Improved Z-source network DC-DC converter and converter for hydrogen fuel cell

Abstract

The invention discloses an improved Z-source network DC-DC converter for a hydrogen fuel cell. The input end of the converter is connected to a DC power supply, and the output end of the converter is connected to an inverter bridge; the direct-current power supply comprises a hydrogen fuel cell; comprising a Z-source network, diodes D0, D1 and D2, capacitors C3 and C4, an inductor L3 and switching tubes S7 and S8. The Z-source network comprises L1, L2, C1 and C2; the output positive electrode of the Z-source network is connected with the negative electrode of the D0, the positive electrode of the S7 and the positive electrode of the D1, and the output negative electrode is connected with the negative electrodes of the S7, the C3 and the C4; the positive electrode of the C3 is connected with the negative electrode of the D1 and the positive electrode of the S8, and the negative electrode of the C3 is connected with the positive electrode of the D2; the negative electrode of the S8 is connected with the negative electrode of the D2 and the positive electrode of the L3; the positive electrode of the C4 is connected with the negative electrode of the L3, the positive electrode of the C4 is also used for connecting the input positive electrode of the inverter bridge, and the negative electrode of the C4 is also used for connecting the input negative electrode of the inverter bridge; the anode of the D0 is connected to the anode of a direct-current power supply; the output cathode of the Z-source network is also connected to the cathode of the DC power supply. The invention also discloses a converter.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed hydrogen fuel cell grid connection, and in particular to an improved Z-source network DC-DC converter and converter for hydrogen fuel cells. Background Art

[0002] As distributed fuel cell power generation systems gradually become an important scenario for current hydrogen power generation, how to ensure that hydrogen fuel cells are stably connected to the DC microgrid and ensure the stability of the connection has become an urgent problem that needs to be solved. Therefore, it is necessary to improve the control of the distributed power grid-connected interface, strengthen harmonic control, optimize power quality, and assist in improving system stability.

[0003] As a typical distributed energy system with soft output characteristics, the hydrogen fuel cell system outputs a DC power with a small voltage and large fluctuations, which cannot directly provide a stable and high voltage for the inverter bridge to convert into the required AC power. In 2004, Professor Peng Fangzheng proposed a Z-source inverter, which uses a unique X-type impedance network to connect the input side and the inverter bridge. In the direct state, the input end and the capacitor are used to magnetize the inductor; in the non-direct state, the inductor is demagnetized, and the boost function is achieved by controlling the duration of the direct state. Therefore, the inverter has the effect of boosting and inverting, overcoming the problem that the traditional inverter can only invert but not boost. However, the traditional Z-source inverter alone still cannot adapt to the wide range of output characteristics of fuel cells, resulting in frequent voltage fluctuations at the upper and lower ends of the bridge arm in the non-direct state, and there is also the problem of inrush current at startup. The existing technology suppresses the inrush current through a current limiting resistor and increases the voltage through a step-up transformer to overcome the problem of insufficient boosting capability of the Z-source inverter and inrush current at startup. However, the existing technology still has the problem that the DC side voltage fluctuates frequently and is unstable, and the fuel cell voltage fluctuates greatly and affects the power quality, which has not been solved.

[0004] Therefore, a new technical solution is urgently needed to solve the technical problems in the existing technology that the DC side voltage is unstable and the hydrogen fuel cell voltage fluctuations affect the power quality. Summary of the invention

[0005] The present invention provides an improved Z-source network DC-DC converter and converter for hydrogen fuel cells, which are used to solve the technical problems in the prior art of unstable DC side voltage and large voltage fluctuation of hydrogen fuel cells affecting power quality.

[0006] To achieve the above object, the present invention provides an improved Z source network DC-DC converter for a hydrogen fuel cell, wherein the input end of the converter is connected to a DC power supply, and the output end is connected to an inverter bridge; the DC power supply includes a hydrogen fuel cell; and includes: a Z source network, a diode D 0 , D 1and D 2 , capacitor C 3 and C 4 , inductance L 3 And the switch tube S 7 and S 8 ; Z source network includes L 1 , L 2 , C 1 and C 2 ;

[0007] The positive output of the Z source network is connected to D 0 The negative electrode, S 7 The positive electrode and D 1 The positive pole is connected to the output negative pole and S 7 , C 3 and C 4 The negative pole of C 3 The positive electrode and D 1 The negative electrode and S 8 The positive electrode of C 3 The negative electrode and D 2 The positive electrode is connected to S 8 The negative electrode and D 2 The negative electrode and L 3 The positive electrode is connected to 4 The positive electrode and L 3 The negative pole of C 4 The positive pole is also used to connect the positive pole of the inverter bridge input, C 4 The negative pole is also used to connect the negative pole of the inverter bridge input; D 0 The positive pole of is used to connect to the positive pole of the DC power supply; the negative pole of the output of the Z source network is also used to connect to the negative pole of the DC power supply;

[0008] S 7 and S 8 It is used to turn on or off according to a preset duty cycle, so that the converter forms one of the first branch, the second branch, the third branch or the fourth branch within the divided interval of the preset switching cycle, thereby completing DC-DC voltage stabilization.

[0009] Preferably, making the converter form one of the first branch, the second branch, the third branch or the fourth branch in the divided intervals of the preset working cycle, thereby completing the DC-DC voltage stabilization includes:

[0010] DC-DC voltage regulation includes the boost process and the buck process connected in sequence:

[0011] The step-up process includes: the order in which the converter forms branches includes a first mode and a second mode that are alternating and continuous; the first mode includes forming a first branch and a second branch that are alternating and continuous, and the second mode includes forming a third branch and a fourth branch that are alternating and continuous;

[0012] The step-down process includes: the order in which the converter forms branches includes an alternating third mode and a fourth mode; the third mode includes forming an alternating first branch and a third branch, and the second mode includes forming an alternating second branch and a fourth branch.

[0013] Preferably, alternating continuously includes two situations:

[0014] Assume that the alternating succession includes both A and B;

[0015] Case 1: Start with A and continue alternating;

[0016] Case 2: Continuous alternation starts from B.

[0017] Preferably, the first branch includes:

[0018] Converter S 7 On, S 8 Shut down to form the first branch;

[0019] The states of the components in the first branch include: D 0 and D 1 Shutdown, D 2 On; L 1 and L 2 Discharge is C 1 and C 2 Charging; L 3 Discharge is C 4 Charging; C 3 Energy storage.

[0020] Preferably, the second branch includes:

[0021] Converter S 7 and S 8 All are turned on to form a second branch;

[0022] The states of the components in the second branch include: D 0 , D 1 and D 2 All off; L 1 and L 2 Discharge is C 1 and C 2 Charging; C 3 Discharge is L 3 Charging; L 3 Discharge is C 4 Charging, C 4 The discharge is used to supply the inverter bridge.

[0023] Preferably, the third branch includes:

[0024] Converter S 7and S 8 All are shut down to form a third branch;

[0025] The states of the components in the third branch include: D 0 , D 1 and D 2 Both are on; DC power supply is L 1 and L 2 Charging; C 1 and C 2 Discharge is C 3 Charging; L 3 Discharge is C 4 Charge.

[0026] Preferably, the fourth branch includes:

[0027] Converter S 7 Shutdown, S 8 Conducting, forming the fourth branch;

[0028] The states of the components in the fourth branch include: D 0 and D 1 On, D 2 Off; DC power supply is L 1 and L 2 Charging; C 1 and C 2 Discharge is C 3 Charging; C 3 Discharge is L 3 Charging, 3 Discharge is C 4 Charging; C 4 The discharge is used to supply the inverter bridge.

[0029] Preferably, it also includes:

[0030] Assume the switching period is T S , C 3 The reference voltage is V C3C , then d 1 It can be expressed by the following relationship:

[0031] d 1 =(K P1 +K i1 / s)(V C3C -V C3 )

[0032] Among them, K P1 and K i1 Respectively represent the capacitance C 3 The proportional coefficient and integral coefficient of the closed-loop control loop;

[0033] Assume the switching period is T S, C 4 The reference voltage is V C4C , then d 2 It can be expressed by the following relationship:

[0034] d 2 =(K P2 +K i2 / s)(V C4C -V C4 )

[0035] Among them, K P2 and K i2 Respectively represent the capacitance C 4 The proportional coefficient and integral coefficient of the closed-loop control loop;

[0036] D 1 and d 2 Respectively with the switching period T S The triangular carrier is compared and the PWM technology is used to control S 7 , S 8 on and off states.

[0037] A converter is also provided, which comprises at least the improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention.

[0038] The present invention has the following beneficial effects:

[0039] The improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention improves the DC / DC topology based on the Z-source network, so that the converter of the present invention can be applied to distributed fuel cell grid-connected systems with large output voltage fluctuation range and slow response speed. Since the DC boost link in the traditional grid-connected system is not added, but the boost inversion function can be achieved at the same time, the circuit structure is simplified, the investment cost is reduced, and the reliability of distributed fuel cell grid connection is improved.

[0040] The converter of the present invention, including the improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention, has the same technical effect as the converter of the present invention.

[0041] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0043] Figure 1 It is a schematic diagram of the converter structure of the preferred embodiment 1 of the present invention.

[0044] Figure 2 This is a schematic diagram of the first branch of the preferred embodiment 1 of the present invention.

[0045] Figure 3 This is a schematic diagram of the second branch of the preferred embodiment 1 of the present invention.

[0046] Figure 4 This is a schematic diagram of the third branch of the preferred embodiment 1 of the present invention.

[0047] Figure 5 Schematic diagram of the fourth branch of the preferred embodiment 1 of the present invention

[0048] Figure 6 It is a schematic diagram of the converter structure of the second preferred embodiment of the present invention.

[0049] Figure 7 1 is a waveform diagram of the voltage across capacitor C3 of the second preferred embodiment of the present invention.

[0050] Figure 8 It is a waveform diagram of the voltage across capacitor C4 (DC side of the inverter) in the second preferred embodiment of the present invention.

[0051] Fig. 9 This is a waveform diagram of the through duty cycle d1 of S7 in the second preferred embodiment of the present invention.

[0052] Fig.10 It is a waveform diagram of the through duty cycle d2 of S8 in the second preferred embodiment of the present invention.

[0053] Fig.11 This is a grid-connected current waveform diagram of the second preferred embodiment of the present invention.

[0054] Fig.12 This is a grid-connected voltage waveform diagram of the second preferred embodiment of the present invention. DETAILED DESCRIPTION

[0055] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0056] Embodiment 1:

[0057] See also Figure 1 In a preferred embodiment of the present invention, an improved Z source network DC-DC converter for a hydrogen fuel cell is provided, wherein the input end of the converter is connected to a DC power supply, and the output end is connected to an inverter bridge; the DC power supply includes a hydrogen fuel cell; the converter includes: a Z source network, a diode D 0 , D 1 and D 2 , capacitor C3 and C 4 , inductance L 3 And the switch tube S 7 and S 8 .

[0058] The Z source network includes the inductor L 1 and L 2 And the capacitor C 1 and C 2 ; L 1 The positive and negative electrodes are respectively 1 and C 2 The positive electrode is connected to L 2 The positive and negative electrodes are respectively 1 and C 2 The negative pole of L 1 The positive and negative poles are the positive poles of the Z source network output; L 2 The positive and negative poles are the negative poles of the Z source network output.

[0059] The positive output of the Z source network is connected to D 0 The negative electrode, S 7 The positive electrode and D 1 The positive pole is connected to the output negative pole and S 7 , C 3 and C 4 The negative pole of C 3 The positive electrode and D 1 The negative electrode and S 8 The positive electrode of C 3 The negative electrode and D 2 The positive electrode is connected to S 8 The negative electrode and D 2 The negative electrode and L 3 The positive electrode is connected to 4 The positive electrode and L 3 The negative pole of C 4 The positive pole is also used to connect the positive pole of the inverter bridge input, C 4 The negative pole is also used to connect the negative pole of the inverter bridge input; D 0 The positive pole of the Z source network is used to connect to the positive pole of the power supply; the positive pole of the output of the Z source network is also used to connect to the negative pole of the power supply.

[0060] S 7 and S 8 It is used to turn on or off according to a preset duty cycle, so that the converter forms one of the first branch, the second branch, the third branch or the fourth branch within the divided interval of the preset switching cycle, thereby completing DC-DC voltage stabilization.

[0061] In a preferred embodiment of the present invention, the converter is made to form one of the first branch, the second branch, the third branch or the fourth branch in the divided interval of the preset working cycle, thereby completing the DC-DC voltage stabilization specifically including:

[0062] See also Figures 2 to 5 , connect the converter to a DC power source, specifically to a DC voltage source V 0 and a stabilizing capacitor C to stabilize the battery voltage 0 .

[0063] DC-DC voltage regulation includes the boost process and the buck process connected in sequence:

[0064] The step-up process includes: the order in which the converter forms branches includes a first mode and a second mode that are alternating and continuous; the first mode includes forming a first branch and a second branch that are alternating and continuous, and the second mode includes forming a third branch and a fourth branch that are alternating and continuous;

[0065] The step-down process includes: the order in which the converter forms branches includes an alternating third mode and a fourth mode; the third mode includes forming an alternating first branch and a third branch, and the second mode includes forming an alternating second branch and a fourth branch.

[0066] Assume that the alternating sequence includes both A and B. The alternating sequence includes two situations:

[0067] Case 1: Start with A and continue alternating;

[0068] Case 2: Continuous alternation starts from B.

[0069] In the preferred embodiment of the present invention, see Figure 2 , the first branch specifically includes:

[0070] Converter S 7 On, S 8 Shut down to form the first branch;

[0071] The states of the components in the first branch include: D 0 and D 1 Shutdown, D 2 On; L 1 and L 2 Discharge is C 1 and C 2 Charging; L 3 Discharge is C 4 Charging; C 3 Energy storage.

[0072] In the preferred embodiment of the present invention, see Figure 3 , the second branch specifically includes:

[0073] Converter S 7 and S 8 All are turned on to form a second branch;

[0074] The states of the components in the second branch include: D 0 , D 1 and D 2 All off; L 1 and L 2 Discharge is C 1 and C 2 Charging; C 3 Discharge is L 3 Charging; L 3 Discharge is C 4 Charging, C 4 The discharge is used to supply the inverter bridge.

[0075] In the preferred embodiment of the present invention, see Figure 4 , the third branch specifically includes:

[0076] Converter S 7 and S 8 All are shut down to form a third branch;

[0077] The states of the components in the third branch include: D 0 , D 1 and D 2 Both are on; DC power supply is L 1 and L 2 Charging; C 1 and C 2 Discharge is C 3 Charging; L 3 Discharge is C 4 Charge.

[0078] In the preferred embodiment of the present invention, see Figure 5 , the fourth branch specifically includes:

[0079] Converter S 7 Shutdown, S 8 Conducting, forming the fourth branch;

[0080] The states of the components in the fourth branch include: D 0 and D 1 On, D 2 Off; DC power supply is L 1 and L 2 Charging; C 1 and C 2 Discharge is C 3 Charging; C 3 Discharge is L 3 Charging, 3 Discharge is C4 Charging; C 4 The discharge is used to supply the inverter bridge.

[0081] In the preferred embodiment of the present invention, assuming that the switching period is T S , C 3 The reference voltage is V C3C , then d 1 It can be expressed by the following relationship:

[0082] d 1 =(K P1 +K i1 / s)(V C3C -V C3 )

[0083] Among them, K P1 and K i1 Respectively represent the capacitance C 3 The proportional coefficient and integral coefficient of the closed-loop control loop;

[0084] Assume the switching period is T S , C 4 The reference voltage is V C4C , then d 2 It can be expressed by the following relationship:

[0085] d 2 =(K P2 +K i2 / s)(V C4C -V C4 )

[0086] Among them, K P2 and K i2 Respectively represent the capacitance C 4 The proportional coefficient and integral coefficient of the closed-loop control loop.

[0087] D 1 and d 2 Respectively with the switching period T S The triangular carrier is compared and the PWM technology is used to control S 7 , S 8 on and off states.

[0088] That is, first actually measure C 3 and C 4 The actual voltage V C3 and V C4 , respectively with their respective reference values ​​V C3C and V C4C The error signal obtained by subtracting is used as the input of the PI controller, and the output is d 1 and d 2, and then use the triangle carrier PWM technology to control the switch tubes S7 and S8 to turn on and off, so that the actual voltage V C3 and V C4 is adjusted, and as time goes by, the error signal approaches 0, that is, the actual voltage V C3 and V C4 Gradually approaching their respective reference values ​​V C3C and V C4C .

[0089] The improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention improves the DC / DC topology based on the Z-source network, so that the converter of the present invention can be applied to distributed fuel cell grid-connected systems with large output voltage fluctuation range and slow response speed. Since the DC boost link in the traditional grid-connected system is not added, but the boost inversion function can be achieved at the same time, the circuit structure is simplified, the investment cost is reduced, and the reliability of distributed fuel cell grid connection is improved.

[0090] Embodiment 2:

[0091] In a preferred embodiment of the present invention, a converter is provided, and the converter at least includes the improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention.

[0092] See also Figure 6 In a preferred embodiment of the present invention, the converter specifically includes a distributed fuel cell system, an improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention, a three-phase inverter bridge, an LC filter, a load and a three-phase AC power supply connected in sequence.

[0093] The three-phase inverter bridge includes a switch tube S 1 , S 2 , S 3 , S 4 , S 5 and S 6 , switch tube S 1 , S 3 and S 5 The emitter of S 2 , S 4 and S 6 The collector connection of S 1 , S 3 and S 5 The collectors of S are connected to each other; 2 , S 4 and S 6 The emitters of the three-phase inverter bridge are connected to each other. At any time, one switch tube is turned on and one switch tube is turned off on the same bridge arm of the three-phase inverter bridge, which is the same as the working mode of the traditional inverter bridge.

[0094] The LC filter includes a filter inductor LCA , L CB and L CC And the filter capacitor C CA , C CB and C CC ,; filter inductance L CA , L CB and L CC The positive poles are connected to the output side of the three-phase inverter bridge; the filter capacitor C CA , C CB and C CC The positive pole of the filter inductor L CA , L CB and L CC The negative pole of the filter capacitor C CA , C CB and C CC The negative poles are grounded respectively.

[0095] Verification part: When the output voltage of the distributed fuel cell is V 0 =323V~213V, the through duty ratio is simulated under the condition of voltage closed loop PI control tracking determination. The DC side voltage of the inverter bridge of the present invention, the grid-connected output three-phase current and voltage waveform, S 7 , S 8 Direct duty cycle d 1 ,d 2 The waveform results are as follows Figures 7 to 12 shown.

[0096] The derivation of the boost factor B includes:

[0097] Set S 7 With S 8 The through duty ratios are d 1 , d 2 , the switching period is T S ;

[0098] Set V L1 , V L2 , V L3 , V C1 , V C2 , V C3 and V C4 They are inductance L 1 , inductance L 2 , inductance L 3 , capacitor C 1 , capacitor C 2 , capacitor C 3 , capacitor C 4 The voltage across the terminals, V S7 For S 7 The voltage across the terminals, and L 1 =L2 =L 3 , C 1 =C 2 =C 3 =C 4 ;

[0099] V C3L With V C4L They are the theoretical values ​​of the boost capacitor voltage and the buck capacitor voltage respectively.

[0100] Under the above conditions, when the converter enters steady-state operation, the following voltage relationship derivation process can be obtained:

[0101] according to Figures 2 to 3 The working principle diagram in the straight-through state shown in the figure can obtain the following relationship:

[0102] V L1 =V C1 =V L2 =V C2 =V L =V C

[0103] V L3 =V L '=V C4L =V C '

[0104] V S7 =0

[0105] according to Figures 4 to 5 The working principle diagram in the non-through state shown in the figure can obtain the following relationship:

[0106] V S7 =V C3L =V 0 =V L +V C

[0107] V L3 =V C4L -V C3L =V L '=V C ' C -V C

[0108] The direct-flow time of the converter is d 1 T S , the non-through time is (1-d 1 )T S .

[0109] Under steady-state conditions, according to the volt-second balance principle, the average voltage of the inductor of the Z source network in one switching cycle is 0. The following relationship can be derived from the above content:

[0110]

[0111] V C '=V C4L =d 2 V C3L

[0112] It can be concluded that the boost factor B of the present invention is:

[0113]

[0114] from Figures 7 to 10 It can be seen that the output voltage of the distributed fuel cell is V 0 =323V~213V, the DC side voltage of the inverter, that is, the capacitor C 4 The voltage is stable at 1000V, d 2 Stable at around 0.63, d 1 It is stable at around 0.39, and the boost factor value corresponding to the total voltage gain of the system is B=3.096~4.695, which is consistent with the derived calculation results.

[0115] from Figure 11 to Figure 12 It can be seen that the output voltage of the distributed fuel cell is V 0 =323V~213V, the output of the converter is an AC current with a peak value of 110A and an AC voltage with a peak value of 311V, with low harmonic content. It realizes the inverter function of converting DC power into AC power when the output voltage of the fuel cell fluctuates in a wide range, and still allows the power grid to obtain good power quality.

[0116] The simulation results show that the circuit structure of the present invention not only has the advantage of stably outputting high-quality AC power when the output voltage of the fuel cell fluctuates in a wide range, but also has low control complexity.

[0117] The converter of the present invention, including the improved Z-source network DC-DC converter for hydrogen fuel cells of the present invention, has the same technical effect as the converter of the present invention.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An improved Z-source network DC-DC converter for a hydrogen fuel cell, wherein the input end of the converter is connected to a DC power supply, and the output end is connected to an inverter bridge; the DC power supply includes a hydrogen fuel cell; characterized in that: include: Z source network, diodes D0, D1 and D2, capacitors C3 and C4, inductor L3 and switch tubes S7 and S8; the Z source network includes L1, L2, C1 and C2; The output positive electrode of the Z source network is connected to the negative electrode of D0, the positive electrode of S7 and the positive electrode of D1, and the output negative electrode is connected to the negative electrodes of S7, C3 and C4; the positive electrode of C3 is connected to the negative electrode of D1 and the positive electrode of S8, and the negative electrode of C3 is connected to the positive electrode of D2; the negative electrode of S8 is connected to the negative electrode of D2 and the positive electrode of L3; the positive electrode of C4 is connected to the negative electrode of L3, the positive electrode of C4 is also used to connect to the positive electrode of the inverter bridge input, and the negative electrode of C4 is also used to connect to the negative electrode of the inverter bridge input; the positive electrode of D0 is used to connect to the positive electrode of the DC power supply; the output negative electrode of the Z source network is also used to connect to the negative electrode of the DC power supply; The S7 and S8 are used to turn on or off according to a preset duty cycle, so that the converter forms one of the first branch, the second branch, the third branch or the fourth branch within the divided interval of the preset switching cycle, thereby completing DC-DC voltage stabilization.

2. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 1, characterized in that: The converter is configured to form one of the first branch, the second branch, the third branch or the fourth branch in the divided intervals of the preset working cycle, thereby completing the DC-DC voltage stabilization, including: The DC-DC voltage regulation includes a voltage step-up process and a voltage step-down process connected in sequence: The step-up process includes: the order in which the converter forms branches includes a first mode and a second mode that are alternating and continuous; the first mode includes forming a first branch and a second branch that are alternating and continuous, and the second mode includes forming a third branch and a fourth branch that are alternating and continuous; The step-down process includes: the order in which the converter forms branches includes an alternating third mode and a fourth mode; the third mode includes forming an alternating first branch and a third branch, and the second mode includes forming an alternating second branch and a fourth branch.

3. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 2, characterized in that: The alternating continuity includes two situations: Assume that the alternating succession includes both A and B; Case 1: Start with A and continue alternating; Case 2: Continuous alternation starts from B.

4. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 3, characterized in that: The first branch comprises: In the converter, S7 is turned on and S8 is turned off, forming the first branch; The states of the components in the first branch include: D0 and D1 are turned off, and D2 is turned on; L1 and L2 are discharged to charge C1 and C2; L3 is discharged to charge C4; and C3 stores energy.

5. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 3, characterized in that: The second branch comprises: S7 and S8 in the converter are both turned on to form the second branch; The states of the components in the second branch include: D0, D1 and D2 are all turned off; L1 and L2 discharge to charge C1 and C2; C3 discharges to charge L3; L3 discharges to charge C4, and C4 discharges to supply the inverter bridge.

6. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 3, characterized in that: The third branch comprises: S7 and S8 in the converter are both turned off to form the third branch; The states of the components in the third branch include: D0, D1 and D2 are all turned on; the DC power supply charges L1 and L2; C1 and C2 discharge to charge C3; L3 discharges to charge C4.

7. The improved Z-source network DC-DC converter for hydrogen fuel cells according to claim 3, characterized in that: The fourth branch comprises: In the converter, S7 is turned off and S8 is turned on, forming the fourth branch; The states of the components in the fourth branch include: D0 and D1 are turned on, D2 is turned off; the DC power supply charges L1 and L2; C1 and C2 discharge to charge C3; C3 discharges to charge L3; L3 discharges to charge C4; C4 discharges to supply the inverter bridge.

8. The improved Z-source network DC-DC converter for hydrogen fuel cells according to any one of claims 1 to 7, characterized in that: Also includes: Assume the switching period is T S , the reference voltage of C3 is V C3C , then d1 can be expressed by the following relationship: d1=(K P1 +K i1 / s)(V C3C -V C3 ) Among them, K P1 and K i1 Respectively represent the proportional coefficient and integral coefficient of the closed-loop control loop of capacitor C3; Assume the switching period is T S , the reference voltage of C4 is V C4C , then d2 can be expressed by the following relationship: d2=(K P2 +K i2 / s)(V C4C -V C4 ) Among them, K P2 and K i2 They represent the proportional coefficient and the integral coefficient of the closed-loop control circuit of capacitor C4 respectively; Set d1 and d2 to switch period T S The triangular carrier is compared with the control circuit, and the on and off states of S7 and S8 are controlled by PWM technology.

9. A converter, characterized in that: The converter comprises at least the improved Z-source network DC-DC converter for hydrogen fuel cells as claimed in any one of claims 1 to 8.

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