Power conversion device and control method

Abstract

A power conversion device (1) comprises: a resonator (30); a primary-side full-bridge circuit (10) having a first switch (Q1), a second switch (Q2), a third switch (Q3) and a fourth switch (Q4); a secondary-side full-bridge circuit (20) having a fifth switch (Q5), a sixth switch (Q6), a seventh switch (Q7) and an eighth switch (Q8); and a controller (40). The controller (40) operates the fifth switch (Q5), the sixth switch (Q6), the seventh switch (Q7) and the eighth switch (Q8) in synchronisation with control signals for the first switch (Q1), the second switch (Q2), the third switch (Q3) and the fourth switch (Q4) by means of drive signals for durations that are the result of subtracting a resonance period of the resonator (30) from the switching periods of the first switch (Q1), the second switch (Q2), the third switch (Q3) and the fourth switch (Q4), and controls the on times of the drive signals using the lengths of the durations as an upper limit.

Description

Power conversion device and control method

[0001] The present disclosure relates to a power conversion device capable of unidirectional or bidirectional power conversion and a control method for the power conversion device.

[0002] Toward the realization of a carbon-neutral society, there is a demand for charging circuits that can efficiently charge home storage batteries or automotive batteries. Such charging circuits require isolated DC-DC converters, and resonant converters are commonly used for their compact size and high efficiency. Among resonant converters, LLC converters have attracted particular attention because they can achieve high efficiency with a simple circuit configuration.

[0003] LLC converters generally use frequency control to control output power. The loads to which power is supplied from LLC converters range from light loads to heavy loads, and to accommodate these, the frequency control range becomes wide, requiring measures to accommodate all operating conditions (e.g., EMC (Electromagnetic Compatibility) measures, etc.).

[0004] In response to this, Patent Document 1 describes an LLC type DC-DC converter that controls output power by making the transformer current have an asymmetric waveform between positive and negative sides through duty control.

[0005] Japanese Patent Application Laid-Open No. 2022-17179

[0006] However, in the DC-DC converter disclosed in Patent Document 1, the transformer current has an asymmetric waveform between positive and negative, which has the effect of worsening common mode noise.

[0007] Therefore, the present disclosure provides a power conversion device and the like that can effectively control output power while suppressing the frequency control range width.

[0008] A power conversion device according to the present disclosure is a power conversion device capable of unidirectional or bidirectional power conversion, and includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, a secondary-side full bridge circuit connected to a secondary side of the resonator, and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth switch element provided on the high side of a third leg. the controller calculates a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element, and operates the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal during the period, and controls an on-time of the drive signal with the length of the period as an upper limit.

[0009] A control method according to the present disclosure is a control method for a power conversion device capable of unidirectional or bidirectional power conversion, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit having a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of a second leg, and a fourth switch element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth switch element provided on the high side of a third leg, and a fifth switch element provided on the low side of the third leg. the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element are provided on the high side of the fourth leg, the seventh switch element on the high side of the fourth leg, and the eighth switch element on the low side of the fourth leg, and the control method calculates a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element, and operates the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal in the period, and controls an on-time of the drive signal with the length of the period as an upper limit.

[0010] 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.

[0011] According to a power conversion device according to an aspect of the present disclosure, it is possible to effectively control output power while suppressing the frequency control range width.

[0012] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device according to an embodiment. FIG. 2 is a diagram for explaining operation of a controller according to an embodiment. FIG. 3 is a diagram for explaining an example of operation in a first mode of a controller according to an embodiment. FIG. 4 is a diagram for explaining an effect of operation in the first mode of a controller according to an embodiment. FIG. 5 is a diagram for explaining an example of operation in a second mode of a controller according to an embodiment. FIG. 6 is a diagram for explaining an example of operation in a phase shift control mode of a controller according to an embodiment. FIG. 7 is a diagram for explaining an example of operation in an intermittent operation mode of a controller according to an embodiment. FIG. 8 is a flowchart showing an example of a control method according to another embodiment.

[0013] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0014] 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.

[0015] (Embodiment) Hereinafter, a power conversion device according to an embodiment will be described.

[0016] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to an embodiment.

[0017] The power conversion device 1 is a power conversion device capable of unidirectional or bidirectional power conversion, such as an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined voltage and outputs it. For example, the power conversion device 1 is an LLC converter. An LLC converter is a circuit that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. In an LLC converter, the input / output voltage ratio (Gain) can be changed by changing the switching frequency, making it possible to output a desired power. However, the following description will be directed to a power conversion device 1 that can control output power without frequency control.

[0018] The power conversion device 1 has terminals t1, t2, t3, and t4. The terminal t1 is an input terminal. The terminal t2 is a ground terminal. The terminal t3 is an output terminal. The terminal t4 is a ground terminal. Note that, since the power conversion device 1 is an isolated DC-DC converter, the terminals t2 and t4 are electrically isolated.

[0019] The power conversion device 1 includes a primary side full bridge circuit 10, a secondary side full bridge circuit 20, a resonator 30, capacitors Cin and Cout, and a controller 40. The capacitors Cin and Cout do not necessarily have to be components of the power conversion device 1.

[0020] The capacitor Cin is an input capacitor connected between the terminal t1 and the terminal t2, and the capacitor Cout is an output capacitor (smoothing capacitor) connected between the terminal t3 and the terminal t4.

[0021] The primary-side full-bridge circuit 10 is connected to the primary side of the resonator 30. The primary-side full-bridge circuit 10 has a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg.

[0022] The primary-side full-bridge circuit 10 has switches Q1, Q2, Q3, and Q4, where the switch Q1 is an example of a first switch element, the switch Q2 is an example of a second switch element, the switch Q3 is an example of a third switch element, and the switch Q4 is an example of a fourth switch element.

[0023] The switch Q1 is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch Q1 is connected to the terminal t1, and the source of the switch Q1 is connected to the drain of the switch Q2.

[0024] The switch Q2 is, for example, an N-channel MOSFET. The drain of the switch Q2 is connected to the source of the switch Q1, and the source of the switch Q2 is connected to the terminal t2.

[0025] The switch Q3 is, for example, an N-channel MOSFET. The drain of the switch Q3 is connected to the terminal t1, and the source of the switch Q3 is connected to the drain of the switch Q4.

[0026] The switch Q4 is, for example, an N-channel MOSFET. The drain of the switch Q4 is connected to the source of the switch Q3, and the source of the switch Q4 is connected to the terminal t2.

[0027] The secondary-side full-bridge circuit 20 is connected to the secondary side of the resonator 30. The secondary-side full-bridge circuit 20 has a fifth switch element provided on the high side of the third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of the fourth leg, and an eighth switch element provided on the low side of the fourth leg. The secondary-side full-bridge circuit 20 also functions as a rectifier circuit capable of full-wave rectification.

[0028] The secondary-side full-bridge circuit 20 has switches Q5, Q6, Q7, and Q8, where the switch Q5 is an example of a fifth switch element, the switch Q6 is an example of a sixth switch element, the switch Q7 is an example of a seventh switch element, and the switch Q8 is an example of an eighth switch element.

[0029] The switch Q5 is, for example, an N-channel MOSFET. The drain of the switch Q5 is connected to the terminal t3, and the source of the switch Q5 is connected to the drain of the switch Q6.

[0030] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the source of the switch Q5, and the source of the switch Q6 is connected to the terminal t4.

[0031] The switch Q7 is, for example, an N-channel MOSFET. The drain of the switch Q7 is connected to the terminal t3, and the source of the switch Q7 is connected to the drain of the switch Q8.

[0032] The switch Q8 is, for example, an N-channel MOSFET. The drain of the switch Q8 is connected to the source of the switch Q7, and the source of the switch Q8 is connected to the terminal t4.

[0033] The resonator 30 includes a transformer T and a capacitor Cr.

[0034] The capacitor Cr is an example of a resonant capacitor and is connected to a node between the switch Q1 and the switch Q2 in the first leg.

[0035] The transformer T is an isolated transformer having 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 via a capacitor Cr to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg. One end of the secondary winding of the transformer T is connected to a node between the switches Q5 and Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the switches Q7 and Q8 in the fourth leg.

[0036] The capacitor Cr may be connected to a node between the switches Q3 and Q4 in the second leg. In this case, one end of the primary winding of the transformer T is connected to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg via the capacitor Cr.

[0037] The controller 40 controls the primary-side full-bridge circuit 10 and the secondary-side full-bridge circuit 20. Specifically, the controller 40 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) included in the power conversion device 1. For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 via a PWM generator (not shown) or the like.

[0038] The controller 40 is, 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 to be executed by the processor. For example, the controller 40 is a microcontroller.

[0039] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 (the period of resonance due to the capacitance of the capacitor Cr and the leakage inductance of the transformer T, etc.) from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q5, Q6, Q7, and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using drive signals during that period. The controller 40 also controls the on-time of the drive signals, with the length of the period as an upper limit.

[0040] Here, the operation of the controller 40 will be described in detail with reference to FIG.

[0041] FIG. 2 is a diagram for explaining the operation of the controller 40 according to the embodiment.

[0042] As shown in Fig. 2, for example, the controller 40 controls the switching of the switches Q1 and Q4 in the same phase, and controls the switching of the switches Q2 and Q3 in the same phase. The controller 40 controls the switches Q1, Q2, Q3, and Q4 so that the phase difference between the switching of the switches Q1 and Q4 and the switching of the switches Q2 and Q3 is 180 degrees. As a result, the control signals for the switches Q1, Q2, Q3, and Q4 become, for example, those shown in Fig. 2. Specifically, the switches Q1 and Q4 repeatedly turn on and off with a duty ratio of 50%, and the switches Q2 and Q3 repeatedly turn on and off with a duty ratio of 50%. When the switches Q1 and Q4 are in the on state, the switches Q2 and Q3 are in the off state, and when the switches Q2 and Q3 are in the on state, the switches Q1 and Q4 are in the off state.

[0043] When the controller 40 turns on the switches Q1 and Q4 and turns off the switches Q2 and Q3, or turns on the switches Q2 and Q3 and turns off the switches Q1 and Q4, a current (primary current) flows through the primary winding of the transformer T. The primary current resonates with the resonant period of the resonator 30. Furthermore, when a current flows through the primary winding of the transformer T, a current (secondary current) flows through the secondary winding of the transformer T. The secondary current also resonates with the resonant period of the resonator 30. As a result, the primary and secondary currents become as shown in FIG. 2 .

[0044] The controller 40 calculates a period obtained by subtracting the resonance period (e.g., the resonance half period shown in FIG. 2 ) of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4 (e.g., the switching half period shown in FIG. 2 , which is the period during which the switches are on with a duty ratio of 50%). This period is a period during which no current is applied to the loads connected to the terminals t3 and t4, and is also called a non-energization period.

[0045] The controller 40 operates the switches Q5, Q6, Q7, and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using the drive signals during the non-energized period. At this time, the controller 40 performs pulse width control for the ON periods of the switches Q5, Q6, Q7, and Q8, as shown in FIG. 2 . As shown in FIG. 2 , the control signals for the switches Q1, Q2, Q3, and Q4 are synchronized with the drive signals for the switches Q5, Q6, Q7, and Q8. The synchronization of the control signals and drive signals means that there is a certain relationship between the ON timing of the control signals and the ON timing of the drive signals. In this specification, the synchronization of the control signals and drive signals means that the drive signals are turned on a certain period after the control signals are turned on.

[0046] The controller 40 has a first mode and a second mode as control modes for switching the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8. First, the first mode will be described.

[0047] Fig. 3 is a diagram for explaining an example of operation in the first mode of the controller 40 according to the embodiment. Fig. 3 shows, from top to bottom, timing charts of the gate signals of the switches Q1, Q4, Q5, and Q8, the gate signals of the switches Q2, Q3, Q6, and Q7, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), the excitation current of the transformer T (transformer excitation current), the voltage input to the primary winding of the transformer T (transformer input voltage), and the excitation voltage of the transformer T (transformer excitation voltage). The same applies to Fig. 5, which will be described later.

[0048] 3 , in the first mode, the controller 40, in response to the drive signal, turns on the switches Q5 and Q8 before the switches Q1 and Q4 change from an on state to an off state. In addition, in the first mode, the controller 40, in response to the drive signal, turns on the switches Q6 and Q7 before the switches Q2 and Q3 change from an on state to an off state. The non-energized period is the period before the switches Q1 and Q4 change from an on state to an off state (the period existing in the latter half of the period in which the switches Q1 and Q4 are on) and the period before the switches Q2 and Q3 change from an on state to an off state (the period existing in the latter half of the period in which the switches Q2 and Q3 are on).

[0049] The upper limit of the length of the period before the switches Q1 and Q4 change from an on state to an off state and the period before the switches Q2 and Q3 change from an on state to an off state is the length of the non-conductive period. In other words, the end of the period before the switches Q1 and Q4 change from an on state to an off state is the timing when the switches Q1 and Q4 turn off, and the start of this period is a time up to the length of the non-conductive period before the switches Q1 and Q4 turn off. Also, the end of the period before the switches Q2 and Q3 change from an on state to an off state is the timing when the switches Q2 and Q3 turn off, and the start of this period is a time up to the length of the non-conductive period before the switches Q2 and Q3 turn off. Therefore, the controller 40 controls the on time of the drive signal with the length of the non-conductive period as the upper limit.

[0050] The power conversion device 1, which is an LLC converter, is a circuit that can obtain a gain of 1 or more (i.e., increase output power) by setting the switching frequency lower than the resonant frequency of the resonator 30 (the resonant frequency due to the capacitance of the capacitor Cr and the leakage inductance of the transformer T, etc.). Setting the switching frequency lower than the resonant frequency of the resonator 30 is equivalent to leading the phase of the resonant current relative to the phase of the input voltage (transformer input voltage) of the resonator 30. In other words, leading the phase of the resonant current relative to the phase of the transformer input voltage can increase the output power. In the first mode, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 while keeping the switching frequency fixed so that the phase of the resonant current leads the phase of the input voltage of the resonant circuit. Here, the operation of the controller 40 in the first mode will be described in detail.

[0051] As shown in part A of FIG. 3, the controller 40 turns on the switches Q6 and Q7 during a non-conducting period, which is a period before the switches Q2 and Q3 are turned off from an on state.

[0052] This causes the polarity of the transformer secondary voltage to reverse, as shown in part B of Fig. 3. It can be seen that the timing of the polarity reversal is earlier than the conventional transformer secondary voltage shown by the dashed line (specifically, the transformer secondary voltage when the switches Q6 and Q7 are not controlled during the non-energized period).

[0053] As shown in part C of FIG. 3, when the polarity of the transformer secondary voltage is reversed, the polarity of the transformer excitation voltage is also reversed in response to the reversal of the polarity of the transformer secondary voltage.

[0054] As shown in part D of Figure 3, the polarity of the transformer excitation voltage reverses earlier than before, causing the transformer excitation current to reach its extreme value earlier than before. Specifically, the phase of the polarity reversal of the transformer excitation voltage advances, leading to an advance in the phase of the transformer excitation current. Because the resonant current is superimposed on the transformer excitation current, if the phase of the transformer excitation current advances, the phase of the resonant current also advances. Therefore, the phase of the resonant current advances relative to the phase of the transformer input voltage, allowing for an increase in output power. Note that by further extending the on-time of switches Q6 and Q7 during the non-energized period, the phase of the resonant current further advances, allowing for a further increase in output power.

[0055] 4 is a diagram illustrating the effect of operation of controller 40 in the first mode according to the embodiment. The horizontal axis of the graph shown in FIG. 4 represents the on-time of switches Q5, Q6, Q7, and Q8 during the non-energized period, and the vertical axis represents the output current. There is a correlation between the output current and the output power, and as the output current increases, the output power also increases.

[0056] As shown in Figure 4, the longer the on time of switches Q5, Q6, Q7, and Q8 during the non-energized period, the larger the output current, i.e., the output power. Specifically, it can be seen that power conversion device 1 has a power adjustment function that can handle loads ranging from a light load of approximately 1 A to a heavy load of approximately 15 A. For example, when the output voltage is 250 V, the output power can be adjusted from 250 W to 3.7 kW.

[0057] In this way, in the first mode, the output power can be increased while the switching frequency is fixed.

[0058] Next, the second mode of the controller 40 will be described.

[0059] FIG. 5 is a diagram for explaining an example of the operation of the controller 40 in the second mode according to the embodiment.

[0060] 5, in the second mode, the controller 40, in response to the drive signal, turns on the switches Q6 and Q7 before the switches Q1 and Q4 change from an on state to an off state, and also turns on the switches Q5 and Q8 before the switches Q2 and Q3 change from an on state to an off state.

[0061] The power conversion device 1, which is an LLC converter, is a circuit that can obtain a gain smaller than 1 (i.e., reduce output power) by setting the switching frequency higher than the resonant frequency of the resonator 30. Setting the switching frequency higher than the resonant frequency of the resonator 30 is equivalent to delaying the phase of the resonant current relative to the phase of the input voltage (transformer input voltage) of the resonator 30. In other words, delaying the phase of the resonant current relative to the phase of the transformer input voltage can reduce output power. In the second mode, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 while keeping the switching frequency fixed so that the phase of the resonant current lags the phase of the input voltage of the resonant circuit. Here, details of the operation of the controller 40 in the second mode are described.

[0062] As shown in part A of FIG. 5, the controller 40 turns on the switches Q6 and Q7 during a non-conducting period, which is a period before the switches Q1 and Q4 are turned off from an on state.

[0063] This causes the polarity of the transformer secondary voltage to reverse, as shown in part B of Fig. 5. It can be seen that the timing of the polarity reversal is delayed compared to the conventional transformer secondary voltage shown by the dashed line (specifically, the transformer secondary voltage when the switches Q6 and Q7 are not controlled during the non-energized period).

[0064] As shown in part C of FIG. 5, when the polarity of the transformer secondary voltage is reversed, the polarity of the transformer excitation voltage is also reversed in response to the reversal of the polarity of the transformer secondary voltage.

[0065] As shown in part D of Figure 5, the polarity of the transformer excitation voltage reverses later than in the past, causing the transformer excitation current to reach its extreme value later than in the past. Specifically, the phase of the transformer excitation voltage's polarity reversal is delayed, resulting in a phase delay in the transformer excitation current. Because the resonant current is superimposed on the transformer excitation current, a phase delay in the transformer excitation current also delays the phase of the resonant current. Therefore, the phase of the resonant current lags relative to the phase of the transformer input voltage, allowing for a reduction in output power. Note that by further extending the on-time of switches Q6 and Q7 during the non-energized period, the phase of the resonant current is further delayed, allowing for a further reduction in output power.

[0066] Although illustrations for explaining the effects of operation of the controller 40 in the second mode according to the embodiment are omitted, the longer the on time of the switches Q5, Q6, Q7, and Q8 during the non-energized period, the smaller the output current, i.e., the output power.

[0067] In this way, in the second mode, the output power can be reduced while the switching frequency is fixed.

[0068] Note that there are cases where the output power of the power conversion device 1 cannot be reduced to the target power simply by delaying the phase of polarity reversal of the transformer excitation voltage through operation of the controller 40 in the second mode. Therefore, the controller 40 may further have at least one of a phase shift control mode in which the phase between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4 is controlled, and an intermittent operation mode in which the switching of the switches Q1, Q2, Q3, and Q4 is intermittently controlled. First, the phase shift control mode will be described.

[0069] Fig. 6 is a diagram for explaining an example of operation in the phase shift control mode of the controller 40 according to the embodiment. Fig. 6 shows, from top to bottom, timing charts of the gate signals of the switches Q1 and Q4, the gate signals of the switches Q2 and Q3, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), the excitation current of the transformer T (transformer excitation current) and the voltage input to the primary winding of the transformer T (transformer input voltage), and the excitation voltage of the transformer T (transformer excitation voltage).

[0070] 6 , in the phase-shift control mode, the controller 40 controls the switching of the switches Q1, Q2, Q3, and Q4 so as to delay the switching phase of the switches Q3 and Q4 relative to the switching phase of the switches Q1 and Q2. Note that in the phase-shift control mode, the controller 40 does not input signals to the gates of the switches Q5, Q6, Q7, and Q8, so that the switches Q5, Q6, Q7, and Q8 are in the off state, and the secondary-side full-bridge circuit 20 functions as a full-wave rectifier circuit using the body diodes of the switches Q5, Q6, Q7, and Q8.

[0071] As a result, the waveform of the transformer input voltage (in other words, the output voltage of the primary-side full-bridge circuit 10) is not a square wave, but rather has a waveform that includes a period when the phase shift causes switch Q1 to be on and switch Q4 to be off, resulting in 0 V, and a period when the phase shift causes switch Q2 to be on and switch Q3 to be off, resulting in 0 V. Therefore, the period during which the transformer excitation voltage is applied is shortened, allowing the gain (output power) to be reduced.

[0072] Next, the intermittent operation mode will be described.

[0073] 7 is a diagram for explaining an example of operation in the intermittent operation mode of the controller 40 according to the embodiment. From the top, Fig. 7 shows a timing chart of the gate signals of the switches Q1 and Q4, the gate signals of the switches Q2 and Q3, and the output current of the power conversion device 1.

[0074] As shown in FIG. 7 , in the intermittent operation mode, the controller 40 intermittently controls the switching of the switches Q1, Q2, Q3, and Q4. Specifically, the controller 40 controls the switches Q1, Q2, Q3, and Q4 so that they are repeatedly turned on and off during a first period, and then controls the switches Q1, Q2, Q3, and Q4 to an off state during a subsequent second period, repeating the control during the first period and the control during the second period. As a result, the output current waveform becomes an intermittent waveform in which the output current is output during the first period and not output during the second period. In the intermittent operation mode, the average current (average power) can be reduced over the long term.

[0075] As described above, the period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4 is a non-energized period during which no current is applied to the load. By turning on the switches Q5, Q6, Q7, and Q8 for a certain period during the non-energized period, the timing at which the polarity of the voltage generated in the secondary winding of the transformer T (the transformer secondary voltage) is reversed can be adjusted. When the polarity of the transformer secondary voltage is reversed, the polarity of the excitation voltage of the transformer T is also reversed in accordance with the reversal of the polarity of the transformer secondary voltage. In other words, the timing at which the polarity of the excitation voltage of the transformer T is reversed (in other words, the phase of polarity reversal of the excitation voltage of the transformer T) can be adjusted.

[0076] For example, advancing the phase of polarity reversal of the excitation voltage of transformer T advances the phase of the excitation current of transformer T. Because the resonant current is superimposed on the excitation current, advancing the phase of the excitation current also advances the phase of the resonant current, thereby increasing the output power of the power conversion device 1. For example, delaying the phase of polarity reversal of the excitation voltage of transformer T delays the phase of the excitation current of transformer T. Because the resonant current is superimposed on the excitation current, delaying the phase of the excitation current also delays the phase of the resonant current, thereby reducing the output power of the power conversion device 1. Therefore, by controlling the on-time of the drive signals to switches Q5, Q6, Q7, and Q8 during the non-energized period, the output power can be controlled without frequency control, thereby effectively controlling the output power while suppressing the frequency control range. Note that in the DC-DC converter described in Patent Document 1, the transformer current has an asymmetric waveform between positive and negative, which can have an adverse effect on common-mode noise, whereas in the power conversion device 1, the transformer current has a symmetric waveform between positive and negative, which is less likely to degrade noise performance.

[0077] For example, being able to suppress the frequency control range width makes it possible to reduce the size of the transformer T, improve efficiency, and reduce the size of the EMC filter. Specifically, since the power conversion device 1 does not need to be operated at a low switching frequency, the transformer T can be reduced in size. Furthermore, since the power conversion device 1 does not need to be operated at a high switching frequency, AC resistance loss is reduced, making it possible to improve efficiency. Furthermore, since the frequency control range width is narrow or a fixed value, EMC measures can be taken with a narrow-band EMC filter, and the EMC filter can be reduced in size.

[0078] Note that the power conversion device 1 can perform bidirectional power conversion, and the terminal t3 can be used as the input terminal and the terminal t1 as the output terminal. In this case, the control performed on the switches Q1, Q2, Q3, and Q4 in the above description is performed on the switches Q5, Q6, Q7, and Q8, and the control performed on the switches Q5, Q6, Q7, and Q8 in the above description is performed on the switches Q1, Q2, Q3, and Q4. In this case, the capacitor Cout becomes the input capacitor and the capacitor Cin becomes the output capacitor.

[0079] (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.

[0080] For example, in the above embodiment, an example was described in which the power conversion device is an LLC converter, but this is not limited to this. For example, the power conversion device may be a resonant converter including a resonator configured in series and parallel of LC, such as an LCC converter or an CLLC converter.

[0081] For example, in the above embodiment, an example of an LLC converter including a transformer magnetizing inductance, a leakage inductance, and a resonant capacitor has been described, but instead of the leakage inductance, a separate inductor equivalent to the leakage inductance may be provided.

[0082] For example, the controller 40 may further have a frequency control mode for controlling the switching frequency, and may adjust the output power by controlling the switching frequency.

[0083] For example, the present disclosure can be realized not only as a power conversion device, but also as a control method for controlling a power conversion device (specifically, a control method including steps (processing) performed by components that constitute the power conversion device (specifically, controller 40)).

[0084] FIG. 8 is a flowchart showing an example of a control method according to another embodiment.

[0085] For example, the control method is a control method for a power conversion device capable of unidirectional or bidirectional power conversion, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit including a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit including a fifth switch element provided on the high side of a third leg, and a sixth switch element provided on the low side of the third leg. The control method includes, as shown in FIG. 8 , a process of calculating a period obtained by subtracting a resonance period of the resonator from the switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element (step S11), operating the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal in the period (step S12), and controlling the on-time of the drive signal with the length of the period as an upper limit (step S13).

[0086] 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.

[0087] 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.

[0088] In the above-described embodiments, each component included in the power conversion device 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.

[0089] Some or all of the functions of the power conversion device according to the above-described embodiments are typically realized as an LSI, 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. 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, may also be used.

[0090] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the power conversion device.

[0091] 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.

[0092] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0093] (Technology 1) A power conversion device capable of unidirectional or bidirectional power conversion includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, a secondary-side full bridge circuit connected to a secondary side of the resonator, and a controller that controls the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth switch element provided on a high side of a third leg, and a fifth switch element provided on the high side of the third leg. a sixth switch element provided on a low side of a fourth leg, a seventh switch element provided on a high side of a fourth leg, and an eighth switch element provided on the low side of the fourth leg, wherein the controller calculates a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element, and operates the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal during the period, and controls an on-time of the drive signal so that the length of the period is an upper limit.

[0094] According to this, the period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is a non-energization period in which no current is applied to the load. By turning on the fifth, sixth, seventh, and eighth switch elements for a certain period during the non-energization period, the timing at which the polarity of the voltage generated in the secondary winding of the transformer (the transformer secondary voltage) is reversed can be adjusted. When the polarity of the transformer secondary voltage is reversed, the polarity of the transformer excitation voltage is also reversed in accordance with the polarity reversal of the transformer secondary voltage. In other words, the timing at which the polarity of the transformer excitation voltage is reversed (in other words, the phase of polarity reversal of the transformer excitation voltage) can be adjusted.

[0095] For example, advancing the phase of polarity reversal of the transformer's excitation voltage advances the phase of the transformer's excitation current. Because the resonant current is superimposed on the excitation current, advancing the phase of the excitation current also advances the phase of the resonant current, thereby increasing the output power of the power conversion device. For example, delaying the phase of polarity reversal of the transformer's excitation voltage delays the phase of the transformer's excitation current. Because the resonant current is superimposed on the excitation current, delaying the phase of the excitation current also delays the phase of the resonant current, thereby reducing the output power of the power conversion device. Therefore, by controlling the on-times of the drive signals for the fifth, sixth, seventh, and eighth switch elements during the non-energized period, the output power can be controlled without frequency control, and the output power can be effectively controlled while suppressing the frequency control range width.

[0096] (Technology 2) The power conversion device according to Technology 1, wherein the controller turns on the fifth switch element and the eighth switch element by the drive signal before the first switch element and the fourth switch element change from an on state to an off state, and turns on the sixth switch element and the seventh switch element by the drive signal before the second switch element and the third switch element change from an on state to an off state.

[0097] This allows the phase of polarity reversal of the excitation voltage of the transformer to be advanced, thereby increasing the output power of the power conversion device.

[0098] (Technology 3) The power conversion device according to Technology 1, wherein the controller turns on the sixth switch element and the seventh switch element by the drive signal before the first switch element and the fourth switch element change from an on state to an off state, and turns on the fifth switch element and the eighth switch element by the drive signal before the second switch element and the third switch element change from an on state to an off state.

[0099] This allows the phase of polarity reversal of the excitation voltage of the transformer to be delayed, thereby reducing the output power of the power conversion device.

[0100] (Technology 4) The controller further controls a phase between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element. The power conversion device according to any one of techniques 1 to 3.

[0101] This allows the output power of the power conversion device to be reduced. For example, in cases where the output power of the power conversion device cannot be reduced to the target power by simply delaying the phase of polarity reversal of the excitation voltage of the transformer, the output power of the power conversion device can be reduced to the target power by controlling the phase.

[0102] (Technology 5) The controller further controls the switching of the first switch element, the second switch element, the third switch element, and the fourth switch element intermittently. The power conversion device according to any one of techniques 1 to 4.

[0103] This allows the output power of the power conversion device to be reduced. For example, if the output power of the power conversion device cannot be reduced to the target power by simply delaying the phase of polarity reversal of the excitation voltage of the transformer, the output power of the power conversion device can be reduced to the target power by controlling the switching intermittently.

[0104] (Technology 6) A control method for a power conversion device capable of unidirectional or bidirectional power conversion, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit including a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, the secondary-side full bridge circuit including a fifth switch element provided on the high side of a third leg, and a fifth switch element provided on the low side of the third leg. a sixth switch element provided on the high side of the fourth leg, a seventh switch element provided on the high side of the fourth leg, and an eighth switch element provided on the low side of the fourth leg, wherein the control method calculates a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element, operates the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal during the period, and controls an on-time of the drive signal with the length of the period as an upper limit.

[0105] This makes it possible to provide a control method that can effectively control output power while suppressing the frequency control range width.

[0106] The present disclosure can be applied to an isolated DC-DC converter or the like.

[0107] REFERENCE SIGNS LIST 1 Power conversion device 10 Primary side full bridge circuit 20 Secondary side full bridge circuit 30 Resonator 40 Controller Cin, Cout, Cr Capacitors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Switch T Transformer t1, t2, t3, t4 Terminals

Claims

1. A power conversion device capable of unidirectional or bidirectional power conversion, comprising: a resonator having a transformer and a resonance capacitor; a primary-side full bridge circuit connected to a primary side of the resonator; a secondary-side full bridge circuit connected to a secondary side of the resonator; and a controller for controlling the primary-side full bridge circuit and the secondary-side full bridge circuit, wherein the primary-side full bridge circuit has a first switch element provided on a high side of a first leg, a second switch element provided on a low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth switch element provided on a high side of a third leg, a sixth switch element provided on a low side of the third leg, a seventh switch element provided on a high side of a fourth leg, and an eighth switch element provided on the low side of the fourth leg, and the controller a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element is calculated; the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element are operated in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal during the period; and an on-time of the drive signal is controlled to have an upper limit of the length of the period.

2. The power conversion device according to claim 1, wherein the controller turns on the fifth switch element and the eighth switch element before the first switch element and the fourth switch element change from an on state to an off state in response to the drive signal, and turns on the sixth switch element and the seventh switch element before the second switch element and the third switch element change from an on state to an off state in response to the drive signal.

3. The power conversion device according to claim 1, wherein the controller turns on the sixth switch element and the seventh switch element before the first switch element and the fourth switch element change from an on state to an off state in response to the drive signal, and turns on the fifth switch element and the eighth switch element before the second switch element and the third switch element change from an on state to an off state in response to the drive signal.

4. The power conversion device according to any one of claims 1 to 3, wherein the controller further controls a phase between switching of the first switch element and the second switch element and switching of the third switch element and the fourth switch element.

5. The power conversion device according to any one of claims 1 to 3, wherein the controller further intermittently controls switching of the first switch element, the second switch element, the third switch element and the fourth switch element.

6. A control method for a power conversion device capable of unidirectional or bidirectional power conversion, the power conversion device comprising: a resonator having a transformer and a resonance capacitor; a primary-side full bridge circuit connected to the primary side of the resonator; and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit having a first switch element provided on the high side of a first leg, a second switch element provided on the low side of the first leg, a third switch element provided on the high side of the second leg, and a fourth switch element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth switch element provided on the high side of a third leg, a sixth switch element provided on the low side of the third leg, a seventh switch element provided on the high side of a fourth leg, and an eighth switch element provided on the low side of the fourth leg, the control method comprising: a control method comprising: calculating a period obtained by subtracting a resonance period of the resonator from switching periods of the first switch element, the second switch element, the third switch element, and the fourth switch element; operating the fifth switch element, the sixth switch element, the seventh switch element, and the eighth switch element in synchronization with control signals for the first switch element, the second switch element, the third switch element, and the fourth switch element by a drive signal during the period; and controlling an on-time of the drive signal with an upper limit of the length of the period.

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