Insulated ac / DC converter

Abstract

The purpose of the present disclosure is to improve power factor. An insulated AC / DC converter (1) according to the present disclosure is provided with a first series circuit (2) in which first to fourth semiconductor switches (S1-S4) are connected in series. A second end (a2) of an AC power supply (PS1) is connected to the first connection point (P1) of the second and third semiconductor switches (S2, S3). A second series circuit (3) of first and second capacitors (C1, C2) is connected in parallel with the first series circuit (2). A third capacitor (C3) is connected between the connection point (P3) of the first and second semiconductor switches (S1, S2) and the connection point (P4) of the third and fourth semiconductor switches (S3, S4). An inductor (L1) is connected between at least one of a first rectifier circuit (4) and the first series circuit (2) and the AC power supply (PS1). A primary winding (11) of a transformer (10) is connected between the first connection point (P1) and a second connection point (P2). A second rectifier circuit (30) rectifies the current flowing through a secondary winding (12) of the transformer (10) and outputs the rectified current to a load (40).

Description

Isolated AC / DC converter

[0001] The present disclosure relates to an isolated AC / DC converter, and more particularly to an isolated AC / DC converter having a flying capacitor type multilevel converter circuit.

[0002] Japanese Patent Application Laid-Open No. 2006-129999 (Patent Document 1) discloses a load control device including a series circuit of first and second switching elements, a series circuit of second and third capacitors connected in parallel to the series circuit of the first and second switching elements, a high-frequency isolation transformer, and a first resonant capacitor. In this load control device, one end of the primary winding of the high-frequency isolation transformer is connected to the midpoint of the series circuit of the first and second switching elements via the first resonant capacitor. The other end of the primary winding of the high-frequency isolation transformer is connected to the midpoint of the series circuit of the second and third capacitors. An LLC resonant circuit is also formed by a series circuit of the first resonant capacitor and leakage inductance connected between the midpoint of the series circuit of the first and second switching elements and one end of the primary winding of the high-frequency isolation transformer, and the first resonant capacitor connected in parallel to the primary winding of the high-frequency isolation transformer. In this load control device, the DC bus voltage is controlled to the desired voltage using PWM control, and at the same time, the output voltage is controlled using PFM control based on the gain characteristics of the LLC resonant circuit, thereby controlling the two control quantities, the DC bus voltage and the output voltage, using different modulation methods.

[0003] Japanese Patent Application Laid-Open No. 2022-18418

[0004] An object of the present disclosure is to provide an isolated AC / DC converter that can improve the power factor with simple control.

[0005] An isolated AC / DC converter according to one aspect of the present disclosure includes a first rectifier circuit, a first series circuit, a second series circuit, a third capacitor, an inductor, a transformer, a second rectifier circuit, and a control circuit. The first rectifier circuit includes a series circuit of a first diode and a second diode, the cathode of which is connected to the anode of the first diode. A first end of an AC power supply is connected to a connection point between the first diode and the second diode. The first series circuit includes a first semiconductor switch, a second semiconductor switch, a third semiconductor switch, and a fourth semiconductor switch connected in series between the cathode of the first diode and the anode of the second diode. A second end of the AC power supply is connected to a connection point between the second semiconductor switch and the third semiconductor switch. The second series circuit includes a series circuit of a first capacitor and a second capacitor and is connected in parallel with the first series circuit. The third capacitor is connected between the connection point of the first semiconductor switch and the second semiconductor switch and the connection point of the third semiconductor switch and the fourth semiconductor switch. The inductor is connected between the AC power supply and at least one of the first rectifier circuit and the first series circuit. The transformer has a primary winding connected between a connection point of the second semiconductor switch and the third semiconductor switch and a connection point of the first capacitor and the second capacitor. The second rectifier circuit is connected to a secondary winding of the transformer and rectifies the current flowing through the secondary winding and outputs the rectified current to a load. The control circuit controls each of the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, and the fourth semiconductor switch to an on state or an off state.

[0006] Fig. 1 is a schematic circuit diagram of an isolated AC / DC converter according to an embodiment of the present disclosure. Fig. 2 is a waveform diagram of a current flowing through an inductor provided in the isolated AC / DC converter and a voltage generated in a primary winding of a transformer. Fig. 3 is a schematic circuit diagram illustrating a current path in a first operation mode in the isolated AC / DC converter. Fig. 4 is a schematic circuit diagram illustrating a current path in a second operation mode in the isolated AC / DC converter. Fig. 5 is a schematic circuit diagram illustrating a current path in a third operation mode in the isolated AC / DC converter. Fig. 6 is a schematic circuit diagram illustrating a current path in a fourth operation mode in the isolated AC / DC converter.

[0007] Hereinafter, isolated AC / DC converters according to embodiments will be described in detail with reference to the drawings. The configurations described in the following embodiments are merely examples of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0008] (Embodiment) (1) Overview As shown in Fig. 1, an isolated AC / DC converter 1 of this embodiment includes a first rectifier circuit 4, a first series circuit 2, a second series circuit 3, a third capacitor C3, an inductor L1, a transformer 10, a second rectifier circuit 30, and a control circuit 20. In Fig. 1 and other figures, the second rectifier circuit 30 is abbreviated as "rectifier circuit."

[0009] The first rectifier circuit 4 includes a series circuit of a first diode D1 and a second diode D2 whose cathode is connected to the anode of the first diode D1. A first terminal a1 of the AC power supply PS1 is connected to a connection point P5 between the first diode D1 and the second diode D2.

[0010] The first series circuit 2 includes a first semiconductor switch S1, a second semiconductor switch S2, a third semiconductor switch S3, and a fourth semiconductor switch S4 connected in series between the cathode of the first diode D1 and the anode of the second diode D2. In the first series circuit 2, a second end a2 of the AC power supply PS1 is connected to a connection point P1 between the second semiconductor switch S2 and the third semiconductor switch S3.

[0011] The second series circuit 3 includes a series circuit of a first capacitor C1 and a second capacitor C2, and is connected in parallel with the first series circuit 2.

[0012] The third capacitor C3 is connected between a connection point P3 between the first semiconductor switch S1 and the second semiconductor switch S2 and a connection point P4 between the third semiconductor switch S3 and the fourth semiconductor switch S4.

[0013] The inductor L1 is connected between the AC power supply PS1 and at least one of the first rectifier circuit 4 and the first series circuit 2. In the circuit shown in Fig. 1, the inductor L1 is connected between the first series circuit 2 and the AC power supply PS1.

[0014] The transformer 10 has a primary winding 11 connected between a connection point P1 between the second semiconductor switch S2 and the third semiconductor switch S3 and a connection point P2 between the first capacitor C1 and the second capacitor C2.

[0015] The second rectifier circuit 30 is connected to the secondary winding 12 of the transformer 10 , rectifies the current flowing through the secondary winding 12 , and outputs the rectified current to a load 40 .

[0016] The control circuit 20 controls each of the first semiconductor switch S1, the second semiconductor switch S2, the third semiconductor switch S3, and the fourth semiconductor switch S4 to an on state or an off state.

[0017] Here, "two circuit elements being connected" refers to a state in which the two circuit elements are electrically connected, and is not limited to a state in which the two circuit elements are directly connected, but may also include a state in which the two circuit elements are indirectly connected via another circuit element. In the following description, the isolated AC / DC converter 1 will sometimes be abbreviated as "converter 1," and the first to fourth semiconductor switches S1 to S4 will sometimes be abbreviated as "first to fourth switches S1 to S4," respectively. Furthermore, the connection point P1 will sometimes be referred to as the first connection point, and the connection point P2 will sometimes be referred to as the second connection point.

[0018] In the converter 1 of this embodiment, the control circuit 20 controls the first to fourth switches S1 to S4 to an on or off state, thereby controlling the charging voltages of the first to third capacitors C1 to C3. Because a voltage higher than the charging voltages of the first capacitor C1 and the second capacitor C2 is never applied to the first to fourth switches S1 to S4, controlling the charging voltages of the first capacitor C1 and the second capacitor C2 makes it possible to suppress the voltages applied to the first to fourth switches S1 to S4, and allows the use of semiconductor switches with low voltage resistance performance as the first to fourth switches S1 to S4.

[0019] Furthermore, in the converter 1 of this embodiment, a current flows through the primary winding 11 of the transformer 10, and power is supplied to the load 40 connected to the secondary winding 12 of the transformer 10, in an operation mode (a first operation mode described below) in which the first switch S1 and the second switch S2 are in an on state and the third switch S3 and the fourth switch S4 are in an off state, and an operation mode (a fourth operation mode described below) in which the third switch S3 and the fourth switch S4 are in an on state and the first switch S1 and the second switch S2 are in an off state. Therefore, the control circuit 20 can adjust the proportion of the first operation mode and the fourth operation mode within one switching period in which the first to fourth switches S1 to S4 are switched, thereby adjusting the power supplied to the load 40. Here, a current roughly proportional to the input voltage Vin from the AC power supply PS1 flows through the inductor L1, so that the power factor can be improved with simple control without the control circuit 20 performing complex control. Furthermore, in converter 1, which is a flying capacitor type multilevel converter equipped with first to third capacitors C1 to C3, control circuit 20 can adjust the power supplied to load 40 without changing the switching periods of first to fourth switches S1 to S4.

[0020] (2) Details The isolated AC / DC converter (converter) 1 according to this embodiment will be described in detail below with reference to the drawings.

[0021] (2.1) Configuration FIG. 1 is a schematic circuit diagram of a converter 1.

[0022] The converter 1 is an isolated AC / DC converter that converts an AC voltage input from an AC power supply PS1 such as a commercial AC power supply into a DC voltage and supplies the DC voltage to a load 40 .

[0023] As described above, the converter 1 includes the first rectifier circuit 4, the first series circuit 2, the second series circuit 3, the third capacitor C3, the inductor L1, the transformer 10, the second rectifier circuit 30, and the control circuit 20. The converter 1 also includes a filter circuit F1. Note that the first rectifier circuit 4, the third capacitor C3, and the transformer 10 are as described in "(1) Overview," and therefore will not be described again.

[0024] As described above, the first series circuit 2 includes first to fourth switches S1 to S4 connected in series between the cathode of the first diode D1 and the anode of the second diode D2. The first to fourth switches S1 to S4 are connected between the cathode of the first diode D1 and the anode of the second diode D2 in the order of the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4. The first to fourth switches S1 to S4 are, for example, N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). Each of the first to fourth switches S1 to S4 is controlled to an on or off state by a control signal input from the control circuit 20 to its gate electrode.

[0025] The second series circuit 3 includes a series circuit of a first capacitor C1 and a second capacitor C2 and is connected in parallel with the first series circuit 2. Here, the capacitance of the first capacitor C1 and the capacitance of the second capacitor C2 are the same. Note that the fact that the circuit constants (e.g., capacitances) of two circuit elements are the same does not necessarily mean that the circuit constants of the two circuit elements are completely identical, but may also include cases where the difference in the circuit constants of the two circuit elements is small enough to be considered a manufacturing error. Because the capacitances of the first capacitor C1 and the second capacitor C2 are set to the same value, the voltage at the connection point P2 between the first capacitor C1 and the second capacitor C2 is half the voltage Vbus across the second series circuit 3.

[0026] The control circuit 20 mainly comprises, for example, a computer system having one or more processors and a memory. The functions of the control circuit 20 are realized by the processor of the computer system executing a program stored in the memory of the computer system. The program may be stored in the memory, or may be provided via a telecommunications line such as the Internet, or may be provided by being recorded on a non-transitory recording medium such as a memory card.

[0027] The control circuit 20 receives, as feedback, for example, a voltage Vbus across the second series circuit 3 including the series circuit of the first capacitor C1 and the second capacitor C2, a charging voltage V3 of the third capacitor C3, and a voltage V1 across the primary winding 11 of the transformer 10. The control circuit 20 controls the power supplied to the load 40 by controlling each of the first to fourth switches S1 to S4 to an on or off state based on the feedback values ​​of the voltage Vbus, the charging voltage V3, and the voltage V1.

[0028] The filter circuit F1 is an LC filter including a coil L2 having a first end connected to the second end a2 of the AC power supply PS1, and a capacitor C4 connected between the first end a1 of the AC power supply PS1 and the second end of the coil L2.

[0029] The inductor L1 is connected between a connection point P1 between the second switch S2 and the third switch S3 and the second end a2 of the AC power supply PS1. More specifically, the inductor L1 is connected between the connection point P1 between the second switch S2 and the third switch S3 and the coil L2.

[0030] A pair of input terminals of the second rectifier circuit 30 are connected to both ends of the secondary winding 12 of the transformer 10. The second rectifier circuit 30 includes, for example, a diode bridge circuit in which a plurality of diodes are bridge-connected. A pair of input terminals of the diode bridge circuit are connected to the secondary winding 12 of the transformer 10. Here, the converter 1 preferably further includes, in a stage subsequent to the second rectifier circuit 30, a smoothing circuit that smooths the pulsating voltage output from the second rectifier circuit 30. The DC voltage rectified by the second rectifier circuit 30 and smoothed by the smoothing circuit is supplied to the load 40.

[0031] (2.2) Description of Operation The operation of the converter 1 of this embodiment will be described with reference to FIGS.

[0032] The control circuit 20 controls each of the first to fourth switches S1 to S4 to an on or off state by outputting a control signal to the gate electrodes of the first to fourth switches S1 to S4.

[0033] In this embodiment, the operation modes of the first to fourth switches S1 to S4 include a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode. In the first operation mode, the first switch S1 and the second switch S2 are in an ON state, and the third switch S3 and the fourth switch S4 are in an OFF state. In the second operation mode, the first switch S1 and the third switch S3 are in an ON state, and the second switch S2 and the fourth switch S4 are in an OFF state. In the third operation mode, the second switch S2 and the fourth switch S4 are in an ON state, and the first switch S1 and the third switch S3 are in an OFF state. In the fourth operation mode, the third switch S3 and the fourth switch S4 are in an ON state, and the first switch S1 and the second switch S2 are in an OFF state. The control circuit 20 controls the operation so as to periodically repeat a first period t1 in which the operation mode is the first operation mode, a second period t2 in which the operation mode is the second operation mode or the third operation mode, a third period t3 in which the operation mode is the fourth operation mode, and a fourth period t4 in which the operation mode is the second operation mode or the third operation mode.

[0034] The control circuit 20 controls the lengths of the first period t1, the second period t2, the third period t3, and the fourth period t4 so that the power supply operates in a discontinuous mode in which the current I1 flowing through the inductor L1 is discontinuous. Specifically, the control circuit 20 controls the lengths of the first period t1 and the third period t3 to be the same. The control circuit 20 controls the lengths of the first period t1, the second period t2, the third period t3, and the fourth period t4 so that the voltage Vbus across the second series circuit 3 is at least twice the peak value of the input voltage Vin input from the AC power supply PS1. Here, the term "the lengths of the two operation modes are the same" does not necessarily mean that the lengths of the two operation modes are exactly the same, but may also include a state in which the difference in the length of the time between the two operation modes is within ±several percent (e.g., ±10%) of either of the lengths of the time.

[0035] The operation of the converter 1 in the first to fourth periods t1 to t4 will now be described with reference to Figures 2 to 6. Figures 2 to 6 describe the current path when the input voltage Vin from the AC power supply PS1 is in a positive half cycle in which the first terminal a1 has a higher potential than the second terminal a2.

[0036] 2 is a waveform diagram of the current I1 flowing through the inductor L1 and the voltage V1 generated in the primary winding 11 of the transformer 10. In FIG. 2, periods t1 to t4 correspond to the first to fourth periods, respectively. Furthermore, period T1 indicates the duration of one switching cycle of the first to fourth switches S1 to S4, and the switching frequency of the first to fourth switches S1 to S4 is, for example, approximately 100 kHz. Note that FIG. 2 shows the waveform diagram of the current I1 and voltage V1 for one switching cycle.

[0037] 3 to 6 are schematic circuit diagrams showing paths through which current flows in the first, second, third, and fourth operation modes, respectively. In FIGS. 3 to 6, the on / off states of the first to fourth switches S1 to S4 are schematically illustrated, and the control circuit 20 is not shown. The dotted arrows A1 to A6 in FIGS. 3 to 6 indicate paths through which current flows. The following describes the current paths when the input voltage Vin from the AC power supply PS1 is in a positive half cycle in which the first terminal a1 has a higher potential than the second terminal a2.

[0038] 3 , when the first period t1 during which the control circuit 20 operates in the first operating mode begins, the control circuit 20 controls the first switch S1 and the second switch S2 to an ON state and controls the third switch S3 and the fourth switch S4 to an OFF state. During the first period t1, the voltage at the connection point P1 between the second switch S2 and the third switch S3 becomes equal to the voltage Vbus. In the first operating mode, a current flows through the path (indicated by the arrow A1) of the AC power supply PS1 → the first diode D1 → the first switch S1 → the second switch S2 → the inductor L1 → the coil L2 → the AC power supply PS1.

[0039] In the first operating mode, the first capacitor C1 is connected in parallel with the primary winding 11 of the transformer 10, so that the voltage V1 across the primary winding 11 of the transformer 10 is equal to the charging voltage (Vbus / 2) of the first capacitor C1 (see FIG. 2). At this time, a current flows through the path (indicated by the arrow A2) of the first capacitor C1 → first switch S1 → second switch S2 → primary winding 11 → first capacitor C1.

[0040] During the first period t1, a current flows through the path indicated by arrow A2, thereby supplying power to the secondary side of the transformer 10, and a current flows through the path indicated by arrow A1, thereby storing energy in the inductor L1. Here, if the inductance of the inductor L1 is L, the current I1 during the first period gradually increases at a slope of Vin / L (see FIG. 2).

[0041] A second rectifier circuit 30 is connected to the secondary winding 12 of the transformer 10. The second rectifier circuit 30 rectifies the current generated in the secondary winding 12 of the transformer 10, and the smoothing circuit smooths the rectified current to generate a DC voltage of a predetermined voltage value, and DC power is supplied to the load 40.

[0042] When the first period t1 ends, the control circuit 20 switches the operation mode of the converter 1 from the first operation mode to the second operation mode or the third operation mode. The control circuit 20 controls the operation mode during the second period t2 to either the second operation mode or the third operation mode depending on the charging voltage V3 of the third capacitor C3. Specifically, if the charging voltage V3 of the third capacitor C3 is less than a predetermined threshold voltage Vth, the control circuit 20 controls the operation mode during the second period to the second operation mode. The threshold voltage Vth is set to half the voltage Vbus. Furthermore, if the charging voltage V3 of the third capacitor C3 is equal to or greater than the threshold voltage Vth, the control circuit 20 controls the operation mode during the second period to the third operation mode.

[0043] 4 is a schematic circuit diagram showing current paths when the device is operating in the second operation mode. When the control circuit 20 controls the operation mode to the second operation mode during the second period, the control circuit 20 controls the first switch S1 and the third switch S3 to an on state and the second switch S2 and the fourth switch S4 to an off state. In the second operation mode, the voltage at the connection point P1 between the second switch S2 and the third switch S3 is equal to the voltage (Vbus / 2) at the connection point P2 between the first capacitor C1 and the second capacitor C2.

[0044] In the second operating mode, current flows through the following path (indicated by arrow A3): AC power supply PS1 → first diode D1 → first switch S1 → third capacitor C3 → third switch S3 → inductor L1 → coil L2 → AC power supply PS1. Inductor L1 releases the energy stored in the first operating mode and charges third capacitor C3. In the second operating mode, the voltage applied to inductor L1 is (Vin-Vbus / 2). Since voltage Vbus is charged to a voltage greater than twice the maximum value of input voltage Vin, (Vin-Vbus / 2)<0. Therefore, current I1 flowing through inductor L1 gradually decreases at a rate of (Vin-Vbus / 2) / L. Note that in the second operating mode, no current flows through primary winding 11 of transformer 10, and no power is supplied to the secondary side of transformer 10.

[0045] 5 is a schematic circuit diagram showing the current paths when the device is operating in the third operation mode. When the control circuit 20 switches the operation mode to the third operation mode during the second period, the control circuit 20 turns on the second switch S2 and the fourth switch S4 and turns off the first switch S1 and the third switch S3. Also in the third operation mode, the voltage at the node P1 between the second switch S2 and the third switch S3 is equal to the voltage (Vbus / 2) at the node P2 between the first capacitor C1 and the second capacitor C2.

[0046] In the third operating mode, while energy remains stored in inductor L1, current flows through the following path (indicated by arrow A4): AC power supply PS1 → first diode D1 → first capacitor C1 → second capacitor C2 → fourth switch S4 → third capacitor C3 → second switch S2 → inductor L1 → coil L2 → AC power supply PS1. At this time, third capacitor C3 discharges, while first capacitor C1 and second capacitor C2 charge. In the third operating mode, the voltage applied to inductor L1 is (Vin-Vbus / 2). Since voltage Vbus is charged to a voltage greater than twice the maximum value of input voltage Vin, (Vin-Vbus / 2)<0. Therefore, current I1 flowing through inductor L1 gradually decreases at a rate of (Vin-Vbus / 2) / L. Note that in the third operating mode, no current flows through primary winding 11 of transformer 10, and no power is supplied to the secondary side of transformer 10.

[0047] When the second period t2 ends, the control circuit 20 controls the operation mode of the converter 1 to the fourth operation mode during the third period t3. During the third period t3, the control circuit 20 controls the third switch S3 and the fourth switch S4 to the on state and the first switch S1 and the second switch S2 to the off state, as shown in Fig. 6. During the third period t3, the voltage at the connection point P1 between the second switch S2 and the third switch S3 becomes zero.

[0048] In the fourth operating mode, current flows through the path of AC power supply PS1 → first diode D1 → first capacitor C1 → second capacitor C2 → fourth switch S4 → third switch S3 → inductor L1 → coil L2 → AC power supply PS1 (path indicated by arrow A5), charging the first capacitor C1 and the second capacitor C2.

[0049] In the fourth operating mode, the second capacitor C2 is connected in parallel with the primary winding 11 of the transformer 10, and the voltage V1 across the primary winding 11 of the transformer 10 is equal to (−Vbus / 2) (see FIG. 2). At this time, a current flows through the path (indicated by the arrow A6) of the second capacitor C2 → primary winding 11 → third switch S3 → fourth switch S4 → second capacitor C2, and power is supplied to the secondary side of the transformer 10.

[0050] In the fourth operating mode, the voltage applied to inductor L1 is (Vin - Vbus), and because Vbus is charged to a voltage greater than twice the maximum value of input voltage Vin, (Vin - Vbus) < 0. Therefore, current I1 flowing through inductor L1 gradually decreases at a slope of (Vin - Vbus) / L1 (see FIG. 2). Because control circuit 20 controls the duration of first period t1 and third period t3 to be the same length, during the third period, Vbus is charged to more than twice the peak value of input voltage Vin, and current I1 becomes zero. Current I1 then does not flow until the device switches back to the first operating mode.

[0051] After the third period t3 ends, the control circuit 20 controls the operation mode of the converter 1 to either the second operation mode or the third operation mode during the fourth period t4. Here, the control circuit 20 controls the operation mode during the fourth period t4 to either the second operation mode or the third operation mode. During the fourth period t4, no current flows through the inductor L1, and no power is transferred from the primary side to the secondary side of the transformer 10. Therefore, the operation mode during the fourth period t4 may be either the second operation mode or the third operation mode. Here, the voltage Vbus is charged to more than twice the peak value of the input voltage Vin, and the third capacitor C3 is also charged to the threshold voltage. Therefore, no current I1 flows through the inductor L1 during the fourth period t4. Furthermore, during the fourth period t4, no current flows through the primary winding 11 of the transformer 10, and no power is supplied to the secondary side of the transformer 10.

[0052] When the operation mode transitions from the fourth operation mode to the first operation mode, two switches (the first switch S1 and the second switch S2) are switched from the OFF state to the ON state, which may result in an inrush current. In this embodiment, the control circuit 20 provides a fourth period in which it operates in the second operation mode or the third operation mode between a third period in which it operates in the fourth operation mode and a first period in which it operates in the fourth operation mode. As a result, at the timing of switching from the third period t3 to the fourth period t4 and at the timing of switching from the fourth period t4 to the first period t1, only one switch is switched from the OFF state to the ON state, thereby suppressing the generation of an inrush current.

[0053] After that, when the fourth period t4 ends, the control circuit 20 switches the operation mode of the converter 1 from the fourth operation mode to the first operation mode. The operation of the first operation mode is as described above. Here, the current I1 is zero from the middle of the third operation mode to the start of the first operation mode. Therefore, the first switch S1 can be switched from the OFF state to the ON state while the current I1 is zero. This reduces the possibility of an inrush current flowing when the first switch S1 is switched from the OFF state to the ON state. Note that, since the current I1 does not flow during the fourth period t4 and power is not supplied to the secondary side of the transformer 10, the fourth period t4 is not essential and may be omitted.

[0054] In this embodiment, the control circuit 20 controls the first to fourth switches S1 to S4 so that a first period t1, a second period t2, a third period t3, and a fourth period t4 are cyclically repeated in this order, thereby controlling the voltage Vbus across the second series circuit 3 and the voltage V1 applied to the primary winding 11 of the transformer 10. The converter 1 of this embodiment is a multilevel converter circuit in which the voltage at the connection point between the second switch S2 and the third switch S3 changes between three levels: Vbus, (Vbus / 2), and 0. The control circuit 20 sets the duration of the first period t1 and the duration of the third period t3 to the same duration, and controls the durations of the first period t1, the second period t2, and the third period t3 so that the voltage Vbus across the second series circuit 3 is at least twice the peak value of the input voltage Vin input from the AC power supply PS1. By performing such control by the control circuit 20, the current I1 becomes zero midway through the third period t3, and switching operation can be performed in a discontinuous mode in which the current I1 is discontinuous. In addition, since the current I1 flows in proportion to the input voltage Vin from the AC power supply PS1, there is also the advantage that the power factor is improved.

[0055] During the negative half cycle of the input voltage Vin from the AC power supply PS1, the control circuit 20 also controls the first to fourth switches S1 to S4 to cyclically repeat a first period t1, a second period t2, a third period t3, and a fourth period t4 in this order. During the negative half cycle of the input voltage Vin, energy is stored in the inductor L1 during the third period t3 in the fourth operating mode, and the energy stored in the inductor L1 is released during the fourth period t4 and the first period t1 after the third period t3. During the negative half cycle, the third capacitor C3 is charged in the third operating mode and discharged in the second operating mode. A detailed description of the operation of the converter 1 during the negative half cycle of the input voltage Vin will be omitted.

[0056] The converter 1 supplies power to the secondary side of the transformer 10 during the first period t1 and the third period t3, and stops the power supply to the secondary side of the transformer 10 during the second period t2 and the fourth period t4. The control circuit 20 sets the duration of the first period t1 and the duration of the third period t3 to be the same, and controls the power supply to the load 40 by adjusting the ratio between the total duration of the first period t1 and the third period t3 and the total duration of the second period t2 and the fourth period t4. The greater the ratio of the duration of the first period t1 to the duration of the third period t3 in one cycle T1 of the switching period, the more power is supplied to the load 40. Therefore, the control circuit 20 can adjust the period during which power is supplied to the secondary side of the transformer 10 by adjusting the ratio between the total duration of the first period t1 and the third period t3 and the total duration of the second period t2 and the fourth period t4. Therefore, the control circuit 20 can adjust the power supplied to the load 40 without changing the switching frequencies of the first to fourth switches S1 to S4.

[0057] (3) Modifications The above embodiment is merely one of various embodiments of the present disclosure. The above embodiment can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0058] Modifications of the above embodiment are listed below. The modifications described below can be applied in appropriate combinations. Hereinafter, the above embodiment may also be referred to as the basic configuration.

[0059] The converter 1 of the present disclosure includes a computer system. The computer system is primarily composed of a processor and memory as hardware. The processor executes a program stored in the memory of the computer system to realize the functions of the control circuit 20 of the converter 1 of the present disclosure. The program may be pre-stored in the memory of the computer system, provided via a telecommunications line, or provided on a non-transitory recording medium readable by the computer system, such as a memory card, optical disk, or hard disk drive. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The integrated circuits, such as ICs and LSIs, are referred to by different names depending on the degree of integration, and include integrated circuits called system LSIs, very large-scale integrations (VLSIs), or ultra-large-scale integrations (ULSIs). Furthermore, field-programmable gate arrays (FPGAs), which are programmed after the LSI is manufactured, or logic devices capable of reconfiguring the connections within the LSI or the circuit partitions within the LSI, can also be used as processors. The electronic circuits may be integrated into one chip or distributed across multiple chips. The chips may be integrated into one device or distributed across multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Therefore, the microcontroller is also composed of one or more electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

[0060] In the above embodiment, the control circuit 20 controls the first to fourth switches S1 to S4 to the on or off state so that the first period t1, the second period t2, the third period t3, and the fourth period t4 are repeated in this order, but the second period t2 and the fourth period t4 are not essential and can be omitted.

[0061] For example, in a positive half cycle in which the first terminal a1 of the AC power supply PS1 has a higher potential than the second terminal a2, no current flows through the inductor L1 during the fourth period t4, and no energy is transmitted to the secondary side of the transformer 10, so the control circuit 20 can omit the fourth period t4. Therefore, the control circuit 20 may set the fourth period t4 to zero and perform control so that the first period t1, the second period t2, and the third period t3 are cyclically repeated, thereby shortening the switching period.

[0062] Furthermore, in the negative half cycle in which the first terminal a1 of the AC power supply PS1 has a lower potential than the second terminal a2, no current flows through the inductor L1 during the second period t2, and no energy is transmitted to the secondary side of the transformer 10, so the control circuit 20 can omit the second period t2. Therefore, the control circuit 20 may set the second period t2 to zero and perform control so that the first period t1, the third period t3, and the fourth period t4 are cyclically repeated, thereby shortening the switching cycle.

[0063] In the above embodiment, the first to fourth semiconductor switches S1 to S4 are N-channel MOSFETs, but the first to fourth semiconductor switches S1 to S4 may also be semiconductor switches such as bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors).

[0064] In the above embodiment, the inductor L1 is connected between the first series circuit 2 and the AC power supply PS1, but the inductor L1 may be connected between the first rectifier circuit 4 and the AC power supply PS1, that is, between the connection point P5 of the first diode D1 and the second diode D2 and the first end a1 of the AC power supply PS1. Furthermore, the inductor L1 may be connected between the first series circuit 2 and the AC power supply PS1, and between the first rectifier circuit 4 and the AC power supply PS1.

[0065] In the above embodiment, the converter 1 includes a filter circuit F1 such as an LC filter, but the circuit configuration of the filter circuit F1 can be changed as appropriate. The filter circuit F1 is not an essential component of the converter 1 and can be omitted as appropriate.

[0066] In addition, in the above embodiment, the second rectifier circuit 30 including a diode bridge circuit is connected to the secondary side of the transformer 10, but the configuration of the second rectifier circuit 30 can be changed as appropriate, and it may also be a full-bridge type converter circuit, etc.

[0067] (Summary) The above-described embodiments and the like disclose the following aspects.

[0068] An isolated AC / DC converter (1) of a first aspect includes a first rectifier circuit (4), a first series circuit (2), a second series circuit (3), a third capacitor (C3), an inductor (L1), a transformer (10), a second rectifier circuit (30), and a control circuit (20). The first rectifier circuit (4) includes a series circuit of a first diode (D1) and a second diode (D2) having a cathode connected to the anode of the first diode (D1), and a first end (a1) of an AC power supply (PS1) is connected to a connection point between the first diode (D1) and the second diode (D2). The first series circuit (2) includes a first semiconductor switch (S1), a second semiconductor switch (S2), a third semiconductor switch (S3), and a fourth semiconductor switch (S4) connected in series between the cathode of the first diode (D1) and the anode of the second diode (D2), and a second end (a2) of the AC power supply (PS1) is connected to a connection point between the second semiconductor switch (S2) and the third semiconductor switch (S3). The second series circuit (3) includes a series circuit of a first capacitor (C1) and a second capacitor (C2) and is connected in parallel with the first series circuit (2). The third capacitor (C3) is connected between the connection point between the first semiconductor switch (S1) and the second semiconductor switch (S2) and the connection point between the third semiconductor switch (S3) and the fourth semiconductor switch (S4). An inductor (L1) is connected between the AC power supply (PS1) and at least one of the first rectifier circuit (4) and the first series circuit (2). The transformer (10) has a primary winding (11) connected between a connection point of the second semiconductor switch (S2) and the third semiconductor switch (S3) and a connection point of the first capacitor (C1) and the second capacitor (C2). The second rectifier circuit (30) is connected to a secondary winding (12) of the transformer (10) and rectifies the current flowing through the secondary winding (12) and outputs the rectified current to a load (40). The control circuit (20) controls each of the first semiconductor switch (S1), the second semiconductor switch (S2), the third semiconductor switch (S3), and the fourth semiconductor switch (S4) to an on state or an off state.

[0069] According to this aspect, in a first operating mode in which the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an ON state and the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an OFF state, a current flows through the primary winding (11) of the transformer (10), and power is supplied to a load (40) connected to the secondary winding (12) of the transformer (10). Also, in a fourth operating mode in which the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an ON state and the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an OFF state, a current flows through the primary winding (11) of the transformer (10), and power is supplied to a load (40) connected to the secondary winding (12) of the transformer (10). Therefore, the control circuit (20) can adjust the proportion of the first operating mode and the fourth operating mode within one switching period in which the first to fourth semiconductor switches (S1 to S4) are switched, thereby adjusting the power supplied to the load (40). Furthermore, since a current roughly proportional to the input voltage from the AC power supply (PS1) flows through the inductor (L1), an isolated AC / DC converter (1) capable of improving the power factor can be realized with simple control.

[0070] In the isolated AC / DC converter (1) of the second aspect, the capacitance of the first capacitor (C1) and the capacitance of the second capacitor (C2) are the same as in the first aspect.

[0071] According to this aspect, the voltage at the connection point between the first capacitor (C1) and the second capacitor (C2) can be set to half the voltage (Vbus) across the second series circuit (3).

[0072] In the isolated AC / DC converter (1) of the third aspect, in the first or second aspect, the operation modes of the first to fourth semiconductor switches (S1 to S4) include a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode. In the first operation mode, the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an ON state, and the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an OFF state. In the second operation mode, the first semiconductor switch (S1) and the third semiconductor switch (S3) are in an ON state, and the second semiconductor switch (S2) and the fourth semiconductor switch (S4) are in an OFF state. In the third operation mode, the second semiconductor switch (S2) and the fourth semiconductor switch (S4) are in an ON state, and the first semiconductor switch (S1) and the third semiconductor switch (S3) are in an OFF state. In the fourth operation mode, the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an ON state, and the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an OFF state. The control circuit (20) controls the operation mode to periodically repeat a first period in which the operation mode is the first operation mode, a second period in which the operation mode is the second operation mode or the fourth operation mode, a third period in which the operation mode is the third operation mode, and a fourth period in which the operation mode is the second operation mode or the third operation mode.

[0073] According to this aspect, by periodically repeating the first period, the second period, and the third period, it is possible to convert the input voltage from the AC power supply (PS1) into a DC voltage and supply it to the load (40).

[0074] In the fourth aspect of the isolated AC / DC converter (1), in the third aspect, the control circuit (20) controls the operation mode to either the second operation mode or the fourth operation mode in accordance with the charging voltage of the third capacitor (C3) in each of the second period and the fourth period.

[0075] According to this aspect, the control circuit (20) can control the operating mode in each of the second and fourth periods to either a second operating mode in which the third capacitor (C3) is charged or a third operating mode in which the third capacitor (C3) is discharged, depending on the charging voltage of the third capacitor (C3).

[0076] In the isolated AC / DC converter (1) of the fifth aspect, in the third or fourth aspect, the control circuit (20) controls the time lengths of the first period, the second period, the third period, and the fourth period so as to operate in a discontinuous mode in which the current flowing through the inductor (L1) is discontinuous.

[0077] According to this aspect, it is possible to suppress the inrush current that occurs during switching.

[0078] In the isolated AC / DC converter (1) of the sixth aspect, in the fifth aspect, the control circuit (20) controls the time length of the first period and the time length of the third period to be the same time length, and controls the time lengths of the first period, the second period, the third period, and the fourth period so that the voltage between both ends of the second series circuit (3) is at least twice the peak value of the input voltage input from the AC power supply (PS1).

[0079] According to this embodiment, it is possible to operate in discontinuous mode.

[0080] In the isolated AC / DC converter (1) of a seventh aspect, in any of the third to sixth aspects, the control circuit (20) controls the converter so that, during a positive half cycle in which the first terminal (a1) of the AC power supply (PS1) is at a higher potential than the second terminal (a2), the fourth period is set to zero, and the first, second, and third periods are periodically repeated. During a negative half cycle in which the first terminal (a1) of the AC power supply (PS1) is at a lower potential than the second terminal (a2), the control circuit (20) controls the converter so that the second period is set to zero, and the first, third, and fourth periods are periodically repeated.

[0081] According to this aspect, the switching period can be shortened.

[0082] In the isolated AC / DC converter (1) of an eighth aspect, in any one of the third to seventh aspects, the control circuit (20) controls the duration of the first period to the duration of the third period to be the same duration. The control circuit (20) controls the power supply to the load (40) by adjusting the ratio between the total duration of the first period and the third period and the total duration of the second period and the fourth period.

[0083] According to this aspect, power is supplied to the load (40) in the first operation mode and the fourth operation mode, and power supply to the load (40) is stopped in the second operation mode and the third operation mode. Therefore, the control circuit (20) can control the power supply to the load (40) by adjusting the ratio between the total time length of the first period and the third period in which the control circuit (20) operates in the first operation mode and the fourth operation mode, respectively, and the total time length of the second period and the fourth period in which the control circuit (20) operates in the second operation mode or the third operation mode.

[0084] In the isolated AC / DC converter (1) of a ninth aspect, in any one of the first to eighth aspects, the second rectifier circuit (30) includes a diode bridge circuit.

[0085] According to this aspect, the second rectifier circuit (30) is configured as a diode bridge circuit that does not require control, so that the configuration of the control circuit (20) can be simplified.

[0086] The configurations according to the second to ninth aspects are not essential for the isolated AC / DC converter (1) and can be omitted as appropriate.

[0087] REFERENCE SIGNS LIST 1 Isolated AC / DC converter 2 First series circuit 3 Second series circuit 4 First rectifier circuit 10 Transformer 11 Primary winding 12 Secondary winding 20 Control circuit 30 Second rectifier circuit 40 Load a1 First terminal a2 Second terminal C1 First capacitor C2 Second capacitor C3 Third capacitor D1 First diode D2 Second diode L1 Inductor PS1 AC power supply S1 First semiconductor switch S2 Second semiconductor switch S3 Third semiconductor switch S4 Fourth semiconductor switch

Claims

1. A first rectifier circuit includes a series circuit of a first diode and a second diode whose cathode is connected to the anode of the first diode, and the first terminal of an AC power supply is connected to the connection point of the first diode and the second diode. A first series circuit includes a first semiconductor switch, a second semiconductor switch, a third semiconductor switch, and a fourth semiconductor switch connected in series between the cathode of the first diode and the anode of the second diode, wherein the second terminal of the AC power supply is connected to the connection point of the second semiconductor switch and the third semiconductor switch. The first series circuit includes a series circuit of a first capacitor and a second capacitor, and the second series circuit is connected in parallel with the first series circuit. A third capacitor connected between the connection point of the first semiconductor switch and the second semiconductor switch and the connection point of the third semiconductor switch and the fourth semiconductor switch, An inductor connected between at least one of the first rectifier circuit and the first series circuit and the AC power supply, A transformer in which a primary winding is connected between the connection point of the second semiconductor switch and the third semiconductor switch and the connection point of the first capacitor and the second capacitor, A second rectifier circuit is connected to the secondary winding of the transformer and rectifies the current flowing through the secondary winding, which is then output to the load. The system comprises a control circuit for controlling each of the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, and the fourth semiconductor switch to an ON state or an OFF state. Isolated AC / DC converter.

2. The capacitance of the first capacitor and the capacitance of the second capacitor are the same. The isolated AC / DC converter according to claim 1.

3. The operating modes of the first to fourth semiconductor switches are: A first operating mode in which the first semiconductor switch and the second semiconductor switch are in the ON state and the third semiconductor switch and the fourth semiconductor switch are in the OFF state, A second operating mode in which the first semiconductor switch and the third semiconductor switch are in the ON state and the second semiconductor switch and the fourth semiconductor switch are in the OFF state, A third operating mode in which the second semiconductor switch and the fourth semiconductor switch are in the ON state and the first semiconductor switch and the third semiconductor switch are in the OFF state, A fourth operating mode is included in which the third semiconductor switch and the fourth semiconductor switch are in the ON state and the first semiconductor switch and the second semiconductor switch are in the OFF state, The aforementioned control circuit is The system is controlled to periodically repeat a first period in which the operating mode is the first operating mode, a second period in which the operating mode is the second or third operating mode, a third period in which the operating mode is the fourth operating mode, and a fourth period in which the operating mode is the second or third operating mode. The isolated AC / DC converter according to claim 1 or 2.

4. The control circuit controls the operating mode to either the second operating mode or the third operating mode in each of the second and fourth periods, according to the charging voltage of the third capacitor. The isolated AC / DC converter according to claim 3.

5. The control circuit controls the duration of the first period, the second period, the third period, and the fourth period so that it operates in a discontinuous mode in which the current flowing through the inductor is discontinuous. The isolated AC / DC converter according to claim 3.

6. The aforementioned control circuit is The length of the first period and the length of the third period are set to be the same length. The durations of the first, second, third, and fourth periods are controlled such that the voltage across the second series circuit is at least twice the peak value of the input voltage received from the AC power supply. The isolated AC / DC converter according to claim 5.

7. The aforementioned control circuit is During a positive half-cycle in which the first terminal of the AC power supply is at a higher potential than the second terminal, the fourth period is set to zero, and the first period, the second period, and the third period are controlled to repeat periodically. During a negative half-cycle in which the first terminal of the AC power supply is at a lower potential than the second terminal, the second period is set to zero, and the first period, the third period, and the fourth period are controlled to repeat periodically. The isolated AC / DC converter according to claim 3.

8. The aforementioned control circuit is The length of the first period and the length of the third period are set to be the same length. The power supplied to the load is controlled by adjusting the ratio of the total time length of the first period and the total time length of the third period to the total time length of the second period and the total time length of the fourth period. The isolated AC / DC converter according to claim 3.

9. The second rectifier circuit includes a diode bridge circuit, The isolated AC / DC converter according to claim 1 or 2.