High-frequency circulating current calculation method for cascade coupling parallel structure of motor simulator

Abstract

The invention provides a high-frequency circulating current calculation method for a motor simulator cascade coupling parallel structure, and the method comprises the following steps: building an equivalent decoupling circuit model of each branch in the cascade coupling parallel structure based on the voltage relation of each branch in the motor simulator cascade coupling parallel structure, wherein the equivalent decoupling circuit of each branch comprises an equivalent voltage source and an equivalent leakage inductor which are connected in series, and the equivalent leakage inductor is determined based on self-inductance and mutual inductance of a choking coil of each branch; a plurality of duty ratio intervals are divided between 0 and 1, and the number of the duty ratio intervals is equal to the number of the branches in the cascade coupling parallel structure; and using the equivalent decoupling circuit model to calculate the high-frequency circulation of each corresponding branch when the duty ratio of the modulation signal of the motor simulator is in each duty ratio interval. According to the method provided by the invention, the high-frequency circulating current of the cascade coupling parallel structure of the motor simulator can be accurately calculated, and effective support is provided for targeted design of a high-frequency circulating current suppression scheme.

Description

Technical Field

[0001] This application belongs to the technical field of electric motor simulator control, and particularly relates to a high-frequency circulating current calculation method for a cascaded coupled parallel structure of an electric motor simulator. Background Art

[0002] An Electric Motor Emulation (EME) is a test equipment for the electric drive system of new energy vehicles. Since it can conduct drive system tests without an actual motor and can simulate various working conditions and perform extreme performance tests such as high temperature and low temperature, it can significantly shorten the R & D cycle of the electric drive system.

[0003] Existing electric 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; at the same time, a carrier phase-shifting algorithm is used to generate multilevels, which can improve the control frequency and reduce the output current harmonics. However, this will cause the switching states of each branch to be inconsistent, generating high-frequency differential-mode circulating current close to the switching frequency.

[0004] High-frequency circulating current will have many adverse effects on the EME system. For example, it will increase the output current harmonics, increase the load of the switching devices, reduce their service life and increase the energy loss, and cause the system efficiency to decrease. In order to suppress the high-frequency circulating current between branches, EME mostly adopts a cascaded coupled parallel structure and uses a common-mode choke to suppress the differential-mode circulating current while hardly affecting the common-mode current. However, the simulation and measurement results show that in the cascaded 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 cause the choke to saturate and lose its suppression ability, which will limit the expansion of the number of branches in the cascaded coupled parallel structure and limit the improvement of EME performance. Therefore, it is necessary to deeply explore the variation 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 its characteristics. However, there has been no report on relevant research work so far. Summary of the Invention

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

[0006] S1, establish an equivalent decoupled circuit model for each branch in the cascaded coupled parallel structure based on the voltage relationship of each branch in the cascaded coupled parallel structure of the electric motor simulator. The equivalent decoupled 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 the chokes of each branch;

[0007] S2. Divide multiple duty cycle intervals between 0 and 1, where the number of duty cycle intervals is equal to the number of branches in the cascaded coupled parallel structure;

[0008] S3. Use the equivalent decoupling circuit model to calculate 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.

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

[0010] S11. Establish the voltage equations of each branch in the cascaded coupled parallel structure;

[0011] S12. Simultaneously combine the voltage equations of each branch in the cascaded coupled parallel structure to obtain the equivalent voltage source - leakage inductance relationship of each branch, where the equivalent voltage source - leakage inductance relationship uses a polynomial containing coupling factors as the coefficient term, and the coupling factor is determined based on the self-inductance and mutual inductance of the choke coils corresponding to each branch;

[0012] S13. Based on the equivalent voltage source - leakage inductance relationships of each branch, establish the equivalent decoupling circuit model, where the equivalent voltage source and equivalent leakage inductance in the equivalent decoupling circuit model are connected in series between the midpoint of each branch and the voltage output terminal of the cascaded coupled parallel structure;

[0013] S14. Based on the equivalent decoupling circuit model, determine the current expression flowing through the equivalent leakage inductance and the voltage expression at the virtual node, where the virtual node is the node between the equivalent voltage source and the equivalent leakage inductance.

[0014] Furthermore, step S3 is specifically: Use the current expression flowing through the equivalent leakage inductance and the voltage expression at the virtual node to sequentially calculate 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.

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

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

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

[0018] Preferably, the self-inductances of the choke coils corresponding to each branch are all equal, and the mutual inductances of the choke coils corresponding to each branch are all 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 cascade-coupled 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], where N is the number of branches of the motor simulator cascade-coupled parallel structure; when the number of branches of the motor simulator cascade-coupled 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 in each branch has a maximum value.

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

[0022]

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

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

[0025]

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

[0027]

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

[0029]

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

[0031]

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

[0033] A method for calculating the high-frequency circulating current of a cascaded and parallel structure of motor simulators provided by an embodiment of the present application establishes an equivalent decoupled circuit model for each branch based on the voltage equations of each branch, divides different duty cycle intervals according to the number of branches, and then obtains a quantitative expression when the modulation signal is in different duty cycle intervals through the equivalent decoupled circuit model. Through the method provided by the present application, it is possible to quantitatively analyze the factors affecting the high-frequency circulating current in the cascaded and parallel structure of motor simulators and the variation law of the high-frequency circulating current amplitude, providing a theoretical basis for subsequent research on high-frequency circulating current suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the architecture of a cascaded and 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 cascaded and parallel structure;

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

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

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

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

[0040] Figure 3 It is a flowchart of the method for calculating the high-frequency circulating current of the cascaded and parallel structure of motor simulators provided by the embodiment of the present application;

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

[0042] Figure 5 It is a schematic diagram of the change of the voltage of each branch of the equivalent decoupled 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 change of the voltage of each branch of the equivalent decoupled circuit model of three branches when the duty cycle is in the interval (1 / 3, 2 / 3);

[0044] Figure 7 Schematic diagram of the voltage variation of each branch of the equivalent decoupling circuit model with three branches when the duty cycle is in the range of [2 / 3, 1).

[0045] Figure 8 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with two branches when the duty cycle is equal to 0.5.

[0046] Figure 9 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.1.

[0047] Figure 10 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.2.

[0048] Figure 11 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.3.

[0049] Figure 12 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.4.

[0050] Figure 13 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.5.

[0051] Figure 14 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.6.

[0052] Figure 15 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.7.

[0053] Figure 16 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.8.

[0054] Figure 17 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with three branches when the duty cycle is equal to 0.9.

[0055] Figure 18 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with four branches when the duty cycle is equal to 0.5.

[0056] Figure 19Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with five branches when the duty cycle is equal to 0.5;

[0057] Figure 20 Schematic diagram of the variation of the high-frequency circulating current in the first branch of the equivalent decoupling circuit model with six branches when the duty cycle is equal to 0.5;

[0058] Figure 21 Schematic diagram of the influence of the coupling factor on the amplitude of the high-frequency circulating current in different branches. Detailed implementation manners

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

[0060] In the description of the embodiments of the present application, it should be noted that if terms such as "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the products in the embodiments of the present application are usually placed during use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to the present application. In addition, in the description of the present application, in order to distinguish different units, the terms "first", "second", etc. are used in this specification, but these are not limited by the manufacturing order and cannot be understood as indicating or implying relative importance. In the detailed description and claims of the present application, their names may be different.

[0061] The terms in this specification are used to describe the embodiments of the present application, but are not intended to limit the present application. It should also be noted that unless otherwise clearly defined and limited, if terms such as "set", "connected", "coupled" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, and it can be the internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be specifically understood.

[0062] Figure 1 Shows a schematic diagram of the cascaded and parallel structure of an electric motor emulator (EME) known to those skilled in the art, as Figure 1 shown. For any phase of the electric motor emulator, multiple branches (such as Figure 1 using three branches) can be connected in parallel, and a common-mode choke is used to suppress the differential-mode circulating current topology.

[0063] Figures 2a to 2eThe high-frequency circulating current conditions in the cascaded coupling topology of the EME are respectively shown when two branches, three branches, four branches, five branches, and six branches are adopted. Referring to the respective figures, it can be seen that the high-frequency circulating current increases with the increase in the number of branches. Excessive circulating current will cause the choke coil to saturate and lose its suppression ability, which will limit the expansion of the number of branches in the cascaded parallel structure and the improvement of the EME performance.

[0064] Since there is currently no research on the mechanism of high-frequency circulating current between branches in the cascaded parallel structure of the motor simulator, there is a lack of an accurate calculation method for the high-frequency circulating current between branches, and it is impossible to quantitatively analyze the influencing factors of the high-frequency circulating current, let alone reduce the circulating current targeted.

[0065] To solve the above problems, the present application provides a method for calculating the high-frequency circulating current in the cascaded parallel structure of a motor simulator, as Figure 3 shown, the method includes the following steps:

[0066] S1. Based on the voltage relationships of the branches in the cascaded parallel structure of the motor simulator, establish an equivalent decoupled circuit model for each branch in the cascaded parallel structure, where the equivalent decoupled 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 the choke coils of each branch;

[0067] S2. Divide multiple duty cycle intervals between 0 and 1, where the number of duty cycle intervals is equal to the number of branches in the cascaded parallel structure;

[0068] S3. Use the equivalent decoupled 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.

[0069] The implementation manners of the above steps will be described in detail below in combination with specific drawings and specific embodiments.

[0070] <Establishing an equivalent decoupled circuit model>

[0071] In step S1, according to the voltage relationships of the branches in the cascaded parallel structure of the motor simulator, an equivalent decoupled circuit model for each branch is established, which serves as the basis for quantitatively calculating the high-frequency circulating current of each subsequent branch under the control of modulation signals with different duty cycles.

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

[0073] S11. Establish the voltage equations of the branches in the cascaded parallel structure.

[0074] Taking the cascaded parallel structure of each phase of the motor simulator including three branches as an example, the establishment process of the voltage equations of each branch will be described below:

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

[0076]

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

[0078] S12, jointly and merging the voltage equations of each branch in the cascade coupled parallel structure to obtain an equivalent voltage source-leakage inductance relationship of each branch, wherein the equivalent voltage source-leakage inductance relationship uses 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 corresponding to each branch.

[0079] Still taking three branches as an example, according to formula (1), by adding the voltage equations of the second and third branches, we can get formula (2):

[0080]

[0081] Substitute (2) into the branch voltage equation and define the coupling factor: The branch voltage equation including the coupling factor k can be obtained as shown in formula (3):

[0082]

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

[0084] From (3), we can see that V L1 It can be considered as consisting of two parts: one part is caused by the change of the current i1 through the self-inductance L, and its coefficient is a polynomial containing k The other part consists of the voltage of the second and third branches (V L2 +V L3 ) whose coefficients are polynomials containing k In this application, Considered as equivalent leakage inductance L k ,Will If it is regarded as an equivalent voltage source, the voltage equation of each branch in the form of formula (3) is also called the equivalent voltage source-leakage inductance relationship of each branch.

[0085] S13. Based on the equivalent voltage source-drain inductance relationships, establish the equivalent decoupling circuit model, where the equivalent voltage source and equivalent drain inductance in the equivalent decoupling circuit model are connected in series between the midpoint of each branch and the voltage output terminal of the cascaded coupled parallel structure.

[0086] Still taking the three-branch case as an example for illustration, using the equivalent voltage source-drain inductance relationships of each branch in the form of Equation (3), the three-branch equivalent decoupling circuit model as shown can be established. Figure 4 In each branch, there is an equivalent voltage source and an equivalent drain inductance connected in series between the midpoint of the branch and the voltage output terminal (the output voltage is V o ) of the entire cascaded coupled parallel structure, and their voltage values and inductance values are determined by Equation (3).

[0087] S14. Based on the equivalent decoupling circuit model, determine the current expression flowing through the equivalent drain inductance and the voltage expression at the virtual node, where the virtual node is the node between the equivalent voltage source and the equivalent drain inductance.

[0088] From Figure 4 the equivalent decoupling circuit model shown, the expressions for the currents flowing through the respective equivalent inductances are as shown in Equation (5):

[0089]

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

[0091]

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

[0093] <Calculate high-frequency circulating current in intervals>

[0094] From Equations (5) and (6), it can be seen that in the decoupling equivalent circuit model of each branch, the interaction between the chokes is decoupled and processed as an equivalent voltage source and an equivalent drain inductance. Among them, the voltage and current changes at the virtual node of each branch are affected by the voltage changes of both this branch and other branches. 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 each branch is different, and it is necessary to discuss in intervals.

[0095] Specifically, in step S2, according to the number of branches in the cascaded parallel structure, a plurality of equal-duty-cycle intervals are divided between 0 and 1. For example, when three branches are adopted, a total of three duty-cycle intervals are divided: 0 < D ≤ 1 / 3, 1 / 3 < D < 2 / 3, 2 / 3 ≤ D < 1, where D is the duty cycle of the modulation signal. Another example is that when two branches are adopted, the two divided duty-cycle intervals are 0 < D ≤ 1 / 2 and 1 / 2 < D < 1 respectively. When other numbers of branches are adopted, a similar method is used to divide the same number of duty-cycle intervals as the number of branches.

[0096] Specifically, in step S3, equations (5) and (6) are respectively used to calculate the high-frequency circulating currents of each branch corresponding to when the duty cycle of the modulation signal of the motor simulator is in each duty-cycle interval.

[0097] Still taking three branches as an example, the calculation method of the high-frequency circulating current in each duty-cycle interval is described below.

[0098] 1) 0 < D ≤ 1 / 3

[0099] When the duty cycle D is in the interval (0, 1 / 3], the voltage changes of each branch are as Figure 5 shown, where V in represents the bus voltage (i.e., U DC ), and T is the switching period. It can be seen through Figure 5 that the voltages of each branch do not overlap with each other, and the voltages and currents of each branch change sequentially in the 6 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 in 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 in 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 change amount in this stage can be expressed as:

[0110]

[0111] For stage ④, V1, V2, V3 and V o satisfy the following equation:

[0112]

[0113] The current change amount in this stage can be expressed as: Δi4 = 0.

[0114] For stage ⑤, V1, V2, V3 and V o satisfy the following equation:

[0115]

[0116] The current change amount in this stage can be expressed as:

[0117]

[0118] For stage ⑥, V1, V2, V3 and V o satisfy the following equation:

[0119]

[0120] The current change amount in this stage can be expressed as: Δi6 = 0.

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

[0122] When the duty cycle D is in the interval (1 / 3, 2 / 3), the voltage changes of each branch are as Figure 6 shown. It can be seen through Figure 6 that the voltages of each branch overlap with each other, and the voltages and currents of each branch change successively in the 6 stages divided by 0, DT, T.

[0123] For stage ①, V1, V2, V3 and V o satisfy the following equation:

[0124]

[0125] The current change amount in this stage can be expressed as:

[0126]

[0127] For stage ②, V1, V2, V3 and V oSatisfy the following equations:

[0128]

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

[0130]

[0131] For stage ③, V1, V2, V3 and V o Satisfy the following equations:

[0132]

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

[0134]

[0135] For stage ④, V1, V2, V3 and V o Satisfy the following equations:

[0136]

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

[0138]

[0139] For stage ⑤, V1, V2, V3 and V o Satisfy the following equations:

[0140]

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

[0142]

[0143] For stage ⑥, V1, V2, V3 and V o Satisfy the following equations:

[0144]

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

[0146]

[0147] 3) 2 / 3 ≤ D < 1

[0148] When the duty cycle D is in the interval [2 / 3, 1), the voltage changes of each branch are as Figure 7 shown. Through Figure 7 it can be seen that the voltages of each branch overlap with each other, and the voltages and currents of each branch are at 0, DT, T

[0149] Change successively in the six divided stages.

[0150] For stage ①, V1, V2, V3, and V o Satisfy the following equation:

[0151]

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

[0153] Δi1 = 0.

[0154] For stage ②, V1, V2, V3, and V o Satisfy the following equation:

[0155]

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

[0157]

[0158] For stage ③, V1, V2, V3, and V o Satisfy the following equation:

[0159]

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

[0161] Δi3 = 0.

[0162] For stage ④, V1, V2, V3, and V o Satisfy the following equation:

[0163]

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

[0165]

[0166] For stage ⑤, V1, V2, V3, and V o Satisfy the following equation:

[0167]

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

[0169] Δi5 = 0.

[0170] For stage ⑥, V1, V2, V3, and V oSatisfy the following equation:

[0171]

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

[0173]

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

[0175] After obtaining the expressions of the high-frequency circulating current when the duty cycle of the modulation signal is in different intervals through the above steps, based on the calculation results of the high-frequency circulating current, the variation of the amplitude of the high-frequency circulating current with the duty cycle of the modulation signal can be further determined, as well as the duty cycle of the modulation signal corresponding to the maximum value of the amplitude of the high-frequency circulating current.

[0176] Still taking the three-branch circuit as an example to illustrate the specific analysis steps:

[0177] 1) 0 < D ≤ 1 / 3

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

[0179]

[0180] Observing equation (19), it can be seen 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 its amplitude reaches the maximum value

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

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

[0183]

[0184] After combining like terms, the terms containing D are eliminated, and finally we get:

[0185]

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

[0187] 3) 2 / 3 ≤ D < 1

[0188] When D ∈ [2 / 3, 1), it can be known from Equations (16) to (18) that the high-frequency circulating current rises in stages ② and ④, falls in stage ⑥, and remains unchanged in stages ①, ③, and ⑤. Moreover, the sum of the rising amplitudes in stages ② and ④ is equal to the falling amplitude in stage ⑥. Therefore, when D ∈ [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, that is:

[0189]

[0190] It can be seen from Equation (21) that when the high-frequency circulating current is in the interval of D ∈ [2 / 3, 1), its amplitude decreases as D increases, and when D = 2 / 3, its amplitude is the maximum value

[0191] Based on the same method, the equivalent decoupling circuit models corresponding to two-branch, four-branch, five-branch, and six-branch are established respectively, and the high-frequency circulating current and its amplitude change of each branch are calculated and analyzed when D is in different duty cycle intervals. The conclusions are shown in Table 1 below:

[0192] Table 1. Calculation results of high-frequency circulating current of cascade-coupled parallel structure when the number of branches is 2 - 6

[0193]

[0194]

[0195] It can be seen from Table 1 that for the above analysis results of two-branch to four-branch, when the number of branches of the cascade-coupled parallel structure of the motor simulator is odd, the amplitude of the high-frequency circulating current increases as D increases 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 as D increases when D is in the interval [(N + 1) / 2N, 1], where N is 3 or 5;

[0196] When the number of branches of the cascaded 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 regardless of 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 in each branch has a maximum value.

[0198] <Specific Embodiment 1>

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

[0200] Figure 8 The high-frequency circulating current situation at a duty cycle of 0.5 in the two-branch topology structure is shown. Figures 9 to 17 The high-frequency circulating current situations at duty cycles of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 in the three-branch topology structure are respectively shown. Figures 18 to 20 The high-frequency circulating current situations of the four-branch, five-branch, and six-branch topology structures at a duty cycle of 0.5 are respectively shown.

[0201] Table 2 below shows the comparison results of the calculated values and simulation values of the high-frequency circulating current in different branches.

[0202] Table 2 Calculated values and simulation values of the high-frequency circulating current in different branches

[0203] Number of branches, duty cycle Calculated value (mA) Simulated value (mA) Duty cycle of two branches: 0.5 41.669 43.42 Duty cycle of three branches: 0.1 14.815 13.27 Duty cycle of three branches: 0.2 29.631 29.26 Duty cycle of three branches: 0.3 44.446 44.26 Duty cycle of three branches: 0.4 49.384 48.89 Duty cycle of three branches: 0.5 49.384 48.89 Duty cycle of three branches: 0.6 49.384 48.89 Duty cycle of three branches: 0.7 44.446 44.26 Duty cycle of three branches: 0.8 29.631 29.45 Duty cycle of three branches: 0.9 14.815 13.29 Duty cycle of four branches: 0.5 83.333 82.50 Duty cycle of five branches: 0.5 106.662 106.0 Duty cycle of six branches: 0.5 152.763 151.2

[0204] Through the appendix Figure 8 To the appendix Figure 20 And Table 2, the effectiveness of the high-frequency circulating current calculation method provided by this application can be verified. In addition, according to the derived high-frequency circulating current expression of the cascaded coupled parallel multi-branch, 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, increases with the increase of the bus voltage V in And increases with the increase of the switching period T, and decreases with the increase of the self-inductance L of the choke coil.

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

[0206] The specific implementation manners of the present application have been described in detail above. For those skilled in the art of this technology, without departing from the principle of the present application, several improvements and modifications can still be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A high-frequency circulating current calculation method for a cascaded and parallel structure of a motor simulator, characterized in that It includes the following steps: S1. Based on the voltage relationships of each branch in the cascaded coupled parallel structure of the motor simulator, establish an equivalent decoupled circuit model for each branch in the cascaded coupled parallel structure. The equivalent decoupled circuit of each branch includes an equivalent voltage source and an equivalent leakage inductance connected in series. The equivalent leakage inductance is determined based on the self-inductance and mutual inductance of the choke coils of each branch; S2. Divide multiple duty cycle intervals between 0 and 1, where the number of duty cycle intervals is equal to the number of branches in the cascaded coupled parallel structure; S3. Use the equivalent decoupled circuit model to calculate the high-frequency circulating currents of the corresponding branches when the duty cycle of the modulation signal of the motor simulator is in each duty cycle interval.

2. The high-frequency circulating current calculation method according to claim 1, characterized in that Step S1 further includes the following steps: S11. Establish the voltage equations of each branch in the cascaded coupled parallel structure; S12. Simultaneously combine the voltage equations of each branch in the cascaded coupled parallel structure to obtain the equivalent voltage source - leakage inductance relationship of each branch. Among them, the equivalent voltage source - leakage inductance relationship uses a polynomial containing coupling factors as the coefficient term, and the coupling factor is determined based on the self-inductance and mutual inductance of the choke coils corresponding to each branch; S13. Based on the equivalent voltage source - leakage inductance relationships of each branch, establish the equivalent decoupled circuit model. Among them, the equivalent voltage source and equivalent leakage inductance in the equivalent decoupled circuit model are connected in series between the midpoint of each branch and the voltage output terminal of the cascaded coupled parallel structure; S14. Based on the equivalent decoupled circuit model, determine the current expression flowing through the equivalent leakage inductance and the voltage expression at the virtual node, where the virtual node is the node between the equivalent voltage source and the equivalent leakage inductance.

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

4. The high-frequency circulating current calculation method according to claim 3, characterized in that It further includes the following steps: Based on the high-frequency circulating current calculation results, determine the variation of the amplitude of the high-frequency circulating current with the duty cycle of the modulation signal, and the duty cycle of the modulation signal corresponding to the maximum value of the amplitude of the high-frequency circulating current.

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

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

7. The high-frequency circulating current calculation method according to claim 6, characterized in that When the number of branches of the cascaded parallel structure of the motor simulator is odd, the amplitude of the high-frequency circulating current increases with the increase of the duty ratio 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], where N is the number of branches of the cascaded parallel structure of the motor simulator; When the number of branches of the cascaded 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].

8. The high-frequency circulating current calculation method according to claim 6, wherein When the duty ratio of the modulation signal of the motor simulator is 0.5, the amplitude of the high-frequency circulating current in each branch has a maximum value.

9. The high-frequency circulating current calculation method according to claim 8, wherein When the number of branches of the cascaded parallel structure of the motor simulator is 2, the maximum value of the amplitude of the high-frequency circulating current in each branch is: where T is the period of the modulation signal, V in is the bus voltage, k = M / L is the coupling factor, and M and L are the mutual inductance and self-inductance of the choke coils corresponding to each branch, respectively; When the number of branches of the cascaded parallel structure of the motor simulator is 3, the maximum value of the amplitude of the high-frequency circulating current in each branch is: When the number of branches of the cascaded parallel structure of the motor simulator is 4, the maximum value of the amplitude of the high-frequency circulating current in each branch is: When the number of branches of the cascaded parallel structure of the motor simulator is 5, the maximum value of the amplitude of the high-frequency circulating current in each branch is: When the number of branches of the cascaded parallel structure of the motor simulator is 6, the maximum value of the amplitude of the high-frequency circulating current in each branch is:

10. The high-frequency circulating current calculation method according to claim 5, wherein 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.

Images