High-frequency zero-sequence circulating current calculation method of three-phase integrated parallel multi-level motor simulator and motor simulator design method

Abstract

The application provides a high-frequency zero-sequence circulating current calculation method of a three-phase integrated parallel multi-level motor simulator, and a motor simulator design method. The calculation method comprises the following steps: determining equivalent circuit models of three-phase branches which are parallel wound on the same choke coil in the three-phase integrated parallel multi-level motor simulator, based on voltage relationships of the three-phase branches; determining high-frequency circulating current variation amounts of the three-phase branches which are parallel wound on each choke coil in seven time periods of a same switching cycle, based on the equivalent circuit models; and determining high-frequency zero-sequence circulating current variation amounts and peak values corresponding to each choke coil, based on the high-frequency circulating current variation amounts of the three-phase branches which are parallel wound on each choke coil. The calculation method provided by the application can accurately obtain high-frequency zero-sequence circulating currents existing in a magnetic ring topology of three-phase parallel wound parallel multi-level motor simulators.

Description

Technical Field

[0001] This application belongs to the field of motor simulator design technology, specifically relating to a high-frequency zero-sequence circulating current calculation method for a three-phase integrated parallel multilevel motor simulator, and a design method for a motor simulator. Background Technology

[0002] Electric motor emulation (EME) is a testing equipment for electric drive systems in new energy vehicles. It is widely used because it can comprehensively test motor controllers without requiring a real motor, and can simulate various extreme and complex operating conditions and perform fault condition tests, significantly shortening the R&D cycle of electric drive systems. Existing motor simulators mostly adopt a topology consisting of multiple parallel branches per phase, i.e., parallel multilevel motor simulators. By increasing the number of parallel branches, the maximum port current of a single phase can be expanded, increasing the equivalent switching frequency and load capacity. Simultaneously, a carrier phase-shifting algorithm is used to generate multilevel signals, thereby improving the simulation accuracy of the motor.

[0003] It is known that such parallel multilevel motor simulators, while increasing the equivalent switching frequency, introduce new circulating current paths and generate high-frequency circulating currents, thereby increasing the load and energy loss of switching devices, reducing system efficiency and device lifespan, and causing problems such as inductor saturation and deterioration of system output accuracy. Although the high-frequency circulating current can be suppressed by the choke structure of the cascaded coupling topology, the applicant has demonstrated in Chinese invention patent CN120263025A that when each phase adopts a cascaded coupling topology, the high-frequency circulating current will still increase with the increase of the number of branches, thus greatly limiting the prospect of expanding the number of parallel branches in each phase.

[0004] To address the aforementioned issues, the applicant proposed a three-phase integrated magnetic ring structure for a parallel multilevel motor simulator in its earlier Chinese invention patent application CN121000079A. This structure aims to overcome the problem of increased high-frequency circulating current as the number of parallel branches increases. However, the relationship between the high-frequency circulating current and various circuit parameters under the new three-phase integrated magnetic ring structure has not yet been thoroughly analyzed. Summary of the Invention

[0005] The first aspect of this application provides a method for calculating high-frequency zero-sequence circulating current in a three-phase combined parallel multilevel motor simulator, comprising the following steps: Based on the voltage relationship of the three-phase branches wound in parallel on the same choke coil in the three-phase combined parallel multilevel motor simulator, the equivalent circuit model of each three-phase branch wound in parallel on each choke coil is determined. Based on the equivalent circuit model, the high-frequency circulating current variation of each of the three-phase branches wound in parallel on each choke coil in the seven time periods of the same switching cycle is determined. Based on the high-frequency circulating current variation of the three-phase branches wound in parallel on each choke, the high-frequency zero-sequence circulating current variation and peak value corresponding to each choke are determined.

[0006] Preferably, the equivalent circuit model of each of the three-phase branches wound in parallel on any choke coil consists of an equivalent DC voltage source and an equivalent inductor. The voltage of any corresponding equivalent DC voltage source is determined by the voltage difference between the other two phase branches across the choke coil and the self-inductance and mutual inductance of the choke coil. The inductance value of the corresponding equivalent inductor is determined by the self-inductance and mutual inductance of the choke coil.

[0007] Furthermore, the seven time periods of the same switching cycle are respectively Time period Time period Time period Time period Time period Time period and Time period, among which Time period Time period and The time periods correspond to the duration during which the midpoint of each of the three-phase branches with the same branch number remains at a high level, and and , and They are symmetrically distributed along the time axis. and On both sides of the center position, This represents the duration of the switching cycle.

[0008] Furthermore, for any choke coil, the change in its corresponding high-frequency zero-sequence circulating current is obtained by adding the changes in the high-frequency circulating current of each of the three-phase branches wound in parallel on the choke coil.

[0009] Furthermore, for any first The expression for the peak value of the high-frequency zero-sequence circulation change corresponding to each choke coil. for: , in, , The first The self-sensing and mutual induction of a choke loop, This is the DC bus voltage.

[0010] A second aspect of this application provides a design method for a motor simulator, the design method comprising the following steps: Obtain the design specifications and inductance parameters of the motor simulator. The design specifications include the values ​​of bus voltage, phase current or rated power, and the inductance parameters include the self-inductance and mutual inductance of each choke. Based on the design specifications of the motor simulator, the total number of parallel branches included in each phase inverter circuit of the motor simulator is determined. Based on the inductance parameters, the peak value of the high-frequency circulating current change corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches is calculated and recorded as the first value. The peak value of the high-frequency zero-sequence circulating current change corresponding to each choke coil in the three-phase combined parallel multilevel simulator is calculated and recorded as the second value. The second value is calculated based on the aforementioned high-frequency zero-sequence circulating current calculation method of the three-phase combined parallel multilevel motor simulator. If the first value is less than the second value, the motor simulator is designed as a cascaded coupled parallel multilevel motor simulator; otherwise, the motor simulator is designed as a three-phase combined parallel multilevel motor simulator.

[0011] Preferably, the peak value of the high-frequency circulating current change corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches is calculated through the following steps: Determine the expression for the high-frequency circulating current change of a single branch in a cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches; Vector synthesis is performed based on the phase shift relationship between adjacent branches wound on each choke coil to determine the high-frequency circulating current change and its peak value corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches.

[0012] The high-frequency zero-sequence circulating current calculation method for a three-phase integrated parallel multilevel motor simulator provided in this application is based on the voltage relationship between the three-phase branches wound in parallel on each choke coil under the three-phase integrated topology. An equivalent circuit model of each branch is established, and according to the level change characteristics of the three branches with the same sequence number on the same choke coil in the same switching cycle, the peak value expression of the high-frequency zero-sequence circulating current of the choke coil is constructed. This enables quantitative analysis of its generation factors and amplitude variation law, and provides a theoretical basis for subsequent high-frequency zero-sequence circulating current suppression research. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the a-phase inverter circuit topology of a conventional cascaded-coupled parallel multilevel motor simulator. Figure 2 For a cascaded coupled parallel multilevel motor simulator, the three phases are respectively cascaded coupled and wound. A schematic diagram of the winding method of a magnetic ring structure; Figure 3 This is a schematic diagram of the topology of a three-phase combined parallel multilevel motor simulator; Figure 4 A schematic diagram of the winding method of a three-phase combined parallel wound magnetic ring for a three-phase combined parallel multilevel motor simulator; Figure 5 This is a flowchart of a high-frequency zero-sequence circulating current calculation method for a three-phase combined parallel multilevel motor simulator provided in the embodiments of this application; Figure 6 A schematic diagram showing the voltage relationship of a three-phase branch with each choke coil wound in parallel. Figure 7 This is a schematic diagram of the equivalent circuit model of each branch in the three-phase combined parallel multilevel motor simulator provided according to the embodiments of this application. Figure 8 This is a schematic diagram of the midpoint potential waveform of each of the three-phase 1-branch according to the embodiments of this application, and a schematic diagram showing the combination. Figure 9 This is a schematic diagram of different midpoint potential combinations of a three-phase 1-branch according to an embodiment of this application; Figure 10 This is a schematic diagram comparing the peak value of the high-frequency zero-sequence circulation change calculated using the method of this application with the simulated value in a specific embodiment; Figure 11 This is a schematic diagram comparing the peak values ​​of high-frequency circulating current changes corresponding to each choke in a cascaded coupled topology and a three-phase combined topology when the number of parallel branches is different, in a specific embodiment. Figure 12 This is a flowchart of a motor simulator design method provided according to an embodiment of this application. Detailed Implementation

[0014] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0015] In the description of the embodiments of this application, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, in the description of this 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, nor should they be construed as indicating or implying relative importance. Their names may differ in the detailed description and claims of this application.

[0016] Figure 1 This is a topology of the a-phase inverter circuit for a conventional cascaded-coupled parallel multilevel motor simulator. Figure 2 This illustrates the winding method of the cascaded coupled magnetic ring structure for each of the three phases in this cascaded coupled parallel multilevel motor simulator, such as... Figure 1 , Figure 2 As shown, in this cascaded coupled motor simulator, each phase... The midpoints of the parallel branches are wrapped together in a cascaded manner. On a choke ring, to form A cascaded, coupled inductor structure in the form of a magnetic ring, wherein the wires leading from the midpoint of the first branch are sequentially wound around the first and second chokes; the wires leading from the midpoint of the second branch are sequentially wound around the second and third chokes; and the wires leading from the midpoints of the remaining branches are wound around two adjacent chokes in the same manner, until the last choke... The wires drawn from the midpoint of the branch are sequentially wound around the first... On each choke and the first choke, the phases of each... The wires from each branch are connected together after being wound around two choke coils, thus forming a three-phase output current. , as well as .

[0017] The applicant disclosed a method in Chinese invention patent CN120263025A that is capable of [processing] each phase in a cascaded coupled motor simulator. Quantitative calculations of the high-frequency parallel branch circulating currents in the choke coils of cascaded coupled parallel branches reveal that, under this cascaded coupling topology, the high-frequency parallel branch circulating current in any phase circuit increases with the total number of branches. The correlation between the high-frequency circulating current and the total number of branches increases with the increase of the number of branches, which makes it impossible to expand the total number of branches per phase according to the simulation requirements of high power or high current conditions, greatly limiting its application prospects.

[0018] To this end, the same applicant disclosed a schematic diagram of the topology of a three-phase integrated parallel multilevel motor simulator in Chinese invention patent CN121000079A, as follows: Figure 3 , Figure 4 As shown, this motor simulator changes the phase of each phase in the cascaded coupled motor simulator. A parallel branch and The choke coils are cascaded and coupled together, and the wires from each branch of the three-phase inverter circuit are wound together in a three-phase parallel configuration. The high-frequency circulating current in each branch is effectively reduced by using a choke coil. Experimental and simulation results prove that this three-phase parallel winding method can ensure that the high-frequency circulating current flowing through the choke coil does not increase with the increase of the total number of parallel branches in each phase inverter circuit.

[0019] However, the aforementioned publicly available information does not address... Quantitative analysis of the high-frequency zero-sequence circulating current in the three-phase branch wound on the choke coil is not possible. Therefore, it is impossible to accurately estimate the amplitude of the high-frequency zero-sequence circulating current based on hardware parameters such as choke coil inductance and mutual inductance, so as not to provide an effective reference for the design of motor simulator.

[0020] To address the aforementioned problems, this application provides a method for calculating the high-frequency zero-sequence circulating current of a three-phase combined parallel multilevel motor simulator through several embodiments, for use in calculating... Figure 3 The high-frequency zero-sequence circulating current of each branch of the three-phase combined parallel multilevel inverter shown is accurately calculated. The calculation results can be used as the basis for designing a parallel multilevel motor simulator, thereby optimizing the performance of the motor simulator.

[0021] Figure 5 A flowchart illustrating this calculation method is shown, as follows: Figure 5 As shown, the calculation method includes the following steps: Step S1: Based on the voltage relationship of the three-phase branches wound in parallel on the same choke coil in the three-phase combined parallel multilevel motor simulator, determine the equivalent circuit model of each of the three-phase branches wound in parallel on each choke coil. Step S2: Based on the equivalent circuit model, determine the high-frequency circulating current variation of each of the three-phase branches wound in parallel on each choke coil during the seven time periods of the same switching cycle. Step S3: Based on the high-frequency circulating current variation of the three-phase branches wound in parallel on each choke, determine the high-frequency zero-sequence circulating current variation and peak value corresponding to each choke.

[0022] The following, in conjunction with the accompanying drawings, provides a detailed explanation of the specific implementation of each step in this calculation method.

[0023] <Establish equivalent circuit models for the three-phase branches connected in parallel and wound on the same choke coil> Step S1 is used to establish the equivalent circuit model of each of the three-phase branches on each choke coil, which provides the basis for the high-frequency zero-sequence circulating current calculation of each branch described later.

[0024] like Figure 3 and Figure 4 As shown, when a branch is extracted from each phase of a three-phase parallel multi-level inverter structure and wound in parallel around the same choke coil to form a three-phase integrated magnetic ring structure, the wires on each choke coil do not behave as... Figure 1 , Figure 2 Instead of being cascaded as shown, they are wound in parallel around the same choke coil to form three parallel inductors, which form corresponding voltage relationships through their self-inductance and mutual inductance.

[0025] Figure 6 right The electrical parameters of each phase branch on the parallel-wound chokes are shown in detail, allowing for analysis of the voltage relationships of the three-phase branches on each magnetic ring. Taking the first choke as an example, this choke has wires wound in parallel from the midpoints of the first branches of the three-phase inverter circuits A, B, and C. These wires, wound on the choke, form the inductances corresponding to the first branches of the three phases. , and The voltage difference across the inductors of each phase , , The expression for (i.e., the voltage difference between the two ends of the section of each phase branch wound around the choke coil) is: (1), in, , , These are the currents drawn from the midpoint of the first branch in a parallel multilevel inverter circuit consisting of phases A, B, and C. This is the self-inductance value of the inductance formed by each branch winding itself around the choke coil (the three-phase branches are wound in the same way on the same choke coil, so the self-inductance value of each branch can be considered equal). This is the mutual inductance value of the inductance experienced by each branch by the other branches wound around the choke coil.

[0026] By canceling the parameters in equation (1), we can obtain equation (2): (2).

[0027] make: , but It can be simplified to: (3), make: (4), (5), Then equation (3) becomes: (6), That is, the inductance of the A-phase 1 branch formed by combining the three phases and winding it around the first choke can be regarded as an equivalent DC voltage source and an equivalent inductance. The voltage of the equivalent DC voltage source is... The voltage difference between phase B and branch C at the first choke coil , And the self-induction of the first choke coil and mutual induction It is determined that the inductance value of the equivalent inductance is determined by the self-inductance of the first choke. and mutual induction Sure.

[0028] right and By performing the same process, we can obtain: (7), (8).

[0029] Obviously, the inductances of B-phase 1 branch and C-phase 2 branch can also be equivalent to their respective equivalent DC voltage sources and equivalent inductances, and their voltage and inductance values ​​can be found in equations (5) and (4). Through the above processing, the decoupling processing of the magnetic ring corresponding to the first branch is achieved, and the equivalent circuit models of the three-phase branches wound in parallel on the first choke are obtained.

[0030] Furthermore, by applying the same process to each of the other magnetic rings, we can obtain the equivalent circuit models for the three-phase branches wound in parallel on the second magnetic ring, the equivalent circuit models for the three-phase branches wound in parallel on the third magnetic ring, and so on, until the... The equivalent circuit models of the three-phase branches wound in parallel on each magnetic ring.

[0031] As can be seen from the above steps, the equivalent circuit model of each of the three-phase branches connected in parallel on any choke coil consists of an equivalent DC voltage source and an equivalent inductor. The voltage of any corresponding equivalent DC voltage source is determined by the voltage difference between the other two phase branches at both ends of the choke coil and the self-inductance and mutual inductance of the choke coil. Its expression can be found in equation (5). The inductance value of the corresponding equivalent inductor is determined by the self-inductance and mutual inductance of the choke coil. Its expression can be found in equation (4).

[0032] Figure 7 The equivalent circuit models of each branch in the three-phase combined parallel multilevel motor simulator obtained through the above steps are shown. In the equivalent circuit model of the inductance of branch A1, the potential at the virtual point connecting the equivalent DC voltage source and the equivalent inductor is denoted as... Correspondingly, the potentials at the virtual points of phase B and branch C1 are denoted as follows: , The potential markings of the corresponding virtual points in the equivalent circuit models of the inductance of each phase and branch are deduced in the same manner.

[0033] <Determine the high-frequency circulating current variations of the three-phase branches on the same choke coil during the seven time periods of the same switching cycle> After completing the above decoupling process and obtaining the equivalent circuit model of each phase and branch, the expression for the high-frequency circulating current change in each direction and branch can be derived. The following explanation still takes the three-phase branch corresponding to the first magnetic ring as an example. The three-phase branches corresponding to other magnetic rings can be processed in the same way.

[0034] According to the equivalent circuit model of branch 1 of phase A, the high-frequency circulating current is mainly caused by the oscillation when current flows through the equivalent inductor. Meanwhile, the current expression is related to the voltage across the inductors of phases B and C, which are wound on the same magnetic ring. , and self-awareness Mutual induction Relatedly, considering the case of any inductor In a very short time interval Inside, the potential at its two ends , It can be considered a constant, therefore, in Inductance flowing inside The change in high-frequency current It can be represented as: (9).

[0035] Since the switching period of each branch is much smaller than the change period of the phase current, the current change calculation method of equation (9) can be used to calculate the high-frequency circulating current change of each branch. Specifically: First of all , , The midpoint potential of the three-phase branch 1 , , Potential at the point of merging with the three-phase branch , , The form of the difference: (10) Then, based on the equivalent circuit model of branch 1 of phase A and equation (6), the equivalent inductance of branch 1 of phase A is obtained. The expression for the pressure drop across the two ends: (11), Finally, according to equation (9), the A phase 1 branch is obtained in a very short time period. Expression for high-frequency circulation change within : (12).

[0036] Similarly, it can be concluded that in a very short time period, branch 1 of phase B and branch 1 of phase C... Expression for high-frequency circulation change within , : (13) (14).

[0037] After obtaining the expressions for equations (12) to (14), they can be directly extended to the branches of other phases without considering the coupling between branches in the same phase. This is because the inverter circuit of the same phase is cascaded and wound around the branch. The topologies of the magnetic rings are different, in Figure 3 In the topology of the three-phase combined parallel multilevel motor simulator shown, each choke coil is wound around only one branch of each of the three phases. Different choke coils naturally have magnetic isolation. Therefore, by decoupling the three-phase branches wound in parallel on the same choke coil using the aforementioned method, the entire circuit is established. With each branch having its own independent equivalent circuit model, it is clear that when generalizing equations (12) to (14), there is no need to consider the total number of parallel branches. The influence of this on the expression for the change in high-frequency circulating current allows us to obtain a general expression for the change in high-frequency circulating current in each phase and branch: (15) in, , , The three phases are A, B, and C respectively. The expression for the change in high-frequency circulating current in the branch is as follows: , , The three phases are A, B, and C respectively. The potential at the midpoint of the branch.

[0038] Establish each phase and branch at an extremely short time interval. After obtaining the expression for the high-frequency circulating current change within the circuit, the high-frequency circulating current change of each branch within a complete switching cycle can be analyzed. It should be noted that, based on the choke winding method of the three-phase combined parallel multilevel motor simulator, the specific value of the high-frequency circulating current change of any branch within a switching cycle is influenced by the switching cycle of its own branch (without loss of generality, assuming...). The midpoint potential and merging point potential within the switching cycle length (indicated by the PWM signal) are determined by the changes in the midpoint potential and merging point potential of the other two phase branches within the same switching cycle. Since the same choke coil winds branches with the same number from the three phases, based on the phase difference (120°) of the modulation signals in the three-phase circuit and the generation sequence of the PWM signals, it can be determined that the start and end times of the switching cycles of the three branches on the same choke coil are aligned. The changes in the midpoint potential of the three branches (i.e., the switching states determined by the PWM signals) exhibit a centrally symmetrical pattern. Combined with the phase changes of the three-phase modulation signals, there are a total of six different combinations of the midpoint potential of the three-phase branches. Figure 8 Taking the choke coil wound around a three-phase branch as an example, the waveforms of the midpoint potentials of each of the three-phase branches under one combination are shown, and the combination is displayed on the same time axis. Figure 9 Five other combinations are shown on the same timeline.

[0039] It should be noted that, Figure 8 , Figure 9 The variation of the midpoint potential of the three-phase branch at different times within the same switching cycle is fundamentally different from the variation of the three parallel branches of the same phase at different times within the same switching cycle in the earlier Chinese invention patent CN120263025A filed by the same applicant. In the cascaded coupling topology provided in Chinese invention patent CN120263025A, the midpoints of the parallel branches of the same phase are cascaded and coupled together. Therefore, the potential change at different times within the same switching cycle is actually determined by the phase's... The parallel branches shift phase sequentially within the same switching cycle. The cycle reflects the high-frequency circulating current changes in the parallel branches of the same phase within a single switching cycle of the cascaded coupled circuits in the same phase inverter circuit. These high-frequency circulating current changes are simultaneously reflected in the coupled connections. The number of potential changes on each choke coil within the same switching cycle is greater than the total number of parallel branches in the same phase. Certain; and Figure 8 , Figure 9 What is shown is the change of the midpoint potential of each of the three-phase branches that are connected in parallel and wound on the same choke coil. Since the expression of the high-frequency circulating current change obtained by the equivalent circuit of any branch of any phase after decoupling also includes the midpoint potential of the other two phase branches with the same branch number, in order to facilitate the classification of the combination of midpoint potentials of the three-phase branches in the same switching cycle, they are displayed in the same time axis.

[0040] In addition, through Figure 8 , Figure 9As can be seen from the combination of the midpoint potentials of the three-phase branches, under this topology of three-phase combined parallel winding, in the same switching cycle (assuming the switching cycle duration is...), Within the same choke coil, the midpoint potential of the three-phase branch can be divided into seven time periods with different states, namely: Time period Time period Time period Time period Time period Time period and Time period, among which Time period Time period and The time periods correspond to the midpoints of the three-phase branches with the same branch number maintaining a high level respectively. The time, and and , and They are symmetrically distributed along the time axis. and On both sides of the center position.

[0041] For example, in Figure 8 middle, The time period is the period during which the midpoint potential of branch A1 (represented by the yellow line) remains at a high level. The period during which the midpoint potential of branch B (represented by the green line) remains high is the time during which the midpoint potential remains high. The time period is the period during which the midpoint potential of branch C1 (indicated by the red line) remains at a high level.

[0042] For example, Figure 9 The midpoint potential combination in the upper left corner represents The time period is the period during which the midpoint potential of branch 1 of phase A remains at a high level. The period during which the midpoint potential of branch C1 is maintained at a high level. The time period is the period during which the midpoint potential of branch 1 of phase B remains at a high level. Figure 9 The other combinations correspond to other possible combinations of the three-phase branch's midpoint potential maintaining a high level during the same period.

[0043] After dividing the time periods as described above, the expression for the high-frequency circulating current change of each phase and branch can be determined based on the midpoint potential of the three-phase branches with the same branch number within each time period. The following is an example... Figure 8 The following explanation uses the A-phase 1 branch as an example under the shown potential combination.

[0044] 1) Time period Depend on: , We can obtain: (16); 2) Time period Depend on: , , We can obtain: (17); 3) Time period Depend on: , , We can obtain: (18); 4) Time period Depend on: , We can obtain: (19); 5) Time period Depend on: , , We can obtain: (20); 6) Time period Depend on: , We can obtain: (twenty one); 7) Time period Depend on: , We can obtain: (twenty two).

[0045] Based on the central symmetry at each moment analyzed above, we can obtain: (twenty three).

[0046] Similarly, the same derivation method can be used to extend the expression for the high-frequency circulating current change of branch 1 of phase A within a complete switching cycle to all other phases and branches.

[0047] <Determine the high-frequency zero-sequence circulation variation and peak value expression for each choke coil> For each choke, the magnitude of the high-frequency zero-sequence circulating current component caused by the three-phase branches wound in parallel is a key factor determining the choke's operating state. If the high-frequency zero-sequence circulating current flowing through a choke is too large, the magnetic flux density within the core formed by the choke will reach its saturation point, causing the choke's inductance to saturate and thus losing its ability to suppress the high-frequency zero-sequence circulating current. In this case, the high-frequency circulating current in the system will increase sharply, potentially triggering overcurrent protection or even burning out the device. Therefore, after obtaining the expression for the change in high-frequency circulating current in the three-phase branches of the same choke, it is necessary to further determine the change in high-frequency zero-sequence circulating current flowing through the choke and its peak value to provide a basis for subsequent optimization of the motor simulator design.

[0048] Specifically, for the first When a choke coil is constructed using a three-phase parallel winding structure, the corresponding change in high-frequency zero-sequence circulating current is... It can be composed of three phases wound in parallel on the choke coil. The sum of the high-frequency circulating current changes of each branch is obtained as follows: (twenty four).

[0049] Based on the analysis above, we can obtain the changes in high-frequency zero-sequence circulating current flowing through each choke coil within the same switching cycle. Taking the first choke coil as an example, the expressions for its corresponding high-frequency zero-sequence circulating current changes in each time period are as follows: 1) Time period (25); 2) Time period (26); 3) Time period (27); 4) Time period (28); 5) Time period (29); 6) Time period (30); 7) Time period (31).

[0050] By using the same processing steps, the expressions for the high-frequency zero-sequence circulating currents corresponding to each of the other choke coils can be obtained.

[0051] Observations (25) to (31) show that, Time period Time period and Time period All are positive, meaning the high-frequency zero-sequence circulating current continues to increase. Therefore, based on the sum of the high-frequency zero-sequence circulating currents in these three time periods, and substituting equation (23), we can obtain the expression for the peak value of the high-frequency zero-sequence circulating current change corresponding to the first choke (the branch of the three phases A, B, and C connected in parallel). : (32).

[0052] By using the same processing steps, expressions for the peak values ​​of the high-frequency zero-sequence circulation changes corresponding to each of the other choke coils can be obtained.

[0053] Observing equation (32), it can be found that for Figure 3 The topology shown has a peak value expression for the high-frequency zero-sequence circulating current change on each choke coil that is independent of the number of branches connected in parallel for each phase, and is only related to the self-inductance and mutual inductance of each choke coil after being connected in parallel with three-phase branches.

[0054] Considering the differences in size, specifications, and material properties among various chokes, different chokes... , The values ​​will inevitably differ. If the difference is small, the inductance parameters of each choke can be considered to be consistent, and the peak value of the high-frequency zero-sequence circulating current change corresponding to each choke can be obtained by using equation (32). If the difference is large enough to be negligible, then any choke can be used to calculate the peak value of the high-frequency zero-sequence circulating current change corresponding to each choke. The self-inductance and mutual inductance of each choke are respectively... , This represents the expression for the peak value of the corresponding high-frequency zero-sequence circulation change. It can be in the form of (33): (33).

[0055] To verify the effectiveness of the calculation method, the peak value of the high-frequency zero-sequence circulating current variation (ZSCC) of the choke under different combinations of self-inductance and mutual inductance was calculated using this method. Table 1 shows the parameters of the motor simulator system used for calculation and simulation. Table 1. Motor Simulator System Parameters Figure 10The calculation results of this method and the comparison with the simulation results are shown. It can be seen that the overall error between the simulation value and the calculated value is controlled within 2%, which can meet the accuracy requirements for inductor selection.

[0056] By obtaining the peak expression for the high-frequency zero-sequence circulating current change corresponding to each choke in the three-phase combined parallel multilevel simulator through the above steps, a quantitative basis can be provided for the design of the parallel multilevel motor simulator. For example, when the bus voltage of the topology is determined, the self-inductance and mutual inductance of the coupled inductor can be quantitatively designed based on the above formula, thereby determining the inductor's permeability and the number of winding turns, realizing the forward design of the inductor. This provides a new approach for the design of any power topology, including motor simulators. Furthermore, if the maximum allowable high-frequency zero-sequence circulating current of the system is known, the maximum allowable operating voltage can also be limited according to the above formula, further demonstrating the practical significance of this method.

[0057] For example, in the process of designing a motor simulator, as the load requirements of the motor simulator increase, the rated power, bus voltage, or phase current of the motor simulator may continue to increase, thus requiring each phase inverter circuit to include more parallel branches. Since the high-frequency circulating current value of the branch corresponding to the three-phase combined topology is independent of the number of branches, while the high-frequency circulating current value of the branch corresponding to the cascaded coupling topology increases with the increase of the number of branches, the comparison results of the two overlap as the number of parallel branches changes.

[0058] Figure 11 The results show the measured high-frequency circulating current of each choke as a function of the number of parallel branches, under the conditions of using the same bus voltage (100V) and selecting the same choke and winding turns. The results show the measured high-frequency circulating current of each choke as a function of the number of parallel branches when the motor simulator adopts the same in-phase cascaded coupling topology and the three-phase combined parallel winding topology. In this case, one choke is selected for measurement for each topology. The measurement can be performed using various high-frequency zero-sequence circulating current measurement methods known to those skilled in the art. For example, three high-precision current probes of the same model are connected to an oscilloscope (channels 1, 2, and 3). After ensuring that the wiring and measurement methods are correct, the power is turned on and the three-phase inverter is put into operation through the program control. At this time, the three channels will simultaneously display the high-frequency circulating current of each of the three phases, i.e., the real-time signal corresponding to equation (15). Then, the equipment is kept running normally, and the display result of the new channel in the oscilloscope is set to be the sum of channels 1, 2, and 3, i.e., the real-time signal corresponding to equation (24). The high-frequency zero-sequence circulating current of the magnetic ring can be obtained.

[0059] As can be seen, when using the cascaded coupling topology, the high-frequency circulating current in the choke increases almost exponentially with the increase of the number of parallel branches. However, the high-frequency circulating current of each branch obtained by actual measurement of the three-phase combined topology remains basically unchanged (the slight difference in the measured values ​​between different numbers of branches is caused by the difference in permeability due to the individual processing error of the magnetic ring). The two cross when transitioning from 5 parallel branches to 6 parallel branches. Therefore, when using 2 to 5 parallel branches, the cascaded coupling topology is more conducive to suppressing the high-frequency circulating current. When the number of parallel branches exceeds 6, the three-phase combined topology should be preferred.

[0060] Based on the above analysis, some embodiments of this application also provide a motor simulator design method, such as... Figure 12 As shown, this design method includes the following steps: The first step is to obtain the design specifications and inductance parameters of the motor simulator. The design specifications include the values ​​of bus voltage, phase current or rated power, and the inductance parameters include the self-inductance and mutual inductance values ​​of each choke. The second step is to determine the total number of parallel branches included in each phase inverter circuit of the motor simulator based on the design specifications of the motor simulator. The third step is to calculate, based on the inductance parameters, the peak value of the high-frequency circulating current change corresponding to each choke in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches, and record it as the first value; and to calculate, based on the peak value of the high-frequency zero-sequence circulating current change corresponding to each choke in the three-phase combined parallel multilevel simulator, and record it as the second value. The second value is calculated based on the aforementioned high-frequency zero-sequence circulating current calculation method of the three-phase combined parallel multilevel motor simulator. Fourth step: If the first value is less than the second value, then the motor simulator is designed as a cascaded coupled parallel multilevel motor simulator; otherwise, the motor simulator is designed as a three-phase combined parallel multilevel motor simulator.

[0061] It should be noted that in the third step, the calculation of the peak value of the high-frequency circulating current change of each choke coil in the cascaded coupled topology parallel multilevel motor simulator should be done in a different way than the three-phase combined topology. This is because the generation mechanism of the high-frequency circulating current in the choke coil is completely different under these two winding topologies.

[0062] Specifically, as analyzed above, under the parallel winding of three-phase branches, the midpoint potential of each phase branch is mirror-symmetric within the period, and there is a 120° phase difference between the three phases. Therefore, the influence of the three-phase branches on the saturation of the choke inductor is the change in the high-frequency zero-sequence circulating current, which is expressed as the sum of the changes in the three-phase high-frequency circulating current in equation (24).

[0063] In a cascaded coupled topology, in-phase The midpoint potential of each branch is in the same switching cycle. The phase shift relationship means that when two adjacent branches are wrapped in the same choke, the high-frequency circulating current in the choke is the result of the vector synthesis of the high-frequency circulating currents of the two branches.

[0064] Therefore, for a cascaded coupled motor simulator, the peak value of the high-frequency circulating current change corresponding to each choke coil can be determined through the following steps: First, determine the expression for the high-frequency circulating current change of a single branch in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches; Then, vector synthesis is performed based on the phase shift relationship between adjacent branches wound on each choke coil to determine the high-frequency circulating current change and its peak value corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches.

[0065] Specifically, the applicant provides a method for calculating high-frequency circulating current under a cascaded coupled topology in Chinese invention patent CN120263025A. This method can determine... When parallel branches are cascaded and coupled, the high-frequency circulating current variation and peak value of each branch can be obtained. Then, based on the high-frequency circulating current variation and peak value of adjacent branches wound on the same choke coil, the existing high-frequency circulating current variation and peak value of each branch can be determined. The phase shift relationship is used to perform vector synthesis on the high-frequency circulating current expressions of the two branches after phase shifting, so as to obtain the high-frequency circulating current change of each choke coil in one switching cycle, and determine its peak value.

[0066] As can be seen from the above implementation process, for a cascaded coupled topology, as the number of parallel branches increases... As the number of parallel branches increases, the phase difference of the high-frequency circulating current between adjacent branches gradually decreases, causing the influence of the two branches on the change in high-frequency circulating current on the choke coil to become more consistent. Simultaneously, in conjunction with the applicant's Chinese invention patent CN120263025A, the peak value of the high-frequency circulating current change in each branch also increases with the number of parallel branches. The value increases with the number of parallel branches. Therefore, for cascaded coupled topologies, the combined effect of these two factors will cause the peak value of the high-frequency circulating current change corresponding to each choke coil to increase with the number of parallel branches. The conclusion that it increases rapidly with the increase of [something] has also been obtained. Figure 11 Support.

[0067] The specific embodiments of this application have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for calculating high-frequency zero-sequence circulating current in a three-phase combined parallel multilevel motor simulator, characterized in that, Includes the following steps: Based on the voltage relationship of the three-phase branches wound in parallel on the same choke coil in the three-phase combined parallel multilevel motor simulator, the equivalent circuit model of each three-phase branch wound in parallel on each choke coil is determined. Based on the equivalent circuit model, the high-frequency circulating current variation of each of the three-phase branches wound in parallel on each choke coil in the seven time periods of the same switching cycle is determined. Based on the high-frequency circulating current variation of the three-phase branches wound in parallel on each choke, the high-frequency zero-sequence circulating current variation and peak value corresponding to each choke are determined.

2. The high-frequency zero-sequence circulating current calculation method for a three-phase combined parallel multilevel motor simulator according to claim 1, characterized in that, The equivalent circuit model of each of the three-phase branches wound in parallel on any choke coil consists of an equivalent DC voltage source and an equivalent inductor. The voltage of any corresponding equivalent DC voltage source is determined by the voltage difference between the other two phase branches across the choke coil and the self-inductance and mutual inductance of the choke coil. The inductance value of the corresponding equivalent inductor is determined by the self-inductance and mutual inductance of the choke coil.

3. The high-frequency zero-sequence circulating current calculation method for a three-phase integrated parallel multilevel motor simulator according to claim 1, characterized in that, The seven time periods of the same switching cycle are respectively Time period Time period Time period Time period Time period Time period and Time period, among which Time period Time period and The time periods correspond to the duration during which the midpoint of each of the three-phase branches with the same branch number remains at a high level, and and , and They are symmetrically distributed along the time axis. and On both sides of the center position, This represents the duration of the switching cycle.

4. The high-frequency zero-sequence circulating current calculation method for a three-phase combined parallel multilevel motor simulator according to claim 3, characterized in that, For any given choke, the change in its corresponding high-frequency zero-sequence circulating current is obtained by adding the changes in the high-frequency circulating current of the three-phase branches that are wound in parallel on the choke.

5. The high-frequency zero-sequence circulating current calculation method for a three-phase combined parallel multilevel motor simulator according to claim 4, characterized in that, For any i The expression for the peak value of the high-frequency zero-sequence circulation change corresponding to each choke coil. for: ， in, , The first The self-sensing and mutual induction of a choke loop, This is the DC bus voltage.

6. A design method for a motor simulator, characterized in that, Includes the following steps: Obtain the design specifications and inductance parameters of the motor simulator. The design specifications include the values ​​of bus voltage, phase current or rated power, and the inductance parameters include the self-inductance and mutual inductance of each choke. Based on the design specifications of the motor simulator, the total number of parallel branches included in each phase inverter circuit of the motor simulator is determined. Based on the inductance parameters, the peak value of the high-frequency circulating current change corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches is calculated and recorded as the first value. The peak value of the high-frequency zero-sequence circulating current change corresponding to each choke coil in the three-phase combined parallel multilevel simulator is calculated and recorded as the second value. The second value is calculated based on the aforementioned high-frequency zero-sequence circulating current calculation method of the three-phase combined parallel multilevel motor simulator. If the first value is less than the second value, the motor simulator is designed as a cascaded coupled parallel multilevel motor simulator; otherwise, the motor simulator is designed as a three-phase combined parallel multilevel motor simulator.

7. The design method of the motor simulator according to claim 6, characterized in that, The following steps are used to calculate the peak value of the high-frequency circulating current change corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches: Determine the expression for the high-frequency circulating current change of a single branch in a cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches; Vector synthesis is performed based on the phase shift relationship between adjacent branches wound on each choke coil to determine the high-frequency circulating current change and its peak value corresponding to each choke coil in the cascaded coupled parallel multilevel motor simulator constructed according to the total number of parallel branches.

Images