A carbon emission reduction system for electrolytic aluminum with efficient access to new energy sources

Abstract

This invention provides a carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources, comprising a photovoltaic array, a DC / DC converter, and electrolytic cells. The low-voltage side of the DC / DC converter is connected to a photovoltaic combiner box, and the high-voltage side is connected to the electrolytic aluminum DC bus. Its topology includes both isolated and non-isolated structures, and the low-voltage side can optionally be connected in parallel with an energy storage device. Energy storage devices can improve the absorption capacity of new energy sources and further enhance the carbon reduction flexibility of electrolytic aluminum plants, but they also increase system construction costs. The electrical energy generated by multiple photovoltaic arrays is collected through a combiner box to the low-voltage side of the DC / DC converter topology. Multiple electrolytic aluminum cells are connected in series to the DC bus as the high-voltage side of the DC / DC converter topology. The two are connected through a single-stage DC / DC converter. This invention eliminates multiple conversion stages, significantly improves energy transmission efficiency, saves equipment costs, and brings about substantial carbon emission reductions in the electrolytic aluminum industry.

Description

Technical Field

[0001] This invention belongs to the field of clean energy supply and power electronic power conversion technology, specifically relating to an electrolytic aluminum carbon emission reduction system based on efficient access to new energy sources. Background Technology

[0002] In the context of carbon neutrality, electrolytic aluminum plants, as high-energy-consuming and high-carbon-emission enterprises, emit more than six times the carbon emissions per ton of electrolytic aluminum compared to per ton of steel. Therefore, promoting carbon emission reduction in electrolytic aluminum plants is urgently needed. Photovoltaic power generation, as a widely used renewable energy source, emits almost no carbon during its generation process, making it an ideal power supply method for electrolytic cells. However, current photovoltaic power generation processes require first connecting the photovoltaic side to the grid through DC distribution cabinets, inverters, and step-up transformers. The electrolytic cells then draw power from the grid through step-down transformers and rectifiers. This multi-stage transformation process from source to user results in low overall transmission efficiency. Summary of the Invention

[0003] To address the aforementioned technical issues, this invention provides a carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources. It employs a single-stage DC / DC topology to directly connect distributed photovoltaic power generation to the electrolytic cell load, eliminating intermediate multi-stage conversion steps and significantly improving energy transmission efficiency. This can save equipment costs for enterprises while also leading to substantial carbon emission reductions in the electrolytic aluminum industry.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources includes multiple photovoltaic arrays, DC / DC converters, and electrolytic cells. The DC / DC converters are configured in parallel as a single-stage DC / DC conversion link. These parallel DC / DC converters are connected to multiple photovoltaic arrays via combiner boxes. The low-voltage side of each DC / DC converter is connected to its respective combiner box, and the high-voltage side is connected to the DC bus of the electrolytic cell. Both are connected to an energy storage device in parallel on the low-voltage side. The electrical energy generated by the multiple photovoltaic arrays is collected to the low-voltage side of the DC / DC converters via the combiner boxes. Multiple electrolytic aluminum cells are connected in series to the DC bus of the electrolytic cell as the high-voltage side of the DC / DC converter. The low-voltage side and the high-voltage side are connected through this single-stage DC / DC conversion link to achieve efficient energy transfer. The topology of the DC / DC converter can be either an isolated DC / DC converter topology or a non-isolated DC / DC converter topology.

[0006] Furthermore, the isolated DC / DC converter topology is used in the rainy southern regions to prevent fault current from being transmitted from the photovoltaic side to the electrolytic cell side; while a non-isolated DC / DC converter topology is used in the dry northern regions to ensure high operating efficiency and economy.

[0007] Furthermore, the isolated DC / DC converter topology is formed by multiple isolated DC / DC converter modules connected in parallel. Each isolated DC / DC converter module consists of three parts: a low-voltage side H-bridge topology, a high-frequency transformer, and a high-voltage side H-bridge topology. The low-voltage side uses IGBTs to form an H-bridge circuit to achieve flexible control of low-voltage photovoltaic power transmission. The high-voltage side uses diodes to form an H-bridge circuit to meet only the power transmission requirements. Energy transmission on the low-voltage side is achieved by controlling the on / off state of the IGBTs. The high-voltage side and the low-voltage side are coupled through a high-frequency transformer to achieve isolation. Both the high-voltage side and the low-voltage side are equipped with anti-reverse current diodes, fuses, and disconnect switches.

[0008] Furthermore, the non-isolated DC / DC converter topology includes a three-level boost circuit, which adopts an IGBT-based three-level structure. The low-voltage side includes an inductor and a capacitor, and the high-voltage side has two capacitors connected in series with a resistor connected in parallel next to the capacitors. Both the high-voltage and low-voltage sides are equipped with anti-reverse current diodes, fuses, and disconnect switches.

[0009] Furthermore, when the current in the system exceeds a set value, the fuse trips and the disconnect switch trips, working together to protect the system from damage to the greatest extent possible.

[0010] Furthermore, the energy storage device is used to adjust in accordance with the real-time power characteristics of photovoltaic power generation.

[0011] Furthermore, the adjustments include: when the weather is sunny and the photovoltaic power generation exceeds the electrolytic cell load, the energy storage device absorbs and stores the excess energy to prevent excessive current in the circuit from causing danger; when the weather is cloudy or rainy and the photovoltaic power generation is lower than the electrolytic cell load demand, the energy storage device releases energy to compensate for the power difference between the two parts, thereby ensuring a reliable supply of the electrolytic cell load; the energy storage device is also used to cooperate with photovoltaics to achieve maximum power point tracking, thereby improving the absorption capacity of new energy sources.

[0012] Furthermore, multiple isolated or non-isolated transformation topologies are connected in parallel to the DC bus of the electrolytic cell.

[0013] Furthermore, based on local sunlight conditions, the power required by the electrolytic cell, the DC bus voltage, and the energy transmitted by the DC / DC converter controlled by the energy storage device, real-time dynamic power balance is achieved without reducing photovoltaic power generation; load demand is rationally allocated by controlling the on / off state of the IGBTs in each DC / DC converter.

[0014] Furthermore, firstly, the current photovoltaic output P is collected. PV and the load demand P of the electrolytic cell load Then, the difference between the two is taken to obtain the net power P of the system. S Based on the net power and the current state of charge (SOC) of the energy storage device, five operating modes are defined. These operating modes specifically include:

[0015] Pattern 1: When P S <0 and SOC>SOC min At that time, all the photovoltaic power is supplied to the electrolytic cell load, and the power difference between the two is |P S |This is compensated for by controlling the discharge of the energy storage device;

[0016] Pattern 2: When P S <0 and SOC≤SOC min At that time, all the photovoltaic power is supplied to the electrolytic cell load, and the power difference between the two is |P S |This can be compensated for by the self-owned power plant or the external power grid;

[0017] Pattern 3: When P S When the value is 0, the energy storage device does not need to operate;

[0018] Pattern 4: When P S >0 and SOC < SOC max At that time, the photovoltaic power generation first supplies the electrolytic cell load, and the power difference between the two is |P S | Used to charge energy storage devices, that is, to store the surplus of photovoltaic power generation into energy storage devices;

[0019] Pattern 5: When P S >0 and SOC≥SOC max At that time, the photovoltaic power generation first supplies the electrolytic cell load, and the power difference between the two is |P S | This can be solved by reducing the active power output of photovoltaic power;

[0020] Among them, SOC max SOC min These are the maximum and minimum states of charge, respectively, determined by the energy storage device itself.

[0021] The beneficial effects of this invention are:

[0022] 1) In this invention, photovoltaic power generation is connected to the low-voltage side of a DC / DC topology via a combiner box. After passing through a first-stage DC-DC converter, the energy is transmitted to the electrolytic cell bus. Multiple DC / DC high-voltage sides are connected in parallel to meet the capacity requirements of the electrolytic cell. This energy conversion method significantly improves energy transfer efficiency and enhances the utilization of photovoltaic power in aluminum electrolysis plants.

[0023] 2) The present invention sets anti-reverse current diodes on the high-voltage side and low-voltage side of the DC / DC topology to ensure that energy flows unidirectionally from the photovoltaic power generation side to the electrolytic cell side, thereby improving the operational reliability of the electrolytic cell equipment.

[0024] 3) The present invention configures fuses and disconnecting switches of different specifications on the high-voltage side and low-voltage side of the DC / DC topology to ensure timely disconnection when a system failure occurs, avoid damage to equipment, and improve system operation safety.

[0025] 4) This invention proposes a novel isolated DC / DC topology for special occasions where faults are prone to occur and equipment operation safety requirements are high. For example, in the humid climate of southern regions, grounding faults are prone to occur on the photovoltaic power generation side. Since the positive and negative busbars of the electrolytic cell are not grounded, the fault current can cause significant damage to the equipment. In this case, the isolated DC / DC topology can ensure that the fault current is not transmitted to the electrolytic cell side, thereby improving the reliability and safety of system operation. However, in northern regions, due to the relatively dry weather, the probability of grounding faults on the photovoltaic power generation side is low, making a non-isolated DC / DC suitable, which can ensure higher operating efficiency and better economic benefits.

[0026] 5) To address the current situation where multiple conversion stages are required between the electrolytic cell and photovoltaic power generation, resulting in low energy utilization efficiency, this invention proposes a novel non-isolated DC / DC topology. The main body of this topology is a three-level boost circuit structure composed of four IGBT switches. Two series capacitors on the high-voltage side are connected in parallel with resistors of the same value, ensuring that the voltage across the two capacitors remains constant. Due to the increased number of voltage levels, the inductor current ripple is reduced, and the inductor size and weight are significantly reduced, thereby improving the overall power density of the device and meeting the high-current load requirements of the electrolytic cell. Simultaneously, compared to a conventional boost circuit, a single IGBT only needs to bear half the DC voltage, reducing the voltage withstand requirements of semiconductor devices and further reducing losses. Anti-reverse current diodes are installed on both the high-voltage busbar and the low-voltage photovoltaic side to ensure unidirectional energy transmission from the low-voltage photovoltaic side to the high-voltage busbar, preventing power extraction from the electrolytic cell. Fuses and disconnect switches are installed on both the high-voltage busbar and the low-voltage photovoltaic side, allowing for rapid disconnection in case of a fault on one side, mitigating the impact of the fault on other devices. The low-voltage side is connected to the energy storage device in parallel via a DC / DC converter to achieve flexible power control.

[0027] 6) Photovoltaic power generation emits almost no carbon, offering a significant advantage over traditional fossil fuel power generation under the "dual carbon target" framework. Photovoltaic carbon reduction = Photovoltaic power generation × (Power generation carbon emission factor - Photovoltaic power generation carbon emission factor). This system uses photovoltaic power generation combined with energy storage devices to supply the electrolyzer load. Compared to grid power supply, it not only achieves near-zero carbon emissions during operation but also provides corresponding carbon reduction indicators. Attached Figure Description

[0028] Figure 1 This is a topology diagram of a non-isolated DC / DC converter with an energy storage device according to the present invention;

[0029] Figure 2 This is a topology diagram of a MW-level isolated DC / DC converter with energy storage device according to the present invention;

[0030] Figure 3 This is a schematic diagram showing the connection of the 40MW photovoltaic-electrolysis cell system within the park;

[0031] Figure 4 This is a coordination control diagram for energy storage devices.

[0032] Figure 5 A diagram of a non-isolated DC / DC converter topology.

[0033] Figure 6 A diagram of a MW-level isolated DC / DC converter topology. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1 As shown, the non-isolated DC / DC converter topology of this invention is based on a traditional boost circuit and uses IGBTs as power switching devices to connect the low-voltage photovoltaic power generation device to the high-voltage electrolytic cell. Since energy flows unidirectionally from the low-voltage photovoltaic side to the high-voltage electrolytic cell, anti-reverse current diodes are configured on both the high-voltage and low-voltage sides to ensure that the power flow direction remains unchanged. Additionally, isolating switches and fuses are configured on both the high-voltage and low-voltage sides to ensure timely disconnection in case of system failure, preventing damage to the photovoltaic power generation and electrolytic cell equipment. This topology connects the low-voltage photovoltaic system and the high-voltage electrolytic cell, achieving voltage conversion and energy transfer. The photovoltaic power generation unit is connected to... Figure 1As shown in the diagram, on the "low-voltage side," energy is transferred to the three-level boost circuit via a series branch consisting of an anti-reverse current diode, a fuse, and a disconnect switch. The low-voltage side of the three-level boost circuit includes an inductor and a capacitor, with the capacitor acting as a voltage regulator. The main topology of the three-level boost circuit consists of four IGBTs. Figure 1 The connection point between the resistor branch, capacitor branch, and IGBT branch shown is the neutral point. By controlling the IGBT to turn on and off at different times using a PWM signal, a high voltage can be obtained on the high-voltage side to meet the requirements of the high-voltage electrolytic cell. Two capacitors are connected in series on the high-voltage side for voltage stabilization, and a resistor connected in parallel next to the capacitors serves to equalize the voltage. Energy flows from the capacitors through a series branch consisting of a disconnecting switch, a fuse, and an anti-reverse current diode to the high-voltage side busbar, supplying the high-voltage DC busbar of the electrolytic aluminum plant's electrolytic cells.

[0036] like Figure 2 As shown, the isolated DC / DC converter topology of this invention utilizes multiple isolated DC / DC converter modules connected in parallel to achieve MW-level power delivery due to the small capacity of a single isolated DC / DC converter module. Similar to the non-isolated topology, energy flows unidirectionally from the low-voltage photovoltaic side to the high-voltage electrolytic cell. Unlike the DAB (dual active bridge) type isolated DC / DC topology, due to the unidirectional energy flow, to reduce costs, the low-voltage side of a single isolated DC / DC converter module still uses an H-bridge topology based on IGBTs, while the high-voltage side uses diodes instead of IGBT devices; that is, the high-voltage side employs an uncontrolled rectifier structure to transmit energy. This topology connects the low-voltage photovoltaic and high-voltage electrolytic cells, achieving both voltage conversion and energy transmission. The photovoltaic power generation unit is connected to... Figure 2As shown in the diagram, on the "low-voltage side," energy is transferred to the isolated DC / DC converter module via a series branch consisting of anti-reverse current diodes, fuses, and disconnecting switches. A single isolated DC / DC converter module consists of three parts: a low-voltage side H-bridge topology, a high-frequency transformer, and a high-voltage side H-bridge topology. The low-voltage side uses IGBTs to form an H-bridge circuit for flexible control of low-voltage photovoltaic power transmission. Since energy is transferred unidirectionally from the low-voltage side to the high-voltage side, the high-voltage side uses diodes to form an H-bridge circuit, only needing to meet power transmission requirements. The high-voltage and low-voltage sides are coupled through a high-frequency transformer to achieve isolation. Because a single isolated DC / DC converter module has a small capacity, it is difficult to meet the power requirements of the electrolytic cell's DC bus. Therefore, multiple isolated DC / DC converter modules are designed to be connected in parallel to improve power transmission capability. After being transferred to the high-voltage side through this parallel topology, energy flows to the high-voltage side busbar via a series branch consisting of disconnecting switches, fuses, and anti-reverse current diodes, supplying the high-voltage DC busbar of the electrolytic aluminum plant. On the low-voltage side, an energy storage device is connected in parallel via a DC / DC converter to enable flexible power control. The high-voltage side only needs to receive energy, and energy transfer is achieved on the low-voltage side by controlling the on / off state of the IGBTs.

[0037] An energy storage device is configured on the low-voltage side and connected in parallel to the low-voltage side of the DC / DC converter topology. Since photovoltaic power generation is significantly affected by weather changes, its energy exhibits randomness and fluctuation. The energy storage device can adjust to the real-time power characteristics of photovoltaic power generation, thereby ensuring continuous and stable energy transmission and reliable power supply to the electrolyzer. For example, in sunny weather, photovoltaic power generation exceeds the electrolyzer load, making real-time power absorption difficult. In this case, the energy storage device absorbs and stores excess energy, preventing excessive current in the circuit and potential hazards. Conversely, in cloudy or rainy weather, photovoltaic power generation is lower than the electrolyzer load demand. The energy storage device releases energy to compensate for the power difference, thus ensuring a reliable supply to the electrolyzer load. In rainy southern regions, the isolated DC / DC converter topology is used to prevent fault current from being transmitted to the electrolyzer side. In some special situations, the isolated converter topology can also be used to ensure the safe and reliable operation of the system. In drier northern regions, the probability of short-circuit faults on the photovoltaic side is low. Using a non-isolated DC / DC converter topology can save on equipment investment costs, effectively reduce losses, and improve system efficiency. In addition, energy storage devices can be used in conjunction with photovoltaics to achieve MPPT (Multi-Level Photovoltaic), maximizing the local capacity for renewable energy absorption.

[0038] The two topologies described above differ significantly, primarily in their handling of equipment failures. Taking a DC ground fault on the low-voltage photovoltaic side as an example, a non-isolated topology allows the fault current to be transmitted to the high-voltage electrolyzer via the DC / DC topology, while an isolated topology prevents this transmission. Furthermore, since neither the positive nor negative busbars of the electrolyzer are grounded, the impact of the low-voltage side fault current on the electrolyzer is substantial; therefore, an isolated topology better ensures safe operation of the equipment.

[0039] In both of the aforementioned topologies, anti-reverse current diodes are configured on both the high-voltage and low-voltage sides to ensure unidirectional energy flow. Since the photovoltaic side is consistently used as the power source and the electrolytic cell side consistently acts as a load consuming energy, it is necessary to ensure unidirectional energy transfer from the photovoltaic side to the electrolytic cell side. This is crucial for the normal operation of the electrolytic cell equipment and to prevent current from flowing back from the electrolytic cell to the renewable energy source in the event of a short circuit or ground fault on the positive or negative busbars.

[0040] In both of the aforementioned topologies, fuses and disconnect switches are installed on both the high-voltage and low-voltage sides as protective devices to enhance system operational safety. Since the DC bus of the high-voltage electrolytic cell lacks a grounding device, a system fault could damage the electrolytic cell equipment. When the current in the system exceeds a set value, the fuse trips and the disconnect switch trips, working together to maximize protection of the equipment from damage.

[0041] For large-scale aluminum electrolysis plants, a single DC / DC topology is insufficient to meet power demands, necessitating the parallel connection of multiple isolated / non-isolated topologies to the DC bus of the electrolytic cells. Combined with energy storage units, the energy transmitted by different DC / DC topologies can be flexibly controlled based on local sunlight conditions, the power requirements of the electrolytic cells, and the DC bus voltage, achieving real-time dynamic power balance without reducing photovoltaic power generation. Furthermore, energy storage enables peak shaving and valley filling, as well as peak-valley arbitrage, while maximizing the utilization of renewable energy sources.

[0042] like Figure 3The diagram shows a 40MW photovoltaic-electrolytic cell system connection within the park. The DC / DC converter in the diagram represents the aforementioned isolated or non-isolated converter. Due to the large operating current of the electrolytic cell, a large-capacity photovoltaic grid connection is required. This invention's carbon emission reduction system for electrolytic aluminum based on efficient new energy grid connection includes multiple photovoltaic arrays, DC / DC converters, and electrolytic cells. Multiple DC / DC converters are used, each connected to multiple photovoltaic arrays. Their low-voltage side is connected to a combiner box, and their high-voltage side is connected to the electrolytic aluminum DC bus. All DC / DC converters are connected in parallel to an energy storage device on the low-voltage side. First, the electrical energy generated by the photovoltaic arrays is collected through the combiner box to the low-voltage side of the DC / DC converter. The voltage is boosted by the DC-DC conversion stage, and the energy is unidirectionally transferred to the electrolytic cell DC bus. The high-voltage sides of multiple DC / DC converters are connected in parallel to the electrolytic cell DC bus to meet its capacity requirements. The power of a single photovoltaic panel is relatively small; its power at its maximum power point is typically only a few hundred watts. To meet the power requirements of the electrolytic aluminum load, multiple photovoltaic panels are first connected in series to form a photovoltaic array, achieving primary energy collection. Then, n photovoltaic arrays are connected to a combiner box for secondary energy collection. The power output of a single combiner box can reach the megawatt level. The combiner box only serves the function of energy collection and does not perform voltage transformation; therefore, the voltage level is still relatively low, requiring a DC / DC converter for voltage boosting. The DC / DC converter shown in the figure is... Figure 1 , Figure 2 The non-isolated and isolated DC / DC converter topologies shown can be selected according to actual needs. The energy generated by photovoltaic power generation is collected in the combiner box and connected to the "low-voltage side" of the converter. After topology transformation, the voltage is boosted to 1235V DC, thereby enabling unidirectional energy transfer from the low-voltage photovoltaic side to the high-voltage electrolytic cell bus, realizing high-efficiency electrolytic aluminum production in the park.

[0043] This invention can also be implemented without an energy storage device, and its topology is as follows: Figure 5 , 6 As shown. The integration of energy storage devices allows for more flexible energy control, but it also increases costs and complicates control strategies. When the low-voltage side of the topology is not connected to energy storage, the IGBT devices can be switched on and off in real time based on photovoltaic power generation and electrolyzer load requirements, thus achieving unidirectional energy transfer from photovoltaic to electrolyzer. Topologies without energy storage are suitable for areas with abundant sunshine. Figure 3 In the photovoltaic-electrolysis cell system shown in the park, the photovoltaic power generation in areas with sufficient sunshine can always meet the power demand of the electrolysis cell load. At this time, by reasonably controlling the DC / DC converter, the real-time balance of photovoltaic-electrolysis cell power can be achieved. The photovoltaic electrolysis of aluminum can be realized without adding energy storage devices, which can reduce the system investment and operation and maintenance costs, and simplify the system control strategy.

[0044] Figure 4 The diagram shown is a coordinated control diagram for an energy storage device. This control process is applicable to devices such as... Figure 1 , 2 The DC / DC converter shown here features an energy storage device. First, it's necessary to collect the current photovoltaic output P. PV and the load demand P of the electrolytic cell load Then, the difference between the two is taken to obtain the net power P of the system. S The system is classified into five operating modes based on its net power and the current state of charge (SOC) of the energy storage device. (SOC diagram follows.) max SOC min These represent the maximum and minimum states of charge, determined by the energy storage device itself. The different operating modes are summarized below:

[0045] Pattern 1: When P S <0 and SOC>SOC min At this time, the photovoltaic power generation is less than the load demand of the electrolyzer, and the energy storage device meets the conditions for discharging. If all the photovoltaic power is supplied to the electrolyzer load, the power difference |P| between the two is... S This is compensated for by controlling the discharge of the energy storage device.

[0046] Pattern 2: When P S <0 and SOC≤SOC min At this time, photovoltaic power generation is less than the load demand of the electrolyzer, but the energy storage device does not meet the conditions for discharging. Therefore, all photovoltaic power is supplied to the electrolyzer load, and the power difference between the two is |P S The shortfall can be made up by the self-owned power plant or the external power grid.

[0047] Pattern 3: When P S When the value is 0, the photovoltaic power generation and the electrolytic cell load demand are balanced, and the energy storage device does not need to work.

[0048] Pattern 4: When P S >0 and SOC < SOC max At this time, photovoltaic power generation exceeds the load demand of the electrolyzer, and the energy storage device meets the conditions for internal charging. The photovoltaic power generation first supplies the electrolyzer load, and the power difference between the two is |P S | Used to charge energy storage devices, that is, to store the surplus of photovoltaic power generation into energy storage devices.

[0049] Pattern 5: When P S >0 and SOC≥SOC max At this time, photovoltaic power generation exceeds the load demand of the electrolyzer, but the energy storage device does not meet the conditions for internal charging. The photovoltaic power generation first supplies the electrolyzer load, and the power difference between the two is |PS This is addressed by reducing the active power output of solar power, which results in "curtailment".

[0050] Compared to traditional photovoltaic-electrolytic aluminum energy flow processes, this invention employs a single-stage DC / DC topology to directly connect photovoltaic power generation to electrolytic aluminum, eliminating multiple intermediate conversion stages and thus improving efficiency. The energy generated by the photovoltaic array is collected in a combiner box to the low-voltage side of the DC / DC topology, and then unidirectionally transferred to the DC bus of the electrolytic cell via an isolated / non-isolated converter, achieving an energy transfer efficiency exceeding 96%. Currently, photovoltaic utilization in electrolytic aluminum plants nationwide requires multiple stages of DC-AC-DC conversion, with traditional photovoltaic-electrolytic aluminum energy transfer efficiencies below 92%. Applying this system can significantly improve energy transfer efficiency and enhance the carbon emission reduction capabilities of electrolytic aluminum plants.

[0051] like Figure 5 As shown, the non-isolated DC / DC converter topology of this invention, without energy storage, is based on a traditional boost circuit and uses IGBTs as power switching devices to connect the low-voltage photovoltaic power generation unit to the high-voltage electrolytic cell. Since energy flows unidirectionally from the low-voltage photovoltaic side to the high-voltage electrolytic cell, anti-reverse current diodes are configured on both the high-voltage and low-voltage sides to ensure that the power flow direction remains unchanged. Additionally, isolating switches and fuses are configured on both the high-voltage and low-voltage sides to ensure timely disconnection in case of system failure, preventing damage to the photovoltaic power generation and electrolytic cell equipment. This topology connects the low-voltage photovoltaic unit and the high-voltage electrolytic cell, achieving voltage conversion and energy transfer. The photovoltaic power generation unit is connected to... Figure 1 As shown in the diagram, on the "low-voltage side," energy is transferred to the three-level boost circuit via a series branch consisting of an anti-reverse current diode, a fuse, and a disconnect switch. The low-voltage side of the three-level boost circuit includes an inductor and a capacitor, with the capacitor acting as a voltage regulator. The main topology of the three-level boost circuit consists of four IGBTs. Figure 1 The connection point between the resistor branch, capacitor branch, and IGBT branch shown is the neutral point. By controlling the IGBT to turn on and off at different times using a PWM signal, a high voltage can be obtained on the high-voltage side to meet the requirements of the high-voltage electrolytic cell. Two capacitors are connected in series on the high-voltage side for voltage stabilization, and a resistor connected in parallel next to the capacitors serves to equalize the voltage. Energy flows from the capacitors through a series branch consisting of a disconnecting switch, a fuse, and an anti-reverse current diode to the high-voltage side busbar, supplying the high-voltage DC busbar of the electrolytic aluminum plant's electrolytic cells.

[0052] like Figure 6As shown, the isolated DC / DC converter topology of this invention, which does not include energy storage, utilizes multiple isolated DC / DC converter modules connected in parallel to achieve MW-level power delivery due to the small capacity of a single isolated DC / DC converter module. Similar to the non-isolated topology, energy flows unidirectionally from the low-voltage photovoltaic side to the high-voltage electrolytic cell. Unlike the DAB (dual active bridge) type isolated DC / DC topology, due to the unidirectional energy flow, to reduce costs, the low-voltage side of a single isolated DC / DC converter module still uses an H-bridge topology based on IGBTs, while the high-voltage side uses diodes instead of IGBT devices; that is, the high-voltage side uses an uncontrolled rectifier structure to transmit energy. This topology connects the low-voltage photovoltaic and high-voltage electrolytic cells, achieving both voltage conversion and energy transmission. The photovoltaic power generation unit is connected to... Figure 2 As shown in the diagram, on the "low-voltage side," energy is transferred to the isolated DC / DC converter module via a series branch consisting of anti-reverse current diodes, fuses, and disconnecting switches. A single isolated DC / DC converter module consists of three parts: a low-voltage side H-bridge topology, a high-frequency transformer, and a high-voltage side H-bridge topology. The low-voltage side uses IGBTs to form an H-bridge circuit for flexible control of low-voltage photovoltaic power transmission. Since energy is transferred unidirectionally from the low-voltage side to the high-voltage side, the high-voltage side uses diodes to form an H-bridge circuit, only needing to meet power transmission requirements. The high-voltage and low-voltage sides are coupled through a high-frequency transformer to achieve isolation. Because a single isolated DC / DC converter module has a small capacity, it is difficult to meet the power requirements of the electrolytic cell's DC bus. Therefore, multiple isolated DC / DC converter modules are designed to be connected in parallel to improve power transmission capability. After being transferred to the high-voltage side through this parallel topology, energy flows to the high-voltage side busbar via a series branch consisting of disconnecting switches, fuses, and anti-reverse current diodes, supplying the high-voltage DC busbar of the electrolytic aluminum plant. On the low-voltage side, an energy storage device is connected in parallel via a DC / DC converter to enable flexible power control. The high-voltage side only needs to receive energy, and energy transfer is achieved on the low-voltage side by controlling the on / off state of the IGBTs.

[0053] This invention combines energy storage and new energy sources to provide auxiliary frequency regulation services for electrolytic cells. As a load in the power system, the conventional approach to frequency regulation for electrolytic cells involves using self-saturating reactors and on-load tap changers to regulate voltage and thus adjust the cell's power. With the system of this invention, the electrolytic cell can simultaneously utilize both renewable energy supply from within the industrial park and grid power. Combined with the energy storage unit and the DC / DC converter topology of this invention, flexible and precise control of renewable energy power supply can be achieved, thereby enabling control of grid power supply, which is more flexible and reliable than current frequency regulation methods.

[0054] The system described in this invention enables deep integration of high-energy-consuming industries such as electrolytic aluminum production with new energy power generation technologies, efficiently utilizing photovoltaic power generation resources and contributing to significant carbon emission reduction in the electrolytic aluminum industry. This invention is feasible and innovative in terms of both its technical approach and product demonstration.

[0055] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources, characterized in that: The system includes multiple photovoltaic arrays, DC / DC converters, and electrolytic cells. The DC / DC converters are configured in parallel as a single-stage DC / DC conversion stage. These parallel DC / DC converters are connected to multiple photovoltaic arrays via combiner boxes. The low-voltage side of each DC / DC converter is connected to its respective combiner box, while the high-voltage side is connected to the DC bus of the electrolytic cell. The low-voltage side can optionally be connected to an energy storage device. The electrical energy generated by the multiple photovoltaic arrays is collected and fed to the low-voltage side of the DC / DC converter via the combiner boxes. Multiple electrolytic aluminum cells are connected in series to the DC bus of the electrolytic cell, serving as the high-voltage side of the DC / DC converter. The low-voltage and high-voltage sides are connected through this single-stage DC / DC conversion stage, achieving efficient energy transfer. The topology of the DC / DC converter can be either an isolated or non-isolated DC / DC conversion topology. The isolated DC / DC converter topology is formed by multiple isolated DC / DC converter modules connected in parallel. Each isolated DC / DC converter module consists of three parts: a low-voltage side H-bridge topology, a high-frequency transformer, and a high-voltage side H-bridge topology. The low-voltage side uses IGBTs to form an H-bridge circuit to achieve flexible control of low-voltage photovoltaic power transmission. The high-voltage side uses diodes to form an H-bridge circuit to meet only the power transmission requirements. Energy transmission on the low-voltage side is achieved by controlling the on / off state of the IGBTs. The high-voltage and low-voltage sides are coupled through a high-frequency transformer to achieve isolation. Both the high-voltage and low-voltage sides are equipped with anti-reverse current diodes, fuses, and disconnect switches.

2. The carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources according to claim 1, characterized in that: In rainy southern regions, the isolated DC / DC converter topology is used to prevent fault current from being transmitted to the electrolytic cell side; in northern regions, a non-isolated DC / DC converter topology is used.

3. The carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources according to claim 1, characterized in that: The non-isolated DC / DC converter topology includes a three-level boost circuit, which adopts an IGBT-based three-level structure. The low-voltage side includes an inductor and a capacitor, and the high-voltage side has two capacitors connected in series with a resistor connected in parallel next to the capacitors. Both the high-voltage and low-voltage sides are equipped with anti-reverse current diodes, fuses, and disconnect switches.

4. The electrolytic aluminum carbon emission reduction system based on efficient access to new energy sources according to claim 3, characterized in that: When the current in the system exceeds the set value, the fuse trips and the disconnecting switch disconnects, working together to protect the system from damage to the greatest extent possible.

5. The carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources according to claim 1, characterized in that: If an energy storage device is connected to the low-voltage side of the DC / DC converter, the energy storage device is used to adjust in accordance with the real-time power characteristics of photovoltaic power generation.

6. The electrolytic aluminum carbon emission reduction system based on efficient access to new energy sources according to claim 5, characterized in that: The adjustments include: when the weather is sunny and the photovoltaic power generation exceeds the electrolyzer load, the energy storage device absorbs and stores the excess energy to prevent excessive current in the circuit from causing danger; when the weather is cloudy or rainy and the photovoltaic power generation is lower than the electrolyzer load demand, the energy storage device releases energy to compensate for the power difference, thereby ensuring a reliable supply to the electrolyzer load; the energy storage device is also used to cooperate with photovoltaics to achieve maximum power point tracking, thereby improving the absorption capacity of new energy sources.

7. A carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources, as described in claim 1 or 3, characterized in that: Multiple isolated or non-isolated transformer topologies are connected in parallel to the DC bus of the electrolytic cell to meet the system capacity requirements.

8. The electrolytic aluminum carbon emission reduction system based on efficient access to new energy sources according to claim 5, characterized in that: Based on local sunlight conditions, the power required by the electrolytic cell, the DC bus voltage, and the energy transmitted by the DC / DC converter controlled by the energy storage device, real-time dynamic power balance is achieved without reducing photovoltaic power generation; load demand is rationally allocated by controlling the on / off state of the IGBTs in each DC / DC converter.

9. The carbon emission reduction system for electrolytic aluminum based on efficient access to new energy sources according to claim 1, characterized in that, First, collect the current photovoltaic output P. PV and the load demand P of the electrolytic cell load Then, the difference between the two is taken to obtain the net power P of the system. S Based on the net power and the current state of charge (SOC) of the energy storage device, five operating modes are defined. These operating modes specifically include: Pattern 1: When P S <0 and SOC>SOC min At that time, all the photovoltaic power generated is supplied to the electrolytic cell load, and the power difference between the two is |P S |This is compensated for by controlling the discharge of the energy storage device; Pattern 2: When P S <0 and SOC≤SOC min At that time, all the photovoltaic power generated is supplied to the electrolytic cell load, and the power difference between the two is |P S |This can be compensated for by the self-owned power plant or the external power grid; Pattern 3: When P S When the value is 0, the energy storage device does not need to work; Pattern 4: When P S >0 and SOC < SOC max At that time, the photovoltaic power generation first supplies the electrolytic cell load, and the power difference between the two is |P S | Used to charge energy storage devices, that is, to store the surplus of photovoltaic power generation into energy storage devices; Pattern 5: When P S >0 and SOC≥SOC max At that time, the photovoltaic power generation first supplies the electrolytic cell load, and the power difference between the two is |P S | This can be solved by reducing the active power output of photovoltaic power plants; Among them, SOC max SOC min These are the maximum and minimum states of charge, respectively, determined by the energy storage device itself.

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