Power supply device

Abstract

To realize a power supply device that can achieve a large input / output voltage range and a lower loss.SOLUTION: When second DC voltage is higher than a predetermined threshold value Vth1, and the second DC voltage is lower than a predetermined threshold value Vth2 larger than the threshold value Vth1, a control circuit 12 controls a DC-DC converter 10 in a resonant frequency mode which maintains a switching frequency of a full-bridge circuit 101 in the vicinity of a resonant frequency of a resonance circuit 102. Further, when the second DC voltage is lower than the predetermined threshold value Vth1, or the second DC voltage is higher than the predetermined threshold value Vth2, the control circuit 12 controls the DC-DC converter 10 in a frequency modulation mode which changes the switching frequency accompanying a change of the second DC voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a power supply device.

Background Art

[0002] With the recent trend of automotive electrification, in-vehicle chargers with high-power output that can be charged in a short time have been developed. The voltage of a lithium-ion battery, which is the energy storage battery of an EV, varies greatly depending on the state of charge, and low loss in a wide output range is desired. In these charging devices, DC-DC converters capable of converting DC power with different voltages are widely used. In addition, as a countermeasure against power outages caused by disasters and for power smoothing, the view of treating the energy storage battery of an EV as an energy source for homes and building facilities has also attracted attention, and the demand for devices that can convert power bidirectionally is increasing. In this case, the above DC-DC converter is required to have the feature of being able to convert power bidirectionally.

[0003] Regarding a bidirectional DC-DC converter, for example, the technology of Patent Document 1 is known. Patent Document 1 discloses a technology in a resonant type DC-DC converter that utilizes the resonance phenomenon of an LC resonance circuit. When supplying power from one DC voltage source to the other DC voltage source, the bridge circuit on the side of one DC voltage source is pulse frequency modulation controlled at a frequency below the resonance frequency of the resonance circuit, and when supplying power in the opposite direction, the bridge circuit on the side of the other DC voltage source is fixed frequency controlled.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the resonant type DC-DC converter described in Patent Document 1, it is difficult to achieve both a wide input / output voltage range and low loss. [Means for solving the problem]

[0006] The power supply device according to the present invention comprises a resonant DC-DC converter that converts voltage between a first DC voltage and a second DC voltage, and a control circuit that controls the DC-DC converter, wherein the DC-DC converter has a switching circuit and a resonant circuit, and the control circuit controls the DC-DC converter in a resonant frequency mode that maintains the switching frequency of the switching circuit near the resonant frequency of the resonant circuit when the second DC voltage is higher than a predetermined first threshold and the second DC voltage is lower than a predetermined second threshold which is higher than the first threshold, and the control circuit controls the DC-DC converter in a frequency modulation mode that changes the switching frequency in accordance with the change in the second DC voltage when the second DC voltage is lower than the first threshold or when the second DC voltage is higher than the second threshold. [Effects of the Invention]

[0007] According to the present invention, a power supply device that can achieve both a wide input / output voltage range and low power loss can be realized. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the configuration of a power supply device according to the first embodiment of the present invention. [Figure 2] This diagram illustrates the operation of a power supply device according to the first embodiment of the present invention. [Figure 3] This is an explanatory diagram of the effect of phase shift control. [Figure 4] This figure shows the configuration of a power supply device according to a second embodiment of the present invention. [Figure 5] This diagram illustrates the operation of a power supply device according to a second embodiment of the present invention. [Figure 6] This figure shows the configuration of a power supply device according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0009] -First Embodiment- Figure 1 is a diagram showing the configuration of a power supply device according to the first embodiment of the present invention. The power supply device 1 shown in Figure 1 receives AC power supplied from an AC power source 2 via a power supply line 3, generates DC power, and outputs it to a load 4, thereby supplying DC power to the load 4. The AC power supplied from the AC power source 2 may be single-phase or three-phase, and the voltage is not limited.

[0010] Power supply unit 1 comprises a resonant DC-DC converter 10, a voltage sensor 11, a control circuit 12, a current sensor 13, an AC-DC converter 14, a voltage sensor 15, a voltage sensor 16, and a current sensor 17. The load 4 that receives DC power from power supply unit 1 could be, for example, a secondary battery such as a lithium-ion battery or a lead-acid battery, or an inverter circuit that converts DC power to AC power.

[0011] The AC-DC converter 14 converts the AC voltage input from the AC power supply 2 into a DC voltage and outputs the converted DC voltage to the DC-DC converter 10. The magnitude of the AC voltage and AC current input from the AC power supply 2 to the AC-DC converter 14 are detected by the voltage sensor 11 and the current sensor 13, respectively, and sensor signals corresponding to the detection results of these sensors are transmitted to the control circuit 12. The voltage sensor 15 detects the magnitude of the DC voltage output from the AC-DC converter 14 and transmits a sensor signal corresponding to the detection result to the control circuit 12.

[0012] The DC-DC converter 10 converts the DC voltage output from the AC-DC converter 14 to another DC voltage and outputs the DC power after voltage conversion to the load 4. The DC-DC converter 10 comprises a full-bridge circuit 101 which is composed of a combination of capacitor C1 and switching elements Q1 to Q4 and operates as a switching circuit, a resonant circuit 102 composed of a resonant capacitor Cr1 and a resonant reactor Lr1, an isolation transformer 103 having a primary winding N1, a secondary winding N2 and an excitation inductance Lm1, a rectifier circuit 104 having diodes D1 and D2, and a capacitor C2.

[0013] Capacitor C1 smooths the DC voltage input to the DC-DC converter 10. The full-bridge circuit 101 has two switching legs, each consisting of switching elements Q1 and Q2, and switching elements Q3 and Q4 connected in series. The DC voltage input to the DC-DC converter 10 is applied across these switching legs. In this state, switching elements Q1 to Q4 switch at predetermined timings according to the control circuit 12, converting the DC voltage into an AC voltage, which is then output to the resonant circuit 102. Semiconductor elements such as MOSFETs and IGBTs are used for the switching elements Q1 to Q4.

[0014] The resonant circuit 102 is connected between the full-bridge circuit 101 and the isolation transformer 103, and has a predetermined resonant frequency determined according to the capacitance value of the resonant capacitor Cr1 and the inductance value of the resonant reactor Lr1. In the power supply device 1 of this embodiment, the resonant phenomenon by this resonant circuit 102 is utilized to improve the efficiency of the DC-DC converter 10.

[0015] The isolation transformer 103 performs voltage conversion on the AC voltage input to the primary winding N1 from the full-bridge circuit 101 via the resonance circuit 102 to another AC voltage at a voltage ratio corresponding to the turns ratio of the primary winding N1 and the secondary winding N2, and outputs it to the rectifier circuit 104. The center-tapped rectifier circuit 104 has diodes D1 and D2 connected to both ends of the secondary winding N2 respectively, and generates a DC voltage by rectifying the AC voltage output to the secondary winding N2 side of the isolation transformer 103 and outputs it to the load 4. The capacitor C2 smoothes the DC voltage output from the rectifier circuit 104 to the load 4. Thereby, a DC voltage is output from the DC-DC converter 10 to the load 4, and the DC power supply is supplied from the power supply device 1 to the load 4.

[0016] Note that the magnitudes of the DC voltage and DC current output from the DC-DC converter 10 to the load 4 are respectively detected by the voltage sensor 16 and the current sensor 17, and sensor signals corresponding to the detection results of these sensors are transmitted to the control circuit 12.

[0017] The control circuit 12 receives the sensor signals respectively transmitted from each of the sensors including the voltage sensor 11 and the current sensor 13 provided on the AC power supply 2 side, the voltage sensor 15 provided between the AC-DC converter 14 and the DC-DC converter 10, and the voltage sensor 16 and the current sensor 17 provided on the load 4 side, thereby obtaining the detection results of the voltage and current by these sensors. Then, based on the detection results of the obtained voltages and currents, the AC-DC converter 14 and the DC-DC converter 10 are controlled.

[0018] -Operation of the First Embodiment- FIG. 2 is a diagram showing the operation of the power supply device according to the first embodiment of the present invention. Hereinafter, an operation example in the case where the load 4 is a secondary battery and the power supply device 1 charges the load 4 using the power of the AC power supply 2 will be described with reference to FIG. 2.

[0019] In FIG. 2, graph 21 represents the output voltage of the AC-DC converter 14 (hereinafter referred to as the "first DC voltage"), graph 22 represents the switching frequency of the full-bridge circuit 101 in the DC-DC converter 10, and graph 23 represents the change in the phase shift amount of the full-bridge circuit 101. In these graphs 21 to 23, the horizontal axis represents the magnitude of the output voltage from the DC-DC converter 10 to the load 4 (hereinafter referred to as the "second DC voltage"), and the vertical axis represents the magnitude of the physical quantity corresponding to each graph (the first DC voltage, the switching frequency, the phase shift amount).

[0020] First, the control circuit 12 sets a function corresponding to graph 21 as a command value for the AC-DC converter 14. This function represents the relationship between the first DC voltage and the second DC voltage, that is, how the output voltage of the AC-DC converter 14 should be set with respect to the output voltage of the DC-DC converter 10 detected by the voltage sensor 16. Thereby, the control circuit 12 can control the AC-DC converter 14 according to graph 21 based on the second DC voltage detected by the voltage sensor 16.

[0021] Then, the control circuit 12 sets the switching frequency of the full-bridge circuit 101 based on the charging voltage (second DC voltage) and charging current of the load 4 detected by the voltage sensor 16 and the current sensor 17 respectively, and the charging command value for the load 4, and controls the switching elements Q1 to Q4 according to this switching frequency. At this time, any one of, for example, a current command, a voltage command, and a power command can be used as the charging command value. Thereby, the control circuit 12 can control the full-bridge circuit 101 according to graph 22 based on the second DC voltage detected by the voltage sensor 16 and change the switching frequency.

[0022] The control circuit 12 compares the value of the second DC voltage detected by the voltage sensor 16 with preset threshold values Vth1 and Vth2 (Vth1 < Vth2), and changes the switching frequency as shown in the graph 22 of FIG. 2 according to the comparison result. That is, when the second DC voltage is higher than the threshold value Vth1 and lower than the threshold value Vth2, the control of the full-bridge circuit 101 in the DC-DC converter 10 is performed so as to maintain the switching frequency near the resonance frequency of the resonance circuit 102. Hereinafter, such a control mode is referred to as a "resonance frequency mode".

[0023] On the other hand, when the second DC voltage is lower than the threshold value Vth1 or higher than the threshold value Vth2, the control of the full-bridge circuit 101 in the DC-DC converter 10 is performed so as to change the switching frequency in accordance with the change in the second DC voltage. Specifically, when the second DC voltage is lower than the threshold value Vth1, the full-bridge circuit 101 in the DC-DC converter 10 is controlled so that as the second DC voltage rises, the switching frequency higher than the resonance frequency changes toward the resonance frequency. Also, when the second DC voltage is higher than the threshold value Vth2, the full-bridge circuit 101 in the DC-DC converter 10 is controlled so that as the second DC voltage rises, the switching frequency lower than the resonance frequency changes away from the resonance frequency. Hereinafter, such a control mode is referred to as a "frequency modulation mode".

[0024] In the power supply device 1 of the present embodiment, by performing the control as described above, the DC-DC converter 10 can perform voltage conversion from the first DC voltage to the second DC voltage in a wide input-output voltage range, and can reduce losses by using the resonance frequency mode within the possible voltage range. Therefore, it is possible to achieve both a wide input-output voltage range and low loss. Also, since the frequency range of the AC voltage applied to the isolation transformer 103 can be narrowed, it is possible to reduce the size of the isolation transformer 103.

[0025] Furthermore, if the switching frequency of the full-bridge circuit 101 is higher than the resonant frequency, that is, if the second DC voltage is lower than the threshold Vth1, the control circuit 12 performs phase shift control on the full-bridge circuit 101. Phase shift control is the process of controlling the switching operation of each switching element Q1 to Q4 of the full-bridge circuit 101 by shifting the switching timing of the two switching legs of the full-bridge circuit 101 so that a phase difference is created between their respective switching timings.

[0026] In controlling the full-bridge circuit 101, the control circuit 12 controls the switching operation of switching elements Q1 to Q4 so that switching elements Q1 and Q4 and switching elements Q2 and Q3 alternately turn ON / OFF at a switching frequency determined from the second DC voltage according to graph 22. In this process, to prevent both switching elements from being ON at the same time in each switching leg, the control circuit ensures that for any two switching elements on the same leg, one is always turned OFF before the other is turned ON.

[0027] When phase shift control is not performed, the control circuit 12 controls the switching operation of switching elements Q1 to Q4 so that the switching timings of switching elements Q1 and Q4 and the switching timings of switching elements Q2 and Q3 match. On the other hand, when phase shift control is performed, the control circuit 12 controls the switching operation of switching elements Q1 to Q4 so that the switching timings of switching elements Q1 and Q4 and the switching timings of switching elements Q2 and Q3 are shifted by the same amount of phase shift for each combination.

[0028] When performing the above-described phase shift control, the control circuit 12 changes the amount of phase shift according to the magnitude of the second DC voltage. Specifically, as shown in Graph 23, the control circuit 12 adjusts the amount of phase shift so that the phase shift is larger when the second DC voltage is low and farther from the threshold Vth1. For example, the relationship between the switching frequency and the amount of phase shift, which is determined according to the second DC voltage, can be pre-implemented in the control circuit 12 using a function or table, and the amount of phase shift can be adjusted according to Graph 23 using this. Alternatively, the amount of phase shift may be adjusted based on the output voltage (second DC voltage) or output power of the DC-DC converter 10 instead of the switching frequency.

[0029] As shown in Graph 22, when the switching frequency reaches a predetermined upper limit frequency in frequency modulation mode, the control circuit 12 performs phase shift control to change the phase shift amount while fixing the switching frequency at this upper limit frequency. This allows the output voltage (second DC voltage) of the DC-DC converter 10 to be controlled by changing the phase shift amount, even when there is an upper limit to the switching frequency.

[0030] -Phase Shift- Figure 3 is an explanatory diagram of the effect of phase shift control. In Figure 3, graph 31 represents the current flowing through the resonant reactor Lr1, and graph 32 represents the current flowing through the excitation inductance Lm1. Without phase shift control, as shown in the left diagram of Figure 3, the switching signal for switching element Q1 and the switching signal for switching element Q4 repeatedly turn ON / OFF at the same timing. On the other hand, with phase shift control, as shown in the right diagram of Figure 3, the switching signal for switching element Q1 and the switching signal for switching element Q4 repeatedly turn ON / OFF at timings shifted by the amount of phase shift. The amount of phase shift at this time is determined so that when the delay-side switching element (switching element Q4 in Figure 3) turns off, the current value of the resonant reactor Lr1 shown in graph 31 and the current value of the excitation inductance Lm1 shown in graph 32 overlap with each other. As a result, the cutoff current in the delay-side switching element can be significantly reduced compared to the case without phase shift control. Therefore, it becomes possible to reduce losses due to the switching operation of the full-bridge circuit 101.

[0031] As explained above, by performing phase shift control, losses due to the switching operation of the full-bridge circuit 101 can be reduced, and the DC-DC converter 10 can be operated with high efficiency. The above-mentioned phase shift amount corresponds to the phase shift amount adjusted according to graph 23 in Figure 2, and as mentioned above, this can be achieved using functions or tables that are pre-implemented in the control circuit 12.

[0032] According to the first embodiment of the present invention described above, the following effects are achieved.

[0033] (1) The power supply unit 1 comprises a resonant DC-DC converter 10 that converts voltage between a first DC voltage and a second DC voltage, and a control circuit 12 that controls the DC-DC converter 10. The DC-DC converter 10 has a full-bridge circuit 101 and a resonant circuit 102, which are switching circuits. When the second DC voltage is higher than a predetermined threshold Vth1 and lower than a predetermined threshold Vth2 which is greater than threshold Vth1, the control circuit 12 controls the DC-DC converter 10 in a resonant frequency mode that maintains the switching frequency of the full-bridge circuit 101 near the resonant frequency of the resonant circuit 102. Furthermore, when the second DC voltage is lower than threshold Vth1, or when the second DC voltage is higher than threshold Vth2, the control circuit 12 controls the DC-DC converter 10 in a frequency modulation mode that changes the switching frequency in accordance with the change in the second DC voltage. In this way, a power supply unit 1 that can achieve both a wide input / output voltage range and low loss can be realized.

[0034] (2) The power supply unit 1 further includes an AC-DC converter 14 that converts an AC voltage to a first DC voltage. In the case of the resonant frequency mode, the control circuit 12 controls the AC-DC converter 14 to increase the first DC voltage in accordance with the increase in the second DC voltage, according to the graph 21 in Figure 2. In this way, a wide input / output voltage range can be achieved in the power supply unit 1 that supplies DC power from AC power.

[0035] (3) The switching circuit includes a full-bridge circuit 101 having two switching legs connected to a first DC voltage. When the switching frequency in frequency modulation mode is higher than the resonant frequency, the control circuit 12 performs phase shift control on the switching circuit so that a phase difference is created between the switching timing of one switching leg and the switching timing of the other switching leg. In this way, losses due to the switching operation of the full-bridge circuit 101 can be reduced.

[0036] (4) When the switching frequency reaches a predetermined upper limit frequency in frequency modulation mode, the control circuit 12 performs phase shift control while fixing the switching frequency to the upper limit frequency. In this way, even if there is an upper limit to the switching frequency due to the characteristics of the switching element, the output voltage of the DC-DC converter 10 can be controlled by changing the amount of phase shift.

[0037] (5) When the control circuit 12 supplies power from the first DC voltage to the second DC voltage, if the second DC voltage is lower than the threshold Vth1, it controls the DC-DC converter 10 so that the switching frequency higher than the resonant frequency changes toward the resonant frequency as the second DC voltage rises. Also, if the second DC voltage is higher than the threshold Vth2, it controls the DC-DC converter 10 so that the switching frequency lower than the resonant frequency changes away from the resonant frequency as the second DC voltage rises. In this way, the power supply device 1 that supplies power from the first DC voltage to the second DC voltage to charge a load such as a secondary battery can appropriately control the DC-DC converter 10 in accordance with voltage fluctuations of the load.

[0038] -Second Embodiment- Figure 4 shows the configuration of a power supply device according to a second embodiment of the present invention. The power supply device 1A shown in Figure 4 differs from the power supply device 1 shown in Figure 1, which was described in the first embodiment, in that it has a bidirectional DC-DC converter 10A instead of the DC-DC converter 10. The DC-DC converter 10A has a secondary resonant circuit 105 and a secondary full-bridge circuit 106 instead of a rectifier circuit 104. The power supply device 1A of this embodiment will be described below, focusing on the differences from the first embodiment.

[0039] The secondary full-bridge circuit 106, like the full-bridge circuit 101, has two switching legs in which switching elements Q5 and Q6, and switching elements Q7 and Q8, are connected in series. In these switching legs, switching elements Q5 to Q8 perform switching operations at predetermined timings in accordance with the control circuit 12, thereby converting the DC voltage applied from the load 4 into an AC voltage, which is output to the secondary resonant circuit 105. Semiconductor elements such as MOSFETs and IGBTs are used for the switching elements Q5 to Q8.

[0040] The secondary resonant circuit 105 is connected between the secondary full-bridge circuit 106 and the isolation transformer 103, and has a predetermined resonant frequency determined according to the capacitance value of the resonant capacitor Cr2 and the inductance value of the resonant reactor Lr2.

[0041] In this embodiment, the isolation transformer 103 performs voltage conversion from the primary winding N1 to the secondary winding N2, as described in the first embodiment, as well as voltage conversion from the secondary winding N2 to the primary winding N1. That is, it converts the AC voltage input to the secondary winding N2 from the secondary full-bridge circuit 106 via the secondary resonant circuit 105 to another AC voltage at a voltage ratio corresponding to the turns ratio of the primary winding N1 and the secondary winding N2, and outputs it to the full-bridge circuit 101 via the resonant circuit 102.

[0042] The full-bridge circuit 101 generates a DC voltage by rectifying the AC voltage output to the primary winding N1 side of the isolation transformer 103 and outputs it to the AC-DC converter 14. In this embodiment, the AC-DC converter 14 is capable of inverter operation and converts the DC voltage generated by the full-bridge circuit 101 into a predetermined AC voltage and outputs it to the AC power supply 2 side. This makes it possible to realize a power supply device 1A as a bidirectional charger that can supply power from the AC power supply 2 to the load 4, as well as supply power from the load 4 to the AC power supply 2 using the load 4 as a DC power supply.

[0043] The control circuit 12 controls the switching operation of the full-bridge circuit 101 or the secondary full-bridge circuit 106 according to the power supply direction of the power supply unit 1A. Specifically, when power is supplied from the AC power supply 2 to the load 4, the switching elements Q1 to Q4 of the full-bridge circuit 101 are controlled based on the sensor signals transmitted from the voltage sensor 11 and current sensor 13, the voltage sensor 15, and the voltage sensor 16 and current sensor 17, respectively, as described in the first embodiment. On the other hand, when power is supplied from the load 4 to the AC power supply 2, the switching elements Q5 to Q8 of the secondary full-bridge circuit 106 are controlled based on the sensor signals transmitted from each of these sensors, respectively.

[0044] -Operation of the second embodiment- Figure 5 is a diagram illustrating the operation of a power supply device according to a second embodiment of the present invention. Figure 5 shows an example of operation when power is supplied from load 4 to AC power supply 2 in power supply device 1A of Figure 4. Below, an example of operation when load 4 is a secondary battery and power supply device 1A uses the power of load 4 to supply power to AC power supply 2 will be explained with reference to Figure 5. Note that the operation when charging load 4 using the power of AC power supply 2 is the same as that described in Figure 2 in the first embodiment, so the explanation will be omitted below.

[0045] In Figure 5, Graph 51 shows the input voltage (first DC voltage) of the AC-DC converter 14, Graph 52 shows the switching frequency of the secondary full-bridge circuit 106 in the DC-DC converter 10A, and Graph 53 shows the change in the phase shift amount of the secondary full-bridge circuit 106. In these graphs 51 to 53, the horizontal axis represents the magnitude of the input voltage (second DC voltage) from the load 4 to the DC-DC converter 10A, and the vertical axis represents the magnitude of the physical quantity corresponding to each graph (first DC voltage, switching frequency, and phase shift amount).

[0046] First, the control circuit 12 sets a function corresponding to the graph 51 as the DC voltage command value for the DC-DC converter 10A. This function represents the relationship between the first DC voltage and the second DC voltage. Then, based on the set DC voltage command value and the DC voltages (the first and second DC voltages) detected by the voltage sensors 15 and 16 respectively, the control circuit 12 sets the switching frequency of the secondary full-bridge circuit 106 and controls the switching elements Q5 to Q8 according to this switching frequency. Thereby, the control circuit 12 can control the secondary full-bridge circuit 106 according to the graphs 51 and 52 and change the switching frequency.

[0047] The control circuit 12 compares the value of the second DC voltage detected by the voltage sensor 16 with the preset threshold values Vth1 and Vth2 (Vth1 < Vth2), and changes the switching frequency as shown in the graph 52 of FIG. 5 according to the comparison result. That is, when the second DC voltage is higher than the threshold value Vth1 and the second DC voltage is lower than the threshold value Vth2, the DC-DC converter 10A is set to the resonance frequency mode, and the control of the secondary full-bridge circuit 106 in the DC-DC converter 10A is performed so as to maintain the switching frequency near the resonance frequency of the secondary resonance circuit 105.

[0048] On the other hand, if the second DC voltage is higher than threshold Vth2, or if the second DC voltage is lower than threshold Vth1, the DC-DC converter 10A is set to frequency modulation mode, and the secondary full-bridge circuit 106 in the DC-DC converter 10A is controlled to change the switching frequency in accordance with the change in the second DC voltage. Specifically, if the second DC voltage is higher than threshold Vth2, the secondary full-bridge circuit 106 in the DC-DC converter 10A is controlled so that the switching frequency, which is higher than the resonant frequency, changes toward the resonant frequency as the second DC voltage decreases. Also, if the second DC voltage is lower than threshold Vth1, the secondary full-bridge circuit 106 in the DC-DC converter 10A is controlled so that the switching frequency, which is lower than the resonant frequency, changes toward the resonant frequency as the second DC voltage decreases.

[0049] In the power supply unit 1A of this embodiment, by performing the control described above, the DC-DC converter 10A can perform not only voltage conversion from the first DC voltage to the second DC voltage, but also voltage conversion from the second DC voltage to the first DC voltage, over a wide input / output voltage range, while utilizing the resonant frequency mode within the possible voltage range to reduce losses. Therefore, it is possible to achieve both a wide input / output voltage range and low losses.

[0050] Furthermore, if the switching frequency of the secondary full-bridge circuit 106 is higher than the resonant frequency, that is, if the second DC voltage is higher than the threshold Vth2, the control circuit 12 performs phase shift control on the secondary full-bridge circuit 106. In other words, it shifts the switching timing of the two switching legs of the secondary full-bridge circuit 106, controlling the switching operation of each switching element Q5 to Q8 of the secondary full-bridge circuit 106 so that a phase difference is created between their respective switching timings.

[0051] In controlling the secondary full-bridge circuit 106, the control circuit 12 controls the switching operation of switching elements Q5 to Q8 so that switching elements Q5 and Q8 and switching elements Q6 and Q7 alternately turn ON / OFF at a switching frequency determined from the second DC voltage according to graph 52. In this process, to prevent both switching elements from being ON at the same time in each switching leg, the control circuit ensures that one switching element on the same leg is always turned OFF before the other is turned ON.

[0052] When phase shift control is not performed, the control circuit 12 controls the switching operation of switching elements Q5 to Q8 so that the switching timings of switching elements Q5 and Q8 and the switching timings of switching elements Q6 and Q7 match. On the other hand, when phase shift control is performed, the control circuit 12 controls the switching operation of switching elements Q5 to Q8 so that the switching timings of switching elements Q5 and Q8 and the switching timings of switching elements Q6 and Q7 are shifted by the same amount of phase shift for each combination.

[0053] When the control circuit 12 performs the above-described phase shift control, it changes the amount of phase shift according to the magnitude of the second DC voltage, similar to the first embodiment. Specifically, as shown in Graph 53, the control circuit 12 adjusts the amount of phase shift so that the amount of phase shift increases as the second DC voltage is higher and further away from the threshold Vth2. For example, the relationship between the switching frequency and the amount of phase shift, which is determined according to the second DC voltage, can be pre-implemented in the control circuit 12 using a function or table, and the amount of phase shift can be adjusted according to Graph 53 using this. Alternatively, the amount of phase shift may be adjusted based on the output voltage (first DC voltage) or output power of the DC-DC converter 10A, rather than the switching frequency.

[0054] According to the second embodiment of the present invention described above, when supplying power from a second DC voltage to a first DC voltage, the control circuit 12 controls the DC-DC converter 10A so that, when the second DC voltage is higher than the threshold Vth2, the switching frequency higher than the resonant frequency changes toward the resonant frequency as the second DC voltage decreases. Also, when the second DC voltage is lower than the threshold Vth1, the control circuit 12 controls the DC-DC converter 10A so that, as the second DC voltage decreases, the switching frequency lower than the resonant frequency changes away from the resonant frequency. In this way, in a power supply device 1A that supplies power from a DC power source to an AC power source by supplying power from a second DC voltage to a first DC voltage, the DC-DC converter 10A can be appropriately controlled in accordance with the voltage fluctuations of the DC power source.

[0055] -Third Embodiment- Figure 6 shows the configuration of a power supply device according to a third embodiment of the present invention. The power supply device 1B shown in Figure 6 differs from the power supply device 1 shown in Figure 1, which was described in the first embodiment, in that it has a DC-DC converter 10B instead of a DC-DC converter 10. The DC-DC converter 10B further includes a voltage sensor 18, a capacitor C3, and a chopper 19, which are inserted between the rectifier circuit 104 and the load 4. The power supply device 1B of this embodiment will be described below, focusing on the differences from the first embodiment.

[0056] The chopper 19 converts the DC voltage generated by the rectifier circuit 104 and smoothed by the capacitor C3 (hereinafter referred to as the "third DC voltage" in this embodiment) into a second DC voltage, which is the output voltage to the load 4, and outputs it to the load 4. In other words, in this embodiment, the chopper 19, which is provided between the rectifier circuit 104 and the second DC voltage, converts the third DC voltage into the second DC voltage and outputs it to the load 4. The voltage sensor 18 detects the magnitude of the third DC voltage and transmits a sensor signal corresponding to the detection result to the control circuit 12.

[0057] In this embodiment, in the case of the resonant frequency mode, the control circuit 12 controls the chopper 19 in addition to controlling the AC-DC converter 14 and switching elements Q1 to Q4 as described in the first embodiment. Specifically, based on the sensor signals transmitted from the voltage sensors 15 and 18, the control circuit 12 controls the chopper 19 so that the ratio of the input voltage of the chopper 19 (third DC voltage) to the first DC voltage remains constant. This allows the DC-DC converter 10B to be operated with the switching frequency fixed at the resonant frequency.

[0058] According to the third embodiment of the present invention described above, the DC-DC converter 10B includes an isolation transformer 103 that converts an AC voltage generated by a switching circuit based on a first DC voltage to another AC voltage at a predetermined voltage ratio, a rectifier circuit 104 that rectifies the AC voltage generated by the voltage conversion of the isolation transformer 103 to generate a third DC voltage, and a chopper 19 provided between the rectifier circuit 104 and the second DC voltage, which converts the third DC voltage to the second DC voltage. In the case of the resonant frequency mode, the control circuit 12 controls the chopper 19 so that the ratio of the third DC voltage to the first DC voltage remains constant. In this way, the resonant frequency mode can be applied over a wide voltage range, and high efficiency can be achieved.

[0059] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, each of the embodiments described above is described in detail for the purpose of clearly illustrating the present invention, and is not necessarily limited to having all of the described configurations. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. In addition, each of the above configurations, functions, processing units, processing means, etc. may be implemented in hardware, in whole or in part, for example, by designing them as integrated circuits. Furthermore, each of the above configurations, functions, etc. may be implemented in software by having a processor interpret and execute a program that implements each function. Information such as programs, tables, files that implement each function can be stored in memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0060] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0061] 1,1A,1B: Power supply unit, 2: AC power supply, 3: Power supply line, 4: Load, 10,10A,10B: DC-DC converter, 11: Voltage sensor, 12: Control circuit, 13: Current sensor, 14: AC-DC converter, 15: Voltage sensor, 16: Voltage sensor, 17: Current sensor, 18: Voltage sensor, 19: Chopper, 101: Full bridge circuit, 102: Resonant circuit, 103: Isolation transformer, 104: Rectifier circuit, 105: Secondary side resonant circuit, 106: Secondary side full bridge circuit

Claims

1. The system comprises a resonant DC-DC converter that converts voltage between a first DC voltage and a second DC voltage, and a control circuit that controls the DC-DC converter. The DC-DC converter has a switching circuit and a resonant circuit, The control circuit controls the DC-DC converter in a resonant frequency mode that maintains the switching frequency of the switching circuit near the resonant frequency of the resonant circuit when the second DC voltage is higher than a predetermined first threshold and the second DC voltage is lower than a predetermined second threshold that is greater than the first threshold. The control circuit is a power supply that controls the DC-DC converter in a frequency modulation mode that changes the switching frequency in accordance with the change in the second DC voltage when the second DC voltage is lower than the first threshold or when the second DC voltage is higher than the second threshold.

2. In the power supply device according to claim 1, The system further includes an AC-DC converter that converts an AC voltage to the first DC voltage, The control circuit is a power supply device that controls the AC-DC converter to increase the first DC voltage in accordance with the increase in the second DC voltage in the resonant frequency mode.

3. In the power supply device according to claim 1, The DC-DC converter includes a transformer that converts an AC voltage generated by the switching circuit based on the first DC voltage into another AC voltage at a predetermined voltage ratio, a rectifier circuit that rectifies the other AC voltage to generate a third DC voltage, and a chopper provided between the rectifier circuit and the second DC voltage, which converts the third DC voltage into the second DC voltage. The control circuit is a power supply device that controls the chopper such that the ratio of the third DC voltage to the first DC voltage remains constant in the resonant frequency mode.

4. In the power supply device according to claim 1, The switching circuit includes a full-bridge circuit connected to the first DC voltage and having a first switching leg and a second switching leg. The control circuit is a power supply device that, when the switching frequency is higher than the resonant frequency in the frequency modulation mode, performs phase shift control on the switching circuit so that a phase difference is created between the switching timing of the first switching leg and the switching timing of the second switching leg.

5. In the power supply device according to claim 4, The control circuit is a power supply device that, in the frequency modulation mode, performs the phase shift control while fixing the switching frequency to the upper limit frequency when the switching frequency reaches a predetermined upper limit frequency.

6. In the power supply device according to claim 1, When the control circuit supplies power from the first DC voltage to the second DC voltage, If the second DC voltage is lower than the first threshold, the DC-DC converter is controlled so that the switching frequency, which is higher than the resonant frequency, changes toward the resonant frequency as the second DC voltage increases. A power supply device that controls the DC-DC converter such that, when the second DC voltage is higher than the second threshold, the switching frequency, which is lower than the resonant frequency, changes away from the resonant frequency as the second DC voltage increases.

7. In the power supply device according to claim 1, When the control circuit supplies power from the second DC voltage to the first DC voltage, If the second DC voltage is higher than the second threshold, the DC-DC converter is controlled so that the switching frequency, which is higher than the resonant frequency, changes toward the resonant frequency as the second DC voltage decreases. A power supply device that controls the DC-DC converter such that, when the second DC voltage is lower than the first threshold voltage, the switching frequency, which is lower than the resonant frequency, changes away from the resonant frequency as the second DC voltage decreases.

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