Control method of hybrid bridge converter

Abstract

The invention discloses a control method of a hybrid bridge converter, and the hybrid bridge converter comprises a first full-bridge circuit, a second full-bridge circuit, a transformer T1, a transformer T2, a three-bridge-arm rectification circuit, an output filter inductor L, and an output capacitor Co. And the secondary side of the hybrid bridge type converter is rectified by a three-bridge-arm rectifying circuit and then transmits the energy to the output through an output filter inductor. According to the control method disclosed by the invention, the reverse recovery of the secondary side rectifying circuit can be maintained in a minimum state in a full input / output voltage range. Therefore, the reverse recovery loss and the peak voltage stress of the rectification circuit are small, the model selection difficulty and the material cost of the rectification circuit are greatly reduced, the power conversion efficiency and the reliability of the product are improved, and the localization of the device is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply, in particular to a control method of hybrid bridge converter. BACKGROUND

[0002] For high power switching power supply, usually adopts bridge circuit topology. But the disadvantage of bridge circuit topology is that when used in wide input voltage range, if the output voltage is higher, the voltage stress platform of rectifier circuit is larger, the reverse recovery loss and stress peak of power tube is also larger, and the power device is difficult to select.

[0003] Based on this, the 2006 IEEE paper entitled "Extra Wide Input Voltage Range and High Efficiency DC-DC Converter Using Hybrid Modulation" proposes a hybrid bridge converter, the primary side adopts two parallel full-bridge circuits, the secondary side adopts series transformer, after rectification by three bridge arms rectifier circuit, the energy is transmitted to the output filter capacitor for filtering and output through the output filter inductor, as shown in the figure. Figure 1 The circuit can realize series operation and parallel operation of two-way full-bridge circuit transformer output end, when the input voltage is low, the secondary side of two-way transformer works in series, the gain is larger, when the input voltage is high, the secondary side of two-way transformer can work alternately, thereby reducing the voltage stress platform of secondary side rectifier tube.

[0004] The existing control technology scheme of hybrid bridge converter is mainly based on the condition that the turns ratio of the primary side two-way transformer is the same. When the turns ratio of the primary side two-way transformer is different, the existing control scheme cannot maintain the reverse recovery of the secondary side rectifier circuit at the minimum state in the full input / output voltage range. The main performance is that in the alternating working state of the first full-bridge circuit and the second full-bridge circuit, the rectifier circuit voltage of the secondary side is directly raised from 0V to the final stress platform. And since the rectifier circuit voltage stress platform is inversely proportional to the transformer turns ratio, the smaller the turns ratio, the larger the stress platform, and the larger the reverse recovery of the power tube. Therefore, for the full-bridge with small turns ratio, the poor reverse recovery characteristic is a problem that the current scheme has not solved. SUMMARY

[0005] In view of the technical defects of the existing hybrid bridge converter, the technical problem to be solved by the present application is to propose a control method of hybrid bridge converter, which can maintain the reverse recovery of the secondary side rectifier circuit at the minimum state in the full input / output voltage range without increasing additional devices.

[0006] In order to achieve the above application purpose, the application concept of the present application is:

[0007] In a first aspect, the present application provides a control method of a hybrid bridge converter, the hybrid bridge converter comprising a first full-bridge circuit, a second full-bridge circuit, a transformer T1, a transformer T2, a three-bridge rectifier circuit, an output filter inductor L and an output capacitor Co, the first full-bridge circuit comprising a power tube S1, a power tube S2, a power tube S3 and a power tube S4, the second full-bridge circuit comprising a power tube S5, a power tube S6, a power tube S7 and a power tube S8;

[0008] The first end of the power tube S1, the first end of the power tube S3, the first end of the power tube S5 and the first end of the power tube S7 are connected to a positive pole of a power supply, the second end of the power tube S2, the second end of the power tube S4, the second end of the power tube S6 and the second end of the power tube S8 are connected to a negative pole of the power supply, the second end of the power tube S1 is connected to the first end of the power tube S2 and the first end of the transformer T1, the second end of the power tube S3 is connected to the first end of the power tube S4 and the second end of the transformer T1, the second end of the power tube S5 is connected to the first end of the power tube S6 and the first end of the transformer T2, the second end of the power tube S7 is connected to the first end of the power tube S8 and the second end of the transformer T2;

[0009] The first input end of the three-bridge rectifier circuit is connected to the third end of the transformer T1, the second input end of the three-bridge rectifier circuit is connected to the fourth end of the transformer T1 and the third end of the transformer T2 respectively, the third input end of the three-bridge rectifier circuit is connected to the fourth end of the transformer T2, the output positive end of the three-bridge rectifier circuit is connected to the first end of the output capacitor Co through the output filter inductor L, and the output negative end of the three-bridge rectifier circuit is connected to the second end of the output capacitor Co;

[0010] The control method comprises:

[0011] When n1

[0012] when n1>n2, in a switching cycle, the power tube S1 and the power tube S3 in the first full-bridge circuit adopt front edge modulation; the power tube S5 and the power tube S7 in the second full-bridge circuit adopt rear edge modulation; wherein, in a switching cycle, the power tube S5 is turned on before the power tube S3 is turned off, and the power tube S7 is turned on before the power tube S1 is turned off;

[0013] wherein, n1 represents the turns ratio of the transformer T1, and n2 represents the turns ratio of the transformer T2.

[0014] Optionally, the power tube S2 and the power tube S1 are driven complementarily; the power tube S4 and the power tube S3 are driven complementarily; the power tube S8 and the power tube S5 are driven identically; and the power tube S6 and the power tube S7 are driven identically.

[0015] Optionally, the control method further comprises:

[0016] when n1<n2, in a switching cycle, the following steps are performed:

[0017] a first stage: turning on the power tube S1, and turning off the power tube S7 after the power tube S1 is turned on;

[0018] a second stage: turning on the power tube S5 after the power tube S7 is turned off;

[0019] a third stage: turning off the power tube S1, and turning on the power tube S3 after the power tube S1 is turned off;

[0020] a fourth stage: turning off the power tube S5 after the power tube S3 is turned on;

[0021] a fifth stage: turning on the power tube S7 after the power tube S5 is turned off;

[0022] when n1>n2, in a switching cycle, the following steps are performed:

[0023] a first stage: turning on the power tube S5, and turning off the power tube S3 after the power tube S5 is turned on;

[0024] a second stage: turning on the power tube S1 after the power tube S3 is turned off;

[0025] a third stage: turning off the power tube S5, and turning on the power tube S7 after the power tube S5 is turned off;

[0026] a fourth stage: turning off the power tube S1 after the power tube S7 is turned on;

[0027] The fifth stage: after the power tube S1 is turned off, the power tube S3 is turned on.

[0028] Optionally, the control method further comprises:

[0029] When n1

[0030] As the input voltage increases, the duty cycles of the power tube S1 and the power tube S3 remain unchanged at 100%, and the duty cycles of the power tube S5 and the power tube S7 gradually decrease from 100%;

[0031] When the duty cycles of the power tube S5 and the power tube S7 decrease to 0, the duty cycles of the power tube S1 and the power tube S3 begin to gradually decrease, and the duty cycles of the power tube S5 and the power tube S7 begin to gradually increase;

[0032] When the duty cycles of the power tube S5 and the power tube S7 increase to the maximum duty cycle limit value, and the duty cycles of the power tube S1 and the power tube S3 have not decreased to 0, the duty cycles of the power tube S5 and the power tube S7 follow the maximum duty cycle limit value;

[0033] When the duty cycles of the power tube S1 and the power tube S3 decrease to 0, the maximum duty cycle of the power tube S5 and the power tube S7 is not limited;

[0034] When n1

[0035] As the input voltage increases, the duty cycles of the power tube S5 and the power tube S7 remain unchanged at 100%, and the duty cycles of the power tube S1 and the power tube S3 gradually decrease from 100%;

[0036] When the duty cycles of the power tube S1 and the power tube S3 decrease to 0, the duty cycles of the power tube S5 and the power tube S7 begin to gradually decrease, and the duty cycles of the power tube S1 and the power tube S3 begin to gradually increase;

[0037] When the duty cycles of the power tube S1 and the power tube S3 increase to the maximum duty cycle limit value, and the duty cycles of the power tube S5 and the power tube S7 have not decreased to 0, the duty cycles of the power tube S1 and the power tube S3 follow the maximum duty cycle limit value;

[0038] When the duty cycles of the power tube S5 and the power tube S7 decrease to 0, the maximum duty cycle of the power tube S1 and the power tube S3 is not limited.

[0039] Optionally, the maximum duty cycle limit value is a ratio of a volt-second product K and an input voltage Vin, wherein the volt-second product K is a preset value.

[0040] In a second aspect, the present application provides a control method of a hybrid bridge converter, the hybrid bridge converter comprising a first half-bridge circuit, a second half-bridge circuit, a transformer T1, a transformer T2, a three-bridge rectifier circuit, an output filter inductor L and an output capacitor Co, the first half-bridge circuit comprising a capacitor C1, a capacitor C2, a power tube S3 and a power tube S4, the second half-bridge circuit comprising a capacitor C5, a capacitor C6, a power tube S7 and a power tube S8, the three-bridge rectifier circuit comprising a power tube D1, a power tube D2, a power tube D3, a power tube D4, a power tube D5 and a power tube D6;

[0041] The first end of the capacitor C1, the first end of the power tube S3, the first end of the capacitor C5 and the first end of the power tube S7 are connected to a positive pole of a power supply, the second end of the capacitor C2, the second end of the power tube S4, the second end of the capacitor C6 and the second end of the power tube S8 are connected to a negative pole of the power supply, the second end of the capacitor C1 is connected to the first end of the capacitor C2 and the first end of the transformer T1, the second end of the power tube S3 is connected to the first end of the power tube S4 and the second end of the transformer T1, the second end of the capacitor C5 is connected to the first end of the capacitor C6 and the first end of the transformer T2, the second end of the power tube S7 is connected to the first end of the power tube S8 and the second end of the transformer T2;

[0042] The first end of the power tube D1, the first end of the power tube D3 and the first end of the power tube D5 are connected to the first end of the output filter inductor L, the second end of the power tube D2, the second end of the power tube D4 and the second end of the power tube D6 are connected to the second end of the output capacitor Co, the second end of the power tube D1 is connected to the first end of the power tube D2 and the third end of the transformer T1, the second end of the power tube D3 is connected to the first end of the power tube D4 and the fourth end of the transformer T1, the second end of the power tube D5 is connected to the first end of the power tube D6 and the fourth end of the transformer T2, the fourth end of the transformer T1 is connected to the third end of the transformer T2, and the second end of the output filter inductor L is connected to the first end of the output capacitor Co;

[0043] The control method comprises:

[0044] When n1n2, in a switching cycle, the power tube S4 and the power tube S3 in the first full-bridge circuit adopt trailing edge modulation; the power tube S8 and the power tube S7 in the second full-bridge circuit adopt leading edge modulation; in a switching cycle, the power tube S7 can be turned off only after the power tube S4 is turned on, and the power tube S8 can be turned off only after the power tube S3 is turned on.

[0045] When n1n2, in a switching cycle, the power tube S4 and the power tube S3 in the first full-bridge circuit adopt trailing edge modulation; the power tube S8 and the power tube S7 in the second full-bridge circuit adopt leading edge modulation; in a switching cycle, the power tube S7 can be turned off only after the power tube S4 is turned on, and the power tube S8 can be turned off only after the power tube S3 is turned on.

[0046] Wherein, n1 represents the turns ratio of the transformer T1, and n2 represents the turns ratio of the transformer T2.

[0047] Optionally, the control method further comprises:

[0048] After the power tube S8 is turned on and before the power tube S3 is turned on, the power tube D1 is in a conductive state; after the power tube S7 is turned on and before the power tube S4 is turned on, the power tube D2 is in a conductive state.

[0049] Optionally, the control method further comprises:

[0050] When n1n2, in a switching cycle, the following steps are performed:

[0051] First stage: turn on the power tube S4, and turn off the power tube S7 after the power tube S4 is turned on;

[0052] Second stage: turn on the power tube S8 after the power tube S7 is turned off;

[0053] Third stage: turn off the power tube S4, and turn on the power tube S3 after the power tube S4 is turned off;

[0054] Fourth stage: turn off the power tube S8 after the power tube S3 is turned on;

[0055] Fifth stage: turn on the power tube S7 after the power tube S8 is turned off;

[0056] When n1n2, in a switching cycle, the following steps are performed:

[0057] First stage: turn on the power tube S8, and turn off the power tube S3 after the power tube S8 is turned on;

[0058] Second stage: turn on the power tube S4 after the power tube S3 is turned off;

[0059] Third stage: turn off the power tube S8, and turn on the power tube S7 after the power tube S8 is turned off;

[0060] Fourth stage: turn off the power tube S4 after the power tube S7 is turned on;

[0061] Fifth stage: turn on the power tube S3 after the power tube S4 is turned off.

[0062] Optionally, the control method further comprises:

[0063] When n1

[0064] As the input voltage rises, the duty cycles of the power tube S3 and the power tube S4 remain unchanged at 100%, and the duty cycles of the power tube S8 and the power tube S7 gradually decrease from 100%;

[0065] When the duty cycles of the power tube S8 and the power tube S7 decrease to 0, the duty cycles of the power tube S4 and the power tube S3 start to gradually decrease, and the duty cycles of the power tube S8 and the power tube S7 start to gradually increase;

[0066] When the duty cycles of the power tube S8 and the power tube S7 increase to the maximum duty cycle limit value, and the duty cycles of the power tube S4 and the power tube S3 have not decreased to 0, the duty cycles of the power tube S8 and the power tube S7 follow the maximum duty cycle limit value;

[0067] When the duty cycles of the power tube S3 and the power tube S4 decrease to 0, the maximum duty cycles of the power tube S7 and the power tube S8 are not limited;

[0068] When n1

[0069] As the input voltage rises, the duty cycles of the power tube S8 and the power tube S7 remain unchanged at 100%, and the duty cycles of the power tube S4 and the power tube S3 gradually decrease from 100%;

[0070] When the duty cycles of the power tube S4 and the power tube S3 decrease to 0, the duty cycles of the power tube S8 and the power tube S7 start to gradually decrease, and the duty cycles of the power tube S4 and the power tube S3 start to gradually increase;

[0071] When the duty cycles of the power tube S4 and the power tube S3 increase to the maximum duty cycle limit value, and the duty cycles of the power tube S7 and the power tube S8 are not reduced to 0, the duty cycles of the power tube S4 and the power tube S3 follow the maximum duty cycle limit value.

[0072] When the duty cycles of the power tube S7 and the power tube S8 are reduced to 0, the maximum duty cycle of the power tube S3 is not limited.

[0073] Optionally, the maximum duty cycle limit value is a ratio of a volt-second product K and an input voltage Vin, wherein the volt-second product K is a preset value.

[0074] In a third aspect, the present application further provides a control method of a hybrid bridge converter, the hybrid bridge converter comprising a first bridge circuit, a second bridge circuit, a transformer T1, a transformer T2 and a secondary-side power tube, the control method comprising: when the secondary-side power tube is off, lifting a voltage across the secondary-side power tube to a first voltage first, and then to a second voltage, so as to reduce reverse-recovery loss and stress spikes of the secondary-side power tube, wherein the second voltage is greater than the first voltage.

[0075] Optionally, the control method further comprises: when the first bridge circuit is not working, clamping a voltage across the transformer T1 to 0V, so as to prevent reverse excitation of the second bridge circuit.

[0076] The working principle of the present application will be analyzed in combination with specific embodiments, which will not be described here. Compared with the prior art, the present application has the following beneficial effects:

[0077] 1) The present application can realize full input / output voltage range, and maintain reverse recovery of the secondary-side rectifier circuit in a minimum state. Thus, reverse-recovery loss and stress spikes of the secondary-side rectifier circuit power tube are greatly reduced, which is more conducive to power tube selection and localization, and reduces device cost.

[0078] 2) The present application can improve the problem that when the second full-bridge of the hybrid bridge converter works, the secondary-side voltage of the transformer T2 excites the primary-side coil of the transformer T1 through the secondary-side coil of the transformer T1, which causes the transformer T1 to increase with the input voltage Vin, and the magnetic flux density of the transformer magnetic core increases, thereby reducing the volume of the transformer magnetic core of the first full-bridge converter.

[0079] 3) The present application can limit the maximum output of the full-bridge circuit of the transformer with a large turn ratio by dynamically limiting the duty cycle of the full-bridge circuit, which is more conducive to power stage device selection, magnetic core design, balanced product temperature rise, and improved design flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0080] Figure 1is the circuit principle diagram of the first and second embodiments of the control method of the hybrid bridge converter of the present application;

[0081] Figure 2 is the main control timing and waveform diagram of the first embodiment of the control method of the hybrid bridge converter of the present application with the change of input voltage;

[0082] Figure 3 is the main control timing and waveform diagram of the second embodiment of the control method of the hybrid bridge converter of the present application with the change of input voltage;

[0083] Figure 4 is the circuit principle diagram of the third and fourth embodiments of the control method of the hybrid bridge converter of the present application;

[0084] Figure 5 is the main control timing and waveform diagram of the third embodiment of the control method of the hybrid bridge converter of the present application with the change of input voltage;

[0085] Figure 6 is the main control timing and waveform diagram of the fourth embodiment of the control method of the hybrid bridge converter of the present application with the change of input voltage.

[0086] The above drawings do not limit the scope of the inventive concept, but illustrate the inventive concept to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0087] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below by referring to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application.

[0088] In the hybrid bridge converter of the present application, two full-bridge transformers adopt different turns ratios. Since the voltage stress platform of the rectifier circuit on the secondary side is inversely proportional to the turns ratio of the transformer, the voltage stress platform of the corresponding rectifier circuit on the secondary side of the full-bridge circuit with large turns ratio is small, and the voltage stress platform of the corresponding rectifier circuit on the secondary side of the full-bridge circuit with small turns ratio is large.

[0089] When the hybrid bridge converter works, the full-bridge circuit with large turns ratio works first, and the voltage of the rectifier circuit on the secondary side is raised to a lower voltage stress platform. Then the full-bridge circuit with small turns ratio works, and the voltage of the rectifier circuit on the secondary side is raised from a lower voltage stress platform to the final stress platform, thereby effectively reducing the reverse recovery loss and stress peak of the power tube of the rectifier circuit on the secondary side.

[0090] Meanwhile, the control method improves the hybrid bridge converter, transformer T2 secondary side voltage through transformer T1 secondary side coil excitation to its primary side coil, resulting in transformer T1 core magnetic flux large problem. And synchronous consideration of the input voltage range hybrid bridge converter gain maximization and continuity.

[0091] First embodiment

[0092] Figure 1 For the first embodiment of the hybrid bridge converter of the application, the primary side uses two full-bridge circuits in parallel, and the secondary side uses a three-leg rectifier circuit for rectification, and the energy is transmitted to the output through the output filter inductor.

[0093] The hybrid bridge converter in this embodiment includes a first full-bridge circuit, a second full-bridge circuit, a transformer T1, a transformer T2, a three-leg rectifier circuit, an output filter inductor L and an output capacitor Co, the first full-bridge circuit includes power tubes S1, power tubes S2, power tubes S3 and power tubes S4, the second full-bridge circuit includes power tubes S5, power tubes S6, power tubes S7 and power tubes S8, the three-leg rectifier circuit includes power tubes D1, power tubes D2, power tubes D3, power tubes D4, power tubes D5 and power tubes D6;

[0094] The first end of the power tube S1, the first end of the power tube S3, the first end of the power tube S5 and the first end of the power tube S7 are connected with the positive electrode of the power supply, the second end of the power tube S2, the second end of the power tube S4, the second end of the power tube S6 and the second end of the power tube S8 are connected with the negative electrode of the power supply, the second end of the power tube S1 is connected with the first end of the power tube S2 and the first end of the transformer T1, the second end of the power tube S3 is connected with the first end of the power tube S4 and the second end of the transformer T1, the second end of the power tube S5 is connected with the first end of the power tube S6 and the first end of the transformer T2, the second end of the power tube S7 is connected with the first end of the power tube S8 and the second end of the transformer T2;

[0095] The first end of the power tube D1, the first end of the power tube D3 and the first end of the power tube D5 are connected with the first end of the output filter inductor L, the second end of the power tube D2, the second end of the power tube D4 and the second end of the power tube D6 are connected with the second end of the output capacitor Co, the second end of the power tube D1 is simultaneously connected with the first end of the power tube D2 and the third end of the transformer T1, the second end of the power tube D3 is simultaneously connected with the first end of the power tube D4 and the fourth end of the transformer T1, the second end of the power tube D5 is simultaneously connected with the first end of the power tube D6 and the fourth end of the transformer T2. The fourth end of the transformer T1 is connected with the third end of the transformer T2, and the second end of the output filter inductor L is connected with the first end of the output capacitor Co.

[0096] Wherein, the power tube S1, the power tube S2, the power tube S3, the power tube S4, the power tube S5, the power tube S6, the power tube S7, the power tube S8, the power tube D1, the power tube D2, the power tube D3, the power tube D4, the power tube D5 and the power tube D6 can be MOS tube, triode or IGBT switch device.

[0097] Figure 2 The main control timing and waveform (n1 < n2) of the hybrid bridge converter with the change of input voltage are the first embodiment of the application. Wherein, the turn ratio n1 of the transformer T1 is less than the turn ratio n2 of the transformer T2, V DE The voltage across the two ends of the secondary side three-bridge arm rectifier circuit of the hybrid bridge converter is V AB The winding voltage of the secondary side of the transformer T1 is V BC The winding voltage of the secondary side of the transformer T2 is V.

[0098] The main features of the control timing are:

[0099] The power tube S1 and the power tube S3 of the first full-bridge circuit adopt trailing edge modulation, that is, in a switching cycle, the turn-on time of the power tube S1 and the power tube S3 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S5 and the power tube S7 of the second full-bridge circuit adopt leading edge modulation, that is, in a switching cycle, the turn-off time of the power tube S5 and the power tube S7 is unchanged, and the turn-on time is controlled by pulse width modulation. The power tube S5 can be turned off after the power tube S3 is turned on, and the power tube S7 can be turned off after the power tube S1 is turned on. The power tube S3 and the power tube S5 have overlapping driving, and the power tube S1 and the power tube S7 have overlapping driving. During the overlapping period, the secondary side coils of the transformer T1 and the transformer T2 are in parallel connection.

[0100] Through the control, when the hybrid bridge converter works, the full-bridge circuit with the large turn ratio works first, and the voltage of the rectifier circuit at the secondary side is raised to a lower voltage stress platform. Then the full-bridge circuit with the small turn ratio works, and the voltage of the rectifier circuit at the secondary side is raised from the lower voltage stress platform to the final stress platform, so that the reverse recovery of the power tube at the secondary side is maintained at a minimum state in the input voltage range, and the reverse recovery loss and stress peak are effectively reduced.

[0101] The power tube S3 / power tube S5 drive overlap time and the power tube S1 / power tube S7 drive overlap time are not prone to be too long, and the voltage across the secondary side rectifier bridge circuit can be maintained at the secondary side voltage corresponding to the transformer with the large turn ratio, and otherwise the maximum gain of the converter output will be reduced.

[0102] The drive of the first full-bridge power tube S2 is complementary to the drive of the power tube S1, and the drive of the power tube S4 is complementary to the drive of the power tube S3. Through this mode, when the power tube S1 and the power tube S3 are both turned off, the primary side voltage of the transformer T1 is clamped to a low level. This prevents the problem that when the second full-bridge of the full-bridge converter works, the secondary side voltage of the transformer T2 passes through the secondary side coil of the transformer T1 to excite the primary side coil, causing the magnetic flux density of the transformer T1 to increase as the input voltage Vin rises, thereby reducing the volume of the transformer magnetic core of the first full-bridge converter.

[0103] When the power tube S1 and the power tube S3 are both turned off, the primary side voltage of the transformer T1 is clamped to a low level, which can also be achieved by another way: when only the power tube S5 and the power tube S8 of the hybrid bridge converter are turned on, the power tube D1 is controlled to be turned on, and when only the power tube S6 and the power tube S7 of the hybrid bridge converter are turned on, the power tube D2 needs to be controlled to be turned on.

[0104] When the hybrid bridge converter alternately works in the first full-bridge circuit and the second full-bridge circuit in a working cycle, i.e., there is no series working state of the output terminals of the secondary sides of the transformers T1 and T2. In order to balance the power of the two full-bridge circuits and optimize the temperature rise of the hybrid bridge converter, the duty cycle of the power tubes S5 and S7 of the second full-bridge circuit needs to be dynamically limited. The maximum duty cycle limit method is as follows: a volt-second product K is set, and the maximum duty cycle limit value is equal to the ratio of the volt-second product K to the input voltage Vin. With the increase of the input voltage, when the duty cycle of the power tubes S5 and S7 is less than the maximum duty cycle limit value, the duty cycle of the power tubes S5 and S7 increases with the increase of the input voltage; when the duty cycle of the power tubes S5 and S7 is greater than or equal to the duty cycle limit, the duty cycle of the power tubes S5 and S7 is controlled by the maximum duty cycle limit value and gradually decreases with the increase of the input voltage. The duty cycle of the power tubes S1 and S3 of the first full-bridge circuit always decreases with the increase of the input voltage. When the duty cycle of the power tubes S1 and S3 decreases to the minimum, the maximum duty cycle of the power tubes S5 and S7 is not limited.

[0105] The value of the volt-second product K is based on that the product of the duty cycle of the second full-bridge circuit at the lowest input voltage of the hybrid bridge converter and the input voltage is equal to the value of the volt-second product K.

[0106] Here, the input voltage range is 36V-75V, the output voltage is 50V, the turn ratio n1 of the transformer T1 is 1:1, and the turn ratio n2 of the transformer T2 is 2:1.

[0107] Now, the working time sequence of the three main input voltage sections will be described. Figure 2 When only the first full-bridge circuit works and the hybrid bridge converter cannot maintain the output voltage equal to the set voltage, the working state of the hybrid bridge converter is the T0-T5 stage, which includes the series connection and gain increasing process of the secondary side windings of the transformers T1 and T2. Here, the input voltage is equal to 36V.

[0108] T0-T1 stage: when the power tubes S1 and S4 are turned on, the power tubes S7 and S6 are still turned on, at this time, the secondary side windings of the transformers T1 and T2 are in parallel. However, due to the fact that the turn ratio of the transformer T2 is twice that of the transformer T1, the secondary side voltage V AB of the transformer T1 is twice the secondary side voltage V BC of the transformer T2, i.e., V AB =2*V BC , which causes the secondary side windings of the transformers T1 and T2 to be unable to be directly connected in parallel, but only the secondary side winding of the transformer T1 transfers energy to the output through the power tubes D1 / D4, the secondary side power tube D5 is cut off, and the secondary side winding of the transformer T2 cannot transfer energy to the output through the power tubes D5 / D4. At this time, the voltage drop VD5 = V AB -V BC , V AB = 2*V BC , V D5 = V BC = 0.5V AB , the reverse recovery voltage of power tube D5 is reduced by half, which can greatly reduce the loss and stress caused by reverse recovery. The turn-off time of power tube S7 / power tube S6 ensures that power tube D5 is turned off, and after power tube S7 / power tube S6 is turned off, V D5 rises to V AB , and the process has no reverse recovery.

[0109] But if power tube S7 / power tube S6 is not in the on state when power tube S1 / power tube S4 is turned on, it means that V BC = 0, and because the voltage drop V D5 = V AB -V BC across power tube D5, V D5 will directly rise from 0V to V AB , and the reverse recovery voltage of power tube D5 will be doubled compared to the control method of the present application, resulting in increased reverse recovery loss and stress.

[0110] T1-T2 stage: at T1, power tube S5 / power tube S8 is turned on, and because power tube S1 / power tube S4 is still on at this time, the secondary winding of transformer T1, T2 is in series. The corresponding secondary power tube D1 / D6 is turned on, and at this time, power tube D4 is turned off under reverse voltage, and its reverse recovery voltage VD4 = V BC = 0.5V AB , the reverse recovery voltage is still relatively small. In addition, the series connection of the secondary winding of transformer T1 / T2 is realized, and at this time, the voltage V DE = V AB + V BC = 18V+36V = 54V across the secondary three-bridge rectifier circuit of the hybrid bridge converter can ensure a low-voltage 50V output, and the output voltage gain is improved.

[0111] T2-T3 stage: power tube S1 / power tube S4 is turned off, and secondary power tube D1 is turned off. Because the voltage across power tube D1 starts to rise, the current flowing through it just changes direction to power tube D3, and power tube D1 has no reverse recovery loss, greatly reducing the reverse recovery loss and stress of the secondary side. At this time, the voltage V DE = V BC = 36V across the secondary three-bridge rectifier circuit of the hybrid bridge converter.

[0112] T3-T4 stage: power tube S2 / power tube S3 is turned on, at this time power tube S5 / power tube S8 is still turned on. Its working principle is the same as that of TO-T1 stage, the transformer T1, T2 secondary winding cannot be directly connected in parallel, but only transformer T1 secondary winding transmits energy to the output through power tube D2 / D3, the secondary power tube D6 is cut off, the transformer T2 secondary winding cannot transmit energy to the output through power tube D3 / D6. At this time, the voltage drop V D6 = V AB -V BC , and because V AB = 2*V BC , V D6 = V BC = 0.5V AB , the reverse recovery voltage of power tube D6 is reduced by half, which can greatly reduce the loss and stress problem brought by its reverse recovery. The turn-off time of power tube S5 / power tube S8 can be turned off after power tube D6 is turned off, after power tube S5 / power tube S8 is turned off, V D5 rises to V AB , and the process has no reverse recovery.

[0113] T4-T5 stage: at T4, power tube S6 / power tube S7 is turned on, because at this time power tube S2 / power tube S3 is still turned on, at this time the secondary windings of transformers T1, T2 are in series. Corresponding to the conduction of secondary power tube D2 / D5, power tube D3 is turned off due to the withstand voltage, and its reverse recovery voltage VD3 = V BC = 0.5V AB , the reverse recovery voltage is still relatively small. In addition, the series connection of the secondary windings of transformers T1 / T2 is realized, and the output voltage gain is improved. At T5, the secondary power tube D2 is turned off, because when the voltage across power tube D2 starts to rise, the current flowing through it just changes direction to power tube D4, power tube D2 has no reverse recovery loss, which greatly reduces the reverse recovery loss and stress of the secondary side. At this time, the voltage across the hybrid bridge rectifier circuit on the secondary side V DE = V BC = 36V.

[0114] Thus, a cycle period under this stage ends. From the working process, it can be seen that the secondary power tube D1 / D2 has no reverse recovery loss, and D3 / D4 / D5 / D6 has reverse recovery loss, but the reverse recovery voltage is half of the VAB voltage, which can greatly reduce the loss and device stress problem brought by the reverse recovery of the secondary power tube.

[0115] When only the first full-bridge circuit is working, it is sufficient to maintain the output voltage equal to the set voltage. Furthermore, when the power transistors S5 and S7 of the second full-bridge circuit have not reached their maximum duty cycle limits, the hybrid bridge converter operates in the T6–T12 stage. During this stage, transformers T1 and T2 operate alternately. This is illustrated using an input voltage of 60V.

[0116] T6-T7 Stage: At time T6, power transistor S1 is turned on. Power transistors S4, S6, and S7 are still turned on, and the secondary windings of transformers T1 and T2 are connected in parallel. The operation at this time is the same as in the T0-T1 stage, so it will not be described again here. At this time, the reverse recovery voltage of power transistor D5 is VD5 = V... BC =0.5V AB The reverse recovery voltage is still only V. AB Half the voltage.

[0117] During the T7-T8 phase: At time T7, power transistor S1 is off, and neither transformers T1 nor T2 transfer energy to the secondary side. All secondary power transistors D1 / D2 / D3 / D4 / D5 / D6 are on for freewheeling. At time T8, power transistors S5 and S8 are on, and transformer T2 begins to transfer energy to the output. Secondary power transistors D1 / D5 / D2 / D4 are off, and their reverse recovery voltages VD1 = VD5 = VD2 = VD4 = V BC =0.5V AB The reverse recovery voltage is still only half of the VAB voltage.

[0118] During the T8-T9 phase: At time T8, power transistors S5, S8, S2, and S4 are turned on. Because power transistors S2 and S4 are on, the primary winding voltage of transformer T1 is clamped to 0V, thus preventing the secondary winding voltage of transformer T2 from being reduced to V. BC By energizing the primary coil of transformer T1 through the secondary coil, the magnetic flux density of the transformer core of transformer T1 increases as the input voltage Vin increases, thus reducing the core volume of the transformer in the first full-bridge converter.

[0119] If only power transistors S5 and S8 are turned on, in addition to D3 and D6 conducting, D2 will also conduct due to the freewheeling current in the output filter inductor L, experiencing a forward voltage drop. At this time, the transformer windings T1 and T2 are directly connected in parallel, causing V... AB =V BC This forces the transformer of the first full-bridge converter to be energized, resulting in an increase in the magnetic flux density of the transformer core. In this embodiment of the invention, by turning on the primary-side power transistors S2 and S4 of the first full-bridge circuit, the voltage of the primary coil of transformer T1 is clamped to 0V. Power transistor D2 will then be cut off due to the reverse voltage drop, effectively preventing this problem.

[0120] T9-T10 stage: at T9 moment, power tube S3 is turned on, at this moment, power tube S2 / power tube S5 / power tube S8 are still turned on, the secondary winding of transformer T1 and T2 is in parallel. The working process at this moment is consistent with T3-T4 stage, so it is not described here. At this moment, the voltage drop V D6 = V AB -V BC , and because V AB = 2*V BC , V D6 = V BC = 0.5V AB , the reverse recovery voltage of power tube D6 is reduced by half, which can greatly reduce the loss and stress problem caused by reverse recovery.

[0121] T10-T11 stage: at T10 moment, power tube S3 is turned off, transformer T1 and T2 do not transmit energy to the secondary side, and the secondary side power tube D1 / D2 / D3 / D4 / D5 / D6 is all turned on for freewheeling. At T11 moment, power tube S7 / power tube S6 is turned on, and transformer T2 starts to transmit energy to the output end. The secondary side power tube D1 / D3 / D2 / D6 is turned off, VD1 = VD3 = VD2 = VD6 = V BC = 0.5V AB , the reverse recovery voltage is still only half of the VAB voltage.

[0122] At T11-T12 stage, power tube S7 / power tube S6 / power tube S2 / power tube S4 is turned on, which ensures that the primary winding voltage of transformer T1 is clamped to 0V, thereby preventing the transformer T2 secondary voltage V BC from increasing through the transformer T1 secondary coil to excite its primary coil, which causes the transformer T1 to increase with the input voltage Vin, and the transformer magnetic core magnetic flux density increases, which reduces the volume of the transformer magnetic core of the first full-bridge converter.

[0123] At this stage, a cycle period ends. From the working process, it can be seen that the secondary side power tube D1 / D2 has no reverse recovery loss, and D3 / D4 / D5 / D6 has reverse recovery loss, but the reverse recovery voltage is half of the VAB voltage, which can greatly reduce the loss and device stress problem caused by the reverse recovery of the secondary side power tube.

[0124] When the input voltage reaches the maximum input voltage, the hybrid bridge converter works in T13-T21 stage, and the transformer T1 and T2 still work alternately, and the working process is consistent with T6-T12 stage, which is not described here.

[0125] From the above working states, it can be seen that when the input voltage is low, 36V, the transformer T1 / T2 is still in series state, and the maximum stress of the secondary power tube is 54V; when the input voltage is close to the output voltage, the transformer T1 / T2 is still in series state, and the maximum stress of the secondary power tube is 75V; when the input voltage is high, 75V, the transformer T1 / T2 is in alternating working state, and the maximum stress of the secondary power tube is 75V. Therefore, in the whole input voltage range, the maximum stress of the secondary power tube is 75V. However, in the traditional bridge topology, when the input voltage is low, 36V, if the maximum stress of the secondary power tube is 54V, when the input voltage is 75V, the stress of the secondary power tube is 112V, which is much higher than the maximum stress of the secondary power tube in the embodiment, 75V, and the reverse recovery loss is also larger, which requires a power tube with a larger voltage resistance, resulting in an increase in system cost and a decrease in efficiency. Therefore, the embodiment has performance and cost advantages.

[0126] Second embodiment

[0127] Figure 3 The main control timing and waveform (n1>n2) of the hybrid bridge converter with the change of the input voltage are the second embodiment of the application, wherein the turn ratio n1 of the transformer T1 is greater than the turn ratio n2 of the transformer T2. Wherein V DE is the voltage across the secondary three-bridge rectifier circuit of the hybrid bridge converter, V AB is the voltage of the secondary winding of the transformer T1, V BC is the voltage of the secondary winding of the transformer T2.

[0128] The main features of the control timing are: the power tube S1 and the power tube S3 of the first full-bridge circuit use leading edge modulation, that is, in a switching cycle, the turn-on time of the power tube S1 and the power tube S3 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S5 and the power tube S7 of the second full-bridge circuit use trailing edge modulation, that is, in a switching cycle, the turn-on time of the power tube S5 and the power tube S7 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S5 can be turned off only after the power tube S3 is turned on, and the power tube S1 can be turned off only after the power tube S7 is turned on. The power tube S3 and the power tube S5 have overlapping driving, and the power tube S1 and the power tube S7 have overlapping driving. During the overlapping period, the secondary coils of the transformer T1 and the transformer T2 are in parallel connection. Through the control, when the hybrid bridge converter works, the full-bridge circuit with a larger turn ratio works first, and the voltage of the secondary rectifier circuit is raised to a lower voltage stress platform. Then the full-bridge circuit with a smaller turn ratio works, and the voltage of the secondary rectifier circuit is raised from a lower voltage stress platform to a final stress platform, so that the reverse recovery of the power tube of the secondary rectifier circuit in the input voltage range is maintained in the minimum state, and the reverse recovery loss and stress peak are effectively reduced.

[0129] The driving overlap time of the power tube S3 / power tube S5 and the driving overlap time of the power tube S1 / power tube S7 cannot be too long, and the voltage across the secondary side rectifier bridge circuit can be maintained at the corresponding secondary side voltage of the transformer with a large turn ratio, otherwise the maximum gain of the converter output will be reduced.

[0130] The driving of the power tube S2 of the first full-bridge circuit is complementary to the driving of the power tube S1, and the driving of the power tube S4 is complementary to the driving of the power tube S3. In this way, when the power tube S1 and the power tube S3 are both turned off, the primary side voltage of the transformer T1 can be clamped to a low level. This prevents the transformer T2 secondary side voltage from exciting the transformer T1 primary side coil through the transformer T1 secondary side coil when the second full-bridge of the full-bridge converter works, which causes the transformer T1 to increase the magnetic flux density of the transformer core as the input voltage Vin increases, thereby reducing the volume of the transformer core of the first full-bridge converter.

[0131] When the power tube S1 and the power tube S3 are both turned off, the primary side voltage of the transformer T1 can also be clamped to a low level by another method: when only the power tube S5 and the power tube S8 of the hybrid bridge converter are turned on, the power tube D1 is controlled to be turned on; when only the power tube S6 and the power tube S7 of the hybrid bridge converter are turned on, the power tube D2 needs to be controlled to be turned on.

[0132] When the first full-bridge circuit and the second full-bridge circuit of the hybrid bridge converter work alternately in a working cycle, i.e., there is no series connection of the transformer T1 and T2 secondary side output terminals. In order to balance the power of the two full-bridge circuits and optimize the temperature rise of the hybrid bridge converter, the duty cycle of the power tube S1 and the power tube S3 of the first full-bridge circuit needs to be dynamically limited. The maximum duty cycle limit method is to set a volt-second product K, and the maximum duty cycle limit value is equal to the ratio of the volt-second product K to the input voltage Vin. As the input voltage increases, when the duty cycle of the power tube S1 and the power tube S3 is less than the maximum duty cycle limit value, the duty cycle of the power tube S1 and the power tube S3 increases as the input voltage increases; when the duty cycle of the power tube S1 and the power tube S3 is greater than or equal to the duty cycle limit, the duty cycle of the power tube S1 and the power tube S3 is controlled by the maximum duty cycle limit value and gradually decreases as the input voltage increases. The duty cycle of the power tube S5 and the power tube S7 of the second full-bridge circuit always decreases as the input voltage increases. When the duty cycle of the power tube S5 and the power tube S7 decreases to the minimum, the maximum duty cycle of the power tube S1 and the power tube S3 is not limited.

[0133] The value of the volt-second product K is based on the product of the duty cycle of the first full-bridge circuit at the lowest input voltage of the hybrid bridge converter and the input voltage, which is equal to the value of the volt-second product K.

[0134] Since the second embodiment has the same working principle as the first embodiment, only the change of the turn ratio results in the change of the driving object, and thus no further description is given herein.

[0135] Third embodiment

[0136] Figure 4 A schematic diagram of the hybrid bridge converter of the third embodiment of the present application is shown in FIG. 3. The primary side of the converter uses two half-bridge circuits in parallel, and the secondary side uses a three-bridge rectifier circuit for rectification. The energy is transferred to the output through an output filter inductor.

[0137] The hybrid bridge converter in this embodiment includes a first half-bridge circuit, a second half-bridge circuit, a transformer T1, a transformer T2, a three-bridge rectifier circuit, an output filter inductor L, and an output capacitor Co. The first half-bridge circuit includes a capacitor C1, a capacitor C2, a power tube S3, and a power tube S4. The second half-bridge circuit includes a capacitor C5, a capacitor C6, a power tube S7, and a power tube S8. The three-bridge rectifier circuit includes a power tube D1, a power tube D2, a power tube D3, a power tube D4, a power tube D5, and a power tube D6.

[0138] The first end of the capacitor C1, the first end of the power tube S3, the first end of the capacitor C5, and the first end of the power tube S7 are connected to the positive pole of the power supply. The second end of the capacitor C2, the second end of the power tube S4, the second end of the capacitor C6, and the second end of the power tube S8 are connected to the negative pole of the power supply. The second end of the capacitor C1 is connected to the first end of the capacitor C2 and the first end of the transformer T1. The second end of the power tube S3 is connected to the first end of the power tube S4 and the second end of the transformer T1. The second end of the capacitor C5 is connected to the first end of the capacitor C6 and the first end of the transformer T2. The second end of the power tube S7 is connected to the first end of the power tube S8 and the second end of the transformer T2.

[0139] The first end of the power tube D1, the first end of the power tube D3, and the first end of the power tube D5 are connected to the first end of the output filter inductor L. The second end of the power tube D2, the second end of the power tube D4, and the second end of the power tube D6 are connected to the second end of the output capacitor Co. The second end of the power tube D1 is connected to the first end of the power tube D2 and the third end of the transformer T1. The second end of the power tube D3 is connected to the first end of the power tube D4 and the fourth end of the transformer T1. The second end of the power tube D5 is connected to the first end of the power tube D6 and the fourth end of the transformer T2. The fourth end of the transformer T1 is connected to the third end of the transformer T2. The second end of the output filter inductor L is connected to the first end of the output capacitor Co.

[0140] Among them, the power tube S3, the power tube S4, the power tube S7, the power tube S8, the power tube D1, the power tube D2, the power tube D3, the power tube D4, the power tube D5, the power tube D6 can be MOS tube, triode or IGBT and other switching devices.

[0141] Figure 5 The main control timing and waveform (n1 DE The voltage across the two ends of the secondary side three-bridge arm rectifier circuit of the hybrid bridge converter is V AB The voltage of the secondary side winding of the transformer T1 is V BC The voltage of the secondary side winding of the transformer T2 is V

[0142] The main features of the control timing are:

[0143] The power tube S3 and the power tube S4 of the first half-bridge circuit adopt trailing edge modulation, that is, in a switching period, the turn-on time of the power tube S4 and the power tube S3 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S7 and the power tube S8 of the second half-bridge circuit adopt leading edge modulation, that is, in a switching period, the turn-off time of the power tube S8 and the power tube S7 is unchanged, and the turn-on time is controlled by pulse width modulation. The power tube S3 can be turned off only after the power tube S8 is turned on, and the power tube S7 can be turned off only after the power tube S4 is turned on. The driving of the power tube S3 and the power tube S8 overlaps, and the driving of the power tube S4 and the power tube S7 overlaps. During the overlap period, the secondary side coils of the transformer T1 and the transformer T2 are in parallel connection.

[0144] Through the control, when the hybrid bridge converter works, the full-bridge circuit with the larger turn ratio works first, and the voltage of the secondary side rectifier circuit is raised to a lower voltage stress platform. Then the full-bridge circuit with the smaller turn ratio works, and the voltage of the secondary side rectifier circuit is raised from a lower voltage stress platform to a final stress platform, so that the reverse recovery of the power tube of the secondary side rectifier circuit in the input voltage range is maintained in the minimum state, and the reverse recovery loss and stress peak are effectively reduced.

[0145] The driving overlap time of the power tube S3 and the power tube S8 and the driving overlap time of the power tube S4 and the power tube S7 should not be too long, so as to ensure that the voltage across the two ends of the secondary side rectifier bridge circuit can be maintained at the corresponding secondary side voltage of the transformer with the larger turn ratio, otherwise the maximum gain of the converter output will be reduced.

[0146] After power transistor S8 is turned on and before S3 is turned on, ensure that power transistor D1 is in the conducting state; after power transistor S7 is turned on and before S4 is turned on, ensure that power transistor D2 is in the conducting state. This ensures that when power transistors S1 and S3 are both turned off, the primary voltage of transformer T1 is clamped to a low level. This prevents the secondary voltage of transformer T2 from energizing the primary coil of transformer T1 through the secondary coil when the second half-bridge of the half-bridge converter is operating, thus preventing an increase in the magnetic flux density of transformer T1 as the input voltage Vin increases. This also reduces the core size of the transformer in the first half-bridge converter.

[0147] When the first and second half-bridge circuits of the hybrid bridge converter operate alternately within one duty cycle, that is, there is no series connection at the secondary output terminals of transformers T1 and T2. To balance the power of the two half-bridge circuits and optimize the temperature rise of the hybrid bridge converter, it is also necessary to dynamically limit the duty cycle of power transistors S8 and S7 in the second half-bridge circuit. The maximum duty cycle limit is determined by setting a volt-second product K, which is equal to the ratio of this volt-second product K to the input voltage Vin. As the input voltage increases, when the duty cycle of power transistors S8 and S7 is less than the maximum duty cycle limit, their duty cycles increase with the increase in input voltage. When the duty cycle of power transistors S8 and S7 is greater than or equal to the duty cycle limit, their duty cycles are controlled by the maximum duty cycle limit and gradually decrease with the increase in input voltage. The duty cycles of power transistors S4 and S3 in the first half-bridge circuit decrease as the input voltage increases. When the duty cycles of power transistors S4 and S3 are reduced to their minimum, the maximum duty cycles of power transistors S8 and S7 are not limited.

[0148] The value of the volt-second product K is determined based on the following: Under the lowest input voltage of the hybrid bridge converter, the product of the duty cycle of the second half-bridge circuit and the input voltage is equal to the value of the volt-second product K.

[0149] The input voltage range is given here as 36V to 75V, the output voltage is 25V, the turns ratio of transformer T1 is n1 = 1:1, and the turns ratio of transformer T2 is n2 = 2:1.

[0150] Now combined Figure 4 The operating timing of the three main input voltage stages is explained. When only the first half-bridge circuit is working, and the hybrid bridge converter is insufficient to maintain the output voltage equal to the set voltage, the hybrid bridge converter operates in the T0 to T5 stage. This stage includes the series gain increase process of the secondary windings of transformers T1 and T2. Here, we assume the input voltage is equal to 36V.

[0151] During the T0-T1 stage: When power transistor S4 is turned on, power transistor S7 is still turned on. At this time, the secondary windings of transformers T1 and T2 are connected in parallel. However, since the turns ratio of transformer T2 is twice that of T1, the secondary voltage V of transformer T1... AB It is the secondary voltage V of transformer T2. BC twice that, i.e., V AB =2*V BC This causes the secondary windings of transformers T1 and T2 to be unable to be directly connected in parallel. Instead, only the secondary winding of transformer T1 transfers energy to the output through power transistors D1 / D4, while power transistor D5 is cut off. Therefore, the secondary winding of transformer T2 cannot transfer energy to the output through power transistors D5 / D4. At this time, the voltage drop V across power transistor D5... D5 =V AB -V BC And because of V AB =2*V BC Therefore, V D5 =V BC =0.5V AB The reverse recovery voltage of power transistor D5 is reduced by half, which greatly reduces the losses and stress caused by reverse recovery. The turn-off time of power transistor S7 should be ensured to be turned off immediately after power transistor D5 is turned off. After power transistor S7 is turned off, V... D5 Upgrade to V AB There is no reverse recovery in this process.

[0152] However, if power transistor S7 is not turned on when power transistor S4 is turned on, it means that V BC =0, and because the voltage drop V across power transistor D5 is... D5 =V AB -V BC This will lead to V D5 Directly from 0V to V AB The reverse recovery voltage of power transistor D5 will be doubled compared to the control method of this invention, resulting in increased reverse recovery loss and stress.

[0153] During the T1-T2 phase: At T1, power transistor S8 is turned on. Since S4 is still on, the secondary windings of transformers T1 and T2 are connected in series. Correspondingly, secondary power transistors D1 / D6 are turned on. At this time, power transistor D4 is turned off due to reverse voltage, and its reverse recovery voltage VD4 = V BC =0.5V AB The reverse recovery voltage is still relatively small. Furthermore, the series connection of the secondary windings of transformers T1 / T2 is implemented, at which point the voltage V across the three-arm rectifier circuit on the secondary side of the hybrid bridge converter is... DE =V AB +V BC =9V + 18V = 27V, which ensures a low-voltage 25V output and improves the output voltage gain.

[0154] T2-T3 stage: power tube S4 is off, and the secondary power tube D1 is off. When the voltage across the power tube D1 begins to rise, the current flowing through it just reverses to the power tube D3, and the power tube D1 has no reverse recovery loss, which greatly reduces the reverse recovery loss and stress of the secondary side. At this time, the voltage across the secondary three-bridge rectifier circuit of the hybrid bridge converter is V DE = V BC = 18V.

[0155] T3-T4 stage: the power tube S3 is on, and the power tube S8 is still on. Its working principle is the same as that in the T0-T1 stage. The transformer T1 and T2 secondary windings cannot be directly connected in parallel, but only the transformer T1 secondary winding transfers energy to the output through the power tubes D2 / D3, and the secondary power tube D6 is cut off, so that the transformer T2 secondary winding cannot transfer energy to the output through the power tubes D3 / D6. At this time, the voltage drop across the power tube D6 is V D6 = V AB -V BC , and because V AB = 2*V BC , V D6 = V BC = 0.5V AB , the reverse recovery voltage of the power tube D6 is reduced by half, which can greatly reduce the loss and stress caused by the reverse recovery. The turn-off time of the power tube S8 can be ensured after the power tube D6 is turned off, and after the power tube S8 is turned off, V D5 rises to V AB , and this process has no reverse recovery.

[0156] T4-T5 stage: at T4, the power tube S7 is on. At this time, the power tube S3 is still on, and the transformer T1 and T2 secondary windings are in series. The corresponding secondary power tubes D2 / D5 are on, and the power tube D3 is off due to the reverse voltage, and the reverse recovery voltage VD3 = V BC = 0.5V AB , which is still relatively small. In addition, the series connection of the transformer T1 / T2 secondary windings is realized, and the output voltage gain is improved. At T5, the secondary power tube D2 is off. When the voltage across the power tube D2 begins to rise, the current flowing through it just reverses to the power tube D4, and the power tube D2 has no reverse recovery loss, which greatly reduces the reverse recovery loss and stress of the secondary side. At this time, the voltage across the secondary three-bridge rectifier circuit of the hybrid bridge converter is V DE = V BC = 18V.

[0157] This completes one cycle of this stage. As can be seen from this process, secondary power transistors D1 / D2 have no reverse recovery loss, while D3 / D4 / D5 / D6 do. However, the reverse recovery voltages are all half of the VAB voltage, which greatly reduces the losses and device stress caused by the reverse recovery of the secondary power transistors.

[0158] When only the first half-bridge circuit is working, it is sufficient to maintain the output voltage equal to the set voltage. Furthermore, when the power transistors S8 and S7 of the second half-bridge circuit have not reached their maximum duty cycle limits, the hybrid bridge converter operates in the T6–T12 stage. During this stage, transformers T1 and T2 operate alternately. This is illustrated using an input voltage of 60V.

[0159] T6-T7 Stage: At time T6, power transistor S4 is turned on, while power transistor S7 remains on. The secondary windings of transformers T1 and T2 are connected in parallel. The operation at this time is consistent with the T0-T1 stage, so it will not be described again here. At this time, the reverse recovery voltage of power transistor D5 is VD5 = V BC =0.5V AB The reverse recovery voltage is still only V. AB Half the voltage.

[0160] During the T7-T8 phase: At time T7, power transistor S4 is off, and neither transformers T1 nor T2 transfer energy to the secondary side. All secondary power transistors D1 / D2 / D3 / D4 / D5 / D6 are turned on for freewheeling. At time T8, power transistor S8 is turned on, and transformer T2 begins to transfer energy to the output. Secondary power transistors D1 / D5 / D2 / D4 are off, and their reverse recovery voltages VD1 = VD5 = VD2 = VD4 = V BC =0.5V AB The reverse recovery voltage is still only half of the VAB voltage.

[0161] During the T8-T9 phase: At time T8, power transistor S8 is turned on. Besides D3 / D6, D2 will also conduct due to the freewheeling current in the output filter inductor L, experiencing a forward voltage drop. At this time, the transformer windings T1 and T2 are directly connected in parallel, causing V... AB =V BC This forces the transformer of the first half-bridge converter to be energized, resulting in an increase in the magnetic flux density of the transformer core. In this embodiment of the invention, by turning on the power transistor D1, the voltage of the primary coil of transformer T1 is clamped to 0V, and the power transistor D2 will also be cut off due to the reverse voltage drop, thus effectively preventing this problem.

[0162] T9-T10 stage: at T9 moment, power tube S3 is turned on, at this moment, power tube S8 is still turned on, and the secondary winding of transformer T1 and T2 is in parallel. The working process at this moment is consistent with T3-T4 stage, and thus, the description is not repeated here. At this moment, the voltage drop V D6 AB BC , and because V AB = 2*V BC , V D6 = V BC = 0.5V AB , the reverse recovery voltage of power tube D6 is reduced by half, and the loss and stress problem caused by the reverse recovery can be greatly reduced.

[0163] T10-T11 stage: at T10 moment, power tube S3 is turned off, and transformer T1 and T2 do not transmit energy to the secondary side, and the secondary side power tubes D1 / D2 / D3 / D4 / D5 / D6 are all turned on for freewheeling. At T11 moment, power tube S7 is turned on, and transformer T2 starts to transmit energy to the output end. The secondary side power tubes D1 / D3 / D2 / D6 are turned off, and VD1 = VD3 = VD2 = VD6 = V BC = 0.5V AB , and the reverse recovery voltage is still only half of the VAB voltage.

[0164] At T11-T12 stage, power tube S7 is turned on, and in addition to D4 / D5, D1 will also be turned on due to the freewheeling of the output filter inductor L and will withstand a forward voltage drop, at this moment, the transformer T1 winding and T2 winding are directly in parallel, so that V AB = V BC , thereby forcing the transformer of the first half-bridge converter to be excited, resulting in an increase in the magnetic flux density of the transformer core. In this embodiment, the transformer T1 primary coil voltage is clamped to 0V by turning on power tube D2, and power tube D1 will also be turned off due to the reverse voltage drop, thereby effectively preventing this problem.

[0165] At this stage, a cycle period ends. From the working process, it can be seen that the secondary side power tubes D1 / D2 have no reverse recovery loss, and D3 / D4 / D5 / D6 have reverse recovery loss, but the reverse recovery voltage is half of the VAB voltage, which can greatly reduce the loss and device stress problem caused by the reverse recovery of the secondary side power tube.

[0166] When the input voltage reaches the maximum input voltage, the hybrid bridge converter works in T13-T19 stage, and the transformer T1 and T2 are still alternately working, and the working process is consistent with T6-T12 stage, and thus, the description is not repeated here.

[0167] ​​From the above working states, it can be seen that when the input voltage is low, 36V, the transformer T1 / T2 is still in series state, and the maximum stress of the secondary power tube is 27V; when the input voltage is close to the output voltage, the transformer T1 / T2 is still in series state, and the maximum stress of the secondary power tube is 37.5V; when the input voltage is high, 75V, the transformer T1 / T2 is in alternating working state, and the maximum stress of the secondary power tube is 37.5V. Therefore, in the whole input voltage range, the maximum stress of the secondary power tube is 37.5V. However, in the traditional bridge topology, when the input voltage is low, 36V, if the maximum stress of the secondary power tube is 37.5V, when the input voltage is 75V, the stress of the secondary power tube is 78.12V, which is much larger than the maximum stress of the secondary power tube in the embodiment, 37.5V, and the reverse recovery loss is also larger, which requires a power tube with a larger withstand voltage, resulting in an increase in system cost and a decrease in efficiency. Therefore, the embodiment has performance and cost advantages.

[0168] Fourth embodiment

[0169] Figure 6 The main control timing and waveform (n1>n2) of the hybrid bridge converter with the change of the input voltage are the fourth embodiment of the present application, wherein the turn ratio n1 of the transformer T1 is greater than the turn ratio n2 of the transformer T2. Wherein V DE is the voltage across the secondary three-bridge rectifier circuit of the hybrid bridge converter, V AB is the voltage of the secondary winding of the transformer T1, V BC is the voltage of the secondary winding of the transformer T2.

[0170] The main features of the control timing are: the power tube S3 and the power tube S4 of the first half-bridge circuit use leading edge modulation, that is, in a switching cycle, the turn-on time of the power tube S4 and the power tube S3 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S7 and the power tube S8 of the second half-bridge circuit use trailing edge modulation, that is, in a switching cycle, the turn-on time of the power tube S8 and the power tube S7 is unchanged, and the turn-off time is controlled by pulse width modulation. The power tube S8 can be turned off only after the power tube S3 is turned on, and the power tube S4 can be turned off only after the power tube S7 is turned on. The driving of the power tube S3 and the power tube S8 overlaps, and the driving of the power tube S4 and the power tube S7 overlaps. During the overlap period, the secondary coils of the transformer T1 and the transformer T2 are in parallel connection. Through the control, when the hybrid bridge converter works, the half-bridge circuit with a larger turn ratio works first, and the voltage of the secondary rectifier circuit is raised to a lower voltage stress platform. Then the half-bridge circuit with a smaller turn ratio works, and the voltage of the secondary rectifier circuit is raised from a lower voltage stress platform to a final stress platform, so that the reverse recovery of the power tube of the secondary rectifier circuit in the input voltage range is maintained in the minimum state, and the reverse recovery loss and stress peak are effectively reduced.

[0171] The driving overlap time of the power tube S3 / power tube S8 and the driving overlap time of the power tube S4 / power tube S7 cannot be too long, and the voltage across the secondary side rectifier bridge circuit can be maintained at the corresponding secondary side voltage of the transformer with a large turn ratio, otherwise the maximum gain of the converter output will be reduced.

[0172] After the power tube S8 is turned on and before the power tube S3 is turned on, the power tube D1 is ensured to be in a conduction state; after the power tube S7 is turned on and before the power tube S4 is turned on, the power tube D2 needs to be in a conduction state. In this way, when the power tube S1 and the power tube S3 are both turned off, the primary side voltage of the transformer T1 is clamped to a low level. This prevents the problem that when the second half-bridge of the half-bridge converter works, the secondary side voltage of the transformer T2 passes through the secondary side coil of the transformer T1 to excite the primary side coil, causing the transformer T1 to increase with the input voltage Vin, and the magnetic flux density of the transformer magnetic core increases, thereby reducing the volume of the transformer magnetic core of the first half-bridge converter.

[0173] When the hybrid bridge converter works in a working cycle, the first half-bridge circuit and the second half-bridge circuit work alternately, that is, there is no series connection of the secondary side output terminals of the transformers T1 and T2. In order to balance the power of the two half-bridge circuits and optimize the temperature rise of the hybrid bridge converter, it is also necessary to dynamically limit the duty cycle of the power tube S4 and the power tube S3 of the first half-bridge circuit. The maximum duty cycle limit value method is: set a volt-second product K, and the maximum duty cycle limit value is equal to the ratio of the volt-second product K to the input voltage Vin. As the input voltage rises, when the duty cycle of the power tube S4 and the power tube S3 is less than the maximum duty cycle limit value, the duty cycle of the power tube S4 and the power tube S3 increases with the increase of the input voltage, and when the duty cycle of the power tube S4 and the power tube S3 is greater than or equal to the duty cycle limit, the duty cycle of the power tube S4 and the power tube S3 is controlled by the maximum duty cycle limit value and gradually decreases with the increase of the input voltage. The duty cycle of the power tube S8 and the power tube S7 of the second half-bridge circuit always decreases with the increase of the input voltage. When the duty cycle of the power tube S8 and the power tube S7 decreases to the minimum, the maximum duty cycle of the power tube S4 and the power tube S3 is not limited.

[0174] The value of the volt-second product K is based on: the product of the duty cycle of the first half-bridge circuit at this time and the input voltage under the lowest input voltage of the hybrid bridge converter is equal to the value of the volt-second product K.

[0175] Since the working principle of the fourth embodiment is the same as that of the third embodiment, only the driving object changes due to the change of the turn ratio, and therefore the details are not repeated here.

[0176] Further, the embodiment of the present application also provides a control method of the hybrid bridge converter, the hybrid bridge converter comprising a first bridge circuit, a second bridge circuit, a transformer T1, a transformer T2 and a secondary power tube, the control method comprising: when the secondary power tube is off, lifting the voltage across the secondary power tube to a first voltage first, and then to a second voltage, so as to reduce the reverse-recovery loss and stress peak of the secondary power tube, wherein the second voltage is greater than the first voltage.

[0177] In an embodiment, the control method further comprises: clamping the voltage across the transformer T1 to 0V when the first bridge circuit is not working, so as to prevent the second bridge circuit from being reversely excited.

[0178] The first bridge circuit and the second bridge circuit can be full-bridge circuits or half-bridge circuits.

[0179] The above-mentioned embodiments should not be regarded as limitations of the present application, and the protection scope of the present application should be defined by the scope defined in the claims. For those skilled in the art, a number of equivalent replacements, improvements and refinements can be made without departing from the spirit and scope of the present application, and the improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A control method for a hybrid bridge converter, the hybrid bridge converter comprising a first full-bridge circuit, a second full-bridge circuit, a transformer T1, a transformer T2, a three-leg rectifier circuit, an output filter inductor L, and an output capacitor Co. The first full-bridge circuit includes power transistors S1, S2, S3, and S4, and the second full-bridge circuit includes power transistors S5, S6, S7, and S8; The first ends of the power transistors S1, S3, S5, and S7 are all connected to the positive power supply, and the second ends of the power transistors S2, S4, S6, and S8 are all connected to the negative power supply. The second end of the power transistor S1 is simultaneously connected to the first end of the power transistor S2 and the first end of the transformer T1. The second end of the power transistor S3 is simultaneously connected to the first end of the power transistor S4 and the second end of the transformer T1. The second end of the power transistor S5 is simultaneously connected to the first end of the power transistor S6 and the first end of the transformer T2. The second end of the power transistor S7 is simultaneously connected to the first end of the power transistor S8 and the second end of the transformer T2; The first input terminal of the three-leg rectifier circuit is connected to the third terminal of the transformer T1. The second input terminal of the three-leg rectifier circuit is respectively connected to the fourth terminal of the transformer T1 and the third terminal of the transformer T2. The third input terminal of the three-leg rectifier circuit is connected to the fourth terminal of the transformer T2. The positive output terminal of the three-leg rectifier circuit is connected to the first end of the output capacitor Co through the output filter inductor L. The negative output terminal of the three-leg rectifier circuit is connected to the second end of the output capacitor Co; Its features are, The control method includes: When n1 < n2, within one switching period, the power transistors S1 and S3 in the first full-bridge circuit adopt trailing-edge modulation; the power transistors S5 and S7 in the second full-bridge circuit adopt leading-edge modulation. Wherein, within one switching period, the power transistor S7 can be turned off only after the power transistor S1 is turned on, and the power transistor S5 can be turned off only after the power transistor S3 is turned on; When n1 > n2, within one switching period, the power transistors S1 and S3 in the first full-bridge circuit adopt leading-edge modulation; the power transistors S5 and S7 in the second full-bridge circuit adopt trailing-edge modulation. Wherein, within one switching period, the power transistor S3 can be turned off only after the power transistor S5 is turned on, and the power transistor S1 can be turned off only after the power transistor S7 is turned on; Wherein, n1 represents the turns ratio of the transformer T1, and n2 represents the turns ratio of the transformer T2.

2. The control method for the hybrid bridge converter according to claim 1, characterized in that: The power transistor S2 and the power transistor S1 are driven complementary; the power transistor S4 and the power transistor S3 are driven complementary; the power transistor S8 and the power transistor S5 are driven the same; the power transistor S6 and the power transistor S7 are driven the same.

3. The control method for the hybrid bridge converter according to claim 1, characterized in that: The control method further includes: When n1 < n2, within one switching period, the following steps are executed: First stage: Turn on the power transistor S1, and after the power transistor S1 is turned on, turn off the power transistor S7; Second stage: After the power transistor S7 is turned off, turn on the power transistor S5; Third stage: Turn off the power transistor S1, and after the power transistor S1 is turned off, turn on the power transistor S3; Fourth stage: After the power transistor S3 is turned on, turn off the power transistor S5; Fifth stage: After the power transistor S5 is turned off, turn on the power transistor S7; When n1 > n2, within one switching period, the following steps are executed: First stage: Turn on the power transistor S5, and after the power transistor S5 is turned on, turn off the power transistor S3; Second stage: After the power transistor S3 is turned off, turn on the power transistor S1; Third stage: Turn off the power transistor S5, and after the power transistor S5 is turned off, turn on the power transistor S7; Fourth stage: After the power transistor S7 is turned on, turn off the power transistor S1; Fifth stage: After the power transistor S1 is turned off, turn on the power transistor S3.

4. The control method for the hybrid bridge converter according to claim 1, characterized in that: The control method further includes: When n1 < n2, within the input voltage range, the control mode between multiple switching periods is: As the input voltage increases, the duty cycles of the power transistors S1 and S3 both remain unchanged at 100%, and the duty cycles of the power transistors S5 and S7 gradually decrease starting from 100%; When the duty cycles of the power transistors S5 and S7 decrease to 0, make the duty cycles of the power transistors S1 and S3 start to gradually decrease, and at the same time, the duty cycles of the power transistors S5 and S7 start to gradually increase; When the duty cycles of the power transistors S5 and S7 increase to the maximum duty cycle limit value, and the duty cycles of the power transistors S1 and S3 have not decreased to 0, the duty cycles of the power transistors S5 and S7 change following the maximum duty cycle limit value; When the duty cycles of the power transistors S ​ ​ ​ ​ When the duty cycles of the power transistors S5 and S7 are reduced to 0, there is no limit on the maximum duty cycles of the power transistors S1 and S3.

5. The control method for the hybrid bridge converter according to claim 4, characterized in that: The maximum duty cycle limit value is the ratio of the volt-second product K to the input voltage Vin, where the volt-second product K is a preset value.

6. A control method for a hybrid bridge converter, the hybrid bridge converter including a first half-bridge circuit, a second half-bridge circuit, a transformer T1, a transformer T2, a three-arm rectifier circuit, an output filter inductor L, and an output capacitor Co. The first half-bridge circuit includes a capacitor C1, a capacitor C2, a power transistor S3, and a power transistor S4. The second half-bridge circuit includes a capacitor C5, a capacitor C6, a power transistor S7, and a power transistor S8. The three-arm rectifier circuit includes a power transistor D1, a power transistor D2, a power transistor D3, a power transistor D4, a power transistor D5, and a power transistor D6; The first end of the capacitor C1, the first end of the power transistor S3, the first end of the capacitor C5, and the first end of the power transistor S7 are all connected to the positive power supply. The second end of the capacitor C2, the second end of the power transistor S4, the second end of the capacitor C6, and the second end of the power transistor S8 are all connected to the negative power supply. The second end of the capacitor C1 is simultaneously connected to the first end of the capacitor C2 and the first end of the transformer T1. The second end of the power transistor S3 is simultaneously connected to the first end of the power transistor S4 and the second end of the transformer T1. The second end of the capacitor C5 is simultaneously connected to the first end of the capacitor C6 and the first end of the transformer T2. The second end of the power transistor S7 is simultaneously connected to the first end of the power transistor S8 and the second end of the transformer T2; The first end of the power transistor D1, the first end of the power transistor D Its features are, ​ ​ When n1 > n2, within one switching period, the power transistors S4 and S3 in the first full-bridge circuit adopt leading-edge modulation; the power transistors S7 and S8 in the second full-bridge circuit adopt trailing-edge modulation; within one switching period, the power transistor S3 can be turned off only after the power transistor S8 is turned on, and the power transistor S4 can be turned off only after the power transistor S7 is turned on; Where, n1 represents the turns ratio of transformer T1, and n2 represents the turns ratio of transformer T2.

7. The control method for the hybrid bridge converter according to claim 6, characterized in that: The control method further includes: Before the power transistor S3 is turned on after the power transistor S8 is turned on, the power diode D1 is in the conducting state; before the power transistor S4 is turned on after the power transistor S7 is turned on, the power diode D2 is in the conducting state.

8. The control method for the hybrid bridge converter according to claim 6, characterized in that: The control method further includes: When n1 < n2, within one switching period, perform the following steps: First stage: Turn on the power transistor S4, and after the power transistor S4 is turned on, turn off the power transistor S7; Second stage: After the power transistor S7 is turned off, turn on the power transistor S8; Third stage: Turn off the power transistor S4, and after the power transistor S4 is turned off, turn on the power transistor S3; Fourth stage: After the power transistor S3 is turned on, turn off the power transistor S8; Fifth stage: After the power transistor S8 is turned off, turn on the power transistor S7; When n1 > n2, within one switching period, perform the following steps: First stage: Turn on the power transistor S8, and after the power transistor S8 is turned on, turn off the power transistor S3; Second stage: After the power transistor S3 is turned off, turn on the power transistor S4; Third stage: Turn off the power transistor S8, and after the power transistor S8 is turned off, turn on the power transistor S7; Fourth stage: After the power transistor S7 is turned on, turn off the power transistor S4; Fifth stage: After the power transistor S4 is turned off, turn on the power transistor S3.

9. The control method for the hybrid bridge converter according to claim 6, characterized in that: The control method further includes: When n1 < n2, within the input voltage range, the control mode between multiple switching periods is: As the input voltage increases, the duty cycles of the power transistors S3 and S4 both remain unchanged at 100%, and the duty cycles of the power transistors S8 and S7 gradually decrease starting from 100%; When the duty cycles of the power transistors S8 and S7 decrease to 0, make the duty cycles of the power transistors S4 and S3 start to gradually decrease, and at the same time, make the duty cycles of the power transistors S8 and S7 start to gradually increase; When the duty cycles of the power transistors S8 and S7 increase to the maximum duty cycle limit value and the duty cycles of the power transistors S4 and S ​ ​ As the input voltage increases, the duty cycle of power transistors S8 and S7 remains constant at 100%, while the duty cycle of power transistors S4 and S3 gradually decreases from 100%. When the duty cycle of power transistor S4 and power transistor S3 is reduced to 0, the duty cycle of power transistor S8 and power transistor S7 begins to gradually decrease, while the duty cycle of power transistor S4 and power transistor S3 begins to gradually increase. When the duty cycle of power transistor S4 and power transistor S3 increases to the maximum duty cycle limit value, and the duty cycle of power transistor S7 and power transistor S8 does not decrease to 0, the duty cycle of power transistor S4 and power transistor S3 follows the maximum duty cycle limit value. When the duty cycles of power transistors S7 and S8 are reduced to 0, the maximum duty cycle of power transistor S3 is not limited.

10. The control method for the hybrid bridge converter according to claim 9, characterized in that: The maximum duty cycle limit is the ratio of the volt-second product K to the input voltage Vin, wherein the volt-second product K is a preset value.

11. A control method for a hybrid bridge converter, the hybrid bridge converter comprising a first bridge circuit, a second bridge circuit, transformer T1, transformer T2, and secondary power transistors, characterized in that: The control method includes: when the secondary power transistor is turned off, the voltage across the secondary power transistor is first raised to a first voltage and then raised to a second voltage, thereby reducing the reverse recovery loss and stress spike of the secondary power transistor, wherein the second voltage is greater than the first voltage.

12. The control method for the hybrid bridge converter according to claim 11, characterized in that: The control method further includes: when the first bridge circuit is not working, clamping the voltage across the transformer T1 to 0V to prevent the second bridge circuit from being reverse-energized.

Images