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

Abstract

The invention provides a three-phase-in-one type parallel multi-level inverter and a motor simulator, the three-phase-in-one type parallel multi-level inverter comprises three phases of inverter circuits, each phase of inverter circuit comprises a plurality of bridge arm branches which are connected in parallel with a direct current bus power supply, the number of the bridge arm branches is equal to that of the inverter circuits, and each bridge arm branch comprises two switching devices which are connected in series; the number of the three-phase one-in-one type magnetic rings is equal to that of the bridge arm branches in any phase of inverter circuit, and each three-phase one-in-one type magnetic ring is formed by spirally winding three wires on the choking coil, one end of each of three wires of each three-phase-in-one magnetic ring is connected with the midpoint of one bridge arm branch in one phase inverter circuit, and the other end of each of the three wires forms a current output end of a corresponding phase according to an in-phase connection mode. According to the inverter provided by the invention, the cascade coupling inductor topological structure of the existing motor simulator is changed, and the problem that the high-frequency circulating current is increased along with the increase of the number of the branches is effectively solved.

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-in-one 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;

[0007] The three-phase-in-one parallel multi-level inverter further comprises a plurality of three-phase-in-one magnetic rings, the number of the three-phase-in-one magnetic rings being equal to the number of the bridge arm branches in any one of the three-phase inverter circuits, and each of the three-phase-in-one magnetic rings is formed by spirally winding three wires on an inductor, wherein one end of each of the three wires of each of the three-phase-in-one magnetic rings is connected to the midpoint of one of the bridge arm branches in one of the three-phase inverter circuits, and the other end forms a current output end of the corresponding phase in a same-phase connection manner.

[0008] The application further provides an electric motor simulator comprising a signal acquisition unit, an electric motor model unit, a driving unit and the three-phase-in-one parallel multi-level inverter.

[0009] The three-phase-in-one parallel multi-level inverter provided by the application changes the connection mode of the three-phase inverter circuits in the existing inverter structure of the electric motor simulator, that is, each of the three-phase inverter circuits is independently connected to the corresponding cascade coupling topology, the wires led out from the midpoints of the bridge arm branches of the three-phase inverter circuits are three-wire wound, the vector sum of the three-phase branch currents of each winding structure is minimized, the common-mode impedance between the branches and the high-frequency circulating current caused thereby are effectively reduced, and the high-frequency circulating current is ensured not to increase with the increase of the bridge arm branches.

[0010] In addition, since the three-phase-in-one winding mode is adopted, the number of the required magnetic rings is equal to the number of the bridge arm branches of any one of the three-phase inverter circuits, which is only one third of the number of the required magnetic rings of the existing parallel multi-level cascade coupling topology, thereby greatly reducing the complexity and the implementation cost of the coupling topology. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 It is a schematic diagram of the architecture of a motor controller test platform;

[0012] Figure 2 It is a schematic diagram of the topology of the a-phase of the inverter of an existing electric motor simulator;

[0013] Figure 3 It is a schematic diagram of the cascade coupling structure of each phase of the inverter of an existing electric motor simulator;

[0014] Figure 4 It is a schematic diagram of the topology of the three-phase-in-one parallel multi-level inverter provided by the embodiment of the application;

[0015] Figure 5A schematic diagram of a connection relationship of a plurality of three-phase integrated magnetic rings according to an embodiment of the present application is provided.

[0016] Figure 6 A physical diagram of a choke according to an embodiment of the present application is provided.

[0017] Figure 7 A schematic diagram of winding on the choke according to an embodiment of the present application is provided.

[0018] Figure 8 A symbolic schematic diagram of a three-phase integrated magnetic ring according to an embodiment of the present application is provided.

[0019] Figure 9 A schematic diagram of a three-phase integrated magnetic ring according to an embodiment of the present application is provided.

[0020] Figure 10 A physical diagram of a three-phase integrated parallel multi-level inverter according to an embodiment of the present application is provided.

[0021] Figure 11 A schematic diagram of a current measurement circuit of each bridge arm branch in specific embodiment one is provided.

[0022] Figure 12 A schematic diagram of A-phase loop current in three-branch parallel in specific embodiment one is provided.

[0023] Figure 13 A schematic diagram of A-phase loop current in four-branch parallel in specific embodiment one is provided. DETAILED DESCRIPTION

[0024] Hereinafter, the present application is further described based on the preferred embodiments and with reference to the accompanying drawings.

[0025] In the description in the embodiments of the present application, it needs to be explained that if the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship when the product of the embodiments of the present application is usually placed, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, in order to distinguish different units, the first, second and the like are used in the specification, but these will not be limited by the order of manufacture, and cannot be understood as indicating or implying relative importance, and the name may be different in the detailed description and the claims of the present application.

[0026] The words in the specification are used for the purpose of describing the embodiments of the present application, but are not intended to limit the present application. It should also be noted that, unless otherwise explicitly specified and limited, if the terms "set", "connected", "connected" appear, they should be understood broadly, for example, they can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, can be directly connected, or indirectly connected through an intermediate medium, can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood concretely.

[0027] Figure 1 An architecture schematic diagram of a drag-to-drag test platform for testing the performance of a motor controller for vehicles is shown, the left half of the drag-to-drag test platform is a motor controller (i.e. the motor control unit part in the figure), and the right side is a motor simulator, as shown in Figure 1 The motor simulator includes a signal acquisition unit, a motor model unit, an inverter unit, and a driving unit. The signal acquisition unit acquires real-time voltages of each phase of the inverter unit and real-time currents of each bridge arm branch, and outputs them to the motor model unit and the driving unit. The motor model unit calculates the target current of each bridge arm branch according to the real-time voltage and current signals acquired by the signal acquisition unit. The driving unit determines and outputs the driving signals of each switching device in the inverter unit according to the real-time current and target current of each bridge arm branch of each phase, so as to track the target current and realize closed-loop control of the motor simulator.

[0028] During the drag-to-drag test, the motor simulator is connected to the inverter midpoint (phase node) of the motor controller under test through cascaded coupled inductors, for providing 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 measured inverter generates equivalent phase current and terminal voltage waveforms as a real motor under normal modulation.

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

[0030] Referring to Figure 2 , Figure 3 , for any one-phase inverter circuit, it includes n bridge arm branches connected in parallel between the DC bus power supply (U dc ) between the DC bus power supply (U Figure 2 In the embodiment, the number of bridge arm branches is 3, and in other embodiments, n can also 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, by increasing the number of bridge arm branches of each phase inverter circuit, the equivalent switching frequency of the inverter can be improved. However, with the increase of the number of bridge arm branches, the circulating current between the branches in the existing cascaded coupling structure will increase rapidly. Although various schemes for reducing high-frequency circulating current are currently disclosed, such as implementing active circulating current suppression through algorithms or adding H-bridge structures between each bridge arm branch to suppress high-frequency circulating current, the above schemes either increase the complexity of system control or are limited to specific application scenarios or increase the cost of the entire system. Meanwhile, the applicant has found through research that, Figure 2 and Figure 3 In the parallel multi-level cascaded coupling structure shown in the above two figures, the high-frequency circulating current inevitably increases with the increase of the number of parallel branches. Therefore, without changing the cascaded coupling topology, no matter what suppression algorithm is used, the problem caused by this inherent characteristic cannot be fundamentally solved.

[0035] Therefore, in the present application, the applicant discloses a three-phase-in-one parallel multi-level inverter with a brand-new topology structure, which can effectively solve the inherent problem of the increase of high-frequency circulating current with the increase of the number of branches in the cascaded coupling parallel multi-level structure used in the existing motor simulator while reducing the hardware cost.

[0036] Figure 4 The circuit structure schematic diagram of the three-phase-in-one parallel multi-level inverter in some specific embodiments is shown, Figure 5 the winding method of the three-phase-in-one magnetic ring contained therein is further shown, Figure 6 and the current flow direction of the inductance circuit composed of each three-phase-in-one magnetic ring is shown.

[0037] Referring to Figure 4 to Figure 6 , the three-phase-in-one parallel multi-level inverter provided by the present application comprises a three-phase inverter circuit and a plurality of three-phase-in-one magnetic rings.

[0038] Specifically, the three-phase inverter circuit is constructed in the same way as the three-phase inverter circuit architecture used in the existing motor simulator, that is, each phase inverter circuit comprises a plurality of bridge arm branches connected in parallel to a DC bus power supply, and each bridge arm branch comprises two switching devices connected in series. For example, in the embodiment shown in Figure 4 , the A-phase, B-phase and C-phase inverter circuits each comprise n (n≥2) switching branches connected in parallel between U dc , and each bridge arm branch comprises two switching devices connected in series.

[0039] The number of three-phase-in-one magnetic rings is equal to the number of bridge arm branches in any 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 combined magnetic rings is also n.

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

[0041] Reference Figure 4 to Figure 6 For example, for the first bridge arm branch (1 branch) of the A-phase, B-phase, and C-phase inverter circuits, respectively, a wire is led out from the midpoint, and the three wires are wound on the same choke coil. The currents flowing out from the midpoints of the three wires are denoted as i a1 , i b1 , i c1 , respectively. Similarly, the wires led out from the midpoints of the 2 branches of the A-phase, B-phase, and C-phase inverter circuits are wound on the same choke coil, and so on, until the wires led out from the midpoints of the n branches of the A-phase, B-phase, and C-phase inverter circuits are wound on the same choke coil. After the above winding is completed, the other ends of the wires led out from the A-phase inverter circuit on each choke coil are combined together as the A-phase current output end of the inverter, and the output current is denoted as i a . The other ends of the wires led out from the B-phase inverter circuit on each choke coil are combined together as the B-phase current output end of the inverter, and the output current is denoted as i b . The other ends of the wires led out from the C-phase inverter circuit on each choke coil are combined together as the C-phase current output end of the inverter, and the output current is denoted as i c .

[0042] Obviously, this winding method changes the commonly used inductance structure of the cascaded coupling of the independent inverter circuits of each phase to an inductance structure in which each magnetic ring is formed by winding one branch of each three-phase inverter circuit on the same choke coil, and then combining the same-phase parts of the n three-phase combined inductance structures. This change not only reduces the number of choke coils from 3n to n, but more importantly, significantly improves the suppression of high-frequency circulating current, and this suppression capability is not weakened by the increase in the number of bridge arm branches.

[0043] The mechanism of this in suppressing high-frequency circulating current is analyzed as follows.

[0044] For the existing power topology with cascaded coupling structure of each phase, increasing the number of bridge arm branches to improve the equivalent switching frequency will increase the path of system circulating current, and the system circulating current will increase. When the system circulating current exceeds a certain value, the magnetic device in the topology structure will be saturated, resulting in smaller impedance and losing the ability to suppress differential mode current.

[0045] The three-phase integrated inductive structure winding method used in the present application can make the magnetic flux generated by the three-phase current winding on the choke coil cancel each other out in the magnetic ring. At this time, the magnetic ring shows a net magnetic flux of zero to the outside, the common-mode impedance is extremely small, and theoretically it can realize the carrying capacity of unlimited current.

[0046] Specifically, the magnetic flux of the coil can be represented 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 of the enclosed area. For a three-wire parallel winding magnetic device, the expression of its magnetic flux satisfies:

[0049]

[0050] Compared with the traditional same-phase different-branch winding method of forming inductance on the same magnetic ring, the present patent adopts a scheme of simultaneously winding different-phase branches on the same magnetic ring in a three-phase topology. This scheme uses the feature that the sum of three-phase currents in a parallel multi-level structure is zero, so that the magnetic flux on each magnetic ring meets the above equation of summing to zero. Treating the three branches wound on the same magnetic ring as a parallel sub-module, the system circulating current of each parallel sub-module can be effectively suppressed.

[0051] That is, the three-phase integrated inductive structure provided by the present application can significantly reduce high-frequency circulating current by winding the midpoint lead of different-phase bridge arm branches on the same magnetic ring, rather than cascading the midpoint lead of each branch of the same phase on the magnetic ring. Moreover, the value of high-frequency circulating current is independent of the number of bridge arm branches, effectively solving the problem of increasing high-frequency circulating current with increasing number of branches, thereby greatly expanding the upper limit of the number of bridge arm branches that can be used by the motor simulator.

[0052] In order to distinguish the existing cascaded inductive structure, as shown in Figure 7 The magnetic ring formed by the three-phase integrated winding in the present application can be represented by three spiral lines, upper, middle and lower.

[0053] Figure 8In some specific embodiments, a physical diagram of a choke coil for winding a wire is shown. For a choke coil, the saturation characteristics of the magnetic device can cause it to lose its choke ability, so preferably, an amorphous nanocrystalline material with high relative magnetic permeability is used to make the choke coil. The outer surface of the choke coil is preferably provided with an insulating material layer (such as Figure 8 In the present application, the surface of the choke coil 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 plate) can be provided between the magnetic rings.

[0054] Considering the size of the magnetic device, the number of turns of the winding wire, and the subsequent demand for space of the inverter after the number of bridge branches is expanded, in some preferred embodiments, the outer diameter of the choke coil 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 be determined by testing the load and specific working conditions of the motor controller, then the wire is wound on the choke coil one turn at a time, and the inductance value is measured in real time, and finally the appropriate number of turns closest to the L value is determined. For example, in some specific embodiments, the required L value is 8mH to 12mH, and the choke coil winding magnetic ring shown in Figure 8 Each wire on the choke coil has a suitable number of turns of 10 to 15 turns.

[0056] In some preferred embodiments, considering the current peak value on each bridge branch and the skin effect of the current during the actual test of the drag experiment, the wire wound on the choke coil is selected to use a Litz wire with a current carrying capacity of not less than 50A.

[0057] Figure 9 In some preferred embodiments of the present application, a connection diagram of a three-phase integrated magnetic ring is shown. As shown in the figure, the three-phase integrated magnetic ring is used to wind the wire (the currents are i a1 , i b1 , i c1 ) drawn from the midpoint of each 1 branch of the three-phase inverter circuit. The difference between this embodiment and the previous embodiment is that in this embodiment, each wire wound on the choke coil is also connected with an additional inductance.

[0058] The position of the additional inductance connected on each wire can be as shown in Figure 9 , located at the winding completion position of the wire on the choke coil to the current output end of the corresponding phase (i.e. the i a end, i b end, i cAlternatively, the additional inductors can also be arranged between the point where the conductive wires are drawn out from the bridge arm branch (the midpoint) and the starting position of the winding of the conductive wires on the choke coil. That is, the additional inductors arranged in series on each conductive wire are located outside the respective choke coils.

[0059] The additional inductors arranged in series on each phase conductive wire after the winding on the choke coil is completed, and the purpose is to make the magnetic ring actively generate leakage inductance. These additional inductors do not participate in the interaction of the coupled inductance in the three-phase-in-one magnetic ring, so when measured by an impedance analyzer, this part does not participate in the measurement of mutual inductance, and is displayed as leakage inductance. The applicant found that when the additional inductors with appropriate inductance values are arranged on each conductive wire, the overall amplitude of the system circulating current will be significantly reduced.

[0060] The inductance value range of the additional inductors should be selected according to the inductance value (i.e. L) of the winding of each conductive wire on the choke coil. The inductance value cannot be too small or too large. If the inductance value is too small, the leakage effect will not be obvious, and if the inductance value is too large, the energy consumption and heat generation of the entire magnetic ring structure will be significantly increased. Preferably, when the inductance value of the winding of each conductive wire on the choke coil is 8mH to 12mH, the inductance value of the additional inductors arranged in series is set to be in the range of 100uH to 300uH.

[0061] In addition, in some preferred embodiments, each phase inverter circuit further comprises a plurality of bus filter capacitors, and the number of bus filter capacitors can be equal to the number of bridge arm branches, thereby filtering the bus voltage of each bridge arm branch in each phase inverter circuit one by one.

[0062] Some embodiments of the present application also provide a motor simulator comprising the three-phase-in-one parallel multi-level inverter, and the motor simulator further comprises a signal acquisition unit, a motor model unit, and a driving unit. The topological structure and control logic of the above functional units can be referred to the embodiments shown in the above motor simulator. Figure 1 The difference between the embodiments shown in the above motor simulator and the embodiments shown in the above motor simulator is that the inverter unit in the above motor simulator is replaced by the three-phase-in-one parallel multi-level inverter provided by the present application. Specific embodiment one

[0064] In order to verify the effect of the three-phase-in-one parallel multi-level inverter provided by the present application on the suppression of high-frequency circulating current, a three-phase-in-one multi-level inverter with four branches (i.e. each phase inverter circuit comprises four bridge arm branches) is built through the present embodiment, and a motor simulator comprising the three-phase-in-one parallel multi-level inverter is used for motor controller drag test.

[0065] Figure 10The physical diagram of the three-phase integrated parallel multi-level inverter is shown. As shown in the figure, the three-phase inverter circuit draws 12 wires, which are grouped according to the bridge arm branch number and then wound on four choke coils to form four three-phase integrated magnetic rings. The other end of the 12 wires is connected together in the same phase to form a three-phase output current terminal.

[0066] In addition, as shown in the figure, a small additional inductance is connected in series on each wire. Figure 8

[0067] The experimental platform adopts the same architecture as the experimental platform of the first embodiment, and the difference lies in that the three-phase integrated inverter provided by the present application is used to replace the inverter unit in the experimental platform of the first embodiment. Figure 1 Figure 1

[0068] The switch device selects the SiC-MOSFET of the CAS120M12BM2 model of the CREE company, the gate opening voltage is set to 18V, the gate closing voltage is set to -5V, and the driving chip of the 1ED020I12-F2 model is selected on this basis, and the corresponding driving circuit is designed. Table 1 shows the experimental parameter setting situation in this embodiment.

[0069] Table 1

[0070]

[0071]

[0072] In order to compare the high-frequency circulating current under different bridge arm branch numbers, the driving program is adjusted to realize current inversion of three-branch parallel and current inversion of four-branch parallel, and the current measurement circuit shown in the figure is used to measure the current on each bridge arm branch. Figure 11

[0073] Figure 12 , Figure 13 The A-phase circulating current situations of three-branch parallel and four-branch parallel are shown in the two figures, and the A-phase voltage command value is 10V, and the B-phase and C-phase voltage command values are -5V. By comparing the two figures, it can be seen that the circulating current amplitude is 620mA under three-branch parallel, and the circulating current amplitude is 618mA under four-branch parallel, which are almost completely consistent, effectively verifying that the three-phase integrated parallel multi-level inverter proposed in the present application will not change obviously with the increase of the branch number. Second embodiment

[0075] ​​​​In the embodiment two, the simulation experiment verifies that the high-frequency circulating current does not increase with the increase of the number of parallel multi-level inverter branches in the three-phase integrated topology provided by the application. The same parameters in Table 1 are used in the embodiment, and the high-frequency circulating current in the case of two branches, six branches, eight branches, ten branches and twelve branches is simulated and calculated respectively. Table 2 is the simulation result, and the existing conventional cascade coupling topology is also listed for comparison. At this time, the command voltage of the three phases is 0V, i.e. the duty ratio is 0.5.

[0076] Table 2

[0077]

[0078] As can be seen from Table 2, when the existing cascade coupling structure is used, the circulating current of each phase increases monotonously with the increase of the number of branches, while the amplitude of the zero sequence circulating current basically remains at 1*e-4 when the number of branches increases using the three-phase integrated topology of the application. -11 A left and right, it is verified that winding different phase branches on the same magnetic ring can significantly reduce the circulating current, which shows that the technical solution disclosed by the application can fundamentally inhibit the problem that the circulating current increases with the increase of the number of branches in the parallel multi-level topology, and provides a strong guarantee for constructing a motor simulator inverter topology with more than ten branches or even twenty branches.

[0079] The specific embodiments of the application are described in detail above, and for those skilled in the art, some improvements and modifications can be made to the application without departing from the principles of the application, and these improvements and modifications also belong to the protection scope of the claims of the application.

Claims

1. A three-phase integrated parallel multi-level inverter applied to a motor simulator, comprising three-phase inverter circuits, each of which comprises an equal number of bridge arm branches connected in parallel with a DC bus power supply, each of the bridge arm branches comprising two switching devices connected in series; characterized in that, Also included are: a plurality of three-phase integrated magnetic rings, the number of which is equal to the number of bridge arm branches in any one phase inverter circuit, each of which is formed by spirally winding three wires on a choke coil, 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 phase inverter circuit, and the other end forms a current output end of the corresponding phase in a same-phase connection manner.

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

3. The three-phase integrated parallel multi-level inverter according to claim 1, characterized in that, the choke coil is made of amorphous nanocrystalline material.

4. The three-phase integrated parallel multi-level inverter according to claim 3, characterized in that, an insulating layer is provided on the surface of the choke coil, or an insulating material is provided between adjacent choke coils.

5. The three-phase integrated parallel multi-level inverter according to claim 4, characterized in that, the outer diameter of the choke coil is 135-140mm, the width is 15-20mm, and the thickness is 20-35mm.

6. The three-phase integrated parallel multi-level inverter according to claim 5, characterized in that, an additional inductor is further connected in series on each wire, and the series connection position of the additional inductor is outside the choke coil.

7. The three-phase integrated parallel multi-level inverter according to claim 6, characterized in that, the inductance value of the wire wound on the choke coil is 8-12mH, and the inductance value of the additional inductor is 100-300uH.

8. The three-phase integrated parallel multi-level inverter according to claim 1, characterized in that, each phase inverter circuit further comprises a plurality of bus filter capacitors for filtering the bus voltage of each bridge arm branch in each phase inverter circuit.

9. An electric motor simulator comprising a signal acquisition unit, an electric motor model unit, a drive unit and an inverter unit, characterized in that, the inverter unit is the three-phase integrated parallel multi-level inverter of claim 1.

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