WO2024257394A1 - Control circuit, electric power converter, and control method - Google Patents

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

This disclosure relates to a control circuit for controlling a power converter.

Patent document 1 discloses an LLC converter.

WO 2023/276024

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

The present disclosure provides a control circuit and the like that can suppress the effects of ripples and reduce the reduction in component lifespan.

The 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 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 the phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency.

The power converter according to the present disclosure includes the above-mentioned control circuit, the first set of switching devices, and the second set of switching devices.

The 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 control method including a determination step of determining a predetermined frequency, a first control step 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 of controlling the phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency.

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

The control circuit according to one embodiment of the present disclosure can suppress the effects of ripples and reduce the reduction in component lifespan.

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

The following describes the embodiment in detail with reference to the drawings.

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

(Embodiment)
A control circuit and a power converter according to an embodiment will be described below.

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.

The power converter 100 is an isolated DC-DC converter that steps up or down the input voltage to a specified voltage and outputs it. For example, the power converter 100 is an LLC converter. An LLC converter is a circuit that utilizes LLC resonance caused by the leakage inductance of a transformer, the excitation inductance, and a resonant capacitor. In an LLC converter, the input/output voltage ratio (Gain) changes by changing the switching frequency, making it possible to output the desired voltage.

The PFC circuit 300 is, for example, an ACDC converter with a PFC (Power Factor Correction) function, and converts the 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.

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 load 400 can be charged at the battery voltage Vbat by the battery current Ibat.

FIG. 2A is a circuit 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.

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

Capacitor 110 is an input capacitor connected between terminals t1 and t2, and capacitor 120 is an output capacitor (smoothing capacitor) connected between terminals t3 and t4.

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.

Switch Q1 is an example of a first switch provided on path P1 connecting terminals t1 and t2. Path P1 is an example of a first path. Switch Q2 is an example of a second switch provided on path P1 and connected in series with switch Q1. Switches Q1 and Q2 are an example of a first set of switching devices consisting of switches Q1 and Q2 connected in series on path P1 connecting terminals t1 and t2.

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, which is connected in parallel with the switch Q1 in the equivalent circuit. 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. 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.

Switch Q2 is, for example, an N-channel MOSFET. In FIG. 2A, the parasitic capacitance of switch Q2 is shown as capacitor C2, and capacitor C2 is connected in parallel with switch Q2 in the equivalent circuit. The drain of switch Q2 is connected to the source of switch Q1, and the source of switch Q2 is connected to terminal t2. Also, in FIG. 2A, the parasitic diode of switch Q2 is shown as diode D2, and in the equivalent circuit, the anode of diode D2 is connected to the source of switch Q2, and the cathode is connected to the drain of switch Q2.

Switch Q3 is an example of a third switch provided on path P2, which connects terminals t1 and t2 and is different from path P1. Path P2 is an example of a second path. Switch Q4 is an example of a fourth switch provided on path P2 and connected in series with switch Q3. Switches Q3 and Q4 are an example of a second set of switching devices consisting of switches Q3 and Q4 connected in series on path P2, which connects terminals t1 and t2 and is different from path P1.

Switch Q3 is, for example, an N-channel MOSFET. In FIG. 2A, the parasitic capacitance of switch Q3 is shown as capacitor C3, which is connected in parallel with switch Q3 in the equivalent circuit. The drain of switch Q3 is connected to terminal t1, and the source of switch Q3 is connected to the drain of switch Q4. Also, in FIG. 2A, the parasitic diode of switch Q3 is shown as diode D3, and in the equivalent circuit, the anode of diode D3 is connected to the source of switch Q3, and the cathode is connected to the drain of switch Q3.

Switch Q4 is, for example, an N-channel MOSFET. In FIG. 2A, the parasitic capacitance of switch Q4 is shown as capacitor C4, and capacitor C4 is connected in parallel with switch Q4 in the equivalent circuit. The drain of switch Q4 is connected to the source of switch Q3, and the source of switch Q4 is connected to terminal t2. Also, in FIG. 2A, the parasitic diode of switch Q4 is shown as diode D4, and in the equivalent circuit, the anode of diode D4 is connected to the source of switch Q4, and the cathode is connected to the drain of switch Q4.

Capacitor Cr1 is connected to node N1 between switch Q1 and switch Q2 on path P1. Capacitor Cr1 is an example of a first resonant capacitor. Node N1 is an example of a first node.

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 switch Q3 and the switch 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, and the transformer T1 can be represented by an ideal transformer Tid, a primary leakage inductance Lr1, and a secondary leakage inductance Lr2. Note that the excitation inductance is not shown. The leakage inductance Lr1 is connected in series to the primary coil of the ideal transformer Tid, and the leakage inductance Lr2 is connected in series to the secondary coil of the ideal transformer Tid. Note that the power converter 100 may include an inductor equivalent to the leakage inductance Lr1 and an inductor equivalent to the leakage inductance Lr2.

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 consisting of four diodes, enabling full-wave rectification.

The control circuit 10 is a circuit for controlling the switching (on and off) of the 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 the gate drive circuits connected to the gates of the switches Q1, Q2, Q3, and Q4 via a PWM generator or the like.

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 is, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory), and can store a program executed by the processor. The control unit 11 and the decision unit 12 are realized by, for example, a processor that executes a program stored in the memory.

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

The control unit 11 has a first control mode that controls the operating frequency of the first set of switching devices (switches Q1 and Q2) and the second set of switching devices (switches Q3 and Q4) with a predetermined frequency as the upper limit, and a second control mode that controls the phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency. The control unit 11 will be described in detail later.

The power converter 100 does not have to be an LLC converter, but may be any isolated DC-DC converter as long as it has at least a first set of switching devices (switches Q1 and Q2), a second set of switching devices (switches Q3 and Q4), and a control circuit 10.

For example, the power converter 100 may be a CLLC converter. Here, an example in which the power converter 100 is a CLLC converter will be described with reference to FIG. 2B.

FIG. 2B is a circuit diagram showing another example of a power converter 100 according to an embodiment.

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 provided. The following will focus on the differences from the power converter 100 when it is an LLC converter (FIG. 2A).

The power converter 100 (CLLC converter) shown in FIG. 2B includes switches Q5, Q6, Q7, and Q8, which together form a rectifier circuit D10.

Switch Q5 is an example of a fifth switch provided on path P3 connecting terminals t3 and t4. Path P3 is an example of a third path. Switch Q6 is an example of a sixth switch provided on path P3 and connected in series with switch Q5. Switches Q5 and Q6 are an example of a third set of switching devices consisting of switches Q5 and Q6 connected in series on path P3 connecting terminals t3 and t4.

Switch Q5 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of switch Q5 is shown as capacitor C5, and capacitor C5 is connected in parallel with switch Q5 in the equivalent circuit. The drain of switch Q5 is connected to terminal t3, and the source of switch Q5 is connected to the drain of switch Q6. Also, in FIG. 2B, the parasitic diode of switch Q5 is shown as diode D5, and in the equivalent circuit, the anode of diode D5 is connected to the source of switch Q5, and the cathode is connected to the drain of switch Q5.

Switch Q6 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of switch Q6 is shown as capacitor C6, and capacitor C6 is connected in parallel with switch Q6 in the equivalent circuit. The drain of switch Q6 is connected to the source of switch Q5, and the source of switch Q6 is connected to terminal t4. Also, in FIG. 2B, the parasitic diode of switch Q6 is shown as diode D6, and in the equivalent circuit, the anode of diode D6 is connected to the source of switch Q6, and the cathode is connected to the drain of switch Q6.

Switch Q7 is an example of a seventh switch provided on path P4, which is different from path P3, connecting terminals t3 and t4. Path P4 is an example of a fourth path. Switch Q8 is an example of an eighth switch provided on path P4 and connected in series with switch Q7. Switches Q7 and Q8 are an example of a fourth set of switching devices consisting of switches Q7 and Q8 connected in series on path P4, which is different from path P3, connecting terminals t3 and t4.

Switch Q7 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of switch Q7 is shown as capacitor C7, and capacitor C7 is connected in parallel with switch Q7 in the equivalent circuit. The drain of switch Q7 is connected to terminal t3, and the source of switch Q7 is connected to the drain of switch Q8. Also, in FIG. 2B, the parasitic diode of switch Q7 is shown as diode D7, and in the equivalent circuit, the anode of diode D7 is connected to the source of switch Q7, and the cathode is connected to the drain of switch Q7.

Switch Q8 is, for example, an N-channel MOSFET. In FIG. 2B, the parasitic capacitance of switch Q8 is shown as capacitor C8, and capacitor C8 is connected in parallel with switch Q8 in the equivalent circuit. The drain of switch Q8 is connected to the source of switch Q7, and the source of switch Q8 is connected to terminal t4. Also, in FIG. 2B, the parasitic diode of switch Q8 is shown as diode D8, and in the equivalent circuit, the anode of diode D8 is connected to the source of switch Q8, and the cathode is connected to the drain of switch Q8.

Capacitor Cr2 is connected to node N3 between switch Q5 and switch Q6 on path P3. Capacitor Cr2 is an example of a second resonant capacitor. Node N3 is an example of a third node.

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

Note that the rectifier circuit D10 of the power converter 100 (LLC converter) shown in FIG. 2B may be composed of four diodes, similar to the power converter 100 (LLC converter) shown in FIG. 2A.

The power converter 100 also 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 the control circuit 10 controls the switching of the switches Q1, Q2, Q3, and Q4 based on the results of these detections. When the power converter 100 has the circuit configuration shown in FIG. 2B, the control circuit 10 may also control the switches Q5, Q6, Q7, and Q8.

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 specified frequency will be described with reference to FIG. 3.

FIG. 3 is a diagram for explaining variable frequency control. The horizontal axis of the graph shown in FIG. 3 is the output voltage (Vbat) of the power converter 100, and the vertical axis is the control amount Ton. The control amount Ton is the on time of the switch, specifically, the time when the switches Q1 and Q4 are on and the switches Q2 and Q3 are off, or the time when 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 control amount Ton, and the higher the operating frequency of each switch, the shorter the control amount 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.

As shown in Figure 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.

For this reason, the control unit 11 has a first control mode that controls the operating frequency of the first set of switching devices (switches Q1 and Q2) and the second set of switching devices (switches Q3 and Q4) with a predetermined frequency as the upper limit, and a second control mode that controls the phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency. This will be explained using Figures 4 and 5.

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

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

For example, the control unit 11 controls the operating frequency of the switches Q1, Q2, Q3, and Q4 with the frequency Fth corresponding to the control period threshold Tth as the upper limit as the predetermined frequency, 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 phase of the switching of the switches Q1 and Q4 is shifted 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 phase of the switching of the switches Q2 and Q3 is shifted 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).

When the output voltage is between Vbat_min and Vth, the control unit 11 performs phase shift control in the second control mode, and when the output voltage is between Vth and Vbat_max, it performs variable frequency control in the first control mode. This makes it possible to shorten the control amount Ton without raising the operating frequency above a predetermined frequency, thereby suppressing losses and enabling power conversion over a wide range.

The bus voltage Vbus, which is the input voltage of the power converter 100, has some voltage fluctuation (ripple) because it is the AC current (AC current Iac) and voltage converted from the system power source 200 by the PFC circuit 300 into a DC current (bus current Ibus) and voltage (bus voltage Vbus). This ripple can be superimposed on the output voltage Vbat via the power converter 100. The output voltage Vbat on which this ripple is superimposed is applied to the capacitor 120, so a charge and discharge operation of the ripple occurs, and loss and temperature rise occur due to the internal resistance of the capacitor. This temperature rise is a factor that reduces the life of the capacitor. Also, if the load 400 is a battery, for the same reason, the ripple can also be a factor that reduces the battery life. Therefore, it is desirable to design so that the ripple is minimized. One way to minimize the ripple is to increase the capacitance value of the capacitor 120, but in that case, it leads to an increase in the size and cost of the power converter. Therefore, the ripple is generally minimized by control design.

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 have a control design that minimizes the ripples superimposed on the output voltage Vbat.

The effect on control responsiveness when ripples are present is explained below using Figures 6A to 6C.

FIG. 6A is a diagram for explaining the control responsiveness in the case of condition 1.

FIG. 6B is a diagram to explain the control responsiveness in the case of condition 2.

Figure 6C is a diagram to explain the control responsiveness in the case of condition 3.

The horizontal axis of the graphs shown in Figs. 6A to 6C is the phase amount Tθ, and the vertical axis is the output current (Ibat) of the power converter 100. The phase amount Tθ is the amount of phase shift between the switching of the first group of switching devices and the switching of the second group of switching devices. When the phase amount Tθ is 0, the control amount Ton is the control period threshold value Tth/2, and as the phase amount Tθ increases, the control amount Ton becomes shorter than the control period threshold value Tth/2. Conditions 1 to 3 shown in Figs. 6A to 6C are conditions 1 to 3 shown in Fig. 4, and the output voltage is larger 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 in condition 1, Ibat2 in condition 2, and Ibat3 in condition 3. For example, assume that ripples occur in conditions 1 to 3.

As shown in FIG. 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 became smaller due to the influence of ripples.

As shown in FIG. 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, 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 became smaller due to the influence of ripples.

As shown in FIG. 6C, under condition 3, when the power converter 100 outputs maximum power, if the output current becomes smaller due to the influence of ripple, for example, there is insufficient phase control responsiveness 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 be increased by the amount that has become smaller due to the influence of ripple. When an uncontrollable region is included in this way, control to suppress the ripple becomes impossible. In other words, if power conversion is performed in this state, the ripple cannot be suppressed, so the amount of heat generated by the capacitor 120 and the load 400 (battery) increases, and there is a risk of shortening the life of the parts.

In response to this, the control circuit 10 is provided with a determination unit 12 that determines the predetermined frequency. In other words, 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 effect achieved by the control circuit 10 being provided with the determination unit 12 will be explained using Figures 7 and 8.

Figure 7 is a diagram to explain how to change the upper limit frequency of phase shift control.

Figure 8 is a diagram to explain the control responsiveness in the case of condition 3 when the upper frequency limit of phase shift control is lowered.

7, for example, the determination unit 12 determines the predetermined frequency to be a frequency corresponding to the control cycle threshold Tth'. As a result, as shown in FIG. 8, when the predetermined frequency corresponds to the control cycle threshold Tth', the output current obtained for the same phase amount Tθ is larger than when the predetermined frequency corresponds to the control cycle threshold Tth. In other words, when the predetermined frequency corresponds to the control cycle threshold Tth', the phase amount Tθ required to obtain the same output current is larger than when the predetermined frequency corresponds to the control cycle threshold Tth. Therefore, when the predetermined frequency corresponds to the control cycle threshold Tth', the phase amount Tθ corresponding to the output current Ibat3 is increased, and since there is sufficient phase control responsiveness for the phase amount Tθ, the phase amount Tθ can be further reduced (i.e., the phase amount Tθ can be brought closer to 0). Therefore, the output current can be increased by the amount that has been reduced due to the influence of the ripple.

As explained above, generally, 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 to control the on-time of the switching devices to perform power conversion, but when the output voltage is low, the operating frequency increases, increasing the switching loss of each switch and the AC loss of the magnetic components. Therefore, in 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-time of the switching devices is 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 makes it possible to perform power conversion over a wide range while suppressing losses.

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 control and respond to a wider range of ripple superposition, and to reduce the reduction in component lifespan.

Note that if the specified frequency is made too small, in other words, if the control period threshold is made too large, there is a risk of large losses, so the determination unit 12 needs to determine an optimal specified frequency.

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 number of output voltage values, and the determination unit 12 determines the predetermined frequency based on this table.

Here, we will explain how to create a table that associates a specific frequency with each output voltage, using Figures 9 to 11.

First, we will use Figure 9 to explain how to estimate the control operating region, which is necessary to create a table in which a specific frequency is associated with each output voltage.

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

For example, the relationship between the control amount Ton and the output current Ibat during rated operation (e.g., Vbat = 250V to 450V, Pmax = 3700W) is calculated using the fundamental wave approximation method. Figure 9 shows the above relationship when the output voltage is 250V, 360V, and 450V. Then, the 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 Figure 9, when the output voltage is 250V, the control operation region ΔTon1 is estimated, when the output voltage is 360V, the control operation region ΔTon2 is estimated, and when the output voltage is 450V, the control operation region ΔTon3 is estimated. Note that FIG. 9 shows output voltages of 250V, 360V, and 450V, but the control operation region ΔTon can be estimated for various output voltages other than 250V, 360V, and 450V.

Next, we will use Figure 10 to explain how to estimate the control period threshold Tth, which is necessary to create a table in which a specific frequency is associated with each output voltage.

FIG. 10 is a diagram for explaining a method for estimating the control period threshold Tth. In the graph shown in FIG. 10, the horizontal axis represents the output voltage (Vbat), and the vertical axis represents the control amount Ton.

As shown in FIG. 10, the maximum control amount Ton_max can be calculated by adding 1/2 of the control operation range ΔTon to the control amount for each output voltage at maximum power (Ton@Pmax). The control period threshold Tth can be estimated from this maximum control amount Ton_max. For example, when the output voltage is 250V, the control period threshold Tth is estimated to be 713ns, when the output voltage is 360V, the control period threshold Tth is estimated to be 825ns, and when the output voltage is 450V, the control period threshold Tth is estimated to be 1763ns.

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

FIG. 11 shows an example of a table in which a specific frequency is associated with each output voltage.

Since 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 a predetermined frequency is associated with each output voltage. Note that FIG. 11 shows the cases where the output voltage is 250V, 360V, and 450V, but the above table associates a predetermined frequency with various output voltages other than 250V, 360V, and 450V. However, a predetermined frequency may also be associated with each output voltage in a certain range. Specifically, a predetermined frequency A may be associated with 250V to 260V, a predetermined frequency B may be associated with 260V to 270V, and so on, and a predetermined frequency Z may be associated with 440V to 450V.

Note that the estimated ripple may vary depending on the environment in which the power converter 100 is applied or the user who uses the power converter 100, and therefore the contents of the table may also 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 or the user who uses the power converter 100.

Next, an example of the operation of the control circuit 10 will be described with reference to FIG. 12.

FIG. 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.

The determination unit 12 determines a predetermined frequency based on the output voltage (Vbat_mes) and notifies the PWM generator 20 of the 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 and 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.

The control unit 11 is, for example, a PI controller, and notifies the PWM generator 20 of the 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. This allows the phase to be controlled to suppress the effects of ripples even when ripples are superimposed. In addition, since a predetermined frequency (control period threshold Tth) that can suppress the effects of ripples by phase control is determined in advance, the output current is prevented from being unable to be fully adjusted by phase control, and the effects of ripples can be suppressed by phase control.

However, there may be cases where the actually occurring ripple is larger than the estimated ripple, and the output current cannot be adjusted by phase control. In this case, 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 explained using Figures 13 to 15.

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

FIG. 14 is a diagram for explaining a method for correcting a specified frequency.

Figure 15 is a diagram to explain how actual ripples can be suppressed by correcting a specific frequency.

13 and 14, the determination unit 12 corrects the control period threshold value Tth to the control period threshold value Tth' based on the ripple (ΔR_mes) actually superimposed on the output current of the power converter 100. Specifically, the determination unit 12 estimates the control operation region ΔTon' required for the actual ripple from the difference (ΔR_err) between the estimated ripple (ΔR_est) and the actual ripple (ΔR_mes), and further estimates the maximum control amount Ton_max', and determines the control period threshold value Tth' from the estimated maximum control amount Ton_max'.

As shown in FIG. 15, by correcting the control cycle threshold Tth to the control cycle threshold Tth', it can be seen that the effect of the actual ripple (ΔR_mes) can be suppressed. 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 effect of the ripple can be suppressed.

Other Embodiments
As described above, the embodiment has been described as an example of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to this, and can be applied to an embodiment in which appropriate changes, substitutions, additions, omissions, etc. are made. For example, the following modified examples are also included in one embodiment of the present disclosure.

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

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

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 determining 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 the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency.

For example, the present disclosure can be realized as a program for causing a computer (processor) to execute the 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.

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, and input/output circuits. In other words, each step is performed by the CPU obtaining data from memory or input/output circuits, etc., performing calculations, and outputting the results of the calculations to memory or input/output circuits, etc.

In the above embodiment, 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.

Some or all of the functions of the control circuit 10 or power converter 100 according to the above embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into one chip, or may be integrated into one chip that includes some or all of the functions. Furthermore, the integrated circuit is not limited to an LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacture, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells inside the LSI may also be used.

Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derived technologies, it is natural that each component included in the control circuit 10 or power converter 100 may be integrated using that technology.

In addition, this disclosure also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art may conceive, and forms realized by arbitrarily combining the components and functions of each embodiment within the scope that does not deviate from the spirit of this disclosure.

(Additional Note)
The above description of the embodiments discloses the following techniques.

(Technology 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 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 the phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency.

Generally, the operating frequencies of the first and second sets of switching devices are controlled to control the on-time of the switching devices and perform power conversion, but when the output voltage is low, the operating frequency increases, increasing the switching loss of each switch and the AC loss of the 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-time of the switching devices is controlled by controlling the phase between the switching of the first and second sets of switching devices. This makes it possible to perform power conversion over a wide range while suppressing losses.

However, ripple from a commercial power source may be superimposed on the input current, and if power conversion is performed with the ripple superimposed, the ripple will also be superimposed on the output voltage. This ripple is applied to the output capacitor and the load battery, causing charging and discharging of the ripple, resulting in loss and temperature rise due to the internal resistance of the capacitor. This temperature rise is a factor that shortens the life of the capacitor and battery. In response to this, if the output current is large due to the ripple, it is possible to control the phase so that the output current is reduced accordingly, and if the output current is small due to the ripple, it is possible to control the phase so that the output current is increased accordingly. However, there are cases where the output current cannot be adjusted completely by phase control, and the effects of the ripple cannot be suppressed. Therefore, by having the control circuit have the function of determining the specified frequency (in other words, the function of changing the specified frequency), the specified frequency can be determined in advance to a frequency that can suppress the effects of the ripple by controlling the phase. Therefore, the effects of the ripple can be suppressed, and the shortening of the life of the parts can be reduced.

(Technology 2) The control circuit described in Technology 1, in which the determination unit determines the predetermined frequency based on the output voltage of the power converter.

In this way, since the specified frequency varies depending on the output voltage, the specified frequency can be determined from the output voltage.

(Technology 3) The control circuit described in Technology 2, in which the determination unit determines the predetermined frequency to be a smaller value as the output voltage increases.

In this way, the higher the output voltage, the smaller the specified frequency becomes, so it is possible to determine a specified frequency that is smaller the higher the output voltage.

(Technology 4) The control circuit described in Technology 2 or 3, in which the determination unit determines the predetermined frequency based on a table in which the predetermined frequency is associated with each output voltage.

By doing this, by preparing a table in advance in which a specific frequency is associated with each output voltage, the specific frequency can be easily determined using the table.

(Technology 5) A control circuit according to any one of techniques 1 to 4, in which the determination unit further corrects the determined predetermined frequency based on a ripple superimposed on the output current of the power converter.

As a result, even if the actual ripple is larger than the expected ripple, a certain frequency can be corrected from the actual superimposed ripple, and the effects of the ripple can be suppressed.

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

This makes it possible to provide a power converter that can suppress the effects of ripples and reduce the reduction in component life.

(Technology 7) The power converter described in Technology 6 further includes a 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 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.

This makes it possible to provide an LLC converter that can suppress the effects of ripples and reduce the reduction in component life.

(Technology 8) The power converter according to Technology 7 further includes 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 the 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, and 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.

This makes it possible to provide a CLLC converter that can suppress the effects of ripples and reduce the reduction in component life.

(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 control method including a determination step of determining a predetermined frequency, a first control step 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 of controlling a phase between the switching of the first set of switching devices and the switching of the second set of switching devices when the operating frequency is the predetermined frequency.

This provides a control method that can suppress the effects of ripples and reduce the reduction in component life.

This disclosure can be applied to power converters such as LLC converters.

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 (9)

A control circuit for controlling a power converter,
The 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 the input terminal and a first ground terminal;
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;
Equipped with
The control circuit includes:
A determination unit that determines a predetermined frequency;
a control unit having a first control mode for controlling an operating frequency 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 in a state in which the operating frequency is the predetermined frequency;
Equipped with
Control circuit. The determination unit determines the predetermined frequency based on an output voltage of the power converter.
2. The control circuit of claim 1. The determination unit determines the predetermined frequency to be a smaller value as the output voltage increases.
3. The control circuit of claim 2. 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.
3. The control circuit of claim 2. The determination unit further corrects the determined predetermined frequency based on a ripple superimposed on the output current of the power converter.
2. The control circuit of claim 1. A control circuit according to any one of claims 1 to 5;
the first set of switching devices;
the second set of switching devices.
Power converter. a first resonant capacitor connected to a first node on the first path between the first switch and the second switch;
a transformer having a primary winding and a secondary winding, one end of the primary winding being connected to the first resonant capacitor and the other end of the primary winding being connected to a second node between the third switch and the fourth switch on the second path;
Further comprising:
7. The power converter of claim 6. 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 the second ground terminal;
a fourth set of switching devices including a seventh switch and an eighth switch connected in series on a fourth path connecting the output terminal and the second ground terminal, the fourth path being different from the third path;
a second resonant capacitor connected to a third node on the third path between the fifth switch and the sixth switch;
Further equipped with
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;
8. The power converter of claim 7. A control method executed by a control circuit for controlling a power converter, comprising:
The 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 the input terminal and a first ground terminal;
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;
Equipped with
The control method includes:
determining a predetermined frequency;
controlling an operating frequency of the first set of switching devices and the second set of switching devices up to the predetermined frequency;
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;
Including,
Control methods.

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