JP7135895B2 - DC DC converter - Google Patents

Description

The present invention relates to DCDC converters.

As a DCDC converter, the power supplied from the power supply is supplied through the transformer, rectifier circuit, and smoothing circuit by alternately turning on and off a switch provided in the low-side power supply line between the power supply and the primary coil of the transformer. Some control the drive of the switch so that the output current reaches the upper limit of the rated output current when the output current exceeds the upper limit of the rated output current while outputting to the load.

As a related technology, there is Patent Document 1.

JP 2017-79520 A

However, since the DCDC converter does not detect the current flowing through the switch, the switch may be destroyed if an overcurrent flows through the switch.

Further, in the DCDC converter, there is a concern that the current requested by the load cannot be output to the load when the output current requested by the load is larger than the upper limit value of the rated output current.

SUMMARY OF THE INVENTION Accordingly, an object of one aspect of the present invention is to prevent a switch from being destroyed due to overcurrent flowing through the switch in a DCDC converter, and to prevent the output current required from the load from exceeding the upper limit of the rated output current. Even if it is large, the current required by the load should be output to the load as much as possible.

A DCDC converter, which is one embodiment of the present invention, includes a transformer, a switch provided on a low-side power supply line between a power supply and a primary coil of the transformer, and a rectifier circuit provided after the secondary coil of the transformer. , a smoothing circuit provided after the rectifier circuit, an input voltage sensor that detects the input voltage of the DCDC converter, an output voltage sensor that detects the output voltage of the DCDC converter, and an output current sensor that detects the output current of the DCDC converter. , a drive section that outputs a control signal to the switch to alternately turn on and off the switch; and a control signal that is obtained from the input voltage and the output voltage command value detected by the input voltage sensor, and that control signal is output to the drive section. and a part.

The driving unit stops the operation of the switch when the peak value of the current flowing through the switch reaches or exceeds the peak current threshold.

As a result, it is possible to prevent the switch from being destroyed due to excessive current flowing through the switch.

Further, when the output current detected by the output current sensor is greater than the upper limit value of the rated output current, the control unit creates a droop control map in which the output current and the output voltage when the DCDC converter does not stop are associated with each other. The output voltage corresponding to the output current detected by the output current sensor is defined as the output voltage threshold, and when the output voltage detected by the output voltage sensor is greater than the output voltage threshold, the output voltage detected by the output voltage sensor is Gradually decrease the output voltage command value until it becomes equal to or less than the output voltage threshold.

As a result, even if the output current is greater than the upper limit of the rated output current, the droop control map can be used to decrease the output voltage and output the current from the DCDC converter to the load without stopping the DCDC converter. The current required by the load can be output to the load as much as possible.

Also, the controller may be configured to change the peak current threshold according to the input voltage detected by the input voltage sensor or the output voltage detected by the output voltage sensor.

Also, the DCDC converter includes a temperature sensor that detects the temperature of cooling water that cools the DCDC converter, and the control unit is configured to change the droop control map to another droop control map according to the temperature detected by the temperature sensor. You may

The present invention prevents a switch from being destroyed due to overcurrent in a DCDC converter, and even if the output current required by the load is greater than the upper limit of the rated output current, the current required by the load is reduced as much as possible. can be output to

It is a figure which shows an example of the DCDC converter of embodiment. It is a figure which shows an example of operation|movement of a control part. It is a figure which shows an example of a droop control map. FIG. 10 is a diagram illustrating an example of the operation of a control unit in modification 1; FIG. 11 is a diagram showing an example of a DCDC converter in modification 2; FIG. 10 is a diagram illustrating an example of the operation of a control unit in modified example 2;

Embodiments will be described in detail below with reference to the drawings.
FIG. 1 is a diagram showing an example of a DCDC converter according to an embodiment.

The DCDC converter 1 shown in FIG. 1 is mounted on a vehicle such as a hybrid vehicle or an electric vehicle, and supplies power supplied from a high-voltage battery Bhi (power supply) to a low-voltage battery Blo or a load Lo2 such as a starter motor or a light. . The high-voltage battery Bhi is composed of a lithium ion battery or the like, and supplies power to a load Lo1 such as an inverter that drives the traction motor. The low-voltage battery Blo is composed of a lead battery or the like, and supplies power to the load Lo2. Note that the DCDC converter 1 supplies power to the load Lo2 in cooperation with the low-voltage battery Blo. That is, when the current requested by the load Lo2 (load requested current) is greater than the output current of the DCDC converter 1, the current short of the current requested by the load Lo2 is output from the low-voltage battery Blo to the load Lo2. .

Further, the DCDC converter 1 is a forward-type isolated DCDC converter, and includes a capacitor C1, a switch SW, a transformer T, a rectifying circuit 2, a smoothing circuit 3, an input voltage sensor SVin, and an output voltage sensor SVout. , an input current sensor SIin, an output current sensor SIout, a drive unit 4 and a control unit 5 . The rectifier circuit 2 includes diodes D1 and D2. The smoothing circuit 3 includes an inductor L and a capacitor C2. The switch SW is assumed to be a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or the like. Also, the ratio of the number of turns of the primary coil L1 and the secondary coil L2 of the transformer T is the number of turns of the primary coil L1:the number of turns of the secondary coil L2=N:1. The input voltage sensor SVin and the output voltage sensor SVout are each composed of a plurality of voltage dividing resistors. Also, the input current sensor SIin and the output current sensor SIout are each configured by a Hall element or the like. Further, the drive unit 4 is configured by an IC (Integrated Circuit) or the like. The control unit 5 is configured by a CPU (Central Processing Unit) or a programmable device (FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)). In addition, the DCDC converter 1 converts the power supplied from the high-voltage battery Bhi to the transformer T by alternately turning on and off the switch SW provided in the low-side power supply line between the high-voltage battery Bhi and the primary coil L1 of the transformer T. It is not limited to a forward-type isolated DCDC converter as long as it outputs through T, a rectifying circuit 2 and a smoothing circuit 3 . For example, a full-bridge method or the like may be used.

A positive terminal of the high-voltage battery Bhi is connected to one terminal of the capacitor C1 and one terminal of the primary coil L1 of the transformer T, and a negative terminal of the high-voltage battery Bhi is connected to the other terminal of the capacitor C1 and the source terminal of the switch SW. It is A drain terminal of the switch SW is connected to the other terminal of the primary coil L1. One terminal of the secondary coil L2 of the transformer T is connected to the cathode terminal of the diode D1 and one terminal of the inductor L, and the other terminal of the secondary coil L2 is connected to the cathode terminal of the diode D2. The other terminal of inductor L is connected to one terminal of capacitor C2 and the positive terminal of low-voltage battery Blo. The anode terminal of diode D1 is connected to the anode terminal of diode D2, the other terminal of capacitor C2, and the negative terminal of low voltage battery Blo.
The input voltage sensor SVin is connected to one terminal of the capacitor C1, detects the voltage applied to the capacitor C1, and outputs the detected voltage to the control unit 5. FIG. The output voltage sensor SVout is connected to one terminal of the capacitor C2, detects the voltage applied to the capacitor C2, and outputs the detected voltage to the control unit 5. The input current sensor SIin is connected between one terminal of the capacitor C<b>1 and one terminal of the primary coil L<b>1 , detects current flowing through the switch SW, and outputs the detected current to the drive unit 4 . The output current sensor SIout is connected between one terminal of the capacitor C2 and the positive terminal of the low-voltage battery Blo, detects the current output from the DCDC converter 1, and outputs the detected current to the control unit 5.

The driving unit 4 alternately turns on and off the switch SW by outputting the control signal output from the control unit 5 to the gate terminal of the switch SW. When the switch SW is turned on, current flows from the high-voltage battery Bhi through the capacitor C1 to the primary coil L1, and current flows from the secondary coil L2 through the inductor L and the capacitor C2 to the low-voltage battery Blo and the load Lo2. When the switch SW is turned off, current flows from the diode D1 through the inductor L and the capacitor C2 to the low-voltage battery Blo and the load Lo2. That is, when the switch SW is alternately turned on and off, the power supplied from the high-voltage battery Bhi is converted into alternating current and transmitted from the primary coil L1 to the secondary coil L2. The power transmitted to the secondary coil L2 is rectified and smoothed by the rectifier circuit 2 and the smoothing circuit 3, and supplied to the low-voltage battery Blo and the load Lo2.

The drive unit 4 uses the current detected by the input current sensor SIin as an input current. By forcibly stopping the operation of the switch SW, the power supply from the DCDC converter 1 to the low-voltage battery Blo and the load Lo2 is prohibited regardless of whether the power is output from the DCDC converter 1 or not. Note that the peak current threshold is the maximum value of the current that flows through the switch SW when the switch SW is not destroyed. As a result, it is possible to prevent the switch SW from being destroyed due to overcurrent flowing through the switch SW.

FIG. 2 is a flow chart showing an example of the operation of the control section 5. As shown in FIG.
First, the control unit 5 acquires an input voltage, an output voltage, an output voltage command value, and an output current (step S1). For example, the control unit 5 acquires the voltage detected by the input voltage sensor SVin as the input voltage. Further, the control unit 5 acquires the voltage detected by the output voltage sensor SVout as the output voltage. Also, the control unit 5 acquires an output voltage command value sent from a higher-level control unit that controls the operation of the entire vehicle. Further, the control unit 5 acquires the current detected by the output current sensor SIout as the output current. In addition, in order to increase the detection accuracy of the output current, the control unit 5 uses the output value of the output current sensor SIout when the actual output current is a predetermined current (for example, zero), and is referred to when acquiring the output current. The output value-output current correspondence information may be corrected. In addition, in order to increase the detection accuracy of the output voltage, the control unit 5 uses the output value of the output voltage sensor SVout when the actual output voltage is a predetermined voltage (for example, zero), and is referred to when acquiring the output voltage. The output value-output voltage correspondence information may be corrected.

Next, when the output current acquired in step S1 or step S8, which will be described later, is equal to or less than the upper limit value of the rated output current (step S2: Yes), the control unit 5 generates a control signal based on the input voltage and the output voltage command value. After obtaining the duty ratio and outputting the control signal to the drive unit 4 (step S3), the process returns to step S1 to obtain the input voltage, the output voltage, the output voltage command value, and the output current again. For example, the control unit 5 obtains the duty ratio of the control signal by calculating “(output voltage command value/input voltage)×number of turns N of primary coil L1”.

On the other hand, when the output current is greater than the upper limit value of the rated output current (step S2: No), the control unit 5 refers to the droop control map and sets the output voltage corresponding to the output current as the output voltage threshold (step S4). .

Here, FIG. 3A is a diagram showing an example of the droop control map. The horizontal axis of the rectangular coordinates shown in FIG. 3(a) indicates the output current, and the vertical axis indicates the output voltage. In addition, the solid line shown in FIG. ) indicates a drooping control map, which is pre-stored inside the control unit 5 . In addition, the hatched portion shown in FIG. 3A indicates that the output current is equal to or less than the upper limit of the rated output current, the output voltage is equal to or less than the upper limit of the rated output voltage, and the output voltage is equal to or less than the lower limit of the rated output voltage. It shows the area when it is above.

The droop control map shown in FIG. 3A is information in which the output current and the output voltage are associated when the DCDC converter 1 does not stop even though the output current is greater than the upper limit value of the rated output current. In other words, the power that is the product of the output current and the output voltage shown in the droop control map is the power that can be output from the DCDC converter 2 without stopping the DCDC converter 1 . As a result, when the output current and output voltage obtained in step S1 of the flowchart shown in FIG. 2 or step S8 described later substantially match the output current and output voltage shown in the droop control map, the DCDC converter 1 is stopped. An output current larger than the upper limit value of the rated output current can be output from the DCDC converter 1 to the load Lo2 without any need.

Next, when the output voltage obtained in step S1 or step S8 described later is equal to or less than the output voltage threshold (step S5: Yes), the control unit 5 proceeds to step S3 and outputs a control signal to the driving unit 4.

On the other hand, when the output voltage obtained in step S1 or step S8, which will be described later, is higher than the output voltage threshold (step S5: No), the control unit 5 reduces the output voltage command value by a certain value (step S6). The duty ratio of the control signal is obtained using the input voltage obtained in S1 or step S8, which will be described later, and the output voltage command value decreased in step S6, and the control signal is output to the drive unit 4 (step S7).

Next, after acquiring the input voltage, the output voltage, and the output current (step S8), the control unit 5 returns to step S2 and determines whether the output current is equal to or less than the upper limit of the rated output current.

As a result, when the output current is higher than the upper limit of the rated output current and the output voltage is higher than the output voltage threshold, the output voltage can be gradually lowered until the output voltage drops below the output voltage threshold. The current and output voltage can be approximately matched with the output current and output voltage indicated in the droop control map, respectively. As described above, when the output current and the output voltage substantially match the output current and the output voltage shown in the droop control map, respectively, the output current greater than the upper limit of the rated output current is generated without stopping the DCDC converter 1. 1 to load Lo2. Therefore, even when the output current is higher than the upper limit value of the rated output current, power can be supplied from the DCDC converter 1 to the load Lo2 without stopping the DCDC converter 1 .

Thus, in the DCDC converter 1 of the embodiment, when the output current is higher than the upper limit of the rated output current and the output voltage is higher than the output voltage threshold, the output voltage is gradually reduced until the output voltage becomes equal to or lower than the output voltage threshold. , power can be supplied from the DCDC converter 1 to the load Lo2 without stopping the DCDC converter 1 even when the output current is greater than the upper limit value of the rated output current. As a result, even if the output current requested by the load Lo2 is greater than the upper limit value of the rated output current, the current requested by the load Lo2 can be output to the load Lo2 as much as possible.

Further, in the DCDC converter 1 of the embodiment, when the peak value of the input current is equal to or higher than the peak current threshold, the operation of the switch SW is forcibly stopped. can be prevented from being destroyed.

The present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the gist of the present invention.

<Modification 1>
FIG. 4 is a flow chart showing an example of the operation of the control unit 5 in Modification 1. As shown in FIG. Note that the configuration of the DCDC converter 1 in Modification 1 is the same as that of the DCDC converter 1 shown in FIG. Further, steps S1 to S8 shown in FIG. 4 are the same as steps S1 to S8 shown in FIG. 2, and therefore description thereof is omitted.

The flowchart shown in FIG. 4 is different from the flowchart shown in FIG. 2 in that the peak current threshold is changed according to the input voltage and the output voltage in step S2' before step S2. Note that the execution timing of step S2' is not limited to before step S2.

For example, the controller 5 increases the peak current threshold as the input voltage increases or as the output voltage decreases.

As the input voltage increases or as the output voltage decreases, the change width per unit time of the current flowing through the switch SW before the current flowing through the switch SW reaches its peak value ((input voltage/winding of the primary coil L1 number N-output voltage)/inductance of inductor L) increases. That is, the higher the input voltage or the lower the output voltage, the higher the peak value of the current flowing through the switch SW.

Therefore, by similarly changing the peak current threshold in accordance with the change in the peak value accompanying the change in the input voltage or the output voltage, as in Modification 1, the switch Stopping the SW can be reduced.

<Modification 2>
FIG. 5 is a diagram showing the DCDC converter 1 in Modification 2. As shown in FIG. 5 that are the same as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The DCDC converter 1 shown in FIG. 5 differs from the DCDC converter 1 shown in FIG. 1 in that it further includes a temperature sensor St for detecting the temperature of cooling water for cooling the DCDC converter 1 .

The temperature sensor St is configured by a thermistor or the like, and outputs the detected temperature to the controller 5 .

FIG. 6 is a diagram showing an example of the operation of the control unit 5 in Modification 2. As shown in FIG. Since steps S1 to S8 shown in FIG. 6 are the same as steps S1 to S8 shown in FIG. 2, the description thereof will be omitted.

The flowchart shown in FIG. 6 differs from the flowchart shown in FIG. 2 in that the droop control map is changed according to the temperature detected by the temperature sensor St in step S4' before step S4.

For example, when the temperature detected by the temperature sensor St does not rise, the control unit 5 uses the droop control map 1 shown in FIG. A drooping control map 2 (each output current of the drooping control map 1 is reduced by a constant value) shown in FIG. 3(b) is used.

In order to suppress breakage of the switch SW due to heat, it is necessary to suppress the heat generation of the switch SW by reducing the output current as the temperature of the cooling water rises.

Therefore, by changing the drooping control map to another drooping control map according to the temperature detected by the temperature sensor St as in Modification 2, the output current can be reduced. can be suppressed.

Note that step S4' shown in FIG. 6 may be executed before step S4 shown in FIG.

1 DCDC converter 2 rectifier circuit 3 smoothing circuit 4 drive unit 5 control unit Bhi high voltage battery Blo low voltage battery Lo1, Lo2 load C1, C2 capacitor SW switch D1, D2 diode T transformer L inductor SVin input voltage sensor SVout output voltage sensor SIin input current Sensor SIout Output current sensor

Claims (3)

A DCDC converter,
a transformer;
a switch provided on a low-side power supply line between the power supply and the primary coil of the transformer;
a rectifier circuit provided after the secondary coil of the transformer;
a smoothing circuit provided after the rectifying circuit;
an input voltage sensor that detects the input voltage of the DCDC converter;
an output voltage sensor that detects the output voltage of the DCDC converter;
an output current sensor that detects the output current of the DCDC converter;
a driving unit that outputs a control signal to the switch to alternately turn on and off the switch;
a control unit that obtains the control signal from the input voltage and the output voltage command value detected by the input voltage sensor and outputs the control signal to the driving unit;
with
The driving unit stops the operation of the switch when a peak value of the current flowing through the switch becomes equal to or greater than a peak current threshold,
When the output current detected by the output current sensor is greater than the upper limit value of the rated output current, the control unit causes the output current and the output voltage to correspond to each other when the DCDC converter does not stop. An output voltage corresponding to the output current detected by the output current sensor with reference to the control map is defined as an output voltage threshold, and when the output voltage detected by the output voltage sensor is greater than the output voltage threshold, the output voltage sensor The output voltage command value is gradually decreased until the output voltage detected by is equal to or lower than the output voltage threshold. The DCDC converter according to claim 1,
The DCDC converter, wherein the control unit changes the peak current threshold according to the input voltage detected by the input voltage sensor or the output voltage detected by the output voltage sensor. The DCDC converter according to claim 1 or claim 2,
A temperature sensor that detects the temperature of cooling water that cools the DCDC converter,
The DCDC converter, wherein the control section changes the droop control map to another droop control map according to the temperature detected by the temperature sensor.

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