JP2022102661A - Ac power supply device - Google Patents

Abstract

To provide an AC power supply device capable of suppressing an increase in loss of a switching element even in a case of a relatively light load.SOLUTION: An AC power supply device (1a) includes a leg in which two arms including switching elements (transistors Q1 and Q2 respectively) are connected in series and a DC voltage is applied to both ends, and converts the DC voltage into an AC voltage. The AC power supply device includes: an inductor (L1) whose one end is connected to a connection point of the two arms; two diodes (D1 and D2) that clamp the potential of another end of the inductor to the potentials of one end and another end of the leg; and a capacitor (C1) having one end connected to the other end of the inductor and another end connected to a predetermined potential. The resonance frequency by the inductor and the capacitor is higher than more than 3 times the on/off frequency of the switching element.SELECTED DRAWING: Figure 1

Description

The present invention relates to an AC power supply device that converts DC power into AC power.

Conventionally, an AC power supply device using a half-bridge or full-bridge class D amplifier is known. The half-bridge class D amplifier outputs a square wave voltage by alternately turning on high-side and low-side switching elements. A full-bridge class D amplifier applies a square wave voltage by alternately repeating control for simultaneously turning on the high-side switching element of one leg and the low-side switching element of the other leg for the combination of the two legs. Output. By providing a resonance circuit at the output of these half bridges or full bridges and applying an output voltage to the load via the resonance circuit, an AC power supply device that supplies AC power close to a sine wave to the load is provided.

Some class D amplifiers enable zero voltage switching (ZVS = Zero Voltage Switching) by making the circuit connected to the output side inductive. ZVS reduces the switching loss at the time of turning on by discharging the capacitance of the output of the switching element to near 0V before the switching element transitions from off to on. In particular, an amplifier that turns on / off the switching element in time with the state of the resonance circuit on the output side is called a class E amplifier.

On the other hand, when a mismatch occurs in the load of the class D amplifier and a large return current flows from the output side, the switching element may be damaged. On the other hand, in Patent Document 1, by providing a diode clamping circuit at the intermediate point of two high frequency filters connected to the output side of the inverter circuit, the potential at the intermediate point is clamped to the potentials at both ends of the power supply. Class E amplifiers are disclosed.

Special Table 2007-591340 Gazette

However, regardless of whether or not the technique disclosed in Patent Document 1 is applied, there is a problem that zero voltage switching cannot be established when the load of the class D amplifier becomes relatively light, and the loss of the switching element increases. rice field.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an AC power supply device capable of suppressing an increase in loss of a switching element even when a relatively light load is applied. To provide.

The AC power supply device according to one aspect of the present invention is an AC power supply device that includes a leg in which two arms including a switching element are connected in series and a DC voltage is applied to both ends, and converts the DC voltage into an AC voltage. There are an inductor with one end connected to the connection points of the two arms, two diodes that clamp the potential of the other end of the inductor to the potentials of one end and the other end of the leg, and the inductor. A capacitor having one end connected to the other end and the other end connected to a predetermined potential is provided, and the resonance frequency of the inductor and the capacitor is higher than three times the on / off frequency of the switching element. ..

In this embodiment, one end of an inductor is connected to the connection point of two arms in a leg to which a DC voltage is applied to both ends, and between the other end of the inductor and one end and the other end of the leg, respectively. A clamp diode is connected. Further, a capacitor is connected between the other end of the inductor and a predetermined potential. The resonance frequency between the inductor and the capacitor is higher than three times the on / off frequency of the switching element. That is, the capacitor is not intended to suppress the harmonics of the switching frequency. With the above configuration, it is possible to secure the reflux current flowing through the inductor before each switching element makes a transition from off to on, so that the output capacitance of the switching element can be discharged more.

The AC power supply device according to one aspect of the present invention includes two sets of the leg, the inductor, the two diodes, and the capacitor.

In this embodiment, since the two legs have the same configuration, as in the case of the half bridge, the return current flowing through the inductor is secured before each switching element transitions from off to on. , The output capacitance of the switching element can be discharged more.

The AC power supply device according to one aspect of the present invention shifts the on / off phases of the switching element included in the high-side arm of one leg and the switching element included in the low-side arm of the other leg to each other. Further, a control unit for controlling the output AC power is provided.

In this embodiment, the output power is controlled by shifting the on / off phase of the switching element included in one leg of the full bridge circuit and the diagonally opposed arms of the other leg. Even when the output power is reduced in this configuration, the recirculation current flowing through the inductor is secured before each switching element transitions from off to on, and the output capacitance of the switching element is secured. Can be discharged more.

The AC power supply device according to one aspect of the present invention further includes a series resonance circuit that resonates with the on / off frequency of the switching element after the inductor.

In this embodiment, since the series resonance circuit in the subsequent stage resonates with the switching frequency, the harmonic of the output can be suppressed.

According to the present invention, it is possible to suppress an increase in loss of a switching element even in the case of a relatively light load.

It is a circuit diagram which shows the structural example of the AC power supply device which concerns on Embodiment 1. FIG. It is a mode transition diagram of the AC power supply device which concerns on Embodiment 1. FIG. It is a waveform diagram which simulated and compared the switching waveform in the AC power supply device which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the structural example of the AC power supply device which concerns on Embodiment 2. It is a mode transition diagram of the AC power supply device which concerns on Embodiment 2. FIG. It is a 1st waveform diagram which simulated and compared the switching waveform in the AC power supply apparatus which concerns on Embodiment 2. FIG. It is a 2nd waveform diagram which simulated and compared the switching waveform in the AC power supply apparatus which concerns on Embodiment 2. FIG.

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration example of the AC power supply device 1a according to the first embodiment. The AC power supply device 1a supplies AC power to, for example, a plasma processing device. The AC power supply device 1a is a class D amplifier of a half bridge including a leg in which two arms including transistors Q1 and Q2 are connected in series. A DC voltage is applied to both ends of the leg from the DC power supply DC1.

The AC power supply device 1a is parallel to the inductor L1 having one end connected to the connection points of the transistors Q1 and Q2, the diodes D1 and D2 having the anode and the cathode connected to the other ends of the inductor L1, respectively, and both ends of the diode D2. It further includes a connected capacitor C1. The cathode of the diode D1 is connected to one end on the positive side of the leg. The anode of the diode D2 is connected to the other end of the leg. That is, the diode D1 clamps the potential of the other end of the inductor L1 to the potential of one end of the leg. The diode D2 clamps the potential of the other end of the inductor L1 to the potential of the other end of the leg. The other end of the leg has a common potential.

Even when one end of the capacitor C1 is connected to the other end of the inductor L1 and the other end is connected to an arbitrary potential, the capacitor C1 is equivalent to the case of FIG. 1 in terms of alternating current. Specifically, the other end of the capacitor C1 may be connected to the cathode of the diode D1. Further, the capacitor C1 may be capacitively divided into two capacitors, one of which may be connected in parallel to the diode D1 and the other of which may be connected in parallel to the diode D2.

The connection points of the diodes D1 and D2 are connected to one end of the primary winding of the transformer T1 via a series resonant circuit of the inductor Lr and the capacitor Cr. The other end of the primary winding is connected to a common potential. The resonance frequencies of the inductor Lr and the capacitor Cr are substantially equal to the switching frequencies of the transistors Q1 and Q2. AC power is supplied from the secondary winding of the transformer T1 to the load Ld via a low-pass filter by the inductor Lf and the capacitor Cf.

The transistors Q1 and Q2 are, for example, FETs (Field Effect Transistors), but may be other switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and HEMTs (High Electron Mobility Transistors). When the transistors Q1 and Q2 are IGBTs or HEMTs, it is preferable to connect an external diode in antiparallel to each IGBT or HEMT. The drain of the transistor Q1 is connected to the DC power supply DC1, and the source is connected to the drain of the transistor Q2 and one end of the inductor L1. The source of transistor Q2 is connected to a common potential.

Signal sources S11 and S12 whose duty is controlled by the control unit 10a are connected to the gates of the transistors Q1 and Q2, respectively. The signal sources S11 and S12 output signals that turn on / off the transistors Q1 and Q2 in opposite phases.

In the above configuration, a rectangular wave-shaped AC voltage is output from the connection points of the transistors Q1 and Q2, which are the connection points of the two arms. Since the harmonics of this AC voltage are suppressed by the resonant circuit of the inductor Lr and the capacitor Cr and the low-pass filter of the inductor Lf and the capacitor Cf, a substantially sinusoidal AC voltage is applied to the load Ld.

In the first embodiment, the frequency of the AC voltage is 3.2 MHz, but the frequency is not limited to this, and is not limited to this, for example, an industrial RF (Radio Frequency) band such as 13.56 MHz, 27.12 MHz, 40.68 MHz. Frequency may be.

The inductor L1 and the capacitor C1 apparently form a low-pass filter, but their resonance frequency, that is, the cutoff frequency as a low-pass filter is higher than three times the frequency of the AC voltage. That is, the inductor L1 to which the capacitor C1 is connected to the other end behaves as an inductive element with respect to the circuit after the other end at the frequency of the AC voltage. On the other hand, the circuit connected to the subsequent stage from the other end of the inductor L1 has a resistance of about 50 Ω at the frequency of the AC voltage. Therefore, the circuit connected to the transistors Q1 and Q2 at the frequency of the AC voltage can be regarded as inductive by the action of the inductor L1.

When the circuit connected to the transistors Q1 and Q2 is inductive, the transistors Q1 and Q2 can be zero voltage switched (ZVS) by a known technique if the conditions are met. This is because the capacitance of the output of each transistor (not shown in FIG. 1) is discharged to near 0V before the transistors Q1 and Q2 transition from off to on, thereby reducing the switching loss at the time of on. It is a technology to reduce.

However, when the AC power output by the AC power supply device 1a is relatively small, the current flowing through the inductor L1 becomes relatively small, and the above-mentioned capacitance is sufficiently applied before the transistors Q1 and Q2 transition from off to on. It becomes impossible to discharge and ZVS cannot be established. In the first embodiment, by providing the diodes D1 and D2 and the capacitor C1, the transistors Q1 and Q2 can be switched to zero voltage even when the AC power output by the AC power supply device 1a is relatively small. .. Hereinafter, a case where the output power of the AC power supply device 1a is relatively small because the duty ratio of the transistors Q1 and Q2 is relatively small or the resistance value of the load Ld is larger than 50Ω will be described.

FIG. 2 is a mode transition diagram of the AC power supply device 1a according to the first embodiment. In FIG. 2, the state of the AC power supply device 1a is described by dividing it into six modes from mode 1 to mode 6 according to the transition of the on / off states of the transistors Q1 and Q2. Of the configurations of the AC power supply device 1a in each mode, the inductor Lr, the capacitor Cr, the signal sources S11 and S12, and the control unit 10a are not shown. The AC power supply device 1a repeats the mode transition in the direction of the white arrow in the figure.

It is assumed that the capacitances Cd1 and Cd2 are connected between the drain sources of the transistors Q1 and Q2, respectively. For each transistor, the one in the on state is referred to as "on". Those that are in the off state do not indicate the state. The broken line in the figure represents the current flowing to and from the DC power supply DC1, and the alternate long and short dash line represents the reflux current that does not flow to the DC power supply DC1. Here, for convenience of explanation, the state of mode 6 will be described as a starting point.

Mode 6 is a state during the transition from off to on of the transistor Q1 and immediately after the transition to on. In the mode 6, when the transistor Q1 is turned on, a current starts to flow from the DC power supply DC1 to the inductor L1 via the transistor Q1 and the capacitor C1. As a result, the capacitor C1 is gradually charged. That is, the presence of the capacitor C1 allows a current to flow through the inductor L1. The capacitance Cd2 is rapidly charged by the current that starts to flow from the DC power supply DC1 through the transistor Q1 by the amount that cannot be fully charged in the mode 5. Further, the capacitance Cd1 is rapidly discharged by the transition from the off to the on of the transistor Q1 by the amount that cannot be completely discharged in the mode 5. The charge current of the capacitance Cd2 and the discharge current of the capacitance Cd1 become the loss of the transistor Q1. In the first embodiment, the loss due to these is minimized.

After that, when the charging of the capacitor C1, the charging of the capacitance Cd2, and the discharging of the capacitance Cd1 are completed, the AC power supply device 1a transitions to the mode 1. In mode 1, the current flowing through the inductor L1 becomes a reflux current that continues to flow through the diode D1 and the transistor Q1. That is, the presence of the diode D1 holds the current flowing through the inductor L1. The capacitor C1 and the capacitance Cd2 are charged to the voltage of the DC power supply DC1.

After that, when the transistor Q1 is turned off, the AC power supply device 1a transitions to the mode 2. In the mode 2, a part of the current flowing through the inductor L1 is a current flowing through the DC power supply DC1 via the capacitance Cd2 and the diode D1. As a result, the capacitance Cd2 is gradually discharged. The capacitance Cd2 can be discharged until the parasitic diode (not shown) of the transistor Q2 conducts. The other part of the current flowing through the inductor L1 is the reflux current flowing through the diode D1 and the capacitance Cd1. As a result, the capacitance Cd1 is gradually charged. That is, even in the mode 2, the presence of the diode D1 holds the current flowing through the inductor L1. Further, before the transistor Q2 is turned on in the next mode 3, the capacitance Cd2 is discharged and the voltage across the ends drops. The capacitor C1 is still charged to the voltage of the DC power supply DC1.

After that, when the transistor Q2 is turned on, the AC power supply device 1a transitions to the mode 3. Mode 3 is a state during the transition from off to on of the transistor Q2 and immediately after the transition to on. In the mode 3, when the transistor Q2 is turned on, the voltage of the capacitor C1 is applied to the inductor L1, and a current in the opposite direction to that in the mode 2 starts to flow. As a result, the capacitor C1 is gradually discharged. That is, the presence of the capacitor C1 allows a current to flow through the inductor L1. The capacitance Cd2 is rapidly discharged by the transition from the off to the on of the transistor Q2 by the amount that cannot be completely discharged in the mode 2. Further, the capacitance Cd1 is rapidly charged by the current that starts to flow from the DC power supply DC1 via the transistor Q2 by the amount that cannot be fully charged in the mode 2. The discharge current of the capacitance Cd2 and the charge current of the capacitance Cd1 become the loss of the transistor Q2. In the first embodiment, the loss due to these is minimized.

After that, when the discharge of the capacitor C1, the discharge of the capacitance Cd2, and the charging of the capacitance Cd1 are completed, the AC power supply device 1a transitions to the mode 4. In the mode 4, the current flowing through the inductor L1 becomes a current that continues to flow through the diode D2 and the transistor Q2. That is, the presence of the diode D2 holds the current flowing through the inductor L1. The capacitance Cd1 is charged to the voltage of the DC power supply DC1.

After that, when the transistor Q2 is turned off, the AC power supply device 1a transitions to the mode 5. In the mode 5, a part of the current flowing through the inductor L1 is a current flowing through the DC power supply DC1 via the capacitance Cd1 and the diode D2. As a result, the capacitance Cd1 is gradually discharged. The capacitance Cd1 can be discharged until the parasitic diode (not shown) of the transistor Q1 conducts. The other part of the current flowing through the inductor L1 is the reflux current flowing through the diode D2 and the capacitance Cd2. As a result, the capacitance Cd2 is gradually charged. That is, even in the mode 5, the presence of the diode D2 keeps the current flowing through the inductor L1. Further, before the transistor Q1 is turned on in the next mode 6, the capacitance Cd1 is discharged and the voltage across the ends drops.

From the above explanation using FIG. 2, it has been clarified that the loss when the transistors Q1 and Q2 are turned on is reduced by the inductor L1, the diodes D1 and D2, and the capacitor C1. Here, in the case of a low output in which the duty ratio of the transistors Q1 and Q2 is fixed to 0.5 and the resistance value of the load Ld is sufficiently larger than 50Ω, how the switching waveforms of the transistors Q1 and Q2 change depending on the presence or absence of the capacitor C1. The result of simulating whether it changes to is explained.

FIG. 3 is a waveform diagram comparing simulations of switching waveforms in the AC power supply device 1a according to the first embodiment. In FIG. 3A, when the capacitor C1 is not provided, the switching voltage between the drain and the source of the transistor Q1 is shown in the upper stage, and the voltage at the other end of the inductor L1 is shown in the lower stage. In FIG. 3B, when the capacitor C1 is present, the switching voltage between the drain and the source of the transistor Q1 is shown in the upper stage, and the voltage at the other end of the inductor L1 is shown in the lower stage. In any waveform diagram, the horizontal axis represents time (μs) and the vertical axis represents voltage (V). The waveform of the switching voltage of the transistor Q2 is delayed by half a cycle from the waveform shown in the upper part of FIGS. 3A and 3B.

According to the upper diagram of FIG. 3A, the transistor Q1 is turned on before the switching voltage is completely lowered, and a switching loss occurs. On the other hand, according to the upper diagram of FIG. 3B, the transistor Q1 is turned on after the switching voltage has completely dropped, and no switching loss has occurred. As shown in the lower part of each of FIGS. 3A and 3B, there is no significant difference in the voltage waveform at the other end of the inductor L1 between the case where the capacitor C1 is not provided and the case where the capacitor C1 is not provided.

As described above, according to the first embodiment, one end of the inductor L1 is connected to the connection point of the two arms in the leg to which the DC voltage is applied to both ends, and the other end of the inductor L1, one end of the leg, and the like. Diodes D1 and D2 for voltage clamping are connected to the end. Further, the capacitor C1 is connected between the other end of the inductor L1 and the common potential. The resonance frequency between the inductor L1 and the capacitor C1 is higher than three times the on / off frequency of the transistors Q1 and Q2. That is, the capacitor C1 is not intended to suppress harmonics of the switching frequency. With this configuration, before the transistors Q1 and Q2 transition from off to on, the recirculation current flowing through the inductor L1 is secured, and the capacitances Cd1 and Cd2 of the outputs of the transistors Q1 and Q2, respectively, are discharged more. be able to. Therefore, even in the case of a relatively light load, it is possible to suppress an increase in the loss of the switching element which is the transistors Q1 and Q2.

Further, according to the first embodiment, since the resonance circuit by the inductor Lr and the capacitor Cr resonates with the switching frequency of the transistors Q1 and Q2, the harmonic of the output can be suppressed.

(Embodiment 2)
The first embodiment is a half bridge in which the class D amplifier has one leg in which two arms are connected in series, whereas the second embodiment is a full bridge in which the class D amplifier has two legs. Is. Both ends of the two legs are both connected to the DC power supply DC1.

FIG. 4 is a circuit diagram showing a configuration example of the AC power supply device 1b according to the second embodiment. In addition to the configuration of the AC power supply device 1a of the first embodiment, the AC power supply device 1a has one end to another leg in which two arms including the transistors Q3 and Q4 are connected in series and a connection point of the transistors Q3 and Q4. Further includes an inductor L2 to which the inductor L2 is connected, diodes D3 and D4 to which an anode and a cathode are connected to the other ends of the inductor L2, respectively, and a capacitor C2 connected in parallel to both ends of the diode D4.

The cathode of the diode D3 is connected to one end on the positive side of each leg. The anode of the diode D4 is connected to the other end of each leg. That is, each of the diodes D3 and D4 clamps the potential of the other end of the inductor L2 to the potential of one end and the other end of each leg. The connection points of the diodes D3 and D4 are connected to the other end of the primary winding of the transformer T1.

The drain of the transistor Q3 is connected to the DC power supply DC1, and the source is connected to the drain of the transistor Q4 and one end of the inductor L2. The source of the transistor Q4 is connected to a common potential. Signal sources S21, S22, S23 and S24 whose phase is controlled by the control unit 10b are connected to the gates of the transistors Q1, Q2, Q3 and Q4, respectively. In addition, the parts corresponding to the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

Each of the signal sources S21 and S22 outputs a signal for turning on / off the transistors Q1 and Q2 in opposite phases. Each of the signal sources S23 and S24 outputs a signal for turning on / off the transistors Q3 and Q4 in opposite phases. The control unit 10b controls the phases of the signal sources S21 and S24 so that the phases on / off of the transistors Q1 and Q4 are shifted from each other, and the phases on which the transistors Q2 and Q3 are turned on / off are shifted to each other. In this way, the phases of the signal sources S22 and S23 are controlled. As a result, the magnitude of the AC power output by the AC power supply device 1b is controlled. That is, the AC power supply device 1b is a so-called phase shift type full bridge type power supply device.

In the AC power supply device 1b, the shorter the time that the transistors Q1 and Q4 are turned on at the same time and the shorter the time that the transistors Q2 and Q3 are turned on at the same time, the lower the output power. When the output power is close to the minimum, the transistors Q1 and Q3 are turned on / off in substantially in-phase, and the transistors Q2 and Q4 are turned on / off in substantially in-phase. Even in such a case, it is possible to sufficiently discharge the capacitance of the output of the transistors Q1, Q2, Q3 and Q4 before the transistors Q1, Q2, Q3 and Q4 transition from off to on. In the following, a case where the output power of the AC power supply device 1b is close to the minimum will be described as an example.

FIG. 5 is a mode transition diagram of the AC power supply device 1b according to the second embodiment. In FIG. 5, the state of the AC power supply device 1b is described by dividing it into six modes from mode 1 to mode 6 according to the transition of the on / off states of the transistors Q1, Q2, Q3 and Q4. Of the configurations of the AC power supply device 1b in each mode, the inductor Lr, the capacitor Cr, the signal sources S21, S22, S23 and S24, and the control unit 10b are not shown. The AC power supply device 1b repeats the mode transition in the direction of the white arrow in the figure.

It is assumed that the capacitances Cd1, Cd2, Cd3 and Cd4 are connected between the drain sources of the transistors Q1, Q2, Q3 and Q4, respectively. For each transistor, the one in the on state is referred to as "on". Those that are in the off state do not indicate the state. The broken line in the figure represents the current flowing to and from the DC power supply DC1, and the alternate long and short dash line represents the reflux current that does not flow to the DC power supply DC1.

Since the currents flowing through the transistors Q1 and Q2, the capacitances Cd1 and Cd2, the diodes D1 and D2, and the capacitor C1 in each mode are exactly the same as those shown in FIG. 2 of the first embodiment, the drawings are shown. Illustration is omitted to avoid complication. That is, FIG. 5 shows the currents flowing through the transistors Q3 and Q4, the capacitances Cd3 and Cd4, the diodes D3 and D4, and the capacitor C2 in each mode. Since these currents are similar to the currents shown in FIG. 2, they are described in the same manner as in FIG. 2 by simply replacing the reference numerals. Therefore, a part of the explanation will be simplified. Here, the state of mode 6 will be described as a starting point.

In the mode 6, when the transistor Q3 is turned on, a current starts to flow from the DC power supply DC1 to the inductor L2 via the transistor Q3 and the capacitor C2. As a result, the capacitor C2 is gradually charged. That is, the presence of the capacitor C2 allows a current to flow through the inductor L2. The capacitance Cd4 is rapidly charged by the current that starts to flow from the DC power supply DC1 through the transistor Q3 by the amount that cannot be fully charged in the mode 5. Further, the capacitance Cd3 is rapidly discharged by the transition from the off to the on of the transistor Q3 by the amount that cannot be completely discharged in the mode 5. The charge current of the capacitance Cd4 and the discharge current of the capacitance Cd3 cause the loss of the transistor Q3. In the second embodiment, the loss due to these is minimized.

After that, when the charging of the capacitor C2, the charging of the capacitance Cd4, and the discharging of the capacitance Cd3 are completed, the AC power supply device 1b transitions to the mode 1. In mode 1, the current flowing through the inductor L2 becomes a current that continues to flow through the diode D3 and the transistor Q3. That is, the presence of the diode D3 holds the current flowing through the inductor L2.

After that, when the transistor Q3 is turned off, the AC power supply device 1b transitions to the mode 2. In the mode 2, a part of the current flowing through the inductor L2 is a current flowing through the DC power supply DC1 via the capacitance Cd4 and the diode D3. As a result, the capacitance Cd4 is gradually discharged. The other part of the current flowing through the inductor L2 is the current flowing through the diode D3 and the capacitance Cd3. As a result, the capacitance Cd3 is gradually charged. That is, even in the mode 2, the presence of the diode D3 holds the current flowing through the inductor L2. Further, before the transistor Q4 is turned on in the next mode 3, the capacitance Cd4 is discharged and the voltage across the ends drops.

After that, when the transistor Q4 is turned on, the AC power supply device 1b transitions to the mode 3. In the mode 3, when the transistor Q4 is turned on, the voltage of the capacitor C2 is applied to the inductor L2, and a current in the opposite direction to that in the mode 2 starts to flow. As a result, the capacitor C2 is gradually discharged. That is, the presence of the capacitor C2 allows a current to flow through the inductor L2. The capacitance Cd4 is rapidly discharged by the transition from the off to the on of the transistor Q4 by the amount that cannot be completely discharged in the mode 2. Further, the capacitance Cd3 is rapidly charged by the current that starts to flow from the DC power supply DC1 via the transistor Q4 by the amount that cannot be fully charged in the mode 2. The discharge current of the capacitance Cd4 and the charge current of the capacitance Cd3 cause the loss of the transistor Q4. In the second embodiment, the loss due to these is minimized.

After that, when the discharge of the capacitor C2, the discharge of the capacitance Cd4, and the charging of the capacitance Cd3 are completed, the AC power supply device 1b transitions to the mode 4. In the mode 4, the current flowing through the inductor L2 becomes a current that continues to flow through the diode D4 and the transistor Q4. That is, the presence of the diode D4 holds the current flowing through the inductor L2.

After that, when the transistor Q4 is turned off, the AC power supply device 1b transitions to the mode 5. In the mode 5, a part of the current flowing through the inductor L2 is a current flowing through the DC power supply DC1 via the capacitance Cd3 and the diode D4. As a result, the capacitance Cd3 is gradually discharged. The other part of the current flowing through the inductor L2 is the current flowing through the diode D4 and the capacitance Cd4. As a result, the capacitance Cd4 is gradually charged. That is, even in the mode 5, the presence of the diode D4 keeps the current flowing through the inductor L2. Further, before the transistor Q3 is turned on in the next mode 6, the capacitance Cd3 is discharged and the voltage across the ends drops.

From the above explanation using FIG. 5, it has been clarified that the loss when the transistors Q3 and Q4 are turned on is reduced by the inductor L2, the diodes D3 and D4, and the capacitor C2. Here, when the output power is 0 W, the result of simulating how the switching waveforms of the transistors Q1 and Q2 change depending on the presence or absence of the capacitor C1 will be described. The same applies to the result of simulating how the switching waveforms of the transistors Q3 and Q4 change depending on the presence or absence of the capacitor C2.

FIG. 6 is a first waveform diagram in which switching waveforms in the AC power supply device 1b according to the second embodiment are simulated and compared. FIG. 6A shows the switching voltage between the drain and the source of the transistor Q1 in the case where the capacitor C1 is not provided. FIG. 6B shows the switching voltage between the drain and the source of the transistor Q1 in the case where the capacitor C1 is present. In any waveform diagram, the horizontal axis represents time (t) and the vertical axis represents voltage (V). The waveform of the switching voltage of the transistor Q2 is delayed by half a cycle from the waveforms shown in FIGS. 6A and 6B.

According to FIG. 6A, the transistors Q1 or Q2 are turned on before the switching voltage drops, and the switching loss is relatively large. On the other hand, according to FIG. 6B, the transistors Q1 or Q2 are turned on after the switching voltage drops halfway, and the switching loss is relatively small.

Next, the influence of the LC resonance frequency of the inductor L1 and the capacitor C1 on the switching waveforms of the transistors Q1 and Q2 will be described. The same applies to the influence of the LC resonance frequency of the inductor L2 and the capacitor C2 on the switching waveforms of the transistors Q3 and Q3.

FIG. 7 is a second waveform diagram in which switching waveforms in the AC power supply device according to the second embodiment are simulated and compared. 7A, 7B, 7C and 7D show the switching voltage between the drain and source of the transistor Q1 when the LC resonance frequencies are 22.5 MHz, 15.9 MHz, 11.3 MHz and 7.12 MHz, respectively. .. In any waveform diagram, the horizontal axis represents time (μs) and the vertical axis represents voltage (V). The waveform of the switching voltage of the transistor Q2 is delayed by half a cycle from the waveforms shown in FIGS. 7A to 7D.

In the case of FIG. 7A where the LC resonance frequency is about 7 times the switching frequency (3.2 MHz) and the case of FIG. 7B where the LC resonance frequency is about 5 times, the transistor Q1 is turned on before the switching voltage is completely reduced. The switching loss is relatively large. In the case of FIG. 7C in which the LC resonance frequency is about 3.5 times the switching frequency and the case of FIG. 7D in which the LC resonance frequency is about 2.2 times, the transistor Q1 is turned on after the switching voltage has completely dropped. Switching loss is relatively small. However, in the case of FIG. 7D, it has been confirmed that a large distortion occurs in the waveform of the output voltage as compared with the case of FIG. 7C. As described above, the loss tends to decrease as the LC resonance frequency decreases, but the distortion that occurs in the waveform of the output voltage tends to increase. Therefore, the LC resonance frequency due to the inductor L1 and the capacitor C1 is preferably 3 times or more the switching frequency. More preferably, it is about 3 to 5 times.

As described above, according to the second embodiment, since the two legs have the same configuration, the transistors Q1 and Q2 pass through the inductor L1 before transitioning from off to on, as in the case of the half bridge. It is possible to secure the flowing return current and discharge more of the capacitances Cd1 and Cd2 of the outputs of the transistors Q1 and Q2, respectively.

Further, according to the second embodiment, the phases of the transistors Q1 and Q4 (and Q2 and Q3) included in the diagonally opposed arms of one leg and the other leg of the full bridge circuit are shifted and output. Control power. Even when the output power is reduced in this configuration, the return current flowing through the inductor L1 is secured before the transistors Q1 and Q2 transition from off to on, and the outputs of the transistors Q1 and Q2 are respectively output. The capacitances Cd1 and Cd2 can be discharged more. Similarly, before the transistors Q3 and Q4 transition from off to on, the reflux current flowing through the inductor L2 is secured to discharge more of the capacitances Cd3 and Cd4 of the outputs of the transistors Q3 and Q4, respectively. Can be done.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims, not the above-mentioned meaning, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. In addition, the technical features described in each embodiment can be combined with each other.

1a, 1b AC power supply 10a, 10b Control unit C1, C2, Cr, Cf Capacitor Cd1, Cd2, Cd3, Cd4 Capacitance D1, D2, D3, D4 Diode DC1 DC power supply L1, L2, Lr, Lf Inductor Ld Load Q1, Q2, Q3, Q4 Transistors S11, S12, S21, S22, S23, S24 Signal Source T1 Transformer

Claims (4)

An AC power supply device in which two arms including a switching element are connected in series and a leg to which a DC voltage is applied is provided at both ends, and the DC voltage is converted into an AC voltage.
An inductor with one end connected to the connection points of the two arms,
Two diodes that clamp the potential of the other end of the inductor to the potentials of one end and the other end of the leg,
One end is connected to the other end of the inductor, and the other end is provided with a capacitor connected to a predetermined potential.
An AC power supply device in which the resonance frequency of the inductor and the capacitor is higher than three times the on / off frequency of the switching element. The AC power supply device according to claim 1, further comprising two sets of the leg, the inductor, the two diodes, and the capacitor. A control unit that controls the output AC power by shifting the on / off phases of the switching element included in the high-side arm of one leg and the switching element included in the low-side arm of the other leg is further added. The AC power supply device according to claim 2. The AC power supply device according to any one of claims 1 to 3, further comprising a series resonance circuit that resonates with the on / off frequency of the switching element after the inductor.

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