LLC converter and method for controlling same

Abstract

The present invention suppresses variation in loss between switches in an LLC converter. An LLC converter (1) is provided with a resonator (20), a primary-side circuit (10), a control unit (40), and a loss calculation unit (50). The primary-side circuit (10) has a first set of switches comprising a first H switch (AH) and a first L switch (AL), and a second set of switches comprising a second H switch (BH) and a second L switch (BL). The control unit (40) executes a control determination sequence for switching between: a first control for controlling each switch so that a switching phase of the first set of switches leads a switching phase of the second set of switches; and a second control for controlling each switch so that the ON period of the first H switch (AH) is included in the ON period of the second L switch (BL) and the ON period of the second H switch (BH) is included in the ON period of the first L switch (AL).

Description

LLC converter and control method thereof

[0001] The present disclosure relates to an LLC converter and a control method thereof.

[0002] Patent Document 1 discloses a technique relating to an operation method of an LLC converter. Specifically, this operation method analyzes the output voltage of the LLC converter, determines whether the output voltage is within a target voltage range, and if it determines that an output voltage within the target voltage range cannot be achieved by frequency control alone, performs phase shift control with the operating frequency increased to its maximum, thereby achieving an output voltage within the target voltage range.

[0003] JP 2016-63745 A

[0004] However, with the technology disclosed in Patent Document 1, when phase-shift control is performed, the turn-off of the switches in the leading leg of the primary-side full-bridge circuit, which has an advanced phase, does not occur at a low current like in a conventional LLC converter, resulting in turn-off loss. Meanwhile, the return current conduction loss during the return period is distributed almost evenly among the switches in the primary-side full-bridge circuit. As a result, the loss in the switches in the leading leg is greater than the loss in the switches in the lagging leg, resulting in loss variation between the switches. When loss variation between switches becomes large, a design tailored to the switches with the larger losses is required, resulting in waste in terms of cost and other factors.

[0005] Therefore, the present disclosure provides an LLC converter and a control method thereof that can suppress variations in loss between switches.

[0006] The LLC converter according to the present disclosure includes a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor, a primary-side circuit connected to the primary side of the resonator, a rectifier circuit connected to the secondary side of the resonator, a control unit, and a loss calculation unit. The primary-side circuit includes a first set of switches and a second set of switches. The first set of switches includes a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal. The second set of switches includes a second high-side switch and a second low-side switch connected in series on a second path connecting the input terminal and the ground terminal, the second path being different from the first path. The control unit controls the output voltage output from the output terminal connected to the rectifier circuit by performing frequency control and phase shift control in combination. The frequency control controls the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The phase shift control is control that controls a phase difference between switching of the first group of switches and switching of the second group of switches. The phase shift control can be executed by switching between first control and second control. The first control is control that controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the phase of switching of the first group of switches leads the phase of switching of the second group of switches, or so that the phase of switching of the second group of switches leads the phase of switching of the first group of switches.The second control controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and the on-period of the second high-side switch is included in an on-period of the first low-side switch, or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and the on-period of the second low-side switch is included in an on-period of the first high-side switch. The loss calculation unit calculates losses generated in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The at least two switches include at least the first high-side switch and the second low-side switch, or at least the second high-side switch and the first low-side switch. The control unit executes a control determination sequence to switch between the first control and the second control so that a loss difference between a maximum loss and a minimum loss among the losses of the at least two switches calculated by the loss calculation unit is reduced.

[0007] A control method according to the present disclosure is a control method for an LLC converter, the LLC converter including a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor, a primary-side circuit connected to the primary side of the resonator, and a rectifier circuit connected to the secondary side of the resonator. The primary-side circuit includes a first set of switches and a second set of switches. The first set of switches includes a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal. The second set of switches includes a second high-side switch and a second low-side switch connected in series on a second path connecting the input terminal and the ground terminal, the second path being different from the first path. The control method controls the output voltage output from the output terminal connected to the rectifier circuit by performing frequency control and phase shift control in combination. The frequency control controls the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The phase shift control is control that controls a phase difference between switching of the first group of switches and switching of the second group of switches. The control method can switch between first control and second control in the phase shift control. The first control is control that controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the phase of switching of the first group of switches leads the phase of switching of the second group of switches, or so that the phase of switching of the second group of switches leads the phase of switching of the first group of switches.The second control controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and the on-period of the second high-side switch is included in an on-period of the first low-side switch, or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and the on-period of the second low-side switch is included in an on-period of the first high-side switch. The control method includes the steps of calculating losses generated in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and switching between the first control and the second control so that a difference between a maximum loss and a minimum loss among the calculated losses of the at least two switches is reduced. The at least two switches include at least the first high-side switch and the second low-side switch, or at least the second high-side switch and the first low-side switch.

[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 an LLC converter according to an aspect of the present disclosure, it is possible to suppress variations in loss between switches.

[0010] 1 is a circuit configuration diagram showing an example of an LLC converter according to an embodiment; FIG. 2 is a timing chart showing an example of first control; FIG. 3 is a timing chart showing an example of second control; FIG. 4 is a diagram showing an example of phase shift control before and after a control determination sequence; FIG. 5 is a diagram showing an example of phase shift control before and after a control determination sequence; and FIG. 6 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, an LLC converter according to an embodiment will be described.

[0014] FIG. 1 is a circuit diagram showing an example of an LLC converter 1 according to an embodiment.

[0015] The LLC converter 1 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined output voltage. The LLC converter 1 is a circuit that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. The LLC converter 1 performs frequency control to change the switching frequency of each switch in the primary side circuit 10, and phase shift control to change the switching phase difference of each switch in the primary side circuit 10, thereby changing the input / output voltage ratio (Gain), thereby enabling the desired power output.

[0016] The LLC converter 1 has terminals t1, t2, t3, and t4. Terminal t1 is an input terminal. Terminal t2 is a ground terminal. Terminal t3 is an output terminal. Terminal t4 is a ground terminal. Since the LLC converter 1 is an isolated DC-DC converter, terminals t2 and t4 are electrically isolated. An input voltage and an input current are input to terminal t1. The input voltage is the voltage between terminals t1 and t2. An output voltage and an output current are output from terminal t3. The output voltage is the voltage between terminals t3 and t4.

[0017] The LLC converter 1 includes a primary side circuit 10 , a resonator 20 , a rectifier circuit 30 , a control unit 40 , and a loss calculation unit 50 .

[0018] The primary circuit 10 is connected to the primary side of the resonator 20. The primary circuit 10 has a first set of switches consisting of switches AH and AL connected in series on a path P1 connecting terminals t1 and t2, and a second set of switches consisting of switches BH and BL connected in series on a path P2 different from path P1 connecting terminals t1 and t2. Path P1 is an example of a first path, and path P2 is an example of a second path. Switch AH is an example of a first high-side switch, and switch AL is an example of a first low-side switch. Switch BH is an example of a second high-side switch, and switch BL is an example of a second low-side switch.

[0019] The switch AH is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch AH is connected to the terminal t1, and the source of the switch AH is connected to the drain of the switch AL.

[0020] The switch AL is, for example, an N-channel MOSFET. The drain of the switch AL is connected to the source of the switch AH, and the source of the switch AL is connected to the terminal t2.

[0021] The switch BH is, for example, an N-channel MOSFET. The drain of the switch BH is connected to the terminal t1, and the source of the switch BH is connected to the drain of the switch BL.

[0022] The switch BL is, for example, an N-channel MOSFET. The drain of the switch BL is connected to the source of the switch BH, and the source of the switch BL is connected to the terminal t2.

[0023] The rectifier circuit 30 is connected to the secondary side of the resonator 20. The output voltage and output current rectified by the rectifier circuit 30 are output from a terminal t3. For example, the rectifier circuit 30 may be a circuit made up of a plurality of switches that perform synchronous rectification in response to the current flowing on the secondary side of the resonator 20. Alternatively, for example, the rectifier circuit 30 may be a circuit made up of a plurality of diodes. For example, these circuits may be a full bridge circuit or a center tap circuit.

[0024] The resonator 20 includes a transformer T, an inductor Lr, and a capacitor Cr.

[0025] The capacitor Cr is an example of a resonant capacitor. For example, the capacitor Cr is connected to a node between the switch AH and the switch AL on the path P1.

[0026] The transformer T is an example of an isolation transformer. The transformer T has a primary winding and a secondary winding that are insulated from each other. One end of the primary winding of the transformer T is connected to a node between the switch AH and the switch AL in the path P1 via a capacitor Cr, and the other end of the primary winding of the transformer T is connected to a node between the switch BH and the switch BL in the path P2. The secondary winding of the transformer T is connected to the rectifier circuit 30.

[0027] The inductor Lr is an example of a resonant inductor. For example, the inductor Lr is connected to a node between the switch AH and the switch AL in the path P1 via the capacitor Cr, and is also connected in series with the capacitor Cr. The inductor Lr may be provided as a separate inductor, or may be provided by utilizing the leakage inductance of the transformer T.

[0028] The capacitor Cr and the inductor Lr may be connected to a node between the switch BH and the switch BL on the path P2. In this case, one end of the primary winding of the transformer T is connected to a node between the switch AH and the switch AL on the path P1, and the other end of the primary winding of the transformer T is connected to a node between the switch BH and the switch BL on the path P2 via the capacitor Cr and the inductor Lr. Also, although the example in which the capacitor Cr is connected to the transformer T via the inductor Lr has been shown, the inductor Lr may also be connected to the transformer T via the capacitor Cr. For example, the capacitor Cr and the inductor Lr shown in FIG. 1 may be interchanged. However, if the inductor Lr is provided by utilizing the leakage inductance of the transformer T, the inductor Lr is placed closer to the transformer T than the capacitor Cr (in other words, the capacitor Cr is connected to the transformer T via the inductor Lr).

[0029] The control unit 40 controls the switching of the switches AH, AL, BH, and BL in the primary side circuit 10. For example, the control unit 40 controls the switching of the switches AH, AL, BH, and BL by controlling a gate drive circuit (not shown) connected to the gates of the switches AH, AL, BH, and BL via a PWM generator (not shown) or the like. Note that if the rectifier circuit 30 is a circuit made up of multiple switches that perform synchronous rectification in response to the current flowing on the secondary side of the resonator 20, the control unit 40 also controls the switching of the multiple switches.

[0030] The control unit 40 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs executed by the processor. For example, the control unit 40 is realized by a microcontroller.

[0031] The control unit 40 controls the output voltage from the terminal t3 connected to the rectifier circuit 30 by simultaneously performing frequency control, which controls the switching frequency of the switches AH, AL, BH, and BL, and phase shift control, which controls the phase difference between the switching of the first group of switches (specifically, the switches AH and AL) and the switching of the second group of switches (specifically, the switches BH and BL). For example, to control the output voltage, the control unit 40 repeats frequency control and phase shift control to optimize the switching frequency of the switches AH, AL, BH, and BL and the phase difference between the switching of the first group of switches and the switching of the second group of switches. For example, to optimize the switching frequency and the phase difference, the control unit 40 may alternate between frequency control and phase shift control, or may repeat frequency control one or more times and phase shift control one or more times. In this way, repeating frequency control and phase shift control allows the switching frequency and phase difference to be optimized to accommodate a wide range of input and output voltages. For example, it is possible to reduce the number of step-down converters required to accommodate low gain, thereby enabling miniaturization.

[0032] Furthermore, the control unit 40 can switch between first control and second control in the phase shift control. When performing the first control in the phase shift control, the control unit 40 controls the switches AH, AL, BH, and BL so that the switching phase of the first set of switches leads the switching phase of the second set of switches, or so that the switching phase of the second set of switches leads the switching phase of the first set of switches. When performing the second control in the phase shift control, the control unit 40 controls the switches AH, AL, BH, and BL so that the on-period of the switch AH is included in the on-period of the switch BL and the on-period of the switch BH is included in the on-period of the switch AL, or so that the on-period of the switch AL is included in the on-period of the switch BH and the on-period of the switch BL is included in the on-period of the switch AH. Details of the first control and the second control will be described later with reference to FIGS. 2 and 3.

[0033] The loss calculation unit 50 calculates losses occurring in at least two of the switches AH, AL, BH, and BL. For example, the calculated losses include turn-off losses that occur when the switches are turned off and reflux current conduction losses that occur when a reflux current flows when the switches are turned on. The at least two switches include at least the switches AH and BL, or at least the switches BH and AL. In other words, the loss calculation unit 50 only needs to calculate losses occurring in at least the switches AH and BL, and it is not necessary to calculate losses occurring in the switches BH and AL. Alternatively, the loss calculation unit 50 only needs to calculate losses occurring in at least the switches BH and AL, and it is not necessary to calculate losses occurring in the switches AH and BL. Note that the loss calculation unit 50 may calculate losses occurring in all of the switches AH, AL, BH, and BL.

[0034] The loss calculation unit 50 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory is, for example, a ROM or RAM, and can store a program executed by the processor. For example, the loss calculation unit 50 is realized by a microcontroller. The control unit 40 and the loss calculation unit 50 may be realized by the same processor (for example, the same microcomputer).

[0035] For example, the loss calculation unit 50 may calculate the losses generated in the at least two switches based on the input voltage and input current input to the terminal t1. The input voltage contributes to the turn-off loss because the turn-off loss increases as the input voltage increases. The input current contributes to the turn-off loss and the return current conduction loss. Therefore, the losses can be calculated based on the input voltage and the input current. For example, by preparing a data set or a calculation formula in advance regarding the relationship between the input voltage and the input current and the turn-off loss and the return current conduction loss, the losses can be easily calculated.

[0036] The loss calculation unit 50 may further calculate the losses occurring in the at least two switches based on the output voltage output from the terminal t3. The output voltage affects the period during which the return current flows, and the higher the output voltage, the smaller the return current conduction loss, which contributes to the return current conduction loss. Therefore, the return current conduction loss can be calculated based on the output voltage.

[0037] Furthermore, when the rectifier circuit 30 is composed of multiple switches that perform synchronous rectification in response to the current flowing on the secondary side of the resonator 20, for example, the loss calculation unit 50 may calculate the loss generated in at least two switches based on the timing when the switches AH and BH are both turned on, or the timing when the switches AL and BL are both turned on, and the on-periods of the multiple switches in the rectifier circuit 30. The timing when the switches AH and BH are both turned on, or the timing when the switches AL and BL are both turned on, is the timing when a reflux current begins to flow. The on-periods of the multiple switches in the rectifier circuit 30 are the periods during which the reflux current flows. In other words, a reflux current flows in the switches AH and BH or the switches AL and BL of the primary-side circuit 10 during the period from the timing when the switches are turned on to the timing when the on-periods of the multiple switches in the rectifier circuit 30 end, i.e., the timing when the multiple switches turn off. Therefore, the return current conduction loss can be calculated based on the timing of the on-state and the on-period (in other words, the turn-off timing) of the multiple switches in the rectifier circuit 30. For example, by preparing a data set or a calculation formula in advance regarding the relationship between the period during which the return current flows and the return current conduction loss, the return current conduction loss can be easily calculated.

[0038] For example, the control unit 40 may control multiple switches in the rectifier circuit 30 and determine the on-periods of the multiple switches based on detection results indicating whether the multiple switches are operating as diodes to pass current. For example, the rectifier circuit 30 may be provided with a detection circuit that detects whether the multiple switches are operating as diodes to pass current, and the control unit 40 may acquire the detection results of the detection circuit. Here, diode operation refers to an operation in which current flows from the source to the drain when the switch is in an off state, i.e., a state in which current is blocked from the drain to the source. For example, this corresponds to an operation in which a forward current flows through the body diode of a Si or SiC MOSFET when it is off. This allows the on-periods of the multiple switches to be determined based on detection results indicating that the multiple switches are operating as diodes to pass current, thereby enabling accurate calculation of the return current conduction loss using the determined on-periods of the multiple switches. The detection circuit that detects whether the multiple switches are operating as diodes to pass current may or may not be a component of the LLC converter 1.

[0039] Furthermore, for example, the control unit 40 may calculate the losses generated in at least two switches based on the elapsed time from when both the switches AH and BL are turned on to when at least one of the switches AH and BL is turned off, or the elapsed time from when both the switches AL and BH are turned on to when at least one of the switches AL and BH is turned off. The phase of the current can be estimated from the elapsed time and the switching frequency, and the phase of the current at the time of turn-off contributes to the turn-off loss. Therefore, the turn-off loss can be calculated based on the input voltage and input current.

[0040] For example, the loss calculation unit 50 may calculate the loss generated in at least two switches based on the surface temperatures of the at least two switches. For example, a temperature detection unit may be provided in at least two switches, and the loss calculation unit 50 may acquire the detection results of the temperature detection unit. Because there is a correlation between the loss generated in a switch and the surface temperature of the switch, it is possible to calculate the loss directly based on the surface temperature. Note that the temperature detection unit may or may not be a component of the LLC converter 1.

[0041] Next, the first control and the second control executed in the phase shift control will be described. First, the first control will be described with reference to FIG.

[0042] FIG. 2 is a timing chart showing an example of the first control. From top to bottom, FIG. 2 shows the gate voltages of the switches AH and AL, the gate voltages of the switches BH and BL, and the resonant current flowing through the primary winding of the transformer T. Non-ZCS timing is timing when zero current switching (ZCS) does not occur; in other words, timing when the switches are turned off while the resonant current is not zero. Also shown are "H" and "L" as freewheeling operation periods. "H" indicates a period when the high-side switches AH and BH are both on, and a freewheeling current flows from one end of the primary winding of the transformer T (upper side of FIG. 1 ) to the capacitor Cr, the switches AH and BH, and the other end of the primary winding of the transformer T (lower side of FIG. 1 ). "L" indicates a period when the low-side switches AL and BL are both on, and a freewheeling current flows from the other end of the primary winding of the transformer T to the switches BL, AL, the capacitor Cr, and one end of the primary winding of the transformer T.

[0043] In the first control, for example, as shown in Fig. 2, the switches AH, AL, BH, and BL are controlled so that the switching phase of the first group of switches (specifically, the switches AH and AL) leads the switching phase of the second group of switches (specifically, the switches BH and BL). By setting a phase difference between the switching of the first group of switches and the switching of the second group of switches, it is possible to shorten the period during which the switches AH and BL are both in the ON state and the period during which the switches BH and AL are both in the ON state, i.e., to shorten the period during which power is transmitted to the secondary side. This makes it possible to achieve a low gain.

[0044] 2 , in the first control, the phase-leading switches (e.g., switches AH and AL) of the first and second switch groups are always turned off at non-ZCS timings, so turn-off loss is biased toward switches AH and AL. Meanwhile, reflux current conduction loss is evenly distributed between the high-side switches AH and BH and the low-side switches AL and BL. Therefore, the total loss is biased toward switches AH and AL, and heat generation in switches AH and AL is greater than that in switches BH and BL.

[0045] In the first control, the switches AH, AL, BH, and BL may be controlled so that the switching phase of the second group of switches (specifically, the switches BH and BL) leads the switching phase of the first group of switches (specifically, the switches AH and AL). In this case, turn-off loss is biased toward the switches BH and BL, and reflux current conduction loss is distributed evenly between the high-side switches AH and BH and the low-side switches AL and BL. Therefore, in this case, the total loss is biased toward the switches BH and BL, and heat generation in the switches BH and BL is greater than that in the switches AH and AL.

[0046] In this way, in the first control, there is a possibility that the variation in loss between the switches will be large.

[0047] Next, the second control will be described with reference to FIG.

[0048] 3 is a timing chart showing an example of the second control, which shows, from the top, the gate voltages of the switches AH and AL, the gate voltages of the switches BH and BL, and the resonant current flowing through the primary winding of the transformer T.

[0049] 3, for example, the switches AH, AL, BH, and BL are controlled so that the on-period of the switch AH is included in the on-period of the switch BL, and the on-period of the switch BH is included in the on-period of the switch AL. That is, the switch AH is turned on after the switch BL is turned on, the switch BL is turned off after the switch AH is turned off, the switch BH is turned on after the switch AL is turned on, and the switch AL is turned off after the switch BH is turned off.

[0050] 3, in the second control, switches that turn off at non-ZCS timings are biased toward switches with short on-periods (e.g., high-side switches AH and BH), so turn-off losses are biased toward the high-side switches AH and BH. Meanwhile, reflux current conduction losses are biased toward switches with long on-periods (e.g., low-side switches AL and BL). Therefore, compared to the first control, the second control has the potential to more evenly distribute the total losses between the high-side switches AH and BH and the low-side switches AL and BL.

[0051] In the second control, the switches AH, AL, BH, and BL may be controlled so that the on-period of the switch AL is included in the on-period of the switch BH, and the on-period of the switch BL is included in the on-period of the switch AH. That is, the switch AL may be turned on after the switch BH is turned on, the switch BH may be turned off after the switch AL is turned off, the switch BL may be turned on after the switch AH is turned on, and the switch AH may be turned off after the switch BL is turned off. In this case, the switches that turn off at non-ZCS timings are biased toward switches with short on-periods (e.g., the low-side switches AL and BL), and therefore, turn-off losses are biased toward the low-side switches AL and BL. Meanwhile, reflux current conduction losses are biased toward switches with long on-periods (e.g., the high-side switches AH and BH). Therefore, compared to the first control, the second control has the possibility of distributing the total loss more evenly between the high-side switches AH and BH and the low-side switches AL and BL.

[0052] In this way, the second control may be able to suppress the variation in loss between switches more effectively than the first control. However, if the return current conduction loss is large, the second control may result in a larger variation in loss between switches than the first control. This is because the return current conduction loss is distributed to each switch in the first control, so even if the return current conduction loss is large, it does not affect the variation in loss between switches.

[0053] Therefore, the control unit 40 executes a control determination sequence for switching between the first control and the second control so as to reduce the loss difference between the maximum loss and the minimum loss among the losses of the at least two switches calculated by the loss calculation unit 50, in other words, so as to reduce the variation in loss between the switches. Specifically, in the control determination sequence, the control unit 40 compares the loss difference when the first control is executed with the loss difference when the second control is executed, and subsequently executes phase shift control using the control with the smaller loss difference.

[0054] For example, the control unit 40 executes the control determination sequence at regular intervals or each time the loss difference falls outside the set threshold range. By repeatedly executing the control determination sequence in this manner, it is possible to maintain a state in which the variation in loss between the switches is suppressed. For example, the control unit 40 updates the set threshold range based on the loss difference after executing the control determination sequence. Because the loss difference varies depending on the operating conditions of the LLC converter 1, it is possible to set an appropriate set threshold range depending on the operating conditions of the LLC converter 1.

[0055] For example, in the control determination sequence, the control unit 40 executes switching from one of the first control and the second control to the other, thereby obtaining the loss difference when the first control is being executed and the loss difference when the second control is being executed, and executes phase shift control using the first control or the second control corresponding to the smaller of the two obtained loss differences until the next time the control determination sequence is executed.

[0056] Here, an example of phase shift control before and after the control determination sequence will be described with reference to FIGS. 4A and 4B.

[0057] 4A and 4B are diagrams illustrating an example of phase shift control before and after a control determination sequence. Loss differences before and after a control determination sequence are shown in FIGS. 4A and 4B. FIG. 4A illustrates an example of phase shift control in the case where the loss difference becomes small after switching from one of the first control and the second control to the other by the control determination sequence. FIG. 4B illustrates an example of phase shift control in the case where the loss difference becomes large after switching from one of the first control and the second control to the other by the control determination sequence.

[0058] As shown in FIG. 4A , when the control unit 40 is executing one of the first and second controls (e.g., the first control), the operating conditions of the LLC converter 1 fluctuate, causing the loss difference to fall outside the set threshold range. In this case, the control unit 40 executes a control determination sequence to switch from one of the first and second controls to the other (e.g., from the first control to the second control). During a switchover verification period after switching from the first control to the second control, the control unit 40 compares the loss difference when the first control is executed with the loss difference when the second control is executed. As shown in FIG. 4A , if the loss difference when the second control is executed is smaller than the loss difference when the first control is executed, the control unit 40 continues to execute phase shift control using the second control until the next execution of the control determination sequence. For example, the control unit 40 updates the set threshold range and sets a new set threshold range based on the loss difference after executing the control determination sequence. Because the loss difference varies depending on the operating conditions of the LLC converter 1, an appropriate set threshold range can be set depending on the operating conditions of the LLC converter 1.

[0059] As shown in FIG. 4B , when the control unit 40 is executing one of the first and second controls (e.g., the first control), the operating conditions of the LLC converter 1 fluctuate, causing the loss difference to fall outside the set threshold range. The control unit 40 executes a control determination sequence to switch from one of the first and second controls to the other (e.g., from the first control to the second control). During a switchover verification period after switching from the first control to the second control, the control unit 40 compares the loss difference when the first control is executed with the loss difference when the second control is executed. As shown in FIG. 4B , if the loss difference when the second control is executed is greater than the loss difference when the first control is executed, the control unit 40 switches from the second control to the first control (i.e., returns to the original control) and executes phase shift control using the first control until the next control determination sequence is executed. For example, the control unit 40 updates the set threshold range to set a new set threshold range based on the loss difference after executing the control determination sequence.

[0060] In this way, when the loss difference becomes small due to switching between the first control and the second control, phase shift control can be performed using the control after switching, and when the loss difference becomes large due to switching between the first control and the second control, phase shift control can be performed using the control before switching.

[0061] The control unit 40 may acquire the ambient temperature of the LLC converter 1. If the acquired ambient temperature is lower than the ambient temperature threshold, the control determination sequence may not be executed and the first control may be executed in the phase shift control. For example, the LLC converter 1 may be equipped with an ambient temperature monitoring unit (e.g., a thermometer) that monitors the ambient temperature of the LLC converter 1. When the ambient temperature is low, variations in loss between the switches do not significantly impede operation, and there is little need to execute the control determination sequence to reduce the loss difference. Therefore, in this case, the operation of the LLC converter 1 can be stabilized by omitting the control determination sequence.

[0062] As described above, when the first control is performed in the phase-shift control, the turn-off loss is biased toward the first set of switches or the second set of switches, while the return current conduction loss is distributed among the switches. On the other hand, when the second control is performed in the phase-shift control, the turn-off loss is biased toward one of the high-side switches AH and BH and the low-side switches AL and BL, while the return current conduction loss is biased toward the other. Because the loss generated in each switch varies depending on the operating conditions of the LLC converter 1, a control decision sequence is executed to switch between the first control and the second control so as to reduce the difference between the maximum and minimum losses of the losses of at least two switches, thereby suppressing the variation in loss among the switches. This allows, for example, optimization of thermal design or device selection and reduction in costs.

[0063] (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.

[0064] For example, the present disclosure can be realized not only as an LLC converter, but also as a control method for an LLC converter including steps (processing) performed by components that make up the LLC converter (e.g., the control unit 40 and the loss calculation unit 50).

[0065] FIG. 5 is a flowchart showing an example of a control method according to another embodiment.

[0066] The control method is a control method for an LLC converter, the LLC converter comprising: a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor; a primary-side circuit connected to the primary side of the resonator; and a rectifier circuit connected to the secondary side of the resonator, the primary-side circuit having: a first set of switches consisting of a first high-side switch and a first low-side switch connected in series on a first path connecting the input terminal and a ground terminal; and a second set of switches consisting of a second high-side switch and a second low-side switch connected in series on a second path different from the first path connecting the input terminal and the ground terminal, the control method controlling an output voltage output from an output terminal connected to the rectifier circuit by simultaneously performing frequency control for controlling a switching frequency of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and phase shift control for controlling a phase difference between switching of the first set of switches and switching of the second set of switches, a first control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the switching phase of the second group of switches leads the switching phase of the first group of switches, or so that the switching phase of the second group of switches leads the switching phase of the first group of switches; and a second control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the on-period of the first high-side switch is included in the on-period of the second low-side switch and the on-period of the second high-side switch is included in the on-period of the first low-side switch, or so that the on-period of the first low-side switch is included in the on-period of the second high-side switch and the on-period of the second low-side switch is included in the on-period of the first high-side switch. As shown in FIG. 5 , the control method can be executed by switching between: a first control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the on-period of the first high-side switch is included in the on-period of the second low-side switch;and a step (step S12) of switching between the first control and the second control so as to reduce a loss difference between a maximum loss and a minimum loss among the calculated losses of the at least two switches, wherein the at least two switches include at least a first high-side switch and a second low-side switch, or at least a second high-side switch and a first low-side switch.

[0067] 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.

[0068] 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, 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.

[0069] In the above-described embodiment, each component included in the LLC converter may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may also 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.

[0070] Some or all of the functions of the LLC converter according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into single chips, 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), which can be programmed after LSI manufacturing, or a reconfigurable processor, which allows the connections and settings of circuit cells within an LSI to be reconfigured.

[0071] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that each component included in the LLC converter can be integrated using that technology.

[0072] 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.

[0073] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0074] (Technology 1) An LLC converter according to Technology 1 includes a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor, a primary-side circuit connected to the primary side of the resonator, a rectifier circuit connected to the secondary side of the resonator, a control unit, and a loss calculation unit. The primary-side circuit includes a first set of switches and a second set of switches. The first set of switches includes a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal. The second set of switches includes a second high-side switch and a second low-side switch connected in series on a second path connecting the input terminal and the ground terminal, the second path being different from the first path. The control unit controls the output voltage output from the output terminal connected to the rectifier circuit by performing frequency control and phase shift control in combination. The frequency control controls the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The phase shift control is control that controls a phase difference between switching of the first group of switches and switching of the second group of switches. The phase shift control can be executed by switching between first control and second control. The first control is control that controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the phase of switching of the first group of switches leads the phase of switching of the second group of switches, or so that the phase of switching of the second group of switches leads the phase of switching of the first group of switches.The second control controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and the on-period of the second high-side switch is included in an on-period of the first low-side switch, or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and the on-period of the second low-side switch is included in an on-period of the first high-side switch. The loss calculation unit calculates losses generated in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The at least two switches include at least the first high-side switch and the second low-side switch, or at least the second high-side switch and the first low-side switch. The control unit executes a control determination sequence to switch between the first control and the second control so that a loss difference between a maximum loss and a minimum loss among the losses of the at least two switches calculated by the loss calculation unit is reduced.

[0075] According to this, when the first control is executed in the phase-shift control, the turn-off loss can be biased to the first set of switches or the second set of switches, while the return current conduction loss can be distributed among the switches. On the other hand, when the second control is executed in the phase-shift control, the turn-off loss can be biased to one of the high-side switch and the low-side switch, while the return current conduction loss can be biased to the other. Because the loss generated in each switch varies depending on the operating status of the LLC converter, a control decision sequence is executed to switch between the first control and the second control so as to reduce the difference between the maximum loss and the minimum loss among the losses of at least two switches, thereby suppressing the variation in loss among the switches. This allows, for example, optimization of thermal design or device selection and reduction in costs.

[0076] (Technology 2) In the LLC converter according to Technology 1, the control unit repeats the frequency control and the phase shift control to control the output voltage, thereby optimizing the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and the phase difference between the switching of the first group of switches and the switching of the second group of switches.

[0077] In this way, by repeating frequency control and phase shift control, the switching frequency and phase difference can be optimized to accommodate a wide range of input and output voltages. For example, it is possible to reduce the number of step-down converters required to accommodate low gain, thereby enabling miniaturization.

[0078] (Technology 3) The LLC converter according to Technology 1 or 2, wherein the loss calculation unit calculates losses occurring in the at least two switches based on an input voltage and an input current input to the input terminals.

[0079] The input voltage contributes to the turn-off loss, and the input current contributes to the turn-off loss and the return current conduction loss. Therefore, the loss can be calculated based on the input voltage and the input current. For example, by preparing a data set or a formula in advance regarding the relationship between the input voltage and the input current and the turn-off loss and the return current conduction loss, the loss can be easily calculated.

[0080] (Technology 4) An LLC converter according to Technology 3, wherein the rectifier circuit includes a plurality of switches that perform synchronous rectification in response to a current flowing through the secondary side of the resonator, and the loss calculation unit further calculates the loss generated in the at least two switches based on a timing when the first high-side switch and the second high-side switch are both turned on or a timing when the first low-side switch and the second low-side switch are both turned on, and an on-period of the plurality of switches.

[0081] According to this, a return current flows in the primary circuit from the time when the switches in the rectifier circuit are turned on to the time when the on-periods of the switches in the rectifier circuit end, i.e., the time when the switches are turned off. Therefore, the return current conduction loss can be calculated based on the time when the switches in the rectifier circuit are turned on and the on-periods of the switches in the rectifier circuit (i.e., the time when the switches are turned off). For example, by preparing a data set or a formula in advance regarding the relationship between the period during which the return current flows and the return current conduction loss, the return current conduction loss can be easily calculated.

[0082] (Technology 5) In the LLC converter according to Technology 4, the control unit further controls the plurality of switches and determines an on-period of the plurality of switches based on a detection result indicating whether the plurality of switches are operating as diodes and passing current.

[0083] This makes it possible to detect the on-periods of multiple switches based on detection results that indicate that multiple switches are operating as diodes and passing current, thereby enabling the return current conduction loss to be calculated with high accuracy.

[0084] (Technology 6) An LLC converter according to any one of technologies 1 to 5, wherein the loss calculation unit calculates losses occurring in the at least two switches based on surface temperatures of the at least two switches.

[0085] According to this, since there is a correlation between the loss generated in the switch and the surface temperature of the switch, the loss can be calculated directly based on the surface temperature.

[0086] (Technology 7) An LLC converter according to any one of technologies 1 to 6, wherein the control unit executes the control determination sequence at regular intervals or whenever the loss difference falls outside a set threshold range.

[0087] According to this, by repeatedly executing the control determination sequence, it is possible to maintain a state in which the variation in loss between the switches is suppressed.

[0088] (Technology 8) In an LLC converter according to Technology 7, the control unit acquires the loss difference when the first control is being executed and the loss difference when the second control is being executed by executing a switch from one of the first control and the second control to the other in the control determination sequence, and executes the phase shift control by the first control or the second control corresponding to the smaller of the two acquired loss differences until the next time the control determination sequence is executed.

[0089] In this way, until the next execution of the control determination sequence, the phase shift control can be executed by the control with the smaller loss difference between the first control and the second control.

[0090] (Technology 9) An LLC converter according to Technology 8, wherein, if the loss difference when executing one of the controls is smaller than the loss difference when executing the other of the controls, the control unit continues to execute the phase shift control using the other of the controls until the next execution of the control determination sequence, and, if the loss difference when executing the other of the controls is larger than the loss difference when executing one of the controls, switches from the other of the controls to the one of the controls, and executes the phase shift control using the one of the controls until the next execution of the control determination sequence.

[0091] In this way, when the loss difference becomes small due to switching between the first control and the second control, phase shift control can be performed using the control after switching, and when the loss difference becomes large due to switching between the first control and the second control, phase shift control can be performed using the control before switching.

[0092] (Technology 10) An LLC converter according to any one of Techniques 7 to 9, wherein the control unit updates the set threshold range based on the loss difference after executing the control determination sequence.

[0093] According to this, since the loss difference varies depending on the operating conditions of the LLC converter, it is possible to set an appropriate set threshold range depending on the operating conditions of the LLC converter.

[0094] (Technology 11) An LLC converter described in any one of Technologies 1 to 10, wherein the control unit further acquires an ambient temperature of the LLC converter, and if the acquired ambient temperature is lower than an ambient temperature threshold, does not execute the control determination sequence in the phase shift control, and executes the first control.

[0095] According to this, when the ambient temperature is low, variations in loss between the switches do not significantly impede operation, and there is little need to execute the control determination sequence to reduce the loss difference. Therefore, in this case, the operation of the LLC converter can be stabilized by omitting the control determination sequence.

[0096] (Technology 12) A control method for an LLC converter, the LLC converter comprising: a resonator having an isolation transformer and a resonant capacitor; a primary-side circuit connected to the primary side of the resonator; and a rectifier circuit connected to the secondary side of the resonator. The primary-side circuit includes a first set of switches and a second set of switches. The first set of switches includes a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal. The second set of switches includes a second high-side switch and a second low-side switch connected in series on a second path connecting the input terminal and the ground terminal, the second path being different from the first path. The control method controls the output voltage output from an output terminal connected to the rectifier circuit by performing frequency control and phase shift control in combination. The frequency control controls the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The phase shift control is control that controls a phase difference between switching of the first group of switches and switching of the second group of switches. The control method can switch between first control and second control in the phase shift control. The first control is control that controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that the phase of switching of the first group of switches leads the phase of switching of the second group of switches, or so that the phase of switching of the second group of switches leads the phase of switching of the first group of switches.The second control controls the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and the on-period of the second high-side switch is included in an on-period of the first low-side switch, or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and the on-period of the second low-side switch is included in an on-period of the first high-side switch. The control method includes the steps of calculating losses generated in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and switching between the first control and the second control so that a difference between a maximum loss and a minimum loss among the calculated losses of the at least two switches is reduced. The at least two switches include at least the first high-side switch and the second low-side switch, or at least the second high-side switch and the first low-side switch.

[0097] This provides a control method that can suppress variations in loss between switches.

[0098] The present disclosure is applicable to LLC converters that can accommodate a wide range of input and output voltages.

[0099] REFERENCE SIGNS LIST 1 LLC converter 10 primary side circuit 20 resonator 30 rectifier circuit 40 control unit 50 loss calculation unit AH, AL, BH, BL switch Cr capacitor Lr inductor T transformer t1, t2, t3, t4 terminal

Claims

1. A power supply comprising: a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor; a primary side circuit connected to the primary side of the resonator; a rectifier circuit connected to the secondary side of the resonator; a control unit; and a loss calculation unit, wherein the primary side circuit has: a first set of switches consisting of a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal; and a second set of switches consisting of a second high-side switch and a second low-side switch connected in series on a second path different from the first path connecting the input terminal and the ground terminal, wherein the control unit controls an output voltage output from an output terminal connected to the rectifier circuit by simultaneously executing frequency control for controlling a switching frequency of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and phase shift control for controlling a phase difference between switching of the first set of switches and switching of the second set of switches, a first control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that a switching phase of the first set of switches leads a switching phase of the second set of switches or so that a switching phase of the second set of switches leads a switching phase of the first set of switches; and a second control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and an on-period of the second high-side switch is included in an on-period of the first low-side switch or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and an on-period of the second low-side switch is included in an on-period of the first high-side switch,an LLC converter, wherein the loss calculation unit calculates losses occurring in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and the at least two switches include at least the first high-side switch and the second low-side switch, or include at least the second high-side switch and the first low-side switch, and the control unit executes a control determination sequence for switching between the first control and the second control so that a loss difference between a maximum loss and a minimum loss among the losses of the at least two switches calculated by the loss calculation unit becomes small.

2. The LLC converter according to claim 1, wherein the control unit repeats the frequency control and the phase shift control to control the output voltage, thereby optimizing the switching frequencies of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and the phase difference between the switching of the first set of switches and the switching of the second set of switches.

3. The LLC converter according to claim 1, wherein the loss calculation unit calculates losses occurring in the at least two switches based on an input voltage and an input current input to the input terminal.

4. The LLC converter according to claim 3, wherein the rectifier circuit is made up of a plurality of switches that perform synchronous rectification in response to a current flowing through the secondary side of the resonator, and the loss calculation unit further calculates the loss generated in the at least two switches based on a timing when the first high-side switch and the second high-side switch are both turned on or a timing when the first low-side switch and the second low-side switch are both turned on, and an on-period of the plurality of switches.

5. The LLC converter according to claim 4, wherein the control unit further controls the plurality of switches and determines an on-period of the plurality of switches based on a detection result indicating whether the plurality of switches are operating as diodes and passing a current.

6. The LLC converter according to claim 1, wherein the loss calculation unit calculates losses occurring in the at least two switches based on surface temperatures of the at least two switches.

7. The LLC converter according to any one of claims 1 to 6, wherein the control unit executes the control determination sequence at regular intervals or each time the loss difference falls outside a set threshold range.

8. The LLC converter as described in claim 7, wherein the control unit acquires the loss difference when the first control is being executed and the loss difference when the second control is being executed by executing a switch from one of the first control and the second control to the other in the control determination sequence, and executes the phase shift control by the first control or the second control corresponding to the smaller of the two acquired loss differences until the control determination sequence is next executed.

9. The LLC converter as described in claim 8, wherein the control unit, if the loss difference when executing the one control is smaller than the loss difference when executing the other control, continues to execute the phase shift control using the other control until the next time the control determination sequence is executed, and, if the loss difference when executing the other control is larger than the loss difference when executing the one control, switches from the other control to the one control and executes the phase shift control using the one control until the next time the control determination sequence is executed.

10. The LLC converter according to claim 7, wherein the control unit updates the set threshold range based on the loss difference after executing the control determination sequence.

11. An LLC converter as described in any one of claims 1 to 5, wherein the control unit further acquires an ambient temperature of the LLC converter, and if the acquired ambient temperature is lower than an ambient temperature threshold value, in the phase shift control, the control decision sequence is not executed and the first control is executed.

12. A control method for an LLC converter, comprising: a resonator having an isolation transformer, a resonant capacitor, and a resonant inductor; a primary-side circuit connected to the primary side of the resonator; and a rectifier circuit connected to the secondary side of the resonator, wherein the primary-side circuit has: a first set of switches consisting of a first high-side switch and a first low-side switch connected in series on a first path connecting an input terminal and a ground terminal; and a second set of switches consisting of a second high-side switch and a second low-side switch connected in series on a second path different from the first path connecting the input terminal and the ground terminal, wherein the control method controls an output voltage output from an output terminal connected to the rectifier circuit by simultaneously executing frequency control for controlling a switching frequency of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and phase shift control for controlling a phase difference between switching of the first set of switches and switching of the second set of switches, wherein the control method further comprises: a first control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that a switching phase of the first set of switches leads a switching phase of the second set of switches or so that a switching phase of the second set of switches leads a switching phase of the first set of switches; and a second control for controlling the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch so that an on-period of the first high-side switch is included in an on-period of the second low-side switch and an on-period of the second high-side switch is included in an on-period of the first low-side switch or so that an on-period of the first low-side switch is included in an on-period of the second high-side switch and an on-period of the second low-side switch is included in an on-period of the first high-side switch,A control method comprising: a step of calculating losses generated in at least two switches among the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch; and a step of switching between the first control and the second control so that a loss difference between a maximum loss and a minimum loss among the calculated losses of the at least two switches becomes small, wherein the at least two switches include at least the first high-side switch and the second low-side switch, or include at least the second high-side switch and the first low-side switch.

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