Composite control device for light-storage stable green hydrogen production considering three-stage smooth switching

Abstract

The invention provides a light storage stable green hydrogen production composite control device considering three-stage smooth switching. The light storage stable green hydrogen production composite control device comprises light storage equipment, a power converter, a control module, a direct current bus and an electrolytic hydrogen production module, the optical storage equipment is controlled by the power converter to transmit electric energy with the direct-current bus; the direct current bus transmits electric energy to the electrolytic hydrogen production module; the control module is used for collecting electric quantity data, obtaining the running state of the electrolytic hydrogen production module according to the electrolytic voltage of the electrolytic tank, and transmitting the running state and the electric quantity data to the power converter; the power converter smoothly switches a control state according to the operation state, the electrical quantity of the optical storage equipment, the direct current bus voltage and the load current, and the control state comprises network following type control and network construction type control. The composite control device provided by the invention can realize safe, stable and efficient operation of electrolytic hydrogen production, ensures the continuity and stability of the hydrogen production process, and improves the efficiency and safety of electrolytic green hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic storage and hydrogen production, and in particular to a composite control device for photovoltaic storage and stable green hydrogen production taking into account three-stage smooth switching. Background Art

[0002] Directly producing hydrogen using new energy sources such as photovoltaics produces green hydrogen with zero carbon emissions; in addition, producing green hydrogen is also an effective technical means to improve the ability to absorb new energy. However, the volatility and intermittency of photovoltaic power generation pose a challenge to the stable power supply required for hydrogen production equipment. Photovoltaic power generation systems rely on sunlight, so their power generation is significantly affected by weather conditions and day and night changes. This inherent volatility and intermittency makes it impossible for photovoltaic power generation to provide electricity continuously and stably, especially at night or when there is insufficient sunlight. Hydrogen production equipment, especially electrolyzers, require stable current and voltage to operate efficiently. The volatility of photovoltaic power generation can cause unstable input to the electrolyzer, and sharp fluctuations in current may cause the electrolyzer to deviate from stable operating conditions, affecting the electrode reaction rate, and thus affecting the efficiency and safety of hydrogen production.

[0003] In order to solve this problem, researchers have proposed a variety of technical solutions. For example, using DC / DC converters to track photovoltaic power changes in real time can effectively suppress the adverse effects of photovoltaic energy fluctuations on energy utilization. In addition, by designing intelligent control algorithms, DC / AC inverters can be controlled to optimize the performance of photovoltaic direct-coupled hydrogen production systems when they are connected to the grid. Adding energy storage systems, such as batteries, can serve as "regulators and stabilizers" for hydrogen production systems, storing the peak power of photovoltaic power generation and releasing it when the light is insufficient, thereby providing a continuous and stable power supply. The above-mentioned "photovoltaic storage" grid-connected hydrogen production can use intelligent energy scheduling, grid optimization and operation strategies to synchronously adjust the operating power of the electrolyzer to fully ensure the smooth operation of the hydrogen production system. However, hydrogen production with grid power is not green hydrogen production, and carbon emissions are generated during the hydrogen production process. In addition, although the above methods focus on studying how to produce hydrogen in a stable state and try to improve the stability of photovoltaic hydrogen production systems through energy storage systems and grid inertia control, they do not fully consider the changing load characteristics when hydrogen production starts and stops.

[0004] For photovoltaic hydrogen production systems, solutions for direct coupling of photovoltaic power generation systems with water electrolysis to produce hydrogen are used. These solutions usually rely on the electricity generated by photovoltaic arrays to directly supply power to electrolyzers for water electrolysis to produce hydrogen. However, these solutions may not fully consider the impact of the volatility and intermittency of photovoltaic power generation on the stability of electrolyzers. Energy storage systems such as batteries are combined with photovoltaic power generation systems to provide a more stable power supply to electrolyzers. This "photovoltaic storage" integrated solution can release stored power when the light is insufficient to maintain the stable operation of the electrolyzer. However, these solutions may not be specifically optimized for the start-stop characteristics of hydrogen production equipment. In addition, a DC / DC converter is used to track photovoltaic power changes in real time to effectively suppress the adverse effects of photovoltaic energy fluctuations on energy utilization. At the same time, the DC / AC inverter is controlled by an intelligent control algorithm to optimize the performance of photovoltaic direct-coupled hydrogen production systems when they are connected to the grid. These technologies mainly focus on improving the stability of photovoltaic hydrogen production systems, but may not cover the load characteristics of the start-stop stage. For the control of photovoltaic arrays, a maximum power point tracking (MPPT) control strategy is adopted to optimize the working state of the photovoltaic array and ensure that the electrolyzer obtains a constant current input. This control strategy helps maintain stable operation of the electrolyzer when light conditions change or the photovoltaic array is partially shaded. Existing technologies may use a single control strategy, such as only using MPPT control or only using grid-type control, but do not implement a composite control strategy that automatically switches between grid-type and grid-type control strategies according to the bus voltage level of the hydrogen production system. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a composite control device for stable green hydrogen production by photovoltaic storage taking into account three-stage smooth switching to adapt to the volatility of photovoltaic power generation and hydrogen production load in three stages of stability, shutdown and startup, and to ensure safe and efficient operation of the electrolyzer.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching, comprising a photovoltaic storage device, a power converter, a control module, a DC bus and an electrolytic hydrogen production module; The photovoltaic storage device is controlled by the power converter to transmit electric energy to the DC bus, or the photovoltaic storage device is controlled by the power converter to transmit electric energy to and from the DC bus; The DC bus transmits electric energy to the electrolysis hydrogen production module; The control module is used to collect electrical quantity data, to obtain the operating state of the electrolytic hydrogen production module according to the electrical quantity data, and to transmit the operating state and the electrical quantity data to the power converter; the electrical quantity data includes the electrical quantity of the photovoltaic storage device, the DC bus voltage, the electrolysis voltage of the electrolytic cell of the electrolytic hydrogen production module and the load current of the electrolytic hydrogen production module; the control module obtains the operating state of the electrolytic hydrogen production module according to the electrolysis voltage of the electrolytic cell; the operating state includes a stable operation stage, a stop process and a start process; The power converter smoothly switches the control state according to the operating state, the electrical quantity of the photovoltaic storage device, the DC bus voltage and the load current, and the control state includes grid-following control and grid-forming control.

[0007] In some embodiments, when the operating state is the stable operating stage, the control state of the power converter is grid-following control; When the operating state is the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the power converter is grid-following control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the control state of the power converter is smoothly switched to grid-forming control; When the operating state is the startup process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control state of the power converter is grid-forming control; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the power converter is smoothly switched to grid-following control.

[0008] In some of the embodiments, the photovoltaic storage device includes a new energy power generation device and an energy storage device, and the power converter includes a first power converter and a second power converter; The new energy power generation equipment is controlled by the first power converter to transmit electric energy to the DC bus; The energy storage device is controlled by the second power converter to transmit electric energy to and from the DC bus.

[0009] In some of the embodiments, the grid-following control includes MPPT control and constant current discharge control, and the grid-building control includes droop control.

[0010] In some embodiments, when the operating state is the stable operating stage: the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; When the operating state is the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the first power converter and the second power converter are smoothly switched to droop control; When the operating state is the startup process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control states of the first power converter and the second power converter are respectively droop control; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the first power converter is smoothly switched to MPPT control, and the control state of the second power converter is smoothly switched to constant current discharge control.

[0011] In some embodiments, the first power converter includes a boost conversion control circuit and a buck conversion control circuit; The output end of the new energy power generation equipment is connected to the input end of the boost conversion control circuit, the output end of the boost conversion control circuit is connected to the input end of the buck conversion control circuit, and the output end of the buck conversion control circuit is connected to the DC bus.

[0012] In some of the embodiments, the boost conversion control circuit includes a new energy side circuit, a boost converter, a transmission line circuit and a first control circuit; The input voltage of the new energy side circuit is the output voltage of the new energy power generation equipment; The first control circuit includes a first outer voltage loop, an intermediate voltage loop and a first inner current loop; The input value of the first outer voltage loop includes the DC bus reference voltage and the input voltage of the new energy side circuit, and the output value of the first outer voltage loop is the reference voltage of the intermediate voltage loop; The input value of the intermediate voltage loop includes the reference voltage of the intermediate voltage loop and the output voltage of the transmission line circuit, and the output value of the intermediate voltage loop is the reference current of the first inner current loop; The input value of the first inner current loop includes a reference current of the first inner current loop and an input current of the new energy side circuit, and the output value of the first inner current loop is a duty cycle of the boost converter.

[0013] In some of these embodiments, the buck conversion control circuit includes a buck converter, an output circuit, and a second control circuit; The second control circuit includes a second outer voltage loop and a second inner current loop; The input value of the second outer voltage loop includes a DC bus reference voltage and a DC bus voltage, and the output value of the second outer voltage loop is a reference current of the second inner current loop; The input value of the second inner current loop includes a reference current of the second inner current loop and an output current of the output circuit, and the output value of the second inner current loop is a duty cycle of the buck converter.

[0014] In some embodiments, the second power converter is a bidirectional DC-DC power converter.

[0015] In some embodiments, when the electrolysis voltage of the electrolytic cell is the first load voltage, the operating state is the stable operation stage; The stopping process includes a stopping start time, a stopping duration phase and a stopping end time; During the stopping process, the electrolysis voltage of the electrolytic cell is first stepped down from the first load voltage to the second load voltage and then stepped up to the third load voltage; the moment when the electrolysis voltage of the electrolytic cell starts to step down from the first load voltage is the stopping start moment; the moment when the electrolysis voltage of the electrolytic cell is stepped up to the third load voltage is the stopping end moment; The startup process includes a startup start time, a startup duration phase, and a startup end time; During the startup process, the electrolysis voltage of the electrolytic cell is first boosted from the third load voltage to the fourth load voltage and then reduced to the first load voltage; the moment when the electrolysis voltage of the electrolytic cell starts to be boosted from the third load voltage is the startup start time; the moment when the electrolysis voltage of the electrolytic cell is reduced to the first load voltage is the startup end time.

[0016] In some embodiments, the preset current is 450A, and the preset voltage is 41.4V.

[0017] Compared with the prior art, the present invention has the following beneficial effects: Based on the dynamic load characteristics of hydrogen production, the present invention combines the control of the power converter over the photovoltaic storage device with the electrolytic hydrogen production module through a control module, avoiding sudden changes of the DC bus and the DC bus in the three stages of stability, stop and start, and realizing safe, stable and efficient operation of the electrolytic hydrogen production module, ensuring the continuity and stability of the hydrogen production process and improving the efficiency and safety of electrolytic green hydrogen production.

[0018] The traditional photovoltaic power generation control strategy is MPPT grid-following control, and energy storage is mostly constant current charge and discharge control. These grid-following controls do not have the ability to adjust the bus voltage level. The present invention realizes the full stability of the DC bus voltage and DC bus current in different operation stages during the entire operation period through the automatic and smooth switching mode of grid-following control and grid-forming control, so that there is no sudden change in voltage, current and temperature during the hydrogen production process, and can match the start, stop and stable operation conditions of hydrogen production.

[0019] Grid-building control and grid-following control belong to different types of control. The existing technology often uses switches to complete the switching between the two control loops, but now there will be large transient fluctuations in the switching process. The present invention innovatively designs a control circuit that combines a boost conversion control circuit with a buck conversion control circuit, which can integrate the two types of control, grid-following control and grid-building control, into a complete set of controls in stages, and realizes automatic and smooth switching of the two control modes by setting the voltage threshold. This control method can not only reduce the loss in the photovoltaic power transmission process, but also realize the automatic and smooth switching of the two control modes through the control that only contains proportional and limiting links. The control strategy does not add a differential link, which avoids system oscillation or instability caused by unreasonable parameter settings and enhances the robustness of the control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of the composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching of the present invention; Figure 2 is a schematic structural diagram of a first power converter in the present invention; Figure 3 is a control block diagram of the first control circuit in the present invention; Figure 4 is a control block diagram of the second control circuit in the present invention; Figure 5 It is a graph showing the change of electrolytic voltage of the electrolytic cell at different operation stages in the calculation example of the present invention; Figure 6 It is a structural schematic diagram of the structure of the electrolysis hydrogen production model in the example of the present invention; Figure 7 It is a comparison chart of the simulation results of the actual water tank temperature and the water tank temperature data of the simulation model; Figure 8 It is a control block diagram of a feedforward PID controller with adaptive delay time in the example of the present invention; Fig. 9 It is a graph showing the change of electrolytic current of the electrolytic cell at different operation stages in the calculation example of the present invention; Fig.10 It is a graph showing the change of the electrolytic cell temperature at different operation stages in the calculation example of the present invention; Fig.11It is a schematic diagram of a composite control method for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching in the calculation example of the present invention; Fig.12 The volt-ampere characteristic curve of the photovoltaic power generation system and the energy storage device in the example of the present invention; Fig.13 is the control output characteristic curve of the 1.8MW photovoltaic power generation system in the example of the present invention; Fig.14 The output voltage characteristic curve of the DC bus of the simulation experiment of the present invention; Fig.15 The output current characteristic curve of the DC bus of the simulation experiment of the example of the present invention. DETAILED DESCRIPTION

[0021] In order to clearly illustrate the technical features of this solution, the following will be combined with the accompanying drawings and examples to describe in detail the implementation methods of this application, so that the application can fully understand how to use technical means to solve technical problems and achieve the corresponding technical effects and implement them accordingly. The embodiments of this application and the various features in the embodiments can be combined with each other without conflict, and the technical solutions formed are all within the scope of protection of this application.

[0022] Fully consider the changing load characteristics when hydrogen production starts and stops. First, the load characteristics of hydrogen production equipment when starting and stopping are very different from those during stable operation: when starting, the electrolyzer needs to set a suitable current density to achieve a cold start of the hydrogen production equipment; when stopping, the current cannot be suddenly interrupted to avoid rapid changes in the internal pressure of the electrolyzer, affecting the safety and life of the equipment. Secondly, photovoltaic power generation has changes in light intensity during the day and night, which in turn produces a start-stop process. Therefore, the start-stop conditions must be considered in the hydrogen production process. If the changing load characteristics when hydrogen production starts and stops are ignored, it will be detrimental to the safety and stability of hydrogen production.

[0023] At present, there are few studies on the control strategy of "photovoltaic storage" green hydrogen production involving the three stages of "start, stop, and stabilize", and there is a lack of "photovoltaic storage" integrated composite control solutions. In order to achieve the stable operation of the photovoltaic storage hydrogen production system and ensure the efficiency of hydrogen production, the present invention fully considers the load characteristics of the different stages of "start, stop, and stabilize" in the green hydrogen production process, ensuring efficient and stable control in each stage; further combined with various working conditions, a three-stage smooth switching "photovoltaic storage" integrated composite control device is proposed.

[0024] See also Figure 1 , an embodiment of the present invention provides a composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching, including a photovoltaic storage device, a power converter, a control module, a DC bus and an electrolytic hydrogen production module; The photovoltaic storage device is controlled by the power converter to transmit electric energy to the DC bus, or the photovoltaic storage device is controlled by the power converter to transmit electric energy to and from the DC bus; The DC bus transmits electrical energy to the electrolysis hydrogen production module; The control module is used to collect electrical quantity data, to obtain the operating status of the electrolytic hydrogen production module according to the electrical quantity data, and to transmit the operating status and electrical quantity data to the power converter; see Figure 1 The control module includes an electric quantity collection unit, which is used to collect electric quantity data, and the electrical quantity data includes the electrical quantity of the photovoltaic storage device, the DC bus voltage, the electrolysis voltage of the electrolytic cell of the electrolytic hydrogen production module, and the load current of the electrolytic hydrogen production module; the control module obtains the operating state of the electrolytic hydrogen production module according to the electrolysis voltage of the electrolytic cell; The power converter smoothly switches the control state according to the operating state, the electrical quantity of the photovoltaic storage device, the DC bus voltage and the load current. The control state includes grid-following control and grid-forming control.

[0025] Through the control module, the power converter's control of the photovoltaic storage device is combined with the electrolytic hydrogen production module to achieve stable control of voltage, current and temperature. The startup process and the stop process are inverse processes to each other. The control state of the power converter over the photovoltaic storage device involves smooth switching between grid-following control and grid-forming control. Under the composite control of smooth switching between grid-following control and grid-forming control, smooth conversion of different operating stages during the entire operation period, that is, different operating state conditions, is achieved, so that the bus voltage and bus current are fully stable in different operating stages during the entire operation period, without sudden changes in voltage and current, and can match the different operating conditions of the electrolytic hydrogen production module, ensuring the safety and stability of the hydrogen production process, while ensuring the maximum hydrogen production efficiency.

[0026] In some of the embodiments, the operation state includes a stable operation stage, a stop process and a start process, that is, the device includes three different operation stages during the entire operation period: a stable operation stage, a stop process and a start process; When the operation state is in the stable operation stage, the control state of the power converter is grid-following control; that is, when the operation state is in the stable operation stage, the power converter adopts grid-following control, and in the stable operation stage, the temperature is stable, the current is constant, and the voltage is constant, that is, constant power operation; When the operation state is the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the power converter is the grid-following control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the control state of the power converter is smoothly switched to the grid-forming control; that is, when the operation state is the stop process, the power converter first adopts the grid-following control, and when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the power converter smoothly switches to the grid-forming control, and the stop process firstly increases the voltage by constant current and then decreases the current by constant current to realize the temperature reduction control; in some embodiments, the preset current is 450A and the preset voltage is 41.4V; When the operating state is the starting process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control state of the power converter is grid-forming control; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the power converter is smoothly switched to grid-following control, that is, when the operating state is the starting process, the power converter first adopts grid-forming control, and when the DC bus voltage is higher than the preset voltage and the load current is lower than the preset current, the power converter smoothly switches to grid-following control, and the starting process first increases the current at constant voltage and then reduces the voltage at constant current to achieve temperature rise control.

[0027] The control module combines the control of the power converter on the photovoltaic storage device with the electrolytic hydrogen production module, realizing stable control of voltage, current and temperature. The startup process and the stop process are inverse processes. The control of the power converter on the photovoltaic storage device involves smooth switching between grid-following control and grid-building control. The electrolytic hydrogen production module works stably during the stable operation stage. The control of the power converter on the photovoltaic storage device is grid-following control, providing the system with maximum power. Under the composite control of smooth switching between grid-following control and grid-building control, the smooth conversion of different working conditions in the three stages can be achieved during the entire operation, making the bus voltage and bus current fully stable in the entire three stages, without voltage and current mutations, and matching the start and stop and stable operation conditions of the electrolytic hydrogen production module, ensuring the safety and stability of the hydrogen production process, while ensuring the maximum hydrogen production efficiency. At the same time, the hydrogen production efficiency in the stable operation stage reaches 86%, which meets the standard requirements.

[0028] See also Figure 1 In some embodiments, the photovoltaic storage device includes a new energy power generation device and an energy storage device, and the power converter includes a first power converter and a second power converter; the photovoltaic storage device is modularized into a new energy power generation device and an energy storage device, and precise control can be performed on different modules, simplifying the control while ensuring the control accuracy; preferably, the new energy power generation device is a photovoltaic power generation system, and the energy storage device is a battery; The new energy power generation equipment is controlled by the first power converter to transmit electric energy to the DC bus; The energy storage device is controlled by the second power converter to transmit electric energy to and from the DC bus. Preferably, the second power converter is a bidirectional DC-DC power converter. The bidirectional DC-DC power converter can realize bidirectional flow of energy. It can output the electric energy in the energy storage device to the DC bus to power the electrolysis hydrogen production module, and can also recover the excess electric energy to the energy storage device when there is surplus electric energy. It has a voltage regulation function, that is, it can automatically adjust the output voltage of the energy storage device according to the change of the DC bus voltage and the load demand, so as to ensure the supply of stable electric energy to the electrolysis hydrogen production module, and further ensure the stability of the electrolysis hydrogen production process.

[0029] The photovoltaic power generation system generates electric energy, which is controlled by the first power converter and transmitted to the DC bus. The battery is controlled by the bidirectional DC-DC power converter to provide stable DC bus voltage support. Preferably, the control module is connected to the DC bus, obtains electric energy from the DC bus, and controls the bidirectional DC-DC power converter and the first power converter according to the load voltage and load current. The power collection is used to monitor the operating status of the entire device to ensure the stable conversion of electric energy.

[0030] In some of the embodiments, the grid-following control includes MPPT control and constant current discharge control, and the grid-building control includes droop control.

[0031] In some embodiments, when the operation state is in the stable operation stage: the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; When the operation state is in the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the first power converter and the second power converter are smoothly switched to droop control; When the operating state is the startup process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control states of the first power converter and the second power converter are droop control respectively; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the first power converter is smoothly switched to MPPT control, and the control state of the second power converter is smoothly switched to constant current discharge control.

[0032] See also Figure 2 , in some embodiments, the first power converter includes a boost conversion control circuit and a buck conversion control circuit; Figure 2In the figure, the photovoltaic panel represents a new energy power generation device, the Boost converter represents a boost converter, the Buck converter represents a buck converter, the circuit between the photovoltaic panel and the Buck converter is a boost conversion control circuit, and the circuit between the Buck converter and the Buck converter and the DC bus is a buck conversion control circuit; The output end of the new energy power generation equipment is connected to the input end of the boost conversion control circuit, the output end of the boost conversion control circuit is connected to the input end of the buck conversion control circuit, and the output end of the buck conversion control circuit is connected to the DC bus.

[0033] See also Figure 2 , in some embodiments, the boost conversion control circuit includes a new energy side circuit, a boost converter, a transmission line circuit and a first control circuit; Figure 2 middle, For the new energy side capacitor, is the inductor on the new energy side, is the transmission line capacitance; the input voltage of the new energy side circuit is the output voltage of the new energy power generation equipment ; See also Figure 3 , the first control circuit includes a first outer voltage loop, an intermediate voltage loop and a first inner current loop; The input value of the first outer voltage loop includes the DC bus reference voltage The input voltage of the new energy side circuit is the output voltage of the new energy power generation equipment , the output value of the first outer voltage loop is the reference voltage of the middle voltage loop , the input voltage of the new energy side circuit and the DC bus reference voltage The deviation of the voltage proportional coefficient of the new energy side Amplify and obtain the reference voltage of the intermediate voltage loop after the limiting link ; The input value of the intermediate voltage loop includes the reference voltage of the intermediate voltage loop and the output voltage of the transmission line circuit The output value of the intermediate voltage loop is the reference current of the first inner current loop. , the output voltage of the transmission line circuit The reference voltage of the intermediate voltage ring The deviation of the transmission line voltage proportionality factor Amplify and obtain the reference current of the first inner current loop after the limiting link ; The input value of the first inner current loop includes the reference current of the first inner current loop and the input current of the new energy side circuit The output value of the first inner current loop is the duty cycle of the boost converter , the input current of the new energy side circuit The reference current of the first inner current loop The deviation of the current proportionality coefficient of the new energy side Amplify and obtain the duty cycle of the boost converter after the limiting link , according to the duty cycle of the boost converter Controls the boost converter.

[0034] See also Figure 2 , in some embodiments, the buck conversion control circuit includes a buck converter, an output circuit, and a second control circuit; Figure 3 middle, is the output side capacitance, is the output side inductance; See also Figure 4 , the second control circuit includes a second outer voltage loop and a second inner current loop; The input value of the second outer voltage loop includes the DC bus reference voltage and DC bus voltage The output value of the second outer voltage loop is the reference current of the second inner current loop. , DC bus reference voltage With DC bus voltage The deviation of the output voltage proportional coefficient Amplify and obtain the reference current of the second inner current loop after the limiting link ; The input value of the second inner current loop includes the reference current of the second inner current loop and the output current of the output circuit The output value of the second inner current loop is the duty cycle of the buck converter , the reference current of the second inner current loop Output current of the output circuit The deviation of the output current proportionality coefficient Amplify and obtain the duty cycle of the buck converter after the limiting link , according to the duty cycle of the buck converter Controls the buck converter.

[0035] The control strategy of the first power converter is realized by combining a boost conversion control circuit with a buck conversion control circuit. The two types of control, grid-following control and grid-forming control, can be integrated in a complete set of controls in stages. Automatic and smooth switching of the two control modes is achieved by setting a voltage threshold, i.e., a preset voltage. This control method combining a boost conversion control circuit with a buck conversion control circuit can not only reduce the loss in the process of photovoltaic power transmission, but also realizes automatic and smooth switching of grid-following control and grid-forming control through control containing only proportional and limiting links.

[0036] The control strategy does not add a differential link, which avoids system oscillation or instability caused by unreasonable parameter settings and enhances the robustness of the control system.

[0037] In some of the embodiments, when the electrolysis voltage of the electrolytic cell is the first load voltage, the operation state is a stable operation stage; The stopping process includes the stopping start time, the stopping duration phase and the stopping end time; During the stopping process, the electrolytic voltage of the electrolytic cell is first stepped down from the first load voltage to the second load voltage and then stepped up to the third load voltage; the moment when the electrolytic voltage of the electrolytic cell starts to step down from the first load voltage is the stopping start moment; the moment when the electrolytic voltage of the electrolytic cell is stepped up to the third load voltage is the stopping end moment; The startup process includes the startup start time, the startup duration phase and the startup end time; During the startup process, the electrolysis voltage of the electrolytic cell is first increased from the third load voltage to the fourth load voltage and then decreased to the first load voltage; the moment when the electrolysis voltage of the electrolytic cell starts to increase from the third load voltage is the startup start time; the moment when the electrolysis voltage of the electrolytic cell is decreased to the first load voltage is the startup end time.

[0038] Calculation example Taking into account the dynamic load characteristics of the electrolyzer hydrogen production module, mainly its start-stop characteristics, the present invention provides an electrolytic hydrogen production model under the premise of considering the influence of gas flow and temperature changes on hydrogen production efficiency, which is used for electrolytic hydrogen production simulation experiments. In this example, it is used to replace the electrolytic hydrogen production module in the composite control device for stable green hydrogen production by light storage considering three-stage smooth switching, including a hydrogen production module, a temperature dynamic module and an electrolysis control model. The hydrogen production module includes an electrolyzer voltage model and an electrolysis heat production model, and the temperature dynamic module includes an electrolyzer temperature model, a water tank temperature model, a heat exchanger temperature model and a chiller; the electrolysis control model is used to control the hydrogen production module and the temperature dynamic module; considering that most of the startup modes of the electrolyzer hydrogen production module are cold start, the operating temperature after startup can reach the expected optimal operating state through heat generation and temperature rise through the electrolysis heat production model, so the electrolytic hydrogen production model adopts the interaction between the hydrogen production module containing electricity, heat and gas and the temperature dynamic model to fit the three operating stages of stable, stopped and started of the actual electrolytic hydrogen production module.

[0039] Preferably, Simulink is used to build a hydrogen electrolysis model; see Figure 6 , is the electrolysis voltage of the electrolytic cell, is the water tank temperature, is the opening degree of the cold water outlet valve, The electrolytic cell generates heat. is the electrolytic cell temperature, and the connecting lines in the figure represent the transfer of related quantities between models; the chiller reduces the temperature of the cooling water to a preset temperature, usually 20°C, and then the chiller delivers the cooling water at the preset temperature to the heat exchanger temperature model. The heat generated by the electrolytic heat generation model is the heat generated by the electrolytic cell reaction. The temperature of the electrolyzer is transferred to the electrolytic cell temperature model to increase the temperature of the electrolyzed water in the electrolytic cell temperature model to form the electrolytic cell temperature , electrolytic cell temperature The water tank temperature is formed by transferring the electrolyzed water to the water tank temperature model , water tank temperature As the electrolyzed water exchanges heat with the cooling water in the heat exchanger temperature model, the cooling water absorbs the heat released by the electrolyzed water, thereby reducing the temperature of the electrolyzed water. The electrolyzed water transfers the heat to the cooling water, and its own temperature decreases and then flows into the electrolytic cell temperature model. Figure 6 The effectiveness of the temperature dynamic simulation model of the electrolyzer in this example is to collect the temperature data of the water tank (actual water tank) in the real electrolysis hydrogen production module ( Figure 7 The actual temperature curve sampled in the simulation results) and the temperature data in the water tank temperature model in the electrolysis hydrogen production model (simulation model) ( Figure 7 By comparing the simulated temperature curve in the simulation model with the actual water tank temperature change curve, it can be seen that the cold start temperature change curve of the simulation model is basically consistent with the temperature change of the actual water tank, and the maximum temperature deviation is 1.6℃.

[0040] Based on the hydrogen production module and the temperature dynamic module, and considering the stability and high efficiency of hydrogen production by electrolysis, this example proposes a feedforward PID controller based on adaptive delay time as the electrolysis control model to control the temperature dynamic model and ensure the temperature of the electrolyzer under stable operation conditions. Around 65℃. Figure 8 In the figure, the feedforward PID controller with adaptive delay time is shown. is the temperature reference value, is the feedforward control quantity, is the feedback control quantity of the PID controller. By comparing with the PID control effect, it is found that the feedforward PID controller with adaptive delay time proposed in the present invention can better fit the actual temperature control requirements.

[0041] Select 3 interpolation points , and , the feedforward control quantity in the feedforward PID controller with adaptive delay time is shown in formula (1): (1) The reference quantity passed to the proportional integrator after adaptive startup adjustment As shown in formula (2): (2) In the formula, is a step function, Switch temperature points for parameters, is the difference between the electrolytic cell temperature and the temperature reference value; The feedback control quantity of the PID controller is shown in formula (3): (3) In the formula, is the proportional coefficient of the PID controller, is the integral coefficient of the PID controller, is the differential coefficient of the PID controller.

[0042] The equipment electrolysis hydrogen production model based on full consideration of gas flow and temperature dynamics can better fit the actual working state. At the same time, the feedforward PID controller with adaptive delay time of variable starting point can ensure the stability of the electrolyzer temperature in the stable operation stage of the electrolyzer hydrogen production model.

[0043] The electrolytic hydrogen production model is used to replace the electrolytic hydrogen production module in the composite control device for stable green hydrogen production by light storage considering three-stage smooth switching. The cross-sectional area of ​​the connecting line is 250 cm -2 The electrolytic cell current of the hydrogen production model at different operation stages during the entire operation period can be found in Fig. 9 、Electrolysis voltage of electrolytic cell Figure 5 , electrolytic cell temperature see Fig.10 : (1) In the stable operation stage, the current density is 1.8A·cm -2 At this time, the temperature of the electrolyzer tends to be constant, and the load voltage, that is, the electrolysis voltage of the electrolyzer, is constant, achieving constant power hydrogen production.

[0044] (2) During the stop process, first ensure that the current density is reduced step by step ((1.8→1→0.6→0.28) A·cm -2 ) operation, set the external cold water switch to the maximum, and start to reduce the temperature. Increase the cooling speed step by step, while avoiding a large drop in the load voltage.

[0045] (3) During the startup process, the current density is maintained at 1.8A·cm-2 The maximum power temperature rises, simulating the working condition of the electrolytic hydrogen production model starting at a constant current density. The temperature of hydrogen production rises to 65°C, and the operation is stable, and the current density is still 1.8A·cm -2 At this time, the temperature is constant, the voltage is constant, and hydrogen is produced at constant power.

[0046] The above three-stage control can ensure that the current density during hydrogen production by electrolysis is between 0.2 and 1.8 cm -2 The safety and stability of hydrogen production are ensured.

[0047] Considering the coupling relationship between the three variables of electrolytic cell temperature, load voltage and load current (i.e. electrolytic current of electrolytic cell), temperature is regarded as the key intermediate quantity to discuss the load characteristic changes of electrolytic cell in the three stages of steady, stop and start. The temperature change curve of electrolytic cell is verified by simulation, such as Fig.10 . Simulate the load voltage changes of hydrogen production by electrolysis in three stages: steady, stop and start. See attached Figure 5 At this point, the electrical characteristics of the electrolyzer are simulated according to the hydrogen production by electrolysis model, and the working characteristic curve of the electrolyzer is fitted using equivalent resistance, so as to obtain the relationship between the load current and the load voltage when the electrolyzer is working.

[0048] The electrolysis hydrogen production model controls and fits the changes in the hydrogen production load characteristics of the three stages, such as Fig.11 shown.

[0049] During the boot process: First, the constant voltage current is increased to complete the pre-start. At this time, the electrolyzer works in the set voltage range (between 41V and 43V). The power converter adopts droop control, the voltage remains basically unchanged, and a small power pre-heating is used to raise the current density to 1.8A cm -2 , that is, the preset current of 450A is reached. At this time, the electrolytic cell uses the maximum heat generation power and is in the heating stage.

[0050] Then the voltage is reduced by constant current and the temperature is increased. At this time, the current density is maintained at 1.8A·cm -2, achieving maximum power temperature rise, simulating the operating condition of the electrolytic hydrogen production module starting at a constant current density; the electrolyzer is cold started, with the aim of raising its operating temperature through electrolysis heat to reach the expected optimal operating state. During the startup process at this stage, the input current of the electrolyzer needs to remain stable to ensure the continuity of the electrolysis reaction. The first power converter performs MPPT control to ensure that the electrolyzer obtains a constant current input by optimizing the working state of the photovoltaic array, even when the lighting conditions change or the photovoltaic array is partially blocked. However, as the temperature of the electrolyzer increases, the resistivity of the electrolyte decreases, which causes the operating voltage of the electrolyzer to decrease. Therefore, the use of MPPT control at this stage can adjust the output voltage of the photovoltaic power generation system according to the voltage changes monitored in real time to adapt to the working requirements of the electrolyzer.

[0051] In the stable operation stage: constant voltage and constant current, stable operation. Under this condition, the current density is still 1.8A·cm -2 , at this time, the temperature is constant, the voltage is constant, and the hydrogen is produced at a constant power. When the electrolyzer is working stably, the photovoltaic panel produces hydrogen at a constant power through the maximum power point tracking (MPPT) technology, and the energy storage system provides the necessary energy buffering and regulation to cope with the volatility of photovoltaic power generation.

[0052] During the stop process: First, the constant current is used to increase the voltage and reduce the temperature. The first power converter performs MPPT control to keep the current stable at 1.8A·cm -2 However, the temperature control loop loses its effectiveness when the external main cold water switch is turned on, and the temperature drops first. Considering the relationship between the volt-ampere characteristic and temperature of the electrolytic cell, the voltage drops as the temperature drops and exceeds the limit (41V-43V).

[0053] Secondly, the constant voltage current is increased. After the pre-cooling process, the electrolytic voltage of the electrolytic cell exceeds the limit (41V-43V) as the temperature drops. At this time, the electrolysis process adopts droop control, and the electrolytic voltage of the electrolytic cell is stable between 41V and 43V. At the same time, the cooling system is still working and the temperature drops. Considering that the volt-ampere characteristics of the electrolytic cell are affected by temperature, the current drops, and the load reduction stop is achieved.

[0054] In this disclosure, the preset current is 450A. According to the volt-ampere characteristics of the photovoltaic power generation system and the energy storage device, see Fig.12 , the voltage range of droop control is 41V-43V.

[0055] Table 1 Design parameters of photovoltaic panels It can be concluded that when the DC bus voltage drops to 41V, the Figure 2The output current of the photovoltaic storage device in needs to be 450A, that is, the output current when the droop control mode is smoothly switched to the MPPT control mode. The calculation shows that the output power at the turning point, that is, the switching point from the droop control mode to the MPPT control mode, is 18450W. According to the detailed values ​​of the design parameters of the photovoltaic panels in Table 1, if a photovoltaic panel with a maximum output power of 200W is used, this example requires 90 photovoltaic panels, and the maximum output current is 450A.

[0056] From the PV curve of the photovoltaic panel, we can see that when the working voltage of the maximum power point is 64V, when the working voltage is between 64V and the turning point voltage, the PV curve is a nonlinear curve, that is, the maximum power working area. At this time, the photovoltaic power generation system works in the MPPT control mode to supply power to the electrolytic hydrogen system; when the voltage is lower than the turning voltage, the PV curve is an approximate linear curve. At this time, the photovoltaic power generation system works in the droop control mode to provide voltage support for the DC system bus. Fig.12 It can be seen that the photovoltaic power generation system switches from the maximum power point area to the low power area on the left, and the current remains basically constant. In order to achieve the goal of "outputting low voltage in the photovoltaic maximum power area and high voltage in the low power area", it is necessary to design a power converter and its control strategy.

[0057] By the attached Figure 3 It can be seen that the first control circuit corresponding to the Boost converter includes a first outer voltage loop, an intermediate voltage loop and a first inner current loop; the DC bus reference voltage Set to 64V, the output voltage of the new energy power generation equipment fed back and DC bus reference voltage The difference gradually increases after passing through the proportion and limiter links, so the output voltage of the new energy power generation equipment Gradually decreases, while outputting the reference voltage of the intermediate voltage loop . The reference voltage of the intermediate voltage loop output by Boost is Gradually increases. Therefore, the voltage control of the first outer voltage loop realizes the transformation of the input link with gradually decreasing voltage into the output link with gradually increasing voltage. The reason why the droop interval working point of the photovoltaic is set to the left of the maximum power point is that the current and power on the right side of the maximum power point change greatly, and it is not easy to achieve stable control. The intermediate voltage loop also outputs the reference current of the first current inner loop through the proportional and limiting links. , close to the photovoltaic constant current, that is, the preset current of 450A. Since the outer loop has a large proportional coefficient and the voltage increases quickly, although the intermediate link has a limited proportional coefficient, the Boost output is easy to exceed the DC bus reference voltage, so the voltage is limited by the amplitude limit. The current inner loop is based on the reference current of the first inner loop current loop. and the input current of the new energy side circuit The difference adjusts the duty cycle.

[0058] The second control circuit corresponding to the Buck converter includes a second outer voltage loop and a second inner current loop, that is, a dual-loop control, to reduce the voltage to 41V; in addition, adding a buck conversion control circuit after the boost conversion control circuit can prevent the problem of the boost conversion control circuit being open-circuited and the output voltage rising infinitely to a certain extent, and the buck conversion control circuit can limit the output voltage to below the input voltage, thereby avoiding this problem.

[0059] A simulation experiment is conducted using a photovoltaic power generation system as an example to verify this example. The simulation experiment uses a 1.8MW power level device, with a DC bus voltage upper limit of 43V and a voltage lower limit of 41V. Fig.13 The photovoltaic control block diagram and simulation results are shown in Figure 2-4 , unifying MPPT control and droop control into the same control loop. The simulation output results are as follows Fig.14 , 15 As shown, it can be seen that according to the bus voltage level, this example can achieve smooth switching of three stages during operation.

[0060] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A composite control device for stable production of green hydrogen by photovoltaic storage considering three-stage smooth switching, characterized by: It includes photovoltaic storage equipment, power converter, control module, DC bus and electrolysis hydrogen production module; The photovoltaic storage device is controlled by the power converter to transmit electric energy to the DC bus, or the photovoltaic storage device is controlled by the power converter to transmit electric energy to and from the DC bus; The DC bus transmits electric energy to the electrolysis hydrogen production module; The control module is used to collect electrical quantity data, to obtain the operating state of the electrolytic hydrogen production module according to the electrical quantity data, and to transmit the operating state and the electrical quantity data to the power converter; the electrical quantity data includes the electrical quantity of the photovoltaic storage device, the DC bus voltage, the electrolysis voltage of the electrolytic cell of the electrolytic hydrogen production module and the load current of the electrolytic hydrogen production module; the control module obtains the operating state of the electrolytic hydrogen production module according to the electrolysis voltage of the electrolytic cell; the operating state includes a stable operation stage, a stop process and a start process; The power converter smoothly switches the control state according to the operating state, the electrical quantity of the photovoltaic storage device, the DC bus voltage and the load current, and the control state includes grid-following control and grid-forming control.

2. According to claim 1, the composite control device for stable green hydrogen production by photovoltaic storage taking into account three-stage smooth switching is characterized by: When the operating state is the stable operating stage, the control state of the power converter is grid-following control; When the operating state is the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the power converter is grid-following control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the control state of the power converter is smoothly switched to grid-forming control; When the operating state is the startup process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control state of the power converter is grid-forming control; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the power converter is smoothly switched to grid-following control.

3. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 2 is characterized in that: The photovoltaic storage device includes a new energy power generation device and an energy storage device, and the power converter includes a first power converter and a second power converter; The new energy power generation equipment is controlled by the first power converter to transmit electric energy to the DC bus; The energy storage device is controlled by the second power converter to transmit electric energy to and from the DC bus.

4. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 3 is characterized by: The grid-following control includes MPPT control and constant current discharge control, and the grid-building control includes droop control.

5. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 4 is characterized in that: When the operating state is the stable operating stage: the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; When the operating state is the stop process: when the DC bus voltage is lower than the preset voltage or the load current is higher than the preset current, the control state of the first power converter is MPPT control, and the control state of the second power converter is constant current discharge control; when the DC bus voltage is not lower than the preset voltage and the load current is not higher than the preset current, the first power converter and the second power converter are smoothly switched to droop control; When the operating state is the startup process: when the DC bus voltage is not lower than the preset voltage or the load current is not higher than the preset current, the control states of the first power converter and the second power converter are respectively droop control; when the DC bus voltage is lower than the preset voltage and the load current is higher than the preset current, the control state of the first power converter is smoothly switched to MPPT control, and the control state of the second power converter is smoothly switched to constant current discharge control.

6. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 5 is characterized in that: The first power converter includes a boost conversion control circuit and a buck conversion control circuit; The output end of the new energy power generation equipment is connected to the input end of the boost conversion control circuit, the output end of the boost conversion control circuit is connected to the input end of the buck conversion control circuit, and the output end of the buck conversion control circuit is connected to the DC bus.

7. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 6 is characterized by: The boost conversion control circuit includes a new energy side circuit, a boost converter, a transmission line circuit and a first control circuit; The input voltage of the new energy side circuit is the output voltage of the new energy power generation equipment; The first control circuit includes a first outer voltage loop, an intermediate voltage loop and a first inner current loop; The input value of the first outer voltage loop includes the DC bus reference voltage and the input voltage of the new energy side circuit, and the output value of the first outer voltage loop is the reference voltage of the intermediate voltage loop; The input value of the intermediate voltage loop includes the reference voltage of the intermediate voltage loop and the output voltage of the transmission line circuit, and the output value of the intermediate voltage loop is the reference current of the first inner current loop; The input value of the first inner current loop includes a reference current of the first inner current loop and an input current of the new energy side circuit, and the output value of the first inner current loop is a duty cycle of the boost converter.

8. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 6 is characterized by: The step-down conversion control circuit includes a step-down converter, an output circuit and a second control circuit; The second control circuit includes a second outer voltage loop and a second inner current loop; The input value of the second outer voltage loop includes a DC bus reference voltage and a DC bus voltage, and the output value of the second outer voltage loop is a reference current of the second inner current loop; The input value of the second inner current loop includes a reference current of the second inner current loop and an output current of the output circuit, and the output value of the second inner current loop is a duty cycle of the buck converter.

9. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to claim 2 is characterized by: When the electrolysis voltage of the electrolytic cell is the first load voltage, the operation state is the stable operation stage; The stopping process includes a stopping start time, a stopping duration phase and a stopping end time; During the stopping process, the electrolysis voltage of the electrolytic cell is first stepped down from the first load voltage to the second load voltage and then stepped up to the third load voltage; the moment when the electrolysis voltage of the electrolytic cell starts to step down from the first load voltage is the stopping start moment; the moment when the electrolysis voltage of the electrolytic cell is stepped up to the third load voltage is the stopping end moment; The startup process includes a startup start time, a startup duration phase, and a startup end time; During the startup process, the electrolysis voltage of the electrolytic cell is first boosted from the third load voltage to the fourth load voltage and then reduced to the first load voltage; the moment when the electrolysis voltage of the electrolytic cell starts to be boosted from the third load voltage is the startup start time; the moment when the electrolysis voltage of the electrolytic cell is reduced to the first load voltage is the startup end time.

10. The composite control device for stable green hydrogen production by photovoltaic storage considering three-stage smooth switching according to any one of claims 2 to 9, characterized in that: The preset current is 450A, and the preset voltage is 41.4V.

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