coupled parallel structure of the motor simulator; When the number of branches in the cascade coupled parallel structure of the motor simulator is even, the amplitude of the high-frequency circulating current is In the range When, increases with the increase of In the range When, decreases with the increase.

7. The high-frequency circulating current calculation method according to claim 5, characterized in that: When the duty cycle of the modulation signal of the motor simulator is 0.5, the amplitude of the high-frequency circulating current of each branch reaches a maximum value.

8. The high-frequency circulating current calculation method according to claim 7, characterized in that: When the number of branches in the cascade coupled parallel structure of the motor simulator is 2, the maximum amplitude of the high-frequency circulating current in each branch is: ， in, is the period of the modulation signal, is the bus voltage, is the coupling factor, 、 are the mutual inductance and self-inductance of the choke coils corresponding to each branch; When the number of branches in the cascade coupled parallel structure of the motor simulator is 3, the maximum amplitude of the high-frequency circulating current in each branch is: ； When the number of branches of the motor simulator cascade coupled parallel structure is 4, the maximum amplitude of the high-frequency circulating current of each branch is: ； When the number of branches of the motor simulator cascade coupled parallel structure is 5, the maximum amplitude of the high-frequency circulating current of each branch is: ； When the number of branches of the motor simulator cascade coupled parallel structure is 6, the maximum amplitude of the high-frequency circulating current of each branch is: 。 9. The high-frequency circulating current calculation method according to claim 4, characterized in that: The high-frequency circulating current increases with the increase of the number of branches, increases with the increase of bus voltage, increases with the increase of switching period, and decreases with the increase of choke coil self-inductance.

Images