Control method, device and system of high-gain modularized multi-level direct-current converter for hydrogen fuel cell

Abstract

The invention discloses a control method of a high-gain modularized multi-level direct-current converter for a hydrogen fuel cell, which comprises the following steps of: setting a reference value of direct-current voltage output by the converter, and measuring an actual value; obtaining the duty ratio of a fourth sub-module according to the reference value and the actual value; obtaining a first signal and a fourth sub-module switching tube driving signal according to the duty ratio of the fourth sub-module; the fourth sub-module switch tube driving signal comprises a second switch tube driving signal; performing phase shift according to the first signal to obtain second and third signals; adding a second switch tube driving signal to the first, second and third signals to obtain switch tube driving signals of the first, second and third sub-modules; switching tubes are controlled according to the switching tube driving signals of all the modules, and two or three sub-modules are periodically selected from the first sub-module, the second sub-module, the third sub-module and the fourth sub-module according to preset conditions to be alternately put into operation. The invention further provides a control device and system of the high-gain modularized multi-level direct-current converter for the hydrogen fuel cell.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a control method, device and system for a high-gain modular multi-level DC converter for a hydrogen fuel cell. Background Art

[0002] As the demand for renewable energy in human society increases, distributed power generation has been widely used. However, the networking of a large proportion of distributed power sources may bring about problems such as the power angle, voltage, and frequency stability of the large system power grid. Therefore, it is necessary to improve the control of the distributed power grid interface, strengthen harmonic control, optimize power quality, and assist in improving system stability.

[0003] The grid-connected system is an important component of the fuel cell distributed power generation system, and the output of distributed energy sources such as fuel cells and solar energy is a DC power supply with a low voltage and large fluctuations. It cannot directly provide a stable and high voltage, nor can it stably supply grid energy. Therefore, it is necessary to use power electronics technology to invert these DC outputs to obtain the required AC power. In 2022, Dr. Zhu Xiaoquan proposed a high-gain modular multilevel resonant DC boost converter based on a quasi-Z source network. It inherits the advantages of MMC (modular multilevel converter). By increasing the switching frequency of the lower bridge arm power switching device, the lower bridge arm only needs to use one submodule, thereby reducing the size and cost of the converter. In addition, the lower bridge arm submodule of the converter can achieve ZVS (zero-voltage-switching), greatly reducing the switching loss of the converter. The converter has good linear characteristics, does not require complex closed-loop control, and can achieve self-balancing of the submodule capacitor voltage in the open-loop state. However, facing the technical problem that the wide range output of distributed fuel cells is difficult to stabilize to a high voltage and thus realize high voltage direct hanging, although the existing control method of the high-gain modular multi-level resonant DC boost converter based on the quasi-Z source network can work stably in the open-loop state, and the sub-module capacitor voltage can achieve self-balancing, but in the existing method, all sub-modules of the converter are put into operation at any time, and too many sub-modules are put into operation for a long time, which will lead to an increase in the converter failure rate and reduce the reliability of the system. At the same time, the converter has not yet been applied to the field of hydrogen fuel cell power generation.

[0004] Therefore, a new technical solution is urgently needed to solve the technical problem that in the existing control method of a high-gain modular multi-level resonant DC boost converter based on a quasi-Z-source network, all sub-modules are put into operation for a long time, resulting in an increased converter failure rate and reduced system reliability. Summary of the invention

[0005] The present invention provides a control method, device and system for a high-gain modular multi-level DC converter for a hydrogen fuel cell, which is used to solve the technical problem that in the existing control method of a high-gain modular multi-level resonant DC boost converter based on a quasi-Z source network, all sub-modules are put into operation for a long time, resulting in an increased converter failure rate and reduced system reliability.

[0006] To achieve the above object, the present invention provides a control method for a high-gain modular multi-level DC converter for a hydrogen fuel cell, comprising:

[0007] A reference value of the converter output DC voltage is set; an actual value of the converter output DC voltage is measured; and a switch duty cycle of the fourth submodule of the converter is obtained through voltage closed-loop control according to the reference value and the actual value of the output DC voltage.

[0008] The first signal and the switch tube driving signal of the fourth submodule are obtained according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube.

[0009] A preset phase shift process is performed on the first signal to obtain the second signal and the third signal respectively; the first signal, the second signal and the third signal are respectively added with the driving signal of the second switching tube, and then the switch tube driving signals of the first submodule, the second submodule and the third submodule of the converter are obtained through a limiter.

[0010] The switch tubes in the converter are controlled according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and two or three submodules are periodically selected from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

[0011] Preferably, obtaining the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule includes:

[0012] The switch duty cycle and frequency of the fourth submodule are set to the preset switching frequency f s The triangular carrier is compared to obtain the first signal.

[0013] The switch duty cycle of the fourth submodule is set to 3 times the preset switching frequency f s The triangular carrier is compared to obtain the driving signal of the first switch tube; the driving signal of the first switch tube is inverted to obtain the driving signal of the second switch tube.

[0014] Preferably, the switch duty cycle of the fourth submodule can be calculated by the following relationship:

[0015]

[0016] Wherein, d represents the switch duty cycle of the fourth submodule; K P is the proportionality coefficient; K i is the integral coefficient; s is a complex variable; U ref Indicates the reference value of the converter output DC voltage; U o Indicates the actual value of the converter output DC voltage.

[0017] Preferably, performing a preset phase shift process on the first signal to obtain the second signal and the third signal respectively comprises:

[0018] Phase shift the driving signal of the first signal Get the second signal.

[0019] Phase shift the driving signal of the first signal Get the third signal.

[0020] in,

[0021] Preferably, controlling the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically selecting two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately comprises:

[0022] When the switch tubes in the converter are controlled according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the converter sequentially forms a first mode, a second mode, a first mode, a third mode, a first mode and a fourth mode at preset time intervals within one working cycle.

[0023] The first mode includes three submodules that are put into operation: a first submodule, a second submodule, and a third submodule.

[0024] The second mode, the third mode, and the fourth mode include two submodules in operation: the fourth submodule and one of the first submodule, the second submodule, or the third submodule.

[0025] Preferably, the first mode includes:

[0026] In the first mode, the switch S 1 , S 2 , S 3 and S 5 Both are turned on, the switch tube S 4 Turn off, the capacitor C 1 , C 2 and C 3 Put into operation, capacitor C 4 In the cut-off state, that is, the first submodule, the second submodule and the third submodule are put into operation; the diode D1 Withstand reverse voltage drop cutoff, low voltage side voltage source V 0 and capacitor C 6 Through the switch tube S 5 The circuit is composed of an inductor L 1 Charging, capacitor C 5 Through the switch tube S 5 is the inductance L 2 Charge.

[0027] Preferably, the second mode includes:

[0028] In the second mode, the switch S 1 and S 4 The switch tube S is turned on. 2 , S 3 and S 5 are all turned off, then the capacitor C 2 and C 3 In the cut-off state, the capacitor C 1 and C 4 put into operation, that is, the first submodule and the fourth submodule are put into operation; diode D 1 Withstand the forward voltage drop and conduct, the inductor L 1 and L 2 Release energy.

[0029] Preferably, the third mode includes:

[0030] In the third mode, the switch tube S 2 and S 4 The switch tube S is turned on. 1 , S 3 and S 5 are all turned off, then the capacitor C 1 and C 3 In the cut-off state, the capacitor C 2 and C 4 put into operation, that is, the second submodule and the fourth submodule are put into operation; diode D 1 Withstand the forward voltage drop and conduct, the inductor L 1 and L 2 Release energy.

[0031] Preferably, the fourth mode includes:

[0032] In the fourth mode, the switch tube S 3 and S 4 The switch tube S is turned on. 1 , S 2 and S 5 are all turned off, then the capacitor C 1 and C 2 In the cut-off state, the capacitor C 3 and C4 put into operation, that is, the third submodule and the fourth submodule are put into operation; diode D 1 Withstand the forward voltage drop and conduct, the inductor L 1 and L 2 Release energy.

[0033] The present invention also provides a control device for a high-gain modular multi-level DC converter for a hydrogen fuel cell, comprising a controller, the controller being used to connect to the converter;

[0034] The controller is also used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage;

[0035] The controller is further used to obtain the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube;

[0036] The controller is also used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to obtain the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter through the limiter after adding the drive signal of the second switch tube to the first signal, the second signal and the third signal respectively;

[0037] The controller is also used to control the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

[0038] The present invention also provides a control system for a high-gain modular multi-level DC converter for a hydrogen fuel cell, comprising a control device and a converter; the control device comprises a controller; the controller is connected to the converter;

[0039] The controller is used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage;

[0040] The controller is further used to obtain the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube;

[0041] The controller is also used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to obtain the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter through the limiter after adding the drive signal of the second switch tube to the first signal, the second signal and the third signal respectively;

[0042] The controller is also used to control the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

[0043] The present invention has the following beneficial effects:

[0044] The control method of the high-gain modular multi-level DC converter for hydrogen fuel cells of the present invention obtains the switch tube duty ratio of the fourth submodule of the converter through voltage closed-loop control according to the reference value and actual value of the output DC voltage, and then obtains the switch tube drive signal of the fourth submodule, providing a data basis for the subsequent switch tube control of the fourth submodule. A first signal is obtained through voltage closed-loop control according to the reference value and actual value of the output DC voltage, and a second signal and a third signal are obtained respectively by performing a preset phase shift process according to the first signal, and the first signal, the second signal and the third signal are respectively added to the drive signal of the second switch tube, and the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter are obtained through a limiter, providing a data basis for the subsequent switch tube control of the first submodule, the second submodule and the third submodule. According to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the switch tube in the converter is controlled, and two or three submodules are periodically selected from the first submodule, the second submodule, the third submodule and the fourth submodule according to the preset combination conditions to be put into operation alternately, so that the method of the present invention reduces the number of submodules put into operation in one switching cycle, improves the control target of the reliable operation of the high-gain modular multi-level DC converter, reduces the failure rate, and improves the system operation reliability; that is, by controlling the various submodules of the converter to be put into operation alternately, the working pressure of the converter submodule is relieved, thereby greatly improving the service life of the converter. This method is suitable for long-term operation.

[0045] The control device of the high-gain modular multi-level DC converter for the hydrogen fuel cell of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0046] The control system of the high-gain modular multi-level DC converter for the hydrogen fuel cell of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0047] 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

[0048] 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:

[0049] Figure 1 It is a schematic structural diagram of a preferred embodiment of the present invention.

[0050] Figure 2 It is a schematic diagram of a method flow of a preferred embodiment of the present invention.

[0051] Figure 3 Schematic diagram of the first mode of the converter according to the preferred embodiment of the present invention.

[0052] Figure 4 Schematic diagram of the second mode of the converter according to the preferred embodiment of the present invention.

[0053] Figure 5 Schematic diagram of the third mode of the converter according to the preferred embodiment of the present invention.

[0054] Figure 6 Schematic diagram of the fourth mode of the converter according to the preferred embodiment of the present invention.

[0055] Figure 7 It is a control block diagram of solving the switch tube driving signal according to a preferred embodiment of the present invention.

[0056] Figure 8 is S of the preferred embodiment of the present invention 1 , S 2 , S 3 and S 4 Duty cycle diagram.

[0057] Fig. 9 Schematic diagram of output voltages of each submodule of a converter according to a preferred embodiment of the present invention.

[0058] Fig.10 Schematic diagram of output voltage of a converter according to a preferred embodiment of the present invention.

[0059] Fig.11 It is a partial enlarged schematic diagram of the output voltage of the converter according to the preferred embodiment of the present invention.

[0060] Fig.12 After the converter of the preferred embodiment of the present invention reaches a steady state, C 1 , C 2 , C 3and C 4 Voltage diagram.

[0061] Fig.13 After the converter of the preferred embodiment of the present invention reaches a steady state, C 5 Voltage diagram.

[0062] Fig.14 After the converter of the preferred embodiment of the present invention reaches a steady state, C 6 Voltage diagram. DETAILED DESCRIPTION

[0063] 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.

[0064] See also Figure 1 The high-gain modular multi-level DC converter of the present invention includes an inductor L 1 , L 2 and L S , capacitor C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , C 7 and C 8 , diode D 1 , D 2 , D 3 and D 4 , switch tube S 1 , S 2 , S 3 , S 4 and S 5 In the preferred embodiment of the present invention, S 4 That is, the first switch tube, S 5 That is the second switching tube.

[0065] Among them, L 1 The first end of the converter is used as the positive input terminal, L 1 The second end of the 1 The positive electrode and C 6 The first end of L 2 The second end is connected to S 4 The negative electrode, S 5 The positive electrode, D 4 The positive electrode, C 3 The second end and C 6 The second end, L 2 The first end of the D 1 The negative electrode and C 5 The first end of S 5 The negative terminal of C5 The second end and C 4 The second end of S is used as the negative input of the converter; 4 The positive terminal is connected to C 4 The first end of S 4 The negative terminal is connected to S 5 The positive electrode of the first switch tube, that is, the negative electrode of the first switch tube is connected to the positive electrode of the second switch tube; D 4 The negative terminal is connected to S 3 The negative electrode; S 3 The positive terminal is connected to C 3 The first end of S 3 The negative electrode and D 4 The negative terminal of D 3 The positive electrode and C 2 The second end, C 2 The first end is connected to S 2 The positive electrode; S 2 The negative terminal of D 3 The negative electrode; S 2 The negative electrode and D 3 The negative terminal of D 2 The positive electrode and C 1 The second end of C 1 The first end is connected to S 1 The positive electrode, S 1 The negative terminal of D 2 The negative electrode; S 1 The negative electrode and D 2 The negative terminal is connected to L S The first end of L S The second end of the C 7 The first end of the converter is used as the positive output terminal; C 7 The second end of the C 8 The first end of C 8 The second end of the converter is used as the negative input electrode of the converter and the negative output electrode of the converter. The positive input electrode and the negative output electrode of the converter are used to connect the distributed hydrogen fuel cell.

[0066] The upper bridge arm and the lower bridge arm of the converter are composed of four submodules, wherein the upper bridge arm of the converter includes the first submodule, the second submodule and the third submodule; the lower bridge arm of the converter includes the fourth submodule. 1 , D 2 and S 1 The second submodule of the converter consists of C 2 , D 3 and S 2 The third submodule of the converter consists of C 3 , D 4 and S 3 The fourth submodule of the converter consists of C4 , S 4 and S 5 constitute.

[0067] In the preferred embodiment of the present invention, the voltage and voltage direction of each component / module / port in the converter are Figure 1 Marked in.

[0068] See also Figure 2 and Figure 7 In a preferred embodiment of the present invention, a control method for a high-gain modular multi-level DC converter for a hydrogen fuel cell is provided. Figure 7 In, S 11 , S 21 , S 31 , S 41 and S 51 Respectively represent the switch tube S 1 , S 2 , S 3 , S 4 and S 5 The driving signal.

[0069] The method of the present invention comprises:

[0070] A reference value of the converter output DC voltage is set; an actual value of the converter output DC voltage is measured; and a switch duty cycle of the fourth submodule of the converter is obtained through voltage closed-loop control according to the reference value and the actual value of the output DC voltage.

[0071] The first signal and the switch tube driving signal of the fourth submodule are obtained according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube.

[0072] In a preferred embodiment of the present invention, obtaining the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule specifically includes:

[0073] The switch duty cycle and frequency of the fourth submodule are set to the preset switching frequency f s The triangular carrier is compared to obtain the first signal.

[0074] The switch duty cycle of the fourth submodule is set to 3 times the preset switching frequency f s The triangular carrier is compared to obtain the driving signal of the first switch tube; the driving signal of the first switch tube is inverted to obtain the driving signal of the second switch tube.

[0075] The switch duty cycle of the fourth submodule can be calculated using the following relationship:

[0076]

[0077] Wherein, d represents the switch duty cycle of the fourth submodule; K P is the proportionality coefficient; K i is the integral coefficient; s is a complex variable; U ref Indicates the reference value of the converter output DC voltage; U O Indicates the actual value of the converter output DC voltage.

[0078] A preset phase shift process is performed on the first signal to obtain the second signal and the third signal respectively; the first signal, the second signal and the third signal are respectively added with the driving signal of the second switching tube, and then the switch tube driving signals of the first submodule, the second submodule and the third submodule of the converter are obtained through a limiter.

[0079] In a preferred embodiment of the present invention, performing a preset phase shift process on the first signal to obtain the second signal and the third signal respectively specifically includes:

[0080] The first signal S 1 * The driving signal phase shift Get the second signal S 2 * .

[0081] The first signal S 1 * The driving signal phase shift Get the third signal S 3 * .

[0082] in,

[0083] According to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the switch tube in the converter is controlled, and two or three submodules are periodically selected from the first submodule, the second submodule, the third submodule and the fourth submodule according to the preset combination conditions to be put into operation alternately. Specifically include:

[0084] When the switch tubes in the converter are controlled according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the converter sequentially forms a first mode, a second mode, a first mode, a third mode, a first mode and a fourth mode at preset time intervals within one working cycle.

[0085] The first mode includes three submodules that are put into operation: a first submodule, a second submodule, and a third submodule.

[0086] The second mode, the third mode, and the fourth mode include two submodules in operation: the fourth submodule and one of the first submodule, the second submodule, or the third submodule.

[0087] In a preferred embodiment of the present invention, by controlling the various submodules of the converter to be put into operation alternately, the operating pressure of the converter submodules can be alleviated, thereby greatly improving the service life of the converter.

[0088] (1) The first mode specifically includes:

[0089] See also Figure 3 , in the first mode, S 1 , S 2 and S 3 are both conducting, then C 1 , C 2 and C 3 Put into operation; S 5 On, S 4 Turn off, then C 4 In the cut-off state, that is, the first submodule, the second submodule and the third submodule are put into operation; D 1 Withstand reverse voltage drop cutoff, low voltage side voltage source V 0 and C 6 By S 5 The circuit is L 1 Charging, C 5 By S 5 For L 2 Charge.

[0090] In the first mode, L 1 and L 2 The voltage U L1 and U L2 It can be expressed by the following relationship:

[0091] U L1 =V 0 +U C6

[0092] U L2 =U C5

[0093] Among them, U C6 Represents C 6 Voltage; U C5 Represents C 5 voltage.

[0094] (2) The second mode specifically includes:

[0095] See also Figure 4 , in the second mode, S 1 and S 4 On, S 2 , S 3 and S 5 If both are turned off, C 2 and C3 In the resection state, C 1 and C 4 Put into operation, that is, the first submodule and the fourth submodule are put into operation; D 1 Withstands forward voltage drop and conducts, L 1 and L 2 Release energy.

[0096] In the second mode, L 1 and L 2 The voltage U L1 and U L2 It can be expressed by the following relationship:

[0097] U L1 =V 0 -U C5

[0098] U L2 =-U C6

[0099] C 4 The voltage across the two ends is U C4 It can be expressed by the following relationship:

[0100] U C4 =U C5 +U C6

[0101] (3) The third mode specifically includes:

[0102] See also Figure 5 , in the third mode, S 2 and S 4 On, S 1 , S 3 and S 5 If both are turned off, C 1 and C 3 In the resection state, C 2 and C 4 Put into operation, that is, the second submodule and the fourth submodule are put into operation; D 1 Withstands forward voltage drop and conducts, L 1 and L 2 Release energy.

[0103] In the third mode, L 1 and L 2 The voltage U L1 and U L2 It can be expressed by the following relationship:

[0104] U L1 =V 0 -U C5

[0105] U L2 =-U C6

[0106] C 4 The voltage across the two ends is U C4 It can be expressed by the following relationship:

[0107] U C4 =U C5 +U C6

[0108] (4) The fourth mode specifically includes:

[0109] See also Figure 6 , in the fourth mode, S 3 and S 4 On, S 1 , S 2 and S 5 If both are turned off, C 1 and C 2 In the resection state, C 3 and C 4 Put into operation, that is, the third submodule and the fourth submodule are put into operation; D 1 Withstands forward voltage drop and conducts, L 1 and L 2 Release energy.

[0110] In the fourth mode, L 1 and L 2 The voltage U L1 and U L2 It can be expressed by the following relationship:

[0111] U L1 =V 0 -U C5

[0112] U L2 =-U C6

[0113] C 4 The voltage U C4 It can be expressed by the following relationship:

[0114] U C4 =U C5 +U C6

[0115] In a preferred embodiment of the present invention, in a working cycle, when the converter enters a steady state, based on the inductance L 1 and L 2 The volt-second balance principle gives:

[0116] (V0 +U C6 )dT S +(V 0 -U C5 )(1-d)T S =0

[0117] U C5 dT S +(-U C6 )(1-d)T S =0

[0118] Wherein, d represents the switch duty cycle of the fourth submodule;

[0119] Then U C5 and U C6 It can be expressed by the following relationship:

[0120] U C5 =(1-d)V 0 / (1-2d)

[0121] U C6 =dV 0 / (1-2d)

[0122] Therefore C 4 The voltage U C4 It can be expressed by the following relationship:

[0123] U C4 =V 0 / (1-2d)

[0124] When the converter works in an ideal state, the capacitor voltages U C1 , U C2 and U C3 Equal, can be expressed as U C , that is: U C1 =U C2 =U C3 =U C ; Lower bridge arm submodule capacitor voltage U C4 It is twice the upper bridge arm submodule capacitor voltage, that is: U C4 =2U C Therefore, the voltages of the upper and lower bridge arms in each working mode can be obtained. In the first mode, the voltages of the upper and lower bridge arms can be expressed as

[0125] U U =3U C

[0126] U L =0

[0127] In the second mode, the third mode and the fourth mode, the upper and lower bridge arm voltages can be expressed as

[0128] U U =U C

[0129] U L =2U C

[0130] Since the upper and lower bridge arms of the converter are connected in series to supply power to the load, the sum of the upper and lower bridge arm voltages in each mode should be equal to the high-voltage side output voltage U O , then:

[0131] U O =U U +U L =3U C

[0132] It can be seen that when the high-gain modular multi-level DC converter is controlled by the method of the present invention, the output voltage U O Still 3U C , ensuring the normal voltage output of the converter, which is consistent with the voltage output effect achieved by the prior art.

[0133] Verification part:

[0134] In the high-gain modular multi-level DC converter of the preferred embodiment of the present invention, L 1 =L 2 =0.0002H;C 5 =C 6 =1500μF; C 7 =C 8 =8000μF; L S =1.60μH; the output voltage of the distributed hydrogen fuel cell V 0 Random wide range fluctuation of 413V~587V; C 1 =C 2 =C 3 =C 4 =800μF; f S =30KHz, U ref =15000V. The simulation results are as follows:

[0135] See also Figure 8 , from top to bottom are S 1 , S 2 and S 3 The duty cycle and S 4 The duty cycle d of the submodule output voltage is Fig. 9 ,exist Fig. 9In the figure, U1, U2, U3 and U4 represent the output voltages of the first submodule, the second submodule, the third submodule and the fourth submodule respectively; it can be seen that three submodules are put into operation in half a cycle, and all output a voltage of 5000V, and two submodules are put into operation in half a cycle, one outputs a voltage of 10000V and the other outputs a voltage of 5000V.

[0136] Fig.10 The output voltage diagram of the high-gain modular multi-level DC converter is shown in Figure 2. Fig.11 for Fig.10 A partial enlarged view of Figure 10 to Figure 11 It can be seen that the output voltage of the high-gain modular multi-level DC converter of the preferred embodiment of the present invention is stabilized at about 15000V at 0.31s, and the fluctuation range is less than 0.5%, achieving a stable boost output from low voltage to high voltage.

[0137] See also Figure 12 to Figure 14 After the high-gain modular multi-level DC converter of the preferred embodiment of the present invention reaches a steady state, C 1 , C 2 , C 3 The voltage is stable at 5000V, C 4 The voltage is stable at around 10000V, C 5 and C 6 The voltage is stable at approximately 4600V and 5000V, with a small fluctuation range, which meets the requirements of the DC power generation system.

[0138] In a preferred embodiment of the present invention, a high-gain modular multi-level resonant DC boost converter based on a quasi-Z-source network is used in a distributed hydrogen fuel cell power generation system, which can adapt to the characteristics of distributed hydrogen fuel cells such as low output voltage, large fluctuation range, and slow response speed, and can achieve high-voltage direct hanging.

[0139] In summary, the control method of the high-gain modular multi-level DC converter for hydrogen fuel cells of the present invention obtains the switch tube duty ratio of the fourth submodule of the converter through voltage closed-loop control according to the reference value and actual value of the output DC voltage, and then obtains the switch tube drive signal of the fourth submodule, providing a data basis for the subsequent switch tube control of the fourth submodule. A first signal is obtained through voltage closed-loop control according to the reference value and actual value of the output DC voltage, and a second signal and a third signal are obtained respectively by performing a preset phase shift process according to the first signal, and the first signal, the second signal and the third signal are respectively added to the drive signal of the second switch tube, and then the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter are obtained through a limiter, providing a data basis for the subsequent switch tube control of the first submodule, the second submodule and the third submodule. According to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the switch tube in the converter is controlled, and two or three submodules are periodically selected from the first submodule, the second submodule, the third submodule and the fourth submodule according to the preset combination conditions to be put into operation alternately, so that the method of the present invention reduces the number of submodules put into operation in one switching cycle, improves the control target of the reliable operation of the high-gain modular multi-level DC converter, reduces the failure rate, and improves the system operation reliability; that is, by controlling the various submodules of the converter to be put into operation alternately, the working pressure of the converter submodule is relieved, thereby greatly improving the service life of the converter. This method is suitable for long-term operation.

[0140] In a preferred embodiment of the present invention, a control device for a high-gain modular multi-level DC converter for a hydrogen fuel cell is also provided, which is used in the method of the present invention, and the device includes a controller, and the controller is used to connect to the converter;

[0141] The controller is also used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage;

[0142] The controller is further used to obtain the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube;

[0143] The controller is also used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to obtain the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter through the limiter after adding the drive signal of the second switch tube to the first signal, the second signal and the third signal respectively;

[0144] The controller is also used to control the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

[0145] The control device of the high-gain modular multi-level DC converter for the hydrogen fuel cell of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0146] In a preferred embodiment of the present invention, a control system of a high-gain modular multi-level DC converter for a hydrogen fuel cell is also provided, comprising a control device and a converter; the control device comprises a controller; the controller is connected to the converter;

[0147] The controller is used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage;

[0148] The controller is further used to obtain the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes the driving signal of the second switch tube;

[0149] The controller is also used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to obtain the switch tube drive signals of the first submodule, the second submodule and the third submodule of the converter through the limiter after adding the drive signal of the second switch tube to the first signal, the second signal and the third signal respectively;

[0150] The controller is also used to control the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

[0151] The control system of the high-gain modular multi-level DC converter for the hydrogen fuel cell of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0152] 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. A control method for a high-gain modular multi-level DC converter for a hydrogen fuel cell, characterized in that: include: Setting the reference value of the converter output DC voltage; Measure the actual value of the converter output DC voltage; Obtaining a switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage; Obtaining a first signal and a switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes a driving signal of the second switch tube; Performing a preset phase shift process on the first signal to obtain a second signal and a third signal respectively; adding the first signal, the second signal and the third signal to the driving signal of the second switch tube respectively, and then obtaining the switch tube driving signals of the first submodule, the second submodule and the third submodule of the converter through a limiter; The switch tubes in the converter are controlled according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and two or three submodules are periodically selected from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

2. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 1, characterized in that: Obtaining the first signal and the switch tube driving signal of the fourth submodule according to the switch tube duty cycle of the fourth submodule includes: The switch duty cycle and frequency of the fourth submodule are set to the preset switching frequency f s The triangular carrier is compared with the first signal to obtain the first signal; The switch duty cycle of the fourth submodule is 3 times the preset switching frequency f s The triangular carrier is compared to obtain a driving signal of the first switch tube; the driving signal of the first switch tube is inverted to obtain a driving signal of the second switch tube; The switch duty cycle of the fourth submodule can be calculated by the following relationship: Wherein, d represents the switch duty cycle of the fourth submodule; K P is the proportionality coefficient; K i is the integral coefficient; s is a complex variable; U ref Indicates the reference value of the converter output DC voltage; U o Indicates the actual value of the converter output DC voltage.

3. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 2, characterized in that: Performing a preset phase shift process on the first signal to obtain a second signal and a third signal respectively comprises: The driving signal of the first signal is phase-shifted obtaining the second signal; The driving signal of the first signal is phase-shifted obtaining the third signal; in, 4. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 3, characterized in that: Controlling the switch tubes in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically selecting two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately comprises: When the switch tubes in the converter are controlled according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, the converter sequentially forms a first mode, a second mode, a first mode, a third mode, a first mode and a fourth mode at preset time intervals within a working cycle; The first mode includes three submodules put into operation: a first submodule, a second submodule and a third submodule; The second mode, the third mode and the fourth mode include two submodules in operation: the fourth submodule and one of the first submodule, the second submodule or the third submodule.

5. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 4, characterized in that: The first mode includes: In the first mode, the switches S1, S2, S3 and S5 are all turned on, and the switch S4 is turned off, then the capacitors C1, C2 and C3 are put into operation, and the capacitor C4 is in a cut-off state, that is, the first submodule, the second submodule and the third submodule are put into operation; the diode D1 is cut off due to the reverse voltage drop, the low-voltage side voltage source V0 and the capacitor C6 form a loop through the switch S5 to charge the inductor L1, and the capacitor C5 charges the inductor L2 through the switch S5.

6. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 5, characterized in that: The second mode includes: In the second mode, the switch tubes S1 and S4 are turned on, and the switch tubes S2, S3 and S5 are all turned off, then the capacitors C2 and C3 are in a cut-off state, and the capacitors C1 and C4 are put into operation, that is, the first submodule and the fourth submodule are put into operation; the diode D1 is turned on under the forward voltage drop, and the inductors L1 and L2 release energy.

7. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 6, characterized in that: The third mode includes: In the third mode, the switch tubes S2 and S4 are turned on, and the switch tubes S1, S3 and S5 are all turned off, then the capacitors C1 and C3 are in a cut-off state, and the capacitors C2 and C4 are put into operation, that is, the second submodule and the fourth submodule are put into operation; the diode D1 is turned on under the forward voltage drop, and the inductors L1 and L2 release energy.

8. The control method of the high-gain modular multi-level DC converter for a hydrogen fuel cell according to claim 7, characterized in that: The fourth mode includes: In the fourth mode, the switch tubes S3 and S4 are turned on, and the switch tubes S1, S2 and S5 are all turned off, then the capacitors C1 and C2 are in a cut-off state, and the capacitors C3 and C4 are put into operation, that is, the third submodule and the fourth submodule are put into operation; the diode D1 is turned on under the forward voltage drop, and the inductors L1 and L2 release energy.

9. A control device for a high-gain modular multi-level DC converter for a hydrogen fuel cell, characterized in that: comprising a controller, the controller being used to be connected to the converter; The controller is also used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage; The controller is further configured to obtain a first signal and a switch tube driving signal of the fourth submodule according to a switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes a driving signal of the second switch tube; The controller is further used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to add the first signal, the second signal and the third signal to the driving signal of the second switch tube respectively, and then obtain the switch tube driving signals of the first submodule, the second submodule and the third submodule of the converter through the limiter; The controller is also used to control the switch tube in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

10. A control system for a high-gain modular multi-level DC converter for a hydrogen fuel cell, characterized in that: It comprises a control device and a converter; the control device comprises a controller; the controller is connected to the converter; The controller is used to set a reference value of the converter output DC voltage, measure the actual value of the converter output DC voltage, and obtain the switch duty cycle of the fourth submodule of the converter through voltage closed-loop control according to the reference value and the actual value of the output DC voltage; The controller is further configured to obtain a first signal and a switch tube driving signal of the fourth submodule according to a switch tube duty cycle of the fourth submodule; the switch tube driving signal of the fourth submodule includes a driving signal of the second switch tube; The controller is further used to perform a preset phase shift process according to the first signal to obtain a second signal and a third signal respectively, and to add the first signal, the second signal and the third signal to the driving signal of the second switch tube respectively, and then obtain the switch tube driving signals of the first submodule, the second submodule and the third submodule of the converter through the limiter; The controller is also used to control the switch tube in the converter according to the switch tube driving signals of the first submodule, the second submodule, the third submodule and the fourth submodule, and periodically select two or three submodules from the first submodule, the second submodule, the third submodule and the fourth submodule according to preset combination conditions to be put into operation alternately.

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