JP2012120294A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce switching loss of a primary side phase shift type DC-DC converter.SOLUTION: The DC-DC converter includes an inverter INV, a transformer Tsf in which a high-frequency output of the inverter is inputted, a rectification circuit Rec which rectifies an output of the transformer, a tap-fitted inductor Lot whose tap is connected to a plus side output terminal of the rectification circuit, with an end connected to a plus-side converter output terminal, and a diode D7 connected between a converter output terminal drawn out of a minus side output terminal of the rectification circuit and the other end of the inductor Lot. A capacitor voltage dividing circuit is connected between input terminals of the inverter. A resonance reactor L2 is connected between the voltage division point and the output terminal of a control phase side of the inverter. Charging/discharging is performed with a snubber capacitor of the leg of control phase through the reactor L2, so that the switching operation of a switch element of the leg of control phase acts as soft switching, for reduced switching loss.

Description

  The present invention relates to a primary-side phase shift DC-DC converter including a full-bridge inverter that converts a DC voltage into a high-frequency voltage and a rectifier circuit that rectifies the output of the inverter.

  A primary-side phase shift DC-DC converter combining a full-bridge inverter and a rectifier circuit is basically configured as shown in FIG. In the figure, INV is a full-bridge inverter that converts the output voltage E of the DC power source 1 to a high-frequency AC voltage Vcd, Tsf is a transformer that receives the output of the inverter INV, and Rec is a DC output that rectifies the high-frequency AC output of the transformer. R is a rectifier circuit for converting to F, F is a filter circuit for removing harmonic components from the output voltage of the rectifier circuit Rec, and Ro is a load.

  The inverter INV includes an upper arm including a switch element Q1, a snubber capacitor C1 connected in parallel to the switch element, and a feedback diode D1 connected in reverse parallel to the switch element Q1, a switch element Q2 and the switch element in parallel. A leg 2 of the reference phase configured by connecting in series a lower arm composed of a connected snubber capacitor C2 and a feedback diode D2 connected in reverse parallel to the switch element Q2, and in parallel to the switch element Q3 and the switch element Q3 Is connected in parallel to the snubber capacitor C3 and the switch element Q4 connected in parallel to the switch element Q4 and the switch element Q4. Connected in series with lower arm consisting of connected feedback diode D4 Consists circuits and leg 3 of the control phase constituted connected in parallel Te.

  In this inverter, the end on the upper arm side and the end on the lower arm side of the parallel circuit of the leg 2 of the reference phase and the leg 3 of the control phase are a positive input terminal a and a negative input terminal b, respectively. The output voltage E of the DC power source 1 is applied between these input terminals. The connection points between the upper arm and the lower arm of the leg 2 of the reference phase and the connection points of the upper arm and the lower arm of the leg 3 of the control phase are respectively the first and second inverter output terminals c and d. The voltage Vcd obtained between these inverter output terminals is applied to the primary coil W1 of the transformer through the series reactor L1.

  The transformer Tsf has a primary coil W1 and a secondary coil W2, and a center tap tc is drawn from the secondary coil W2. The rectifier circuit Rec includes a diode D5 having an anode connected to one end of a secondary coil W2 of the transformer, a diode D6 having an anode connected to the other end of the secondary coil W2, and a cathode commonly connected to the cathode of the diode D5. The common connection point of the cathodes of the diodes D5 and D6 and the center tap tc of the secondary coil of the transformer serve as the positive output terminal e and the negative output terminal f of the rectifier circuit Rec, respectively.

  The filter circuit F has one end connected between the inductor (choke coil) Lo connected to the plus output terminal e of the rectifier circuit Rec, and the other end of the inductor Lo and the minus output terminal f of the rectifier circuit Rec. It consists of a capacitor Co. A plus-side converter output terminal g and a minus-side converter output terminal h are drawn from the other end of the inductor Lo and a minus-side output terminal f of the rectifier circuit Rec, respectively, and a load Ro is connected between these converter output terminals.

  FIG. 5 shows the voltage waveform and current waveform of each part of the DC-DC converter shown in FIG. 5A shows drive signals S1 and S2 supplied to the gates of the switching elements Q1 and Q2 of the leg 2 of the reference phase, respectively, and FIG. 5B shows the gates of the switching elements Q3 and Q4 of the leg 3 of the control phase. The drive signals S3 and S4 respectively supplied are shown in FIG. FIG. 5C shows the voltage (output voltage of the inverter) Vcd input to the transformer, and FIG. 5D shows the current I1 flowing through the primary coil W1 of the transformer. In FIG. 5, T indicates one cycle of the output voltage of the inverter.

  In the DC-DC converter shown in FIG. 4, the switch elements Q1 to Q4 are turned on when the drive signals S1 to S4 are applied to the respective gates, and the drive signals S1 to S4 are applied. The on state is maintained, and the off state is obtained when the drive signals S1 to S4 are removed. In this DC-DC converter, as shown in FIGS. 5A and 5B, the switch elements Q1 and Q2 of the inverter INV are alternately turned on with a conduction angle of approximately 180 °, The switch elements Q4 and Q3 at the diagonal positions of the switch elements Q1 and Q2 have a conduction angle of approximately 180 at a timing delayed by a predetermined phase angle α with respect to the timing at which the switch elements Q1 and Q2 are turned on. Alternately turned on as °. In order to prevent the DC power supply 1 from being short-circuited, an appropriate dead time is applied during a period during which the switch elements Q1, Q2 of the same leg are turned on and during a period during which the switch elements Q3, Q4 are turned on. Time is provided.

  As described above, the switch elements Q1 to Q4 are turned on and off, whereby the output voltage E of the DC power supply 1 is converted into the high-frequency AC voltage Vcd. This AC voltage Vcd is transformed by a transformer, rectified by a rectifier circuit Rec and converted into a DC voltage Vr, a harmonic component is removed by a filter circuit F, and the DC output voltage Eo is applied to a load Ro.

  In the DC-DC converter shown in FIG. 4, the drive signals S1 and S4 are supplied, and the switch element Q1 of the upper arm of the reference phase leg and the switch element Q4 of the lower arm of the control phase leg are in the ON state. , Current I1 in the direction of the arrow flows from DC power source 1 through switch element Q1, series reactor L1, transformer primary coil W1, and switch element Q4. At this time, a voltage in a direction in which current flows through the diode D5 is induced in the secondary coil of the transformer, and a load current Id5 flows from the half W21 of the secondary coil W2 through the diode D5, the choke coil Lo, and the load Ro. The current I1 flowing through the primary coil of the transformer Tsf is a current obtained by superimposing the exciting current of the transformer Tsf on the current induced on the primary side of the transformer Tsf by the load current Id5.

  In this state, the drive signal S1 is set to zero to turn off the switching element Q1 of the upper arm of the reference phase leg. At this time, the snubber capacitor C1 connected in parallel to the switch element Q1 is connected to the DC power supply 1 → the capacitor C1 → the series reactor by the output voltage E of the DC power supply 1 and the energy accumulated in the series reactor L1 and the exciting inductance of the transformer. The electromagnetic energy stored in the circuit inductance is absorbed by the snubber capacitor C1 by charging through the path of L1 → primary coil W1 → switching element Q4 → DC power supply 1. The charging current of the capacitor C1 flowing at this time is a current I1 in which the exciting current of the transformer Tsf is superimposed on the current induced on the primary side of the transformer Tsf by the load current flowing in the secondary coil of the transformer Tsf.

  The snubber capacitor C1 at both ends of the switch element Q1 on the upper arm of the reference phase leg to be turned off is gradually charged as the switch element Q1 is turned off, so that the voltage Vc1 at both ends thereof rises almost linearly. I will do it. As a result, when the switch element Q1 is turned off, an increase in voltage at both ends thereof is alleviated, and zero voltage switching (ZVS) of the switch element Q1 is achieved.

  As described above, when the snubber capacitor C1 connected to both ends of the switch element Q1 of the upper arm of the reference phase leg to be turned off is charged, the diode D1 connected in parallel to the switch element Q1 is reversed. Biased so that no current flows through the diode D1.

  Further, when the snubber capacitor C1 is charged, the electric charge accumulated in the snubber capacitor C2 connected to both ends of the lower-arm switch element (switch element to be turned on next) Q2 of the leg 2 of the reference phase is transferred to the capacitor C2. → Series reactor L1 → Primary coil W1 of transformer → Switch element Q4 on lower arm of control phase → Discharge through the path of capacitor C2. As a result, the voltage Vc2 across the snubber capacitor C2 connected in parallel to the switch element Q2 of the lower arm of the reference phase leg to be turned on next decreases linearly. When the discharge of the snubber capacitor C2 is completed, the reverse bias of the feedback diode D2 connected in reverse parallel to the switch element Q2 is released, so that the primary energy is stored in the series reactor L1 and the magnetizing inductance of the transformer. The forward current Id2 flows through the diode D2 through the path of the coil W1, the switching element Q4, the diode D2, the series reactor L1, and the primary coil W1. This forward current Id2 is a current (transformer primary current I1) in which the exciting current of the transformer Tsf is superimposed on the current induced in the primary coil of the transformer by the load current flowing through the secondary coil of the transformer Tsf. As a result of the forward current flowing through the diode D2, the voltage across the switch element Q2 of the lower arm of the reference phase leg 2 to be turned on next is almost zero, and the switch element Q2 to which the drive signal S2 is applied is supplied. Turns on with almost zero current. Thereby, zero voltage switching (ZVS) and zero current switching (ZCS) of the switching element Q2 are achieved.

  The period in which the forward current Id2 flows through the diode D2 by the energy accumulated in the series reactor L1 and the exciting inductance of the transformer when the drive signal S1 is set to zero, and the switching element Q2 of the lower arm of the reference phase leg 2 and control In the period in which the switching element Q4 of the lower arm of the phase leg 3 is in the ON state at the same time, the circulation in the direction indicated by the arrow in the path of the primary coil W1, the switching element Q4, the diode D2, the series reactor L1, and the primary coil W1. Current I1 flows. On the secondary side of the transformer Tsf during which this circulating current flows, the current flows back through the closed circuit of the secondary coil W21 → the diode D5 → the inductor Lo → the load Ro → the secondary coil W21. The circulating current I1 is a current in which the exciting current of the transformer is superimposed on the current induced in the primary coil of the transformer by the return current flowing on the secondary side of the transformer. In FIG. 5, the part which flows as the circulating current of the current I1 is hatched.

  When the switch element Q2 of the lower arm of the reference phase leg and the switch element Q4 of the lower arm of the control phase leg are in the ON state, the drive signal is used to turn off the switch element Q4 of the lower arm of the control phase leg. S4 is set to zero. At this time, the switch elements Q1 and Q3 are in the OFF state, and the snubber capacitor C4 of the lower arm of the control phase leg is connected to the series reactor L1 by the electromagnetic energy accumulated in the series reactor L1 and the exciting inductance of the transformer. → Transformer primary coil W1 → Capacitor C4 → Diode D2 → Charge through a series reactor L1. At this time, the charging current flowing through the capacitor C4 is a current I1 in which the exciting current of the transformer is superimposed on the current induced in the primary coil of the transformer by the load current flowing through the secondary side of the transformer Tsf. As a result, the voltage Vc4 across the capacitor C4 rises almost linearly and the voltage across the switch element Q4 rises almost linearly. Therefore, when the switch element Q4 turns off, Rise is moderated. Thereby, ZVS of the switch element Q4 is achieved.

  Further, in the process of turning off the switch element Q4, the snubber capacitor C3 at both ends of the switch element Q3 of the upper arm of the control phase is switched between the capacitor C3 → the capacitance of the DC power source 1 → the leg of the reference phase whose reverse bias is released. Since the discharge is performed in the path of the diode D2, the series reactor L1, the primary coil W1, and the capacitor C3, the voltage Vc3 across the capacitor C3 decreases almost linearly. Since the reverse bias of the diode D3 is released when the discharge of the capacitor C3 is completed, the transformer primary coil W1 → diode D3 → DC is generated by the electromagnetic energy accumulated in the series reactor L1 and the exciting inductance of the transformer Tsf. The forward current Id3 flows through the diode D3 through the path of the capacitance of the power supply 1 → the diode D2 → the series reactor L1 → the primary coil W1 of the transformer. This forward current Id3 is a current (primary current I1) in which the exciting current of the transformer is superimposed on the current flowing in the primary coil of the transformer by the load current flowing in the secondary coil of the transformer Tsf. When the forward current Id3 flows through the diode D3, the voltage across the switch element Q3 is made substantially zero. In this state, by applying the drive signal S3 to the switch element Q3, the switch element Q3 is turned on in a state where the current is substantially zero, and zero current switching (ZCS) of the switch element Q3 is achieved. Accordingly, the switch element Q2 of the lower arm of the reference phase leg and the switch element Q3 of the upper arm of the control phase leg are simultaneously turned on.

  When the switching element Q2 of the lower arm of the reference phase leg and the switching element Q3 of the upper arm of the control phase leg are simultaneously turned on, the switching element Q3, the transformer primary coil W1, the series reactor L1, A current I1 in the direction opposite to the direction of the arrow flows through the switch element Q2. At this time, a voltage in the direction in which the current flows through the diode D6 is induced in the secondary coil W2 of the transformer, and the load current Id6 flows from the half W22 of the secondary coil through the diode D6, the choke coil Lo, and the capacitor Co. At this time, the current I1 flowing through the primary coil of the transformer is a current obtained by superimposing the exciting current of the transformer on the current induced in the primary coil of the transformer by the load current Id6.

  Next, the drive signal S2 is set to zero in order to turn off the switching element Q2 of the lower arm of the leg 2 of the reference phase. At this time, the capacitor C2 is charged by the current I1 flowing through the path of the DC power source 1 → the switch element Q3 → the primary coil W1 of the transformer → the series reactor L1 → the capacitor C2 → the DC power source 1, and the voltage Vc2 across the switch element Q2 is almost equal. Ascend linearly. As a result, when the switch element Q2 of the lower arm of the reference phase leg is turned off, an increase in voltage at both ends thereof is mitigated, and ZVS of the switch element Q2 is achieved.

  Further, in the process of turning off the switching element Q2, the snubber capacitor C1 at both ends of the switching element Q1 on the upper arm of the reference phase leg is routed from the capacitor C1, the switching element Q3, the transformer primary coil W1, the series reactor L1, and the capacitor C1. When the discharge is completed, the reverse bias of the diode D1 is released. As a result, the energy accumulated in the exciting inductances of the series reactor L1 and the transformer Tsf causes the transformer primary coil W1, the series reactor L1, the diode D1, the switch element Q3, and the transformer primary coil W1 to forward to the diode D1. A current Id1 flows. This forward current Id1 is a current (transformer primary current I1) in which the exciting current of the transformer Tsf is superimposed on the current induced in the primary coil of the transformer by the load current flowing through the secondary coil of the transformer Tsf. Thus, the forward current flows through the diode D1, so that the voltage across the switch element Q1 is substantially zero. In this state, the drive signal S1 is generated to turn on the switching element Q1 of the upper arm of the reference phase leg in a state where the current is almost zero, thereby achieving ZVS and ZCS. As a result, the switch element Q1 of the upper arm of the reference phase leg and the switch element Q3 of the upper arm of the control phase leg are simultaneously turned on.

  The primary coil W1 → the series reactor L1 → in the period when the forward current flows through the diode D1 and the switch elements Q1 and Q3 are simultaneously turned on by the energy stored in the series reactor L1 and the magnetizing inductance of the transformer. A circulating current I1 in the direction opposite to the direction of the arrow flows through the path of the diode D1, the switching element Q3, and the primary coil W1. On the secondary side of the transformer Tsf during which the circulating current flows, the current flows back through a closed circuit of the secondary coil W22 → the diode D6 → the inductor Lo → the load Ro → the secondary coil W22. A primary current that is induced in the primary coil of the transformer by the return current is superimposed on the circulating current I1.

  After the switching element Q1 of the upper arm of the reference phase leg is turned on, the drive signal S3 of the switching element Q3 of the upper arm of the control phase leg is set to zero at a predetermined timing. At this time, the capacitor C3 is charged through the path of the transformer primary coil W1, the series reactor L1, the diode D1, and the capacitor C3 by the excitation inductance of the primary coil W1 of the transformer Tsf and the energy stored in the series reactor L1. . As a result, the voltage Vc3 across the capacitor C3 rises almost linearly, and when the switch element Q3 is turned off, the rise in voltage across the capacitor C3 is alleviated. Thereby, ZVS of the switching element Q3 is achieved.

  In the process of turning off the switch element Q3, the capacitor C4 connected to both ends of the switch element Q4 of the lower arm of the control phase leg 3 is connected to the capacitor C4 → the primary coil W1 → the series reactor L1 → the diode D1 → the DC power supply 1 The capacitor is discharged along the path of the capacitor C4. When this discharge is completed, the reverse bias of the diode D4 is released. Therefore, the primary coil W1 → the series reactor L1 → the diode D1 → the capacitance of the DC power supply 1 → the diode D4 → the primary coil W1 in the order of the diode D4. A direction current Id4 flows. The forward current Id4 is a current in which an excitation current is superimposed on a current induced in the primary coil of the transformer by a load current flowing through the secondary coil of the transformer Tsf. When the forward current Id4 flows through the diode D4, the voltage across the switch element Q4 is made substantially zero. By generating the drive signal S4 in this state, the switch element Q4 of the lower arm of the control phase leg is turned on in a state where the current is almost zero, and ZVS and ZCS are achieved.

  The inverter INV converts the output voltage E of the DC power source 1 into the AC voltage Vcd by repeating the above operation. This AC voltage is converted into an AC voltage transformed by the transformer Tsf, and this AC voltage is converted into a DC voltage Vr by performing both-wave rectification by the rectifier circuit Rec, and then a harmonic component is removed from the DC voltage Vr by the filter circuit F. Then, the DC voltage Eo from which the harmonic component is removed is applied from the filter circuit F to the load Ro. The magnitude of the DC voltage applied to the load is determined by the phase angle α between the timing when the switching element of the reference phase leg is turned on and the timing when the switching element of the control phase leg in the diagonal position is turned on. Is controlled in the range of 0 ° to approximately 180 °.

  As described above, in the DC-DC converter shown in FIG. 4, a large circulating current flows between the reference phase leg 2 and the control phase leg 3 during the period indicated by the oblique lines in FIG. It is inevitable that the conduction loss generated in the element increases and the conversion efficiency decreases. In order to solve this problem, the DC-DC converter shown in Patent Document 1 has been proposed. In the DC-DC converter shown in Patent Document 1, the rectifier circuit Rec is used as shown in FIG. As an inductor provided in the subsequent filter circuit F, a tapped inductor Lot in which a tap to is drawn out in the middle is used. In this DC-DC converter, a positive-side converter output terminal g and a negative-side converter output terminal h are drawn from one end of the tapped inductor Lot and a negative-side output terminal f of the rectifier circuit Rec, respectively, and the other end of the tapped inductor Lot. The flywheel diode D7 is connected between the negative converter output terminal h and the anode facing the negative converter output terminal h. The tap to of the tapped inductor Lot is connected to the positive output terminal e of the rectifier circuit Rec.

  FIG. 7 shows voltage and current waveforms at various parts of the DC-DC converter shown in FIG. 7A to 7D show drive signals S1 to S4 applied to the switch elements Q1 to Q4, respectively, and FIG. 7E shows the output voltage Vcd of the inverter by a solid line and the output current I1 by a broken line. . Further, (F) to (I) indicate the voltages Vq1 to Vq4 across the switching elements Q1 to Q4 by solid lines, respectively, the currents Iq1 to q4 flowing through the switching elements Q1 to Q4 and the currents Id1 to Q4 flowing through the feedback diodes D1 to D4 Id4 is indicated by a broken line. Further, (J) shows the output voltage Vr of the rectifier circuit Rec, and (K) shows the current Id5 flowing through the diode D5 of the rectifier circuit Rec by a solid line and the current Id6 flowing through the diode D6 by a broken line. (L) indicates the voltage Vd7 across the diode D7 by a solid line, and the current Id7 flowing through the diode D7 by a broken line.

  In the DC-DC converter shown in FIG. 6, as shown in FIG. 7A, when the drive signal S1 becomes zero at time t1, charging of the capacitor C1 is started. As shown, the current Iq1 flowing through the switch element Q1 becomes zero. As the charging of the capacitor C1 proceeds, the voltage Vq1 across the switch element Q1 slowly increases. Thereby, the ZVS of the switch element Q1 is achieved. When charging of the capacitor C1 is started at time t1, the capacitor C2 is discharged through the series reactor L1, the primary coil W1 of the transformer, and the switch element S4, so that the voltage Vq2 across the switch element Q2 decreases. When the discharge of the capacitor C2 is completed at time t2, the reverse bias of the diode D2 is released and the forward current Id2 flows through the diode D2 as shown in FIG. 7G, so that the voltage Vq2 across the switch element Q2 is almost equal. Kept at zero.

  At time t2, the discharge of the capacitor C2 is completed, and when the forward current Id2 flows through the diode D2, the current Id7 begins to flow through the diode D7 of the filter circuit F with a voltage induced in the inductor Lot by the output voltage Vr of the rectifier circuit. For this reason, the current Id5 flowing through the diode D5 decreases. At this time, since the current induced on the primary side of the transformer by the current Id5 decreases, as shown in FIGS. 7E and 7I, the primary current I1 and the current Iq4 flowing through the switch element Q4 decrease. The forward current Id2 flowing through the diode D2 also decreases. When the drive signal S2 is generated at time t3 when the voltage Vq2 across the switch element Q2 is maintained at substantially zero, the switch element Q2 is turned on in a state of zero current, and ZCS is achieved.

  When the current Id7 flowing through the diode D7 is saturated, on the secondary side of the transformer, the current flows back through the closed circuit of the diode D7 → the inductor Lot → the capacitor Co and the load Ro → the diode D7, and the secondary coil of the transformer Tsf As shown in FIG. 7K, the current Id5 flowing through the diode D5 becomes zero. In this state, the primary current I1 of the transformer is only the exciting current of the transformer Tsf.

  At time t4, the drive signal S4 becomes zero. At this time, the capacitor C4 is only charged with the exciting current of the transformer, so that the capacitor C4 is hardly charged and the switching element Q4 is not ZVS. After the drive signal S4 is set to zero, the switch element Q4 is turned off when the predetermined turn-off time has elapsed, and the current Iq4 is cut off. At this time, vibration occurs due to the capacitance and inductance of the circuit. Next, when the drive signal S3 is generated, the switch element Q3 transitions to the on state, and the turn-on of the switch element Q3 is completed at time t5.

  When the drive signal S2 becomes zero at time t6, charging of the capacitor C2 is started, and the current Iq2 flowing through the switch element Q2 becomes zero. As charging of the capacitor C2 progresses, the voltage Vq2 across the switch element Q2 slowly increases. As a result, ZVS of the switch element Q2 is achieved. When charging of the capacitor C2 is started at time t6, discharging of the capacitor C1 is started, so that the voltage Vq1 across the switch element Q1 decreases. When the discharge of the capacitor C1 is completed at time t7, the reverse bias of the diode D1 is released and the forward current Id1 flows through the diode D1 as shown in FIG. 7F, so that the voltage Vq1 across the switch element Q1 is almost equal. Kept at zero.

  When the discharge of the capacitor C1 is completed at time t7, the current Id7 starts to flow through the diode D7 of the filter circuit F due to the voltage induced in the inductor Lot by the output voltage Vr of the rectifier circuit F, and the current Id6 flowing through the diode D6 decreases. . At this time, the current induced on the primary side of the transformer by the current Id6 decreases, so that the forward current Id1 flowing through the primary current I1 and the diode D1 decreases as shown in FIGS. 7E and 7F. Go. When the drive signal S1 is generated at time t8 when the voltage Vq1 across the switch element Q1 is maintained at substantially zero, the switch element Q1 is turned on with zero current, and ZCS is achieved.

  As described above, in the DC-DC converter shown in FIG. 6, after the switch element Q1 is turned off, the diode D2 is turned on, and the tapped inductor is supplied during the period in which current flows back to the secondary side circuit of the transformer Tsf. By the action of Lot, by flowing the current Id7 through the closed circuit of the inductor Lot → load → diode D7 → inductor Lot, the primary side and the secondary side of the transformer are separated, and the return current flowing on the secondary side of the transformer Since it is possible to prevent the current from flowing to the primary side of the transformer, the current Id2 flowing through the diode D2 can be attenuated as shown in FIG. 7G, which occurs when the circulating current flows. Loss can be reduced.

  Similarly, when the diode D1 is turned on after the switch element Q2 is turned off, a current Id7 is caused to flow through the closed circuit of the inductor Lot → load → diode D7 → inductor Lot with a transient voltage induced in the inductor Lot. Since the primary side and the secondary side are separated from each other and the current flowing to the primary side of the transformer can be prevented by the return current flowing through the secondary side of the transformer, the diode as shown in FIG. The current Id1 flowing through D1 can be attenuated, and loss caused when the circulating current flows can be reduced.

JP-A-6-14544

  In the DC-DC converter shown in FIG. 6, when the switch element Q1 of the leg 2 of the reference phase is turned off and when the switch element Q2 is turned off, the current flowing through the switch elements Q1 and Q2 is converted into the snubber capacitor C1 and Since the current flowing through the switch elements Q1 and Q2 is reduced to zero and the voltage across the switch elements Q1 and Q2 can be slowly raised as the snubber capacitors C1 and C2 are charged, Zero voltage switching (ZVS) of the switching elements Q1 and Q2 in the leg of the reference phase can be performed. Further, when turning on the switching elements Q1 and Q2 of the leg of the reference phase, the capacitors C1 and C2 that are sufficiently charged by the output of the DC power supply are discharged, and a forward current flows through the feedback diodes D1 and D2. Therefore, the voltage across the switching elements Q1 and Q2 can be reduced, and zero voltage switching (ZVS) and zero current switching (ZCS) can be performed. Therefore, when the switching elements Q1 and Q2 of the reference phase leg are turned on and off, almost no switching loss occurs.

  On the other hand, when the switching elements Q3 and Q4 of the leg 3 of the control phase are turned off, the primary side and the secondary side of the transformer Tsf are disconnected by the action of the tapped inductor Lot, so that the primary coil of the transformer Tsf Since the current flowing through the transformer is only the exciting current of the transformer and the charging current of the capacitors C3 and C4 is only the exciting current of the transformer Tsf, the capacitors C3 and C4 can hardly be charged. For this reason, when the switch elements Q3 and Q4 are turned off, the voltages at both ends cannot be raised, and ZVS of the switch elements Q3 and Q4 cannot be performed. Further, when the switching elements Q3 and Q4 of the control phase leg are turned off, the primary side and the secondary side of the transformer Tsf are disconnected, so that only the excitation current of the transformer can be supplied to the feedback diodes D3 and D4. Therefore, since the forward current cannot sufficiently flow through the feedback diodes D3 and D4, ZCS cannot be performed when the switch elements Q3 and Q4 are turned on.

  As described above, in the DC-DC converter shown in FIG. 6, ZVS cannot be performed when the switch elements Q3 and Q4 of the control phase leg are turned off, and the switch elements Q3 and Q4 are turned on. Since ZCS cannot be performed at this time, it is inevitable that switching loss occurs in these switch elements.

  In the DC-DC converter shown in FIG. 6, during actual operation, the capacitors C3 and C4 are repeatedly turned on and off when the switch elements Q3 and Q4 of the control phase leg are turned off depending on circuit constants and input / output conditions. Oscillating current flows and loss occurs. This loss becomes a value that cannot be ignored when the inverter INV operates at a frequency of several hundred kHz or more.

  FIG. 8 shows an example of actual operation waveforms when the inverter is operated at 300 kHz in the DC-DC converter shown in FIG. In FIG. 8, a shows the waveforms of the voltages Vq3 and Vq4 across the switch elements Q3 and Q4, and b shows the waveforms of the currents Iq3 and Iq4 flowing through the switch elements Q3 and Q4. As shown in the figure, in the DC-DC converter shown in FIG. 6, when the switch elements Q3 and Q4 of the control phase leg are turned on at time ta and turned off at time tb, the current Iq3 is small. When Iq4 flows and the operating frequency of the inverter is high, this switching loss becomes a value that cannot be ignored, which causes a decrease in conversion efficiency.

  An object of the present invention is to provide an inductor with a tap in a filter circuit provided on the output side of a rectifier circuit that rectifies a secondary output of a transformer that transforms an output of an inverter, and to turn on / off a switching element of a reference phase leg In the primary side phase shift type DC-DC converter which aims to reduce the switching loss, the switching loss at the time of turning on and off the switching element of the control phase leg is reduced to further improve the efficiency.

  In the present invention, a reference phase leg and a control phase leg in which upper and lower arms are configured by a switch element, a snubber capacitor connected in parallel to the switch element, and a feedback diode connected in reverse parallel to the switch element are connected in parallel. Then, the upper arm side end and lower arm side end of the parallel circuit of the reference phase leg and the control phase leg are respectively the plus side and minus side input terminals, and the upper and lower arms of the reference phase leg are Using the connection point and the connection point of the upper and lower arms of the control phase leg as the first and second inverter output terminals, respectively, the DC voltage applied between the input terminals is converted into a high-frequency AC voltage to convert the first and second Rectifying the induced voltage of the secondary coil of the transformer, the full-bridge inverter that outputs from the inverter output terminal of 2, the transformer in which the output of the inverter is input to the primary coil Rectifier circuit, a tapped inductor with a tap connected to the plus side output terminal of the rectifier circuit, a positive side converter output terminal and a minus side drawn from one end of the tapped inductor and the minus side output terminal of the rectifier circuit, respectively. The present invention is directed to a DC-DC converter including a converter output terminal and a flywheel diode having an anode connected to the negative converter output terminal side between the other end of the tapped inductor and the negative converter output terminal. .

  In the present invention, in order to achieve the above object, a capacitor voltage dividing circuit is connected between the input terminals of the inverter, and a resonant reactor is provided between the voltage dividing point of the capacitor voltage dividing circuit and the second inverter output terminal. Connected.

  The snubber capacitor connected in parallel to each switch element may be composed of an external capacitor or a parasitic capacitor included in each switch element. Further, both an external capacitor and a parasitic capacitor may be used as the snubber capacitor.

  With the above configuration, the capacitor voltage dividing circuit can be used as a voltage source to charge and discharge the capacitors at both ends of the upper and lower switch elements of the control phase leg through the resonant reactor. A ZVS operation can be performed when the upper arm and lower arm switch elements are turned off, and a ZVS operation and a ZCS operation can be performed when the switch elements are turned on.

  Therefore, according to the present invention, in addition to the circulating current reduction effect obtained by the action of the tapped inductor provided in the filter circuit, the effect of reducing the switching loss of the switching element of the control phase can be obtained, and the primary side phase shift The conversion efficiency of the DC-DC converter of the system can be improved.

  The rectifier circuit includes first and second rectifier diodes having an anode connected to one end and the other end of a secondary coil of a transformer, and a cathode connected in common, the first and second rectifier diodes. May be constituted by a double-wave rectifier circuit in which the intermediate tap provided on the common connection point of the cathode and the secondary coil of the transformer are respectively the positive output terminal and the negative output terminal, and the induced voltage of the secondary coil of the transformer is You may comprise by the diode bridge full wave rectifier circuit applied between alternating current input terminals.

  When the excitation inductance of the transformer is small, it is preferable to connect a series reactor in series with the primary coil of the transformer.

  According to the present invention, the capacitor voltage dividing circuit is connected between the input terminals of the inverter, and the voltage dividing point of the capacitor voltage dividing circuit and the second inverter output terminal (the capacitor of the upper arm and the capacitor of the lower arm of the control phase) And a capacitor voltage dividing circuit as a voltage source to charge and discharge the capacitors at both ends of the upper and lower arm switching elements of the control phase through the resonant reactor. Therefore, the ZVS operation can be performed when the switch elements of the upper arm and the lower arm of the control phase leg are turned off, and the ZVS operation and the ZCS operation can be performed at the turn-on. Therefore, according to the present invention, in addition to the circulating current reduction effect obtained by the action of the tapped inductor provided in the filter circuit, the effect of reducing the switching loss of the switching element of the control phase can be obtained, and the primary side phase shift The conversion efficiency of the DC-DC converter of the system can be improved.

1 is a circuit diagram showing an embodiment of a DC-DC converter according to the present invention. It is a wave form diagram which showed the waveform of the voltage of each part of FIG. 1, and an electric current. FIG. 2 is a waveform diagram showing measured waveforms during the on / off operation of voltages and energization currents at both ends of a control phase switch element of the DC-DC converter shown in FIG. 1. It is the circuit diagram which showed the fundamental structure of the DC-DC converter of a primary side phase shift system. FIG. 5 is a waveform diagram showing voltage and current waveforms at various parts in FIG. 4. FIG. 6 is a circuit diagram illustrating a configuration of a primary-side phase shift DC-DC converter disclosed in Patent Document 1. FIG. 7 is a waveform diagram showing waveforms of voltages and currents at various parts in FIG. 6. FIG. 7 is a waveform diagram showing measured waveforms at the time of on / off operation of voltages and energization currents of switch elements in the control phase of the DC-DC converter shown in FIG. 6.

  With reference to FIG. 1 thru | or FIG. 3, one Embodiment of the DC-DC converter concerning this invention is described. In FIG. 1, parts that are the same as the parts of the DC-DC converter shown in FIG. 6 are given the same reference numerals as those shown in FIGS.

  As in the DC-DC converter shown in FIG. 6, the DC-DC converter shown in FIG. 1 is a full-bridge inverter INV, a transformer Tsf to which the output of the inverter INV is input, and a high-frequency AC output of the transformer Tsf. , And a filter circuit F that removes harmonic components from the output voltage of the rectifier circuit Rec. A load Ro is connected between the output terminals of the filter circuit F.

  The inverter INV includes an upper arm including a switch element Q1, a snubber capacitor C1 connected in parallel to the switch element, and a feedback diode D1 connected in reverse parallel to the switch element Q1, a switch element Q2 and the switch element in parallel. A leg 2 of the reference phase configured by connecting in series a lower arm composed of a connected snubber capacitor C2 and a feedback diode D2 connected in reverse parallel to the switch element Q2, and in parallel to the switch element Q3 and the switch element Q3 Is connected in parallel to the snubber capacitor C3 and the switch element Q4 connected in parallel to the switch element Q4 and the switch element Q4. Connected in series with lower arm consisting of connected feedback diode D4 Consists circuits and leg 3 of the control phase constituted connected in parallel Te. Each switch element is a semiconductor switch element that transitions to an on state when a drive signal is applied, maintains an on state while the drive signal is applied, and transitions to an off state when the drive signal is removed. Use. As each switch element, it is preferable to use an element having a small switch loss, such as a MOSFET or an IGBT.

  In the illustrated inverter INV, the upper arm end and the lower arm end of the parallel circuit of the reference phase leg 2 and the control phase leg 3 are respectively connected to the positive input terminal a and the negative input terminal b. The output voltage E of the DC power source 1 is applied between these input terminals. The connection points between the upper arm and the lower arm of the leg 2 of the reference phase and the connection points of the upper arm and the lower arm of the leg 3 of the control phase are respectively the first and second inverter output terminals c and d. The voltage Vcd obtained between these inverter output terminals is applied to the primary coil W1 of the transformer through the series reactor L1.

  The transformer Tsf has a primary coil W1 and a secondary coil W2, and a center tap tc is drawn from the secondary coil W2. The rectifier circuit Rec includes a diode D5 having an anode connected to one end of a secondary coil W2 of the transformer, a diode D6 having an anode connected to the other end of the secondary coil W2, and a cathode commonly connected to the cathode of the diode D5. The common connection point of the cathodes of the diodes D5 and D6 and the center tap tc of the secondary coil of the transformer serve as the positive output terminal e and the negative output terminal f of the rectifier circuit Rec, respectively.

  The filter circuit F includes a tapped inductor Lot whose tap to is connected to the plus side output terminal e of the rectifier circuit Rec, one end of the tapped inductor Lot, and the plus side drawn from the minus side output terminal f of the rectifier circuit Rec. A flywheel diode D7 having an anode connected to the negative converter output terminal h side between the converter output terminal g and the negative converter output terminal h and the other end of the tapped inductor Lot and the negative converter output terminal h. And.

  The above configuration is the same as that of the DC-DC converter shown in FIG. In the present embodiment, a capacitor voltage dividing circuit CD comprising a series circuit of capacitors C5 and C6 is connected between the input terminals a and b of the inverter INV, and the voltage dividing point of the capacitor voltage dividing circuit CD is connected to the second voltage dividing point CD. A resonant reactor L2 is connected to the inverter output terminal d.

  FIG. 2 shows voltage and current waveforms at various parts of the DC-DC converter of FIG. In FIG. 2, (A) through (D) show drive signals S1 through S4 applied to the switch elements Q1 through Q4, respectively. In FIG. 2E, the output voltage Vcd of the inverter is indicated by a solid line, and the output current I1 is indicated by a broken line. 2 (F) to (I) show the voltages Vq1 to Vq4 across the switching elements Q1 to Q4 by solid lines, respectively, the current Iq1 flowing through the switching elements Q1 to Q4 and the current flowing through the feedback diodes D1 to D4. Id1 to Id4 are indicated by broken lines. 2 (J) shows the current IL2 flowing through the resonant reactor L2, FIG. 2 (K) shows the output voltage Vr of the rectifier circuit Rec, and (L) shows the current Id5 flowing through the diode D5 of the rectifier circuit Rec as a solid line. The current Id6 flowing through the diode D6 is indicated by a broken line. Further, (M) indicates the voltage Vd7 across the diode D7 by a solid line, and the current Id7 flowing through the diode D7 by a broken line.

  In the DC-DC converter shown in FIG. 1, when the capacitances of the capacitors C5 and C6 are sufficiently large and the respective capacitances are equal, C5 and C6 are each a voltage source that generates a voltage of E / 2. A current having a constant slope flows through the resonant reactor L2 by turning on and off the switching elements Q3 and Q4 in the control phase.

  In the DC-DC converter of FIG. 1, when the switch element Q4 of the lower arm of the control phase is in the ON state, the path of the capacitor C6 → resonance reactor L2 → switch element Q4 → capacitor C6 and DC power supply 1 → capacitor C5 → Resonance reactor L2 → Switch element Q4 → The current IL2 in the direction of the arrow shown in FIG. This current IL2 increases with a constant slope. When time is t and the inductance of the resonant reactor L2 is represented by L2, the current flowing through the resonant reactor L2 when the switching element Q4 is in the ON state can be represented by IL2 = (E / L2) × t. Further, when the switch element Q3 of the upper arm of the control phase is in the ON state, the path of the capacitor C5 → switch element Q3 → resonance reactor L2 → capacitor C5 and DC power source 1 → switch element Q3 → resonance reactor L2 → capacitor C6 → DC A current IL2 flows through the path of the power supply 1. The slope of this current is opposite to the slope of the current flowing through the resonant reactor L2 when the switch element Q4 is in the on state. The current flowing through the resonant reactor L2 when the switch element Q3 is in the on state can be expressed as IL2 = − (E / L2) × t.

  Therefore, the current Iq3 flowing through the switch element Q3 when the switch element Q3 is in the on state has a waveform obtained by adding IL2 to Iq3 in FIG. 7, and the current flowing through the switch element Q4 when the switch element Q4 is in the on state. Iq4 has a waveform obtained by adding IL2 to Iq4 in FIG.

  Further, the current Id3 flowing through the feedback diode D3 in FIG. 1 has a waveform obtained by adding IL2 to Id3 in FIG. 7, and the current Id4 flowing through the feedback diode D4 in FIG. 1 has a waveform obtained by adding IL2 to Id4 in FIG. . Assuming that the currents flowing through the capacitors C5 and C6 are IC5 and IC6, respectively, the current IL2 flowing through the resonance reactor L2 is expressed as IL2 = IC5 + IC6.

  When the switch element Q4 of the control phase is turned off, the current flowing due to the energy stored in the reactor L2 during the period when the switch element Q4 is in the ON state is added to the exciting current of the transformer Tsf to charge the capacitor C4. The capacitor C3 is discharged. In this case, charging of the capacitor C4 is performed by the path of the transformer primary coil W1, the capacitor C4, the diode D2, the reactor L1, the transformer primary coil W1, and the path of the reactor L2, the capacitor C4, the capacitor C6, and the reactor L2. . The capacitor C3 is discharged through a path of the capacitor C3 → DC power supply 1 → diode D2 → reactor L1 → transformer primary coil W1 → capacitor C3 and a path of capacitor C3 → capacitor C5 → reactor L2 → capacitor C3.

  When the switch element Q3 of the control phase is turned off, the current flowing by the energy stored in the reactor L2 during the period when the switch Q3 is on is added to the exciting current of the transformer Tsf, and charging of the capacitor C3 and the capacitor C4 is discharged. In this case, the charging of the capacitor C3 is performed through the path of the transformer primary coil W1, the reactor L1, the diode D1, the capacitor C3, and the transformer primary coil W1, and the path of the reactor L2, the capacitor C5, the capacitor C3, and the reactor L2. . Further, the capacitor C4 is discharged through the path of the capacitor C4 → the primary coil W1 of the transformer → the reactor L1 → the diode D1 → the DC power source 1 → the capacitor C4, and the path of the capacitor C4 → the reactor L2 → the capacitor C6 → the capacitor C4.

  The resonant reactor L2 accumulates energy when the switch elements Q3 and Q4 are in the ON state, and a dead time period from when the switch element Q3 is turned off to when the switch element Q4 is turned on with the accumulated energy, In addition, the capacitors C3 and C4 are charged and discharged during a dead time from when the switch element Q4 is turned off to when the switch element Q3 is turned on.

  In the DC-DC converter shown in FIG. 1, as shown in FIG. 2A, when the drive signal S1 becomes zero at time t1, the turn-off operation of the switch element Q1 is started and the charging of the capacitor C1 is started. Since the process is started, as shown in FIG. 1F, the current Iq1 flowing through the switch element Q1 is made zero. As the charging of the capacitor C1 proceeds, the voltage Vq1 across the switch element Q1 slowly increases. As a result, when the switch element Q1 is turned off, an increase in voltage at both ends thereof is alleviated, and zero voltage switching (ZVS) of the switch element Q1 is achieved.

  When the turn-off operation of the switch element Q1 is started at the time t1, the capacitor C2 is discharged along the path of the capacitor C2, the series reactor L1, the transformer primary coil W1, the switch element S4, and the capacitor C2, so that both ends of the switch element Q2 Voltage Vq2 decreases. When the discharge of the capacitor C2 is completed at time t2, the reverse bias of the diode D2 is released, and the energy accumulated in the series reactor L1 and the primary coil W1 causes the series reactor L1 → the primary coil W1 of the transformer → the switch element Q4 → A forward current Id2 flows through the diode D2 through the path of the diode D2 → the series reactor L1, as shown in FIG. This forward current Id2 is a current (transformer primary current I1) in which the exciting current of the transformer Tsf is superimposed on the current induced in the primary coil of the transformer by the current Id5 flowing through the secondary coil of the transformer Tsf. In this way, the forward current flows through the diode D2, so that the voltage Vq2 across the switch element Q2 is kept substantially zero.

  When the discharge of the capacitor C2 is completed at the time t2 and the forward current Id2 flows through the diode D2, the current Id7 (see FIG. 5) is applied to the diode D7 of the filter circuit F with a voltage induced in the inductor Lot by the output voltage Vr of the rectifier circuit. 2M) starts to flow, the current Id5 (FIG. 2L) flowing through the diode D5 decreases. At this time, since the current induced on the primary side of the transformer by the current Id5 decreases, as shown in FIGS. 2E and 2I, the primary current I1 and the current Iq4 flowing through the switch element Q4 decrease. The forward current Id2 flowing through the diode D2 (FIG. 2G) also decreases. When the drive signal S2 is generated at time t3 while the voltage Vq2 across the switch element Q2 is maintained at substantially zero, the switch element Q2 is turned on in a state of zero current, and zero current switching (ZCS) is achieved.

  As shown in FIG. 2 (M), when the current Id7 flowing through the diode D7 is saturated, the secondary side of the transformer Tsf passes through the closed circuit of the diode D7 → the inductor Lot → the capacitor Co and the load Ro → the diode D7. In a recirculating state, no current flows through the secondary coil of the transformer Tsf, and the current Id5 flowing through the diode D5 becomes zero as shown in FIG. In this state, the primary current I1 of the transformer is only the exciting current of the transformer Tsf.

  When the drive signal S4 becomes zero at time t4, the turn-off operation of the switch element Q4 is started, the path of the transformer primary coil W1, the capacitor C4, the diode D2, the reactor L1, the transformer primary coil W1, and the resonant reactor L2 → capacitor. The capacitor C4 is charged along the path C4 → capacitor C6 → resonance reactor L2. As a result, the voltage across the switch element Q4 rises linearly, and the turn-off is performed by ZVS.

  When the turn-off operation of the switch element Q4 is started at time t4, the path of the capacitor C3 → DC power supply 1 → diode D2 → reactor L1 → transformer primary coil W1 → capacitor C3, capacitor C3 → capacitor C5 → resonance reactor L2 → The capacitor C3 is discharged along the path of the capacitor C3. When the discharge of the capacitor C3 is completed, the reverse bias of the diode D3 is released. Therefore, the transformer primary coil W1, the diode D3, the DC power supply 1, the diode D2, the series reactor L1, the path of the primary coil W1, and the capacitor C6 → resonance. A forward current flows in the diode D3 through the path of the reactor L2, the diode D3, the DC power supply 1, the capacitor C6, and the path of the capacitor C5, the resonant reactor L2, the diode D3, and the capacitor C5, and the voltage across the switch element Q3 is almost equal. Zeroed out. When drive signal S3 is applied in this state, turn-off operation of switch element Q3 is performed at ZVS and ZCS, and the turn-on is completed at time t5.

  During the dead time period from the time t4 to the time t5, a transient phenomenon occurs in the LC circuits of L2, C3, and C4. If the dead time is sufficiently shortened so that no vibration occurs due to the transient decrease, FIG. As shown in (J), the current IL2 flowing through the reactor L2 changes from increasing to decreasing at time t4 without vibration, and becomes a continuous triangular waveform. When the switch element Q3 is turned on at time t5, the direction of the current IL2 flowing through the resonant reactor L2 is forcibly reversed, and the path of the capacitor C5 → switch element Q3 → reactor L2 → capacitor C5 and the DC power source 1 → switch element Q3. The current IL2 in the direction opposite to the arrow in the figure flows through the path of the resonance reactor L2, the capacitor C6, and the DC power source 1. This current IL2 increases with time.

  When the drive signal S2 is set to zero at time t6, the switch element Q2 is turned off, and the DC power source 1 → switch element Q3 → transformer primary coil W1 → series reactor L1 → capacitor C2 → DC power source 1 The capacitor C2 is charged by the flowing current I1. The charging current I1 of the capacitor C2 is a current obtained by superimposing the exciting current of the transformer on the current induced in the primary coil of the transformer by the load current Id6 (FIG. 2L) flowing through the secondary coil of the transformer Tsf. Since the capacitor C2 is charged in this way, the voltage Vq2 across the switch element Q2 rises almost linearly, and the rise in voltage across the both ends is mitigated, so that the switch element Q2 is turned off by ZVS. .

  In the process of turning off the switch element Q2, the snubber capacitor C1 at both ends of the switch element Q1 of the upper arm of the reference phase leg is in the path of capacitor C → switch element Q3 → transformer primary coil W1 → series reactor L1 → capacitor C1. When the discharge is completed, the reverse bias of the diode D1 is released. As a result, the energy accumulated in the exciting inductances of the series reactor L1 and the transformer Tsf causes the transformer primary coil W1, the series reactor L1, the diode D1, the switch element Q3, and the transformer primary coil W1 to forward to the diode D1. A current Id1 flows. This forward current Id1 is a current (transformer primary current I1) in which the exciting current of the transformer Tsf is superimposed on the current induced in the primary coil of the transformer Tsf by the load current Id6 flowing through the secondary coil of the transformer Tsf. . As a result of the forward current flowing through the diode D1, the voltage across the switch element Q1 becomes almost zero. In this state, when the drive signal S1 is given at time t8, the switch element Q1 is turned on by ZVS and ZCS.

  As described above, the capacitor voltage dividing circuit CD is connected between the input terminals of the inverter, and a resonant reactor is connected between the voltage dividing point of the voltage dividing circuit and the second inverter output terminal, and this resonant reactor L2 is connected. When the current IL2 is supplied through the capacitor C3 and the capacitor C3 and C4 in the control phase are charged, a loss due to the current IL2 occurs. This loss causes the capacitor IL and the capacitor C3 and C4 to be charged and discharged. By setting the required minimum size, it is possible to significantly reduce the switching loss that occurs when ZVS and ZCS of the switching elements Q3 and Q4 are not performed.

  FIG. 3 shows an example of actual operation waveforms when the inverter is operated at 300 kHz in the DC-DC converter shown in FIG. In FIG. 3, “a” shows waveforms of voltages Vq3 and Vq4 across the switching elements Q3 and Q4 of the control phase leg, and “b” shows waveforms of currents Iq3 and Iq4 flowing through the switching elements Q3 and Q4. As shown in the figure, in the DC-DC converter shown in FIG. 1, when the switching elements Q3 and Q4 of the control phase leg are turned on at time ta, the ZVS and ZCS operations are performed, and when the switch elements Q3 and Q4 are turned off at time tb. Therefore, the switching loss of the switch element of the control phase leg can be reduced.

  In the above embodiment, the rectifier circuit provided on the secondary side of the transformer is a double-wave rectifier circuit. However, the rectifier circuit Rec provided on the secondary side of the transformer is a well-known circuit composed of a full bridge circuit in which each arm is configured by a diode. A diode bridge full-wave rectifier circuit may be used. When the rectifier circuit Rec is a diode bridge full-wave rectifier circuit, an induced voltage of the secondary coil is applied between the AC input terminals of the full-wave rectifier circuit without providing a center tap on the secondary coil of the transformer Tsf. .

  As described above, according to the present invention, the capacitor voltage dividing circuit is connected between the input terminals of the inverter, and the voltage dividing point of the capacitor voltage dividing circuit and the second inverter output terminal (the capacitor of the upper arm of the control phase) And a capacitor at both ends of the switching elements of the upper arm and the lower arm of the control phase leg through the resonant reactor using a capacitor voltage divider as a voltage source. Therefore, the ZVS operation can be performed when the upper and lower arm switch elements of the control phase leg are turned off, and both the ZVS operation and the ZCS operation can be performed at the time of turn-on. . Therefore, according to the present invention, in addition to the circulating current reduction effect obtained by the action of the tapped inductor provided in the filter circuit, the effect of reducing the switching loss of the switching element of the control phase can be obtained, and the primary side phase shift The conversion efficiency of the DC-DC converter of the system can be improved.

1 DC power supply 2 Reference phase leg 3 Control phase leg INV Full bridge inverter Q1 Reference phase leg upper arm snubber capacitor C1 Reference phase leg upper arm snubber capacitor D1 Reference phase leg upper arm feedback diode Q2 Reference phase leg lower arm switch element C2 Reference phase leg lower arm snubber capacitor D2 Reference phase leg lower arm feedback diode Q3 Control phase leg upper arm switch element C3 Control phase leg Upper arm snubber capacitor D3 Control phase leg upper arm feedback diode Q4 Control phase leg lower arm snubber capacitor C4 Control phase leg lower arm snubber capacitor D4 Control phase leg lower arm feedback diode Tsf Transformer W1 Primary coil W2 Secondary coil L1 Series reactor Rec Adjustment Circuit D5 first rectifier diode D6 second rectifier diode D7 flywheel diode Lot tapped inductor Co capacitor Ro load

Claims (4)

The leg of the reference phase and the control phase in which the upper and lower arms are constituted by the switch element, the snubber capacitor connected in parallel to the switch element, and the feedback diode connected in reverse parallel to the switch element, are connected in parallel, The upper arm end and lower arm end of the parallel circuit of the reference phase leg and the control phase leg are the positive and negative input terminals, respectively, and the connection points of the upper and lower arms of the reference phase leg And the connection points of the upper and lower arms of the control phase leg are respectively the first and second inverter output terminals, and the DC voltage applied between the input terminals is converted into a high-frequency AC voltage to convert the first and second Rectifying the induced voltage of the full-bridge inverter that is output from the inverter output terminal, the transformer in which the output of the inverter is input to the primary coil, and the secondary coil of the transformer A rectifier circuit, a tapped inductor having a tap connected to the plus side output terminal of the rectifier circuit, a plus side converter output terminal and a minus side drawn from one end of the tapped inductor and the minus side output terminal of the rectifier circuit, respectively. In a DC-DC converter comprising: a side converter output terminal; and a flywheel diode having an anode connected to the negative converter output terminal side between the other end of the tapped inductor and the negative converter output terminal ,
A capacitor voltage divider connected between the input terminals of the inverter;
A resonant reactor connected between a voltage dividing point of the capacitor voltage dividing circuit and the second inverter output terminal;
A DC-DC converter comprising:   The rectifier circuit includes first and second rectifier diodes, each having an anode connected to one end and the other end of the secondary coil of the transformer, and a cathode connected in common. 2. The DC-DC according to claim 1, comprising a double-wave rectifier circuit in which a common connection point of a cathode of a diode and an intermediate tap provided in a secondary coil of the transformer are respectively used as a positive output terminal and a negative output terminal. converter.   2. The DC-DC converter according to claim 1, wherein the rectifier circuit includes a diode bridge full-wave rectifier circuit provided so that a voltage induced in a secondary coil of the transformer is applied to an AC input terminal.   4. The DC-DC converter according to claim 1, wherein a series reactor is connected in series with a primary coil of the transformer.

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