JP7658293B2 - Power Conversion Equipment - Google Patents

Description

This disclosure relates to a power conversion device.

In recent years, the output current required of 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 losses in the secondary circuit. In response to this problem, 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).

Chinese Patent Publication No. 105743356

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

This disclosure describes a power conversion device that can reduce losses in the secondary circuit while suppressing an increase in circuit size, and can control the current division ratio of the circuit through which the output current flows without using a current detection device.

The power conversion device according to one aspect of the present disclosure is a forward type power conversion device. This power conversion device 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 side ground potential, a second rectifying element connected between the other end of the secondary winding and the 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 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 side 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.

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 between 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.

In some embodiments, the control device may switch the conductive/non-conductive states of the first switching element and the second switching element so that the duty ratio of the first switching element is equal to the duty ratio of the second switching element. In this case, 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.

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.

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 losses in the first rectifying element compared to when the first rectifying element is a diode.

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 losses in the second rectifier element compared to when the second rectifier element is a diode.

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 losses in the third rectifier element compared to when the third rectifier element is a diode.

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 the circuit through which the output current flows without using a current detection device.

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

The power conversion device according to one embodiment will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate descriptions will be omitted.

With reference to FIG. 1, the circuit configuration of a power conversion device according to one embodiment will be described. FIG. 1 is a diagram showing an example of the circuit configuration of a power conversion device according to one 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 the 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.

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.

Each switching element is a circuit element that can switch 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. In the case of a MOSFET, the main terminals are the drain and 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 emitter. A gate voltage is applied from the control device 16 to the gate of each switching element, thereby switching the main terminals of the switching element between a conductive state and a non-conductive state. In this specification, the conductive/non-conductive state between the main terminals of a switching element or rectifier element is simply referred to as the "conductive/non-conductive state of the switching element or rectifier element."

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 side marked with a black circle and the side not marked with a black circle of both the primary winding 11a and the secondary winding 11b are referred to as the positive terminal and the negative terminal, respectively. 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. The other end (source) of the switching element Qp is connected to the primary side ground potential.

The capacitor 12 and the rectifier 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 rectifier element Q2 are connected to each other at a connection point CP1 (first connection point). The other end (source) of the rectifier element Q2 is connected to the secondary ground potential.

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.

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

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.

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

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.

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.

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 the current path in phase Φ1 shown in Fig. 2. Fig. 4 is a diagram showing the current path in phases Φ2 and Φ4 shown in Fig. 2. Fig. 5 is a diagram showing the current path in phase Φ3 shown in Fig. 2.

As shown in FIG. 2, the control device 16 synchronously switches the conductive/non-conductive state of the switching element Qp and the conductive/non-conductive state of the rectifier element Q1. Specifically, the control device 16 controls the rectifier element Q1 to a conductive state during a period in which the switching element Qp is in a conductive state, and controls the rectifier 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 rectifier element Q2. Specifically, the control device 16 controls the rectifier element Q2 to a non-conductive state during a period in which the switching element Qp is in a conductive state, and controls the rectifier element Q2 to a conductive state during a period in which the switching element Qp is in a non-conductive state.

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 the switching element Qp and the switching element Q3 are not both in a conductive state, and includes the 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.

The duty ratio of the switching element Qp _{is d1} , and the duty ratio of the switching element Q3 is _d3 . The duty ratio is the ratio of the time during one cycle during which the switching element is in a conductive state. In other words, the switching element Qp is in a conductive state for a time ( _d1 x T) obtained by multiplying the duty ratio _d1 by the time T of one cycle. The switching element Q3 is in _a conductive state for a time ( _d3 x T) obtained by multiplying the duty ratio d3 by the time T of one cycle. Since the switching elements Qp and Q3 are not in a conductive state at the same time, the time difference Δ x T is greater than the time ( _d1 x T).

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 states of the switching elements Qp and Q3 at regular intervals so that the duty ratio _d1 and the duty ratio _d3 are equal to each other.

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 is explained below. In the following explanation, 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.

<Phase Φ1>
As shown in Fig. 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) is generated in the secondary winding 11b so that the potential of the positive terminal is higher than the potential of the negative terminal. As a result, a current I 1 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 rectifying element Q1 in this order, and returns to the negative terminal of the secondary winding 11b. At this time, a voltage obtained by subtracting the voltage V _C (see FIG. 6) across the capacitor 12 and the output voltage V _O (see FIG. 6) of the power conversion device 1 from the voltage V _S generated in the secondary winding 11b is applied to the inductor 13. Therefore, the current I ₁ flowing through the inductor 13 increases. The capacitor 12 is charged by the current I ₁ .

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 output voltage _VO is applied to the inductor 14 in the reverse direction, so that the current _I2 flowing through the inductor 14 decreases.

<Phase Φ2>
As shown in Fig. 4, in phase Φ2, the rectifier elements Q2 and Q4 are in a conducting state, and the switching elements Qp, Q3 and the rectifier element Q1 are in a non-conducting state. The switching element Qp and the rectifier element Q1 go from a conducting state to a non-conducting state, and the rectifier element Q2 goes from a non-conducting state to a conducting state. Therefore, due to the continuity of the current _I1 , the current _I1 flows through a current path that goes from the other end of the inductor 13 to 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 output voltage _V0 is applied to the inductor 13 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.

<Phase Φ3>
As shown in Fig. 5, in phase Φ3, the rectifier element Q2 and the switching element Q3 are in a conducting state, and the switching element Qp and the rectifier elements Q1 and Q4 are in a non-conducting state. Even when the phase is switched from Φ2 to Φ3, 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 non-conducting state to a conducting state and the rectifier element Q4 goes from a conducting state to a non-conducting state, a voltage obtained by subtracting the output voltage _V0 from the voltage _Vc across the inductor 14 is applied to the inductor 14. As a result, the current _I2 starts to increase. The capacitor 12 is discharged by the current _I2 .

<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 current path from the other end of the inductor ₁₄ to the positive output terminal 1P, the load, and the rectifier element Q4 in this order, and returns to one end of the inductor 14, due to the continuity of the current _I2 . At this time, the output voltage _VO is applied to the inductor 14 in the reverse direction, so the current _I2 flowing through the inductor 14 starts to decrease. In phase Φ4, the capacitor 12 is neither charged nor discharged.

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, causing the switching element Qp to be damaged. Active clamp circuits, regenerative circuits, snubber circuits, etc. are known as circuits for processing the energy stored in the excitation inductor. 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.

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.

As shown in equation (1), the voltage V _S is determined by the input voltage V _P , the number of turns N _P of the primary winding 11a and the number of turns N _S of the secondary winding 11b.

Due to the balance of the ET product in the inductor 13, the relationship of equation (2) holds among the voltage V _S , the voltage across both ends V _C , the output voltage V _O , the duty ratio d ₁ of the inductor 13, and the time T of one period.

Equation (3) is obtained from equation (2).

Due to the balance of the ET product in the inductor 14, the relationship of equation (4) holds among the voltage V _C across both ends, the output voltage V _O , the duty ratio d ₃ of the inductor 14, and the time T of one period.

Equation (5) is obtained from equation (4).

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

Due to charge balance in the capacitor 12, the relationship of equation (8) holds among the current I ₁ , the current I ₂ , the duty ratio d ₁ , the duty ratio d ₃ , and the time T of one period.

Equation (9) is obtained from equation (8).

As described above, it is understood that the voltage V _S , the voltage across both ends V _C , the output voltage V _O , the current I ₁ , and the current I ₂ do not depend on the time difference ratio Δ.

When the duty ratio d ₁ and the duty ratio d ₃ are equal, the following equations (10) to (12) are obtained from the equations (6), (7), and (9), respectively.

In this case, the maximum value of the output voltage _V0 is one-fourth of the voltage _Vs. The voltage _Vc across the capacitor 12 is half of the voltage _Vs. Furthermore, the currents _I1 (the average values) and _I2 (the average values) become equal regardless of the inductances 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 make the currents _I1 (the average values) and _I2 (the average values) equal.

Next, the output current waveform is expanded into a Fourier series to consider changes in harmonic components due to the duty ratio d ₁ , duty ratio d ₃ , and time difference ratio Δ. A Fourier series expansion of the output current i _O (t) can be obtained by simple calculation. If the Fourier series expansion of the output current i _O (t) is given by equation (13), the Fourier coefficients a ₀ , a _n , and b _n are expressed by equations (14) to (16), respectively. Note that inductance L ₁ is the inductance of inductor 13, and inductance L ₂ is the inductance of inductor 14.

According to the formulas (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. At this time, 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 set to 0.5, both the Fourier coefficients _an and _bn can be set to 0 when n is an odd number.

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 is generated in the secondary winding 11b. Then, a voltage obtained by subtracting the voltage V _C across the capacitor 12 and the output voltage V _O from the voltage V _S is applied to the inductor 13. As a result, the current I ₁ flowing through the inductor 13 increases, and the capacitor 12 is charged. At this time, the output voltage V _O is applied to the inductor 14 in the reverse direction, so the current I ₂ flowing through the inductor 14 decreases. On the other hand, when the switching element Q3 is set to a conductive state and the switching element Qp is set to a non-conductive state, a voltage obtained by subtracting the output voltage V _O from the voltage V _C across the capacitor 12 is applied to the inductor 14. As a result, the current I ₂ flowing through the inductor 14 increases, and the capacitor 12 is discharged. At this time, the output voltage V _O is applied to the inductor 13 in the reverse direction, so the current I ₁ flowing through the inductor 13 decreases. In this way, without connecting the transformers in parallel, the current flows in a distributed manner through the inductors 13 and 14. This makes it possible to reduce losses in the secondary circuit, particularly DC losses due to the resistance components of the inductors 13 and 14, while suppressing an increase in the circuit size.

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.

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 and the average value of the current _I2 equal.

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

In the above embodiment, the rectifying element Q1 is a switching element. The control device 16 controls the rectifying element Q1 to a conductive state during the period when the switching element Qp is in a conductive state, and controls the rectifying element Q1 to a non-conductive state during the period when the switching element Qp is in a non-conductive state. Since a current flows through the rectifying element Q1 during the period when the switching element Qp is in a conductive state, a current flows through the switching element (transistor) by setting the rectifying element Q1 to a conductive state during that 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 Q1 compared to when the rectifying element Q1 is a diode.

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 the period when the switching element Qp is in a conducting state, and controls the rectifying element Q2 to a conducting state during the period when the switching element Qp is in a non-conducting state. Since a current flows through the rectifying element Q2 during the 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 that 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.

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 the period when the switching element Q3 is in a conducting state, and controls the rectifying element Q4 to a conducting state during the period when the switching element Q3 is in a non-conducting state. Since a current flows through the rectifying element Q4 during the 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 that 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.

One embodiment of the present disclosure has been described in detail above, but the power conversion device according to the present disclosure is not limited to the above embodiment.

The power conversion device 1 does not need to include a capacitor 15.

At least one of the rectifying 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 differs from the power conversion device 1 mainly in that it includes rectifying elements D1 (second rectifying element), D2 (first rectifying element), and D4 (third rectifying element) instead of the rectifying elements Q1, Q2, and Q4. The rectifying elements D1, D2, and D4 are diodes. When the rectifying elements D1, D2, and D4 are diodes, the main terminals are the anode and the cathode.

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

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 element D1, the rectifying element D2, and the rectifying element D4 are diodes, the control device 16 does not need to control these rectifying elements. Therefore, it is possible to simplify the circuit configuration.

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 (6)

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. 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 the duty ratio of the first switching element and the duty ratio of the second switching element are equal. The power conversion device according to claim 1 or 2, wherein the control device adjusts 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. 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. 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. 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.

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