Converter device

Abstract

The present disclosure addresses the problem of providing a converter device capable of reducing noise and increasing the power factor. A converter device (A1) comprises a first inverter (3), a transformer (Tr1), a second inverter (4), and a control circuit (5). The control circuit (5) controls the first inverter (3) so that a first switching element (Q1) and a second switching element (Q2) are alternately in on-states and the on-times thereof are the same. The control circuit (5) controls the second inverter (4) so that a third switching element (Q3) and a fourth switching element (Q4) are alternately in on-states and the on-times thereof are the same as the on-time of the first switching element (Q1). The control circuit (5) controls the switching frequencies of the first switching element (Q1) and the second switching element (Q2) so that the half voltage value of a DC bus voltage (Vdc) becomes a first predetermined value and controls the switching frequencies in accordance with an AC voltage (Vin).

Description

Converter device

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

[0002] An example of the converter device described in Patent Document 1 will be described. 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. Further, the converter device described in Patent Document 1 aims to improve the power factor to achieve a high power factor.

[0003] In the converter device described in Patent Document 1, noise reduction may be desired.

[0004] International Publication No. 2023 / 243321

[0005] An object of the present disclosure is to provide a converter device capable of achieving noise reduction and high power factor improvement.

[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 transformer has its primary winding electrically connected between the connection point of the first and second switching elements and the connection point of the first and second capacitors. 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 second inverter has its secondary winding 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 such that the first switching element and the second switching element are alternately turned on, and the on time of the first switching element and the on time of the second switching element are the same.The control circuit controls the second inverter such that the third switching element and the fourth switching element alternately turn on, the on time of the third switching element and the on time of the fourth switching element are the same, and the on time of the third switching element is the same as the on time of the first switching element. The control circuit controls the switching frequencies of the first switching element and the second switching element such that the voltage value of half the DC bus voltage, which is the output voltage of the second series circuit of the first inverter, becomes a first predetermined value. The control circuit controls the switching frequencies according to the AC voltage.

[0007] Figure 1 is a circuit diagram of the converter device according to Embodiments 1 to 3. Figure 2 is a timing chart showing the operation of the same converter device. Figure 3 is a schematic graph showing the noise level of the output voltage for the converter device of the comparative example. Figure 4 is a schematic graph showing the noise level of the output voltage for the converter device according to Embodiments 1 to 3. Figure 5 is a graph showing the relationship between the input voltage and input current for the converter device of the comparative example. Figure 6 is a graph showing the change in modulation rate due to the control circuit for the converter device according to Embodiments 2 to 3.

[0008] 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.

[0009] (Embodiment 1) Hereinafter, a converter device according to Embodiment 1 will be described with reference to Figures 1 to 2 and Figure 4.

[0010] (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 a pair of input terminals 11 and 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 and 14.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] (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.

[0015] (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.

[0016] (1.3) Rectifier The rectifier 2 rectifies the AC voltage Vin of the AC power supply 8. The rectifier 2 is 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.

[0017] (1.4) First Inverter The first inverter 3 is 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The capacitance of capacitor C2 is 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 difference (absolute value of the difference) between the capacitance of capacitor C1 and the capacitance of capacitor C2 is within the margin of error (for example, 10%).

[0022] (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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] (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.

[0035] (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.

[0036] 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, for example, 50%.

[0037] The duty cycle represents the ratio of the high-level period to the total period of time 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, period T1 represents the high-level period (on time) of control signal S1. In Figure 2, period T2 represents the low-level period (off time) of control signal S1. In Figure 2, period T3 represents the total period of the high-level period (period T1) and low-level period (period T2) of control signal S1.

[0038] 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 (for example, a PWM signal). The duty cycle of the control signal S2 is, for example, 50%.

[0039] In other words, the control circuit 5 controls the first inverter 3 so that the duty cycles of the two switching elements Q1 and Q2 are the same. To put it another way, the control circuit 5 controls the first inverter 3 so that the on-time of switching element Q1 and the on-time of switching element Q2 are the same.

[0040] Note that the phrase "the on-time of the switching element Q1 and the on-time of the switching element Q2 are the same time" does not only refer to the case where the on-time of the switching element Q1 and the on-time of the switching element Q2 are exactly the same time, but also includes cases where, for example, the difference (absolute value of the difference) between the on-time of the switching element Q1 and the on-time of the switching element Q2 is at the error level (e.g., 5%).

[0041] The control circuit 5 synchronizes the control signal S1 and the control signal S2 and outputs the control signal S1 and the control signal S2 to the first inverter 3. Further, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 such that the control signal S1 and the control signal S2 have a trade-off relationship. For example, as shown in FIG. 2, when the signal level of the control signal S1 is high, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 such that the signal level of the control signal S2 is low. Also, when the signal level of the control signal S1 is low, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 such that the signal level of the control signal S2 is high.

[0042] In other words, when the switching element Q1 is in the on-state, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 such that the switching element Q2 is in the off-state. Also, when the switching element Q1 is in the off-state, the control circuit 5 outputs the control signal S1 and the control signal S2 to the first inverter 3 such that the switching element Q2 is in the on-state. In short, the control circuit 5 controls the first inverter 3 so that the switching element Q1 and the switching element Q2 are alternately in the on-state.

[0043] 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 pulsed signal (e.g., a PWM 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, 50%.

[0044] Further, 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 for switching the switching element Q4 to either an on state or an off state. The control signal S4 is, for example, a pulsed signal (e.g., a PWM signal). The duty of the control signal S4 is the same as the duty of the control signal S2. The duty of the control signal S4 is, for example, 50%.

[0045] The control circuit 5 synchronizes the control signal S3 and the control signal S4 and outputs the control signal S3 and the control signal S4 to the second inverter 4. Further, the control circuit 5 outputs the control signal S3 and the control signal S4 to the second inverter 4 such that the control signal S3 and the control signal S4 have a trade-off relationship. That is, the control circuit 5 controls the second inverter 4 such that the switching element Q3 and the switching element Q4 are alternately in an on state.

[0046] Further, 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 for switching the switching element Q5 to either an on state or an off state. The control signal S5 is, for example, a pulsed signal (e.g., a PWM signal). The duty of the control signal S5 is the same as the duty of the control signal S4. The duty of the control signal S5 is, for example, 50%.

[0047] 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 (for example, a PWM signal). The duty cycle of the control signal S6 is the same as the duty cycle of the control signal S3. The duty cycle of the control signal S6 is, for example, 50%.

[0048] The control circuit 5 synchronizes control signals S5 and S6 and outputs them to the second inverter 4. Furthermore, the control circuit 5 outputs control signals S5 and S6 to the second inverter 4 in such a trade-off relationship. In other words, the control circuit 5 controls the second inverter 4 so that switching elements Q5 and Q6 are alternately turned on.

[0049] Furthermore, the control circuit 5 synchronizes control signals S4 and S5 and outputs control signals S4 and S5 to the second inverter 4. In short, the control circuit 5 controls the second inverter 4 so that switching element Q5 performs the same switching operation as switching element Q4 (see Figure 2). Also, the control circuit 5 synchronizes control signals S3 and S6 and outputs control signals S3 and S6 to the second inverter 4. In short, the control circuit 5 controls the second inverter 4 so that switching element Q6 performs the same switching operation as switching element Q3 (see Figure 2). That is, the control circuit 5 synchronizes the four control signals S3 to S6 and outputs the four control signals S3 to S6 to the second inverter 4.

[0050] Furthermore, "same switching operation" does not only mean, for example, that the switching operation of switching element Q5 is exactly the same as the switching operation of switching element Q4, but also includes cases where there is a slight delay between the switching operation of switching element Q5 and the switching operation of switching element Q4.

[0051] As shown in Figure 2, the control circuit 5 outputs the control signal S3 to the switching element Q3 such that the control signal S3 has a phase difference θ with respect to the control signal S1. In other words, the control circuit 5 outputs 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 θ with respect to the control signal to the first inverter 3 (for example, control signal S1). Therefore, 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 enabling control of the output voltage of the second inverter 4.

[0052] The control circuit 5 shown in Figure 1 detects the output voltage Vo of the output filter C4. Based on the output voltage Vo, the control circuit 5 determines the phase difference θ. The control circuit 5 also detects the output voltage (DC bus voltage) Vdc of the second series circuit 32 of the first inverter 3. Based on the DC bus voltage Vdc, the control circuit 5 determines the switching frequency fsw.

[0053] The control circuit 5 includes, for example, a first processing unit 51, a first control unit 52, a second processing unit 53, a second control unit 54, and a generation unit 55.

[0054] The first processing unit 51, for example, determines the voltage value of the output voltage Vo of the output filter C4 and the first output voltage command value Vo ＊ It is configured to calculate the difference (difference voltage value) between the first output voltage command value Vo ＊ This is a reference value for the output voltage Vo, and is pre-stored in the memory of the control circuit 5, for example. The first processing unit 51 is electrically connected to the first control unit 52.

[0055] The first control unit 52 is configured, for example, to perform PI control. The first control unit 52 generates a phase difference θ for performing feedback control to bring the differential voltage value obtained by the first processing unit 51 closer to zero, and outputs it to the generation unit 55. The first control unit 52 is electrically connected to the generation unit 55. Although the first control unit 52 is configured to perform PI control, it may also be configured to perform PID control or P control.

[0056] The second processing unit 53, for example, determines the voltage value of the output voltage (DC bus voltage) Vdc of the second series circuit 32 of the first inverter 3 and the second output voltage command value Vdc ＊ It is configured to calculate the difference (difference voltage value) between the two values. Second output voltage command value Vdc ＊ This is a reference value for the DC bus voltage Vdc, and is pre-stored, for example, in the memory of the control circuit 5. The second processing unit 53 is electrically connected to the second control unit 54.

[0057] The second control unit 54 is configured, for example, to perform PI control. The second control unit 54 generates a switching frequency fsw for performing feedback control to bring the differential voltage value obtained by the second processing unit 53 closer to zero, and outputs it to the generation unit 55. The second control unit 54 is electrically connected to the generation unit 55. Although the second control unit 54 is configured to perform PI control, it may also be configured to perform PID control or P control.

[0058] The generation unit 55 generates a control signal S1 based on the phase difference θ from the first control unit 52 and the switching frequency fsw from the second control unit 54, and outputs the control signal S1 to the switching element Q1 of the first inverter 3. That is, the generation unit 55 generates a control signal S1 that includes the phase difference θ and the switching frequency fsw, and outputs the control signal S1 to the switching element Q1. The generation unit 55 is electrically connected to the gate terminal of the switching element Q1. The generation unit 55 is also electrically connected to the gate terminals of each of the five switching elements Q2 to Q6. The generation unit 55 outputs five control signals S2 to S6 to the corresponding switching elements Q2 to Q6, respectively. Note that the operation of the generation unit 55 in generating the five control signals S2 to S6 is the same as the operation of the generation unit 55 in generating the control signal S1, except that the target switching element is different.

[0059] Incidentally, the control circuit 5 controls the switching frequency fsw of switching elements Q1 and Q2 so that, for example, the voltage value is half of the DC bus voltage Vdc, which is a first predetermined value. For example, the control circuit 5 finds the switching frequency fsw such that the voltage value is half of the DC bus voltage Vdc, which is a first predetermined value, and generates control signals S1 and S2 including this switching frequency fsw, which it outputs to the first inverter 3. The first predetermined value is, for example, stored in the memory of the control circuit 5.

[0060] In this embodiment, the voltage value of half the DC bus voltage Vdc is determined by the capacitances of capacitors C1 and C2, and corresponds to, for example, the voltage across capacitor C1. Note that "the voltage value of half the DC bus voltage Vdc" is not limited to cases where the voltage value of half the DC bus voltage Vdc is exactly half the voltage value, but also includes cases where there is an error (for example, ±10%) in the voltage value of half the DC bus voltage Vdc.

[0061] Furthermore, the control circuit 5 controls the switching frequency fsw of switching elements Q1 and Q2 according to the AC voltage Vin. For example, the control circuit 5 controls the switching frequency fsw of switching elements Q1 and Q2 according to the phase of the AC voltage Vin. Specifically, the control circuit 5 controls the switching frequency fsw so that it increases as the phase of the AC voltage Vin changes from zero to π / 2. Also, the control circuit 5 controls the switching frequency fsw so that it decreases as the phase of the AC voltage Vin changes from π / 2 to π. Also, the control circuit 5 controls the switching frequency fsw so that it increases as the phase of the AC voltage Vin changes from π to 3π / 2. Also, the control circuit 5 controls the switching frequency fsw so that it decreases as the phase of the AC voltage Vin changes from 3π / 2 to 2π.

[0062] Here, we will describe a comparative example of a converter device in which the control circuit controls each of the six switching elements at a constant switching frequency. In the comparative example of a converter device, when the switching frequency of each of the six switching elements is constant, noise is generated in the output voltage of the converter device within a specific frequency range, as shown in Figure 3, for example. In Figure 3, frequency f0 represents the frequency of the fundamental wave (first fundamental wave) of the comparative example of a converter device (the switching frequency of the comparative example of a converter device). In Figure 3, frequency 3f0 represents the frequency of the third harmonic of the first fundamental wave. In Figure 3, frequency 5f0 represents the frequency of the fifth harmonic of the first fundamental wave.

[0063] On the other hand, in the converter device A1 of this embodiment, the switching frequency fsw is controlled (changed) according to the AC voltage Vin, so, as shown in Figure 4, for example, the noise level of the output voltage Vo within a specific frequency range is lower than that of the comparative example converter device. Therefore, the converter device A1 can achieve lower noise than the comparative example converter device. In Figure 4, frequency f1 represents the frequency (switching frequency fsw) of the fundamental wave (second fundamental wave) of the converter device A1. In Figure 4, frequency 3f1 represents the frequency of the third harmonic of the second fundamental wave. In Figure 4, frequency 5f1 represents the frequency of the fifth harmonic of the second fundamental wave.

[0064] Furthermore, in the comparative example converter device, when the control circuit controls each of the six switching elements at a constant switching frequency, a distortion component is generated in the current I2 that flows when electrical energy is released by the first inductor, as shown in Figure 5, for example. Therefore, in the comparative example converter device, a distortion component is superimposed on the input current I0 of the converter device, causing the power factor to decrease. Note that the current I0 in Figure 5 represents the waveform of the input current (AC current) of the comparative example converter device. The voltage V0 in Figure 5 represents the waveform of the input voltage (AC voltage) of the comparative example converter device. The current I1 in Figure 5 represents the waveform of the current that flows when electrical energy is stored by the first inductor in the comparative example converter device. The current I2 in Figure 5 represents the waveform of the current that flows when electrical energy is released by the first inductor in the comparative example converter device.

[0065] On the other hand, in the converter device A1 of this embodiment, the switching frequency fsw is controlled (changed) according to the AC voltage Vin, so that the generation of distortion components in the current i1 (see Figure 1) that flows when electrical energy is released by the first inductor L1 can be suppressed. Therefore, in converter device A1, since distortion components are not superimposed on the input current Iin (see Figure 1) of converter device A1, it is possible to improve the power factor, and it is possible to achieve a higher power factor than the converter device of the comparative example. Furthermore, since a higher power factor can be achieved in converter device A1, it is also possible to achieve higher efficiency.

[0066] Therefore, the converter device A1 of this embodiment makes it possible to achieve low noise and high power factor.

[0067] The control circuit 5 shown in Figure 1 preferably controls the switching elements Q1 and Q2 of the first inverter 3 so that, for example, the voltage value of the DC bus voltage Vdc is at least twice the maximum value of the AC voltage Vin (for example, 141V if the AC voltage Vin is 100V). Furthermore, the control circuit 5 preferably changes the phase difference between the output voltage V1 of the first inverter 3 and the input voltage V2 of the second inverter 4 so that the voltage value of the output voltage Vo of the second inverter 4 becomes a second predetermined value. Specifically, the control circuit 5 increases the phase difference when the voltage value of the output voltage Vo of the second inverter 4 is less than the second predetermined value. Also, the control circuit 5 decreases the phase difference when the voltage value of the output voltage Vo of the second inverter 4 is greater than the second predetermined value. As a result, in the converter device A1, the mode of the current i1 flowing through the first inductor L1 is always a current discontinuity mode, which makes it possible to further improve the power factor and achieve a higher power factor. However, it is desirable that the phase difference between the output voltage V1 of the first inverter 3 and the input voltage V2 of the second inverter 4 be greater than 0 and less than (one period of the AC voltage Vin) / 4.

[0068] (2) Modified Control Circuit 5 controls the switching frequency fsw according to the phase of the AC voltage Vin, but for example, the switching frequency fsw may be controlled according to the increase or decrease in the absolute value of the instantaneous value of the AC voltage Vin.

[0069] For example, the control circuit 5 may control the switching frequency fsw such that the switching frequency fsw increases as the absolute value of the instantaneous value of the AC voltage Vin increases. Alternatively, the control circuit 5 may control the switching frequency fsw such that the switching frequency fsw decreases as the absolute value of the instantaneous value of the AC voltage Vin decreases. In this case as well, the converter device A1 can achieve low noise and high power factor.

[0070] Furthermore, the control circuit 5 may control the switching frequency fsw so that it increases when the absolute value of the instantaneous AC voltage Vin is greater than or equal to the first threshold. Alternatively, the control circuit 5 may control the switching frequency fsw so that it decreases when the absolute value of the instantaneous AC voltage Vin is less than the first threshold. Even in this case, the converter device A1 can achieve low noise and high power factor. The first threshold is stored in the memory of the control circuit 5, for example.

[0071] The first control unit 52 is configured to perform PI control, but may also be configured to perform feedback control (FB control), feedforward control (FF control), etc. The second control unit 54 is configured to perform PI control, but may also be configured to perform feedback control (FB control), feedforward control (FF control), etc.

[0072] 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.

[0073] 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.

[0074] The connection point 21 between diode D1 and diode D2 may be, for example, a connection point provided on the circuit between the anode of diode D1 and the cathode of diode D2, or it may be the anode of diode D1, or it may be the cathode of diode D2.

[0075] 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.

[0076] 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.

[0077] The second inductor L2 may be, for example, the leakage inductance of the transformer Tr1.

[0078] 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 (a third capacitor and a 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 controls the second inverter 4 so that the two switching elements Q3 and Q4 are turned on alternately.

[0079] In this case, the high-potential terminal of the third capacitor is electrically connected to the drain terminal of the 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 the 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.

[0080] 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.

[0081] (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.

[0082] The converter device A2 according to Embodiment 2 will be described below.

[0083] (1) The converter device control circuit 5 changes the modulation ratio of switching elements Q1 and Q2 according to a voltage value that is half the DC bus voltage Vdc of the second series circuit 32 in the first inverter 3. The modulation ratio is the rate by which the switching frequency fsw of switching elements Q1 and Q2 is changed.

[0084] Specifically, the control circuit 5 controls the switching frequency fsw such that the modulation ratio decreases as the voltage value of half the DC bus voltage Vdc increases (see Figure 6). Also, the control circuit 5 controls the switching frequency fsw such that the modulation ratio increases as the voltage value of half the DC bus voltage Vdc decreases (see Figure 6). As a result, the converter device A2 controls (changes) the switching frequency fsw according to the AC voltage Vin, similar to the converter device A1 of Embodiment 1, making it possible to reduce noise and increase the power factor.

[0085] Note that the voltage V3 in Figure 6 represents the waveform of the AC voltage Vin of the AC power supply 8. The modulation rate K1 in Figure 6 represents the change in modulation rate when the DC bus voltage Vdc is a first voltage value (e.g., 450V). The modulation rate K2 in Figure 6 represents the change in modulation rate when the DC bus voltage Vdc is a second voltage value (e.g., 320V) which is a voltage value smaller than the first voltage value.

[0086] Here, the modulation index is preferably a value within the range of 1 to √2, as shown in Figure 6. This allows the converter device A2 to further suppress the generation of distortion components in the current i1 (see Figure 1) that flows when electrical energy is released by the first inductor L1. Therefore, the converter device A2 can further improve the power factor and achieve an even higher power factor.

[0087] (2) Modified Example The control circuit 5 is configured to control the switching frequency fsw so that the modulation ratio decreases as the voltage value of half of the DC bus voltage Vdc increases, and to control the switching frequency fsw so that the modulation ratio increases as the voltage value of half of the DC bus voltage Vdc decreases, but is not limited to this configuration. For example, the control circuit 5 may be configured to control the switching frequency fsw so that the modulation ratio decreases when the voltage value of half of the DC bus voltage Vdc is greater than or equal to the second threshold, and to control the switching frequency fsw so that the modulation ratio increases when the voltage value of half of the DC bus voltage Vdc is less than the second threshold. The second threshold is stored in the memory of the control circuit 5 in advance. Even in this case, the converter device A2 can achieve low noise and high power factor.

[0088] (Embodiment 3) The converter device A3 according to Embodiment 3 (see Figure 1) differs from the converter device A2 according to Embodiment 2 in that the control of the control circuit 5 is different. Regarding the converter device A3 according to Embodiment 3, components similar to those in the converter device A2 according to Embodiment 2 are denoted by the same reference numerals and their descriptions are omitted.

[0089] The converter device A3 according to Embodiment 3 will be described below.

[0090] (1) The converter device control circuit 5 changes the modulation rate of switching elements Q1 and Q2 based on a voltage ratio which is the ratio of half the DC bus voltage Vdc of the second series circuit 32 in the first inverter 3 to the maximum value of the AC voltage Vin.

[0091] The control circuit 5 controls the switching frequency fsw of switching element Q1 and second switching element Q2 so that the modulation ratio decreases as the voltage ratio increases. The control circuit 5 also controls the switching frequency fsw so that the modulation ratio increases as the voltage ratio decreases. As a result, the converter device A3 controls (changes) the switching frequency fsw according to the AC voltage Vin, similar to the converter device A2 of Embodiment 2, making it possible to reduce noise and increase the power factor.

[0092] (2) Modified Control Circuit 5 is configured to control the switching frequency fsw so that the modulation ratio decreases as the voltage ratio increases, and so that the modulation ratio increases as the voltage ratio decreases, but is not limited to this configuration. The control circuit 5 may also be configured to control the switching frequency fsw so that the modulation ratio decreases when the voltage ratio is greater than or equal to the third threshold, and so that the modulation ratio increases when the voltage ratio is less than the third threshold. The third threshold is stored in the memory of the control circuit 5 in advance. Even in this case, the converter device A3 can achieve low noise and high power factor.

[0093] The embodiments 1 to 3 and their modifications described above are only a part of the various embodiments and modifications of this disclosure.

[0094] 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.

[0095] (Aspects) The following aspects are disclosed in this specification.

[0096] The converter devices (A1 to A3) 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) so that the first switching element (Q1) and the second switching element (Q2) are alternately turned on, and the on-time of the first switching element (Q1) and the on-time of the second switching element (Q2) are the same. The control circuit (5) controls the second inverter (4) so ​​that the third switching element (Q3) and the fourth switching element (Q4) are alternately turned on, and the on-time of the third switching element (Q3) and the on-time of the fourth switching element (Q4) are the same, and the on-time of the third switching element (Q3) is the same as the on-time of the first switching element (Q1). The control circuit (5) controls the switching frequencies (fsw) of the first switching element (Q1) and the second switching element (Q2) so that the voltage value of half the DC bus voltage (Vdc), which is the output voltage (Vdc) of the second series circuit (32) of the first inverter (3), becomes a first predetermined value. The control circuit (5) controls the switching frequency (fsw) according to the AC voltage (Vin).

[0097] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0098] The converter devices (A1 to A3) according to the second embodiment further include a fifth switching element (Q5) and a sixth switching element (Q6) in the second inverter (4) according to the first embodiment. The control circuit (5) further controls the second inverter (4) such that the fifth switching element (Q5) performs the same switching operation as the fourth switching element (Q4), and the sixth switching element (Q6) performs the same switching operation as the third switching element (Q3).

[0099] 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) of the first inverter (3) so that the voltage value of the DC bus voltage (Vdc) is twice or more the maximum value of the AC voltage (Vin). The control circuit (5) changes the phase difference between the output voltage (V1) of the first inverter (3) and the input voltage (V2) of the second inverter (4) so ​​that the voltage value of the output voltage (Vo) of the second inverter (4) becomes a second predetermined value.

[0100] According to this embodiment, it is possible to further improve the power factor and achieve a higher power factor.

[0101] In the converter device (A1 to A3) according to the fourth embodiment, in the third embodiment, the control circuit (5) increases the phase difference when the voltage value of the output voltage (Vo) of the second inverter (4) is less than a second predetermined value. The control circuit (5) decreases the phase difference when the voltage value of the output voltage (Vo) of the second inverter (4) is greater than a second predetermined value.

[0102] In the converter device (A1) according to the fifth embodiment, in any one of the first to fourth embodiments, the control circuit (5) controls the switching frequency (fsw) according to the phase of the AC voltage (Vin).

[0103] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0104] In the sixth embodiment of the converter device (A1), in any one of the first to fourth embodiments, the control circuit (5) controls the switching frequency (FSW) such that the switching frequency (FSW) increases as the absolute value of the instantaneous AC voltage (Vin) increases. The control circuit (5) controls the switching frequency (FSW) such that the switching frequency (FSW) decreases as the absolute value of the instantaneous AC voltage (Vin) decreases.

[0105] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0106] In the converter device (A1) according to the seventh embodiment, in any one of the first to fourth embodiments, the control circuit (5) controls the switching frequency (FSW) to increase when the absolute value of the instantaneous AC voltage (Vin) is greater than or equal to a first threshold. The control circuit (5) controls the switching frequency (FSW) to decrease when the absolute value of the instantaneous AC voltage (Vin) is less than the first threshold.

[0107] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0108] In the converter device (A2) according to the eighth embodiment, in any one of the first to fourth embodiments, the control circuit (5) changes the modulation rate, which is the rate at which the switching frequency (fsw) is changed, according to a voltage value of half the DC bus voltage (Vdc).

[0109] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0110] In the ninth embodiment of the converter device (A2), in the eighth embodiment, the control circuit (5) controls the switching frequency (fsw) such that the modulation ratio decreases as the voltage value of half of the DC bus voltage (Vdc) increases. The control circuit (5) controls the switching frequency (fsw) such that the modulation ratio increases as the voltage value of half of the DC bus voltage (Vdc) decreases.

[0111] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0112] In the converter device (A2) according to the tenth embodiment, in the eighth embodiment, the control circuit (5) controls the switching frequency (fsw) such that the modulation ratio decreases when the voltage value of half of the DC bus voltage (Vdc) is equal to or greater than the second threshold. The control circuit (5) controls the switching frequency (fsw) such that the modulation ratio increases when the voltage value of half of the DC bus voltage (Vdc) is less than the second threshold.

[0113] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0114] In the eleventh embodiment of the converter device (A3), in the eighth embodiment, the control circuit (5) changes the modulation ratio according to a voltage ratio which is the ratio of half the DC bus voltage (Vdc) to the maximum value of the AC voltage (Vin). The control circuit (5) controls the switching frequency (fsw) such that the modulation ratio decreases as the voltage ratio increases. The control circuit (5) controls the switching frequency (fsw) such that the modulation ratio increases as the voltage ratio decreases.

[0115] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0116] In the converter device (A3) according to the twelfth embodiment, in the eighth embodiment, the control circuit (5) changes the modulation ratio according to a voltage ratio which is the ratio of half the DC bus voltage (Vdc) to the maximum value of the AC voltage (Vin). When the voltage ratio is greater than or equal to a third threshold, the control circuit (5) controls the switching frequency (fsw) so that the modulation ratio becomes smaller. When the voltage ratio is less than the third threshold, the control circuit (5) controls the switching frequency (fsw) so that the modulation ratio becomes larger.

[0117] According to this embodiment, it is possible to reduce noise and increase the power factor.

[0118] In the converter device (A2 to A3) according to the 13th embodiment, in any one of the 8th to 12th embodiments, the modulation rate is a value within the range of 1 to √2.

[0119] According to this embodiment, it is possible to further improve the power factor and to further increase the power factor.

[0120] 2 Rectifier 3 First Inverter 4 Second Inverter 5 Control Circuit 8 AC Power Supply 21 Connection Point (Connection point of the first and second diodes) 31 First Series Circuit 32 Second Series Circuit 34 Connection Point (Connection point of the first and second switching elements) 35 Connection Point (Connection point of the first and second capacitors) 44 Input Terminal 45 Input Terminal 46 Output Terminal 47 Output Terminal 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) fsw Switching Frequency 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 (4th switching element) Q5 Switching element (5th switching element) Q6 Switching element (6th switching element) Tr1 Transformer V1 Output voltage (output voltage of the 1st inverter) V2 Input voltage (input voltage of the 2nd inverter) Vdc Output voltage (DC bus voltage) Vin AC voltage Vo Output voltage (output voltage of the 2nd 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; The inverter comprises: 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 so that the first switching element and the second switching element alternately turn on, and the on time of the first switching element and the on time of the second switching element are the same; controls the second inverter so that the third switching element and the fourth switching element alternately turn on, and the on time of the third switching element and the on time of the fourth switching element are the same, and the on time of the third switching element is the same as the on time of the first switching element; controls the switching frequencies of the first and second switching elements so that the voltage value of half the DC bus voltage, which is the output voltage of the second series circuit of the first inverter, becomes a first predetermined value; and controls the switching frequencies according to the AC voltage.Converter device.

2. 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 fourth switching element, and the sixth switching element performs the same switching operation as the third switching element.

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 of the first inverter so that the voltage value of the DC bus voltage is twice or more the maximum value of the AC voltage, and changes the phase difference between the output voltage of the first inverter and the input voltage of the second inverter so that the voltage value of the output voltage of the second inverter becomes a second predetermined value.

4. The converter device according to claim 3, wherein the control circuit increases the phase difference when the voltage value of the output voltage of the second inverter is less than the second predetermined value, and decreases the phase difference when the voltage value of the output voltage of the second inverter is greater than the second predetermined value.

5. The converter device according to any one of claims 1 to 4, wherein the control circuit controls the switching frequency according to the phase of the AC voltage.

6. The converter device according to any one of claims 1 to 4, wherein the control circuit controls the switching frequency such that the switching frequency increases as the absolute value of the instantaneous value of the AC voltage increases, and controls the switching frequency such that the switching frequency decreases as the absolute value of the instantaneous value of the AC voltage decreases.

7. The converter device according to any one of claims 1 to 4, wherein the control circuit controls the switching frequency so that the switching frequency is higher when the absolute value of the instantaneous value of the AC voltage is greater than or equal to a first threshold, and controls the switching frequency so that the switching frequency is lower when the absolute value of the instantaneous value of the AC voltage is less than the first threshold.

8. The converter device according to any one of claims 1 to 4, wherein the control circuit changes the modulation rate, which is the rate at which the switching frequency is changed, according to a voltage value of half the DC bus voltage.

9. The converter device according to claim 8, wherein the control circuit controls the switching frequency such that the modulation ratio decreases as the voltage value of half the DC bus voltage increases, and controls the switching frequency such that the modulation ratio increases as the voltage value of half the DC bus voltage decreases.

10. The converter device according to claim 8, wherein the control circuit controls the switching frequency to reduce the modulation ratio when the voltage value of half the DC bus voltage is greater than or equal to a second threshold, and controls the switching frequency to increase the modulation ratio when the voltage value of half the DC bus voltage is less than the second threshold.

11. The converter device according to claim 8, wherein the control circuit changes the modulation rate according to a voltage ratio which is the ratio of half the DC bus voltage to the maximum value of the AC voltage, controls the switching frequency such that the modulation rate decreases as the voltage ratio increases, and controls the switching frequency such that the modulation rate increases as the voltage ratio decreases.

12. The converter device according to claim 8, wherein the control circuit changes the modulation rate according to a voltage ratio which is the ratio of half the DC bus voltage to the maximum value of the AC voltage, controls the switching frequency to decrease the modulation rate when the voltage ratio is greater than or equal to a third threshold, and controls the switching frequency to increase the modulation rate when the voltage ratio is less than the third threshold.

13. The converter device according to any one of claims 8 to 12, wherein the modulation rate is a value within the range of 1 to √2.

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