JP2017085689A - Power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply device that is highly efficient over a wide load range.SOLUTION: The power supply device comprises: a DC power source; an inverter converting a DC voltage from the DC power source into an AC voltage; and a control unit for controlling the operation of the inverter. The inverter circuit comprises: a switching circuit comprised of switching elements Q1 and Q2, a resonance coil Lr, and a resonance capacitor Cr. When the output power Pout from the inverter is smaller than a predetermined threshold power Pth, the control unit performs control in such a manner that the switching frequency fsw of the switching circuit is in a first mode lower than the resonance frequency fr of the resonance circuit. When the output power Pout from the inverter is larger than a predetermined threshold power Pth, the control unit performs control in such a manner that the switching frequency fsw of the switching circuit is in a second mode higher than the resonance frequency fr.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power supply device that converts a DC voltage into an AC voltage of a different voltage, and more particularly to a resonant power supply device.

  An induction heating cooker causes a high-frequency current to flow from a high-frequency inverter to a heating coil, generates an eddy current in a metal heated object disposed in the vicinity of the coil, and generates heat by the electric resistance of the heated object itself.

  In a high-frequency inverter used for an induction heating cooker, a resonance type inverter is generally used. In this resonance type inverter circuit, when the switching element is turned off at the timing when the current flowing through the switching element becomes small due to the resonance, the cutoff current is small, so that the switching loss is small and high efficiency can be obtained. However, in general, the resonance type inverter controls the output by changing the switching frequency. When the output power is reduced, the switching frequency is increased to cause a switching loss and the efficiency is lowered.

  As a conventional technique for solving such a problem, there is Patent Document 1. Patent Document 1 discloses a current resonance type power supply device that changes the on-time ratio of an inverter at a light load to prevent a high switching frequency.

Japanese Patent Laying-Open No. 2015-70708

  In the power supply device disclosed in Patent Document 1, an increase in switching loss at the time of low power output is suppressed by combining frequency control and on-time ratio control. However, even at low power output, the switching frequency operates only in a range higher than the resonance frequency, and a large switching loss still occurs.

  An object of the present invention is to provide a highly efficient power supply device in a wide load range.

  In order to achieve the above object, a power supply apparatus according to the present invention includes a DC power supply, a switching circuit that converts a DC voltage from the DC power supply into an AC voltage, a control unit that controls the operation of the switching circuit, and a resonance coil. The control unit includes a resonance circuit including Lr and a resonance capacitor Cr. When the input power Pin to the switching circuit is smaller than a predetermined threshold power Pth, the switching frequency fsw of the switching circuit is When control is performed so that the first mode is lower than the resonance frequency fr of the circuit, and the input power Pin to the switching circuit is larger than a predetermined threshold power Pth, the switching frequency fsw of the switching circuit is the resonance frequency. Control is performed so that the second mode becomes higher than fr.

  According to the present invention, a highly efficient electromagnetic induction heating device can be provided in a wide load range.

1 is a circuit configuration diagram of a power supply device 1 according to a first embodiment. The flowchart which shows the flow of the process which the power supply device 1 of Example 1 performs. The conceptual diagram which showed the relationship between the input electric power Pin of Example 1, and switching frequency fsw, or duty ratio dutyQ1, dutyQ2 of switching element Q1, Q2. A graph showing the relationship between the switching frequency fsw and the input power Pin of the first embodiment together with the resonance characteristics of the resonance circuit 30. Operation waveforms at operation points 1 to 4 shown in FIGS. The conceptual diagram which showed the relationship between the input electric power Pin of Example 2, and switching frequency fsw, or duty ratio dutyQ1, dutyQ2 of switching element Q1, Q2. Graph showing the relationship between the switching frequency fsw and the input power Pin of Example 2 together with the resonance characteristics of the resonance circuit 30 Operation waveforms at operation points 1 to 4 shown in FIGS. The conceptual diagram which showed the relationship between the input electric power Pin of Example 3, and switching frequency fsw or duty ratio dutyQ1, dutyQ2 of switching element Q1, Q2. The relationship between the switching frequency fsw and the input power Pin of Example 3 is shown together with the resonance characteristics of the resonance circuit 30, and the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2. Graph Operation waveforms at operation points 1 to 4 shown in FIGS. The conceptual diagram which showed the relationship between the input electric power Pin of Example 4, switching frequency fsw, or duty ratio dutyQ1, dutyQ2 of switching element Q1, Q2. The relationship between the switching frequency fsw and the input power Pin of the fourth embodiment is shown together with the resonance characteristics of the resonance circuit 30, and the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2. Graph Operation waveforms at operation points 1 to 4 shown in FIGS. Circuit configuration diagram of power supply device 2 in Embodiment 5

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit configuration diagram of a power supply device 1 according to the present embodiment. The power supply device 1 includes a switching circuit 20 that inputs the voltage of the DC power supply 10, a resonance circuit 30, input power detection means 40 for the switching circuit, and a control unit 50 that controls the on / off state of the switching elements included in the switching circuit. It is constituted by.

  The switching circuit 20 includes switching elements Q1 and Q2, and diodes D1 and D2 are connected in reverse parallel to the switching elements Q1 and Q2, respectively. Here, when MOSFETs are used as the switching elements Q1 and Q2, parasitic diodes of the MOSFETs can be used, so that the diodes D1 and D2 can be omitted. The switching circuit 20 is connected between a node Nd1 that is a positive electrode point of the DC power supply 10 and a node Nd2 that is a negative electrode point, and converts a DC voltage supplied from the DC power supply 10 into a high-frequency AC voltage. Then, it is applied to the resonance circuit 30.

  The resonance circuit 30 includes a resonance coil Lr and resonance capacitors Cr1 and Cr2 connected in series, and high frequency power is supplied from the switching circuit 20 to the resonance coil Lr.

  FIG. 2 is a flowchart showing a flow of processing executed by the power supply device 1. In step 1 (S1), the control unit 50 reads the input power Pin detected by the power detection means 40. In step 2 (S2), the control unit 50 determines whether or not the input power Pin is smaller than the threshold power Pth. When the input power Pin is larger than the threshold power Pth (S2 → Yes), the process of the control unit 50 proceeds to step 3 (S3). In step 3, the control unit 50 transitions to the first mode, which is an operation mode when the power supply device 1 is lightly loaded. When the input power Pin is smaller than the threshold power Pth (S2 → No), the process of the control unit 50 proceeds to step 4 (S4). In step 4, the control unit 50 makes a transition to the second mode, which is an operation mode when the power supply device 1 is under heavy load. In step 5 (S5), the control unit 50 generates a drive signal corresponding to the determined drive mode, outputs the drive signal to the switching elements Q1, Q2, and drives the power supply device 1. After executing the process of step 5, the process of the control unit 50 returns to START (RETURN).

  The operation of the power supply device 1 will be described with reference to FIGS. In this specification, the on-time ratio of the switching element Q1 is defined as duty Q1, the on-time ratio of the switching element Q2 is defined as duty Q2, and the resonance frequency by the resonance coil Lr and the resonance capacitors Cr1, Cr2 is defined as fr. In the present embodiment, by setting the switching frequency fsw of the switching circuit to be lower than the resonance frequency fr in the first mode when the load is light, low power can be output while suppressing an increase in switching loss.

  FIG. 3A is a conceptual diagram illustrating a relationship between the input power Pin and the switching frequency fsw in the first embodiment. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the lower limit value of the switching frequency fsw in the second mode, and f3. Is the upper limit value of the switching frequency fsw in the first mode, and f4 is the lower limit value of the switching frequency fsw in the first mode. First, when the rated power Pmax is input to the power supply device 1, the switching frequency fsw operates at a frequency f2 higher than the resonance frequency fr. Thereafter, the input power Pin is reduced by increasing the switching frequency fsw. When the input power Pin reaches the threshold power Pth, the switching frequency fsw is shifted to f3. At this time, in this embodiment, f3 is set to a range lower than the resonance frequency fr and higher than 1/2 of the resonance frequency fr, that is, 1/2 fr to fr. Thereafter, the input power Pin is reduced by reducing the switching frequency fsw, and reaches the lower limit input power Pmin when the switching frequency fsw becomes f4.

  FIG. 3b is a conceptual diagram showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In this embodiment, the on-time ratio is fixed at 0.5 regardless of the input power Pin.

  As described above, by setting the threshold power Pth, the switching frequency fsw can be operated in a region lower than the resonance frequency fr at a light load. Therefore, the power supply device 1 of the present invention has a wide input power range. While enabling operation, it is possible to reduce the increase in switching frequency at light load and obtain high efficiency.

  FIG. 4 is a graph showing the relationship between the switching frequency fsw and the input power Pin together with the resonance characteristics of the resonance circuit 30. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the lower limit value of the switching frequency fsw in the second mode, and f3. Is the upper limit value of the switching frequency fsw in the first mode, and f4 is the lower limit value of the switching frequency fsw in the first mode. In the second mode in which the input power is in the range of Pth to Pmax, in the first mode in which the switching frequency fsw is on the slow phase side having a resonance characteristic higher than the resonance frequency fr, and the input power is in the range of Pth to Pmin. The switching frequency fsw is in the range of 1/2 fr to fr, that is, the fast phase side of the resonance characteristics is used.

  Therefore, in the second mode, when the input power Pin is decreased, the switching frequency fsw is increased. In the first mode, when the input voltage Pin is decreased, the switching frequency fsw is decreased. By operating in this way, it is possible to operate in a wide input power range.

  In this embodiment, when the input power Pin is finely adjusted in the vicinity of the threshold power Pth, the switching frequency fsw changes continuously and suddenly. In this case, in order to suppress a sudden change in the switching frequency fsw, the adjustment is made between the threshold power for changing from the first mode to the second mode and the threshold power for changing from the second mode to the first mode. It is better to provide sensitivity (hysteresis).

  Next, the relationship between the switching elements Q1, Q2 and the current flowing through the resonance coil Lr will be described with reference to FIG. In FIG. 5, Q1VGE and Q2VGE represent gate voltages of the switching elements Q1 and Q2, respectively. ILr represents the current of the resonance coil Lr, and the direction flowing from Nd3 to Nd4 is positive.

  5a and 5b show operation waveforms at the operation point 1 and the operation point 2 shown in FIGS. 3 and 4, respectively. The switching elements Q1 and Q2 operate to cut off the resonance current caused by the resonance coil Lr and the resonance capacitors Cr1 and Cr2.

  FIG. 5c shows an operation waveform at the operation point 3 shown in FIGS. 3 and 4, and the operation is performed under the condition that the switching frequency fsw is shifted to f3 lower than the resonance frequency fr with the same input power as that of the operation point 2. The waveform is shown. Since f3 is lower than fr, the resonance current flows for more than a half cycle within the switching half cycle of the switching elements Q1, Q2.

  FIG. 5d shows an operation waveform at the operation point 4 shown in FIGS. 3 and 4, and shows an operation waveform when the input power is further reduced from the operation point 3. FIG. As shown in FIG. 5d, the effective current flowing through the resonance coil Lr is reduced due to the effect of reducing the switching frequency fsw, so that the input power is reduced. When the switching frequency fsw reaches f4, the minimum input power Pmin is obtained.

  As described above, in the power supply device 1, the switching frequency is reduced to a range lower than the resonance frequency at a light load, thereby reducing the switching loss.

  Next, Example 2 will be described. The basic configuration is the same as that of the first embodiment, but in this embodiment, the switching frequency fsw is reduced to a range of ½ or less of the resonance frequency fr in the first mode.

  The operation of the power supply device 1 according to this embodiment will be described with reference to FIGS.

  FIG. 6A is a conceptual diagram showing the relationship between the input power Pin and the switching frequency fsw in the present embodiment. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the lower limit value of the switching frequency fsw in the second mode, f5 Is the upper limit value of the switching frequency fsw in the first mode, and f6 is the lower limit value of the switching frequency fsw in the first mode.

  In the present embodiment, unlike the first embodiment, in the first mode, the switching frequency fsw is reduced to a range of 1/2 or less of the resonance frequency fr. First, when the rated power Pmax is input to the power supply device 1, the switching frequency fsw operates at a frequency f2 higher than the resonance frequency fr. Thereafter, the input power Pin is reduced by increasing the switching frequency fsw. When the input power Pin reaches the threshold power Pth, the switching frequency fsw is shifted to f6 that is lower than the resonance frequency fr. At this time, in this embodiment, f6 is set to a range lower than 1/2 of the resonance frequency fr and higher than 1/3 of the resonance frequency fr, that is, 1 / 2fr to 1 / 3fr. Thereafter, the input power Pin is reduced by increasing the switching frequency fsw, and reaches the lower limit input power Pmin when the switching frequency fsw becomes f5.

  FIG. 6B is a conceptual diagram showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In this embodiment, the on-time ratio is fixed at 0.5 regardless of the input power Pin.

  FIG. 7 is a graph showing the relationship between the switching frequency fsw and the input power Pin, together with the resonance characteristics of the resonance circuit 30. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the switching frequency when the rated power is input, and f5 is the first power. The upper limit value of the switching frequency fsw in the mode, and f6 is the lower limit value of the switching frequency fsw in the first mode. In the present embodiment, in the first mode in which the input power is in the range of Pth to Pmax, the switching frequency fsw is in the range of Pth to Pmin, using the slow phase side having the resonance characteristics higher than the resonance frequency fr. In the second mode, the switching frequency fsw is in the range of 1/2 fr to 1/3 fr, that is, the slow phase side in the triple resonance characteristic. Therefore, in this embodiment, when the input power Pin is decreased in both the first mode and the second mode, the switching frequency fsw is increased.

  Also in the present embodiment, similarly to the first embodiment, when the input power Pin is finely adjusted in the vicinity of the threshold power Pth, the switching frequency fsw continuously changes suddenly. In this case, in order to suppress a sudden change in the switching frequency fsw, the adjustment is made between the threshold power for changing from the first mode to the second mode and the threshold power for changing from the second mode to the first mode. It is better to provide sensitivity (hysteresis).

  Next, the relationship between the switching elements Q1, Q2 and the current flowing through the resonance coil Lr will be described with reference to FIG. 8a and 8b show operation waveforms at the operation points 1 and 2 shown in FIGS. 5 and 6, respectively. The switching elements Q1 and Q2 operate to cut off the resonance current by the resonance coil Lr and the resonance capacitors Cr1 and Cr2.

  FIG. 8c shows the operation waveform at the operation point 3 shown in FIGS. 6 and 7, and the operation under the condition that the switching frequency fsw is lowered to f6 lower than the resonance frequency fr while keeping the same input power as the operation point 2. The waveform is shown. Since f6 is lower than half of fr, that is, ½fr, the resonance current flows for one period or more in the switching half cycle of the switching elements Q1 and Q2.

  FIG. 8 d shows an operation waveform at the operation point 4 shown in FIGS. 6 and 7, and shows an operation waveform when the input power is further reduced from the operation point 6. As shown in FIG. 8d, due to the effect of reducing the switching frequency fsw, the current flowing through the resonance coil Lr is reduced, so that the input power is reduced. When the switching frequency fsw reaches f5, the minimum input power Pmin is obtained.

  As described above, in this embodiment, the switching frequency at light load can be further reduced as compared with Embodiment 1, and the efficiency at light load can be further increased.

  Further, by applying the first embodiment and the second embodiment, in the first mode, both the fast phase side and the slow phase side can be used in any resonance part generated by the multiple resonance characteristic of the resonance circuit 30. . That is, in the first mode, the present invention can be applied in any range where the switching frequency fsw is lower than the resonance frequency fr.

  Next, Example 3 will be described. The basic configuration is the same as that of the first embodiment, but in this embodiment, the switching frequency fsw is reduced to a range below the resonance frequency fr in the first mode, and in the first mode, The input power is adjusted by operating the on-time ratio of the switching element in a range lower than 0.5 and operating the other switching element in the range higher than 0.5.

  In this embodiment, the operation when the on-time ratio dutyQ1 of the switching element Q1 is reduced and the on-time ratio dutyQ2 of the switching element Q2 is increased in the first mode will be described.

  The operation of the power supply device 1 in this embodiment will be described with reference to FIGS.

  FIG. 9a is a conceptual diagram showing the relationship between the input power Pin and the switching frequency fsw in the present embodiment. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the switching frequency when the rated power is input, and f7 is the first power. The switching frequency fsw in the mode.

  In the present embodiment, unlike the first embodiment, in the first mode, the switching frequency fsw is reduced to a range below the resonance frequency fr and the operation is performed at the fixed frequency f7. First, when the rated power Pmax is input to the power supply device 1, the switching frequency fsw operates at a frequency f2 higher than the resonance frequency fr. Thereafter, the input power Pin is reduced by increasing the switching frequency fsw. When the input power Pin reaches the threshold power Pth, the switching frequency fsw is shifted to f7 that is lower than the resonance frequency fr. At this time, in this embodiment, in the first mode, the switching frequency fsw is operated as the fixed frequency f7, and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 are changed.

  FIG. 9b is a conceptual diagram showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In the present embodiment, in the second mode in which the input power Pin is Pmax to Pth, the on-time ratio is fixed at 0.5 for both the switching elements Q1 and Q2. In the first mode in which the input power Pin is lower than Pth, the input power Pin is reduced by reducing the on-time ratio dutyQ1 of the switching element Q1 and increasing the on-time ratio dutyQ2 of the switching element Q2, so that the dutyQ1 becomes dutymin. When the duty Q2 reaches the duty max, the lower limit input power Pmin is reached.

  FIG. 10 a is a graph showing the relationship between the switching frequency fsw and the input power Pin, together with the resonance characteristics of the resonance circuit 30. In the figure, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the switching frequency at the rated power output, and f7 is the switching frequency fsw in the first mode. is there. In the present embodiment, in the second mode in which the input power is in the range of Pth to Pmax, the switching frequency fsw is on the slow phase side having a resonance characteristic higher than the resonance frequency fr, and the input power is in the range of Pth to Pmin. In the first mode, the switching frequency fsw is operated at a fixed frequency lower than the resonance frequency fr.

  FIG. 10B is a graph showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In the present embodiment, the duty Q1 is fixed to 0.5 in the second mode in which the input power Pin is Pmax to Pth. In the first mode in which the input power Pin is Pth to Pmin, the duty Q1 is operated in a range lower than 0.5, and the duty Q2 is operated in a range higher than 0.5.

  Also in this embodiment, as in the first and second embodiments, when the input power Pin is finely adjusted in the vicinity of the threshold power Pth, the switching frequency fsw changes continuously and suddenly. In this case, in order to suppress a sudden change in the switching frequency fsw, the adjustment is made between the threshold power for changing from the first mode to the second mode and the threshold power for changing from the second mode to the first mode. It is better to provide sensitivity (hysteresis).

  Next, the relationship between the switching elements Q1, Q2 and the current flowing through the resonance coil Lr will be described with reference to FIG. 11a and 11b show operation waveforms at the operation point 1 and the operation point 2 shown in FIGS. 9 and 10, respectively. The switching elements Q1 and Q2 operate to cut off the resonance current by the resonance coil Lr and the resonance capacitors Cr1 and Cr2.

  FIG. 11c shows the operation waveform at the operation point 3 shown in FIGS. 9 and 10, and the operation under the condition that the switching frequency fsw is lowered to f7 lower than the resonance frequency fr while maintaining the same input power as that of the operation point 2. The waveform is shown. Since f7 is lower than fr, the resonance current flows in the switching half cycle of the switching elements Q1, Q2 for more than a half cycle.

  FIG. 11 d shows an operation waveform at the operation point 4 shown in FIGS. 9 and 10, and shows an operation waveform when the input power is further reduced from the operation point 3. As shown in FIG. 11d, the effective current flowing through the resonance coil Lr is reduced due to the effect of reducing the on-time ratio dutyQ1 of the switching element Q1, so that the input power is reduced. Here, when dutymin is set to 0, when the on-time ratio dutyQ1 of the switching element Q1 becomes 0, the input power also becomes 0.

  As described above, in this embodiment, as in Embodiments 1 and 2, the switching frequency at light load can be reduced while enabling operation in a wide load range, and the efficiency at light load can be reduced. Can be high.

  In the first mode, even when the on-time ratio dutyQ2 of the switching element Q2 is increased and the on-time ratio dutyQ1 of the switching element Q1 is decreased, the effects described in this embodiment can be obtained. In the present invention, when the input power Pin is finely adjusted in the vicinity of Pth, the switching frequency fsw continuously changes suddenly. In this case, the switching is performed by giving a width to Pth and giving a hysteresis characteristic at the switching point. It is possible to suppress a sudden change in the frequency fsw.

    Next, Example 4 will be described. The basic configuration is the same as that of the first embodiment, but in this embodiment, the switching frequency fsw is reduced to a range below the resonance frequency fr in the first mode, and the switching is performed in the first mode. The input power is adjusted by operating the on-time ratios dutyQ1 and dutyQ2 of the elements Q1 and Q2 in a range lower than 0.5.

  The operation of the power supply device 1 according to the present embodiment will be described with reference to FIGS.

  FIG. 12A is a conceptual diagram showing the relationship between the input power Pin and the switching frequency fsw in the present embodiment. In the figure, Pmin is the minimum input power, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the switching frequency at the rated power output, and f8 is the first power. The switching frequency fsw in the mode.

  In the present embodiment, as in the third embodiment, in the first mode, the switching frequency fsw is reduced to a range below the resonance frequency fr and is operated at a fixed frequency. First, when the rated power Pmax is input to the power supply device 1, the switching frequency fsw operates in a range higher than the resonance frequency fr. Thereafter, the input power Pin is reduced by increasing the switching frequency fsw. When the input power Pin reaches the threshold power Pth, the switching frequency fsw is shifted to f8 that is lower than the resonance frequency fr. At this time, in this embodiment, in the first mode, the switching frequency fsw is operated as the fixed frequency f8, and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 are changed.

  FIG. 12B is a conceptual diagram showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In the present embodiment, in the second mode in which the input power Pin is Pmax to Pth, the on-time ratio is fixed at 0.5 for both the switching elements Q1 and Q2. In the first mode in which the input power Pin is lower than Pth, the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 are both reduced, and when the dutyQ1 and dutyQ2 reach the dutymin, the lower limit input power Pmin is reached.

  FIG. 13 a is a graph showing the relationship between the switching frequency fsw and the input power Pin together with the resonance characteristics of the resonance circuit 30. In the figure, Pth is the threshold power, Pmax is the rated input power, f1 is the upper limit value of the switching frequency fsw in the second mode, f2 is the switching frequency at the rated power output, and f8 is the switching frequency fsw in the first mode. is there. In the present embodiment, in the second mode in which the input power is in the range of Pth to Pmax, the switching frequency fsw is on the slow phase side having a resonance characteristic higher than the resonance frequency fr, and the input power is in the range of Pth to Pmin. In the first mode, the switching frequency fsw is operated at a fixed frequency lower than the resonance frequency fr.

  FIG. 13b is a graph showing the relationship between the input power Pin and the on-time ratios dutyQ1 and dutyQ2 of the switching elements Q1 and Q2 in the present embodiment. In the present embodiment, in the second mode in which the input power Pin is Pmax to Pth, the duty Q1 is fixed to 0.5, and in the first mode in which the input power Pin is Pth to Pmin, the duty Q1 and the duty Q2 are set. Both are operated in a range lower than 0.5.

  Also in this embodiment, as in the first to third embodiments, when the input power Pin is finely adjusted in the vicinity of the threshold power Pth, the switching frequency fsw changes continuously and suddenly. In this case, in order to suppress a sudden change in the switching frequency fsw, the adjustment is made between the threshold power for changing from the first mode to the second mode and the threshold power for changing from the second mode to the first mode. It is better to provide sensitivity (hysteresis).

  Next, the relationship between the switching elements Q1, Q2 and the current flowing through the resonance coil Lr will be described with reference to FIG. 14a and 14b show operation waveforms at the operation points 1 and 2 shown in FIGS. 12 and 13, respectively. The switching elements Q1 and Q2 operate to cut off the resonance current caused by the resonance coil Lr and the resonance capacitor Cr.

  FIG. 14c shows the operation waveform at the operation point 3 shown in FIGS. 12 and 13, and the operation under the condition that the switching frequency fsw is lowered to f8 lower than the resonance frequency fr while maintaining the same input power as the operation point 2. The waveform is shown. Since f8 is lower than fr, the resonance current flows in the switching half cycle of the switching elements Q1, Q2 for more than a half cycle.

  FIG. 14 d shows an operation waveform at the operation point 4 shown in FIGS. 12 and 13, and shows an operation waveform when the input power is further reduced from the operation point 3. As shown in FIG. 13d, the effective current flowing through the resonance coil Lr is reduced due to the effect of reducing the on-time ratios duty Q1 and Q2 of the switching elements Q1 and Q2, so that the input power is reduced. When the on-duty ratios Duty Q1 and Q2 of the switching elements Q1 and Q2 are 0, the input power is also 0.

  As described above, in this embodiment, as in Embodiments 1 to 3, the switching frequency at light load can be reduced while enabling operation in a wide load range, and the efficiency at light load can be reduced. Can be high. In the present invention, when the input power Pin is finely adjusted in the vicinity of Pth, the switching frequency fsw continuously changes suddenly. In this case, the switching is performed by giving a width to Pth and giving a hysteresis characteristic at the switching point. It is possible to suppress a sudden change in the frequency fsw.

  FIG. 15 is a circuit configuration diagram of the power supply device 2 according to the fifth embodiment. This power supply device 2 controls the ON / OFF state of the switching element provided in the switching circuit 21, the resonance circuit 31, the rectifier circuit 24, the output power detection means 41 from the rectifier circuit, and the switching circuit that inputs the voltage of the DC power source 10. The control unit 50 and the load 60 are configured to supply power to the load 60 from the DC power supply 10.

  The switching circuit 21 includes a switching leg 22 in which an upper arm switching element Q1 and a lower arm switching element Q2 are connected in series at a node Nd5, and a switching leg 23 in which an upper arm switching element Q3 and a lower arm switching element Q4 are connected in series at a node Nd6. Are connected in parallel, and both ends of the switching legs 21 and 22, that is, between the nodes Nd 1 and Nd 2 are input to the switching circuit 21, and between the nodes Nd 5 and Nd 6 are output to the switching circuit 21. The switching circuit 21 has an advantage that the withstand voltage of the switching element is lower than the switching circuit 20 of the first embodiment.

  The output of the switching circuit 21 is connected to a resonance coil Lr, a winding N1 of a transformer Tr, and a resonance capacitor Cr. Here, the exciting inductance Lm of the transformer Tr is defined in parallel with the winding N1. Here, in the power supply device 2 of the present embodiment, the resonance coil Lr and the resonance capacitor Cr only need to exist between the output of the switching circuit 21 and the smoothing capacitor C1, for example, the resonance coil Lr is connected in series with the winding N2. May be inserted. Further, the leakage inductance of the transformer Tr may be used as the resonance coil Lr.

  A winding N2 magnetically coupled to the winding N1 is connected to an input of a rectifier circuit 24 in which diodes D3 to D6 are bridge-connected, and a smoothing capacitor C1 is connected to an output of the rectifier circuit 24. The load 60 is connected in parallel to the smoothing capacitor C1, and the power supply device 2 outputs the power input from the DC power supply 10 to both ends of the smoothing capacitor C1. An output power detection means 41 is connected to the smoothing capacitor C1, and the power detection means 41 is connected to the control unit 50.

  The power supply device 2 applies a voltage to the winding N1 by the switching elements Q1 to Q4 connected in a full bridge, and applies a voltage generated in the winding N2 to the smoothing capacitor C1 via the diodes D3 to D6. Output to.

  In this switching circuit 21, the switching elements Q1 and Q3 on the upper arm side and the switching elements Q2 and Q4 on the lower arm side perform on / off driving opposite to each other. A circuit operation similar to the on / off drive of the element Q1 and the switching element Q2 can be realized.

  Further, when the on-time ratio shown in the third and fourth embodiments is reduced, a general phase shift method is used in which the phases of the on / off drive of the switching leg 21 and the on / off drive of the switching leg 22 are shifted. Thus, the operation of varying the on-time ratios dutyQ1 and dutyQ2 of Q1 shown in the third and fourth embodiments can be realized.

  As described above, the power supply device of the present invention includes a DC power supply, a switching circuit that converts a DC voltage from the DC power supply into an AC voltage, a control unit that controls the operation of the switching circuit, and a resonance coil Lr. , A resonance circuit including a resonance capacitor Cr, and when the input power Pin to the switching circuit is smaller than a predetermined threshold power Pth, the control unit sets the switching frequency fsw of the switching circuit to the resonance circuit. If the input power Pin to the switching circuit is larger than a predetermined threshold power Pth, the switching frequency fsw of the switching circuit is set to the resonance frequency fr. Control is performed so that the second mode becomes higher. As a result, an increase in the switching frequency at light load can be reduced and high efficiency can be obtained while enabling operation in a wide output power range.

  The present invention can be applied to a wide range of devices that allow a current to flow from a high-frequency switching circuit to a circuit having a resonance element, thereby obtaining an effect. For example, induction heating devices, LED lighting, converters that convert the power of solar cells and fuel cells, power supplies for information devices such as servers, chargers and DC-DC converters for electric vehicles, non-contact power supply devices, power supplies for X-ray tubes It can be widely applied to resonance-type power supply devices using high-frequency inverters, such as power supplies for laser machines and bidirectional converters for battery charging and discharging.

  DESCRIPTION OF SYMBOLS 1, 2 ... Power supply device 20, 21 ... Switching circuit, 22, 23 ... Switching leg, 24 ... Rectifier circuit, 30, 31 ... Resonance circuit, 40, 41 ... Power detection means, 50 ... Control part, 60 ... Load, Q1, Q2, Q3, Q4 ... switching element, D1, D2, D3, D4, D5, D6 ... diode, Lr ... resonant coil, Cr, Cr1, Cr2 ... resonant capacitor, C1 ... smoothing capacitor, Tr ... transformer, Lm ... Excitation inductance, N1, N2 ... winding, Nd1, Nd2, Nd3, Nd4, Nd5, Nd6 ... node.

Claims (9)

A DC power supply, a switching circuit for converting a DC voltage from the DC power supply to an AC voltage, a resonance circuit including a resonance capacitor and a resonance inductor connected between AC terminals of the switching circuit, and controlling the operation of the switching circuit And a control unit for
When the input power to the switching circuit is smaller than a predetermined threshold power, the control unit controls the switching frequency of the switching circuit to be in a first mode lower than the resonance frequency of the resonance circuit. And
When the input power to the switching circuit is larger than a predetermined threshold power, the switching circuit is controlled to be in a second mode in which the switching frequency is higher than the resonance frequency of the resonance circuit. Power supply.   2. The power supply device according to claim 1, wherein the switching circuit includes a first switching leg in which first and second switching elements are connected in series, a first and second resonant capacitor, and the switching circuit. A first resonance capacitor series connection body connected in parallel to the first switching leg, wherein both ends of the first switching leg are between DC terminals, and a series connection point of the first and second switching elements; The power supply device is characterized in that between the first and second resonant capacitors connected in series is between the AC terminals.   2. The power supply device according to claim 1, wherein the switching circuit includes a second switching leg in which third and fourth switching elements are connected in series, and fifth and sixth switching elements in series, and A third switching leg connected in parallel to the second switching leg, wherein both ends of the second switching leg are between the DC terminals, and the third connection point of the third and fourth switching elements and the fifth switching leg A power supply device characterized in that a portion between the series connection points of the sixth switching elements is between AC terminals.   4. The power supply device according to claim 1, wherein the control unit adjusts the output power by adjusting a switching frequency of the switching circuit in the first mode. .   5. The power supply device according to claim 1, wherein the control unit adjusts output power by adjusting an on-time ratio of the switching circuit in the first mode. apparatus.   6. The power supply device according to claim 1, wherein the control unit adjusts output power by adjusting an on time of the switching circuit in the first mode. .   7. The power supply device according to claim 1, further comprising an induction heating coil at an output of the switching circuit. A DC power supply, a switching circuit that converts a DC voltage from the DC power supply to an AC voltage, a primary winding connected to the output of the switching circuit, and the primary and secondary windings are magnetically coupled. A transformer, a rectifier circuit for rectifying the current of the secondary winding, a resonant capacitor and a resonant inductor connected in series between the output of the switching circuit and the input of the rectifier circuit, A control unit for controlling the operation,
When the output power from the power supply device is smaller than a predetermined threshold power, the control unit controls the switching frequency of the switching circuit to be in a first mode lower than the resonance frequency of the resonance circuit. And
When the output power from the power supply device is larger than a predetermined threshold power, control is performed so that the switching mode of the switching circuit becomes a second mode in which the switching frequency is higher than the resonance frequency of the resonance circuit. Power supply. A DC power supply, a switching circuit for converting a DC voltage from the DC power supply to an AC voltage, a resonance circuit including a resonance capacitor and a resonance inductor connected between AC terminals of the switching circuit, and controlling the operation of the switching circuit And a control unit for
The control unit controls the input voltage using both a first mode in which the input voltage is decreased by decreasing the switching frequency fsw and a second mode in which the input voltage is decreased by increasing the switching frequency fsw. A power supply device characterized by that.

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