JP5322858B2 - DC / DC converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a DC/DC converter that is operated even if an intermediate capacitor is opened to fail, sends energy equivalent to that when the DC/DC converter is normal even in the case of short-circuit failure, and can step up and down voltage. <P>SOLUTION: In the step-down operation, a change to a pattern for mutually and simultaneously turning on/off first and second switching elements S1, S2 is made when the open-circuit failure of the intermediate capacitor C1 is detected, and a change to a pattern for continuously keeping the second switching element S2 on and turning on/off the first switching element S1 is made when the short-circuit failure of the intermediate capacitor C1 is detected. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a DC / DC converter that converts a DC voltage into a DC voltage that is stepped up or stepped down.

  The conventional DC / DC converter performs the voltage conversion from direct current to direct current by controlling the amount of energy stored in and discharged from the coil by using the on / off operation of the switching element. In addition, since this coil has a problem that it is large and heavy, the voltage applied to the coil is reduced using charging / discharging of the intermediate capacitor, and the inductance value required for the coil is reduced, thereby reducing the size of the coil. A technique for reducing the weight is disclosed (for example, see Patent Document 1).

Japanese Examined Patent Publication No. 6-67181

  However, in the case of the conventional DC / DC converter, when the intermediate capacitor has an open failure, the current path is lost and the boosting and stepping-down operations are impossible. In addition, when a short-circuit failure occurs in the intermediate capacitor, the intermediate capacitor becomes a resistor, and energy cannot be transmitted in cooperation with the coil, resulting in a problem that boosting and stepping down operations are impossible.

  The present invention has been made in order to solve the above-described problems. The DC / DC converter is operated even when the intermediate capacitor has an open failure, and the DC / DC converter fails even when a short-circuit failure occurs. An object of the present invention is to obtain a DC / DC converter that can transmit energy equivalent to that of a non-powered state and can perform step-up and step-down operations.

A DC / DC converter according to the present invention includes a low-voltage side smoothing capacitor that holds a low-voltage side voltage, a negative-voltage side terminal connected to a negative-side terminal of the low-voltage side smoothing capacitor, and a high-voltage side smoothing capacitor that holds a high-voltage side voltage. A first semiconductor element arm connected to the negative terminal of the side smoothing capacitor, one end connected to the other end of the first semiconductor element arm, and the other end connected to the positive terminal of the low voltage side smoothing capacitor via the coil The second semiconductor element arm, one end connected to the other end of the second semiconductor element arm, the third semiconductor element arm connected to the other end of the third semiconductor element arm, and the other end connected to the high-voltage side smoother A fourth semiconductor element arm connected to the positive terminal of the capacitor, and one end connected to an intermediate connection point between the first semiconductor element arm and the second semiconductor element arm and the other end to the third half Comprising a body element arm and an intermediate capacitor connected to an intermediate connection point between the fourth semiconductor element arms,
Each of the first and second semiconductor element arms has a function of a switching element and a diode element connected in reverse parallel to the switching element,
Each of the third and fourth semiconductor element arms has a function of a diode element,
A step-up operation for converting the input voltage of the low-voltage side smoothing capacitor into a boosted voltage by the on / off switching function of the switching elements provided in the first and second semiconductor element arms, and outputting the boosted voltage to the high-voltage side smoothing capacitor;
Each of the third and fourth semiconductor element arms has a function of a switching element and a diode element connected in reverse parallel to the switching element,
Both the first and second semiconductor element arms have the function of a diode element,
By the on / off switching function of the switching element provided in the third and fourth semiconductor element arms, it is possible to perform a step-down operation in which the voltage of the input high-voltage side smoothing capacitor is converted to a step-down voltage and output to the low-voltage side smoothing capacitor. In the DC / DC converter,
Means for detecting an open-circuit failure or a short-circuit failure of the intermediate capacitor, and when the open-circuit failure or the short-circuit failure is detected, the switching provided to the first and second semiconductor element arms or the third and fourth semiconductor element arms The step-up operation or the step-down operation can be continued by changing the on / off switching pattern of the element to a predetermined pattern different from the normal pattern.

  As described above, according to the present invention, when an open circuit fault or a short circuit fault occurs in the intermediate capacitor, the on / off switching of the switching element provided in the first and second semiconductor element arms or the third and fourth semiconductor element arms is performed. The step-up operation or step-down operation can be continued by changing the pattern to a predetermined pattern different from the normal pattern, so that step-up operation or step-down operation can be performed without relying on the charge / discharge function of the intermediate capacitor. .

It is a circuit diagram of the DC / DC converter in Embodiment 1 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage rise operation which makes an output voltage 2 times the input voltage of the DC / DC converter in Embodiment 1 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage rise operation which makes the output voltage 1 time or more and 2 times or less of input voltage of the DC / DC converter in Embodiment 1 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage rise operation which makes the output voltage 2 times or more of input voltage of the DC / DC converter in Embodiment 1 of this invention. It is an equivalent circuit when the intermediate capacitor C1 of the DC / DC converter according to Embodiment 1 of the present invention has an open fault. It is a figure which shows a gate signal and voltage waveform at the time of the open circuit failure of the intermediate | middle capacitor | condenser C1 of the DC / DC converter in Embodiment 1 of this invention. It is an equivalent circuit when the intermediate capacitor C1 of the DC / DC converter in Embodiment 1 of the present invention has a short circuit failure. It is a figure which shows a gate signal and voltage waveform at the time of the short circuit failure of the intermediate | middle capacitor | condenser C1 of the DC / DC converter in Embodiment 1 of this invention. It is a circuit diagram of the DC / DC converter in Embodiment 2 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage fall operation which makes the output voltage 0.5 times the input voltage of the DC / DC converter in Embodiment 2 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage fall operation which makes the output voltage 0.5 times or more and 1 time or less of input voltage of the DC / DC converter in Embodiment 2 of this invention. It is a figure which shows the gate signal and voltage waveform at the time of the pressure | voltage fall operation which makes the output voltage 0.5 times or less of input voltage of the DC / DC converter in Embodiment 2 of this invention. It is an equivalent circuit when the intermediate capacitor C1 of the DC / DC converter in Embodiment 2 of the present invention has an open fault. It is a figure which shows a gate signal and voltage waveform at the time of the open circuit failure of the intermediate | middle capacitor | condenser C1 of the DC / DC converter in Embodiment 2 of this invention. It is an equivalent circuit when the intermediate capacitor C1 of the DC / DC converter in Embodiment 2 of the present invention has a short-circuit fault. It is a figure which shows a gate signal and voltage waveform at the time of the short circuit failure of the intermediate | middle capacitor | condenser C1 of the DC / DC converter in Embodiment 2 of this invention. It is a circuit diagram of the DC / DC converter in Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of a DC / DC converter according to Embodiment 1 of the present invention. The DC / DC converter shown in FIG. 1 converts an input voltage Vin, which is a low-voltage side voltage, into a boosted high-voltage side voltage and outputs it as an output voltage Vout.

  The main circuit components include an input-side smoothing capacitor Cin that is a low-voltage side smoothing capacitor that holds the input voltage Vin, an output-side smoothing capacitor Cout that is a high-voltage side smoothing capacitor that holds the output voltage Vout, and energy storage and release. , The intermediate capacitor C1 that charges and discharges electric charge in cooperation with the coil L, and the first to fourth semiconductor element arms that are connected in series and are sequentially arranged from the negative electrode side.

  The first and second semiconductor element arms are connected in antiparallel to the first and second switching elements S1 and S2, such as an IGBT, and the switching elements S1 and S2, respectively, with the polarity shown in the figure. The first and second diodes D1, D2 and the third and fourth semiconductor element arms are respectively composed of third and fourth diode elements D3, D4.

  Further, the connection configuration of these elements will be described. The low voltage side smoothing capacitor Cin has a positive terminal (upper terminal in FIG. 1) connected to one end of the coil L, and a negative terminal connected to the negative terminal of the high voltage smoothing capacitor Cout and the first switching element S1. Connected to the emitter terminal. The other end of the coil L is connected to the collector terminal of the second switching element S2. The cathode terminal of the fourth diode element D4 is connected to the positive terminal of the high voltage side smoothing capacitor Cout. The intermediate capacitor C1 has one end connected to the anode terminal of the fourth diode element D4 and the other end connected to the collector terminal of the first switching element S1.

  Next, three operations of the DC / DC converter shown in FIG. 1 will be described with reference to FIGS. Here, for the sake of simplicity, the voltage of the intermediate capacitor C1 is shown to be constant in the voltage waveform of each figure. The voltage waveform diagram also shows the voltages at points A and B in FIG.

First, the operation when the output voltage Vout is twice the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S1 and S2 are both turned on / off repeatedly with an on-duty ratio of 0.5 and a phase shift of 180 °.
First, in a period t1, the switching element S1 is turned on and S2 is turned off.
Cin → L → D3 → C1 → S1 → Cin
A current flows through the path, and the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the coil L and the intermediate capacitor C1. At this time, the coil L absorbs the voltage difference between the input-side smoothing capacitor Cin and the intermediate capacitor C1, and serves to prevent a current from flowing suddenly.

In period t2, switching element S1 is turned off, S2 is turned on,
Cin → L → S2 → C1 → D4 → Cout → Cin
A current flows through the path, and the voltage of the series circuit of the input side smoothing capacitor Cin, the coil L, and the intermediate capacitor C1 is applied to the output side smoothing capacitor Cout. At this time, the coil L absorbs a voltage difference between the sum of the voltages of the input-side smoothing capacitor Cin and the intermediate capacitor C1 and the voltage of the output-side smoothing capacitor Cout, and prevents the current from flowing suddenly. Thus, a voltage obtained by boosting the input voltage Vin twice as the output voltage Vout is obtained.

  Next, an operation when the output voltage Vout is set to a value between 1 and 2 times the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S1 and S2 are both turned on / off repeatedly with an on-duty ratio of 0.5 or less and a phase shift of 180 °. Further, by adjusting the duty ratio, the output voltage Vout can be adjusted, and the output voltage increases as the on-duty ratio increases.

First, in period t3, both switching elements S1 and S2 are turned off,
Cin → L → D3 → D4 → Cout → Cin
A current flows through the path, and at this time, the coil L releases energy. In period t4, switching element S1 is turned on, S2 is turned off,
Cin → L → D3 → C1 → S1 → Cin
In this path, a current flows, the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L is applied to the intermediate capacitor C1, the coil L accumulates energy, and the intermediate capacitor C1 is charged. At this time, since the coil L releases energy in the period t3, a voltage opposite to the voltage of the input side smoothing capacitor Cin is applied, and the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L is the input voltage Vin. The intermediate capacitor C1 is charged to a voltage lower than the input voltage Vin.

In a period t5, both the switching elements S1 and S2 are turned off,
Cin → L → D3 → D4 → Cout → Cin
A current flows through the path, and at this time, the coil L releases energy. In period t6, switching element S1 is turned off, S2 is turned on,
Cin → L → S2 → C1 → D4 → Cout → Cin
The current flows through the path, and the voltage of the series circuit of the input side smoothing capacitor Cin, the coil L, and the intermediate capacitor C1 is applied to the output side smoothing capacitor Cout, and the coil L accumulates energy. At this time, since the coil L releases energy in the period t5, a voltage opposite to the voltage of the input side smoothing capacitor Cin is applied, and the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L is the input voltage Vin. Lower than. Further, since the intermediate capacitor C1 is also charged to a voltage lower than the input voltage Vin in the period t5, a voltage lower than twice the input voltage Vin is applied to the output voltage Vout. As described above, when the output voltage is 1 to 2 times the input voltage, the coil L performs an operation such that the input voltage is lowered.

  Finally, an operation for setting the output voltage Vout to twice or more the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S1 and S2 are both turned on / off repeatedly with an on-duty ratio of 0.5 or more and a phase shift of 180 °. Further, by adjusting the duty ratio, the output voltage Vout can be adjusted, and the output voltage increases as the on-duty ratio increases.

First, in period t7, both switching elements S1 and S2 are turned on,
Cin → L → S2 → S1 → Cin
A current flows through the path, and energy is accumulated in the coil L. In period t8, switching element S1 is turned on, S2 is turned off,
Cin → L → D3 → C1 → S1 → Cin
The current flows through the path of (2), the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L is applied to the intermediate capacitor C1, and the coil L releases energy. At this time, since energy is stored in the coil L in the period t7, a voltage in the same direction as the input voltage Vin is applied, and the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L becomes higher than the input voltage Vin. The intermediate capacitor C1 is charged to a voltage higher than the input voltage Vin.

In a period t9, both the switching elements S1 and S2 are turned on,
Cin → L → S2 → S1 → Cin
A current flows through the path, and energy is accumulated in the coil L. In period t10, switching element S1 is turned off, S2 is turned on,
Cin → L → S2 → C1 → D4 → Cout → Cin
A current flows through the path, a voltage of a series circuit of the coil L, the intermediate capacitor C1, and the input side smoothing capacitor Cin is applied to the output side smoothing capacitor Cout, and the coil L releases energy. Since energy is stored in the coil L in the period t9, a voltage in the same direction as the input voltage Vin is applied, and the voltage of the series circuit of the input side smoothing capacitor Cin and the coil L becomes higher than the input voltage Vin. Furthermore, since the intermediate capacitor C1 is charged to a voltage higher than the input voltage Vin in the period t8, a voltage higher than twice the input voltage is applied to the output side smoothing capacitor Cout. As described above, when the output voltage Vout is twice or more the input voltage Vin, the coil L performs an operation such that the input voltage Vin is increased.

The DC / DC converter of FIG. 1 can boost the input voltage and output it by performing the above operation.
However, if the intermediate capacitor C1 has an open failure, the circuit described above is not configured and the boosting operation is not performed. In addition, when a short circuit failure occurs, the failed intermediate capacitor C1 becomes a resistor, and energy cannot be sent well. In other words, the DC / DC converter stops its step-up operation due to the failure of the intermediate capacitor C1, causing an operational trouble.
Therefore, the DC / DC converter according to the first embodiment of the present application can continue the boosting operation by changing the operation method of the switching element from the normal method when the intermediate capacitor C1 has an open failure or a short circuit failure. It improves operational reliability.

  The failure of the intermediate capacitor C1 is not shown in FIG. 1, but, for example, the intermediate capacitor C1 and the output voltage Vout are always detected, and the open failure or short circuit of the intermediate capacitor C1 is based on the output values of both. Means for determining the occurrence of a failure is provided, and the determination is made based on the output of the determination means.

First, FIG. 5 shows an equivalent circuit when the intermediate capacitor C1 has an open failure. FIG. 6 shows an operation waveform when the intermediate capacitor C1 has an open failure. At this time, the switching elements S1 and S2 are repeatedly turned on / off simultaneously. The output voltage Vout can be adjusted by adjusting the on-duty ratio of the switching elements S1 and S2, and the output voltage increases as the on-duty ratio increases.
The operation at this time is Cin → L → S2 → S1 → Cin when the switching elements S1 and S2 are simultaneously turned on in the period t11.
The current flows through the path, energy is accumulated in the coil L, and when the switching elements S1 and S2 are simultaneously turned off in the period t12,
Cin → D3 → D4 → Cout → Cin
A current flows through the path (1), and a voltage higher than the input voltage Vin is obtained as the output voltage Vout by the energy previously stored in the coil L. By performing such an operation, the DC / DC converter can boost the voltage even if the intermediate capacitor C1 is in an open failure.

Next, FIG. 7 shows an equivalent circuit when the intermediate capacitor C1 is short-circuited. FIG. 8 shows an operation waveform when the intermediate capacitor C1 is short-circuited. At this time, the switching element S2 is always on, and the switching element S1 is repeatedly turned on / off. The output voltage Vout can be adjusted by adjusting the on-duty ratio of the switching element S1, and the output voltage increases as the on-duty ratio increases.
The operation at this time is the period t13, the switching element S2 is always on, and when S1 is on,
Cin → L → S2 → S1 → Cin
When energy is accumulated in the coil L through the path and the switching element S1 is turned off in the period t14,
Path 1: Cin → L → S2 → C1 (short circuit) → D4 → Cout → Cin,
Or
Path 2: Cin → L → D3 → D4 → Cout → Cin
The current flows through the path with the smaller loss, and the output voltage higher than the input voltage is obtained by the energy previously stored in the coil L.

  When the current flows through the path 1, the loss is smaller than when the switching elements S1 and S2 are simultaneously turned on / off. By performing such an operation, the DC / DC converter can boost the voltage even if the first capacitor C1 is short-circuited.

As described above, in the DC / DC converter according to Embodiment 1 of the present application, even when an open circuit fault or a short circuit fault occurs in the intermediate capacitor C1, the on / off switching pattern of the switching elements S1 and S2 is different from the normal pattern. By making the change, the boosting operation can be continued.
In this way, it is not necessary to prepare the intermediate capacitor C1 in preparation for its failure, and the amount of parts is reduced. Even if the intermediate capacitor C1 fails, the switching element operation method is changed from the normal method to increase the voltage. It is possible to continue operation and improve operational reliability.
For example, when an EV (electric vehicle) or HEV (hybrid car) equipped with a DC / DC converter according to the present invention fails to operate normally due to a failure of an intermediate capacitor on the road, the switching pattern is changed. Thus, the operation as the converter can be continued, and the EV and HEV can be moved without interfering with the following vehicle.

Embodiment 2. FIG.
FIG. 9 is a circuit diagram showing a configuration of the DC / DC converter according to Embodiment 2 of the present invention. The DC / DC converter shown in FIG. 9 converts the input voltage Vin, which is a high-voltage side voltage, into a low-voltage side voltage that is stepped down and outputs it as an output voltage Vout.

  The main circuit components include an input-side smoothing capacitor Cin that is a high-voltage side smoothing capacitor that holds the input voltage Vin, an output-side smoothing capacitor Cout that is a low-voltage side smoothing capacitor that holds the output voltage Vout, and energy storage and release. , The intermediate capacitor C1 that charges and discharges electric charge in cooperation with the coil L, and the first to fourth semiconductor element arms that are connected in series and are sequentially arranged from the negative electrode side.

  Then, with the polarities shown in the figure, the first and second semiconductor element arms are respectively from the first and second diode elements D1 and D2, and the third and fourth semiconductor element arms are, for example, IGBT or the like The third and fourth switching elements S3, S4 and the third and fourth diode elements D3, D4 connected in antiparallel with the switching elements S3, S4.

  Further, the connection configuration of these elements will be described. The low-voltage side smoothing capacitor Cout has its positive-side terminal (upper terminal in FIG. 9) connected to one end of the coil L, and its negative-side terminal connected to the negative-side terminal of the high-voltage-side smoothing capacitor Cin and the first diode element D1. Connected to the anode terminal. The other end of the coil L is connected to the cathode terminal of the second diode element D2. The collector terminal of the fourth switching element S4 is connected to the positive terminal of the high voltage side smoothing capacitor Cin. The intermediate capacitor C1 has one end connected to the emitter terminal of the fourth switching element S4 and the other end connected to the cathode terminal of the first diode element D1.

  Next, three operations of the DC / DC converter shown in FIG. 9 will be described with reference to FIGS. Here, for the sake of simplicity, the voltage of the intermediate capacitor C1 is shown to be constant in the voltage waveform of each figure. The voltage waveform diagram also shows the voltages at points A and B in FIG.

First, the operation when the output voltage Vout is 0.5 times the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S3 and S4 are both turned on / off repeatedly with an on-duty ratio of 0.5 and a phase shift of 180 °.
First, in period t15, switching element S3 is turned off, S4 is turned on,
Cin → S4 → C1 → D2 → L → Cout → Cin
The current flows through the path, and the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the intermediate capacitor C1, the coil L, and the output side smoothing capacitor Cout. At this time, the coil L absorbs a voltage difference between the voltage of the input-side smoothing capacitor Cin and the sum of the voltages of the intermediate capacitor C1 and the output-side smoothing capacitor Cout, and prevents the current from flowing suddenly.

In period t16, switching element S3 is turned on, S4 is turned off,
C1->S3->L->Cout->D1-> C1
The current flows through the path (1), the voltage of the series circuit of the intermediate capacitor C1 and the coil L is applied to Cout, and the voltage obtained by stepping down the input voltage Vin by 0.5 times is obtained. At this time, the coil L absorbs the voltage difference between the voltage of the intermediate capacitor C1 and the voltage of the output-side smoothing capacitor Cout, and prevents the current from flowing suddenly.

  Next, an operation when the output voltage Vout is set to a value not less than 0.5 times and not more than 1 time the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S3 and S4 are both turned on / off repeatedly with an on-duty ratio of 0.5 or more and a phase shift of 180 °. Further, by adjusting the duty ratio, the output voltage Vout can be adjusted, and the output voltage increases as the on-duty ratio increases.

First, in a period t17, by turning on both switching elements S3 and S4,
Cin → S4 → S3 → L → Cout → Cin
The current flows through the path, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the output side smoothing capacitor Cout and the coil L, and energy is stored in the coil L. Next, in period t18, switching element S3 is turned off and S4 is turned on.
Cin → S4 → C1 → D2 → L → Cout → Cin
In this path, a current flows, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the intermediate capacitor C1, the coil L, and the output side smoothing capacitor Cout, and the energy stored in the coil L is released.

Next, in the period t19, both the switching elements S3 and S4 are turned on.
Cin → S4 → S3 → L → Cout → Cin
A current flows through the path, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the coil L and the output side smoothing capacitor Cout, and energy is accumulated in the coil L. In the period t20, the switching element S3 is turned on and S4 is turned off.
C1->S3->L->Cout->D1-> C1
A current flows through the path, the voltage of the intermediate capacitor C1 is applied to the series circuit of the coil L and the output-side smoothing capacitor Cout, and the energy stored in the coil L is released. At this time, a voltage in the same direction as the voltage of the intermediate capacitor C1 is applied to the coil L, and the voltage of the series circuit of the intermediate capacitor C1 and the coil L is higher than 0.5 times the input voltage. In this manner, a voltage obtained by stepping down the input voltage by 0.5 times to 1 time is output.

  Finally, the operation when the output voltage Vout is 0.5 times or less of the input voltage Vin will be described. The operation waveform at this time is shown in FIG. At this time, the switching elements S3 and S4 are both turned on / off repeatedly with an on-duty ratio of 0.5 or less and a phase shift of 180 °. Further, by adjusting the duty ratio, the output voltage Vout can be adjusted, and the output voltage increases as the on-duty ratio increases.

First, in the period t21, both switching elements S3 and S4 are turned off.
D1->D2->L->Cout-> D1
The current flows through the path, and energy is released from the coil L. Next, in period t22, switching element S3 is turned off and S4 is turned on.
Cin → S4 → C1 → D2 → L → Cout → Cin
The current flows through this path, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the intermediate capacitor C1, the coil L, and the output side smoothing capacitor Cout, and energy is stored in the coil L.

Next, in a period t23, both switching elements S3 and S4 are turned off.
D1->D2->L->Cout-> D1
The current flows through the path, and energy is released from the coil L. In the period t24, the switching element S3 is turned on and S4 is turned off.
C1->S3->L->Cout->D1-> C1
A current flows through the path, the voltage of the intermediate capacitor C1 is applied to the series circuit of the coil L and the output-side smoothing capacitor Cout, and the energy stored in the coil L is released. At this time, a voltage opposite to the voltage of the intermediate capacitor C1 is applied to the coil L, and the voltage of the series circuit of the intermediate capacitor C1 and the coil L becomes lower than 0.5 times the input voltage. In this way, a voltage obtained by stepping down the input voltage to 0.5 times or less is output.

The DC / DC converter of FIG. 9 can step down and output the input voltage by performing the above operation.
However, here, when the intermediate capacitor C1 has an open failure, the circuit described above is not configured and the step-down operation is not performed. In addition, when a short circuit failure occurs, the failed intermediate capacitor C1 becomes a resistor, and energy cannot be sent well. In other words, the DC / DC converter stops its step-down operation due to the failure of the intermediate capacitor C1, causing an operational problem.
Therefore, the DC / DC converter according to Embodiment 2 of the present application enables the continuation of the step-down operation by changing the operation method of the switching element from the normal method when the intermediate capacitor C1 has an open failure or a short circuit failure. It improves operational reliability.

  Although the failure of the intermediate capacitor C1 is not shown in FIG. 9, for example, the intermediate capacitor C1 and the input voltage Vin are always detected, and the open failure or short circuit of the intermediate capacitor C1 is based on the output values of both. Means for determining the occurrence of a failure is provided, and the determination is made based on the output of the determination means.

First, FIG. 13 shows an equivalent circuit when the intermediate capacitor C1 has an open failure. FIG. 14 shows an operation waveform when the intermediate capacitor C1 has an open failure. At this time, the switching elements S3 and S4 repeat ON / OFF simultaneously. The output voltage Vout can be adjusted by adjusting the on-duty ratio of the switching elements S3 and S4. The larger the on-duty ratio, the higher the output voltage.
The operation at this time is as follows: when the switching elements S3 and S4 are simultaneously turned on in the period t25,
Cin → S4 → S3 → L → Cout → Cin
The current flows through the path, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the coil L and the output side smoothing capacitor Cout, and energy is stored in the coil L. When switching elements S3 and S4 are turned off at the same time in period t26,
D1->D2->L->Cout-> D1
The current flows through the path (1), the energy previously stored in the coil L is released, and a voltage lower than the input voltage Vin is obtained as the output voltage Vout. By performing such an operation, the DC / DC converter can step down the voltage even if the intermediate capacitor C1 is in an open failure.

Next, FIG. 15 shows an equivalent circuit when the intermediate capacitor C1 is short-circuited. FIG. 16 shows an operation waveform when the short-circuit fault occurs in the intermediate capacitor C1. At this time, the switching element S3 is always on, and the switching element S4 is repeatedly turned on / off. The output voltage Vout can be adjusted by adjusting the on-duty ratio of the switching element S4. The larger the on-duty ratio, the higher the output voltage.
The operation at this time is a period t27, the switching element S3 is always on, and the switching element S4 is turned on.
Cin → S4 → S3 → L → Cout → Cin
The current flows through the path, the voltage of the input side smoothing capacitor Cin is applied to the series circuit of the coil L and the output side smoothing capacitor Cout, and energy is stored in the coil L. When switching element S4 is turned off in period t28,
Path 1: D1 → C1 (short circuit) → S3 → L → Cout → D1,
Or
Path 2: D1->D2->L->Cout-> D1
The current flows through the path with the smaller loss, and the output voltage lower than the input voltage Vin is obtained by the energy previously stored in the coil L.

  When current flows in the path 1, the loss is smaller than when the switching elements S3 and S4 are simultaneously turned on / off. By performing such an operation, the DC / DC converter can step down the voltage even if the intermediate capacitor C1 is short-circuited.

As described above, in the DC / DC converter according to Embodiment 2 of the present application, even if an open failure or a short-circuit failure occurs in the intermediate capacitor C1, the on / off switching pattern of the switching elements S3 and S4 is different from the normal pattern. By making the change, the step-down operation can be continued.
In this way, it is not necessary to prepare the intermediate capacitor C1 in preparation for the failure, and the amount of parts is reduced. Even if the intermediate capacitor C1 breaks down, the switching element operation method is changed from the normal method to reduce the voltage. It is possible to continue operation and improve operational reliability.

Embodiment 3 FIG.
FIG. 17 is a circuit diagram showing a configuration of a DC / DC converter according to Embodiment 3 of the present invention. The DC / DC converter shown in FIG. 17 can send energy in both directions by performing a step-up operation when energy is sent from the Vin side to the Vout side and a step-down operation when sending energy from the Vout side to the Vin side.

  The main circuit components include an input-side smoothing capacitor Cin that is a low-voltage side smoothing capacitor that holds the input voltage Vin, an output-side smoothing capacitor Cout that is a high-voltage side smoothing capacitor that holds the output voltage Vout, and energy storage and release. , The intermediate capacitor C1 that charges and discharges electric charge in cooperation with the coil L, and the first to fourth semiconductor element arms that are connected in series and are sequentially arranged from the negative electrode side.

  The first to fourth semiconductor element arms are connected in antiparallel to the first to fourth switching elements S1 to S4 such as IGBT and the switching elements S1 to S4, respectively, with the polarity shown in the figure. The first to fourth diode elements D1 to D4.

  Further, the connection configuration of these elements will be described. The low voltage side smoothing capacitor Cin has a positive terminal (upper terminal in FIG. 17) connected to one end of the coil L, and a negative terminal connected to the negative terminal of the high voltage smoothing capacitor Cout and the first switching element S1. Connected to the emitter terminal. The other end of the coil L is connected to the collector terminal of the second switching element S2. The collector terminal of the fourth switching element S4 is connected to the positive terminal of the high-voltage side smoothing capacitor Cout. The intermediate capacitor C1 has one end connected to the emitter terminal of the fourth switching element S4 and the other end connected to the collector terminal of the first switching element S1.

  Next, during the step-up operation of the DC / DC converter shown in FIG. 17, the switching elements S3 and S4 are always off, and both the third and fourth semiconductor element arms function as diode elements. Then, the first and second switching elements S1 and S2 are turned on and off in the same pattern as in the first embodiment, so that energy is transmitted from the Vin side to the Vout side, including when the intermediate capacitor C1 fails. Boosting operation can be performed.

  Further, during the step-down operation, the switching elements S1 and S2 are always turned off, and both the first and second semiconductor element arms function as diode elements. Then, the third and fourth switching elements S3 and S4 are turned on / off in exactly the same pattern as in the second embodiment, so that energy is transmitted from the Vout side to the Vin side including the time when the intermediate capacitor C1 fails. The step-down operation can be performed.

  As described above, the DC / DC converter according to the third embodiment of the present application can perform a bidirectional conversion operation of a step-up operation for sending energy from the Vin side to the Vout side and a step-down operation for sending energy from the Vout side to the Vin side. Even if an open circuit fault or a short circuit fault occurs in the intermediate capacitor C1, during the step-up operation, the step-up operation can be continued by changing the on / off switching pattern of the switching elements S1, S2 to a pattern different from the normal pattern. Sometimes, the step-down operation can be continued by changing the on / off switching pattern of the switching elements S3 and S4 to a pattern different from the normal pattern.

L coil, C1 intermediate capacitor, S1 to S4, first to fourth switching elements,
D1 to D4 First to fourth diode elements.

Claims (8)

A low-voltage side smoothing capacitor that holds a low-voltage side voltage, a negative-side terminal connected to a negative-side terminal of the low-voltage side smoothing capacitor and a high-voltage side smoothing capacitor that holds a high-voltage side voltage, and one end connected to the negative-side terminal of the low-voltage side smoothing capacitor A first semiconductor element arm connected, a second semiconductor element having one end connected to the other end of the first semiconductor element arm and the other end connected to the positive terminal of the low-voltage side smoothing capacitor via a coil An arm, one end connected to the other end of the second semiconductor element arm, one end connected to the other end of the third semiconductor element arm, and the other end connected to the positive electrode of the high-voltage side smoothing capacitor A fourth semiconductor element arm connected to the side terminal, and one end connected to an intermediate connection point between the first semiconductor element arm and the second semiconductor element arm and the other end connected to the third semiconductor element arm; An intermediate capacitor connected to an intermediate connection point between the conductor element arm fourth semiconductor element arms,
Each of the first and second semiconductor element arms has a function of a switching element and a diode element connected in reverse parallel to the switching element,
Each of the third and fourth semiconductor element arms has a function of a diode element,
The step-up operation of converting the input voltage of the low-voltage side smoothing capacitor into a boosted voltage and outputting it to the high-voltage side smoothing capacitor by the on / off switching function of the switching elements provided in the first and second semiconductor element arms Or
Each of the third and fourth semiconductor element arms has a function of a switching element and a diode element connected in reverse parallel to the switching element,
Each of the first and second semiconductor element arms has a function of a diode element,
Step-down operation for converting the input voltage of the high-voltage side smoothing capacitor into a step-down voltage and outputting it to the low-voltage side smoothing capacitor by the on / off switching function of the switching elements provided in the third and fourth semiconductor element arms In a DC / DC converter capable of
Means for detecting an open fault or a short-circuit fault of the intermediate capacitor, and when the open fault or the short-circuit fault is detected, the first and second semiconductor element arms or the third and fourth semiconductor element arms are provided. A DC / DC converter characterized in that the step-up operation or the step-down operation can be continued by changing the on / off switching pattern of the provided switching element to a predetermined pattern different from the normal pattern. When an opening failure of the intermediate capacitor is detected in the boost operation,
The first switching element provided in the first semiconductor element arm and the second switching element provided in the second semiconductor element arm are changed to a pattern for simultaneously turning on and off each other. The DC / DC converter according to 1. When a short circuit failure of the intermediate capacitor is detected in the boost operation,
The second switching element provided in the second semiconductor element arm is always turned on, and the first switching element provided in the first semiconductor element arm is changed to a pattern for turning on and off. Item 4. The DC / DC converter according to Item 1. When an open fault of the intermediate capacitor is detected in the step-down operation,
The third switching element provided in the third semiconductor element arm and the fourth switching element provided in the fourth semiconductor element arm are changed to a pattern for simultaneously turning on and off each other. The DC / DC converter according to 1. When a short circuit fault of the intermediate capacitor is detected in the step-down operation,
The third switching element provided in the third semiconductor element arm is always turned on, and the pattern is changed to a pattern in which the fourth switching element provided in the fourth semiconductor element arm is turned on / off. Item 4. The DC / DC converter according to Item 1. Each of the first and second semiconductor element arms is constituted by a switching element and a diode element connected in reverse parallel to the switching element, and each of the third and fourth semiconductor element arms is constituted by a diode element. 4. The DC / DC converter according to claim 1, wherein the step-up operation is performed. Each of the third and fourth semiconductor element arms is composed of a switching element and a diode element connected in reverse parallel to the switching element, and each of the first and second semiconductor element arms is composed of a diode element. The DC / DC converter according to claim 1, wherein the step-down operation is performed. Each of the first to fourth semiconductor element arms includes a switching element and a diode element connected in reverse parallel to the switching element.
When performing the boosting operation, the third and fourth switching elements constituting the third and fourth semiconductor element arms are always turned off,
6. The method according to claim 1, wherein when the step-down operation is performed, the first and second switching elements constituting the first and second semiconductor element arms are always turned off. The DC / DC converter described.

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