Description:
FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. TITLE OF THE INVENTION
DIRECT CURRENT AIR CONDITIONING SYSTEM FOR LOCOMOTIVE CABIN

2. APPLICANTS

NAME : TRANS ACNR SOLUTIONS PRIVATE LIMITED
NATIONALITY : IN
ADDRESS : G-19, 20, 31 & 32, RIICO Industrial Area, Shahjahanpur, Alwar, Rajasthan-301706 India

2. PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to the field of air conditioning systems. More specifically, the present disclosure pertains to direct current (DC) air conditioning systems for locomotive cabins that operate directly using the DC power supply available from locomotives without requiring alternating current (AC) conversion.

BACKGROUND
In modern railway systems, locomotive cabins are typically equipped with air conditioning systems to provide comfortable working environments for train operators. These air conditioning systems are powered by the electrical systems of the locomotives. Conventionally, locomotives, particularly diesel locomotives, are equipped with auxiliary alternators that generate three-phase alternating current (AC) power, typically at around 55 volts AC. This AC power is then converted to direct current (DC) power, typically at around 74 volts DC, through bridge rectifiers installed in the locomotives. The DC power serves as the primary power source for various electrical applications within the locomotive, including the cabin air conditioning systems.
However, several problems are associated with conventional locomotive cabin air conditioning systems. The DC power supplied from the locomotive’s auxiliary generator through bridge rectifiers often contains significant power repulsions, which can deteriorate further when the locomotive operates at lower speeds or idles. Additionally, conventional air conditioning systems typically require multiple power conversion stages between the locomotive’s DC power supply and the air conditioning components, such as compressors and fans. These power conversions generally involve boosting the input DC voltage to a higher DC voltage and then inverting it to AC power to operate the compressor and fans. Furthermore, the capacitor banks provided in conventional cabin air conditioners are often not designed with sufficient capacitance to adequately reduce the repulsions in the power supply, particularly under varying locomotive operating conditions.
To address these issues, various solutions have been implemented in conventional systems. These include the use of power conversion modules that boost the input voltage from the typical 74VDC to approximately 400VDC, followed by inverters that convert this boosted DC voltage to 220VAC to power the compressor and other components. Additionally, some systems incorporate filtering capacitors and power conditioning circuits in attempts to mitigate power quality issues. Further solutions include the use of variable frequency drives to control the speed of AC compressors and fans, as well as control panel that regulate the operation of the air conditioning system based on cabin temperature and other operational parameters.
Despite these implementations, conventional solutions still present significant limitations. The multiple power conversion stages required to operate standard AC components introduce numerous potential points of failure in the system. Each power conversion stage not only adds complexity but also introduces energy losses, reducing overall system efficiency. The power repulsions from the locomotive’s DC supply can cause stress on the electronic components of the power conversion stages, leading to premature failures of power drive circuits. Additionally, the instability caused by varying input power from the locomotive, combined with fixed-load requirements of the air conditioning system, can lead to operational issues and system failures. Conventional solutions also typically result in larger, heavier systems with higher maintenance requirements due to the numerous components involved in power conversion and conditioning.
Therefore, there exists a need for an improved air conditioning system for locomotive cabins that can operate reliably with the DC power supplied by locomotives without requiring multiple power conversion stages, while effectively handling power quality issues and providing efficient and reliable cooling performance under varying operating conditions.

SUMMARY
The present disclosure addresses the aforementioned needs by providing a direct current (DC) air conditioning system for locomotive cabins that operates directly from the locomotive’s DC power supply without requiring conversion to alternating current (AC). The disclosed air conditioning system eliminates potential failure points and power losses associated with traditional power conversion components, while providing stable and efficient cooling performance.
In one aspect, the present disclosure provides an air conditioning system for a cabin of a locomotive having a direct current (DC) power source. The air conditioning system includes a DC power input configured to receive DC power directly from the DC power source of the locomotive, a capacitor bank coupled to the DC power input and configured to process the received DC power to reduce repulsions, a DC compressor coupled to the capacitor bank and configured to provide variable cooling capacity and operate directly using the processed DC power without alternating current (AC) conversion, at least one DC fan coupled to the capacitor bank and configured to provide variable cooling airflow and operate directly using the processed DC power without AC conversion, and a control unit configured to regulate operation of the DC compressor and the at least one DC fan by adjusting the variable cooling capacity and the variable cooling airflow.
In another aspect, the air conditioning system includes a reverse polarity protection circuit coupled between the DC power input and the capacitor bank, configured to protect electrical components in the system if the polarity of the applied voltage is reversed, enhancing the system’s reliability in harsh operating environments.
In yet another aspect, the air conditioning system includes a pre-charge circuit coupled between the DC power input and the capacitor bank, configured to gradually charge the capacitor bank before activating system loads. This feature reduces initial current spikes and prevents electrical stress on the system components when the air conditioning system is powered on.
In a further aspect, the air conditioning system includes a DC-DC buck converter coupled to the DC power input, configured to convert the input DC power to a lower DC voltage for operating low voltage components in the air conditioning system, allowing for efficient power management across different voltage requirements.
The air conditioning system of the present disclosure provides several advantages, including elimination of AC power conversion components, reduced complexity, improved reliability, enhanced energy efficiency, and stable performance under varying locomotive operating conditions. By utilizing DC components with built-in soft start functions and appropriate power conditioning, the system effectively addresses the power quality issues associated with locomotive DC power supplies.

BRIEF DESCRIPTION OF DRAWINGS
A more complete appreciation of the present invention and many of the attendant aspects thereof will be readily obtained as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawings:
FIG. 1 illustrates a circuit diagram of a direct current (DC) air conditioning system for a locomotive cabin, in accordance with an embodiment of the present disclosure; and
FIG. 2 illustrates a block diagram of a conventional air conditioning system for a locomotive cabin, provided for comparative purposes.

DETAILED DESCRIPTION OF THE INVENTION
The present disclosure provides detailed description of embodiments of an air conditioning system for a locomotive cabin. The following detailed description is presented to enable any person skilled in the art to make and use the disclosed subject matter. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the disclosed embodiments. Descriptions of specific embodiments or applications are provided only as examples. Various modifications to the embodiments described herein will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the disclosure.
As used herein, “direct current (DC) power” refers to electrical power in which the flow of electric charge does not change direction, maintaining a unidirectional flow, as contrasted with alternating current (AC) power.
As used herein, “capacitor bank” refers to a group of multiple capacitors arranged in a specific configuration to achieve desired electrical characteristics for processing electrical power.
As used herein, “DC compressor” refers to a refrigerant compressor that operates directly from DC power without requiring conversion to AC power.
As used herein, “variable cooling capacity” refers to the ability of a compressor to adjust the amount of cooling produced by operating at different speeds or power levels.
As used herein, “alternating current (AC) conversion” refers to the process of converting direct current (DC) power to alternating current (AC) power, typically using an inverter or similar power conversion device.
As used herein, “DC fan” refers to a fan with a motor that operates directly from DC power without requiring conversion to AC power.
As used herein, “variable cooling airflow” refers to the ability of a fan to adjust the volume of air moved per unit time by operating at different speeds.
As used herein, “control unit” refers to an electronic device or system that monitors various parameters and generates control signals to regulate the operation of components in the air conditioning system.
As used herein, “reverse polarity protection circuit” refers to an electrical circuit designed to protect electrical components from damage if the polarity of the applied voltage is reversed.
As used herein, “pre-charge circuit” refers to an electrical circuit designed to limit the initial current flow to a capacitor bank when power is first applied to the system.
As used herein, “DC-DC buck converter” refers to a type of DC-DC power converter that reduces an input voltage to a lower output voltage.
As used herein, “soft start function” refers to a feature that allows electrical components to gradually increase their power consumption when starting, rather than immediately drawing full operating power.
As used herein, “brushless DC (BLDC)” refers to a type of electric motor that uses electronic commutation rather than mechanical brushes to control the power distribution to the motor.
Referring to FIG. 1, illustrated is a circuit diagram of an air conditioning system 100 for a cabin of a locomotive, in accordance with an embodiment of the present disclosure. The air conditioning system 100 is designed to operate directly from a direct current (DC) power source of the locomotive without requiring conversion to alternating current (AC), thereby eliminating potential failure points and power losses associated with traditional power conversion components.
As shown in FIG. 1, the locomotive implements a locomotive power supply 10 including a three-phase auxiliary generator 12 that generates three-phase alternating current (AC) power, typically at around 55 volts AC (55VAC). The three-phase auxiliary generator 12 is typically configured to operate across a range of speeds, such as from approximately 775 to 2888 rpm, with a frequency range of approximately 26 Hz to 97 Hz, and is typically rated at approximately 18 kW of power output. This three-phase AC power from the auxiliary generator 12 is input to a bridge rectifier 14 that converts the three-phase AC power to DC power. The bridge rectifier 14 typically receives an input voltage of approximately 55VAC and outputs a nominal DC voltage of approximately 74 volts DC (74VDC). The output of the bridge rectifier 14 is connected to positive and negative bus bars 16, 18 of the locomotive, which distribute the DC power to various systems, including the air conditioning system 100. The bus bars 16, 18 are typically connected to a battery 20 of about 72V for the locomotive engine, which provides backup power to auxiliary load (without back power to air conditioning system).
The air conditioning system 100 includes a DC power input 102 configured to receive DC power directly from the bridge rectifier 14 of the locomotive power supply 10 through the bus bars 16, 18. The DC power input 102 serves as the interface between the locomotive’s electrical system and the air conditioning system 100. The DC power input 102 is designed to handle the voltage and current requirements of the air conditioning system 100 and to accommodate the characteristics of the locomotive’s DC power supply, including any voltage fluctuations or transients that may occur during locomotive operation.
The air conditioning system 100 further includes a reverse polarity protection circuit 104 coupled to the DC power input 102. The reverse polarity protection circuit 104 is configured to protect the electrical components in the air conditioning system 100 if the polarity of the applied voltage is reversed. This protection is particularly important in locomotive applications, where maintenance activities or electrical system issues could potentially lead to incorrect connections or polarity reversals. The reverse polarity protection circuit 104 prevents damage to sensitive electronic components in the air conditioning system 100 by blocking current flow when reverse polarity is detected, thereby ensuring the longevity and reliability of the system in harsh operating environments.
In various embodiments, the reverse polarity protection circuit 104 may be implemented using various techniques and components. For example, the reverse polarity protection circuit 104 may include a diode connected in series with the power input, which allows current to flow only in the correct direction while blocking current in the reverse direction. Alternatively, the reverse polarity protection circuit 104 may use a MOSFET-based solution that provides lower power losses compared to a diode-based solution. The specific implementation of the reverse polarity protection circuit 104 may be selected based on factors such as the expected current levels, power loss considerations, and space constraints of the application.
The air conditioning system 100 also includes a capacitor bank 106 coupled to the output of the reverse polarity protection circuit 104. The capacitor bank 106 is configured to process the received DC power to reduce repulsions in the power supply. In the context of locomotive applications, “repulsions” refer to voltage and current fluctuations, ripples, or transients in the DC power supply that can occur due to various factors, including variations in the auxiliary generator’s output, load changes, or electrical noise in the locomotive’s electrical system. These repulsions can adversely affect the performance and reliability of electronic components in the air conditioning system 100 if not properly managed.
The capacitor bank 106 consists of multiple capacitors arranged in a configuration that optimizes the filtering performance and voltage handling capability of the bank. The capacitors in the capacitor bank 106 are sized and selected to effectively reduce the repulsions present in the locomotive’s DC power supply, particularly at idle engine speeds when repulsions can be more pronounced. The capacitor bank 106 smoothens the DC power by absorbing and releasing energy as needed to compensate for voltage fluctuations, effectively acting as an energy buffer that provides a more stable DC voltage to the downstream components of the air conditioning system 100. The design of the capacitor bank 106 takes into account factors such as the expected magnitude and frequency of repulsions, the power requirements of the air conditioning system 100, and the physical constraints of the installation environment.
Connected to the capacitor bank 106 is a pre-charge circuit 108. The pre-charge circuit 108 is configured to gradually charge the capacitor bank 106 before activating the system loads. When a large capacitor bank such as the capacitor bank 106 is suddenly connected to a power source, it can draw a very large initial current, known as an inrush current, as it charges. This inrush current can stress or damage components in both the air conditioning system 100 and the locomotive’s electrical system. The pre-charge circuit 108 prevents these issues by limiting the initial current flow to the capacitor bank 106 when the air conditioning system 100 is powered on.
The pre-charge circuit 108 typically includes current-limiting components such as resistors or thermistors that are temporarily placed in series with the capacitor bank 106 during the initial charging phase. Once the capacitor bank 106 has charged to a sufficient level, these current-limiting components are bypassed, allowing full current flow during normal operation. The operation of the pre-charge circuit 108 may be controlled by a control unit (as discussed later in detail) of the air conditioning system 100, which monitors the charging status of the capacitor bank 106 and manages the transition from the pre-charge state to the normal operating state. The pre-charge circuit 108 is designed to provide protection against inrush currents while minimizing the impact on the start-up time of the air conditioning system 100.
In some embodiments, the pre-charge circuit 108 is configured to gradually increase current flow to the capacitor bank 106 to limit inrush current when the air conditioning system 100 powers on, based on system load conditions. This adaptive approach allows the pre-charge circuit 108 to optimize the charging process based on factors such as the initial state of charge of the capacitor bank 106, the available power from the locomotive’s DC supply, and the specific requirements of the air conditioning system 100 at start-up. By tailoring the pre-charge process to the actual conditions, the pre-charge circuit 108 provides effective protection while minimizing unnecessary delays in system availability.
The air conditioning system 100 further includes a DC-DC buck converter 110 coupled to the capacitor bank 106. The DC-DC buck converter 110 is configured to convert the input DC power, typically at around 74VDC, to a lower DC voltage, such as 24VDC, for operating low voltage components in the air conditioning system 100. This voltage conversion is necessary because different components within the air conditioning system 100 may have different voltage requirements, and providing a dedicated lower voltage supply for certain components can improve overall system efficiency and reliability.
The DC-DC buck converter 110 uses switching technology to efficiently step down the voltage while minimizing power losses. Unlike linear voltage regulators that dissipate excess power as heat, the DC-DC buck converter 110 achieves high efficiency by transferring power from input to output with minimal losses, typically achieving efficiency rates of 85% to 95% depending on the specific design and operating conditions. The DC-DC buck converter 110 is designed to handle the expected load variations of the low voltage components and to maintain a stable output voltage despite fluctuations in the input voltage from the locomotive’s DC power supply. Additionally, the DC-DC buck converter 110 may include protective features such as overcurrent protection, thermal shutdown, and output overvoltage protection to ensure safe and reliable operation under various conditions.
The air conditioning system 100 further includes a DC compressor 112 coupled to the capacitor bank 106. The DC compressor 112 is an automotive grade 74VDC electronically commutated compressor configured to provide variable cooling capacity and operate directly using the processed DC power from the capacitor bank 106. This direct use of DC power represents a significant departure from conventional locomotive cabin air conditioning systems, which typically require the DC power to be converted to AC power to operate standard AC compressors. By eliminating this power conversion stage, the air conditioning system 100 reduces complexity, improves reliability, and increases overall energy efficiency.
The DC compressor 112 in the air conditioning system 100 comprises an electronically commutated DC (eDC) compressor with a built-in soft start function that eliminates the need for an external inverter or drive circuit. The built-in soft start function allows the DC compressor 112 to gradually ramp up its speed when starting, reducing mechanical stress on the compressor components and minimizing the initial current surge. This feature is particularly important in locomotive applications, where the electrical system may have limited capacity to handle large current surges. The electronic commutation in the DC compressor 112 uses electronic circuit to control the current flow through the motor windings, providing precise control over the compressor’s operation without the need for mechanical commutation components that are subject to wear.
The DC compressor 112 is capable of operating at variable speeds to match the cooling requirements of the locomotive cabin. This variable capacity capability allows the air conditioning system 100 to efficiently respond to changing cooling demands, which may vary based on factors such as ambient temperature, cabin temperature and locomotive driver comfort settings. The DC compressor 112 can modulate its cooling capacity by adjusting its operating speed, providing the right amount of cooling without unnecessary energy consumption. The control of the DC compressor 112 is managed by the control unit (as discussed in the proceeding paragraphs), which determines the appropriate compressor speed based on various inputs and system parameters.
The air conditioning system 100 also includes at least one DC fan 114 coupled to the capacitor bank 106 through the DC-DC buck converter 110. The at least one DC fan 114 is configured to provide variable cooling airflow and operate directly using the processed DC power from the capacitor bank 106 without requiring conversion to alternating current (AC). Similar to the DC compressor 112, the direct use of DC power by the at least one DC fan 114 eliminates the need for power conversion stages, contributing to the overall simplicity, reliability, and efficiency of the air conditioning system 100.
In the embodiment shown in FIG. 1, the at least one DC fan 114 comprises at least one brushless DC (BLDC) fan and at least one BLDC blower, both configured to operate at variable speeds to provide the variable cooling airflow. The BLDC fan is typically located in the outdoor unit of the air conditioning system 100 and is responsible for moving air across the condenser coil to facilitate heat rejection to the ambient environment. The BLDC blower is typically located in the indoor unit of the air conditioning system 100 and is responsible for circulating conditioned air within the locomotive cabin. Both the BLDC fan and the BLDC blower utilize brushless DC motor technology, which offers advantages such as higher efficiency, reduced noise, longer lifespan, and more precise speed control compared to traditional brushed DC motors.
The BLDC fan and blower in the at least one DC fan 114 are typically designed to operate at a nominal voltage of 24VDC, which is provided by the DC-DC buck converter 110. Operating these fans at a lower voltage than the main system voltage allows for more efficient and quieter operation, as well as compatibility with standard 24VDC fan designs that are widely available in the market. The variable speed capability of the at least one DC fan 114 allows the air conditioning system 100 to adjust the airflow based on the cooling requirements, providing just the right amount of air movement for the current conditions and thereby optimizing energy consumption and comfort.
The air conditioning system 100 further includes a control unit (not shown in the circuit diagram of FIG. 1) configured to regulate operation of the DC compressor 112 and the at least one DC fan 114 by adjusting the variable cooling capacity and the variable cooling airflow. The control unit serves as the central intelligence of the air conditioning system 100, monitoring various system parameters and environmental conditions, processing this information according to control algorithms, and generating control signals for the various components of the system. The control unit typically includes a microcontroller or microprocessor, along with associated circuitry for signal conditioning, communication interfaces, and power management.
The control unit receives inputs from various sensors within the air conditioning system 100, which may include temperature sensors for measuring cabin temperature, ambient temperature, refrigerant temperatures at various points in the refrigeration cycle, and other relevant parameters. Based on these inputs and predefined control algorithms, the control unit determines the appropriate operating parameters for the DC compressor 112 and the at least one DC fan 114 to maintain the desired cabin temperature while optimizing energy efficiency.
In various embodiments, the control unit is further configured to adjust the variable cooling capacity and the variable cooling airflow based on at least one of: ambient temperature, cabin temperature, driver comfort settings, and locomotive operating conditions. This adaptive control approach allows the air conditioning system 100 to provide optimal comfort and efficiency across a wide range of operating conditions. For example, the control unit may reduce the cooling capacity during periods of low heat load, such as when the ambient temperature is moderate or when the cabin is lightly occupied, thereby conserving energy. Conversely, the control unit may increase the cooling capacity during periods of high heat load, such as when the ambient temperature is high or when the cabin is fully occupied, to maintain comfortable conditions.
The control unit may also implement various advanced control strategies to enhance the performance and efficiency of the air conditioning system 100. These strategies may include predictive control algorithms that anticipate changes in cooling requirements based on patterns of usage or environmental conditions, adaptive control algorithms that learn and adjust to the specific characteristics of the installation environment, and fault detection and diagnostic algorithms that monitor the system for signs of abnormal operation or impending issues. The control unit may also provide interfaces for maintenance personnel to access system information, adjust settings, and diagnose problems, either through a local user interface or through remote connectivity options.
The air conditioning system 100 of the present disclosure is configured to operate with input DC power having voltage variations between 55V and 90VDC while maintaining stable cooling performance without AC conversion. This wide input voltage range capability is an important feature for locomotive applications, where the actual voltage from the locomotive’s DC power supply may vary significantly depending on factors such as the auxiliary generator’s speed, the state of charge of the locomotive’s batteries, and the overall load on the electrical system. By accommodating this wide range of input voltages, the air conditioning system 100 can provide reliable cooling performance across the full range of locomotive operating conditions, from idle to full power.
In an exemplary embodiment of the air conditioning system 100, the DC compressor 112 is a 72VDC compressor, which is well-matched to the nominal 74VDC power supply from the locomotive. This voltage match minimizes the need for voltage conversion or regulation for the compressor, contributing to the overall efficiency of the system. The at least one DC fan 114 comprises 24V brushless DC (BLDC) condenser fans and blowers, which operate at a lower voltage provided by the DC-DC buck converter 110. This dual-voltage approach allows the air conditioning system 100 to optimize the voltage level for each component based on its specific requirements, balancing performance, efficiency, and compatibility with standard components.
The air conditioning system 100 operates by receiving DC power from the locomotive’s power source through the DC power input 102. The received DC power first passes through the reverse polarity protection circuit 104, which ensures that the power is connected with correct polarity. The protected DC power then flows to the capacitor bank 106 through the pre-charge circuit 108 manages the initial charging of the capacitor bank 106 when the system is powered on, preventing damaging inrush currents, which processes the DC power to reduce repulsions and provide a more stable power source for the downstream components.
From the capacitor bank 106, a portion of the processed DC power flows directly to the DC compressor 112, which operates at the nominal system voltage of approximately 74VDC. Another portion of the processed DC power flows to the DC-DC buck converter 110, which steps down the voltage to approximately 24VDC for the at least one DC fan 114. The control unit monitors various system parameters and environmental conditions, and based on this information, generates control signals for the DC compressor 112 and the at least one DC fan 114 to regulate the cooling capacity and airflow of the air conditioning system 100.
In the refrigeration cycle of the air conditioning system 100, the DC compressor 112 compresses refrigerant gas, raising its pressure and temperature. The hot, high-pressure refrigerant then flows to a condenser (not shown in FIG. 1), where it releases heat to the ambient environment with the assistance of the BLDC condenser fans of the at least one DC fan 114. The refrigerant then passes through an expansion device (not shown), which reduces its pressure and temperature. The cold, low-pressure refrigerant then flows through an evaporator (not shown), where it absorbs heat from the cabin air that is circulated by the BLDC blowers of the at least one DC fan 114. The refrigerant then returns to the DC compressor 112 to repeat the cycle. Throughout this process, the control unit adjusts the speed of the DC compressor 112 and the at least one DC fan 114 to maintain the desired cabin temperature while optimizing energy efficiency.
The air conditioning system 100 utilizes all components with built-in soft start functions instead of controlling them through any external drive. This approach helps to stabilize the input power from the locomotive for the air conditioning system 100. Soft start functions gradually ramp up the current draw when components such as the DC compressor 112 and the at least one DC fan 114 are started, rather than immediately drawing full operating current. This gradual start-up reduces stress on the components themselves, as well as on the locomotive’s electrical system, leading to improved reliability and longevity of the air conditioning system 100.
The built-in soft start functions in the components of the air conditioning system 100 operate independently of each other, but under the coordinated control of the control unit. For example, when the air conditioning system 100 is powered on, the control unit may sequence the start-up of different components to further manage the overall current draw. The control unit might first start the at least one DC fan 114 at a low speed, then gradually increase the fan speed while simultaneously starting the DC compressor 112, which itself would ramp up gradually due to its built-in soft start function. This coordinated approach to system start-up provides additional protection against excessive current draws or voltage dips in the locomotive’s electrical system.
Another aspect of the air conditioning system 100 is its ability to operate in various environmental conditions. Locomotives often operate in diverse climates and weather conditions, from extreme heat to extreme cold, and from dry to humid environments. The air conditioning system 100 is designed to provide reliable cooling performance across this wide range of conditions.
Referring now to FIG. 2, illustrated is a circuit diagram of a conventional air conditioning system 200 for a locomotive cabin, provided for comparative purposes. The conventional air conditioning system 200 is shown connected to the same locomotive power supply 10 as the air conditioning system 100 of FIG. 1, including the three-phase auxiliary generator 12, the bridge rectifier 14, the bus bars 16, 18, and the battery 20. However, the architecture and operation of the conventional air conditioning system 200 differ significantly from those of the air conditioning system 100 of the present disclosure.
The conventional air conditioning system 200 includes a DC-DC boost converter 202 that receives the nominal 74VDC power from the locomotive’s bus bars 16, 18 and boosts it to a higher voltage, typically around 400VDC. This voltage boosting is necessary to provide a suitable input voltage for the inverter 204, which converts the boosted DC voltage to three-phase 220VAC at a frequency of approximately 50Hz for the compressor 206, and single-phase 220VAC for the condenser fan and blower 208. The compressor 206 is typically a standard three-phase AC compressor that requires a three-phase AC power supply for operation, while the condenser fan and blower 208 are typically standard AC fans that require a single-phase AC power supply.
The architecture of the conventional air conditioning system 200 involves multiple power conversion stages between the locomotive’s DC power supply and the air conditioning components. The DC-DC boost converter 202 and the inverter 204 represent two separate power conversion stages, each introducing complexity, potential points of failure, and energy losses to the system. The multiple power conversions are necessary because the conventional air conditioning system 200 utilizes standard AC components such as the compressor 206 and the condenser fan and blower 208, which cannot operate directly from the locomotive’s DC power supply.
The conventional air conditioning system 200 faces several challenges related to the locomotive’s DC power supply. The DC power from the locomotive’s auxiliary generator through the bridge rectifier 14 often contains significant power repulsions, which can deteriorate further when the locomotive operates at lower speeds or idles. These repulsions can stress the electronic components of the DC-DC boost converter 202 and the inverter 204, potentially leading to premature failures. Additionally, the stability of the power conversion stages can be affected by variations in the input power from the locomotive and the load requirements of the air conditioning components, particularly during start-up or changes in operating conditions.
The conventional air conditioning system 200 also typically lacks advanced power conditioning features such as the adequate capacitor bank 106, the reverse polarity protection circuit 104, and the pre-charge circuit 108 of the air conditioning system 100 of the present disclosure. Without these features, the conventional system may be more susceptible to issues related to power quality, polarity errors, and inrush currents. Additionally, the conventional system may not be able to accommodate as wide a range of input voltage variations as the air conditioning system 100 of the present disclosure, potentially leading to operational issues when the locomotive’s DC power supply deviates from its nominal voltage.
Comparing the present air conditioning system 100 (as shown in FIG. 1) with the conventional air conditioning system 200 (as shown in FIG. 2) reveals several advantages of the present disclosure. The air conditioning system 100 eliminates the need for multiple power conversion stages by utilizing DC components that can operate directly from the locomotive’s DC power supply. This elimination of power conversion stages reduces complexity, potential points of failure, and energy losses in the system. The air conditioning system 100 also includes advanced power conditioning features such as the capacitor bank 106, the reverse polarity protection circuit 104, and the pre-charge circuit 108, which enhance the system’s reliability and performance in the challenging electrical environment of a locomotive.
Additionally, the air conditioning system 100 of the present disclosure offers improved control and efficiency using variable-speed DC components such as the DC compressor 112 and the at least one DC fan 114, which can adjust their operation to match the actual cooling requirements. This variable-speed capability, combined with the intelligent control provided by the control unit, allows the air conditioning system 100 to optimize its performance based on factors such as ambient temperature, cabin temperature, driver comfort settings, and locomotive operating conditions.
Furthermore, the air conditioning system 100 of the present disclosure offers advantages in terms of physical size, weight, and installation requirements. By eliminating the need for bulky power conversion components such as the DC-DC boost converter 202 and the inverter 204, the air conditioning system 100 can be more compact and lighter than the conventional air conditioning system 200. This reduction in weight can be particularly advantageous in locomotive applications, where weight constraints may be significant considerations. Additionally, the simpler electrical architecture of the air conditioning system 100 may simplify installation and maintenance procedures, potentially reducing the total cost of ownership over the system’s lifecycle.
While specific embodiments of the air conditioning system for a locomotive cabin have been described, it should be understood that various modifications, adaptations, and variations may be made to the embodiments described herein. For example, while the embodiments described herein focus on cooling applications, the air conditioning system could be adapted to provide heating functionality as well, either through a heat pump configuration or through the addition of electric heating elements. Similarly, while the embodiments described herein utilize specific voltage levels such as 74VDC for the main system and 24VDC for the fans, other voltage levels could be utilized based on the specific requirements of the application and the available power supply from the locomotive.
Additionally, various alternative configurations of the components within the air conditioning system are possible. For example, the capacitor bank could be implemented with different types of capacitors, such as electrolytic capacitors, film capacitors, or hybrid configurations, depending on factors such as cost, size, reliability, and performance requirements. Similarly, the control unit could be implemented using various hardware platforms, from simple microcontrollers to more advanced processors, depending on the complexity of the control algorithms and the interface requirements of the system.
It is to be understood that the present disclosure is not limited to the exact construction and compositions that have been described above and illustrated in the accompanying drawings, and that various modifications, changes, and variations may be apparent from this detailed description without departing from the spirit and scope of the invention as defined in the appended claims. The foregoing description of the specific embodiments reveals the general nature of the present disclosure such that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

Dated 10th day of April, 2025 Ankush Mahajan
Agent for the Applicant (IN/PA-1523)
OF CoreIP Legal Services Pvt. Ltd. , Claims:CLAIMS
WE CLAIM
1. An air conditioning system for a cabin of a locomotive having a direct current (DC) power source, the air conditioning system comprising:
a direct current (DC) power input configured to receive DC power directly from the DC power source of the locomotive;
a capacitor bank coupled to the DC power input and configured to process the received DC power to reduce repulsions;
a DC compressor coupled to the capacitor bank and configured to provide variable cooling capacity and operate directly using the processed DC power without alternating current (AC) conversion;
at least one DC fan coupled to the capacitor bank and configured to provide variable cooling airflow and operate directly using the processed DC power without AC conversion; and
a control unit configured to regulate operation of the DC compressor and the at least one DC fan by adjusting the variable cooling capacity and the variable cooling airflow.
2. The air conditioning system of claim 1, further comprising a reverse polarity protection circuit coupled between the DC power input and the capacitor bank, wherein the reverse polarity protection circuit is configured to protect electrical components in the system if polarity of applied voltage is reversed.
3. The air conditioning system of claim 1, further comprising a pre-charge circuit coupled between the DC power input and the capacitor bank, wherein the pre-charge circuit is configured to gradually charge the capacitor bank before activating system loads to reduce initial current spikes.
4. The air conditioning system of claim 3, wherein the pre-charge circuit is configured to gradually increase current flow to the capacitor bank to limit inrush current when the air conditioning system powers on, based on system load conditions.
5. The air conditioning system of claim 1, further comprising a DC-DC buck converter coupled to the DC power input and configured to convert the input DC power to a lower DC voltage for operating low voltage components in the air conditioning system.
6. The air conditioning system of claim 1, wherein the DC compressor comprises an electronically commutated DC compressor with a built-in soft start function that eliminates the need for an external inverter or drive circuit.
7. The air conditioning system of claim 1, wherein the at least one DC fan comprises at least one brushless DC condenser fan and at least one brushless DC blower, both configured to operate at variable speeds to provide the variable cooling airflow thereby.
8. The air conditioning system of claim 1, wherein the control unit is further configured to adjust the variable cooling capacity and the variable cooling airflow based on at least one of: ambient temperature, cabin temperature, driver comfort settings, and locomotive operating conditions.
9. The air conditioning system of claim 1, wherein the air conditioning system is configured to operate with input DC power having voltage variations between 55V and 90VDC while maintaining stable cooling performance without AC conversion.
10. The air conditioning system of claim 1, wherein the DC compressor is a 72VDC compressor, and wherein the at least one DC fan comprises 24V brushless DC (BLDC) condenser fans.
Dated 10th day of April, 2025 Ankush Mahajan
Agent for the Applicant (IN/PA-1523)
OF CoreIP Legal Services Pvt. Ltd.