JP2013243852A - Series resonant converter system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a series resonant converter system that improves power efficiency without increasing the number of components.SOLUTION: When an inverter circuit in which two legs each comprising upper and lower arms each comprising a switching element having an antiparallel diode and a parallel capacitor are connected in parallel across a DC power supply converts a direct current input from the DC power supply to an alternating current to supply power to a secondary side via a transformer 11 by means of series resonance of a pair of resonant capacitors Ca, Cb on the secondary side of the transformer 11 and a resonant inductance L, a control device 15 turns off either of the switching element of the upper arm of the first or second leg and the switching element of the lower arm of the second or first leg forming a set in an on state first, and after a current flowing through the switching element to be turned off later becomes an exciting current of the transformer, feeds an off signal to that switching element.

Description

  The present invention relates to a series resonance type converter system using a series resonance action of inductance and capacitance.

  As a converter having high power conversion efficiency, a series resonance type converter using a series resonance of an inductance of a resonance inductance and a capacitance of a resonance capacitor is widely used.

  As a series resonance type converter with high power conversion efficiency, the zero current that switches the switching element when the current flowing through the switching element of the primary side inverter circuit is almost zero by using the series resonance of the resonance capacitor and the resonance inductance mainly. Some switching loss is reduced by switching (see, for example, Patent Document 1).

  Further, as a series resonance type converter, a resonance capacitor is provided on each of the primary side and the secondary side, and when the load voltage and the load current change greatly, the resonance capacitance in the series resonance circuit including the resonance inductance and the resonance capacitor is large. Is automatically changed to improve the resonance current waveform so that it is sinusoidal or close to a sine waveform, and to improve the power efficiency of the series resonance converter over a wide load range (see Patent Document 2). ).

  In general, in a full-bridge inverter circuit, two legs having switching elements as upper and lower arms are connected in parallel, and an upper arm switching element on one leg and a lower arm switching element on the other leg are connected. On-off control is alternately performed as a set, and direct current input from the input terminal is converted into alternating current.

  In that case, as shown in FIG. 7, the drive signal of each switching element controls the output by changing the frequency (cycle) of the on-time start point with the on-time To fixed for all four switching elements. ing. Now, assuming that the switching elements of the upper and lower arms of one leg are switching elements S1 and S2, and the switching elements of the upper and lower arms of the other leg are switching elements S3 and S4, the switching elements S1 and S4 are one set. The switching elements S2 and S3 form the other set and are alternately turned on / off.

  For example, if switching elements S2 and S3 are simultaneously turned off at time t1, then switching elements S1 and S4 are simultaneously turned on at time t2. At time t3, the switching elements S1 and S4 are simultaneously turned off, and at time t4, the switching elements S2 and S3 are simultaneously turned on. Hereinafter, similarly, after the time point t5, the switching elements S1 and S4 and the switching elements S2 and S3 are paired and alternately turned on and off. In this case, the on-time To of all the switching elements S1, S2, S3, S4 is constant. The output is controlled by adjusting the timing of turning on the switching elements S1 and S2 and the timing of turning on the switching elements S2 and S3.

JP 2010-4724 A JP 2011-114978 A

  However, although the thing of patent document 1 can be used in a comparatively wide output voltage range, in the area | region where an output voltage is low, when the switching element of the inverter circuit of a primary side switches off, it does not become zero current switching. Loss occurs. The loss increases as the output voltage decreases. This is because when the output voltage is lowered, series resonance between the resonance capacitor and the resonance inductance is not performed.

  On the other hand, in Patent Document 2, the power efficiency can be improved over a wide load range. However, since a resonant capacitor is required on each of the primary side and the secondary side, the number of parts increases and the cost increases. .

  Further, in Patent Documents 1 and 2, when the switching element is turned on, energy stored in the parasitic capacitance of the switching element is consumed by the turned on switching element, resulting in a loss.

  An object of the present invention is to provide a series resonance type converter system capable of improving power efficiency without increasing the number of parts.

  A series resonance type converter system according to a first aspect of the present invention includes a bridge circuit in which a first leg and a second leg, each having a switching element as an upper and lower arm, are connected in parallel between DC power sources, and the switching element. An anti-parallel diode connected in anti-parallel, and a parallel capacitor connected in parallel to each of the switching elements, the switching element of the upper arm of the first or second leg, and the second or first The inverter circuit having an inverter circuit which is alternately turned on and off alternately with a switching element of the lower arm of the leg and converts a direct current input from the direct current power source into an alternating current, a primary winding and a secondary winding Connected to one terminal of the secondary winding of the transformer and two transformers that input the alternating current converted in step 1 to the primary winding and output from the secondary winding. A pair of resonance capacitors connected in series between the output terminals, and a pair of reverse charge suppression elements connected in parallel to the pair of resonance capacitors to prevent each resonance capacitor from being charged in reverse polarity; , Connected to the other terminal of the secondary winding of the transformer, connected in series between the two output terminals, and prevents current from being fed back from the pair of resonant capacitors to the DC power source. A pair of unidirectional elements, a resonance inductance that acts in series with the pair of resonant capacitors, and the switching elements that are in the set are alternately turned on and off, and the first set that is in the on state Or one of the switching element of the upper arm of the second leg and the switching element of the lower arm of the second or first leg. It is off, characterized in that the current flowing through the switching element is turned off and a control unit for turning off the switching element to turn off is delayed after said became exciting current of the transformer to delay the.

  The series resonance type converter system according to a second aspect of the present invention is the serial resonance type converter system according to the first aspect, wherein the control device includes a switching element of the arm that is delayed and turned off after the switching element of the arm that is turned off and delayed is turned on. While the discharge current of the parallel capacitor connected in parallel finishes flowing, the exciting current of the transformer flows while flowing through the anti-parallel diode of the switching element of the other arm of the same leg as the switching element of the arm that has been delayed and turned off. An ON signal is given to the switching element to be turned on of the switching element of the other arm and the other set of switching elements.

  A series resonance converter system according to a third aspect of the present invention is the serial resonance type converter system according to the first aspect, wherein the control device fixes an ON signal of a switching element to be turned off first among the switching elements to be the pair, Of the switching elements to be turned off after being delayed until the ON signal is given to the switching elements on the other leg of the same leg as the switching elements of the arm to be turned off after the on signal of the switching element to be turned off is delayed. The dead time is fixed.

  According to a fourth aspect of the present invention, there is provided a series resonance type converter system according to the first aspect of the invention, wherein the control device provides four switchings in which both of the upper and lower arm switching elements do not give an ON signal for each of the two legs. Each element dead time is fixed, and the time during which an ON signal is simultaneously applied to the switching element of the upper arm of the one leg and the switching element of the lower arm of the other leg is fixed. To do.

  A series resonance type converter system according to a fifth aspect of the present invention is the serial resonance type converter system according to the second aspect of the present invention, wherein the switch element in the switching element having a smaller impedance than the antiparallel diode through which the exciting current of the transformer flows is conducted in the reverse direction. And conducting in the forward direction.

  According to the present invention, the switching elements of the upper arm of the first or second leg and the lower arm of the second or first leg that are in the set in the on state when alternately switching on and off the switching elements that are the set. The switching element that is turned off later is turned off after the current flowing in the switching element that is turned off and delayed is turned off after the current flowing through the switching element is turned off. , It can be turned off while the current flowing therethrough is suppressed. Moreover, it can turn on in the state which suppressed the voltage of the two switching elements used as the group turned on next by the effect | action of the resonance inductance and the antiparallel diode and parallel capacitor | condenser of a switching element.

The block diagram of the series resonance type converter system which concerns on embodiment of this invention. The timing diagram which shows an example of on-off control of the switch element of the switching element in embodiment of this invention. FIG. 3 is a circuit diagram of a series resonant converter system formed when each switching element is on / off controlled at the timing shown in FIG. 2. FIG. 3 is a waveform diagram of voltage and current of each switching element when each switching element is on / off controlled at the timing shown in FIG. 2. FIG. 5 is a waveform diagram of voltages and currents of switching elements S1 and S2 obtained by extending the time axis of the T period in FIG. The timing diagram which shows another example of on-off control of the switching element in embodiment of this invention. The timing diagram of on-off control of the switching element of the conventional full bridge inverter circuit.

  Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of a series resonance type converter system according to an embodiment of the present invention.

  The series resonance type converter is almost the same as that shown in FIG. 5 of Patent Document 1, and the feedback diode of the switching element constituting the primary side inverter circuit of Patent Document 1 is the reverse of the embodiment of the present invention. Corresponds to a parallel diode. That is, the antiparallel diode of the embodiment of the present invention corresponds to an antiparallel diode connected in antiparallel to the built-in diode of the switching element or the switch element of the switching element. The parallel capacitor according to the embodiment of the present invention corresponds to a parasitic capacitance of the switching element or a capacitor connected in parallel to the switching element of the switching element. Although the parallel capacitor is not shown in Patent Document 1, the parallel capacitor is clearly illustrated in the embodiment of the present invention because it is necessary to consider the operation of the parallel capacitor.

  In an embodiment of the present invention, taking into account the anti-parallel diode and parallel capacitor of the switching element, the control device makes the voltage across the switching element almost zero just before the switching element is turned on, and is used in a wide output voltage range. Even in this case, of the four switching elements, on / off control of the switching elements is performed so that the switching loss at the time of turning off the two switching elements can be reduced.

  In FIG. 1, first, a series resonance type converter will be described. The primary side and the secondary side of the series resonant converter are connected via a transformer 11 having a primary winding 11a and a secondary winding 11b.

  The primary side of the transformer 11 has an inverter circuit 13 connected in parallel to the DC power source 12 on the input terminal side. The inverter circuit 13 includes a leg 14 a having a switching element S 1 as an upper arm and a switching element S 2 as a lower arm, and a leg 14 b having a switching element S 3 as an upper arm and the switching element S 4 as a lower arm, in parallel between the DC power supplies 12. To form a bridge circuit (full bridge circuit).

  The switching elements S1 and S2 include antiparallel diodes D1 and D2 and parallel capacitors C1 and C2 in parallel with the switching elements Q1 and Q2. Similarly, the switching elements S3 and S4 have antiparallel diodes D3 and D4 and parallel capacitors C3 and C4 in parallel with the switching elements Q3 and Q4.

  The inverter circuit 13 is alternately turned on and off in pairs with the switching element S1 (S3) of the upper arm of one leg 14a (14b) and the switching element S4 (S2) of the lower arm of the other leg 14b (14a). . That is, the switching elements S1 and S4 form a pair, and the switching elements S3 and S2 form a pair, which are alternately turned on and off to convert the direct current input from the direct current power source 12 into alternating current.

  The connection point between the switching elements S1 and S2 is connected to one terminal of the primary winding 11a of the transformer 11 via the resonance inductance L, and the connection point between the switching elements S3 and S4 is the primary winding of the transformer 11. 11a is connected to the other terminal. Thereby, the alternating current converted by the inverter circuit 13 is output from the primary winding 11a of the transformer 11 to the secondary winding 11b of the transformer 11 and supplied to the secondary side.

  The secondary side of the transformer 11 includes a pair of resonance capacitors Ca and Cb, reverse charge suppression diodes Da and Db connected in parallel to the pair of resonance capacitors Ca and Cb, a pair of unidirectional elements Dc and Dd, and an output. A smoothing capacitor Cc is provided on the terminal side. The pair of reverse charge suppression diodes Da and Db prevent the resonance capacitors Ca and Cb from being charged with reverse polarity.

  The resonant capacitors Ca and Cb are connected to one end of the secondary winding of the transformer 11 and connected in series between two output terminals to which a load is connected. The resonant capacitors Ca and Cb act together with the resonant inductance L to resonate in series. The unidirectional elements Dc and Dd are connected to the other terminal of the secondary winding 11b of the transformer 11, connected in series between the two output terminals, and connected to the DC power source 12 from the pair of resonance capacitors Ca and Cb. To prevent the current from being fed back. The resonance inductance L may be connected to the secondary winding 11b side of the transformer 11.

  The control device 15 turns off one of the switching element S1 (S3) of the upper arm of one leg 14a (14b) and the switching element S4 (S2) of the lower arm of the other leg 14b (14a). , And the on / off control of the paired switching elements is performed alternately.

  For example, when the switching element S1 (S3) of the upper arm of one leg 14a (14b) is turned off first, the switching element S4 (S2) of the lower arm of the other leg 14b (14a) is turned off. Turn off late.

  Alternatively, when the switching element S2 (S4) of the lower arm of one leg 14a (14b) is turned off first, the switching element S4 (S1) of the upper arm of the other leg 14b (14a) to be paired is turned on. Turn off late. In addition, the switching elements forming a set with these combinations are alternately turned on and off.

  In the following description, the switching element S4 of the lower arm of one leg 14b is turned off first, the switching element S1 of the upper arm of the other leg 14a in the pair is turned off with delay, and the upper arm of one leg 14b is turned off. A case will be described in which the switching element S3 is turned off first, and the switching element S2 of the lower arm of the other leg 14a in the pair is turned off with a delay.

  FIG. 2 is a timing chart showing an example of on / off control of the switch element of the switching element in the embodiment of the present invention. In contrast to the conventional example shown in FIG. 7, instead of fixing the on-time To of all the switching elements S1, S2, S3, S4, the on-time To of the switching element S4 of the lower arm of the leg 14b and the leg 14b The on-time To of the upper-arm switching element S3 is fixed, and the dead time Td during which both the upper- and lower-arm switching elements S1 and S2 of the leg 14a are off is fixed. Here, the dead time is such that the switching element S1 (Q2) of one switching element S1 (S2) is turned off and then the other switching element S2 ( This is a predetermined time required when the switch element Q2 (Q1) of S1) is delayed and turned on.

  As shown in FIG. 2, at time t1, when an ON signal for simultaneously turning on the switching element Q1 of the switching element S1 and the switching element Q4 of the switching element S4 is given, and a fixed on-time To elapses. At t2, the switching element S4 is turned off first.

  When the switching element is an element that maintains the on state when the on signal is continuously applied, the switching element is turned off by stopping the application of the on signal. On the other hand, if the element is in an on state once it is on, it is turned off by applying an off signal.

  At time t3 after the switching element S4 is turned off first, the switching element Q1 of the switching element S1 is turned off. At the time t3 when the ON signal of the switching element Q1 of the switching element S1 is finished and the switching element Q1 is turned OFF, the other switching element S2 of the same leg 14b as the OFF switching element S1 is in the OFF state.

  Therefore, at a time point 4 when the fixed dead time Td has elapsed from the time point t3, an ON signal for simultaneously turning on the switching element Q2 of the switching element S2 and the switching element Q3 of the switching element S3 which are in another set is given. Thereafter, at the time t5 when the fixed on-time To elapses, the switching element S3 is first turned off. Further, the switching element S2 is turned off at a subsequent time point t6.

  Hereinafter, similarly, at time t7 when the fixed dead time Td has elapsed from time t6, an on signal for simultaneously turning on the switching element Q1 of the switching element S1 and the switching element Q4 of the switching element S4 is given, At time t8 when the fixed on-time To elapses, the switching element S4 is turned off first. Thereafter, at time t9, the switching element S1 is turned off. The same applies after time t10.

  Thus, after the current flowing through the switching element that is turned off with delay becomes the exciting current of the transformer, the switching element that is turned off with delay is turned off, so that the current flowing through the switching element S1 (S2) that is turned off later is suppressed. And it turns off in the state by which the electric current was suppressed. Further, the switching of the two switching elements S2, S3 (S1, S4) to be turned on next by the action of the resonance inductance L and the antiparallel diodes D1 to D4 of the switching elements S1 to S4 and the parallel capacitors C1 to C4. The voltage of the element is also suppressed. And it turns on in the state which suppressed the voltage.

  Next, an operation when the output voltage Eo of the series resonance type converter system is low will be described. FIG. 3 is a circuit diagram of a series resonant converter system formed when each switching element S1, S2, S3, S4 is controlled to be turned on and off at the timing shown in FIG. 2, and FIG. 4 shows the switching elements S1, S2, FIG. 5 is a waveform diagram of the voltages and currents of the switching elements S1 and S2 obtained by extending the time axis of the T period in FIG.

  Now, both the switching element Q2 of the switching element S2 and the switching element Q3 of the switching element S3 of the series resonant converter system shown in FIG. 1 are off, and the switching element Q1 of the switching element S1 and the switch of the switching element S4 Assume that both of the elements Q4 are turned on. Among the states where both the switching element Q1 of the switching element S1 and the switching element Q4 of the switching element S4 are turned on, the circuit shown in FIG. 3A is formed in the state from the time point t1 to the time point t2 in FIG. A sinusoidal current flows due to resonance between the resonance inductance L and the resonance capacitors Ca and Cb. The arrow in FIG. 3A indicates the direction of current.

  Since the output voltage Eo is low, in this state, when the resonance capacitor Cb is charged to the output voltage Eo and the resonance capacitor Ca is discharged to 0 V at time t2 in FIG. 4, the circuit of FIG. 3B is formed. Is done. That is, the reverse charge suppression diodes Da and Dd are turned on, and no current flows through the resonance capacitors Ca and Cb, so that resonance stops. That is, the resonance inductance L is applied with the voltage of the input voltage Ein− (N1 / N2) Eo, and the current becomes linear. N1 / N2 is the turn ratio of the transformer T. In this case, the current does not decrease as the output voltage Eo decreases.

  Next, assuming that the switching element Q4 of the switching element S4 is turned off first at time t3 in FIG. 4, the circuit in FIG. 3C is formed. A current flows through the switching element Q1 of the switching element S1, and the voltage of the parallel capacitor C4 increases and the voltage of the parallel capacitor C3 decreases due to resonance between the resonance inductance L and the parallel capacitors C3 and C4 of the switching elements S3 and S4. To do.

  Then, when the voltage of the parallel capacitor C3 becomes 0V, the circuit of FIG. 3D is formed, the antiparallel diode D3 of the switching element S3 becomes conductive, the voltage applied to the transformer T becomes almost 0V, and the resonance inductance L The voltage applied to is-(N1 / N2) Eo. Therefore, the current decreases linearly (time points t3 to t4 in FIG. 4).

  When the currents of the reverse charge suppression diode Da and the unidirectional element Dd become 0 A, the reverse charge suppression diodes Da and Db are cut off and no current flows on the secondary side. Thereby, the circuit of FIG. 3E is formed. At this time, the exciting current of the transformer T flows through the switch element Q1 and the parallel diode D3. If the switching element Q1 of the switching element S1 is turned off in a state where this exciting current is flowing, the exciting current is very small, so that it can be practically turned off with zero current.

  Next, if the switching element Q1 of the switching element S1 is turned off at time t5 in FIG. 4, the circuit of FIG. 3 (f) is formed, and the voltage of the parallel capacitor C1 is generated by resonance by the resonance inductance L and the parallel capacitors C1 and C2. Increases, and the voltage of the parallel capacitor C2 decreases. At this time, a current also flows through the resonance capacitors Ca and Cb. However, since the capacitances of the resonance capacitors Ca and Cb are much larger than the capacitances of the parallel capacitors C1 and C2, the resonance is hardly affected. Therefore, the voltage of the parallel capacitor C2 can be lowered to 0V by adjusting the value of the excitation inductance of the transformer to an appropriate value of the excitation current. In this case, the energy stored in the parallel capacitor C2 of the switching element S2 is regenerated in the DC power source 12, and therefore hardly loses.

  In FIG. 5, if the switching element Q1 of the switching element S1 is turned off at time t5, the parallel capacitor C1 of the switching element S1 is charged due to resonance by the resonance inductance L and the parallel capacitors C1 and C2. Still has current. When charging of the parallel capacitor C1 ends at time t51 and no current flows through the switching element S1, the voltage across the switching element S1 becomes the input voltage Ein. The time from when the switching element Q1 of the switching element S1 is turned off until no current flows through the parallel capacitor C1, that is, until no current flows through the switching element S1, is the minimum dead time Td0.

  On the other hand, if the switching element S2 of the same leg as the switching element S1 is turned off at the time t5, the switching element S1 is turned off by the resonance inductance L and the parallel capacitors C1 and C2, and the parallel capacitor C2 of the switching element S2. Is discharged and the voltage of the parallel capacitor C2 drops. At time t51, the parallel capacitor C2 is completely discharged, and when the voltage of the parallel capacitor C2 becomes 0 V, the antiparallel diode D2 is turned on, and the circuit shown in FIG. 3G is formed.

  When the anti-parallel diode D2 is conducting, that is, an on signal is given to the switching element Q2 of the switching element S2 at the time t6 after the minimum dead time Td0 has elapsed since the switching element Q1 of the switching element S1 is turned off. Thus, the dead time Td is set so as to be in a conductive state. Since the switching element Q2 of the switching element S2 is rendered conductive in the forward direction when the antiparallel diode D2 is conducting, the switching element Q2 can be turned on with zero voltage when current starts to flow in the forward direction.

  As described above, in the embodiment of the present invention, the switch element Q1 of the switching element S1 that is turned on is turned off at the time t5 when only the excitation current flows. The timing at which the switching element S1 is turned off is the timing at which the switching element S1 is turned off later than the switching element S4, and is determined by appropriately setting the dead time Td. The dead time Td is the time from when the switching element Q1 of the switching element S1 is turned off to when the switching element Q2 of the switching element S2 is brought into a conductive state.

  In this way, the voltage of the switching element S2 to be turned on is lowered to zero, and the switching element S2 is turned on at the time t6 when the antiparallel diode D2 is turned on after the time t51 when the voltage of the switching element S2 becomes zero. An ON signal is given to make it conductive. Accordingly, the switching element S2 can be turned on with zero voltage, so that no switching loss occurs.

  As shown in FIG. 5, when the switching element S2 is turned on by applying an ON signal to the switching element S2 at time t6 when the antiparallel diode D2 is conducting, the switching element of the switching element is an element capable of conducting in the reverse direction. In addition, if the impedance of the switch element is smaller than that of the antiparallel diode, a current flows through the switch element in the reverse direction. When the reverse current flowing through the switch element becomes zero, the switch element is conducted in the forward direction. The current loss can be reduced by the current flowing through the switch element having a smaller impedance than the antiparallel diode.

  In the above description, the ON time To of the switching elements S3 and S4 of the upper and lower arms of the leg 14b is fixed, and the dead time Td during which both the switching elements S1 and S2 of the upper and lower arms of the leg 14a are OFF is fixed. The same applies to the case where the ON time To with the switching elements S1, S2 of the upper and lower arms of the leg 14a is fixed and the dead time Td during which both the switching elements S3, S4 of the upper and lower arms of the leg 14b are OFF is fixed. . The on-time To of the switching elements S1 and S3 of the upper arms of the two legs 14a and 14b is fixed, and the dead time Td of the switching elements S2 and S4 of the lower arms of the legs 14a and 14b, that is, the switching elements of the lower arm The time from when the switching element Q2 (Q4) of S2 (S4) is turned off to when the switching element Q1 (Q3) of the switching element S1 (S3) of the other upper arm is rendered conductive may be fixed. . Similarly, the on-time To of the switching elements S2 and S4 of the lower arms of the two legs 14a and 14b may be fixed, and the dead time Td of the switching elements S1 and S3 of the upper arms of the legs 14a and 14b may be fixed. Also, as shown in FIG. 6, the dead time of the upper and lower arm switching elements is fixed for each of the two legs, and the upper arm switching element of one leg and the lower arm switching element of the other leg are combined. You may make it fix the ON time which is ON simultaneously.

  FIG. 6 is a timing chart showing another example of the on / off control of the switching element in the embodiment of the present invention. As shown in FIG. 6, the dead time Td of the switching elements S1, S2 and the dead time Td of the switching elements S3, S4 are fixed, and the switching element S1 (S2) and the switching element S4 (S3) are turned on simultaneously. Frequency modulation is performed by shifting the phase (phase shift) so that the time To becomes constant. In this case, the same effect as that shown in FIG. 2 can be obtained.

  In the embodiment of the present invention, the switching element Q1 (Q3) of the switching element S1 (S3) of the upper arm of the first or second leg and the switching element of the lower arm of the second or first leg that form a pair. Although an example in which an ON signal is simultaneously applied to the switching element Q4 (Q2) of S4 (S2) has been shown, the current flows in the antiparallel diode D1 (D3) and the antiparallel diode D4 (D2). It does not have to be at the same time.

  As described above, according to the embodiment of the present invention, with respect to the series resonant converter shown in FIG. 5 of Patent Document 1, the function of making the voltage applied to the switching element almost zero immediately before the switching element is turned on ( Zero voltage switching) and the ability to reduce the switching loss at the time of turn-off of two of the four switching elements even when used in a wide output voltage range, the control device 15 has the number of parts. Without increasing it, power loss at turn-off or turn-on can be reduced and power efficiency can be improved.

  The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Transformer, 11a ... Primary winding, 11b ... Secondary winding, 12 ... DC power supply, 13 ... Inverter circuit, S1-S4 ... Switching element, 14 ... Leg, Q1-Q4 ... Switch element, D1-D4 ... Reverse parallel diode, C1 to C4 ... Parallel capacitor, L ... Resonance inductance, Ca, Cb ... Resonance capacitor, Da, Db ... Reverse charge suppression diode, Dc, Dd ... Unidirectional element, Cc ... Smoothing capacitor, 15 ... Controller

Claims (5)

A bridge circuit in which a first leg and a second leg having switching elements as upper and lower arms are connected in parallel between DC power sources, an anti-parallel diode connected in anti-parallel to each of the switching elements, and the switching element Each having a parallel capacitor connected in parallel to each other, and the switching elements of the upper arm of the first or second leg and the switching elements of the lower arm of the second or first leg are alternately assembled into a set. An inverter circuit that converts the direct current input from the direct current power source into alternating current;
A transformer having a primary winding and a secondary winding, the alternating current converted by the inverter circuit being input to the primary winding and output from the secondary winding;
A pair of resonant capacitors connected to one terminal of the secondary winding of the transformer and connected in series between two output terminals;
A pair of reverse charge suppression elements connected in parallel to the pair of resonant capacitors, respectively, to prevent each resonant capacitor from being charged in reverse polarity;
Connected to the other terminal of the secondary winding of the transformer, connected in series between the two output terminals, and prevents current from being fed back from the pair of resonant capacitors to the DC power supply. A pair of unidirectional elements;
A resonant inductance that acts in series with the pair of resonant capacitors to resonate;
In the on / off control of the switching elements constituting the set alternately, the switching elements of the upper arm of the first or second leg and the lower arm of the second or first leg that are in the on state are switched. And a control device for turning off the switching element that is turned off after the current flowing in the switching element that is turned off with delay is turned off after the current flowing through the switching element that is turned off with delay becomes the exciting current of the transformer. A series resonance type converter system.   The control device is configured such that the discharge current of the parallel capacitor connected in parallel with the switching element of the arm to be delayed and turned off after the switching element of the arm to be turned off and delayed is ended after the end of the ON signal. The switching element to be turned on of the switching element of the other arm and the other set of switching elements while flowing to the antiparallel diode of the switching element of the other arm of the same leg as the switching element of the arm turned off and delayed The series resonance type converter system according to claim 1, wherein an on signal is provided.   The control device fixes an ON signal of a switching element to be turned off first among the switching elements in the group, and delays and turns off after completion of an ON signal of the switching element to be turned off among the switching elements in the group. 2. The series resonance type converter system according to claim 1, wherein a dead time of the delayed switching element until the ON signal is given to the switching element of the other arm of the same leg as the switching element of the arm is fixed.   The control device fixes the dead times of the four switching elements that do not give an ON signal to both of the upper and lower arm switching elements for each of the two legs, and switches the upper arm of the one leg that forms a pair. 2. The series resonance type converter system according to claim 1, wherein a time during which an ON signal is simultaneously applied to the element and the switching element of the lower arm of the other leg is fixed.   3. The series resonance according to claim 2, wherein the switch element in the switching element having an impedance smaller than that of the antiparallel diode through which the exciting current of the transformer flows is made to conduct in the reverse direction and then conducted in the forward direction. Type converter system.

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