JP7629759B2 - DC/DC Converter - Google Patents

Description

The present invention relates to a DC/DC converter.

There is a known power supply system that supplies power to a motor drive device via a DC/DC converter that steps up or steps down the voltage supplied from a power source such as a battery. This power supply system is provided with a large-capacity power supply stabilization capacitor to absorb the ripple current flowing through the motor and stabilize the power supply voltage.

The power supply stabilization capacitor is connected in parallel to the motor drive device, which is the load of the battery. Patent Document 1 discloses a precharge circuit that precharges the power supply stabilization capacitor when the power is turned on. The precharge circuit prevents excessive inrush current from flowing from the power supply to the power supply stabilization capacitor when the power is turned on. This prevents failure of semiconductor elements arranged in the DC/DC converter in the power supply system.

JP 2007-336609 A

However, in the above-mentioned power supply system, if the motor drive device suddenly stops while the precharge circuit is supplying power to the motor drive device after performing preliminary charging, current will flow from the power supply to the power supply stabilization capacitor if the voltage of the power supply stabilization capacitor is lower than the power supply voltage.

At this time, the switching element in the DC/DC converter is OFF. Therefore, the current flowing from the power supply to the power supply stabilization capacitor passes through the body diode that is parasitic on the switching element. This current passage causes the body diode to heat up.

One aspect of the present invention has been made in consideration of the above problems, and aims to realize a DC/DC converter that can reduce heat generation within the DC/DC converter.

In order to solve the above problems, a DC/DC converter according to one aspect of the present invention includes a one-phase converter composed of an inductor, an upper switching element, and a lower switching element, and a control unit that switches the upper switching element between ON and OFF and switches the lower switching element between ON and OFF, and the control unit turns the upper switching element ON when a predetermined determination condition is satisfied.

In the above configuration, if an abnormality occurs in an electric vehicle equipped with a DC/DC converter and the electric vehicle stops boost control, and the output voltage of the DC/DC converter is lower than the input voltage, a direct current will flow from the input side to the output side of the DC/DC converter.

According to the above configuration, when a predetermined judgment condition is satisfied, the control unit turns on the upper switching element. As a result, the direct current flowing from the input side to the output side of the DC/DC converter does not flow through the body diode, which is a parasitic diode of the upper switching element, but flows through the channel portion of the upper switching element, which has a smaller resistance than the body diode. Therefore, the DC/DC converter can reduce heat generation within the DC/DC converter.

It is preferable that the control unit turns on the upper switching element when the DC current flowing through the inductor exceeds a current threshold.

With the above configuration, the control unit can determine whether or not a predetermined determination condition is satisfied by measuring the direct current flowing through the inductor of the DC/DC converter.

It is preferable that the control unit turns on the upper switching element when the output voltage of the DC/DC converter becomes lower than the input voltage of the DC/DC converter by a voltage threshold or more.

According to the above configuration, the control unit can determine whether or not a predetermined determination condition is satisfied by measuring the output voltage and input voltage of the DC/DC converter.

The control unit may turn on the upper switching element when the output voltage of the DC/DC converter becomes lower than the input voltage of the DC/DC converter by a voltage threshold or more and the direct current flowing through the inductor becomes equal to or greater than a current threshold.

It is preferable that the system is provided with a plurality of single-phase converters, and that the DC/DC converter is a multi-phase DC/DC converter.

The above configuration makes it possible to reduce heat generation within the DC/DC converter, even in the case of a multi-phase DC/DC converter.

According to one aspect of the present invention, heat generation within a DC/DC converter can be reduced.

1 is a schematic configuration diagram of an electric vehicle equipped with a DC/DC converter according to a first embodiment of the present invention; 4 shows a flowchart of a control process of the DC/DC converter. 4 is a diagram for explaining a current path when the electric vehicle performs precharging. FIG. 4 is a diagram for explaining a current path when the electric vehicle starts boost control. FIG. 10A and 10B are diagrams illustrating the operation of the upper switching element and the lower switching element when the electric vehicle starts boost control. 10A and 10B are diagrams illustrating other operations of the upper and lower switching elements when the electric vehicle starts boost control. 4 is a diagram for explaining a current path when the electric vehicle stops boost control. FIG. FIG. 11 is a schematic configuration diagram of an electric vehicle equipped with a DC/DC converter according to a second embodiment of the present invention.

[Embodiment 1]
Hereinafter, the first embodiment of the present invention will be described in detail.

<Electric vehicle configuration>
1 is a schematic configuration diagram of an electric vehicle equipped with a DC/DC converter 1 according to the present embodiment 1. In the present embodiment 1, an embodiment in which the DC/DC converter 1 is a DC/DC converter equipped in an electric vehicle will be described as an example.

As shown in FIG. 1, the electric vehicle includes a DC/DC converter 1, a high-voltage power supply 2, a power supply control unit 3, a contactor 4, a precharge circuit 5, a storage capacitor 7, an inverter 8, and a motor 9.

The high-voltage power supply 2 supplies a DC voltage to the DC/DC converter 1 via the contactor 4 or the precharge circuit 5. For example, the high-voltage power supply 2 supplies a DC voltage of 200 V to the DC/DC converter 1.

The power supply control unit 3 turns the contactor 4 ON or OFF. The power supply control unit 3 also turns the contactor 51 included in the precharge circuit 5 ON or OFF. Details of the precharge circuit 5 will be described later.

When the power supply control unit 3 turns contactor 4 ON and contactor 51 OFF, current flows from the high voltage power supply 2 through contactor 4 to the DC/DC converter 1. When the power supply control unit 3 turns contactor 4 OFF and contactor 51 ON, current flows from the high voltage power supply 2 through the precharge circuit 5 to the DC/DC converter 1. When the power supply control unit 3 turns contactor 4 OFF and contactor 51 OFF, current does not flow from the high voltage power supply 2 to the DC/DC converter 1.

The contactor 4 is, for example, a relay-type electromagnetic switch.

The precharge circuit 5 is a circuit for preventing an inrush current from flowing from the high voltage power supply 2 to the DC/DC converter 1 when the high voltage power supply 2 is started. The precharge circuit 5 includes the above-mentioned contactor 51 and a resistor 52 connected in series to the contactor 51. The contactor 51 is, for example, a relay-type electromagnetic switch.

If an inrush current flows into the DC/DC converter 1, the semiconductor elements in the DC/DC converter 1 may break down. For this reason, when the high voltage power supply 2 is started, the power supply control unit 3 turns off the contactor 4 and turns on the contactor 51, causing the DC current flowing from the high voltage power supply 2 to the DC/DC converter 1 to pass through the precharge circuit 5. The DC current flows through resistor 52 of the precharge circuit 5, and the current value of the DC current drops by the resistance value of resistor 52. Therefore, the precharge circuit 5 can prevent an inrush current from flowing into the DC/DC converter 1.

The DC/DC converter 1 charges the storage capacitor 7. The storage capacitor 7 supplies DC current to the inverter 8 by discharging.

The inverter 8 converts the direct current supplied from the storage capacitor 7 into alternating current.

The motor 9 is driven by an alternating current supplied from the inverter 8. Note that, although there is one motor 9 in the example of FIG. 1, there may be multiple motors.

<Functional configuration of DC/DC converter>
The DC/DC converter 1 is a circuit that converts a DC voltage supplied from a high voltage power supply 2. For example, when the DC voltage of the high voltage power supply 2 is 200 V, the DC/DC converter 1 converts the DC voltage of 200 V to a DC voltage of 450 V. The DC/DC converter can also step down the DC voltage supplied from the high voltage power supply 2.

The DC/DC converter 1 includes a first input terminal T1, a second input terminal T2, an inductor L1, an upper switching element Fu1, a lower switching element Fd1, a smoothing capacitor C, a first output terminal T3, a second output terminal T4, and a control unit 10. The DC/DC converter 1 may further include a first voltmeter D1, a second voltmeter D2, and an ammeter E1.

The first input terminal T1 is connected to the positive terminal of the high voltage power supply 2 via the contactor 4 or the precharge circuit 5. The second input terminal T2 is connected to the negative terminal of the high voltage power supply 2.

The inductor L1, the upper switching element Fu1, and the lower switching element Fd1 form a one-phase converter. The upper switching element Fu1 is, for example, a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor). The lower switching element Fd1 is, for example, a MOS-FET.

One terminal of the inductor L1 is connected to the first input terminal, and the other terminal is connected to the source of the upper switching element Fu1. The inductor L1 stores or discharges the DC current supplied from the high-voltage power supply 2.

The gate of the upper switching element Fu1 is connected to the control unit 10, and the drain is connected to the first output terminal T3.

The gate of the lower switching element Fd1 is connected to the control unit 10, the drain is connected to the other terminal of the inductor L1 and the source of the upper switching element, and the source is connected to the second input terminal T2 and the second output terminal T4.

A body diode Bu1 is formed between the source and drain of the upper switching element Fu1. The body diode Bu1 is a parasitic diode of the upper switching element Fu1. When the upper switching element Fu1 is ON, the current flowing through the upper switching element Fu1 does not flow through the body diode Bu1, but through a channel portion with a smaller resistance than the body diode Bu1. When the upper switching element Fu1 is OFF, the current flowing through the body diode Bu1.

A body diode Bd1 is formed between the source and drain of the lower switching element Fd1. The body diode Bd1 is a parasitic diode of the lower switching element Fd1. When the lower switching element Fd1 is ON, the current flowing through the lower switching element Fd1 does not flow through the body diode Bd1, but through a channel portion with a smaller resistance than the body diode Bd1. When the lower switching element Fd1 is OFF, the current flowing through the body diode Bd1.

The upper switching element Fu1 is turned ON when the control unit 10 inputs an H-level gate signal Gu1 to its gate. On the other hand, the upper switching element Fu1 is turned OFF when the control unit 10 inputs an L-level gate signal Gu1 to its gate.

The lower switching element Fd1 is turned ON when an H-level gate signal Gd1 is input to its gate from the control unit 10. On the other hand, the lower switching element Fd1 is turned OFF when an L-level gate signal Gd1 is input to its gate from the control unit 10.

The smoothing capacitor C is connected between the first output terminal T3 and the second output terminal T4. The smoothing capacitor C smoothes the output voltage Vout that is output between the first output terminal T3 and the second output terminal T4.

The first voltmeter D1 is connected between the first input terminal T1 and the second input terminal T2. The first voltmeter D1 measures the input voltage Vin between the first input terminal T1 and the second input terminal T2. The first voltmeter D1 outputs the measurement result H1 to the control unit 10.

The second voltmeter D2 is connected between the first output terminal T3 and the second output terminal T4. The second voltmeter D2 measures the output voltage Vout between the first output terminal T3 and the second output terminal T4. The second voltmeter D2 outputs the measurement result H2 to the control unit 10.

The ammeter E1 is connected between the inductor L1 and the first input terminal T1. The ammeter E1 measures the direct current I1 flowing through the inductor L1. The ammeter E1 outputs the measurement result J1 to the control unit 10.

<Control process of DC/DC converter>
Fig. 2 is a flowchart showing the control process of the DC/DC converter 1. When the high-voltage power supply 2 of the electric vehicle shown in Fig. 1 is started, control of the DC/DC converter 1 is started.

Step S101:
The electric vehicle performs pre-charging to store electricity in the storage capacitor 7. More specifically, the power supply control unit 3 turns the contactor 4 OFF and the contactor 51 ON. The control unit 10 turns the upper switching element Fu1 OFF and the lower switching element Fd1 OFF. Note that if a large current is required for pre-charging, the control unit 10 may turn the upper switching element Fu1 ON. Next, the process proceeds to step S102.

Here, we explain the current path when an electric vehicle is precharging.

Figure 3 is a diagram to explain the current path when an electric vehicle is precharging.

When an electric vehicle performs precharging, the DC/DC converter 1 stores the direct current I1 in the storage capacitor 7.

As shown in FIG. 3, a DC current I1 flows from a high-voltage power supply 2 through a DC/DC converter 1 to a storage capacitor 7. The paths of the DC current I1 include a current path R1 and a current path R2.

Current path R1 is a path through which DC current I1 flows through the body diode Bu1 of the upper switching element Fu1. Current path R1 is a path that corresponds to when the upper switching element Fu1 is OFF. Current path R2 is a path through which DC current I1 flows through the channel portion of the upper switching element Fu1. Current path R2 is a path that corresponds to when the upper switching element Fu1 is ON.

Step S102:
The electric vehicle starts boost control. The boost control is a control for supplying power to the inverter 8 for rotating the motor 9. More specifically, the power supply control unit 3 turns the contactor 4 ON and turns the contactor 51 OFF. The control unit 10 turns the upper switching element Fu1 OFF and controls the lower switching element Fd1 with PWM (Pulse Width Modulation). When the load applied to the motor 9 is high, the control unit 10 may also PWM control the upper switching element Fu1. However, the control unit 10 PWM controls the upper switching element Fu1 so that the ON period of the upper switching element Fu1 and the OFF period of the lower switching element Fd1 coincide with each other, and the OFF period of the upper switching element Fu1 and the ON period of the lower switching element Fd1 coincide with each other. Next, the process proceeds to step S103.

Here, we explain the current path when an electric vehicle starts boost control.

Figure 4 is a diagram to explain the current path when an electric vehicle starts boost control.

The electric vehicle starts boost control when power is stored in the storage capacitor 7 through precharging. Boost control stores the output voltage Vout of the DC/DC converter 1 in the storage capacitor 7. At this time, the control unit 10 PWM controls the lower switching element Fd1. When the motor 9 is under a low load, the control unit 10 turns off the upper switching element Fu1. When the motor 9 is under a high load, the control unit 10 also PWM controls the upper switching element Fu1.

As shown in FIG. 4, the paths of DC current I1 include current path R3, current path R4, and current path R5.

Current path R3 is a path through which DC current I1 flows through the channel portion of the lower switching element Fd1. Current path R3 is a path that corresponds to when the lower switching element Fd1 is ON. Current path R4 is a path through which DC current I1 flows through the body diode Bu1 of the upper switching element Fu1. Current path R4 is a path that corresponds to when the lower switching element Fd1 is OFF and the upper switching element Fu1 is OFF. Current path R5 is a path through which DC current I1 flows through the channel portion of the upper switching element Fu1. Current path R5 is a path that corresponds to when the upper switching element Fu1 is ON.

Figure 5 is a diagram explaining the operation of the upper switching element Fu1 and the lower switching element Fd1 when the electric vehicle starts boost control. Figure 5 corresponds to the case where the load applied to the motor 9 is low.

As shown in FIG. 5, the upper switching element Fu1 is OFF during the period from time t10 to time t14. On the other hand, the lower switching element Fd1 is ON during the period from time t10 to time t11, OFF during the period from time t11 to time t12, ON during the period from time t12 to time t13, and OFF during the period from time t13 to time t14. The period from time t10 to time t11 is the same as the period from time t12 to time t13. The period from time t11 to time t12 is the same as the period from time t13 to time t14. That is, the control unit 10 PWM controls the lower switching element Fd1 based on the following duty ratio.

Duty ratio: (period from time t10 to time t11)/(period from time t10 to time t12).

Figure 6 is a diagram explaining another operation of the upper switching element Fu1 and the lower switching element Fd1 when the electric vehicle starts boost control. Figure 6 corresponds to the case where the load applied to the motor 9 is high.

As shown in FIG. 6, the upper switching element Fu1 is OFF during the period from time t20 to time t21, ON during the period from time t21 to time t22, OFF during the period from time t22 to time t23, and ON during the period from time t23 to time t24. The period from time t20 to time t21 is the same as the period from time t22 to time t23. The period from time t21 to time t22 is the same as the period from time t23 to time t24. That is, the control unit 10 PWM controls the upper switching element Fu1 based on the following duty ratio.

Duty ratio: (period from time t21 to time t22)/(period from time t21 to time t23).

On the other hand, the lower switching element Fd1 is ON from time t20 to time t21, OFF from time t21 to time t22, ON from time t22 to time t23, and OFF from time t23 to time t24. The period from time t20 to time t21 is the same as the period from time t22 to time t23. The period from time t21 to time t22 is the same as the period from time t23 to time t24. That is, the control unit 10 PWM controls the lower switching element Fd1 based on the following duty ratio.

Duty ratio: (period from time t20 to time t21)/(period from time t20 to time t22).

Step S103:
The electric vehicle stops the boost control. More specifically, the control unit 10 turns off the upper switching element Fu1 and turns off the lower switching element Fd1. The boost control stop in step S103 means a stop caused by an abnormality occurring in the electric vehicle. An abnormality in the electric vehicle refers to, for example, a state in which the inverter 8 or the motor 9 breaks down and stops their operation. Specific examples of abnormalities occurring in the electric vehicle include (1) a situation in which the inverter 8 has a short circuit failure at a timing when the inverter 8 should not operate, causing a current to flow into the inverter 8 side, and (2) a situation in which the contactor 4, which should normally be turned off, does not turn off when the boost control is stopped. When an abnormality occurs in the electric vehicle, the electric vehicle stops the boost control and also stops the control of the DC/DC converter 1. Next, the process proceeds to step S104.

Here, we explain the current path when an electric vehicle stops boost control.

Figure 7 is a diagram to explain the current path when an electric vehicle stops boost control.

As shown in FIG. 7, DC current I1 flows from the high voltage power supply 2 through the DC/DC converter 1 to the storage capacitor 7. The path of DC current I1 is current path R5. Current path R5 is a path through which DC current I1 flows through the channel portion of the upper switching element Fu1. This is the path that corresponds to when the upper switching element Fu1 is ON.

Step S104:
The control unit 10 receives the measurement result H1 from the first voltmeter D1 and the measurement result H2 from the second voltmeter D2. The control unit 10 obtains the input voltage Vin from the measurement result H1 and the output voltage Vout from the measurement result H2. If the input voltage Vin and the output voltage Vout satisfy the determination condition (YES in step S104), the process proceeds to step S105. On the other hand, if the input voltage Vin and the output voltage Vout do not satisfy the determination condition (NO in step S104), the process proceeds to step S106.

The above-mentioned judgment condition is that the output voltage Vout is lower than the input voltage Vin by at least the voltage threshold Th1. The voltage threshold Th1 is, for example, 10 V. However, the voltage threshold Th1 depends on the design value of the maximum current of the DC/DC converter 1, the rating of the body diode of the switching element mounted on the DC/DC converter 1, etc.

Step S105: The control unit 10 turns on the upper switching element Fu1. The control unit 10 keeps the lower switching element Fd1 OFF. Next, proceed to step S106.

Here, we will explain the current path when the control unit 10 turns on the upper switching element Fu1.

Figure 7 is a diagram to explain the current path when the control unit 10 turns on the upper switching element Fu1.

As shown in FIG. 7, the path of DC current I1 is current path R5. Current path R5 is a path through which DC current I1 flows through the channel portion of the upper switching element Fu1. Current path R5 is the path that corresponds when the upper switching element Fu1 is ON.

Step S106: If there is a request to start boost control (YES in step S106), return to step S102. Otherwise (NO in step S106), end this control process.

Effects of First Embodiment
When an abnormality occurs in the electric vehicle and the electric vehicle stops the boost control, if the output voltage Vout is lower than the input voltage Vin, a direct current flows from the high voltage power supply 2 to the DC/DC converter 1. At this time, since the upper switching element Fu1 is OFF, the direct current flows through the body diode Bu1 of the upper switching element Fu1. According to the DC/DC converter 1, when the above-mentioned judgment condition is satisfied, that is, when the output voltage Vout is lower than the input voltage Vin by the voltage threshold value Th1 or more, the control unit 10 turns on the upper switching element Fu1. As a result, the direct current flowing from the high voltage power supply 2 to the DC/DC converter 1 flows through a channel portion having a smaller resistance than the body diode Bu1. The heat generated when the direct current flows through the body diode Bu1 is greater than the heat generated when the direct current flows through the channel portion of the upper switching element Fu1. Therefore, according to the DC/DC converter 1, the heat generation in the DC/DC converter 1 can be reduced.

<Modification 1>
The only difference between this modified example 1 and the above-described embodiment 1 is the determination condition used in step S104 in FIG.

In this first modification, the condition used in step S104 in FIG. 2 is that the DC current I1 flowing through the inductor L1 is equal to or greater than the current threshold value Th2. The current threshold value Th2 is, for example, 10 A. However, the current threshold value Th2 depends on the design value of the maximum current of the DC/DC converter 1, the rating of the body diode of the switching element mounted on the DC/DC converter 1, etc.

<Modification 2>
The only difference between the present modified example 2 and the above-described embodiment 1 is the determination condition used in step S104 in FIG.

In this modification example 2, the determination condition used in step S104 in FIG. 2 is that both the determination condition in the first embodiment and the determination condition in the first modification example are satisfied.

According to this modified example 2, the accuracy of the judgment process in step S104 in FIG. 2 can be improved compared to when judgment is made using only one of the judgment conditions of the above-mentioned embodiment 1 or the judgment conditions of the above-mentioned modified example 1. Furthermore, according to this modified example 2, it is possible to prevent overlooking of the direct current flowing from the high-voltage power supply 2 to the DC/DC converter 1 compared to when judgment is made using only one of the judgment conditions of the above-mentioned embodiment 1 or the judgment conditions of the above-mentioned modified example 1.

[Embodiment 2]
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

Figure 8 is a schematic diagram of an electric vehicle equipped with a DC/DC converter 1N according to the second embodiment. The DC/DC converter 1N differs from the DC/DC converter 1 in that the DC/DC converter 1 has a single-phase converter, whereas the DC/DC converter 1N has a multi-phase converter.

Specifically, as shown in FIG. 8, the DC/DC converter 1N includes a first-phase converter consisting of an inductor L1, an upper switching element Fu1, and a lower switching element Fd1; a second-phase converter consisting of an inductor L2, an upper switching element Fu2, and a lower switching element Fd2; a third-phase converter consisting of an inductor L3, an upper switching element Fu3, and a lower switching element Fd3; and an n-th phase converter consisting of an inductor Ln, an upper switching element Fun, and a lower switching element Fdn. Here, "n" in n-th phase is an integer equal to or greater than 2.

The functions and operations of the inductor, upper switching element, and lower switching element that constitute the converter of each phase are similar to those of the inductor L1, upper switching element Fu1, and lower switching element Fd1 of the DC/DC converter 1, so their explanation will not be repeated. However, with regard to the PWM control shown in Figures 5 and 6 above, the phases of the pulses are shifted from each other between the phases.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

1, 1N DC/DC converter 2 High voltage power supply 3 Power supply control unit 4, 51 Contactor 5 Precharge circuit 7 Storage capacitor 8 Inverter 9 Motor 10 Control unit 52 Resistor Bu1, Bd1 Body diode D1 First voltmeter D2 Second voltmeter E1 Ammeter Fu1, Fu2, Fu3, Fun Upper switching elements Fd1, Fd2, Fd3, Fdn Lower switching elements L1, L2, L3, Ln Inductor T1 First input terminal T2 Second input terminal T3 First output terminal T4 Second output terminal Th1 Voltage threshold Th2 Current threshold Vin Input voltage Vout Output voltage

Claims (3)

a one-phase converter including an inductor, an upper switching element, and a lower switching element;
A DC/DC converter including a control unit that switches the upper switching element between ON and OFF and switches the lower switching element between ON and OFF,
The control unit turns on the upper switching element when an output voltage of the DC/DC converter becomes lower than an input voltage of the DC/DC converter by a voltage threshold value or more . a one-phase converter including an inductor, an upper switching element, and a lower switching element;
a control unit that switches the upper switching element between ON and OFF and switches the lower switching element between ON and OFF;
A DC/DC converter comprising:
The control unit is
The output voltage of the DC/DC converter is lower than the input voltage of the DC/DC converter by a voltage threshold or more, and
When the DC current flowing through the inductor exceeds the current threshold,
a second switching element connected to the first switching element; A plurality of the one-phase converters are provided,
3. The DC/DC converter according to claim 1, wherein the DC/DC converter is a multi-phase DC/DC converter.

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