JP5605701B2 - Snubber circuit and power conversion circuit - Google Patents

Description

  The present invention relates to a power conversion circuit mounted on a power conversion device and a snubber circuit used in the power conversion circuit. The present invention is particularly effective when used in a non-insulated power converter.

  Examples of the snubber circuit used in the non-insulated power converter include an RC snubber circuit, an RCD snubber circuit, and an active snubber circuit described in Non-Patent Document 1 (Basics of Switching Converter, Kosuke Harada et al. Corona). Further, there is a circuit disclosed in Patent Document 1 (Snubber circuit and power conversion device, Japanese Patent Laid-Open No. 2000-333439).

The operation of the conventional snubber circuit will be described below.
First, the RC snubber circuit is composed of a series circuit of a resistor and a capacitor. This snubber circuit is connected in parallel with the main switch. When the main switch transitions from on to off, charging the snubber circuit capacitor suppresses the voltage transition speed of the main switch and reduces the switching loss of the main switch. However, the energy stored in the capacitor is consumed by the resistance of the snubber circuit.

  The RCD snubber circuit is configured by a series circuit of a parallel circuit of a resistor and a capacitor and a diode. This snubber circuit is connected in parallel with the main switch. When the main switch transitions from on to off, the capacitor of the snubber circuit is charged via the diode, whereby the voltage transition speed of the main switch is suppressed and the switching loss of the main switch is reduced. However, the energy stored in the snubber capacitor is consumed by the resistance of the snubber circuit. In the case of the RCD snubber circuit, there is less loss than the RC snubber circuit, and the effect of suppressing the transition speed of the voltage of the main switch is great.

  The active snubber circuit includes a small power conversion circuit, and is configured by a series circuit of the power conversion circuit, a parallel circuit of a capacitor, and a diode. This snubber circuit is connected in parallel with the main switch. When the main switch transitions from on to off, charging the snubber circuit capacitor via the diode suppresses the voltage transition speed of the main switch and reduces the switching loss of the main switch. The energy stored in the snubber capacitor is regenerated by the power conversion circuit in the snubber circuit. However, the active snubber circuit has a problem that the circuit configuration is complicated.

  Note that the LC snubber circuit and the switch snubber circuit shown in Non-Patent Document 1 do not operate in a non-insulated power converter because the magnetic flux of the main inductor is not reset.

  The snubber circuit disclosed in Patent Document 1 is a circuit that can be considered as a modification of the RCD snubber circuit. The snubber circuit has a configuration in which a capacitor is further connected in parallel to a diode of the RCD snubber circuit. A parallel circuit of a resistor and a capacitor, a diode and a capacitor Consists of a series circuit. This snubber circuit is connected in parallel with the main switch. When the main switch transitions from on to off, the voltage transition speed of the main switch is greatly suppressed by charging the capacitor of the snubber circuit via the diode. However, when the main switch transitions from OFF to ON, the energy stored in the snubber capacitor is discharged at once, and a large current pulse is generated in the main switch. For this reason, there is a problem that new power loss occurs.

  As described above, in the conventional snubber circuit, the attempt to reduce the switching loss of the main switch has been successful to some extent, but the reduction of the switching loss is insufficient and the power loss is still large. There are problems such as a complicated structure and a large mounting cost.

JP 2003-333439 A

Kosuke Harada, Tamotsu Ninomiya, Kenbun Ken, "Fundamentals of Switching Converter" Corona (1992.3.25, 2009.5.20) P.103-107

  The object of the present invention is to solve the above-mentioned problems and to reduce the power loss in the snubber circuit and to regenerate the power while the snubber circuit has a simple circuit configuration and to sufficiently reduce the switching loss of the main switch. It is to provide a snubber circuit.

  Another object of the present invention is to provide a highly efficient power conversion circuit using the snubber circuit.

In order to achieve the above object, a snubber circuit according to the present invention is a snubber circuit that is added to a power conversion circuit including a switching means including a main switch element and a commutation switch element connected in series. inductors, capacitors, first diode and second diode, a first terminal and a second terminal respectively connected to the high potential side and the low potential side of the DC power source input comprises a one end of the inductor is the switching means connected to the midpoint, the series circuit consisting of the auxiliary switching device and the inductor is connected in parallel with the main switching device, and one end of the capacitor is connected to the midpoint of the switching means, the condenser and the second a series circuit consisting of the diode is connected in parallel with the commutation switching element, it from the auxiliary switching device and the inductor The midpoint of the series circuit, the midpoint of the series circuit composed of the capacitor and a second diode, respectively connecting both ends of the first diode, the auxiliary switching device is connected at a high potential side to the first terminal The first diode has a cathode connected to the low potential side of the auxiliary switch element, the inductor has one end connected to the low potential side of the auxiliary switch element, and the capacitor has one end other than the inductor. And the other end is connected to the anode of the first diode. The second diode has an anode connected to the second terminal and a cathode connected to the other end of the capacitor. A third terminal is provided at a connection point with the capacitor .

The snubber circuit according to the present invention is a snubber circuit added to a power conversion circuit including a switching means composed of a main switch element and a commutation switch element connected in series, wherein an auxiliary switch element, an inductor, a capacitor, A first terminal and a second terminal connected to a high potential side and a low potential side of the input DC power source, respectively, and one end of the inductor is connected to the midpoint of the switching means. A series circuit composed of the auxiliary switch element and the inductor is connected in parallel to the main switch element, one end of the capacitor is connected to a midpoint of the switching means, and a series circuit composed of the capacitor and the second diode is The middle point of the series circuit composed of the auxiliary switch element and the inductor is connected in parallel to the commutation switch element. Both ends of the first diode are connected to the middle point of the series circuit composed of the capacitor and the second diode, respectively, the auxiliary switch element is connected to the second terminal on the low potential side, and the first diode is The anode is connected to the high potential side of the auxiliary switch element, the inductor has one end connected to the high potential side of the auxiliary switch element, and the capacitor includes the other end of the inductor and the cathode of the first diode. The second diode has a cathode connected to the first terminal, an anode connected to the cathode of the first diode, and a third terminal provided at a connection point between the inductor and the capacitor. It is characterized by that.

The step-down power converter according to the present invention includes a DC input power source, an input capacitor, a main switch element and a commutation switch connected in series, and a switching circuit connected in parallel to the input capacitor. Means, an auxiliary switch element, an inductor, a capacitor, a first diode and a second diode, and one end of the inductor is connected to a midpoint of the switching means, and a series circuit including the auxiliary switch element and the inductor is The auxiliary switch is connected in parallel, one end of the capacitor is connected to the midpoint of the switching means, and a series circuit composed of the capacitor and the second diode is connected in parallel to the commutation switch element, and the auxiliary switch The midpoint of the series circuit consisting of the element and inductor, the capacitor and the second diode The midpoint of Ranaru series circuit composed of an snubber circuit, each connected to both ends of the first diode, and a smoothing filter to generate a DC output voltage output smoothed from the switching means, the.

Furthermore, the step-down power converter circuit according to the present invention includes a DC input power source, an input capacitor, a main switch element and a commutation switch connected in series, and a switching circuit connected in parallel to the input capacitor. And the first terminal and the second terminal are respectively connected to the high potential side and the low potential side of the DC input power supply, and the third terminal is connected to the midpoint of the switching means. The snubber circuit according to claim 1 or 2 and a smoothing filter that generates a DC output voltage obtained by smoothing the output from the switching means .

  The snubber circuit according to the present invention reduces the loss that occurs during switching by mitigating steep voltage changes and current changes during the on / off operation of the switching elements constituting the switching converter circuit, and reduces the parasitic diodes of the switching elements. Reduce current due to accumulated charge. In addition, the snubber circuit according to the present invention can regenerate the power energy absorbed by the snubber circuit, and can reduce power loss in the snubber circuit. The snubber circuit according to the present invention has a simple circuit configuration.

  On the other hand, since the power conversion circuit according to the present invention includes the snubber circuit according to the present invention, almost no switching loss occurs during the switching operation of the switching converter circuit. Therefore, the power conversion circuit according to the present invention can realize a highly efficient power conversion device.

1 is a circuit diagram showing a power conversion circuit 1 and a snubber circuit 2 according to an embodiment of the present invention. It is a circuit diagram which shows the power converter circuit 1 and the snubber circuit 2 which concern on the 2nd Embodiment of this invention. It is a circuit diagram which shows the power converter circuit 1 and the snubber circuit 2 which concern on the 3rd Embodiment of this invention. It is a circuit diagram which shows the power converter circuit 1 and the snubber circuit 2 which concern on the 4th Embodiment of this invention. FIGS. 5A to 5C are a drive signal (upper side) for on / off control of the switch elements S1 to S3, respectively, and a diagram (lower side) showing an actual on / off state. FIG. 6 is a waveform diagram showing the waveform of the voltage (V _S2 ) of the commutation switch element S2 and the waveform of the voltage (V _D2 ) of the second diode D2. FIG. 7A is a waveform diagram of the current I _L1 flowing through the inductor L1, and FIG. 7B is a waveform diagram of the current I _L2 flowing through the inductor L2.

  A power conversion circuit including a snubber circuit according to the present invention will be specifically described on the basis of the following first to fourth embodiments. The following embodiment is an example of the present invention, and Is not limited to these embodiments. 2 to 4, parts that are substantially the same as those in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.

[First Embodiment]
The power conversion circuit 1 of the first embodiment has a circuit configuration of a switching type DC-DC converter (switched-mode dc-dc converter), and is a step-down power conversion circuit in which an output voltage is lower than an input voltage. is there.

In FIG. 1, the power conversion circuit 1 is connected to a DC input power supply (voltage V _{in +} ) at a positive input terminal 3a, and is connected to a DC input power supply (voltage V _in− ) at a negative input terminal 3b. The power conversion circuit 1 is connected to the capacitor C1 as an input capacitor, the chopper switching means 5 connected in parallel to the capacitor C1, and the input power source and the chopper switching means 5. The snubber circuit 2 and a smoothing filter 6 for generating a DC output voltage obtained by smoothing the output from the chopper switching means 5.

  The capacitor C1 in FIG. 1 functions as an input capacitor, and is connected to a DC input power source at the positive input terminal 3a and the negative input terminal 3b. The chopper switching means 5 includes a main switch element S1 connected to the positive side of the input power source and a commutation switch element S2 connected to the other end of the switch element S1 and connected to the negative side of the input power source. Consists of That is, the series circuit composed of the switch elements S1 and S2 is connected so as to be parallel to the capacitor C1 and connected between the input terminals 3a and 3b at both ends of the series. The switch elements S1 and S2 can be configured using field effect transistors or the like. The constituent elements PD1 and PD2 are parasitic diodes of the switch elements, and correspond to the switch elements S1 and S2, respectively.

  In the snubber circuit 2 of the first embodiment, one end of the auxiliary switch element S3 is connected to the positive input terminal 3a, and the other end of the switch element S3 is connected to the high potential side terminal of the inductor L2. And connected to the cathode of the first diode D1. The snubber circuit 2 is connected to the connection point 5m between the switch elements S1 and S2 at the other end 2m of the inductor L2. A second diode D2 is connected between the first diode D1 and the negative DC input power supply. The anode of the second diode D2 is the negative DC input power supply, and the cathode of the second diode D2 is the first diode D1. Each is connected to the anode. A capacitor C3 is connected between the connection point of the diodes D1 and D2 and the other end 2m of the inductor L2.

The connection point 5m between the switch elements S1 and S2 and the connection point 2m to which the inductor L2 and the capacitor C3 are connected are connected to the inductor L1, and between the output side of the inductor L1 and the negative DC input power source, A capacitor C2 is connected. The connection point 4a between the output side of the inductor L1 and the capacitor C2 serves as a terminal for positive output (voltage _{Vout +} ), and the connection point 4b between the capacitor C2 and the negative DC input power supply serves as negative output (voltage _{Vout). -} ) Terminal. The smoothing filter 6 is composed of the inductor L1 and the capacitor C2 as described above, and a DC output voltage is taken out from the connection point 4a as the positive terminal and the connection point 4b as the negative terminal.

  In the circuit of FIG. 1, when the snubber circuit 2 of the present invention is not used, it is necessary to operate the switching converter circuit by alternately switching on and off the switch elements S1 and S2 and smoothing the voltage with the inductor L1. There is. However, in this case, when the commutation switch element S2 is turned off and the main switch element S1 is turned on, a very large current flows through the main switch element S1 due to the charge accumulated in the parasitic diode PD2. In addition, when the main switch element S1 is turned off and the commutation switch element S2 is turned on, the current of the inductor L1 flows transiently through the main switch element S1 at both ends of the main switch element S1. A large voltage is generated and a large amount of power is lost in the main switch element S1. For this reason, a large loss occurs in the switching converter circuit.

Next, the operation of the snubber circuit 2 in FIG. 1 will be described with reference to FIGS. 5 to 7A and 7B.
The upper diagrams of FIGS. 5A to 5C show the drive signals of the switch elements S1 to S3, and the switch elements S1 to S3 are the drive signals of FIGS. 5A to 5C, respectively. ON / OFF control. However, the actual switch elements S1 to S3 perform an on / off operation shown on the lower side of FIGS. 5 (a) to 5 (c). FIG. 6 shows the waveform of the voltage (V _S2 ) of the commutation switch element S2 and the waveform of the voltage (V _D2 ) of the second diode D2. FIGS. 7A and 7B show waveforms of currents I _L1 and I _L2 flowing through the inductors L1 and L2, respectively. The horizontal axis is a time axis, and is common to FIGS. 5 to 7 (a) and (b), and the phenomenon corresponds to the same time axis, and the operation of the snubber circuit 2 is the same. The waveform when in a steady operation state is shown.

When the commutation switch element S2 that is on / off controlled by the drive signal shown in FIG. 5A receives an instruction from on to off at the time t _1a , the component of the current I _L1 of the inductor L1 changes. That is, until just before time t ₁ , the current I _L1 is equal to the current I _S2 that has been flowing through the commutation switch element S2 of the power converter. However, immediately after the commutation switch element S2 is turned off, the current I _PD2 flowing through the parasitic diode PD2 of the commutation switch element S2 becomes relatively large with respect to the current I _S2 , and the current I _L1 becomes the current I _PD2 . (FIG. 7A). Incidentally, t ₁ and t _1a is a point a certain time period determined by the switching frequency of the power converter circuit (timing).

Further, (between t ₃ time points from time point t ₁ in FIG. 5 (a)) between the state of the commutation switching element S2 off until the transition to the main switching device S1 on, turning on the auxiliary switch element S3 As a result, the current I _{L1 of the} inductor L1 is caused to pass through the auxiliary switch element S3 and the inductor L2. Thereby, the loss accompanying the switching operation of the switch elements S1 and S2 can be reduced.

When assisted t _2a point immediately after commutation switching element S2 off switch element S3 receives a drive signal to the on state, the auxiliary switching element S3 is transitioned to the ON state at t ₂ time, current I _L2 in the inductor L2 is It increases from 0 with time (FIG. 7B). When the current I _L2 of the inductor _L2 becomes equal to the current I _{L1 of the} inductor L1 (FIGS. 7A and 7B), the current I _PD2 of the parasitic diode _PD2 becomes 0 (FIG. 7A), and the main switch element S1 The voltage across the begins to decrease. In FIG. 7A, the time point when the current of PD2 decreases to zero is defined as tc. As soon as the voltage across the main switch element S1 reaches zero, that is, the voltage across the commutation switch element S2 reaches V _{in +} -V _in- (V _{S2 in} FIG. 6), a current flows through the parasitic diode PD1. start. Although t ₂ is set after t _1, it is preferable to set t ₂ at the same time as or immediately after t ₁ .

Soon after the voltage across the commutation switch element S2 reaches V _{in +} −V _in− , the main switch element S1 is controlled to receive a drive signal for turning on at time t _3a . Thus, without substantially generating a switching loss, at t ₃ time points, it is possible to transition from state commutation switching element S2 on to the main switching device S1 on state. Note that t ₃ is preferably set to be the same as or immediately after the time when the voltage at the connection point 5m reaches V _{in +} .

After the main switch device S1 is shifted to ON, t ₄ time of the auxiliary switch element S3 receives a drive signal to the OFF state at t _4a time, immediately auxiliary switch element S3 is a transition to the OFF state (FIG. 5 (c) ). At this time, the energy stored in the inductor L2 charges the capacitor C3 via the first diode D1. As a result, the voltage across the capacitor C3 is raised to the input voltage (V _{in +} −V _in− ) of the power conversion circuit. At this time, the voltage V _D2 of the second diode D2 decreases to 0 because the capacitor C3 is charged (V _{D2 in} FIG. 6). Note that t ₄ is preferably set immediately after t ₃ .

Next, the main switching device S1 is subjected to the driving signal to the off state at t _5a point, main switching device S1 is a transition to the OFF state (t ₅ the time in Figure 5 (a)). During the transition from the state of the main switching element S1 off to commutation switching element S2 on, i.e., from t ₅ the time in FIG. 5 (a), the charge stored in the capacitor C3 is discharged (Fig. 7 ( a) I _D2 ). The current I _L1 at this time is equal to the current I _D2 flowing through the second diode D2, and the charge (C ₃ V) stored in the capacitor C3 is discharged.

Immediately after the charge (C ₃ V) is discharged, that is, immediately after the time point t ₅ , the voltage of the capacitor C3 becomes substantially equal to the voltage V _S2 across the commutation switch element S2. As shown by V _S2 in FIG. 6, the voltage across the capacitor C3 and the commutation switch element S2 decreases with time, and the voltage across the capacitor C3 and the commutation switch element S2 becomes zero. Then, the current I _PD2 starts to flow through the parasitic diode PD2 (FIG. 7A). Incidentally, t ₅ is a time to be determined corresponding to the target value of the input and output voltage ratio of the power conversion circuit. In general, t ₅ is given in correspondence with a ratio (time ratio) of time that the main switch element S1 is on.

At the time point t _6a , the commutation switch element S2 receives the drive signal to turn on, and the commutation switch element S2 quickly transitions to the on state (time t _{6 in} FIG. 5B), thereby commutation. During a predetermined time until the switch element S2 transitions from on to off, the current I _{L1 of the} inductor L1 flows through the commutation switch element S2. Then, after a predetermined time, if the commutation switching element S2 is changed from on to off, again as above t ₁ when the time of the transition to the per pass switch element S2 is turned off, the above switching operation of the switching elements S1 to S3 are repeated It is. Note that t ₆ is preferably the same as or just after the time when the voltage at the connection point 5 m reaches V _in− .

As described above, by repeating the switching operation to switching elements S1 to S3 is a predetermined time elapses from the time point t _1, with almost no generation switching losses per pass switching element from the main switching element S1 on state Transition to the S2 on state is possible.

As described above, the switch elements S1 to S3 are controlled by the drive signals shown in the upper diagrams of FIGS. 5A to 5C, respectively, but actually, FIGS. 5A to 5C are used. On / off operation is performed as shown below. Therefore, the timing (time point) to the transition of the drive signals for turning on and off the switching elements S1 to S3, as t _1a to t _6a respectively so as to correspond to the timing t ₁ to t ₆ switching elements S1 to S3 are turned on and off, the switch The elements S1 to S3 have been described as described above.

Thus, in practice, it is necessary to consider the time required to drive each switch element, while the time required to drive each switch element, that is, t ₁ -t _1a , t ₂ -t _2a ,... since t ₆ -t _2a are not identical, taking into account the difference in time required for this drive, it is necessary to drive each switch element.

A method for generating the timing for driving the switch elements S1 to S3 will be described. First, t _2a may be set after a certain time after t _1a . Although t _3a may be set after a certain time from t _1a , the voltage between both ends of the main switch element S1 is observed, and when that voltage becomes close to 0 (that is, the voltage at the connection point 5m is V _{in +} It is preferable that t _3a be a point in time when the _frequency is near. Further, t _4a may be set after a certain time after t _3a .

Further, t _5a corresponds to a target value of the voltage ratio between the input and output of the power conversion circuit, and the timing output by the control circuit included in the power conversion circuit is used. That is, a control circuit (not shown) is connected to the switch elements S1 to S3, and the switch elements S1 to S3 are on / off controlled by the control circuit.

Specifically, the control circuit of the power conversion circuit performs control so that the main switch element S1 is repeatedly turned on and off at a predetermined switching frequency. In this control, t _3a and t _5a are controlled so that the output voltage of the power conversion circuit becomes a predetermined voltage value by changing the ratio of the ON time and the OFF time of the main switch element S1.

The commutation switch S2 and the auxiliary switch S3 also generate timing in conjunction with the time when the main switch S1 is turned on and turned off, and control t _1a , t _2a , t _4a, and t _6a .

Further, t _6a may be set after a certain time from t _5a , but when the voltage between both ends of the advancing switch element S2 is observed, the time when the voltage becomes close to 0 (that is, the voltage at the connection point 5m is It is also possible to set t _6a as the time point when it becomes near V _in− .

[Second Embodiment]
The power conversion circuit 1 according to the second embodiment shown in FIG. 2 is a step-down power conversion circuit in which the output voltage is lower than the input voltage. The components 1 to 6 in FIG. 2 are equivalent in function and effect to the components 1 to 6 in FIG.

  The snubber circuit 2 of the second embodiment is connected to the negative input terminal 3b at the low potential side terminal of the switch element S3, and the high potential side terminal of the switch element S3 is connected to the low potential side terminal of the inductor L2. Connected to the anode of the diode D1. The snubber circuit 2 is connected to the connection point 5m between the switch elements S1 and S2 at the high potential side terminal 2m of the inductor L2. Between the diode D1 and the positive DC input power supply, the anode of the diode D2 is connected to the cathode of the diode D1, and the cathode of the diode D2 is connected to the terminal 4a of the positive DC input power supply. The inductor L2 and the capacitor C3 are connected between the high potential side terminal of the switch element S3 and the anode of the diode D2, and are connected between the low potential side terminal of the switch element S3 and the cathode of the diode D2. This is different from the snubber circuit 2 of the first embodiment.

Next, the operation of the snubber circuit 2 of the second embodiment will be described. Since the basic operation is substantially the same as that of the snubber circuit 2 of the first embodiment, detailed description thereof is omitted. The difference is the direction of the current in the discharge path of the charge C ₃ V stored in the capacitor C3 during the transition from the switch element S1 off state to the switch element S2 on state.
Path: Inductor L1 → Capacitor C3 → Diode D2
The energy of the snubber circuit 2 is regenerated in the DC power supply output or the capacitor C2.

In addition, the current I _L2 of the inductor L2 is between the time when the switch element S3 is turned on immediately after the switch element S2 is turned off and the time when the switch element S3 is turned off.
Path: Inductor L1 → Inductor L2
The electric current flows at, and energy is supplied to the snubber circuit 2.

[Third Embodiment]
The power conversion circuit 1 of the third embodiment shown in FIG. 3 is a boost type power conversion circuit in which the output voltage is higher than the input voltage. The third embodiment differs from the structure of the first embodiment in that the chopper switching means 5 and the capacitor C1 are connected to the DC output 4 side, and the smoothing filter 6 is connected to the DC input power supply 3 side. However, the components 1 to 6 in FIG. 3 are equivalent to the components 1 to 6 in FIG.

  The snubber circuit 2 of the third embodiment is connected to the positive input terminal 3a at the high potential side terminal of the switch element S3, and the low potential side terminal of the switch element S3 is connected to the high potential side terminal of the inductor L2. Connected to the cathode of the diode D1. The snubber circuit 2 is connected to the connection point 5m between the switch elements S1 and S2 at the low potential side terminal 2m of the inductor L2. Between the diode D2 and the negative DC output, the cathode of the diode D2 is connected to the anode of the diode D1, and the anode of the diode D2 is connected to the negative DC output terminal 4b. Note that the circuit connection and basic operation of the snubber circuit 2 are the same as those of the snubber circuit 2 of the first embodiment.

Next, the operation of the snubber circuit 2 of the third embodiment will be described. Since the basic operation is substantially the same as that of the snubber circuit 2 of the first embodiment, detailed description thereof is omitted. The direction of the current in the discharge path of the charge C ₃ V stored in the capacitor C3 during the transition from the switch element S1 off state to the switch element S2 on state is the same as in the first embodiment.
Path: Diode D2 → Capacitor C3 → Inductor L1
The energy of the snubber circuit 2 is regenerated in the DC power supply output or the capacitor C1.

In addition, the current I _L2 of the inductor L2 is between the time when the switch element S3 is turned on immediately after the switch element S2 is turned off and the time when the switch element S3 is turned off.
Path: Inductor L2 → Inductor L1
The electric current flows at, and energy is supplied to the snubber circuit 2.
[Fourth Embodiment]
The power conversion circuit 1 according to the fourth embodiment shown in FIG. 4 is a boost type power conversion circuit in which the output voltage is higher than the input voltage. The components 1 to 6 in FIG. 4 are equivalent in function and effect to the components 1 to 6 in FIG.

  The snubber circuit 2 of the fourth embodiment is connected to the negative output terminal 4b at the low potential side terminal of the switch element S3, and the high potential side terminal of the switch element S3 is connected to the low potential side terminal of the inductor L2. Connected to the anode of the diode D1. The snubber circuit 2 is connected to the connection point 5m between the switch elements S1 and S2 at the high potential side terminal 2m of the inductor L2. Between the diode D1 and the positive DC input power supply, the cathode of the diode D1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the positive DC output terminal 4a. The inductor L2 and the capacitor C3 are connected between the high potential side terminal of the switch element S3 and the anode of the diode D2, and are connected between the low potential side terminal of the switch element S3 and the cathode of the diode D2. This is different from the snubber circuit 2 of the third embodiment.

Next, the operation of the snubber circuit 2 of the fourth embodiment will be described. Since the basic operation is substantially the same as that of the snubber circuit 2 of the first embodiment, detailed description thereof is omitted. The difference is the direction of the current in the discharge path of the charge C ₃ V stored in the capacitor C3 during the transition from the switch element S1 off state to the switch element S2 on state.
Path: Inductor L1 → Capacitor C3 → Diode D2
The energy of the snubber circuit 2 is regenerated in the DC input power source or the capacitor C2.

In addition, the current I _L2 of the inductor L2 is between the time when the switch element S3 is turned on immediately after the switch element S2 is turned off and the time when the switch element S3 is turned off.
Path: Inductor L1 → Inductor L2
The electric current flows at, and energy is supplied to the snubber circuit 2.

  The switch elements S1 to S3 are field effect transistors (FETs), IGBTs, or junction transistors. In addition, by providing a diode suitable for high-power high-speed switching such as a high-speed recovery diode or Schottky barrier diode in parallel with the switch element, better electrical characteristics than the parasitic diode of the switch element can be obtained, and the loss of the power conversion circuit Can be further reduced. It is preferable that the main switch S1 and the commutation switch S2 have a small on-state resistance value, and the auxiliary switch element S3 has a high switching speed.

  Next, in order to confirm the effect by this invention, the power conversion efficiency was measured using the power converter circuit 1 of Embodiment 4. FIG. The loss of the power conversion circuit is calculated by calculating the difference between the input power and the output power to the power conversion circuit as the loss of the power conversion circuit.

Further, each part of the circuit shown in FIG. 4 was selected as follows.
Inductor L1 = 80μH
Inductor L2 = 10μH
Capacitor C3 = 0.022μF
Switching frequency = 34.5 kHz
Note that Schottky barrier diodes were used as the diodes D1 and D2, and field effect transistors were used as the switch elements S1 to S3.

  In the power conversion circuit 1 of Embodiment 4 configured as described above, the input voltage was set to 42.4V, the input power was set to 97.7W, and the output voltage was set to 48.1V.

  When the snubber circuit of the present invention was not operated, the loss of the power conversion circuit was 2.89 W, but when the snubber circuit of the present invention was operated, the loss of the power conversion circuit was reduced to 1.84 W. That is, with the snubber circuit of the present invention, the loss of the power conversion circuit could be reduced by 1/3 or more.

DESCRIPTION OF SYMBOLS 1 Power converter circuit 2 Snubber circuit 3 DC input power supply 3a Positive electrode terminal on the DC input side 3b Negative electrode terminal on the DC input side 4 DC output 4a Positive electrode terminal on the DC output side 4b Negative electrode terminal on the DC output side 5 Switching means 5m Middle point of switching means 6 Smoothing filter C3 Capacitor D1 First diode D2 Second diode L1 Inductor L2 Inductor S1 Main switch means S2 Commutation switch means S3 Auxiliary switch means

Claims (4)

In a snubber circuit added to a power conversion circuit provided with switching means composed of a main switch element and a commutation switch element connected in series,
An auxiliary switch element, an inductor, a capacitor, a first diode and a second diode, and a first terminal and a second terminal respectively connected to a high potential side and a low potential side of an input DC power source ;
One end of the inductor is connected to the midpoint of the switching means, the series circuit consisting of the auxiliary switching element and the inductor is connected in parallel to the main switching device,
One end of the capacitor is connected to the midpoint of the switching means, the series circuit composed of the capacitor and a second diode is connected in parallel with the commutation switching element,
The midpoint of the series circuit consisting of the auxiliary switching element and the inductor, the midpoint of the series circuit composed of the capacitor and a second diode, respectively connecting both ends of the first diode,
The auxiliary switch element is connected to the first terminal on the high potential side,
The first diode has a cathode connected to the low potential side of the auxiliary switch element,
The inductor has one end connected to the low potential side of the auxiliary switch element,
The capacitor has one end connected to the other end of the inductor and the other end connected to the anode of the first diode,
The second diode has an anode connected to the second terminal and a cathode connected to the other end of the capacitor;
A third terminal is provided at a connection point between the inductor and the capacitor;
A snubber circuit characterized by that. In a snubber circuit added to a power conversion circuit provided with switching means composed of a main switch element and a commutation switch element connected in series,
An auxiliary switch element, an inductor, a capacitor, a first diode and a second diode, and a first terminal and a second terminal respectively connected to a high potential side and a low potential side of an input DC power source;
One end of the inductor is connected to the midpoint of the switching means, and a series circuit composed of the auxiliary switch element and the inductor is connected in parallel to the main switch element,
One end of the capacitor is connected to the midpoint of the switching means, and a series circuit composed of the capacitor and a second diode is connected in parallel to the commutation switch element,
Both ends of the first diode are connected to the midpoint of the series circuit composed of the auxiliary switch element and the inductor and the midpoint of the series circuit composed of the capacitor and the second diode,
The auxiliary switch element is connected to the second terminal on the low potential side,
The first diode has an anode connected to the high potential side of the auxiliary switch element,
One end of the inductor is connected to the high potential side of the auxiliary switch element,
The capacitor is connected between the other end of the inductor and the cathode of the first diode;
The second diode has a cathode connected to the first terminal and an anode connected to the cathode of the first diode;
A third terminal is provided at a connection point between the inductor and the capacitor;
A snubber circuit characterized by that . DC input power supply,
An input capacitor;
Switching means comprising a main switch element and a commutation switch connected in series and connected in parallel to the input capacitor;
An auxiliary switch element, an inductor, a capacitor, a first diode and a second diode;
One end of the inductor is connected to the midpoint of the switching means, and a series circuit composed of the auxiliary switch element and the inductor is connected in parallel to the main switch element,
One end of the capacitor is connected to the midpoint of the switching means, and a series circuit composed of the capacitor and a second diode is connected in parallel to the commutation switch element,
A snubber circuit for connecting both ends of the first diode to the midpoint of the series circuit composed of the auxiliary switch element and the inductor, and the midpoint of the series circuit composed of the capacitor and the second diode ;
A smoothing filter for generating a DC output voltage obtained by smoothing the output from the switching means ;
A step-down power conversion circuit comprising: DC input power supply,
An input capacitor;
Switching means comprising a main switch element and a commutation switch connected in series and connected in parallel to the input capacitor;
The first terminal and the second terminal are connected to the high potential side and the low potential side of the DC input power source, respectively, and the third terminal is connected to the midpoint of the switching means.
Snubber circuit according to claim 1 or 2,
A smoothing filter for generating a DC output voltage obtained by smoothing the output from the switching means;
A step-down power conversion circuit comprising:

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