Method for reducing heating of support capacitor in vehicle-mounted driving system and support capacitor

Abstract

The invention relates to the technical field of vehicle-mounted driving control, in particular to a method for reducing heating of a supporting capacitor in a vehicle-mounted driving system and the supporting capacitor, and the supporting capacitor is connected with a motor A and a motor B through a semiconductor module A and a semiconductor module B. The signal processor is used for inputting PWM gate signals to the semiconductor module A and the semiconductor module B for driving control; the frequency phases of PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180 degrees; or the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are the same in frequency phase. According to the invention, the ripple current generated by the support capacitor in the vehicle-mounted driving system can be mutually counteracted, the ripple current in the direct current support capacitor is reduced, and the heating of the capacitor is reduced, so that the support capacitor with a small volume can be used for production, the manufacturing cost is reduced, and the market competitiveness is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle-mounted drive control, and in particular to a method for reducing the heating of a support capacitor in a vehicle-mounted drive system and the support capacitor. Background Art

[0002] In recent years, with the rapid growth of new energy vehicles, pure electric vehicles and hybrid vehicles have come into being. The emergence of new energy vehicles has enabled automobiles to play a vital role in energy conservation and emission reduction.

[0003] Case (1): In pure electric vehicles, Figure 1 The figure shows a schematic diagram of the structure of a dual-motor (left-wheel drive motor and right-wheel drive motor) drive system in the prior art. The left-wheel drive motor and the right-wheel drive motor of the drive system are controlled by a signal processor. Under this condition, the semiconductor module A of the left-wheel drive and the semiconductor module B of the right-wheel drive share a DC support capacitor. In the prior art, no special processing is performed on the phase of the PWM gate signal of the left and right wheels, which causes the ripple current flowing into the DC support capacitor to become the algebraic superposition of the ripple currents of the two motors. Case (2), in a hybrid vehicle, if Figure 2 The figure shows the structure of the hybrid motor (drive motor, generator) drive system in the prior art. In this drive system, the drive motor is responsible for driving the vehicle, the generator cooperates with the engine to generate electricity, and the drive semiconductor module of the drive motor and the semiconductor module of the generator share a DC support capacitor. In this application, the PWM carrier will change with the change of the motor sine wave, and the speed and working conditions of the drive motor and the generator are inconsistent, so the PWM carrier frequency will be inconsistent.

[0004] In case (1), the ripple current flowing through the supporting capacitor is large, which will cause serious heating problems, limit the output current of the controller, and thus limit the motor current. At the same time, under the condition of the same capacitance value, the capacitor ripple current and voltage are in an integral relationship. The ripple voltage flowing through the capacitor is large, causing the ripple voltage across the capacitor to increase. Under extreme conditions, it may cause control instability. In case (2), when the carrier waves are different (when the drive motor and generator are in their respective working states and are both in high power states), the second harmonic components of the PWM frequency generated by the motor and generator cannot cancel each other out and require support capacitors to absorb them, which increases the heating of the capacitors.

[0005] Therefore, regardless of case (1) or case (2), the support capacitor will generate heat. In order to solve the problem of support capacitor heating, the prior art usually increases its capacitance value, uses a larger support capacitor, and adds a heat dissipation structure to the capacitor, which undoubtedly increases the product and reduces its market competitiveness. In view of this, we propose a method for reducing the heating of the support capacitor in a vehicle drive system and the support capacitor. Summary of the invention

[0006] The object of the present invention is to provide a method for reducing the heating of a support capacitor in a vehicle drive system and the support capacitor, so as to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for reducing heating of a support capacitor in a vehicle drive system, wherein the support capacitor is connected to a motor A and a motor B through a semiconductor module A and a semiconductor module B respectively; a signal processor is used to input a PWM gate signal to the semiconductor module A and the semiconductor module B for driving control; The PWM gate signal frequencies output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180°; or, the PWM gate signal frequencies output by the signal processor to the semiconductor module A and the semiconductor module B are the same in phase.

[0008] Preferably, when the motor A and the motor B are the left wheel drive motor and the right wheel drive motor in the vehicle drive system, the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180° in phase.

[0009] Preferably, when the motor A and the motor B are the drive motor and the generator in the vehicle drive system, the PWM gate signal frequency output by the signal processor to the semiconductor module A and the semiconductor module B is the same.

[0010] A supporting capacitor is also provided. The method uses the supporting capacitor, which includes a positive copper bar, a negative copper bar, and a capacitor core; A first recess is provided in the middle of the positive copper bar, and a plurality of first contact points are provided; A second recess is provided in the middle of the negative electrode copper bar, and a plurality of groups of second contacts are provided; The second concave portion of the negative copper bar is buckled into the first concave portion of the positive copper bar, and there is a certain gap between the bottom surface of the second concave portion and the top surface of the first concave portion; The first contacts and the second contacts are arranged alternately; The capacitor core is fixed in the second recess.

[0011] Preferably, a gap between the bottom surface of the second recess and the top surface of the first recess is less than 20 mm.

[0012] Preferably, an insulating layer is laid in the gap.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. Methods for reducing the heating of the supporting capacitor in the vehicle drive system: In pure electric vehicles, in the control of dual motors (left and right drive motors), the gate signals for the two motors are generated by a DSP (signal processor). The gate signals have the same frequency and a phase difference of 180°, which partially offsets the ripple current on the supporting capacitor, reducing the ripple current and the heating of the capacitor. In hybrid vehicles, when the generator and drive motor are working under low power conditions, they each use PWM frequency control; when the motor and generator are both working under high power conditions, the same frequency PWM control is used to make the ripple currents generated by the motor and generator offset each other, reducing the ripple current in the DC support capacitor and reducing the heating of the capacitor.

[0014] 2. The gap between the positive and negative copper bars of the support capacitor is less than 20mm, which reduces the generation of parasitic inductance, makes it easier to offset the current components, and prevents abnormal heating of the capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of a dual-motor (left motor and right motor) drive system in the prior art; Figure 2 It is a schematic diagram of the structure of a hybrid motor (drive motor, generator) drive system in the prior art; Figure 3 is a relationship diagram between the reference carrier wave and the modulated wave in the standard state in Example 1; Figure 4 The relationship diagram of the carrier wave and the modulated wave after the PWM phase is staggered by 180° in Example 1; Figure 5 The gate signal waveform diagram after PWM phase shift of 180° in Example 1; Figure 6 The non-misaligned and 180°-misaligned ripple currents in Example 1, and the superimposed ripple current waveforms; Figure 7 This is a ripple current diagram of the left and right drive motors in Example 1 when PWM phase shift is not performed; Figure 8 1 is a diagram of ripple current and ripple voltage in non-PWM interleaving in Example 1; Fig. 9 1 is a diagram of ripple current and ripple voltage when PWM is staggered in Example 1; Fig.10 is the frequency of the ripple current Vs under the PWM reference phase condition in Example 1; Fig.11 is the ripple current Vs frequency under the condition of PWM phase difference of 180° in Example 1; Fig.12 is the frequency of the ripple current Vs after superposition in Example 1; Fig.13 This is a relationship diagram between the reference carrier wave and the modulated wave of the drive motor and the generator under low power conditions in Example 2; Fig.14 This is a relationship diagram of the reference carrier wave and the modulated wave of the drive motor and the generator under high power conditions in Example 2; Fig.15 is a frequency component diagram of the ripple current of the generator and the drive motor in Example 2; Fig.16 is a frequency component diagram of the ripple current of the generator and the drive motor after offset in Example 2; Fig.17 A diagram showing the design of the supporting capacitor structure in the present invention; Fig.18 This is the second diagram of the support capacitor structure design in the present invention.

[0016] In the figure: 1. Positive copper busbar; 2. Negative copper busbar; 3. Capacitor core; 4. Gap. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] A method for reducing the heating of a support capacitor in a vehicle drive system, wherein the support capacitor is connected to a motor A and a motor B through a semiconductor module A and a semiconductor module B respectively; a signal processor is used to input a PWM gate signal to the semiconductor module A and the semiconductor module B for driving control; the frequency phases of the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180°; or, the frequency phases of the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are the same. Example

[0019] like Figure 1The figure shows a schematic diagram of the structure of a dual-motor (left wheel drive motor, right wheel drive motor) drive system in the prior art. In the prior art, no special processing is performed on the phases of the PWM gate signals of the left and right wheels, which causes the ripple current flowing into the DC support capacitor to become the algebraic superposition of the ripple currents of the two motors, thereby causing a large ripple current flowing through the support capacitor, which will cause serious heating problems.

[0020] In one embodiment, when the motor A and the motor B are the left wheel drive motor and the right wheel drive motor in the vehicle drive system, the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180°.

[0021] The PWM gate signal (pulse width modulation) output from the DSP (signal processor) is staggered by 180°, causing the ripple current to be out of phase. After the phase shift, the odd-numbered frequencies of the ripple currents of the left and right motors will cancel each other out, leaving only the even-numbered frequency components. In this way, the overall ripple current becomes smaller, and the small-capacitance support capacitor can also meet the heating and ripple voltage requirements.

[0022] For the sake of simplicity, the PWM pulse generation method is described using the triangle wave generation method. In other embodiments, the space rotation vector method and other methods may also be used for description, but the PWM phase shift principle is the same. Figure 3 As shown, Figure 3 This is the relationship diagram between the reference carrier and the modulated wave under standard conditions. Figure 3 Series 2 is the PWM carrier, and series 3, 4, and 5 are the sine waves of the drive motor (the left and right motors are the same sine waves under most working conditions); Figure 4 As shown, Figure 4 This is the relationship diagram between the carrier wave and the modulated wave after the PWM phase is shifted by 180°. It is not difficult to find that Figure 3 and Figure 4 The only difference is that the carrier phase changes, while the sine wave driven by the motor remains unchanged, which does not affect the motor control.

[0023] When the PWM carrier phase changes, the PMW pulse also changes phase; Figure 5 As shown, Figure 5 The following are the gate signal waveforms after the PWM phase is staggered by 180°. Series 1 is the reference PWM phase gate signal, and series 2 is the gate signal when the phase is staggered by 180°. The PWM cycle and pulse width are the same, but the reference PWM phase gate signal and the gate signal when the phase is staggered by 180° are 180° apart. At this time, when the left motor uses the reference PWM gate signal and the right motor uses the gate signal staggered by 180° to drive the motor, the ripple current on the capacitor will be partially offset.

[0024] like Figure 6 As shown, Figure 6Series 1 is the ripple current waveform of the left motor after non-staggered 180°, and series 2 is the ripple current waveform after PWM staggered. The superposition of the two is the ripple current waveform loaded on the capacitor, which is series 3. If PWM phase stagger is not performed, the ripple current phases of the left and right drive motors are the same, then the superimposed ripple current will be twice the series 1 (or series 2) curve, see for details. Figure 7 ;like Figure 7 As shown, Figure 7 The ripple current curve on the left or right in the middle is series 1, while series 2 is the superimposed ripple current curve (without PWM phase shift).

[0025] Therefore, the ripple voltage on the supporting capacitor is affected by the PWM stagger, which is much less than the ripple voltage without PWM stagger. For the comparison of ripple voltage and ripple current when PWM is non-staggered and staggered by 180° under the same capacitance value, see Figure 8 and Fig. 9 .

[0026] In addition, if we convert the current waveforms from the time domain to the frequency domain when the PWM is misaligned and non-misaligned, we can easily find that the components will cancel each other out near the odd multiples of the switching frequency. Fig.10 and Fig.11 . After the final cancellation, it becomes Fig.12 As shown. This also mathematically proves that when the PWM phases are staggered during dual motor control, the ripple current can be reduced, so that the original large capacitance design can be replaced by a small capacitance, which also proves the feasibility of this technical solution. Example

[0027] like Figure 2 The figure shows a schematic diagram of the structure of a hybrid motor (drive motor, generator) drive system in the prior art. In this application, the PWM carrier will change with the change of the motor sine wave, and the speed and working conditions of the drive motor and the generator are inconsistent, so the PWM carrier frequency will be inconsistent. When the carrier is different (the drive motor and the generator are in their respective working states and are both in a high-power state), the secondary harmonic components of the PWM frequency generated by the motor and the generator cannot offset each other, and need to be absorbed by supporting capacitors, which increases the heating of the capacitors.

[0028] In one embodiment, when the motor A and the motor B are the driving motor and the generator in the vehicle driving system, the PWM gate signal frequency output by the signal processor to the semiconductor module A and the semiconductor module B is the same.

[0029] When the drive motor and generator are both running at high power, the PWM frequency of the drive motor and generator is adjusted to the same frequency control, which can offset the Cos component of the 2nd harmonic frequency of the PWM frequency. The reason is that the motor and generator have opposite energy directions. Although they are at different speeds, the Cos component of the 2nd harmonic is completely consistent with the PWM frequency, which can ignore the different sinusoidal frequencies and reduce the ripple current. When the ripple current becomes smaller, it can effectively reduce the internal loss of the capacitor, reduce or reduce the heat dissipation capacity of the capacitor, thereby making the shape design more flexible and prolonging the life of the capacitor.

[0030] On the other hand, when the motor is running at low speed and low power, the PWM frequency is linked with the sine wave frequency to achieve good efficiency, and there is no need to use the same frequency as the PWM carrier of the generator. Because the ripple current through the capacitor is small under this working condition, even if the same PWM frequency is used, it does not make much sense to reduce heat generation.

[0031] like Fig.13 As shown, under low power conditions, the PWM control of the generator and the drive motor can be completely independent. Fig.13 In the figure, the triangle wave of series 2 is the PWM carrier wave, and the carrier wave frequency is completely different. Series 3, series 4, and series 5 are three-phase signals. Since the motor and generator are in two completely different working states, the amplitude and frequency of the three-phase signals are also different at this time, and the motors are in their respective working states at this time. Since the ripple current is small, the current superimposed on the capacitor will not cause thermal problems at this time.

[0032] like Fig.14 As shown, series 2 is a triangular wave carrier, and the carrier frequencies of the upper and lower working conditions are the same. Series 3, series 4, and series 5 sine waves are different. When the drive motor and generator are both in high-power working state, the drive motor and generator are changed to the same PWM frequency (that is, the triangular wave is the same frequency), while series 3, series 4, and series 5 sine waves do not need to be the same frequency or the same amplitude. This is because the working state of the motor and the generator is almost impossible to be the same.

[0033] like Fig.15 As shown in the figure, the frequency components of the ripple current of the generator and the drive motor are respectively Fig.15 In this example, the switching frequency (i.e., the triangular wave frequency is 10KHz), so the 2, 4, 6 times components of 10KHz...are not affected by the modulated wave (sine wave). And because the current directions of the motor and generator are opposite when they are working, the 20KHz, 40KHz, and 60KHz current components can be offset. The ripple current components after offset are shown in Fig.16 , which obviously becomes smaller at the above frequency points, which means that the high-frequency ripple current borne by the capacitor can be reduced, which can effectively reduce the heating and loss of the capacitor. Example

[0034] In order to make the current components offset on the film capacitor components, the positive and negative copper bars inside the capacitor need to reduce the parasitic inductance as much as possible. The positive and negative copper bars inside the capacitor need to be introduced into a laminated structure. In the prior art, the distance between the positive and negative copper bars is affected by the size of the capacitor core. The distance between the positive and negative copper bars is greater than 20mm, which invisibly increases the parasitic inductance, making it impossible to completely offset the ripple current components that could have been offset. Instead, current oscillation will be formed, causing abnormal heating inside the capacitor.

[0035] The present invention also provides a support capacitor. The methods of Embodiment 1 and Embodiment 2 use the support capacitor as an energy conversion element in a vehicle drive system. Specifically, Fig.17 As shown, the supporting capacitor includes: a positive copper bar 1, a negative copper bar 2, and a capacitor core 3; a first recess is provided in the middle of the positive copper bar, and a plurality of first contacts are provided; a second recess is provided in the middle of the negative copper bar, and a plurality of second contacts are provided; the second recess of the negative copper bar is buckled into the first recess of the positive copper bar, and there is a certain gap 4 between the bottom surface of the second recess and the top surface of the first recess; the first contacts and the second contacts are arranged alternately; the capacitor core is fixed in the second recess, an insulating layer is laid in the gap 4, and the gap between the bottom surface of the second recess and the top surface of the first recess is less than 20 mm.

[0036] In another embodiment, the support capacitor can also be designed as follows Fig.18 The structure shown.

[0037] In order to offset the ripple current in Examples 1 and 2, a laminated copper busbar method is adopted, in which the positive and negative copper busbars are stacked together with an insulating layer sandwiched between them, and the capacitor core is arranged on one side of the laminated copper busbar to reduce the parasitic inductance inside the capacitor, so that the ripple current in the capacitor can be partially offset.

[0038] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for reducing heating of a support capacitor in a vehicle drive system, wherein the support capacitor is connected to a motor A and a motor B through a semiconductor module A and a semiconductor module B respectively; a signal processor is used to input a PWM gate signal to the semiconductor module A and the semiconductor module B for driving control; the method is characterized in that: The signal processor outputs PWM gate signals with frequency phases staggered by 180° to semiconductor module A and semiconductor module B; or, The signal processor outputs PWM gate signals with the same frequency and phase to semiconductor module A and semiconductor module B.

2. The method for reducing heating of a support capacitor in a vehicle-mounted drive system according to claim 1, characterized in that: When the motor A and the motor B are the left wheel drive motor and the right wheel drive motor in the vehicle drive system, the PWM gate signals output by the signal processor to the semiconductor module A and the semiconductor module B are staggered by 180° in phase.

3. The method for reducing heating of a support capacitor in a vehicle-mounted drive system according to claim 1, characterized in that: When the motor A and the motor B are the driving motor and the generator in the vehicle driving system, the PWM gate signal frequency output by the signal processor to the semiconductor module A and the semiconductor module B is the same.

4. A support capacitor, used in the method according to any one of claims 1 to 3, characterized in that: Including positive copper busbar, negative copper busbar and capacitor core; A first recess is provided in the middle of the positive copper bar, and a plurality of first contact points are provided; A second recess is provided in the middle of the negative electrode copper bar, and a plurality of groups of second contacts are provided; The second concave portion of the negative copper bar is buckled into the first concave portion of the positive copper bar, and there is a certain gap between the bottom surface of the second concave portion and the top surface of the first concave portion; The first contacts and the second contacts are arranged alternately; The capacitor core is fixed in the second recess.

5. The support capacitor according to claim 4, characterized in that: The gap between the bottom surface of the second recess and the top surface of the first recess is less than 20 mm.

6. The support capacitor according to claim 5, characterized in that: An insulating layer is laid in the gap.

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