Main circuit apparatus for an electric train using a hydrogen fuel cell

Abstract

The present disclosure relates to a technology for a main circuit device of a demand electric train, which eliminates the DC / DC converter for voltage step-up to fundamentally eliminate the risk of fire in secondary batteries due to high-voltage operation, and simplifies and lightens the drive system.

Description

Technology Field

[0001] The present invention relates to a technology for an electric vehicle that uses a hydrogen fuel cell as its primary power source. Background Technology

[0003] As global efforts toward carbon neutrality accelerate, the demand for eco-friendly power sources to replace fossil fuels is surging in the transportation sector. Particularly in railway systems responsible for large-scale transport, hydrogen fuel cell-based hydrogen electric multiple units (HEVs) are emerging as a key next-generation technology. These HEVs can replace diesel locomotives and operate in non-electrified sections lacking fixed power supply infrastructure, such as overhead power lines. Since HEVs directly generate electricity by reacting hydrogen loaded onto the vehicle with oxygen from the air, they are a zero-emission mode of transportation that emits only pure water (H2O) during operation.

[0004] Generally, the main circuit system of a hydrogen electric multiple unit (EMU) developed for commercialization is configured as a hybrid system using both hydrogen fuel cells and secondary batteries. First, the hydrogen fuel cell stack, which serves as the core power source, generates the primary DC voltage (e.g., DC 750V) required for vehicle operation. However, since this voltage may be too low to efficiently drive a high-capacity traction motor, a DC / DC converter included in the main circuit system of the hydrogen electric multiple unit is responsible for stepping this voltage up to a high voltage of approximately DC 1,500V. This stepped-up high-voltage DC power is transmitted to a traction control inverter (VVVF), where it is converted into variable voltage, variable frequency AC power, and finally drives the traction motor to generate the train's propulsion force.

[0005] At the same time, secondary batteries play an important role in enhancing the stability and efficiency of the system. When a large output is required instantaneously, such as when the vehicle accelerates rapidly or climbs an uphill slope, the secondary battery supplements the power that may be insufficient from the output of the hydrogen fuel cell alone. Conversely, kinetic energy generated when the train decelerates or brakes is converted into electricity through regenerative braking, stored in the secondary battery, and recycled when needed.

[0006] However, these conventional high-voltage-based main circuit systems for hydrogen electric vehicles have several fundamental limitations in terms of stability and efficiency.

[0007] The biggest concern is the safety of secondary batteries. As the main circuit of hydrogen electric trains operates at a high voltage of 1,500V, secondary batteries also undergo repeated charging and discharging in the same high-voltage environment. These harsh conditions impose significant electrical and thermal stress on the battery cells, which poses a potential risk of causing thermal runaway, potentially leading to fire or explosion. Given the nature of railway vehicles used by numerous passengers, this safety issue is a top priority that must be resolved.

[0008] Furthermore, there are issues regarding the physical and economic inefficiencies of the system. The high-capacity DC / DC converter, required to boost the voltage of the main circuit units in hydrogen electric vehicles, is a core component that is bulky, heavy, and expensive in itself. This converter occupies limited space within the vehicle, hindering design flexibility, and increases the overall vehicle weight, leading to unnecessary energy consumption. In addition, energy loss inevitably occurring during the power conversion process acts as a factor that degrades the overall efficiency of the system. Ultimately, the presence of the DC / DC converter increases system complexity, adds potential failure risks, and causes manufacturing and maintenance costs to rise. Prior art literature

[0009] Korean Patent Publication No. 10-2018-0131439 The problem to be solved

[0010] The present invention is proposed in consideration of the above circumstances and aims to provide a main circuit device for a hydrogen electric train that lowers the voltage of the main circuit device system of the hydrogen electric train to increase the operational stability of the secondary battery and minimize the risk of fire.

[0011] In addition, the present invention has another objective of simplifying the in-vehicle device configuration, increasing space utilization, and reducing the overall weight and cost of the system by eliminating the DC / DC converter for voltage boosting. means of solving the problem

[0013] To achieve the above objective, the main circuit device of a hydrogen electric train according to an embodiment of the present invention includes a hydrogen fuel cell that generates a first DC voltage, a secondary battery connected in parallel with the hydrogen fuel cell to a common DC link operating at the first DC voltage, and a propulsion inverter connected to the common DC link to drive a traction motor, wherein the propulsion inverter receives the first DC voltage directly from the common DC link without passing through a DC / DC converter that steps up the voltage.

[0014] The first DC voltage can be DC 750V.

[0015] The secondary battery can discharge to supply auxiliary power to the propulsion inverter when the vehicle accelerates, and can charge and store regenerative braking energy generated from the traction motor when the vehicle brakes.

[0016] The main circuit device of a hydrogen electric vehicle according to an embodiment of the present invention may further include an SIV (auxiliary power supply unit) connected to a common DC link to supply power to the vehicle's lighting and heating / cooling devices.

[0017] The main circuit device of a hydrogen electric vehicle according to an embodiment of the present invention may further include a controller that controls the secondary battery to discharge when the power demand of the propulsion inverter exceeds the preset output capacity of the hydrogen fuel cell. Effects of the invention

[0019] According to the present invention, the main circuit device of a hydrogen electric train removes the DC / DC converter for voltage step-up, thereby lowering the voltage of the main circuit device system of the hydrogen electric train from the existing DC 1500V level to the DC 750V level, which significantly reduces the electrical and thermal stress applied to the secondary battery, fundamentally blocking the possibility of thermal runaway, which is the main cause of battery fires, and thus has the effect of dramatically improving the operational stability of the railway vehicle.

[0020] In addition, by completely eliminating the DC / DC converter from the main circuit unit of the hydrogen electric multiple unit—which is bulky, heavy, and requires a separate cooling device—significant installation space can be secured, greatly increasing the flexibility of vehicle design. Furthermore, the overall weight reduction of the vehicle reduces the burden on the tracks and improves operational energy efficiency.

[0021] Furthermore, the main circuit unit of a hydrogen electric train is designed to significantly simplify the overall system configuration by removing critical high-power components. This reduces potential failure points, thereby improving the system's overall reliability and durability. Additionally, the elimination of expensive parts and related devices eliminates the need for costly components, resulting in reduced initial manufacturing costs and long-term maintenance expenses.

[0022] In addition, the main circuit device of the hydrogen electric train eliminates the power conversion step for voltage boosting, thereby fundamentally removing power that would otherwise be lost as thermal energy in the converter, which increases the overall energy efficiency of the system and reduces hydrogen consumption, resulting in the effect of directly improving the operational economics of the vehicle. Brief explanation of the drawing

[0024] FIG. 1 is a block diagram illustrating the configuration of a hydrogen linkage cell propulsion system of a typical electric train. FIG. 2 is a block diagram illustrating the main circuit device of a hydrogen electric train according to an embodiment of the present invention. FIG. 3 is a drawing for explaining an example of detailed operation reflecting the capacitance and current values ​​of each component included in a main circuit device according to an embodiment of the present invention. Specific details for implementing the invention

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0026] The embodiments are provided to more fully explain the invention to those skilled in the art, and the following embodiments may be modified in various different forms, and the scope of the invention is not limited to the following embodiments. Rather, these embodiments are provided to make the disclosure more faithful and complete and to fully convey the spirit of the invention.

[0027] A hydrogen electric train is driven by a hydrogen fuel cell as a power source. The hydrogen electric train includes a main circuit unit that controls power using a hydrogen fuel cell.

[0028] Referring to FIG. 1, the main circuit device of a typical hydrogen electric vehicle comprises a hydrogen tank (10), a hydrogen fuel cell (20), a DC / DC converter (30), a secondary battery (40), a VVVF inverter (50), a PMSM (60, traction motor), a static inverter (70), an LCL filter (72), a TR (74, transformer), a grid (80), and a control battery charger (90).

[0029] The power flow of the hydrogen train begins when hydrogen stored at high pressure in the hydrogen tank (10) is supplied to the hydrogen fuel cell (20). The hydrogen fuel cell (20) produces primary direct current (DC) power required for driving the vehicle through an electrochemical reaction. Since the voltage produced at this time (e.g., DC 750V) may be inefficient for directly driving a large-capacity traction motor, it is stepped up to a high voltage (e.g., 1500Vdc) suitable for the main circuit device of the hydrogen electric train through a DC / DC converter (30). This step-up process is a key component of the prior art to reduce cable losses (I²R losses) by lowering the current during the same power transmission by using high voltage, and to optimize the efficiency of the propulsion inverter and motor designed for high voltage.

[0030] The boosted 1500Vdc power forms a DC link that serves as the common power line of the system, to which the main devices are connected in parallel. A VVVF inverter (50) converts this high-voltage DC into three-phase AC with variable voltage and variable frequency to precisely control a permanent magnet synchronous motor, such as a PMSM (60, traction motor). This enables the torque and speed required in all operating areas, such as starting, acceleration, constant speed driving, and deceleration of the train.

[0031] The secondary battery (40) is directly connected to the DC link and plays an important role in maximizing the system's dynamic responsiveness and energy efficiency. In sections where the output of the hydrogen fuel cell (20) alone is insufficient or the response may be slow, such as when the train accelerates rapidly or climbs, the secondary battery (40) quickly discharges to supplement the insufficient power (Power Assist). Conversely, when the train brakes, the PMSM (60) operates as a generator to convert kinetic energy into electrical energy (regenerative braking), and this regenerative energy is stored in the secondary battery (40) and reused during the next acceleration.

[0032] In addition, various auxiliary power devices are connected to the DC link. A static inverter (70), an LCL filter (72) that removes harmonics to ensure power quality, and a TR (transformer) (74) that converts the voltage to match the external grid voltage are grid connection devices required to send the vehicle's energy to the external grid (80) (V2G) or to operate the vehicle system by receiving power from the outside. A control battery charger (90) converts the high voltage of the DC link to a low voltage to supply stable power to various essential electronic equipment, such as the train's integrated control unit (VCU), lighting, and communication equipment.

[0033] However, the main circuit device of this conventional hydrogen electric train has the following fundamental problems. As the main circuit device of the hydrogen electric train operates at a high voltage of 1500V, the secondary battery (40) also repeatedly charges and discharges in the same high voltage environment. These harsh conditions apply significant electrical and thermal stress to the battery cells, which can cause a thermal runaway phenomenon and pose a potential risk of fire or explosion. Given the nature of railway vehicles used by numerous passengers, this safety issue is a top priority that must be resolved.

[0034] In addition, there are issues regarding the physical and economic inefficiency of the system. The high-capacity DC / DC converter (30) for boosting the voltage of the main circuit device of the hydrogen electric vehicle is a core component that is bulky, heavy, and expensive. This converter occupies a limited space in the vehicle, hindering design flexibility and increasing the overall weight of the vehicle, thereby causing unnecessary energy consumption. Furthermore, energy loss inevitably occurring during the power conversion process acts as a factor that lowers the overall efficiency of the system. Ultimately, the presence of the DC / DC converter (30) increases the complexity of the system, adds potential failure possibilities, and causes manufacturing and maintenance costs to rise.

[0035] The main circuit device of a hydrogen electric train according to an embodiment of the present invention is proposed to fundamentally solve the complexity and safety issues of the high-voltage system of a conventional hydrogen electric train main circuit device (see FIG. 1), by completely eliminating the DC / DC converter for voltage boosting and directly linking all major power devices at the basic output voltage level of the fuel cell.

[0036] Referring to FIG. 2, the main circuit device of a hydrogen electric vehicle according to an embodiment of the present invention is configured to include a hydrogen fuel cell (110), a secondary battery (120), a VVVF inverter (130, integrated inverter), an IM (140, traction motor), a SIV (150, auxiliary power supply), and a control battery charger (160).

[0037] The fuel cell (110) is the primary power source of the hydrogen electric train. The fuel cell (110) stably produces DC power (750V DC) required for the basic operation of the electric train through the electrochemical reaction of hydrogen and oxygen. The fuel cell (110) operates in the most efficient range to avoid sudden load fluctuations under the control of the electric train controller (VCU) and supplies a base load to the system. The power produced by the fuel cell (110) is transmitted to the inverter (130) and auxiliary power supply units (150, 160) through a DC link.

[0038] The secondary battery (120) stores energy and assists dynamic output. When power exceeding the output of the fuel cell (110) is required during rapid acceleration or uphill driving, the secondary battery (120) quickly discharges according to the command of the VCU to replenish the insufficient energy (i.e., discharge (output assistance)). When the electric vehicle decelerates, the secondary battery (120) receives and stores regenerative energy generated from the traction motor (140) at DC 750V via the inverter (130) (i.e., charge (regenerative braking)). At this time, all charging and discharging of the secondary battery (120) are performed at a low voltage of 750V rather than 1500V, thereby minimizing stress on the battery cells and the risk of thermal runaway.

[0039] The VVVF inverter (130, integrated inverter) is the core control device of the main circuit device. The VVVF inverter (130) receives power from the DC 750V link during propulsion and converts it into three-phase AC power of variable voltage variable frequency (VVVF) to precisely control the speed and torque of the traction motor (140). During braking, the VVVF inverter (130) converts (rectifies) the AC regenerative energy generated from the traction motor (140) back into DC 750V and stores it in the secondary battery (120).

[0040] The traction motor (140) converts electrical energy into mechanical rotational force to drive the electric train.

[0041] The traction motor (140) generates rotational force using alternating current power supplied from the VVVF inverter (130) during propulsion to drive the wheels. Based on FIG. 2, the traction motor (140) shares the total required output, including the first traction motor (142), the second traction motor (144), the third traction motor (146), and the fourth traction motor (146).

[0042] The traction motor (140) operates as a generator using the kinetic energy of the electric train during braking, and produces regenerative energy in the form of alternating current and sends it back to the inverter (130).

[0043] The SIV (150, auxiliary power supply, Static Inverter) supplies power to all auxiliary systems other than the propulsion of the electric train. The SIV (150) receives power directly from a DC 750V link and converts it into stable AC and DC power required for the train's lighting, HVAC, broadcasting and communication equipment, door control, etc.

[0044] The control battery charger (160) charges and supplies power to the battery for the core control system and emergency power of the electric train. The control battery charger (160) receives power from a DC 750V link and converts it into low-voltage DC (e.g., DC 24V or 100V) suitable for the control circuit. This power supplies power to core control equipment, such as the electric train's VCU, while keeping the control battery (accumulator) always fully charged to maintain control power in case of an emergency.

[0045] The main circuit device has a simple and efficient structure in which the fuel cell (110), which is the main power source of the vehicle, and the secondary battery (120), which is an energy storage device, are directly connected in parallel to a common low-voltage DC link (e.g., DC 750V). This DC link serves as a single channel for all major power devices of the vehicle to exchange energy, and since there is no intermediate process of stepping up to 1500V as in the prior art, the entire system operates stably at the basic output voltage level of the fuel cell (110).

[0046] The VVVF inverter (130, integrated inverter) receives DC 750V power directly from a low-voltage DC link. This inverter (130) is designed to be optimized for low-voltage, high-current environments and converts the input DC power into three-phase AC power of variable voltage and variable frequency to precisely drive a number of traction motors (140, IM).

[0047] Power management during vehicle operation is achieved through the organic cooperation of the fuel cell (110) and the secondary battery (120). When stable output is required, such as during constant speed driving, the fuel cell (110) supplies most of the power as the primary power source. On the other hand, when a large amount of power is required instantaneously, such as during rapid acceleration or uphill driving, the vehicle controller supplies a powerful auxiliary output to the inverter (130) simultaneously through the discharge of the secondary battery (120) along with the stable output of the fuel cell (110).

[0048] When the vehicle brakes, the regenerative braking function is activated. The AC power produced by the traction motor (140) operating as a generator is converted into DC power of 750V through the inverter (130) and returned to the DC link. This regenerative energy is immediately stored in a secondary battery (120) directly connected to the DC link to maximize energy efficiency. In particular, since both charging and discharging of the secondary battery (120) are performed at a low voltage of 750V rather than 1500V, the electrical and thermal stress applied to the battery cells is significantly reduced, drastically lowering the risk of battery thermal runaway and fire and ensuring a stable power supply.

[0049] In addition, the SIV (150) that supplies power to various auxiliary systems such as the train's lighting, heating and cooling, and communication equipment, and the control battery charger (160) for the control system are also directly connected to the low-voltage DC link without a separate complex voltage conversion process. This simplifies the configuration of the auxiliary power system and contributes to increasing the space efficiency and reliability of the entire system.

[0050] Referring to FIG. 3, the detailed operation reflecting the capacity and current values ​​of each component included in the main circuit device of a hydrogen electric train according to an embodiment of the present invention is described as follows.

[0051] When the hydrogen electric train is running normally (normal continuous operation (continuous output operation)), four traction motors (142, 144, 146, 148) each operate with a continuous capacity of 130 kW, requiring a total propulsion force of 520 kW. The hydrogen fuel cell (110) stably supplies 200 kW of power as the main power source. The insufficient power (520 kW - 200 kW = 320 kW) is supplemented by discharging the secondary battery (120). This combined power (520 kW) is supplied to the traction motors (140) through the VVVF inverter (130). At this time, the inverter operates stably within a continuous capacity range of approximately 760 kW.

[0052] When the hydrogen electric train accelerates rapidly (maximum acceleration (peak output operation)), each traction motor (140) requires a total output of 664 kW using a maximum peak (reverse) capacity of 166 kW. The hydrogen fuel cell (110) supplies a maximum capacity of 200 kW. The secondary battery (120) momentarily discharges a very high output of 464 kW (664 kW - 200 kW) to handle the peak power required for acceleration. At this time, the VVVF inverter (130) operates within a peak current range of approximately 1048 A and transmits the total power of 664 kW received from the two power sources to the traction motors (140).

[0053] When the hydrogen electric train performs maximum regenerative braking (max braking), each traction motor (140) acts as a generator and can individually produce up to 229 kW of power. Theoretically, a total of 916 kW (229 kW x 4) of regenerative energy can be generated from the four motors, but this is limited by the regenerative capacity limit of 802 kW of the VVVF inverter (130). Therefore, up to 802 kW of regenerative power is returned to the DC 750V link through the inverter (130). All of this regenerative power is stored in the secondary battery (120) to increase energy efficiency.

[0054] When supplying auxiliary power to a hydrogen electric vehicle, power for lighting, heating and cooling, communication equipment, etc., is supplied through the SIV (150) regardless of the vehicle's operation. The SIV continuously receives 50 kW of power from a DC 750V link and converts it into the necessary AC or DC power. The control battery charger (160) also receives the power required for the control system from the DC link.

[0055] As such, the main circuit device according to the embodiment of the present invention can simultaneously solve the problems of space occupation, weight, cost, reduced efficiency, and system complexity associated with the prior art by eliminating the DC / DC converter.

[0056] In addition, the main circuit device according to the embodiment of the present invention can further operate the entire system at a low voltage to dramatically improve the safety of the secondary battery, thereby providing a technical basis for realizing a safer and more economical hydrogen electric vehicle.

[0057] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0059] 10: Hydrogen tank 20: Hydrogen fuel cell 30: DC / DC converter 40: Secondary battery 50: VVVF Inverter 60: PMSM (Traction Motor) 70: Static inverter 72: LCL filter 74: TR (Transformer) 80: Grid 90: Control battery charger 110: Fuel cell 120: Secondary battery 130: VVVF (Integrated Inverter) 140: IM (Traction Motor) 150: SIV (Auxiliary Power Supply) 160: Control Battery Charger

Claims

Claim 1 A main circuit device of a hydrogen electric vehicle comprises: a hydrogen fuel cell that generates a first DC voltage; a secondary battery connected in parallel with the hydrogen fuel cell to a common DC link operating at the first DC voltage; a propulsion inverter connected to the common DC link to drive a traction motor; an SIV connected to the common DC link to supply power to the vehicle's lighting and heating / cooling devices; and a control battery charger connected to the common DC link to receive power from the common DC link, convert it into DC power suitable for a control circuit, and charge a control battery; wherein the propulsion inverter receives the first DC voltage directly from the common DC link without passing through a DC / DC converter that steps up the voltage. Claim 2 In claim 1, the main circuit device of a hydrogen electric train, wherein the first DC voltage is DC 750V. Claim 3 In claim 1, the secondary battery is a main circuit device of a hydrogen electric vehicle that discharges when the vehicle accelerates to supply auxiliary power to the propulsion inverter, and charges and stores regenerative braking energy generated from the traction motor when the vehicle brakes. Claim 4 In claim 1, the auxiliary power supply unit is a main circuit unit of a hydrogen electric vehicle connected to the common DC link and supplying power to the vehicle's lighting and heating / cooling devices. Claim 5 A main circuit device of a hydrogen electric vehicle according to claim 1, further comprising a controller that controls the secondary battery to discharge when the power requirement of the propulsion inverter exceeds the preset output capacity of the hydrogen fuel cell.

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