A flow-fed bidirectional DC-DC converter based on magnetic integration and double transformers

Abstract

The application provides a flow-fed bidirectional DC-DC converter based on magnetic integration and double transformers, which comprises a feed inductance, a low-voltage end basic full-bridge circuit, a high-voltage end basic full-bridge circuit, a high-voltage end basic half-bridge circuit and a double transformer, the input end of the low-voltage end basic full-bridge circuit is connected with a low-voltage terminal, the input end of the low-voltage end basic full-bridge circuit and the low-voltage terminal are further connected in series with the feed inductance, the output end of the low-voltage end basic full-bridge circuit is connected with the input end of the double transformer, the output end of the low-voltage end basic full-bridge circuit and the input end of the double transformer are further connected in series with the leakage inductance, the output end of the double transformer is connected with the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit respectively, and the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit are connected in parallel to a high-voltage terminal. The application has the beneficial effects that the transformer leakage inductance current peak value is controllable, the voltage gain range is expanded, and the soft switching performance in the full load range of the converter is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switching power supply, and particularly relates to a flow-fed bidirectional DC-DC converter based on magnetic integration and double transformers. BACKGROUND

[0002] The bidirectional DC-DC converter can realize bidirectional transmission and conversion of electric energy, and is widely applied to fields such as electric vehicles, uninterruptible power supplies (UPS), renewable energy power generation systems (photovoltaic power generation, fuel cells) and energy storage systems.

[0003] On the one hand, in many application scenarios, the input voltage, output voltage and transmission power are required to change in a large range. For example, in a renewable energy power generation system, a hybrid power system using a fuel cell and a super capacitor, the output voltage of the fuel cell (150V-300V / 255V-425V) changes in a range of nearly two times, and the super capacitor also changes in a large voltage range for different load conditions and charging and discharging processes. Therefore, the input voltage, output voltage and transmission power of the bidirectional DC-DC converter connected to the high-voltage bus and the super capacitor should also change in a large range.

[0004] On the other hand, the Boost-derived current-fed bidirectional DC-DC converter has the advantages of small input current ripple, high boost ratio, low high-frequency (HF) transformer turn ratio, inherent short-circuit protection, no duty cycle loss and easy current control, and has attracted widespread attention in recent years. Typical applications include auxiliary DC-DC converters for connecting low-voltage (LV) energy storage and high-voltage (HV) DC buses, renewable energy power generation and multi-voltage level hybrid DC microgrids. However, the current-fed DC-DC converter has the inherent defect that large voltage spikes will occur between low-voltage switches due to current mismatch, and the amplitude of the spike voltage may be several times the maximum blocking voltage. By using traditional active commutation techniques, including single-phase shift modulation (SPSM) and double-phase shift modulation (DPSM), the voltage can be naturally clamped, but due to the limitation of variable parameters, this technique can only work in a limited operating region, and it is difficult to achieve soft switching in a wide power range. SUMMARY

[0005] The application provides a flow-fed bidirectional DC-DC converter based on magnetic integration and double transformers, which comprises a feeding inductor, a low-voltage end basic full-bridge circuit, a high-voltage end basic full-bridge circuit, a high-voltage end basic half-bridge circuit, a leakage inductor and double transformers, wherein the input end of the low-voltage end basic full-bridge circuit is connected with a low-voltage terminal, the feeding inductor is connected in series between the input end of the low-voltage end basic full-bridge circuit and the low-voltage terminal, the output end of the low-voltage end basic full-bridge circuit is connected with the input end of the double transformers, the leakage inductor is connected in series between the output end of the low-voltage end basic full-bridge circuit and the input end of the double transformers, the output end of the double transformers is connected with the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit respectively, and the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit are connected in parallel to a high-voltage terminal.

[0006] As a further improvement of the application, the flow-fed bidirectional DC-DC converter further comprises a first filter capacitor, one end of the first filter capacitor is connected with a positive pole of the low-voltage terminal and one end of the feeding inductor respectively, and the other end of the first filter capacitor is connected with a negative pole of the low-voltage terminal and the low-voltage end basic full-bridge circuit respectively.

[0007] As a further improvement of the application, the flow-fed bidirectional DC-DC converter further comprises a second filter capacitor and a third filter capacitor, wherein,

[0008] one end of the second filter capacitor is connected with the high-voltage end basic full-bridge circuit, the high-voltage end basic half-bridge circuit and a high-voltage terminal V HV + respectively, and the other end of the second filter capacitor is connected with the other end of the third filter capacitor and the output end of the double transformers respectively;

[0009] one end of the third filter capacitor is further connected with the output end of the double transformers, and the other end of the third filter capacitor is further connected with the high-voltage end basic half-bridge circuit, the high-voltage end basic full-bridge circuit and a high-voltage terminal V HV - respectively.

[0010] As a further improvement of the application, the double transformers comprise a first transformer and a second transformer, one end of the primary side of the first transformer is connected with the other end of the leakage inductor, the other end of the primary side of the first transformer is connected with one end of the primary side of the second transformer, the secondary side of the first transformer is connected with the high-voltage end basic full-bridge circuit, the other end of the primary side of the second transformer is connected with the low-voltage end basic full-bridge circuit, the other end of the first filter capacitor and the low-voltage terminal respectively, one end of the secondary side of the second transformer is connected with the high-voltage end basic half-bridge circuit, and the other end of the secondary side of the second transformer is connected with the other end of the second filter capacitor and one end of the third filter capacitor respectively.

[0011] As a further improvement of the application, the low-voltage end basic full-bridge circuit comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, wherein,

[0012] One end of the first switch tube is connected with the other end of the power supply inductor and one end of the third switch tube respectively, and the other end of the first switch tube is connected with one end of the second switch tube and one end of the leakage inductor respectively.

[0013] One end of the second switch tube is also connected with one end of the leakage inductor, and the other end of the second switch tube is connected with the negative pole of the low-voltage terminal and the other end of the fourth switch tube respectively.

[0014] One end of the third switch tube is also connected with one end of the first switch tube, and the other end of the third switch tube is connected with one end of the fourth switch tube and the other end of the primary side of the second transformer respectively.

[0015] One end of the fourth switch tube is also connected with the other end of the primary side of the second transformer, and the other end of the fourth switch tube is also connected with the negative pole of the low-voltage terminal.

[0016] As a further improvement of the application, the high-voltage end basic full-bridge circuit comprises a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube, wherein,

[0017] One end of the fifth switch tube is connected with one end of the secondary side of the first transformer and one end of the sixth switch tube respectively, and the other end of the fifth switch tube is connected with the seventh switch tube, the high-voltage end basic half-bridge circuit, one end of the second filter capacitor and the positive pole of the high-voltage terminal respectively.

[0018] One end of the sixth switch tube is also connected with one end of the secondary side of the first transformer, and the other end of the sixth switch tube is connected with the other end of the eighth switch tube, the high-voltage end basic half-bridge circuit, the other end of the third filter capacitor and the negative pole of the high-voltage terminal respectively.

[0019] One end of the seventh switch tube is also connected with the high-voltage end basic half-bridge circuit, one end of the second filter capacitor and the positive pole of the high-voltage terminal respectively, and the other end of the seventh switch tube is also connected with the other end of the secondary side of the first transformer and one end of the eighth switch tube respectively.

[0020] One end of the eighth switch tube is also connected with one end of the secondary side of the first transformer, and the other end of the eighth switch tube is also connected with the high-voltage end basic half-bridge circuit and the other end of the third filter capacitor respectively.

[0021] As a further improvement of the application, the high-voltage end basic half-bridge circuit comprises a ninth switch tube and a tenth switch tube, wherein,

[0022] One end of the ninth switch tube is connected with one end of the second filter capacitor and the positive pole of the high voltage terminal respectively, and the other end of the ninth switch tube is connected with one end of the secondary side of the second transformer and one end of the tenth switch tube respectively.

[0023] One end of the tenth switch tube is also connected with one end of the secondary side of the second transformer, and the other end of the tenth switch tube is connected with the other end of the eighth switch tube, the other end of the sixth switch tube, the other end of the third filter capacitor and the negative pole of the high voltage terminal respectively.

[0024] As a further improvement of the application, the feeding inductor, the first transformer and the second transformer adopt an "E-I-E" shaped magnetic core structure.

[0025] As a further improvement of the application, the middle column of the two E-shaped magnetic cores is opened with an air gap, the two sides of the E-shaped magnetic core are used as mutual inductance channels without air gap, the primary and secondary side coils of the first transformer and the second transformer are symmetrically wound on the two outer magnetic columns of each E-shaped magnetic core, the inductor coils are wound on the middle columns of the two E-shaped magnetic cores, and the two inductor coils are connected in series to form the feeding inductor; the leakage inductor is wound on the middle column of the magnetic core.

[0026] As a further improvement of the application, the secondary side of the first transformer is connected with a full-bridge structure, and the turn ratio is 1:n1, and the secondary side of the second transformer is connected with a half-bridge structure, and the turn ratio is 1:n2.

[0027] The application has the following advantages: 1. The flow-fed bidirectional DC-DC converter solves the defects of the limited input and output voltage range of the traditional active commutation technology, realizes the controllable transformer leakage current peak through the topology structure of the double transformer, expands the range of voltage gain, and guarantees the soft switching performance in the full load range of the converter; 2. Different composite phase-shift modulation methods are adopted to realize the switching of three working modes of the converter to meet the needs of different working conditions in actual application, and realize higher voltage gain and power transmission limit. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the circuit principle diagram of the flow-fed bidirectional DC-DC converter of the application;

[0029] Figure 2 is the integrated magnetic core structure and simplified magnetic flux distribution diagram of the flow-fed bidirectional DC-DC converter of the application;

[0030] Figure 3 is the double transformer excitation voltage and alternating current magnetic flux waveform diagram of the flow-fed bidirectional DC-DC converter of the application;

[0031] Figure 4 is a diagram of the dual transformer operation modes of the current-fed bidirectional DC-DC converter of the present invention; Figure 4(a) shows forward power transmission (P>0), and Figure 4(b) shows reverse power transmission (P<0);

[0032] Figure 5 shows the detailed operating waveforms and equivalent circuit diagrams of the current-fed bidirectional DC-DC converter of the present invention during forward power transmission in Mode I, at various time intervals; Figure 5(a) before time t0; Figure 5(b) t0-t1; Figure 5(c) t1-t2; Figure 5(d) t2-t β Figure 5(e)t β -t α Figure 5(f)t α -t x Figure 5(g) Figure 5(h)

[0033] Figures 6(a) and 6(b) show the leakage inductance current i of the current-fed bidirectional DC-DC converter in Mode II. Llk Waveform diagram and equivalent circuit diagram of the rising phase;

[0034] Figure 7 shows the leakage inductance current i of the current-feed bidirectional DC-DC converter of the present invention in Mode III. Llk Waveform diagram and equivalent circuit diagram of the rising phase;

[0035] Figure 8 shows the actual operating regions of the current-fed bidirectional DC-DC converter of the present invention under different modes; Figure 8(a) is mode I, Figure 8(b) is mode II, Figure 8(c) is mode III, and Figure 8(d) is modes I, II, and III.

[0036] Figure 9 This is a flowchart of the modulation strategy for the current-feed bidirectional DC-DC converter of the present invention. Detailed Implementation

[0037] This invention discloses a current-fed bidirectional DC-DC converter based on magnetic integration and dual transformers, such as... Figure 1 As shown, this current-fed bidirectional DC-DC converter is installed at the low-voltage terminal V. LV and high voltage terminal V HV Between, bidirectional to the low-voltage terminal V LV or high voltage terminal V HV Provides DC power, low-voltage terminal V LV and high voltage terminal V HV The first filter capacitor C is connected in parallel. LV Second filter capacitor C HV1 Third filter capacitor C HV2 This current-fed bidirectional DC-DC converter also includes a low-voltage side feed inductor L and a first switching transistor S.1a , the second switch tube S 2a , the third switch tube S 3a , the fourth switch tube S 4a , the basic full-bridge structure, high-frequency double transformer (first transformer Tr1 and second transformer Tr2) and its total series equivalent leakage inductance L lk , the high-voltage side by the fifth switch tube S 1b , the sixth switch tube S 2b , the seventh switch tube S 3b , the eighth switch tube S 4b , the basic full-bridge structure and by the ninth switch tube S 5b , the tenth switch tube S 6b , the basic half-bridge structure.

[0038] Low-voltage side topology, connected to the low-voltage terminal V LV , including series feeding inductance L and low-voltage end basic full-bridge circuit, while suppressing current ripple, realizing Boost voltage, for easy analysis, the first switch tube S 1a , the second switch tube S 2a , the bridge arm A is called, the third switch tube S 3a , the fourth switch tube S 4a , the bridge arm B is called.

[0039] High-voltage side topology, including high-voltage end basic full-bridge circuit and basic half-bridge topology circuit in parallel combination, for easy analysis, the fifth switch tube S 1b , the sixth switch tube S 2b , the bridge arm C is called, the seventh switch tube S 3b , the eighth switch tube S 4b , the bridge arm D is called, the ninth switch tube S 5b , the tenth switch tube S 6b , the bridge arm E is called, the output side is connected to the high-voltage terminal V HV .

[0040] Double transformer (first transformer T r1 and second transformer T r2 ) secondary side is independently connected to two high-voltage side H bridge, the secondary side of the first transformer T r1 Connects the full-bridge structure, the turns ratio is 1:n1; the secondary side of the second transformer T r2 Connects the half-bridge structure, the turns ratio is 1:n2.

[0041] The flow-fed bidirectional DC-DC converter of the application can work in a single transformer mode due to the parallel configuration of the high-voltage side. When the high-voltage side bridge arm fails, the transformer is switched to make the converter switch to a half-bridge operation mode based on SPSM or a full-bridge operation mode based on DPSM, thereby improving the reliability of the converter to a certain extent.

[0042] In the flow-fed bidirectional DC-DC converter topology of the application, the primary sides of the two transformers are connected in series, and the currents flowing through the primary side windings of the two transformers are the same; the high-voltage side is in a parallel structure, and the leakage current i Llk of the transformer is controlled by the common control of the primary side voltage v r1 of the first transformer T CD and the primary side voltage v r2 of the second transformer T EF . In order to make the peak value of i Llk controllable and reduce the circulating current under non-full load conditions, it is necessary to offset v CD and v EF to each other, and the voltage applied to the leakage inductance L lk is zero, and i Llk stops rising.

[0043] The feeding inductance L LV of the low-voltage side is connected to the positive pole of the low-voltage terminal V 1a , and the other end is connected to the input end of the low-voltage side basic full-bridge topology; the bridge arm A midpoint of the first switch S 2a , the second switch S lk comprises one end of the leakage inductance L lk , the other end of the leakage inductance L r1 is connected to one end of the primary side of the first transformer T r1 , and the other end of the primary side of the first transformer T r2 is connected in series with the primary side of the second transformer T r2 ; the other end of the primary side of the second transformer T 3a is connected to the midpoint of the bridge arm B composed of the third switch S 4a and the fourth switch S HV .

[0044] The bridge arm C and the bridge arm D of the high-voltage side together constitute a basic full-bridge topology, the bridge arm D and the filter capacitor constitute a basic half-bridge topology, and the two are connected in parallel to the high-voltage terminal V 1b ; the midpoint of the bridge arm C composed of the fifth switch S 2b and the sixth switch S r1 is connected to one end of the secondary side of the first transformer T 3b , and the midpoint of the bridge arm D composed of the seventh switch S 4b and the eighth switch S r1 is connected to one end of the secondary side of the first transformer Tthe other end of the secondary side; the ninth switch S 5b , the tenth switch S 6b The midpoint of the bridge arm E composed of the second transformer T r2 is connected to the second transformer T HV1 One end of the secondary side, the midpoint of two high-voltage side filter capacitors (second filter capacitor C HV2 ) is connected to the second transformer T r2 The other end of the secondary side.

[0045] The power supply inductance L and the high-frequency double transformer (the first transformer T r1 and the second transformer T r2 ) are designed using magnetic integration technology, as shown in Figure 2 In the "E-I-E" core structure, the middle column of the two E-shaped cores is opened with an air gap, and the two sides of the E-shaped core are used as mutual inductance channels without air gap.

[0046] On the two outer magnetic columns of each E-shaped core, the primary and secondary side coils of the first transformer T r1 and the second transformer T r2 are symmetrically wound. Because the magnetic resistance of the middle column with an air gap is large, the main magnetic flux Φ Tr1 and Φ Tr2 of the two transformer windings mainly flows through the outer magnetic columns of the E-shaped core. The excitation voltage and its alternating magnetic flux waveform of the double transformer in the converter are shown in Figure 3 .

[0047] The inductance coil is wound on the middle column of the two E-shaped cores, and the two inductances are connected in series as the power supply inductance L of the converter. The main magnetic flux Φ L of the power supply inductance mainly flows through the middle column of the E-shaped core and then evenly divides into the outer magnetic columns. The auxiliary inductance is wound on the middle column of the core and connected in series with the secondary side coil of the transformer, so as to design the leakage inductance L lk of the transformer according to requirements.

[0048] Specifically, to ensure that the voltage applied to the leakage inductance L lk is zero, it is necessary to cancel each other out by converting v CD and v EF to the primary side, so the amplitude of v CD is twice that of v EF , n1=2n2.

[0049] In the composite phase-shift modulation, three control variables β, α and are considered, where β is defined as the phase shift angle between the driving signal of the low-voltage side first switch S 1a and the high-voltage side fifth switch S 1b , and β is negative, indicating that the fifth switch S 1bThe phase of the driving signal is ahead of the first switch S 1a on the low-voltage side 1b ; α is defined as the fifth switch S 4b on the high-voltage side 1b and the eighth switch S 5b on the high-voltage side Llk ; and the phase shift angle between the driving signals, all in the unit of radian. The relationship between the above three variables affects the working mode of the flow-fed bidirectional DC-DC converter, and there are three working modes in the embodiment of the present application, and different working modes correspond to different secondary-side leakage inductance currents i 2a of the transformer.

[0050] Taking the working mode I of the converter proposed in the embodiment of the present application as an example, the working principle of the flow-fed bidirectional DC-DC converter when the forward power transmission (P>0) is explained in detail, as shown in Fig. 5.

[0051] For the sake of simplicity, the charging and discharging processes of the parasitic capacitances of the switches and the dead time of the high-voltage switches are ignored, and the steady-state theoretical waveforms of the converter proposed in the embodiment of the present application at different time intervals in a half switching period are analyzed in detail. The flow-fed bidirectional DC-DC converter of the present application repeats the working process symmetrically in the second half cycle:

[0052] Stage one (before t0), the second switch S 3a and the third switch S 1b on the low-voltage side are turned on, the fifth switch S 3b on the high-voltage side is forwardly turned on, and the seventh switch S 6b and the tenth switch S Llk on the high-voltage side are reversely turned on.

[0053] Further, the leakage inductance current i CD remains constant in the reverse direction, the secondary-side voltage v EF of the transformer is at zero level, v AB is negative; the primary-side voltage v HV of the transformer is –V HV / 2n2. The voltages across the non-conducting low-voltage switches and high-voltage switches are naturally clamped at V HV / 2n2 and V HV , respectively.

[0054] Stage two (t0 to t1), the low-voltage side switches are all turned on, and the high-voltage side switches remain unchanged.

[0055] Further, the voltage of –V lk / 2n2 is applied to the leakage inductance L Llk .The leakage current i Llk increases with a fixed slope S2a . S3a decreases linearly S1a . S4a increases from zero, thus reducing the turn-on loss; at time t1, i Llk = 0 and i S2a = i S3a = i S1a = i S4a = I LV / 2.

[0056] Phase three (t1 to t2), all low-voltage side switch tubes are turned on, and the fifth switch tube S 1b , the seventh switch tube S 3b and the tenth switch tube S 6b achieve natural commutation.

[0057] Further, the current through the low-voltage switch tube increases or decreases with the same slope as in the previous phase; at time t2, i Llk = i S1a = i S4a = I LV and i S2a = i S3a = 0; i Llk and i S1a , i S4a The expression of current change is:

[0058]

[0059] Phase four (t2 to t β ): i Llk and i S1a , i S4a continue to increase with the original slope, the second switch tube S 2a and the third switch tube S 3a are turned on in reverse, forming a circulating current, which helps the ZCS turn-off of the second switch tube S 2a and the third switch tube S 3a ; at time t β , i Llk reaches the peak i Llk,peak .

[0060] Phase five (t β to t α ): S 3b is turned off, and the body diode of S 4b continues to flow, and S 4b can achieve ZVS turn-on, at which time v CD becomes V HV .

[0061] Further, the voltage of the primary side of the double transformer cancels each other, the voltage on the leakage inductance L lk is zero, so i Llk and i S1a , i S4a remain the peak value of the last stage, at the moment of t α , the second switch S 2a , the third switch S 3a can realize ZCS turn-off.

[0062] Stage six (t α to t x ): the tenth switch S 6b turns off, the high voltage side current is continued by the body diode of the ninth switch S 5b , the ninth switch S 5b can realize ZVS turn-on;

[0063] Further, v EF becomes V HV / 2, i Llk and i S1a , i S4a start to decrease; at the moment of t x , i Llk = i S1a = i S4a = I LV and i S2a = i S3a = 0; i Llk and i S1a , i S4a The expression of the current change is:

[0064]

[0065] Stage seven (t x to t φ ): the feeding inductance L starts to discharge, i Llk and i S1a , i S4a remain constant value I LV , the transformer primary side voltage v AB becomes V HV / n1+V HV / 2n2, the power is transmitted to the load side in the positive direction, the fifth switch S 1b turns off and its body diode starts to continue to flow, so that it realizes ZCS turn-off.

[0066] Stage eight (t φ to T s / 2): the power is transmitted in the positive direction, the sixth switch S 2b turns on, v CDto zero level; meanwhile v AB and the low voltage side switch tube end voltage is reduced to V HV / 2n2.

[0067] The waveform of the flow-fed bidirectional DC-DC converter in mode II and mode III in a half switch period is different from that in mode I only in the rising (falling) stage of the double transformer leakage current i Llk . Therefore, in order to simplify the description, the following will only analyze the working principle of the leakage current i Llk in the rising stage of mode II and mode III.

[0068] As shown in Fig. 6, for mode II, the working principle of the flow-fed bidirectional DC-DC converter in the leakage current i Llk rising stage of the present application is as follows:

[0069] In stage one (t0 to t β ), all the low voltage side switch tubes are forward conducting, and the sixth switch tube S 2b , the seventh switch tube S 3b and the tenth switch tube S 6b of the high voltage side are reverse conducting.

[0070] Further, the transformer secondary side voltage v CD is -V HV , v EF is -V HV / 2; the transformer primary side voltage v AB is zero. The sum of the secondary side voltages of the double transformer is converted to the primary side, which makes the leakage current i Llk rise at a faster speed; the switch tube currents i S2a , i S3a linearly decrease, i S1a , i S4a start to increase from zero; at t β , i Llk =I1; i Llk and i S1a current change expressions are as follows:

[0071]

[0072] In stage two (t β to t x ), all the low voltage side switch tubes are forward conducting, and the fifth switch tube S 1b , the seventh switch tube S 3b and the tenth switch tube S 6b of the high voltage side are forward conducting.

[0073] Further, the transformer secondary side voltage v CD is zero, vEF For –V HV / 2; Transformer primary voltage v AB The value is zero. The secondary voltage of the dual transformer, after being referred to the primary side, causes the leakage inductance current i to be zero. Llk Rise at a relatively slow rate; i S2a i S3a It continues to decrease linearly, and i S1a i S4a Continue to increase; at t x At that moment, i Llk =I LV i Llk and i S1a The expression for the change in current is:

[0074]

[0075] As shown in Figure 7, for mode III, the converter has a leakage inductance current i Llk The working principle of the ascending phase is as follows:

[0076] Phase 1 (t0 to t) β All low-voltage side switches are forward-biased, and the sixth high-voltage side switch S... 2b Eighth switch S 4b 10th switch S 6b Forward guidance.

[0077] Furthermore, the secondary voltage v of the transformer CD v is zero EF For –V HV / 2; Transformer primary voltage v AB The value is zero. The sum of the secondary voltages of a dual transformer, when referred to the primary side, will result in a leakage inductance current i. Llk The current of the switching transistor rises at a relatively slow rate; S2a i S3a linearly decrease, i S1a i S4a Increment starting from zero; at t β At that moment, i Llk =I2;i Llk and i S1a The expression for the change in current is:

[0078]

[0079] Phase Two (t) β To t x All low-voltage side switches are forward-biased, and the sixth high-voltage side switch S... 2b Seventh switch S 3b 10th switch S 6b Forward guidance.

[0080] Further, the transformer secondary side voltage v CD is –V HV , v EF is –V HV / 2; the transformer primary side voltage v AB is zero. The secondary side voltage of the double transformer is converted to the primary side, which makes the leakage inductance current i Llk rise at a faster speed; i S2a , i S3a continues to linearly decrease, and i S1a , i S4a continues to increase; at the moment t x , i Llk =I LV ; i Llk and i S1a The expression of the current change is:

[0081]

[0082] According to the above analysis, the rising speed of the leakage inductance current i Llk is accelerated at the moments t0 to t β of mode II and t β to t x of mode III, respectively. If only v EF acts on the rising stage of the commutation, i.e., v CD is zero in this stage, the rising slope of i Llk is V HV / 2n2L lk , at this time, mode II and mode III are degenerated to mode I to some extent; however, if v CD is also effective in this stage, the slope of i Llk becomes V HV / 2n2L lk +V HV / n1L lk .

[0083] Further, if v CD is always –V HV in this stage, the leakage inductance current i Llk will rise at the maximum slope. At this time, in the fixed rising time, the flow-fed bidirectional DC-DC converter of the present application can obtain a greater current value, which will directly affect the transmission power of the converter. Therefore, mode II and mode III can expand the transmission power capacity of the flow-fed bidirectional DC-DC converter of the present application.

[0084] For the convenience of understanding the scheme and effects of the embodiments of the present application, a specific design example is given below. Those skilled in the art should understand that the example is only for the convenience of understanding the present application, and any specific details thereof are not intended to limit the present application in any way.

[0085] In the specific design example, the low-voltage-side input voltage V LV = 20V~40V, and the nominal value is 20V; the high-voltage-side voltage V HV = 150V~600V, and the nominal value is 300V; the rated full load power P max,r = 200W; the switching frequency f s = 100kHz; the duty ratio d1 of the low-voltage-side switching tube driving signal = 0.6~0.8; the duty ratio of the high-voltage-side switching tube driving signal after considering the dead time is 0.48; the input inductance current ripple is less than 1A; and the charging time x is limited within 0.1~0.3.

[0086] The value of the input inductance L is calculated according to the current ripple:

[0087]

[0088] Specifically, for ΔI LV = 1A, L = 60μH.

[0089] For the convenience of design, the turns ratio of the double transformer is considered to be symmetrical, that is:

[0090] n1 = 2n2

[0091]

[0092] Specifically, for V LV = 20V, n1 = 6, and n2 = 3.

[0093] The calculation of the leakage inductance L lk is based on the rated full load power P max,r . Through analysis, it is known that the leakage inductance values in the three working modes are the same, and the calculation formula is:

[0094]

[0095] Specifically, for x = 0.3 and d max = 0.8, L lk = 7.5μH.

[0096] According to the above working principle analysis and calculation, the expressions of the leakage inductance current, the switching current, the voltage gain, and the transmission power of the transformer in the three working modes can be obtained, as shown in Table 1.

[0097] Table 1 Parameter expressions of the converter in different working modes

[0098]

[0099]

[0100] wherein,

[0101] The voltage gain expression in Table 1 shows that the voltage gain relationship not only depends on the turns ratio n1, n2 of the double transformer and the charging time x of the input inductor, but also depends on the newly introduced control variable This shows that compared with the SPSM and DPSM, the converter topology of the embodiment effectively expands the voltage gain range by adding a new control variable;

[0102] The actual working area of the converter in different modes described in the embodiment of the application is analyzed, as shown in Figure 8.

[0103] The maximum transmission power of the converter in mode II is twice that in mode I, and for the current-fed converter, the maximum transmission power is closely related to the maximum input current I LV . Analysis of the working principle shows that when v CD and v EF work simultaneously, the leakage inductance current i Llk has a fast rising stage; but for mode I, during the rising stage of the leakage inductance current i Llk , v CD is always zero, only v EF works, so the rising slope of the leakage inductance current i Llk is half of the former.

[0104] Therefore, in the same rising time, the maximum leakage inductance current I Llk,peak that can be reached by mode I is only half of that of mode II and mode III, that is, the maximum transmission power of mode I is only half of that of mode II; but in the power transmission range, by comparing the effective value of the leakage inductance current I Llk , it can be known that the leakage current of mode I is smaller, and part of the loss of the converter in operation can be reduced in this mode.

[0105] Further, the converter topology described in the embodiment is essentially a boost circuit, when the converter works in mode III, the actual charging time of the input inductor L should be (mode III is negative), and in a half cycle, the sum of the charging and discharging time of the input inductor is 0.5 times the unit value, so the charging time of the input inductor in this mode is longer than that in mode I and mode II, and the corresponding discharging time is shorter.

[0106] Therefore, the mode III can effectively improve the voltage gain of the whole converter. In theory, the voltage gain of the mode III can reach infinity. Therefore, when the output voltage is required to be greater than 300V, the converter can be operated in the mode III.

[0107] As shown in FIG. 1, the control strategy of the converter topology of the embodiment in three working modes is as follows: Figure 9

[0108] Firstly, according to the conditions of the input voltage and the output voltage, when the output voltage is required to be greater than 300V, the mode III is entered. If the output voltage is required to be in the range of 150-300V, the transmission power needs to be judged. If the transmission power is in the range of the mode I, the mode I is selected, at this time, the effective value of the leakage inductance current is the smallest, and the transmission loss of the converter is the smallest; if the transmission power exceeds the maximum value of the mode I, the mode II is selected.

[0109] The duty ratio d2 of the driving signal of the high-voltage side switch tube is kept as 0.5, and the upper and lower switch tubes of the same bridge arm are complementarily turned on;

[0110] The duty ratio d1 of the driving signal of the low-voltage side switch tube is set as The diagonal switch tube driving signals are the same, and the upper and lower switch tubes of the same bridge arm are complementarily turned on and overlap.

[0111] According to the phase relationship of the high-voltage side switch tube driving signal waveform, the working mode of the flow-fed bidirectional DC-DC converter is judged:

[0112] When the phase of the driving signal of the fifth switch tube S 1b of the high-voltage side is ahead of the phase of the driving signal of the first switch tube S 1a of the low-voltage side, the phase of the driving signal of the eighth switch tube S 4b of the high-voltage side, and the phase of the driving signal of the ninth switch tube S 5b of the high-voltage side, the converter operates in the working mode I;

[0113] Under the working mode I, the three control variables of the converter have the following size relationship: β < 0,

[0114] When the phase of the driving signal of the fifth switch tube S 1b of the high-voltage side lags behind the phase of the driving signal of the first switch tube S 1a of the low-voltage side, the phase of the driving signal of the fifth switch tube S 1b of the high-voltage side is ahead of the phase of the driving signal of the eighth switch tube S 4b of the high-voltage side, and the phase of the driving signal of the ninth switch tube S 5b of the high-voltage side, the flow-fed bidirectional DC-DC converter operates in the working mode II;

[0115] ​Under the working mode II, the three control variables of the flow-fed bidirectional DC-DC converter are in the following size relationship: 0≤β≤x, 0≤α≤0.5-β,

[0116] When the fifth switch S 1b The phase of the driving signal lags behind the first switch S 1a And the ninth switch S 5b The phase of the driving signal leads ahead of the eighth switch S 1b The phase of the driving signal lags behind the first switch S 4b The fifth switch S

[0117] Under the working mode III, the three control variables of the flow-fed bidirectional DC-DC converter are in the following size relationship: 0≤β≤0.5,

[0118] Compared with the traditional full-bridge or half-bridge bidirectional DC-DC converter, the converter topology proposed in the embodiment expands the operating range of the converter by using the dual-transformer structure of the integrated magnetic core structure. In addition, new modes (mode II and mode III) based on mode I are proposed, higher voltage gain and power transmission limit are realized, and the soft switching of the converter in the full load range is ensured.

[0119] The flow-fed bidirectional DC-DC converter based on magnetic integration and dual transformer disclosed in the application combines a new topology structure and a modulation strategy, widens the working area of the converter, i.e. wide input and output voltage range, high voltage gain, wide power transmission range and wide soft switching range, and further improves the performance of the bidirectional DC-DC converter.

[0120] The flow-fed bidirectional DC-DC converter has the following advantages: 1. The flow-fed bidirectional DC-DC converter solves the defect that the input and output voltage range of the traditional active commutation technology has limitations, realizes controllable transformer leakage inductance current peak value through the topology structure of the dual transformer, expands the range of voltage gain, and ensures the soft switching performance of the converter in the full load range; 2. Different composite phase-shift modulation methods are adopted to realize the switching of the three working modes of the converter to meet the requirements of different working conditions in actual application occasions, realize higher voltage gain and power transmission limit.

[0121] The above content is a further detailed description of the application in combination with the specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, some simple deductions or substitutions can be made without departing from the concept of the application, and all of them should be regarded as falling within the protection scope of the application.

Claims

1. A magnetic integration and dual transformer based flow-fed bidirectional DC-DC converter, characterized in that: The power supply circuit comprises a feeding inductor (L), a low-voltage end basic full-bridge circuit, a high-voltage end basic full-bridge circuit, a high-voltage end basic half-bridge circuit, a leakage inductor (L lk ), a double transformer, an input end of the low-voltage end basic full-bridge circuit is connected with a low-voltage terminal (V V LV ), a feeding inductor (L) is further connected in series between the input end of the low-voltage end basic full-bridge circuit and a low-voltage terminal (V V LV ), an output end of the low-voltage end basic full-bridge circuit is connected with an input end of the double transformer, the leakage inductor (L lk ) is further connected in series between the output end of the low-voltage end basic full-bridge circuit and the input end of the double transformer, output ends of the double transformer are respectively connected with the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit, the high-voltage end basic full-bridge circuit and the high-voltage end basic half-bridge circuit are connected in parallel and then connected to a high-voltage terminal (V V HV ). The double transformer comprises a first transformer (Tr1) and a second transformer (Tr2); The feeding inductor (L), the first transformer (Tr1) and the second transformer (Tr2) adopt an "E-I-E" shaped magnetic core structure; The E-shaped magnetic core is provided with two E-shaped magnetic cores, and the middle columns of the two E-shaped magnetic cores are opened to form air gaps. The two sides of the E-shaped magnetic core are used as mutual inductance channels, and no air gap is arranged. The primary and secondary side coils of the first transformer (1) and the second transformer (2) are symmetrically wound on the two outer magnetic columns of each E-shaped magnetic core. Inductance coils are wound on the middle columns of the two E-shaped magnetic cores, and the two inductance coils are connected in series to form the feeding inductance (L). T r1 ) and the second transformer (2) are symmetrically wound on the two outer magnetic columns of each E-shaped magnetic core. Inductance coils are wound on the middle columns of the two E-shaped magnetic cores, and the two inductance coils are connected in series to form the feeding inductance (L). T r2 ​ 2. The flow-fed bidirectional DC-DC converter of claim 1, wherein: This flow-fed bidirectional DC-DC converter also includes a first filter capacitor ( C LV ), the first filter capacitor ( C LV One end is connected to the low-voltage terminal ( V LV The positive terminal is connected to one end of the feed inductor (L), and the first filter capacitor ( C LV The other end is connected to the low-voltage terminal ( V LV The negative terminal and the low-voltage terminal are basically connected to the full-bridge circuit.

3. The flow-fed bidirectional DC-DC converter of claim 1 or 2, characterized in that: The flow-fed bidirectional DC-DC converter further comprises a second filter capacitor (C2) C HV1 ), a third filter capacitor (C3) C HV2 , wherein, The second filter capacitor ( C HV1 One end is connected to the high-voltage end basic full-bridge circuit, the high-voltage end basic half-bridge circuit, and the high-voltage terminal ( V HV The positive terminal is connected, and the second filter capacitor ( C HV1 The other end is connected to the third filter capacitor ( C HV2 One end is connected to the output end of the dual transformer; The third filter capacitor ( C HV2 ) is also connected with the double transformer output end at one end, and the third filter capacitor ( C HV2 ) is also connected with the high-voltage end basic half-bridge circuit, the high-voltage end basic full-bridge circuit and the high-voltage terminal ( V HV ) negative electrode at the other end, respectively.

4. The flow-fed bidirectional DC-DC converter of claim 3, wherein: One end of the primary side of the first transformer (Tr1) is connected with the other end of the leakage inductance (L lk ), the other end of the primary side of the first transformer (Tr1) is connected with one end of the primary side of the second transformer (Tr2), the secondary side of the first transformer (Tr1) is connected with the high-voltage end basic full-bridge circuit, the other end of the primary side of the second transformer (Tr2) is respectively connected with the low-voltage end basic full-bridge circuit, the other end of the first filter capacitor (C C LV ), the low-voltage terminal (V V LV ), one end of the secondary side of the second transformer (Tr2) is connected with the high-voltage end basic half-bridge circuit, the other end of the secondary side of the second transformer (Tr2) is respectively connected with the other end of the second filter capacitor (C C HV1 ), and one end of the third filter capacitor (C C HV2 ).

5. The flow-fed bidirectional DC-DC converter of claim 4, wherein: The low-voltage end basic full-bridge circuit comprises a first switch tube (S 1a ), a second switch tube (S 2a ), a third switch tube (S 3a ) and a fourth switch tube (S 4a ), wherein, The first switch (S) 1a One end of the transistor is connected to the other end of the feed inductor (L) and the third switch (S). 3a One end is connected, and the first switch (S) 1a The other end is connected to the second switching transistor (S) 2a One end, the leakage inductance (L) lk One end is connected; One end of the second switch tube (S 2a ) is also connected with one end of the drain inductor (L lk ), and the other end of the second switch tube (S 2a ) is connected with the negative pole of the low-voltage terminal (V V LV ) and the other end of the fourth switch tube (S 4a ) respectively; One end of the third switch tube (S 3a ) is also connected with one end of the first switch tube (S 1a ), and the other end of the third switch tube (S 3a ) is respectively connected with one end of the fourth switch tube (S 4a ) and the other end of the primary side of the second transformer (Tr2). One end of the fourth switch tube (S 4a ) is also connected with the other end of the primary side of the second transformer (Tr2), and the other end of the fourth switch tube (S 4a ) is also connected with the negative pole of the low-voltage terminal (V V LV ).

6. The flow-fed bidirectional DC-DC converter of claim 5, wherein: The high-voltage end basic full-bridge circuit comprises a fifth switch tube (S 1b ), a sixth switch tube (S 2b ), a seventh switch tube (S 3b ) and an eighth switch tube (S 4b ), wherein, One end of the fifth switch tube (S 1b ) is connected with one end of the secondary side of the first transformer (Tr1) and one end of the sixth switch tube (S 2b ) respectively, and the other end of the fifth switch tube (S 1b ) is connected with the seventh switch tube (S 3b ), the high-voltage end of the basic half-bridge circuit, the first end of the second filter capacitor (C C HV1 ) and the positive electrode of the high-voltage terminal (V V HV ) respectively. The sixth switch tube (S 2b ) has one end connected with one end of the secondary side of the first transformer (Tr1), and the other end of the sixth switch tube (S 2b ) is connected with the other end of the eighth switch tube (S 4b ), the basic half-bridge circuit of the high-voltage end, the other end of the third filter capacitor (C C HV2 ), and the negative electrode of the high-voltage terminal (V V HV ). One end of the seventh switch tube (S 3b ) is also connected with the high-voltage end of the basic half-bridge circuit, one end of the second filter capacitor (C C HV1 ), the positive electrode of the high-voltage terminal (V V HV ), and the other end of the seventh switch tube (S 3b ) is also connected with the other end of the secondary side of the first transformer (Tr1) and one end of the eighth switch tube (S 4b ). One end of the eighth switch tube (S 4b ) is also connected with one end of the secondary side of the first transformer (Tr1), and the other end of the eighth switch tube (S 4b ) is also connected with the high voltage end basic half-bridge circuit and the other end of the third filter capacitor (C C HV2 ), respectively.

7. The flow-fed bidirectional DC-DC converter of claim 6, wherein: The high-voltage end basic half-bridge circuit comprises a ninth switch tube (S 5b ), a tenth switch tube (S 6b ), wherein, One end of the ninth switch tube (S 5b ) is connected with one end of the second filter capacitor (C C HV1 ) and the positive electrode of the high-voltage terminal (V V HV ) respectively, and the other end of the ninth switch tube (S 5b ) is connected with one end of the secondary side of the second transformer (Tr2) and one end of the tenth switch tube (S 6b ) respectively. One end of the tenth switch tube (S 6b ) is also connected with one end of the secondary side of the second transformer (Tr2), and the other end of the tenth switch tube (S 6b ) is respectively connected with the other end of the eighth switch tube (S 4b ), the other end of the sixth switch tube (S 2b ), the other end of the third filter capacitor (C C HV2 ), and the negative electrode of the high-voltage terminal (V V HV ).

8. The flow-fed bidirectional DC-DC converter of claim 1, wherein: The leakage inductance (L lk ) is wound in the core leg; the first transformer (Tr1) is connected with full-bridge structure at the secondary side, with a turns ratio of 1:n1, and the second transformer (Tr2) is connected with half-bridge structure at the secondary side, with a turns ratio of 1:n2.

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