Control circuit, electric power converter, and control method

Abstract

This control circuit comprises: a determination unit for determining a predetermined frequency; and a control unit that has a first control mode for controlling operating frequencies of a first set of switching devices (a first switch and a second switch) and a second set of switching devices (a third switch and a fourth switch) with a predetermined frequency as an upper limit, and a second control mode for controlling the phase between the switching of the first set of switching devices and the switching of the second set of switching devices while the operating frequency is at a predetermined frequency.

Description

Control circuit, power converter and control method

[0001] The present disclosure relates to a control circuit for controlling a power converter.

[0002] Patent Document 1 discloses an LLC converter.

[0003] International Publication No. 2023 / 276024

[0004] In the LLC converter disclosed in Patent Document 1, ripple from the commercial power supply may be superimposed on the input current, and if power conversion is performed with ripple superimposed, the amount of heat generated may increase and the lifespan of components may be shortened.

[0005] Therefore, the present disclosure provides a control circuit and the like that can suppress the effects of ripples and reduce the reduction in the lifespan of components.

[0006] A control circuit according to the present disclosure is a control circuit for controlling a power converter, the power converter comprising: a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal, the second set of switching devices being connected in series; and the control circuit comprises: a determination unit that determines a predetermined frequency; and a control unit having a first control mode that controls the operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit; and a second control mode that controls the phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is the predetermined frequency.

[0007] A power converter according to the present disclosure includes the above control circuit, the first set of switching devices, and the second set of switching devices.

[0008] A control method according to the present disclosure is a control method executed by a control circuit that controls a power converter, the power converter comprising: a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal, the second set of switching devices including a determination step of determining a predetermined frequency; a first control step of controlling operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit; and a second control step of controlling a phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is the predetermined frequency.

[0009] 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.

[0010] According to a control circuit and the like according to an aspect of the present disclosure, the influence of ripples can be suppressed, and a reduction in the lifespan of components can be reduced.

[0011] FIG. 1 is a configuration diagram showing an application example of a power converter according to an embodiment. FIG. 2A is a circuit configuration diagram showing an example of a power converter according to an embodiment. FIG. 2B is a circuit configuration diagram showing another example of a power converter according to an embodiment. FIG. 3 is a diagram for explaining variable frequency control of a power converter according to an embodiment. FIG. 4 is a diagram for explaining a combination of variable frequency control and phase shift control of a power converter according to an embodiment. FIG. 5 is a diagram for explaining a controlled variable of a power converter according to an embodiment. FIG. 6A is a diagram for explaining control responsiveness under condition 1 of a power converter according to an embodiment. FIG. 6B is a diagram for explaining control responsiveness under condition 2 of a power converter according to an embodiment. FIG. 6C is a diagram for explaining control responsiveness under condition 3 of a power converter according to an embodiment. FIG. 7 is a diagram for explaining a change in the upper limit frequency of phase shift control of a power converter according to an embodiment. FIG. 8 is a diagram for explaining control responsiveness under condition 3 when the upper limit frequency of phase shift control of a power converter according to an embodiment is lowered. FIG. 9 is a diagram for explaining a method for estimating a control operation region of a power converter according to an embodiment. FIG. 10 is a diagram for explaining a method for estimating a control period threshold of a power converter according to an embodiment. Fig. 11 is a diagram showing an example of a table in which a predetermined frequency is associated with each output voltage of a power converter according to an embodiment. Fig. 12 is a diagram for explaining an example of operation of a control circuit according to an embodiment. Fig. 13 is a diagram for explaining another example of operation of a control circuit according to an embodiment. Fig. 14 is a diagram for explaining a method of correcting a predetermined frequency of a power converter according to an embodiment. Fig. 15 is a diagram for explaining that actual ripples can be suppressed by correcting the predetermined frequency of a power converter according to an embodiment. Fig. 16 is a flowchart showing an example of a control method according to another embodiment.

[0012] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0013] 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.

[0014] (Embodiments) A control circuit and a power converter according to embodiments will be described below.

[0015] Fig. 1 is a configuration diagram showing an application example of a power converter 100 according to an embodiment. In addition to the power converter 100, Fig. 1 shows a system power supply 200, a PFC (Power Factor Correction) circuit 300, capacitors 110 and 120, and a load 400.

[0016] The power converter 100 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined output voltage. For example, the power converter 100 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 voltage.

[0017] The PFC circuit 300 is, for example, an AC-DC converter having a PFC (Power Factor Correction) function, and converts an AC current (AC current Iac) and voltage from the system power supply 200 into a DC current (bus current Ibus) and voltage (bus voltage Vbus). The load 400 is, for example, a battery.

[0018] The power converter 100 converts the DC current and voltage from the PFC circuit 300 into DC current (battery current Ibat) and voltage (battery voltage Vbat) of different values. The battery current Ibat can charge the load 400 at the battery voltage Vbat.

[0019] 2A is a circuit configuration diagram showing an example of a power converter 100 according to an embodiment. In addition to the power converter 100, Fig. 2A shows a PFC circuit 300, capacitors 110 and 120, and a load 400. Note that the capacitors 110 and 120 may be provided in the power converter 100.

[0020] The power converter 100 includes terminals t1, t2, t3, and t4. The terminal t1 is an input terminal. The terminal t2 is an example of a first ground terminal. The terminal t3 is an output terminal. The terminal t4 is an example of a second ground terminal. Note that, since the power converter 100 is an isolated DC-DC converter, the terminal t1 or the terminal t2 is electrically isolated from the terminal t3 or the terminal t4, respectively.

[0021] The capacitor 110 is an input capacitor connected between the terminal t1 and the terminal t2, and the capacitor 120 is an output capacitor (smoothing capacitor) connected between the terminal t3 and the terminal t4.

[0022] The power converter 100 includes switches Q1, Q2, Q3 and Q4, a capacitor Cr1, a rectifier circuit D10, a transformer T1 and a control circuit 10.

[0023] The switch Q1 is an example of a first switch provided on a path P1 connecting the terminal t1 and the terminal t2. The path P1 is an example of a first path. The switch Q2 is an example of a second switch provided on the path P1 and connected in series with the switch Q1. The switches Q1 and Q2 are an example of a first set of switching devices made up of the switches Q1 and Q2 connected in series on the path P1 connecting the terminal t1 and the terminal t2.

[0024] The switch Q1 is, for example, an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In FIG. 2A, the parasitic capacitance of the switch Q1 is shown as a capacitor C1, and the capacitor C1 is connected in parallel to the switch Q1 in the equivalent circuit. The drain of the switch Q1 is connected to a terminal t1, and the source of the switch Q1 is connected to the drain of the switch Q2. Also in FIG. 2A, the parasitic diode of the switch Q1 is shown as a diode D1, and the anode of the diode D1 is connected to the source of the switch Q1 and the cathode is connected to the drain of the switch Q1 in the equivalent circuit.

[0025] The switch Q2 is, for example, an N-channel MOSFET. In Fig. 2A, the parasitic capacitance of the switch Q2 is shown as capacitor C2, and the capacitor C2 is connected in parallel to the switch Q2 in the equivalent circuit. 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 terminal t2. In Fig. 2A, the parasitic diode of the switch Q2 is shown as diode D2, and in the equivalent circuit, the anode of the diode D2 is connected to the source of the switch Q2 and the cathode is connected to the drain of the switch Q2.

[0026] The switch Q3 is an example of a third switch provided on a path P2 that connects the terminal t1 and the terminal t2 and is different from the path P1. The path P2 is an example of a second path. The switch Q4 is an example of a fourth switch provided on the path P2 and connected in series with the switch Q3. The switches Q3 and Q4 are an example of a second set of switching devices made up of the switches Q3 and Q4 connected in series on the path P2 that connects the terminal t1 and the terminal t2 and is different from the path P1.

[0027] The switch Q3 is, for example, an N-channel MOSFET. In FIG. 2A, the parasitic capacitance of the switch Q3 is shown as a capacitor C3, which is connected in parallel with the switch Q3 in the equivalent circuit. 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. In FIG. 2A, the parasitic diode of the switch Q3 is shown as a diode D3, and in the equivalent circuit, the anode of the diode D3 is connected to the source of the switch Q3 and the cathode is connected to the drain of the switch Q3.

[0028] The switch Q4 is, for example, an N-channel MOSFET. In FIG. 2A, the parasitic capacitance of the switch Q4 is shown as a capacitor C4, which is connected in parallel with the switch Q4 in the equivalent circuit. 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. In FIG. 2A, the parasitic diode of the switch Q4 is shown as a diode D4, and in the equivalent circuit, the anode of the diode D4 is connected to the source of the switch Q4 and the cathode is connected to the drain of the switch Q4.

[0029] The capacitor Cr1 is connected to a node N1 between the switch Q1 and the switch Q2 on the path P1. The capacitor Cr1 is an example of a first resonant capacitor. The node N1 is an example of a first node.

[0030] The transformer T1 has a primary winding and a secondary winding. One end of the primary winding is connected to the capacitor Cr1, and the other end of the primary winding is connected to a node N2 between the switches Q3 and Q4 on the path P2. The node N2 is an example of a second node. Both ends of the secondary winding are connected to the rectifier circuit D10. FIG. 2A shows an equivalent circuit of the transformer T1, which can be represented by an ideal transformer Tid, a primary-side leakage inductance Lr1, and a secondary-side leakage inductance Lr2. Note that the excitation inductance is not shown. The leakage inductance Lr1 is connected in series with the primary coil of the ideal transformer Tid, and the leakage inductance Lr2 is connected in series with the secondary coil of the ideal transformer Tid. Note that the power converter 100 may also include inductors corresponding to the leakage inductances Lr1 and Lr2.

[0031] The rectifier circuit D10 is connected to the secondary winding of the transformer T1. For example, the rectifier circuit D10 has a full-bridge configuration made up of four diodes, and is capable of full-wave rectification.

[0032] The control circuit 10 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q3, and Q4) included in the power converter 100. For example, the control circuit 10 controls the switching of the switches Q1, Q2, Q3, and Q4 by controlling a gate drive circuit connected to the gates of the switches Q1, Q2, Q3, and Q4 via a PWM generator or the like.

[0033] The control circuit 10 includes a control unit 11 and a decision unit 12. The control circuit 10 is a computer including, for example, a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store a program to be executed by the processor. The control unit 11 and the decision unit 12 are realized by the processor that executes the program stored in the memory.

[0034] The determination unit 12 determines the predetermined frequency. Details of the determination unit 12 will be described later.

[0035] The control unit 11 has a first control mode in which the operating frequencies of the first set of switching devices (switches Q1 and Q2) and the second set of switching devices (switches Q3 and Q4) are controlled with a predetermined frequency as an upper limit, and a second control mode in which the control unit 11 controls the phase between the switching of the first set of switching devices and the switching of the second set of switching devices while the operating frequencies are set to the predetermined frequency. Details of the control unit 11 will be described later.

[0036] It should be noted that power converter 100 does not have to be an LLC converter, and may be any isolated DC-DC converter as long as it includes at least a first set of switching devices (switches Q1 and Q2), a second set of switching devices (switches Q3 and Q4), and control circuit 10.

[0037] For example, the power converter 100 may be a CLLC converter. An example in which the power converter 100 is a CLLC converter will now be described with reference to FIG.

[0038] FIG. 2B is a circuit configuration diagram illustrating another example of the power converter 100 according to the embodiment.

[0039] The power converter 100 (LLC converter) shown in Fig. 2B differs from the power converter 100 (LLC converter) shown in Fig. 2A in that the components of the rectifier circuit D10 are different and that a capacitor Cr2 is further included. The following description will focus on the differences from the case where power converter 100 is an LLC converter (the case of Fig. 2A).

[0040] The power converter 100 (LLC converter) shown in FIG. 2B includes switches Q5, Q6, Q7, and Q8, which configure a rectifier circuit D10.

[0041] The switch Q5 is an example of a fifth switch provided on the path P3 connecting the terminal t3 and the terminal t4. The path P3 is an example of a third path. The switch Q6 is an example of a sixth switch provided on the path P3 and connected in series with the switch Q5. The switches Q5 and Q6 are an example of a third set of switching devices consisting of the switches Q5 and Q6 connected in series on the path P3 connecting the terminal t3 and the terminal t4.

[0042] The switch Q5 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of the switch Q5 is shown as a capacitor C5, which is connected in parallel with the switch Q5 in the equivalent circuit. 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. In FIG. 2B, the parasitic diode of the switch Q5 is shown as a diode D5, and in the equivalent circuit, the anode of the diode D5 is connected to the source of the switch Q5 and the cathode is connected to the drain of the switch Q5.

[0043] The switch Q6 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of the switch Q6 is shown as a capacitor C6, which is connected in parallel with the switch Q6 in the equivalent circuit. 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. In FIG. 2B, the parasitic diode of the switch Q6 is shown as a diode D6, and in the equivalent circuit, the anode of the diode D6 is connected to the source of the switch Q6 and the cathode is connected to the drain of the switch Q6.

[0044] The switch Q7 is an example of a seventh switch provided on a path P4 that connects the terminals t3 and t4 and is different from the path P3. The path P4 is an example of a fourth path. The switch Q8 is an example of an eighth switch provided on the path P4 and connected in series with the switch Q7. The switches Q7 and Q8 are an example of a fourth set of switching devices made up of the switches Q7 and Q8 connected in series on the path P4 that connects the terminals t3 and t4 and is different from the path P3.

[0045] The switch Q7 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of the switch Q7 is shown as a capacitor C7, which is connected in parallel with the switch Q7 in the equivalent circuit. 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. In FIG. 2B, the parasitic diode of the switch Q7 is shown as a diode D7, and in the equivalent circuit, the anode of the diode D7 is connected to the source of the switch Q7 and the cathode is connected to the drain of the switch Q7.

[0046] The switch Q8 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of the switch Q8 is shown as a capacitor C8, which is connected in parallel with the switch Q8 in the equivalent circuit. 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. In FIG. 2B, the parasitic diode of the switch Q8 is shown as a diode D8, and in the equivalent circuit, the anode of the diode D8 is connected to the source of the switch Q8 and the cathode is connected to the drain of the switch Q8.

[0047] The capacitor Cr2 is connected to a node N3 between the switch Q5 and the switch Q6 on the path P3. The capacitor Cr2 is an example of a second resonant capacitor. The node N3 is an example of a third node.

[0048] The transformer T1 has one end of a secondary winding connected to the capacitor Cr2 and the other end connected to a node N4 on the path P4 between the switches Q7 and Q8. The node N4 is an example of a fourth node.

[0049] The rectifier circuit D10 of the power converter 100 (LLC converter) shown in FIG. 2B may be configured with four diodes, similar to the power converter 100 (LLC converter) shown in FIG. 2A.

[0050] Furthermore, power converter 100 includes a voltage detection circuit that detects the output voltage (battery voltage Vbat) and a current detection circuit that detects the output current (battery current Ibat), and control circuit 10 controls the switching of switches Q1, Q2, Q3, and Q4 based on the results of these detections. Furthermore, when power converter 100 has the circuit configuration shown in FIG. 2B , control circuit 10 may also control switches Q5, Q6, Q7, and Q8.

[0051] Next, a case where the control unit 11 controls the switching of the switches Q1, Q2, Q3, and Q4 only in the first control mode (in other words, only variable frequency control) regardless of the predetermined frequency will be described with reference to FIG.

[0052] FIG. 3 is a diagram illustrating variable frequency control. The horizontal axis of the graph shown in FIG. 3 represents the output voltage (Vbat) of the power converter 100, and the vertical axis represents the controlled variable Ton. The controlled variable Ton is the on-time of the switches, specifically, the time during which the switches Q1 and Q4 are on and the switches Q2 and Q3 are off, or the time during which the switches Q2 and Q3 are on and the switches Q1 and Q4 are off. The lower the operating frequency of each switch, the longer the controlled variable Ton. The higher the operating frequency of each switch, the shorter the controlled variable Ton. Furthermore, Pmax is the maximum power that the power converter 100 can output, and Pmin is the minimum power that the power converter 100 can output. Vbat_max is the maximum voltage of the load 400 (battery), and Vbat_min is the minimum voltage of the load 400.

[0053] As shown in FIG. 3 , it is necessary to output a voltage (Vbat_min to Vbat_max) within the operating range of the load 400. To output a high voltage, the control amount Ton must be increased, i.e., the operating frequency of each switch must be reduced. On the other hand, to output a low voltage, the control amount Ton must be reduced, i.e., the operating frequency of each switch must be increased. However, if the operating frequency of each switch is increased, the switching loss of each switch and the AC loss of magnetic components such as the transformer T1 increase.

[0054] For this reason, the control unit 11 has a first control mode in which the operating frequencies of the first set of switching devices (switches Q1 and Q2) and the second set of switching devices (switches Q3 and Q4) are controlled with a predetermined frequency as the upper limit, and a second control mode in which the phase between the switching of the first set of switching devices and the switching of the second set of switching devices is controlled while the operating frequencies are set to the predetermined frequency. This will be described with reference to FIGS. 4 and 5.

[0055] FIG. 4 is a diagram for explaining a combination of variable frequency control (control in the first control mode) and phase shift control (control in the second control mode).

[0056] FIG. 5 is a diagram for explaining the control amount Ton.

[0057] For example, the control unit 11 controls the operating frequencies of the switches Q1, Q2, Q3, and Q4 with a predetermined frequency Fth corresponding to the control period threshold Tth as the upper limit, and controls the phase between the switching of the switches Q1 and Q2 and the switching of the switches Q3 and Q4 when the operating frequency is the predetermined frequency Fth. That is, in the second control mode, as shown in FIG. 5 , the control unit 11 shifts the phase of the switching of the switches Q1 and Q4 from a state in which the on-time (control amount Ton) of each of the switches Q1 and Q4 is equal to the control period threshold Tth / 2, thereby shortening the period in which the on-times of the switches Q1 and Q4 overlap (control amount Ton). Also, in the second control mode, the control unit 11 shifts the phase of the switching of the switches Q2 and Q3 from a state in which the on-time (control amount Ton) of each of the switches Q2 and Q3 is equal to the control period threshold Tth / 2, thereby shortening the period in which the on-times of the switches Q2 and Q3 overlap (control amount Ton).

[0058] The control unit 11 performs phase shift control in the second control mode when the output voltage is between Vbat_min and Vth, and performs variable frequency control in the first control mode when the output voltage is between Vth and Vbat_max. This allows the control amount Ton to be shortened without increasing the operating frequency above a predetermined frequency, thereby enabling power conversion over a wide range while suppressing losses.

[0059] The bus voltage Vbus, which is the input voltage of the power converter 100, is obtained by converting AC current (AC current Iac) and voltage from the system power supply 200 to DC current (bus current Ibus) and voltage (bus voltage Vbus) via the PFC circuit 300, resulting in slight voltage fluctuations (ripple). This ripple can be superimposed on the output voltage Vbat via the power converter 100. The output voltage Vbat with this ripple superimposed on it is applied to the capacitor 120, causing charging and discharging operations equivalent to the ripple, resulting in losses and temperature rise due to the internal resistance of the capacitor. This temperature rise reduces the capacitor's lifespan. Furthermore, if the load 400 is a battery, the ripple can also reduce the battery's lifespan for the same reason. Therefore, it is desirable to design the power converter to minimize the ripple. One way to minimize the ripple is to increase the capacitance of the capacitor 120, but this leads to an increase in the size and cost of the power converter. For this reason, the ripple is generally minimized through control design.

[0060] Therefore, in designing the power converter 100, it is necessary to assume that the bus voltage Vbus is not a constant value but has ripples, and to design a control that minimizes the ripples superimposed on the output voltage Vbat.

[0061] The influence of the ripple on the control response will be described below with reference to FIGS. 6A to 6C.

[0062] FIG. 6A is a diagram for explaining the control response in the case of Condition 1. FIG.

[0063] FIG. 6B is a diagram for explaining the control response in the case of Condition 2.

[0064] FIG. 6C is a diagram for explaining the control response in the case of Condition 3.

[0065] The horizontal axis of the graphs shown in FIGS. 6A to 6C represents the phase shift Tθ, and the vertical axis represents the output current (Ibat) of the power converter 100. The phase shift Tθ is the amount of phase shift between the switching of the first set of switching devices and the switching of the second set of switching devices. When the phase shift Tθ is 0, the control variable Ton is equal to the control period threshold Tth / 2. As the phase shift Tθ increases, the control variable Ton decreases from the control period threshold Tth / 2. Conditions 1 to 3 shown in FIGS. 6A to 6C correspond to conditions 1 to 3 shown in FIG. 4, with the output voltage increasing in the order of condition 1, condition 2, and condition 3. As shown in FIG. 4, when the power converter 100 outputs maximum power, the output current is Ibat1 under condition 1, Ibat2 under condition 2, and Ibat3 under condition 3. For example, assume that ripples occur under conditions 1 to 3.

[0066] As shown in Figure 6A, under condition 1, when the power converter 100 outputs maximum power, if the output current becomes smaller due to the influence of ripples, for example, there is sufficient phase control responsiveness for the phase amount Tθ corresponding to the output current Ibat1, so by further reducing the phase amount Tθ (i.e., bringing the phase amount Tθ closer to 0), the output current can be increased by the amount that has become smaller due to the influence of ripples.

[0067] As shown in Figure 6B, under condition 2, when the power converter 100 outputs maximum power, if the output current becomes smaller due to the influence of ripples, for example, there is sufficient phase control responsiveness for the phase amount Tθ corresponding to the output current Ibat2. Therefore, by further reducing the phase amount Tθ (i.e., by bringing the phase amount Tθ closer to 0), the output current can be increased by the amount that has become smaller due to the influence of ripples.

[0068] As shown in FIG. 6C , under condition 3, when the power converter 100 outputs maximum power, if the output current is reduced due to the influence of ripple, the phase control responsiveness is insufficient for the phase amount Tθ corresponding to the output current Ibat3. Specifically, since the phase amount Tθ (phase shift amount) cannot be reduced to 0 or less, it may not be possible to control the output current to increase by the amount reduced due to the influence of ripple. If an uncontrollable region is included, it becomes impossible to control the ripple to be suppressed. In other words, if power conversion is performed under this condition, the ripple cannot be suppressed, which may increase the heat generation of the capacitor 120 and the load 400 (battery), resulting in a shortened component life.

[0069] In response to this, the control circuit 10 includes a determination unit 12 that determines the predetermined frequency. That is, the control circuit 10 has a function of changing the upper limit frequency (predetermined frequency) of the phase shift control, in other words, the control cycle threshold, depending on the situation. The effects achieved by including the determination unit 12 in the control circuit 10 will be described with reference to FIGS. 7 and 8.

[0070] FIG. 7 is a diagram for explaining the change of the upper limit frequency of the phase shift control.

[0071] FIG. 8 is a diagram for explaining the control response in the case of Condition 3 when the upper limit frequency of the phase shift control is lowered.

[0072] As shown in FIG. 7 , for example, the determination unit 12 determines the predetermined frequency to be a frequency corresponding to the control period threshold Tth′. As a result, as shown in FIG. 8 , when the predetermined frequency corresponds to the control period threshold Tth′, a larger output current is obtained for the same phase amount Tθ compared to when the predetermined frequency corresponds to the control period threshold Tth. In other words, when the predetermined frequency corresponds to the control period threshold Tth′, a larger phase amount Tθ is required to obtain the same output current compared to when the predetermined frequency corresponds to the control period threshold Tth. Therefore, when the predetermined frequency corresponds to the control period threshold Tth′, the phase amount Tθ corresponding to the output current Ibat3 increases, and the phase control responsiveness to the phase amount Tθ is sufficient. Therefore, the phase amount Tθ can be further reduced (i.e., the phase amount Tθ can be brought closer to zero). Therefore, the output current can be increased by the amount that has been reduced due to the influence of ripples.

[0073] As described above, power conversion is generally performed by controlling the operating frequencies of the first set of switching devices (switches Q1 and Q2) and the second set of switching devices (switches Q3 and Q4), thereby controlling the on-times of the switching devices. However, when the output voltage is low, the operating frequency increases, resulting in increased switching losses in each switch and increased AC losses in the magnetic components. Therefore, when controlling the operating frequency, a predetermined frequency is set as the upper limit of the operating frequency. When conversion to a voltage lower than the voltage that can be converted by controlling the operating frequency with the predetermined frequency as the upper limit is performed, the on-times of the switching devices are controlled by controlling the phase between the switching of the first set of switching devices (switches Q1 and Q2) and the switching of the second set of switching devices (switches Q3 and Q4). This allows power conversion to be performed over a wide range while suppressing losses.

[0074] As described above, by having not only the control cycle threshold value Tth but also the control cycle threshold value Tth', it is possible to respond to the ripple superimposition over a wider range, and it is possible to reduce the reduction in the lifespan of parts.

[0075] Note that if the predetermined frequency is set too low, in other words, if the control cycle threshold is set too high, there is a risk of loss increasing, and therefore the determination unit 12 needs to determine an optimum predetermined frequency.

[0076] For example, the determination unit 12 determines the predetermined frequency based on the output voltage of the power converter 100. Specifically, the control circuit 10 stores a table in which the optimum predetermined frequency value is associated with each of a plurality of output voltage values, and the determination unit 12 determines the predetermined frequency based on this table.

[0077] Here, a method for creating a table in which a predetermined frequency is associated with each output voltage will be described with reference to FIGS.

[0078] First, a method for estimating a control operation region, which is necessary for creating a table in which a predetermined frequency is associated with each output voltage, will be described with reference to FIG.

[0079] 9 is a diagram for explaining a method for estimating the control operation region, in which the horizontal axis of the graph shown in Fig. 9 represents the control amount Ton, and the vertical axis represents the output current (Ibat) of the power converter 100.

[0080] For example, the relationship between the control amount Ton and the output current Ibat during rated operation (e.g., Vbat = 250 V to 450 V, Pmax = 3700 W) is calculated using the fundamental wave approximation method. FIG. 9 shows the above relationship when the output voltage is 250 V, 360 V, and 450 V. Then, a control operation region ΔTon is estimated when an estimated ripple (ΔR_est) is superimposed. The control operation region ΔTon is the control width of the control amount Ton required to suppress the influence of the ripple when the estimated ripple is superimposed. As shown in FIG. 9, when the output voltage is 250 V, a control operation region ΔTon1 is estimated, when the output voltage is 360 V, a control operation region ΔTon2 is estimated, and when the output voltage is 450 V, a control operation region ΔTon3 is estimated. Although FIG. 9 shows output voltages of 250V, 360V, and 450V, the control operation region ΔTon can be estimated for various output voltages other than 250V, 360V, and 450V.

[0081] Next, a method for estimating the control period threshold value Tth required to create a table in which a predetermined frequency is associated with each output voltage will be described with reference to FIG.

[0082] 10 is a diagram for explaining a method for estimating the control period threshold Tth, in which the horizontal axis of the graph shown in Fig. 10 represents the output voltage (Vbat) and the vertical axis represents the control amount Ton.

[0083] 10 , the maximum control amount Ton_max can be calculated by adding half the control operation range ΔTon to the control amount (Ton@Pmax) for each output voltage at maximum power. The control period threshold Tth can be estimated from this maximum control amount Ton_max. For example, when the output voltage is 250 V, the control period threshold Tth is estimated to be 713 ns, when the output voltage is 360 V, the control period threshold Tth is estimated to be 825 ns, and when the output voltage is 450 V, the control period threshold Tth is estimated to be 1763 ns.

[0084] Then, the control period threshold value Tth estimated for each output voltage is converted into a predetermined frequency, and a table is created in which the predetermined frequency is associated with each output voltage.

[0085] FIG. 11 is a diagram showing an example of a table in which a predetermined frequency is associated with each output voltage.

[0086] Because the operating frequency of the switch corresponds to the control amount Ton, the control period threshold value Tth (maximum control amount Ton_max) can be converted to a predetermined frequency, and a table can be created in which the predetermined frequency is associated with each output voltage. While FIG. 11 shows output voltages of 250 V, 360 V, and 450 V, the table also associates predetermined frequencies with various output voltages other than 250 V, 360 V, and 450 V. However, predetermined frequencies may also be associated with each output voltage within a certain range. Specifically, predetermined frequency A may be associated with 250 V to 260 V, predetermined frequency B may be associated with 260 V to 270 V, and so on, and predetermined frequency Z may be associated with 440 V to 450 V.

[0087] The estimated ripple may vary depending on the environment in which the power converter 100 is applied and the user who uses the power converter 100. Therefore, the contents of the table may vary depending on the estimated ripple. In other words, a dedicated table may be created depending on the environment in which the power converter 100 is applied and the user who uses the power converter 100.

[0088] Next, an example of the operation of the control circuit 10 will be described with reference to FIG.

[0089] 12 is a diagram for explaining an example of the operation of the control circuit 10 according to the embodiment. In FIG. 12, the control circuit 10, the PWM generator 20, and the power converter 100 are shown.

[0090] The determination unit 12 determines a predetermined frequency based on the output voltage (Vbat_mes), and notifies the PWM generator 20 of a control period threshold Tth corresponding to the predetermined frequency. This makes it possible to perform phase shift control when the operating frequency is the predetermined frequency, in the case where a voltage smaller than the output voltage that can be output when the operating frequency is equal to or lower than the predetermined frequency is output.

[0091] The control unit 11 is, for example, a PI controller, and notifies the PWM generator 20 of a phase amount Tθ such that the output current (Ibat_mes) of the power converter 100 becomes the target current (Ibat_trg), i.e., such that the error Ibat_err becomes zero. As a result, even when a ripple is superimposed, the phase is controlled to suppress the influence of the ripple. Furthermore, since a predetermined frequency (control period threshold Tth) that can suppress the influence of the ripple by controlling the phase is determined in advance, it is possible to prevent the output current from being unable to be adjusted by controlling the phase, and the influence of the ripple can be suppressed by controlling the phase.

[0092] However, there may be cases where the actually occurring ripple is larger than the estimated ripple and the output current cannot be adjusted by controlling the phase. Therefore, the determination unit 12 may correct the determined predetermined frequency based on the ripple superimposed on the output current of the power converter 100. This will be described with reference to FIGS. 13 to 15.

[0093] FIG. 13 is a diagram for explaining another example of the operation of the control circuit 10 according to the embodiment.

[0094] FIG. 14 is a diagram for explaining a method of correcting a predetermined frequency.

[0095] FIG. 15 is a diagram for explaining that the actual ripple can be suppressed by correcting a predetermined frequency.

[0096] 13 and 14 , the determiner 12 corrects the control period threshold Tth to a control period threshold Tth′ based on the ripple (ΔR_mes) that is actually superimposed on the output current of the power converter 100. Specifically, the determiner 12 estimates a control operation region ΔTon′ required for the actual ripple, and furthermore a maximum control amount Ton_max′, from the difference (ΔR_err) between the estimated ripple (ΔR_est) and the actual ripple (ΔR_mes), and determines the control period threshold Tth′ from the estimated maximum control amount Ton_max′.

[0097] 15, it can be seen that the influence of the actual ripple (ΔR_mes) can be suppressed by correcting the control cycle threshold value Tth to the control cycle threshold value Tth′. In this way, even if the actual ripple is larger than the expected ripple, a predetermined frequency can be corrected from the actually superimposed ripple, and the influence of the ripple can be suppressed.

[0098] (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.

[0099] For example, the present disclosure can be realized not only as the control circuit 10 or the power converter 100, but also as a control method including steps (processing) performed by the components that make up the control circuit 10.

[0100] FIG. 16 is a flowchart showing an example of a control method according to another embodiment.

[0101] The control method is executed by a control circuit 10 that controls a power converter 100. The power converter 100 includes a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting a first input / output terminal and a second input / output terminal, and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the first input / output terminal and the second input / output terminal. As shown in FIG. 16 , the control method includes a determination step (step S11) of a predetermined frequency, a first control step (step S12) of controlling the operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit, and a second control step (step S13) of controlling the phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is the predetermined frequency.

[0102] 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.

[0103] 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.

[0104] In the above-described embodiments, each component included in the control circuit 10 or the power converter 100 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.

[0105] Some or all of the functions of the control circuit 10 or power converter 100 according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually implemented on a single chip, or some or all of them may be integrated on a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within an LSI.

[0106] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derived technologies, that technology may naturally be used to integrate each component included in the control circuit 10 or the power converter 100 into an integrated circuit.

[0107] 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.

[0108] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0109] (Technology 1) A control circuit for controlling a power converter includes: a first set of switching devices including a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices including a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal; the control circuit includes a determination unit that determines a predetermined frequency; and a control unit having a first control mode that controls operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit; and a second control mode that controls a phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is the predetermined frequency.

[0110] Generally, power conversion is performed by controlling the operating frequencies of the first and second sets of switching devices, thereby controlling the on-times of the switching devices. However, when the output voltage is low, the operating frequency increases, resulting in increased switching losses in each switch and increased AC losses in magnetic components. Therefore, when controlling the operating frequency, a predetermined frequency is set as the upper limit of the operating frequency, and when conversion to a voltage lower than the voltage that can be converted by controlling the operating frequency with the predetermined frequency as the upper limit is performed, the on-times of the switching devices are controlled by controlling the phase between the switching of the first and second sets of switching devices. This allows power conversion to be performed over a wide range while suppressing losses.

[0111] However, ripple from the commercial power supply may be superimposed on the input current. If power conversion is performed with this ripple superimposed, the ripple will also be superimposed on the output voltage. This ripple is then applied to the output capacitor or the load battery, causing charging and discharging operations equivalent to the ripple, resulting in losses and temperature rise due to the internal resistance of the capacitor. This temperature rise reduces the lifespan of the capacitor and battery. To address this issue, phase control can be used to reduce the output current when the ripple increases the output current, or to increase the output current when the ripple decreases the output current. However, phase control may not be sufficient to fully adjust the output current and thus may not be able to suppress the effects of ripple. Therefore, by having a control circuit with the function of determining a predetermined frequency (or, in other words, the function of changing the predetermined frequency), the predetermined frequency can be pre-determined to a frequency that can suppress the effects of ripple through phase control. This suppresses the effects of ripple and reduces the shortening of component lifespan.

[0112] (Technology 2) The control circuit according to Technology 1, wherein the determination unit determines the predetermined frequency based on an output voltage of the power converter.

[0113] According to this, since the predetermined frequency differs depending on the output voltage, the predetermined frequency can be determined from the output voltage.

[0114] (Technology 3) The control circuit according to Technology 2, wherein the determination unit determines the predetermined frequency to be a smaller value as the output voltage increases.

[0115] According to this, the higher the output voltage, the lower the predetermined frequency, and therefore, the higher the output voltage, the lower the predetermined frequency can be determined.

[0116] (Technology 4) The control circuit according to Technology 2 or 3, wherein the determination unit determines the predetermined frequency based on a table in which the predetermined frequency is associated with each of the output voltages.

[0117] According to this, by preparing in advance a table in which a predetermined frequency is associated with each output voltage, the predetermined frequency can be easily determined using the table.

[0118] (Technology 5) The control circuit according to any one of Techniques 1 to 4, wherein the determination unit further corrects the determined predetermined frequency based on a ripple superimposed on the output current of the power converter.

[0119] This makes it possible to correct a predetermined frequency from the actually superimposed ripple, even if the actual ripple is larger than the expected ripple, thereby suppressing the influence of the ripple.

[0120] (Technology 6) A power converter comprising the control circuit according to any one of technologies 1 to 5, the first set of switching devices, and the second set of switching devices.

[0121] This makes it possible to provide a power converter that can suppress the effects of ripples and reduce the reduction in the lifespan of components.

[0122] (Technology 7) The power converter according to Technology 6, further comprising: a resonant capacitor connected to a first node on the first path between the first switch and the second switch; and a transformer having a primary winding and a secondary winding, one end of the primary winding connected to the resonant capacitor and the other end of the primary winding connected to a second node on the second path between the third switch and the fourth switch.

[0123] This makes it possible to provide an LLC converter that can suppress the effects of ripples and reduce the reduction in the lifespan of components.

[0124] (Technology 8) The power converter according to Technology 7 further includes: a third set of switching devices including a fifth switch and a sixth switch connected in series on a third path connecting the output terminal and a second ground terminal; a fourth set of switching devices including a seventh switch and an eighth switch connected in series on a fourth path different from the third path connecting the output terminal and the second ground terminal; and a second resonant capacitor connected to a third node on the third path between the fifth switch and the sixth switch, wherein one end of the secondary winding of the transformer is connected to the second resonant capacitor and the other end of the secondary winding is connected to a fourth node on the fourth path between the seventh switch and the eighth switch.

[0125] This makes it possible to provide a CLLC converter that can suppress the effects of ripples and reduce the reduction in the lifespan of components.

[0126] (Technology 9) A control method executed by a control circuit that controls a power converter, the power converter comprising: a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal, the second set of switching devices including: a determination step of determining a predetermined frequency; a first control step of controlling operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit; and a second control step of controlling a phase between switching of the first set of switching devices and switching of the second set of switching devices while the operating frequency is at the predetermined frequency.

[0127] This makes it possible to provide a control method that can suppress the influence of ripples and reduce the reduction in the lifespan of components.

[0128] The present disclosure can be applied to power converters such as LLC converters.

[0129] 10 Control circuit 11 Control unit 12 Determination unit 20 PWM generator 100 Power converter 110, 120, C1, C2, C3, C4, C5, C6, C7, C8, Cr1, Cr2 Capacitor 200 System power supply 300 PFC circuit 400 Load D1, D2, D3, D4, D5, D6, D7, D8 Diode D10 Rectifier circuit Lr1, Lr2 Leakage inductance N1, N2, N3, N4 Node P1, P2, P3, P4 Path Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Switch T1 Transformer Tid Ideal transformer t1, t2, t3, t4 Terminal

Claims

1. A control circuit for controlling a power converter, the power converter comprising: a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal, the second set of switching devices being connected in series on a second path different from the first path, the control circuit comprising: a determination unit for determining a predetermined frequency; and a control unit having a first control mode for controlling the operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit, and a second control mode for controlling a phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is the predetermined frequency.

2. The control circuit according to claim 1, wherein the determination unit determines the predetermined frequency based on an output voltage of the power converter.

3. The control circuit according to claim 2, wherein the determination section determines the predetermined frequency to be a smaller value as the output voltage increases.

4. The control circuit according to claim 2, wherein the determination unit determines the predetermined frequency based on a table in which a value of the predetermined frequency is associated with each of a plurality of values ​​of the output voltage.

5. The control circuit according to claim 1, wherein the determination unit further corrects the determined predetermined frequency based on a ripple superimposed on the output current of the power converter.

6. A power converter comprising: a control circuit according to any one of claims 1 to 5; the first set of switching devices; and the second set of switching devices.

7. The power converter according to claim 6, further comprising: a first resonant capacitor connected to a first node between the first switch and the second switch on the first path; and a transformer having a primary winding and a secondary winding, one end of the primary winding connected to the first resonant capacitor and the other end of the primary winding connected to a second node between the third switch and the fourth switch on the second path.

8. The power converter according to claim 7, further comprising: a third set of switching devices consisting of a fifth switch and a sixth switch connected in series on a third path connecting the output terminal and a second ground terminal; a fourth set of switching devices consisting of a seventh switch and an eighth switch connected in series on a fourth path different from the third path connecting the output terminal and the second ground terminal; and a second resonant capacitor connected to a third node between the fifth switch and the sixth switch on the third path, wherein the transformer has one end of the secondary winding connected to the second resonant capacitor and the other end of the secondary winding connected to a fourth node between the seventh switch and the eighth switch on the fourth path.

9. A control method executed by a control circuit that controls a power converter, the power converter comprising: a first set of switching devices consisting of a first switch and a second switch connected in series on a first path connecting an input terminal and a first ground terminal; and a second set of switching devices consisting of a third switch and a fourth switch connected in series on a second path different from the first path connecting the input terminal and the first ground terminal, the control method including the steps of: determining a predetermined frequency; controlling operating frequencies of the first set of switching devices and the second set of switching devices with the predetermined frequency as an upper limit; and controlling a phase between switching of the first set of switching devices and switching of the second set of switching devices when the operating frequency is at the predetermined frequency.

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