Modular multilevel hydrogen power supply for high voltage direct current grid and control method

Abstract

The application discloses a modular multilevel hydrogen production power supply for a high-voltage direct-current power grid and a control method, belongs to the technical field of high-voltage direct-current hydrogen production, and solves the problem of how to design a non-isolated hydrogen production power supply to meet the demand of a high-voltage direct-current power grid directly supplying power to a hydrogen production electrolytic cell. The application adopts a cross connection capacitor to connect the upper and lower bridge arm midpoints of a modular multilevel converter, the cross connection capacitor is used to transmit AC power, the power balance between the bridge arms is realized by controlling the current of the cross connection capacitor, and the capacitor voltage fluctuation of the full-bridge converter is greatly reduced. Meanwhile, the modular multilevel converter adopts a full-bridge converter in series, and has a direct-current fault blocking function. The power supply has the advantages of no transformer, high transformation ratio and low cost. The control method combines output current control and capacitor voltage control, effectively controls the output side current and suppresses the capacitor voltage fluctuation of the bridge arm full-bridge module, realizes the minimization of the bridge arm circulating current, and has good output precision and anti-interference capability.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage direct current hydrogen production technology, and relates to a modular multilevel hydrogen production power supply and control method for high-voltage direct current power grids. Background Technology

[0002] With economic and social development, human demand for energy is increasing daily, but my country still relies heavily on fossil fuels. Among renewable energy sources, hydrogen, as a zero-carbon energy carrier, is widely used in my country's energy internet. Of all hydrogen production methods, natural gas production and petroleum gasification account for a significant portion, but both methods generate substantial carbon dioxide emissions. Water electrolysis for hydrogen production, however, is geared towards future carbon neutrality and even carbon-negative emissions, eliminating carbon pollution and possessing relatively mature technology.

[0003] With the continuous development of clean energy, especially the large-scale application of renewable energy sources such as solar and wind power, high-voltage direct current (HVDC) grids have become an effective means of connecting distributed energy sources to the main power grid. In such HVDC grids, how to efficiently and stably convert electrical energy into hydrogen energy has become a technically significant issue.

[0004] Traditional hydrogen production power supplies mostly consist of rectifiers made up of transformers and thyristors. This type of isolated hydrogen production power supply suffers from high energy loss and low efficiency. Modular multilevel converters have advantages such as modular design, low harmonic content in the output waveform, flexible structure, and easy expansion. They are non-isolated hydrogen production power supplies and do not require large transformers to achieve power conversion and voltage step-up / step-down, which reduces the complexity, size, weight, and cost of the system. Summary of the Invention

[0005] The purpose of this invention is to design a non-isolated hydrogen production power source to meet the demand of direct power supply from the high-voltage DC grid to the hydrogen electrolyzer.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0007] A modular multilevel hydrogen production power supply for a high-voltage direct current (HVDC) grid employs at least one modular multilevel converter (10) connected in parallel to the positive and negative terminals of the HVDC grid. The modular multilevel converter (10) includes: an upper bridge arm (11), a lower bridge arm (12), a filter inductor L1, a filter inductor L2, and a bridging capacitor C1. The upper bridge arm (11), the filter inductor L1, the filter inductor L2, and the lower bridge arm (12) are connected in series, wherein the non-series terminal of the upper bridge arm (11) serves as the positive terminal of the HVDC input. The common point of the series connection of filter inductor L1 and filter inductor L2 serves as the positive terminal of the low-voltage DC output, and the non-series terminal of the lower bridge arm (12) serves as the negative terminal of the high-voltage DC input and the negative terminal of the low-voltage DC output. The upper bridge arm (11) of the modular multilevel converter (10) uses 2N1 full-bridge converters connected in series, and the lower bridge arm (12) uses 2N2 full-bridge converters connected in series. A terminal is led out from the midpoint of the 2N1 and 2N2 full-bridge converters connected in series, respectively, to connect the two ends of the bridging capacitor C1.

[0008] Furthermore, the full-bridge converter includes: a full-bridge capacitor C, fully controlled devices S1 to S4, and diodes D1 to D4, wherein the fully controlled devices S1 to S4 and diodes D1 to D4 constitute an H-bridge structure, and the full-bridge capacitor C is connected in parallel with the H-bridge structure.

[0009] Furthermore, the full-bridge converter operates in three states, with power transferred from the high-voltage side to the low-voltage side: bypass state, charging state, and discharging state. 1) In the bypass state, current flows through diode D1 and fully controlled device S3, or through fully controlled device S2 and diode D4, but does not flow through the capacitor. 2) In the charging state, current flows through diode D1, capacitor C, and diode D4, at which point the capacitor is in a charging state. 3) In the discharging state, current flows through diode D2, capacitor C, and fully controlled device S3, at which point the capacitor is in a discharging state. By controlling the operating state of the full-bridge converter, a corresponding output voltage is obtained on the output side.

[0010] A control method for a modular multilevel hydrogen production power supply for a high-voltage DC grid includes: a DC voltage control and current sharing control unit, a capacitor voltage control unit, and a dominant voltage control unit.

[0011] The DC voltage control and current sharing control unit: measures the low-voltage side voltage v L With low-voltage side reference voltage v L,ref After comparison and adjustment by the PI controller, the target current i on the low-voltage side is generated. L * ;The low-voltage side target current i L *Divide by the number X of modular multilevel converters (10) and then divide by the low-voltage side current i of each modular multilevel converter (10). L,x After comparison and adjustment by the PI controller, the low-voltage side reference voltage v of each modular multilevel converter (10) is generated. L,x ;

[0012] The capacitor voltage control unit includes: intra-arm capacitor voltage control, inter-arm capacitor voltage balance control, and full-bridge converter capacitor voltage control;

[0013] The aforementioned bridge arm capacitor voltage control: The bridge arm capacitor reference voltage V... c * The average capacitor voltage v in the full-bridge converter within the upper arm (11) and lower arm (12) of a modular multilevel converter (10) is related to the average capacitor voltage v. c,str,x After comparison and adjustment by the PI controller, its output is then compared with the feedback current i. com After comparison and adjustment by the PI controller, the output is the adjusted voltage component Δv. c,str,x ;

[0014] The bridge arm capacitor voltage balance control includes bridge arm capacitor voltage outer loop control and AC current inner loop control. The capacitor voltage balance between the upper and lower bridge arms is achieved by controlling the AC current component. The average capacitor voltage v of the upper bridge arm (11) and lower bridge arm (12) in the modular multilevel converter (10) is calculated. c,x,1 v c,x,2 The signal is compared with the feedforward signal I after adjustment by the PI controller. ac,fwd Add them together, then multiply by sin(ωt+θ) x ), θ x =360° / X, thus generating an instantaneous AC reference current i ac,x * , and the measured alternating current i ac,x The comparison is performed, and the adjustment voltage Δv is generated after adjustment by the PI controller. c,val,x ;

[0015] The full-bridge converter capacitor voltage control: The capacitor reference voltage V... c * The measured voltage v of a single full-bridge converter capacitor c,x,i,h,j After comparison and adjustment by the PI controller, it is compared with the instantaneous current i of the corresponding upper or lower half of the bridge arm. x,i,h Multiply to generate the adjusted voltage Δv x,i,h,j ;

[0016] The dominant voltage v of the dominant voltage control unit rem,x and v ac,xWith adjustment of voltage component Δv c,str,x Δv c,val,x and Δv x,i,j Combined, a capacitor voltage reference for the full-bridge converter in the bridge arm is synthesized, and the switching devices are controlled by pulse width modulation based on the capacitor voltage reference of the full-bridge converter in the bridge arm.

[0017] Furthermore, the feedback current i com It is the current component flowing through the entire modular multilevel converter (10), and its calculation formula is as follows:

[0018] i com =0.5(i x,1,s +i x,2,f +i x,F (1)

[0019] Among them, i x,1,s i represents the current in the lower half of the upper arm of the xth modular multilevel converter (10). x,2,f i represents the current in the upper half of the lower arm of the xth modular multilevel converter (10). x,F This represents the cross-connect capacitor current of the xth modular multilevel converter (10).

[0020] Furthermore, the calculation formula for the feedforward signal is as follows:

[0021]

[0022] Among them, V H Indicates high voltage DC input, V L Indicates low-voltage DC output, i L,x V represents the output current of the xth modular multilevel converter (10). ac This represents the amplitude of the AC component of the voltage in half of the bridge arm.

[0023] Furthermore, the dominant voltage v rem,x and v ac,x It is calculated using the following formula:

[0024] v rem,x =V H -V L,x (3)

[0025] v ac,x =d ac V H (4)

[0026]

[0027]

[0028] Where, d ac Here, r is the AC voltage factor, and d is the voltage ratio. min It represents the AC voltage factor when the AC voltage component is at its minimum.

[0029] Furthermore, the calculation formula for the capacitor voltage reference of the full-bridge converter in the bridge arm is as follows:

[0030]

[0031] Among them, symbols The "±" symbol is used to distinguish between the upper and lower halves of the bridge arm.

[0032] The advantages of this invention are:

[0033] The technical solution of this invention uses a bridging capacitor to connect the midpoints of the upper and lower bridge arms of a modular multilevel converter. The bridging capacitor is used to transmit AC power. By controlling the current of the bridging capacitor, power balance between the bridge arms is achieved, thereby significantly reducing the capacitor voltage fluctuation of the full-bridge converter. At the same time, the modular multilevel converter uses a series full-bridge converter, which has a DC fault blocking function. Compared with the prior art, the power supply of this invention has the advantages of no transformer, high turns ratio, and low cost. In order to achieve stable operation of the converter, a control method combining output current control and capacitor voltage control is adopted, which can effectively control the output side current and suppress the capacitor voltage fluctuation of the full-bridge module of the bridge arm. At the same time, it can also minimize the circulating current of the bridge arm, and has good output accuracy and anti-interference capability. Attached Figure Description

[0034] Figure 1 This is a circuit topology diagram of a modular multilevel hydrogen production power supply for a high-voltage DC grid that uses only one modular multilevel converter.

[0035] Figure 2 The circuit topology diagram for a non-isolated hydrogen production power supply for a high-voltage DC grid using multiple parallel modular multilevel converters is shown.

[0036] Figure 3 This is a structural diagram of a modular multilevel converter.

[0037] Figure 4 The operating state diagram of a full-bridge converter for a modular multilevel converter;

[0038] Figure 5 A control block diagram for a modular multilevel hydrogen production power supply used in a high-voltage DC power grid;

[0039] Figure 6 The circuit topology diagram of a modular multilevel hydrogen production power supply using three modular multilevel converters for a high-voltage DC grid is shown.

[0040] Figure 7 The simulated waveform of the bridge arm voltage;

[0041] Figure 8 This is the simulated waveform of the output current. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0044] 1. Power supply topology

[0045] like Figure 1 The diagram shows the circuit topology of a modular multilevel hydrogen production power supply for a high-voltage DC grid using only one modular multilevel converter (10). The modular multilevel converter (10) includes: an upper bridge arm (11), a lower bridge arm (12), a filter inductor L1, a filter inductor L2, and a bridging capacitor C1. The upper bridge arm (11), the filter inductor L1, the filter inductor L2, and the lower bridge arm (12) are connected in series. The non-series terminal of the upper bridge arm (11) serves as the positive terminal of the high-voltage DC input, the common point of the series connection of the filter inductor L1 and the filter inductor L2 serves as the positive terminal of the low-voltage DC output, and the non-series terminal of the lower bridge arm (12) serves as the negative terminal of the high-voltage DC input and the negative terminal of the low-voltage DC output. The two ends of the bridging capacitor C1 are connected to the midpoint terminals of the upper bridge arm (11) and the lower bridge arm (12), respectively.

[0046] like Figure 2 The diagram shows a circuit topology for a non-isolated hydrogen production power supply for a high-voltage DC grid using multiple parallel modular multilevel converters (10). One parallel common terminal of the multiple modular multilevel converters (10) serves as the input high-voltage DC positive terminal, and the other parallel common terminal serves as the input high-voltage DC negative terminal and the output low-voltage DC negative terminal. The common point of the series connection of the filter inductors L1 and L2 of the multiple modular multilevel converters (10) serves as the output low-voltage DC positive terminal.

[0047] like Figure 3As shown, the upper bridge arm (11) of each modular multilevel converter (10) consists of 2N1 full-bridge converters connected in series, and the lower bridge arm (12) consists of 2N2 full-bridge converters connected in series. N1 can be equal to N2 or not. A terminal is led out from the midpoint of the 2N1 and 2N2 full-bridge converters connected in series, respectively, to connect the two ends of the bridging capacitor C1.

[0048] like Figure 3 or Figure 4 As shown, the full-bridge converter includes: a full-bridge capacitor C, fully controlled devices S1 to S4, and diodes D1 to D4. The fully controlled devices S1 to S4 and diodes D1 to D4 form an H-bridge structure, and the full-bridge capacitor C is connected in parallel with the H-bridge structure.

[0049] 2. Working principle of the power supply

[0050] Taking power transmission from the high-voltage side to the low-voltage side as an example, the operating principle of the topology of this invention is explained as follows:

[0051] The operating states of a full-bridge converter can be divided into three types according to the charging and discharging states of the capacitor: bypass state, charging state, and discharging state. 1) In the bypass state, the current flows through diode D1 and fully controlled device S3, or through fully controlled device S2 and diode D4, but does not flow through the capacitor. 2) In the charging state, the current flows through diode D1, capacitor C, and diode D4, and the capacitor is in a charging state. 3) In the discharging state, the current flows through diode D2, capacitor C, and fully controlled device S3, and the capacitor is in a discharging state. By controlling the operating state of the full-bridge converter, the corresponding output voltage is obtained on the output side.

[0052] 3. Power supply control method

[0053] The stable operation of the converter depends on the constant voltage of the full-bridge converter capacitors. The full-bridge converter voltage depends on the coordination between the capacitors and the fully controlled devices. The modulation signal mainly controls the operating state of the fully controlled devices. Therefore, optimizing the modulation strategy is an important guarantee for the stable operation of the converter. To ensure stable output voltage, balanced current in each group, and prevent overvoltage and overcurrent in any part of the system, the output voltage and the output current of each group are selected as the controlled objects, and a control strategy of voltage outer loop and current inner loop is adopted.

[0054] There are two types of imbalance in the full-bridge capacitor voltage: imbalance between capacitor voltages within the same bridge arm and deviation between capacitor voltages between the upper and lower bridge arms. Imbalance in the capacitor voltage within the same bridge arm is caused by uneven charging and discharging. This invention introduces in-arm capacitor voltage control and full-bridge converter capacitor voltage control for balancing. The flow of DC current between the bridge arms causes energy to be gradually consumed in the capacitors of one bridge arm of the full-bridge converter, while energy gradually increases in the other arm, resulting in the average voltage of the upper and lower bridge arms deviating from the nominal value. To counteract this imbalance, this invention employs in-arm capacitor voltage balancing control, utilizing controlled AC circulating current to facilitate active power exchange between the upper and lower bridge arms.

[0055] like Figure 5 As shown, the control method of the modular multilevel hydrogen production power supply for high voltage DC grid of the present invention includes: DC voltage control and current sharing control unit, capacitor voltage control unit and dominant voltage control unit;

[0056] The DC voltage control and current sharing control unit: measures the low-voltage side voltage v L With low-voltage side reference voltage v L,ref After comparison and adjustment by the PI controller, the target current i on the low-voltage side is generated. L * ;The low-voltage side target current i L * Divide by the number X of modular multilevel converters (10) and then divide by the low-voltage side current i of each modular multilevel converter (10). L,x After comparison and adjustment by the PI controller, the low-voltage side reference voltage v of each modular multilevel converter (10) is generated. L,x .

[0057] The capacitor voltage control unit includes: intra-arm capacitor voltage control, inter-arm capacitor voltage balance control, and full-bridge converter capacitor voltage control.

[0058] Bridge arm capacitor voltage control: The reference voltage V of the bridge arm capacitor is... c * The average capacitor voltage v in the full-bridge converter within the upper arm (11) and lower arm (12) of a modular multilevel converter (10) is related to the average capacitor voltage v. c,str,x After comparison and adjustment by the PI controller, its output is then compared with the feedback current i. com After comparison and adjustment by the PI controller, the output is the adjusted voltage component Δv. c,str,x .

[0059] The feedback current i comIt is the current component flowing through the entire modular multilevel converter (10), and its calculation formula is as follows:

[0060] i com =0.5(i x,1,s +i x,2,f +i x,F (1)

[0061] Among them, i x,1,s i represents the current in the lower half of the upper arm of the xth modular multilevel converter (10). x,2,f i represents the current in the upper half of the lower arm of the xth modular multilevel converter (10). x,F This represents the cross-connect capacitor current of the xth modular multilevel converter (10).

[0062] Inter-arm capacitor voltage balance control: This includes outer loop control of the bridge arm capacitor voltage and inner loop control of the AC current. The capacitor voltage balance between the upper and lower bridge arms is achieved by controlling the AC current component. The average capacitor voltage v of the upper bridge arm (11) and lower bridge arm (12) in the modular multilevel converter (10) is calculated. c,x,1 v c,x,2 The signal is compared with the feedforward signal I after adjustment by the PI controller. ac,fwd Add them together, then multiply by sin(ωt+θ) x ), θ x =360° / X, thus generating an instantaneous AC reference current i ac,x * , and the measured alternating current i ac,x The comparison is performed, and the adjustment voltage Δv is generated after adjustment by the PI controller. c,val,x .

[0063] The formula for calculating the feedforward signal is as follows:

[0064]

[0065] Among them, V H Indicates high voltage DC input, V L Indicates low-voltage DC output, i L,x V represents the output current of the xth modular multilevel converter (10). ac This represents the amplitude of the AC component of the voltage in half of the bridge arm.

[0066] Full-bridge converter capacitor voltage control: The capacitor reference voltage V... c * The measured voltage v of a single full-bridge converter capacitor c,x,i,h,j After comparison and adjustment by the PI controller, it is compared with the instantaneous current i of the corresponding upper or lower half of the bridge arm. x,i,hMultiply to generate the adjusted voltage Δv x,i,h,j .

[0067] The two dominant voltages v of the dominant voltage control unit rem,x and v ac,x It is calculated using the following formula:

[0068] v rem,x =V H -V L,x (3)

[0069] v ac,x =d ac V H (4)

[0070]

[0071]

[0072] Where, d ac Here, r is the AC voltage factor, and d is the voltage ratio. min This represents the AC voltage factor when the AC voltage component is at its minimum.

[0073] Dominant component v rem,x and v ac,x With adjustment of voltage component Δv c,str,x Δv c,val,x and Δv x,i,h,j By combining these factors, a capacitor voltage reference for the full-bridge converter in the bridge arm is synthesized, and the calculation formula is as follows:

[0074]

[0075] Among them, symbols Or "±" is used to distinguish between the upper and lower halves of the bridge arm;

[0076] Finally, based on the capacitor voltage reference of the full-bridge converter in the bridge arm, the switching devices are controlled by pulse width modulation.

[0077] 4. Simulation test

[0078] like Figure 6 As shown, the circuit topology of this invention is simulated using three modular multilevel converters (10). Each bridge arm consists of six full-bridge converters connected in series. The circuit parameters are shown in the table below:

[0079] Input voltage <![CDATA[V H ]]> 2000 V Output voltage <![CDATA[V L ]]> 1000 V Full-bridge capacitor C 5000 μF Filter inductor <![CDATA[L1、L2]]> 5 mH Switching frequency f 800 Hz bridging capacitor <![CDATA[C1]]> 500 μF

[0080] like Figure 7The figure shows the simulated waveform of the bridge arm voltage of the present invention. Capacitor voltage equalization control is added at time 1s. V1, V2, and V3 are the voltages of bridge arm 1, bridge arm 2, and bridge arm 3, respectively. It can be seen from the waveform that the bridge arm voltages of the three bridge arms gradually balance from time 1s, and the voltage balance effect is good.

[0081] like Figure 8 The figure shows the simulated waveform of the output current of the present invention. Output current equalization control is added at time 1s, i L,1 i L,2 i L,3 The waveforms show the output currents of the three groups. It can be seen from the waveforms that the output currents of the three groups gradually balance from time 1 second, and the current balancing effect is good.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a modular multilevel hydrogen production power supply for a high-voltage direct current (HVDC) grid, wherein the modular multilevel hydrogen production power supply employs at least one modular multilevel converter (10) connected in parallel to the positive and negative terminals of the HVDC grid; the modular multilevel converter (10) comprises: The upper bridge arm (11), lower bridge arm (12), filter inductor L1, filter inductor L2, and bridging capacitor C1 are connected in series. The upper bridge arm (11), filter inductor L1, filter inductor L2, and lower bridge arm (12) are connected in series. The non-series end of the upper bridge arm (11) is used as the input high voltage DC positive terminal, the common point of the series connection of filter inductor L1 and filter inductor L2 is used as the output low voltage DC positive terminal, and the non-series end of the lower bridge arm (12) is used as the input high voltage DC negative terminal and the output low voltage DC negative terminal. The upper bridge arm (11) of the modular multilevel converter (10) uses 2N1 full-bridge converters connected in series, and the lower bridge arm (12) uses 2N2 full-bridge converters connected in series. A terminal is led out from the midpoint of the 2N1 and 2N2 full-bridge converters connected in series to connect the two ends of the bridging capacitor C1. The control method is characterized by comprising: a DC voltage control and current sharing control unit, a capacitor voltage control unit, and a dominant voltage control unit; The DC voltage control and current sharing control unit: measures the low-voltage side voltage v L With low-voltage side reference voltage v L,ref After comparison and adjustment by the PI controller, the target current i on the low-voltage side is generated. L * ;The low-voltage side target current i L * Divide by the number of modular multilevel converters (10) X, and then divide by the low-voltage side current i of each modular multilevel converter (10). L,x After comparison and adjustment by the PI controller, the low-voltage side reference voltage v of each modular multilevel converter (10) is generated. L,x ; The capacitor voltage control unit includes: intra-arm capacitor voltage control, inter-arm capacitor voltage balance control, and full-bridge converter capacitor voltage control; The aforementioned bridge arm capacitor voltage control: The bridge arm capacitor reference voltage V... c * The average capacitor voltage v in the full-bridge converter within the upper arm (11) and lower arm (12) of a modular multilevel converter (10) is related to the average capacitor voltage v. c,str,x After comparison and adjustment by the PI controller, its output is then compared with the feedback current i. com After comparison and adjustment by the PI controller, the output is the adjusted voltage component Δv. c,str,x ; The bridge arm capacitor voltage balance control includes bridge arm capacitor voltage outer loop control and AC current inner loop control. The capacitor voltage balance between the upper and lower bridge arms is achieved by controlling the AC current component. The average capacitor voltage v of the upper bridge arm (11) and lower bridge arm (12) in the modular multilevel converter (10) is calculated. c,x,1 v c,x,2 The signal is compared with the feedforward signal I after adjustment by the PI controller. ac,fwd Add them together, then multiply by sin(ωt+θ) x ), θ x =360° / X, thus generating an instantaneous AC reference current i ac,x * , and the measured alternating current i ac,x The comparison is performed, and the adjustment voltage Δv is generated after adjustment by the PI controller. c,val,x ; The full-bridge converter capacitor voltage control: The capacitor reference voltage V... c * The measured voltage v of a single full-bridge converter capacitor c,x,i,h,j After comparison and adjustment by the PI controller, it is compared with the instantaneous current i of the corresponding upper or lower half of the bridge arm. x,i,h Multiply to generate the adjusted voltage Δv x,i,h,j ; The dominant voltage v of the dominant voltage control unit rem,x and v ac,x With adjustment of voltage component Δv c,str,x Δv c,val,x and Δv x,i,j Combined, a capacitor voltage reference for the full-bridge converter in the bridge arm is synthesized, and the switching devices are controlled by pulse width modulation based on the capacitor voltage reference of the full-bridge converter in the bridge arm.

2. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC grid according to claim 1, characterized in that, The full-bridge converter includes: a full-bridge capacitor C, fully controlled devices S1 to S4, and diodes D1 to D4. The fully controlled devices S1 to S4 and diodes D1 to D4 form an H-bridge structure, and the full-bridge capacitor C is connected in parallel with the H-bridge structure.

3. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC grid according to claim 2, characterized in that, The full-bridge converter operates in three states, transferring power from the high-voltage side to the low-voltage side: bypass state, charging state, and discharging state. 1) In the bypass state, current flows through diode D1 and fully controlled device S3, or through fully controlled device S2 and diode D4, but does not flow through the capacitor. 2) In the charging state, current flows through diode D1, capacitor C, and diode D4, at which point the capacitor is in a charging state. 3) In the discharging state, current flows through diode D2, capacitor C, and fully controlled device S3, at which point the capacitor is in a discharging state. By controlling the operating state of the full-bridge converter, a corresponding output voltage is obtained on the output side.

4. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC power grid according to claim 1, characterized in that, The feedback current i com It is the current component flowing through the entire modular multilevel converter (10), and its calculation formula is as follows: （1） Among them, i x,1,s i represents the current in the lower half of the upper arm of the xth modular multilevel converter (10). x,2,f i represents the current in the upper half of the lower arm of the xth modular multilevel converter (10). x,F This represents the cross-capacitor current of the xth modular multilevel converter (10).

5. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC power grid according to claim 4, characterized in that, The formula for calculating the feedforward signal is as follows: （2） Among them, V H Indicates high voltage DC input, V L Indicates low-voltage DC output, i L,x V represents the output current of the xth modular multilevel converter (10). ac This represents the amplitude of the AC component of the voltage in half of the bridge arm.

6. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC power grid according to claim 5, characterized in that, The dominant voltage v rem,x and v ac,x It is calculated using the following formula: （3） （4） （5） （6） Where, d ac Here, r is the AC voltage factor, and d is the voltage ratio. min It represents the AC voltage factor when the AC voltage component is at its minimum.

7. The control method for a modular multilevel hydrogen production power supply for a high-voltage DC power grid according to claim 6, characterized in that, The formula for calculating the capacitor voltage reference of the full-bridge converter in the bridge arm is as follows: （7） Among them, the symbol " " or "±" are used to distinguish between the upper and lower halves of the bridge arm.

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