Power Conversion Equipment

Abstract

To control a voltage conversion device having a coupling reactor more stably.SOLUTION: A power conversion device (10) converts an input voltage (Vin) into a predetermined output voltage (Vout). The power conversion device (10) includes a coupling reactor (1) having a first reactor (L1) and a second reactor (L2) which are magnetically coupled to each other, a first switching element (Tr1), a second switching element (Tr2), a first capacitor (C1), a second capacitor (C2), and a controller (15). The controller (15) increases the switching frequencies of the first switching element (Tr1) and the second switching element (Tr2) under light load.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Conventionally, some DC-DC converters have an interleaved circuit configuration in which converter circuits are parallelized in order to achieve high power. In order to miniaturize this interleaved circuit configuration, it has been proposed to use a coupling reactor in which the reactors of each phase are magnetically coupled.

[0003] For example, Patent Document 1 discloses a converter including a first reactor of a first phase and a second reactor of a second phase that are coupled to each other. A first high-side switch and a first low-side switch are connected to the first reactor. A second high-side switch and a second low-side switch are connected to the second reactor. In this converter, the conduction of the body diode of the second low-side switch is controlled in response to the on-state of the first high-side switch depending on the strength of the coupling between the first reactor and the second reactor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Pat. No. 10,326,369 Summary of the Invention [Problem to be solved by the invention]

[0005] In a step-up DC-DC converter equipped with a coupling reactor, when the converter is driven in discontinuous current mode (DCM) under a light load where the on-duty ratio of the switching pulse applied to the switching element is less than 50%, a reverse current is generated in the coupling reactor. This can cause a dead zone phenomenon where the output voltage does not follow changes in the on-duty ratio. When this dead zone phenomenon occurs, the control of the power conversion device becomes unstable, and there is a risk of the output voltage oscillating.

[0006] An object of one aspect of the present invention is to provide a more stable control of a voltage conversion device including a coupling reactor. [Means for solving the problem]

[0007] In order to solve the above problems, a voltage conversion device according to one embodiment of the present invention is a power conversion device that converts an input voltage into a predetermined output voltage, and includes a coupled reactor having a first reactor and a second reactor that are magnetically coupled to each other, a first switching element connected to the output side of the first reactor, a second switching element connected to the output side of the second reactor, and a control unit that controls the driving of the first switching element and the second switching element, wherein the control unit increases the switching frequency of the first switching element and the second switching element under light load.

[0008] The current flowing through either the first reactor or the second reactor at the boundary between the discontinuous current mode and the continuous current mode depends on the inverse of the switching frequency. As a result, the value of the above current decreases by increasing the switching frequency. Therefore, the boundary where the discontinuous current mode and the continuous current mode switch is shifted toward the continuous current mode. Therefore, the range of the discontinuous current mode can be narrowed and the range of the continuous current mode can be widened. Therefore, the dead zone that occurs when the power conversion device is operating in the discontinuous current mode under light load can be narrowed.

[0009] In the power conversion device according to aspect 2 of the present invention, the control unit changes the on-duty ratio of a control signal that switches the first switching element and the second switching element in accordance with the magnitude of the load, and increases the switching frequency when the on-duty ratio is less than 50%.

[0010] According to the above configuration, it is possible to determine whether to increase the switching frequency depending on whether the on-duty ratio is less than 50%, which makes it possible to easily control switching between the discontinuous current mode and the continuous current mode.

[0011] In a power conversion device according to a third aspect of the present invention, the power conversion device operates in a discontinuous current mode and a continuous current mode, and a current Icrm flowing through either the first reactor or the second reactor at a boundary between the discontinuous current mode and the continuous current mode is expressed as follows: SW The self-reactance of the first reactor and the second reactor is L, and the coupling coefficient of the coupling reactor is k. Then, Icrm = AVi{1-A(1+k)} / 2Lf SW (1-A)(1-k 2 ) It is expressed by:

[0012] According to the above configuration, switching between the discontinuous current mode and the continuous current mode can be easily controlled by utilizing the switching frequency dependency of the current Icrm.

[0013] The power conversion device according to a fourth aspect of the present invention further includes a first capacitor connected to the input side of the coupling reactor, and a second capacitor connected to the output side of the coupling reactor.

[0014] According to the above configuration, the ripple current can be removed by the first capacitor, and the energy stored in the coupling reactor is supplied to the second capacitor and then released, thereby increasing the output of the power conversion device.

[0015] The power conversion device according to a fifth aspect of the present invention further includes a first diode connected to an output side of the first switching element, and a second diode connected to an output side of the second switching element.

[0016] According to the above configuration, by connecting a first diode to the output side of the first switching element and connecting a second diode to the output side of the second switching element, it is possible to prevent a current from flowing back from the first capacitor to the coupling reactor.

[0017] In a power conversion device according to aspect 6 of the present invention, the first switching element and the second switching element are vertical MOS field effect transistors, the drain of the first switching element is connected to the anode of the first diode, and the drain of the second switching element is connected to the anode of the second diode.

[0018] According to the above configuration, by using vertical MOS field effect transistors as the switching elements, it is possible to increase the breakdown voltage and perform high-speed switching.

[0019] A power conversion device according to aspect 7 of the present invention further includes a third switching element connected to the output side of the first switching element and a fourth switching element connected to the output side of the second switching element, and the control unit controls the driving of the third switching element and the fourth switching element so that the third switching element is turned off when the first switching element is turned on, the third switching element is turned on when the first switching element is turned off, the fourth switching element is turned off when the second switching element is on, and the fourth switching element is turned on when the second switching element is off.

[0020] According to the above configuration, by connecting the third switching element to the output side of the first switching element and connecting the fourth switching element to the output side of the second switching element, it is possible to prevent a current from flowing back from the first capacitor to the coupling reactor. In addition, since a synchronous rectification circuit configuration is formed, it is possible to improve the conversion efficiency compared to the power conversion device according to the fifth aspect. Effect of the Invention

[0021] According to one aspect of the present invention, it is possible to more stably control a voltage conversion device including a coupling reactor. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram showing a schematic configuration of a power supply device including a power conversion device according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram showing current paths of each phase in a current continuous mode in the power conversion device. [Diagram 3] 4 is a graph showing a relationship between a time change in an on-duty ratio of a first switching element and a second switching element and a time change in an output voltage in the power conversion device. [Figure 4] 4 is a diagram showing a state in which a reverse current flows through a coupling reactor in the power conversion device. FIG. [Diagram 5]4 is a diagram corresponding to FIG. 3 when a dead zone occurs in a coupling reactor of the power conversion device. FIG. [Figure 6] FIG. 11 is a waveform diagram showing waveforms of currents flowing through a first reactor and a second reactor constituting a coupling reactor when the on-duty ratio is less than 50%. [Figure 7] FIG. 4 is a diagram showing a relationship between a switching period and a current flowing through the first reactor and the second reactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] [Embodiment] Hereinafter, a power supply device 100 including a power conversion device 10 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.

[0024] <Outline of power supply unit configuration> Fig. 1 is a diagram showing a schematic configuration of a power supply device 100 including a power conversion device 10. As shown in Fig. 1, the power supply device 100 includes a power source E and the power conversion device 10. The power supply device 100 is mounted on a vehicle such as an electric vehicle or a hybrid vehicle, and is connected to a motor 30.

[0025] The power conversion device 10 is a device that converts a direct current input voltage Vin supplied from a power source E into a predetermined output voltage Vout. The power conversion device 10 is, for example, a DC-DC converter such as a boost converter. The power source E is, for example, a high-voltage power source of about 200 [V]. The power conversion device 10 is connected to an inverter 20 and supplies an output voltage Vout to the inverter 20. Note that the power conversion device 10 is not limited to a DC-DC converter, and may also be used in a power factor correction (PFC) circuit.

[0026] An inverter 20 is connected to the power supply device 100. A three-phase AC motor 30 is connected to the inverter 20. The inverter 20 converts the output voltage Vout supplied from the power conversion device 10 into a three-phase AC voltage and outputs it to the motor 30. The motor 30 functions as a drive source for driving the vehicle.

[0027] [Power conversion device configuration] As shown in FIG. 1, the power conversion device 10 includes a coupling reactor 1, a first switching element Tr1, a second switching element Tr2, a first diode D1, a second diode D2, a first capacitor C1, a second capacitor C2, and a control unit 15.

[0028] An input terminal Pin of the power conversion device 10 is connected to the positive electrode of a power source E. Meanwhile, an input terminal Nin of the power conversion device 10 is connected to the negative electrode of the power source E. Also, an output terminal Pout of the power conversion device 10 is connected to an input terminal 21 on the positive electrode side of an inverter 20. Meanwhile, an output terminal Nout of the power conversion device 10 is connected to an input terminal 22 on the negative electrode side of the inverter 20. The power conversion device 10 boosts an input voltage Vin input from the power source E to a predetermined output voltage Vout.

[0029] The coupling reactor 1 includes a first reactor L1 having a coil wound around a core 11, and a second reactor L2 having a coil wound around the core 11. The first reactor L1 and the second reactor L2 of the coupling reactor 1 are magnetically coupled to each other. The first reactor L1 and the second reactor L2 are differential coupling reactors wound in different directions. This makes it possible to cancel out the DC magnetic flux of each phase generated in the core 11, and improve the margin for magnetic saturation. Therefore, the size of the core 11 can be reduced while suppressing magnetic saturation.

[0030] An input side terminal T11 of the first reactor L1 is connected to the positive electrode of a power source E. An input side terminal T21 of the second reactor L2 is connected to the positive electrode of the power source E. A first switching element Tr1 and a first diode D1 are connected to an output side terminal T12 of the first reactor L1. A second switching element Tr2 and a second diode D2 are connected to an output side terminal T22 of the second reactor L2.

[0031] The first switching element Tr1 and the second switching element Tr2 are, for example, power MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors). The on and off operations of the first switching element Tr1 and the second switching element Tr2 are controlled by the control unit 15. Note that the first switching element Tr1 and the second switching element Tr2 are not limited to power MOSFETs, and may also be IGBTs (Insulated Gate Bipolar Transistors).

[0032] A first body diode Db1 is formed between the source s1 and drain d1 of the first switching element Tr1. The first body diode Db1 is a parasitic diode of the first switching element Tr1. When the first switching element Tr1 is on, a current flows through a channel portion having a smaller resistance than the first body diode Db1. On the other hand, when the first switching element Tr1 is off, a current flows through the first body diode Db1.

[0033] A second body diode Db2 is formed between the source s2 and drain d2 of the second switching element Tr2. The second body diode Db2 is a parasitic diode of the second switching element Tr2. When the second switching element Tr2 is on, a current flows through a channel portion having a smaller resistance than the second body diode Db2. On the other hand, when the second switching element Tr2 is off, a current flows through the second body diode Db2.

[0034] The drain d1 of the first switching element Tr1 is connected to the terminal T12 on the output side of the first reactor L1 and the anode of the first diode D1. The source s1 of the first switching element Tr1 is connected to the input terminal Nin and the output terminal Nout. The gate g1 of the first switching element Tr1 is connected to the control unit 15.

[0035] The drain d2 of the second switching element Tr2 is connected to the terminal T22 on the output side of the second reactor L2 and the anode of the second diode D2. The source s2 of the second switching element Tr2 is connected to the input terminal Nin and the output terminal Nout. The gate g2 of the second switching element Tr2 is connected to the control unit 15.

[0036] One end P1 of the first capacitor C1 is connected between the input terminal Pin and the terminal T11 on the input side of the first reactor L1. The other end N1 of the first capacitor C1 is connected between the input terminal Nin and the output terminal Nout. The first capacitor C1 is a smoothing capacitor, and reduces ripples contained in the input voltage Vin supplied from the power source E to the power conversion device 10.

[0037] One end P2 of the second capacitor C2 is connected to the positive terminal 21 of the inverter 20 via the output terminal Pout. The other end N2 of the second capacitor C2 is connected to the negative terminal 22 of the inverter 20 via the output terminal Nout.

[0038] 1, the control unit 15 controls the on and off operation of the first switching element Tr1 by outputting a control signal Sig1. The control unit 15 also controls the on and off operation of the second switching element Tr2 by outputting a control signal Sig2. As a result, the control unit 15 supplies the energy stored in the first reactor L1 and the second reactor L2 to the inverter 20 via the second capacitor C2.

[0039] The control unit 15 changes the on-duty ratio of the control signal for switching the first switching element Tr1 and the second switching element Tr2 according to the magnitude of the load. Specifically, the control unit 15 increases the on-duty ratio when the load is large (heavy load), and decreases the on-duty ratio when the load is small (light load).

[0040] <Operation of power conversion device> Next, an example of the operation of the power conversion device 10 will be described with reference to Fig. 2. Fig. 2 is a diagram showing a current path of each phase in a current continuous mode in the power conversion device 10. Fig. 3 is a graph showing the relationship between the time change of the on-duty ratio A and the time change of the output voltage Vout in the power conversion device 10.

[0041] The power conversion device 10 shown in FIG.

[0042] In operation mode 1, the first switching element Tr1 is on and the second switching element Tr2 is off.

[0043] In operation mode 2, the first switching element Tr1 is off and the second switching element Tr2 is on.

[0044] In operation mode 3, the first switching element Tr1 and the second switching element Tr2 are in an off state.

[0045] In operation mode 4, the first switching element Tr1 and the second switching element Tr2 are in an ON state. In each of operation modes 1 to 4, the first reactor L1 and the second reactor L2 operate in a state in which they are magnetically coupled to each other.

[0046] The control unit 15 drives the first switching element Tr1 and the second switching element Tr2 with a half-cycle shift, i.e., a 180° phase shift. When the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, the control unit 15 controls the driving of the first switching element Tr1 and the second switching element Tr2 so that the pattern of operation mode 1 → operation mode 3 → operation mode 2 → operation mode 3 is repeated, for example.

[0047] On the other hand, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is greater than 50%, the control unit 15 controls the driving of the first switching element Tr1 and the second switching element Tr2 so that the pattern of operation mode 1 → operation mode 4 → operation mode 2 → operation mode 4 is repeated. Also, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is 50%, the control unit 15 alternately repeats operation mode 1 and operation mode 2. Note that the above-mentioned operation pattern of the power conversion device 10 is an example and can be changed as appropriate.

[0048] When the on-duty ratio A is 50% or more, as shown in Fig. 3, the output voltage Vout changes so as to follow the change in the on-duty ratio A. In this way, when the on-duty ratio A is 50% or more, the control of the output voltage Vout is stable.

[0049] [Occurrence of reverse current] Next, the conditions under which a reverse current occurs in the first reactor L1 or the second reactor L2 of the coupling reactor 1 and the conditions under which a reverse current does not occur will be described with reference to Figs. 3 to 5 and Table 1. Fig. 3 is a graph showing the relationship between the time change of the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 in the power conversion device 10 of Fig. 1 and the time change of the output voltage Vout. Fig. 4 is a diagram showing a state in which a reverse current flows in the second reactor L2 of the power conversion device 10 of Fig. 1. Fig. 5 is a diagram equivalent to Fig. 3 when a dead band phenomenon occurs in the coupling reactor 1 of the power conversion device 10 of Fig. 1. Here, the "dead band phenomenon" refers to a phenomenon in which the output voltage Vout does not follow the change in the on-duty ratio A. In addition, as shown in Fig. 5 from time t2 to t3, the region in which the dead band phenomenon occurs is called the "dead band region".

[0050] The following Table 1 shows the conditions under which a reverse current occurs. In Table 1, continuous conduction mode (CCM) refers to a mode in which a current flows continuously through the first reactor L1 or the second reactor L2. On the other hand, discontinuous conduction mode (DCM) refers to a mode in which the current flowing through the first reactor L1 or the second reactor L2 has a period during one cycle where it becomes zero.

[0051] In addition, since a general DC-DC converter must be designed with the intention of always operating in continuous current mode even under light load, it usually operates in a state in which discontinuous current mode and continuous current mode coexist. Therefore, the power conversion device 10 is also assumed to operate in a state in which discontinuous current mode and continuous current mode coexist.

[0052] [Table 1]

[0053] As shown in Table 1, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is 50% or more, no reverse current is generated in the first reactor L1 or the second reactor L2. Also, when the first switching element Tr1 and the second switching element Tr2 are driven in the current continuous mode, no reverse current is generated in the first reactor L1 or the second reactor L2.

[0054] On the other hand, for example, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, when the second switching element Tr2 is driven in a discontinuous current mode, as shown in FIG. 4, a reactor current I L2 A reverse current indicated by -1 occurs.

[0055] Specifically, when the state changes from the above-mentioned operation mode 1 to operation mode 3, that is, during the period when the first switching element Tr1 is turned off and the first reactor L1 is discharging to the output side, when the second switching element Tr2 is off, the second body diode Db2 becomes conductive, causing a reverse current to be generated in the second reactor L2.

[0056] The reverse current in the second reactor L2 is the reactor current I L1 When -1 flows to the output side, the reactor current I L2 This occurs due to the flow of −1. For this reason, as shown by t2 to t3 in FIG. 5, a dead band region appears in which the output voltage Vout does not follow the change in the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2.

[0057] [Current flowing at the boundary between discontinuous current mode and continuous current mode] Next, the relationship between the current (boundary current) flowing through the reactor at the boundary where the current discontinuous mode and the current continuous mode switch, and the switching frequencies of the first switching element Tr1 and the second switching element Tr2 will be described.

[0058] FIG. 6 is a waveform diagram showing the waveforms of the currents flowing through the first reactor L1 and the second reactor L2 that form the coupling reactor when the on-duty ratio is less than 50%.

[0059] In the following description with reference to Fig. 6, the first mode will be referred to as mode M1, the third mode following the first mode as mode M2, the second mode as mode M3, and the third mode following the second mode as mode M4. In the following description, the currents flowing through the first reactors L1 and L2 will be referred to as I L1 ,I L2 It is called.

[0060] In addition, in the description below with reference to Table 2, the input voltage Vin is referred to as Vi, and the output voltage Vout is referred to as Vo.

[0061] As shown in FIG. 6, when the on-duty ratio A is less than 50%, the reactor current I flowing through the first reactor L1 in the modes M1 to M4 is L1 changes as follows:

[0062] In mode M1, the first switching element Tr1 is turned on for an on-time ton. This causes a reactor current I of di1 [A] to flow to the first reactor L1 via the first switching element Tr1. L1 As a result of this current flowing in, magnetic energy is stored in the first reactor L1.

[0063] In mode M2, when the first switching element Tr1 turns off for the off-time toff (= ton), part of the magnetic energy stored in the first reactor L1 is released. As a result, a negative reactor current I of di2 [A] (|di1| > |di2|) L1 flows out from the first reactor L1 to the first diode D1.

[0064] In mode M3, the second switching element Tr2 turns on for the on-time ton. As a result, a reactor current I of slight di3 [A] (|di2| > |di3|) L1 flows into the first reactor L1 through the second switching element Tr2.

[0065] In mode M4, when the first switching element Tr1 and the second switching element Tr2 turn off for the off-time toff, the rest of the magnetic energy stored in the first reactor L1 is released. As a result, a negative reactor current I of di4 [A] (di2 < di4 < 0) L1 flows out from the first reactor L1 to the first diode D1.

[0066] Note that the reactor current I in modes M1 to M4 L1 is equal to the reactor current I in modes M3, M4, M1, and M2 respectively L2 .

[0067] Here, in each of modes M1 to M4 of the first phase (first reactor L1) and the second phase (second reactor L2), the input voltage Vi and the difference between the input voltage Vi and the output voltage Vo (Vi - Vo) are expressed as in the following equations shown in Table 2. In Table 2, L represents the self-inductance of each of the first reactor L1 and the second reactor L2, and M represents the mutual inductance in the coupled reactor 1.

[0068]

Table 2

[0069] By rearranging the equations for ton from the first and second phases of mode M1 in Table 2, equation (1) is derived.

[0070] Voton / (L+M)=di1-di3 …(1) By rearranging the equations for toff from the first and second phases of mode M2 ​​in Table 2, equation (2) is derived.

[0071] di2=di41=(Vi-Vo)toff / (LM) …(2) For mode M3, the phase is simply exchanged with mode M1, so the same equation as equation (1) is derived. For mode M4, the phase is simply exchanged with mode M2, so the same equation as equation (2) is derived.

[0072] The periodic average current Iave of the first phase is expressed by the following equation (3), where T is the switching period of the first phase (first switching element Tr1).

[0073] Iave=di1{(ton / 2)+toff+(ton / 2)} / T =di1 / 2 …(3) Furthermore, when the sign of the current gradient is taken into consideration, di1+di3 is equal to -(di2+di4), and therefore can be obtained as shown in equation (4).

[0074] di1+di3=-2(Vi-Vo)toff / (LM) …(4) Equation (1) and equation (4), A=ton / (ton+toff)=ton f SW Therefore, di1 can be calculated as follows. Here, A represents the on-duty ratio, and f SW represents the switching frequency of the first switching element Tr1.

[0075] di1=(LM)VoA-(L+M)(Vi-Vo)(1-2A) / 2f SW (L2-M2) In the above equation, Vi=(1-A)Vo and M=kL (k is the coupling coefficient of the coupling reactor 1), so that di1 is expressed as in equation (5).

[0076] di1=AVo{1-A(1+k)} / f SW (1-D(1+k)) …(5) Therefore, the boundary current Icrm represented by the periodic average current Iave of the first phase is expressed as the following equation (6) from equations (3) and (5).

[0077] Icrm=Iave=AVi{1-A(1+k)} / 2Lf SW (1-A)(1-k 2 ) …(6) Thus, the boundary current Icrm is SW The switching frequency f SW It depends on the inverse of

[0078] [Changing the boundary between discontinuous current mode and continuous current mode] The boundary current Icrm and switching frequency f SW From the relationship, the switching frequency f SW Increasing the switching frequency f SW By increasing the switching frequency f, the area in which the regulator operates in discontinuous current mode can be narrowed. SW is the switching period T SW Since the on-duty ratio A is inversely related to the switching period T SW By shortening the time, the above-mentioned boundary current value is reduced, and the region in which the device operates in the discontinuous current mode can be narrowed.

[0079] Therefore, when the on-duty ratio A is less than 50%, that is, when the load is light, the control unit 15 sets the switching frequency f SW The operation of the first switching element Tr1 and the second switching element Tr2 is controlled so as to increase the current.

[0080] Next, the switching frequency f SW The effect of increasing the switching period T SW and the current (boundary current) flowing through the coupling reactor 1. Here, the switching frequency f SW (Switching period T SW ) are controlled to be equal, and the reactor current I L1 ,I L2 are equal as described above (see FIG. 6).

[0081] The above equation (6) is expressed as the switching period T SW As shown in Figure 7, the switching period T SW The boundary current Icrm is proportional to the switching frequency f SW Before increasing (switching period T SW A boundary Bm1 between a range DCM1 of the discontinuous current mode and a range CCM1 of the continuous current mode (before the current is shortened) is at a position determined by a boundary current Icrm1.

[0082] In contrast, the switching frequency f SW Increase the switching period T SW By shortening the current limit (Bm1), the boundary current Icrm1 changes to a smaller boundary current Icrm2. This causes the boundary Bm1 to shift to the boundary Bm2 on the left side. Therefore, the range DCM1 of the discontinuous current mode narrows to a narrower range DCM2, and the range CCM1 of the continuous current mode expands to a wider range CCM2.

[0083] [Effects of the embodiment] As described above, by narrowing the range of the discontinuous current mode, it is possible to narrow the dead band region that occurs in the discontinuous current mode when the on-duty ratio A is less than 50%, and therefore it is possible to further stabilize the control of the power conversion device 10 including the coupling reactor 1.

[0084] In addition, it is possible to determine whether or not to increase the switching frequency depending on whether the on-duty ratio A is less than 50%. This makes it possible to easily control switching between the discontinuous current mode and the continuous current mode.

[0085] In addition, as expressed by equation (6), by utilizing the switching frequency dependency of the current Icrm, it is possible to easily control switching between the discontinuous current mode and the continuous current mode.

[0086] Also, ripple can be reduced by connecting the first capacitor C1 in parallel between the power source E and the coupling reactor 1. Also, by connecting the second capacitor C2 to the output side of the coupling reactor 1, the energy stored in the coupling reactor 1 is supplied to the second capacitor C2 and then released to the inverter 20, thereby increasing the output of the power conversion device 10.

[0087] In addition, by connecting a first diode D1 to the output side of the first switching element Tr1 and connecting a second diode D2 to the output side of the second switching element Tr2, it is possible to prevent current from flowing back from the second capacitor C2 to the coupling reactor 1.

[0088] Furthermore, by using a power MOSFET, which is a vertical MOS field effect transistor, as the first switching element Tr1 or the second switching element Tr2, it is possible to increase the breakdown voltage and perform high-speed switching.

[0089] Other embodiments In the power conversion device 10 according to the above embodiment, a case has been described in which one coupling reactor 1 in which a two-phase first reactor L1 and a two-phase second reactor L2 are magnetically coupled is provided. However, the present invention is not limited to this, and two coupling reactors 1 each consisting of a four-phase reactor may be provided.

[0090] In the power conversion device 10 of the embodiment described above, the first diode D1 is connected to the output side of the first reactor L1, and the second diode D2 is connected to the output side of the second reactor L2, but the configuration is not limited to this. Instead of the first diode D1 and the second diode D2, a synchronous rectification type circuit configuration in which a third switching element and a fourth switching element are arranged may be used.

[0091] That is, the power conversion device 10 may have a circuit configuration in which a third switching element is connected to the output side of the first switching element Tr1, and a fourth switching element is connected to the output side of the second switching element Tr2. FETs or the like can be used as the third switching element and the fourth switching element.

[0092] The on and off operations of the third switching element and the fourth switching element are controlled by the control unit 15. Specifically, the control unit 15 controls the third switching element to be on when the first switching element Tr1 is off, and the fourth switching element to be on when the second switching element Tr2 is off. The control unit 15 also controls the third switching element to be off when the first switching element Tr1 is on, and the fourth switching element to be off when the second switching element Tr2 is on. This makes it possible to prevent a current from flowing back from the second capacitor C2 to the coupling reactor 1 when the first switching element Tr1 is on and when the second switching element Tr2 is on.

[0093] In this case, by using a secondary battery as the power source E, the power conversion device 10 can convert the power generated by the motor 30 into direct current and charge the power source E. Furthermore, the synchronous rectification circuit configuration can improve conversion efficiency compared to the asynchronous rectification circuit configuration including the first diode D1 and the second diode D2.

[0094] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. In addition, the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. [Explanation of symbols]

[0095] 1. Coupling reactor 10 Power conversion device 11 cores 15 Control section 20 Inverter 100 Power supply L1 First reactor L2 Second reactor Tr1 First switching element Tr2 Second switching element C1 First capacitor C2 Second capacitor D1 First diode D2 Second diode Vin Input voltage Vout Output voltage A On-duty ratio

Claims

1. A power conversion device that converts an input voltage into a predetermined output voltage, a coupling reactor including a first reactor and a second reactor that are magnetically coupled to each other; a first switching element connected to an output side of the first reactor; a second switching element connected to an output side of the second reactor; a control unit that controls driving of the first switching element and the second switching element; Equipped with The power conversion device according to claim 1, wherein the control unit increases a switching frequency of the first switching element and the second switching element when a light load is applied.

2. 2. The power conversion device according to claim 1, wherein the control unit changes an on-duty ratio of a control signal that switches the first switching element and the second switching element in accordance with a magnitude of a load, and increases the switching frequency when the on-duty ratio is less than 50%.

3. The power conversion device operates in a discontinuous current mode and a continuous current mode, A current Icrm flowing through either the first reactor or the second reactor at the boundary between the discontinuous current mode and the continuous current mode is expressed as follows: ＳＷ The self-reactance of the first reactor and the second reactor is L, and the coupling coefficient of the coupling reactor is k. Then, Icrm=AVi{1-A(1+k)} / 2Lf ＳＷ (1-A)(1-k ２ ) 3. The power conversion device according to claim 2, wherein the power conversion device is expressed by:

4. A first capacitor connected to an input side of the coupling reactor; a second capacitor connected to an output side of the coupling reactor; The power conversion device according to any one of claims 1 to 3, further comprising:

5. a first diode connected to an output side of the first switching element; a second diode connected to an output side of the second switching element; The power conversion device according to claim 4, further comprising:

6. the first switching element and the second switching element are vertical MOS field effect transistors, the drain of the first switching element and the anode of the first diode are connected; 6. The power conversion device according to claim 5, wherein the drain of the second switching element and the anode of the second diode are connected together.

7. a third switching element connected to an output side of the first switching element; a fourth switching element connected to an output side of the second switching element; Further comprising:

5. The power conversion device according to claim 4, wherein the control unit controls driving of the third switching element and the fourth switching element so that the third switching element is turned off when the first switching element is turned on, the third switching element is turned on when the first switching element is turned off, the fourth switching element is turned off when the second switching element is turned on, and the fourth switching element is turned on when the second switching element is turned off.

Images