A midpoint balancing circuit for a vehicle-mounted three-level motor controller and a vehicle

Abstract

The application relates to a midpoint balancing circuit for a vehicle-mounted three-level motor controller and a vehicle, which solves the problem of midpoint potential imbalance of a vehicle-mounted T-shaped three-level circuit without increasing cost. The circuit comprises a first resistor, a second resistor, a first capacitor, a second capacitor, a vertical bridge circuit with three vertical bridge arms, a horizontal bridge circuit with three horizontal bridge arms and a neutral point. One end of the first resistor is connected with a positive pole of a bus, the other end is connected with the neutral point; one end of the second resistor is connected with a negative pole of the bus, the other end is connected with the neutral point; and the first resistor and the second resistor are connected in series; two ends of the first capacitor are respectively connected with the positive pole of the bus and the neutral point, and two ends of the second capacitor are respectively connected with the negative pole of the bus and the neutral point; two ends of each vertical bridge arm of the vertical bridge circuit are respectively connected with the positive pole and the negative pole of the bus, and an output end of each vertical bridge arm of the vertical bridge circuit is connected with a motor; one end of each horizontal bridge arm of the horizontal bridge circuit is respectively connected with an output end of one vertical bridge arm, and the other end is connected with the neutral point; the first resistor and the second resistor are passive discharge resistors provided on the vehicle-mounted three-level motor controller.

Description

Technical Field

[0001] This application relates to the field of vehicle motor controllers, specifically a midpoint balancing circuit for an on-board three-level motor controller and a vehicle. Background Technology

[0002] Traditional T-type three-level circuits, such as Figure 1 As shown, a three-phase full-bridge control of a permanent magnet synchronous motor is used, and a three-level control circuit is implemented by generating three levels through a T-shaped bridge arm. The existing circuit suffers from low-frequency voltage fluctuations at the midpoint O. Because the potential at midpoint O is affected by the medium and small vectors in the modulation algorithm, low-frequency fluctuations occur. If not properly controlled, the voltage at point O can damage IGBTs and other switching devices, causing electrical failure.

[0003] At present, two main methods are used to solve the above problem;

[0004] One approach is to increase the capacitance of C1 and C2. This method can indeed suppress the midpoint potential to some extent, but it will increase the cost and volume many times over.

[0005] As shown in the formula below, Vo_Ripple - Midpoint voltage ripple, Io_max - Maximum current, M - Modulation ratio, ω - Electrical angular frequency, Cp - Bus capacitance, η is a coefficient; if the midpoint voltage ripple Vo_Ripple needs to be reduced by half, then the bus capacitance Cp also needs to be doubled, which will double the cost and volume.

[0006] Second, a closed-loop midpoint potential control algorithm is added. This method can indeed suppress the problem of midpoint potential imbalance. However, the closed-loop midpoint potential algorithm is too complex, and the PID parameters require a lot of debugging and calibration work, so its practical value is not high. In addition, a high-cost MCU is required to perform these overly complex algorithm calculations. Summary of the Invention

[0007] This application provides a midpoint balancing circuit and vehicle for an on-board three-level motor controller, which solves the problem of midpoint potential imbalance in on-board T-type three-level circuits without increasing costs.

[0008] The technical solution of this application is as follows:

[0009] A neutral point balancing circuit for an on-board three-level motor controller includes: a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a vertical bridge circuit with three vertical arms, a horizontal bridge circuit with three horizontal arms, and a neutral point O.

[0010] One end of the first resistor R1 is connected to the positive terminal of the busbar, and the other end is connected to the neutral point O.

[0011] One end of the second resistor R2 is connected to the negative terminal of the busbar, and the other end is connected to the neutral point O; and the first resistor R1 and the second resistor R2 are connected in series.

[0012] The two ends of the first capacitor C1 are connected to the positive terminal of the busbar and the neutral point O, respectively; the two ends of the second capacitor C2 are connected to the negative terminal of the busbar and the neutral point O, respectively.

[0013] The two ends of each vertical bridge arm of the vertical bridge circuit are connected to the positive and negative poles of the busbar, respectively, and the output end of each vertical bridge arm of the vertical bridge circuit is connected to the motor.

[0014] Each horizontal bridge arm of the horizontal bridge circuit is connected at one end to the output terminal of a vertical bridge arm, and at the other end to the neutral point O.

[0015] The first resistor R1 and the second resistor R2 are passive discharge resistors built into the vehicle-mounted three-level motor controller.

[0016] Preferably, each vertical bridge arm of the vertical bridge circuit includes two switching transistors connected in series, and the connection point of the two switching transistors is the output terminal of the corresponding vertical bridge arm.

[0017] Preferably, each arm of the crossbridge circuit includes two switching transistors connected in reverse series.

[0018] This application also provides a vehicle including the aforementioned midpoint balancing circuit for an on-board three-level motor controller.

[0019] The beneficial effects of this application are as follows:

[0020] When a midpoint current I1 is present, the current in the capacitors will be drawn away, causing an imbalance in the midpoint potential. The voltage across the first capacitor C1 and the voltage across the second capacitor C2 will be inconsistent. After adding the first resistor R1 and the second resistor R2, currents I2 and I3 will be generated in the circuit. At this time, the voltage across C2...

[0021] VC2 = (R2*V1 - I1*R1*R2) / (R1+R2). This formula shows that the fluctuation of the voltage VC2 across the second capacitor C2 is related not only to the midpoint current I1, but also to the values ​​of the first resistor R1 and the second resistor R2. If the first resistor R1 and the second resistor R2 are set appropriately, the voltage fluctuation of the second capacitor C2 can be effectively suppressed. Attached Figure Description

[0022] Figure 1 This is a circuit diagram of the prior art;

[0023] Figure 2 This is a circuit diagram from an embodiment of this application;

[0024] Figure 3 This is a schematic diagram of the simulation circuit in the embodiments of this application;

[0025] Figure 4 The following are schematic diagrams of simulation waveforms and simulation results for existing technologies;

[0026] Figure 5 The diagram shows the simulation waveforms and simulation results in the embodiments of this application. Detailed Implementation

[0027] Reference Figure 2 This application provides a midpoint balancing circuit for an on-board three-level motor controller, including: a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a vertical bridge circuit with three vertical bridge arms, a horizontal bridge circuit with three horizontal bridge arms, and a neutral point O.

[0028] One end of the first resistor R1 is connected to the positive terminal of the busbar, and the other end is connected to the neutral point O.

[0029] One end of the second resistor R2 is connected to the negative terminal of the busbar, and the other end is connected to the neutral point O; and the first resistor R1 and the second resistor R2 are connected in series.

[0030] The two ends of the first capacitor C1 are connected to the positive terminal of the busbar and the neutral point O, respectively; the two ends of the second capacitor C2 are connected to the negative terminal of the busbar and the neutral point O, respectively.

[0031] The two ends of each vertical bridge arm of the vertical bridge circuit are connected to the positive and negative poles of the busbar, respectively, and the output end of each vertical bridge arm of the vertical bridge circuit is connected to the motor.

[0032] Each horizontal bridge arm of the horizontal bridge circuit is connected at one end to the output terminal of a vertical bridge arm, and at the other end to the neutral point O.

[0033] The first resistor R1 and the second resistor R2 are passive discharge resistors built into the vehicle-mounted three-level motor controller.

[0034] Preferably, each vertical bridge arm of the vertical bridge circuit includes two switching transistors connected in series, and the connection point of the two switching transistors is the output terminal of the corresponding vertical bridge arm.

[0035] Preferably, each arm of the crossbridge circuit includes two switching transistors connected in reverse series.

[0036] In this embodiment, a first resistor R1 and a second resistor R2 are used as midpoint balancing resistors to perform midpoint voltage balance control; and since the first resistor R1 and the second resistor R2 are passive discharge resistors built into the vehicle motor controller (after power failure, the voltage on the capacitor is discharged within a specified time), no additional cost is added.

[0037] Combination Figure 2 The working principle of the circuit described in this application is as follows: When a midpoint current I1 exists, the current in the capacitor is drawn away, resulting in an imbalance in the midpoint potential, and the voltage across the first capacitor C1 is inconsistent with the voltage across the second capacitor C2. After adding the first resistor R1 and the second resistor R2, currents I2 and I3 are generated in the circuit. At this time, the voltage VC2 across C2 is calculated as (R2*V1 - I1*R1*R2) / (R1+R2). From this formula, it can be seen that the fluctuation of the voltage VC2 across the second capacitor C2 is related not only to the midpoint current I1 but also to the values ​​of the first resistor R1 and the second resistor R2. If the first resistor R1 and the second resistor R2 are set appropriately, the fluctuation of the voltage VC2 across the second capacitor C2 can be effectively suppressed.

[0038] as follows Figure 3 As shown, a circuit simulation model is built, where V1 simulates the power output, the first resistor R1 and the second resistor R2 are used for passive discharge and midpoint balancing, the first capacitor C1 and the second capacitor C2 are the upper and lower filter capacitors of the bus, IGBT1, IGBT2, IGBT3, IGBT4, IGBT5 and IGBT6 are the main circuit switching devices, and SA1, SA2, SA3, SA4, SA5 and SA6 are T-type three-level freewheeling switches. R1 = R2 = 30000Ω, V1 = 750V.

[0039] When a passive resistor is not used as the midpoint resistor, the test waveform is as follows: Figure 4 It can be determined that when I1 = 0.75mA, the midpoint potential will drop to around 91V, which is completely unable to balance the midpoint potential.

[0040] In a circuit with a midpoint balancing resistor, the test waveform is as follows: Figure 5 As shown, it can be determined that the midpoint voltage fluctuation to 363.7V meets the requirements.

[0041] Where I1 = 0.76mA, I2 = 12.88mA, and I3 = 12.1mA, according to Kirchhoff's voltage theorem and current theorem, VC2 = (R2*V1 - I1*R1*R2) / (R1+R2) = 363.6V;

[0042] I2 = (VC2 - V1) / R1 = 12.9mA; I3 = VC2 / R2 = 12.1mA. This means the theoretical calculations match the simulation data, and using the passive discharge resistor as the midpoint balancing resistor can effectively balance the midpoint potential. Therefore, without increasing cost, by appropriately setting the discharge resistor value based on the magnitude of the I1 current, the midpoint potential balance problem can be effectively solved.

Claims

1. A midpoint balancing circuit for an on-board three-level motor controller, characterized in that, include: First resistor (R1), second resistor (R2), first capacitor (C1), second capacitor (C2), vertical bridge circuit with three vertical arms, horizontal bridge circuit with three horizontal arms, and neutral point (O). One end of the first resistor (R1) is connected to the positive terminal of the busbar, and the other end is connected to the neutral point (O); One end of the second resistor (R2) is connected to the negative terminal of the busbar, and the other end is connected to the neutral point (O); and the first resistor (R1) and the second resistor (R2) are connected in series. The two ends of the first capacitor (C1) are connected to the positive terminal and the neutral point (O) of the busbar, respectively, and the two ends of the second capacitor (C2) are connected to the negative terminal and the neutral point (O) of the busbar, respectively. The two ends of each vertical bridge arm of the vertical bridge circuit are connected to the positive and negative poles of the busbar, respectively, and the output end of each vertical bridge arm of the vertical bridge circuit is connected to the motor. One end of each horizontal bridge arm of the horizontal bridge circuit is connected to the output terminal of a vertical bridge arm, and the other end is connected to the neutral point (O). The first resistor (R1) and the second resistor (R2) are passive discharge resistors built into the vehicle-mounted three-level motor controller.

2. The midpoint balancing circuit for an on-board three-level motor controller according to claim 1, characterized in that, Each vertical bridge arm of the vertical bridge circuit includes two switching transistors connected in series, and the connection point of the two switching transistors is the output terminal of the corresponding vertical bridge arm.

3. The midpoint balancing circuit for an on-board three-level motor controller according to claim 2, characterized in that, Each arm of the bridge circuit includes two switching transistors connected in reverse series.

4. A vehicle, characterized in that, Including the midpoint balancing circuit for an on-board three-level motor controller as described in any one of claims 1-3.

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