JP5325991B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter, and more particularly, to a power converter that performs soft switching.

  Soft switching inverters that perform soft switching have been developed. Soft switching includes zero current switching in which the current flowing through the switch element is zeroed to turn the switch element on and off, and zero voltage switching in which the voltage applied to the switch element is zeroed to turn on and off the switch element. In the soft switching inverter, switching noise and switching loss can be reduced by such soft switching.

  Examples of soft switching inverters are Frederik W. Combrink et al, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL.21, NO.1, JANUARY 2006 (Non-patent Document 1) and Japanese Translation of PCT Publication No. 5-502365 (Patent Document 1). Is disclosed.

Japanese National Patent Publication No. 5-502365

Frederik W. Combrink et al, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL.21, NO.1, JANUARY 2006

  However, in the soft switching inverter described in Non-Patent Document 1, switching loss occurs in the main diodes Dn and Dp. For example, the main diode Dn will be described. In the sequence shown in FIG. 2, the snubber capacitor Crn is charged to the power supply voltage level during the period from time 0 to time t1. In the period from time t4 to time t5, the main switch Gn is turned off and the main switch Gp is turned on. Then, commutation from the main diode Dn to the main switch Gp starts. Then, the current flowing from the DC power source Vp through the main switch Gp increases and becomes equal to the load current. At the same time, the current flowing through the main diode Dn becomes zero and the main diode Dn is turned off, and this commutation is completed.

  Here, since the snubber capacitor Crn is charged to the power supply voltage level, the power supply voltage is applied to the main diode Dn at the moment when the main diode Dn is turned off. In general, the switching loss that occurs when a diode is turned off is substantially proportional to the voltage applied to the diode immediately after the diode is turned off. For this reason, in the soft switching inverter described in Non-Patent Document 1, a large switching loss occurs in the main diode Dn. Further, Patent Document 1 does not disclose a configuration for solving such a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a power conversion device capable of reducing switching loss in a main diode connected in parallel with the main switch. .

  A power converter according to an aspect of the present invention includes a first DC power source having a first electrode and a second electrode, a first electrode connected to the second electrode of the first DC power source, and a second electrode A power converter for converting DC power supplied from a second DC power supply having AC power to AC power to be supplied to a load, the first end coupled to the first electrode of the first DC power supply; A first main switch having a second end coupled to the load, and a first main switch connected in parallel with the first main switch such that a conduction direction is opposite to that of the first main switch. The first snubber capacitor, the first snubber capacitor connected in parallel with the first main switch and the first main diode, and the first snubber so as to have the same conduction direction as the first main switch. A first capacitor connected in series, and A first snubber diode connected between the capacitor and the second end of the first main switch; a connection node between the first DC power source and the second DC power source; and the first snubber capacitor. And a first auxiliary switch and a first auxiliary reactor connected in series with each other and connected to a connection node of the first snubber diode, and coupled to a second end of the first main switch. A second main switch having a first end and a second end coupled to the second electrode of the second DC power supply, the second main switch being provided to have the same conduction direction as the first main switch; The second main diode connected in parallel with the second main switch, and in parallel with the second main switch and the second main diode, so that the conduction direction is opposite to that of the second main switch. The second connected And the second snubber capacitor and the first end of the second main switch are connected in series so that the conduction direction of the capacitor is the same as that of the second main switch. A second snubber diode connected between the first DC power source and the second DC power source and the first auxiliary switch or the first auxiliary reactor, and the second snubber. A second auxiliary switch and a second auxiliary reactor connected between the capacitor and the connection node of the second snubber diode and connected in series with each other; and a voltage applied to the first snubber capacitor is predetermined. When the voltage exceeds a predetermined value or when the voltage applied to the second snubber capacitor exceeds a predetermined value, the first DC power supply and the second DC power supply A protection circuit for allowing a charging current to flow from the first to the first snubber capacitor or the second snubber capacitor to another current path, the first main switch, the second main switch, the second And a control circuit that controls on and off of the one auxiliary switch and the second auxiliary switch. The control circuit controls the second snubber by turning on the second auxiliary switch while the second main diode is on during a positive period in which current flows from the power converter to the load. The first snubber is controlled by turning on the first auxiliary switch while the first main diode is on during a negative period in which a capacitor is discharged and current flows from the load to the power converter. Discharge the capacitor.

  According to the present invention, the switching loss in the main diode connected in parallel with the main switch can be reduced.

It is a figure which shows the structure of the soft switching inverter which concerns on the 1st Embodiment of this invention. It is a figure which shows the flow of an electric current when the soft switching inverter which concerns on the 1st Embodiment of this invention performs power conversion in time series. It is a figure which shows the flow of an electric current when the soft switching inverter which concerns on the 1st Embodiment of this invention performs power conversion in time series. It is a figure which shows the switch control procedure when the soft switching inverter which concerns on the 1st Embodiment of this invention performs power conversion. It is a figure which shows the flow of an electric current when the soft switching inverter which concerns on the 1st Embodiment of this invention performs power conversion in time series. It is a figure which shows the flow of an electric current when the soft switching inverter which concerns on the 1st Embodiment of this invention performs power conversion in time series. It is a figure which shows the structure of the modification of the soft switching inverter which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the soft switching inverter which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the soft switching inverter which concerns on the 3rd Embodiment of this invention. It is a figure which shows the structure of the soft switching inverter which concerns on the 4th Embodiment of this invention. It is a figure which shows the switch control procedure when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion. It is a figure which shows the electric current flow at the time series when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion. It is a figure which shows the electric current flow at the time series when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion. It is a figure which shows the electric current flow at the time series when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion. It is a figure which shows the electric current flow at the time series when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion. It is a figure which shows the other example of a switch control procedure when the soft switching inverter which concerns on the 5th Embodiment of this invention performs power conversion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing a configuration of a soft switching inverter according to a first embodiment of the present invention.

  Referring to FIG. 1, a soft switching inverter (power conversion device) 101 includes power supply terminals TP, TC, TN, an AC output terminal TOUT, main switches Gp, Gn, main diodes Dp, Dn, and a snubber capacitor Crp. , Crn, snubber diodes Drp, Drn, auxiliary switches Srp, Srn, auxiliary reactors Lrp, Lrn, a control circuit 11, and a protection circuit 51. Protection circuit 51 includes a transformer Tr and a clamp diode Df. The transformer Tr includes primary windings Ls1, Ls2 and a secondary winding Lf. The soft switching inverter 101 may be configured to include DC power supplies Vp and Vn.

  The main switches Gp and Gn are, for example, IGBTs (Insulated Gate Bipolar Transistors). The auxiliary switches Srp and Srn are, for example, reverse blocking thyristors.

  DC power supplies Vp and Vn are connected in series. That is, the DC power supply Vp has a positive electrode connected to the power supply terminal TP and a negative electrode connected to the power supply terminal TC. DC power supply Vn has a negative electrode of DC power supply Vp, a positive electrode connected to power supply terminal TC, and a negative electrode connected to power supply terminal TN.

  Main switch Gp has a collector coupled to the positive electrode of DC power supply Vp and an emitter coupled to a load via AC output terminal TOUT. That is, the main switch Gp has a collector connected to the power supply terminal TP and an emitter connected to the first end of the primary winding Ls1 of the transformer Tr. The main diode Dp is connected in parallel with the main switch Gp so that the conduction direction is opposite to that of the main switch Gp. That is, the main diode Dp has a cathode connected to the collector of the main switch Gp and an anode connected to the emitter of the main switch Gp. The snubber capacitor Crp is connected in parallel with the main switch Gp and the main diode Dp. The snubber diode Drp is connected in parallel with the main switch Gp and the main diode Dp so as to have the same conduction direction as the main switch Gp, and is connected in series with the snubber capacitor Crp. That is, snubber diode Drp has an anode connected to the second end of snubber capacitor Crp and the second end of auxiliary reactor Lrp, and a cathode connected to the emitter of main switch Gp and the anode of main diode Dp. Auxiliary switch Srp and auxiliary reactor Lrp are connected between a connection node of DC power supply Vp and DC power supply Vn, that is, between a power supply terminal TC and a connection node of snubber capacitor Crp and snubber diode Drp, and are connected in series with each other. That is, auxiliary switch Srp has an anode connected to power supply terminal TC and a cathode connected to the first end of auxiliary reactor Lrp. Auxiliary reactor Lrp has a first end connected to the cathode of auxiliary switch Srp and a second end connected to a connection node of snubber capacitor Crp and snubber diode Drp.

  The main switch Gn has a collector coupled to the emitter of the main switch Gp and an emitter coupled to the negative electrode of the DC power supply Vn, and is provided so as to have the same conduction direction as the main switch Gp. That is, the main switch Gn has a collector connected to the second end of the primary winding Ls2 of the transformer Tr and an emitter connected to the power supply terminal TN. The main diode Dn is connected in parallel with the main switch Gn so that the conduction direction is opposite to that of the main switch Gn. That is, the main diode Dn has a cathode connected to the collector of the main switch Gn and an anode connected to the emitter of the main switch Gn. The snubber capacitor Crn is connected in parallel with the main switch Gn and the main diode Dn. The snubber diode Drn is connected in parallel with the main switch Gn and the main diode Dn so as to have the same conduction direction as the main switch Gn, and is connected in series with the snubber capacitor Crn. In other words, snubber diode Drn has a cathode connected to the first end of snubber capacitor Crn and the second end of auxiliary reactor Lrn, and an anode connected to the collector of main switch Gn and the cathode of main diode Dn. Auxiliary switch Srn and auxiliary reactor Lrn are connected between DC power supply Vp and a connection node between DC power supply Vn and auxiliary switch Srp, that is, between power supply terminal TC and a connection node of snubber capacitor Crn and snubber diode Drn, and connected in series with each other. Has been. That is, auxiliary switch Srn has a cathode connected to power supply terminal TC and an anode connected to the first end of auxiliary reactor Lrn. Auxiliary reactor Lrn has a first end connected to the anode of auxiliary switch Srn and a second end connected to a connection node of snubber capacitor Crn and snubber diode Drn.

  The protection circuit 51 is connected between the emitter of the main switch Gp and the collector of the main switch Gn. In the protection circuit 51, the primary windings Ls1 and Ls2 are connected between the emitter of the main switch Gp and the collector of the main switch Gn. That is, the primary winding Ls1 has a first end connected to the emitter of the main switch Gp and the cathode of the snubber diode Drp, and a second end connected to the AC output terminal TOUT and the first end of the primary winding Ls2. And have. The primary winding Ls2 has a first end connected to the AC output terminal TOUT and the second end of the primary winding Ls1, and a second end connected to the collector of the main switch Gn and the anode of the snubber diode Drn. Have. The primary windings Ls1 and Ls2 have the same winding direction.

  The secondary winding Lf is connected between the positive electrode of the DC power source Vp and the negative electrode of the DC power source Vn, and is magnetically coupled to the primary windings Ls1 and Ls2. That is, the secondary winding Lf has a first end connected to the anode of the clamp diode Df and a second end connected to the power supply terminal TN. The secondary winding Lf has a winding direction opposite to that of the primary windings Ls1 and Ls2. Further, the turns ratio of the primary winding and the secondary winding of the transformer Tr is 1: n, for example, n> 2.

  The clamp diode Df is connected between the positive electrode of the DC power supply Vp and the negative electrode of the DC power supply Vn, and is connected in series with the secondary winding Lf. That is, the clamp diode Df has a cathode connected to the power supply terminal TP and an anode connected to the first end of the secondary winding Lf.

  The soft switching inverter 101 switches the DC power supplied from the DC power supplies Vp and Vn by the main switches Gp and Gn which are main arms, thereby converting the DC power supplied from the DC power supply Vp and the DC power supply Vn into AC power. The voltage is converted and supplied to the load via the AC output terminal TOUT.

  The snubber capacitor Crp is provided to prevent voltage from being applied to the main switch Gp when the main switch Gp is turned off. The snubber capacitor Crn is provided to prevent a voltage from being applied to the main switch Gn when the main switch Gn is turned off.

  FIG. An anode reactor Lbp of the soft switching inverter shown in FIG. 2 is provided to prevent current from flowing through the main switch Gp when the main switch Gp is turned on. The anode reactor Lbn is provided to prevent current from flowing through the main switch Gn when the main switch Gn is turned on. On the other hand, in the soft switching inverter 101, the anode reactors Lbp and Lbn are not provided, but the primary windings Ls1 and Ls2 of the transformer Tr also serve as the anode reactors Lbp and Lbn.

  The control circuit 11 performs switching control on the main switches Gp and Gn and the auxiliary switches Srp and Srn, respectively.

  The protection circuit 51 has a current path PT between the positive electrode of the DC power supply Vp and the negative electrode of the DC power supply Vn. By using the transformer Tr, the protection circuit 51 suppresses the maximum voltage applied to the main switches Gp and Gn to the maximum value VM smaller than twice the output voltage of the DC power sources Vp and Vn.

  Next, the operation when the soft switching inverter according to the first embodiment of the present invention performs power conversion will be described with reference to the drawings. First, the operation in the positive period in which current flows from the soft switching inverter 101 to the load will be described, and then the operation in the negative period in which current flows from the load to the soft switching inverter 101 will be described.

[Period operation]
2 and 3 are diagrams showing a current flow in time series when the soft switching inverter according to the first embodiment of the present invention performs power conversion. FIG. 4 is a diagram showing a switch control procedure when the soft switching inverter according to the first embodiment of the present invention performs power conversion. Here, the output voltage of the DC power supply Vp is Vp, and the output voltage of the DC power supply Vn is Vn.

  2 and 3, “+, −” attached to the side of the snubber capacitors Crp and Crn indicates the state in which the charge is accumulated in the snubber capacitor and the polarity of the charge, and “0” indicates the snubber capacitor. It shows a state where the charge is zero.

  The horizontal axis in FIG. 4 indicates time, and the numbers of “positive period” along the horizontal axis indicate the steps shown in FIGS. 2 and 3.

  2 to 4, first, main switch Gp is on-controlled, main switch Gn is off-controlled, and auxiliary switches Srp and Srn are off-controlled, and from DC power supply Vp to load through main switch Gp. The description starts from a state where a current is flowing (step 1).

  In this state, the main switch Gp is turned off. Then, the current from the DC power supply Vp is commutated to the snubber capacitor Crp. As a result, the snubber capacitor Crp is charged, and the main diode Dn becomes conductive when the voltage at the snubber capacitor Crp becomes equal to the output voltages (Vp + Vn) of the DC power supplies Vp and Vn. When the main diode Dn becomes conductive, a current from the DC power supply Vn flows to the load through the main diode Dn. (Step 2).

  Here, when the main switch Gp is controlled to be off at the start of step 2, a current flows to the snubber capacitor Crp. When the main switch Gp is turned off, since the electric charge of the snubber capacitor Crp is zero, no voltage is applied to the main switch Gp. Thereby, zero volt switching is realized.

  Next, the current flowing from the snubber capacitor Crp to the snubber diode Drp decreases due to resonance between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crp is charged by the resonance current between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, the voltage difference between the output voltages (Vp + Vn) of the DC power sources Vp and Vn and the voltage Vc at the snubber capacitor Crp is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vp + Vn) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc in the snubber capacitor Crp increases and the secondary voltage of the transformer Tr reaches the output voltage (Vp + Vn), the clamp diode Df is turned on and the snubber diode Drp is turned off. The maximum value VM of the voltage Vc at this time is expressed by the following equation.

VM = (1 + 2 / n) × (Vp + Vn)
Then, a current flows as indicated by a broken line shown in Step 3 of FIG. 2, the current flowing to the snubber capacitor Crp becomes zero, and the snubber capacitor Crp is not charged. As a result, the voltage Vc at the snubber capacitor Crp is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 3).

  Next, the main switch Gn is turned on when the predetermined time Tb has elapsed since the main switch Gp was turned off. However, since the current from the main diode Dn to the load has a current polarity opposite to that of the main switch Gn, the main switch Gn does not conduct and the current continues to flow to the load through the main diode Dn (step 4). That is, when the main switch Gn is on-controlled, no current flows through the main switch Gn. Thereby, zero current switching is realized.

  Next, the auxiliary switch Srn is turned on when a predetermined time Td has elapsed since the main switch Gn was turned on. Thereby, discharge of the snubber capacitor Crn starts. When this discharge is completed and the voltage at the snubber capacitor Crn becomes zero, the snubber diode Drn becomes conductive (step 5).

  Next, when the snubber diode Drn becomes conductive, the voltage from the DC power source Vn is applied to the auxiliary reactor Lrn. Therefore, the current flowing through the auxiliary switch Srn is attenuated, and when it becomes zero, both the auxiliary switch Srn and the snubber diode Drn are turned off (step 6).

  Next, when the auxiliary switch Srn is turned on, the main switch Gn is turned off when a predetermined time Tc has elapsed. That is, the main switch Gn is turned off in a state where the main diode Dn continues to be conductive and the current from the DC power source Vn flows to the load through the main diode Dn (step 7). At this time, the main switch Gn is on-controlled, but is not conducting, so there is no change in state.

  Next, the main switch Gp is turned on when a predetermined time Tb elapses after the main switch Gn is turned off. Then, commutation from the main diode Dn to the main switch Gp starts. Then, the current flowing from the DC power source Vp through the main switch Gp increases and becomes equal to the load current. At the same time, the current flowing through the main diode Dn becomes zero and the main diode Dn is turned off, and this commutation is completed.

  Here, the snubber diode Drn becomes conductive at the moment when the main diode Dn is turned off. At this time, since the electric charge of the snubber capacitor Crn is zero, the current flowing from the DC power source Vp through the main switch Gp flows to the snubber capacitor Crn. That is, since no voltage is applied to the main diode Dn, no switching loss occurs in the main diode Dn. Thereby, zero volt switching is realized (step 8).

  Next, the current flowing from the snubber capacitor Crn to the snubber diode Drn decreases due to resonance between the snubber capacitor Crn and the excitation inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crn is charged by a resonance current between the snubber capacitor Crn and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, a difference voltage between the output voltage (Vp + Vn) of the DC power sources Vp and Vn and the voltage Vc at the snubber capacitor Crn is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vp + Vn) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc in the snubber capacitor Crn rises and the secondary voltage of the transformer Tr reaches the output voltage (Vp + Vn), the clamp diode Df is turned on and the snubber diode Drn is turned off. The maximum value VM of the voltage Vc at this time is expressed by the following equation.

VM = (1 + 2 / n) × (Vp + Vn)
Then, a current flows as indicated by a broken line shown in Step 9 of FIG. 3, the current flowing to the snubber capacitor Crn becomes zero, and the snubber capacitor Crn is not charged. As a result, the voltage Vc at the snubber capacitor Crn is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 9).

  Next, the current from the DC power source Vp flows to the load through the main switch Gp (step 10).

  Next, the auxiliary switch Srp is turned on when a predetermined time Td has elapsed since the main switch Gp was turned on. As a result, the snubber capacitor Crp begins to discharge. When this discharge is completed and the voltage at the snubber capacitor Crp becomes zero, the snubber diode Drp conducts (step 11).

  Next, when the snubber diode Drp is turned on, a voltage from the DC power source Vp is applied to the auxiliary reactor Lrp. For this reason, the current flowing through the auxiliary switch Srp attenuates, and when it becomes zero, both the auxiliary switch Srp and the snubber diode Drp are turned off and the state returns to the state of Step 1 (Step 12).

  In the soft switching inverter according to the first embodiment of the present invention, when the snubber capacitor Crp or Crn is overcharged to a voltage higher than the power supply voltage Vs by resonance, the voltage Vc at the snubber capacitor becomes the voltage value VM. When it reaches, the energy to flow current through the primary windings Ls1 and Ls2 of the transformer Tr moves to the secondary winding Lf of the transformer Tr, and the charging current does not flow through the snubber capacitor. For this reason, the charging of the snubber capacitor is stopped, and the maximum voltage of the snubber capacitor is clamped to VM. Here, by setting the turn ratio n of the transformer Tr to n> 2, VM becomes equal to or less than twice Vs. Further, if n is increased, VM≈ (Vp + Vn). Therefore, the voltage Vc at the snubber capacitor can be suppressed to a value as close as possible to the power supply voltage Vs.

[Negative period operation]
5 and 6 are diagrams showing the current flow in time series when the soft switching inverter according to the first embodiment of the present invention performs power conversion. Here, the output voltage of the DC power supply Vp is Vp, and the output voltage of the DC power supply Vn is Vn.

  In FIG. 5 and FIG. 6, “+, −” attached to the side of the snubber capacitors Crp and Crn indicates the state in which the charge is accumulated in the snubber capacitor and the polarity of the charge, and “0” indicates the snubber capacitor. It shows a state where the charge is zero.

  The horizontal axis in FIG. 4 indicates time, and the numbers of “negative periods” arranged along the horizontal axis indicate the steps shown in FIGS. 5 and 6.

  4 to 6, first, main switch Gn is on-controlled, main switch Gp is off-controlled, and auxiliary switches Srn and Srp are off-controlled, and from DC power supply Vn to load through main switch Gn. The description starts from the state in which current is flowing (step 21).

  In this state, the main switch Gn is turned off. Then, the current from the load is commutated to the snubber capacitor Crn. As a result, the snubber capacitor Crn is charged, and the main diode Dp conducts when the voltage at the snubber capacitor Crn becomes equal to the output voltages (Vn + Vp) of the DC power supplies Vn and Vp. When the main diode Dp becomes conductive, a current from the load flows to the DC power source Vp through the main diode Dp (step 22).

  Here, when the main switch Gn is controlled to be off at the start of step 22, a current flows to the snubber capacitor Crn. When the main switch Gn is turned off, no charge is applied to the main switch Gn because the electric charge of the snubber capacitor Crn is zero. Thereby, zero volt switching is realized.

  Next, the current flowing from the snubber diode Drn to the snubber capacitor Crn decreases due to resonance between the snubber capacitor Crn and the exciting inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crn is charged by a resonance current between the snubber capacitor Crn and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, the difference voltage between the output voltage (Vn + Vp) of the DC power sources Vn and Vp and the voltage Vc at the snubber capacitor Crn is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vn + Vp) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc at the snubber capacitor Crn rises and the secondary voltage of the transformer Tr reaches the output voltage (Vn + Vp), the clamp diode Df is turned on and the snubber diode Drn is turned off. The maximum value VM of the voltage Vc at this time is expressed by the following equation.

VM = (1 + 2 / n) × (Vn + Vp)
Then, a current flows as shown by a broken line in step 23 of FIG. 5, the current flowing to the snubber capacitor Crn becomes zero, and the snubber capacitor Crn is not charged. As a result, the voltage Vc at the snubber capacitor Crn is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 23).

  Next, the main switch Gp is turned on when a predetermined time Tb elapses after the main switch Gn is turned off. However, since the current from the load to the main diode Dp has a current polarity opposite to that of the main switch Gp, the main switch Gp does not conduct, and the current continues to flow to the DC power source Vp through the main diode Dp (step 24). That is, when the main switch Gp is on-controlled, no current flows through the main switch Gp. Thereby, zero current switching is realized.

  Next, the auxiliary switch Srp is turned on when a predetermined time Td has elapsed since the main switch Gp was turned on. As a result, the snubber capacitor Crp begins to discharge. When this discharge is completed and the voltage at the snubber capacitor Crp becomes zero, the snubber diode Drp conducts (step 25).

  Next, when the snubber diode Drp is turned on, a voltage from the DC power source Vp is applied to the auxiliary reactor Lrp. Therefore, the current flowing through the auxiliary switch Srp is attenuated, and when it becomes zero, both the auxiliary switch Srp and the snubber diode Drp are turned off (step 26).

  Next, when the auxiliary switch Srp is turned on, the main switch Gp is turned off when the predetermined time Tc has elapsed. In other words, the main switch Gp is turned off in a state where the main diode Dp continues to be conductive and the current from the load flows to the DC power source Vp through the main diode Dp (step 27). At this time, the main switch Gp is on-controlled, but is not conducting, so there is no change in state.

  Next, the main switch Gn is turned on when the predetermined time Tb has elapsed since the main switch Gp was turned off. Then, commutation from the main diode Dp to the main switch Gn starts. Then, the current flowing from the DC power source Vn through the main switch Gn increases and becomes equal to the load current. At the same time, the current flowing through the main diode Dp becomes zero, and the main diode Dp is turned off, and this commutation is completed.

  Here, the snubber diode Drp conducts at the moment when the main diode Dp is turned off. At this time, since the electric charge of the snubber capacitor Crp is zero, the current from the DC power source Vp flows to the snubber capacitor Crp. That is, since no voltage is applied to the main diode Dp, no switching loss occurs in the main diode Dp. Thereby, zero volt switching is realized (step 28).

  Next, the current flowing from the snubber capacitor Crp to the snubber diode Drp decreases due to resonance between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crp is charged by the resonance current between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, a difference voltage between the output voltage (Vn + Vp) of the DC power sources Vn and Vp and the voltage Vc at the snubber capacitor Crp is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vn + Vp) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc at the snubber capacitor Crp increases and the secondary voltage of the transformer Tr reaches the output voltage (Vn + Vp), the clamp diode Df is turned on and the snubber diode Drp is turned off. The maximum value VM of the voltage Vc at this time is expressed by the following equation.

VM = (1 + 2 / n) × (Vn + Vp)
Then, a current flows as indicated by a broken line shown in step 29 of FIG. 6, the current flowing to the snubber capacitor Crp becomes zero, and the snubber capacitor Crp is not charged. As a result, the voltage Vc at the snubber capacitor Crp is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 29).

  Next, a current from the load flows to the DC power source Vn through the main switch Gn (step 30).

  Next, the auxiliary switch Srn is turned on when a predetermined time Td has elapsed since the main switch Gn was turned on. Thereby, discharge of the snubber capacitor Crn starts. When this discharge is completed and the voltage at the snubber capacitor Crn becomes zero, the snubber diode Drn becomes conductive (step 31).

  Next, when the snubber diode Drn becomes conductive, the voltage from the DC power source Vn is applied to the auxiliary reactor Lrn. For this reason, the current flowing through the auxiliary switch Srn is attenuated, and when it becomes zero, both the auxiliary switch Srn and the snubber diode Drn are turned off, and the state returns to the state of step 21 (step 32).

  In the soft switching inverter according to the first embodiment of the present invention, when the snubber capacitor Crn or Crp is about to be overcharged to a voltage higher than the power supply voltage Vs by resonance, the voltage Vc at the snubber capacitor becomes the voltage value VM. When it reaches, the energy to flow current through the primary windings Ls1 and Ls2 of the transformer Tr moves to the secondary winding Lf of the transformer Tr, and the charging current does not flow through the snubber capacitor. For this reason, the charging of the snubber capacitor is stopped, and the maximum voltage of the snubber capacitor is clamped to VM. Here, by setting the turn ratio n of the transformer Tr to n> 2, VM becomes equal to or less than twice Vs. Further, if n is increased, VM≈ (Vn + Vp), so that the voltage Vc at the snubber capacitor can be suppressed to a value as close as possible to the power supply voltage Vs.

  The soft switching inverter 101 repeats the operations of Steps 1 to 12 shown in FIGS. 2 and 3 as the positive period operation, and the operations of Steps 21 to 32 shown in FIGS. 5 and 6 as the negative period operation. Repeat. Soft switching inverter 101 supplies alternating current power to the load by alternately performing such positive period operation and negative period operation.

  Incidentally, the soft switching inverter described in Non-Patent Document 1 has a problem that a switching loss occurs in a main diode connected in parallel with the main switch.

  However, in the soft switching inverter according to the first embodiment of the present invention, the control circuit 11 controls the snubber capacitor Crn by turning on the auxiliary switch Srn while the main diode Dn is on during the positive period. In the negative period, the snubber capacitor Crp is discharged by turning on the auxiliary switch Srp while the main diode Dp is on.

  With such a configuration, the voltage applied when the main diode connected in parallel with the main switch is turned off can be made zero, so that the switching loss in the main diode can be reduced.

  In the soft switching inverter according to the first embodiment of the present invention, the control circuit 11 controls the main switch Gn to be on when the predetermined time has elapsed since the main switch Gp is turned off, and the main switch Gn is turned on. When the predetermined time elapses, the auxiliary switch Srn is turned on. After the auxiliary switch Srn is turned on, the main switch Gn is turned off when the predetermined time elapses. After the main switch Gn is turned off, the main switch Gn is turned off. The switch Gp is turned on, the auxiliary switch Srp is turned on when a predetermined time elapses after the main switch Gp is turned on, and the main switch Gp is turned off when a predetermined time elapses after the auxiliary switch Srp is turned on.

  By performing such switch control, the same switch control can be performed in both the positive period and the negative period. That is, since the switch control procedure can be made the same regardless of the polarity of the load current, it is not necessary to change the switch control procedure by determining the polarity of the load current, and the control can be simplified.

  The soft switching inverter described in Non-Patent Document 1 is premised on a case where the load current is large to some extent. For example, FIG. In the sequence shown in FIG. 2, when the load current is very small, the charging of the snubber capacitor Crp in the period from the time 0 to the time t1 becomes extremely slow, and thus the time until the operation shifts to the operation in the period from the time t1 to the time t3. Becomes longer. That is, the commutation time to the main diode Dn becomes very long.

  In order to avoid such a phenomenon, it can be considered that the main switch Gn is turned on when a predetermined time elapses from time 0, that is, the time when the main switch Gp is turned off. When the main switch Gn is turned on during the charging of the snubber capacitor Crp from the time 0 to the time t1, the snubber capacitor Crp is charged by resonance between the snubber capacitor Crp and the anode reactors Lbp and Lbn. When the voltage of the snubber capacitor Crp reaches the power supply voltage, the current flowing through the main switch Gn starts to decrease. When the current flowing through the main switch Gn becomes zero, the main switch Gn is turned off and the main diode Dn is turned on, thereby shifting to the operation from the time t2 to the time t3.

  However, when the snubber capacitor Crp is charged using the resonance as described above, the snubber capacitor Crp is overcharged to a voltage higher than the power supply voltage. When the load current is extremely close to zero, the snubber capacitor Crp is charged up to twice the power supply voltage by the resonance. Since the charging voltage of the snubber capacitor Crp is applied to the main switch Gn and the main diode Dn, these elements are required to have a breakdown voltage (Break Down Voltage) that is twice or more the power supply voltage. For this reason, there existed a problem that a soft switching inverter became large and cost also took.

  However, in the soft switching inverter according to the first embodiment of the present invention, the protection circuit 51 supplies the snubber capacitor Crp with a charging current that tends to flow from the DC power source Vp and the DC power source Vn to the snubber capacitor Crp or the snubber capacitor Crn. When the voltage applied to the capacitor exceeds a predetermined value, or when the voltage applied to the snubber capacitor Crn exceeds the predetermined value, the positive electrode of the DC power source Vp and the negative electrode of the DC power source Vn via the current path PT Shed in between.

  More specifically, the protection circuit 51 includes the voltage difference between the output voltage of the DC power supply Vp and the DC power supply Vn and the voltage applied to the snubber capacitor Crp, or the output voltage of the DC power supply Vp and the DC power supply Vn and the snubber capacitor. In response to the voltage difference from the voltage applied to Crn, a voltage obtained by boosting the received voltage is generated. Based on the generated voltage, the positive electrode of the DC power supply Vp and the DC power supply Vn are connected via the current path PT. Switches whether or not a charging current flows between the negative electrodes.

  That is, in the soft switching inverter according to the first embodiment of the present invention, the maximum charging voltage of the snubber capacitor is set to the power supply voltage by inserting a transformer and setting the turns ratio to 1: n (n> 2). To within 2 times. In other words, when the snubber capacitor is overcharged to a voltage higher than the power supply voltage due to resonance, the protection circuit 51 turns to the primary winding of the transformer when the voltage applied to the snubber capacitor reaches a predetermined voltage. The energy to pass current is transferred to the secondary winding of the transformer. As a result, the charging current stops flowing through the snubber capacitor and charging is stopped, and the voltage applied to the snubber capacitor is clamped. By setting the turn ratio n of the transformer Tr to n> 2, the clamp voltage becomes less than twice the power supply voltage, and if n is increased, the voltage applied to the snubber capacitor is suppressed to a value close to the power supply voltage. can do.

  Therefore, since the voltage applied to the main switch and the main diode is also limited, the breakdown voltage of these elements can be lowered, so that the apparatus can be downsized and the cost can be reduced. Conversely, by using elements having the same breakdown voltage without changing the breakdown voltage of these elements, an output voltage higher than that of the prior art can be obtained. That is, since the voltage utilization factor of the main switch and the main diode is improved by suppressing the charging voltage of the snubber capacitor, a higher output voltage can be obtained using elements having the same breakdown voltage.

  The protection circuit is not limited to the configuration shown in FIG. 1, and the voltage applied to the snubber capacitor Crp exceeds a predetermined value or the voltage applied to the snubber capacitor Crn exceeds a predetermined value. In this case, any configuration may be employed as long as the charging current that is about to flow from the DC power source Vp and the DC power source Vn to the snubber capacitor Crp or the snubber capacitor Crn is released to another current path.

  FIG. 7 is a diagram showing a configuration of a modification of the soft switching inverter according to the first embodiment of the present invention.

  With reference to FIG. 7, the soft switching inverter includes a protection circuit 52 instead of the protection circuit 51 as compared with the soft switching inverter 101. Protection circuit 52 includes a transformer Tr, a clamp diode Df, and a DC power supply Vb. DC power supply Vb has a positive electrode connected to the cathode of clamp diode Df and a negative electrode connected to the anode of clamp diode Df.

  In the soft switching inverter according to the first embodiment of the present invention, the cathode of the clamp diode Df is connected to the positive electrode of the DC power supply Vp. However, the present invention is not limited to this. That is, as shown in FIG. 7, the protection circuit 52 may include a DC power supply Vb different from the DC power supplies Vp and Vn.

  When the voltage applied to the snubber capacitor Crp exceeds a predetermined value or when the voltage applied to the snubber capacitor Crn exceeds a predetermined value, the protection circuit 52 detects the snubber capacitor Crp from the DC power source Vp and the DC power source Vn. Alternatively, a charging current that is about to flow to the snubber capacitor Crn is passed to the DC power source Vb via the clamp diode Df.

  With such a configuration, the voltage applied to the snubber capacitor can be applied to the DC power sources Vp and Vn without boosting the difference voltage between the output voltage of the DC power sources Vp and Vn and the voltage Vc of the snubber capacitor by the transformer Tr. For example, the clamp diode Df can be turned on before the output voltage is doubled, for example, so that the voltage applied to the snubber capacitor can be limited to less than twice the output voltage of the DC power supplies Vp and Vn. .

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to a soft switching inverter provided with an alternative circuit for a transformer as compared with the soft switching inverter according to the first embodiment. The contents other than those described below are the same as those of the soft switching inverter according to the first embodiment.

  FIG. 8 is a diagram showing a configuration of the soft switching inverter according to the second embodiment of the present invention.

  Referring to FIG. 8, soft switching inverter 102 includes a protection circuit 53 instead of protection circuit 51 as compared with the soft switching inverter according to the first embodiment of the present invention. Protection circuit 53 includes an anode reactor Lb, a clamp diode Df, and a DC power supply Vb. Anode reactor Lb has a first end connected to the emitter of main switch Gp and a second end connected to the collector of main switch Gn. The DC power supply Vb and the clamp diode Df are connected in series between both ends of the anode reactor Lb. That is, DC power supply Vb has a positive electrode connected to the cathode of clamp diode Df and a negative electrode connected to the first end of anode reactor Lb. The clamp diode Df has an anode connected to the second end of the anode reactor Lb.

  When the voltage applied to the snubber capacitor Crp exceeds a predetermined value or when the voltage applied to the snubber capacitor Crn exceeds a predetermined value, the protection circuit 53 generates a snubber capacitor Crp from the DC power source Vp and the DC power source Vn. Alternatively, the charging current that is about to flow to the snubber capacitor Crn is released to the DC power source Vb via the clamp diode Df.

  Thus, it is possible not to use a transformer in the protection circuit. On the other hand, in the configuration using a transformer in the protection circuit as in the soft switching inverter according to the first embodiment of the present invention, it is not necessary to separately provide a DC power supply, and therefore the configuration can be simplified.

  Since other configurations and operations are the same as those of the soft switching inverter according to the first embodiment, detailed description thereof will not be repeated here.

<Third Embodiment>
The present embodiment relates to a soft switching inverter in which an anode reactor is added as compared with the soft switching inverter according to the first embodiment. The contents other than those described below are the same as those of the soft switching inverter according to the first embodiment.

  FIG. 9 is a diagram showing a configuration of the soft switching inverter according to the third embodiment of the present invention.

  Referring to FIG. 9, soft switching inverter 103 further includes anode reactors Lbp and Lbn as compared with the soft switching inverter according to the first embodiment of the present invention.

  Anode reactor Lbp has a first end connected to the cathode of snubber diode Drp, the emitter of main switch Gp, and the anode of main diode Dp, and a second end connected to the first end of primary winding Ls1. . Anode reactor Lbn has a first end connected to the second end of primary winding Ls2, and a second end connected to the anode of snubber diode Drn, the collector of main switch Gn, and the cathode of main diode Dn. .

  Since other configurations and operations are the same as those of the soft switching inverter according to the first embodiment, detailed description thereof will not be repeated here.

<Fourth embodiment>
The present embodiment relates to a soft switching inverter in which an anode reactor is added as compared with the soft switching inverter according to the first embodiment. The contents other than those described below are the same as those of the soft switching inverter according to the first embodiment.

  FIG. 10 is a diagram showing a configuration of the soft switching inverter according to the fourth embodiment of the present invention.

  Referring to FIG. 10, soft switching inverter 104 further includes anode reactors Lbp and Lbn as compared with the soft switching inverter according to the first embodiment of the present invention.

  The anode reactor Lbp has a first end connected to the power supply terminal TP and the cathode of the clamp diode Df, a first end of the snubber capacitor Crp, a collector of the main switch Gp, and a second end connected to the cathode of the main diode Dp. Have The anode reactor Lbn is connected to the first end connected to the power supply terminal TN and the second end of the secondary winding Lf, the second end of the snubber capacitor Crn, the emitter of the main switch Gn, and the anode of the main diode Dn. And a second end.

  Since other configurations and operations are the same as those of the soft switching inverter according to the first embodiment, detailed description thereof will not be repeated here.

<Fifth embodiment>
The present embodiment is different from the first embodiment in the timing of the on control of the auxiliary switches Srp and Srn. The contents other than those described below are the same as those of the soft switching inverter according to the first embodiment. Therefore, the configuration of the soft switching inverter according to the present embodiment is the same as the configuration shown in FIG.

  FIG. 11 is a diagram illustrating a switch control procedure when the soft switching inverter according to the fifth embodiment of the present invention performs power conversion.

  With reference to FIG. 11 and FIG. 4, in the fifth embodiment, the control circuit 11 simultaneously turns on the main switch Gp and the auxiliary switch Srp. Similarly, the control circuit 11 simultaneously controls the main switch Gn and the auxiliary switch Srn on. In this respect, the switching control according to the fifth embodiment is different from the switching control according to the first embodiment.

  The on-time of the auxiliary switch Srp and the on-time of the auxiliary switch Srn are Te. The time Tc from when the auxiliary switch Srp is turned on until the main switch Gp is turned off is equal to the on time of the main switch Gp. Similarly, the time Tc from when the auxiliary switch Srn is turned on until the main switch Gn is turned off is equal to the on time of the main switch Gn.

  Furthermore, the operation of the soft switching inverter according to the fifth embodiment differs from the operation of the soft switching inverter according to the first embodiment in the following points. Regarding the operation in the positive period, the operations in steps 4, 11, and 12 are omitted, and the operations in steps 5, 8, and 9 are replaced with the operations in steps 5A, 8A, and 9A, respectively. Similarly, regarding the operation in the negative period, the operations in steps 24, 31, and 32 are omitted, and the operations in steps 25, 28, and 29 are replaced with the operations in steps 25A, 28A, and 29A, respectively.

  Hereinafter, regarding the operation of the soft switching inverter according to the fifth embodiment, the operations of Steps 5A, 8A, 9A, 25A, 28A, and 29A will be described in detail. Since the operation of the soft switching inverter in the other steps shown in FIG. 11 is the same as the operation of the corresponding steps shown in FIGS. 2, 3, 5, 6, detailed description will not be repeated hereinafter.

[Period operation]
12 and 13 are diagrams showing the current flow in time series when the soft switching inverter according to the fifth embodiment of the present invention performs power conversion.

  Referring to FIGS. 11, 12 and 13, the operations of steps 1 and 2 are first executed. Thereby, commutation from the main switch Gp to the main diode Dn, that is, commutation through the current path PT is completed (step 3).

  Next, when the predetermined time Tb has elapsed since the main switch Gp was turned off, the main switch Gn and the auxiliary switch Srn are simultaneously turned on. At this time, the main switch Gn does not conduct and current continues to flow to the load through the main diode Dn, so that zero current switching is realized. Also, the snubber capacitor Crn starts to discharge. When this discharge is completed and the voltage at the snubber capacitor Crn becomes zero, the snubber diode Drn becomes conductive (step 5A).

  Following the operation of step 5A, the operations of steps 6 and 7 are executed. After the operation of step 7, the operation of step 8A is executed. Specifically, the main switch Gp and the auxiliary switch Srp are simultaneously turned on when a predetermined time Tb has elapsed since the main switch Gn was turned off. Thereby, commutation from the main diode Dn to the main switch Gp starts. Then, the current flowing from the DC power source Vp through the main switch Gp increases and becomes equal to the load current. At the same time, the current flowing through the main diode Dn becomes zero and the main diode Dn is turned off, and this commutation is completed (step 8A). .

  At the moment when the main diode Dn is turned off, the snubber diode Drn becomes conductive. At this time, since the electric charge of the snubber capacitor Crn is zero, the current flowing from the DC power source Vp through the main switch Gp flows to the snubber capacitor Crn. That is, since no voltage is applied to the main diode Dn, no switching loss occurs in the main diode Dn. Thereby, zero volt switching is realized. Further, when the auxiliary switch Srp is turned on at the start of step 8A, the auxiliary switch Srp starts to conduct and simultaneously the discharge of the snubber capacitor Crp starts. When this discharge is completed and the voltage at the snubber capacitor Crp becomes zero, the snubber diode Drp conducts. When the snubber diode Drp is turned on, a voltage from the DC power source Vp is applied to the auxiliary reactor Lrp (step 8A).

  The current flowing from the snubber capacitor Crn to the snubber diode Drn is decreased by the resonance between the snubber capacitor Crn and the exciting inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crn is charged by a resonance current between the snubber capacitor Crn and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, a difference voltage between the output voltage (Vp + Vn) of the DC power sources Vp and Vn and the voltage Vc at the snubber capacitor Crn is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vp + Vn) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc at the snubber capacitor Crn increases and the secondary voltage of the transformer Tr reaches the output voltage (Vp + Vn), the clamp diode Df is turned on and the snubber diode Drn is turned off (step 9A).

The maximum value VM of the voltage Vc at this time is expressed by the following equation.
VM = (1 + 2 / n) × (Vp + Vn)
Then, a current flows as shown by a broken line in Step 9A of FIG. 13, the current flowing to the snubber capacitor Crn becomes zero, and the snubber capacitor Crn is not charged. As a result, the voltage Vc at the snubber capacitor Crn is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 9A).

  A current from the DC power source Vp flows to the load through the main switch Gp (step 10). Furthermore, the current flowing through the auxiliary switch Srp is attenuated to zero. When the current becomes 0, both the auxiliary switch Srp and the snubber diode Drp are turned off. Therefore, the operation of the soft switching inverter returns to step 1.

[Negative period operation]
14 and 15 are diagrams showing the current flow in time series when the soft switching inverter according to the fifth embodiment of the present invention performs power conversion.

  Referring to FIGS. 11, 14 and 15, first, operations of steps 21, 22 and 23 are sequentially executed. At the start of step 22, when the main switch Gn is turned off, a current flows to the snubber capacitor Crn. When the main switch Gn is turned off, since the electric charge of the snubber capacitor Crn is zero, no voltage is applied to the main switch Gn. Thereby, zero volt switching is realized.

  Next, the main switch Gp and the auxiliary switch Srp are simultaneously turned on when the predetermined time Tb has elapsed since the main switch Gn was turned off. At this time, the main switch Gp does not conduct, and current continues to flow to the DC power source Vp through the main diode Dp, so that zero current switching is realized. In addition, the snubber capacitor Crp starts to discharge. When this discharge is completed and the voltage at the snubber capacitor Crp becomes zero, the snubber diode Drp conducts (step 25A).

  Following the operation of step 25A, the operations of steps 26 and 27 are executed. After the operation of step 27, the operation of step 28A is executed. Specifically, the main switch Gn and the auxiliary switch Srn are simultaneously turned on when a predetermined time Tb has elapsed since the main switch Gp was turned off. This starts commutation from the main diode Dp to the main switch Gn. Then, the current flowing from the DC power source Vn through the main switch Gn increases to be equal to the load current, and at the same time, the current flowing through the main diode Dp becomes zero and the main diode Dp is turned off, and this commutation is completed (step 28A). .

  At the moment when the main diode Dp is turned off, the snubber diode Drp becomes conductive. At this time, since the electric charge of the snubber capacitor Crp is zero, the current from the DC power source Vp flows to the snubber capacitor Crp. That is, since no voltage is applied to the main diode Dp, no switching loss occurs in the main diode Dp. Thereby, zero volt switching is realized. Further, when the auxiliary switch Srn is turned on at the start of step 28A, the auxiliary switch Srn starts to conduct and simultaneously the discharge of the snubber capacitor Crn starts. When this discharge is completed and the voltage at the snubber capacitor Crn becomes zero, the snubber diode Drn becomes conductive. When the snubber diode Drn becomes conductive, the voltage from the DC power source Vn is applied to the auxiliary reactor Lrn (step 28A).

  The current flowing from the snubber capacitor Crp to the snubber diode Drp decreases due to resonance between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2.

  Further, the snubber capacitor Crp is charged by the resonance current between the snubber capacitor Crp and the exciting inductance in the primary windings Ls1 and Ls2 of the transformer Tr. At this time, a difference voltage between the output voltage (Vn + Vp) of the DC power sources Vn and Vp and the voltage Vc at the snubber capacitor Crp is applied to the series circuit of the primary windings Ls1 and Ls2 of the transformer Tr. The primary windings Ls1 and Ls2 each share a voltage that is ½ of the difference voltage. That is, the value VL of the voltage applied to the primary windings Ls1 and Ls2 is expressed by the following equation.

VL = {(Vn + Vp) -Vc} / 2
Since the turns ratio of the transformer Tr is 1: n, a voltage of n × VL is induced on the secondary side. When the voltage Vc at the snubber capacitor Crp increases and the secondary voltage of the transformer Tr reaches the output voltage (Vn + Vp), the clamp diode Df is turned on and the snubber diode Drp is turned off. The maximum value VM of the voltage Vc at this time is expressed by the following equation.

VM = (1 + 2 / n) × (Vn + Vp)
Then, a current flows as indicated by a broken line shown in step 29 of FIG. 6, the current flowing to the snubber capacitor Crp becomes zero, and the snubber capacitor Crp is not charged. As a result, the voltage Vc at the snubber capacitor Crp is clamped to VM. Thereafter, when the current flowing through the clamp diode Df decreases and eventually becomes zero, the clamp diode Df is turned off, and commutation through the current path PT is completed (step 29A).

  A current from the load flows to the DC power source Vn through the main switch Gn (step 10). Furthermore, the current flowing through the auxiliary switch Srn is attenuated to zero. When the current becomes 0, both the auxiliary switch Srp and the snubber diode Drn are turned off. Therefore, the operation of the soft switching inverter returns to step 21.

  Thus, according to the fifth embodiment of the present invention, the control circuit 11 simultaneously controls the main switch Gn and the auxiliary switch Srn to be turned on when a predetermined time has elapsed since the main switch Gp was turned off. Similarly, the control circuit 11 simultaneously turns on the main switch Gp and the auxiliary switch Srp when a predetermined time elapses after the main switch Gn is turned off. As a result, it is possible to perform control more simplified than the switching control according to the first embodiment.

  Further, as shown in FIG. 16, the main switch Gp and the auxiliary switch Srp may be simultaneously controlled to be on and off, and the main switch Gn and the auxiliary switch Srn may be simultaneously controlled to be on and off. The operation of the soft switching inverter in this case is the same as the operation shown in FIGS. When the control circuit 11 performs the switching control shown in FIG. 16, the control of the control circuit 11 can be further simplified.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  11 control circuit, 51, 52, 53 protection circuit, 101 soft switching inverter (power conversion device), Vp, Vn DC power supply, TP, TC, TN power supply terminal, TOUT AC output terminal, Gp, Gn main switch, Dp, Dn Main diode, Crp, Crn snubber capacitor, Drp, Drn snubber diode, Srp, Srn auxiliary switch, Lrp, Lrn auxiliary reactor, Tr transformer, Df clamp diode, Ls1, Ls2 primary winding, Lf secondary winding, Vb DC power supply, Lb, Lbp, Lbn Anode reactor.

Claims (4)

A first DC power source (Vp) having a first electrode and a second electrode, a first electrode connected to a second electrode of the first DC power source (Vp), and a second DC having a second electrode A power conversion device that converts DC power supplied from a power source (Vn) into AC power and supplies it to a load,
A first main switch (Gp) having a first end coupled to the first electrode of the first DC power supply (Vp) and a second end coupled to the load;
A first main diode (Dp) connected in parallel with the first main switch (Gp) so that a conduction direction is opposite to that of the first main switch (Gp);
A first snubber capacitor (Crp) connected in parallel with the first main switch (Gp) and the first main diode (Dp);
The first snubber capacitor (Crp) and the first main switch are connected in series with the first snubber capacitor (Crp) so that the conduction direction is the same as that of the first main switch (Gp). A first snubber diode (Drp) connected between the second end of (Gp);
Connected between a connection node of the first DC power supply (Vp) and the second DC power supply (Vn) and a connection node of the first snubber capacitor (Crp) and the first snubber diode (Drp). And a first auxiliary switch (Srp) and a first auxiliary reactor (Lrp) connected in series with each other;
A first end coupled to a second end of the first main switch (Gp) and a second end coupled to a second electrode of the second DC power source (Vn); A second main switch (Gn) provided to have the same conduction direction as the main switch (Gp) of
A second main diode (Dn) connected in parallel with the second main switch (Gn) so that a conduction direction is opposite to that of the second main switch (Gn);
A second snubber capacitor (Crn) connected in parallel with the second main switch (Gn) and the second main diode (Dn);
The second snubber capacitor (Crn) and the second main switch are connected in series with the second snubber capacitor (Crn) so as to have the same conduction direction as the second main switch (Gn). A second snubber diode (Drn) connected between the first end of (Gn);
A connection node between the first DC power source (Vp) and the second DC power source (Vn) and the first auxiliary switch (Srp) or the first auxiliary reactor (Lrp) and the second snubber capacitor A second auxiliary switch (Srn) and a second auxiliary reactor (Lrn) connected in series between each other (Crn) and a connection node of the second snubber diode (Drn);
When the voltage applied to the first snubber capacitor (Crp) exceeds a predetermined value or when the voltage applied to the second snubber capacitor (Crn) exceeds a predetermined value, the first snubber capacitor (Crp) In order to flow a charging current from the DC power source (Vp) and the second DC power source (Vn) to the first snubber capacitor (Crp) or the second snubber capacitor (Crn) to another current path. Protection circuit (51, 52, 53),
A control circuit (11) for controlling on and off of the first main switch (Gp), the second main switch (Gn), the first auxiliary switch (Srp), and the second auxiliary switch (Srn). )
The control circuit (11) turns on the second auxiliary switch (Srn) while the second main diode (Dn) is on during a positive period in which current flows from the power converter to the load. The second snubber capacitor (Crn) is discharged by the control, and the first main diode (Dp) is turned on during the negative period in which current flows from the load to the power converter. A power converter that discharges the first snubber capacitor (Crp) by turning on one auxiliary switch (Srp).   The control circuit (11) controls the second main switch (Gn) to turn on when the predetermined time elapses after the first main switch (Gp) is turned off to control the second main switch (Gn). The second auxiliary switch (Srn) is turned on when a predetermined time has elapsed since the ON control of the second auxiliary switch (Srn) and the second main switch (Srn) is turned on when the second auxiliary switch (Srn) is turned on. Gn) is turned off, the first main switch (Gp) is turned on when a predetermined time elapses after the second main switch (Gn) is turned off, and the first main switch (Gp) is turned on. The first auxiliary switch (Srp) is turned on when a predetermined time elapses after being turned on, and the first main switch (Gp) is turned on when the predetermined time elapses after the first auxiliary switch (Srp) is turned on. ) Off control, Power converter according to paragraph 1 range determined.   The control circuit (11) simultaneously turns on the second main switch (Gn) and the second auxiliary switch (Srn) when a predetermined time elapses after the first main switch (Gp) is turned off. The second auxiliary switch (Srn) is turned off, the second main switch (Gn) is turned off, and the second main switch (Gn) is turned off. The first main switch (Gp) and the first auxiliary switch (Srp) are simultaneously turned on, and the first auxiliary switch (Srp) is turned off, and then the first main switch (Gp) is turned on. The power conversion device according to claim 1, which is turned off.   The control circuit (11) simultaneously turns on the second main switch (Gn) and the second auxiliary switch (Srn) when a predetermined time elapses after the first main switch (Gp) is turned off. The second main switch (Gn) and the second auxiliary switch (Srn) are simultaneously turned off after a predetermined on-period has elapsed, and the second main switch (Gn) and the second main switch (Gn) The first main switch (Gp) and the first auxiliary switch (Srp) are simultaneously turned on when a predetermined time elapses after the auxiliary switch (Srn) is turned off. The power conversion device according to claim 1, wherein the first main switch (Gp) and the first auxiliary switch (Srp) are simultaneously turned off.

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