Power converter

Abstract

This invention provides a power converter that enables smooth charging and discharging of a DC blocking capacitor near zero crossing. [Solution] A power converter comprising a circuit including a leg in which a high-side switching element and a low-side switching element are connected in series, a buffer capacitor connected between both ends of the leg, and one or more capacitors connected to the midpoint of the leg via an inductor, the one end not connected to the inductor being connected to either the upper or lower terminal of the leg, which controls the voltage of the capacitor by utilizing the resonance state between the combined capacitance of the buffer capacitor and the capacitors and the reactance of the inductor.

Description

Technical Field

[0001] The present invention relates to a power converter.

Background Art

[0002] As shown in FIG. 9, a power converter that enables power exchange between an AC power supply on the primary side and a DC power supply on the secondary side is known.

[0003] In a configuration that does not use a single synchronous rectifier, as shown in FIG. 10, the on-time (duty ratio) of the upper and lower switching elements of the legs on the primary side and the secondary side is reversed depending on the sign of the input voltage V in . Therefore, as shown in FIG. 11, a sudden change in the duty ratio occurs near the timing when the sign inversion of the input voltage V in occurs (hereinafter referred to as near the zero crossing).

[0004] Here, the voltages V b1 , C b2 of the DC blocking capacitors C cb1 , V cb2 are the product of the output voltage V out and the duty ratio D (or 1 - D), and near the zero crossing, the voltages V b1 , C b2 of the DC blocking capacitors C cb1 , V cb2 suddenly change from 0V to the output voltage V out or from the output voltage V out to 0V. Such rapid charging and discharging of the DC blocking capacitors C b1 , C b2 may generate a large charging current or discharging current, resulting in vibration of the input / output current as shown in FIG. 12.

[0005] Also, the voltages V b1 , C b2 of the DC blocking capacitors C cb1 , V cb2One method for gradually changing the duty cycle is to apply a filter to the duty cycle D. However, even if the duty cycle D is processed to change gradually, the DC blocking capacitor C b1 ,C b2 Uncontrolled LC resonance occurs between the transformer's secondary inductor L2 and the reactor component, causing an increase in the current of the transformer's secondary inductor L2 and distortion in the primary input current, as shown in Figure 13. Furthermore, applying filtering to the duty cycle D deviates from the originally intended optimal duty cycle D, leading to a significant increase in the transformer's current amplitude due to the increase in circulating current. Moreover, the filtering deviates from the optimal duty cycle D, increasing the likelihood of soft switching failure, which may result in circuit damage due to the increased current amplitude and soft switching failure. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to improve power quality and prevent overcurrents to various components by smoothly charging and discharging DC blocking capacitors near zero crossing, thereby reducing fluctuations in input and output currents. [Means for solving the problem]

[0007] One aspect of the present invention is a power converter comprising a circuit including a leg in which a high-side switching element and a low-side switching element are connected in series, a buffer capacitor connected between both ends of the leg, and one or more capacitors connected to the midpoint of the leg via an inductor, the one end not connected to the inductor being connected to either the upper or lower terminal of the leg, and characterized in that the voltage of the capacitor is varied by utilizing the resonance state between the combined capacitance of the buffer capacitor and the capacitors and the reactance of the inductor.

[0008] Here, when increasing the voltage of the capacitor, it is preferable to control the system to transfer energy from the buffer capacitor to the capacitor and the inductor as a first state in which energy is transferred by turning on the high-side switching element or the low-side switching element so that the buffer capacitor, the inductor and the capacitor are connected in series, thereby generating LC resonance, and then to control the system to transfer energy from the inductor to the capacitor as a second state in which the capacitor and the inductor are connected in series by operating the leg. When decreasing the voltage of the capacitor, it is preferable to control the system to transfer energy from the capacitor to the inductor as a second state in which energy is transferred by turning on the high-side switching element or the low-side switching element so that the buffer capacitor, the inductor and the capacitor are connected in series, thereby generating LC resonance, and then to transfer energy from the capacitor and the inductor to the buffer capacitor as a first state in which energy is transferred by turning on the high-side switching element or the low-side switching element so that the buffer capacitor, the inductor and the capacitor are connected in series.

[0009] Furthermore, it is preferable to perform control that alternately repeats the first state and the second state multiple times.

[0010] Furthermore, of the switching timing from the first state to the second state and the switching timing from the second state to the first state, the switching timing with the larger current value flowing through the inductor is preferably a first timing where the current value is less than the rated current of the switching element.

[0011] Furthermore, it is preferable that the switching timing for the smaller current value flowing through the inductor be a second timing where the current value is less than a predetermined set value that is smaller than the current value at the first timing.

[0012] Furthermore, the second timing is preferably the timing when the current value is approximately 0.

[0013] Furthermore, it is preferable to turn off the switching element included in the leg and utilize the passive conduction state due to the operation of the antiparallel diode of the switching element, thereby automatically opening the leg due to the antiparallel diode blocking as the current flowing through the inductor decreases, and thus terminating the control.

[0014] Furthermore, it is preferable to perform the control that varies the voltage of the capacitor between the voltage of the capacitor corresponding to when the duty cycle, which indicates the on-time ratio of the high-side switching element, is 0, and the voltage of the capacitor corresponding to when the duty cycle is 1.

[0015] Furthermore, it is preferable to have a configuration with two capacitors, where the wiring is such that when the voltage of one capacitor increases, the voltage of the other capacitor decreases.

[0016] Furthermore, the device preferably comprises an AC power supply, a rectifier circuit for rectifying the AC power supply, and a second inductor connected to the rectifier circuit, wherein the second inductor has a circuit configuration of an isolated AC / DC converter that can be electromagnetically coupled with the inductor.

[0017] Furthermore, it is preferable to apply energy transfer control utilizing the resonance state when the duty cycle of the single-phase AC voltage output from the AC power supply changes. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a power converter that smoothly charges and discharges the DC blocking capacitor near zero crossing, reduces fluctuations in input and output currents, improves power quality, and prevents overcurrent to each component. [Brief explanation of the drawing]

[0019] [Figure 1] This is a circuit diagram showing the configuration of a power conversion circuit in an embodiment of the present invention. [Figure 2]This figure illustrates a control method for a power conversion circuit in an embodiment of the present invention. [Figure 3] This figure shows the time changes of various signals in the operating mode switching process of a power conversion circuit in an embodiment of the present invention. [Figure 4] This figure shows the time changes of various signals in the operating mode switching process of a power conversion circuit in an embodiment of the present invention. [Figure 5] This figure shows the time changes of various signals in the operating mode switching process of a power conversion circuit in an embodiment of the present invention. [Figure 6] This figure shows the time changes of various signals in the operating mode switching process of a power conversion circuit in an embodiment of the present invention. [Figure 7] This figure shows an example of a single configuration of a DC blocking capacitor in an embodiment of the present invention. [Figure 8] This figure shows two examples of configurations for a DC blocking capacitor in an embodiment of the present invention. [Figure 9] This is a circuit diagram showing the configuration of a power conversion circuit in conventional technology. [Figure 10] This diagram illustrates the switching between positive and negative input voltages. [Figure 11] This diagram illustrates the abrupt change in duty cycle in conventional technology. [Figure 12] This figure shows the current oscillations during zero-crossing. [Figure 13] This figure shows the current oscillations when the duty cycle is filtered. [Modes for carrying out the invention]

[0020] [Basic circuit configuration] In the embodiment of the present invention, the power converter 100 has a primary switching element S as shown in Figure 1. r1H S r1L S 1H S 1L, capacitor C1, transformer primary side inductor L1, transformer secondary side inductor L2, DC block capacitor C b1 , C b2 , switching element S 3H S 3L It is composed of a buffer capacitor C2.

[0021] The power converter 100 is connected to the primary side of the AC power supply V in and the DC power supply V connected to the secondary side out It is used to exchange power between [the two parties].

[0022] Switching element S r1H and switching element S r1L These are connected in series to form the first leg. Also, the switching element S 1H and switching element S 1L The first and second legs are connected in series to form a second leg. The ends of the first and second legs are connected to each other. A capacitor C1 is also connected in common to both ends of the first and second legs.

[0023] Primary AC power supply V in The switching element S in the first leg is r1H and switching element S r1L The connection point and the switching element S in the second leg 1H and switching element S 1L It is connected between the connection point and via an inductor L1 that constitutes the transformer.

[0024] Switching element S 3H and switching element S 3L This constitutes the third leg. A capacitor C2 and a DC power supply V are connected to both ends of the third leg. out These are connected in parallel. Also, a DC block capacitor C is connected across the third leg. b1 and DC block capacitor C b2 The following are connected in series. DC block capacitor C b1 and DC block capacitor C b2The connection point and the switching element S in the third leg 3H and switching element S 3L The inductor L2 on the secondary side of the transformer is connected between the connection point and the other point.

[0025] [Operation mode switching process using a single pulse] In the power converter 100, by devising the switching control of each switching element, it is possible to switch the operating mode at zero crossing while suppressing the influence on the input current and output current. Specifically, the reactor component of the inductor L2 on the secondary side of the transformer and the DC block capacitor C b1 , C b2 By generating a controlled LC resonance between the two, a DC block capacitor C is created. b1 , C b2 The battery is rapidly charged and discharged. In this embodiment, a single pulse signal is used to perform the operating mode switching process at the time of zero crossing. A key feature is that the time required for switching is short, ranging from a few to tens of microseconds.

[0026] The operation mode switching process using a single pulse will be explained below with reference to Figures 2 and 3. The operation mode switching process is performed by modes 1 to 3. Here, the input voltage V in This section explains the case where the value crosses zero from positive to negative.

[0027] Mode 1 is the normal operating mode immediately before switching. Just before zero crossing, the upper DC blocking capacitor C b1 Voltage V cb1 The output voltage is V out Equal to the lower DC blocking capacitor C b2 Voltage V cb2 The voltage is 0V.

[0028] In Mode 2, the switching element S of the upper arm in the third leg on the secondary side 3H Turn on DC blocking capacitor C b1 Discharge begins from the DC blocking capacitor C b2Charging begins. As shown in Figure 2, the charge / discharge current flows through the inductor L2 on the secondary side of the transformer.

[0029] Here, the switching element S of the upper arm in mode 2. 3H The duration for which it is turned on (on period) can be determined in one of the following two ways. (1) DC block capacitor C b1 Voltage V cb1 and DC block capacitor C b2 Voltage V cb2 Until they become equal (2) DC block capacitor C b1 ,C b2 and the combined capacitance C of buffer capacitor C2 s and the reactor component L of the inductor L2 on the secondary side of the transformer m Resonance period T s Until 1 / 6 of an hour has elapsed

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[0030] In case (1), the effects of variations in combined capacitance and reactor components can be ignored, making it preferable in that it can achieve ideal switching. On the other hand, DC block capacitor C b1 ,C b2 Voltage V cb1 ,V cb2 A voltage sensor is required to measure the voltage. Since adding a voltage sensor increases manufacturing costs, it is preferable to implement it without a sensor, as in (2), in order to reduce manufacturing costs.

[0031] In Mode 3, DC block capacitor C b1 ,C b2Until the charging and discharging of 3H and the switching element S 3L of the switching element S 3L are both turned off. The current flowing through the switching element S 3H in the upper arm is diverted to the body diode of the switching element S 3L in the lower arm, and the charging and discharging of the DC block capacitors C b1 , C b2 continues.

[0032] In mode 3, the timing to complete the charging and discharging can be determined in the following three ways. (1) The timing b1 when the voltage V cb1 of the upper DC block capacitor C b2 becomes 0V and the voltage V cb2 of the lower DC blocking capacitor C out becomes the output voltage V (2) The timing when the current flowing through the inductor L2 on the secondary side of the transformer becomes 0A (here, the current being 0 does not have to be exactly zero, it can be approximately zero. Approximately zero means a value that can suppress the influence on the input current and output current to a necessary extent and enable the switching of the operation mode at the zero crossing.) (3) The timing when 1 / 6 of the resonant period T b1 , C b2 of the combined capacitance C s of the DC block capacitors C m and the buffer capacitor C2 and the reactance component L s of the inductor L2 on the secondary side of the transformer has elapsed

[0033] Mode 3 also holds when the switching element S 3H in the upper arm is turned off and the switching element S 3L in the lower arm is turned on. However, when the switching element S 3L in the lower arm is turned on, after the charging and discharging of the DC block capacitors C b1 , C b2 is completed, the current flows backward and the DC block capacitor Cb1 Charge the DC block capacitor C b2 This can cause the DC block capacitor C to discharge, which can lead to a state where the DC block capacitor C b1 ,C b2 Voltage V cb1 ,V cb2 The lower arm's switching element S may vibrate, potentially causing distortion in the input and output currents. 3L Turn off the switching element S 3L By utilizing the body diode, it is preferable to prevent reverse current flow and achieve smooth switching.

[0034] Depending on the mode 1-3, the DC block capacitor C b1 ,C b2 After charging and discharging are complete, control returns to the normal operating mode.

[0035] Furthermore, it is preferable to keep the primary side transformer from flowing during operation mode switching control. Therefore, the primary side switching element S r1H S r1L S 1H S 1L It is preferable to turn all of them off.

[0036] Furthermore, in this embodiment, the operation mode switching control when the input voltage switches from positive to negative has been described, but when switching from negative to positive, the switching element S of the upper arm in the third leg 3H and the switching element S of the lower arm 3L The on / off relationship can be reversed. Also, in a configuration where multiple transformer coils (inductances) are provided on the secondary side of the transformer, the same control can be applied to the DC blocking capacitors connected to each transformer coil (inductance). For example, if there are two transformer coils (inductances) on the secondary side, there will be four DC blocking capacitors, and the same control as above can be applied to the legs to which each is connected.

[0037] As described above, by applying single-pulse operation mode switching processing, it is possible to suppress voltage oscillations of the DC blocking capacitor near zero crossing, as shown in Figure 3, and reduce input current distortion, as shown in Figure 4.

[0038] [Multiple pulse operation mode switching process] In single-pulse operation mode switching processing, a single pulse signal is used to switch the DC block capacitor C b1 ,C b2 To complete the charging and discharging, the current flowing on the secondary side of the transformer becomes large, several hundred amperes, as shown in Figure 3. The peak value of this current is at the DC block capacitor C. b1 ,C b2 It varies depending on the capacitance and the reactor component of the inductor L2 on the secondary side of the transformer. DC block capacitor C b1 ,C b2 The larger the capacitance and the greater the amount of energy transferred during switching, the smaller the reactor component of inductor L2, and the shorter the switching time, the greater the current peak value. This current is related to the DC block capacitor C b1 ,C b2 or each switching element S on the secondary side 3H S 3L The same current flows through it. Therefore, the increase in the peak value of the current is due to the DC block capacitor C b1 ,C b2 Increase in the effective current value and each switching element S 3H S 3L This causes an increase in current stress. For example, DC block capacitor C b1 ,C b2 Constraints on the capacitors that can be used as switching elements S 3H S 3L This may cause problems such as damage.

[0039] Therefore, by using two or more pulses in the operating mode switching process, it becomes possible to suppress the increase in the current peak value while enabling zero-crossing switching without affecting the input / output current.

[0040] Figures 5 and 6 show the time variations of various signals during the operating mode switching process of the power conversion circuit. Multi-pulse operating mode switching is achieved by repeatedly alternating between modes 2 and 3 of the single-pulse operating mode switching process multiple times.

[0041] As shown in Figure 5, the switching element S of the upper arm 3H Mode 2 corresponds to the period when the gate signal is high, and Mode 3 corresponds to the period when it is low. In Mode 2, the current on the secondary side of the transformer increases, and in Mode 3, this current decreases.

[0042] In the multi-pulse operation mode switching process, in mode 2, as the current on the secondary side of the transformer increases, the system switches to mode 3 when it reaches a predetermined first threshold current value. In mode 3, the current is reduced to a second threshold current value, which is smaller than the first threshold current value. After the current has decreased to the second threshold current value, the system switches back to mode 2. In this way, modes 2 and 3 are repeated alternately multiple times, and the DC block capacitor C is switched off when the peak value of the current no longer exceeds the first threshold current value. b1 ,C b2 The system determines that charging and discharging is complete and returns to normal operation control. b1 ,C b2 Voltage V cb1 ,V cb2 The charging and discharging process may be determined to be complete when the value exceeds or falls below a predetermined threshold.

[0043] Here, the absolute value of the first threshold current is set to a value smaller than the absolute value of the second threshold current. Furthermore, the second threshold current is preferably approximately 0 or 0. (Here, "approximately 0" means a value that allows for switching of the operating mode at zero crossing while suppressing the influence on the input and output currents to the necessary extent.)

[0044] By using multi-pulse operation mode switching processing, the peak value of the current on the secondary side of the transformer can be controlled, and the DC block capacitor C b1 ,C b2or switching element S 3H S 3L It can be controlled with a current value that matches its rating.

[0045] Furthermore, in the multi-pulse operation mode switching process, the timing of mode transitions can be determined not only by the current threshold as described above, but also by analyzing the pulse pattern in advance using simulations, and using a predetermined pulse pattern based on the results of those simulations. This method makes it possible to implement multi-pulse operation mode switching without providing sensors such as current sensors.

[0046] Furthermore, even in multi-pulse operation mode switching control, it is preferable to keep the primary side transformer free of current. Therefore, the primary side switching element S r1H S r1L S 1H S 1L It is preferable to turn all of them off.

[0047] Furthermore, in this embodiment, the operation mode switching control when the input voltage switches from positive to negative has been described, but when switching from negative to positive, the switching element S of the upper arm in the third leg 3H and the switching element S of the lower arm 3L The on / off relationship can be reversed. Also, in a configuration where multiple transformer coils (inductances) are provided on the secondary side of the transformer, the same control can be applied to the DC blocking capacitors connected to each transformer coil (inductance). For example, if there are two transformer coils (inductances) on the secondary side, there will be four DC blocking capacitors, and the same control as above can be applied to the legs to which each is connected.

[0048] By applying the multi-pulse operation mode switching control described above, it is possible to suppress voltage oscillations of the DC blocking capacitor near the zero crossing, as shown in Figure 5, and reduce input current distortion, as shown in Figure 6.

[0049] [Blocking Capacitor Configuration] The cases of one DC blocking capacitor and two DC blocking capacitors in the power converter 100 will be explained below.

[0050] Figure 7 shows the DC blocking capacitor C b The configuration of a power converter 100 is shown, which is equipped with one DC blocking capacitor C. In this configuration, when the voltage is reduced during single-pulse switching or multi-pulse switching, the DC blocking capacitor C b The energy stored in the buffer capacitor C fo It flows into, current I cb This occurs. Also, when increasing the voltage, a buffer capacitor C is needed. fo The energy stored in the DC blocking capacitor C b A current I flows into it in the reverse direction. cb This occurs. In other words, DC blocking capacitor C b When the voltage rises, the buffer capacitor C fo From DC blocking capacitor C b Energy is transferred to the DC blocking capacitor C. b When the voltage decreases, the DC blocking capacitor C b from buffer capacitor C fo Energy is transferred to the buffer capacitor C during the switching operation. fo The voltage may fluctuate, potentially causing distortion in the input and output currents.

[0051] Figure 8 shows DC blocking capacitor C b The configuration of the power converter 100, which is provided with two DC blocking capacitors C, is shown. In this configuration, as described above, one of the DC blocking capacitors C b1 When the capacitor voltage rises, the other DC blocking capacitor C b2 The voltage decreases. Conversely, the DC blocking capacitor C b2 When the capacitor voltage rises, the other DC blocking capacitor C b1The voltage decreases. In other words, in this configuration, the energy discharged from the DC blocking capacitor whose voltage decreases is transferred to the other DC blocking capacitor whose voltage increases. By making this energy balance as equal as possible, the buffer capacitor C fo Voltage fluctuation (current I cb This can reduce the noise to almost zero, thereby suppressing the impact on input and output current.

[0052] Thus, in order to suppress distortion of input and output currents, it is preferable to configure the power converter 100 using two or more DC blocking capacitors so that the energy balance between them is equal.

[0053] [Structure of the present invention] [Configuration 1] A leg in which high-side switching elements and low-side switching elements are connected in series, A buffer capacitor connected between both ends of the aforementioned leg, The circuit includes one or more capacitors connected to the midpoint of the leg via an inductor, the capacitor having one end not connected to the inductor connected to either the upper or lower terminal of the leg, A power converter characterized by controlling the voltage of the capacitor by utilizing the resonance state between the combined capacitance of the buffer capacitor and the capacitor and the reactance of the inductor. [Configuration 2] The power converter described in Configuration 1, When increasing the voltage of the capacitor, the first state is created in which LC resonance is generated by turning on the high-side switching element or the low-side switching element so that the buffer capacitor, the inductor, and the capacitor are connected in series, and energy is transferred from the buffer capacitor to the capacitor and the inductor. Subsequently, the leg is operated to connect the capacitor and the inductor in series, thereby creating a second state in which energy is transferred from the inductor to the capacitor. When reducing the voltage of the capacitor, the leg is operated to bring it to a second state, and energy is transferred from the capacitor to the inductor by connecting the capacitor and the inductor in series. Subsequently, the high-side switching element or the low-side switching element is turned on to generate an LC resonance, thereby creating a first state in which energy is transferred from the capacitor and the inductor to the buffer capacitor. A power converter characterized by the following features. [Configuration 3] The power converter described in configuration 2, A power converter characterized by performing control that alternately repeats the first state and the second state multiple times. [Structure 4] The power converter described in configuration 3, A power converter characterized in that the switching timing between the first state and the second state and the switching timing between the second state and the first state, whichever has a larger current value flowing through the inductor, is a first timing in which the current value is less than the rated current of the switching element. [Composition 5] The power converter described in configuration 4, A power converter characterized in that the switching timing for the smaller current value flowing through the inductor is a second timing where the current value is less than a predetermined set value which is smaller than the current value at the first timing. [Composition 6] The power converter described in configuration 5, The power converter is characterized in that the second timing is the timing when the current value is approximately 0. [Composition 7] A power converter according to any one of items 2 to 6 of the configuration, A power converter characterized by turning off the switching element included in the leg and utilizing the passive conduction state due to the operation of the antiparallel diode of the switching element, thereby automatically opening the leg due to the antiparallel diode blocking as the current flowing through the inductor decreases, and thus terminating the control. [Structure 8] A power converter according to any one of items 1 to 7, A power converter characterized by performing the control to vary the voltage of the capacitor between the voltage of the capacitor corresponding to when the duty cycle, which indicates the on-time ratio of the high-side switching element, is 0, and the voltage of the capacitor corresponding to when the duty cycle is 1. [Composition 9] A power converter as described in any one of items 1 to 8, The configuration includes two of the aforementioned capacitors. A power converter characterized in that it is wired such that when the voltage of one capacitor increases, the voltage of the other capacitor decreases. [Configuration 10] A power converter according to any one of items 1 to 9, A power converter comprising an AC power source, a rectifier circuit for rectifying the AC power source, and a second inductor connected to the rectifier circuit, wherein the second inductor has a circuit configuration of an isolated AC / DC converter that can be electromagnetically coupled with the inductor. [Composition 11] The power converter described in configuration 10, A power converter characterized by applying energy transfer control utilizing the resonance state during duty cycle changes of the single-phase AC voltage output from the AC power source. [Explanation of Symbols]

[0054] 100 Power converter.

Claims

1. A leg in which high-side switching elements and low-side switching elements are connected in series, A buffer capacitor connected between both ends of the aforementioned leg, The circuit includes one or more capacitors connected to the midpoint of the leg via an inductor, the capacitor having one end not connected to the inductor connected to either the upper or lower terminal of the leg, A power converter characterized by controlling the voltage of the capacitor by utilizing the resonance state between the combined capacitance of the buffer capacitor and the capacitor and the reactance of the inductor.

2. A power converter according to claim 1, When increasing the voltage of the capacitor, the first state is created in which LC resonance is generated by turning on the high-side switching element or the low-side switching element so that the buffer capacitor, the inductor, and the capacitor are connected in series, and energy is transferred from the buffer capacitor to the capacitor and the inductor. Subsequently, the leg is operated to connect the capacitor and the inductor in series, thereby creating a second state in which energy is transferred from the inductor to the capacitor. When reducing the voltage of the capacitor, the leg is operated to bring it to a second state, and energy is transferred from the capacitor to the inductor by connecting the capacitor and the inductor in series. Subsequently, the high-side switching element or the low-side switching element is turned on to generate LC resonance, creating a first state in which energy is transferred from the capacitor and the inductor to the buffer capacitor. A power converter characterized by the following features.

3. A power converter according to claim 2, A power converter characterized by performing control that alternately repeats the first state and the second state multiple times.

4. A power converter according to claim 3, A power converter characterized in that the switching timing between the first state and the second state and the switching timing between the second state and the first state, whichever has a larger current value flowing through the inductor, is a first timing in which the current value is less than the rated current of the switching element.

5. A power converter according to claim 4, A power converter characterized in that the switching timing for the smaller current value flowing through the inductor is a second timing where the current value is less than a predetermined set value which is smaller than the current value at the first timing.

6. A power converter according to claim 5, The power converter is characterized in that the second timing is the timing when the current value is approximately zero.

7. A power converter according to claim 2, A power converter characterized by turning off the switching element included in the leg and utilizing the passive conduction state due to the operation of the antiparallel diode of the switching element, thereby automatically opening the leg due to the antiparallel diode blocking as the current flowing through the inductor decreases, and thus terminating the control.

8. A power converter according to any one of claims 1 to 7, A power converter characterized by performing the control to vary the voltage of the capacitor between the voltage of the capacitor corresponding to when the duty cycle, which indicates the on-time ratio of the high-side switching element, is 0, and the voltage of the capacitor corresponding to when the duty cycle is 1.

9. A power converter according to claim 1, The configuration includes two of the aforementioned capacitors. A power converter characterized in that it is wired such that when the voltage of one capacitor increases, the voltage of the other capacitor decreases.

10. A power converter according to claim 1, A power converter comprising an AC power source, a rectifier circuit for rectifying the AC power source, and a second inductor connected to the rectifier circuit, wherein the second inductor has a circuit configuration of an isolated AC / DC converter that can be electromagnetically coupled with the inductor.

11. A power converter according to claim 10, A power converter characterized by applying energy transfer control utilizing the resonance state during duty cycle changes of the single-phase AC voltage output from the AC power source.

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