Mining machine power conversion system

Abstract

The invention pertains to a method of power conversion in an electric drive system of a mining or construction machine. The method involves receiving an alternating current (AC) voltage from an external power source, boosting and rectifying the received AC voltage, and then reducing the boosted and rectified voltage. The reduced voltage is then galvanically isolated, providing an isolated direct current (DC) voltage for a DC bus of the electric drive system. This method allows for efficient power conversion and management in heavy-duty machinery used in mining and construction applications. A power conversion unit implementing the method and an electric mining and / or construction machine comprising such a power conversion unit are also described.

Description

113724Mining Machine Power Conversion SystemField

[0001] The technology pertains to the field of electrical engineering, specifically focusing on power conversion systems. It is particularly relevant to the mining industry, where such systems are utilized in mining machines for various operations including drilling, excavation, and construction.Background

[0002] Mining and / or construction machines, such as rock drilling rigs, are used for several purposes, such as exploration drilling, which aims to identify the location and quality of a mineral, and production mining and quarrying, used in the productioncycle for mining or construction. Other application areas are road construction and structural construction.

[0003] Traditionally, mining and / or construction machines have been driven by combustion engines. However, in recent years, growing environmental concerns have driven the mining industry to reducing or phasing out the traditional combustion engines to reduce and eventually stop the emission of greenhouse gases from fossil fuels.

[0004] In the mining industry the solution is focused on electrification of the machine park. Electrification has some challenges, mainly in the capacity of today’s electric batteries, especially in a rock drilling rig, where the demands for power and energy are high during rock drilling. This is solved in that the rock drilling rig can be connected to an external electrical network when performing its rock drilling work cycle.

[0005] The prior art in this context pertains to the power conversion systems used in electric mining and / or construction machines. These systems traditionally rely on an on-board passive voltage conversion device, such as a transformer, to step down the high voltage Alternating Current (AC) received directly from an external electrical power grid. The output AC voltage from the transformer is then converted to a Direct Current (DC) voltage, using an AC-DC converter, which is used to charge the onboard battery storage, such as an ultracapacitor bank.113724

[0006] While these transformers serve the purpose of stepping down the high voltage AC power, they present several challenges. One of the primary issues is the large size and weight of the transformers. The substantial iron cores and copper windings used in these transformers contribute significantly to their size and weight. This not only increases the overall volume required for the electric mining machine, making it less efficient in terms of space utilization, but also adds to the total weight of the machine. This can negatively impact the machine's mobility and energy efficiency. The heavy weight can also lead to increased wear and tear on the machine's components and higher energy consumption during operation.

[0007] Another issue arises when a lower voltage is used on the cable reel with the same amount of power draw. This increases the size and weight of the cable reel, requiring either a larger cable reel or a reduction in the length of the cable. Both scenarios are undesirable as they either increase the machine's size and weight or limit its operational range.

[0008] In summary, the prior art presents significant challenges in terms of the size, weight, and efficiency of power conversion systems in electric mining machines. These challenges stem from the use of large and heavy transformers for voltage conversion and the limitations associated with using lower voltages on the cable reel.Summary

[0009] An object of the present invention is to provide a power conversion unit in which the problems of prior art solutions are eliminated or at least mitigated. This particularly relates to the size and weight of the unit, mainly relating to the transformer.

[0010] According to a first aspect of the disclosure, a method of converting power in an electric drive system of an electrically powered mining and / or construction machine is provided. The method comprises receiving an AC voltage from an external power source, boosting and rectifying the received AC voltage, bucking the boosted and rectified voltage from the external power source, and galvanically isolating the bucked voltage. This process thereby provides an isolated DC voltage for a DC bus of the electric drive system. The advantage of this method is that it113724 ensures a stable and isolated DC voltage supply, which is for the reliable operation of the electric drive system in harsh mining and construction environments.

[0011] Optionally in some examples, the method comprises the additional step of further bucking the galvanically isolated voltage before being provided to the DC bus of the electric drive system. This additional step allows for finer control of the voltage levels, ensuring that the voltage supplied to the DC bus is precisely tailored to the operational requirements of the electric drive system. The advantage of this step is that it enhances the efficiency and adaptability of the power conversion process, making the system more versatile for different operational scenarios.

[0012] Optionally in some examples, the step of galvanically isolating the bucked voltage comprises switching the bucked voltage at a predetermined frequency, sending the switched voltage to a primary winding of a transformer, and rectifying a voltage received at a secondary winding of the transformer. This method ensures that the voltage is not only isolated but also converted efficiently through high- frequency switching, which reduces the size and weight of the transformer. The advantage of this approach is that it allows for a more compact and lightweight design, which is beneficial for mobile mining and construction machines.

[0013] Optionally in some examples, the predetermined frequency is above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz. Operating at such high frequencies allows for the use of smaller and more efficient transformer and other components, which contributes to the overall reduction in size and weight of the power conversion system. The advantage of this high-frequency operation is that it significantly improves the power density and efficiency of the system, making it more suitable for demanding applications in mining and construction.

[0014] According to a second aspect of the disclosure, a power conversion system for a mining and / or construction machine connectable to an external power source and comprising an electric drive system is provided. The electric drive system comprises a power conversion unit that includes a voltage boost stage connectable to the external power source and configured to boost incoming AC voltage from the external power source, a first buck stage connected to the voltage boost stage and configured to buck voltage from the voltage boost stage, and an isolation stage113724 connected to the first buck stage and connectable to a bus of the electric drive system and configured to galvanically separate the bus from the external power source. The advantage of this system is that it provides a comprehensive solution for converting and managing power in an electric drive system, ensuring stable and isolated DC voltage supply for various operational needs.

[0015] Optionally in some examples, the power conversion system comprises a second buck stage connected to the isolation stage and configured to buck voltage from the isolation stage. This additional buck stage allows for further refinement of the voltage levels, ensuring that the voltage supplied to the bus is optimal for the specific requirements of the electric drive system. The advantage of this additional stage is that it enhances the flexibility and precision of the power conversion process, making the system more adaptable to different operational conditions.

[0016] Optionally in some examples, the isolation stage comprises a switched DC- to-DC converter, comprising a transformer, wherein the switched DC-to-DC converter is adapted for switching above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz. This high-frequency switching allows for the use of smaller and more efficient transformer, which reduces the overall size and weight of the power conversion system. The advantage of this high-frequency operation is that it improves the power density and efficiency of the system, making it more suitable for mobile and space-constrained applications in mining and construction.

[0017] Optionally in some examples, the isolation stage is configured to separate the vehicle's electrical network from the grid and protect against high voltage faults. This configuration ensures that the vehicle's electrical systems are protected from potential faults and surges in the external power grid, enhancing the safety and reliability of the electric drive system. The advantage of this protective feature is that it provides an additional layer of safety, ensuring that the vehicle's electrical systems remain operational and protected in the event of grid-related issues.

[0018] Optionally in some examples, the isolation stage comprises a transformer which is adapted for switching above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz.113724

[0019] Optionally in some examples, the power conversion unit further comprises a second buck stage connected to the isolation stage and configured to buck voltage from the isolation stage.

[0020] According to a third aspect of the disclosure, an electrically powered mining and / or construction machine is provided. The machine comprises a power conversion unit that includes a voltage boost stage connectable to the external power source and configured to boost incoming AC voltage from the external power source, a first buck stage connected to the voltage boost stage and configured to buck voltage from the voltage boost stage, and an isolation stage connected to the first buck stage and connected to a bus of the electric drive system and configured to galvanically separate the bus from the external power source. The machine further comprises an electric drive unit, a bus interconnecting an output of the power conversion unit and an input of the electric drive unit, and a control unit adapted to control the power conversion unit to perform the method according to any of the previously described methods. The advantage of this machine is that it integrates a sophisticated power conversion system with an electric drive unit, providing a reliable and efficient solution for electrically powered mining and construction operations.

[0021] Optionally in some examples, the isolation stage comprises a transformer which is adapted for switching above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz. This high-frequency switching capability allows for the use of smaller and more efficient transformer, contributing to the overall reduction in size and weight of the power conversion system. The advantage of this feature is that it enhances the power density and efficiency of the machine, making it more suitable for mobile and space-constrained applications in mining and construction.

[0022] Optionally in some examples, the power conversion unit further comprises a second buck stage connected to the isolation stage and configured to buck voltage from the isolation stage. This additional buck stage allows for further refinement of the voltage levels, ensuring that the voltage supplied to the bus is optimal for the specific requirements of the electric drive system. The advantage of this additional stage is that it enhances the flexibility and precision of the power conversion process, making the system more adaptable to different operational conditions.113724

[0023] According to a fourth aspect of the disclosure, a non-transitory computer- readable source medium that stores a program configured to execute the method of any one of the previously described methods in an electrically powered mining and / or construction machine is provided. The advantage of this aspect is that it allows for the implementation of the power conversion method through software, providing a flexible and upgradable solution for managing power in electrically powered mining and construction machines.

[0024] According to a fifth aspect of the disclosure, a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of the previously described methods in an electrically powered mining and / or construction machine is provided. The advantage of this aspect is that it enables the automation and optimization of the power conversion process through software, enhancing the efficiency and reliability of the electric drive system in mining and construction applications.Brief Description of the Drawings

[0025] Examples are described in more detail below with reference to the appended drawings.Figure 1 shows a schematic view of a mining and / or construction machine in the form of a surface drilling rig.Figure 2 shows a simplified block diagram of an exemplary electric drive system in a mining and / or construction machine.Figure 3 shows a block diagram of a power conversion unit with an AC to DC boost stage, a DC to DC buck stage, and a DC to DC isolation stage.Figure 4 shows a block diagram of a power conversion unit with an AC to DC boost stage, a first DC to DC buck stage, a DC to DC isolation stage, and a second DC to DC buck stage.Figure 5a shows a design of the AC to DC boost stage.Figure 5b shows a design of the first DC to DC buck stage.113724Figure 5c shows a design of the DC to DC isolation stage.Figure 5d shows a design of the second DC to DC buck stage.Detailed description

[0026] The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.

[0027] Fig. 1 shows a schematic representation of a mining and / or construction machine in the form of a mining machine or rock drilling rig, generally designated 2. The rock drilling rig 2 comprises a carriage 4 and a rock drill machine 6 attached to the front of the carriage 4. The rock drilling machine 6 is arranged on and connected to the carriage 4 by means of a boom 8, so that the rock drilling machine 6 can be arranged in different positions in relation to the carriage 4 and to the rock to be drilled. Together, the carriage 4, the rock drilling machine 6 and the boom 8 form the main part of the rock drilling rig 2. The carriage 4 is further provided with propulsion means 9, such as wheels or continuous track and propulsion equipment.

[0028] The rock drilling rig 2 further comprises an electric drive system 100, which is connectable to an external grid via a cable interface 12. The rock drilling rig 2 is provided with operative power from either an external energy source, not shown in Fig. 1 , via the cable interface 12, or an internal energy source comprised in the electric drive system 100, such as an electric battery, a super capacitor, or a fuel cell, or a combination thereof. The cable interface 12 may incorporate various safety features, such as overcurrent protection, surge protection, and grounding mechanisms, to safeguard the machine and operators from electrical hazards.

[0029] Operative power is power that either powers the propulsion means 9 and / or the rock drilling machine 6. When the rock drilling rig 2 is operated, a control unit of the electric drive system 100 is configured to selectively control operating power from the external energy source or the internal energy source, as will be described below. A work cycle normally comprises a plurality of work tasks. The control unit is further configured to selectively charge the internal energy source with energy from the external electrical source, as will be described below.113724

[0030] The mining and / or construction machine 2 has been described as a rock drilling rig, but it may also be a production, exploration, excavation, and / or construction mining rig for surface and underground applications. The mining and / or construction machine 2 has an electric drive system 100 as a component.

[0031] Figure 2 provides a simplified block diagram of a typical electric drive system 100 integrated into a mining and / or construction machine 2. This illustration aims to present a clear and concise overview of the system's architecture and the interconnection of its primary components, emphasizing the functional relationship between the invention and the broader system it operates within.

[0032] The diagram shows the electric drive system 100 as a network of interconnected components, each playing a role in the system's overall operation. The external power source 10, representing an external electrical grid, supplies power to the system. This power is then channeled through the cable interface 12, which serves as the connection point between the external power source 10 and the machine's internal electrical system. The power conversion unit 200, a central element of the invention, receives the incoming power and converts it into a suitable form for the electric drive unit 110. A bus 104 acts as the primary conduit for electrical power distribution within the system, connecting the power conversion unit 200 to the electric drive unit 110. The DC voltage present on the DC bus 104 possesses specific characteristics that are crucial for the proper operation of the electric drive system 100. These characteristics include the voltage level, ripple, and current capacity.

[0033] Finally, a control unit 106 oversees and regulates the operation of the entire system, ensuring optimal performance and safety. The control unit 106 may be a component of the electric drive system 100 but may alternatively be provided externally of the electric drive system 100.

[0034] This figure effectively illustrates how the invention, embodied in the power conversion unit 200, seamlessly integrates into a complex electromechanical system. It highlights the system's reliance on the invention for efficient power conversion and distribution, enabling the mining and / or construction machine 2 to perform its intended tasks.113724

[0035] The electric drive unit 110 is a component of the electric drive system 100. The electric drive unit 110 may convert electrical power to mechanical power for different functions. For example, the electric drive unit 110 may be an electric motor adapted to drive a load device in the form of a compressor, or to drive a load in the form of one or more hydraulic pumps.

[0036] The power conversion unit 200 is a component of the electric drive system 100 and may have a preferred input voltage of about 1000 V AC. The power conversion unit 200 according to the invention may reduce the size and weight of the electric mining machine, creating a more desirable product for mines to use. Smaller machines are easier to operate, transport, and service. The power conversion unit 200 converts high voltage AC power from the external power source 10 to a stable DC voltage suitable for the mining machine's operations performed by the electric drive unit 110 and other components. The power conversion unit 200 comprises a voltage boost stage 210, a first buck stage 220, an isolation stage 230, and optionally a second buck stage 240, as will be described below with reference to Figures 3 and 4.

[0037] Figure 3 provides a block diagram representation of the power conversion unit 200, detailing its key functional stages. This illustration aims to provide a deeper understanding of the power conversion process by breaking down the unit into its constituent stages and highlighting the flow of power through the system. The figure emphasizes the sequential operation of these stages, illustrating how each stage contributes to the overall functionality of the power conversion unit 200.

[0038] The diagram depicts the power conversion unit 200 as a series of interconnected stages, each responsible for a specific aspect of power conversion. An AC to DC boost stage 210 receives the incoming AC voltage from the external power source 10 and boosts it to a higher DC voltage level. This boosted DC voltage is then fed into a DC to DC buck stage 220, which reduces the voltage to a lower DC level suitable for the subsequent stage. The DC to DC isolation stage 230 then galvanically isolates the bucked DC voltage, ensuring electrical separation between the input and output sides of the power conversion unit 200. This isolation is crucial for safety and protection of the downstream electrical components.113724

[0039] This figure effectively illustrates the step-by-step power conversion process within the power conversion unit 200, highlighting the role of each stage in transforming the incoming AC voltage into a usable DC voltage for the electric drive system 100. It emphasizes the importance of voltage boosting, bucking, and isolation in achieving efficient and reliable power conversion for the mining and / or construction machine 2.

[0040] The voltage boost stage 210 is a component of the power conversion unit 200 and is preferably designed to boost to a voltage range of 1800 - 2200 V DC, most preferably to about 2000 V DC. The voltage boost stage 210 boosts the incoming voltage from AC to a stable DC voltage. For instance, for 1000 V AC this corresponds to 1633 V, add in minimum boost factor and safety factor and that changes to 2000 V. The voltage boost stage 210 enables the conversion of AC voltage to a stable DC voltage, which is necessary for downstream DC-DC conversion stages. In addition, the voltage boost stage 210 provides the flexibility to handle a broad range of input voltages, making the system adaptable to different power grid conditions. In some configurations, the voltage boost stage 210 may include a three phase boost stage with three legs, each with two switches, inductors on incoming lines and a stabilizing capacitor, as will be described in more detail below with reference to Figure 5a.

[0041] The first buck stage 220 is a component of the power conversion unit 200.The first buck stage 220 is connected to an output of the voltage boost stage 210. The voltage is preferably bucked to the range of 800 - 1000 V DC, preferably to 920 V DC. The first buck stage 220 bucks the voltage so that it can be received by the switching isolation stage 230 and may include a capacitor, an inductor, a rectifier, and a power switch, such as an nmos switch, as will be described in more detail below with reference to Figure 5b.

[0042] The isolation stage 230 is a component of the power conversion unit 200. The isolation stage 230 is connected to the first buck stage 220. The isolation stage 230 exists as a requirement so that the electric mining and / or construction machine 2 is part of a separate network from the grid and is protected in case of high voltage faults from other devices on the grid to the vehicle. The isolation stage 230 separates the vehicle's electrical network from the grid and protects against high voltage faults.In this embodiment, the isolation stage 230 is a switched DC-to-DC converter. Due to the higher frequency seen in this device than would normally be seen in a 50hz transformer, the transformer is significantly smaller. The isolation stage 230 may include a capacitor, a diode, a power switch, such as an nmos switch, an inductor, and a transformer, as will be described in more detail below with reference to Figure 5c. The transformer preferably has a turn ratio of 1 :1 .

[0043] Figure 4 provides a block diagram representation of an alternative embodiment of the power conversion unit 200, detailing its internal structure and the interconnection of its key functional stages. This alternative embodiment is similar to the one described above with reference to Figure 3, but it also comprises a second buck stage 240.

[0044] The second buck stage 240 is an integral component of an alternative embodiment of the power conversion unit 200, playing a role in regulating the voltage supplied to the electric drive system 100. This stage is positioned after the isolation stage 230 to further reduce the DC voltage to a level suitable for the electric drive unit 110 and other components within the mining and / or construction machine 2. The second buck stage 240 contributes to the system's efficiency by ensuring that the voltage supplied to the electric drive unit 110 is optimized for its operational requirements. This optimized voltage level maximizes the performance and efficiency of the electric drive unit 110, ultimately enhancing the overall energy efficiency of the mining and / or construction machine 2. The second buck stage 240 comprises several key components, each contributing to its voltage regulation function. These components may include a capacitor, an inductor, a diode, and a power switch, such as an nmos switch, all working in concert to achieve precise voltage control, as will be described in more detail below with reference to Figure 5d. The specific configuration and arrangement of these components may vary depending on the specific design requirements of the power conversion unit 200 and the intended application of the mining and / or construction machine 2. In essence, the second buck stage 240 acts as a fine-tuning mechanism within the power conversion unit 200, ensuring that the final DC voltage delivered to the electric drive system 100 is precisely regulated to meet the demands of the mining and / or construction machine 2 during its operation.

[0045] Figure 5a provides a detailed schematic diagram of the boost stage 210, a critical component within the power conversion unit 200 of the electric drive system 100 for a mining and / or construction machine 2. This stage is responsible for receiving the incoming AC voltage from the external power source 10 and boosting it to a higher DC voltage level. This conversion is essential for ensuring the efficient operation of the subsequent stages within the power conversion unit 200.

[0046] The schematic diagram in Figure 5a illustrates the arrangement of electrical components within the AC to DC boost stage 210. In the shown embodiment, the first boost stage 210 is a three phase boost stage with three legs 212a-c provided between positive and negative, each leg with two power electronic switches, with inductors 214a-c on incoming lines connected to a mid-point of a respective leg 212a-c, and a stabilizing capacitor 216 provided between positive and negative.

[0047] Figure 5b provides a detailed schematic diagram of the first DC to DC buck stage 220, another essential stage within the power conversion unit 200. This stage is positioned after the AC to DC boost stage 210 and is responsible for reducing the boosted DC voltage to a lower level suitable for the subsequent isolation stage 230. This voltage reduction is crucial for ensuring the efficient and safe operation of the isolation process.

[0048] The schematic diagram in Figure 5b illustrates a specific arrangement of electrical components within the first DC to DC buck stage 220. The diagram shows the interconnection between various components, including a capacitor 228 provided for voltage smoothing, an inductor 226 for current smoothing, a rectifier 224 between positive and negative, and a power electronic switch in the form of an nmos switch 222, each contributing to the overall functionality of the first DC to DC buck stage 220.

[0049] Figure 5c provides a detailed schematic diagram of the DC to DC isolation stage 230, a critical stage within the power conversion unit 200. This stage is responsible for galvanically isolating the bucked DC voltage received from the preceding first DC to DC buck stage 220. Galvanic isolation is essential for ensuring electrical separation between the input and output sides of the power conversion unit 200, enhancing safety, and protecting downstream components from voltage surgesor faults. This isolation prevents the propagation of electrical disturbances between different parts of the system, ensuring reliable operation and safeguarding sensitive electronics. The schematic diagram in Figure 5c illustrates the specific arrangement of electrical components within the DC to DC isolation stage 230, highlighting the configuration required for achieving effective galvanic isolation. The diagram shows the interconnection between various components, including a capacitor 238 stabilizing the voltage from the DC to DC isolation stage 230, a diode 237, a power electronic switch in the form of an nmos power switch 236, an inductor 234, and a transformer 232, each contributing to the overall functionality of this stage. This detailed illustration of the DC to DC isolation stage 230 in Figure 5c helps understanding how the bucked DC voltage is galvanically isolated while maintaining the desired voltage level. The diagram provides insights into the role of each component in the isolation process, emphasizing the importance of this stage in ensuring the safe and efficient operation of the power conversion unit 200 and the overall electric drive system 100.

[0050] The transformer 232 may have a switching frequency above 200 khz, more preferably above 500 khz, most preferably above 700 khz. By switching the current provided to the primary winding of the transformer 232, in combination with reduced voltage provided by the first buck stage 220, the weight and dimensions of the transformer 232 may be reduced. Also, in a preferred embodiment, the transformer 232 has a turn ratio of 1 : 1 .

[0051] Figure 5d provides a detailed schematic diagram of an embodiment of the second DC to DC buck stage 240, an optional stage within the power conversion unit 200, see Figure 4. This stage is positioned after the isolation stage 230 and is responsible for further reducing the DC voltage to a level suitable for the electric drive unit 110 and other components within the mining and / or construction machine 2. This stage ensures that the final DC voltage delivered to the electric drive system 100 is precisely regulated to meet the demands of the mining and / or construction machine 2 during its operation.

[0052] The schematic diagram in Figure 5d illustrates the specific arrangement of electrical components within an embodiment of the second DC to DC buck stage 240. The diagram shows the interconnection between various components: acapacitor 248, an inductor 246, a diode 244, and a power switch in the form of an nmos switch 242, each contributing to the overall functionality of this stage.

[0053] A method of converting power in an electric drive system of an electrically powered mining and / or construction machine will now be described.

[0054] The process begins with receiving an AC voltage from an external power source 10, which serves as the primary electrical supply for the mining and / or construction machine 2. This external power source 10 could be an electrical grid or a dedicated generator, providing the necessary power for the machine's operation. The AC voltage received is typically a high voltage, such as 1000 V AC or higher, suitable for transmission over long distances but requiring conversion for use by the machine's internal systems.

[0055] The connection to the external power source 10 is the initial point of contact for receiving electrical power into the mining and / or construction machine 2. This connection is established through a designated interface, typically a cable interface 12, designed to handle the high voltage AC power supplied by the external source. The cable interface 12 ensures a secure and reliable connection, allowing the machine to draw power safely and efficiently.

[0056] The AC voltage received from the external power source 10 possesses specific characteristics that are crucial for the proper operation of the mining and / or construction machine 2. These characteristics include the voltage level, frequency, and number of phases, preferably three phases.

[0057] The received AC voltage, being in alternating current (AC) form, is unsuitable for direct use by the electric drive system 100, which typically operates on direct current (DC). Therefore, the next step involves boosting and rectifying the AC voltage. Boosting refers to increasing the voltage level, while rectification converts the AC voltage into a DC voltage. This process is handled by the voltage boost stage 210 within the power conversion unit 200.

[0058] The voltage boost stage 210 functionality centers around increasing the voltage level of the incoming AC power to a higher DC voltage. This is achieved through a process that typically involves rectification and voltage boosting.113724Rectification converts the AC voltage into a pulsating DC voltage, which is then smoothed using capacitor 238 to reduce voltage ripples. Voltage boosting then steps up the DC voltage to the desired higher level.

[0059] The voltage boost stage 210 utilizes electronic switches, typically transistors, to control the flow of current and manipulate the voltage levels. These switches are controlled by a control circuit, described above as control unit 106, that monitors the input and output voltages and adjusts the switching frequency and duty cycle to achieve the desired voltage boost. The boosted DC voltage from this stage is then fed into the subsequent stages for further processing and regulation.

[0060] The rectification process is a crucial step in converting the alternating current (AC) voltage received from the external power source 10 into a direct current (DC) voltage suitable for use by the electric drive system 100. This process involves converting the bidirectional AC waveform into a unidirectional DC waveform, essentially allowing the current to flow in only one direction.

[0061] After the AC voltage is boosted and rectified into a DC voltage, it undergoes a bucking process. Bucking, in this context, refers to reducing the voltage level to a more manageable and suitable level for subsequent stages within the power conversion unit 200. This step is crucial to ensure that the voltage levels are compatible with the components in the following stages, particularly the isolation stage 230. The first buck stage 220 is responsible for this voltage reduction process.

[0062] The first buck stage 220 plays a crucial role in regulating the voltage levels within the power conversion unit 200 before the isolation process. Its primary function is to reduce the boosted DC voltage received from the voltage boost stage 210 to a lower, more manageable level suitable for the isolation stage 230. This voltage reduction is essential for ensuring the efficiency and safety of the isolation process, as well as for protecting the downstream components from excessive voltage levels.

[0063] The first buck stage 220 achieves this voltage reduction through a process called buck conversion, which involves controlling the flow of current through an inductor 226. By rapidly switching the current flow on and off at a high frequency, the first buck stage 220 effectively controls the amount of energy transferred to the output, thereby regulating the output voltage.113724

[0064] The specific voltage level to which the first buck stage 220 reduces the boosted DC voltage is determined by the design parameters of the power conversion unit 200 and the requirements of the isolation stage 230. This stage ensures that the voltage levels are compatible with the isolation components and processes, preventing potential issues and ensuring the smooth operation of the power conversion process. In a preferred embodiment, the voltage is reduced to 800 - 1000 V DC, preferably to 920 V DC.

[0065] Once the voltage is bucked to an appropriate level, it undergoes galvanic isolation. Galvanic isolation is a crucial safety feature that electrically separates two circuits, preventing the flow of direct current between them. In the context of this invention, the isolation stage 230 ensures that the DC power from the external power source 10 is isolated from the DC bus 104 and the electric drive unit 110. This isolation is essential for protecting the system and operators from ground faults and other electrical hazards. It also helps to reduce noise and interference between different parts of the electrical system.

[0066] This isolation is particularly important in the context of the mining and / or construction machine 2, where the power conversion unit 200 handles high voltage levels and operates in potentially harsh environments. The isolation stage 230 ensures that any faults or disturbances on the input side, such as voltage surges or ground faults, do not directly impact the output side, protecting the electric drive unit 110 and other sensitive components.

[0067] The galvanic isolation process within the isolation stage 230 relies on the principle of electromagnetic induction, utilizing the transformer 232 to achieve electrical separation between the input and output circuits. This process ensures that there is no direct current path between the two sides, preventing the flow of DC current while still allowing the transfer of power.

[0068] After galvanic isolation, the isolated DC voltage is ready to be supplied to the DC bus 104. The DC bus 104 acts as the primary power distribution network within the electric drive system 100, delivering the isolated DC voltage to various components, including the electric drive unit 110. This stage ensures that the isolated113724DC voltage is readily available for the electric drive unit 110 and other components, enabling the mining and / or construction machine 2 to perform its intended functions.

[0069] The connection to the DC bus 104 ensures that the isolated DC voltage is readily available to the electric drive unit 110 and other components, enabling the mining and / or construction machine 2 to perform its intended functions. The DC bus 104 acts as a central power hub, distributing the converted and isolated DC power to where it's needed within the system.

[0070] While the isolated DC voltage on the DC bus 104 is ready for distribution, it might still be at a higher voltage level than what's required by certain components, particularly the electric drive unit 110. Therefore, a further bucking process is often employed to fine-tune the voltage level to match the specific requirements of the electric drive unit 110. This additional voltage reduction is handled by the second buck stage 240, ensuring that the electric drive unit 110 receives the optimal voltage for efficient and reliable operation.

[0071] The second buck stage 240 plays a role in fine-tuning the voltage level delivered to the electric drive unit 110. While the isolated DC voltage on the DC bus 104 is already regulated, it might still be at a higher voltage level than what's optimally required by the electric drive unit 110 for its specific operating conditions.

[0072] The second buck stage 240 acts as a final voltage regulation stage, further reducing the DC voltage from the DC bus 104 to precisely match the requirements of the electric drive unit 110. This fine-tuning of the voltage level ensures that the electric drive unit 110 receives the optimal voltage for its current operating conditions, maximizing its performance and efficiency. In a preferred embodiment, the voltage received from the isolation stage 230 is further reduced from, in the above example, 920 V DC to 500 - 800 V DC, depending on the operating voltage of the bus 104.

[0073] The second buck stage 240 achieves this voltage regulation using a similar principle as the first buck stage 220, employing a buck converter topology to step down the voltage level. However, the second buck stage 240 is typically designed with tighter voltage regulation capabilities, ensuring that the electric drive unit 110 receives a stable and precisely controlled voltage supply, regardless of fluctuations in the input voltage or load conditions.113724

[0074] The process of bucking the voltage, both in the first buck stage 220 and the second buck stage 240, often involves switching the DC voltage on and off at a high frequency. This switching is controlled by electronic switches, typically transistors, operating at a predetermined frequency. The frequency of this switching is a crucial design parameter that affects the efficiency, size, and cost of the power conversion unit 200. Higher switching frequencies generally lead to smaller and lighter components but might come at the cost of slightly reduced efficiency. The specific switching frequency is chosen based on a trade-off between these factors and the overall performance requirements of the system.

[0075] The voltage level refers to the magnitude of the electrical potential difference between the positive and negative terminals of the DC bus 104, typically measured in volts (V). This voltage level is determined by the output of the second buck stage 240 and is carefully regulated to meet the specific requirements of the electric drive unit 110 and other connected components.

[0076] Current capacity refers to the maximum amount of current that the DC bus 104 can safely handle without overheating or experiencing damage. This capacity is determined by the physical characteristics of the busbars and conductors used in the DC bus 104 construction and is designed to accommodate the peak current demands of the electric drive unit 110 and other connected components.

[0077] Preferred embodiments of a method of converting power in an electric drive system of an electrically powered mining and / or construction machine, a power conversion system for a mining and / or construction machine, and a mining and / or construction machine comprising such a power conversion system have been described. It will be realized that these can be varied with the scope of the appended claims without departing from the inventive idea. For example, a three-phase external power source have been described as the source providing the electric power. The voltage boost stage could be modified to handle single-phase or two-phase voltage as well.

Claims

Claims1 . A method of converting power in an electric drive system (100) of an electrically powered mining and / or construction machine (2), the method comprising the following steps:- receiving an AC voltage from an external power source (10),- boosting and rectifying the AC voltage from the external power source (10);- bucking the boosted and rectified voltage, and- galvanically isolating the bucked voltage, thereby providing an isolated DC voltage for a DC bus (104) of the electric drive system (100).

2. The method according to claim 1 , comprising the additional step of further bucking the galvanically isolated voltage before being provided to the DC bus (104) of the electric drive system (100).

3. The method according to claim 1 or 2, wherein the step of galvanically isolating the bucked voltage comprises switching the bucked voltage at a predetermined frequency, sending the switched voltage to a primary winding of a transformer, and rectifying a voltage received at a secondary winding of the transformer.

4. The method according to claim 3, wherein the predetermined frequency is above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz.

5. A power conversion unit (200) for a mining and / or construction machine (2) connectable to an external power source (10) and comprising an electric drive system (100), the power conversion unit (200) comprising o a voltage boost stage (210) connectable to the external power source (10) and configured to boost and rectify incoming AC voltage from the external AC power source (10);o a first buck stage (220) connected to the voltage boost stage (210) and configured to buck voltage from the voltage boost stage (210), and o an isolation stage (230) connected to the first buck stage (220) and connectable to a bus (104) of the electric drive system (100) and configured to galvanically separate the bus (104) from the external power source (10).

6. The power conversion unit (200) according to claim 5, comprising a second buck stage (240) connected to the isolation stage (230) and configured to buck voltage from the isolation stage (230).

7. The power conversion unit (200) according to claim 5 or 6, wherein the isolation stage (230) comprises a switched DC-to-DC converter, comprising a transformer (232), wherein the switched DC-to-DC converter is adapted for switching above 200 kHz, more preferably above 500 kHz, and most preferably above 700 kHz8. The power conversion unit (200) according to any of claims 5 to 7, wherein the isolation stage (230) is configured to separate the vehicle's electrical network from the grid and protect against high voltage faults.

9. An electrically powered mining and / or construction machine (2) comprising a power conversion unit (200) comprising- a voltage boost stage (210) connectable to the external power source (10) and configured to boost incoming AC voltage from the external power source (10);- a first buck stage (220) connected to the voltage boost stage (210) and configured to buck voltage from the voltage boost stage (210), and- an isolation stage (230) connected to the first buck stage (220) and connected to a bus (104) of an electric drive system (100) and configured to galvanically separate the bus (104) from the external power source (10), the electrically powered mining and / or construction machine (2) further comprisingan electric drive unit (110),- wherein the bus (104) interconnects an output of the power conversion unit (200) and an input of the electric drive unit (110); and- a control unit (106) adapted to control the power conversion unit (200) to perform the method according to any one of claims 1-4.

10. The electrically powered mining and / or construction machine (2) according to claim 9, wherein the isolation stage (230) comprises a transformer (232) which is adapted for switching above 200 kHz, more preferably above 500 kHz, most preferably above 700 kHz.11 . The electrically powered mining and / or construction machine (2) according to claim 9 or 10, wherein the power conversion unit (200) further comprises a second buck stage (240) connected to the isolation stage (230) and configured to buck voltage from the isolation stage (230).

12. A non-transitory computer-readable source medium that stores a program configured to execute the method of any one of claims 1 to 4 in an electrically powered mining and / or construction machine (2) according to claim 9.

13. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of claims 1 to 4 in an electrically powered mining and / or construction machine (2) according to claim 9.

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