An alternating current grid-connected two-stage conversion type hydrogen production power supply and a control method thereof

Abstract

A two-stage AC grid-connected converter hydrogen production power supply and its control method are disclosed, belonging to the field of hydrogen production power supply technology. The invention addresses how to design a small-sized, high-power-density two-stage converter hydrogen production power supply that can suppress AC side harmonic distortion rate and improve power factor. The power supply's front-end uses a modular multilevel converter for AC / AC conversion, converting the mains frequency AC grid power V... A The AC power is converted to intermediate frequency and then transmitted to the subsequent full-bridge converter via an intermediate frequency transformer. The subsequent full-bridge converter performs AC / DC conversion to power the hydrogen electrolyzer. The power supply of this invention can suppress AC side harmonic distortion rate and improve power density. Compared with traditional converters that require three-stage conversion power supplies, the power supply topology of this invention has only two power conversion stages, which improves efficiency and reduces cost. The use of an intermediate frequency transformer for isolation results in a smaller size and further improves the overall power density of the power supply.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production power technology, and relates to an AC grid-connected two-stage conversion hydrogen production power supply and its control method. Background Technology

[0002] With my country's economic development, the country's demand for energy is increasing. While using fossil fuels, it has begun to vigorously develop different types of clean energy. Hydrogen energy, as a zero-carbon, clean, and efficient energy carrier, is accounting for an increasing proportion of my country's energy consumption year by year. To produce hydrogen more efficiently, hydrogen production power source technology, which plays a crucial role in the process, is constantly developing. Hydrogen production power sources can convert electrical energy and hydrogen energy in a green and efficient manner, and this technology is receiving increasing attention.

[0003] In the application of low-voltage, high-current systems for hydrogen production power supplies, in order to suppress the AC side harmonic distortion rate, the traditional topology uses a three-phase current-type PWM rectifier as the topology of the hydrogen production power supply, such as the literature "Analysis of a Novel Low-Voltage, High-Current Three-Phase PWM Rectifier" (Chen Chao et al., School of Electrical and Information Engineering, Sichuan University, 2017). This topology can suppress the AC side harmonic distortion rate while meeting the requirements of low voltage and high current. However, this topology is a three-stage power electronic converter, which has the disadvantages of complex control methods and large DC filter inductance. Summary of the Invention

[0004] The purpose of this invention is to design a two-stage converter hydrogen production power supply that is small in size and has high power density, which can suppress AC side harmonic distortion rate and improve power factor.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0006] A two-stage converter-type AC grid-connected hydrogen production power supply includes: a single-phase grid-connected circuit (10), a front-end modular multilevel converter (11), an intermediate frequency transformer (12), and a rear-end full-bridge converter (13); the single-phase grid-connected circuit (10) consists of a bus capacitor C1, a bus capacitor C2, and an AC grid power supply V. A Bus inductance L A Reactor L X Reactor L YThe front-end modular multilevel converter (11) consists of two bridge arms. The first bridge arm is composed of a first converter module (111), inductor L1, inductor L2, and second converter module (112) connected in series. The common point of series connection of inductor L1 and inductor L2 serves as the midpoint of the first bridge arm. The second bridge arm is composed of a third converter module (113), a fourth converter module (114), inductor L3, and inductor L4 connected in series. The common point of series connection of inductor L3 and inductor L4 serves as the midpoint of the second bridge arm. The non-series terminals of the first converter module (111) and the third converter module (113) are connected together as one input / output terminal of the front-end modular multilevel converter (11). The non-series terminals of the second converter module (112) and the fourth converter module (114) are connected together as the other input / output terminal of the front-end modular multilevel converter (11).

[0007] The common point of the series connection of bus capacitor C1 and bus capacitor C2 is grounded. The non-series terminal of bus capacitor C1 is connected to one input terminal of the front-end modular multilevel converter (11), and the non-series terminal of bus capacitor C2 is connected to the other input terminal of the front-end modular multilevel converter (11). The AC grid power supply V A One end is connected to the common point of series connection between bus capacitor C1 and bus capacitor C2, and the AC mains power supply V A The other end is connected to the bus inductance L A One end is connected to the bus inductance L A The other end is connected to reactor L respectively X one end and reactor L Y One end is connected to reactor L X The other end is connected to the midpoint of the first bridge arm, reactor L Y The other end is connected to the midpoint of the second bridge arm;

[0008] The two ends of the primary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the two bridge arms of the subsequent full-bridge converter (13); the intermediate frequency transformer (12) is used to provide electrical isolation and connect the front-stage modular multilevel converter (11) with coupled phase-to-phase inductors on the high-voltage side to the subsequent full-bridge converter (13) on the low-voltage side.

[0009] Furthermore, each converter module consists of multiple half-bridge converters connected in series. The half-bridge converters operate in four different states, as follows: When the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module.

[0010] Furthermore, the working principle of the power supply is as follows: AC mains power supply V A The front-end modular multilevel converter (11) is powered by a single-phase grid-connected circuit (10). The front-end modular multilevel converter (11) converts the AC grid power V of the power frequency into AC power V. A The AC power is converted to medium frequency and then transmitted to the subsequent full-bridge converter (13) through the medium frequency transformer (12). The subsequent full-bridge converter (13) converts the AC power to DC power to supply the hydrogen electrolyzer.

[0011] A control method for the aforementioned AC grid-connected two-stage converter hydrogen production power supply includes: control of the average voltage and input current of the front-stage modular multilevel converter bridge arm, control of the voltage difference between the upper and lower converter modules of the front-stage modular multilevel converter bridge arm, and control of the output DC side voltage of the rear-stage full-bridge converter.

[0012] The method for controlling the average voltage and input current of the front-end modular multilevel converter bridge arm is as follows: by collecting the voltage V of the first bridge arm, the first converter module (111), the second converter module (112), the third converter module (113), and the fourth converter module (114) of the front-end modular multilevel converter (11), the method is as follows: X1 V X2 V Y1 V Y2 Take V X1 V X2 V Y1 V Y2 Average voltage V B V B With the average voltage command value V d The difference is calculated, and the modulation signal is obtained through the first PI controller. Then, it is multiplied by the sinωt signal to obtain the current command value i used for input current control. a_ref Then collect the bus inductance L A current i aand the current command value i controlled by the input current. a_ref The difference is calculated, and the modulation signal U is obtained through the second PI controller. * ;

[0013] The specific method for controlling the voltage difference between the upper and lower converter modules of the front-end modular multilevel converter bridge arm is as follows: The acquired voltage V... X2 With V X1 The difference is calculated, and the modulation signal U is obtained through the third PI controller. X Then modulate the signal U X Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; at the same time, the modulation signal U is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; * Subtract the modulating signal U X The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the second commutator module (112) of the first bridge arm; the collected voltage V is then sent to the carrier phase-shift modulator to obtain the PWM control signal of the second commutator module (112) of the first bridge arm; Y2 With V Y1 The difference is calculated, and the modulation signal U is obtained through the fourth PI controller. Y Then modulate the signal U Y Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the third commutator module (113) of the second bridge arm; at the same time, the modulation signal U is... * Subtract the modulating signal U Y The difference is sent to the carrier phase shift modulator to obtain the PWM control signal of the fourth commutator module (114) of the second bridge arm;

[0014] The specific method for controlling the output DC-side voltage of the subsequent full-bridge converter is as follows: The output voltage V is collected. O With the output voltage command value V O_ref The difference is calculated, and the difference is used by the fifth PI controller and PWM stage to obtain pulses that control the switching of the subsequent full-bridge converter, thereby controlling the output voltage V. O .

[0015] Furthermore, the control strategy of the first PI controller is as follows:

[0016] i a_ref =k pia (V B -V d )+k iia ∫(V B -V d )dt

[0017] Where, k pia k is the proportional element parameter of the first PI controller. iiaThese are the integral parameters of the first PI controller. Furthermore, the control strategy of the second PI controller is as follows:

[0018] U * =k pu* (i a -i a_ref )+k iu* ∫(i a -i a_ref )dt

[0019] Where, k pu* k is the proportional element parameter of the second PI controller. iu* These are the parameters of the integral element of the second PI controller.

[0020] Furthermore, the control strategy of the third PI controller is as follows:

[0021] U x =k pux (V x2 -V x1 )+k iux ∫(V x2 -V x1 )dt

[0022] Where, k pux k is the proportional element parameter of the third PI controller. iux These are the parameters for the integral element of the third PI controller.

[0023] Furthermore, the control strategy of the fourth PI controller is as follows:

[0024] U y =k puy (V y2 -V y1 )+k iuy ∫(V y2 -V y1 )dt

[0025] Where, k puy k is the proportional element parameter of the fourth PI controller. iuy These are the parameters for the integral element of the fourth PI controller.

[0026] The advantages of this invention are:

[0027] The power supply of this invention uses a modular multilevel converter for AC / AC conversion in its front-end stage, converting the mains AC power V from the power grid frequency. AThe AC power is converted to intermediate frequency and then transmitted to the subsequent full-bridge converter via an intermediate frequency transformer. The subsequent full-bridge converter performs AC / DC conversion to power the hydrogen electrolyzer. The power supply of this invention can suppress AC side harmonic distortion rate and improve power density. Compared with traditional converters that require three-stage conversion power supplies, the power supply topology of this invention has only two power conversion stages, which improves efficiency and reduces cost. The use of an intermediate frequency transformer for isolation results in a smaller size and further improves the overall power density of the power supply. Attached Figure Description

[0028] Figure 1 This is a topology diagram of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention;

[0029] Figure 2 This is a structural diagram of the converter module of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0030] Figure 3 This is a block diagram showing the control of the average voltage and input current of the front-end modular multilevel converter bridge arm of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0031] Figure 4 This is a block diagram of the voltage difference control of the upper and lower converter modules of the front-end modular multilevel converter bridge arm of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0032] Figure 5 This is a block diagram of the output DC-side voltage control of the rear full-bridge converter of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0033] Figure 6(a) Simulation results of the capacitor voltage of the upper and lower converter modules of the first bridge arm of the front-end modular multilevel converter of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0034] Figure 6(b) shows the simulation results of the current and circulating current of the upper and lower converter modules of the first bridge arm of the front-end modular multilevel converter of the AC grid-connected two-stage conversion hydrogen production power supply of the present invention.

[0035] Figure 6(c) shows the simulation results of the output DC-side voltage of the subsequent full-bridge converter (13) of the present invention. Detailed Implementation

[0036] 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.

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0038] Example 1

[0039] I. Power Supply Topology

[0040] like Figure 1 As shown, the topology of the AC grid-connected two-stage converter hydrogen production power supply of this embodiment includes: a single-phase grid-connected access circuit (10), a front-end modular multilevel converter (11), an intermediate frequency transformer (12), and a rear-end full-bridge converter (13); the single-phase grid-connected access circuit (10) consists of a bus capacitor C1, a bus capacitor C2, and an AC grid power supply V. A Bus inductance L A Reactor L X Reactor L Y The front-end modular multilevel converter (11) consists of two bridge arms. The first bridge arm is composed of a first converter module (111), inductor L1, inductor L2, and second converter module (112) connected in series. The common point of series connection of inductor L1 and inductor L2 serves as the midpoint of the first bridge arm. The second bridge arm is composed of a third converter module (113), a fourth converter module (114), inductor L3, and inductor L4 connected in series. The common point of series connection of inductor L3 and inductor L4 serves as the midpoint of the second bridge arm. The non-series terminals of the first converter module (111) and the third converter module (113) are connected together as one input / output terminal of the front-end modular multilevel converter (11). The non-series terminals of the second converter module (112) and the fourth converter module (114) are connected together as the other input / output terminal of the front-end modular multilevel converter (11).

[0041] The common point of the series connection of bus capacitor C1 and bus capacitor C2 is grounded. The non-series terminal of bus capacitor C1 is connected to one input terminal of the front-end modular multilevel converter (11), and the non-series terminal of bus capacitor C2 is connected to the other input terminal of the front-end modular multilevel converter (11). The AC grid power supply V A One end is connected to the common point of series connection between bus capacitor C1 and bus capacitor C2, and the AC mains power supply V A The other end is connected to the bus inductance L A One end is connected to the bus inductance L A The other end is connected to reactor L respectively X one end and reactor L Y One end is connected to reactor L X The other end is connected to the midpoint of the first bridge arm, reactor L YThe other end is connected to the midpoint of the second bridge arm.

[0042] The two ends of the primary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the two bridge arms of the subsequent full-bridge converter (13); the intermediate frequency transformer (12) is used to provide electrical isolation and connect the front-stage modular multilevel converter (11) with coupled phase-to-phase inductors on the high-voltage side to the subsequent full-bridge converter (13) on the low-voltage side.

[0043] like Figure 2 The diagram shows the converter module structure of the front-end modular multilevel converter (11). Each converter module consists of multiple half-bridge converters connected in series. The half-bridge converters operate in four different states, as follows: When the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module. Therefore, the external voltage of the bridge arm can be adjusted by controlling the operating state of the half-bridge converter.

[0044] II. Working principle of the power supply

[0045] AC mains power supply V A The front-end modular multilevel converter (11) is powered by a single-phase grid-connected circuit (10). The front-end modular multilevel converter (11) converts the AC grid power V of the power frequency into AC power V. A The AC power is converted to medium frequency and then transmitted to the subsequent full-bridge converter (13) through the medium frequency transformer (12). The subsequent full-bridge converter (13) converts the AC power to DC power to supply the hydrogen electrolyzer.

[0046] III. Power Supply Control Methods

[0047] The control method of the AC grid-connected two-stage converter hydrogen production power supply in this embodiment includes: control of the average voltage and input current of the front-stage modular multilevel converter bridge arm, control of the voltage difference between the upper and lower converter modules of the front-stage modular multilevel converter bridge arm, and control of the output DC side voltage of the rear-stage full-bridge converter.

[0048] like Figure 3The diagram shows the block diagram for controlling the average voltage and input current of the bridge arms of the front-end modular multilevel converter. This is achieved by collecting the voltage V1 of the first bridge arm, the first converter module (111), the second converter module (112), the third converter module (113), and the fourth converter module (114) of the second bridge arm of the front-end modular multilevel converter (11). X1 V X2 V Y1 V Y2 Take V X1 V X2 V Y1 V Y2 Average voltage V B V B With the average voltage command value V d The difference is calculated, and the modulation signal is obtained through the first PI controller. Then, it is multiplied by the sinωt signal to obtain the current command value i used for input current control. a_ref Then collect the bus inductance L A current i a and the current command value i controlled by the input current. a_ref The difference is calculated, and the modulation signal U is obtained through the second PI controller. * .

[0049] The control strategy of the first PI controller is as follows:

[0050] i a_ref =k pia (V B -V d )+k iia ∫(V B -V d )dt

[0051] Where, k pia k is the proportional element parameter of the first PI controller. iia These are the integral parameters of the first PI controller. The control strategy of the second PI controller is as follows:

[0052] U * =k pu* (i a -i a_ref )+k iu* ∫(i a -i a_ref )dt

[0053] Where, k pu* k is the proportional element parameter of the second PI controller. iu* These are the parameters of the integral element of the second PI controller.

[0054] like Figure 4The diagram shown is a block diagram of the voltage difference control of the upper and lower converter modules of the front-end modular multilevel converter bridge arm. The acquired voltage V... X2 With V X1 The difference is calculated, and the modulation signal U is obtained through the third PI controller. X Then modulate the signal U X Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; at the same time, the modulation signal U is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; * Subtract the modulating signal U X The difference is sent to the carrier phase shift modulator to obtain the PWM control signal of the second commutator module (112) of the first bridge arm;

[0055] The collected voltage V Y2 With V Y1 The difference is calculated, and the modulation signal U is obtained through the fourth PI controller. Y Then modulate the signal U Y Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the third commutator module (113) of the second bridge arm; at the same time, the modulation signal U is... * Subtract the modulating signal U Y The difference is sent to the carrier phase shift modulator to obtain the PWM control signal of the fourth commutator module (114) of the second bridge arm.

[0056] The control strategy of the third PI controller is as follows:

[0057] U x =k pux (V x2 -V x1 )+k iux ∫(V x2 -V x1 )dt

[0058] Where, k pux k is the proportional element parameter of the third PI controller. iux These are the parameters for the integral element of the third PI controller.

[0059] The control strategy of the fourth PI controller is as follows:

[0060] U y =k puy (V y2 -V y1 )+k iuy ∫(V y2 -V y1 )dt

[0061] Where, kpuy k is the proportional element parameter of the fourth PI controller. iuy These are the parameters for the integral element of the fourth PI controller.

[0062] like Figure 5 The diagram shown is a block diagram of the output DC-side voltage control of the subsequent full-bridge converter, where the output voltage V is collected. O With the output voltage command value V O_ref The difference is calculated, and the difference is used by the fifth PI controller and PWM stage to obtain pulses that control the switching of the subsequent full-bridge converter, thereby controlling the output voltage V. O .

[0063] IV. Simulation Verification

[0064] The circuit simulation parameters of the AC grid-connected two-stage converter hydrogen production power supply according to an embodiment of the present invention are as follows:

[0065] Grid voltage 10kV Rated voltage command value of converter module 2100V Grid frequency 50Hz Number of serial submodules 10 Grid-connected reactance value 4mH Bridge arm reactance value 12mH Converter module switching frequency 1kHz DC capacitor value of converter module 1000μF Output DC capacitor 10000μF Output voltage 1.7kV

[0066] As shown in Figures 6(a), 6(b), and 6(c), the simulation results show that under the control method proposed in this invention, the voltage of all converter modules in the first bridge arm is around 2100V. When the balance control is added at 1s, the voltage fluctuation of the sub-modules is reduced. After 1.3s, the output DC voltage command value is changed to 1.8kV, and the voltage reaches the target value after 0.1s, which has a good control effect.

[0067] 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. An AC grid-connected two-stage converter hydrogen production power supply, characterized in that, include: The system consists of a single-phase grid-connected circuit (10), a front-end modular multilevel converter (11), an intermediate frequency transformer (12), and a rear-end full-bridge converter (13); the single-phase grid-connected circuit (10) comprises a bus capacitor C1, a bus capacitor C2, and an AC grid power supply V. A Bus inductance L A Reactor L X Reactor L Y The front-end modular multilevel converter (11) consists of two bridge arms. The first bridge arm is composed of a first converter module (111), inductor L1, inductor L2, and second converter module (112) connected in series. The common point of series connection of inductor L1 and inductor L2 serves as the midpoint of the first bridge arm. The second bridge arm is composed of a third converter module (113), a fourth converter module (114), inductor L3, and inductor L4 connected in series. The common point of series connection of inductor L3 and inductor L4 serves as the midpoint of the second bridge arm. The non-series terminals of the first converter module (111) and the third converter module (113) are connected together as one input / output terminal of the front-end modular multilevel converter (11). The non-series terminals of the second converter module (112) and the fourth converter module (114) are connected together as the other input / output terminal of the front-end modular multilevel converter (11). The common point of the series connection of bus capacitor C1 and bus capacitor C2 is grounded. The non-series terminal of bus capacitor C1 is connected to one input terminal of the front-end modular multilevel converter (11), and the non-series terminal of bus capacitor C2 is connected to the other input terminal of the front-end modular multilevel converter (11). The AC grid power supply V A One end is connected to the common point of series connection between bus capacitor C1 and bus capacitor C2, and the AC mains power supply V A The other end is connected to the bus inductance L A One end is connected to the bus inductance L A The other end is connected to reactor L respectively X one end and reactor L Y One end is connected to reactor L X The other end is connected to the midpoint of the first bridge arm, reactor L Y The other end is connected to the midpoint of the second bridge arm; The two ends of the primary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary side of the intermediate frequency transformer (12) are respectively connected to the midpoint of the two bridge arms of the subsequent full-bridge converter (13); the intermediate frequency transformer (12) is used to provide electrical isolation and connect the front-stage modular multilevel converter (11) with coupled phase-to-phase inductors on the high-voltage side to the subsequent full-bridge converter (13) on the low-voltage side.

2. The AC grid-connected two-stage converter hydrogen production power supply according to claim 1, characterized in that, Each converter module consists of multiple half-bridge converters connected in series. The half-bridge converters operate in four different states, as follows: When the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is positive, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned off, and the corresponding switch S2 is turned on, resulting in a voltage of 0 for the half-bridge module; when the current im of the half-bridge converter is negative, switch S1 in the half-bridge module is turned on, and the corresponding switch S2 is turned off, resulting in a voltage of Vd for the half-bridge module.

3. The AC grid-connected two-stage converter hydrogen production power supply according to claim 2, characterized in that, The working principle of the power supply is as follows: AC mains power supply V A The front-end modular multilevel converter (11) is powered by a single-phase grid-connected circuit (10). The front-end modular multilevel converter (11) converts the AC grid power V of the power frequency into AC power V. A The AC power is converted to medium frequency and then transmitted to the subsequent full-bridge converter (13) through the medium frequency transformer (12). The subsequent full-bridge converter (13) converts the AC power to DC power to supply the hydrogen electrolyzer.

4. A control method for an AC grid-connected two-stage conversion hydrogen production power supply as described in any one of claims 1 to 3, characterized in that, include: The control of average voltage and input current of the front-stage modular multilevel converter bridge arm, the control of voltage difference between the upper and lower converter modules of the front-stage modular multilevel converter bridge arm, and the control of output DC side voltage of the rear-stage full-bridge converter. The method for controlling the average voltage and input current of the front-end modular multilevel converter bridge arm is as follows: by collecting the voltage V of the first bridge arm, the first converter module (111), the second converter module (112), the third converter module (113), and the fourth converter module (114) of the front-end modular multilevel converter (11), the method is as follows: X1 V X2 V Y1 V Y2 Take V X1 V X2 V Y1 V Y2 Average voltage V B V B With the average voltage command value V d The difference is calculated, and the modulation signal is obtained through the first PI controller. Then, it is multiplied by the sinωt signal to obtain the current command value i used for input current control. a_ref Then collect the bus inductance L A current i a and the current command value i controlled by the input current. a_ref The difference is calculated, and the modulation signal U is obtained through the second PI controller. * ; The specific method for controlling the voltage difference between the upper and lower converter modules of the front-end modular multilevel converter bridge arm is as follows: The acquired voltage V... X2 With V X1 The difference is calculated, and the modulation signal U is obtained through the third PI controller. X Then modulate the signal U X Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; at the same time, the modulation signal U is sent to the carrier phase-shift modulator to obtain the PWM control signal of the first commutator module (111) of the first bridge arm; * Subtract the modulating signal U X The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the second commutator module (112) of the first bridge arm; the collected voltage V is then sent to the carrier phase-shift modulator to obtain the PWM control signal of the second commutator module (112) of the first bridge arm; Y2 With V Y1 The difference is calculated, and the modulation signal U is obtained through the fourth PI controller. Y Then modulate the signal U Y Subtract the modulating signal U * The difference is sent to the carrier phase-shift modulator to obtain the PWM control signal of the third commutator module (113) of the second bridge arm; at the same time, the modulation signal U is... * Subtract the modulating signal U Y The difference is sent to the carrier phase shift modulator to obtain the PWM control signal of the fourth commutator module (114) of the second bridge arm; The specific method for controlling the output DC-side voltage of the subsequent full-bridge converter is as follows: The output voltage V0 and the output voltage command value V0 are collected. 0_ref The difference is calculated, and the difference is used by the fifth PI controller and the PWM stage to obtain the pulses that control the switching of the subsequent full-bridge converter, thereby controlling the output voltage V0.

5. The control method according to claim 4, characterized in that, The control strategy of the first PI controller is as follows: and a_ref =k pia (V B -V d )+k iia ∫(V B -V d )dt Where, k pia k is the proportional element parameter of the first PI controller. iia These are the parameters of the integral element of the first PI controller.

6. The control method according to claim 5, characterized in that, The control strategy of the second PI controller is as follows: U * =k pu* (i a -i a_ref )+k iu* ∫(i a -i a_ref )dt Where, k pu* k is the proportional element parameter of the second PI controller. iu* These are the parameters of the integral element of the second PI controller.

7. The control method according to claim 6, characterized in that, The control strategy of the third PI controller is as follows: U x =k pux (V x2 -V x1 )+k iux ∫(V x2 -V x1 )dt Where, k pux k is the proportional element parameter of the third PI controller. iux These are the parameters for the integral element of the third PI controller.

8. The control method according to claim 7, characterized in that, The control strategy of the fourth PI controller is as follows: you y =k puy (V y2 -V y1 )+k iuy ∫(V y2 -V y1 )dt Where, k puy k is the proportional element parameter of the fourth PI controller. iuy These are the parameters for the integral element of the fourth PI controller.

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