A foreword

I have proposed one kind is mixed with the high-current DC-DC converter of parallel undervoltage, its primary side adopts the structure of symmetrical semi-bridge, and secondaly side adopts the current-doubling to commutate the structure. Can reduce the electric current ripple on the Filtering capacitance greatly while adopting this kind of structure, thus has reduced and filtered the size of inductive magnitude and whole DC-DC converter greatly. This kind of converter operates the environment in the switching frequency of input voltage and 100kHz of 48V.

Structural analysis of the high-current DC-DC converter of rect. undervoltage of 2 current-doubling

The schematic circuit diagram that the current-doubling commutates the high-current DC-DC converter of undervoltage is shown as in Fig. 1, primary side adopts the structure of symmetrical semi-bridge, secondaly side adopts the current-doubling to commutate the structure, SR1 must end when S1 turns on, L1 charges; SR2 must end when S2 turns on, L2 charges, so filtering inductive current will transplant on the Filtering capacitance and superpose. Fig. 2 provides the control strategy of the switch.

Schematic circuit diagram of the high-current DC-DC converter of rect. undervoltage of the current-doubling of Fig. 1

Control strategy of switch of Fig. 2

Can be found out through the above-mentioned analysis, the current-doubling commutates 2 pieces of filtering inductive current of structural secondaly side to superpose on the Filtering capacitance each other, thus make the output current ripple quite small.

Synchronous rectifier in the structure drive, deal with according to extra signal, make it become it very much complicated not to control, but simple to use in this kind of semi-bridge – topological structure of current-doubling since the driving means is very difficult, because in the structure, fetch appropriate the intersection of point and driving signal in synchronous rectifier in circuit directly, , for zero hour, synchronous rectifier will end as the driving signal within Dead Time. In order to use in the semi-bridge – topological structure of current-doubling from the driving means, must use the auxiliary winding.

Take single semi-bridge – topological structure of current-doubling as examples, see Fig. 3, VSEC is the voltage of secondaly side of the voltage transformer, Vgs for driving voltage of synchronous rectifier that obtain by auxiliary winding, can find out even during the time of the inert zone, the driving voltage of the synchronous rectifier can not be zero either, guarantee it from the application of the driving means in this kind of topological structure.

Self-driving synchronous rectifier circuit of Fig. 3 and oscillogram

In addition, because MOSFET turns on pressure drop and increases in case of heavy current, thus will produce the greater feed-through to loss, for this reason should adopt a plurality of MOSFET to connect the method in parallel to reduce lossing.

3 interlocks and connects the high-current DC-DC converter of undervoltage in parallel

3.1 Schematic circuit diagram

In sum, it has very good characteristics that the current-doubling commutates the high-current DC-DC converter of undervoltage, introduce and mixed with connecting technology in parallel on this basis, form a kind of new structure, called and connected the high-current DC-DC converter of undervoltage in parallel, can further reduce the output current ripple.

Fig. 4 interlocks and connects the schematic circuit diagram of the high-current DC-DC converter of undervoltage commutate and interlock to connect in parallel for the example with simplest 2 pieces of current-doubling in parallel .

Fig. 4 interlocks and connects the schematic circuit diagram of the high-current DC-DC converter of undervoltage in parallel

3.2 Switch control strategy of the converter

Mixed with the switch control strategy of connecting the high-current DC-DC converter of undervoltage in parallel being shown in Fig. 5.

Fig. 5 interlocks and connects the switch control strategy of the high-current DC-DC converter of undervoltage in parallel

3.3 Interlock and connect the high-current DC-DC converter characteristic of undervoltage in parallel

The advantage of this kind of topological structure maximum is the structure reduction of the primary side of the voltage transformer at first, it becomes very simple to control. Secondly, the realization of this method must adopt the synchronous rectifying circuit, because interlock the realization of the parallel circuit require upper and lower electric potential of secondary of voltage transformer to take turns in order that, there is one as the positive potential within a time quantum, the others are all zero potential. But in this kind of topological structure, because the primary sides of 2 voltage transformers connect in series together, and the secondary is parallel, so function as the rectifier if with the Schottky diode, then the input voltage, in the partial pressure of original edge of 2 voltage transformers, but the Schottky diode does not have a gated function, in this way the waveform of the voltage transformer secondaly side will be totally symmetric, the upper and lower complete reclosing of electric current of 2 pieces of rectifying circuit, it is mixed with the parallel purpose to reach the electric current.

In this way, employ the synchronous rectifier to finish this function, utilize the two-way conductive characteristic of MOSFET at the same time, to it leaks source currents to be distributed in both sides of coordinate abscissa axis synchronous rectifier tube. The detailed analysis of such structural course is as follows:

1S1 turns on, S2 ends; S3 ends, S4, S5, S6 turns on. Because of S4, S5, the feed-through of S6, the first voltage transformer secondary coil lower end is the zero potential, on the second voltage transformer secondary coil, the lower end is the zero potential, the inductance L1 upper electric current rises, L2, L3, L4 upper electric current drops.

2S2 turns on, S1 ends; S4 ends, S3, S5, S6 turns on. Because of S3, S5, the feed-through of S6, on the first voltage transformer secondary coil is the zero potential, on the second voltage transformer secondary coil, the lower end is the zero potential, the inductance L2 upper electric current rises, L1, L3, L4 upper electric current drops.

3S1 turns on, S2 ends; S5 ends, S3, S4, S6 turns on. Because of S3, S4, the feed-through of S6, the second voltage transformer secondary coil lower end is the zero potential, on the first voltage transformer secondary coil, the lower end is the zero potential, the inductance L3 upper electric current rises, L1, L2, L4 upper electric current drops.

4S2 turns on, S1 ends; S6 ends, S3, S4, S5 turns on. Because of S3, S4, the feed-through of S5, on the second voltage transformer secondary coil is the zero potential, on the first voltage transformer secondary coil, the lower end is the zero potential, the inductance L4 upper electric current rises, L1, L2, L3 upper electric current drops.

Various types of the above neglects the voltage drop of the rectifier, and VSEC is the magnitude of voltage of the voltage transformer secondaly side.

According to the above-mentioned analysis being knowing, employ synchronous rectifier, connect in series through the primary side of the voltage transformer and parallel method of secondary, can realize this kind interlocks and connects the semi-bridge – topological structure of current-doubling in parallel. Its advantage mainly has the following several respect:

1Have simplified topological structure and control strategy effectively.

2In a situation that the frequency maitains unchanged, if peak-peak value of the ripple must, this kind of structure can reduce and filter the inductive value effectively, thus accelerate the dynamic response time of the whole converter.

3It is mixed with the parallel semi-bridge – topological structure of current-doubling to compare to mixed with the parallel semi-bridge – topological structure AND NOT of current-doubling, primary side and feed-through of secondaly side loss similarly, but because adopt and mixed with connecting technology in parallel, the switching frequency of secondaly side is original half, the corresponding switching loss is original half too. Because the switching loss of the converter takes very large proportion in the whole loss is counted, so, interlock and connect the efficiency that technology can raise the converter greatly in parallel.

4 simulation analysis

Employ Pspice software to carry on emulation to the circuit. The parameter of the circuit is as follows: Switching frequency is 100kHz, the duty ratio is 40%, the input voltage is 48V, the filtering inductance is 2 H, the Filtering capacitance is 820 F, the output current is 60A, the output voltage is 1125V.

Fig. 6 shows in order to filter the inductive electric current waveform, can be found out from Fig. 6, 4 filtering inductive electric current is charged in turn, if a filtering inductance is being charged, other 3 pieces of inductance must be discharging, within Dead Time, 4 pieces of filtering inductance are discharging.

7 Fig. and respectively for interlock, connect converter and single current-doubling in parallel, commutate the intersection of converter and structural the intersection of output current and the intersection of ripple and waveform 8 of Fig., can be found out from Fig. 7, 4 filtering inductive electric current is superposed on the Filtering capacitance, can reduce the ripple of the electric current a lot.

Filtering inductive current waveform of Fig. 6

Fig. 7 interlocks and connects the structural output current ripple waveform of the converter in parallel

The single current-doubling of Fig. 8 commutates the structural output current ripple waveform of the converter

5 experimental results

Through theoretical research and simulation analysis, can find out, it has good characteristics that mixed with the high-current DC-DC converter of parallel undervoltage, on condition that output as 1125V/60A, the output current ripple can be dropped to very small. In order to further explain such topological structural feasibility, prove with the experimental result. The circuit of experiment is shown in Fig. 4, experimental parameter and artificial and the same, received the experiment waveform shown in Fig. 9 finally. In Fig. 9, Vgs drives the voltage waveform for the gate electrode of one MOSFET of primary side, Vds is the bar source voltage waveform of corresponding MOSFET, can be found out from Fig. 9, the theory analysis results of resulting waveform of experimental result and Fig. 5 are very identical, methods put forward are feasible. Among them, the voltage transformer selects GU22 magnetic core made of R2KB soft magnetic ferrite, the turn of the original secondary side is 8 circles and 1 circle respectively; The inductance selects the ring shaped core T5-10-215 made of wide permanent magnetic conductive material IJ50h, the turn is 8 circles.

Experiment waveform of Fig. 9

Through emulation and experimental analysis, draw the following conclusions: As to the high-current DC-DC converter of undervoltage, can be by it is parallel to be mixed withing, further reduce the output current ripple, the result is very obvious; Or in case of same output current ripple, can reduce the filtering electricity greatly

A foreword

I have proposed one kind is mixed with the high-current DC-DC converter of parallel undervoltage, its primary side adopts the structure of symmetrical semi-bridge, and secondaly side adopts the current-doubling to commutate the structure. Can reduce the electric current ripple on the Filtering capacitance greatly while adopting this kind of structure, thus has reduced and filtered the size of inductive magnitude and whole DC-DC converter greatly. This kind of converter operates the environment in the switching frequency of input voltage and 100kHz of 48V.

Structural analysis of the high-current DC-DC converter of rect. undervoltage of 2 current-doubling

The schematic circuit diagram that the current-doubling commutates the high-current DC-DC converter of undervoltage is shown as in Fig. 1, primary side adopts the structure of symmetrical semi-bridge, secondaly side adopts the current-doubling to commutate the structure, SR1 must end when S1 turns on, L1 charges; SR2 must end when S2 turns on, L2 charges, so filtering inductive current will transplant on the Filtering capacitance and superpose. Fig. 2 provides the control strategy of the switch.

Schematic circuit diagram of the high-current DC-DC converter of rect. undervoltage of the current-doubling of Fig. 1

Control strategy of switch of Fig. 2

Can be found out through the above-mentioned analysis, the current-doubling commutates 2 pieces of filtering inductive current of structural secondaly side to superpose on the Filtering capacitance each other, thus make the output current ripple quite small.

Synchronous rectifier in the structure drive, deal with according to extra signal, make it become it very much complicated not to control, but simple to use in this kind of semi-bridge – topological structure of current-doubling since the driving means is very difficult, because in the structure, fetch appropriate the intersection of point and driving signal in synchronous rectifier in circuit directly, , for zero hour, synchronous rectifier will end as the driving signal within Dead Time. In order to use in the semi-bridge – topological structure of current-doubling from the driving means, must use the auxiliary winding.

Take single semi-bridge – topological structure of current-doubling as examples, see Fig. 3, VSEC is the voltage of secondaly side of the voltage transformer, Vgs for driving voltage of synchronous rectifier that obtain by auxiliary winding, can find out even during the time of the inert zone, the driving voltage of the synchronous rectifier can not be zero either, guarantee it from the application of the driving means in this kind of topological structure.

Self-driving synchronous rectifier circuit of Fig. 3 and oscillogram

In addition, because MOSFET turns on pressure drop and increases in case of heavy current, thus will produce the greater feed-through to loss, for this reason should adopt a plurality of MOSFET to connect the method in parallel to reduce lossing.

3 interlocks and connects the high-current DC-DC converter of undervoltage in parallel

3.1 Schematic circuit diagram

In sum, it has very good characteristics that the current-doubling commutates the high-current DC-DC converter of undervoltage, introduce and mixed with connecting technology in parallel on this basis, form a kind of new structure, called and connected the high-current DC-DC converter of undervoltage in parallel, can further reduce the output current ripple.

Fig. 4 interlocks and connects the schematic circuit diagram of the high-current DC-DC converter of undervoltage commutate and interlock to connect in parallel for the example with simplest 2 pieces of current-doubling in parallel .

Fig. 4 interlocks and connects the schematic circuit diagram of the high-current DC-DC converter of undervoltage in parallel

3.2 Switch control strategy of the converter

Mixed with the switch control strategy of connecting the high-current DC-DC converter of undervoltage in parallel being shown in Fig. 5.

Fig. 5 interlocks and connects the switch control strategy of the high-current DC-DC converter of undervoltage in parallel

3.3 Interlock and connect the high-current DC-DC converter characteristic of undervoltage in parallel

The advantage of this kind of topological structure maximum is the structure reduction of the primary side of the voltage transformer at first, it becomes very simple to control. Secondly, the realization of this method must adopt the synchronous rectifying circuit, because interlock the realization of the parallel circuit require upper and lower electric potential of secondary of voltage transformer to take turns in order that, there is one as the positive potential within a time quantum, the others are all zero potential. But in this kind of topological structure, because the primary sides of 2 voltage transformers connect in series together, and the secondary is parallel, so function as the rectifier if with the Schottky diode, then the input voltage, in the partial pressure of original edge of 2 voltage transformers, but the Schottky diode does not have a gated function, in this way the waveform of the voltage transformer secondaly side will be totally symmetric, the upper and lower complete reclosing of electric current of 2 pieces of rectifying circuit, it is mixed with the parallel purpose to reach the electric current.

In this way, employ the synchronous rectifier to finish this function, utilize the two-way conductive characteristic of MOSFET at the same time, to it leaks source currents to be distributed in both sides of coordinate abscissa axis synchronous rectifier tube. The detailed analysis of such structural course is as follows:

1S1 turns on, S2 ends; S3 ends, S4, S5, S6 turns on. Because of S4, S5, the feed-through of S6, the first voltage transformer secondary coil lower end is the zero potential, on the second voltage transformer secondary coil, the lower end is the zero potential, the inductance L1 upper electric current rises, L2, L3, L4 upper electric current drops.

2S2 turns on, S1 ends; S4 ends, S3, S5, S6 turns on. Because of S3, S5, the feed-through of S6, on the first voltage transformer secondary coil is the zero potential, on the second voltage transformer secondary coil, the lower end is the zero potential, the inductance L2 upper electric current rises, L1, L3, L4 upper electric current drops.

3S1 turns on, S2 ends; S5 ends, S3, S4, S6 turns on. Because of S3, S4, the feed-through of S6, the second voltage transformer secondary coil lower end is the zero potential, on the first voltage transformer secondary coil, the lower end is the zero potential, the inductance L3 upper electric current rises, L1, L2, L4 upper electric current drops.

4S2 turns on, S1 ends; S6 ends, S3, S4, S5 turns on. Because of S3, S4, the feed-through of S5, on the second voltage transformer secondary coil is the zero potential, on the first voltage transformer secondary coil, the lower end is the zero potential, the inductance L4 upper electric current rises, L1, L2, L3 upper electric current drops.

Various types of the above neglects the voltage drop of the rectifier, and VSEC is the magnitude of voltage of the voltage transformer secondaly side.

According to the above-mentioned analysis being knowing, employ synchronous rectifier, connect in series through the primary side of the voltage transformer and parallel method of secondary, can realize this kind interlocks and connects the semi-bridge – topological structure of current-doubling in parallel. Its advantage mainly has the following several respect:

1Have simplified topological structure and control strategy effectively.

2In a situation that the frequency maitains unchanged, if peak-peak value of the ripple must, this kind of structure can reduce and filter the inductive value effectively, thus accelerate the dynamic response time of the whole converter.

3It is mixed with the parallel semi-bridge – topological structure of current-doubling to compare to mixed with the parallel semi-bridge – topological structure AND NOT of current-doubling, primary side and feed-through of secondaly side loss similarly, but because adopt and mixed with connecting technology in parallel, the switching frequency of secondaly side is original half, the corresponding switching loss is original half too. Because the switching loss of the converter takes very large proportion in the whole loss is counted, so, interlock and connect the efficiency that technology can raise the converter greatly in parallel.

4 simulation analysis

Employ Pspice software to carry on emulation to the circuit. The parameter of the circuit is as follows: Switching frequency is 100kHz, the duty ratio is 40%, the input voltage is 48V, the filtering inductance is 2 H, the Filtering capacitance is 820 F, the output current is 60A, the output voltage is 1125V.

Fig. 6 shows in order to filter the inductive electric current waveform, can be found out from Fig. 6, 4 filtering inductive electric current is charged in turn, if a filtering inductance is being charged, other 3 pieces of inductance must be discharging, within Dead Time, 4 pieces of filtering inductance are discharging.

Fig. 7 and Fig. 8 show and commutate the structural output current ripple waveform of the converter in order to interlock to connect converter and single current-doubling in parallel respectively, can be found out from Fig. 7, 4 filtering inductive electric current is superposed on the Filtering capacitance, can reduce the ripple of the electric current a lot.

Filtering inductive current waveform of Fig. 6

Fig. 7 interlocks and connects the structural output current ripple waveform of the converter in parallel

The single current-doubling of Fig. 8 commutates the structural output current ripple waveform of the converter

5 experimental results

Through theoretical research and simulation analysis, can find out, it has good characteristics that mixed with the high-current DC-DC converter of parallel undervoltage, on condition that output as 1125V/60A, the output current ripple can be dropped to very small. In order to further explain such topological structural feasibility, prove with the experimental result. The circuit of experiment is shown in Fig. 4, experimental parameter and artificial and the same, received the experiment waveform shown in Fig. 9 finally. In Fig. 9, Vgs drives the voltage waveform for the gate electrode of one MOSFET of primary side, Vds is the bar source voltage waveform of corresponding MOSFET, can be found out from Fig. 9, the theory analysis results of resulting waveform of experimental result and Fig. 5 are very identical, methods put forward are feasible. Among them, the voltage transformer selects GU22 magnetic core made of R2KB soft magnetic ferrite, the turn of the original secondary side is 8 circles and 1 circle respectively; The inductance selects the ring shaped core T5-10-215 made of wide permanent magnetic conductive material IJ50h, the turn is 8 circles.

Experiment waveform of Fig. 9

Through emulation and experimental analysis, draw the following conclusions: As to the high-current DC-DC converter of undervoltage, can be by it is parallel to be mixed withing, further reduce the output current ripple, the result is very obvious; Or in case of same output current ripple, can reduce the filtering inductance greatly, thus reduce the size of the whole converter and improve the transient response characteristic of the converter. 2 pieces of current-doubling discussed commutate the structure and interlock and connect the case in parallel to accommodate a plurality of current-doubling and commutate the structure and mixed with the parallel situation too.