Power conversion device and control method

Abstract

Provided is a power conversion device in which high efficiency of power transmission can be achieved while establishing ZVS corresponding to a wide input / output voltage conversion ratio. A power conversion device 1 comprises: a switch (SW1); a (SW2) that is connected in series with the switch (SW1); an inductor (L1) that is connected to a connection node that connects the switch (SW1) and the switch (SW2); a voltage detection circuit (20) that detects the voltage applied across the switch (SW1) and outputs the comparison result between the voltage across the switch (SW1) and a set threshold; and a control unit (10) that controls the switching operations of the switches (SW1) and (SW2). The control unit (10) controls a dead time period from the turn-off of the switch (SW1) to the turn-on of the switch (SW2) in accordance with the comparison result.

Description

Power conversion device and control method

[0001] The present disclosure relates to a power conversion device and a control method thereof.

[0002] Patent Document 1 describes a power conversion device for performing so-called soft switching (for example, zero voltage switching (ZVS)).

[0003] Japanese Patent Application Laid-Open No. 2019-134674

[0004] In the technology disclosed in Patent Document 1, when performing ZVS, the energy required for ZVS, i.e., the negative current, is adjusted by controlling the on-period of the synchronous rectifier switch. However, in order to achieve ZVS in response to a wide input / output voltage conversion ratio, an excessive negative current may be required, which may result in a decrease in the efficiency of power transmission.

[0005] Therefore, the present disclosure provides a power conversion device and a control method that can achieve ZVS in response to a wide input / output voltage conversion ratio while achieving high efficiency in power transmission.

[0006] A power conversion device according to the present disclosure includes a first switch, a second switch connected in series with the first switch, an inductor connected to a connection node connecting the first switch and the second switch, a first input / output terminal connected to a terminal of the first switch that is not connected to the connection node, a second input / output terminal connected to a terminal of the inductor that is not connected to the connection node, a third input / output terminal connected to a terminal of the second switch that is not connected to the connection node, a voltage detection circuit that detects a voltage applied to both ends of the first switch and outputs a comparison result between the voltage applied to both ends and a set threshold value, and a control unit that controls the switching operations of the first switch and the second switch, and the control unit controls a dead time period from when the first switch is turned off to when the second switch is turned on according to the comparison result.

[0007] A control method according to the present disclosure is a control method for a power conversion device including a first switch, a second switch connected in series with the first switch, an inductor connected to a connection node connecting the first switch and the second switch, a first input / output terminal connected to a terminal of the first switch that is not connected to the connection node, a second input / output terminal connected to a terminal of the inductor that is not connected to the connection node, and a third input / output terminal connected to a terminal of the second switch that is not connected to the connection node, the control method including an acquisition step of acquiring a comparison result between a voltage applied to both ends of the first switch and a set threshold value, and a control step of controlling a dead time period from when the first switch is turned off to when the second switch is turned on in accordance with the comparison result.

[0008] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0009] According to a power conversion device and a control method according to an aspect of the present disclosure, it is possible to achieve ZVS in response to a wide range of input / output voltage conversion ratios, while achieving high efficiency in power transmission.

[0010] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device according to an embodiment. FIG. 1 is a diagram for explaining that ZVS is no longer established when the input / output voltage conversion ratio changes. FIG. 2 is a diagram for explaining that ZVS is no longer established when the input / output voltage conversion ratio changes. FIG. 3 is a diagram for explaining that a negative current increases when ZVS is established by controlling the on-period of a synchronous rectifier switch when the input / output voltage conversion ratio increases. FIG. 4 is a diagram for explaining that a negative current increases when ZVS is established by controlling the on-period of a synchronous rectifier switch when the input / output voltage conversion ratio increases. FIG. 5 is a diagram for explaining that a negative current increases when ZVS is established by controlling the on-period of a synchronous rectifier switch when the input / output voltage conversion ratio decreases. FIG. 6 is a diagram for explaining that a negative current increases when ZVS is established by controlling the on-period of a synchronous rectifier switch when the input / output voltage conversion ratio decreases. FIG. 7 is a diagram for explaining that an increase in negative current can be suppressed when ZVS is established by controlling the on-period and dead time of the synchronous rectifier switch when the input / output voltage conversion ratio increases. FIG. 1 is a diagram for explaining that, when the input / output voltage conversion ratio increases, ZVS is established by controlling the on-period and dead time period of the synchronous rectifier switch, thereby suppressing an increase in negative current. FIG. 2 is a diagram for explaining that, when the input / output voltage conversion ratio decreases, ZVS is established by controlling the on-period and dead time period of the synchronous rectifier switch, thereby suppressing an increase in negative current. FIG. 3 is a diagram for explaining that, when the input / output voltage conversion ratio decreases, ZVS is established by controlling the on-period and dead time period of the synchronous rectifier switch, thereby suppressing an increase in negative current. FIG. 4 is a diagram for explaining that, when the input / output voltage conversion ratio decreases, ZVS is established by controlling the on-period and dead time period of the synchronous rectifier switch, thereby suppressing an increase in negative current. FIG. 5 is a diagram for explaining an example of search control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 6 is a diagram for explaining an example of optimization control after search control when the input / output voltage conversion ratio is smaller than the predetermined ratio. FIG. 7 is a diagram for explaining a first example of initial control when the input / output voltage conversion ratio is smaller than the predetermined ratio. FIG. 8 is a diagram for explaining a second example of initial control when the input / output voltage conversion ratio is smaller than the predetermined ratio. FIG. 9 is a diagram for explaining a third example of initial control when the input / output voltage conversion ratio is smaller than the predetermined ratio.FIG. 10 is a diagram showing a fourth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 11 is a diagram showing a fifth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 12 is a diagram showing a sixth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 13 is a diagram showing a seventh example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 14 is a diagram showing an eighth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 15 is a diagram showing a ninth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio. FIG. 16 is a diagram showing a first example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio. FIG. 17 is a diagram showing a second example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio. FIG. 18 is a diagram showing a third example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio. FIG. 19 is a flowchart showing an example of a control method according to another embodiment.

[0011] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0012] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0013] (Embodiment) Hereinafter, a power conversion device according to an embodiment will be described.

[0014] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to an embodiment.

[0015] The power conversion device 1 is a step-down converter (buck converter) that steps down an input voltage to a predetermined voltage and outputs the voltage. The power conversion device 1 includes input / output terminals t1, t2, and t3. The input / output terminal t1 is an example of a first input / output terminal, the input / output terminal t2 is an example of a second input / output terminal, and the input / output terminal t3 is an example of a third input / output terminal. The input / output terminal t1 is an input terminal to which a voltage is input, the input / output terminal t2 is an output terminal from which a voltage is output, and the input / output terminal t3 is a ground terminal connected to ground. The voltage at the input / output terminal t1 refers to the voltage between the input / output terminal t1 and the input / output terminal t3, and is the input voltage input to the power conversion device 1. The voltage at the input / output terminal t2 refers to the voltage between the input / output terminal t2 and the input / output terminal t3, and is the output voltage output from the power conversion device 1.

[0016] The power conversion device 1 includes switches SW1 and SW2, an inductor L1, a control unit 10, a voltage detection circuit 20, an input voltage detection circuit 30, and an output voltage detection circuit 40. The switch SW1 is an example of a first switch, and the switch SW2 is an example of a second switch.

[0017] The switches SW1 and SW2 are provided on a path connecting the input / output terminal t1 and the input / output terminal t3. In the path, the switch SW2 is connected in series with the switch SW1. The switch SW2 is also called a synchronous rectification switch.

[0018] The inductor L1 is connected to the connection node connecting the switch SW1 and the switch SW2.

[0019] The input / output terminal t1 is connected to the terminal of the switch SW1 that is not connected to the connection node. The input / output terminal t2 is connected to the terminal of the inductor L1 that is not connected to the connection node. The input / output terminal t3 is connected to the terminal of the switch SW2 that is not connected to the connection node.

[0020] The switches SW1 and SW2 are, for example, N-channel metal oxide semiconductor field effect transistors (MOSFETs), and the input / output terminal t1 is connected to the drain of the switch SW1, and the input / output terminal t3 is connected to the source of the switch SW2. The inductor L1 is connected to the connection node connecting the source of the switch SW1 and the drain of the switch SW2.

[0021] The voltage detection circuit 20 detects the voltage applied to the switch SW1 and outputs the result of comparing the voltage across the switch SW1 with a set threshold to the control unit 10. The voltage detection circuit 20 is, for example, a comparator. The set threshold is a threshold for determining whether or not ZVS of the switch SW1 is established, and is, for example, 0 V. For example, ZVS is established when the switch SW1 is turned on when the voltage across the switch SW1 is equal to or lower than the set threshold, but ZVS is not established when the switch SW1 is turned on when the voltage across the switch SW1 is higher than the set threshold.

[0022] The input voltage detection circuit 30 detects the input voltage between the input / output terminal t1 and the input / output terminal t3, and outputs the detection result to the control unit 10.

[0023] The output voltage detection circuit 40 detects the output voltage between the input / output terminal t2 and the input / output terminal t3, and outputs the detection result to the control unit 10.

[0024] The control unit 10 controls the switching operations of the switches SW1 and SW2. The control unit 10 is, for example, a microcontroller unit (MCU). The control unit 10 controls the switching operations of the switches SW1 and SW2 via gate drivers connected to the gates of the switches SW1 and SW2. The control unit 10 may also have the functions of the voltage detection circuit 20, the input voltage detection circuit 30, or the output voltage detection circuit 40.

[0025] The following describes a power conversion device 1 that can achieve high efficiency in power transmission while establishing ZVS in response to a wide input / output voltage conversion ratio. To achieve this, the control unit 10 controls the dead time period in accordance with the comparison result in the voltage detection circuit 20, as will be described in detail later. The dead time period is a period during which both switches SW1 and SW2 are off, and more specifically, is a period from when switch SW1 is turned off to when switch SW2 is turned on.

[0026] First, the relationship between the input / output voltage conversion ratio and the feasibility of ZVS will be described with reference to Figures 2A and 2B. The input / output voltage conversion ratio is the magnitude of the output voltage relative to the input voltage, and when the input voltage is V ｉｎ and the output voltage is V ｏ In this case, V ｏ / V ｉｎ is.

[0027] 2A and 2B are diagrams for explaining that a change in the input / output voltage conversion ratio causes ZVS to no longer be established. ｇｓ＿ＣＴＲ ), the gate-source voltage of the switch SW2 (V ＧＳ＿ＳＲ ), input / output voltage difference (V ｉｎ -V ｏ ), the drain-source voltage of the switch SW1 (V ｄｓ＿ＣＴＲ ), the current flowing through the inductor L1 (I Ｌ ) is shown as a time domain waveform. The drain-source voltage of the switch SW1 is also called the voltage across the switch SW1. In FIG. 2B, the horizontal axis represents the drain-source voltage (V ｄｓ＿ＣＴＲ ) that is, the voltage across the switch SW1, and the vertical axis represents the current (I Ｌ ) and the impedance of the load connected to the input / output terminal t2 (Z ｎ ) (a value corresponding to the current flowing through inductor L1) is shown.

[0028] 2A and 2B indicates a state where ZVS is established. "I" shown in FIGS. 2A and 2B indicates a state where the input / output voltage conversion ratio is increased from the state of "II" (in other words, a state where the output voltage is no longer large relative to the input voltage, or further in other words, a state where V ｉｎ -V ｏ "III" is a state in which the input / output voltage conversion ratio is small (in other words, the output voltage is large relative to the input voltage, or in other words, V ｉｎ -V ｏ This indicates a state in which ZVS is no longer established.

[0029] 2A and 2B is a dead time period, which is a fixed value here. Specifically, resonance of the voltage across the switch SW1 (V in FIG. 2A) occurs during the period when the switches SW1 and SW2 are off (dead time period) due to the parasitic capacitance of the switches SW1 and SW2 and the inductance of the inductor L1. ｄｓ＿ＣＴＲ If one period of the resonance (resonance) is 360°, then, for example, Tdead2=111°.

[0030] "Toff1" shown in FIG. 2B corresponds to the on-period of switch SW2 in state "I," "Toff2" corresponds to the on-period of switch SW2 in state "II," and "Toff3" corresponds to the on-period of switch SW2 in state "III." It can be seen that the on-period of switch SW2 is shortened to increase the input-output voltage conversion ratio from state "II" to state "I," and the negative current flowing through inductor L1 decreases accordingly. It can also be seen that the on-period of switch SW2 is lengthened to decrease the input-output voltage conversion ratio from state "II" to state "III," and the negative current flowing through inductor L1 increases accordingly. In this way, when the on-period of switch SW2 is shortened, the negative current decreases, and when the on-period of switch SW2 is lengthened, the negative current increases.

[0031] As shown in FIG. 2A, in the state “II”, when the switch SW1 is turned on, that is, V ｇｓ＿ＣＴＲ When the voltage across the switch SW1 (V ｄｓ＿ＣＴＲ ) is almost 0 V, and ZVS is established. The fact that ZVS is established in the state "II" is also shown in FIG. 2B. Specifically, V ｉｎ -V ｏ 2A and 2B, in the "II" state, the current flowing through inductor L1 is also approximately zero when switch SW1 is turned on, and ideal ZVS is established.

[0032] As shown in FIG. 2A, in the "I" state, when the switch SW1 is turned on, the voltage across the switch SW1 is higher than 0V, and ZVS is not established. As described above, the dead time period is fixed here, and the dead time period ends before the voltage across the switch SW1 falls to 0V. The fact that ZVS is not established in the "I" state is also shown in FIG. 2B. Specifically, V in the "I" state ｉｎ -V ｏ The tip of the curve that rotates clockwise from the tip of the arrow "Toff1" by Tdead2=111° with this as its center is the timing when switch SW1 turns on, and the coordinate of the horizontal axis of this tip at this timing (voltage across switch SW1) is greater than 0 V, and ZVS is not established.

[0033] As shown in FIG. 2A, in the state "III", when the switch SW1 is turned on, the voltage across the switch SW1 is higher than 0V, and ZVS is not established. As described above, the dead time period is fixed here, and the dead time period does not end even after the voltage across the switch SW1 falls to 0V. The dead time period ends when the voltage across the switch SW1 increases due to resonance. The fact that ZVS is not established in the state "III" is also shown in FIG. 2B. Specifically, V in the state "III" ｉｎ -V ｏ The tip of the curve that rotates clockwise from the tip of the arrow "Toff3" by Tdead2=111° with this as its center is the timing when switch SW1 turns on, and the coordinate of the horizontal axis of this tip at this timing (voltage across switch SW1) is greater than 0 V, and ZVS is not established.

[0034] In this way, the change in the input / output voltage conversion ratio causes ZVS to no longer be established.

[0035] Next, conventional methods for achieving ZVS and their problems when the input / output voltage conversion ratio changes will be described with reference to Figures 3A and 3B and Figures 4A and 4B. First, the case where the input / output voltage conversion ratio increases will be described with reference to Figures 3A and 3B.

[0036] 3A and 3B are diagrams for explaining that when the input / output voltage conversion ratio becomes large and ZVS is established by controlling the on-period of switch SW2 (synchronous rectification switch), the negative current increases.

[0037] When the input / output voltage conversion ratio increases to state "I", extending the on period of switch SW2 to state "I'" shown in Figure 3A, specifically extending Toff1 to Toff1' as shown in Figure 3B, allows switch SW1 to be turned on when the voltage across switch SW1 is 0 V or less, thereby achieving ZVS. However, as shown in Figure 3B, an excessive negative current is required, which reduces the efficiency of power transmission.

[0038] Next, a case where the input / output voltage conversion ratio is small will be described with reference to FIGS. 4A and 4B.

[0039] 4A and 4B are diagrams for explaining that when the input / output voltage conversion ratio becomes small, the negative current increases when ZVS is established by controlling the on-period of the switch SW2 (synchronous rectification switch).

[0040] When the input / output voltage conversion ratio decreases to state "III," extending the on period of switch SW2 to state "III'" shown in Fig. 4A, specifically extending Toff3 to Toff3' as shown in Fig. 4B, enables switch SW1 to be turned on when the voltage across switch SW1 is 0 V or less, thereby achieving ZVS. However, as shown in Fig. 4B, an excessive negative current is required, which reduces the efficiency of power transmission.

[0041] In contrast, in the power conversion device 1 of the present disclosure, the control unit 10 controls the dead time period in accordance with the comparison result in the voltage detection circuit 20, or controls the on-period of the switch SW2 in addition to the dead time period depending on the input-output voltage conversion ratio, thereby achieving ZVS and suppressing an increase in negative current. This will be described using Figures 5A and 5B and Figures 6A and 6B. First, a case in which the dead time period and the on-period of the switch SW2 are controlled when the input-output voltage conversion ratio increases (for example, when the state changes from "II" to "I") will be described using Figures 5A and 5B.

[0042] 5A and 5B are diagrams illustrating how, when the input / output voltage conversion ratio increases, ZVS can be established by controlling the on-period and dead-time period of switch SW2 (synchronous rectification switch), thereby suppressing an increase in negative current.

[0043] As shown in FIGS. 5A and 5B , when the input-output voltage conversion ratio increases to enter the “I” state, ZVS is not established, as described with reference to FIGS. 2A and 2B . Furthermore, when the “I′” state is entered by controlling the on-period of switch SW2, ZVS can be established, but negative current increases, as described with reference to FIGS. 3A and 3B . On the other hand, by extending the dead time period and the on-period of switch SW2, as shown in FIG. 5A , specifically by extending Tdead2 to Tdead2″ and Toff1 to Toff1″, as shown in FIGS. 5A and 5B , switch SW1 can be turned on when the voltage across switch SW1 is 0 V or less, thereby establishing ZVS. In this case, the increase in negative current is also suppressed, demonstrating the establishment of ideal ZVS.

[0044] Next, a case where the dead time period and the on period of switch SW2 are controlled when the input / output voltage conversion ratio becomes smaller (for example, when the state changes from "II" to "III") will be described with reference to Figures 6A and 6B.

[0045] 6A and 6B are diagrams illustrating how, when the input / output voltage conversion ratio becomes small, ZVS can be established by controlling the on-period and dead time period of switch SW2 (synchronous rectification switch), thereby suppressing an increase in negative current.

[0046] As shown in FIGS. 6A and 6B , when the input-output voltage conversion ratio decreases to state "III," ZVS is not established, as described with reference to FIGS. 2A and 2B . Furthermore, when state "III'" is established by controlling the on-period of switch SW2, ZVS can be established, but negative current increases, as described with reference to FIGS. 4A and 4B . On the other hand, by shortening the dead time and extending the on-period of switch SW2, as shown in FIG. 6A , specifically, by shortening Tdead2 to Tdead2" and extending Toff3 to Toff3" as shown in FIGS. 6A and 6B , switch SW1 can be turned on when the voltage across switch SW1 is 0 V or less, thereby establishing ZVS. In this case, the increase in negative current is also suppressed, and it can be seen that ideal ZVS is established.

[0047] The control unit 10 calculates an input / output voltage conversion ratio from the input voltage detected by the input voltage detection circuit 30 and the output voltage detected by the output voltage detection circuit 40, and if the calculated input / output voltage conversion ratio is smaller than a predetermined ratio, the control unit 10 controls the dead time period and the on period of the switch SW2 according to the comparison result of the voltage detection circuit 20, thereby establishing ZVS and suppressing an increase in negative current. For example, the predetermined ratio is 0.5, and the control unit 10 determines that if the input / output voltage conversion ratio is smaller than 0.5, in other words, if the output voltage is smaller than half the input voltage, or further in other words, if V ｉｎ -V ｏ >0.5V ｉｎ In this case, the dead time period and the ON period of the switch SW2 are controlled according to the result of the comparison.

[0048] Depending on the input / output voltage conversion ratio, there may be a shortage of energy (negative current) required for ZVS. For example, if the input / output voltage conversion ratio is smaller than a predetermined ratio, specifically, if it is smaller than 0.5, the negative current required for ZVS is insufficient. In response to this, the negative current can be increased by lengthening the on-period of switch SW2. Therefore, by controlling the on-period of switch SW2 in addition to the dead time period, ZVS can be more reliably achieved over a wide range of input / output voltage conversion ratios, while improving the efficiency of power transmission.

[0049] When the calculated input / output voltage conversion ratio is equal to or greater than a predetermined ratio, the control unit 10 controls the dead time period in accordance with the comparison result of the voltage detection circuit 20, thereby establishing ZVS and suppressing an increase in negative current. For example, the predetermined ratio is 0.5, and the control unit 10 determines that when the input / output voltage conversion ratio is 0.5 or greater, in other words, when the output voltage is half or greater than the input voltage, or further in other words, when V ｉｎ -V ｏ ≦0.5V ｉｎ In this case, the dead time period is controlled in accordance with the comparison result, and the ON period of the switch SW2 is not controlled in accordance with the comparison result.

[0050] When the input / output voltage conversion ratio is smaller than a predetermined ratio, specifically, when it is smaller than 0.5, the negative current required for ZVS is insufficient. Therefore, in this case, by controlling the on-period of switch SW2 in addition to the dead time period, it is possible to more reliably establish ZVS over a wide range of input / output voltage conversion ratios while improving the efficiency of power transmission. Furthermore, when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, specifically, equal to or greater than 0.5, the negative current required for ZVS is not insufficient. Therefore, by controlling the dead time period without controlling the on-period of switch SW2, it is possible to establish ZVS over a wide range of input / output voltage conversion ratios while improving the efficiency of power transmission.

[0051] Next, the operation of the power conversion device 1 (specifically, the operation of the control unit 10) when the input / output voltage conversion ratio is smaller than a predetermined ratio will be described in detail with reference to FIGS. 7 to 17. FIG.

[0052] The control unit 10 performs search control at least once to search for a combination of the dead time period and the on period of the switch SW2 that can establish ZVS and suppress an increase in negative current. Here, the search control will be described with reference to FIG. 7.

[0053] FIG. 7 is a diagram showing an example of search control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0054] The search control is to control the switches SW1 and SW2 so that the voltage across the switch SW1 does not become equal to or less than a set threshold (e.g., 0 V), i.e., so that ZVS is not established, by shortening the on-period of the switch SW2 and extending the dead time period so that the voltage across the switch SW1 becomes equal to or less than the set threshold, i.e., so that ZVS is established. A combination of the successive "SR-SW shortening" control and "Tdead extension" control shown in FIG. 7 constitutes one search control. The control unit 10 performs this search control at least once. Specifically, the control unit 10 performs the search control until the voltage across the switch SW1 does not become equal to or less than the set threshold when the dead time period is extended. Because the voltage across the switch SW1 may not become equal to or less than the set threshold when the dead time period is extended in one search control, the control unit 10 may perform the search control only once. Furthermore, when the dead time period is extended, the control unit 10 may perform the search control multiple times until the voltage across the switch SW1 is not equal to or lower than the set threshold value. Fig. 7 shows an example in which the search control is performed multiple times.

[0055] Furthermore, the control unit 10 performs optimization control when, during at least one search control, the voltage across the switch SW1 does not become equal to or less than the set threshold value when the dead time period is extended. Here, the optimization control will be described with reference to FIG. 8.

[0056] FIG. 8 is a diagram showing an example of optimization control after search control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0057] The optimization control is to control the switches SW1 and SW2 so as to extend the ON period of the switch SW2 and shorten the dead time period. The combination of the "SR-SW extension" control and the "Tdead shortening" control shown in FIG. 8 is the optimization control.

[0058] In this way, the on-period of switch SW2 is shortened so that the voltage across switch SW1 does not become equal to or less than the set threshold, in other words, so that ZVS is not established, and the dead time period is extended so that the voltage across switch SW1 becomes equal to or less than the set threshold, in other words, so that ZVS is established, and this search control is performed at least once until ZVS is no longer established even when the dead time period is extended. In other words, by shortening the on-period of switch SW2 to reduce the negative current required for ZVS, the dead time period is controlled, and an optimal combination of the dead time period and the on-period of switch SW2 that establishes ZVS without excessive negative current is searched for.

[0059] After at least one search control has been performed, the on-period of switch SW2 is slightly shorter than the optimal on-period due to the search for the optimal combination, as shown in the graph on the lower right of Figure 7, and the negative current required for ZVS is insufficient. Therefore, after at least one search control has been performed, as shown in Figure 8, the on-period of switch SW2 can be extended to set the negative current to the minimum value required for ZVS, and ZVS can be achieved by shortening the dead time. Therefore, it is possible to achieve ZVS while improving the efficiency of power transmission.

[0060] Note that ZVS may not be established even when search control is performed, depending on the on-period of switch SW2 before search control is performed. Therefore, for example, when the input / output voltage conversion ratio is smaller than a predetermined ratio and the voltage across switch SW1 before search control is performed is higher than a set threshold, that is, when ZVS is not established, the control unit 10 performs initial control to extend the dead time period before search control is performed. This makes it possible to determine whether the on-period of switch SW2 before search control is performed is long enough to establish ZVS. This will be described with reference to first to third examples.

[0061] First, a first example of the initial control will be described with reference to FIG.

[0062] FIG. 9 is a diagram showing a first example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0063] In a first example of the initial control, the control unit 10 performs a first control ("extending Tdead" control shown in FIG. 9) that extends the dead time period during the initial control. As shown in the graph on the right side of FIG. 9, if the voltage across the switch SW1 becomes equal to or less than the set threshold before the dead time period reaches the upper dead time limit during the first control, that is, if ZVS is established, the control unit 10 starts search control using, as an initial value, the dead time period when the voltage across the switch SW1 becomes equal to or less than the set threshold during the first control (Tdead shown in the graph on the right side of FIG. 9).

[0064] In this way, if ZVS is established before the dead time reaches the upper dead time limit during the first control for extending the dead time, it can be determined that the on-period of switch SW2 is long enough to establish ZVS. Therefore, when the on-period of switch SW2 is long enough to establish ZVS, search control for shortening the on-period of switch SW2 can be started.

[0065] The upper limit of dead time is the upper limit of dead time required to establish ZVS, and is determined by the capacitance of switch SW1, the inductance of inductor L1, and the range of the input-output voltage conversion ratio. The range of the input-output voltage conversion ratio is the range from the minimum to the maximum of the input-output voltage conversion ratio, calculated from the expected maximum and minimum input voltages, and the expected maximum and minimum output voltages. The same applies to the upper limit of dead time described below, so a description of the upper limit of dead time will be omitted below.

[0066] Next, a second example of the initial control will be described with reference to FIG.

[0067] FIG. 10 is a diagram showing a second example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0068] In a second example of the initial control, the control unit 10 performs a first control ("Tdead extension" control shown in FIG. 10) to extend the dead time period during the initial control. As shown in the graph on the upper right side of FIG. 10, if the voltage across the switch SW1 does not become equal to or less than the set threshold even when the dead time period reaches the upper limit of the dead time during the first control, i.e., if ZVS is not established, the control unit 10 performs a second control ("SR-SW extension" control shown in FIG. 10) to extend the on-period of the switch SW2. As shown in the graph on the lower left side of FIG. 10, if the voltage across the switch SW1 becomes equal to or less than the set threshold before the on-period of the switch SW2 reaches the upper limit of the on-period during the second control, i.e., if ZVS is established, the control unit 10 performs a third control ("Tdead shortening" control shown in FIG. 10) to shorten the dead time period. As shown in the graph on the lower right side of Figure 10, if the voltage across switch SW1 becomes higher than the set threshold during the third control, that is, if ZVS is no longer established, the control unit 10 starts search control using, as initial values, the on period of switch SW1 when the voltage across switch SW1 becomes equal to or lower than the set threshold during the second control and the dead time period when the voltage across switch SW1 becomes higher than the set threshold during the third control (SR_SW and Tdead shown in the graph on the lower right side of Figure 10).

[0069] In this way, if ZVS is not established even when the dead time reaches the upper limit during the first control for extending the dead time, it can be determined that the on-period of switch SW2 is not long enough to establish ZVS, and therefore, the second control for extending the on-period of switch SW2 is performed in the initial control. If ZVS is established before the on-period of switch SW2 reaches the upper limit during the second control, it can be determined that the on-period of switch SW2 is long enough to establish ZVS through the second control. Furthermore, in order to determine whether the on-period of switch SW2 is long enough to establish ZVS, the dead time is extended to the upper limit during the first control, and therefore, search control for extending the dead time cannot be started. Therefore, the third control for shortening the dead time until ZVS is no longer established can be performed. As a result, search control for shortening the on-period of switch SW2 and extending the dead time can be started when the on-period of switch SW2 is long enough to establish ZVS and the dead time is not too long.

[0070] The on-period upper limit is the upper limit of the on-period of switch SW2 required to establish ZVS, which is determined by the capacitance component of switch SW1, the inductance of inductor L1, and the range of the input / output voltage conversion ratio. Note that the same applies to the on-period upper limit described below, and therefore, a description of the on-period upper limit will be omitted below.

[0071] Next, a third example of the initial control will be described with reference to FIG.

[0072] FIG. 11 is a diagram showing a third example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0073] In a third example of the initial control, the control unit 10 performs a first control ("Tdead extension" control shown in FIG. 11) to extend the dead time period during the initial control. As shown in the graph in the upper center of FIG. 11, if the voltage across the switch SW1 does not become equal to or less than the set threshold even when the dead time period reaches the dead time upper limit during the first control, i.e., if ZVS is not established, the control unit 10 performs a second control ("SR-SW extension" control shown in FIG. 11) to extend the on-period of the switch SW2. As shown in the graph in the upper right of FIG. 11, if the voltage across the switch SW1 does not become equal to or less than the set threshold even when the on-period of the switch SW2 reaches the on-period upper limit during the second control, i.e., if ZVS is not established, the control unit 10 performs a third control ("Tdead shortening" control shown on the left side of FIG. 11) to shorten the dead time period. As shown in the graph on the lower left side of Fig. 11 , if the voltage across switch SW1 becomes equal to or lower than the set threshold during the third control, that is, if ZVS is established, the control unit 10 performs fourth control (the "Tdead shortening" control on the right side of Fig. 11 ) to further shorten the dead time period. As shown in the graph on the lower right side of Fig. 11 , if the voltage across switch SW1 becomes higher than the set threshold during the fourth control, that is, if ZVS is no longer established, the control unit 10 starts search control using, as initial values, the on-period of switch SW2, which is the on-period upper limit, and the dead time period when the voltage across switch SW1 becomes higher than the set threshold during the fourth control (SR_SW and Tdead shown in the graph on the lower right side of Fig. 11 ).

[0074] In this way, if ZVS is not established even when the dead time reaches the upper dead time limit during the first control for extending the dead time, it can be determined that the on-period of switch SW2 is not long enough to establish ZVS, and therefore, a second control for extending the on-period of switch SW2 is performed in the initial control. If ZVS is not established even when the on-period of switch SW2 reaches the upper dead time limit during the second control, it is possible that the dead time is too long, and therefore, a third control for shortening the dead time is performed in the initial control. If ZVS is established during the third control, it can be determined that the dead time is too long, and therefore, a fourth control for further shortening the dead time until ZVS is no longer established in the initial control. As a result, it is possible to start search control for shortening the on-period of switch SW2 and extending the dead time when the on-period of switch SW2 is long enough to establish ZVS and is not too long.

[0075] In the first to third examples, initial control is performed to extend the dead time before the search control is performed when ZVS is not established before the search control is performed. However, this is not limited to this. For example, when the input / output voltage conversion ratio is smaller than a predetermined ratio, if the voltage across switch SW1 before the search control is performed is higher than a set threshold, i.e., when ZVS is not established, the control unit 10 may perform initial control to extend the on-period of switch SW2 before the search control is performed. This makes it possible to make the on-period of switch SW2 before the search control sufficient to establish ZVS. This will be described using a fourth and fifth example.

[0076] First, a fourth example of the initial control will be described with reference to FIG.

[0077] FIG. 12 is a diagram showing a fourth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0078] In a fourth example of initial control, the control unit 10 performs first control ("SR-SW extend" control shown in FIG. 12) to extend the on-period of the switch SW2 during the initial control. As shown in the graph on the right side of FIG. 12, if the voltage across the switch SW1 becomes equal to or less than the set threshold before the on-period of the switch SW2 reaches its upper on-period limit during the first control, that is, if ZVS is established, the control unit 10 starts search control using, as an initial value, the on-period of the switch SW2 when the voltage across the switch SW1 becomes equal to or less than the set threshold during the first control (SR-SW shown in the graph on the right side of FIG. 12).

[0079] In this way, if ZVS is established before the on-period of switch SW2 reaches the on-period upper limit during the first control that extends the on-period of switch SW2, it can be determined that the on-period of switch SW2 has become long enough to establish ZVS, and search control can be started to shorten the on-period of switch SW2 when the on-period of switch SW2 is long enough to establish ZVS.

[0080] Next, a fifth example of the initial control will be described with reference to FIG.

[0081] FIG. 13 is a diagram showing a fifth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0082] In a fifth example of initial control, the control unit 10 performs a first control (the "SR-SW extension" control shown in FIG. 13) to extend the on-period of the switch SW2 during the initial control. As shown in the graph on the upper right side of FIG. 13, if the on-period of the switch SW2 reaches the on-period upper limit value during the first control but the voltage across the switch SW1 does not become equal to or less than the set threshold, i.e., if ZVS is not established, the control unit 10 performs a second control (the "Tdead shortening" control shown on the left side of FIG. 13) to shorten the dead time period. As shown in the graph on the lower left side of FIG. 13, if the voltage across the switch SW1 becomes equal to or less than the set threshold during the second control, i.e., if ZVS is established, the control unit 10 performs a third control (the "Tdead shortening" control shown on the right side of FIG. 13) to further shorten the dead time period. As shown in the graph on the lower right side of Figure 13, if the voltage across switch SW1 becomes higher than the set threshold during the third control, that is, if ZVS is no longer established, the control unit 10 starts search control using, as initial values, the on-period of switch SW2, which is the upper limit of the on-period, and the dead time period when the voltage across switch SW1 becomes higher than the set threshold during the third control (SR-SW and Tdead shown from the left to the lower right side of Figure 13).

[0083] In this way, if ZVS is not established even when the on-period of switch SW2 reaches the on-period upper limit during first control, which extends the on-period of switch SW2, it is possible that the dead time is too long, so second control, which shortens the dead time, is performed in initial control. If ZVS is established during second control, it can be determined that the dead time was too long, so third control, which further shortens the dead time until ZVS is no longer established during initial control, is performed. In this way, it is possible to start search control, which shortens the on-period of switch SW2 and extends the dead time, when the on-period of switch SW2 is long enough to establish ZVS and the dead time is not too long.

[0084] It should be noted that there are cases where ZVS is already established before search control is performed. In such cases, ZVS may be established in a state where the dead time period is long and the negative current is excessive. Therefore, a sixth example of initial control that is performed when ZVS is already established before search control is performed will be described. The sixth example of initial control will be described with reference to FIG. 14 .

[0085] FIG. 14 is a diagram showing a sixth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0086] In a sixth example of initial control, when the input / output voltage conversion ratio is smaller than a predetermined ratio, and when the voltage across switch SW1 before performing search control is equal to or lower than a set threshold, that is, when ZVS is established, control unit 10 performs initial control to shorten the dead time period before performing search control (control to shorten Tdead shown in FIG. 14 ). As shown in the graph on the right side of FIG. 14 , when the voltage across switch SW1 becomes higher than the set threshold during initial control, that is, when ZVS is no longer established, control unit 10 starts search control with the dead time period (Tdead shown in the graph on the right side of FIG. 14 ) when the voltage across switch SW1 becomes higher than the set threshold during initial control as an initial value.

[0087] In this way, if ZVS is already established before search control is performed, there is a possibility that ZVS is established in a state where the dead time period is long and the negative current is excessive. Therefore, if ZVS is established before search control is performed, initial control is performed to shorten the dead time period until ZVS is no longer established before search control is performed, so that search control can be started in a state where the dead time period is not too long.

[0088] Note that if ZVS is already established before search control is performed, it is possible that ZVS is established when the on-period of switch SW2 is long and the negative current is excessive. Therefore, for example, if the input / output voltage conversion ratio is smaller than a predetermined ratio and the voltage across switch SW1 before search control is performed is equal to or lower than a set threshold, i.e., when ZVS is established, the control unit 10 performs initial control to shorten the on-period of switch SW2 before search control is performed. This makes it possible to start search control without the on-period of switch SW2 being too long. This will be described with seventh to ninth examples.

[0089] First, a seventh example of the initial control will be described with reference to FIG.

[0090] FIG. 15 is a diagram showing a seventh example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0091] In the seventh example of initial control, the control unit 10 performs a first control (the "SR-SW shortening" control shown in FIG. 15) that shortens the on-period of the switch SW2 during the initial control. As shown in the central graph in FIG. 15, if the voltage across the switch SW1 becomes higher than the set threshold before the on-period of the switch SW2 reaches its lower limit during the first control, that is, if ZVS is no longer established, the control unit 10 performs a second control (the "Tdead extending" control shown in FIG. 15) that lengthens the dead time. As shown in the graph on the right side of Figure 15, if the voltage across switch SW1 becomes equal to or lower than the set threshold value before the dead time period reaches the upper dead time limit during the second control, that is, if ZVS is established, the control unit 10 starts search control using as initial values ​​the on period of switch SW2 when the voltage across switch SW1 becomes higher than the set threshold value during the first control and the dead time period when the voltage across switch SW1 becomes equal to or lower than the set threshold value during the second control (SR-SW and Tdead shown in the graph on the right side of Figure 15).

[0092] In this way, if ZVS is no longer established by the time the on-period of switch SW2 reaches the on-period lower limit during the first control that shortens the on-period of switch SW2, it can be determined that the on-period of switch SW2 was too long. However, shortening the on-period of switch SW2 through the first control may result in the on-period of switch SW2 being insufficiently long to establish ZVS. Therefore, in order to determine whether the on-period of switch SW2 is long enough to establish ZVS, the second control that extends the dead time is performed during the initial control. If ZVS is established by the time the dead time reaches the dead time upper limit during the second control, it can be determined that the on-period of switch SW2 is long enough to establish ZVS, and the search control can be started without the on-period of switch SW2 being too long.

[0093] The on-period lower limit is the lower limit of the on-period of switch SW2 required to establish ZVS, which is determined by the capacitance component of switch SW1, the inductance of inductor L1, and the range of the input / output voltage conversion ratio. Note that the on-period lower limit described below has the same meaning, so a description of the on-period lower limit will be omitted below.

[0094] Next, an eighth example of the initial control will be described with reference to FIG.

[0095] FIG. 16 is a diagram showing an eighth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0096] In the eighth example of the initial control, the control unit 10 performs a first control (the "SR-SW shortening" control shown in FIG. 16) to shorten the on-period of the switch SW2 during the initial control. As shown in the graph in the upper center of FIG. 16, if the voltage across the switch SW1 becomes higher than the set threshold before the on-period of the switch SW2 reaches the on-period lower limit during the first control, that is, if ZVS is no longer established, the control unit 10 performs a second control (the "Tdead extending" control shown in FIG. 16) to lengthen the dead time period. As shown in the graph in the upper right of FIG. 16, if the voltage across the switch SW1 does not become equal to or lower than the set threshold even when the dead time period reaches the dead time upper limit during the second control, that is, if ZVS is not established, the control unit 10 performs a third control (the "Tdead shortening" control shown on the left side of FIG. 16) to shorten the dead time period. As shown in the graph on the lower left side of Figure 16, if the voltage across switch SW1 becomes equal to or less than the set threshold before the dead time period reaches the dead time lower limit during the third control, that is, if ZVS is established, the control unit 10 performs fourth control ("Tdead shortening" control on the right side of Figure 16) to further shorten the dead time period. As shown in the graph on the lower right side of Figure 16, if the voltage across switch SW1 becomes higher than the set threshold during the fourth control, that is, if ZVS is no longer established, the control unit 10 starts search control using as initial values ​​the on-period of switch SW2 when the voltage across switch SW1 became higher than the set threshold during the first control and the dead time period when the voltage across switch SW1 became higher than the set threshold during the fourth control (SR-SW and Tdead shown in the graph on the lower right of Figure 16).

[0097] In this way, if ZVS is no longer established by the time the on-period of switch SW2 reaches the on-period lower limit during the first control for shortening the on-period of switch SW2, it can be determined that the on-period of the switch SW2 was too long. However, it is possible that ZVS was established in a state where the dead time period was long and the negative current was excessive. Therefore, to determine whether the dead time period is too long, the second control for extending the dead time period is performed during the initial control. If ZVS is not established even when the dead time period reaches the upper dead time limit during the second control, it is possible that the dead time period is too long, so the third control for shortening the dead time period is performed during the initial control. If ZVS is established during the third control, it can be determined that the dead time period was too long, so the fourth control for further shortening the dead time period until ZVS is no longer established during the initial control. This allows the search control to be started when the on-period of switch SW2 is not too long and the dead time period is not too long.

[0098] The dead time lower limit is the lower limit of the dead time period required to establish ZVS, which is determined by the capacitance component of switch SW1, the inductance of inductor L1, and the range of the input / output voltage conversion ratio. Note that the same applies to the on-period lower limit described below, so a description of the dead time lower limit will be omitted below.

[0099] Next, a ninth example of the initial control will be described with reference to FIG.

[0100] FIG. 17 is a diagram showing a ninth example of initial control when the input / output voltage conversion ratio is smaller than a predetermined ratio.

[0101] In the ninth example of the initial control, the control unit 10 performs a first control (the "SR-SW shortening" control shown in FIG. 17) to shorten the on-period of the switch SW2 during the initial control. As shown in the graph in the upper center of FIG. 17, if the voltage across the switch SW1 becomes higher than the set threshold before the on-period of the switch SW2 reaches the on-period lower limit during the first control, that is, if ZVS is no longer established, the control unit 10 performs a second control (the "Tdead extending" control shown in FIG. 17) to lengthen the dead time period. As shown in the graph in the upper right of FIG. 17, if the voltage across the switch SW1 does not become equal to or lower than the set threshold even when the dead time period reaches the dead time upper limit during the second control, that is, if ZVS is not established, the control unit 10 performs a third control (the "Tdead shortening" control shown in FIG. 17) to shorten the dead time period. As shown in the graph on the lower left side of Figure 17, if the voltage across switch SW1 does not become equal to or less than the set threshold even when the dead time period reaches the dead time lower limit during the third control, i.e., if ZVS is not established, the control unit 10 performs a fourth control (the "SR-SW extension" control shown in Figure 17) that extends the on-period of switch SW2. As shown in the graph on the lower right side of Figure 17, if the voltage across switch SW2 becomes equal to or less than the set threshold before the on-period of switch SW2 reaches the on-period upper limit during the fourth control, i.e., if ZVS is established, the control unit 10 starts search control using, as initial values, the dead time period that is the dead time lower limit and the on-period of switch SW2 when the voltage across switch SW1 becomes equal to or less than the set threshold during the fourth control (SR-SW and Tdead shown in the graph on the lower right side of Figure 17).

[0102] Thus, if ZVS is no longer established by the time the on-period of switch SW2 reaches the on-period lower limit during the first control for shortening the on-period of switch SW2, it can be determined that the on-period of switch SW2 was too long. However, it is also possible that ZVS was established when the dead time period was long and the negative current was excessive. Therefore, to determine whether the dead time period is too long, the second control for extending the dead time period is performed during the initial control. If ZVS is not established even when the dead time period reaches the dead time upper limit during the second control, it is possible that the dead time period is too long, and therefore the third control for shortening the dead time period is performed during the initial control. If ZVS is not established during the third control, it can be determined that the dead time period is not too long, but that the on-period of switch SW2, shortened by the first control, is not long enough to establish ZVS. Therefore, the fourth control for extending the on-period of switch SW2 until ZVS is established during the initial control is performed. This allows the search control to be started without the ON period of the switch SW2 being too long.

[0103] Next, the operation of the power conversion device 1 when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio will be described.

[0104] When the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, control unit 10 controls the dead time period in accordance with the comparison result in voltage detection circuit 20, and does not control the on period of switch SW2 in accordance with the comparison result in voltage detection circuit 20. In other words, when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, the on period of switch SW2 is not controlled, and only the dead time period is controlled.

[0105] When the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, specifically, when it is 0.5 or greater (that is, when the output voltage is equal to or greater than half of the input voltage), the negative current required for ZVS is sufficient. Therefore, by controlling the dead time period without controlling the on period of switch SW2, it is possible to achieve ZVS in response to a wide range of input / output voltage conversion ratios while achieving high efficiency in power transmission.

[0106] Next, details of optimization control for optimizing the dead time period when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio will be described with reference to first to third examples using Figures 18 to 20. Note that optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio is control for optimizing the dead time period so that the dead time period is a period in which ZVS can be established and the negative current does not become excessive.

[0107] First, a first example of optimization control will be described with reference to FIG.

[0108] FIG. 18 is a diagram showing a first example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio.

[0109] In a first example of optimization control, when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, and the voltage across switch SW1 is equal to or less than a set threshold, that is, when ZVS is established, control unit 10 performs first control to shorten the dead time period (two "Tdead shortening" controls shown in FIG. 18). As shown in the graphs on the upper right and lower left of FIG. 18, if the voltage across switch SW1 becomes higher than the set threshold before the dead time period reaches the lower limit value during the first control, that is, when ZVS is no longer established, control unit 10 performs control to extend the dead time period ("Tdead extending" control shown in FIG. 18) until the voltage across switch SW1 becomes equal to or less than the set threshold, that is, until ZVS is established.

[0110] In this way, if ZVS is already established before controlling the dead time period, ZVS is established when the dead time period is long and the negative current is excessive. Therefore, a first control is performed to shorten the dead time period until ZVS is no longer established. This makes it possible to search for an optimal dead time period that can establish ZVS without causing excessive negative current. The dead time period after the first control is performed is slightly shorter than the optimal dead time period, and ZVS is not established. Therefore, by extending the dead time period after the first control is performed, ZVS can be established without causing excessive negative current. Therefore, it is possible to achieve high efficiency power transmission while maintaining ZVS.

[0111] Next, a second example of optimization control will be described with reference to FIG.

[0112] FIG. 19 is a diagram showing a second example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio.

[0113] In a second example of optimization control, when the input-output voltage conversion ratio is equal to or greater than a predetermined ratio, and the voltage across switch SW1 is higher than a set threshold, that is, when ZVS is not established, control unit 10 performs first control to extend the dead time period (two "Tdead extension" controls shown in FIG. 19 ). As shown in the graphs on the upper right and lower left of FIG. 19 , if the voltage across switch SW1 becomes equal to or lower than the set threshold before the dead time period reaches the upper dead time limit during the first control, that is, when ZVS is established, control unit 10 performs control to maintain the dead time period when the voltage across switch SW1 becomes equal to or lower than the set threshold during the first control ("maintenance" control shown in FIG. 19 ).

[0114] In this way, if ZVS is not established before controlling the dead time period, the dead time period may be too short, and therefore a first control is performed to extend the dead time period until ZVS is established. This makes it possible to search for an optimal dead time period that allows ZVS to be established without excessive negative current. Since the dead time period after the first control is performed is the optimal dead time period, maintaining this dead time period allows ZVS to be established without excessive negative current. Therefore, it is possible to achieve high efficiency power transmission while maintaining ZVS.

[0115] Next, a third example of optimization control will be described with reference to FIG.

[0116] FIG. 20 is a diagram showing a third example of optimization control when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio.

[0117] In a third example of optimization control, when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, and the voltage across switch SW1 is higher than a set threshold, that is, when ZVS is not established, control unit 10 performs first control to extend the dead time period (the "Tdead extension" control in the upper part of FIG. 20). As shown in the graph in the center of the upper part of FIG. 20, when the dead time period reaches the upper dead time limit during the first control but the voltage across switch SW1 does not become equal to or less than the set threshold, that is, when ZVS is not established, control unit 10 performs second control to shorten the dead time period (the "Tdead shortening" control in the upper part of FIG. 20). As shown in the graph on the right side of the upper row of Fig. 20 , if the voltage across switch SW1 becomes equal to or lower than the set threshold before the dead time period reaches the lower limit value of dead time during the second control, that is, if ZVS is established, the control unit 10 performs third control to further shorten the dead time period (the two "Tdead shortening" controls in the lower row of Fig. 20 ). As shown in the graphs on the left side and the center of the lower row of Fig. 20 , if the voltage across switch SW1 becomes higher than the set threshold before the dead time period reaches the lower limit value of dead time during the third control, that is, if ZVS is no longer established, the control unit 10 performs control to extend the dead time period (the "Tdead extend" control in the lower row of Fig. 20 ) until the voltage across switch SW1 becomes equal to or lower than the set threshold, that is, until ZVS is established.

[0118] In this way, if ZVS is not established before controlling the dead time period, the dead time period may be too long, so a first control is performed to extend the dead time period until ZVS is established. If ZVS is not established even when the dead time period reaches the upper dead time limit during the first control, it can be determined that the dead time period is too long, and a second control is performed to shorten the dead time period. If ZVS is established during the second control, a third control is performed to further shorten the dead time period until ZVS is no longer established. The dead time period after the third control is performed is slightly shorter than the optimal dead time period, and ZVS is not established. Therefore, by extending the dead time period after the third control is performed, ZVS can be established without excessive negative current. Therefore, it is possible to achieve ZVS while improving the efficiency of power transmission.

[0119] As described above, in the present disclosure, at least the dead time period is controlled, and the on-period of switch SW2 is also controlled depending on the input-output voltage conversion ratio. Controlling the dead time period allows adjustment of the period during which a negative current necessary for achieving ZVS flows. Therefore, by adjusting the dead time period so that ZVS is achieved without excessive negative current, high power transmission efficiency is achieved. Whether ZVS is achieved can be determined by comparing the voltage across switch SW1 with a set threshold (specifically, a threshold for determining whether ZVS is achieved, e.g., 0 V). Therefore, by controlling the dead time period according to the comparison result of the voltage across switch SW1 with the set threshold, ZVS can be achieved without excessive negative current even when the input-output voltage conversion ratio changes. Therefore, high power transmission efficiency can be achieved while maintaining ZVS over a wide range of input-output voltage conversion ratios.

[0120] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0121] For example, in the above embodiment, an example was described in which the power conversion device 1 is equipped with an input voltage detection circuit 30 and an output voltage detection circuit 40, but the power conversion device 1 does not have to be equipped with the input voltage detection circuit 30 and the output voltage detection circuit 40.

[0122] For example, the present disclosure can be realized not only as the power conversion device 1 but also as a control method including steps (processing) performed by components (for example, the control unit 10) that make up the power conversion device 1.

[0123] FIG. 21 is a flowchart showing an example of a control method according to another embodiment.

[0124] The control method is a control method for a power conversion device including a first switch, a second switch connected in series with the first switch, an inductor connected to a connection node connecting the first switch and the second switch, a first input / output terminal connected to a terminal of the first switch not connected to the connection node, a second input / output terminal connected to a terminal of the inductor not connected to the connection node, and a third input / output terminal connected to a terminal of the second switch not connected to the connection node, and includes the following steps: As shown in Fig. 21 , the control method includes an acquisition step (step S11) of acquiring a comparison result between a voltage applied to the first switch and a set threshold, and a control step (step S12) of controlling a dead time period from when the first switch is turned off to when the second switch is turned on, depending on the comparison result.

[0125] For example, the control method further includes a calculation step of calculating an input / output voltage conversion ratio from the input voltage between the first input / output terminal and the third input / output terminal and the output voltage between the second input / output terminal and the third input / output terminal, and in the control step, if the input / output voltage conversion ratio is smaller than a predetermined ratio, the dead time period and the on-period of the second switch are controlled in accordance with the comparison result, and if the input / output voltage conversion ratio is equal to or greater than the predetermined ratio, the dead time period is controlled in accordance with the comparison result, and the on-period of the second switch is not controlled in accordance with the comparison result.

[0126] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0127] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU (Central Processing Unit), memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0128] In the above embodiment, each component included in the power conversion device 1 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0129] Some or all of the functions of the power conversion device 1 according to the above embodiment are typically realized as an LSI (Large Scale Integration), which is an integrated circuit. These may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI.

[0130] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derived technologies, it is natural that each component included in the power conversion device 1 can be integrated using that technology.

[0131] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0132] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0133] (Technology 1) A power conversion device according to Technology 1 includes a first switch, a second switch connected in series with the first switch, an inductor connected to a connection node connecting the first switch and the second switch, a first input / output terminal connected to a terminal of the first switch not connected to the connection node, a second input / output terminal connected to a terminal of the inductor not connected to the connection node, a third input / output terminal connected to a terminal of the second switch not connected to the connection node, a voltage detection circuit configured to detect a voltage applied to the first switch and output a comparison result between the voltage applied to both ends and a set threshold, and a control unit configured to control switching operations of the first switch and the second switch, wherein the control unit controls a dead time period from when the first switch is turned off until when the second switch is turned on in response to the comparison result.

[0134] According to this, by controlling the dead time period, it is possible to adjust the period during which the negative current necessary to establish ZVS flows, and therefore, by adjusting the dead time period so that ZVS is established without excessive negative current, it is possible to improve the efficiency of power transmission. Whether ZVS is established can be determined by comparing the voltage applied to the first switch with a set threshold (specifically, a threshold for determining whether ZVS is established, e.g., 0 V). Therefore, by controlling the dead time period in accordance with the comparison result of the voltage applied to the first switch with the set threshold, ZVS can be established without excessive negative current even when the input-output voltage conversion ratio changes. Therefore, it is possible to achieve high efficiency of power transmission while maintaining ZVS over a wide range of input-output voltage conversion ratios.

[0135] (Technology 2) The power conversion device according to Technology 2 is the power conversion device according to Technology 1, wherein the control unit controls the dead time period and the ON period of the second switch according to the comparison result.

[0136] Depending on the input / output voltage conversion ratio, there may be a shortage of energy (negative current) required for ZVS. In response to this, the negative current can be increased by extending the on-period of the second switch. Therefore, by controlling the on-period of the second switch in addition to the dead time period, ZVS can be established more reliably in response to a wide range of input / output voltage conversion ratios, while improving the efficiency of power transmission.

[0137] (Technology 3) The power conversion device according to Technology 3 is the power conversion device according to Technology 2, further comprising: an input voltage detection circuit that detects an input voltage between the first input / output terminal and the third input / output terminal; and an output voltage detection circuit that detects an output voltage between the second input / output terminal and the third input / output terminal. When an input / output voltage conversion ratio calculated from the input voltage and the output voltage is smaller than a predetermined ratio, the control unit controls the dead time period and the on period of the second switch according to the comparison result.

[0138] According to this, when the input / output voltage conversion ratio (the magnitude of the output voltage relative to the input voltage: output voltage / input voltage) is smaller than a predetermined ratio, specifically, when it is smaller than 0.5 (i.e., when the output voltage is less than half the input voltage), the negative current required for ZVS is insufficient. Therefore, in this case, by controlling the on period of the second switch in addition to the dead time period, it is possible to more reliably establish ZVS in response to a wide range of input / output voltage conversion ratios while improving the efficiency of power transmission.

[0139] (Technology 4) In the power conversion device according to Technology 4, in the power conversion device according to Technology 3, when the input / output voltage conversion ratio is smaller than the predetermined ratio, the control unit performs search control at least once to shorten the on-period of the second switch so that the voltage across the second switch does not become equal to or less than the set threshold, and to extend the dead time period so that the voltage across the second switch becomes equal to or less than the set threshold. When the voltage across the second switch does not become equal to or less than the set threshold when the dead time period is extended during the at least one search control, the control unit performs control to extend the on-period of the second switch and shorten the dead time period.

[0140] According to this, the on-period of the second switch is shortened so that the voltage across the first switch does not fall below the set threshold, in other words, ZVS is not established. This search control, which extends the dead time period so that ZVS is established, is performed at least once until ZVS is no longer established even when the dead time period is extended. In other words, by shortening the on-period of the second switch to reduce the negative current required for ZVS, the dead time period is controlled, thereby searching for an optimal combination of the dead time period and the on-period of switch SW2 that establishes ZVS without excessive negative current. After at least one search control, the on-period of the second switch is slightly shorter than the optimal on-period due to the search for the optimal combination, and the negative current required for ZVS is insufficient. Therefore, by extending the on-period of the second switch after at least one search control, the negative current can be reduced to the minimum value required for ZVS, and by shortening the dead time period, ZVS can be established. Therefore, it is possible to achieve high efficiency in power transmission while achieving ZVS.

[0141] (Technology 5) The power conversion device described in Technology 5 is the power conversion device described in Technology 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio, and when the voltage across both ends before performing the search control is higher than the set threshold, the control unit performs initial control to extend the dead time period before performing the search control.

[0142] Depending on the ON period of the second switch before the search control is performed, ZVS may not be established even if the search control is performed. Therefore, if ZVS is not established before the search control is performed, initial control is performed to extend the dead time period. This makes it possible to determine whether the ON period of the second switch before the search control is performed is long enough to establish ZVS.

[0143] (Technology 6) In the power conversion device according to Technology 6, in the power conversion device according to Technology 5, the control unit performs first control to extend the dead time period during the initial control, and if the voltage between both ends becomes equal to or less than the set threshold before the dead time period reaches a dead time upper limit value during the first control, starts the searching control with the dead time period when the voltage between both ends becomes equal to or less than the set threshold value during the first control as an initial value. The dead time upper limit value is an upper limit value of the dead time determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

[0144] According to this, if ZVS is established before the dead time reaches the upper limit during the first control of extending the dead time, it can be determined that the on-period of the second switch is long enough to establish ZVS. Therefore, when the on-period of the second switch is long enough to establish ZVS, search control for shortening the on-period of the second switch can be started.

[0145] (Technology 7) In the power conversion device according to Technology 7, in the power conversion device according to Technology 5, the control unit performs a first control to extend the dead time in the initial control, and if the voltage across the second switch does not become equal to or less than the set threshold even when the dead time reaches a dead time upper limit during the first control, performs a second control to extend an on-period of the second switch, and if the voltage across the second switch becomes equal to or less than the set threshold before the on-period of the second switch reaches an on-period upper limit during the second control, performs a third control to shorten the dead time, and if the voltage across the second switch becomes higher than the set threshold during the third control, starts the searching control using, as initial values, the on-period of the second switch when the voltage across the second switch became equal to or less than the set threshold during the second control and the dead time when the voltage across the second switch became higher than the set threshold during the third control. The dead time upper limit is an upper limit of the dead time determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input-output voltage conversion ratio. The upper limit of the on-period is an upper limit of the on-period of the second switch determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input / output voltage conversion ratio.

[0146] According to this, if ZVS is not established even when the dead time reaches the upper limit during the first control for extending the dead time, it can be determined that the on-period of the second switch is not long enough to establish ZVS, and therefore, the second control for extending the on-period of the second switch is performed in the initial control. If ZVS is established before the on-period of the second switch reaches the upper limit during the second control, it can be determined that the on-period of the second switch is long enough to establish ZVS by the second control. Furthermore, to determine whether the on-period of the second switch is long enough to establish ZVS, the first control extends the dead time to the upper limit, and therefore, the search control for extending the dead time cannot be started. Therefore, the third control for shortening the dead time until ZVS is no longer established can be started when the on-period of the second switch is long enough to establish ZVS and the dead time is not too long.

[0147] (Technology 8) In the power conversion device described in Technology 8, in the power conversion device described in Technology 5, the control unit performs a first control to extend the dead time period in the initial control, and if the voltage across the second switch does not become equal to or less than the set threshold even when the dead time period reaches a dead time upper limit value during the first control, performs a second control to extend an on-period of the second switch, and if the voltage across the second switch does not become equal to or less than the set threshold even when the on-period of the second switch reaches an on-period upper limit value during the second control, performs a third control to shorten the dead time period, and if the voltage across the second switch becomes equal to or less than the set threshold during the third control, performs a fourth control to further shorten the dead time period, and if the voltage across the second switch becomes higher than the set threshold during the fourth control, starts the search control using as initial values ​​the on-period of the second switch that is the on-period upper limit value and the dead time period when the voltage across the second switch became higher than the set threshold during the fourth control. The dead time upper limit is an upper limit of the dead time period determined by the capacitance of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The on-period upper limit is an upper limit of the on-period of the second switch determined by the capacitance of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio.

[0148] According to this, if ZVS is not established even when the dead time reaches the upper dead time limit during the first control for extending the dead time, it can be determined that the on-period of the second switch is not long enough to establish ZVS, and therefore, a second control for extending the on-period of the second switch is performed in the initial control. If ZVS is not established even when the on-period of the second switch reaches the upper dead time limit during the second control, it is possible that the dead time is too long, and therefore, a third control for shortening the dead time is performed in the initial control. If ZVS is established during the third control, it can be determined that the dead time is too long, and therefore, a fourth control for further shortening the dead time until ZVS is no longer established in the initial control. As a result, it is possible to start search control for shortening the on-period of the second switch and extending the dead time when the on-period of the second switch is long enough to establish ZVS and the dead time is not too long.

[0149] (Technology 9) The power conversion device described in Technology 9 is the power conversion device described in Technology 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio and the voltage across both ends before performing the search control is higher than the set threshold, the control unit performs initial control to extend the on-period of the second switch before performing the search control.

[0150] Depending on the on-period of the second switch before the search control is performed, ZVS may not be established even if the search control is performed. Therefore, if ZVS is not established before the search control is performed, initial control is performed to extend the on-period of the second switch. This makes it possible to make the on-period of the second switch before the search control be long enough to establish ZVS.

[0151] (Technology 10) In the power conversion device according to Technology 10, in the power conversion device according to Technology 9, the control unit performs a first control that extends an on-period of the second switch during the initial control, and if the voltage across the second switch becomes equal to or less than the set threshold before the on-period of the second switch reaches an on-period upper limit during the first control, starts the searching control with the on-period of the second switch when the voltage across the second switch becomes equal to or less than the set threshold during the first control as an initial value. The on-period upper limit is an upper limit of the on-period of the second switch determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

[0152] According to this, if ZVS is established before the on-period of the second switch reaches the on-period upper limit value during the first control in which the on-period of the second switch is extended, it can be determined that the on-period of the second switch has become long enough to establish ZVS, and search control can be started in which the on-period of the second switch is shortened when the on-period of the second switch is long enough to establish ZVS.

[0153] (Technology 11) In the power conversion device described in Technology 11, in the power conversion device described in Technology 9, the control unit performs a first control to extend an on-period of the second switch during the initial control, and if the on-period of the second switch reaches an on-period upper limit value but the voltage across the second switch does not become equal to or less than the set threshold value during the first control, performs a second control to shorten the dead time period, and if the voltage across the second switch becomes equal to or less than the set threshold value during the second control, performs a third control to further shorten the dead time period, and if the voltage across the second switch becomes higher than the set threshold value during the third control, starts the searching control using, as initial values, the on-period of the second switch that is set to the on-period upper limit value and the dead time period when the voltage across the second switch becomes higher than the set threshold value during the third control. The on-period upper limit value is an upper limit value of the on-period of the second switch determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

[0154] According to this, if ZVS is not established even when the on-period of the second switch reaches the on-period upper limit during first control, which extends the on-period of the second switch, it is possible that the dead time period is too long, so second control, which shortens the dead time period, is performed in initial control. If ZVS is established during second control, it can be determined that the dead time period was too long, so third control, which further shortens the dead time period until ZVS is no longer established during initial control, is performed. As a result, it is possible to start search control, which shortens the on-period of the second switch and extends the dead time period, when the on-period of the second switch is long enough to establish ZVS and the dead time period is not too long.

[0155] (Technology 12) The power conversion device described in Technology 12 is the power conversion device described in Technology 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio, if the voltage between both ends before performing the search control is equal to or smaller than the set threshold, the control unit performs initial control to shorten the dead time period before performing the search control, and if the voltage between both ends becomes higher than the set threshold during the initial control, starts the search control with an initial value that is the dead time period when the voltage between both ends becomes higher than the set threshold during the initial control.

[0156] If ZVS is already established before search control is performed, there is a possibility that ZVS is established in a state where the dead time period is long and the negative current is excessive. Therefore, if ZVS is established before search control is performed, initial control is performed to shorten the dead time period until ZVS is no longer established before search control is performed, so that search control can be started in a state where the dead time period is not too long.

[0157] (Technology 13) The power conversion device described in Technology 13 is the power conversion device described in Technology 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio, and when the voltage across both ends before performing the search control is equal to or lower than the set threshold, the control unit performs initial control to shorten the on-period of the second switch before performing the search control.

[0158] If ZVS is already established before search control is performed, there is a possibility that ZVS is established in a state where the on-period of the second switch is long and the negative current is excessive. Therefore, if ZVS is established before search control is performed, initial control is performed to shorten the on-period of the second switch. This makes it possible to start search control in a state where the on-period of the second switch is not too long.

[0159] (Technology 14) In the power conversion device described in Technology 14, in the power conversion device described in Technology 13, the control unit performs a first control to shorten an on-period of the second switch during the initial control, and if the voltage across the second switch becomes higher than the set threshold before the on-period lower limit value during the first control, performs a second control to extend the dead time period. If the voltage across the second switch becomes equal to or lower than the set threshold before the dead time period reaches the dead time upper limit value during the second control, the control unit starts the search control with the on-period of the second switch when the voltage across the second switch becomes higher than the set threshold during the first control and the dead time period when the voltage across the second switch becomes equal to or lower than the set threshold during the second control as initial values. The on-period lower limit value is a lower limit value of the on-period of the second switch determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The dead time upper limit value is an upper limit value of the dead time period determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio.

[0160] According to this, if ZVS is no longer established by the time the on-period of the second switch reaches the on-period lower limit during the first control that shortens the on-period of the second switch, it can be determined that the on-period of the second switch was too long. However, shortening the on-period of the second switch through the first control may result in the on-period of the second switch being insufficiently long to establish ZVS. Therefore, in order to determine whether the on-period of the second switch is long enough to establish ZVS, the second control that extends the dead time is performed in the initial control. If ZVS is established by the time the dead time reaches the dead time upper limit during the second control, it can be determined that the on-period of the second switch is long enough to establish ZVS, and the search control can be started without the on-period of the second switch being too long.

[0161] (Technology 15) In the power conversion device described in Technology 15, in the power conversion device described in Technology 13, the control unit performs a first control to shorten an on-period of the second switch in the initial control, and if the voltage across the second switch becomes higher than the set threshold before the on-period of the second switch reaches an on-period lower-limit value during the first control, performs a second control to extend the dead time period, and if the voltage across the second switch does not become equal to or lower than the set threshold even when the dead time period reaches an upper dead time limit value during the second control, performs a third control to shorten the dead time period, and if the voltage across the second switch becomes equal to or lower than the set threshold before the dead time period reaches a lower dead time limit value during the third control, performs a fourth control to further shorten the dead time period, and if the voltage across the second switch becomes higher than the set threshold during the fourth control, starts the search control using as initial values ​​the on-period of the second switch when the voltage across the second switch became higher than the set threshold during the first control and the dead time period when the voltage across the second switch became higher than the set threshold during the fourth control. The on-period lower limit is a lower limit of the on-period of the second switch determined by the capacitance of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The dead-time upper limit is an upper limit of the dead-time period determined by the capacitance of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The dead-time lower limit is a lower limit of the dead-time period determined by the capacitance of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio.

[0162] According to this, if ZVS is no longer established by the time the on-period of the second switch reaches the on-period lower limit during the first control for shortening the on-period of the second switch, it can be determined that the on-period of the second switch was too long. However, it is possible that ZVS was established when the dead time period was long and the negative current was excessive. Therefore, to determine whether the dead time period is too long, a second control for extending the dead time period is performed during the initial control. If ZVS is not established even when the dead time period reaches the upper dead time limit during the second control, it is possible that the dead time period is too long, so a third control for shortening the dead time period is performed during the initial control. If ZVS is established during the third control, it can be determined that the dead time period was too long, so a fourth control for further shortening the dead time period is performed during the initial control until ZVS is no longer established. This allows the search control to be started when the on-period of the second switch is not too long and the dead time period is not too long.

[0163] (Technology 16) In a power conversion device described in Technology 16, in the power conversion device described in Technology 13, the control unit performs a first control to shorten an on-period of the second switch in the initial control, and if the voltage across the second switch becomes higher than the set threshold before the on-period of the second switch reaches an on-period lower limit during the first control, performs a second control to extend the dead time period, and if the voltage across the second switch does not become equal to or lower than the set threshold even when the dead time period reaches an upper dead time limit during the second control, performs a third control to shorten the dead time period, and if the voltage across the second switch does not become equal to or lower than the set threshold even when the dead time period reaches a lower dead time limit during the third control, performs a fourth control to extend the on-period of the second switch, and if the voltage across the second switch becomes equal to or lower than the set threshold before the on-period of the second switch reaches an on-period upper limit during the fourth control, starts the searching control using as initial values ​​the dead time period that is the dead time lower limit and the on-period of the second switch when the voltage across the second switch became equal to or lower than the set threshold during the fourth control. The on-period lower limit is a lower limit of the on-period of the second switch determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The dead-time upper limit is an upper limit of the dead-time period determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The dead-time lower limit is a lower limit of the dead-time period determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio. The on-period upper limit is an upper limit of the on-period of the second switch determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input-output voltage conversion ratio.

[0164] According to this, if ZVS is no longer established by the time the on-period of the second switch reaches the on-period lower limit during the first control for shortening the on-period of the second switch, it can be determined that the on-period of the second switch was too long. However, it is also possible that ZVS was established when the dead time period was long and the negative current was excessive. Therefore, to determine whether the dead time period is too long, a second control for extending the dead time period is performed during the initial control. If ZVS is not established even when the dead time period reaches the dead time upper limit during the second control, it is possible that the dead time period is too long, so a third control for shortening the dead time period is performed during the initial control. If ZVS is not established during the third control, it can be determined that the on-period of the second switch is not long enough to establish ZVS, not because the dead time period is too long, but because the on-period of the second switch was shortened by the first control. Therefore, a fourth control for extending the on-period of the second switch is performed during the initial control until ZVS is established. This allows the search control to be started when the on-period of the second switch is not too long.

[0165] (Technology 17) A power conversion device according to Technology 17 is the power conversion device according to Technology 1, further comprising: an input voltage detection circuit that detects an input voltage between the first input / output terminal and the third input / output terminal; and an output voltage detection circuit that detects an output voltage between the second input / output terminal and the third input / output terminal. When an input / output voltage conversion ratio calculated from the input voltage and the output voltage is equal to or greater than a predetermined ratio, the control unit controls the dead time period in accordance with the comparison result, and does not control the on period of the second switch in accordance with the comparison result.

[0166] According to this, when the input / output voltage conversion ratio (the magnitude of the output voltage relative to the input voltage: output voltage / input voltage) is a predetermined ratio or higher, specifically, when it is 0.5 or higher (that is, when the output voltage is half or more of the input voltage), the negative current required for ZVS is sufficient. Therefore, by controlling the dead time period without controlling the on period of the second switch, it is possible to achieve ZVS in response to a wide range of input / output voltage conversion ratios while achieving high efficiency in power transmission.

[0167] (Technology 18) In the power conversion device according to Technology 18, in the power conversion device according to Technology 17, the control unit performs a first control to shorten the dead time period when the input-output voltage conversion ratio is equal to or greater than the predetermined ratio and the voltage across the dead time period is equal to or less than the set threshold, and if the voltage across the dead time period becomes higher than the set threshold before the dead time period reaches a dead time lower limit value during the first control, performs a control to extend the dead time period until the voltage across the dead time period becomes equal to or less than the set threshold. The dead time lower limit value is a lower limit value of the dead time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input-output voltage conversion ratio.

[0168] According to this, if ZVS is already established before controlling the dead time period, ZVS is established in a state where the dead time period is long and the negative current is excessive, and therefore, a first control is performed to shorten the dead time period until ZVS is no longer established. This makes it possible to search for an optimal dead time period that can establish ZVS without causing excessive negative current. The dead time period after the first control is performed is slightly shorter than the optimal dead time period, and ZVS is not established. Therefore, by extending the dead time period after the first control is performed, ZVS can be established without causing excessive negative current. This makes it possible to achieve high efficiency power transmission while maintaining ZVS.

[0169] (Technology 19) In the power conversion device according to Technology 19, in the power conversion device according to Technology 17, the control unit performs a first control to extend the dead time period when the voltage across the terminals is higher than the set threshold when the input / output voltage conversion ratio is equal to or greater than the predetermined ratio, and performs a control to maintain the dead time period when the voltage across the terminals becomes equal to or less than the set threshold before the dead time period reaches a dead time upper limit value during the first control. The dead time upper limit value is an upper limit value of the dead time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

[0170] According to this, if ZVS is not established before controlling the dead time period, the dead time period may be too short, and therefore a first control is performed to extend the dead time period until ZVS is established. This makes it possible to search for an optimal dead time period that allows ZVS to be established without excessive negative current. Since the dead time period after the first control is performed is the optimal dead time period, maintaining this dead time period allows ZVS to be established without excessive negative current. Therefore, it is possible to achieve high efficiency power transmission while maintaining ZVS.

[0171] (Technology 20) In the power conversion device described in Technology 20, in the power conversion device described in Technology 17, the control unit performs a first control to extend the dead time period when the input-output voltage conversion ratio is equal to or greater than the predetermined ratio and the voltage across the dead time period is higher than the set threshold, performs a second control to shorten the dead time period when the voltage across the dead time period does not become equal to or lower than the set threshold even when the dead time period reaches a dead time upper limit during the first control, performs a third control to further shorten the dead time period when the voltage across the dead time period becomes equal to or lower than the set threshold before the dead time period reaches a dead time lower limit during the second control, and performs a control to extend the dead time period until the voltage across the dead time period becomes equal to or lower than the set threshold before the dead time period reaches the dead time lower limit during the third control. The dead time upper limit is an upper limit of the dead time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input-output voltage conversion ratio. The dead time lower limit is a lower limit of the dead time period determined by the capacitance component of the first switch, the inductance of the inductor, and the range of the input / output voltage conversion ratio.

[0172] According to this, if ZVS is not established before controlling the dead time period, the dead time period may be too long, so a first control is performed to extend the dead time period until ZVS is established. If ZVS is not established even when the dead time period reaches the dead time upper limit value during the first control, it can be determined that the dead time period is too long, and a second control is performed to shorten the dead time period. If ZVS is established during the second control, a third control is performed to further shorten the dead time period until ZVS is no longer established. The dead time period after the third control is performed is slightly shorter than the optimal dead time period, and ZVS is not established. Therefore, by extending the dead time period after the third control is performed, ZVS can be established without excessive negative current. Therefore, it is possible to achieve high efficiency power transmission while maintaining ZVS.

[0173] (Technology 21) A control method disclosed in Technology 21 is a control method for a power conversion device including a first switch, a second switch connected in series with the first switch, an inductor connected to a connection node connecting the first switch and the second switch, a first input / output terminal connected to a terminal of the first switch that is not connected to the connection node, a second input / output terminal connected to a terminal of the inductor that is not connected to the connection node, and a third input / output terminal connected to a terminal of the second switch that is not connected to the connection node, and includes the following steps: an acquisition step of acquiring a comparison result of a voltage applied to the first switch and a set threshold value, and a control step of controlling a dead time period from when the first switch is turned off to when the second switch is turned on, based on the comparison result.

[0174] This makes it possible to provide a control method that enables high efficiency power transmission while establishing ZVS in response to a wide range of input / output voltage conversion ratios.

[0175] (Technology 22) A control method according to Technology 22 is the control method according to Technology 21, further comprising a calculation step of calculating an input / output voltage conversion ratio from the input voltage between the first input / output terminal and the third input / output terminal and the output voltage between the second input / output terminal and the third input / output terminal. In the control step, if the input / output voltage conversion ratio is smaller than a predetermined ratio, the dead time period and the on-period of the second switch are controlled in accordance with the comparison result, and if the input / output voltage conversion ratio is equal to or greater than the predetermined ratio, the dead time period is controlled in accordance with the comparison result, and the on-period of the second switch is not controlled in accordance with the comparison result.

[0176] When the input / output voltage conversion ratio is smaller than a predetermined ratio, specifically, when it is smaller than 0.5, the negative current required for ZVS is insufficient. Therefore, in this case, by controlling the on-period of the second switch in addition to the dead time period, it is possible to more reliably establish ZVS over a wide range of input / output voltage conversion ratios while improving the efficiency of power transmission. Furthermore, when the input / output voltage conversion ratio is equal to or greater than a predetermined ratio, specifically, equal to or greater than 0.5, the negative current required for ZVS is not insufficient. Therefore, by controlling the dead time period without controlling the on-period of the second switch, it is possible to establish ZVS over a wide range of input / output voltage conversion ratios while improving the efficiency of power transmission.

[0177] The present disclosure can be applied to a power conversion device and a control method. The power conversion device and control method of the present disclosure can achieve ZVS in response to a wide input / output voltage conversion ratio while achieving high efficiency in power transmission. In this way, the power conversion device and control method of the present disclosure are industrially useful.

[0178] REFERENCE SIGNS LIST 1 Power conversion device 10 Control unit 20 Voltage detection circuit 30 Input voltage detection circuit 40 Output voltage detection circuit L1 Inductor SW1, SW2 Switches t1, t2, t3 Input / output terminals

Claims

1. A power conversion device comprising: a first switch; a second switch connected in series with the first switch; an inductor connected to a connection node connecting the first switch and the second switch; a first input / output terminal connected to a terminal of the first switch that is not connected to the connection node; a second input / output terminal connected to a terminal of the inductor that is not connected to the connection node; a third input / output terminal connected to a terminal of the second switch that is not connected to the connection node; a voltage detection circuit that detects a voltage applied to both ends of the first switch and outputs a comparison result between the voltage at both ends and a set threshold; and a control unit that controls switching operations of the first switch and the second switch, wherein the control unit controls a dead time period from when the first switch is turned off to when the second switch is turned on in accordance with the comparison result.

2. The power conversion device according to claim 1, wherein the control unit controls the dead time period and the on-period of the second switch in accordance with the result of the comparison.

3. The power conversion device according to claim 2, further comprising: an input voltage detection circuit that detects an input voltage between the first input / output terminal and the third input / output terminal; and an output voltage detection circuit that detects an output voltage between the second input / output terminal and the third input / output terminal, wherein the control unit controls the dead time period and the on period of the second switch in accordance with a result of the comparison when an input / output voltage conversion ratio calculated from the input voltage and the output voltage is smaller than a predetermined ratio.

4. The power conversion device according to claim 3, wherein the control unit, when the input / output voltage conversion ratio is smaller than the predetermined ratio, performs at least one search control to shorten the on-period of the second switch so that the voltage at both ends does not become equal to or less than the set threshold and extends the dead-time period so that the voltage at both ends becomes equal to or less than the set threshold, and when, during at least one search control, the voltage at both ends does not become equal to or less than the set threshold when the dead-time period is extended, performs control to extend the on-period of the second switch and shorten the dead-time period.

5. The power conversion device according to claim 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio and the voltage between both ends before performing the search control is higher than the set threshold, the control unit performs initial control to extend the dead time period before performing the search control.

6. The control unit performs a first control to extend the dead-time period in the initial control, and if the voltage between both ends becomes equal to or lower than the set threshold before the dead-time period reaches a dead-time upper limit value during the first control, starts the search control with the dead-time period when the voltage between both ends becomes equal to or lower than the set threshold value during the first control as an initial value, and the dead-time upper limit value is an upper limit value of the dead time determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

7. The control unit performs a first control to extend the dead time period in the initial control, and if the voltage across both ends does not become equal to or less than the set threshold even when the dead time period reaches a dead time upper limit value during the first control, performs a second control to extend an on-period of the second switch, and if the voltage across both ends becomes equal to or less than the set threshold before the on-period of the second switch reaches an on-period upper limit value during the second control, performs a third control to shorten the dead time period, and if the voltage across both ends becomes higher than the set threshold during the third control, starts the search control using as initial values ​​the on-period of the second switch when the voltage across both ends becomes equal to or less than the set threshold during the second control and the dead time period when the voltage across both ends becomes higher than the set threshold during the third control, the dead time upper limit value being an upper limit value of the dead time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, The power conversion device according to claim 5 , wherein the on-period upper limit is an upper limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

8. The control unit performs a first control to extend the dead time period in the initial control, and when the voltage at both ends does not become equal to or less than the set threshold value even when the dead time period reaches a dead time upper limit value during the first control, performs a second control to extend an on-period of the second switch, and when the voltage at both ends does not become equal to or less than the set threshold value during the second control even when the on-period of the second switch reaches an on-period upper limit value during the second control, performs a third control to shorten the dead time period, and when the voltage at both ends becomes equal to or less than the set threshold value during the third control, performs a fourth control to further shorten the dead time period, and when the voltage at both ends becomes higher than the set threshold value during the fourth control, starts the search control with the on-period of the second switch which is set to the on-period upper limit value and the dead time period when the voltage at both ends becomes higher than the set threshold value during the fourth control as initial values, and the dead time upper limit value is an upper limit value of the dead time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, The power conversion device according to claim 5 , wherein the on-period upper limit is an upper limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

9. The power conversion device according to claim 4, wherein when the input / output voltage conversion ratio is smaller than the predetermined ratio and the voltage between both ends before performing the search control is higher than the set threshold, the control unit performs initial control to extend the on-period of the second switch before performing the search control.

10. The power conversion device according to claim 9, wherein the control unit performs a first control to extend the on-period of the second switch in the initial control, and if the voltage across the second switch becomes equal to or lower than the set threshold before the on-period of the second switch reaches an on-period upper limit during the first control, starts the search control with the on-period of the second switch when the voltage across the second switch becomes equal to or lower than the set threshold during the first control as an initial value, and the on-period upper limit is an upper limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

11. The power conversion device according to claim 9, wherein the control unit performs a first control to extend an on-period of the second switch in the initial control, and if the on-period of the second switch reaches an on-period upper limit value during the first control but the voltage across both ends does not become equal to or lower than the set threshold value, performs a second control to shorten the dead-time period, and if the voltage across both ends becomes equal to or lower than the set threshold value during the second control, performs a third control to further shorten the dead-time period, and if the voltage across both ends becomes higher than the set threshold value during the third control, starts the search control with the on-period of the second switch which is set to the on-period upper limit value and the dead-time period when the voltage across both ends became higher than the set threshold value during the third control as initial values, and the on-period upper limit value is an upper limit value of the on-period of the second switch which is determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

12. The power conversion device according to claim 4, wherein the control unit performs initial control to shorten the dead time period before performing the search control when the input / output voltage conversion ratio is smaller than the predetermined ratio and when the end-to-end voltage before performing the search control is equal to or lower than the set threshold value, and when the end-to-end voltage becomes higher than the set threshold value during the initial control, starts the search control with the dead time period at the time when the end-to-end voltage became higher than the set threshold value during the initial control as an initial value.

13. The power conversion device according to claim 4, wherein the control unit performs initial control to shorten an on-period of the second switch before performing the search control when the input / output voltage conversion ratio is smaller than the predetermined ratio and when the voltage between both ends before performing the search control is equal to or lower than the set threshold value.

14. The power conversion device according to claim 13, wherein the control unit performs a first control to shorten an on-period of the second switch in the initial control, and, if the voltage across both ends becomes higher than the set threshold before the on-period of the second switch reaches an on-period lower limit value during the first control, performs a second control to extend the dead-time period, and, if the voltage across both ends becomes equal to or lower than the set threshold before the dead-time period reaches a dead-time upper limit value during the second control, starts the search control with the on-period of the second switch when the voltage across both ends became higher than the set threshold during the first control and the dead-time period when the voltage across both ends became equal to or lower than the set threshold during the second control as initial values, wherein the on-period lower limit value is a lower limit value of the on-period of the second switch determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input-output voltage conversion ratio, and the dead-time upper limit value is an upper limit value of the dead-time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input-output voltage conversion ratio.

15. The control unit performs a first control to shorten the on-period of the second switch in the initial control, and if the voltage across the second switch becomes higher than the set threshold before the on-period of the second switch reaches an on-period lower limit during the first control, performs a second control to extend the dead-time period, and if the voltage across the second switch does not become equal to or lower than the set threshold even when the dead-time period reaches an upper dead-time limit during the second control, performs a third control to shorten the dead-time period, and if the voltage across the second switch becomes equal to or lower than the set threshold before the dead-time period reaches a lower dead-time limit during the third control, performs a fourth control to further shorten the dead-time period, and if the voltage across the second switch becomes higher than the set threshold during the first control and the dead-time period when the voltage across the second switch becomes higher than the set threshold during the fourth control, the search control is started with an initial value being the on-period of the second switch when the voltage across the second switch became higher than the set threshold during the first control and the dead-time period when the voltage across the second switch became higher than the set threshold during the fourth control, 14. The power conversion device according to claim 13, wherein the on-period lower limit is a lower limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, the dead-time upper limit is an upper limit of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, and the dead-time lower limit is a lower limit of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

16. The control unit performs a first control to shorten the on-period of the second switch in the initial control, performs a second control to extend the dead-time period if the voltage at both ends becomes higher than the set threshold before the on-period of the second switch reaches an on-period lower limit during the first control, performs a third control to shorten the dead-time period if the voltage at both ends does not become equal to or lower than the set threshold even when the dead-time period reaches an upper limit during the second control, performs a fourth control to extend the on-period of the second switch if the voltage at both ends does not become equal to or lower than the set threshold even when the dead-time period reaches a lower limit during the third control, and starts the search control with the dead-time period which is the dead-time lower limit and the on-period of the second switch when the voltage at both ends becomes equal to or lower than the set threshold during the fourth control as initial values ​​if the voltage at both ends becomes equal to or lower than the set threshold before the on-period of the second switch reaches an on-period upper limit during the fourth control, 14. The power conversion device according to claim 13, wherein the on-period lower limit is a lower limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, the dead-time upper limit is an upper limit of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, the dead-time lower limit is a lower limit of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio, and the on-period upper limit is an upper limit of the on-period of the second switch determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

17. A power conversion device as claimed in claim 1, comprising: an input voltage detection circuit that detects an input voltage between the first input / output terminal and the third input / output terminal; and an output voltage detection circuit that detects an output voltage between the second input / output terminal and the third input / output terminal, wherein the control unit controls the dead time period in accordance with a result of the comparison when an input / output voltage conversion ratio calculated from the input voltage and the output voltage is equal to or greater than a predetermined ratio, and does not control the on-period of the second switch in accordance with the result of the comparison.

18. The power conversion device according to claim 17, wherein the control unit performs a first control to shorten the dead-time period when the input / output voltage conversion ratio is equal to or greater than the predetermined ratio and the voltage at both ends is equal to or less than the set threshold, and performs a control to extend the dead-time period until the voltage at both ends becomes equal to or less than the set threshold if the voltage at both ends becomes higher than the set threshold before the dead-time period reaches a dead-time lower limit value during the first control, wherein the dead-time lower limit value is a lower limit value of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

19. The power conversion device according to claim 17, wherein the control unit performs a first control to extend the dead-time period when the input / output voltage conversion ratio is equal to or greater than the predetermined ratio and the voltage at both ends is higher than the set threshold, and performs a control to maintain the dead-time period at the time when the voltage at both ends became equal to or lower than the set threshold during the first control if the voltage at both ends becomes equal to or lower than the set threshold before the dead-time period reaches a dead-time upper limit value during the first control, and the dead-time upper limit value is an upper limit value of the dead-time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

20. The control unit performs a first control to extend the dead-time period when the voltage at both ends is higher than the set threshold value when the input / output voltage conversion ratio is equal to or greater than the predetermined ratio; performs a second control to shorten the dead-time period when the voltage at both ends does not become equal to or less than the set threshold value even when the dead-time period reaches a dead-time upper limit value during the first control; performs a third control to further shorten the dead-time period when the voltage at both ends becomes equal to or less than the set threshold value before the dead-time period reaches a dead-time lower limit value during the second control; performs a control to extend the dead-time period until the voltage at both ends becomes equal to or less than the set threshold value during the third control when the voltage at both ends becomes higher than the set threshold value before the dead-time period reaches the dead-time lower limit value; the dead-time upper limit value is an upper limit value of the dead-time period determined by a capacitance component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio; The power conversion device according to claim 17 , wherein the dead time lower limit is a lower limit of the dead time period determined by a capacitive component of the first switch, an inductance of the inductor, and a range of the input / output voltage conversion ratio.

21. A control method for a power conversion device including: a first switch; a second switch connected in series with the first switch; an inductor connected to a connection node connecting the first switch and the second switch; a first input / output terminal connected to a terminal of the first switch on a side not connected to the connection node; a second input / output terminal connected to a terminal of the inductor on a side not connected to the connection node; and a third input / output terminal connected to a terminal of the second switch on a side not connected to the connection node, the control method comprising: an acquisition step of acquiring a comparison result between a voltage applied to both ends of the first switch and a set threshold value; and a control step of controlling a dead time period from when the first switch is turned off to when the second switch is turned on in accordance with the comparison result.

22. The control method according to claim 21, further comprising a calculation step of calculating an input / output voltage conversion ratio from an input voltage between the first input / output terminal and the third input / output terminal and an output voltage between the second input / output terminal and the third input / output terminal, wherein in the control step, when the input / output voltage conversion ratio is smaller than a predetermined ratio, the dead time period and the on-period of the second switch are controlled in accordance with the comparison result, and when the input / output voltage conversion ratio is equal to or greater than the predetermined ratio, the dead time period is controlled in accordance with the comparison result and the on-period of the second switch is not controlled in accordance with the comparison result.

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