JP2017112758A - Voltage conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make noise, resulting from ripple of an electric current flowing in a reactor, inaudible to an operator.SOLUTION: To step up a step up/down converter, switching control for transistors T21, T22 is exerted such that on-timings of the transistors T21, T22 differ from each other while both the switching frequencies of the transistors T21, T22, as a lower arm, have a predetermined frequency fup(=1/Tup). Here, the predetermined frequency fup is set to a frequency higher than 1/2 of the upper limit frequency fmax of an audible region and equal to or lower than the upper limit frequency fmax of the audible region.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a voltage converter.

  2. Description of the Related Art Conventionally, a voltage conversion device has been proposed that includes a buck-boost converter having a reactor, two upper arm switching elements (transistors), two lower arm switching elements (transistors), and four diodes. (For example, refer to Patent Document 1). Here, one terminal of the reactor is connected to the positive electrode line of the first power line to which the battery is connected. The two upper arm switching elements are connected in parallel to the positive line of the second power line to which the motor is connected and the other terminal of the reactor. The two lower arm switching elements are connected in parallel to the other terminal of the reactor and the negative lines of the first and second power lines. The four diodes are connected in parallel to each of the four switching elements in the reverse direction. In this voltage converter, when the step-up / step-down converter is boosted, both are turned on / off at the same timing based on the difference between the threshold voltages (voltages at which on / off is switched) of the two lower arm switching elements. An on / off signal is supplied to both to turn off. Also, when the buck-boost converter is stepped down, an on / off signal is supplied to both of them so that they are turned on / off at the same timing based on the difference in threshold voltages of the two upper arm switching elements. To do. Such control prevents an imbalance between the amount of current and the amount of heat generated between the parallel switching elements.

JP 2009-225531 A

  In such a voltage converter, a ripple (pulsation) occurs in the reactor current in synchronization with the on / off cycle (switching cycle) of the switching elements of the two upper arms and the lower arm. And this ripple causes the magnetic attractive force acting on the reactor to fluctuate and generate noise. If the noise frequency is in the audible range, the driver may feel noise due to the noise. On the other hand, it is also conceivable that the frequency of the reactor current ripple is made higher than the audible range by making the switching frequency of each switching element higher than the audible range. However, in this case, since the calorific value of each element becomes relatively large, there is a possibility that a bad effect such as a relatively short life of each element may occur.

  The main purpose of the voltage converter of the present invention is to suppress the driver from feeling noise caused by the ripple of current flowing through the reactor.

  The voltage converter of the present invention employs the following means in order to achieve the main object described above.

The voltage converter of the present invention is
A reactor having one terminal connected to the first positive line of the first power line connected to the battery, a second positive line of the second power line connected to the motor, and the other terminal of the reactor are parallel to each other. Are connected in parallel to n (where n is an integer of 2 or more) upper arm switching elements, the other terminal of the reactor, and the first and second negative lines of the first and second power lines. N lower arm switching elements connected, and 2n diodes connected in parallel in opposite directions to each of the n upper arm switching elements and the n lower arm switching elements, A buck-boost converter,
Control means for controlling the n upper arm switching elements and the n lower arm switching elements;
A voltage conversion device comprising:
The control means includes
When the step-up / step-down converter is boosted, the switching frequency of each of the n lower arm switching elements is set to a first predetermined frequency and each of the n lower arm switching elements is turned on. Controlling the switching elements of the n lower arms such that are different from each other,
When the step-up / down converter is stepped down, the switching frequency of each of the n upper arm switching elements is set to a second predetermined frequency, and each of the n upper arm switching elements is turned on. Controlling the switching elements of the n upper arms so that are different from each other,
The first predetermined frequency and the second predetermined frequency are determined within a range greater than 1 / n of the upper limit frequency of the audible range and less than or equal to the upper limit frequency.
This is the gist.

  In this voltage converter of the present invention, when the step-up / step-down converter is boosted (when power is supplied from the first power line to the second power line with voltage step-up by the step-up / down converter) The switching elements of the n lower arms are controlled so that the switching frequencies of the switching elements of the arms are all set to the first predetermined frequency and the ON timings of the switching elements of the n lower arms are different from each other. Here, the first predetermined frequency is determined within a range greater than 1 / n of the upper limit frequency of the audible range and less than or equal to the upper limit frequency. As described above, since the ON timings of the n lower arm switching elements are made different from each other, the frequency (average value) of the ripple of the reactor current may be set to a frequency n times the first predetermined frequency. In addition, the ripple amount of the reactor current can be reduced to reduce the sound pressure of noise caused by the ripple. Since the first predetermined frequency is set to a frequency larger than 1 / n of the upper limit frequency (for example, 20 kHz) of the audible range, the reactor current ripple frequency can be made larger than the upper limit frequency of the audible range. Thereby, it can suppress making a driver | operator feel the noise resulting from the ripple of the electric current of a reactor. Moreover, since the first predetermined frequency is set to a frequency equal to or lower than the upper limit frequency of the audible range, the amount of heat generated by each element is larger than that in which the first predetermined frequency is set to a frequency higher than the upper limit frequency of the audible range. Can be suppressed.

  In the voltage conversion device of the present invention, when the step-up / down converter is stepped down (when power is supplied from the second power line to the first power line with voltage step-down by the step-up / down converter), n The n upper arm switching elements are controlled so that the switching frequency of each of the upper arm switching elements is the second predetermined frequency and the ON timing of each of the n upper arm switching elements is different from each other. To do. Here, like the first predetermined frequency, the second predetermined frequency is determined within a range larger than 1 / n of the upper limit frequency of the audible range and equal to or lower than the upper limit frequency. As described above, since the ON timings of the n upper arm switching elements are made different from each other, the frequency (average value) of the ripple of the reactor current may be set to a frequency n times the second predetermined frequency. In addition, the ripple amount of the reactor current can be reduced to reduce the sound pressure of noise caused by the ripple. Since the second predetermined frequency is set to a frequency larger than 1 / n of the upper limit frequency of the audible range, the frequency of the ripple of the reactor current can be made larger than the upper limit frequency of the audible range. Thereby, it can suppress making a driver | operator feel the noise resulting from the ripple of the electric current of a reactor. Moreover, since the second predetermined frequency is set to a frequency equal to or lower than the upper limit frequency of the audible range, the amount of heat generated by each element is larger than that in which the second predetermined frequency is set to a frequency higher than the upper limit frequency of the audible range. Can be suppressed.

  In such a voltage converter of the present invention, when the control means performs the step-up operation of the step-up / down converter, the ON timing of each of the n lower arm switching elements is the reciprocal of the first predetermined frequency. When the buck-boost converter is controlled to deviate by a time corresponding to 1 / n (1 / (n · first predetermined frequency)), each of the n upper arm switching elements is controlled. May be controlled so as to be shifted by a time corresponding to 1 / n of the reciprocal of the second predetermined frequency (1 / (n · second predetermined frequency)).

It is a block diagram which shows the outline of a structure of the electric vehicle 20 carrying the voltage converter 40 as one Example of this invention. It is a block diagram which shows the outline of a structure of the electric vehicle 20B of a 1st comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage rise operation of the buck-boost converter 46B in the case of a 1st comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage rise operation of the buck-boost converter 46C in the case of a 2nd comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage rise operation of the buck-boost converter 46 in the case of an Example. It is explanatory drawing which shows an example of the mode of the electric current IL of the reactor L at the time of the pressure | voltage rise operation of the buck-boost converters 46, 46B, and 46C of an Example, a 1st comparative example, and a 2nd comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage fall operation of the buck-boost converter 46B in the case of a 1st comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage fall operation | movement of the buck-boost converter 46C in the case of a 2nd comparative example. It is explanatory drawing which shows the mode of the electric current flow at the time of the pressure | voltage fall operation of the buck-boost converter 46 in the case of an Example. It is explanatory drawing which shows an example of the mode of the electric current IL of the reactor L at the time of pressure | voltage fall operation of the buck-boost converters 46, 46B, and 46C of an Example, a 1st comparative example, and a 2nd comparative example. It is a block diagram which shows the outline of a structure of the electric vehicle 120 of a modification. It is explanatory drawing which shows an example of the mode of the electric current IL of the reactor L at the time of the pressure | voltage rise operation of the buck-boost converters 146 and 46C of a modification and a 2nd comparative example.

  Next, the form for implementing this invention is demonstrated using an Example.

  FIG. 1 is a configuration diagram showing an outline of a configuration of an electric vehicle 20 equipped with a voltage conversion device 40 as an embodiment of the present invention. As shown in FIG. 1, the electric vehicle 20 of the embodiment includes a motor 32, an inverter 34, a battery 36, a step-up / down converter 46, and an electronic control unit 50. Here, the voltage converter 40 of the embodiment corresponds to the step-up / step-down converter 46 and the electronic control unit 50.

  The motor 32 is configured as, for example, a synchronous generator motor, and a rotor is connected to a drive shaft 26 that is connected to drive wheels 22a and 22b via a differential gear 24. The inverter 34 is used to drive the motor 32, is connected to the motor 32, and is connected to the buck-boost converter 46 via the high voltage system power line 42. The battery 36 is configured as, for example, a lithium ion secondary battery or a nickel hydride secondary battery, and is connected to the buck-boost converter 46 via the low voltage system power line 44.

  The step-up / down converter 46 is connected to a high voltage system power line 42 to which the inverter 34 is connected and a low voltage system power line 44 to which the battery 36 is connected. This step-up / step-down converter 46 includes a reactor L, transistors T11, T12, T21, and T22 as four switching elements, and four diodes D11, D12, D21, and D22. One terminal of the reactor L is connected to the positive electrode line 44 a of the low voltage system power line 44. The transistors T11 and T12 are connected in parallel to the positive line 42a of the high voltage system power line 42 and the other terminal of the reactor L. The transistors T21 and T22 are connected in parallel to the other terminal of the reactor L and the negative voltage lines 42b and 44b of the low voltage system power line 44 and the high voltage system power line 42. The diodes D11 and D12 are connected to the transistors T11 and T12 in parallel in the reverse direction (so that the direction of the positive line 42a from the other terminal of the reactor L is the forward direction). The diodes D21 and D22 are connected to the transistors T21 and T22 in parallel in the reverse direction (so that the direction of the other terminal of the reactor L from the negative lines 42b and 44b is the forward direction). This step-up / down converter 46 supplies the power of the low voltage system power line 44 to the high voltage system power line 42 with a voltage step-up or the power of the high voltage system power line 42 with a voltage step-down. To the system power line 44. Hereinafter, the transistors T11 and T12 may be referred to as “upper arm”, and the transistors T21 and T22 may be referred to as “lower arm”.

  A smoothing capacitor 43 is attached to the positive line 42a and the negative line 42b of the high voltage system power line 42. A smoothing capacitor 45 is attached to the positive electrode line 44 a and the negative electrode line 44 b of the low voltage system power line 44.

  Although not shown, the electronic control unit 50 is configured as a microprocessor centered on a CPU, and includes a ROM for storing a processing program, a RAM for temporarily storing data, and an input / output port in addition to the CPU.

Signals from various sensors are input to the electronic control unit 50 via input ports. Examples of signals input to the electronic control unit 50 include the following.
The rotational position θm of the rotor of the motor 32 from the rotational position detection sensor that detects the rotational position of the rotor of the motor 32
The phase currents Iu and Iv from the current sensor that detects the current flowing in each phase of the motor 32
The voltage VH of the capacitor 43 (high voltage system power line 42) from the voltage sensor 43a attached between the terminals of the capacitor 43.
The voltage VL of the capacitor 45 (low voltage system power line 44) from the voltage sensor 45a attached between the terminals of the capacitor 45.
The current IL of the reactor L from the current sensor 46a that detects the current flowing through the reactor L of the step-up / down converter 46
-Ignition signal from the ignition switch 60-Shift position SP from the shift position sensor 62 that detects the operation position of the shift lever 61
Accelerator opening degree Acc from the accelerator pedal position sensor 64 that detects the depression amount of the accelerator pedal 63
-Brake pedal position BP from the brake pedal position sensor 66 that detects the amount of depression of the brake pedal 65
・ Vehicle speed V from the vehicle speed sensor 68

Various control signals are output from the electronic control unit 50 through an output port. Examples of the signal output from the electronic control unit 50 include the following.
A switching control signal for a plurality of switching elements (not shown) of the inverter 34 A switching control signal for the transistors T11, T12, T21, T22 of the buck-boost converter 46

The electronic control unit 50 performs the following calculations.
The rotational speed Nm of the motor 32 based on the rotational position θm of the rotor of the motor 32 from the rotational position detection sensor

  In the electric vehicle 20 of the embodiment configured as described above, the electronic control unit 50 sets the required torque Tp * required for traveling based on the accelerator opening Acc, the brake pedal position BP, and the vehicle speed V, and sets the required request. The torque Tp * is set to the torque command Tm * of the motor 32. Subsequently, the target voltage VH * of the high voltage system power line 42 is set based on the torque command Tm * of the motor 32 and the rotation speed Nm, and the target power as the product of the torque command Tm * of the motor 32 and the rotation speed Nm. Based on Pm * and the target voltage VH * and voltage VH of the high voltage system power line 42, a target current IL * as a target value of the current flowing through the reactor L is set. Then, the switching of the plurality of switching elements of the inverter 34 is controlled so that the motor 32 is driven by the torque command Tm *, and the transistor of the step-up / down converter 46 is set so that the current IL flowing through the reactor L becomes the target current IL *. Switching control of T11, T12, T21, and T22 is performed. Hereinafter, control of the buck-boost converter 46 by the electronic control unit 50 will be described.

  First, a description will be given of the step-up operation of the step-up / step-down converter 46 (when the electric power is supplied from the battery 36 to the motor 32 with the voltage step-up by the step-up / down converter 46). At this time, the electronic control unit 50 first sets the total target duty ratio Dup * of the lower arms (transistors T21 and T22) so that the current IL of the reactor L becomes the target current IL *. Subsequently, a half value of the target duty ratio Dup * is set to each of the target duty ratios Dup1 * and Dup2 * of the transistors T21 and T22.

  Then, the switching control of the transistors T21 and T22 is performed using the target duty ratios Dup1 * and Dup2 * so that the switching frequencies of the transistors T21 and T22 are both set to the predetermined frequency fup and the ON timings of the transistors T21 and T22 are different from each other. Do. In the embodiment, the predetermined frequency fup is set to a frequency larger than one half of the upper limit frequency fmax (for example, 20 kHz) of the audible range and lower than the upper limit frequency fmax of the audible range, for example, 11 kHz, 12 kHz, and 13 kHz. In the embodiment, the on-timing of the transistors T21 and T22 is shifted by a time (1 / (2 · fup) corresponding to one half of the reciprocal of the predetermined frequency fup.

  Note that when the step-up / step-down converter 46 is boosted, the transistor T11 may be held off, turned off when the transistor T21 is on, and turned on when the transistor T21 is off. Also good. The transistor T12 can be considered similarly to the transistor T11.

  Next, a description will be given of the step-down operation of the step-up / step-down converter 46 (when electric power is supplied from the motor 32 to the battery 36 with voltage step-down by the step-up / step-down converter 46). At this time, the electronic control unit 50 first sets the total target duty ratio Ddn * of the upper arms (transistors T11 and T12) so that the current IL of the reactor L becomes the target current IL *. Subsequently, a half value of the target duty ratio Ddn * is set to each of the target duty ratios Ddn1 * and Ddn2 * of the transistors T11 and T12.

  Then, the switching control of the transistors T11 and T12 is performed using the target duty ratios Ddn1 * and Ddn2 * so that the switching frequencies of the transistors T11 and T12 are both set to the predetermined frequency fdn and the ON timings of the transistors T11 and T12 are different from each other. Do. In the embodiment, the predetermined frequency fdn is set to a frequency larger than one half of the upper limit frequency fmax of the audible range and lower than the upper limit frequency fmax of the audible range, for example, 11 kHz, 12 kHz, 13 kHz. The predetermined frequency fdn may be the same frequency as the predetermined frequency fup, or may be a frequency different from the predetermined frequency fup. In the embodiment, the on-timing of the transistors T11 and T12 is shifted by a time (1 / (2 · fdn) corresponding to one half of the reciprocal of the predetermined frequency fdn.

  When the step-up / step-down converter 46 is stepped down, the transistor T21 may be held off, turned off when the transistor T11 is turned on, and turned on when the transistor T11 is turned off. Also good. The transistor T22 can be considered similarly to the transistor T21.

  By performing such control, the following effects can be obtained. Here, the electric vehicle 20B of the first comparative example and the electric vehicle 20C of the second comparative example will be described.

  First, the electric vehicle 20B of the first comparative example will be described. As for the hardware configuration, as shown in the configuration diagram of the electric vehicle 20B of the first comparative example in FIG. 2, transistors T12 and T22 and diodes D12 and D22 are provided in place of the buck-boost converter 46 of the electric vehicle 20 of the embodiment. The configuration is the same as that of the electric vehicle 20 of the embodiment except that the buck-boost converter 46B is used (having the reactor L, the two transistors T11 and T21, and the two diodes D11 and D21). The control of the buck-boost converter 46B by the electronic control unit 50 is performed as follows. When the step-up / step-down converter 46B is boosted, the switching control of the transistor T21 is performed using the target duty ratio Dup * with the switching frequency of the transistor T21 being a predetermined frequency fup. When the step-up / step-down converter 46B is stepped down, the switching control of the transistor T11 is performed using the target duty ratio Ddn * with the switching frequency of the transistor T11 as the predetermined frequency fdn.

  Next, the electric vehicle 20C of the second comparative example will be described. About a hardware structure, it was set as the structure same as the electric vehicle 20 of an Example. That is, the buck-boost converter 46C of the electric vehicle 20C of the second comparative example is the same as the buck-boost converter 46 of the electric vehicle 20 of the embodiment. Therefore, the illustration of the electric vehicle 20C is omitted. The control of the buck-boost converter 46C by the electronic control unit 50 is performed as follows. When the step-up / step-down converter 46C is boosted, the target duty ratio Dup * is set so that both the switching frequencies of the transistors T21 and T22 are set to the predetermined frequency fup and the ON timings of the transistors T21 and T22 are aligned (synchronized). It was assumed that the switching control of the transistors T21 and T22 was performed. When the buck-boost converter 46C is stepped down, the target duty ratio Ddn * is set so that the switching frequencies of the transistors T11 and T12 are both set to the predetermined frequency fdn and the ON timings of the transistors T11 and T12 are aligned (synchronized). It is assumed that the switching control of the transistors T11 and T12 is performed.

  Next, a description will be given of the state of the step-up / step-down converters 46, 46B, 46C in the embodiment, the first comparative example, and the second comparative example during the boosting operation. FIG. 3 is an explanatory diagram showing the state of current flow during the step-up operation of the buck-boost converter 46B in the case of the first comparative example. FIG. 3A shows a state when the transistor T21 is on, and FIG. 3B shows a state when the transistor T21 is off. FIG. 4 is an explanatory diagram showing the state of current flow during the step-up operation of the buck-boost converter 46C in the case of the second comparative example. FIG. 4A shows a state when both the transistors T21 and T22 are on, and FIG. 4B shows a state when both the transistors T21 and T22 are off. FIG. 5 is an explanatory diagram showing the state of current flow during the step-up operation of the buck-boost converter 46 in the case of the embodiment. FIG. 5A shows a state when the transistor T21 is on and the transistor T22 is off. FIG. 5B shows a state when the transistor T21 is off and the transistor T22 is on. ) Shows a state when both of the transistors T21 and T22 are off.

  As shown in FIG. 3, during the step-up operation of the step-up / step-down converter 46B in the case of the first comparative example, the following occurs. When the transistor T21 is on, a current path is formed for the battery 36, the positive line 44a, the reactor L, the transistor T21, and the negative line 44b as indicated by the thick arrows in FIG. 3A, and energy is accumulated in the reactor L. The When the transistor T21 is turned off, the battery 36, the positive line 44a, the reactor L, the diode D11, the positive line 42a, the capacitor 43, and the motor 32 (not shown), as indicated by the thick arrows in FIG. The current path of the negative electrode line 42b and the negative electrode line 44b is formed, and the energy of the reactor L is supplied to the high voltage system power line 42 (capacitor 43 and motor 32) together with the energy of the low voltage system power line 44 (battery 36).

  When the step-up / step-down converter 46C is boosted in the second comparative example, as shown in FIG. When both of the transistors T21 and T22 are on, a current path of the battery 36, the positive electrode line 44a, the reactor L, the transistors T21, T22, and the negative electrode line 44b is formed as shown by a thick arrow in FIG. Energy is stored in When both the transistors T21 and T22 are turned off, the battery 36, the positive line 44a, the reactor L, the diodes D11 and D12, the positive line 42a, the capacitor 43, and the motor 32 (see FIG. 3B). The current path of the negative electrode line 42b and the negative electrode line 44b is formed, and the energy of the reactor L is supplied to the high voltage system power line 42 (capacitor 43 and motor 32) together with the energy of the power line 44 (battery 36). The

  When the step-up / step-down converter 46 is boosted in the embodiment, as shown in FIG. When the transistor T21 is on and the transistor T22 is off, the current path of the battery 36, the positive line 44a, the reactor L, the transistor T21, and the negative line 44b is formed as shown by the thick arrow in FIG. Energy is stored in When both the transistors T21 and T22 are turned off, the battery 36, the positive line 44a, the reactor L, the diodes D11 and D12, the positive line 42a, the capacitor 43, and the motor 32 (see FIG. 5C). The current path of the negative electrode line 42b and the negative electrode line 44b is formed, and the energy of the reactor L is supplied to the power line 42 (capacitor 43 and motor 32) together with the energy of the low voltage system power line 44 (battery 36). The When the transistor T21 is off and the transistor T22 is on, a current path of the battery 36, the positive line 44a, the reactor L, the transistor T22, and the negative line 44b is formed as shown in FIG. Energy is stored. When both the transistors T21 and T22 are turned off, the state shown in FIG.

  FIG. 6 is an explanatory diagram showing an example of the state of the current IL of the reactor L during the step-up operation of the step-up / step-down converters 46, 46B, 46C in the embodiment, the first comparative example, and the second comparative example. In the figure, “Tup” is the switching cycle time of each transistor and corresponds to the reciprocal of the switching frequency (predetermined frequency fup).

  As shown in FIG. 6, in the first comparative example and the second comparative example, the cycle time of the ripple of the current IL of the reactor L is the same as the switching cycle time Tup. That is, the ripple frequency of the current IL of the reactor L becomes the same as the predetermined frequency fup. The ripple causes the magnetic attractive force acting on the reactor L to fluctuate and generate noise. When the frequency of this noise is in the audible range, the driver may feel noise due to this noise. On the other hand, it is also conceivable that the ripple frequency of the current IL of the reactor L is made higher than the upper limit frequency fmax of the audible range by making the switching frequency higher than the upper limit frequency fmax of the audible range. However, in this case, since the calorific value of each element becomes relatively large, there is a possibility that a bad effect such as a relatively short life of each element may occur.

  On the other hand, in the embodiment, the cycle time of the current IL of the reactor L is ½ of the switching cycle time Tup. That is, the ripple frequency of the current IL of the reactor L is twice the predetermined frequency fup. Thereby, the ripple amount (pulsation amount) of the current IL of the reactor L can be reduced, and the sound pressure of noise caused by the ripple can be reduced. As described above, since the predetermined frequency fup is set to a frequency larger than one half of the upper limit frequency fmax of the audible range, the ripple frequency of the current IL of the reactor L is set larger than the upper limit frequency fmax of the audible range. be able to. Thereby, it can suppress making a driver | operator feel the noise resulting from the ripple of the electric current IL of the reactor L. FIG. In addition, since the predetermined frequency fup is set to a frequency equal to or lower than the upper limit frequency fmax of the audible range, the amount of heat generated by each element is larger than that in which the predetermined frequency fup is higher than the upper limit frequency fmax of the audible range. Can be suppressed.

  Next, the state during the step-down operation of the step-up / step-down converters 46, 46B, 46C of the embodiment, the first comparative example, and the second comparative example will be described. FIG. 7 is an explanatory diagram showing the state of current flow during the step-down operation of the buck-boost converter 46B in the case of the first comparative example. FIG. 7A shows a state when the transistor T11 is on, and FIG. 7B shows a state when the transistor T11 is off. FIG. 8 is an explanatory diagram showing the state of current flow during the step-down operation of the step-up / down converter 46C in the case of the second comparative example. FIG. 8A shows a state when both the transistors T11 and T12 are on, and FIG. 8B shows a state when both the transistors T11 and T12 are off. FIG. 9 is an explanatory diagram showing a state of current flow during the step-down operation of the step-up / down converter 46 in the case of the embodiment. FIG. 9A shows a state when the transistor T11 is on and the transistor T12 is off, and FIG. 9B shows a state when the transistor T11 is off and the transistor T12 is on. ) Shows a state when both the transistors T11 and T12 are off.

  At the time of step-down operation of the buck-boost converter 46B in the case of the first comparative example, as shown in FIG. When the transistor T11 is on, as shown by the thick arrow in FIG. 7A, the capacitor 43 and the motor 32 (not shown), the positive line 42a, the transistor T11, the reactor L, the positive line 44a, the battery 36, and the negative line 44b and the negative electrode line 42b are formed, and energy is accumulated in the reactor L. When the transistor T11 is turned off, the current path of the reactor L, the positive electrode line 44a, the battery 36, the negative electrode line 44b, and the diode D21 is formed as shown by the thick arrow in FIG. 3B, and the energy of the reactor L is changed. It is supplied to the low voltage system power line 44 (battery 36).

  At the time of the step-down operation of the step-up / down converter 46C in the case of the second comparative example, as shown in FIG. When the transistors T11 and T12 are on, as shown by the thick arrows in FIG. 8A, the capacitor 43 and the motor 32 (not shown), the positive line 42a, the transistors T11 and T12, the reactor L, the positive line 44a, the battery 36, the current path of the negative electrode line 44b and the negative electrode line 42b is formed, and energy is accumulated in the reactor L. When the transistors T11 and T12 are turned off, a current path of the reactor L, the positive electrode line 44a, the battery 36, the negative electrode line 44b, and the diodes D21 and D22 is formed as shown by the thick arrows in FIG. L energy is supplied to the low voltage system power line 44 (battery 36).

  In the step-down operation of the step-up / down converter 46 in the embodiment, as shown in FIG. When transistor T11 is on and transistor T12 is off, capacitor 43 and motor 32 (not shown), positive line 42a, transistor T11, reactor L, positive line 44a, as shown by the thick arrow in FIG. A current path of the battery 36, the negative electrode line 44b, and the negative electrode line 42b is formed, and energy is stored in the reactor L. When both the transistors T11 and T12 are turned off, the current paths of the reactor L, the positive line 44a, the battery 36, the negative line 44b, and the diodes D21 and D22 are formed as shown by the thick arrows in FIG. 9C. The energy of the reactor L is supplied to the power line 44 (battery 36). When the transistor T11 is off and the transistor T12 is on, as shown in FIG. 9B, the capacitor 43 and the motor 32 (not shown), the positive line 42a, the transistor T12, the reactor L, the positive line 44a, the battery 36, the current path of the negative electrode line 44b and the negative electrode line 42b is formed, and energy is accumulated in the reactor L. When the transistors T11 and T12 are both turned off, the state shown in FIG.

  FIG. 10 is an explanatory diagram illustrating an example of a state of the current IL of the reactor L during the step-down operation of the step-up / step-down converters 46, 46B, and 46C in the embodiment, the first comparative example, and the second comparative example. In the figure, “Tdn” is the switching cycle time of each transistor and corresponds to the reciprocal of the switching frequency (predetermined frequency fdn).

  As shown in FIG. 10, in the first comparative example and the second comparative example, the period time of the ripple of the current IL of the reactor L is the same as the switching period time Tup. That is, the ripple frequency of the current IL of the reactor L is the same as the predetermined frequency fdn. The ripple causes the magnetic attractive force acting on the reactor L to fluctuate and generate noise. When the frequency of this noise is in the audible range, the driver may feel noise due to this noise. On the other hand, it is also conceivable that the ripple frequency of the current IL of the reactor L is made higher than the upper limit frequency fmax of the audible range by making the switching frequency higher than the upper limit frequency fmax of the audible range. However, in this case, since the calorific value of each element becomes relatively large, there is a possibility that a bad effect such as a relatively short life of each element may occur.

  On the other hand, in the embodiment, the cycle time of the current IL of the reactor L is ½ of the switching cycle time Tdn. That is, the ripple frequency of the current IL of the reactor L is twice the predetermined frequency fdn. Thereby, the ripple amount (pulsation amount) of the current IL of the reactor L can be reduced, and the sound pressure of noise caused by the ripple can be reduced. As described above, since the predetermined frequency fdn is set to a frequency larger than one half of the upper limit frequency fmax of the audible range, the ripple frequency of the current IL of the reactor L is set larger than the upper limit frequency fmax of the audible range. be able to. Thereby, it can suppress making a driver | operator feel the noise resulting from the ripple of the electric current IL of the reactor L. FIG. In addition, since the predetermined frequency fdn is set to a frequency that is equal to or lower than the upper limit frequency fmax of the audible range, the amount of heat generated by each element is larger than that in which the predetermined frequency fdn is higher than the upper limit frequency fmax of the audible range. Can be suppressed.

  In the electric vehicle 20 of the embodiment described above, when the step-up / step-down converter 46 is boosted, the switching frequencies of the transistors T21 and T22 are both set to the predetermined frequency fup, and the ON timings of the transistors T21 and T22 are different from each other ( Switching control of the transistors T21 and T22 is performed so as to be shifted by a time corresponding to one half of the inverse of the predetermined frequency fup (1 / (2 · fup)). Here, the predetermined frequency fup is set to a frequency that is greater than one half of the upper limit frequency fmax of the audible range and less than or equal to the upper limit frequency fmax of the audible range. When the step-up / step-down converter 46 performs a step-down operation, the switching frequencies of the transistors T11 and T12 are both set to the predetermined frequency fdn, and the ON timings of the transistors T11 and T12 are different from each other (two times the reciprocal of the predetermined frequency fdn). The switching control of the transistors T11 and T12 is performed so as to be shifted by a time corresponding to 1 (1 / (2 · fdn)). Here, the predetermined frequency fdn is set to a frequency that is greater than one half of the upper limit frequency fmax of the audible range and lower than or equal to the upper limit frequency fmax of the audible range. Accordingly, the ripple amount of the current IL of the reactor L can be reduced to reduce the sound pressure of noise caused by the ripple, and the ripple frequency of the current IL of the reactor L can be set to the upper limit frequency fmax of the audible range. It is possible to suppress the noise caused by the ripple of the current IL of the reactor L from being felt by the driver. In addition, it is possible to suppress an increase in the amount of heat generated by each element, as compared with the case where the predetermined frequency fdn is set higher than the upper limit frequency fmax of the audible range.

  In the electric vehicle 20 of the embodiment, when the step-up / step-down converter 46 is boosted, the value of one half of the total target duty ratio Dup * of the lower arm (transistors T21, T22) is set to each of the transistors T21, T22. The target duty ratios Dup1 * and Dup2 * are set. When the step-up / step-down converter 46 is stepped down, a value half the total target duty ratio Ddn * of the upper arms (transistors T11 and T12) is set to the target duty ratio Ddn1 * of each of the transistors T11 and T12. , Ddn2 *. However, when considering an increase in loss in the step-up / down converter 46 in the embodiment relative to the case of the first comparative example or the second comparative example, when the step-up / down converter 46 is boosted, the target duty ratio Dup * When the value obtained by adding the loss increase to the half value is set to the target duty ratios Dup1 * and Dup2 *, and the step-up / down converter 46 is stepped down, the target duty ratio Ddn * is halved. A value obtained by adding an increase in loss to the value of may be set as the target duty ratios Ddn1 * and Ddn2 *.

  In the electric vehicle 20 of the embodiment, the step-up / step-down converter 46 includes a reactor L, four transistors T11, T12, T21, and T22, and four diodes D11, D12, D13, and D14. However, the buck-boost converter 46 may include a reactor L, 2n (n is an integer of 3 or more) transistors, and 2n diodes. FIG. 11 is an explanatory diagram illustrating an example of a configuration of an electric vehicle 120 according to a modification. The step-up / down converter 146 of the electric vehicle 120 includes a reactor L, six transistors T11, T12, T13, T21, T22, and T23 and six diodes D11, D12, D13, D21, D22, and D23. That is, this corresponds to when n is 3. The transistors T11, T12, and T13 are connected in parallel to the positive line 42a of the high voltage system power line 42 and the other terminal of the reactor L. The transistors T21, T22, T23 are connected in parallel to the other terminal of the reactor L and the low voltage system power line 44 and the negative electrode lines 42b, 44b of the high voltage system power line 42. The diodes D11, D12, D13, D21, D22, and D23 are connected in parallel to the transistors T11, T12, T13, T21, T22, and T23 in the reverse direction.

  In this electric vehicle 120, when the step-up / step-down converter 146 is boosted, the switching frequencies of the transistors T21, T22, and T23 are all set to a predetermined frequency fup2, and the ON timings of the transistors T21, T22, and T23 are different from each other (predetermined) Switching control of the transistors T21, T22, and T23 is performed so that the time corresponds to one third of the reciprocal of the frequency fup (shifted by 1 / (3 · fup2)), where the predetermined frequency fup2 is in the audible range. The frequency is larger than one third of the upper limit frequency fmax and lower than the upper limit frequency fmax of the audible range, for example, 8 kHz, 9 kHz, 10 kHz, etc. When the step-up / down converter 146 is operated in a step-down operation, the transistors T11, Both switching frequency of T12 and T13 The transistors T11, T11, T12, T13 are set to have the constant frequency fdn2 and the ON timings of the transistors T11, T12, T13 are different from each other (the time corresponding to one third of the reciprocal of the predetermined frequency fdn (shifted by 1 / (3 · fdn2)) Switching control is performed at T12 and T13, where the predetermined frequency fdn2 is a frequency that is greater than one third of the upper limit frequency fmax of the audible range and lower than or equal to the upper limit frequency fmax of the audible range, for example, 8 kHz, 9 kHz, 10 kHz, etc. It was.

  FIG. 12 is an explanatory diagram showing an example of the state of the current IL of the reactor L during the step-up operation of the step-up / step-down converters 146 and 46C of this modified example and the second comparative example. In the figure, “Tup2” is the switching cycle time of each transistor and corresponds to the reciprocal of the switching frequency (predetermined frequency fup2). As shown in FIG. 12, the cycle time of the ripple of the current IL of the reactor L is the same as the switching cycle time Tup2 in the second comparative example, and is one third of the switching cycle time Tup2 in this modification. That is, the ripple frequency of the current IL of the reactor L is the same as the predetermined frequency fup2 in the second comparative example, and is three times the predetermined frequency fup in this modification. Thereby, the ripple amount (pulsation amount) of the current IL of the reactor L can be further reduced, and the sound pressure of noise caused by the ripple can be further reduced. Then, by setting the predetermined frequency fup2 to a frequency larger than one third of the upper limit frequency fmax of the audible range, the ripple frequency of the current IL of the reactor L can be made larger than the upper limit frequency fmax of the audible range, It is possible to suppress the driver from feeling noise due to the ripple of the current IL of the reactor L. In FIG. 12, the effect of the step-up / step-down converter 146 during the step-up operation has been described. However, the step-down / step-up converter 146 can be considered in the same manner as this.

  In the electric vehicle 20 of the embodiment, the step-up / step-down converter 46 in the case of including the reactor L, the four transistors T11, T12, T21, T22 and the four diodes D11, D12, D21, D22 are included. The control has been described. Moreover, in the electric vehicle 120 of a modification, the step-up / step-down converter having a reactor L, six transistors T11, T12, T13, T21, T22, T23 and six diodes D11, D12, D13, D21, D22, D23. The control of the step-up / step-down converter 146 when provided with 46 has been described. In light of these, the same applies to a case where a buck-boost converter having a reactor L, 2n transistors (n upper-arm transistors and n lower-arm transistors) and 2n diodes is provided. It is considered that the buck-boost converter should be controlled. When the step-up / step-down converter is boosted, the switching frequency of each of the n lower arm switching elements is set to a predetermined frequency fup3, and the ON timing of each of the n lower arm switching elements is different from each other ( Switching control of the switching elements of the n lower arms is performed so that the time corresponds to 1 / n of the inverse of the predetermined frequency fup3 (1 / (n · fup3)). Here, the predetermined frequency fup3 is greater than 1 / n of the upper limit frequency fmax of the audible range and is equal to or lower than the upper limit frequency fmax. When the buck-boost converter is stepped down, the switching frequency of each of the n upper arm switching elements is set to a predetermined frequency fdn3, and the ON timing of each of the n upper arm switching elements is different from each other ( Switching control of the switching elements of the n upper arms is performed so as to shift by a time corresponding to 1 / n of the inverse of the predetermined frequency fdn3 (1 / (n · fdn3)). Here, the predetermined frequency fdn3 is set to a frequency that is larger than 1 / n of the upper limit frequency fmax of the audible range and lower than or equal to the upper limit frequency fmax. By doing this, it is possible to achieve the same effects as in the embodiment.

  In the embodiment, the voltage conversion device 40 is mounted on the electric vehicle 20 together with the traveling motor 32 and the battery 36. However, the voltage conversion device may be mounted on a hybrid vehicle that includes a traveling engine and a battery in addition to the traveling motor and a fuel cell vehicle that includes a fuel cell in addition to the traveling motor and battery. It is good also as what is mounted in.

  The correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems will be described. In the embodiment, the step-up / step-down converter 46 having the reactor L, the transistors T11, T12, T21, T22 and the diodes D11, D12, D21, D22 corresponds to a “step-up / step-down converter”, and the electronic control unit 50 is “control means”. It corresponds to.

  The correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problem is the same as that of the embodiment described in the column of means for solving the problem. Therefore, the elements of the invention described in the column of means for solving the problems are not limited. That is, the interpretation of the invention described in the column of means for solving the problems should be made based on the description of the column, and the examples are those of the invention described in the column of means for solving the problems. It is only a specific example.

  As mentioned above, although the form for implementing this invention was demonstrated using the Example, this invention is not limited at all to such an Example, In the range which does not deviate from the summary of this invention, it is with various forms. Of course, it can be implemented.

  The present invention is applicable to the voltage conversion device manufacturing industry and the like.

  20, 20B, 20C, 120 Electric vehicle, 22a, 22b Drive wheel, 24 differential gear, 26 Drive shaft, 32 Motor, 34 Inverter, 36 Battery, 40 Voltage converter, 42 High voltage system power line, 42a Positive line, 42b Negative line, 43 capacitor, 43a Voltage sensor, 44 Low voltage system power line, 44a Positive line, 44b Negative line, 45 capacitor, 45a Voltage sensor, 46, 46B, 46C, 146 Buck-boost converter, 46a Current sensor, 50 Electronic control Unit, 60 Ignition switch, 61 Shift lever, 62 Shift position sensor, 63 Accelerator pedal, 64 Accelerator pedal position sensor, 65 Brake pedal, 66 Brake pedal position sensor, 68 Vehicle speed Sensor, D11, D12, D13, D21, D22, D23 Diode, L reactor, T11, T12, T13, T21, T22, T23 transistor.

Claims (1)

A reactor having one terminal connected to the first positive line of the first power line connected to the battery, a second positive line of the second power line connected to the motor, and the other terminal of the reactor are parallel to each other. Are connected in parallel to n (where n is an integer of 2 or more) upper arm switching elements, the other terminal of the reactor, and the first and second negative lines of the first and second power lines. N lower arm switching elements connected, and 2n diodes connected in parallel in opposite directions to each of the n upper arm switching elements and the n lower arm switching elements, A buck-boost converter,
Control means for controlling the n upper arm switching elements and the n lower arm switching elements;
A voltage conversion device comprising:
The control means includes
When the step-up / step-down converter is boosted, the switching frequency of each of the n lower arm switching elements is set to a first predetermined frequency and each of the n lower arm switching elements is turned on. Controlling the switching elements of the n lower arms such that are different from each other,
When the step-up / down converter is stepped down, the switching frequency of each of the n upper arm switching elements is set to a second predetermined frequency, and each of the n upper arm switching elements is turned on. Controlling the switching elements of the n upper arms so that are different from each other,
The first predetermined frequency and the second predetermined frequency are determined within a range greater than 1 / n of the upper limit frequency of the audible range and less than or equal to the upper limit frequency.
Voltage converter.

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