Motor simulator and test platform for NPA three-phase motor

Abstract

The application provides a motor simulator for an NPA three-phase motor and a test platform, and the motor simulator for the NPA three-phase motor comprises: a four-bridge-arm inverter, which comprises three-phase bridge-arm branches and phase bridge-arm branches for simulating three-phase current characteristics and neutral-point electrical characteristics of the NPA three-phase motor; a four-branch interface filter for filtering the current output by the four-bridge-arm inverter; a four-branch signal acquisition unit for acquiring current and phase voltage signals; an NPA motor model unit for generating target current on the EME side based on a motor mathematical model of the NPA three-phase motor; a four-branch closed-loop current control unit for controlling the switching of power devices in each bridge-arm branch of the four-bridge-arm inverter by using a closed-loop current control strategy based on neutral-point current tracking and phase compensation; and a DC power supply on the EME side connected between the common anode and the common cathode of the four-bridge-arm inverter. The technical scheme of the application can accurately simulate the electrical characteristics of the NPA three-phase motor.

Description

Technical Field

[0001] This application belongs to the field of motor control technology and relates to motor simulator technology. Specifically, it provides a motor simulator and a drag testing platform for NPA three-phase motors. Background Technology

[0002] An Electric Motor Emulator (EME) is a power-level hardware-in-the-loop (HIL) testing device that uses a power electronic converter to simulate the electrical characteristics of a real motor and tests the Motor Drive Unit (MDU). The "MDU-EME" drag-and-drop testing architecture can flexibly, efficiently, and safely perform MDU performance tests under various motor operating conditions, effectively solving the problems of large size, high cost, limited dynamic performance, and low efficiency of traditional drag-and-drop testing methods based on real motors and mechanical loads.

[0003] A neutral point accessible three-phase motor, or NPA (Neutral Point Accessible) for short, is a new type of motor that expands applications by bringing the common connection point (neutral point) of the three-phase star (Y-type) windings to the outside of the motor as an independent electrical terminal. This structure expands the motor's control freedom from the traditional two-dimensional (dq axis) to three-dimensional (dq0 axis), making the zero-sequence current (i0) or the neutral point lead current an independently controllable variable. Bringing out the neutral point allows the motor windings to function not only as energy consumers but also as a bidirectional energy conversion interface, enabling applications beyond driving and power generation, such as busbar interaction, low-voltage fast charging, and bidirectional charging and discharging for vehicle connectivity.

[0004] Currently, various three-phase motors using the NPA architecture, such as NPA-PMSM (neutral point-leaded permanent magnet synchronous motor), have received widespread attention in engineering applications. To ensure the reliability of NPA three-phase motor drive systems, rigorous verification of the control functions and reliability of their MDUs under various operating conditions before commissioning has become a key aspect of system development. However, most existing EMEs are designed for traditional three-phase motors without a neutral point, and their electrical models and control architectures do not include independent simulation capabilities for voltage and current at the neutral point. Therefore, EME testing schemes for NPA three-phase motors still have significant deficiencies and cannot meet the hardware-in-the-loop testing requirements of the unique three-dimensional current control strategy of NPA three-phase motors. Summary of the Invention

[0005] This application provides a motor simulator for NPA three-phase motors through embodiments, including: A four-arm inverter includes three-phase arm branches for simulating the three-phase current characteristics of an NPA three-phase motor, and neutral point electrical characteristics for simulating the NPA three-phase motor. Xiangqiao arm branch road; The four-branch interface filter is used to filter the current output by the four-arm inverter. The four-branch signal acquisition unit is used to acquire current and phase voltage signals; The NPA motor model unit generates the target current on the EME side based on the mathematical model of the NPA three-phase motor. A four-branch closed-loop current control unit, employing neutral point current tracking and... A phase-compensated closed-loop current control strategy controls the switching of power devices in each arm branch of a four-arm inverter. The EME-side DC power supply is connected between the common anode and common cathode of the four-arm inverter.

[0006] This application also provides a towing test platform for NPA three-phase motors through embodiments, including a towing connected motor drive unit under test and the aforementioned motor simulator for NPA three-phase motors.

[0007] The embodiments of this application provide a motor simulator for NPA three-phase motors and a test platform for using the simulator, which have at least the following beneficial effects: 1) Fully supports electrical performance simulation of neutral-point-leaded three-phase motors, through additional settings Phase power bridge arms enable physical simulation of the motor neutral point, overcoming the limitation of typical simulators that only support... Insufficient modeling and control of axes, including the missing 0 axis; 2) By optimizing the tracking target and compensation strategy, the mutual cancellation effect between the PI regulation output and the SVPWM common-mode voltage caused by directly tracking the zero-sequence current is avoided, ensuring high voltage utilization. At the same time, the zero potential reference point drift problem caused by the power supply isolation between the MDU side and the EME side is automatically avoided. Meanwhile, the influence of common-mode voltage disturbance on the 0-axis current can be effectively suppressed. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of an NPA three-phase motor application scenario; Figure 2 This is a schematic diagram of another NPA three-phase motor application scenario; Figure 3 This is a schematic diagram of another NPA three-phase motor application scenario; Figure 4 This is a schematic diagram of another NPA three-phase motor application scenario; Figure 5This is a schematic diagram of the architecture of an existing MDU-EME drag-and-drop testing platform; Figure 6 A schematic diagram illustrating the scheme analysis for performing NPA three-phase motor simulation using an existing EME; Figure 7 This is a schematic diagram of the architecture of a motor simulator for an NPA three-phase motor and a drag test platform for an NPA three-phase motor, provided according to embodiments of this application. Figure 8 This is a schematic diagram of the architecture of a drag test platform for a specific application scenario of an NPA three-phase motor, according to an embodiment of this application. Figure 9 This is a schematic diagram of the architecture of a drag test platform for another specific application scenario of an NPA three-phase motor, according to an embodiment of this application. Figure 10 This is a schematic diagram of the architecture of a drag test platform for another specific application scenario of an NPA three-phase motor, according to an embodiment of this application. Figure 11 This is a schematic diagram of a four-branch closed-loop current control architecture that tracks zero-sequence current. Figure 12 This is a schematic diagram of a four-branch closed-loop current control architecture that tracks the neutral point current. Figure 13 A schematic diagram illustrating the working principle of the PWM module in a four-branch closed-loop current control architecture for tracking neutral point current. Figure 14 This is a schematic diagram of the architecture of a four-branch closed-loop current control unit in a motor simulator for an NPA three-phase motor provided according to an embodiment of this application. Figure 15 The position is provided according to the embodiments of this application. Axis PI controller and A schematic diagram of a phase PI controller; Figure 16 This is a physical diagram of the test platform for NPA three-phase motors constructed according to the embodiments of this application; Figure 17 To adopt Figure 11 The diagram shows the simulation results of the NPA three-phase motor electrical performance of the four-branch closed-loop current control strategy. Figure 18 To adopt Figure 14 The diagram shows the simulation results of the NPA three-phase motor electrical performance of the four-branch closed-loop current control strategy. Figure 19 A schematic diagram comparing the current when n-phase compensation is off and when n-phase compensation is on; Figure 20A schematic diagram comparing the harmonic components of different closed-loop current control strategies. Detailed Implementation

[0009] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0010] As introduced in the background technology section, with the iteration of power electronics technology and frequency conversion control technology, the neutral point lead-out three-phase motor, namely the NPA three-phase motor, has broken through the functional limitations of the traditional three-phase motor topology by adding an extra degree of control freedom, and provides a structural foundation for the expansion of applications in various scenarios such as new energy vehicles.

[0011] For example, in Figure 1 In the scenario depicting the interaction between the low-voltage DC power supply and the high-voltage bus, the low-voltage power supply of EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) is mismatched with the high-voltage bus voltage. Using a traditional independent DC-DC converter would increase the vehicle's size, weight, and cost, and reduce its range. Employing a neutral-point NPA-PMSM allows the low-voltage DC power supply to be directly connected to the motor's neutral point. Through zero-sequence voltage compensation control, normal PMSM operation and DC bus voltage regulation can be simultaneously achieved, improving system integration.

[0012] For example, in Figure 2 In the scenario of adapting EV and HEV batteries to 800V low-voltage fast charging, conventional DC fast charging architecture cannot directly charge 800V batteries. Adding an on-board DC-DC boost converter will also increase size, weight, cost and reduce range. By using the NPA-PMSM integrated charger, the zero-sequence circuit formed by the motor neutral point and windings can achieve double voltage boost without additional components, simplifying the system structure and reducing costs and energy consumption.

[0013] For example, in Figure 3 In the phase loss fault-tolerant drive and boost scenario shown, to meet the reliability requirements of three-phase motor drive, the boost-type four-bridge inverter connects the DC power supply between the motor neutral point and the fourth bridge arm: during normal operation, the equivalent two-stage drive topology achieves boost, and during a phase loss fault, the motor only needs two normal phases to operate. Injecting a specific current component corrects the reference values ​​of the direct-axis current and neutral point current to ensure stability, without the need for complex topology reconfiguration.

[0014] For example, in Figure 4In the bidirectional fast charging scenario of vehicle interconnection shown, with NPA-PMSM as the core, an integrated bidirectional DC-DC converter can be built by connecting the neutral point of the motor windings of two electric vehicles to the negative terminal of the vehicle's transmission system bus. This allows for bidirectional power flow control without the need to reconfigure the motor windings, add a mechanical clutch, or adjust the transmission inverter, providing a low-cost solution for emergency vehicle charging.

[0015] Figures 1 to 4 Taking the NPA-PMSM (neutral point lead-out permanent magnet synchronous motor) as an example to illustrate the application of the neutral point lead-out topology in drive-boosting, those skilled in the art should understand that the NPA-PMSM in the above figures can also be replaced by other three-phase motors using the NPA architecture, such as NPA-HESM (Hybrid Excitation Synchronous Motor), NPA-EESM (Electrically Excited Synchronous Motor), or NPA-IM (Induction Motor). Apart from differences in the motor's own excitation method, rotor structure, and equivalent electrical parameters, these NPA three-phase motors share similarities in the use of neutral point lead-out terminals and the mechanisms for achieving functional expansion. Figures 1 to 4 The embodiments shown are essentially the same.

[0016] To ensure the operational safety of NPA three-phase motors in the aforementioned application scenarios, it is necessary to verify the control functions and reliability performance of the motor drive unit (MDU) used in the NPA three-phase motor, especially to conduct extreme condition tests in the aforementioned application scenarios. This places the following simulation requirements on the EME for NPA three-phase motors: (1) The EME must be equipped with four physical ports (corresponding to respectively) Mutually, Mutually, The simulator (including phase and neutral point leads) can accurately reproduce the electrical characteristics of the motor ports under all operating conditions to meet the simulation requirements of NPA three-phase motors. In particular, when the phase lines are open and the motor is rotating, the simulator must accurately simulate the phase voltage. , , This is to ensure effective simulation of the back electromotive force. Under this operating condition, the neutral point voltage should be stabilized near the midpoint of the DC bus to provide a sufficiently large positive and negative voltage range to the phase voltages; (2) Analyze the input-output relationship under the change of the 0-axis (zero-sequence axis) in the NPA three-phase motor model, especially to find the factors that affect the simulation accuracy of the zero-sequence current, so as to provide a theoretical basis for targeted processing; (3) Design a controller that is compatible with the power topology and motor model of the EME-side inverter, especially to solve the neutral point current tracking error caused by the adjustment of the power topology and motor model.

[0017] However, most existing motor simulators (EMEs) are based on traditional three-phase AC motor designs without a neutral point. Their power topology, signal acquisition and control output relationship, and controller tracking target do not take into account the structural characteristics of a neutral point, and therefore cannot meet the need for accurate simulation of the electrical characteristics at the neutral point of an NPA three-phase motor.

[0018] For example, Figure 5 This paper illustrates an EME for a conventional three-phase motor (without a separately led-out neutral point) and the architecture of an MDU-EME-based drag test platform built using this EME. The motor simulator is powered by a DC power supply (voltage: [voltage value missing]) on the EME side. The system consists of a signal acquisition unit, a motor model unit, a closed-loop control unit, an EME-side inverter, and an interface filter (IF). The EME-side inverter's phases ( Mutually, Mutually, The midpoint of the bridge arm branch and each phase of the MDU-side inverter (phase) Mutually, Mutually, The midpoints of the (phase) bridge arm branches are connected one-to-one in phase through interface filters to achieve energy conversion and filtering between the MDU and EME.

[0019] During the towing experiment, the phase voltage output by the MDU is acquired by the signal acquisition unit of the EME and input into the motor model unit. The motor model is used to calculate the current that the actual motor should generate, which is then used as the target current on the EME side and output to the closed-loop control unit. The closed-loop control unit calculates the control voltage of each phase on the EME side and generates the corresponding PWM signal to drive the switching devices of the inverter on the EME side, thereby simulating the output current of the real motor.

[0020] Figure 5 The EME shown, designed for traditional neutral-point-unexposed three-phase motors, has significant drawbacks in its power topology when simulating NPA three-phase motors. The following section combines... Figure 6 A detailed analysis will be conducted.

[0021] Figure 6 This illustrates an alternative approach for NPA three-phase motor simulation using an EME designed for conventional three-phase motors: Option 1: Take the neutral point out end Directly connected to the midpoint of the DC bus .

[0022] This scheme relies on Kirchhoff's current law, indirectly constraining the neutral point current through three-phase current control, theoretically enabling four-current tracking. However, the DC component in the neutral point current causes continuous charging and discharging of the DC bus capacitor, leading to voltage fluctuations at the midpoint of the series capacitor and consequently, loss of control stability. Furthermore, under long-term high-current conditions, it accelerates capacitor aging and may even damage power devices.

[0023] Option 2: Take the neutral point out end Connect to the auxiliary inductor terminal .

[0024] like Connected to the front end of the current sensor Then at the three-phase port and An external circulating current is formed directly between the phase ports without passing through the current sensor, making it impossible to independently control the current at the neutral point, thus failing to meet the port current simulation requirements of the NPA three-phase motor. like Connected to the back end of the current sensor Although the external three-phase current and the current at the neutral point can be controlled, the current distribution flowing through the inverter is unrestrained, which can easily generate internal circulating current, increase system losses, and in severe cases, cause the power module to overheat and be damaged.

[0025] It is evident that selecting a neutral point on the DC side of a traditional three-arm bridge topology will cause voltage fluctuations, while selecting a neutral point on the AC side will introduce circulating current.

[0026] The aforementioned defects cannot be solved simply by adding voltage or current sensors. The root cause lies in the insufficient control degrees of freedom. Therefore, in order to meet the simulation requirements of NPA three-phase motors, it is necessary to fundamentally modify the traditional three-arm topology to add additional control degrees of freedom to independently adjust the voltage and current at the neutral point. Then, based on the newly added degrees of freedom, a corresponding signal acquisition and closed-loop control scheme should be designed to accurately reproduce the neutral point electrical characteristics of the NPA three-phase motor.

[0027] To achieve the above objectives, this application proposes a novel motor simulator for NPA three-phase motors, and a test platform for using the motor simulator. Figure 7 The architecture of the motor simulator for NPA three-phase motors is shown in some embodiments, as well as the architecture of the towing test platform for NPA three-phase motors composed of the novel motor simulator and the MDU towing unit.

[0028] like Figure 7As shown, the motor simulator for NPA three-phase motors includes a four-arm inverter, a four-branch interface filter, a four-branch signal acquisition unit, an NPA motor model unit, a four-branch closed-loop current control unit, and an EME-side DC power supply.

[0029] in: The four-arm inverter includes three-phase arm branches for simulating the three-phase current characteristics of an NPA three-phase motor, and neutral point electrical characteristics for simulating the NPA three-phase motor. Xiangqiao arm branch road; The four-branch interface filter is used to filter the current output from the four-arm inverter. The four-branch signal acquisition unit is used to acquire current and phase voltage signals; The NPA motor model unit generates the target current on the EME side based on the mathematical model of the NPA three-phase motor. The four-branch closed-loop current control unit adopts a neutral point current tracking and... A phase-compensated closed-loop current control strategy controls the switching of power devices in each arm branch of a four-arm inverter. The EME-side DC power supply is connected between the common anode and common cathode of the four-arm inverter to provide a stable DC bus voltage for the four-arm inverter on the EME side.

[0030] like Figure 7 As shown, when it is necessary to test the performance of the motor drive unit driving the NPA three-phase motor in different application scenarios, the motor drive unit under test and the motor simulator for the NPA three-phase motor can be connected in a drag connection to form a drag test platform for the NPA three-phase motor. The motor drive unit under test includes a drive controller, an MDU-side inverter, and an MDU-side DC power supply.

[0031] Specifically, the drive controller is a drive controller for NPA three-phase motors. A closed-loop control strategy is set based on the type of NPA three-phase motor to be tested to control the switching of power devices in each bridge arm branch of the MDU-side inverter. The DC power supply on the MDU side is used to provide power injection to the drive unit of the motor under test.

[0032] Furthermore, such as Figure 7 As shown, between the MDU side and the EME side, the MDU-side inverter and the MDU-side DC power supply are connected to the motor simulator facing the NPA three-phase motor via a neutral point lead-out method. Specifically, the three-phase lines in the EME-side four-arm inverter ( Mutually, Mutually, (phase) and the three-phase lines of the MDU-side inverter ( Mutually, Mutually, (phase) connection method and Figure 5 They are consistent, all connected one-to-one through the corresponding filter inductors of the four-branch interface filters. Phase line (i.e.) (Midpoint lead-out of phase bridge arm branch) passes through the four-branch interface filter After the corresponding filter inductor, a neutral point simulation terminal N is formed. This terminal N is used to simulate the electrical characteristics at the neutral point of an NPA three-phase motor, such as current and voltage characteristics.

[0033] Therefore, the MDU-side inverter and MDU-side DC power supply are connected to the motor simulator for the NPA three-phase motor via a neutral point lead-out method. The key is that the neutral point simulation terminal N is connected to the MDU-side inverter and MDU-side DC power supply via a neutral point lead-out method.

[0034] It should be noted that, depending on the application scenario being tested, different neutral point lead-out connection methods can be used between the neutral point analog terminal N and the MDU-side inverter and MDU-side DC power supply. For example, Figure 8 , Figure 9 , Figure 10 Three specific embodiments of the drag test platform for NPA three-phase motors are shown respectively. These three drag test platforms correspond to... Figure 1 , Figure 2 , Figure 3 The application scenarios are as follows: driving DC bus voltage regulation, low-voltage fast charging, and phase loss fault-tolerant driving and boosting scenarios, to test the ability of the motor drive unit under test to drive an NPA three-phase motor.

[0035] like Figure 8 As shown, the negative terminal of the DC power supply on the MDU side is connected to the common cathode of the three-phase inverter on the MDU side, and the positive terminal is connected to the neutral point analog terminal N. The three bridge arm branches of the three-phase inverter on the MDU side are connected in parallel to the high-voltage DC bus.

[0036] like Figure 9 As shown, the DC power supply on the MDU side is connected in parallel with the DC bus capacitor of the three-phase inverter on the MDU side. At the same time, a fast DC charger is connected between the common cathode and the neutral point analog terminal N of the inverter on the MDU side.

[0037] like Figure 10 As shown, the MDU-side inverter is a four-arm inverter, designed for connection with the EME-side inverter. Distinguish between the phase bridge arm and the neutral point analog terminal N. The midpoint of the fourth bridge arm branch of the MDU-side inverter is denoted as N'. Then, the DC power supply of the MDU side is connected between point N' and the neutral point analog terminal N.

[0038] Obviously, in the above specific towing test platform architectures, both the motor simulator for the NPA three-phase motor and the motor drive unit under test adopt a neutral point lead-out towing connection method. Furthermore, the DC power supply on the MDU side, as the power source for the motor drive unit under test, can be a bidirectional DC power supply or a device with bidirectional power conversion characteristics, such as an actual vehicle battery, which can both output power to the MDU side and absorb power from the MDU side.

[0039] The following is based on Figure 8 Taking the drive-DC bus voltage regulation scenario shown as an example, this paper provides a detailed explanation of each functional unit of the motor simulator for NPA three-phase motors. It is understood that... Figures 8 to 10 The only difference in the embodiments shown is the connection method between the neutral point analog terminal N and the MDU-side device, therefore... Figure 8 The implementation method of each functional unit inside the motor simulator, as illustrated by the example, is also applicable to... Figure 9 , Figure 10 The example shown.

[0040] <Four-arm inverter and its power supply method, four-branch interface filter> like Figure 8 As shown, in the motor simulator for NPA three-phase motors provided in this application, the EME-side inverter adopts a four-arm inverter, which includes four arm branches. Each arm branch consists of two power devices, such as SiC MOSFETs and IGBTs. Among them, three arm branches are similar to the inverter structure of conventional motor simulators. Figure 5 As shown in the diagram, the midpoints of these three bridge arm branches are respectively used as... Mutually, Harmony The current output terminals of the three phases are used to output the three-phase current (to simulate the three-phase current characteristics of an NPA three-phase motor). Correspondingly, these three bridge arm branches are respectively called... Xiangqiao arm branch road, Xiangqiao arm branch road and Xiangqiao arm branch road.

[0041] In addition, such as Figure 8 As shown, the four-arm inverter also includes an arm branch for simulating the neutral point electrical characteristics of an NPA three-phase motor. In the embodiments of this application, this arm branch is referred to as... In a phase bridge arm branch, the midpoint between the two power devices in the bridge arm branch is denoted as point n.

[0042] The four-branch interface filter is used to filter the current output at the midpoint of the four bridge arm branches to obtain the three-phase current and neutral point current used to simulate the output characteristics of a real NPA three-phase motor.

[0043] Specifically, refer to Figure 8 The four-branch interface filter includes filter inductors corresponding to each bridge arm branch of the four-arm inverter, which can be referred to as... Phase filter inductor, Phase filter inductor, Phase filter inductor and Phase filter inductor, correspondingly, Phase filter inductor, Phase filter inductor, Phase filter inductor and The first terminal of the phase filter inductor is respectively connected to Xiangqiao arm branch road, Xiangqiao arm branch road, Xiangqiao arm branch road and Midpoint connection of the bridge arm branch.

[0044] When using this motor simulator designed for NPA three-phase motors for drag testing Phase filter inductor, Phase filter inductor, The second terminal of the phase filter inductor is connected to the inverter on the MDU side. Xiangqiao arm branch road, Xiangqiao arm branch road and The midpoints of the bridge arm branches are connected one-to-one. The second end of the phase filter inductor serves as a terminal that simulates the electrical characteristics at the neutral point of a real motor. As mentioned above, in the embodiments of this application, this terminal is referred to as the neutral point simulation terminal N.

[0045] In some alternative embodiments, the four-branch interface filter uses filter inductors with the same inductance value connected to each bridge arm branch, without loss of generality, to This represents the inductance value of the filter inductor connected to the midpoint of each bridge arm branch, in... This indicates the value of its parasitic resistance. In some alternative instances, the inductance value of the filter inductor in the n-phase bridge arm branch can also be set differently from that of the other three bridge arm branches.

[0046] The common anode and common cathode of the four-arm inverter are connected to the EME-side DC power supply, thus providing a stable DC bus voltage for the four-arm inverter. The voltage difference between its positive and negative terminals is denoted as... Accordingly, the common cathode of the four-arm inverter is represented by point g.

[0047] Furthermore, in Figure 8 In the application scenario shown, the DC power supply on the MDU side is connected between the common cathode (represented by point G) and the neutral point analog terminal N of the MDU-side inverter, and the voltage difference between its positive and negative terminals is as follows: indicates that the power supply is configured to inject power into the entire MDU, and through this neutral point lead-out connection method, the regulation of the DC bus voltage can be achieved

[0048] <Four-branch signal acquisition unit> The four-branch signal acquisition unit is configured to collect current and voltage signals, wherein, as Figure 8 shown, the collected current signals are the phase, phase, phase current signals output by the four-leg inverter, and the collected phase current signals are fed back to the four-branch current closed-loop control unit described later, serving as feedback quantities for tracking the target current.

[0049] It can be understood that, due to the , , three-phase lines of the MDU-side inverter are connected to the , , three-phase lines through filter inductors, the three-phase current signals on both sides are consistent. Therefore, the current signals collected by the signal acquisition unit are actually three-phase current signals that are connected in a drag-to-drag manner and pass through interface filtering.

[0050] The voltage signals collected by the four-branch signal acquisition unit are phase voltage signals output by the MDU-side inverter. The phase voltage signals, as the EME-side reference voltage of the motor inverter, are input to the NPA motor model unit described later, so as to calculate the EME-side target current of the motor simulator.

[0051] It should be noted that, due to the adoption of the neutral point lead-out method, the zero-axis voltage parameter needs to be introduced in the target current calculation process , which is different from the manner in which the EME of a conventional three-phase motor only needs to collect two line voltage signals (such as , ), and the other line voltage can be directly calculated from the three-phase voltage relationship. In the motor simulator for NPA three-phase motors proposed in the present application, the voltage signals collected by the four-branch signal acquisition unit on the MDU side are three paths of phase voltage signals from the midpoint of the three-phase bridge arm branches of the MDU-side inverter relative to the neutral point simulation terminal N, that is , and .

[0052] <NPA motor model unit> The NPA motor model unit converts the voltage signals collected by the four-branch signal acquisition unit (i.e., the EME-side reference voltage) into the target current of the motor simulator through a motor mathematical model that can characterize the current-voltage conversion characteristics of the NPA three-phase motor.​

[0053] It should be noted that the original voltage signals acquired by the four-branch signal acquisition unit are three-phase voltage signals, and the motor model generally uses... The coordinate system is described using an axial coordinate system. Therefore, before transforming using the mathematical model of the motor, a coordinate system transformation is required through Clark+Park transformation. ),Will , and Convert to stator in axial coordinate system shaft voltage , shaft voltage and zero-sequence voltage The coordinate transformation method described above is known to those skilled in the art; for example, it can be performed before the signal acquisition unit outputs a voltage signal to the motor model unit. , , )arrive( , , The transformation can also be received in the motor model unit. , , After that, this conversion is performed before solving for the target current.

[0054] The mathematical model of the motor used in the NPA motor model unit is determined according to the type of motor to be simulated. Taking the neutral point lead-out permanent magnet synchronous motor (NPA-PMSM) as an example, when this type of motor needs to be simulated, the NPA motor model simulation unit solves for the target current on the EME side using the following mathematical model: (1), in, , , The stators of NPA-PMSM are respectively shaft voltage, Axis voltage and zero-sequence voltage, , , The stators of NPA-PMSM are respectively shaft current, shaft current and zero-sequence current, , , The stators of NPA-PMSM are respectively Shaft inductance, Shaft inductance and zero-sequence inductance, For stator winding resistance, The electric angular velocity of the NPA-PMSM For NPA-PMSM magnetization.

[0055] It is understandable that when it is necessary to simulate other types of NPA three-phase motors, such as neutral point lead-out hybrid excitation synchronous motors (NPA-HESM), it is only necessary to replace the motor mathematical model in equation (1) with the motor mathematical model corresponding to NPA-HESM.

[0056] At the same time, based on Kirchhoff's current law and , , and The constant amplitude transformation relationship of the shaft current can be used to obtain the zero-sequence current. With the flow point current (In the embodiments of this application, the flow point) The relationship between the current (called neutral point lead current, or simply neutral point current) and the neutral point lead current is as follows: (2).

[0057] Specifically, the motor model unit acquires and converts the signal obtained by the signal acquisition unit. , , After that, it is used as the voltage reference value and substituted into the differential equation system of equation (1) to solve for the obtained value. , , This refers to the EME side that performs closed-loop current control on the motor simulator (for NPA-PMSM). Target current of shaft , , Furthermore, according to equation (2), the target current at the neutral point on the EME side can be determined simultaneously. .

[0058] As mentioned above, if it is necessary to simulate other types of NPA three-phase motors, simply replace equation (1) accordingly.

[0059] As can be seen, the mathematical model of the motor used in the NPA motor model unit is consistent with that of a typical three-phase motor. Without considering abnormal operating conditions such as shaft current, a typical three-phase motor can essentially be regarded as a zero-sequence current motor. The special case of an NPA three-phase motor with a constant value of zero, from the perspective of engineering applications of motor simulators, the differences in the above motor mathematical models are mainly reflected in the two dimensions of input and output.

[0060] In terms of model input, i.e., signal acquisition, as mentioned earlier, a motor simulator for a typical three-phase motor needs to acquire at least two voltage signals. However, a motor simulator for an NPA three-phase motor, because its voltage equation requires the introduction of the zero-axis voltage parameter, needs to acquire at least three phase voltage signals to convert them into voltage signals. , , .

[0061] In the model output dimension, The mathematical model of the NPA three-phase motor in the axial coordinate system can output the three-dimensional components of the target current on the EME side. , , Therefore, it is necessary to adjust the three sets of currents on the EME side. , , Independent tracking control is implemented for each phase. In contrast, for motor simulators designed for typical three-phase motors, the constraints between the three-phase currents... The natural value is 0, therefore only the value needs to be adjusted. , Two-dimensional current components can be used for tracking and control.

[0062] <Challenges in accurately simulating the electrical characteristics of NPA three-phase motors> The closed-loop current control unit is used to drive the four-arm inverter, enabling the current filtered by the four-branch interface filter to accurately track the target current calculated by the NPA motor mathematical model. As analyzed earlier, the target current includes, in addition to the conventional... In addition to the target shaft current, it also includes a target current related to the zero-sequence current, which, compared to typical motor simulators, only requires control of the target shaft current. The accurate simulation of shaft currents, particularly zero-sequence currents, faces the following challenges.

[0063] A. Time-varying voltage reference point introduced by power supply isolation according to Figure 8 The four-arm inverter topology shown has an independent EME-side DC power supply on the EME side, which is not grounded with the MDU-side DC power supply. While this isolation design brings safety and system independence, it also causes uncertainty in the voltage reference point at the control level.

[0064] Depend on Figure 8 The MDU-EME dual-drive architecture can establish the following voltage-current relationship: (3), in, , , The stator on the MDU side uses point G (i.e., the common cathode of the MDU-side inverter) as the zero potential reference point. shaft voltage, Axis voltage and zero-sequence voltage, , , These are the MDU sides with point G as the zero potential reference point. shaft voltage, Axis voltage and zero-sequence voltage, , , After interface filtering shaft current, Shaft current and zero-sequence current are determined by analyzing the three-phase current flowing through the filter inductor. After axis transformation, As mentioned earlier, these are the inductance values ​​of each filter inductor in the four-branch interface filter. This is the parasitic resistance value of the filter inductor.

[0065] Furthermore, according to the definitions of voltage and duty cycle, we can obtain: (4), in, , , for , , Three-phase average duty cycle converted to Equivalent value after axial coordinate system This refers to the DC bus voltage of the MDU-side inverter. The voltage at the neutral point of an NPA three-phase motor relative to point G can be understood as the voltage when simulating an NPA three-phase motor using a motor simulator. This is the neutral point analog terminal. The voltage relative to point G.

[0066] From equation (4), it can be seen that under the NPA three-phase motor architecture, from The conversion of the axial voltage duty cycle is independent of the zero potential reference point; therefore, in In the axial coordinate system, the motor simulator axis, The zero potential reference point g of the shaft reference voltage (i.e., the common cathode of the four-bridge arm inverter) and the zero potential reference point G of the motor drive unit can be decoupled. Even if there is a difference between the two zero potential reference points, the validity of the first two equations in (3) is still unaffected. That is, the first two equations in (3) can be written as: (5).

[0067] in, , Taking point G as the zero reference point, , Point g is taken as the zero potential reference point.

[0068] However, for the third equation in (3), due to the change in the conversion relationship of the duty cycle of the NPA three-phase motor, When the zero potential reference points g and G of the EME side voltage and the MDU side voltage are inconsistent, equation (3) should be written as: (6).

[0069] It is evident that the voltage-current relationship along the 0-axis is related to the difference between the potential reference points on the EME and MDU sides. The time-varying nature of this difference in zero-potential reference points significantly increases the difficulty of controlling the zero-sequence current compared to other methods. Shaft current control.

[0070] B. Problems with using open-loop control The basic principle of a typical open-loop current design for a motor simulator is to directly calculate the target voltage output of the EME by using known motor simulation parameters and coupling network parameters, combined with the voltage equation given by the motor mathematical model, without using current or voltage sensors for feedback. This shortens the control loop and improves dynamic response.

[0071] The situation is different for motor simulators designed for NPA three-phase motors. The following explanation still uses NPA-PMSM as an example, and the conclusions can be extended to other types of NPA three-phase motors.

[0072] As mentioned earlier, since the motor simulator's filter uses an LR structure, the phase currents on the EME side and the MDU side are equal, that is: (7), in, .

[0073] Combining equations (1) and (3) and performing a Laplace transform, while considering the time-varying nature of the voltage difference between point g and point G, we can obtain: (8), in, For the Laplace operator, , , , , , , , , , Each by , , , , , , (Right now ), , , The Laplace transform is performed to obtain... It is then obtained by performing a Laplace transform on the potential difference between point g and point G.

[0074] As can be seen from equation (8), for the NPA motor architecture, the motor simulator's The target voltage for the 0 axis can be directly solved, and its solution method is consistent with the control logic of a typical motor simulator. However, the target voltage for the 0 axis exhibits... as well as Since all of these are unknown quantities, the target voltage cannot be directly solved using only formula (8), meaning that open-loop control cannot be used.

[0075] C. Target selection under current closed-loop control The current closed-loop control approach for the motor simulator involves building a PI current closed-loop controller in the EME to control the interface filter current. Adjustments are made to dynamically track the reference current calculated by the motor mathematical model, where, as mentioned earlier, the motor mathematical model uses the terminal voltage of the MDU. As an input driver, the PI controller is a single-input single-output (SISO) controller, i.e. axis, The 0 axis and the 0 axis each achieve closed-loop current control through their own independent PI controllers.

[0076] The following explanation will still use NPA-PMSM as an example. Referring to typical motor current controller design methods, it is usually possible to ignore the contents of equation (1). The terms are used to derive the first-order transfer function of the NPA-PMSM permanent magnet synchronous motor (PMSM) (subscript...). (This refers to the motor), that is: (9).

[0077] Similar to the motor model, in In the axial coordinate system, the single-input single-output (SISO) transfer function of the interface filter is shown in the following equation (subscript...). (Represents interface filter) (10).

[0078] Based on equations (9) and (10), we can establish the following: Figure 11 The example shown is shaft current, The closed-loop current control framework, with shaft current and zero-sequence current as the tracking target, is shown in the figure. This framework can be applied to the closed-loop current control framework (tracking) of a conventional three-phase motor. Shaft target current, The target current of the axis (the zero-sequence target current is naturally 0) is obtained by extending it, that is, in addition to being used for the target current of the axis, the target current of the zero sequence is naturally 0. Axis target current , Axis target current The PI controller performs tracking to output separately. Shaft control voltage and Shaft control voltage In addition, an extra one was added for tracking the zero-sequence target current. The PI controller receives the zero-sequence target current calculated by the motor model unit and feedback from the four-arm inverter. (Specifically, The three-phase line current can be connected via the interface filter. , , (Obtained through coordinate transformation), and zero-axis control voltage is generated based on the deviation between the two. .

[0079] Each PI controller is a single-input single-output (SISO) controller, that is... Each shaft is controlled by its own independent PI controller for closed-loop current control. The outputs of the three PI controllers... , , Inverse Clark and inverse Park transformations are performed together to obtain the three-phase control voltage. , , At the same time, 0.5 is used directly as Switching duty cycle of power devices in phase bridge arm Soon Relative to point The control voltage is fixed at 1 / 2. .

[0080] , , The input PWM module can then generate SVPWM (Space Vector Pulse Width Modulation) algorithm. , , ,and Together, the power devices in each arm branch of the four-arm inverter are switched on and off. In the embodiments of this application, this method, in addition to tracking the conventional... In addition to the target shaft current, the zero-sequence target current is also tracked to realize a control strategy that simulates the current characteristics of each phase of the NPA three-phase motor. This strategy is called the closed-loop current control strategy based on zero-sequence current tracking.

[0081] However, when adopting Figure 11 The closed-loop control architecture shown, when using zero-sequence current as the tracking target, suffers from a situation where the output zero-sequence current is the common-mode voltage of the three-phase output after closed-loop modulation. Since one of the core mechanisms of SVPWM modulation is to optimize modulation performance by adjusting the three-phase common-mode voltage, the closed-loop regulation of the PI controller will cancel out the SVPWM regulation of the common-mode voltage, resulting in the inability to achieve the target of improving the voltage utilization of the motor simulator (EME). Furthermore, because... Set to a constant of 0.5, point Zero voltage reference point on the EME side The voltage difference between them remains constant, therefore The phase bridge arm does not participate in active modulation and is not capable of compensating for the time-varying problem of the pressure difference between g and G.

[0082] Apart from Figure 11 The closed-loop current control architecture shown is based on the neutral point electrical characteristics of the NPA three-phase motor. The phase output voltage is controllable, and at the same time, considering With neutral point current The proportional relationship in equation (2) exists, therefore, it is also possible to... The neutral point target current is obtained by conversion. and with As a tracking target, thereby indirectly achieving the goal of Control.

[0083] Specifically, with Corresponding interface filter transfer function for: (11), in, For flowing through The current of the phase filter inductor, For the MDU side Phase terminal voltage, i.e., the neutral point voltage of the motor. For the motor simulator side Phase terminal voltage, i.e. Voltage at the midpoint of the phase bridge arm for The inductance value of the phase filter inductor, for The parasitic resistance value of the phase filter inductor.

[0084] Based on the above analysis, we can establish Figure 12 The example shown is shaft current, The shaft current and neutral point current form a closed-loop current control framework for tracking the target. For example... Figure 12 As shown, in this closed-loop current control framework, besides the components used for... Shaft target current, In addition to the PI controller for tracking the target current of the shaft, a controller for tracking the target current of the neutral point is added. PI controller.

[0085] Specifically, the three target currents, after passing through their respective PI controllers, output to the EME side. Shaft control voltage , Shaft control voltage and neutral point control voltage .in, , go through Transformed into EME side three-phase control voltage , , , and then with They then enter the PWM module together.

[0086] The PWM module is based on the three-phase control voltage of the EME side. , , and EME-side neutral point control voltage PWM signals are generated for each arm branch of the four-arm inverter to control the switching of the power devices in each arm branch.

[0087] Figure 13 The internal structure of the PWM module under the closed-loop current control architecture based on neutral point current tracking is shown in the figure. The three-phase control voltage... , , The SVPWM (Space Vector Pulse Width Modulation) algorithm is used to determine... , , Timing; Neutral point control voltage Then a conventional PWM algorithm, such as the SPWM algorithm, is used. Determined by comparison with carrier wave Duty cycle of the bridge arm branch Time sequence, finally, utilize , , , Each bridge arm branch generates its own timing sequence for PWM signals, and these PWM signals are used to control the switching of the power devices in the four bridge arm branches. In the embodiments of this application, Figure 12 , Figure 13 In addition to the conventional tracking methods employed In addition to the target shaft current, the target neutral point current is also tracked to achieve a control strategy that simulates the electrical characteristics of the NPA three-phase motor. This strategy is called the closed-loop current control strategy based on neutral point current tracking.

[0088] The applicant proved through theoretical analysis that the following method was adopted. Figure 12 , Figure 13 The closed-loop current control architecture shown can solve the drift problem of the zero-potential reference point between the EME side and the MDU side by changing the tracking target, but it also... Three-phase common-mode voltage and phase control are introduced during the phase control process. The disturbance caused by coupling affects the tracking accuracy of the PI controller for the neutral point current. The following is a detailed analysis of the disturbance generation mechanism.

[0089] consider The voltage equation across the phase filter inductor is: (12) Considering the relationship between the zero-sequence current and the neutral point current, and combining equations (1) and (6), we can obtain: (13) in, For EME side Zero potential reference point Point voltage, As mentioned above, this is the zero-sequence voltage on the EME side with G as the zero-potential reference point.

[0090] Although in equation (13) and Both are unknowns, but their differences can still be solved because It can eliminate common-mode components, and the specific expression is as follows: (14) in For point The voltage, whose zero potential reference point is... , , The midpoints of the three-phase bridge arm branches are consistent, for example, they can be the common cathode (i.e., point g) of a four-bridge arm inverter or the midpoint of the DC bus.

[0091] From equations (13) and (14), we can obtain: (15).

[0092] Using equation (15), we can establish a system based on... The PI control architecture that a closed-loop control strategy for phase current tracking should possess: (16) in, The target current at the neutral point can be written as , This serves as the final neutral point control voltage. for The bandwidth of the PI controller.

[0093] Analysis of equations (15) and (16) leads to the following conclusions: First, the control architecture based on equation (15) is independent of the difference between the zero potential reference points on the EME side and the MDU side. Therefore, the closed-loop current control strategy based on neutral point current tracking can solve the reference point drift problem existing in the zero-sequence current control strategy.

[0094] Secondly, it can be seen from equation (16) that, under the architecture of tracking the neutral point target current, to achieve precise control of the zero-sequence current or the neutral point current, the following factors need to be considered simultaneously, among which: In equation (16) The first item This is the form of a conventional PI controller, which can be used to construct... The phase PI controller is tuned to obtain its control parameters. and , and They are respectively The inductance and parasitic resistance of the phase filter inductor are as described above. and That is, can and and They can be the same, or they can be different; The second term in equation (16) ,in The zero-sequence voltage on the MDU side can be obtained in real time by transforming the coordinate system based on the three-phase voltages acquired by the four-branch signal acquisition units. This means that it can be superimposed on the command voltage so that the motor simulator can correctly simulate the zero-sequence voltage characteristics of the tested NPA three-phase motor; The third term in equation (16) This reflects that when using a closed-loop current control strategy based on neutral point current tracking, an additional three-phase common-mode voltage term will appear in the transfer function of the control loop. If, like... Figure 12 , Figure 13 As shown in the control architecture, only a PI loop is used. Phase control, then , , The common-mode voltage of the three-phase line, especially the third harmonic caused by the use of SVPWM modulation, will couple into the circuit. Phase control loop, thereby controlling The control is disrupted.

[0095] It is evident that directly adopting Figure 12 , Figure 13 The control architecture still suffers from three-phase current coupling interference, and the closed-loop current control strategy based on neutral point current tracking needs to be optimized to address this issue.

[0096] Based on neutral point current tracking and Phase-compensated closed-loop current control strategy Equations (15) and (16) reflect the problems with the closed-loop control strategy for neutral point current tracking, while also providing a solution for suppressing common-mode voltage interference, namely: Through The output of the phase PI controller Phase control voltage Superimposed feedforward compensation voltage term It can achieve accurate tracking of the zero-sequence voltage characteristics of NPA three-phase motors; Furthermore, through Introducing a common-mode compensation term in phase control can offset the effect of SVPWM modulation on the EME side. The effect of the phase PI controller, and the expression for this term is the common-mode voltage. Therefore, it is only necessary to construct based on the three-phase common-mode voltage characteristics of the EME side. The phase compensation module can compensate for... The common-mode voltage interference present in the phase closed-loop control is effectively suppressed.

[0097] After clarifying the above-mentioned disturbance generation mechanisms and solutions, we can proceed with... Figure 12 , Figure 13 The control architecture shown has been improved to address the issue of being affected by three-phase common-mode voltage disturbances when tracking the neutral point current.

[0098] Figure 14The following is a schematic diagram of the architecture of a four-branch closed-loop current control unit provided by some preferred embodiments of this application, such as... Figure 14 As shown, the four-branch current control unit includes Axis PI controller Axis PI controller, Phase PI controller, coordinate transformation module, first PWM module, second PWM module and Phase compensation module.

[0099] in, Axis PI controller is used to implement the control of Tracking the target current of the shaft, its input quantity is Target current of shaft and after interface filtering shaft current The output is from the EME side. Shaft control voltage ; Axis PI controller is used to implement the control of Tracking the target current of the shaft, its input quantity is Target current of shaft and after interface filtering shaft current The output is from the EME side. Shaft control voltage .

[0100] The coordinate transformation module uses Transformation, will , Converted to three-phase control voltage on the EME side , , The first PWM module is then input, and based on the three-phase control voltage on the EME side, it determines the voltage in the four-arm inverter using the SVPWM algorithm. Xiangqiao arm branch road, Xiangqiao arm branch road, Duty cycle of the bridge arm branch ( , , And PWM signals, thereby controlling , , Switches of various power devices in the three-phase bridge arm branch.

[0101] Phase PI controller and The phase compensation module works in conjunction with the neutral point target current to achieve tracking. Specifically, The input to the phase PI controller is the neutral point target current. and the neutral point current after interface filtering The output is the neutral point control voltage on the EME side. .in, The zero-sequence target current can be determined using equation (2). The result of the conversion is The zero-sequence current after interface filtering can be used to... Multiply by the scaling factor -3 to get the result.

[0102] Furthermore, The output of the phase PI controller Superimposed feedforward compensation voltage term Then it enters the second PWM module, which can use conventional PWM algorithms, such as the SPWM algorithm, based on the EME-side neutral point control voltage after feedforward voltage compensation. The comparison result with the carrier wave is determined. Duty cycle before compensation of the bridge arm branch , Subsequently The phase compensation module performs common mode compensation, and... Converted to compensated duty cycle .

[0103] Based on the preceding analysis, and considering the relationship between output voltage and duty cycle, it can be determined that... Figure 14 middle The specific architecture of the phase compensation module. For example... Figure 14 As shown, The phase compensation module generates the first PWM module , , A averaging operation is performed to obtain the common-mode compensation term, and then this common-mode compensation term is used to adjust the output of the second PWM module. Perform common-mode compensation to obtain the compensated duty cycle. This ultimately generates the control for the four-arm inverter. PWM signal of the power device in the phase bridge arm branch.

[0104] In this application, the four-branch closed-loop current control unit adopts... Figure 14 The control strategy shown is called neutral point current tracking and... A phase-compensated closed-loop current control strategy.

[0105] In some specific embodiments, PI controller for the axis and The method for determining the PI parameters of the PI controller for the axis can be the same as that in a traditional motor simulator. The axis PI controller is consistent. Figure 15Some specific embodiments are shown. The PI controller for the axis is expressed in the form of a transfer function, as shown in the figure. The transfer function of the PI controller for the axis can be uniformly expressed as: (17) also, Figure 15 It also shows The transfer function form of a phase PI controller: (18).

[0106] <Experimental Verification> To verify the simulation performance of the motor simulator for NPA three-phase motors provided in this application, a system was built as follows: Figure 16 The drag test platform shown has the following topology. Figure 8 As shown, the simulation object is NPA-PMSM, and the experimental parameters are listed in Table 1.

[0107] Table 1 To suppress switching noise and improve the control accuracy of the motor simulator (EME), a low-pass filter with a cutoff frequency of 2kHz was applied to the DC input in the dq0 coordinate system. In the experiment, the highest motor speed was 83.33Hz (1000rpm), far below the filter's cutoff frequency; therefore, the impact of this low-pass filter on the fundamental current component was negligible. Furthermore, the voltage signal from the motor model was not acquired using an actual voltage acquisition module, but rather through internal system signal transmission. It should be clarified that the method of voltage signal acquisition (acquisition or internal transmission) does not change the system's operating principle. Although the voltage acquisition may deviate from the actual voltage, the voltage acquisition error does not affect the validity of the experimental conclusions.

[0108] Figure 17 This illustrates a control strategy that employs tracking zero-sequence current (i.e., Figure 11 The simulation results of the electrical performance of the NPA three-phase motor under the closed-loop current control framework shown can be seen that, based on the PI controller... In a current closed-loop control system, the common-mode voltage output by the PI controller cancels out the common-mode voltage effect of the SVPWM, ultimately leading to a decrease in EME voltage utilization; when the target At 5A, as the motor speed increases from 500rpm to 1000rpm, the voltage utilization rate calculated from the EME output target voltage continuously increases; when this utilization rate is greater than 1, the MDU bus voltage fluctuation amplitude increases significantly, thus affecting... This affects the tracking performance.

[0109] Figure 18 This demonstrates the use of neutral point current tracking and... When using a phase-compensated closed-loop current control strategy, simulation results of the electrical performance of an NPA three-phase motor show that, compared to tracking... The shaft current scheme, which tracks the neutral point current, fully preserves the voltage utilization improvement effect of SVPWM without being canceled out by the PI common-mode output. Furthermore, the zero-sequence voltage and current do not fluctuate drastically, indicating that this control strategy can accurately simulate the electrical performance of NPA three-phase motors.

[0110] Figure 19 For a rotational speed of 800 rpm, the target Under the condition of shaft current = 5A, for Verification of phase compensation effect: No verification was performed 1.54 seconds prior. Phase compensation activates at 1.54s. Phase compensation results show that when using a closed-loop current control strategy based on neutral point current tracking, without... Phase compensation, then the bus voltage and zero-sequence current The fluctuation range has increased significantly. Figure 20 This illustrates a zero-sequence current tracking strategy compared to the neutral point current-based strategy provided in this application. A schematic diagram illustrating the current and voltage harmonic components of a phase-compensated closed-loop current control strategy shows that the third harmonic component is significantly enhanced under the zero-sequence current tracking strategy, further verifying the effect of increasing... Phase compensation's ability to suppress the effects of common-mode voltage disturbances.

[0111] 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 motor simulator for NPA three-phase motors, characterized in that, include: A four-arm inverter includes three-phase arm branches for simulating the three-phase current characteristics of an NPA three-phase motor, and neutral point electrical characteristics for simulating the NPA three-phase motor. Xiangqiao arm branch road; The four-branch interface filter is used to filter the current output by the four-arm inverter. The four-branch signal acquisition unit is used to acquire current and phase voltage signals; The NPA motor model unit generates the target current on the EME side based on the mathematical model of the NPA three-phase motor. A four-branch closed-loop current control unit, employing neutral point current tracking and... A phase-compensated closed-loop current control strategy controls the switching of power devices in each arm branch of a four-arm inverter. The EME-side DC power supply is connected between the common anode and common cathode of the four-arm inverter.

2. The motor simulator for NPA three-phase motors according to claim 1, characterized in that, The four-branch interface filter includes Phase filter inductor, Phase filter inductor, Phase filter inductor and Phase filter inductor, where: The Phase filter inductor, Phase filter inductor, The first terminal of the phase filter inductor is connected to the four-arm inverter. Xiangqiao arm branch road, Xiangqiao arm branch road, Midpoint connection of the bridge arm branch; The The first terminal of the phase filter inductor is connected to the four-arm inverter. The midpoint of the phase bridge arm branch is connected, and the second end is a neutral point analog terminal.

3. The motor simulator for NPA three-phase motors according to claim 2, characterized in that, When performing a drag test between the motor simulator for the NPA three-phase motor and the drive unit of the motor under test: The Phase filter inductor, Phase filter inductor, The second terminal of the phase filter inductor is connected to the motor drive unit under test. Xiangqiao arm branch road, Xiangqiao arm branch road and The midpoints of the bridge arm branches are connected one-to-one; The neutral point analog terminal is connected to the motor drive unit under test in a neutral point lead-out manner.

4. The motor simulator for NPA three-phase motors according to claim 3, characterized in that, When performing a drag test between the motor simulator for the NPA three-phase motor and the drive unit of the motor under test: The current signals acquired by the four-branch signal acquisition unit are three-phase current signals that are connected in pairs and filtered by the interface. The voltage signals acquired by the four-branch signal acquisition unit are the three-phase voltage signals of the midpoint of the three-phase bridge arm branch of the motor drive unit under test relative to the neutral point analog terminal.

5. The motor simulator for NPA three-phase motors according to claim 2, characterized in that, The four-branch closed-loop current control unit includes Axis PI controller Axis PI controller, Phase PI controller, coordinate transformation module, first PWM module, second PWM module and Phase compensation module; The Axis PI controller based Shaft target current and after interface filtering Axis current generation EME side Shaft control voltage, the Axis PI controller based Shaft target current and after interface filtering Axis current generation EME side Shaft control voltage; The coordinate transformation module is used to transform the EME side. Shaft control voltage, EME side The shaft control voltage is converted into the three-phase control voltage on the EME side; The first PWM module determines the three-phase control voltage on the EME side. Xiangqiao arm branch road, Xiangqiao arm branch road, Duty cycle and PWM signal of the phase bridge arm branch; The The phase PI controller generates the neutral point control voltage on the EME side based on the neutral point target current and the neutral point current after interface filtering; The second PWM module determines the neutral point control voltage on the EME side based on the feedforward voltage compensation. Duty cycle before compensation for the bridge arm branch; The The phase compensation module is based on the Xiangqiao arm branch road, Xiangqiao arm branch road, The duty cycle of the phase bridge arm branch, for the aforementioned The duty cycle of the phase bridge arm branch is compensated before compensation to determine the aforementioned... The duty cycle and PWM signal of the phase bridge arm branch after compensation.

6. The motor simulator for NPA three-phase motors according to claim 5, characterized in that, The first PWM module determines the SVPWM algorithm. Xiangqiao arm branch road, Xiangqiao arm branch road, Duty cycle of the bridge arm branch , , ; The second PWM module determines the... Duty cycle before compensation for the bridge arm branch.

7. The motor simulator for NPA three-phase motors according to claim 6, characterized in that, The The phase compensation module generates the first PWM module , , A mean operation is performed to obtain a common mode compensation term, and then the common mode compensation term is used to compensate the duty cycle before compensation to obtain the duty cycle after compensation.

8. The motor simulator for NPA three-phase motors according to any one of claims 1 to 7, characterized in that, The NPA three-phase motor is any one or more of the following: neutral point lead-out permanent magnet synchronous motor, neutral point lead-out electrically excited synchronous motor, neutral point lead-out hybrid excited synchronous motor, and neutral point lead-out asynchronous motor.

9. A test platform for NPA three-phase motors, characterized in that, It includes a motor drive unit for the tested motor connected to a tow cable and a motor simulator for an NPA three-phase motor as described in claim 1.

10. The test platform for NPA three-phase motors according to claim 9, characterized in that, The motor drive unit under test includes: a drive controller, an MDU-side inverter, and an MDU-side DC power supply, wherein: The drive controller is a drive controller for NPA three-phase motors. A closed-loop control strategy is set based on the type of NPA three-phase motor to be tested in order to control the switching of power devices in each bridge arm branch of the MDU-side inverter. The DC power supply on the MDU side is the power source for the motor drive unit under test.

11. The test platform for NPA three-phase motors according to claim 10, characterized in that, The MDU-side inverter and MDU-side DC power supply are connected to the motor simulator for the NPA three-phase motor via a neutral point lead-out method. The connection method between the neutral point simulation terminal of the motor simulator for the NPA three-phase motor and the MDU-side inverter and MDU-side DC power supply is determined based on the application scenario of the test.

12. The test platform for NPA three-phase motors according to any one of claims 9 to 11, characterized in that, The difference between the zero potential reference point of the MDU-side inverter and the four-arm inverter is a time-varying variable.

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