Wind power off-grid hydrogen production system and black start method thereof

Abstract

The present disclosure relates to a wind power off-grid hydrogen production system and a black start method thereof. The system comprises a fan side and a hydrogen production side. The fan side comprises a wind turbine, a machine side converter, a grid side converter, a first DC bus capacitor, a first transformer, a third switch, a fourth switch and a second filter inductor. The hydrogen production side comprises an electrolyzer, a second DC bus capacitor, a second transformer, an AC-DC converter, a DC-DC converter, a black start power supply, an inverter, a first switch, a second switch and a first filter inductor. The black start power supply comprises a hydrogen fuel cell, and the hydrogen fuel source of the hydrogen fuel cell comprises hydrogen produced by the electrolyzer. Thus, the system can realize wind power off-grid hydrogen production without additional electrochemical energy storage devices, thereby improving the safety and greenness of the wind power off-grid hydrogen production system and significantly reducing engineering investment and engineering layout difficulty.

Description

Technical Field

[0001] This disclosure relates to the field of off-grid hydrogen production from wind power, and more particularly to an off-grid hydrogen production system from wind power and its black start method. Background Technology

[0002] A major factor hindering the rapid advancement of green hydrogen projects is grid connection. On the one hand, high-voltage grid connection for integrated wind-solar-hydrogen systems above 220kV may impact grid security and stability, and the pre-approval process is complex. On the other hand, various grid fees, such as capacity fees and grid access fees, significantly increase the cost of green hydrogen production. If off-grid wind power production could be achieved, eliminating grid access, it would not only allow wind power to be consumed locally but also reduce capacity fees, leading to a substantial decrease in the cost of electricity for hydrogen production. Off-grid wind power production is widely considered an effective way to improve the cost competitiveness of green hydrogen. Off-grid wind power production refers to the method where wind turbines convert wind energy into electrical energy, which is then directly supplied to electrolysis hydrogen production equipment without passing through the grid.

[0003] Current off-grid wind power hydrogen production systems all require substantial electrochemical energy storage, increasing equipment investment. For every 10 minutes of additional energy storage, the cost per standard cubic meter of produced hydrogen increases by 0.1 yuan, significantly reducing the price competitiveness of hydrogen products. Furthermore, frequent power fluctuations in the system affect the lifespan of energy storage devices, raising safety concerns associated with electrochemical energy storage itself. Even the black-start power supply in an off-grid wind power hydrogen production system, as proposed in Chinese invention patent CN119518874A, is a type of electrochemical energy storage device. Therefore, if off-grid wind power hydrogen production systems can maintain safety, stability, and high efficiency without the need for electrochemical energy storage, it will significantly reduce engineering investment and layout complexity, improve system efficiency and safety, and become the future development trend of off-grid wind power hydrogen production technology. Summary of the Invention

[0004] In view of this, this disclosure proposes a wind power off-grid hydrogen production system and its black start method, which enables the system to achieve wind power off-grid hydrogen production without the need for any additional electrochemical energy storage devices, thereby improving the safety and greenness of the wind power off-grid hydrogen production system, significantly reducing engineering investment and engineering layout difficulty, and effectively achieving stable startup of the system from the shutdown state to the operating state.

[0005] According to one aspect of this disclosure, a wind power off-grid hydrogen production system is provided, comprising: a wind turbine side and a hydrogen production side. The wind turbine side includes: a wind turbine generator, a turbine-side converter, a grid-side converter, a first DC bus capacitor, a first transformer, a third switch, a fourth switch, and a second filter inductor. The hydrogen production side includes: an electrolyzer, a second DC bus capacitor, a second transformer, an AC-DC converter, a DC-DC converter, a black-start power supply, an inverter, a first switch, a second switch, and a first filter inductor. The stator of the wind turbine generator is connected to the first low-voltage side of the first transformer via the fourth switch. The rotor of the wind turbine generator is connected to the AC side of the turbine-side converter. The first DC bus capacitor is connected in parallel between the DC side of the turbine-side converter and the DC side of the grid-side converter. The AC side of the grid-side converter... The AC side of the inverter is connected to the second low-voltage side of the first transformer via the second filter inductor and the third switch. The black-start power supply is connected to the DC side of the inverter. The AC side of the inverter is connected to the low-voltage side of the second transformer via the second filter inductor and the first switch. The high-voltage side of the second transformer is connected to the high-voltage side of the first transformer via the second switch. The low-voltage side of the second transformer is also connected to the AC side of the AC-DC converter. The second DC bus capacitor is connected in parallel between the DC side of the AC-DC converter and the first DC side of the DC-DC converter. The second DC side of the DC-DC converter is connected to the electrolyzer. The black-start power supply includes a hydrogen fuel cell, and the hydrogen fuel source for the hydrogen fuel cell includes hydrogen produced by the electrolyzer.

[0006] In one possible implementation, the system further includes: a first controller, a second controller, a third controller, and a fourth controller; the first controller includes a first voltage control mode, a first power control mode, and an active power control mode; the first voltage control mode is used to control the generator-side converter based on the first low-voltage side voltage of the first transformer and the stator voltage of the wind turbine generator, the first power control mode is used to control the generator-side converter based on the active power and reactive power of the wind turbine generator, and the active power control mode is used to control the generator-side converter based on the active power of the wind turbine generator; the second controller is used to control the grid-side converter based on the voltage and current on both sides of the grid-side converter; the third controller is used to control the inverter based on the voltage and current on the low-voltage side of the second transformer and the current on the AC side of the inverter; the fourth controller includes a second power control mode and a second voltage control mode, the second power control mode is used to control the DC-DC converter based on the electrolytic power input to the electrolytic cell, and the second voltage control mode is used to control the DC-DC converter based on the voltage across the second DC bus capacitor.

[0007] In one possible implementation, the system further includes: a slip angular frequency generator, the slip angular frequency generator including a first generation mode and a second generation mode; the first generation mode is used to generate a slip angular frequency based on the difference between the rotor angular frequency of the wind turbine and the angular frequency of the first low-voltage side voltage of the first transformer; the second generation mode is used to generate a slip angular frequency based on the difference between the rotor angular frequency of the wind turbine and a preset angular frequency reference value; wherein, the slip angular frequency is used to input to the first controller to control the wind turbine by controlling the machine-side converter based on the slip angular frequency.

[0008] According to another aspect of this disclosure, a black start method is provided for the aforementioned wind power off-grid hydrogen production system. The black start method is used to start the system from a shut-off state to an operating state. When the system is in the shut-off state, the first switch, the second switch, the third switch, and the fourth switch are all open. The black start method includes: closing the first switch and the second switch, starting the black start power supply and the inverter, and controlling the inverter through the third controller to convert the DC power output by the black start power supply into AC power until the system AC voltage reaches a steady state; when the system AC voltage reaches a steady state, closing the third switch, starting the grid-side converter, and controlling the grid-side converter through the second controller to convert the input AC power into DC power until the voltage across the first DC bus capacitor reaches a steady state; when the voltage across the first DC bus capacitor reaches a steady state, starting the turbine-side converter and the wind turbine, and controlling the turbine-side converter through the first controller in the first voltage control mode to make the stator voltage of the wind turbine consistent with the operating voltage. The voltage on the first low-voltage side of the first transformer is equal to the voltage on the first low-voltage side of the first transformer. When the stator voltage is equal to the voltage on the first low-voltage side of the first transformer, the fourth switch is closed, and the generator-side converter is controlled by the first controller in the first power control mode to make the wind turbine power of the wind turbine generator reach a steady state, the wind turbine power including active power and reactive power. When the wind turbine power reaches a steady state, the DC-DC converter and the electrolytic cell are started, and the DC-DC converter is controlled by the fourth controller in the second power control mode to make the electrolytic power input to the electrolytic cell reach a steady state. When the electrolytic power input to the electrolytic cell reaches a steady state, the first switch is opened, and the DC-DC converter is controlled by the fourth controller in the second voltage control mode to keep the voltage across the second DC bus capacitor stable, and the generator-side converter is controlled by the first controller in the active power control mode to make the active power of the wind turbine generator reach a steady state and the reactive power passively change, so as to realize the system starting from the off state to the running state.

[0009] According to various aspects of this disclosure, hydrogen fuel cells can be deployed on the hydrogen production side of the electrolyzer as a black start energy source, and the hydrogen fuel source of the hydrogen fuel cells can be directly used as hydrogen produced by the electrolyzer. This allows the system to achieve off-grid hydrogen production from wind power without the need for any additional electrochemical energy storage devices, further improving the safety and stability of the off-grid hydrogen production system from wind power, significantly reducing engineering investment and layout difficulty, and effectively enabling the system to be stably started from a shut-down state to an operating state.

[0010] Other features and aspects of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0011] The accompanying drawings, which are included in and form part of this specification, illustrate exemplary embodiments, features, and aspects of this disclosure together with the specification and serve to explain the principles of this disclosure.

[0012] Figure 1 A schematic diagram of a wind power off-grid hydrogen production system according to an embodiment of the present disclosure is shown.

[0013] Figure 2 A schematic diagram of a wind power off-grid hydrogen production system including a control system is shown according to an embodiment of the present disclosure.

[0014] Figure 3 A flowchart illustrating a black start method for a wind power off-grid hydrogen production system according to an embodiment of the present disclosure is shown.

[0015] Figure 4 , Figure 5 and Figure 6 A schematic diagram of simulation results is shown for controlling a wind power off-grid hydrogen production system using a black-start method according to an embodiment of the present disclosure. Detailed Implementation

[0016] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0017] As used herein, the terms “comprising,” “including,” “having,” or variations thereof are open-ended and include one or more of the stated features, integrals, elements, steps, components, or functions, but do not exclude the presence or addition of one or more other features, integrals, elements, steps, components, functions, or groups thereof.

[0018] When an element is referred to as “connected,” “coupled,” “responding,” or a variation thereof relative to another element, it may be directly connected, coupled, or responding to another element, or there may be an intermediate element present.

[0019] Although the terms first, second, third, etc., may be used herein to describe various elements / operations, these elements / operations should not be limited by these terms. These terms are only used to distinguish one element / operation from another. Therefore, without departing from the teachings of the inventive concept, a first element / operation in some embodiments may be referred to as a second element / operation in other embodiments.

[0020] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0021] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0022] Figure 1 A schematic diagram of a wind power off-grid hydrogen production system according to an embodiment of the present disclosure is shown. Figure 1 As shown, the system can include a wind turbine side and a hydrogen production side. The wind turbine side includes: a wind turbine generator, a turbine-side converter, a grid-side converter, and a first DC bus capacitor (i.e., C in the figure). DFIG The first transformer, the third switch B3, the fourth switch B4, and the second filter inductor L2; the hydrogen production side includes: an electrolyzer, a second DC bus capacitor C ELZ The system includes a second transformer, an alternating current (AC) to direct current (DC) converter, a DC-DC converter, a black start power supply, an inverter, a first switch B1, a second switch B2, and a first filter inductor L1.

[0023] The stator of the wind turbine is connected to the first low-voltage side of the first transformer via the fourth switch B4; the rotor of the wind turbine is connected to the AC side of the turbine-side converter; and the first DC bus capacitor C... DFIG The inverter is connected in parallel between the DC side of the generator-side converter and the DC side of the grid-side converter; the AC side of the grid-side converter is connected to the second low-voltage side of the first transformer via the second filter inductor L2 and the third switch B3; the black-start power supply is connected to the DC side of the inverter; the AC side of the inverter is connected to the low-voltage side of the second transformer via the first filter inductor L1 and the first switch B1, which is equivalent to connecting the inverter and the black-start power supply in parallel on the AC line of the electrolytic cell side; the high-voltage side of the second transformer is connected to the high-voltage side of the first transformer via the second switch B2; the low-voltage side of the second transformer is connected to the AC side of the AC-DC converter; the second DC bus capacitor C... ELZ It is connected in parallel between the DC side of the AC-DC converter and the first DC side of the DC-DC converter; the second DC side of the DC-DC converter is connected to the electrolytic cell.

[0024] The wind turbine (hereinafter referred to as wind turbine) can be, for example, a double-fed induction generator (DFIG), which, in addition to the generator body, also includes blades, gearboxes, nacelles, and other structures. This disclosure does not limit the type or structure of the wind turbine.

[0025] The turbine-side converter, grid-side converter, and first DC bus capacitor can form a back-to-back converter. The turbine-side converter is mainly used to control the rotor voltage and rotor current input to the wind turbine, thereby controlling the wind turbine's output power (i.e., stator power), output current (i.e., stator current), output voltage (i.e., stator voltage), and output frequency (i.e., stator frequency). The grid-side converter is mainly used to stabilize the voltage across the first DC bus capacitor (hereinafter referred to as the first DC bus capacitor). Only when the first DC bus capacitor is stable can it provide stable excitation to the wind turbine rotor. After the excitation is stable, the turbine-side converter can control the rotor current. Since there is a certain mathematical relationship between the rotor current, stator current, and stator voltage, controlling the rotor current is equivalent to controlling the wind turbine's stator voltage and stator current.

[0026] The first transformer can be, for example, a box-type transformer, and the third transformer can be, for example, a rectifier phase-shifting transformer; this is not a limitation of the embodiments disclosed herein. The first and second transformers can either step down the AC power input from the high-voltage side or step up the AC power input from the low-voltage side. For example, during the black start phase, the DC power generated by the black start energy is converted to AC power by an inverter, then stepped up by the second transformer and transmitted to the high-voltage side of the first transformer. After being stepped down by the first transformer, it is supplied to the wind turbine side to achieve the black start process. Alternatively, when the system is in operation, the AC power generated by the wind turbine can be stepped up by the first transformer and transmitted to the high-voltage side of the second transformer. After being stepped down by the second transformer, it is supplied to the electrolyzer to achieve the electrolytic hydrogen production process. The first and second transformers and the AC transmission lines connecting them can constitute a microgrid. The black start process allows both the wind turbine and the electrolyzer to be smoothly and stably connected to this microgrid, enabling the wind turbine to stably supply power to the electrolyzer after the system starts up and operates.

[0027] The AC-DC converter can be, for example, a 24-pulse uncontrolled rectifier, and the DC-DC converter can be, for example, a multi-interleaved parallel Buck converter; this disclosure does not limit the specific embodiments. The AC-DC converter can convert the alternating current output from the second transformer into direct current, and the DC-DC converter is mainly used to convert the direct current output from the AC-DC converter to adjust the electrolytic voltage, electrolytic current, and electrolytic power input to the electrolytic cell, thereby changing the load characteristics of the electrolytic cell.

[0028] The inverter can be viewed as a DC / AC inverter, mainly used to convert the DC power output from the black start power supply into AC power, specifically into three-phase AC power, thereby providing a stable three-phase AC voltage to the system so that the system can smoothly start from the off state to the running state.

[0029] It is known that black start is a critical and essential technology for off-grid wind power-to-hydrogen AC systems. Existing black start solutions typically use mains power or electrochemical energy storage devices as the black start power source. However, mains power solutions are costly and unstable, while electrochemical energy storage solutions have low safety and high cost. For example, the off-grid wind power-to-hydrogen system proposed in Chinese Invention Patent CN119518874A requires the wind turbine to charge the black start power source during operation. Therefore, the black start power source used is also an electrochemical energy storage device, which has low safety and needs to be deployed on the wind turbine side, requiring additional equipment such as transformers. Therefore, in order to reduce costs and improve system safety and stability, this disclosure proposes using a hydrogen fuel cell as the black start power source. The hydrogen fuel source for the hydrogen fuel cell can include hydrogen produced by an electrolyzer. Since the hydrogen production system itself is a hydrogen source, deploying hydrogen fuel cells as a black start power source on the hydrogen production side is a low-cost, high-safety, and high-stability solution. The hydrogen fuel cell can use hydrogen produced by the electrolyzer as a fuel source, so there is no need to charge the black start power source during system operation, which makes the black start power source have a longer service life, higher safety, lower cost, and can reduce engineering investment and engineering layout difficulty.

[0030] It should be understood that the electrical structure of the wind power off-grid hydrogen production system proposed in the above embodiments of this disclosure is one possible implementation provided by the embodiments of this disclosure. In fact, those skilled in the art can set other required electrical components according to actual needs, for example... Figure 1 The DC-DC converter shown in the figure can also be connected in parallel with the electrolytic cell via a third DC bus capacitor (C3 in the figure), or a switch can be connected in parallel between the DC-DC converter and the electrolytic cell. The first switch B1 near the inverter can also be connected with a grounded capacitor (C4 in the figure), or the grounded capacitor can be left unconnected. This disclosure does not limit the embodiments in this way.

[0031] It should be noted that, Figure 1 This is a topology diagram of a wind power off-grid hydrogen production system provided in an embodiment of this disclosure. Those skilled in the art should understand that... Figure 1The topology diagram showing a single wind turbine and a single electrolyzer connected via an AC transmission line can be expanded to connect a wind farm (including multiple wind turbines) and an electro-hydrogen plant (including multiple electrolyzers) via an AC transmission line (e.g., a 220kV or 35kV transmission line), forming an off-grid wind power hydrogen production system in an engineering sense.

[0032] The aforementioned off-grid hydrogen production system mainly includes a black start phase and an off-grid operation phase. The black start phase primarily involves using a black start power supply to initiate the system from a shutdown state to an operational state. The specific black start process will be described in detail later and will not be elaborated here. The off-grid operation phase is the stage after the system has successfully started and is in operation. During operation, the wind turbine converts wind energy into electrical energy, which is then supplied to the electrolyzer for hydrogen electrolysis. The control logic for the off-grid operation phase can be referenced in the detailed descriptions of relevant technologies. For example, the control logic for the wind turbine and electrolyzer in the control method for an off-grid hydrogen production system proposed in Chinese Invention Patent CN119518874A can be used to implement the off-grid operation phase, which will not be elaborated upon here.

[0033] According to the system of this disclosure, hydrogen fuel cells are deployed on the hydrogen production side of the electrolyzer as black start energy sources, and the hydrogen fuel source of the hydrogen fuel cells can be directly used from the hydrogen produced by the electrolyzer. This allows the system to achieve off-grid hydrogen production from wind power without the need for any additional electrochemical energy storage devices, further improving the safety and stability of the off-grid hydrogen production system from wind power, and also significantly reducing engineering investment and layout difficulty.

[0034] Figure 2 This diagram illustrates a structural schematic of a wind power off-grid hydrogen production system including a control system according to an embodiment of the present disclosure, as shown below. Figure 2 As shown, the control system in the off-grid hydrogen production system includes a first controller, a second controller, a third controller, and a fourth controller. The first controller controls the turbine-side converter, the second controller controls the grid-side converter, the third controller controls the inverter, and the fourth controller controls the DC-DC converter. In practical applications, each controller in the above control system can be a proportional-integral (PI) controller. The PI control algorithm used by the PI controller combines proportional control and integral control, enabling precise adjustment of the error (i.e., the difference between the reference value and the actual value).

[0035] The first controller includes a first voltage control mode (S1=0), a first power control mode (S1=1), and an active power control mode (S1=2). Switching between these modes is achieved via a switching switch S1. The first voltage control mode controls the generator-side converter based on the first low-voltage side voltage of the first transformer and the stator voltage of the wind turbine. The first power control mode controls the generator-side converter based on the active and reactive power of the wind turbine. The active power control mode controls the generator-side converter based on the active power of the wind turbine. In practical applications, the first controller can employ a dual-closed-loop PI control method, with the inner loop for current control and the outer loop for voltage control, power control, or active power control. Specifically, the outer voltage loop in the first voltage control mode can control the actual value u of the first low-voltage side voltage of the first transformer. gabc The actual value of the stator voltage u of the wind turbine sabc The value is compared with the corresponding reference value, and a reference value for the wind turbine rotor current is generated by the PI controller; the power outer loop in the first power control mode can generate the actual value P of the wind turbine's active power. s and the actual value of reactive power Q s The value is compared with the corresponding reference value, and a reference value for the wind turbine rotor current is generated by the PI controller; the power outer loop in the active power control mode can generate the actual value P of the wind turbine active power. s The reference value is compared with the corresponding reference value, and the PI controller generates a reference value for the fan rotor current; the inner current loop can then compare the reference value and the actual value of the fan rotor current. rabc The data is compared and then processed by a PI controller and a Space Vector Pulse Width Modulation (SVPWM) unit to generate a control signal for the machine-side converter. This control signal can be a Pulse Width Modulation (PWM) signal generated by the SVPWM unit. It is known that the machine-side converter contains multiple switching elements. The PWM signal generated by the SVPWM unit can control the ratio of the on-time to off-time of these switching elements within the entire switching cycle, thereby ensuring that the actual value of the wind turbine's rotor current reaches the reference value. The rotor current is also the AC current on the machine-side converter.

[0036] The second controller is specifically used to control the grid-side converter based on the voltage and current on both sides of the grid-side converter. The grid-side converter can also employ a dual-closed-loop PI control method, with the inner loop for current control and the outer loop for voltage control. Specifically, the outer voltage loop compares the actual value of the first DC bus voltage (i.e., the DC side voltage of the grid-side converter, which is also the voltage across the first DC bus capacitor) with the corresponding reference value, and generates a reference value for the AC side current of the grid-side converter via the PI controller. The inner current loop compares the reference value of the AC side current of the grid-side converter with the actual value of the AC side current obtained from real-time sampling, and generates the corresponding control signal via the PI controller and the SVPWM generator. It is known that the grid-side converter contains multiple switching elements. The control signal generated by the SVPWM can be a PWM signal, which can control the proportion of the on-time and off-time of the internal switching elements of the grid-side converter to the entire switching cycle, thereby ensuring that the first DC bus voltage and the AC side voltage of the grid-side converter each reach their corresponding reference values.

[0037] The third controller specifically controls the inverter based on the voltage and current on the low-voltage side of the second transformer and the current on the AC side of the inverter. Specifically, the voltage and current on the low-voltage side of the second transformer can be the voltage and current on the side of the first filter inductor L1 closest to the low-voltage side of the second transformer, or the voltage and current flowing into the low-voltage side of the second transformer. It should be understood that due to the influence of the first filter inductor, grounding capacitor, etc., on the transmission line from the inverter to the second transformer, there is a certain deviation between the AC output from the inverter's AC side and the AC input to the low-voltage side of the second transformer. The AC input to the low-voltage side of the second transformer is the actual AC input to the microgrid and transmitted to the wind turbine side. Therefore, controlling the inverter based on the voltage and current on the low-voltage side of the second transformer can ensure that the AC input to the low-voltage side of the second transformer reaches the preset reference value requirement. In practical applications, the inverter can also adopt a dual closed-loop PI control method, with the inner loop for current control and the outer loop for voltage control. Specifically, the voltage outer loop can control the actual value of the voltage on the low-voltage side of the second transformer. and the actual value of the low-voltage side current The value is compared with the corresponding reference value, and the PI controller generates a reference value for the inverter's AC side current. The inner current loop can compare the reference value of the inverter's AC side current with the actual value of the real-time sampled inverter AC side current. The data is compared and then processed by a PI controller and an SVPWM generator to generate the corresponding control signal. It is known that the inverter contains multiple switching elements. The control signal generated by the SVPWM generator can be a PWM signal, which can control the ratio of the on-time and off-time of the switching elements within the inverter to the total switching cycle. This allows the AC current on the inverter to reach the corresponding reference value, and consequently, the low-voltage voltage on the second transformer to reach the corresponding reference value, thus providing stable three-phase AC power to the microgrid and wind turbine.

[0038] The fourth controller includes a second power control mode (when S2 = 0) and a second voltage control mode (when S2 = 1). Switching between these modes is achieved via the switching switch S2. The second power control mode controls the DC-DC converter based on the electrolytic power input to the electrolytic cell (i.e., the power output from the second DC side of the DC-DC converter). The second voltage control mode controls the DC-DC converter based on the second DC bus capacitor C. ELZ The voltage at both ends (i.e., the voltage on the first DC side of the DC-DC converter, hereinafter referred to as the second DC bus voltage) controls the DC-DC converter. The fourth controller can employ a dual closed-loop PI control method, with the inner loop for current control and the outer loop for voltage or power control. In the second control mode, the power outer loop can control the actual value of the electrolytic power input to the electrolytic cell. The reference value is compared with the corresponding reference value, and the PI controller generates a reference value for the second DC-side current of the DC-DC converter. The voltage outer loop of the second voltage mode can then output the actual value u of the second DC bus voltage. dc The reference value is compared with the corresponding reference value, and the PI controller generates a reference value for the second DC-side current of the DC-DC converter (i.e., the electrolytic current input to the electrolytic cell); the inner current loop can compare the reference value of the second DC-side current of the DC-DC converter with the actual value of the second DC-side current actually acquired. The values ​​are compared, and a DC-DC duty cycle reference value d is generated by the PI controller. Then, a corresponding PWM control signal is generated based on the DC-DC duty cycle reference value d. It can be seen that there are multiple switching elements inside the DC-DC converter. The PWM control signal generated by SVPWM can control the ratio of the on-time and off-time of the switching elements inside the inverter to the entire switching cycle, making the actual duty cycle of the DC-DC converter equal to the duty cycle reference value d, thereby ensuring the actual value of the electrolytic power... Or the actual value of the second DC bus voltage u dc Each reaches its corresponding reference value.

[0039] In practical applications, when generating control signals using the inner current loop of the first controller, the slip angular frequency ω is also required. sl(i.e., the rotor angular frequency ω of the wind turbine) r Angular frequency ω of the microgrid voltage s The difference between them), where the angular frequency of the microgrid voltage can include the first low-voltage side voltage u of the first transformer. gabc The angular frequency, or the angular frequency of the microgrid voltage, can also be a custom-defined angular frequency reference value (2πf). ref To meet different control needs, such as Figure 2 As shown, the system may further include: a slip angular frequency generator, which includes a phase-locked loop (PLL) that can be used to lock the first low-voltage side voltage u of the first transformer. gabc To obtain u from the phase gabc The angular frequency may also include a switching switch S3 for switching between a first generation mode and a second generation mode, and a differencer for calculating ω. r With ω s ω is obtained by subtracting. sl The slip angular frequency generator includes a first generation mode (when S3 = 0) and a second generation mode (when S3 = 1); the first generation mode is used to generate the rotor angular frequency ω of the wind turbine generator. r The first low-voltage side voltage u of the first transformer gabc The difference between the angular frequencies generates the slip angular frequency ω. sl The second generation mode is used based on the rotor angular frequency ω of the wind turbine. r Compared with the preset angular frequency reference value 2πf ref The difference between them generates the slip angular frequency ω. sl Among them, the slip angular frequency ω sl Used as input to the first controller to control the wind turbine generator based on the slip angular frequency via the control unit-side converter.

[0040] Among them, the black start phase is based on the slip angular frequency ω sl The implementation method of controlling the wind turbine will be described in detail later when introducing the black start method. The implementation method of controlling the wind turbine based on the slip angular frequency during the offline operation stage can be found in the relevant record of slip frequency in the control method of a wind power off-grid hydrogen production system proposed in Chinese invention patent CN119518874A, which will not be elaborated here.

[0041] Based on the above Figure 2 The wind power off-grid hydrogen production system shown is Figure 3A flowchart illustrating a black start method for a wind power off-grid hydrogen production system according to an embodiment of this disclosure is shown. This black start method is used to start the system from a shut-off state to an operating state. When the system is in the shut-off state, the first switch B1, the second switch B2, the third switch B3, and the fourth switch B4 are all open. The first controller defaults to a first voltage control mode (i.e., S1 = 0), the fourth controller defaults to a second power control mode (i.e., S2 = 0), and the slip frequency generator defaults to a first generation mode (i.e., S3 = 0). Figure 3 As shown, the method includes:

[0042] Step S11: Close the first switch B1 and the second switch B2 to start the black start power supply and the inverter, and control the inverter through the third controller to convert the DC power output by the black start power supply into AC power until the AC voltage of the system reaches a steady state.

[0043] Step S12: When the system AC voltage reaches a steady state, close the third switch B3, start the grid-side converter, and control the grid-side converter through the second controller to convert the input AC power into DC power until the first DC bus capacitor C... DFIG The voltage across the terminals reaches a steady state;

[0044] Step S13, in the first DC bus capacitor C DFIG Once the voltage at both ends reaches a steady state, the generator-side converter and wind turbine are started. The generator-side converter is then controlled by the first controller in the first voltage control mode to ensure that the stator voltage u of the wind turbine is within a stable range. sabc The first low-voltage side voltage u of the first transformer gabc equal;

[0045] Step S14, under the stator voltage u sabc The first low-voltage side voltage u of the first transformer gabc Under the condition of equal power, close the fourth switch B4 and control the machine-side converter through the first controller in the first power control mode so that the wind turbine power of the wind turbine generator reaches a steady state. The wind turbine power includes active power and reactive power.

[0046] Step S15: When the wind turbine power reaches a steady state, start the DC-DC converter and the electrolytic cell, and control the DC-DC converter in the second power control mode through the fourth controller so that the electrolytic power input to the electrolytic cell reaches a steady state.

[0047] Step S16: When the electrolytic power input to the electrolytic cell reaches a steady state, disconnect the first switch and control the DC-DC converter in the second voltage control mode through the fourth controller to make the second DC bus capacitor C ELZThe voltage at both ends is kept stable, and the generator-side converter is controlled by the first controller in active power control mode so that the active power of the wind turbine generator reaches a steady state and the reactive power changes passively, so as to start the system from the shutdown state to the running state.

[0048] In step S11, after closing the first switch B1 and the second switch B2, and starting the black-start power supply and the inverter, the black-start power supply generates DC power. The inverter converts the DC power generated by the black-start power supply into AC power, which is transmitted to the low-voltage side of the second transformer. After being stepped up by the second transformer, it is transmitted to the high-voltage side of the first transformer. After being stepped down by the first transformer, it is output from the first low-voltage side and the second low-voltage side to their respective lines. That is, AC power is transmitted to the microgrid composed of the first transformer, the second transformer, and the AC transmission line connected to them. The system AC voltage can be understood as the AC voltage of the microgrid. The system AC voltage reaching a steady state can include the low-voltage side voltage of the second transformer reaching a steady state, the voltage between the first transformer and the second transformer reaching a steady state, and the voltages of both the first low-voltage side and the second low-voltage side of the first transformer reaching a steady state. Any voltage reaching a steady state can be understood as the phase, amplitude, frequency, etc. of the AC voltage reaching a steady state, that is, reaching the corresponding reference value.

[0049] Based on this, in step S11 above, the inverter is controlled by the third controller to convert the DC power output from the black-start power supply into AC power until the system AC voltage reaches a steady state, including:

[0050] Step S111: Collect the actual value of the AC side current of the inverter, the actual value of the low-voltage side voltage of the second transformer, and the actual value of the low-voltage side current of the second transformer.

[0051] Step S112: Determine the reference value of the AC side current of the inverter based on the actual value of the low-voltage side voltage of the second transformer, the actual value of the low-voltage side current of the second transformer, the preset reference value of the low-voltage side voltage of the second transformer, and the frequency reference value.

[0052] Step S113: Based on the reference value of the AC side current of the inverter, the actual value of the AC side current of the inverter, and the actual value of the low-voltage side voltage of the second transformer, a first control signal is generated. The first control signal is used to control the switching elements inside the inverter to turn on and off so that the actual value of the AC side current of the inverter reaches the corresponding reference value, thereby making the actual value of the low-voltage side voltage of the second transformer reach the corresponding reference value and the frequency of the low-voltage side voltage stabilize at the frequency reference value. Wherein, the system AC voltage reaching a steady state includes the actual value of the low-voltage side voltage of the second transformer reaching the corresponding reference value and the frequency of the low-voltage side voltage stabilizing at the frequency reference value.

[0053] In step S111, those skilled in the art can use any known current and voltage sampling technique to actually acquire the actual value of the AC side current of the inverter (i.e., the current of the first filter inductor L1 near the inverter). The actual value of the low-voltage side voltage of the second transformer (i.e., the voltage on the side of the first filter inductor L1 closest to the second transformer). The actual value of the low-voltage side current of the second transformer (i.e., the current on the side of the first filter inductor L1 closest to the second transformer). This disclosure does not limit the scope of the embodiments. Specifically, the data actually collected in the system... as well as All values ​​are in a three-phase stationary coordinate system (abc coordinate system). For ease of control, a coordinate transformation to the adc-dq coordinate system is required, that is, the values ​​in the abc coordinate system are transformed. as well as Convert to a two-phase rotating coordinate system (dq coordinate system) The data is then input into the third controller for calculation, whereby... and These represent the actual values ​​of the d-axis and q-axis components of the AC side current of the inverter, respectively. and These represent the actual values ​​of the d-axis and q-axis components of the low-voltage side voltage of the second transformer, respectively. and These represent the actual values ​​of the d-axis and q-axis components of the low-voltage side current of the second transformer, respectively. It should be understood that this disclosure does not limit the specific implementation of the adc-dq coordinate system transformation.

[0054] based on In step S112 above, the reference value of the low-voltage side voltage and the frequency reference value of the second transformer can be set by those skilled in the art according to actual needs, and this embodiment of the present disclosure does not impose any limitations on this. Specifically, a preset frequency reference value (which can be related to the aforementioned angular frequency reference value 2πf) can be set first. ref They can be the same or different; this can be customized. For example, they can both be set to 50Hz, which keeps the AC voltage of the entire system at 50Hz. The reference angle θ is obtained by integration. ref and with this reference angle θ ref The reference value of the low-voltage side voltage of the second transformer is used as a benchmark. By performing an adc-dq coordinate transformation, the reference values ​​of the d-axis components of the low-voltage side voltage of the second transformer in the dq coordinate system are obtained. and q-axis component reference value This is done by using a preset frequency reference value. Transform into and By incorporating this into subsequent calculations, frequency control of the system's AC voltage can be achieved. Then, using formulas (1-1) and (1-2), the reference value of the d-axis component of the inverter's AC side current in the dq coordinate system can be calculated. and q-axis component reference value This means that the reference value of the AC side current of the inverter is calculated:

[0055]

[0056] Where ω represents the angular frequency of the microgrid voltage, C4 represents the capacitance value of the grounding capacitor C4, and PI represents the PI control algorithm, which can refer to existing technologies. For example, PI can be expressed as... K P K represents the proportional adjustment gain. I The integral adjustment gain is represented by s, the complex frequency variable is represented by s, and 1 / s represents the integral element. This disclosure does not limit the specific implementation of this embodiment.

[0057] Based on the above In step S113, the reference value of the d-axis component of the AC side current of the inverter can be obtained first using formulas (2-1) and (2-2). and q-axis component reference value Actual value of the d-axis component of the AC side current of the inverter and q-axis component actual values And the actual value of the d-axis component of the low-voltage side voltage of the second transformer. and q-axis component actual values Calculate the reference value of the d-axis component of the AC side voltage of the inverter. and q-axis component reference value

[0058]

[0059] Where ω represents the angular frequency of the microgrid voltage, and L1 represents the inductance value of the first filter inductor L1; then, it is passed through an SVPWM generator based on and A first control signal is generated; wherein, the implementation method of the SVPWM generator generating the first control signal can refer to the prior art, and this disclosure embodiment does not limit it. As mentioned above, the control signal output by the SVPWM generator can be a PWM signal. Therefore, the first control signal can control the on and off of the switching elements inside the inverter so that the actual value of the AC side current of the inverter reaches the corresponding reference value, thereby making the actual value of the low-voltage side voltage of the second transformer reach the corresponding reference value and the frequency of the low-voltage side voltage stabilize at the frequency reference value (this is because based on the frequency reference value, the actual value of the low-voltage side voltage of the second transformer reaches the corresponding reference value, and the frequency of the low-voltage side voltage stabilizes at the frequency reference value). Transform into and It participates in the generation of the first control signal, thus enabling control of the voltage frequency.

[0060] In this context, the system AC voltage reaching steady state can also be understood as the black-start power supply and inverter providing a stable three-phase AC voltage to the system. When the system AC voltage reaches steady state (i.e., both the voltage and frequency reach their reference values), the voltage on the second low-voltage side of the first transformer also reaches steady state. In this case, the third switch B3 is closed, the grid-side converter is started, and the second controller controls the grid-side converter to convert the input AC power into DC power until the first DC bus capacitor C... DFIG The voltage at both ends reaches a steady state. The main function of the grid-side converter can include maintaining a constant voltage on the first DC bus. Only when the voltage on the first DC bus is constant can the wind turbine rotor be energized. After stable energization, the machine-side current transformer can control the rotor current. There is a certain mathematical relationship between the rotor current and the stator voltage and stator current. Therefore, controlling the rotor current also controls the stator voltage and stator current.

[0061] Based on this, in step S12 above, the grid-side converter is controlled by the second controller to convert the input AC power into DC power until the voltage across the first DC bus capacitor reaches a steady state, including:

[0062] Step S121: Collect the actual value of the voltage across the first DC bus capacitor, the actual value of the second low-voltage side voltage of the first transformer (i.e., the voltage of the second filter inductor L2 near the first transformer), and the actual value of the AC side current of the grid-side converter (i.e., the current of the second filter inductor L2 near the grid-side converter).

[0063] Step S122: Determine the reference value of the AC side current of the grid-side converter based on the preset reference value of the voltage across the first DC bus capacitor and the actual value of the voltage across the first DC bus capacitor.

[0064] Step S123: Based on the reference value of the AC side current of the grid-side converter, the actual value of the AC side current of the grid-side converter, and the actual value of the second low-voltage side voltage of the first transformer, a second control signal is generated. The second control signal is used to control the on and off of the internal switching elements of the grid-side converter so that the actual value of the voltage across the first DC bus capacitor reaches the corresponding reference value. Wherein, the voltage across the first DC bus capacitor reaching a steady state includes the actual value of the voltage across the first DC bus capacitor reaching the corresponding reference value.

[0065] In step S121, those skilled in the art can use any known current and voltage sampling technique in the art to actually collect the first DC bus capacitance C. DFIG Actual value of voltage across terminals The actual value u of the second low-voltage side voltage of the first transformer labc And the actual value i of the AC side current of the grid-side converter. cabc This disclosure does not limit the scope of the embodiments. It should be understood that the actual u collected in the system... labc i cabc All values ​​are in the abc coordinate system. For ease of control, u in the abc coordinate system can be... labc i cabc Convert i to dq coordinate system cd i cq u ld u lq The voltage is then input into the second controller for calculation. Specifically, the second low-voltage side voltage u of the first transformer can be locked via a PLL. labc The phase is used to obtain the reference angle. and with this reference angle u as a benchmark labc and i cabc Perform an adc-dq coordinate transformation to obtain i cd i cq u ld u lq ; where i cd and i cq These represent the actual values ​​of the d-axis and q-axis components of the AC side current of the grid-side converter, respectively. ld and u lq These represent the actual values ​​of the d-axis and q-axis components of the second low-voltage side voltage of the first transformer, respectively.

[0066] In step S122, a PI control algorithm can be used based on a reference value of the voltage across the first DC bus capacitor. The actual value of the voltage across the first DC bus capacitor The reference values ​​of the d-axis component of the AC side current of the grid-side converter in the dq coordinate system are calculated. Among them, the reference value of the voltage across the first DC bus capacitor The settings can be customized by those skilled in the art according to actual needs, and this disclosure does not limit such customization. Optionally, the reference value of the q-axis component of the AC side current of the grid-side converter... This can be set by skilled technicians according to actual needs. Since the q-axis component of the AC current on the grid side can represent reactive power, it is generally desirable for the reactive power to be 0. It can be set to 0; or, it can be determined by actually measuring the actual value Q of the reactive power input to the second low-voltage side of the first transformer. lThen, the PI control algorithm is used to determine the reactive power based on the actual value Q. l The q-axis component reference value of the AC side current of the grid-side converter is calculated by comparing it with the preset power reference value (i.e., 0). The method for measuring reactive power can refer to existing technologies, and this disclosure does not limit the embodiments thereto.

[0067] Based on the above u ld u lq i cd i cq In step S123, formulas (3-1) and (3-2) can be used to determine the result based on... u ld u lq i cd and i cq Calculate the reference value of the d-axis component of the AC side voltage of the grid-side converter. and q-axis component reference value

[0068] Where ω represents the angular frequency of the microgrid voltage, and L2 represents the inductance value of the second filter inductor L2; then, it is passed through an SVPWM generator based on and A second control signal is generated; wherein, the implementation method of generating the first control signal through the SVPWM device can refer to the prior art, and this embodiment of the present disclosure is not limited thereto. As described above, the control signal output by the SVPWM device can be a PWM signal. Therefore, the second control signal can control the on and off of the switching elements inside the grid-side converter so that the AC side voltage of the grid-side converter reaches the corresponding reference value, thereby making the actual value of the voltage across the first DC bus capacitor reach the corresponding reference value.

[0069] As described above, when the system also includes a slip angular frequency generator, the slip angular frequency generator generates the slip angular frequency ω in the first generation mode before the electrolytic power input to the electrolytic cell reaches a steady state. sl That is, based on the rotor angular frequency ω of the wind turbine. r The first low-voltage side voltage u of the first transformer gabc The difference between the angular frequencies is used to generate the slip angular frequency; after the electrolytic power input to the electrolytic cell reaches a steady state, the slip angular frequency generator generates the slip angular frequency in the second generation mode, which is based on the rotor angular frequency ω of the wind turbine generator. r Compared with the preset angular frequency reference value 2πf ref The difference between them generates the slip angular frequency ω. slIn this way, before the electrolytic power input to the electrolytic cell stabilizes (or during the black start phase), the frequency of the AC voltage controlled by the black start power supply and inverter can be established (this is due to the first low-voltage side voltage u of the first transformer). gabc The angular frequency depends on the angular frequency of the three-phase AC voltage generated by the black start power supply and the inverter. At this time, the wind turbine follows the frequency generated by the black start power supply and the inverter. After the electrolytic power input to the electrolytic cell reaches a steady state (which is equivalent to the system starting off-grid operation), the wind turbine performs open-loop frequency control based on its own set angular frequency reference value. This can maintain the frequency of the entire system within the permissible range, which is beneficial to improving the stability of the system from the stop state to the running state.

[0070] Based on the aforementioned slip frequency, in step S13, the first controller controls the generator-side converter in the first voltage control mode to make the stator voltage of the wind turbine equal to the first low-voltage side voltage of the first transformer, including:

[0071] Step S131: Collect the actual value of the first low-voltage side voltage of the first transformer, the actual value of the stator voltage of the wind turbine generator, and the actual value of the rotor current of the wind turbine generator. The rotor current is the AC side current of the generator-side converter.

[0072] Step S132: Determine the reference value of the rotor current based on the actual value of the first low-voltage side voltage of the first transformer, the preset reference value of the first low-voltage side voltage of the first transformer, and the actual value of the stator voltage of the wind turbine.

[0073] Step S133: Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angle frequency generated by the slip angle frequency generator in the first generation mode, a third control signal is generated. The third control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the stator voltage of the wind turbine equal to the first low-voltage side voltage of the first transformer.

[0074] In step S131, those skilled in the art can use any known current and voltage sampling technique in the art to actually acquire the actual value u of the first low-voltage side voltage of the first transformer. gabc The actual value of the stator voltage u of the wind turbine generator sabc And the actual value i of the rotor current of the wind turbine. rabc This disclosure does not limit the scope of the embodiments. It should be understood that the actual u collected in the system... gabc u sabc i rabc All values ​​are in the abc coordinate system. For ease of control, u in the abc coordinate system can be... gabc usabc i rabc Convert to dq coordinate system u gd u gq u sd u sq i rd i rq The input is then fed into the first controller for calculation; for example, it can be locked by the PLL in the slip angular frequency generator. gabc The phase obtained by ω s To obtain a reference angle and with this reference angle u as a benchmark gabc u sabc Perform an adc-dq coordinate transformation to obtain u gd u gq u sd u sq This disclosure provides embodiments for i rabc to i rd i rq The conversion process is not restricted; where u gd and u gq The actual values ​​of the d-axis and q-axis components of the first low-voltage side voltage of the first transformer are represented respectively. sd and u sq The actual values ​​of the d-axis and q-axis components of the stator voltage of the wind turbine generator, i rd and i rq These represent the actual values ​​of the d-axis and q-axis components of the rotor current of the wind turbine, respectively.

[0075] In step S132, the reference value of the first low-voltage side voltage of the first transformer can be customized according to the actual needs of those skilled in the art, and this embodiment of the present disclosure does not impose any limitations on this. Similarly, the reference value of the first low-voltage side voltage of the first transformer can be transformed into the adc-dq coordinate system. For example, it can be based on the aforementioned reference angle. Based on the benchmark Reference value of the d-axis component of the first low-voltage side voltage of the first transformer and q-axis component reference value Therefore, the PI control algorithm can be used based on u sd and The reference value of the q-axis component of the rotor current in the dq coordinate system was calculated. And through PI control algorithm based on u gd and The reference values ​​of the d-axis component of the rotor current in the dq coordinate system were calculated. This gives us a reference value for the rotor current.

[0076] Based on the above i rd i rq and the slip angular frequency ω generated in the first generation mode sl In step S133, the formulas (4-1) and (4-2) can be used first according to... i rd i rq ω sl Generate the d-axis component reference value of the fan rotor reference voltage and q-axis component reference value

[0077] Among them, L r This refers to the self-inductance of the rotor winding (i.e., the magnetic field generated by the change in current in the fan rotor winding inducing the same winding itself). and The feedforward compensation term in the first voltage control mode is a constant related to the circuit parameters and can be customized by those skilled in the art according to actual needs. This embodiment does not impose any limitations on this. Then, the SVPWM is used based on... and A third control signal is generated; the implementation of generating the third control signal through the SVPWM device can refer to existing technology, and this disclosure does not limit it. As mentioned above, the control signal output by the SVPWM device can be a PWM signal. Therefore, the third control signal can control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the stator voltage of the wind turbine equal to the first low-voltage side voltage of the first transformer, that is, completing the no-load stator voltage build-up of the wind turbine. The fact that the stator voltage of the wind turbine is equal to the first low-voltage side voltage of the first transformer (i.e., the phase, amplitude, and frequency of the stator voltage are equal to the first low-voltage side voltage of the second transformer) can be understood as the grid connection condition for the wind turbine to connect to the microgrid. Only when the stator voltage of the wind turbine is equal to the first low-voltage side voltage of the first transformer can the wind turbine smoothly connect to the microgrid to stably supply power to the electrolyzer.

[0078] In step S14, when the stator voltage is equal to the voltage on the first low-voltage side of the first transformer (i.e., the grid connection condition is met), the wind turbine can be connected to the microgrid by closing the fourth switch. Simultaneously, the first controller can be switched from the first voltage control mode to the first power control mode to achieve steady-state wind turbine power. Wind turbine power is divided into active power and reactive power. Active power refers to the useful power generated by the wind turbine, i.e., the power converted into electrical energy output. Reactive power is the power generated by the wind turbine during power generation, used for the conversion of electric and magnetic fields within the circuit; reactive power is not converted into electrical energy output. For active power, the maximum output power reference value (i.e., active power reference value) of the wind turbine can be calculated based on the Maximum Power Point Tracking (MPPT) algorithm by real-time acquisition of the wind turbine's rotor speed. The actual output power of the wind turbine (i.e., the actual active power value) can be calculated by real-time sampling of the voltage and current on the first low-voltage side of the second transformer. Regarding reactive power, the reactive power reference value can be set by those skilled in the art according to actual needs, for example, it can be set to 0; the actual reactive power value can be obtained by measurement, and the method for measuring reactive power can refer to the prior art, which is not limited in this disclosure.

[0079] Based on this, in step S14 above, the first controller controls the machine-side converter in the first power control mode to make the wind turbine power reach a steady state, including:

[0080] Step S141: Collect the actual value P of the active power of the wind turbine generator. s The actual value of reactive power Q of a wind turbine generator s The actual value of the rotor current i of the wind turbine rabc ;

[0081] Step S142, based on the preset reference value of active power. Preset reference value for reactive power The actual value of active power P s and the actual value of reactive power Q s To determine the reference value of the rotor current of the wind turbine;

[0082] Step S143: Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angle frequency generated by the slip angle frequency generator in the first generation mode, a fourth control signal is generated. The fourth control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power and the actual value of the reactive power of the wind turbine reach the corresponding reference value. Among them, the wind turbine power reaching steady state includes the actual value of the active power and the actual value of the reactive power of the wind turbine reaching the corresponding reference value.

[0083] In step S141, this embodiment of the disclosure applies to P. s Q s and i rabc The data acquisition method is not limited; for example, it can be achieved by actually acquiring the stator voltage u of the wind turbine. sabc and stator current i sabc The actual value P of the active power of the wind turbine was obtained. s =u sabc i sabc ; and can also i rabc Convert to i rd i rq This embodiment of the invention does not limit its participation in subsequent calculations. Furthermore, in step S142, a PI control algorithm can be used based on... and P s Reference value for the d-axis component of the generated rotor current And, based on the PI control algorithm and Q s Reference value for generating the q-axis component of the rotor current

[0084] Based on the determination in step S142 and Actual value of the q-axis component of the rotor current i rq and the actual value of the d-axis component i rd and slip frequency ω sl We can first use formulas (5-1) and (5-2) according to... i rd i rq ω sl Generate the d-axis component reference value of the fan rotor reference voltage and q-axis component reference value

[0085]

[0086] Among them, L rFor the rotor winding self-inductance (i.e., the magnetic field generated by the change of current in the fan rotor winding induction on the same winding itself), u rdc and u rqc The feedforward compensation term under the power control mode (i.e., the first power control mode and the active power control mode) is a constant related to the circuit parameters and can be customized by those skilled in the art according to actual needs. This disclosure does not limit this setting. Then, it is passed through an SVPWM device based on... and A fourth control signal is generated; the implementation of generating the fourth control signal through the SVPWM device can refer to existing technology, and this disclosure does not limit this embodiment. As mentioned above, the control signal output by the SVPWM device can be a PWM signal. Therefore, the fourth control signal can control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power and the actual value of the reactive power of the wind turbine reach the corresponding reference value.

[0087] In step S15, the wind turbine power reaches a steady state, meaning the wind turbine can output stable power or stable electrical energy. At this time, the DC-DC converter and electrolytic cell can be started to connect the electrolytic cell to the microgrid. In the second power control mode, the fourth controller controls the DC-DC converter to maintain the system power balance by adjusting the electrolytic power input to the electrolytic cell (i.e., the output power of the DC-DC converter) to achieve a steady state, thereby maintaining the system voltage stability. The system power balance can be understood as the wind turbine output power = power loss of the transmission line + electrolytic power consumed by the electrolytic cell.

[0088] In step S15, the fourth controller, in the second power control mode, determines the power output based on the actual value of the electrolytic power input to the electrolytic cell. Preset reference value of electrolysis power and the actual value of the second DC-side current of the DC-DC converter. The DC-DC converter is controlled to ensure that the electrolytic power input to the electrolytic cell reaches the corresponding reference value. Specifically, this can be achieved first through a PI control algorithm based on... and Reference value for generating the second DC-side current of the DC-DC converter Then, through the PI control algorithm, based on and Generate DC-DC duty cycle reference value Then, a sixth control signal is generated based on the DC-DC duty cycle reference value d using a Sine Pulse Width Modulation (SPWM) device. This sixth control signal can be a PWM signal. Therefore, the sixth control signal can control the on / off switching of the internal switching elements of the grid-side converter to ensure that the duty cycle of the DC-DC converter is equal to the duty cycle reference value d. This allows the electrolytic power input to the electrolytic cell to reach the corresponding reference value, thus facilitating system power balance when the electrolytic cell is connected to the microgrid and maintaining the stability of the microgrid's voltage amplitude and frequency. It should be understood that the actual value of the electrolytic power... The actual value of the second DC-side current of the DC-DC converter can be sampled. The actual value of the second DC side voltage To calculate Reference value of electrolysis power The settings can be customized by those skilled in the art according to actual needs, and this disclosure does not limit the specific settings.

[0089] It should be understood that when the wind turbine power and the electrolytic power input to the electrolytic cell reach a steady state through steps S11 to S15, it indicates that both the wind turbine and the electrolytic cell have been successfully started and stably connected to the microgrid. Therefore, in step S16, the first switch can be disconnected (equivalent to shutting off the black-start power supply, at which point the system enters the off-grid operation phase), and simultaneously the fourth controller can be switched from the second power control mode to the second voltage control mode to maintain a constant electrolytic cell bus voltage (i.e., the voltage across the second DC bus capacitor). This allows the electrolytic cell to act as an active power relaxation node during the system offline operation phase. That is, given a reference value for the electrolytic cell bus voltage, the fourth controller's voltage outer loop calculates the reference value for the changing electrolytic cell bus current, which is equivalent to obtaining a reference value for the changing electrolytic power, without artificial intervention. An electrolysis power reference value is set so that the electrolysis power can change in real time to maintain the active power balance of the system and the stability of the electrolytic cell bus voltage. At the same time, the first controller can be switched from the first power control mode to the active power control mode, and at this time the slip angular frequency generator switches to the second generation mode to generate the slip angular frequency based on the preset reference angular frequency. In this way, during the off-grid operation phase of the system, the wind turbine is used as the reactive power relaxation node, that is, only the active power reference value is given, without manually setting the reactive power reference value. The first controller calculates the changing rotor current reference value, which can realize active power control and frequency control, and at the same time enable the reactive power exchanged between the wind turbine and the microgrid to change in real time to maintain the reactive power balance of the system and the stability of the wind turbine bus voltage (i.e., the voltage across the first DC bus capacitor).

[0090] Therefore, in step S16, the fourth controller, in the second voltage control mode, determines the voltage based on the actual value u across the second DC bus capacitor. dc The preset reference value of the voltage across the second DC bus capacitor. and the actual value of the second DC-side current of the DC-DC converter. Control the DC-DC converter to keep the voltage across the second DC bus capacitor stable at the corresponding reference value. Specifically, this can be achieved first through a PI control algorithm based on... and u dc The reference value for generating the second DC-side current of the DC-DC converter. Then, through the PI control algorithm, based on and Generate DC-DC duty cycle reference value Then, a seventh control signal is generated based on the DC-DC duty cycle reference value d using a Sine Pulse Width Modulation (SPWM) device. This seventh control signal can be a PWM signal. Therefore, the sixth control signal can control the switching elements inside the grid-side converter to ensure that the duty cycle of the DC-DC converter is equal to the duty cycle reference value d, thereby maintaining the voltage across the second DC bus capacitor at the corresponding reference value. It should be understood that u dc and The reference value of the voltage across the second DC bus capacitor can be obtained by sampling using voltage and current sampling techniques known in the art. The settings can be customized by those skilled in the art according to actual needs, and this disclosure does not limit the specific settings.

[0091] In step S16, controlling the generator-side converter in active power control mode via the first controller to bring the active power of the wind turbine generator to a steady state may include:

[0092] Step S161: Collect the actual value P of the active power of the wind turbine. s And the actual value i of the rotor current of the wind turbine. rabc ;

[0093] Step S162: Determine the reference value of the rotor current of the wind turbine generator based on the preset reference value of active power and the actual value of active power.

[0094] Step S163: Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angular frequency generated by the slip angular frequency generator in the second generation mode, a fifth control signal is generated. The fifth control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power of the wind turbine reach the corresponding reference value and the rotor angular frequency stabilize at the preset angular frequency reference value. Wherein, the active power of the wind turbine reaches a steady state including the actual value of the active power of the wind turbine reaching the corresponding reference value and the rotor angular frequency stabilizing at the preset angular frequency reference value.

[0095] In step S161, this embodiment of the disclosure applies to P. s and i rabc The data acquisition method is not limited; for example, it can be achieved by actually acquiring the stator voltage u of the wind turbine. sabc and stator current i sabc The actual value P of the active power of the wind turbine was obtained. s =u sabc i sabc ; and can also i rabc Convert to i rd i rq This embodiment of the invention does not limit its participation in subsequent calculations. Furthermore, in step S162, a PI control algorithm can be used based on... and P s Reference value for the d-axis component of the generated rotor current And directly use the q-axis component reference value of the rotor current If we set it to 0, since the reference value of the q-axis component of the rotor current can reflect the reactive power of the fan, we can consider the reactive power of the fan to be 0.

[0096] In step 163, the d-axis component reference value of the fan rotor reference voltage can be calculated by referring to the above formulas (5-1) and (5-2). and q-axis component reference value The difference lies in the slip angular frequency ω used in step 163. sl It is determined by the rotor angular frequency ω r and the preset angular frequency reference value (2πf) ref As determined by ); then, based on the SVPWM device and A fifth control signal is generated; the implementation of generating the fifth control signal through the SVPWM device can refer to existing technology, and this disclosure does not limit it. As mentioned above, the control signal output by the SVPWM device can be a PWM signal. Therefore, the fifth control signal can control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power of the wind turbine reach the corresponding reference value and stabilizing the rotor angular frequency at the preset angular frequency reference value.

[0097] It should be understood that after completing steps S11 to S16, the system officially enters the offline operation phase, that is, the system successfully starts from the stopped state to the running state. Based on the black start method of steps S11 to S16 above, the black start working principle can be briefly described as follows: First, the hydrogen fuel cell is turned on as the black start power source, providing a stable three-phase AC voltage to the system; then, the blower performs no-load voltage building control to establish a stable voltage, and then executes active power control; then, the electrolyzer is turned on, first performing low active power control, with the blower performing power balancing; then, the electrolyzer switches to voltage control mode to maintain a constant voltage on the electrolyzer bus; finally, the blower performs open-loop frequency control according to the set frequency reference value; at the same time, the black start power source is disconnected, and the system enters the off-grid operation mode. Essentially, during the black start phase, the black start power supply effectively assumes the responsibility of active and reactive power relaxation nodes, and is also responsible for controlling the system voltage frequency (e.g., controlling it to 50Hz). At this time, the wind turbine follows the frequency of the black start power supply. During off-grid operation, the wind turbine acts as a reactive power relaxation node, meaning no reactive power reference value is specified for the wind turbine, and its reactive power passively changes to maintain system reactive power balance. The electrolyzer bus acts as an active power relaxation node, meaning no active or reactive power reference values ​​are specified on the electrolyzer side, and its power passively changes to maintain constant voltage on the electrolyzer bus. The wind turbine itself controls the system voltage frequency (e.g., controlling it to 50Hz). This ensures that the system can maintain power balance, voltage stability, and frequency fluctuations within permissible ranges throughout the entire process.

[0098] Based on the above Figure 3 The black start method shown in this disclosure also includes a black start timing sequence as shown in Table 1, to concisely describe the changes in the actions of various switches, controllers, and devices during the black start process:

[0099] Table 1 Black Startup Sequence

[0100]

[0101]

[0102] Based on the black-start timing shown in Table 1 above, the black-start process can be summarized as follows: In response to receiving the black-start start command, the hydrogen fuel cell, acting as the black-start power source, is switched on and operates in grid-connected control mode. The outer loop of the third controller is a voltage loop, and the inner loop is a current loop, providing a stable three-phase AC voltage to the system. Subsequently, the wind turbine performs no-load voltage building control, the grid-side converter controls the first DC bus voltage, and the outer loop of the first controller of the turbine-side converter controls the stator voltage to build up voltage and achieve smooth grid connection. After grid connection, the outer loop of the first controller switches to a power loop and then performs power control. Subsequently, the electrolyzer is switched on, and the outer loop of the fourth controller is a power loop, first performing low active power control, with the black-start power source performing power balancing. Subsequently, the electrolyzer switches to the second voltage control mode to maintain a constant electrolyzer bus voltage. Finally, the wind turbine performs frequency control according to the set frequency reference value, while maintaining the system's reactive power balance. Finally, the black-start power source is disconnected, and the system enters the off-grid operation phase.

[0103] Figure 4 , Figure 5 and Figure 6 The diagram illustrates the simulation results of controlling a wind power off-grid hydrogen production system using a black-start method according to an embodiment of this disclosure. For example, the simulation results can be obtained by conducting a black-start simulation experiment using a single wind turbine powering a single electrolyzer platform built with Matlab / Simulink. The simulation shows the black-start state before 0.85s, where the system is connected to the grid using the black-start power supply; after 0.85s, the black-start power supply is switched off, and the system enters a purely off-grid operation state. Figure 4 As shown, the active and reactive power absorbed by the stator from the microgrid, the total active and reactive power supplied by the wind turbine to the microgrid, and the active and reactive power supplied by the grid-side converter to the microgrid all change smoothly and in a balanced manner before and after the black-start power supply is switched off (i.e., around 0.85s); and, as Figure 5 As shown, the changes in electrolytic current, electrolytic voltage, electrolytic power, and the voltage on the high-voltage side of the DC-DC converter (i.e., the voltage across the second DC bus capacitor) before and after the black-start power supply is switched off (i.e., around 0.85s) are all smooth and stable. Figure 6 As shown, the changes in the first DC bus voltage and the system frequency (including the microgrid voltage frequency) before and after the black-start power supply is cut off (i.e., around 0.85s) are also stable or even remain unchanged. Therefore, the black-start method proposed in this embodiment can enable the wind power off-grid hydrogen production system to start smoothly without grid connection, and the wind turbine can achieve MPPT during off-grid operation, resulting in a balance between active and reactive power, and stable system voltage and frequency.

[0104] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0105] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A black start method applied to a wind power off-grid hydrogen production system, characterized in that, The wind power off-grid hydrogen production system includes a wind turbine side and a hydrogen production side, a first controller, a second controller, a third controller, and a fourth controller. On the wind turbine side, the stator of the wind turbine is connected to the first low-voltage side of the first transformer via the fourth switch B4, and the rotor is connected to the AC side of the turbine-side converter. A first DC bus capacitor is connected in parallel between the DC side of the turbine-side converter and the DC side of the grid-side converter. The AC side of the grid-side converter is connected to the second low-voltage side of the first transformer via a second filter inductor and a third switch B3. On the hydrogen production side, the electrolyzer is connected to the second DC side of the DC-DC converter, and a second DC bus capacitor is connected in parallel between the DC side of the AC-DC converter and the... Between the first DC side of the DC-DC converter, the AC side of the AC-DC converter is connected to the low-voltage side of the second transformer, and the high-voltage side of the second transformer is connected to the high-voltage side of the first transformer via the second switch B2. The DC side of the inverter is connected to the black-start power supply, and the AC side is connected to the low-voltage side of the second transformer via the first filter inductor and the first switch B1. The black-start power supply includes a hydrogen fuel cell, and the hydrogen fuel source for the hydrogen fuel cell includes hydrogen produced by an electrolyzer. The black-start method is used to start the system from a shut-off state to an operating state. When the system is in a shut-off state, B1, B2, B3, and B4 are all disconnected. The black-start method includes: Close B1 and B2 to start the black start power supply and inverter, and use the third controller to control the inverter to convert the DC power output from the black start power supply into AC power until the system AC voltage reaches a steady state. When the AC voltage of the system reaches a steady state, close B3, start the grid-side converter, and control the grid-side converter through the second controller to convert the input AC power into DC power until the voltage across the first DC bus capacitor reaches a steady state. When the voltage across the first DC bus capacitor reaches a steady state, the machine-side converter and the wind turbine are started, and the machine-side converter is controlled by the first controller in the first voltage control mode so that the stator voltage of the wind turbine is equal to the first low-voltage side voltage of the first transformer. When the stator voltage is equal to the first low-voltage side voltage of the first transformer, B4 is closed, and the machine-side converter is controlled by the first controller in the first power control mode so that the wind turbine power of the wind turbine generator reaches a steady state. The wind turbine power includes active power and reactive power. When the wind turbine power reaches a steady state, the DC-DC converter and the electrolytic cell are started, and the DC-DC converter is controlled by the fourth controller in the second power control mode so that the electrolytic power input to the electrolytic cell reaches a steady state. When the electrolytic power input to the electrolytic cell reaches a steady state, B1 is disconnected, and the DC-DC converter is controlled by the fourth controller in the second voltage control mode to keep the voltage across the second DC bus capacitor stable. The generator-side converter is controlled by the first controller in the active power control mode to make the active power of the wind turbine reach a steady state and the reactive power passively change, so as to start the system from the shutdown state to the operating state.

2. The method of claim 1, wherein, The process of controlling the inverter via a third controller to convert the DC power output from the black-start power supply into AC power until the system AC voltage reaches a steady state includes: The actual values ​​of the AC side current of the inverter, the actual values ​​of the low-voltage side voltage of the second transformer, and the actual values ​​of the low-voltage side current of the second transformer are collected. The reference value of the AC side current of the inverter is determined based on the actual value of the low-voltage side voltage of the second transformer, the actual value of the low-voltage side current of the second transformer, the preset reference value of the low-voltage side voltage of the second transformer, and the frequency reference value. A first control signal is generated based on the reference value of the AC side current of the inverter, the actual value of the AC side current of the inverter, and the actual value of the low-voltage side voltage of the second transformer. The first control signal is used to control the switching elements inside the inverter to turn on and off so that the actual value of the AC side current of the inverter reaches the corresponding reference value, thereby making the actual value of the low-voltage side voltage of the second transformer reach the corresponding reference value and the frequency of the low-voltage side voltage stabilize at the frequency reference value. The system AC voltage reaching a steady state includes the actual value of the low-voltage side voltage of the second transformer reaching the corresponding reference value and the frequency of the low-voltage side voltage stabilizing at the frequency reference value.

3. The method of claim 1, wherein, The process of controlling the grid-side converter via the second controller to convert the input AC power into DC power until the voltage across the first DC bus capacitor reaches a steady state includes: The actual values ​​of the voltage across the first DC bus capacitor, the actual voltage of the second low-voltage side of the first transformer, and the actual AC current of the grid-side converter are collected. Based on the preset reference value of the voltage across the first DC bus capacitor and the actual value of the voltage across the first DC bus capacitor, the reference value of the AC side current of the grid-side converter is determined. A second control signal is generated based on the reference value of the AC side current of the grid-side converter, the actual value of the AC side current of the grid-side converter, and the actual value of the second low-voltage side voltage of the first transformer. The second control signal is used to control the switching elements inside the grid-side converter to turn on and off so that the actual value of the voltage across the first DC bus capacitor reaches the corresponding reference value. The steady-state condition of the voltage across the first DC bus capacitor includes the actual value of the voltage across the first DC bus capacitor reaching the corresponding reference value.

4. The method of claim 1, wherein, The system further includes: a slip angular frequency generator, the slip angular frequency generator including a first generation mode and a second generation mode; The first generation mode is used to generate a slip angular frequency based on the difference between the rotor angular frequency of the wind turbine and the angular frequency of the first low-voltage side voltage of the first transformer. The second generation mode is used to generate a slip angular frequency based on the difference between the rotor angular frequency of the wind turbine and a preset angular frequency reference value; The slip angle frequency is input to the first controller to control the wind turbine generator by controlling the machine-side converter based on the slip angle frequency.

5. The method of claim 4, wherein, If the system also includes a slip angular frequency generator, the slip angular frequency generator generates a slip angular frequency in the first generation mode before the electrolytic power input to the electrolytic cell reaches a steady state. After the electrolytic power input to the electrolytic cell reaches a steady state, the slip angular frequency generator generates the slip angular frequency in the second generation mode.

6. The method of claim 5, wherein, The step of controlling the generator-side converter via a first controller in a first voltage control mode to make the stator voltage of the wind turbine equal to the first low-voltage side voltage of the first transformer includes: The actual values ​​of the first low-voltage side voltage of the first transformer, the actual values ​​of the stator voltage of the wind turbine, and the actual values ​​of the rotor current of the wind turbine are collected. The rotor current is the AC side current of the generator-side converter. The reference value of the rotor current is determined based on the actual value of the first low-voltage side voltage of the first transformer, the preset reference value of the first low-voltage side voltage of the first transformer, and the actual value of the stator voltage of the wind turbine. Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angle frequency generated by the slip angle frequency generator in the first generation mode, a third control signal is generated. The third control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the stator voltage of the wind turbine equal to the first low-voltage side voltage of the first transformer.

7. The method of claim 5, wherein, The step of controlling the machine-side converter through the first controller in the first power control mode to make the wind turbine power reach a steady state includes: The actual values ​​of the active power, reactive power, and rotor current of the wind turbine are collected. The reference value of the rotor current of the wind turbine is determined based on the preset reference value of active power, the preset reference value of reactive power, the actual value of active power, and the actual value of reactive power. Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angle frequency generated by the slip angle frequency generator in the first generation mode, a fourth control signal is generated; the fourth control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power and the actual value of the reactive power of the wind turbine reach the corresponding reference value. The steady-state state of the wind turbine power includes the actual value of the active power of the wind turbine reaching the corresponding reference value and the actual value of the reactive power reaching the corresponding reference value.

8. The method of claim 5, wherein, The step of controlling the generator-side converter in active power control mode via the first controller to achieve a steady state of active power for the wind turbine includes: The actual values ​​of the active power and rotor current of the wind turbine are collected. The reference value of the rotor current of the wind turbine is determined based on the preset reference value of active power and the actual value of the active power. Based on the reference value of the rotor current, the actual value of the rotor current, and the slip angular frequency generated by the slip angular frequency generator in the second generation mode, a fifth control signal is generated. The fifth control signal is used to control the on and off of the switching elements inside the grid-side converter so that the actual value of the rotor current of the wind turbine reaches the corresponding reference value, thereby making the actual value of the active power of the wind turbine reach the corresponding reference value and the rotor angular frequency stabilize at the preset angular frequency reference value. The active power of the wind turbine reaching a steady state includes the actual value of the active power of the wind turbine reaching the corresponding reference value and the rotor angular frequency stabilizing at a preset angular frequency reference value.

9. The method of claim 1, wherein, In the second power control mode, the fourth controller controls the DC-DC converter based on the actual value of the electrolytic power input to the electrolytic cell, the preset reference value of the electrolytic power, and the actual value of the second DC side current of the DC-DC converter, so that the electrolytic power input to the electrolytic cell reaches the corresponding reference value. In the second voltage control mode, the fourth controller controls the DC-DC converter based on the actual value of the voltage across the second DC bus capacitor, the preset reference value of the voltage across the second DC bus capacitor, and the actual value of the second DC side current of the DC-DC converter, so that the voltage across the second DC bus capacitor remains stable at the corresponding reference value.

10. The method of claim 1, wherein, The first controller includes a first voltage control mode, a first power control mode, and an active power control mode; the first voltage control mode is used to control the generator-side converter based on the first low-voltage side voltage of the first transformer and the stator voltage of the wind turbine; the first power control mode is used to control the generator-side converter based on the active power and reactive power of the wind turbine; and the active power control mode is used to control the generator-side converter based on the active power of the wind turbine. The second controller is used to control the grid-side converter based on the voltage and current on both sides of the grid-side converter; The third controller is used to control the inverter based on the voltage and current on the low-voltage side of the second transformer and the current on the AC side of the inverter. The fourth controller includes a second power control mode and a second voltage control mode. The second power control mode is used to control the DC-DC converter based on the electrolytic power input to the electrolytic cell, and the second voltage control mode is used to control the DC-DC converter based on the voltage across the second DC bus capacitor.

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