Power Conversion Equipment

Abstract

To provide a power converter which can reduce loss in a secondary-side circuit while an increase of a circuit scale is suppressed, and can control a current division ratio of a circuit in which output current is shunted and flows without using a current detection device.SOLUTION: A power converter 1 includes: a switching element Qp which is connected to a primary winding 11a in series; a capacitor 12 and a rectifier element Q2, which are connected in series between a positive electrode terminal of a secondary winding 11b and secondary side ground potential; a rectifier element Q1 connected between a negative electrode terminal of the secondary winding 11b and the secondary side ground potential; an inductor 13 connected between a connection point CP1 and a positive electrode output terminal 1P; a switching element Q3 and an inductor 14, which are connected in series between the positive electrode terminal of the secondary winding 11b and the positive electrode output terminal 1P; and a rectifier element Q4 connected between a connection point CP2 and the secondary side ground potential. A controller 16 alternately sets the switching element Qp and the switching element Q3 in a conduction state at a constant period.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, the output current required for DC / DC converters has been increasing. As the output current increases, the current flowing through the secondary circuit of the transformer increases, resulting in increased loss in the secondary circuit. To address this issue, a configuration has been proposed in which the secondary circuit, including the transformer, is connected in parallel to distribute the current flowing through the secondary circuit (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] China Patent Application Publication No. 105743356 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the circuit configuration described in Patent Document 1 requires two transformers, which increases the circuit size. In order to control the balance of currents flowing through the two parallel circuits, a current detection device is generally provided in each of the two parallel circuits.

[0005] The present disclosure describes a power conversion device that can reduce losses in a secondary circuit while suppressing an increase in circuit size, and can control the current division ratio of a circuit through which an output current flows in a divided manner without using a current detection device. [Means for solving the problem]

[0006] A power converter according to one aspect of the present disclosure is a forward type power converter. The power converter includes a transformer having a primary winding and a secondary winding, a first switching element connected in series with the primary winding, a capacitor and a first rectifying element connected in series between one end of the secondary winding and a secondary ground potential, a second rectifying element connected between the other end of the secondary winding and the secondary ground potential, a positive output terminal, a negative output terminal connected to the secondary ground potential, a first inductor connected between a first connection point between the capacitor and the first rectifying element and the positive output terminal, a second switching element and a second inductor connected in series between one end of the secondary winding and the positive output terminal, a third rectifying element connected between a second connection point between the second switching element and the second inductor and the secondary ground potential, and a control device that switches the conductive / non-conductive states of the first switching element and the second switching element. The control device alternately sets the first switching element and the second switching element to a conductive state at a constant period.

[0007] In this power conversion device, when the first switching element is set to a conductive state and the second switching element is set to a non-conductive state, a voltage is generated in the secondary winding, and a voltage obtained by subtracting the voltage across the capacitor and the output voltage from the voltage generated in the secondary winding is applied to the first inductor. As a result, the current flowing through the first inductor increases, and the capacitor is charged. At this time, the output voltage is applied to the second inductor in the reverse direction, so the current flowing through the second inductor decreases. On the other hand, when the second switching element is set to a conductive state and the first switching element is set to a non-conductive state, a voltage obtained by subtracting the output voltage from the voltage across the capacitor is applied to the second inductor. As a result, the current flowing through the second inductor increases, and the capacitor is discharged. At this time, the output voltage is applied to the first inductor in the reverse direction, so the current flowing through the first inductor decreases. In this way, the current flows in a distributed manner in the first inductor and the second inductor without paralleling the transformer. Therefore, it is possible to reduce losses in the secondary circuit, including DC losses in the first inductor and the second inductor, while suppressing an increase in the circuit size. Furthermore, by adjusting the duty ratio of the first switching element and the duty ratio of the second switching element, the ratio (current division ratio) of the current flowing through the first inductor and the current flowing through the second inductor can be changed. Therefore, it is possible to control the current division ratio of the circuit through which the output current flows in a divided manner without using a current detection device.

[0008] In some embodiments, the control device may switch the conductive / non-conductive states of the first switching element and the second switching element such that the duty ratio of the first switching element is equal to the duty ratio of the second switching element, whereby the average value of the current flowing through the first inductor can be made equal to the average value of the current flowing through the second inductor.

[0009] In some embodiments, the control device may adjust the time difference between when the first switching element is switched from a non-conductive state to a conductive state and when the second switching element is switched from a non-conductive state to a conductive state. In this case, the harmonic components of the output current can be adjusted. For example, the harmonic components present in a specific frequency band can be reduced.

[0010] In some embodiments, the first rectifying element may be a switching element. The control device may control the first rectifying element to a non-conductive state during a period in which the first switching element is in a conductive state, and control the first rectifying element to a conductive state during a period in which the first switching element is in a non-conductive state. In this case, it is possible to reduce loss in the first rectifying element compared to a case in which the first rectifying element is a diode.

[0011] In some embodiments, the second rectifier element may be a switching element. The control device may control the second rectifier element to a conductive state during a period in which the first switching element is in a conductive state, and control the second rectifier element to a non-conductive state during a period in which the first switching element is in a non-conductive state. In this case, it is possible to reduce loss in the second rectifier element compared to a case in which the second rectifier element is a diode.

[0012] In some embodiments, the third rectifier element may be a switching element. The control device may control the third rectifier element to a non-conductive state during a period in which the second switching element is in a conductive state, and control the third rectifier element to a conductive state during a period in which the second switching element is in a non-conductive state. In this case, it is possible to reduce loss in the third rectifier element compared to a case in which the third rectifier element is a diode. Effect of the Invention

[0013] According to the present disclosure, it is possible to reduce losses in the secondary circuit while suppressing an increase in circuit size, and to control the current division ratio of a circuit through which an output current flows in a divided manner without using a current detection device. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating an example of a circuit configuration of a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing the switching timing of each switching element shown in FIG. [Diagram 3] FIG. 3 is a diagram showing a current path in phase Φ1 shown in FIG. [Figure 4] FIG. 4 is a diagram showing current paths in phases Φ2 and Φ4 shown in FIG. [Diagram 5] FIG. 5 is a diagram showing a current path in phase Φ3 shown in FIG. [Figure 6] FIG. 6 is a diagram showing a circuit model for analyzing the steady state of the power conversion device shown in FIG. [Figure 7] FIG. 7 is a diagram showing another example of the circuit configuration of the power conversion circuit shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, a power conversion device according to an embodiment will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicated description will be omitted.

[0016] With reference to FIG. 1, a circuit configuration of a power conversion device according to an embodiment will be described. FIG. 1 is a diagram showing an example of a circuit configuration of a power conversion device according to an embodiment. The power conversion device 1 shown in FIG. 1 is a device (DC / DC converter) that converts direct current voltage. The power conversion device 1 is used in electric vehicles such as hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs), and electric vehicles (EVs). In this case, the power conversion device 1 converts, for example, the voltage of a high-voltage battery into an auxiliary voltage. The power conversion device 1 is a forward-type power conversion device. The forward type is a method in which a primary winding of a transformer is excited in only one direction, and energy is transmitted to the secondary side via the transformer only during the excitation period of the primary winding.

[0017] The power conversion device 1 includes a transformer 11, a capacitor 12, an inductor 13 (first inductor), an inductor 14 (second inductor), a capacitor 15, a control device 16, a switching element Qp (first switching element), a rectifying element Q1 (second rectifying element), a rectifying element Q2 (first rectifying element), a switching element Q3 (second switching element), a rectifying element Q4 (third rectifying element), a positive output terminal 1P, and a negative output terminal 1N. In this embodiment, switching elements are used as the rectifying element Q1, the rectifying element Q2, and the rectifying element Q4.

[0018] Each switching element is a circuit element capable of switching the electrical state between its main terminals between a conductive state (ON state) and a non-conductive state (OFF state). In this embodiment, the switching element is a metal oxide semiconductor field effect transistor (MOSFET) with an anti-parallel diode connected thereto. In the case of a MOSFET, the main terminals are the drain and the source. The cathode of the anti-parallel diode is connected to the drain of the MOSFET, and the anode of the anti-parallel diode is connected to the source of the MOSFET. The switching element may be an insulated gate bipolar transistor (IGBT) with an anti-parallel diode connected in parallel. In the case of an IGBT, the main terminals are the collector and the emitter. A gate voltage is applied to the gate of each switching element from the control device 16, thereby switching the main terminals of the switching element between a conductive state and a non-conductive state. In this specification, the conductive state / non-conductive state between the main terminals of a switching element or a rectifying element is simply referred to as the "conductive state / non-conductive state of a switching element or a rectifying element".

[0019] The transformer 11 has a primary winding 11a and a secondary winding 11b. Specifically, the primary winding 11a and the secondary winding 11b are wound around a core. When a voltage is applied to the primary winding 11a so that the potential on the side marked with a black circle in FIG. 1 is higher than the potential on the side not marked with a black circle, a voltage is generated in the secondary winding 11b so that the voltage on the side marked with a black circle of the secondary winding 11b is higher than the potential on the side not marked with a black circle. Hereinafter, the sides marked with a black circle of the primary winding 11a and the secondary winding 11b are referred to as positive terminals and the sides not marked with a black circle are referred to as negative terminals. An input voltage is applied to the positive terminal of the primary winding 11a. The negative terminal of the primary winding 11a is connected to the primary side ground potential via a switching element Qp. The switching element Qp is connected in series with the primary winding 11a. Specifically, one end (drain) of the switching element Qp is connected to the negative terminal of the primary winding 11a, and the other end (source) of the switching element Qp is connected to the primary side ground potential.

[0020] The capacitor 12 and the rectifying element Q2 are connected in series between the positive terminal of the secondary winding 11b and the secondary ground potential. Specifically, one end of the capacitor 12 is connected to the positive terminal of the secondary winding 11b. The other end of the capacitor 12 and one end (drain) of the rectifying element Q2 are connected to each other at a connection point CP1 (first connection point). The other end (source) of the rectifying element Q2 is connected to the secondary ground potential.

[0021] The inductor 13 is connected between the connection point CP1 and the positive output terminal 1P. Specifically, one end of the inductor 13 is connected to the connection point CP1, and the other end of the inductor 13 is connected to the positive output terminal 1P.

[0022] The rectifying element Q1 is connected between the negative terminal of the secondary winding 11b and the secondary ground potential. Specifically, one terminal (drain) of the rectifying element Q1 is connected to the negative terminal of the secondary winding 11b, and the other terminal (source) of the rectifying element Q1 is connected to the secondary ground potential.

[0023] The switching element Q3 and the inductor 14 are connected in series between the positive terminal of the secondary winding 11b and the positive output terminal 1P. Specifically, one end (drain) of the switching element Q3 is connected to the positive terminal of the secondary winding 11b. The other end (source) of the switching element Q3 and one end of the inductor 14 are connected to each other at a connection point CP2 (second connection point). The other end of the inductor 14 is connected to the positive output terminal 1P.

[0024] The rectifying element Q4 is connected between the connection point CP2 and the secondary ground potential. Specifically, one end (drain) of the rectifying element Q4 is connected to the connection point CP2, and the other end (source) of the rectifying element Q4 is connected to the secondary ground potential.

[0025] Capacitor 15 is connected between positive output terminal 1P and negative output terminal 1N. Specifically, one end of capacitor 15 is connected to positive output terminal 1P, and the other end of capacitor 15 is connected to negative output terminal 1N. Negative output terminal 1N is connected to the secondary side ground potential.

[0026] The control device 16 is a circuit that switches the conductive / non-conductive state of each switching element. The control device 16 switches the conductive / non-conductive state of each switching element by supplying a gate voltage to each switching element.

[0027] Next, the operation of the power conversion device 1 will be described with reference to Figs. 2 to 5. Fig. 2 is a diagram showing the switching timing of each switching element shown in Fig. 1. In Fig. 2, the hatched periods indicate that the corresponding switching elements are in a conductive state. Fig. 3 is a diagram showing a current path in phase Φ1 shown in Fig. 2. Fig. 4 is a diagram showing a current path in phases Φ2 and Φ4 shown in Fig. 2. Fig. 5 is a diagram showing a current path in phase Φ3 shown in Fig. 2.

[0028] As shown in Fig. 2, the control device 16 switches the conductive / non-conductive state of the switching element Qp and the conductive / non-conductive state of the rectifying element Q1 in synchronization with each other. Specifically, the control device 16 controls the rectifying element Q1 to a conductive state during a period in which the switching element Qp is in a conductive state, and controls the rectifying element Q1 to a non-conductive state during a period in which the switching element Qp is in a non-conductive state. The control device 16 complementarily switches the conductive / non-conductive state of the switching element Qp and the conductive / non-conductive state of the rectifying element Q2. Specifically, the control device 16 controls the rectifying element Q2 to a non-conductive state during a period in which the switching element Qp is in a conductive state, and controls the rectifying element Q2 to a conductive state during a period in which the switching element Qp is in a non-conductive state.

[0029] The control device 16 alternately sets the switching element Qp and the switching element Q3 to a conductive state. Here, "alternately sets the switching element Qp and the switching element Q3 to a conductive state" means that both the switching element Qp and the switching element Q3 are not in a conductive state, and includes a case where there is a time when both are in a non-conductive state. In this embodiment, the control device 16 switches the switching element Q3 from a non-conductive state to a conductive state in response to the passage of a time difference Δ×T after the switching element Qp is switched from a non-conductive state to a conductive state. The control device 16 complementarily switches the conductive / non-conductive state of the switching element Q3 and the conductive / non-conductive state of the rectifying element Q4. Specifically, the control device 16 controls the rectifying element Q4 to a non-conductive state during a period when the switching element Q3 is in a conductive state, and controls the rectifying element Q4 to a conductive state during a period when the switching element Q3 is in a non-conductive state.

[0030] The duty ratio of switching element Qp is d1, and the duty ratio of switching element Q3 is d3. The duty ratio is the proportion of time during one cycle that a switching element is in a conductive state. In other words, switching element Qp is in a conductive state for a time (d1×T) obtained by multiplying duty ratio d1 by the time T of one cycle. Switching element Q3 is in a conductive state for a time (d3×T) obtained by multiplying duty ratio d3 by the time T of one cycle. Since switching element Qp and switching element Q3 are never in a conductive state at the same time, the time difference Δ×T is greater than the time (d1×T).

[0031] In this embodiment, the control device 16 controls the switching timing of each switching element to adjust the duty ratio d1, the duty ratio d3, and the time difference Δ×T. For example, the control device 16 switches the conductive / non-conductive state of the switching element Qp and the switching element Q3 at a constant period so that the duty ratio d1 and the duty ratio d3 are equal to each other.

[0032] As described above, by switching the conductive / non-conductive state of each switching element, phase Φ1, phase Φ2, phase Φ3, and phase Φ4 are repeated in that order. The current path in each phase will be described below. In the following description, it is assumed that the circuit of the power conversion device 1 is in a steady state. Note that in actual operation, a dead time period is included in addition to phases Φ1 to Φ4.

[0033] <Phase Φ1> 3, in phase Φ1, the switching element Qp and the rectifying elements Q1 and Q4 are in a conducting state, and the rectifying element Q2 and the switching element Q3 are in a non-conducting state. Since the switching element Qp changes from a non-conducting state to a conducting state, an input voltage is applied to the primary winding 11a so that the potential of the positive terminal is higher than the potential of the negative terminal, and a voltage V S(see FIG. 6) occurs such that the potential of the positive terminal is higher than the potential of the negative terminal. As a result, a current I1 flows through a current path that runs from the positive terminal of the secondary winding 11b through the capacitor 12, the inductor 13, the positive output terminal 1P, the load, and the rectifier element Q1 in this order, and returns to the negative terminal of the secondary winding 11b. At this time, the inductor 13 is connected to the voltage V S From the above, the voltage across the capacitor 12, V C (See FIG. 6) and the output voltage V of the power conversion device 1 O (see FIG. 6) is applied. Therefore, the current I1 flowing through the inductor 13 increases. The capacitor 12 is charged by the current I1.

[0034] Even when the phase is switched from Φ4 to Φ1, the current path of the current I2 flowing through the inductor 14 does not change. Specifically, the current I2 flows through a current path that runs from the other end of the inductor 14 through the positive output terminal 1P, the load, and the rectifier element Q4 in this order, and returns to one end of the inductor 14. At this time, the inductor 14 is connected to the output voltage V O is applied in the reverse direction, the current I2 flowing through the inductor 14 decreases.

[0035] <Phase Φ2> As shown in Fig. 4, in phase Φ2, the rectifier elements Q2 and Q4 are in a conductive state, and the switching elements Qp, Q3 and the rectifier element Q1 are in a non-conductive state. The switching element Qp and the rectifier element Q1 change from a conductive state to a non-conductive state, and the rectifier element Q2 changes from a non-conductive state to a conductive state. Therefore, due to the continuity of the current I1, the current I1 flows through a current path that runs from the other end of the inductor 13 through the positive output terminal 1P, the load, and the rectifier element Q2 in this order, and returns to one end of the inductor 13. At this time, the inductor 13 is supplied with a current equal to the output voltage V O is applied in the reverse direction, so the current I1 starts to decrease. Even when the phase is switched from Φ1 to Φ2, the current path of the current I2 does not change, so the current I2 continues to decrease. In phase Φ2, the capacitor 12 is neither charged nor discharged.

[0036] <Phase Φ3> As shown in Fig. 5, in phase Φ3, rectifier element Q2 and switching element Q3 are in a conductive state, and switching element Qp and rectifier elements Q1 and Q4 are in a non-conductive state. Even when phase Φ2 is switched to phase Φ3, the current path of current I1 does not change, so current I1 continues to decrease. Since switching element Q3 goes from a non-conductive state to a conductive state, and rectifier element Q4 goes from a conductive state to a non-conductive state, inductor 14 has a voltage V C to output voltage V O Then, a voltage obtained by subtracting 1 from 1 is applied. This causes the current I2 to start increasing. The capacitor 12 is discharged by the current I2.

[0037] <Phase Φ4> As shown in FIG. 4, in phase Φ4, the rectifier elements Q2 and Q4 are in a conducting state, and the switching elements Qp and Q3 and the rectifier element Q1 are in a non-conducting state. The current path in phase Φ4 is the same as the current path in phase Φ2. Specifically, even when switching from phase Φ3 to phase Φ4, the current path of the current I1 does not change, so the current I1 continues to decrease. Since the switching element Q3 goes from a conducting state to a non-conducting state and the rectifier element Q4 goes from a non-conducting state to a conducting state, the current I2 flows through the continuity of the current I2 from the other end of the inductor 14 through the positive output terminal 1P, the load, and the rectifier element Q4 in this order, and returns to one end of the inductor 14. At this time, the inductor 14 is supplied with a current equal to the output voltage V O is applied in the reverse direction, the current I2 through the inductor 14 starts to decrease. During phase Φ4, the capacitor 12 is neither charged nor discharged.

[0038] In a forward DC / DC converter, a circuit for processing the energy stored in the excitation inductor of the transformer after the switching element Qp becomes non-conductive is usually provided on the primary side. Without this circuit, an excessive voltage may be applied to the switching element Qp due to the energy stored in the excitation inductor, and the switching element Qp may be damaged. Known circuits for processing the energy stored in the excitation inductor include an active clamp circuit, a regenerative circuit, and a snubber circuit. In this embodiment, a circuit for processing the energy stored in the excitation inductor is also provided as appropriate, but since this is a common technique, illustrations and explanations are omitted here.

[0039] Next, the steady state of the power conversion device 1 will be described with reference to Fig. 6. Fig. 6 is a diagram showing a circuit model for analyzing the steady state of the power conversion device shown in Fig. 1. Note that each current value and voltage value is an average value in one switching period. The following analysis also includes a case where the duty ratio d1 and the duty ratio d3 are different.

[0040] As shown in equation (1), the voltage V S is the input voltage V P and the number of turns N of the primary winding 11a P and the number of turns N of the secondary winding 11b S It is determined by.

number

[0041] The balance of the ET product at inductor 13 results in a voltage V S , voltage across both ends V C , output voltage V O , the duty ratio d1 of the inductor 13, and the time T of one period, the relationship of equation (2) is established.

number

[0042] Equation (3) can be obtained from equation (2).

number

[0043] The ET product balance at inductor 14 results in a voltage V C , output voltage V O , the duty ratio d3 of the inductor 14, and the time T of one period, the relationship of equation (4) is established.

number

[0044] Equation (5) is obtained from equation (4).

number

[0045] Equations (6) and (7) are obtained from equations (3) and (5).

number

number

[0046] Due to charge balance in the capacitor 12, the relationship of equation (8) holds among the current I1, the current I2, the duty ratio d1, the duty ratio d3, and the time T of one period.

number

[0047] Equation (9) can be obtained from equation (8).

number

[0048] As mentioned above, the voltage V S , voltage across both ends VC , output voltage V O , current I1, and current I2 do not depend on the time difference ratio Δ.

[0049] When the duty ratio d1 and the duty ratio d3 are equal, the formulas (10) to (12) are obtained from the formulas (6), (7), and (9), respectively.

number

number

number

[0050] In this case, the output voltage V O The maximum value of is the voltage V S The voltage across capacitor 12, V C is the voltage V S 1 / 2. Furthermore, the current I1 (average value) and the current I2 (average value) become equal regardless of the inductance of the inductors 13 and 14. Therefore, there is no need to provide a current detection sensor or perform current balance control in order to equalize the current I1 (average value) and the current I2 (average value).

[0051] Next, the output current waveform is expanded into a Fourier series to consider the changes in the harmonic components due to the duty ratio d1, the duty ratio d3, and the time difference ratio Δ. A simple calculation shows that the output current i O The Fourier series expansion of (t) is obtained. The output current i O If the Fourier series expansion of (t) is expressed as equation (13), the Fourier coefficient a0 and the Fourier coefficient a n , and the Fourier coefficient b n are respectively expressed by equations (14) to (16). Note that inductance L1 is the inductance of inductor 13, and inductance L2 is the inductance of inductor .

number

number

number

number

[0052] According to equations (15) and (16), it can be seen that the magnitude of a specific high-frequency component can be adjusted by adjusting the time difference ratio Δ. Therefore, by adjusting the time difference ratio Δ, it is possible to reduce noise as well as ripples in the output current and output voltage. In this case, if the duty ratios d1 and d3 are constant, there is no effect on the output voltage even if the time difference ratio Δ is changed. For example, under the condition that the duty ratios d1 and d3 are equal and the inductances L1 and L2 are equal, if the time difference ratio Δ is 0.5, when n is an odd number, the Fourier coefficient a n and the Fourier coefficient b n can both be set to 0.

[0053] In the power conversion device 1 described above, when the switching element Qp is set to a conductive state and the switching element Q3 is set to a non-conductive state, a voltage V S Then, the voltage V S The voltage across capacitor 12, V C and the output voltage V O The voltage obtained by subtracting 1 from 1 is applied to the inductor 13. This increases the current I1 flowing through the inductor 13, charging the capacitor 12. At this time, the inductor 14 has an output voltage V O is applied in the reverse direction, the current I2 flowing through the inductor 14 decreases. On the other hand, when the switching element Q3 is set to the conductive state and the switching element Qp is set to the non-conductive state, the voltage VC to output voltage V O The voltage obtained by subtracting 1 from 1 is applied to the inductor 14. This increases the current I2 flowing through the inductor 14, discharging the capacitor 12. At this time, the inductor 13 outputs the output voltage V O is applied in the reverse direction, so that the current I1 flowing through inductor 13 decreases. In this way, the current flows distributedly through inductors 13 and 14 without paralleling the transformers. This makes it possible to reduce losses in the secondary circuit, particularly DC losses due to the resistance components of inductors 13 and 14, while suppressing an increase in the circuit size.

[0054] According to formula (9), by adjusting the duty ratios d1 and d3, it is possible to change the ratio (current division ratio) between the average value of the current I1 flowing through the inductor 13 and the average value of the current I2 flowing through the inductor 14. Therefore, it is possible to control the current division ratio of the circuit through which the output current flows in a divided manner without using a current detection device.

[0055] The control device 16 may switch the conductive / non-conductive states of the switching element Qp and the switching element Q3 so that the duty ratio d1 and the duty ratio d3 are equal. In this case, the average value of the current I1 flowing through the inductor 13 and the average value of the current I2 flowing through the inductor 14 can be automatically made equal without performing additional current balance control. With this configuration, for example, when the inductors 13 and 14 have the same specifications, the DC loss in the inductors 13 and 14 is minimized by making the average value of the current I1 equal to the average value of the current I2.

[0056] According to the formulas (15) and (16), the control device 16 can adjust the harmonic components of the output current by adjusting the time difference ratio Δ. For example, it is possible to reduce harmonic components that exist in a specific frequency band such as the AM (Amplitude Modulation) band.

[0057] In the above embodiment, the rectifier element Q1 is a switching element. The control device 16 controls the rectifier element Q1 to a conductive state during a period when the switching element Qp is in a conductive state, and controls the rectifier element Q1 to a non-conductive state during a period when the switching element Qp is in a non-conductive state. Since a current flows through the rectifier element Q1 during a period when the switching element Qp is in a conductive state, a current flows through the switching element (transistor) by setting the rectifier element Q1 to a conductive state during the period. The voltage drop in the switching element (transistor) is smaller than the voltage drop in a diode. Therefore, it is possible to reduce the loss in the rectifier element Q1 compared to when the rectifier element Q1 is a diode.

[0058] In the above embodiment, the rectifying element Q2 is a switching element. The control device 16 controls the rectifying element Q2 to a non-conducting state during a period when the switching element Qp is in a conducting state, and controls the rectifying element Q2 to a conducting state during a period when the switching element Qp is in a non-conducting state. Since a current flows through the rectifying element Q2 during a period when the switching element Qp is in a non-conducting state, a current flows through the switching element (transistor) by setting the rectifying element Q2 to a conducting state during the period. The voltage drop in the switching element (transistor) is smaller than the voltage drop in a diode. Therefore, it is possible to reduce the loss in the rectifying element Q2 compared to when the rectifying element Q2 is a diode.

[0059] In the above embodiment, the rectifying element Q4 is a switching element. The control device 16 controls the rectifying element Q4 to a non-conducting state during a period when the switching element Q3 is in a conducting state, and controls the rectifying element Q4 to a conducting state during a period when the switching element Q3 is in a non-conducting state. Since a current flows through the rectifying element Q4 during a period when the switching element Q3 is in a non-conducting state, a current flows through the switching element (transistor) by setting the rectifying element Q4 to a conducting state during the period. The voltage drop in the switching element (transistor) is smaller than the voltage drop in a diode. Therefore, it is possible to reduce the loss in the rectifying element Q4 compared to when the rectifying element Q4 is a diode.

[0060] Although one embodiment of the present disclosure has been described in detail above, the power conversion device according to the present disclosure is not limited to the above embodiment.

[0061] The power conversion device 1 does not necessarily have to include the capacitor 15.

[0062] At least one of the rectifier elements Q1, Q2, and Q4 may be a diode. Fig. 7 is a diagram showing another example of the circuit configuration of the power conversion circuit shown in Fig. 1. The power conversion device 1A shown in Fig. 7 is mainly different from the power conversion device 1 in that it includes a rectifier element D1 (second rectifier element), a rectifier element D2 (first rectifier element), and a rectifier element D4 (third rectifier element) instead of the rectifier elements Q1, Q2, and Q4. The rectifier elements D1, D2, and D4 are diodes. When the rectifier elements D1, D2, and D4 are diodes, the main terminals are the anode and the cathode.

[0063] The cathode of rectifier element D1 is connected to the negative terminal of secondary winding 11b, and the anode of rectifier element D1 is connected to the secondary ground potential. The cathode of rectifier element D2 is connected to the other end of capacitor 12 via connection point CP1, and the anode of rectifier element D2 is connected to the secondary ground potential. The cathode of rectifier element D4 is connected to connection point CP2, and the anode of rectifier element D4 is connected to the secondary ground potential.

[0064] In the power conversion device 1A, the same effects as those of the power conversion device 1 can be achieved with respect to the configuration common to the power conversion device 1. Furthermore, in the power conversion device 1A, since the rectifying elements D1, D2, and D4 are diodes, the control device 16 does not need to control these rectifying elements. Therefore, it is possible to simplify the circuit configuration. [Explanation of symbols]

[0065] 1,1A...power conversion device, 1N...negative output terminal, 1P...positive output terminal, 11...transformer, 11a...primary winding, 11b...secondary winding, 12...capacitor, 13...inductor (first inductor), 14...inductor (second inductor), 15...capacitor, 16...control device, CP1...connection point (first connection point), CP2...connection point (second connection point), D1...rectifier element (second rectifier element), D2...rectifier element (first rectifier element), D4...rectifier element (third rectifier element), Q1...rectifier element (second rectifier element), Q2...rectifier element (first rectifier element), Q3...switching element (second switching element), Q4...rectifier element (third rectifier element), Qp...switching element (first switching element).

Claims

1. A forward type power conversion device, a transformer having a primary winding and a secondary winding; a first switching element connected in series with the primary winding; a capacitor and a first rectifying element connected in series between one end of the secondary winding and a secondary side ground potential; a second rectifier element connected between the other end of the secondary winding and a secondary side ground potential; A positive output terminal; A negative output terminal connected to the secondary side ground potential; a first inductor connected between a first connection point between the capacitor and the first rectifying element and the positive output terminal; a second switching element and a second inductor connected in series between the one end of the secondary winding and the positive output terminal; a third rectifier element connected between a second connection point between the second switching element and the second inductor and the secondary side ground potential; a control device for switching between a conductive state and a non-conductive state of the first switching element and the second switching element; Equipped with The control device alternately sets the first switching element and the second switching element to a conductive state at a constant cycle.

2. 2. The power conversion device according to claim 1, wherein the control device switches the conductive / non-conductive states of the first switching element and the second switching element so that a duty ratio of the first switching element and a duty ratio of the second switching element are equal to each other.

3. 3 . The power conversion device according to claim 1 , wherein the control device adjusts a time difference between when the first switching element is switched from a non-conductive state to a conductive state and when the second switching element is switched from a non-conductive state to a conductive state. 4 .

4. the first rectifying element is a switching element, The power conversion device according to any one of claims 1 to 3, wherein the control device controls the first rectifier element to a non-conductive state during a period in which the first switching element is in a conductive state, and controls the first rectifier element to a conductive state during a period in which the first switching element is in a non-conductive state.

5. the second rectifying element is a switching element, The control device controls the second rectifier element to a conductive state during a period in which the first switching element is in a conductive state, and controls the second rectifier element to a non-conductive state during a period in which the first switching element is in a non-conductive state. The power conversion device according to any one of claims 1 to 4.

6. the third rectifying element is a switching element, The control device controls the third rectifier element to a non-conductive state during a period in which the second switching element is in a conductive state, and controls the third rectifier element to a conductive state during a period in which the second switching element is in a non-conductive state. The power conversion device according to any one of claims 1 to 5.

Images