Converter device

Abstract

The present disclosure addresses the problem of providing a converter device capable of controlling output power at a light load with high efficiency. A converter device (A1) comprises a rectifier (2), a first inverter (3), a first inductor (L1), a transformer (Tr1), a second inverter (4), a second inductor (L2), and a control circuit (5). The control circuit (5) controls the first inverter (3) and the second inverter (4) so that a first switching element (Q1) and a third switching element (Q3) perform switching operations at the same timing and a second switching element (Q2) and a fourth switching element (Q4) perform switching operations at the same timing. The control circuit (5) controls the ON periods or the OFF periods of the first switching element (Q1) and the second switching element (Q2) in accordance with the output voltage (Vo) of the second inverter (4).

Description

Converter device

[0001] The present disclosure generally relates to a converter device, and more particularly to a converter device including a transformer.

[0002] The converter device described in Patent Document 1 will be exemplified. The converter device described in Patent Document 1 includes a rectifier, a half-bridge inverter, an input inductor, a transformer, an inductor, a full-bridge inverter, and a control device. The half-bridge inverter has two semiconductor switching elements. The full-bridge inverter has four semiconductor switching elements. The control device controls the two semiconductor switching elements and the four semiconductor switching elements.

[0003] In the converter device described in Patent Document 1, for example, the switching frequency of the semiconductor switching element may increase during light load (when the output power is small), and it is difficult to control the output power during light load with high efficiency.

[0004] International Publication No. 2023 / 243321

[0005] An object of the present disclosure is to provide a converter device capable of controlling the output power during light load with high efficiency.

[0006] A converter device according to one aspect of the present disclosure comprises a rectifier, a first inverter, a first inductor, a transformer, a second inverter, a second inductor, and a control circuit. The rectifier includes a first diode and a second diode connected in series with the first diode. The rectifier rectifies the AC voltage of an AC power supply. The first inverter has a first series circuit and a second series circuit connected in parallel, and the first series circuit and the second series circuit are connected in parallel with the rectifier. The first series circuit is a series circuit in which a first switching element and a second switching element are connected in series. The second series circuit is a series circuit in which a first capacitor and a second capacitor are connected in series. The first inductor is provided in the circuit between the first output terminal of the AC power supply and the connection point of the first diode and the second diode, or in the circuit between the second output terminal of the AC power supply and the connection point of the first switching element and the second switching element. The transformer has a primary winding and a secondary winding. The primary winding of the transformer is electrically connected between the connection point of the first switching element and the second switching element and the connection point of the first capacitor and the second capacitor. The second inverter is composed of a half-bridge inverter or a full-bridge inverter including a pair of input terminals, a pair of output terminals, a third switching element and a fourth switching element. The secondary winding of the second inverter is electrically connected between the pair of input terminals. The second inductor is provided in the circuit between the first inverter and the primary winding, or in the circuit between the secondary winding and the second inverter. The control circuit controls the first inverter and the second inverter. The control circuit controls the first inverter and the second inverter so that the duty cycles of the first switching element, the second switching element, the third switching element and the fourth switching element are the same. The control circuit controls the first inverter and the second inverter so that the first switching element and the third switching element switch at the same timing, and the second switching element and the fourth switching element switch at the same timing.The control circuit controls the on-period or off-period of the first switching element and the second switching element according to the output voltage of the second inverter.

[0007] A converter device according to one aspect of the present disclosure comprises a rectifier, a first inverter, a first inductor, a transformer, a second inverter, a second inductor, and a control circuit. The rectifier includes a first diode and a second diode connected in series with the first diode. The rectifier rectifies the AC voltage of an AC power supply. The first inverter has a first series circuit and a second series circuit connected in parallel, and the first series circuit and the second series circuit are connected in parallel with the rectifier. The first series circuit is a series circuit in which a first switching element and a second switching element are connected in series. The second series circuit is a series circuit in which a first capacitor and a second capacitor are connected in series. The first inductor is provided in the circuit between the first output terminal of the AC power supply and the connection point of the first diode and the second diode, or in the circuit between the second output terminal of the AC power supply and the connection point of the first switching element and the second switching element. The transformer has a primary winding and a secondary winding. The primary winding of the transformer is electrically connected between the connection point of the first switching element and the second switching element and the connection point of the first capacitor and the second capacitor. The second inverter consists of a diode bridge including a pair of input terminals, a pair of output terminals and four diodes. The secondary winding of the second inverter is electrically connected between the pair of input terminals. The second inductor is provided in the circuit between the first inverter and the primary winding, or in the circuit between the secondary winding and the second inverter. The control circuit controls the first inverter. The control circuit controls the first inverter so that the duty cycles of the first switching element and the second switching element are the same. The control circuit controls the on or off period of the first switching element and the second switching element according to the output voltage of the second inverter.

[0008] Figure 1 is a circuit diagram of a converter device according to Embodiments 1 and 2. Figure 2 is a timing chart showing the operation of the same converter device. Figure 3 is a timing chart showing the operation of the same converter device when the polarity of the AC voltage is positive. Figure 4 is a timing chart showing the operation of the same converter device when the polarity of the AC voltage is negative. Figure 5 is a waveform diagram showing the operation of the converter device according to Embodiment 1 when the on-period of the first switching element and the second switching element is controlled. Figure 6 is another waveform diagram showing the operation of the same converter device when the on-period of the first switching element and the second switching element is controlled. Figure 7 is a graph showing the relationship between the on-period of the first switching element and the second switching element and the output power of the second inverter for the same converter device. Figure 8 is a waveform diagram showing the operation of the converter device according to Embodiment 2 when the off-period of the first switching element and the second switching element is controlled. Figure 9 is another waveform diagram showing the operation of the same converter device when the off-period of the first switching element and the second switching element is controlled. Figure 10 is a circuit diagram of a converter device according to Embodiment 3.

[0009] The converter devices according to Embodiments 1 to 3 will be described below with reference to the drawings. The configurations described in each of the embodiments below are merely examples of the present disclosure. The present disclosure is not limited to the embodiments below, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0010] (Embodiment 1) Hereinafter, a converter device according to Embodiment 1 will be described with reference to Figures 1 to 7.

[0011] (1) Converter device embodiment 1, converter device A1, is an isolated AC-DC converter equipped with a transformer Tr1, as shown in Figure 1. Converter device A1 includes, for example, a pair of input terminals 11, 12, an input filter 6, a first inductor L1, a rectifier 2, a first inverter 3, a second inductor L2, a transformer Tr1, a second inverter 4, an output filter C4, a control circuit 5, and a pair of output terminals 13, 14.

[0012] The pair of input terminals 11 and 12 are electrically connected to an AC power source 8, for example, via a pair of power lines (not shown). That is, the converter device A1 is electrically connected to the AC power source 8 between the pair of input terminals 11 and 12. For example, input terminal 11 is electrically connected to the first output terminal 81 of the AC power source 8. Input terminal 12 is electrically connected to the second output terminal 82 of the AC power source 8. The AC power source 8 includes, for example, a commercial power grid. The voltage between the pair of input terminals 11 and 12 is the voltage (AC voltage) Vin input from the AC power source 8. The AC voltage Vin is, for example, a sinusoidal AC voltage.

[0013] The pair of output terminals 13 and 14 are electrically connected to a load (not shown) via, for example, a pair of connecting wires (not shown). In other words, the converter device A1 has the load electrically connected between the pair of output terminals 13 and 14.

[0014] Loads include, for example, information equipment, home appliances, communication equipment, lighting fixtures, and wiring devices. Information equipment includes, for example, smartphones, tablet devices, and laptop computers. Home appliances include, for example, televisions and air conditioners. Communication equipment includes, for example, wireless adapters that enable wireless communication. Lighting fixtures include, for example, LED lighting fixtures. Wiring devices include, for example, electrical outlets and wall switches.

[0015] (1.1) Input Filter The input filter 6 is an EMI (Electromagnetic Interference) filter. The input filter 6 is, for example, an L-type filter composed of an inductor L3 and a capacitor C3. The first end of the inductor L3 is electrically connected to the input terminal 11. The second end of the inductor L3 is electrically connected to the first end of the capacitor C3. The second end of the capacitor C3 is electrically connected to the input terminal 12.

[0016] (1.2) The first inductor L1 is provided in the circuit between the first output terminal 81 of the AC power supply 8 and the rectifier 2. More specifically, the first inductor L1 is provided in the circuit between the input filter 6 and the rectifier 2. Specifically, the first terminal of the first inductor L1 is electrically connected to the second terminal of the inductor L3 of the input filter 6. The second terminal of the first inductor L1 is electrically connected to the rectifier 2.

[0017] (1.3) Rectifier The rectifier 2 rectifies the AC voltage Vin of the AC power supply 8. The rectifier 2 is, for example, a half-wave rectifier. The rectifier 2 includes, for example, two diodes D1 and D2, with diode D1 and diode D2 connected in series with each other. The cathode of diode D1 is electrically connected to the first inverter 3. The anode of diode D1 is electrically connected to the second terminal of the first inductor L1. Also, the anode of diode D1 is electrically connected to the cathode of diode D2. The anode of diode D2 is electrically connected to the first inverter 3.

[0018] (1.4) First Inverter The first inverter 3 is, for example, a half-bridge inverter. The first inverter 3 includes, for example, two switching elements Q1 and Q2 and two capacitors C1 and C2. The first inverter 3 has a first series circuit 31 in which switching elements Q1 and Q2 are connected in series with each other, and a second series circuit 32 in which capacitors C1 and C2 are connected in series with each other, connected in parallel. The first series circuit 31 is electrically connected in parallel with the rectifier 2. The second series circuit 32 is electrically connected in parallel with the first series circuit 31. In other words, the second series circuit 32 is electrically connected in parallel with the rectifier 2.

[0019] Each of the two switching elements Q1 and Q2 is, for example, a GaN-based GIT (Gate Injection Transistor). Each of the two switching elements Q1 and Q2 has a first main terminal, a second main terminal, and a control terminal. In the following description to aid in understanding the embodiment, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0020] The drain terminal of switching element Q1 is electrically connected to the cathode of diode D1 of rectifier 2. The drain terminal of switching element Q1 is also electrically connected to the first terminal of capacitor C1. The second terminal of capacitor C1 is electrically connected to the primary winding N1 of transformer Tr1 (described later). The second terminal of capacitor C1 is also electrically connected to the first terminal of capacitor C2. The second terminal of capacitor C2 is electrically connected to the source terminal of switching element Q2.

[0021] The source terminal of switching element Q2 is electrically connected to the anode of diode D2 of rectifier 2. The gate terminal of switching element Q2 is electrically connected to control circuit 5. The drain terminal of switching element Q2 is electrically connected to the second terminal of capacitor C3 of input filter 6. In addition, the drain terminal of switching element Q2 is electrically connected to the source terminal of switching element Q1. The gate terminal of switching element Q1 is electrically connected to control circuit 5.

[0022] The capacitance of capacitor C2 is, for example, the same as the capacitance of capacitor C1. Note that "the capacitance of capacitor C2 is the same as the capacitance of capacitor C1" does not only mean that the capacitance of capacitor C2 is exactly the same as the capacitance of capacitor C1, but also includes cases where, for example, the capacitances of capacitors C1 and C2 each have an error of ±20% from their nominal values.

[0023] (1.5) Transformer and second inductor Transformer Tr1 has a primary winding N1 and a secondary winding N2. The first end of the primary winding N1 is electrically connected to the connection point 34 of switching elements Q1 and Q2 in the first inverter 3 via the second inductor L2. In other words, the second inductor L2 is provided in the circuit between the first inverter 3 and the primary winding N1 of transformer Tr1. Specifically, the first end of the second inductor L2 is electrically connected to the connection point 34 of switching elements Q1 and Q2. The second end of the second inductor L2 is electrically connected to the first end of the primary winding N1 of transformer Tr1.

[0024] The connection point 34 between switching element Q1 and switching element Q2 may be, for example, a connection point provided on the circuit between the source terminal of switching element Q1 and the drain terminal of switching element Q2, or it may be the source terminal of switching element Q1, or it may be the drain terminal of switching element Q2.

[0025] The second end of the primary winding N1 is electrically connected to the connection point 35 of capacitors C1 and C2 in the first inverter 3. In other words, the primary winding N1 is electrically connected between the connection point 34 of switching elements Q1 and Q2 in the first inverter 3 and the connection point 35 of capacitors C1 and C2 in the first inverter 3.

[0026] The connection point 35 between capacitors C1 and C2 may be, for example, a connection point provided on the circuit between the second end of capacitor C1 and the first end of capacitor C2, or it may be the second end of capacitor C1, or it may be the first end of capacitor C2.

[0027] The first end of the secondary winding N2 is electrically connected to the connection point 44 in the second inverter 4, which will be described later. The second end of the secondary winding N2 is electrically connected to the connection point 45 in the second inverter 4, which will be described later.

[0028] (1.6) Second Inverter The second inverter 4 is, for example, a full-bridge inverter. The second inverter 4 includes, for example, four switching elements Q3 to Q6. Each of the four switching elements Q3 to Q6 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). More specifically, each of the four switching elements Q3 to Q6 is, for example, an n-channel MOSFET. The n-channel MOSFET is, for example, a normally-off Si-based MOSFET. Each of the four switching elements Q3 to Q6 has a first main terminal, a second main terminal, and a control terminal. Each of the four switching elements Q3 to Q6 also has a parasitic diode. In the following, to aid in understanding the description of the embodiment, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0029] The drain terminal of switching element Q3 is electrically connected to the drain terminal of switching element Q5. The gate terminal of switching element Q3 is electrically connected to the control circuit 5. The source terminal of switching element Q3 is electrically connected to the first end of the secondary winding N2 of transformer Tr1. In addition, the source terminal of switching element Q3 is electrically connected to the drain terminal of switching element Q4. The gate terminal of switching element Q4 is electrically connected to the control circuit 5. The source terminal of switching element Q4 is electrically connected to the source terminal of switching element Q6.

[0030] The source terminal of switching element Q6 is electrically connected to output filter C4. The gate terminal of switching element Q6 is electrically connected to control circuit 5. The drain terminal of switching element Q6 is electrically connected to the second end of the secondary winding N2 of transformer Tr1. The drain terminal of switching element Q6 is also electrically connected to the source terminal of switching element Q5. The gate terminal of switching element Q5 is electrically connected to control circuit 5. The drain terminal of switching element Q5 is electrically connected to output filter C4.

[0031] In this embodiment, the connection point 44 between switching element Q3 and switching element Q4 is the input terminal (first input terminal) of the second inverter 4. Also, the connection point 45 between switching element Q5 and switching element Q6 is the input terminal (second input terminal) of the second inverter 4. In other words, the secondary winding N2 of transformer Tr1 is electrically connected between the pair of input terminals 44 and 45 of the second inverter 4.

[0032] The connection point 44 between switching element Q3 and switching element Q4 may, for example, be a connection point provided on the circuit between the source terminal of switching element Q3 and the drain terminal of switching element Q4, or it may be the source terminal of switching element Q3, or it may be the drain terminal of switching element Q4. Similarly, the connection point 45 between switching element Q5 and switching element Q6 may, for example, be a connection point provided on the circuit between the source terminal of switching element Q5 and the drain terminal of switching element Q6, or it may be the source terminal of switching element Q5, or it may be the drain terminal of switching element Q6.

[0033] In this embodiment, the connection point 46 between switching element Q3 and switching element Q5 is the output terminal (first output terminal) of the second inverter 4. Also, the connection point 47 between switching element Q4 and switching element Q6 is the output terminal (second output terminal) of the second inverter 4. In other words, the second inverter 4 includes a pair of input terminals 44 and 45, a pair of output terminals 46 and 47, and four switching elements Q3 to Q6.

[0034] The connection point 46 between switching element Q3 and switching element Q5 may, for example, be a connection point provided on the circuit between the drain terminal of switching element Q3 and the drain terminal of switching element Q5, or it may be the drain terminal of switching element Q3, or it may be the drain terminal of switching element Q5. Also, the connection point 47 between switching element Q4 and switching element Q6 may, for example, be a connection point provided on the circuit between the source terminal of switching element Q4 and the source terminal of switching element Q6, or it may be the source terminal of switching element Q4, or it may be the source terminal of switching element Q6.

[0035] (1.7) Output Filter The output filter C4 smooths the output voltage of the second inverter 4. The output filter C4 is, for example, an electrolytic capacitor. The first terminal (high potential side terminal) of the output filter C4 is electrically connected to the drain terminal of the switching element Q5 in the second inverter 4. The first terminal of the output filter C4 is also electrically connected to the output terminal 13. The second terminal (low potential side terminal) of the output filter C4 is electrically connected to the source terminal of the switching element Q6 in the second inverter 4. The second terminal of the output filter C4 is also electrically connected to the output terminal 14. In other words, the output filter C4 is electrically connected between the pair of output terminals 46 and 47 of the second inverter 4.

[0036] (1.8) Control Circuit The control circuit 5 is implemented, for example, by a computer system having one or more processors and one or more memories. In other words, the functions of the control circuit 5 are realized by one or more processors executing a program stored in memory. The program may be pre-stored in memory, provided via a telecommunication line such as the Internet, or provided on a non-temporary recording medium such as a memory card.

[0037] The control circuit 5 controls the first inverter 3. More specifically, the control circuit 5 controls two switching elements Q1 and Q2. The control circuit 5 outputs a control signal S1 to the switching element Q1. The control signal S1 is a signal for controlling the switching element Q1. More specifically, the control signal S1 is a signal that switches the switching element Q1 to either an on state or an off state. As shown in Figure 2, the control signal S1 is, for example, a pulsed signal (for example, a PWM signal). The duty cycle of the control signal S1 is within the range of 0% to 50%. For example, the duty cycle of the control signal S1 is 40%.

[0038] The duty cycle represents the ratio of the high-level period to the total period during which the signal level of control signal S1 is high (high-level period) and the low-level period (low-level period). In Figure 2, the period Ton represents the high-level period (on period) of control signal S1. In Figure 2, the period Toff represents the low-level period (off period) of control signal S1. In Figure 2, the period Tsw represents the total period of the high-level period (period Ton) and the low-level period (period Toff) of control signal S1. In other words, the period Tsw in Figure 2 represents the switching period of control signal S1.

[0039] Furthermore, the control circuit 5 shown in Figure 1 outputs a control signal S2 to the switching element Q2. The control signal S2 is a signal for controlling the switching element Q2. More specifically, the control signal S2 is a signal that switches the switching element Q2 to either an on state or an off state. The control signal S2 is, for example, a pulsed signal. The duty cycle of the control signal S2 is within the range of 0% to 50%. For example, the duty cycle of the control signal S2 is 40%.

[0040] In other words, the control circuit 5 controls the first inverter 3 so that the duty cycle of control signal S1 and the duty cycle of control signal S2 are the same. To put it another way, the control circuit 5 controls the first inverter 3 so that the on-period Ton of switching element Q1 and the on-period Ton of switching element Q2 are the same.

[0041] Note that the "same duty" includes not only the case where the duty of control signal S1 is exactly the same as the duty of control signal S2, but also, for example, the case where the difference (absolute value of the difference) between the duty of control signal S1 and the duty of control signal S2 is of the error level (for example, 5%).

[0042] As shown in FIG. 2, when the signal level of control signal S1 is high level, control circuit 5 outputs control signals S1 and S2 to first inverter 3 such that the signal level of control signal S2 becomes low level. Also, when the signal level of control signal S1 is low level, control circuit 5 outputs control signals S1 and S2 to first inverter 3 such that the signal level of control signal S2 becomes high level.

[0043] In other words, when switching element Q1 is in the on state, control circuit 5 outputs control signals S1 and S2 to first inverter 3 such that switching element Q2 is in the off state. Also, when switching element Q1 is in the off state, control circuit 5 outputs control signals S1 and S2 to first inverter 3 such that switching element Q2 is in the on state. In short, control circuit 5 controls first inverter 3 such that switching element Q1 and switching element Q2 are alternately in the on state.

[0044] Control circuit 5 controls switching element Q1 and switching element Q2 so as to include a period T2 (hereinafter referred to as "first dead time period") during which switching element Q1 and switching element Q2 are in the off state between the time point when switching element Q1 turns off (in the example of FIG. 2, time point t2) and the time point when switching element Q2 turns on (in the example of FIG. 2, time point t3). Note that the "time point when switching element Q1 turns off" means the time point when switching element Q1 switches from the on state to the off state. Also, the "time point when switching element Q2 turns on" means the time point when switching element Q2 switches from the off state to the on state.

[0045] Further, the control circuit 5 controls the switching elements Q1 and Q2 so as to include a period T4 (hereinafter referred to as "second dead time period") during which the switching elements Q1 and Q2 are in an off state between the time point when the switching element Q2 turns off (time point t5 in the example of FIG. 2) and the time point when the switching element Q1 turns on (time point t6 in the example of FIG. 2).

[0046] Therefore, as shown in FIG. 2, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 so that the on period Ton (first on time T1) of the switching element Q1, the first dead time period T2, the on period Ton (second on period T3) of the switching element Q2, and the second dead time period T4 are repeated in order. As a result, in the converter device A1, as shown in FIG. 2, the current i1 flowing through the first inductor L1 changes.

[0047] Note that the period Ta in FIG. 2 is a period (charging period) during which electrical energy is stored in the first inductor L1. In other words, the period Ta is a period during which a charging current flows through the first inductor L1. The period Tb in FIG. 2 is a period (discharging period) during which the electrical energy stored in the first inductor L1 is discharged. In other words, the period Tb is a period during which a discharging current flows through the first inductor L1. The period Tc in FIG. 2 is a period (zero current period) during which no current flows through the first inductor L1.

[0048] The control circuit 5 shown in FIG. 1 controls the second inverter 4. More specifically, the control circuit 5 controls four switching elements Q3 to Q6. The control circuit 5 outputs a control signal S3 to the switching element Q3. The control signal S3 is a signal for controlling the switching element Q3. More specifically, the control signal S3 is a signal for switching the switching element Q3 to either an on state or an off state. The control signal S3 is, for example, a pulse-shaped signal. The duty of the control signal S3 is the same as the duty of the control signal S1. The duty of the control signal S3 is, for example, 40%.

[0049] Furthermore, the control circuit 5 outputs a control signal S4 to the switching element Q4. The control signal S4 is a signal for controlling the switching element Q4. More specifically, the control signal S4 is a signal that switches the switching element Q4 to either an on state or an off state. The control signal S4 is, for example, a pulsed signal. The duty cycle of the control signal S4 is the same as the duty cycle of the control signal S2. The duty cycle of the control signal S4 is, for example, 40%.

[0050] Furthermore, the control circuit 5 outputs a control signal S5 to the switching element Q5. The control signal S5 is a signal for controlling the switching element Q5. More specifically, the control signal S5 is a signal that switches the switching element Q5 to either an on state or an off state. The control signal S5 is, for example, a pulsed signal. The duty cycle of the control signal S5 is the same as the duty cycle of the control signal S3. The duty cycle of the control signal S5 is, for example, 40%.

[0051] Furthermore, the control circuit 5 outputs a control signal S6 to the switching element Q6. The control signal S6 is a signal for controlling the switching element Q6. More specifically, the control signal S6 is a signal that switches the switching element Q6 to either an on state or an off state. The control signal S6 is, for example, a pulsed signal. The duty cycle of the control signal S6 is the same as the duty cycle of the control signal S4. The duty cycle of the control signal S6 is, for example, 40%.

[0052] The control circuit 5 outputs control signals S3 and S5 to the second inverter 4 so that they synchronize with control signal S1. In short, the control circuit 5 controls the second inverter 4 so that switching elements Q3 and Q5 perform the same switching operation as switching element Q1 (see Figures 3 and 4).

[0053] Furthermore, "same switching operation" does not only mean, for example, that the switching operation of switching element Q3 is exactly the same as the switching operation of switching element Q1, but also includes cases where there is a slight delay between the switching operation of switching element Q3 and the switching operation of switching element Q1. Also, the duty cycles of control signals S1, S3, and S5 in Figures 3 and 4 are shown as an example of 25%, but these duty cycles are not limited to these cases.

[0054] Furthermore, the control circuit 5 outputs control signals S4 and S6 to the second inverter 4 so that they synchronize with control signal S2. In short, the control circuit 5 controls the second inverter 4 so that switching elements Q4 and Q6 perform the same switching operation as switching element Q2 (see Figures 3 and 4). Note that the duty cycles of control signals S2, S4, and S6 in Figures 3 and 4 are shown as an example of 25%, but these duty cycles are not limited.

[0055] The control circuit 5 shown in Figure 1 detects, for example, the output voltage of the second inverter 4 (specifically, the output voltage Vo of the output filter C4). The control circuit 5 also controls the on-period Ton of switching elements Q1 and Q2 according to the output voltage Vo. In other words, the control circuit 5 controls the duty cycle of switching elements Q1 and Q2 according to the output voltage Vo.

[0056] Furthermore, the output voltage Vo of output filter C4 is the same as the output voltage of the second inverter 4. The statement "the output voltage Vo of output filter C4 is the same as the output voltage of the second inverter 4" does not only mean that the output voltage Vo of output filter C4 is exactly the same as the output voltage of the second inverter 4, but also includes cases where, for example, the difference (absolute value of the difference) between the output voltage Vo of output filter C4 and the output voltage of the second inverter 4 is within the margin of error (for example, 5%).

[0057] Furthermore, the control circuit 5 detects the AC voltage Vin of the AC power supply 8. Based on the polarity of the AC voltage Vin, the control circuit 5 controls the switching elements Q1 and Q2.

[0058] The control circuit 5 includes, for example, a detection unit 52, a control unit 53, a generation unit 54, and a determination unit 55.

[0059] The detection unit 52 detects, for example, the voltage value of the output voltage Vo of the second inverter 4. The detection unit 52 also detects, for example, the voltage value of the AC voltage Vin. The detection unit 52 is electrically connected, for example, to a pair of input terminals 11 and 12. The detection unit 52 is also electrically connected, for example, to a pair of output terminals 13 and 14. The detection unit 52 is also electrically connected to the control unit 53.

[0060] The control unit 53 is configured, for example, to perform PI control. The control unit 53 calculates the deviation (deviation value) between the voltage value of the output voltage Vo detected by the detection unit 52 and the output voltage command value, and determines the ON period Ton for performing feedback control to bring the deviation value closer to zero. The output voltage command value is, for example, a reference value of the output voltage Vo. The output voltage command value is, for example, stored in the memory of the control circuit 5. The control unit 53 is electrically connected to the generation unit 54.

[0061] The generation unit 54 generates a control signal S1 that includes the ON period Ton determined by the control unit 53, and outputs the control signal S1 to the switching element Q1 of the first inverter 3. The generation unit 54 is electrically connected to the gate terminal of the switching element Q1. The generation unit 54 is also electrically connected to the gate terminals of each of the five switching elements Q2 to Q6. The generation unit 54 outputs five control signals S2 to S6 to the corresponding switching elements Q2 to Q6, respectively. Note that the operation of the generation unit 54 in generating the five control signals S2 to S6 is the same as the operation of the generation unit 54 in generating the control signal S1, except that the target switching element is different.

[0062] The determination unit 55 determines the polarity of the AC voltage Vin based on the voltage value of the AC voltage Vin detected by the detection unit 52.

[0063] If the polarity of the AC voltage Vin determined by the determination unit 55 is positive, the generation unit 54 outputs control signals S1 and S2 to the first inverter 3 so that switching element Q1 turns on before switching element Q2, as shown in Figure 3. In other words, if the polarity of the AC voltage Vin determined by the determination unit 55 is positive, the control circuit 5 controls switching element Q1 and the second switching element Q2 so that switching element Q1 turns on before switching element Q2.

[0064] In Figure 3, the period Ton represents the ON period of switching elements Q1 and Q2. In Figure 3, the period Toff represents the OFF period of switching element Q1. In Figure 3, the period Tsw represents the switching period of switching element Q1. In Figure 3, the period T1 represents the period when the three switching elements Q1, Q3, and Q5 are in the ON state. In Figure 3, the period T2 represents the period when the six switching elements Q1 to Q6 are in the OFF state. In Figure 3, the period T3 represents the period when the three switching elements Q2, Q4, and Q6 are in the ON state. In Figure 3, the period T4 represents the period when the six switching elements Q1 to Q6 are in the OFF state.

[0065] Furthermore, if the polarity of the AC voltage Vin determined by the determination unit 55 is negative, the generation unit 54 outputs control signals S1 and S2 to the first inverter 3 so that the switching element Q2 turns on before the switching element Q1, as shown in Figure 4. In other words, if the polarity of the AC voltage Vin determined by the determination unit 55 is negative, the control circuit 5 controls the switching element Q1 and the second switching element Q2 so that the switching element Q2 turns on before the switching element Q1.

[0066] In Figure 4, the period Ton represents the ON period of switching elements Q1 and Q2. In Figure 4, the period Toff represents the OFF period of switching element Q2. In Figure 4, the period Tsw represents the switching period of switching element Q2. In Figure 4, the period T5 represents the period when the three switching elements Q2, Q4, and Q6 are in the ON state. In Figure 4, the period T6 represents the period when the six switching elements Q1 to Q6 are in the OFF state. In Figure 4, the period T7 represents the period when the three switching elements Q1, Q3, and Q5 are in the ON state. In Figure 4, the period T8 represents the period when the six switching elements Q1 to Q6 are in the OFF state.

[0067] Incidentally, the control circuit 5 controls switching elements Q1 and Q2 such that the on-period Ton of switching elements Q1 and Q2 is variable, and the switching period Tsw of switching elements Q1 and Q2 is constant. Furthermore, the control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4, for example.

[0068] For example, the control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 so that the on-period Ton of switching elements Q1 and Q2 increases as the output voltage Vo of the second inverter 4 increases (see Figure 5). Also, the control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 so that the on-period Ton of switching elements Q1 and Q2 decreases as the output voltage Vo of the second inverter 4 decreases (see Figure 6). In other words, as shown in Figure 7, the converter device A1 can adjust the output power to a predetermined power by changing the on-period Ton of switching elements Q1 and Q2.

[0069] Therefore, in converter device A1, it is possible to control the output power without changing the switching period Tsw (switching frequency) of switching elements Q1 and Q2. This makes it possible to control the output power efficiently even under light load conditions (for example, when the output power is low). In other words, converter device A1 can efficiently control the output power under light load conditions. Furthermore, because converter device A1 can control the output power during light load operation, it is also possible to respond to load fluctuations efficiently.

[0070] In Figures 5 and 6, the period Tsw1 represents the switching period of switching elements Q1 and Q2. In Figure 5, the period Ton1 represents the ON period Ton of switching elements Q1 and Q2 when the output voltage Vo of the second inverter 4 increases. In Figure 6, the period Ton2 represents the ON period Ton of switching elements Q1 and Q2 when the output voltage Vo of the second inverter 4 decreases.

[0071] In this case, it is preferable that the control circuit 5 shown in Figure 1 controls the switching elements Q1 and Q2 so that the mode of the current i1 flowing through the first inductor L1 becomes a current discontinuity mode. This makes it possible to improve the power factor in the converter device A1, thereby achieving a higher power factor and higher efficiency.

[0072] The control circuit 5 controls switching elements Q1 and Q2 so that when the polarity of the AC voltage Vin is positive, switching element Q1 turns on before switching element Q2. Furthermore, the control circuit 5 controls switching elements Q1 and Q2 so that when the polarity of the AC voltage Vin is negative, switching element Q2 turns on before switching element Q1. As a result, in the converter device A1, a mode occurs in which current i1 flows through the first inductor L1 during the periods when switching elements Q1 and Q2 are in the off state (in the example in Figure 3, the first dead time period T2 and the second dead time period T4). Therefore, in the converter device A1, since no current flows from the source terminal to the drain terminal of switching elements Q1 and Q2 during the periods when switching elements Q1 and Q2 are in the off state, the deterioration of conduction losses in switching elements Q1 and Q2 can be reduced.

[0073] Furthermore, the control circuit 5 determines the on-time Ton for feedback control based on the deviation between the value detected by the detection unit 52 (voltage value of the output voltage Vo) and a reference value. This makes it possible for the converter device A1 to stabilize the output power and respond to load fluctuations.

[0074] (2) The modified form detection unit 52 detects the voltage value of the output voltage Vo of the second inverter 4, but may also detect the current value of the output current Io of the second inverter 4, or the voltage value of the output voltage (DC bus voltage) Vdc of the second series circuit 32 of the first inverter 3. Alternatively, the detection unit 52 may detect two values, for example, the voltage value of the output voltage Vo of the second inverter 4 and the current value of the output current Io of the second inverter 4. Alternatively, the detection unit 52 may detect three values, for example, the voltage value of the output voltage Vo of the second inverter 4, the current value of the output current Io of the second inverter 4, and the voltage value of the DC bus voltage Vdc.

[0075] In other words, the detection unit 52 is configured to detect at least one value of the output voltage Vo of the second inverter 4, the output current Io of the second inverter 4, and the output voltage Vdc of the second series circuit 32 of the first inverter 3.

[0076] The control unit 53 is configured to determine the on-time Ton based on the deviation between the voltage value of the output voltage Vo detected by the detection unit 52 and a reference value, but is not limited to this configuration. The control unit 53 may be configured to determine the on-time Ton based on, for example, the voltage value of the output voltage Vo detected by the detection unit 52 and the current value of the output current Io detected by the detection unit 52. For example, the control unit 53 may be configured to determine the on-time Ton based on the deviation between the voltage value of the output voltage Vo and the output voltage command value (first reference value) and the deviation between the current value of the output current Io and the output current command value (second reference value). This makes it possible to further stabilize the output power in the converter device A1.

[0077] Furthermore, the control unit 53 may be configured to determine the on-time Ton based on, for example, the voltage value of the output voltage Vo detected by the detection unit 52, the current value of the output current Io detected by the detection unit 52, and the voltage value of the DC bus voltage Vdc detected by the detection unit 52. For example, the control unit 53 may be configured to determine the on-time Ton based on the deviation between the voltage value of the output voltage Vo and the output voltage command value (first reference value), the current value of the output current Io and the output current command value (second reference value), and the deviation between the voltage value of the DC bus voltage Vdc and the DC bus voltage command value (third reference value). This makes it possible to further stabilize the output power in the converter device A1.

[0078] The control unit 53 is configured to perform PI control, but it may also be configured to perform feedback control (FB control), feedforward control (FF control), or the like.

[0079] The control circuit 5 is configured to control the on-period Ton of switching elements Q1 and Q2 in accordance with the increase or decrease of the output voltage Vo of the second inverter 4, but is not limited to this configuration. The control circuit 5 may be configured to control the on-period Ton of switching elements Q1 and Q2 based on a comparison result between the voltage value of the output voltage Vo of the second inverter 4 and a threshold value. Specifically, the control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 to increase when the voltage value of the output voltage Vo of the second inverter 4 is greater than or equal to a threshold value. Also, the control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 to decrease when the voltage value of the output voltage Vo of the second inverter 4 is less than a threshold value. The threshold value is stored in advance in the memory of the control circuit 5.

[0080] The control circuit 5 may output the control signal S3 to the switching element Q3 such that the control signal S3 has a phase difference with respect to the control signal S1. That is, the control circuit 5 may output a plurality of control signals (for example, control signals S1 to S6) to the first inverter 3 and the second inverter 4 such that the control signal to the second inverter 4 (for example, control signal S3) has a phase difference with respect to the control signal to the first inverter 3 (for example, control signal S1). For example, the control circuit 5 may be configured to output the control signal to the second inverter 4 to the second inverter 4 with a delay compared to the control signal to the first inverter 3. As a result, the converter device A1 has a phase shift function and can change the phase difference between, for example, the output voltage V1 of the first inverter 3 (see Figure 1) and the input voltage V2 of the second inverter 4 (see Figure 1), thereby controlling the output voltage Vo of the second inverter 4 and further stabilizing the output power.

[0081] The input filter 6 is not limited to an L-type filter; for example, it may be a T-type filter, a π-type filter, a common-mode filter, or the like.

[0082] The first inductor L1 is provided in the circuit between the first output terminal 81 of the AC power supply 8 and the connection point 21 of diodes D1 and D2 of the rectifier 2, but it may also be provided in the circuit between the second output terminal 82 of the AC power supply 8 and the connection point 34 of switching elements Q1 and Q2 of the first inverter 3. In this case, the first terminal of the first inductor L1 is electrically connected to the second terminal of capacitor C3 of the input filter 6. The second terminal of the first inductor L1 is electrically connected to the connection point 34 of switching elements Q1 and Q2.

[0083] The second inductor L2 is provided in the circuit between the connection point 34 of switching elements Q1 and Q2 of the first inverter 3 and the first end of the primary winding N1 of the transformer Tr1, but it may also be provided in the circuit between the connection point 35 of capacitors C1 and C2 of the first inverter 3 and the second end of the primary winding N1 of the transformer Tr1.

[0084] Furthermore, although the second inductor L2 is provided in the circuit between the first inverter 3 and the primary winding N1 of the transformer Tr1, it may also be provided in the circuit between the secondary winding N2 of the transformer Tr1 and the second inverter 4. For example, the second inductor L2 may be provided in the circuit between the first end of the secondary winding N2 of the transformer Tr1 and the connection point 44 between the switching elements Q3 and Q4 of the second inverter 4. Alternatively, the second inductor L2 may be provided in the circuit between the second end of the secondary winding N2 of the transformer Tr1 and the connection point 45 between the switching elements Q5 and Q6 of the second inverter 4.

[0085] The second inductor L2 may be, for example, the leakage inductance of the transformer Tr1.

[0086] The second inverter 4 is a full-bridge inverter including four switching elements Q3 to Q6, but it may also be a half-bridge inverter including, for example, two switching elements Q3 and Q4 and two capacitors (third capacitor and fourth capacitor). In this case, two capacitors are used instead of switching elements Q5 and Q6 of the second inverter 4, and the control circuit 5 only needs to control the two switching elements Q3 and Q4 in the second inverter 4. In this case, the high-potential terminal of the third capacitor is electrically connected to the drain terminal of switching element Q3. The high-potential terminal of the third capacitor is also electrically connected to the high-potential terminal of the output filter C4. The low-potential terminal of the third capacitor is electrically connected to the second end of the secondary winding N2 of the transformer Tr1. The low-potential terminal of the third capacitor is also electrically connected to the high-potential terminal of the fourth capacitor. The low-potential terminal of the fourth capacitor is electrically connected to the source terminal of switching element Q4. The low-potential terminal of the fourth capacitor is also electrically connected to the low-potential terminal of the output filter C4.

[0087] The pair of output terminals 13 and 14 are electrically connected to the load, but they may also be electrically connected to the load via a DC-DC converter that converts the output voltage (DC voltage) Vo of the converter device A1 to a predetermined DC voltage.

[0088] (Embodiment 2) The converter device A2 according to Embodiment 2 (see Figure 1) differs from the converter device A1 according to Embodiment 1 in that the control of the control circuit 5 is different. Regarding the converter device A2 according to Embodiment 2, components similar to those in the converter device A1 according to Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted.

[0089] The converter device A2 according to Embodiment 2 will be described below.

[0090] (1) The converter device control circuit 5 controls the off period Toff (see Figure 2) of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4.

[0091] To explain in more detail, the control unit 53 of the control circuit 5 calculates the deviation (deviation value) between the voltage value of the output voltage Vo detected by the detection unit 52 and the output voltage command value, and determines the off period Toff for performing feedback control to bring the deviation value closer to zero.

[0092] The generation unit 54 generates a control signal S1 that includes the off period Toff determined by the control unit 53, and outputs the control signal S1 to the switching element Q1 of the first inverter 3. The generation unit 54 outputs five control signals S2 to S6 to the corresponding switching elements Q2 to Q6, respectively. Note that the operation of the generation unit 54 in generating the five control signals S2 to S6 is the same as the operation of the generation unit 54 in generating the control signal S1, except that the target switching elements are different.

[0093] The control circuit 5 controls switching elements Q1 and Q2 such that the off period Toff of switching elements Q1 and Q2 is variable, and the on period Ton of switching elements Q1 and Q2 is constant.

[0094] For example, the control circuit 5 controls the off-period Toff of switching elements Q1 and Q2 so that the off-period Toff of switching elements Q1 and Q2 decreases as the output voltage Vo of the second inverter 4 increases (see Figure 8). Also, the control circuit 5 controls the off-period Toff of switching elements Q1 and Q2 so that the off-period Toff of switching elements Q1 and Q2 increases as the output voltage Vo of the second inverter 4 decreases (see Figure 9).

[0095] In other words, the control circuit 5 controls the switching period Tsw of switching elements Q1 and Q2 according to the output voltage Vo. That is, the control circuit 5 controls the off period Toff of switching elements Q1 and Q2 so that the switching period Tsw of switching elements Q1 and Q2 decreases as the output voltage Vo of the second inverter 4 increases. Also, the control circuit 5 controls the off period Toff of switching elements Q1 and Q2 so that the switching period Tsw of switching elements Q1 and Q2 increases as the output voltage Vo of the second inverter 4 decreases.

[0096] Therefore, in converter device A2, the switching period Tsw (switching frequency) of switching elements Q1 and Q2 is changed, but under light load conditions (for example, when the output power is low), the switching period Tsw increases, that is, the switching frequency decreases. As a result, converter device A2 can control the output power with high efficiency even under light load conditions. In other words, converter device A2 can also control the output power under light load conditions with high efficiency. Furthermore, because converter device A2 can control the output power during light load operation, it can also respond to load fluctuations with high efficiency.

[0097] In Figures 8 and 9, period Ton3 represents the ON period Ton of switching elements Q1 and Q2. In Figure 8, period Toff1 represents the OFF period Toff of switching elements Q1 and Q2 when the output voltage Vo of the second inverter 4 increases. In Figure 8, period Tsw2 represents the switching period Tsw when the output voltage Vo of the second inverter 4 increases. In Figure 9, period Toff2 represents the OFF period Toff of switching elements Q1 and Q2 when the output voltage Vo of the second inverter 4 decreases. In Figure 9, period Tsw3 represents the switching period Tsw of switching elements Q1 and Q2 when the output voltage Vo of the second inverter 4 decreases.

[0098] Furthermore, the control circuit 5 determines the off-time Toff for feedback control based on the deviation between the value detected by the detection unit 52 (voltage value of the output voltage Vo) and a reference value. This makes it possible for the converter device A2 to stabilize the output power and respond to load fluctuations.

[0099] (2) Modified configuration The control circuit 5 is configured to control the off period Toff of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4, but is not limited to this configuration. The control circuit 5 may be configured to control the second dead time period T4 of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4.

[0100] For example, the control circuit 5 controls the second dead time period T4 of switching elements Q1 and Q2 so that the second dead time period T4 of switching elements Q1 and Q2 decreases as the output voltage Vo of the second inverter 4 increases. Also, the control circuit 5 controls the second dead time period T4 of switching elements Q1 and Q2 so that the second dead time period T4 of switching elements Q1 and Q2 increases as the output voltage Vo of the second inverter 4 decreases. Even in this case, the converter device A2 can control the output power at light load with high efficiency because the switching period Tsw increases at light load.

[0101] (Embodiment 3) The converter device A3 according to Embodiment 3 (see Figure 10) differs from the converter device A1 according to Embodiment 1 (see Figure 1) in that the configuration of the second inverter 4 is different. Regarding the converter device A3 according to Embodiment 3, components similar to those in the converter device A1 according to Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted.

[0102] The converter device A3 according to Embodiment 3 will be described below.

[0103] The second inverter 4 is a diode bridge including four diodes D3 to D6, as shown in Figure 10, for example.

[0104] The anode of diode D3 is electrically connected to the first end of the secondary winding N2 of transformer Tr1. Also, the anode of diode D3 is electrically connected to the cathode of diode D4. The anode of diode D4 is electrically connected to the anode of diode D6.

[0105] The anode of diode D6 is electrically connected to the second terminal (low-potential terminal) of output filter C4. The cathode of diode D6 is electrically connected to the second terminal of the secondary winding N2 of transformer Tr1. The cathode of diode D6 is also electrically connected to the anode of diode D5. The cathode of diode D5 is also electrically connected to the cathode of diode D3. Furthermore, the cathode of diode D5 is electrically connected to the first terminal (high-potential terminal) of output filter C4.

[0106] In this embodiment, the connection point 40 of diodes D3 and D4 is the input terminal (first input terminal) of the second inverter 4. Also, the connection point 41 of diodes D5 and D6 is the input terminal (second input terminal) of the second inverter 4. In other words, the secondary winding N2 of transformer Tr1 is electrically connected between the pair of input terminals 40 and 41 of the second inverter 4.

[0107] The connection point 40 of diodes D3 and D4 may, for example, be a connection point provided on the circuit between the anode of diode D3 and the cathode of diode D4, or it may be the anode of diode D3, or it may be the cathode of diode D4. Similarly, the connection point 41 of diodes D5 and D6 may, for example, be a connection point provided on the circuit between the anode of diode D5 and the cathode of diode D6, or it may be the anode of diode D5, or it may be the cathode of diode D6.

[0108] In this embodiment, the connection point 42 of diode D3 and diode D5 is the output terminal (first output terminal) of the second inverter 4. Also, the connection point 43 of diode D4 and diode D6 is the output terminal (second output terminal) of the second inverter 4. In other words, the second inverter 4 includes a pair of input terminals 40, 41, a pair of output terminals 42, 43, and four diodes D3 to D6.

[0109] The connection point 42 between diode D3 and diode D5 may, for example, be a connection point located on the circuit between the cathode of diode D3 and the cathode of diode D5, or it may be the cathode of diode D3, or it may be the cathode of diode D5. Similarly, the connection point 43 between diode D4 and diode D6 may, for example, be a connection point located on the circuit between the anode of diode D4 and the anode of diode D6, or it may be the anode of diode D4, or it may be the anode of diode D6.

[0110] The control circuit 5 controls the first inverter 3. More specifically, the control circuit 5 controls the first inverter 3 so that the duty cycles of switching elements Q1 and Q2 are the same.

[0111] Furthermore, the control circuit 5, similar to the control circuit 5 of Embodiment 1, controls the on-period Ton of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4. As a result, the converter device A3 can control the output power at light load with high efficiency, similar to the converter device A1 of Embodiment 1.

[0112] The control circuit 5 controls the on-period Ton of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4. However, similar to the control circuit 5 in Embodiment 2, the off-period Toff of switching elements Q1 and Q2 may also be controlled according to the output voltage Vo of the second inverter 4. Furthermore, the control circuit 5 may also control the second dead time period T4 of switching elements Q1 and Q2 according to the output voltage Vo of the second inverter 4.

[0113] The embodiments 1 to 3 and their modifications described above are only a part of the various embodiments and modifications of this disclosure.

[0114] This disclosure is not limited to the embodiments described above, and it is possible to combine and apply at least some of the configurations of each embodiment and modification as appropriate.

[0115] (Aspects) The following aspects are disclosed in this specification.

[0116] The converter devices (A1, A2) according to the first embodiment include a rectifier (2), a first inverter (3), a first inductor (L1), a transformer (Tr1), a second inverter (4), a second inductor (L2), and a control circuit (5). The rectifier (2) includes a first diode (D1) and a second diode (D2) connected in series with the first diode (D1). The rectifier (2) rectifies the AC voltage (Vin) of the AC power supply (8). The first inverter (3) has a first series circuit (31) and a second series circuit (32) connected in parallel, and the first series circuit (31) and the second series circuit (32) are connected in parallel with the rectifier (2). The first series circuit (31) is a series circuit in which a first switching element (Q1) and a second switching element (Q2) are connected in series. The second series circuit (32) is a series circuit in which the first capacitor (C1) and the second capacitor (C2) are connected in series. The first inductor (L1) is provided in the circuit between the first output terminal (81) of the AC power supply (8) and the connection point (21) of the first diode (D1) and the second diode (D2), or in the circuit between the second output terminal (82) of the AC power supply (8) and the connection point (34) of the first switching element (Q1) and the second switching element (Q2). The transformer (Tr1) has a primary winding (N1) and a secondary winding (N2). The primary winding (N1) of the transformer (Tr1) is electrically connected between the connection point (34) of the first switching element (Q1) and the second switching element (Q2) and the connection point (35) of the first capacitor (C1) and the second capacitor (C2). The second inverter (4) is composed of a half-bridge inverter or a full-bridge inverter including a pair of input terminals (44, 45), a pair of output terminals (46, 47), a third switching element (Q3), and a fourth switching element (Q4). The second inverter (4) has a secondary winding (N2) electrically connected between the pair of input terminals (44, 45). The second inductor (L2) is provided in the circuit between the first inverter (3) and the primary winding (N1), or in the circuit between the secondary winding (N2) and the second inverter (4). The control circuit (5) controls the first inverter (3) and the second inverter (4).The control circuit (5) controls the first inverter (3) and the second inverter (4) so ​​that the duty cycles of the first switching element (Q1), the second switching element (Q2), the third switching element (Q3), and the fourth switching element (Q4) are the same. The control circuit (5) controls the first inverter (3) and the second inverter (4) so ​​that the first switching element (Q1) and the third switching element (Q3) switch at the same timing, and the second switching element (Q2) and the fourth switching element (Q4) switch at the same timing. The control circuit (5) controls the on-period (Ton) or off-period (Toff) of the first switching element (Q1) and the second switching element (Q2) according to the output voltage (Vo) of the second inverter (4).

[0117] According to this embodiment, it is possible to control the output power at light loads with high efficiency.

[0118] The converter device (A3) according to the second embodiment includes a rectifier (2), a first inverter (3), a first inductor (L1), a transformer (Tr1), a second inverter (4), a second inductor (L2), and a control circuit (5). The rectifier (2) includes a first diode (D1) and a second diode (D2) connected in series with the first diode (D1). The rectifier (2) rectifies the AC voltage (Vin) of the AC power supply (8). The first inverter (3) has a first series circuit (31) and a second series circuit (32) connected in parallel, and the first series circuit (31) and the second series circuit (32) are connected in parallel with the rectifier (2). The first series circuit (31) is a series circuit in which a first switching element (Q1) and a second switching element (Q2) are connected in series. The second series circuit (32) is a series circuit in which the first capacitor (C1) and the second capacitor (C2) are connected in series. The first inductor (L1) is provided in the circuit between the first output terminal (81) of the AC power supply (8) and the connection point (21) of the first diode (D1) and the second diode (D2), or in the circuit between the second output terminal (82) of the AC power supply (8) and the connection point (34) of the first switching element (Q1) and the second switching element (Q2). The transformer (Tr1) has a primary winding (N1) and a secondary winding (N2). The primary winding (N1) of the transformer (Tr1) is electrically connected between the connection point (34) of the first switching element (Q1) and the second switching element (Q2) and the connection point (35) of the first capacitor (C1) and the second capacitor (C2). The second inverter (4) is composed of a diode bridge including a pair of input terminals (40, 41), a pair of output terminals (42, 43), and four diodes (D3 to D6). The second inverter (4) has a secondary winding (N2) electrically connected between the pair of input terminals (40, 41). The second inductor (L2) is provided in the circuit between the first inverter (3) and the primary winding (N1), or in the circuit between the secondary winding (N2) and the second inverter (4). The control circuit (5) controls the first inverter (3). The control circuit (5) controls the first inverter (3) so that the duty cycles of the first switching element (Q1) and the second switching element (Q2) are the same.The control circuit (5) controls the on-period (Ton) or off-period (Toff) of the first switching element (Q1) and the second switching element (Q2) according to the output voltage (Vo) of the second inverter (4).

[0119] According to this embodiment, it is possible to control the output power at light loads with high efficiency.

[0120] In the converter device (A1 to A3) according to the third embodiment, in the first or second embodiment, the control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) such that the mode of the current (i1) flowing through the first inductor (L1) becomes a current discontinuity mode.

[0121] According to this embodiment, it is possible to achieve a higher power factor and higher efficiency.

[0122] The converter device (A1 to A3) according to the fourth embodiment, in any one of the first to third embodiments, the control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) such that the first switching element (Q1) and the second switching element (Q2) alternately turn on, and that there are periods (T2, T4) in which the first switching element (Q1) and the second switching element (Q2) are in an off state between the time when the first switching element (Q1) turns off (t2) and the time when the second switching element (Q2) turns on (t3), and between the time when the second switching element (Q2) turns off (t5) and the time when the first switching element (Q1) turns on (t6). The control circuit (5) has a determination unit (55) for determining the polarity of the AC voltage (Vin). The control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the first switching element (Q1) turns on before the second switching element (Q2) if the polarity of the AC voltage (Vin) determined by the determination unit (55) is positive. The control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the second switching element (Q2) turns on before the first switching element (Q1) if the polarity of the AC voltage (Vin) determined by the determination unit (55) is negative.

[0123] According to this embodiment, the deterioration of conduction loss in the first switching element (Q1) and the second switching element (Q2) can be reduced.

[0124] In the converter devices (A1, A3) according to the fifth embodiment, in any one of the first to fourth embodiments, the control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the duty cycle of the first switching element (Q1) and the second switching element (Q2) is within the range of 0% to 50%. The control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the on period (Ton) of the first switching element (Q1) and the second switching element (Q2) is variable and the switching period (Tsw) of the first switching element (Q1) and the second switching element (Q2) is constant.

[0125] According to this embodiment, it is possible to control the output power at light loads with high efficiency.

[0126] In the sixth embodiment, the converter devices (A1, A3) have a detection unit (52) in the fifth embodiment. The detection unit (52) detects at least one of the following values: the output voltage (Vo) of the second inverter (4), the output current (Io) of the second inverter (4), and the output voltage (Vdc) of the second series circuit (32) of the first inverter (3). The control circuit (5) determines an on-period (Ton) for performing feedback control based on the deviation between the above value detected by the detection unit (52) and a reference value.

[0127] According to this embodiment, it is possible to stabilize the output power and respond to load fluctuations.

[0128] In the seventh embodiment of the converter device (A2), in any one of the first to fourth embodiments, the control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the duty cycle of the first switching element (Q1) and the second switching element (Q2) is within the range of 0% to 50%. The control circuit (5) controls the first switching element (Q1) and the second switching element (Q2) so that the off period (Toff) of the first switching element (Q1) and the second switching element (Q2) is variable and the on period (Ton) of the first switching element (Q1) and the second switching element (Q2) is constant.

[0129] According to this embodiment, it is possible to control the output power at light loads with high efficiency.

[0130] The converter device (A2) according to the eighth embodiment, in the seventh embodiment, has a control circuit (5) which includes a detection unit (52). The detection unit (52) detects at least one of the following values: the output voltage (Vo) of the second inverter (4), the output current (Io) of the second inverter (4), and the output voltage (Vdc) of the second series circuit (32) of the first inverter (3). The control circuit (5) determines an off period (Toff) for performing feedback control based on the deviation between the above value detected by the detection unit (52) and a reference value.

[0131] According to this embodiment, it is possible to stabilize the output power and respond to load fluctuations.

[0132] The converter devices (A1, A2) according to the ninth embodiment further include, in the first embodiment, a second inverter (4) further comprising a fifth switching element (Q5) and a sixth switching element (Q6). The control circuit (5) further controls the second inverter (4) such that the fifth switching element (Q5) performs the same switching operation as the third switching element (Q3), and the sixth switching element (Q6) performs the same switching operation as the fourth switching element (Q4).

[0133] According to this embodiment, it is possible to control the output power at light loads with high efficiency.

[0134] 2 Rectifier 3 First Inverter 4 Second Inverter 5 Control Circuit 8 AC Power Supply 21 Connection Point 31 First Series Circuit 32 Second Series Circuit 34 Connection Point (Connection Point between First Switching Element and Second Switching Element) 35 Connection Point (Connection Point between First Capacitor and Second Capacitor) 40 Connection Point (Input Terminal) 41 Connection Point (Input Terminal) 42 Connection Point (Output Terminal) 43 Connection Point (Output Terminal) 44 Connection Point (Input Terminal) 45 Connection Point (Input Terminal) 46 Connection Point (Output Terminal) 47 Connection Point (Output Terminal) 52 Detection Unit 55 Determination Unit 81 First Output Terminal 82 Second Output Terminal A1-A3 Converter Device C1 Capacitor (First Capacitor) C2 Capacitor (Second Capacitor) D1 Diode (First Diode) D2 Diode (Second Diode) D3 Diode D4 Diode D5 Diode D6 Diode i1 Current Io Output current L1 First inductor L2 Second inductor N1 Primary winding N2 Secondary winding Q1 Switching element (first switching element) Q2 Switching element (second switching element) Q3 Switching element (third switching element) Q4 Switching element (fourth switching element) Q5 Switching element (fifth switching element) Q6 Switching element (sixth switching element) t2 Time point t3 Time point t5 Time point t6 Time point T2 Period T4 Period Ton On period Toff Off period Tr1 Transformer Tsw Switching period Vin AC voltage Vdc Output voltage (output voltage of second series circuit) Vo Output voltage (output voltage of second inverter)

Claims

1. A rectifier that rectifies the AC voltage of an AC power supply, including a first diode and a second diode connected in series with the first diode; a first inverter in which a first series circuit in which a first switching element and a second switching element are connected in series, and a second series circuit in which a first capacitor and a second capacitor are connected in series are connected in parallel, and the first series circuit and the second series circuit are connected in parallel with the rectifier; a first inductor provided in the circuit between the first output terminal of the AC power supply and the connection point of the first diode and the second diode, or in the circuit between the second output terminal of the AC power supply and the connection point of the first switching element and the second switching element; a transformer having a primary winding and a secondary winding, with the primary winding electrically connected between the connection point of the first switching element and the second switching element and the connection point of the first capacitor and the second capacitor; a second inverter comprising a half-bridge inverter or a full-bridge inverter including a pair of input terminals, a pair of output terminals, a third switching element and a fourth switching element, with the secondary winding electrically connected between the pair of input terminals; A converter device comprising: a second inductor provided in the circuit between the first inverter and the primary winding, or in the circuit between the secondary winding and the second inverter; and a control circuit for controlling the first inverter and the second inverter, wherein the control circuit controls the first inverter and the second inverter so that the duty cycles of the first switching element, the second switching element, the third switching element and the fourth switching element are the same; controls the first inverter and the second inverter so that the first switching element and the third switching element switch at the same timing, and the second switching element and the fourth switching element switch at the same timing; and controls the on-period or off-period of the first switching element and the second switching element according to the output voltage of the second inverter.

2. A rectifier that rectifies the AC voltage of an AC power supply, including a first diode and a second diode connected in series with the first diode; a first inverter in which a first series circuit in which a first switching element and a second switching element are connected in series, and a second series circuit in which a first capacitor and a second capacitor are connected in series are connected in parallel, and the first series circuit and the second series circuit are connected in parallel with the rectifier; a first inductor provided in the circuit between the first output terminal of the AC power supply and the connection point of the first diode and the second diode, or in the circuit between the second output terminal of the AC power supply and the connection point of the first switching element and the second switching element; a transformer having a primary winding and a secondary winding, with the primary winding electrically connected between the connection point of the first switching element and the second switching element and the connection point of the first capacitor and the second capacitor; a second inverter comprising a diode bridge including a pair of input terminals, a pair of output terminals and four diodes, with the secondary winding electrically connected between the pair of input terminals; A converter device comprising: a second inductor provided in the circuit between the first inverter and the primary winding, or in the circuit between the secondary winding and the second inverter; and a control circuit for controlling the first inverter, wherein the control circuit controls the first inverter so that the duty cycles of the first switching element and the second switching element are the same, and controls the on-period or off-period of the first switching element and the second switching element according to the output voltage of the second inverter.

3. The converter device according to claim 1 or claim 2, wherein the control circuit controls the first switching element and the second switching element such that the mode of the current flowing through the first inductor is a current discontinuity mode.

4. The converter device according to any one of claims 1 to 3, wherein the control circuit controls the first switching element and the second switching element so that the first switching element and the second switching element are alternately turned on, and includes a period in which the first switching element and the second switching element are off between the time the first switching element is turned off and the time the second switching element is turned on, and between the time the second switching element is turned off and the time the first switching element is turned on; and has a determination unit for determining the polarity of the AC voltage; if the polarity of the AC voltage determined by the determination unit is positive, the first switching element and the second switching element are controlled so that the first switching element is turned on before the second switching element; and if the polarity of the AC voltage determined by the determination unit is negative, the first switching element and the second switching element are controlled so that the second switching element is turned on before the first switching element.

5. The converter device according to any one of claims 1 to 4, wherein the control circuit controls the first switching element and the second switching element so that the duty cycle of the first switching element and the second switching element is within the range of 0% to 50%, and controls the first switching element and the second switching element so that the ON period of the first switching element and the second switching element is variable and the switching period of the first switching element and the second switching element is constant.

6. The converter device according to claim 5, wherein the control circuit has a detection unit that detects at least one value of the output voltage of the second inverter, the output current of the second inverter, and the output voltage of the second series circuit of the first inverter, and determines the ON period for performing feedback control based on the deviation between the value detected by the detection unit and a reference value.

7. The converter device according to any one of claims 1 to 4, wherein the control circuit controls the first switching element and the second switching element so that the duty cycle of the first switching element and the second switching element is within the range of 0% to 50%, and controls the first switching element and the second switching element so that the off period of the first switching element and the second switching element is variable and the on period of the first switching element and the second switching element is constant.

8. The converter device according to claim 7, wherein the control circuit has a detection unit that detects at least one value of the output voltage of the second inverter, the output current of the second inverter, and the output voltage of the second series circuit of the first inverter, and determines the off period for performing feedback control based on the deviation between the value detected by the detection unit and a reference value.

9. The converter device according to claim 1, wherein the second inverter further includes a fifth switching element and a sixth switching element, and the control circuit further controls the second inverter such that the fifth switching element performs the same switching operation as the third switching element, and the sixth switching element performs the same switching operation as the fourth switching element.

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