Three-phase-in-one parallel multi-level inverter and motor simulator

Abstract

The application provides a three-phase integrated parallel multi-level inverter and a motor simulator. The three-phase integrated parallel multi-level inverter comprises three-phase inverter circuits, each of which comprises an equal number of bridge arm branches connected in parallel with a DC bus power supply, and each bridge arm branch comprises two switching devices connected in series; and the three-phase integrated parallel multi-level inverter further comprises an equal number of three-phase integrated magnetic rings as the number of bridge arm branches in any one of the three-phase inverter circuits, each of which is formed by spirally winding three wires on an inductor, wherein one end of each of the three wires of each three-phase integrated magnetic ring is connected to the midpoint of one bridge arm branch in one three-phase inverter circuit, and the other end forms a current output end of a corresponding phase in a same-phase connection mode. The inverter provided by the application changes the cascaded coupling inductance topology structure of the existing motor simulator, and effectively solves the problem that the high-frequency circulating current increases with the increase of the number of branches.

Description

Technical Field

[0001] This application belongs to the field of motor simulator control technology, specifically providing a three-phase integrated parallel multilevel inverter and a motor simulator. Background Technology

[0002] Motor simulators are high-end testing equipment for new energy vehicles. They enable power level testing of motor controllers without the need for a real motor, thereby improving testing safety, flexibility, and reproducibility. Their engineering application value is even more prominent for more dangerous high-speed testing conditions. For a motor simulator, its equivalent switching frequency is equal to the product of the number of branches in each phase and the switching frequency of the switching devices in each branch. A higher equivalent switching frequency can effectively improve the quality of the motor simulator's output current. Currently, the main methods for increasing the equivalent switching frequency are increasing the number of branches and increasing the switching frequency of the power devices in each branch.

[0003] However, as the switching frequency of power devices increases, their losses also increase significantly, leading to overheating and potential equipment safety issues. While increasing the number of branches can improve the equivalent switching frequency, the commonly used parallel multilevel cascaded coupling topology causes a rapid increase in circulating current between branches. This saturates the magnetic components, causing a rapid drop in system impedance and a loss of differential-mode current suppression capability. Ultimately, this results in a decrease in the quality of the system output current and reduces the overall performance of the motor simulator.

[0004] While various strategies for suppressing high-frequency circulating currents in existing parallel multilevel cascaded coupling topologies have been disclosed, these strategies either increase algorithmic complexity or are limited by specific application scenarios. Furthermore, the applicant proposed a method in Chinese Invention Patent CN120263025A to calculate the high-frequency circulating currents present in existing motor simulator topologies. This method reveals that in the parallel multilevel cascaded coupling topologies used in existing motor simulators, the high-frequency circulating current inevitably increases with the increase of parallel branches. Clearly, this inherent characteristic of existing parallel multilevel cascaded coupling topologies significantly limits the performance improvement of motor simulators. Summary of the Invention

[0005] To address the inherent problem of increased high-frequency circulating current in the coupled parallel multilevel structure used in existing motor simulators, where the number of branches increases, this application provides a three-phase combined parallel multilevel inverter for use in motor simulators, where the high-frequency circulating current does not increase with the number of branches.

[0006] The three-phase integrated parallel multilevel inverter includes a three-phase inverter circuit. Each phase inverter circuit includes an equal number of bridge arm branches connected in parallel with the DC bus power supply. Each bridge arm branch includes two switching devices connected in series.

[0007] The three-phase integrated parallel multilevel inverter also includes several three-phase integrated magnetic rings. The number of the three-phase integrated magnetic rings is equal to the number of bridge arm branches in any one phase inverter circuit. Each three-phase integrated magnetic ring is formed by three wires spirally wound around a choke coil. One end of each of the three wires of each three-phase integrated magnetic ring is connected to the midpoint of a bridge arm branch in a one-phase inverter circuit, and the other end forms the current output terminal of the corresponding phase in a same-phase connection manner.

[0008] This application also provides a motor simulator through embodiments, including a signal acquisition unit, a motor model unit, a drive unit, and an inverter unit, wherein the inverter unit is the aforementioned three-phase combined parallel multilevel inverter.

[0009] The three-phase combined parallel multilevel inverter provided in this application changes the existing motor simulator inverter structure where the three-phase inverter circuits are independently connected to their corresponding cascaded coupling topology. By winding the wires led out from the midpoint of each bridge arm branch of the three-phase inverter circuit in three parallel sections, the vector sum between the currents of the three-phase branches in each winding structure is minimized, thereby effectively reducing the common-mode impedance between the branches and the resulting high-frequency circulating current, and ensuring that the high-frequency circulating current does not increase with the increase of the bridge arm branches.

[0010] Furthermore, due to the adoption of a three-phase combined winding method, the number of magnetic rings required is the same as the number of bridge arm branches of any one-phase inverter circuit, which is only one-third of the number of magnetic rings required by the existing parallel multi-level cascaded coupling topology, greatly reducing the complexity and implementation cost of the coupling topology. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the architecture of a motor controller-to-drag test platform;

[0012] Figure 2 This is a schematic diagram of the a-phase topology of an inverter in an existing motor simulator.

[0013] Figure 3 This is a schematic diagram of the cascaded coupling structure of each phase in the inverter of an existing motor simulator.

[0014] Figure 4 This is a schematic diagram of the topology of a three-phase combined parallel multilevel inverter provided according to an embodiment of this application;

[0015] Figure 5This is a schematic diagram showing the circuit connection relationship of multiple three-phase integrated magnetic rings according to the embodiments of this application;

[0016] Figure 6 A physical diagram of the choke provided according to an embodiment of this application;

[0017] Figure 7 This is a schematic diagram of winding wire on a choke coil according to an embodiment of this application;

[0018] Figure 8 This is a schematic diagram of a three-phase integrated magnetic ring provided according to an embodiment of this application;

[0019] Figure 9 This is a schematic diagram of a three-phase integrated magnetic ring provided according to an embodiment of this application;

[0020] Figure 10 A physical diagram of a three-phase combined parallel multilevel inverter provided according to an embodiment of this application;

[0021] Figure 11 This is a schematic diagram of the current measurement circuit for each bridge arm branch in specific embodiment one;

[0022] Figure 12 This is a schematic diagram of the A-phase circulating current in the three-branch parallel connection in Specific Embodiment 1;

[0023] Figure 13 This is a schematic diagram of the A-phase circulating current in a specific embodiment 1 with four branches connected in parallel. Detailed Implementation

[0024] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0025] 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.

[0026] The vocabulary used in this specification is for illustrative purposes and is not intended to limit the scope of this application. It should also be noted that, unless otherwise expressly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection via an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of these terms in this application.

[0027] Figure 1 This diagram illustrates the architecture of a towing test platform used for testing the performance of automotive motor controllers. The left half of the platform represents the motor controller (i.e., the motor control unit in the diagram), and the right half represents the motor simulator. Figure 1 As shown, the motor simulator includes a signal acquisition unit, a motor model unit, an inverter unit, and a drive unit. The signal acquisition unit acquires the real-time voltage of each phase and the real-time current of each bridge arm branch of the inverter unit and outputs them to the motor model unit and the drive unit. The motor model unit calculates the target current of each bridge arm branch based on the real-time voltage and current signals acquired by the signal acquisition unit. The drive unit determines and outputs the drive signals of each switching device in the inverter unit based on the real-time current and target current of each bridge arm branch of each phase, thereby enabling the tracking of the target current and realizing closed-loop control of the motor simulator.

[0028] During the test, the motor simulator is connected to the inverter midpoint (phase node) of the motor controller under test through a cascaded coupling inductor to provide an equivalent motor load for each phase. If necessary, a filter network is connected in series / parallel between the two to suppress switching harmonics and limit circulating current, so that the inverter under test can generate phase current and terminal voltage waveforms equivalent to those of a real motor under normal modulation.

[0029] Figure 2 It shows Figure 1 The specific structure of a single-phase inverter circuit in the inverter unit (taking phase a as an example), Figure 3 The circuit diagrams of the cascaded inductor structures in the three-phase inverter circuits a, b, and c are shown respectively.

[0030] refer to Figure 2 , Figure 3 For any single-phase inverter circuit, there is a power supply (U) connected in parallel to the DC bus. dc There are n bridge arm branches between () and () where n is an integer greater than or equal to 2, for example, Figure 2 In this embodiment, the number of bridge arm branches is 3. In other embodiments, n can be 2, 4, 5 or more.

[0031] Furthermore, each bridge arm branch includes two switching devices connected in series. The switching devices can be Si / SiCMOSFETs (with built-in body diodes) or IGBT modules with anti-parallel diodes, etc. The gate of each switching device is given a complementary PWM signal and a dead time is set by the driving unit. The upper and lower transistors are controlled to conduct in an interlocked manner, thereby switching the voltage state of the midpoint of the bridge arm branch (the connection point of the upper and lower switching devices, also known as the phase node of the bridge arm branch).

[0032] A conductor is led out from the midpoint of each bridge arm branch, and then wound around n choke coils in a cascaded manner to form an inductor structure in the form of n cascaded coupled magnetic rings, for example, like... Figure 2 In the three bridge arm branches, the first wire is wound sequentially around the first and second chokes, the second wire is wound sequentially around the second and third chokes, and the third wire is wound sequentially around the third choke and the first choke, thus forming three coupled inductors. Figure 2 , Figure 3 In the diagram, each group of two spirals distributed horizontally and vertically represents a magnetic ring wound with two wires.

[0033] For any cascaded coupling structure of a single phase, the input of each inductor structure is the current at the midpoint of its respective bridge arm branch, and the outputs of each inductor structure are connected together to form the output current of that phase: e.g. Figure 3 As shown, the current at the midpoint of the n bridge arm branches of phase a is i a1 i a2 ,…,i an The current at the midpoint of the n bridge arm branches of phase b is i b1 i b2 ,…,i bn The current at the midpoint of the n bridge arm branches of phase c is i c1 i c2 ,…,i cn The output terminals of each inductor in phase a are connected together to output the phase current i of that phase. a The outputs of each inductor in phase b are connected together to output the phase current i of that phase. b The outputs of each inductor in phase c are connected together to output the phase current i of that phase. c .

[0034] As analyzed in the background section, increasing the number of arm branches in each phase inverter circuit can improve the equivalent switching frequency of the inverter. However, with the increase in the number of arm branches, the circulating current between branches in the existing cascaded coupling structure increases rapidly. Although various schemes for reducing high-frequency circulating current have been disclosed, such as implementing active circulating current suppression through algorithms or adding hardware such as H-bridge structures between each arm branch to suppress high-frequency circulating current, these schemes either increase the complexity of system control, are limited by specific application scenarios, or increase the overall system cost. Meanwhile, the applicant has discovered through research that… Figure 2 and Figure 3 In the parallel multilevel cascaded coupling structure shown, the high-frequency circulating current inevitably increases with the increase of parallel branches. Therefore, without changing this cascaded coupling topology, no matter what suppression algorithm is used, it is impossible to fundamentally solve the problem caused by this inherent characteristic.

[0035] Therefore, in this application, the applicant discloses a three-phase combined parallel multilevel inverter with a novel topology, which can effectively solve the inherent problem of high-frequency circulating current increasing with the number of branches in the coupled parallel multilevel structure used in existing motor simulators while reducing hardware costs.

[0036] Figure 4 The diagram shows a circuit structure schematic of the three-phase combined parallel multilevel inverter in some specific embodiments. Figure 5 The winding method of the three-phase integrated magnetic ring included therein is further illustrated. Figure 6 This shows the current flow direction of the inductor circuit formed by each three-phase integrated magnetic ring.

[0037] refer to Figures 4 to 6 The three-phase integrated parallel multilevel inverter provided in this application includes a three-phase inverter circuit and several three-phase integrated magnetic rings.

[0038] Specifically, the three-phase inverter circuit is structured the same as the three-phase inverter circuit architecture used in existing motor simulators. Each phase inverter circuit includes an equal number of bridge arm branches connected in parallel with the DC bus power supply, and each bridge arm branch includes two switching devices connected in series. For example, in... Figure 4 In the embodiment shown, each of the A-phase, B-phase, and C-phase inverter circuits includes n (n≥2) inverters connected in parallel to U. dc The switching branches between the bridge arms each include two switching devices connected in series.

[0039] The number of three-phase integrated magnetic rings is equal to the number of bridge arm branches in any single-phase inverter circuit, for example, like Figure 4 and Figure 6As shown, when each phase inverter circuit includes n bridge arm branches, the number of three-phase integrated magnetic rings is also n.

[0040] Specifically, each three-phase integrated magnetic ring is formed by three wires spirally wound around a choke coil. One end of each of the three wires of each three-phase integrated magnetic ring is connected to the midpoint of a bridge arm branch in a phase inverter circuit, and the other end forms the current output terminal of the corresponding phase in a same-phase connection manner.

[0041] refer to Figures 4 to 6 For example, for the first bridge arm branch (branch 1) of each of the A-phase, B-phase, and C-phase inverter circuits, wires are drawn from their midpoints and wound together on the same choke coil. The current flowing from the midpoint of each of these three wires is denoted as i. a1 i b1 i c1 Similarly, the wires leading from the midpoints of the two branches of each of the A-phase, B-phase, and C-phase inverter circuits are wound around the same choke coil, ..., until the wires leading from the midpoints of the n branches of each of the A-phase, B-phase, and C-phase inverter circuits are wound around the same choke coil. After completing the above winding, the other ends of the wires leading from the A-phase inverter circuit on each choke coil are combined together to form the A-phase current output terminal of the inverter, and the output current is denoted as i. a Combine the other ends of the wires leading from the B-phase inverter circuit on each choke coil to form the B-phase current output terminal of the inverter, and denote the output current as i. b The other ends of the wires leading from the C-phase inverter circuit on each choke coil are combined together to form the C-phase current output terminal of the inverter, and the output current is denoted as i. c .

[0042] Clearly, this winding method transforms the commonly used cascaded coupling inductor structure where each phase of the inverter circuit is independently constructed into an inductor structure where each magnetic ring's inductor structure is formed by taking one branch from each of the three-phase inverter circuits and winding them together on the same choke coil. Then, the in-phase portions of the resulting n three-phase combined inductor structures are merged. This change not only reduces the number of choke coils from 3n to n, but more importantly, it significantly improves the ability to suppress high-frequency circulating currents, and this suppression ability is not weakened by the increase in the number of bridge arm branches.

[0043] The mechanism by which it suppresses high-frequency circulating currents will be analyzed below.

[0044] For existing power topologies that use cascaded coupling structures with each phase set independently, increasing the equivalent switching frequency by increasing the number of bridge arm branches will increase the path of the system circulating current and increase the system circulating current. When the system circulating current exceeds a certain value, the magnetic devices in the topology will saturate, resulting in a decrease in impedance and loss of the ability to suppress differential mode current.

[0045] The three-phase integrated inductor structure winding method adopted in this application utilizes the relative positive and negative relationship between the currents of the three-phase wires simultaneously wound on the choke coil, which allows the magnetic flux generated to cancel each other out inside the magnetic ring. At this time, the magnetic ring appears to have zero net magnetic flux and extremely low common-mode impedance, theoretically enabling it to carry infinitely large currents.

[0046] Specifically, the magnetic flux of the coil can be expressed as:

[0047] φ = BScosθ,

[0048] Where B is the magnetic field strength, S is the area enclosed by the closed curve, and θ is the angle between the magnetic field and the plane containing the enclosed area. For a magnetic device with three wires wound in parallel, under ideal conditions, the expression for its magnetic flux satisfies:

[0049]

[0050] Compared to the traditional winding method where different branches of the same phase are wound around the same magnetic ring to form an inductor, this patent adopts a scheme in which branches of different phases in a three-phase topology are wound around the same magnetic ring simultaneously. This scheme utilizes the characteristic that the sum of the three-phase line currents in a parallel multi-level structure is 0, so that the magnetic flux on each magnetic ring conforms to the above equation that the sum is zero. The three branches wound around the same magnetic ring are regarded as a parallel sub-module, which can effectively suppress the circulating current of each parallel sub-module in the system.

[0051] The three-phase combined inductor structure provided in this application, by winding the midpoint lead wires of the bridge arm branches of different phases around the same magnetic ring instead of cascading the midpoint lead wires of each branch of the same phase around the magnetic ring, can not only significantly reduce the high-frequency circulating current, but also make the value of the high-frequency circulating current independent of the number of bridge arm branches. This effectively solves the problem that the high-frequency circulating current increases with the number of branches, thereby greatly expanding the upper limit of the number of bridge arm branches that can be used in the motor simulator.

[0052] To distinguish it from existing cascaded coupled inductor structures, such as Figure 7 As shown, the magnetic ring formed by the three-phase winding in this application can be represented by three spiral lines, one above, one in the middle, and one below.

[0053] Figure 8The diagram shows physical images of chokes used for winding wires in some specific embodiments. For chokes, the saturation characteristics of the magnetic device can cause them to lose their choking ability; therefore, it is preferable to fabricate the choke using an amorphous or nanocrystalline material with high relative permeability. An insulating material layer (such as...) is preferably disposed on the outer surface of the choke. Figure 8 (The choke coil surface is covered with insulating cloth). In addition, in order to achieve insulation between the magnetic rings, preferably, an insulating material (such as an insulating layer made of acrylic sheet) can be provided between the magnetic rings.

[0054] Considering the size of the magnetic devices, the number of turns of the winding wire, and the space requirements for the inverter after the expansion of the number of subsequent bridge arm branches, in some preferred embodiments, the outer diameter of the choke is 135 to 140 mm, the width is 15 to 20 mm, and the thickness is 20 to 35 mm.

[0055] In the specific winding process of the magnetic ring, the required inductance value L can first be determined by testing the load and specific operating conditions of the motor controller. Then, the wire is wound around the choke coil turn by turn, and the inductance value is measured in real time to finally determine the appropriate number of turns closest to the L value. For example, in some specific embodiments, the required L value is 8mH to 12mH, using... Figure 8 The choke shown is wound with a magnetic ring, and the appropriate number of turns for each wire to be wound on the choke is 10 to 15.

[0056] In some preferred embodiments, considering the peak current and skin effect of the current on each bridge arm branch during the actual testing of the drag test, the conductors wound around the choke are selected to be Litz wires with a current carrying capacity of not less than 50A.

[0057] Figure 9 The diagram shows a connection schematic of a three-phase integrated magnetic ring used in some preferred embodiments of this application. As shown, the three-phase integrated magnetic ring is used to wind wires drawn from the midpoint of each branch of the three-phase inverter circuit (with currents i... a1 i b1 i c1 The difference between this embodiment and the previous one is that in this embodiment, each wire wound around the choke coil is connected in series with an additional inductor.

[0058] The location of the additional inductance connected in series on each conductor can be as follows: Figure 9 As shown, the current output terminal of the corresponding phase is located at the position where the conductor is finished winding on the choke coil (i.e., the i-th phase formed by the in-phase connection of the conductors led out from n magnetic rings). a end,i b end,i cThe additional inductance can be placed between the ends of the conductors, or it can be placed between the point where the conductor leaves the bridge arm branch (midpoint) and the starting position of the conductor winding on the choke coil. That is, the additional inductance connected in series on each conductor is located outside each choke coil.

[0059] After each phase conductor is wound around the choke coil, an additional inductor is connected in series. The purpose of this is to enable the magnetic ring to actively generate leakage inductance. Since these additional inductors do not participate in the interaction of the coupled inductors in the three-phase combined magnetic ring, they are not included in the mutual inductance measurement during impedance analysis and are displayed as leakage inductance. The applicant found that when an additional inductor with an appropriate inductance value is set on each conductor, the overall amplitude of the system circulating current is significantly reduced.

[0060] The inductance value of the additional inductor should be selected based on the inductance (L) of each wire wound around the choke coil. It should not be too small or too large. If the inductance is too small, the leakage inductance effect will be insignificant; if the inductance is too large, the energy consumption and heat generation of the entire magnetic ring structure will increase significantly. Preferably, when the inductance of each wire wound around the choke coil is 8mH to 12mH, the inductance value of the additional inductor connected in series with it should be set between 100uH and 300uH.

[0061] In addition, in some preferred embodiments, each phase inverter circuit also includes several bus filter capacitors. The number of bus filter capacitors can be equal to the number of bridge arm branches, so as to filter the bus voltage of each bridge arm branch in each phase inverter circuit in a one-to-one correspondence.

[0062] Some embodiments of this application also provide a motor simulator including the three-phase combined parallel level inverter. The motor simulator further includes a signal acquisition unit, a motor model unit, and a drive unit. The topology and control logic of each of the above functional units can be referred to Figure 1 The embodiment shown differs in that the inverter unit is replaced with the three-phase combined parallel multilevel inverter proposed in this application. Specific Implementation Example 1

[0064] To verify the high-frequency circulating current suppression effect of the three-phase integrated parallel multilevel inverter provided in this application, a three-phase integrated multilevel inverter with four branches (i.e., each phase inverter circuit includes four bridge arm branches) was built in this embodiment, and a motor controller drag test was conducted using a motor simulator containing the three-phase integrated parallel multilevel inverter.

[0065] Figure 10The figure shows a physical diagram of the three-phase integrated parallel multilevel inverter. As shown, the three-phase inverter circuit has a total of 12 wires. After being grouped according to the bridge arm branch number, they are wound around the four chokes to form four three-phase integrated magnetic rings. The other ends of the 12 wires are connected together in the same phase to form the three-phase output current terminals.

[0066] In addition, like Figure 8 As shown, a small additional inductor is connected in series with each wire.

[0067] The drag test platform adopts the same as Figure 1 The architecture is the same, the difference being that the three-phase combined inverter provided in this application is used instead. Figure 1 The inverter unit in the middle.

[0068] The switching device selected is the CREE CAS120M12BM2 SiC-MOSFET, with a gate turn-on voltage of 18V and a gate turn-off voltage of -5V. Based on this, a driver chip of model 1ED020I12-F2 is selected, and the corresponding driver circuit is designed. Table 1 shows the experimental parameter settings in this embodiment.

[0069] Table 1

[0070]

[0071]

[0072] To compare the high-frequency circulating current under different numbers of bridge arm branches, the driver program was adjusted to implement two scenarios: current inversion with three branches in parallel and current inversion with four branches in parallel. The following methods were then used for each scenario. Figure 11 The current measurement circuit shown is used to measure the current on each bridge arm branch.

[0073] Figure 12 , Figure 13 The figures show the circulating current of phase A in both three-branch parallel and four-branch parallel configurations. The commanded voltage for phase A is 10V, while the commanded voltages for phases B and C are -5V. Comparing the two figures, the circulating current amplitude is 620mA in the three-branch parallel configuration and 618mA in the four-branch parallel configuration. These two values ​​are almost identical, effectively verifying that the circulating current of the proposed three-phase combined parallel multilevel inverter does not change significantly with the increase in the number of branches. Specific Implementation Example 2

[0075] Specific embodiment two verifies through simulation experiments that, under the condition of a large number of parallel branches, the high-frequency circulating current of the three-phase integrated topology provided in this application does not increase with the increase of the number of branches of the parallel multilevel inverter. In this embodiment, the same parameters as in Table 1 are used to simulate and calculate the high-frequency circulating current under two branches, six branches, eight branches, ten branches and twelve branches respectively. Table 2 shows the simulation results, which also lists the comparison with the existing conventional cascaded coupling topology. At this time, the command voltage of the three phases is 0V, that is, the duty cycle is 0.5.

[0076] Table 2

[0077]

[0078] As shown in Table 2, when using the existing cascaded coupling structure, the circulating current of each phase increases monotonically with the increase of the number of branches. However, when using the three-phase combined topology of this application, the amplitude of the zero-sequence circulating current remains basically at 1*e as the number of branches increases. -11 Around A, it was verified that winding different phase branches around the same magnetic ring can significantly reduce circulating current. This shows that the technical solution disclosed in this application can fundamentally suppress the problem of circulating current increasing with the number of branches in parallel multi-level topology, providing a strong guarantee for constructing motor simulator inverter topologies with more than ten or even twenty branches.

[0079] 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 three-phase combined parallel multilevel inverter, applied to a motor simulator, comprising a three-phase inverter circuit, each phase inverter circuit including an equal number of bridge arm branches connected in parallel with the DC bus power supply, each bridge arm branch including two switching devices connected in series, and the equivalent switching frequency of the motor simulator being equal to the product of the number of branches in each phase and the switching frequency of the switching transistors in each branch; characterized in that, Also includes: Several three-phase integrated magnetic rings are provided, the number of which is equal to the number of bridge arm branches in any one-phase inverter circuit. Each three-phase integrated magnetic ring is formed by three wires spirally wound around a choke coil. One end of each of the three wires of each three-phase integrated magnetic ring is connected to the midpoint of a bridge arm branch in a one-phase inverter circuit, and the other end forms the current output terminal of the corresponding phase in a same-phase connection manner. The three-phase bridge arm branches connected by the three wires wound on the same three-phase integrated magnetic ring have the same branch number. By utilizing the relative positive and negative relationship between the currents of the three-phase wires wound on the choke coil at the same time, the magnetic flux generated by them cancels each other out inside the magnetic ring, so that the magnetic ring appears to have a net magnetic flux of zero.

2. The three-phase combined parallel multilevel inverter according to claim 1, characterized in that, The current carrying capacity of the wire wound around the choke coil is not less than 50A.

3. The three-phase combined parallel multilevel inverter according to claim 1, characterized in that, The choke is made of amorphous nanocrystalline material.

4. The three-phase combined parallel multilevel inverter according to claim 3, characterized in that, An insulating layer is provided on the surface of the choke, or an insulating material is provided between adjacent chokes.

5. The three-phase combined parallel multilevel inverter according to claim 4, characterized in that, The choke has an outer diameter of 135 to 140 mm, a width of 15 to 20 mm, and a thickness of 20 to 35 mm.

6. The three-phase combined parallel multilevel inverter according to claim 5, characterized in that, An additional inductor is connected in series with each conductor, and the additional inductor is connected outside the choke coil.

7. The three-phase combined parallel multilevel inverter according to claim 6, characterized in that, The inductance of the wire wound around the choke is 8mH to 12mH, and the inductance of the additional inductance is 100uH to 300uH.

8. The three-phase combined parallel multilevel inverter according to claim 1, characterized in that, Each phase inverter circuit also includes several bus filter capacitors, which are used to filter the bus voltage of each bridge arm branch in each phase inverter circuit.

9. A motor simulator, comprising a signal acquisition unit, a motor model unit, a drive unit, and an inverter unit, characterized in that, The inverter unit is the three-phase integrated parallel multilevel inverter as described in claim 1.

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