Step-up converter circuit and electric transport machine including same

Abstract

A step-up converter circuit (1) comprises a reactor (L1), a first half-bridge circuit (11), a second half-bridge circuit (12), a first step-up capacitor (C1), a second step-up capacitor (C2), a smoothing capacitor (C0) for smoothing the outputs that are inputted in parallel from the first and second half-bridge circuits, and a switching control circuit (15) for carrying out phase control of a switching operation between the first half-bridge circuit and the second half-bridge circuit. The voltage of the first step-up capacitor is superimposed on the voltage of a voltage source and outputted from the first half-bridge circuit, and the voltage of the second step-up capacitor is superimposed on the voltage of the voltage source and outputted from the second half-bridge circuit.

Description

Boost converter circuit and electric transport equipped with same

[0001] The present invention relates to a boost converter circuit.

[0002] A boost converter (boost converter) is a DC-DC conversion device for obtaining an output at a voltage higher than the input voltage, and is sometimes called a boost chopper, boost converter, etc. A reactor is provided in a boost chopper type boost converter used in a power conditioner circuit in solar power generation, hybrid electric vehicles (HEVs), electric vehicles (EVs), other electric transport vehicles, etc.

[0003] Patent Document 1 listed below discloses a DC-DC converter including a reactor, an inverter circuit including at least one bit inverter connected downstream of the reactor and having a capacitor and a bridge circuit, a smoothing capacitor that smoothes the output of the inverter circuit, a short-circuit switch that switches between a charge mode and a discharge mode, and a control unit.

[0004] Japanese Patent Application Laid-Open No. 2022-132132

[0005] In existing boost converters that include a reactor, the ripple factor increases along with the reactor current, particularly in high-power applications, and a high-inductance reactor must be used to suppress this, resulting in a problem of increased reactor size. In this regard, the DC-DC converter disclosed in Patent Document 1 uses a switched capacitor that can be configured with low inductance, thereby achieving a smaller reactor.

[0006] However, in the DC-DC converter disclosed in Patent Document 1, when bit inverters are connected in multiple stages to increase the output voltage magnification, there is a problem in that the switching timing control of each switch element becomes complicated in order to ensure a low ripple rate of the reactor current.

[0007] The present invention has been made in view of the above problems, and provides a boost converter circuit that enables the boost reactor to be miniaturized even in high-power applications.

[0008] One aspect of the present invention is a boost converter circuit comprising: a reactor that can be connected in series to a DC voltage source; a first half-bridge circuit connected in parallel to the reactor; a first boost capacitor whose charging and discharging are switched by the switching operation of the first half-bridge circuit; a second half-bridge circuit connected in parallel to the reactor on the output side of the first half-bridge circuit; a second boost capacitor whose charging and discharging are switched by the switching operation of the second half-bridge circuit; a smoothing capacitor to which outputs from the first half-bridge circuit and the second half-bridge circuit are input in parallel and which smoothes the output voltage; and a switching control circuit which performs phase control of the switching operation between the first half-bridge circuit and the second half-bridge circuit, wherein the voltage of the first boost capacitor is superimposed on the voltage of the voltage source as the first boost capacitor is discharged and the voltage is output from the first half-bridge circuit, and the voltage of the second boost capacitor is superimposed on the voltage of the voltage source as the second boost capacitor is discharged and the voltage is output from the second half-bridge circuit.

[0009] Another aspect of the present invention is a bidirectional converter circuit including the above-mentioned boost converter circuit, a first terminal capable of connecting the voltage source and the reactor, a second terminal capable of outputting the voltage smoothed by the smoothing capacitor, a plurality of reverse-conducting switching elements including a reverse-conducting switching element provided on an output line of the first half-bridge circuit and an output line of the second half-bridge circuit, and a control circuit that controls the conduction directions of the plurality of reverse-conducting switching elements to switch the input and output of power of the boost converter circuit in reverse directions, thereby causing the boost converter circuit to also operate as a buck converter circuit. Another aspect of the present invention is an electric transport including the above-mentioned boost converter circuit or the above-mentioned bidirectional converter circuit.

[0010] According to the above-described aspects, it is possible to provide a boost converter circuit that enables the boost reactor to be miniaturized even in high-power applications.

[0011] Fig. 1 is a circuit diagram of a boost converter circuit (present circuit) according to a first embodiment; Fig. 2 is a diagram showing an example of operation of the boost converter circuit (present circuit) according to the first embodiment; Fig. 3 is a circuit diagram of a boost converter circuit (present circuit) according to a second embodiment; Fig. 4 is a circuit diagram of a bidirectional converter circuit as a modified example; Fig. 5 is a circuit diagram of a boost converter circuit (present reference circuit) according to a reference example, which is a graph showing simulation results of Example 1;

[0012] Hereinafter, embodiments of the present invention will be described. Note that the following embodiments are merely examples, and the present invention is not limited to the configurations of the following embodiments.

[0013] First Embodiment FIG. 1 is a circuit diagram of a boost converter circuit 1 according to a first embodiment. The boost converter circuit 1 according to the first embodiment (hereinafter sometimes referred to as the present circuit) is configured to be connectable to a voltage source V1 and a load R1, and boosts the DC voltage of the voltage source V1 to a desired voltage and supplies the voltage to the load R1. The voltage source V1 is a DC voltage source that is capable of supplying a substantially constant voltage even when the magnitude of the load R1 fluctuates. The voltage source V1 may also be a circuit (such as an ADDC converter circuit) that converts an AC voltage output from an AC voltage source into a DC voltage and outputs the DC voltage. Hereinafter, in the description of the present circuit 1, the side closer to the load R1 will be referred to as the "rear stage" or "output side," and the side closer to the voltage source V1 will be referred to as the "front stage" or "input side."

[0014] [Circuit Configuration] This circuit 1 includes a reactor L1, half-bridge circuits 10 and 20, boost capacitors C1 and C2, a smoothing capacitor C0, and a switching control circuit 15. The reactor L1 is provided between a voltage source V1 and the half-bridge circuit 10, and is connected in series to the voltage source V1. This circuit 1 operates to reduce the ripple factor of the current flowing through this reactor L1, thereby achieving a miniaturization of the reactor L1.

[0015] Half-bridge circuits 10 and 20 are connected in parallel to a voltage source V1 and a reactor L1, respectively. In the example of Fig. 1, half-bridge circuit 20 is connected to the output side of half-bridge circuit 10. Half-bridge circuit 10 includes a pair of switching elements S11 and S12 connected in series with each other, and half-bridge circuit 20 includes a pair of switching elements S21 and S22 connected in series with each other.

[0016] The half-bridge circuit 10 is controlled by a switching control circuit 15 (described later) to perform a switching operation. Specifically, the pair of switching elements S11 and S12 is controlled to alternately perform a complementary on-off switching operation (one is turned on and the other is turned off). The half-bridge circuit 20 is similarly controlled by the switching control circuit 15 (described later) to perform a switching operation. Specifically, the pair of switching elements S21 and S22 is controlled to alternately perform a complementary on-off switching operation (one is turned on and the other is turned off). This complementary switching operation between the pair of switching elements constituting the half-bridge circuit is referred to as the switching operation of the half-bridge circuit. The switching elements S11, S12, S21, and S22 are semiconductor switching elements such as field effect transistors (FETs), metal oxide semiconductor field effect transistors (MOSFETs), and insulated gate bipolar transistors (IGBTs).

[0017] The boost capacitor C1 is arranged so that the direction of current flowing through it is switched by the switching operation of the half-bridge circuit 10, and as a result, the charging and discharging of the boost capacitor C1 is switched by the switching operation. The boost capacitor C1 is connected in parallel with the switching element S12 with respect to the reactor L1. More specifically, one terminal of the boost capacitor C1 is connected to a branch line extending from between the switching element pair (between switching element S11 and switching element S12) of the half-bridge circuit 10, and the other terminal is connected to the output line LN1 of the half-bridge circuit 10.

[0018] The boost capacitor C2 is arranged so that the direction of current flowing therethrough is switched by the switching operation of the half-bridge circuit 20, and as a result, charging and discharging of the boost capacitor C2 are switched by this switching operation. The boost capacitor C2 is connected in parallel with the switching element S22 across the reactor L1. More specifically, one terminal of the boost capacitor C2 is connected to a branch line extending from between the switching element pair (between switching element S21 and switching element S22) of the half-bridge circuit 20, and the other terminal is connected to the output line LN5 of the half-bridge circuit 20.

[0019] The smoothing capacitor C0 receives the outputs from the half-bridge circuits 10 and 20 in parallel and smoothes the output voltage. Specifically, the smoothing capacitor C0 is provided on the output side of the half-bridge circuits 10 and 20, is connected to the output terminal to which the load R1 is connected, and smoothes the outputs from the output line LN1 of the half-bridge circuit 10 and the output line LN5 of the half-bridge circuit 20.

[0020] As described above, the switching control circuit (hereinafter sometimes simply referred to as the control circuit) 15 controls the switching operation of the half-bridge circuit 10 and the switching operation of the half-bridge circuit 20, and also performs phase control of the switching operation between the half-bridge circuit 10 and the half-bridge circuit 20. The phase control by the control circuit 15 may be in the form of setting the phase difference of the switching operation between the half-bridge circuit 10 and the half-bridge circuit 20 to a value determined according to the impedance of the load R1, or may be in the form of adjusting the phase difference according to fluctuations in the impedance of the load R1. In the latter case, for example, the control circuit 15 is configured to include a circuit element that feeds back the output state from the circuit 1 to detect impedance fluctuations in the load R1, and a circuit element that adjusts the phase difference according to the fed-back output state. The output state that is fed back to detect the impedance of the load R1 is, for example, the output current or output voltage from the circuit 1, or both.

[0021] When the phase difference between the switching operations of the half-bridge circuits 10 and 20 is 180 degrees, the half-bridge circuits 10 and 20 are referred to as performing anti-phase switching operations between the circuits. In such anti-phase switching operations between the half-bridge circuits 10 and 20, the high-potential side switching elements S12 and S22 are in anti-phase with each other, and the low-potential side switching elements S11 and S21 are in anti-phase with each other. For example, when the duty ratio of the switching operations is set to 50% or less, when the switching element S11 is in the on state and the switching element S12 is in the off state, the anti-phase switching operations result in the switching element S21 being in the off state and the switching element S22 being in the on state, and when the switching element S11 is in the off state and the switching element S12 is in the on state, the switching element S21 being in the on state and the switching element S22 being in the off state. The phase control of the control circuit 15 is not limited to control for switching operations in which the half-bridge circuits 10 and 20 are in opposite phases (phase difference of 180 degrees), but also includes control (phase difference of less than 180 degrees) in which, when the duty ratio of the switching operations is set to 50% or less, the on / off states of the low-potential side switching element S11 of the half-bridge circuit 10 and the high-potential side switching element S22 of the half-bridge circuit 20 are different within one cycle, and the on / off states of the high-potential side switching element S12 of the half-bridge circuit 10 and the low-potential side switching element S21 of the half-bridge circuit 20 are different within one cycle.

[0022] The on / off control of each of the switching elements S11, S12, S21, and S22 by the control circuit 15 can be appropriately realized depending on the configuration of each switching element, and the specific method of realizing this control is not limited. For example, when MOSFETs are used as each switching element, the control circuit 15 is connected to each MOSFET so as to be able to apply a gate-source voltage (hereinafter sometimes referred to as a VGS voltage) to each MOSFET. The control circuit 15 alternately applies a VGS voltage exceeding a threshold voltage to each MOSFET in a switching element pair, thereby alternately switching the on / off state of each MOSFET.

[0023] By such control of the control circuit 15, the discharge of the boost capacitor C1 causes the voltage of the boost capacitor C1 to be superimposed on the voltage of the voltage source V1 and output from the output line LN1 of the half-bridge circuit 10, and the discharge of the boost capacitor C2 causes the voltage of the boost capacitor C2 to be superimposed on the voltage of the voltage source V1 and output from the output line LN5 of the half-bridge circuit 20. In this circuit 1, the output from the output line LN1 of the half-bridge circuit 10 and the output from the output line LN5 of the half-bridge circuit 20 are input in parallel to the smoothing capacitor C0 and smoothed by the smoothing capacitor C0.

[0024] The boost converter circuit 1 further includes rectifying diodes D1, D2, D3, and D4 as other circuit components. The diode D1 branches off from the connection point between the reactor L1 and the switching element S12 and is provided for rectification on a line connecting the connection point between the boost capacitor C1 and the output line LN1, with its cathode facing the output side. The diode D2 branches off from the connection point between the reactor L1 and the switching element S22 and is provided for rectification on a line connecting the connection point between the boost capacitor C2 and the output line LN5, with its cathode facing the output side. The diode D3 is provided on the output line LN1 with its cathode facing the output side, and the diode D4 is provided on the output line LN5 with its cathode facing the output side. That is, the diode D3 is provided closer to the output side than the diode D1, and the diode D4 is provided closer to the output side than the diode D2. The output line LN1 of the half-bridge circuit 10 and the output line LN5 of the half-bridge circuit 20 are connected to one terminal of a smoothing capacitor C0.

[0025] [Circuit Operation] The operation of the boost converter circuit 1 having the circuit configuration described above will be described below with reference to Fig. 2. Fig. 2 is a diagram showing an example of the operation of the boost converter circuit 1 according to the first embodiment.

[0026] In the half-bridge circuit 10, when the switching element S11 is in the ON state and the switching element S12 is in the OFF state, the output voltage of the voltage source V1 causes a current to flow through the path I1 shown in Fig. 2. That is, the current flows through the reactor L1, the diode D1, the boost capacitor C1, and the switching element S11. As a result, the boost capacitor C1 is charged with the voltage (Vin) of the voltage source V1.

[0027] In the half-bridge circuit 20, when the switching element S21 is in the ON state and the switching element S22 is in the OFF state, the output voltage of the voltage source V1 causes a current to flow through the path I3 shown in Fig. 2. That is, the current flows through the reactor L1, the diode D2, the boost capacitor C2, and the switching element S21. As a result, the boost capacitor C2 is charged with the voltage (Vin) of the voltage source V1.

[0028] Next, in the half-bridge circuit 10, when the switching element S11 is turned off and the switching element S12 is turned on, a current flows through the path I2 shown in Fig. 2. That is, the current flows through the path passing through the reactor L1, the switching element S12, the boost capacitor C1, the diode D3, and the smoothing capacitor C0. Then, in the half-bridge circuit 20, when the switching element S21 is turned off and the switching element S22 is turned on, a current flows through the path I4 shown in Fig. 2. That is, the current flows through the path passing through the reactor L1, the switching element S22, the boost capacitor C2, the diode D4, and the smoothing capacitor C0. In this way, a voltage (2×Vin) obtained by superimposing the voltage (Vin) of the boost capacitor C1 charged as described above onto the voltage (Vin) of the voltage source V1, and a voltage (2×Vin) obtained by superimposing the voltage (Vin) of the boost capacitor C2 charged as described above onto the voltage (Vin) of the voltage source V1 are applied in parallel to the smoothing capacitor C0, smoothed, and output to the load R1.

[0029] As described above, circuit 1 can double the input voltage from voltage source V1 (2×Vin) and output it. Furthermore, by providing reactor L1 in the upstream stage of the circuit, circuit 1 can suppress the occurrence of steep peak currents in the charging current of each capacitor through resonance between reactor L1 and the downstream boost capacitors C1 and C2 and smoothing capacitor C0. This also suppresses peak currents in each switching element, allowing the use of inexpensive semiconductor switch elements as the switching elements.

[0030] Additionally, in this circuit 1, the two-phase structure of the half-bridge circuits 10 and 20 and the phase control of the switching operation between the half-bridge circuits 10 and 20 reduce the ripple factor of the current flowing through the reactor L1, resulting in a successful miniaturization of the reactor L1. As will be described in detail in the Examples section, the inventors have discovered that the switching operation between the half-bridge circuits 10 and 20 in the operation of this circuit 1 can further reduce the ripple factor when the phase difference between the half-bridge circuits 10 and 20 is less than 180 degrees (particularly in the range of 90 degrees to 120 degrees).

[0031] Second Embodiment Fig. 3 is a circuit diagram of a boost converter circuit 2 according to a second embodiment. The boost converter circuit 2 according to the second embodiment (hereinafter, sometimes referred to as the present circuit) will be described below with reference to Fig. 3. In the following description, the configuration different from the first embodiment will be mainly described, and the description of the configuration similar to the first embodiment will be omitted as appropriate. The present circuit 2 is also configured to be connectable to a voltage source V1 and a load R1. However, the present circuit 2 can boost the DC voltage of the voltage source V1 to four times the voltage and supply it to the load R1.

[0032] [Circuit Configuration] In addition to the circuit configuration of the circuit 1 shown in FIG. 1, the circuit 2 further includes boost capacitors C11, C12, C13, and C14, and diodes D11, D12, D13, and D14.

[0033] The boost capacitors C11, C12, C13, and C14 are boost capacitors similar to the boost capacitors C1 and C2 described above, but to make the explanation easier to understand, they may be referred to as additional boost capacitors to distinguish them from the boost capacitors C1 and C2.

[0034] One terminal of the boost capacitor C11 is connected to the output line LN1 of the half-bridge circuit 10, and the other terminal is connected to a branch line LN6 extending from between the switching element pair (the pair of switching element S21 and switching element S22) of the half-bridge circuit 20. Therefore, the boost capacitor C11 corresponds to a first additional boost capacitor. One terminal of the boost capacitor C12 is connected to the output line LN5 of the half-bridge circuit 20, and the other terminal is connected to a branch line LN2 extending from between the switching element pair (the pair of switching element S11 and switching element S12) of the half-bridge circuit 10. Therefore, the boost capacitor C12 corresponds to a second additional boost capacitor.

[0035] One terminal of the boost capacitor C13 is connected to the output line LN1 of the half-bridge circuit 10, and the other terminal is connected to a branch line LN2 extending from between the switching element pair (the pair of switching element S11 and switching element S12) of the half-bridge circuit 10. Therefore, the boost capacitor C13 corresponds to a third additional boost capacitor. One terminal of the boost capacitor C14 is connected to the output line LN5 of the half-bridge circuit 20, and the other terminal is connected to a branch line LN6 extending from between the switching element pair (the pair of switching element S21 and switching element S22) of the half-bridge circuit 20. Therefore, the boost capacitor C14 corresponds to a fourth additional boost capacitor.

[0036] In this manner, in this circuit 2, the first additional boost capacitor (C11) and the third additional boost capacitor (C13) are alternately arranged in one stage toward the output side of the output line LN1 of the half-bridge circuit 10, and the second additional boost capacitor (C12) and the fourth additional boost capacitor (C14) are alternately arranged in one stage toward the output side of the output line LN5 of the half-bridge circuit 20.

[0037] The diodes D11, D12, D13, and D14 are rectifying diodes similar to the diodes D1, D2, D3, D4, etc. The diodes D11 and D13 are provided on the output line LN1 of the half-bridge circuit 10 with their cathodes facing the output side, and the diodes D12 and D14 are provided on the output line LN5 of the half-bridge circuit 20 with their cathodes facing the output side. Specifically, the diode D11 is provided between the boost capacitor C11 and the boost capacitor C13, the diode D12 is provided between the boost capacitor C12 and the boost capacitor C13, the diode D13 is provided between the node where the output line LN1 and the output line LN5 are connected and the boost capacitor C13, and the diode D14 is provided between the node where the output line LN1 and the output line LN5 are connected and the boost capacitor C14.

[0038] [Circuit Operation] The following describes the operation of the present circuit 2. First, in the present circuit 2, the boost capacitors C1 and C2 are charged with the voltage (Vin) of the voltage source V1 by the same circuit operation as in the first embodiment.

[0039] Thereafter, due to the phase control of the control circuit 15, the switching elements S11 and S22 are turned off, and at the timing when the switching elements S12 and S21 are turned on, a current flows through the path passing through the reactor L1, the switching element S12, the boost capacitor C1, the diode D3, the additional boost capacitor C11, and the switching element S21, and the additional boost capacitor C11 is charged with a voltage (2×Vin) obtained by superimposing the voltage (Vin) of the boost capacitor C1 on the voltage (Vin) of the voltage source V1. Furthermore, at the timing when switching elements S11 and S22 are turned on and switching elements S12 and S21 are turned off, a current flows through a path passing through reactor L1, switching element S22, boost capacitor C2, diode D4, additional boost capacitor C12, and switching element S11, and additional boost capacitor C12 is charged with a voltage (2×Vin) obtained by superimposing the voltage (Vin) of boost capacitor C2 on the voltage (Vin) of voltage source V1.

[0040] In subsequent cycles, when switching elements S11 and S22 are turned off and switching elements S12 and S21 are turned on, current flows through the path passing through reactor L1, switching element S12, additional boost capacitor C12, diode D12, additional boost capacitor C14, and switching element S21, and additional boost capacitor C14 is charged with a voltage (3×Vin) obtained by superimposing the voltage of boost capacitor C12 (2×Vin) on the voltage (Vin) of voltage source V1. Then, at the timing when switching elements S11 and S22 are turned on and switching elements S12 and S21 are turned off, current flows through a path passing through reactor L1, switching element S22, additional boost capacitor C11, diode D11, additional boost capacitor C13, and switching element S11, and additional boost capacitor C13 is charged with a voltage (3×Vin) obtained by superimposing the voltage of boost capacitor C11 (2×Vin) on the voltage (Vin) of voltage source V1.

[0041] In a subsequent period, when the switching elements S11 and S22 are turned off and the switching elements S12 and S21 are turned on, a current flows through the path passing through the reactor L1, the switching element S12, the additional boost capacitor C13, and the diode D13, and a voltage (4×Vin) obtained by superimposing the voltage (Vin) of the voltage source V1 and the voltage (3×Vin) of the boost capacitor C13 is applied to the smoothing capacitor C0. Also, when the switching elements S11 and S22 are turned on and the switching elements S12 and S21 are turned off, a current flows through the path passing through the reactor L1, the switching element S22, the additional boost capacitor C14, and the diode D14, and a voltage (4×Vin) obtained by superimposing the voltage (Vin) of the voltage source V1 and the voltage (3×Vin) of the boost capacitor C14 is applied to the smoothing capacitor C0. In this way, a voltage (4×Vin) that is four times the input voltage is input in parallel from the output line LN1 of the half-bridge circuit 10 and the output line LN5 of the half-bridge circuit 20, smoothed by the smoothing capacitor C0, and output to the load R1. In this way, according to the present circuit 2, a voltage that is four times the input voltage (4×Vin) is output.

[0042] Therefore, according to this circuit 2, it is possible to set the boost factor by adding multiple stages of combinations of capacitors and diodes. Furthermore, according to this circuit 2, not only can the input voltage be boosted four times, but also, by controlling the phase of the switching operation of each switching element pair, it is possible to reduce the ripple factor of the current flowing through the reactor L1, thereby making it possible to reduce the size of the reactor L1, as in the first embodiment.

[0043] [Modifications] The contents of each of the above-described embodiments can be modified as appropriate. The boost converter circuits 1 and 2 according to the first and second embodiments are not limited to the circuit configuration examples shown in the drawings.

[0044] As described above, Circuit 1 has a circuit configuration capable of boosting the input voltage by two times and outputting it, and Circuit 2 has a circuit configuration capable of boosting the input voltage by four times and outputting it, but using the same concept as Circuits 1 and 2, it is also possible to configure the circuit to output the input voltage at a desired boost multiple, such as three times, five times, six times, etc. For example, if the additional boost capacitors C13 and C14 are removed from the circuit configuration of Circuit 2 shown in Figure 3, it can be modified to a circuit that boosts the input voltage by three times and outputs it. In this case, diodes D13 and D14 can also be removed.

[0045] Furthermore, by alternately providing first and third additional boost capacitors in two or more stages toward the output side of the output line LN1 of the half-bridge circuit 10, and alternately providing second and fourth additional boost capacitors in two or more stages toward the output side of the output line LN5 of the half-bridge circuit 20, and by providing an equal number of first, second, third and fourth additional boost capacitors, it is possible to boost the input voltage to an even multiple, such as six times (two stages), eight times (three stages), or ten times (four stages).

[0046] In this case, when the first additional boost capacitor in the nth (n is 1 or more) stage is discharged, the voltage of the first additional boost capacitor in the nth stage is superimposed on the voltage of the voltage source, charging the third additional boost capacitor in the nth stage; when the second additional boost capacitor in the nth stage is discharged, the voltage of the second additional boost capacitor in the nth stage is superimposed on the voltage of the voltage source, charging the fourth additional boost capacitor in the nth stage; and when the third additional boost capacitor in the nth stage is discharged, the voltage of the third additional boost capacitor in the nth stage is superimposed on the voltage of the voltage source, charging the first additional boost capacitor in the (n+1)th stage. When the n-th stage fourth additional boost capacitor is discharged, the voltage of the n-th stage fourth additional boost capacitor is superimposed on the voltage of the voltage source to charge the n+1-th stage second additional boost capacitor, when the final stage third additional boost capacitor is discharged, the voltage of the final stage third additional boost capacitor is superimposed on the voltage of the voltage source to be output from the output line LN1 of the half-bridge circuit 10, when the final stage fourth additional boost capacitor is discharged, the voltage of the final stage fourth additional boost capacitor is superimposed on the voltage of the voltage source to be output from the output line LN5 of the half-bridge circuit 20. Furthermore, by providing the same number of first additional boost capacitors and second additional boost capacitors, and by configuring the circuit so that the same number of third additional boost capacitors and fourth additional boost capacitors are provided, but one stage less than the first additional boost capacitors and second additional boost capacitors, it is possible to output a boosted voltage that is an odd number, such as 5 times (two stages and one stage), 7 times (three stages and two stages), or 9 times (four stages and three stages).

[0047] Furthermore, the boost converter circuits according to the above-described embodiments and modifications can be modified into a step-up / step-down bidirectional converter circuit by replacing some of the circuit components. Fig. 4 is a circuit diagram of a bidirectional converter circuit 1 as a modification. Fig. 4 illustrates a bidirectional converter circuit 1 that is a modification of the boost converter circuit 1 shown in Fig. 1. That is, in the bidirectional converter circuit 1, the rectifying diodes D1, D2, D3, and D4 are replaced with reverse-conducting switching elements RS1, RS2, RS3, and RS4, and both ends are turned into terminals (terminals TM1, TM2, TM3, and TM4).

[0048] The reverse-conducting switching elements RS1, RS2, RS3, and RS4 may be, for example, insulated gate bipolar transistors (RC-IGBTs) with built-in reverse-conducting diodes. The reverse-conducting switching elements may be configured in any manner as long as they can switch their conduction direction using a control voltage or the like. Terminals TM1 and TM2 correspond to first terminals that can connect a voltage source V1 and a reactor L1, and terminals TM3 and TM4 correspond to second terminals that can output a voltage smoothed by a smoothing capacitor C0.

[0049] The bidirectional converter circuit 1 further includes a control circuit capable of controlling the conduction direction of the reverse-conducting switching elements RS1, RS2, RS3, and RS4. This control circuit may be realized by the switching control circuit 15 described above, or may be realized as a circuit separate from the switching control circuit 15. When this control circuit is realized by the switching control circuit 15, the control circuit 15 controls the conduction direction of the reverse-conducting switching elements RS1, RS2, RS3, and RS4 in addition to controlling the switching operation of the half-bridge circuits 10 and 20 described above, thereby enabling switching of the direction of power input and output (direction of current) within the circuit. Specifically, as in the above-described embodiments and modifications, when the terminals TM1 and TM2 are the power input side and the terminals TM3 and TM4 are the power output side, the bidirectional converter circuit 1 operates as a boost converter circuit and can be described as operating in boost mode. On the other hand, when the terminals TM1 and TM2 are on the power output side and the terminals TM3 and TM4 are on the power input side, the bidirectional converter circuit 1 operates as a step-down converter circuit and can be described as operating in step-down mode. In this way, by controlling the conduction directions of the reverse-conducting switching elements RS1, RS2, RS3, and RS4, the operation mode of the bidirectional converter circuit 1 can be switched between step-up mode and step-down mode.

[0050] As an application example of the bidirectional converter circuit 1, when a charging station for an electric vehicle such as an electric aircraft or electric vehicle, or a home power source is connected to terminals TM1 and TM2 via an AC-DC converter or the like, and a storage battery installed in the electric vehicle is connected to terminals TM3 and TM4, the control circuit 15 controls the reverse-conducting switching element so that the circuit operates in step-up mode. This allows the bidirectional converter circuit 1 to operate as a step-up converter circuit as described above, boosting the power input from terminals TM1 and TM2 and supplying it to the storage battery connected to terminals TM3 and TM4. Furthermore, when an electronic device in the electric vehicle is connected to terminals TM1 and TM2 and the storage battery is connected to terminals TM3 and TM4, the control circuit 15 controls the reverse-conducting switching element so that the circuit operates in step-down mode. As a result, the bidirectional converter circuit 1 operates as a step-down converter circuit by allowing current to flow in the opposite direction to that in the above-described embodiments and modifications, and can step down the power input from the terminals TM3 and TM4 and supply it to an electronic device connected to the terminals TM1 and TM2.

[0051] The bidirectional converter circuit 1 as such a modification can operate as a bidirectional converter circuit for step-up and step-down by controlling the direction of input and output of power in the boost converter circuits according to the above-described embodiments and modifications. Note that a bidirectional converter circuit as a modification can be realized not only by modifying the boost converter circuit 1 shown in Fig. 1 but also by modifying the boost converter circuit 2 shown in Fig. 3 in the same way.

[0052] The above content will be explained in more detail below with reference to examples, but the following examples do not limit the above content in any way.

[0053] Example 1 shows the results of verifying the effects of the first embodiment described above. Example 1 shows the results of simulating the boost converter circuit (present circuit) 1 of the first embodiment shown in FIG. 1 using SPICE simulator software (LTspice (registered trademark)).

[0054] In this simulation, circuit 1 was configured to receive an input voltage of 100 V from voltage source V1 and output a boosted voltage to load R1 with a resistance of 5 Ω, with the capacitances of boost capacitors C1 and C2 set to 500 μF, the capacitance of smoothing capacitor C0 set to 1000 μF, and the inductance of reactor L1 set to 1 μH. Regarding the switching control of control circuit 15, the frequency was set to 30 kHz, the on-duty was set to 49.5%, and the phase difference of the switching operation between half-bridge circuit 10 and half-bridge circuit 20 was set to 111.6°.

[0055] The simulation results are as follows: Output voltage: 197.51 (V) Output current: 39.502 (A) Output power: 7.802 (kW) Input current: 79.029 (A) Input power: 7.903 (kW) Ripple current of reactor L1: 2.463 (App) Ripple factor: 3.1% Output efficiency: 98.7%

[0056] 5 is a graph showing the simulation results of Example 1. In the graph of FIG. 5, symbol L1 indicates the waveform of the ripple current of reactor L1, symbol S11 indicates the voltage applied to switching element S11, and symbol S21 indicates the voltage applied to switching element S21. When the voltage of symbol S11 is HIGH (approximately 20 V), switching element S11 is in the ON state. When the voltage of symbol S11 is LO (approximately 0 V), switching element S11 is in the OFF state. When the voltage of symbol S21 is HIGH (approximately 20 V), switching element S21 is in the ON state. When the voltage of symbol S21 is LO (approximately 0 V), switching element S21 is in the OFF state. As shown in FIG. 5, due to the phase control (phase difference: 111.6°) of control circuit 15, there is a timing when both switching elements S11 and S21 are in the HI state.

[0057] The ripple current (2.463 App) mentioned above indicates the average value of the difference between the peak current value and the valley current value in the ripple current waveform (L1) shown in Figure 5, the ripple factor (3.1%) indicates the ratio of the ripple current (2.463 App) to the input current (79.029 A), and the output efficiency (98.7%) indicates the ratio of the output power (7.802 kW) to the input power (7.903 kW).

[0058] The simulation results demonstrate that Circuit 1 can boost the input voltage (100 V) to approximately double (197.51 V) and output it, while also reducing the ripple factor (3.1%) of the reactor current, even with a small reactor L1 (1 μF). The ripple factor of existing boost converters (boost choppers) that handle relatively large input power, such as an input voltage (100 V) and an input current (79.029 A), typically exceeds 20%, even when using a large reactor (a reactor with an inductance of several tens of μF, more than five times that of Circuit 1). Therefore, Circuit 1 significantly reduces the ripple factor (3.1%) even when using a small reactor. Because a large ripple factor directly translates into large losses in the reactor L1, reducing the ripple factor, as in Circuit 1, achieves high output efficiency (98.7%). To achieve such a reduction in the ripple factor, instead of performing switching operations in opposite phases between the half-bridge circuits 10 and 20 (phase difference of 180 degrees), the duty ratio of the switching operations is set to 50% or less, and the phase difference (111.6°) is set so as to include the timing within one period when the on / off states of the low-potential side switching element S11 of the half-bridge circuit 10 and the high-potential side switching element S22 of the half-bridge circuit 20 are different, and the on / off states of the high-potential side switching element S12 of the half-bridge circuit 10 and the low-potential side switching element S21 of the half-bridge circuit 20 are different.

[0059] 5, it can be seen that the peak current can be suppressed by converting the capacitor charging current into a pseudo-sine wave using the LCR filter characteristics (reactor L1, boost capacitor, etc.) of this circuit 1. Furthermore, because this effect can be achieved at a relatively low switching frequency of 30 kHz, an inexpensive magnetic material can be used for reactor L1.

[0060] In Example 1, further simulations were performed under the same simulation conditions as above, but with the resistance value of the load R1 changed from the set value (5Ω) to 1Ω, 10Ω, 50Ω, and 200Ω, and the simulation results are shown below.

[0061] According to Table 1, it has been demonstrated that, by adjusting the phase difference of the switching operation, this circuit 1 can boost the input voltage by approximately two times and output it while reducing the ripple factor, even when the load resistance is changed to 1 Ω, 5 Ω, 10 Ω, 50 Ω, or 200 Ω. Furthermore, a small reactor L1 is used. Thus, this circuit 1 can adapt to load fluctuations while keeping the ripple factor low, even with a small reactor L1, through the phase control of the control circuit 15.

[0062] Example 2 shows the results of a simulation of a boost converter circuit according to a reference example (hereinafter, sometimes referred to as the present reference circuit) 3 using the same simulator software as in Example 1. Fig. 6 is a circuit diagram of the boost converter circuit according to the reference example (the present reference circuit) 3. As shown in Fig. 6, the present reference circuit 3 has a circuit configuration in which the half-bridge circuit 20, the boost capacitor C2, the diode D2, and the diode D4 are deleted from the circuit configuration of the present circuit 1.

[0063] In the simulation of Example 2, the reference circuit 3 was configured to receive an input voltage of 100 V from a voltage source V1 and output a boosted voltage to a load R1 having a resistance of 5 Ω, with the capacitance of the boost capacitor C1 set to 70 μF, the capacitance of the smoothing capacitor C0 set to 100,000 μF, and the inductance of the reactor L1 set to 2 μH. Furthermore, with regard to the switching control of the control circuit 15, the frequency was set to 30 kHz, and the on-duty was set to 49.5%.

[0064] The simulation results are as follows: Output voltage: 196.11 (V) Output current: 39.222 (A) Output power: 7.692 (kW) Input current: 78.198 (A) Input power: 7.820 (kW) Ripple current of reactor L1: 23.57 (App) Ripple factor: 30.1% Output efficiency: 98.4%

[0065] As described above, in Example 2, it is possible to boost the input voltage by approximately double and output it, as in Example 1, and the input power and output power also show approximately the same numerical values ​​as in Example 1, but the ripple factor of the reactor current (30.1%) is higher (approximately 10 times) than in Example 1. One factor behind this is thought to be that, unlike Circuit 1, Reference Circuit 3 has only one phase of the half-bridge circuit and operates in a single phase, and it can be said that a reduction in the ripple factor is achieved by the multi-phase configuration of the half-bridge circuit of Circuit 1 and the phase control of the control circuit 15.

[0066] Example 3 shows the results of verifying the effects of the second embodiment described above. Example 3 shows the results of simulating the boost converter circuit (present circuit) 2 of the second embodiment shown in FIG. 3 using the same simulator software as in Example 1.

[0067] The simulation conditions for Example 3 were as follows: the capacitances of the boost capacitors C1 and C2 and the additional boost capacitors C11, C12, C13, and C14 were set to 500 μF, the capacitance of the smoothing capacitor C0 was set to 1000 μF, and the inductance of the reactor L1 was set to 1 μH. Furthermore, the frequency of the switching control of the control circuit 15 was set to 30 kHz, and the on-duty was set to 49.5%.

[0068] The simulation results are as follows:

[0069] The simulation results demonstrate that the present circuit 2 can boost the input voltage (100 V) by approximately four times (371.35 V, 395.93 V) and output it. It also demonstrates that even with such high output voltages, the ripple factor of the reactor current (3.0%, 2.6%) can be reduced using a small reactor L1. Furthermore, it has been demonstrated that the present circuit 2, which enables boosted output by connecting capacitors and diodes in multiple stages, can boost the input voltage by approximately four times and output it while reducing the ripple factor, even when the load resistance is changed to 1 Ω or 50 Ω, by adjusting the phase difference of the switching operation (180°, 154.9°). The reactor L1 can also remain small. In this way, the present circuit 2, which achieves boosted output by connecting capacitors and diodes in multiple stages, can adapt to load fluctuations while keeping the ripple factor low, even with a small reactor L1, through phase control by the control circuit 15.

[0070] The demonstration results of each of the above examples show that the boost converter circuits 1 and 2 in the above-described embodiments enable miniaturization of the boost reactor even in high-power applications. As a result, the boost converter circuits 1 and 2 in the above-described embodiments and modifications, and the bidirectional converter circuit 1 as a modification, can be said to be suitable for boost converter circuits or bidirectional converter circuits in power conversion mechanisms provided in electric transports such as electric aircraft, electric vehicles, etc.

[0071] The above content can also be specified as follows: However, the above content is not limited to the following description.

[0072] <1> A boost converter circuit comprising: a reactor that can be connected in series to a DC voltage source; a first half-bridge circuit connected in parallel to the reactor; a first boost capacitor whose charging and discharging are switched by a switching operation of the first half-bridge circuit; a second half-bridge circuit connected in parallel to the reactor on an output side of the first half-bridge circuit; a second boost capacitor whose charging and discharging are switched by a switching operation of the second half-bridge circuit; a smoothing capacitor to which outputs from the first half-bridge circuit and the second half-bridge circuit are input in parallel, and which smoothes the output voltage; and a switching control circuit which performs phase control of the switching operation between the first half-bridge circuit and the second half-bridge circuit, wherein the voltage of the first boost capacitor is superimposed on the voltage of the voltage source by discharging the first boost capacitor and the voltage of the second boost capacitor is superimposed on the voltage of the voltage source by discharging the second boost capacitor and the voltage is output from the second half-bridge circuit. <2> The boost converter circuit according to <1>, wherein the switching control circuit adjusts a phase difference of the switching operation between the first half-bridge circuit and the second half-bridge circuit in accordance with an impedance fluctuation on a load side to which an output from the boost converter circuit is supplied.<3> The power supply further comprises: a first additional boost capacitor having one terminal connected to the output line of the first half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the second half-bridge circuit; and a second additional boost capacitor having one terminal connected to the output line of the second half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the first half-bridge circuit, wherein the first boost capacitor has one terminal connected to the output line of the first half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the first half-bridge circuit; and the second boost capacitor has one terminal connected to the output line of the second half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the second half-bridge circuit, <1> or <2>, wherein the first additional boost capacitor is discharged so that the voltage of the first boost capacitor is superimposed on the voltage of the voltage source, thereby charging the first additional boost capacitor; the second additional boost capacitor is discharged so that the voltage of the second boost capacitor is superimposed on the voltage of the voltage source, thereby charging the second additional boost capacitor; the first additional boost capacitor is discharged so that the voltage of the first additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from an output line of the first half-bridge circuit; and the second additional boost capacitor is discharged so that the voltage of the second additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from an output line of the second half-bridge circuit.<4> The boost converter circuit according to <3>, further comprising: a third additional boost capacitor having one terminal connected to the output line of the first half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the first half-bridge circuit; and a fourth additional boost capacitor having one terminal connected to the output line of the second half-bridge circuit and the other terminal connected to a branch line extending from between the switching element pairs of the second half-bridge circuit, wherein the first additional boost capacitor is discharged so that the voltage of the first boost capacitor is superimposed on the voltage of the voltage source to charge the third additional boost capacitor, the second boost capacitor is discharged so that the voltage of the second boost capacitor is superimposed on the voltage of the voltage source to charge the fourth additional boost capacitor, the third additional boost capacitor is discharged so that the voltage of the third additional boost capacitor is superimposed on the voltage of the voltage source to output the voltage from the output line of the first half-bridge circuit, and the fourth additional boost capacitor is discharged so that the voltage of the fourth additional boost capacitor is superimposed on the voltage of the voltage source to output the voltage from the output line of the second half-bridge circuit.<5> The first additional boost capacitor and the third additional boost capacitor are alternately provided in two or more stages toward the output side of the output line of the first half-bridge circuit, the second additional boost capacitor and the fourth additional boost capacitor are alternately provided in two or more stages toward the output side of the output line of the second half-bridge circuit, and the first additional boost capacitor, the second additional boost capacitor, the third additional boost capacitor and the fourth additional boost capacitor are provided in equal numbers, When the first additional boost capacitor of the nth stage (n is 1 or more) is discharged, the voltage of the first additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the third additional boost capacitor of the nth stage; when the second additional boost capacitor of the nth stage is discharged, the voltage of the second additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the fourth additional boost capacitor of the nth stage; when the third additional boost capacitor of the nth stage is discharged, the voltage of the third additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the first additional boost capacitor of the (n+1)th stage. 5. The boost converter circuit according to claim 4, wherein, upon discharging of the fourth additional boost capacitor of the nth stage, the voltage of the fourth additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source to charge the second additional boost capacitor of the (n+1)th stage; upon discharging of the third additional boost capacitor of the final stage, the voltage of the third additional boost capacitor of the final stage is superimposed on the voltage of the voltage source to be output from the output line of the first half-bridge circuit; and upon discharging of the fourth additional boost capacitor of the final stage, the voltage of the fourth additional boost capacitor of the final stage is superimposed on the voltage of the voltage source to be output from the output line of the second half-bridge circuit.<6> A bidirectional converter circuit comprising: the boost converter circuit according to any one of <1> to <5>, a first terminal connectable to the voltage source and the reactor, a second terminal capable of outputting the voltage smoothed by the smoothing capacitor, a plurality of reverse-conducting switching elements including a reverse-conducting switching element provided respectively on an output line of the first half-bridge circuit and an output line of the second half-bridge circuit, and a control circuit capable of switching the input and output of power of the boost converter circuit in reverse directions by controlling the conduction directions of the plurality of reverse-conducting switching elements, thereby causing the boost converter circuit to also operate as a step-down converter circuit. <7> An electric transport equipped with a power conversion mechanism including the boost converter circuit according to any one of <1> to <6> or the bidirectional converter circuit according to <6>.

[0073] 1 Boost converter circuit (main circuit) 2 Boost converter circuit (main circuit) 3 Boost converter circuit (reference circuit) 10 Half-bridge circuit 20 Half-bridge circuit 15 Switching control circuit (control circuit) V1 Voltage source L1 Reactor S11, S12, S21, S22 Switching elements C1, C2, C11, C12, C13, C14 Boost capacitor C0 Smoothing capacitor D1, D2, D3, D4, D11, D12, D13, D14 Diodes LN1, LN5 Output line LN2, LN6 Branch line R1 Load RS1, RS2, RS3, RS4 Reverse-conducting switching element

Claims

a reactor that can be connected in series with a DC voltage source; a first half-bridge circuit connected in parallel to the reactor; a first boost capacitor whose charging and discharging are switched by a switching operation of the first half-bridge circuit; a second half-bridge circuit connected in parallel to the reactor on an output side of the first half-bridge circuit; a second boost capacitor whose charging and discharging are switched by a switching operation of the second half-bridge circuit; an output from the first half-bridge circuit and an output from the second half-bridge circuit input in parallel to a smoothing capacitor that smoothes the output voltage; a switching control circuit that performs phase control of a switching operation between the first half-bridge circuit and the second half-bridge circuit; Equipped with When the first boost capacitor is discharged, the voltage of the first boost capacitor is superimposed on the voltage of the voltage source and output from the first half-bridge circuit, and when the second boost capacitor is discharged, the voltage of the second boost capacitor is superimposed on the voltage of the voltage source and output from the second half-bridge circuit. Boost converter circuit. 　 the switching control circuit adjusts a phase difference of a switching operation between the first half-bridge circuit and the second half-bridge circuit in accordance with a fluctuation in impedance on a load side to which an output from the boost converter circuit is supplied.

2. The boost converter circuit of claim 1. 　 a first additional boost capacitor having one terminal connected to an output line of the first half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the second half-bridge circuit; a second additional boost capacitor having one terminal connected to the output line of the second half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the first half-bridge circuit; Further provided with the first boost capacitor has one terminal connected to an output line of the first half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the first half-bridge circuit; the second boost capacitor has one terminal connected to an output line of the second half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the second half-bridge circuit; When the first boost capacitor is discharged, the voltage of the first boost capacitor is superimposed on the voltage of the voltage source, thereby charging the first additional boost capacitor; when the second boost capacitor is discharged, the voltage of the second boost capacitor is superimposed on the voltage of the voltage source, thereby charging the second additional boost capacitor; when the first additional boost capacitor is discharged, the voltage of the first additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the first half-bridge circuit; when the second additional boost capacitor is discharged, the voltage of the second additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the second half-bridge circuit.

2. The boost converter circuit of claim 1. 　 a third additional boost capacitor having one terminal connected to an output line of the first half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the first half-bridge circuit; a fourth additional boost capacitor having one terminal connected to the output line of the second half-bridge circuit and the other terminal connected to a branch line extending between the switching element pairs of the second half-bridge circuit; Further provided with When the first boost capacitor is discharged, the voltage of the first boost capacitor is superimposed on the voltage of the voltage source, thereby charging the third additional boost capacitor; when the second boost capacitor is discharged, the voltage of the second boost capacitor is superimposed on the voltage of the voltage source, thereby charging the fourth additional boost capacitor; when the third additional boost capacitor is discharged, the voltage of the third additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the first half-bridge circuit; when the fourth additional boost capacitor is discharged, the voltage of the fourth additional boost capacitor is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the second half-bridge circuit.

4. The boost converter circuit of claim 3. 　 the first additional boost capacitor and the third additional boost capacitor are alternately provided in two or more stages toward the output side of the output line of the first half-bridge circuit, the second additional boost capacitor and the fourth additional boost capacitor are alternately provided in two or more stages toward the output side of the output line of the second half-bridge circuit, the first additional boost capacitor, the second additional boost capacitor, the third additional boost capacitor, and the fourth additional boost capacitor are provided in equal numbers, When the first additional boost capacitor of the nth stage (n is 1 or more) is discharged, the voltage of the first additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the third additional boost capacitor of the nth stage; when the second additional boost capacitor of the nth stage is discharged, the voltage of the second additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the fourth additional boost capacitor of the nth stage; when the third additional boost capacitor of the nth stage is discharged, the voltage of the third additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the first additional boost capacitor of the (n+1)th stage. When the fourth additional boost capacitor of the nth stage is discharged, the voltage of the fourth additional boost capacitor of the nth stage is superimposed on the voltage of the voltage source, thereby charging the second additional boost capacitor of the (n+1)th stage; when the third additional boost capacitor of the final stage is discharged, the voltage of the third additional boost capacitor of the final stage is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the first half-bridge circuit; when the fourth additional boost capacitor of the final stage is discharged, the voltage of the fourth additional boost capacitor of the final stage is superimposed on the voltage of the voltage source, thereby outputting the voltage from the output line of the second half-bridge circuit.

5. The boost converter circuit of claim 4. 　 a boost converter circuit according to claim 1; a first terminal capable of connecting the voltage source and the reactor; a second terminal capable of outputting a voltage smoothed by the smoothing capacitor; a plurality of reverse-conducting switching elements including a reverse-conducting switching element respectively provided on an output line of the first half-bridge circuit and an output line of the second half-bridge circuit; a control circuit that controls the conduction directions of the plurality of reverse-conducting switching elements to reversely switch the input and output of power to the boost converter circuit, thereby causing the boost converter circuit to also operate as a buck converter circuit; A bidirectional converter circuit comprising: 　 An electric transport equipped with a power conversion mechanism including the boost converter circuit according to any one of claims 1 to 5 or the bidirectional converter circuit according to claim 6.

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