A Two-Phase Interleaved Flying Capacitor Bidirectional DC-DC Converter Based on Coupled Inductors

Abstract

The present invention discloses a two-phase interleaved flying capacitor bidirectional DC converter based on coupled inductors, which relates to the field of power electronics technology. The DC converter is two-phase interleaved and parallel-connected, and the inductors between the two phases are magnetically coupled. It includes four groups of bridge arms, four flying capacitors, a pair of coupled inductors, and two filter capacitors. Among them, the coupled inductors are reversely coupled. Each group of bridge arms is composed of four power switches connected in series, with a total of sixteen power switches. The characteristics of the present invention are that it can perform bidirectional step-up and step-down. The voltage stress of each power switch is half of the voltage bus. Interleaved parallel connection can reduce the ripple of the output current while increasing the conversion efficiency of the converter. The magnetic integration technology further reduces the inductance and the volume of the converter, reduces the phase current ripple of each phase inductor, and improves the dynamic performance of the converter at the same time. It has good application and development prospects for the energy storage link of new energy distributed power generation systems such as light and wind.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a two-phase interleaved flying capacitor bidirectional DC converter based on a coupled inductor. Background Art

[0002] Energy storage is an important part in photovoltaic and wind power generation systems. When energy storage batteries are used in combination with renewable energy sources, it can make the power generation of renewable energy sources match the grid demand in terms of time, intensity, etc., reduce the randomness of renewable energy power generation, reduce the voltage fluctuation of the DC microgrid, and improve the power generation quality. The energy storage medium is usually connected to the high-voltage bus through a bidirectional DC / DC converter, which can realize the bidirectional flow of energy between the energy storage medium and the DC bus, and can realize the control and efficient utilization of energy in the system.

[0003] Currently, the commonly used bidirectional DC / DC power converter devices can be divided into two structures: isolated topology and non-isolated topology according to whether there is electrical isolation between the input and the output. Due to the presence of a transformer, the isolated topology has higher safety, but the presence of the transformer will lead to a reduction in system efficiency and a large volume, which is not suitable for high-power energy storage systems. The non-isolated bidirectional power converter is commonly used in energy storage systems and overcomes the above disadvantages. At the same time, due to the increasing demand for high-voltage and large-capacity converters, the device voltage stress of traditional converters is challenged. Therefore, multilevel topologies have received attention. However, the current ripple of the existing DC converters with multilevel topologies is still relatively large, which greatly reduces the performance of the converter. Summary of the Invention

[0004] In view of the above problems and technical requirements, the inventor of the present invention has proposed a two-phase interleaved flying capacitor bidirectional DC converter based on a coupled inductor. The technical solution of the present invention is as follows:

[0005] A two-phase interleaved flying capacitor bidirectional DC converter based on coupled inductors, comprising a first to a fourth bridge arm arranged in sequence, a pair of coupled inductors, and four flying capacitors. The middle parts of the first bridge arm and the fourth bridge arm are connected through the first coupled inductor to form an a-phase H-bridge. The middle parts of the second bridge arm and the third bridge arm are connected through the second coupled inductor to form a b-phase H-bridge, and the first and second coupled inductors are reversely coupled. Among them, each group of bridge arms includes a first to a fourth power switch tube connected in series in sequence, and the connection end of the second and third power switch tubes is used as the middle part of the bridge arm. The two ends of the flying capacitor are respectively connected to the connection ends of the first and second power switch tubes and the connection ends of the third and fourth power switch tubes. The first power switch tubes of the first and second bridge arms are connected to form a first end, the fourth power switch tubes of the first and second bridge arms are connected to form a second end, a DC power supply is connected in parallel between the first end and the second end, the first power switch tubes of the third and fourth bridge arms are connected to form a third end, the fourth power switch tubes of the third and fourth bridge arms are connected to form a fourth end, a load is connected in parallel between the third end and the fourth end, and the second end and the fourth end are connected. The bidirectional step-up and step-down of the DC converter is realized by using interleaved individual PWM to control each power switch tube.

[0006] A further technical solution thereof is that the bidirectional step-up and step-down of the DC converter is realized by using interleaved individual PWM to control each power switch tube, including:

[0007] When the DC converter operates in the step-up and step-down modes of the step-up / step-down mode, the driving signals of the first power switch tube and the second power switch tube of the first bridge arm differ by 180°, and the driving signals of the first power switch tube and the fourth power switch tube of the first bridge arm, and the second power switch tube and the third power switch tube are complementary; the driving signals of the first power switch tube of the first bridge arm and the first power switch tube of the second bridge arm, and the second power switch tube of the first bridge arm and the second power switch tube of the second bridge arm differ by 90°; the driving signals of the first power switch tube of the first bridge arm and the fourth power switch tube of the fourth bridge arm, the second power switch tube of the first bridge arm and the third power switch tube of the fourth bridge arm, the third power switch tube of the first bridge arm and the second power switch tube of the fourth bridge arm, and the fourth power switch tube of the first bridge arm and the first power switch tube of the fourth bridge arm are the same; the driving signals of the first power switch tube of the second bridge arm and the fourth power switch tube of the third bridge arm, the second power switch tube of the second bridge arm and the third power switch tube of the third bridge arm, the third power switch tube of the second bridge arm and the second power switch tube of the third bridge arm, and the fourth power switch tube of the second bridge arm and the first power switch tube of the third bridge arm are the same.

[0008] A further technical solution thereof is that when the DC converter operates in the step-down mode of the step-up / step-down mode, the duty cycle includes two cases of 0 < D < 0.25 and 0.25 ≤ D < 0.5, where D represents the duty cycle;

[0009] When in the buck mode and the duty cycle is 0 < D < 0.25, the operating states of the H-bridges of phases a and b of the DC converter are the same throughout the entire operating cycle. The operating states of the H-bridge of phase a are as follows:

[0010] State 1: The first power switch and the third power switch of the first arm, and the second power switch and the fourth power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0011] State 2: The second power switch and the fourth power switch of the first arm, and the first power switch and the third power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0012] State 3: The third power switch and the fourth power switch of the first arm, and the first power switch and the second power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0013] When in the buck mode and the duty cycle is 0.25 ≤ D < 0.5, the operating states of the H-bridges of phases a and b of the DC converter are the same as the above three states throughout the entire operating cycle. The difference is that the operating times of State 1 and State 3 are different, resulting in a change in the final output.

[0014] A further technical solution is that when the DC converter operates in the boost mode of the buck-boost mode, the duty cycle includes two cases: 0.5 ≤ D < 0.75 and 0.75 ≤ D < 1;

[0015] When in the boost mode and the duty cycle is 0.5 ≤ D < 0.75, the operating states of the H-bridges of phases a and b of the DC converter are the same throughout the entire operating cycle. The operating states of the H-bridge of phase a are as follows:

[0016] State 1: The first power switch and the third power switch of the first arm, and the second power switch and the fourth power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0017] State 2: The second power switch and the fourth power switch of the first arm, and the first power switch and the third power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0018] State 3: The first power switch and the second power switch of the first arm, and the third power switch and the fourth power switch of the fourth arm are turned on simultaneously, and the remaining power switches are turned off;

[0019] When in the boost mode and the duty cycle is 0.75 ≤ D < 1, the operating states of the H-bridges of phases a and b of the DC converter are the same as the above three states throughout the entire operating cycle. The difference is that the operating times of State 1 and State 3 are different, resulting in a change in the final output.

[0020] A further technical solution thereof is that the voltages of the first and second coupled inductors are as follows:

[0021]

[0022] where U La is the voltage across the first coupled inductor, and U Lb is the voltage across the second coupled inductor; La and Lb are the self-inductance values of the first and second coupled inductors respectively; i La , i Lb are the currents of the first and second coupled inductors respectively; M is the mutual inductance value of the first and second coupled inductors;

[0023] The voltages of the two flying capacitors on the conducting line are respectively stabilized at half of the input and output voltages, which is expressed as:

[0024]

[0025] where U Cfly1 is the voltage of the flying capacitor on the input-side bridge arm, and U Cfly2 is the voltage of the flying capacitor on the output-side bridge arm; U i is the input voltage, and U o is the output voltage;

[0026] The relationship between the input and output voltages is:

[0027]

[0028] where D is the duty cycle in the current operating state of the DC converter;

[0029] According to the states of the power switching tubes in the current operating state of the DC converter, the relationships between the voltages of the first and second coupled inductors and the changes in inductance and current are derived based on Equations (1)-(3) as:

[0030]

[0031] When two independent inductors are used, the voltages of the independent inductors are respectively:

[0032]

[0033] Substituting La = Lb = L into Equation (5), the relationship between the current slope of the independent inductor and the inductor voltage is obtained as:

[0034]

[0035] Substitute La = Lb = L, M = -0.6L, and the duty cycle in the current working state of the DC converter into Equation (4) to obtain the relationship between the current slopes of the first and second coupled inductors and the inductor voltage. By comparing with Equation (6), the conclusion is drawn that using coupled inductors reduces the inductor current ripple of the DC converter throughout the entire cycle.

[0036] A further technical solution thereof is that the DC converter further includes a first filter capacitor and a second filter capacitor. A first filter capacitor is also connected in parallel between the first terminal and the second terminal, and a second filter capacitor is also connected in parallel between the third terminal and the fourth terminal.

[0037] The beneficial technical effects of the present invention are:

[0038] The two-phase interleaved flying capacitor bidirectional DC converter based on coupled inductors provided by the present invention uses a three-level topology to reduce the voltage stress of the power switching tubes to one-half of the bus-side voltage; through the interleaved parallel technology, the overall conversion power of the DC converter is increased, and at the same time, the voltage and current ripples on the output side are greatly reduced; the magnetic integration technology is used to reversely couple the filter inductors of the two phases, which reduces the phase current ripple of each phase inductor while improving the dynamic performance of the converter and reducing the volume of the converter, making the energy flow between the energy storage medium and the DC bus voltage more efficient and rapid, and having good application and development prospects for the energy storage link of new energy distributed power generation systems such as light and wind. Brief Description of the Drawings

[0039] Figure 1 is the topology diagram of the bidirectional DC converter provided by this application.

[0040] Figure 2 is the driving waveform diagram of each power switching tube when the converter provided by this application is in the buck mode and the duty cycle 0 < D < 0.25.

[0041] Figure 3 is the working mode diagram of the converter provided by this application when it is in the buck mode and the duty cycle is 0 < D < 0.25.

[0042] Figure 4 is the comparison diagram of the current ripples of the independent inductor and the coupled inductor when the converter provided by this application is in the buck mode and the duty cycle is 0 < D < 0.25.

[0043] Figure 5 is the driving waveform diagram of each power switching tube when the converter provided by this application is in the boost mode and the duty cycle is 0.5 ≤ D < 0.75.

[0044] Figure 6 is the working mode diagram of the converter provided by this application when it is in the boost mode and the duty cycle is 0.5 ≤ D < 0.75.

[0045] Figure 7 It is a comparison diagram of the current ripples of the independent inductor and the coupled inductor when the converter provided by this application is in the boost mode and the duty cycle is 0.5 ≤ D < 0.75. Specific embodiments

[0046] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings.

[0047] This application provides a two-phase interleaved flying capacitor bidirectional DC converter based on a coupled inductor, which includes a first to a fourth bridge arm arranged in sequence, a pair of coupled inductors, four flying capacitors, and two filter capacitors. The middle parts of the first bridge arm and the fourth bridge arm are connected by a first coupled inductor to form an a-phase H-bridge, and the middle parts of the second bridge arm and the third bridge arm are connected by a second coupled inductor to form a b-phase H-bridge, and the first and second coupled inductors are reversely coupled. Among them, each group of bridge arms includes a first to a fourth power switch tube connected in series in sequence, and the connection end of the second and third power switch tubes serves as the middle part of the bridge arm. The two ends of the flying capacitor are respectively connected to the connection end of the first and second power switch tubes and the connection end of the third and fourth power switch tubes. The first power switch tubes of the first and second bridge arms are connected to form a first end, and the fourth power switch tubes of the first and second bridge arms are connected to form a second end. A DC power supply and a first filter capacitor are connected in parallel between the first end and the second end. The first power switch tubes of the third and fourth bridge arms are connected to form a third end, and the fourth power switch tubes of the third and fourth bridge arms are connected to form a fourth end. A load and a second filter capacitor are connected in parallel between the third end and the fourth end, and the second end and the fourth end are connected. The separate PWM of each power switch tube is used in an interleaved manner to achieve the bidirectional step-up and step-down of the DC converter.

[0048] Specifically, as Figure 1 shown, this example gives the specific structure of the above DC converter, including: The first bridge arm includes S a11 , S a12 , S a13 , S a14 four power switch tubes, the second bridge arm includes S b11 , S b12 , S b13 , S b14 four power switch tubes, the third bridge arm includes S b21 , S b22 , S b23 , S b24 four power switch tubes, the fourth bridge arm includes S a21 , S a22 , S a23 , S a24 four power switch tubes, a pair of coupled inductors L a , L b , four flying capacitors C flya1, C flya2 , C flyb1 , C flyb2 , the first filter capacitor C i , the second filter capacitor C o

[0049] The connection method of the DC converter is as follows (taking the step-up / step-down from left to right as an example): the low-voltage side DC power supply E bat is connected in parallel with the first filter capacitor C i on the input side. The front bridge arm (i.e., the first bridge arm) of the a-phase H-bridge is composed of S a11 , S a12 , S a13 , S a14 connected in series. One end of the first filter capacitor C i is connected to the collector of the power switch tube S a11 , and the other end is connected to the emitter of the power switch tube S a14 ; one end of the flying capacitor C flya1 is connected to the emitter of the power switch tube S a11 and the collector of the power switch tube S a12 , and the other end is connected to the emitter of the power switch tube S a13 and the collector of the power switch tube S a14 ; one end of the first coupling inductor L a is connected to the middle of the first bridge arm, that is, between the emitter of the power switch tube S a12 and the collector of the power switch tube S a13 , and the same-named end is connected to the middle of the rear bridge arm of the a-phase H-bridge, that is, between the emitter of the power switch tube S a22 and the collector of the power switch tube S a23 ; the rear bridge arm (i.e., the fourth bridge arm) of the a-phase H-bridge is composed of S a21 , S a22 , S a23 , S a24 connected in series. One end of the flying capacitor C flya2 is connected to the emitter of the power switch tube S a21 and the collector of the power switch tube S a22 , and the other end is connected to the emitter of the power switch tube S a23 and the collector of the power switch tube S a24 ; the front bridge arm (i.e., the second bridge arm) of the b-phase H-bridge is composed of S b11 , S b12 , S b13 , S b14 connected in series. One end of the flying capacitor C flyb1 is connected to the emitter of the power switch tube S b11 and the collector of the power switch tube S b12 connected, and the other end is connected to the power switch tube Sb13 The emitter of b14 is connected to the collector of the power switch tube S b ; The same-name terminal of the second coupling inductor L b12 is connected to the middle of the second bridge arm, that is, between the emitter of the power switch tube S b13 and the collector of the power switch tube S b22 ; The other end is connected to the middle of the rear bridge arm of the b-phase H-bridge, that is, between the emitter of the power switch tube S b23 and the collector of the power switch tube S b21 ; The rear bridge arm of the b-phase H-bridge (i.e., the third bridge arm) is composed of S b22 , S b23 , S b24 connected in series, and the flying capacitor C flyb2 has one end connected to the emitter of the power switch tube S b21 and the collector of the power switch tube S b22 , and the other end connected to the emitter of the power switch tube S b23 and the collector of the power switch tube S b24 ; The first and second coupling inductors L a , L b are reversely coupled; One end of the second filter capacitor C o on the output side is connected to the collectors of the power switch tubes S a21 , S b21 , and the other end is connected to the emitters of the power switch tubes S a24 , S b24 ; The load R is in parallel with the second filter capacitor C o , with one end connected to one end of the second filter capacitor C o and the collectors of the power switch tubes S a21 , S b21 , and the other end connected to the other end of the second filter capacitor C o and the emitters of the power switch tubes S a24 , S b24 .

[0050] In this example, an interleaved individual PWM is used to control each power switch tube to achieve bidirectional buck-boost of the DC converter, including:

[0051] When the DC converter operates in the buck and boost modes of the buck-boost mode, the drive signals of the first power switch tube S a11 and the second power switch tube S a12 of the first bridge arm differ by 180°, and the drive signals of the first power switch tube S a11 and the fourth power switch tube S a14 , and the drive signals of the second power switch tube S a12 and the third power switch tube Sa13 The drive signals are complementary. The first power switch tube S of the first arm a11 and the first power switch tube S of the second arm b11 , the second power switch tube S of the first arm a12 and the second power switch tube S of the second arm b12 have drive signals that differ by 90°. The first power switch tube S of the first arm a11 and the fourth power switch tube S of the fourth arm a24 , the second power switch tube S of the first arm a12 and the third power switch tube S of the fourth arm a23 , the third power switch tube S of the first arm a13 and the second power switch tube S of the fourth arm a22 , the fourth power switch tube S of the first arm a14 and the first power switch tube S of the fourth arm a21 have the same drive signals. The first power switch tube S of the second arm b11 and the fourth power switch tube S of the third arm b24 , the second power switch tube S of the second arm b12 and the third power switch tube S of the third arm b23 , the third power switch tube S of the second arm b13 and the second power switch tube S of the third arm b22 , the fourth power switch tube S of the second arm b14 and the first power switch tube S of the third arm b21 have the same drive signals.

[0052] The buck-boost mode of the DC converter is divided into two cases where the duty cycle is greater than and less than 0.5. At the same time, due to the coupled inductor, the operating mode of the DC converter is divided into four cases according to the duty cycle: 0 < D < 0.25, 0.25 ≤ D < 0.5, 0.5 ≤ D < 0.75, and 0.75 ≤ D < 1. Based on the conduction rules of the above power switch tubes, this example mainly makes a detailed analysis of the working modes in two cases: when the DC converter is in the buck mode of the buck-boost mode and the duty cycle is 0 < D < 0.25, and when it is in the boost mode of the buck-boost mode and the duty cycle is 0.5 ≤ D < 0.75.

[0053] (1) When the converter is in the buck mode and the duty cycle is 0 < D < 0.25, each power switch tube operates according to the Figure 2 shown drive signals. During the entire working cycle, the DC converter has 8 modes and 5 working states, as Figure 3 shown, where b, d, f, and h are the same working state.

[0054] Working state 1, asFigure 3 As shown in (a): S a11 , S a13 , S a22 , S a24 and S b13 , S b14 , S b21 , S b22 conduct simultaneously. For phase a, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, the front-side bus voltage charges the first coupling inductor L a . Combining the discharge of the second coupling inductor L b at this time and the coupling effect of its discharge voltage on L a causes the inductor voltage of L a to increase, so the inductor current of phase a increases; for phase b, at this time, the second coupling inductor L b is discharging and in the freewheeling stage, but at this time L a is charging, and its charging voltage has a strong reverse coupling effect on L b , making the inductor current of phase b increase slowly at this time.

[0055] During this process, the voltages of the first and second coupling inductors are:

[0056]

[0057] where U La is the voltage across the first coupling inductor, U Lb is the voltage across the second coupling inductor; La and Lb are the self-inductance values of the first and second coupling inductors respectively; i La , i Lb are the currents of the first and second coupling inductors respectively; M is the mutual inductance value of the first and second coupling inductors.

[0058] The voltages of the two flying capacitors on the conduction line are respectively stabilized at half of the input and output voltages, expressed as:

[0059]

[0060] where U Cfly1 is the voltage of the flying capacitor Cflya1 on the input-side bridge arm, U Cfly2 is the voltage of the flying capacitor Cflya2 on the output-side bridge arm; U i is the input voltage, U o is the output voltage.

[0061] The relationship between the input and output voltages is:

[0062]

[0063] Among them, D is the duty cycle in the current working state of the DC converter. In this example, it is assumed that D = 0.2.

[0064] According to the states of the power switch tubes in the current working state of the DC converter, based on Equations (1)-(3), the relationships between the voltages of the first and second coupled inductors and the changes in inductance and current are derived as follows:

[0065]

[0066] When two independent inductors are used, the voltages of the independent inductors are respectively:

[0067]

[0068] Since the coupled inductor structure is designed with La = Lb = L, M = -0.6L, and D = 0.2 substituted into Equation (4), the relationships between the current slopes of the first and second coupled inductors and the inductor voltages are obtained as follows:

[0069]

[0070] Substituting La = Lb = L into Equation (5), the relationships between the current slopes of the independent inductors and the inductor voltages are obtained as follows:

[0071]

[0072] Comparing Equation (6) with Equation (7), it can be concluded that the current slope of the coupled inductor is smaller than that of the independent inductor.

[0073] Working state 2, as shown in Figure 3 (b): S a13 , S a14 , S a21 , S a22 and S b13 , S b14 , S b21 , S b22 conduct simultaneously. For phase a, at this time, the first coupled inductor L a is in the freewheeling stage, and the inductor current of phase a decreases; for phase b, the second coupled inductor L b is also in the freewheeling stage, and the inductor current of phase b decreases. The calculation method of the current slope is the same as that in working state 1, so the conclusion obtained is also the same and will not be elaborated here.

[0074] Working state 3, as shown in Figure 3 (c): S a13 , S a14 , S a21 , S a22 and S b11 , S b13 , S b22, S b24 conduct simultaneously. For phase a, at this time, the first coupled inductor L a is in the freewheeling stage. However, considering that L b is being charged at this time, and the charging voltage has a strong reverse coupling effect on L a , causing the inductor current of phase a to increase slowly; for phase b, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, the front-side bus voltage charges the second coupled inductor L b . Considering that L a is discharging at this time, and the discharging voltage has a coupling effect on L b , increasing the inductor voltage of L b . Therefore, the inductor current of phase b increases. The current slope calculation method is the same as that in operating state 1, so the conclusion is also the same and will not be elaborated here.

[0075] Operating state 4, as shown in Figure 3 (e): S a12 , S a14 , S a21 , S a23 and S b13 , S b14 , S b21 , S b22 conduct simultaneously. For phase a, according to the relationship of the flying capacitor voltage, it can be known that at this time, the flying capacitor Cfiya1 charges the first coupled inductor L a . Considering that the second coupled inductor L b is discharging at this time, and the discharging voltage has a coupling effect on L a , increasing the inductor voltage of L a . Therefore, the inductor current of phase a increases; for phase b, at this time, L b is in the freewheeling stage. However, L a is being charged at this time, and the charging voltage has a strong reverse coupling effect on L b , causing the inductor current of phase b to increase slowly at this time. The current slope calculation method is the same as that in operating state 1, so the conclusion is also the same and will not be elaborated here.

[0076] Operating state 5, as shown in Figure 3 (g): S a13 , S a14 , S a21 , S a22 and S b12 , S b14 , S b21 , S b23 conduct simultaneously. For phase a, at this time, the first coupled inductor L a is in the freewheeling stage. However, at this time, the second coupled inductor L bFor charging, the charging voltage has a strong reverse coupling effect on L a produces a strong reverse coupling effect, causing the inductor current of phase a to increase slowly at this time; for phase b, according to the relationship of the flying capacitor voltage, at this time the flying capacitor Cfiyb1 charges the second coupled inductor L b For charging, combined with the discharge of L a at this time, its discharge voltage has a coupling effect on L b which causes the inductor voltage of L b to increase, so the inductor current of phase b increases. The current slope calculation method is the same as that in operating state 1, so the conclusion is also the same and will not be elaborated here.

[0077] The comparison diagram of the current ripple of the coupled inductor and the current ripple of the independent inductor in the entire operating cycle is as shown in Figure 4 where the upper figure is the current ripple of the independent inductor and the lower figure is the current ripple of the coupled inductor of this application. It can be seen from this that after using the coupled inductor, the inductor current ripple of the DC converter is significantly suppressed, improving the conversion efficiency of the converter, proving the conclusion that the use of the coupled inductor reduces the inductor current ripple of the DC converter throughout the cycle; and after using the coupled inductor, the magnetic core is reduced, and the volume of the coupled inductor is also significantly reduced compared to the independent inductor, making the volume of the converter smaller and improving the power density of the converter.

[0078] (2) When the converter is in the boost mode and the duty cycle is 0.5 ≤ D < 0.75, each power switch operates according to the Figure 5 shown drive signal. There are 8 modes and 5 operating states in the DC converter throughout the operating cycle, as shown in Figure 6 where b, d, f, and h are the same operating state.

[0079] Operating state 1, as shown in Figure 6 (a): S a11 , S a12 , S a23 , S a24 and S b12 , S b14 , S b21 , S b23 conduct simultaneously. For phase a, according to the relationship between the front-side bus voltage and the flying capacitor voltage, at this time the front-side bus voltage charges the first coupled inductor L a . Combined with the discharge of the second coupled inductor L b at this time, its discharge voltage has a coupling effect on L a which causes the inductor voltage of L a to increase, so the inductor current of phase a increases rapidly; for phase b, according to the relationship of the flying capacitor voltage at this time, L b is in the discharge stage at this time, but at this time La is charged, and its charging voltage affects L b produces a strong reverse coupling effect, causing the inductor current of phase b to increase slowly.

[0080] Operating state 2, as shown in Figure 6 (b): S a11 , S a13 , S a22 , S a24 and S b12 , S b14 , S b21 , S b23 conduct simultaneously. For phase a, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, the first coupling inductor L a discharges. Combining the fact that the second coupling inductor L b discharges at this time, and the coupling effect of its discharge voltage on L a makes the discharge process of L a slower. Therefore, the inductor current of phase a decreases slowly; for phase b, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, L b discharges. Combining the fact that L a discharges at this time, and the coupling effect of its discharge voltage on L b makes the discharge process of L b slower. Therefore, the inductor current of phase b decreases slowly.

[0081] Operating state 3, as shown in Figure 6 (c): S a11 , S a13 , S a22 , S a24 and S b11 , S b12 , S b23 , S b24 conduct simultaneously. For phase a, at this time, according to the relationship of the flying capacitor voltage, it can be known that the first coupling inductor L a is in the discharge stage. However, at this time, the second coupling inductor L b is charged, and its charging voltage has a strong reverse coupling effect on L a , causing the inductor current of phase a to increase slowly; for phase b, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, the front-side bus voltage charges L b . Combining the fact that L a discharges at this time, and the coupling effect of its discharge voltage on L b makes the inductor voltage of L b increase. Therefore, the inductor current of phase b increases rapidly.

[0082] Operating state 4, as shown in Figure 6As shown in (e): S a11 、S a12 、S a23 、S a24 and S b12 、S b14 、S b21 、S b23 conduct simultaneously. For phase a, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that at this time, the front-side bus voltage charges the first coupled inductor L a . Combining with the fact that the second coupled inductor L b discharges at this time, and the coupled influence of its discharge voltage on L a causes the inductor voltage of L a to increase. Therefore, the inductor current of phase a increases rapidly; for phase b, according to the relationship of the flying capacitor voltage at this time, it can be known that L b is in the discharge stage at this time, but L a is charging at this time, and its charging voltage has a strong reverse coupling influence on L b , making the inductor current of phase b increase slowly.

[0083] Operating state 5, as Figure 6 (g) shows: S a12 、S a14 、S a21 、S a23 and S b11 、S b12 、S b23 、S b24 conduct simultaneously. For phase a, according to the relationship of the flying capacitor voltage at this time, it can be known that the first coupled inductor L a is in the discharge stage at this time, but the second coupled inductor L b is charging at this time, and its charging voltage has a strong reverse coupling effect on L a , making the inductor current of phase a increase slowly; for phase b, according to the relationship between the front-side bus voltage and the flying capacitor voltage, it can be known that the front-side bus voltage charges L b at this time. Combining with the fact that L a discharges at this time, and the coupled influence of its discharge voltage on L b causes the inductor voltage of L b to increase. Therefore, the inductor current of phase b increases rapidly.

[0084] The current slope calculation methods under the above five working conditions are the same as the current slope calculation methods under the buck mode, so the conclusions are also the same and will not be repeated here. The comparison diagram of the current ripple of the coupled inductor and the current ripple of the independent inductor summarized in the entire working cycle is shown in Figure 7, where the upper figure is the current ripple of the independent inductor, and the lower figure is the current ripple of the coupled inductor of the present application. It can be seen that after using the coupled inductor, the inductor current ripple of the converter is significantly suppressed, which improves the conversion efficiency of the converter, proving the conclusion that the use of coupled inductors reduces the inductor current ripple of the DC converter throughout the cycle; and after using the coupled inductor, the magnetic core is reduced, and the volume of the coupled inductor is also significantly reduced compared to the independent inductor, which makes the volume of the converter smaller and improves the power density of the converter.

[0085] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A two-phase interleaved flying capacitor bidirectional DC converter based on coupled inductors, characterized in that It includes a first to a fourth bridge arm arranged in sequence, a pair of coupled inductors and four flying capacitors. The middle parts of the first bridge arm and the fourth bridge arm are connected through the first coupled inductor to form an a-phase H bridge. The middle parts of the second bridge arm and the third bridge arm are connected through the second coupled inductor to form a b-phase H bridge, and the first and second coupled inductors are reversely coupled. Wherein, each group of bridge arms includes a first to a fourth power switch tube connected in series in sequence, and the connection end of the second and third power switch tubes is used as the middle part of the bridge arm. The two ends of the flying capacitor are respectively connected to the connection end of the first and second power switch tubes and the connection end of the third and fourth power switch tubes. The first power switch tubes of the first and second bridge arms are connected to form a first end, and the fourth power switch tubes of the first and second bridge arms are connected to form a second end. A DC power supply is connected in parallel between the first end and the second end. The first power switch tubes of the third and fourth bridge arms are connected to form a third end, and the fourth power switch tubes of the third and fourth bridge arms are connected to form a fourth end. A load is connected in parallel between the third end and the fourth end, and the second end and the fourth end are connected. The bidirectional buck-boost of the DC converter is realized by using staggered individual PWM to control each power switch tube.

2. The interleaved two-phase flying capacitor bidirectional DC converter based on coupled inductors according to claim 1, wherein The bidirectional buck-boost of the DC converter is realized by using staggered individual PWM to control each power switch tube, including: When the DC converter works in the boost and buck modes of the buck-boost mode, the driving signals of the first power switch tube and the second power switch tube of the first bridge arm differ by 180°. The driving signals of the first power switch tube and the fourth power switch tube of the first bridge arm, and the second power switch tube and the third power switch tube are complementary. The driving signals of the first power switch tube of the first bridge arm and the first power switch tube of the second bridge arm, and the second power switch tube of the first bridge arm and the second power switch tube of the second bridge arm differ by 90°. The driving signals of the first power switch tube of the first bridge arm and the fourth power switch tube of the fourth bridge arm, the second power switch tube of the first bridge arm and the third power switch tube of the fourth bridge arm, the third power switch tube of the first bridge arm and the second power switch tube of the fourth bridge arm, and the fourth power switch tube of the first bridge arm and the first power switch tube of the fourth bridge arm are the same. The driving signals of the first power switch tube of the second bridge arm and the fourth power switch tube of the third bridge arm, the second power switch tube of the second bridge arm and the third power switch tube of the third bridge arm, the third power switch tube of the second bridge arm and the second power switch tube of the third bridge arm, and the fourth power switch tube of the second bridge arm and the first power switch tube of the third bridge arm are the same.

3. The interleaved two-phase flying capacitor bidirectional DC converter based on coupled inductors according to claim 2, wherein When the DC converter works in the buck mode of the buck-boost mode, the duty cycle includes two cases of 0 < D < 0.25 and 0.25 ≤ D < 0.5, where D represents the duty cycle. When in the buck mode and the duty cycle is 0 < D < 0.25, the working states of the a-phase and b-phase H bridges of the DC converter are the same during the entire working cycle. The working states of the a-phase H bridge are respectively: State 1: The first power switch and the third power switch of the first bridge arm, and the second power switch and the fourth power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; State 2: The second power switch and the fourth power switch of the first bridge arm, and the first power switch and the third power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; State 3: The third power switch and the fourth power switch of the first bridge arm, and the first power switch and the second power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; When in the buck mode and the duty cycle is 0.25 ≤ D < 0.5, the operating states of the a-phase and b-phase H-bridges of the DC converter during the entire operating cycle are the same as the above three states. The difference is that the operating times of State 1 and State 3 are different, resulting in a change in the final output.

4. The interleaved two-phase flying capacitor bidirectional DC-DC converter based on coupled inductors according to claim 2, wherein The duty cycle of the DC converter in the boost mode of the buck-boost mode includes two cases: 0.5 ≤ D < 0.75 and 0.75 ≤ D < 1; When in the boost mode and the duty cycle is 0.5 ≤ D < 0.75, the operating states of the a-phase and b-phase H-bridges of the DC converter are the same during the entire operating cycle. The operating states of the a-phase H-bridge are as follows: State 1: The first power switch and the third power switch of the first bridge arm, and the second power switch and the fourth power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; State 2: The second power switch and the fourth power switch of the first bridge arm, and the first power switch and the third power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; State 3: The first power switch and the second power switch of the first bridge arm, and the third power switch and the fourth power switch of the fourth bridge arm are turned on simultaneously, and the remaining power switches are turned off; When in the boost mode and the duty cycle is 0.75 ≤ D < 1, the operating states of the a-phase and b-phase H-bridges of the DC converter during the entire operating cycle are the same as the above three states. The difference is that the operating times of State 1 and State 3 are different, resulting in a change in the final output.

5. The interleaved two-phase flying-capacitor bidirectional DC-DC converter based on coupled inductors according to any one of claims 1-4, characterized in that, The voltages of the first and second coupled inductors are: Among them, U La is the voltage across the first coupled inductor, and U Lb is the voltage across the second coupled inductor; La and Lb are the self-inductance values of the first and second coupled inductors respectively; i La , i Lb are the currents of the first and second coupled inductors respectively; M is the mutual inductance value of the first and second coupled inductors; The voltages of the two flying capacitors on the conduction line are respectively stabilized at half of the input and output voltages, expressed as: Among them, U Cfly1 is the flying capacitor voltage of the input side bridge arm, and U Cfly2 is the flying capacitor voltage of the output side bridge arm; U i is the input voltage, and U o is the output voltage; The relationship between the input and output voltages is: where D is the duty cycle of the DC converter in the current operating state; According to the power switch states of the DC converter in the current operating state, the relationship between the voltages of the first and second coupled inductors and the changes in inductance and current is derived based on Equations (1)-(3) as: When two independent inductors are used, the voltages of the independent inductors are respectively: Substituting La = Lb = L into Equation (5), the relationship between the current slope of the independent inductor and the inductor voltage is obtained as: Substitute La = Lb = L, M = -0.6L, and the duty cycle of the DC converter in the current operating state into Equation (4) to obtain the relationship between the current slopes and inductance voltages of the first and second coupled inductors. By comparing with Equation (6), the conclusion is drawn that the use of coupled inductors reduces the inductor current ripple of the DC converter throughout the cycle.

6. The interleaved two-phase flying capacitor bidirectional DC converter based on coupled inductors according to claim 5, wherein, The DC converter further includes a first and a second filter capacitor. A first filter capacitor is also connected in parallel between the first terminal and the second terminal, and a second filter capacitor is also connected in parallel between the third terminal and the fourth terminal.

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