High voltage direct mount power conversion system and method without phase shifting transformer

Abstract

The application provides a high-voltage direct-hanging power conversion system and method without phase-shifting transformer, and relates to the technical field of oil and gas exploitation. The system comprises a plurality of cascaded power units, wherein each power unit comprises a rectifier device and an isolation device; the power units are electrically isolated from each other based on the isolation devices; the input end of the rectifier device is connected with a multi-phase high-voltage alternating current power grid, and the rectifier device is used for rectifying alternating current signals of the high-voltage alternating current power grid into direct current signals; the input end of the isolation device is connected with the output end of the rectifier device, and the isolation device is used for converting the direct current signals into direct current bus voltage signals; the output ends of the isolation devices in the plurality of power units are connected in parallel to form a common direct current bus, and the common direct current bus is used for supplying power to connected loads. Through the fusion architecture of cascaded rectification and high-frequency isolation, the power frequency phase-shifting transformer in the traditional scheme is cancelled, the system volume is effectively reduced, and the driving efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of oil and gas extraction technology, and more specifically, to a high-voltage direct-connect power conversion system and method without a phase-shifting transformer. Background Technology

[0002] Currently, in the field of high-voltage, high-power motor drives (e.g., 10kV input, 6kV output), the mainstream technology is the unit-series multilevel voltage source inverter (also known as a high-high voltage source inverter). Its typical structure usually includes: a phase-shifting transformer: the primary side is connected to a 10kV power grid, and the secondary side has multiple isolated windings (e.g., 5-6 groups per phase), with the phases of each group of windings staggered by a certain angle (e.g., +20°, 0°, -20°) to form multi-pulse rectification. Power units: each secondary winding is connected to a power unit, which internally consists of "diode uncontrolled rectification + common DC bus capacitor + IGBT single-phase inverter bridge". Series output: the output terminals of multiple power units in each phase are connected in series to form a high-voltage AC (e.g., 6kV) direct drive motor. In addition, related fields are also exploring cascaded converters without input transformers, such as modular multilevel converters (MMC) or floating capacitor topologies, but these solutions typically lack electrical isolation and are complex to control, and have not yet been widely applied in the field of high-power fracturing.

[0003] The solution including a phase-shifting transformer has the following drawbacks: **Extremely Large Size and Weight:** The phase-shifting transformer is a power frequency (50 / 60Hz) electromagnetic component. The core and windings account for over 40% of the total system weight, making the equipment bulky and inconvenient for well site relocation and skid mounting. **High Cost:** Multi-winding phase-shifting transformers have complex structures and require high manufacturing precision (the short-circuit impedance of each winding must be strictly consistent). Their cost accounts for approximately 40% of the total cost, making cost reduction through mass production difficult. **Efficiency Loss:** The transformer itself has iron and copper losses, resulting in low overall system efficiency. **Difficult Heat Dissipation:** Dry-type transformers use forced air cooling, which becomes a bottleneck for large capacities, and the fans consume a lot of power and generate high noise. **Limited Functionality:** Diode rectification cannot achieve energy feedback; braking energy can only be consumed through the braking resistor, making it unsuitable for applications requiring rapid braking. **Poor Scalability:** The transformer needs to be custom-designed according to specific voltage / power levels, and cannot be reused between different projects, extending the delivery cycle. While non-isolated cascaded solutions (such as MMC) eliminate the input transformer, they lack electrical isolation, leading to issues like common-mode interference and safety concerns. Furthermore, their complex control and high cost have prevented them from becoming mainstream. Therefore, existing high-voltage, high-power motor drive systems perform poorly and cannot meet practical application requirements. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a high-voltage direct-connect power conversion system and method without phase-shifting transformer, so as to improve the problem of poor drive system performance in the prior art.

[0005] To address the aforementioned issues, in a first aspect, embodiments of this application provide a high-voltage direct-connected power conversion system without a phase-shifting transformer, the system comprising: multiple cascaded power units; Each of the power units includes a rectifier and an isolation device; the power unit is electrically isolated from other power units based on the isolation device. The input terminal of the rectifier is connected to a multiphase high-voltage AC power grid, and the rectifier is used to rectify the AC signal of the high-voltage AC power grid into a DC signal. The input terminal of the isolation device is connected to the output terminal of the rectifier device, and the isolation device is used to convert the DC signal into a DC bus voltage signal. The outputs of the isolation devices in multiple power units are connected in parallel to form a common DC bus, which is used to supply power to the connected loads.

[0006] In the above implementation process, the system comprises multiple cascaded power units, each including corresponding rectifiers and isolation devices. Each power unit is electrically isolated from other cascaded power units based on its isolation devices, achieving a fusion system architecture of cascaded rectification and high-frequency isolation. The input terminals of the rectifiers are connected to the multi-phase high-voltage AC power grid, converting the AC signal from the grid into a DC signal. The input terminals of the isolation devices are connected to the output terminals of the rectifiers, transforming the DC signal output by the rectifiers into a DC bus voltage signal. The output terminals of multiple isolation devices in the power units are connected in parallel to form a common DC bus, which supplies power to the connected loads. The system eliminates the need for a power frequency phase-shifting transformer, effectively reducing system size and improving power supply and drive performance and efficiency. The output voltage of the common DC bus can be flexibly configured as AC (any voltage) or DC, and it features four-quadrant operation, modular hot-swappable design, and multi-source access. It is particularly suitable for high-power scenarios with extremely high requirements for size, efficiency, and reliability, such as oil and gas fracturing, data centers, energy storage, and rail transportation, meeting the usage needs of various high-power scenarios.

[0007] Optionally, the system further includes: multiple inverter units; The input terminals of multiple inverter units are connected in parallel to the common DC bus; Each of the inverter units is used to invert the DC bus voltage signal on the common DC bus into an AC drive signal; The output terminals of multiple inverter units are connected in series to form a high-voltage AC output terminal; wherein, the high-voltage AC output terminal is used to drive the connected AC motor.

[0008] In the above implementation process, in scenarios requiring AC drive, the system can also include multiple inverter units. The inputs of these inverter units are connected in parallel to a common DC bus. Each inverter unit can convert the DC bus voltage signal on the common DC bus into an AC drive signal. The outputs of the multiple inverter units are connected in series to form a high-voltage AC output terminal, which drives the connected AC motor. Furthermore, when the AC motor decelerates, energy can be fed back to the common DC bus through the inverter units, achieving bidirectional energy transfer.

[0009] Optionally, the number m of the inverter units connected in series in the high-voltage AC output terminal is determined according to the output voltage requirement of the corresponding phase winding; the target line voltage in the output voltage requirement is determined based on the scenario requirements; the AC motor includes a multi-phase independent winding motor, and the number of independent segments in each phase winding is equal to the number of independent winding segments.

[0010] In the above implementation process, the number of inverter units connected in series to form the high-voltage AC output terminal is m. That is, the high-voltage AC output terminal is formed by connecting the output terminals of m inverter units in series. The specific value of m can be determined according to the output voltage requirements of the corresponding phase winding. The target line voltage in the output voltage requirement can be selected and determined based on the scenario requirements, such as 3300V, 6000V, or 10kV, etc. The AC motor can include a multi-phase independent winding motor, and the number of independent segments in each phase winding is equal to m. That is, the number of inverter units connected in series m matches the number of winding segments of the AC motor, forming an integrated "driver-motor" structure. This significantly shortens the required output cable length, allowing the inverter unit and the AC motor to be installed close to each other, improving electromagnetic compatibility.

[0011] Optionally, an external power supply interface is provided on the common DC bus; The external power interface is used to connect the common DC bus and external equipment; wherein, the external equipment includes: energy storage equipment or power generation unit.

[0012] In the above implementation process, an external power interface is provided on the common DC bus. The external power interface can connect the common DC bus to one or more external devices with DC power sources, such as energy storage devices and power generation units, so as to realize the energy transfer between the external devices and the common DC bus, thereby achieving charging, energy storage and other effects.

[0013] Optionally, the rectifier includes a single-phase H-bridge topology, and the power switching device in the single-phase H-bridge topology includes an IGBT or a SiC MOSFET.

[0014] In the above implementation process, the rectifier can be configured as a single-phase H-bridge topology. The power switching devices in the single-phase H-bridge topology can include IGBTs or SiC MOSFETs to achieve efficient and independent rectification functions.

[0015] Optionally, the power switching device is an automotive-grade IGBT or a SiC MOSFET.

[0016] In the above implementation process, the power switching devices in the single-phase H-bridge topology can be set as automotive-grade IGBTs or SiC MOSFETs with various voltage specifications, using certified devices to meet the usage requirements of various application scenarios.

[0017] Optionally, the isolation device includes a dual active bridge converter, which includes an input-side H-bridge, an output-side H-bridge, a high-frequency transformer, and a resonant inductor; the dual active bridge converter supports bidirectional energy flow.

[0018] In the above implementation process, the isolation device can be set as a dual active bridge converter. The dual active bridge converter can include multiple devices such as an input-side H-bridge, an output-side H-bridge, a high-frequency transformer, and a resonant inductor to achieve electrical isolation and signal conversion effects. Furthermore, the dual active bridge converter can adopt a phase-shift control strategy, which controls the magnitude and direction of power flow by adjusting the phase difference φ between the drive signals of the input-side H-bridge and the output-side H-bridge, thereby achieving four-quadrant operation and supporting bidirectional energy flow.

[0019] Optionally, the system further includes: a main controller; The main controller is connected to each of the power units and is used to determine the modulation command for each of the power units.

[0020] In the above implementation process, in order to control the operation of multiple power units as a whole, a main controller can be set up in the system. The main controller is connected to each power unit to determine the modulation command to control each power unit.

[0021] Optionally, the power unit may further include a sub-controller; The sub-controller is connected to the main controller via optical fiber communication; The sub-controller connects the rectifier and the isolation device, and is used to control the rectifier and the isolation device to operate based on the modulation command.

[0022] In the above implementation process, to enable independent control of the internal operation of each power unit, a sub-controller can be set in the power unit. The sub-controller and the main controller can be connected via optical fiber communication to improve data transmission efficiency, thereby improving control response efficiency. The sub-controller connects the rectifier and the isolation device, and can control the rectifier and the isolation device to operate based on the modulation commands sent by the main controller, so as to achieve independent control of each power unit.

[0023] Optionally, the main controller is configured with a feedforward control strategy, and the main controller is further configured to: acquire the power demand of the connected load; and adjust the modulation command based on the power demand and the feedforward control strategy.

[0024] In the above implementation process, the main controller is configured with a feedforward control strategy, which can obtain the actual power demand of the load connected to the common DC bus, and adjust the modulation command accordingly based on the power demand and the feedforward control strategy, so that each power unit can achieve its corresponding driving effect.

[0025] Optionally, the multiple power units include redundant units and working units; The main controller is also configured to: determine the working status of each working unit; if it is determined that the working status of any working unit is abnormal, isolate the abnormal working unit within a preset time, start the redundant unit to work, and adjust the working parameters of the normal working unit.

[0026] In the above implementation process, considering the possibility of sudden abnormal situations, multiple power units can be divided into redundant units and working units. The main controller can determine the working status of each working unit. When the working status of any working unit becomes abnormal, the abnormal working unit can be isolated within a preset event, and the shut-down redundant unit can be started to work. Since the working of the working unit has changed, the working parameters of the normal working unit can also be adjusted accordingly to ensure that the entire system can still operate normally in the event of an abnormal situation.

[0027] Secondly, embodiments of this application also provide a high-voltage direct-connection power conversion method without a phase-shifting transformer. The method is applied to the system described in any one of the first aspects above. The system includes: multiple cascaded power units; wherein each power unit includes: a rectifier and an isolation device; the power unit is electrically isolated from other power units based on the isolation device; the input terminal of the rectifier is connected to a multiphase high-voltage AC power grid, and the input terminal of the isolation device is connected to the output terminal of the rectifier. The method includes: The rectifier device rectifies the AC signal from the high-voltage AC power grid into a DC signal. The isolation device converts the DC signal into a DC bus voltage signal. The output terminals of the isolation devices in the multiple power units are connected in parallel to form a common DC bus, which is used to supply power to the connected loads.

[0028] In the above implementation process, the AC signal from the high-voltage AC power grid is rectified into a DC signal by a rectifier, and the DC signal output by the rectifier is converted into a DC bus voltage signal by an isolation device. The output terminals of multiple isolation devices in multiple power units are connected in parallel to form a common DC bus, which can supply power to the connected loads.

[0029] Optionally, the system further includes: a plurality of inverter units; The input terminals of multiple inverter units are connected in parallel to the common DC bus; The method further includes: The inverter unit converts the DC signal on the common DC bus into an AC drive signal. The output terminals of multiple inverter units are connected in series to form a high-voltage AC output terminal; wherein, the high-voltage AC output terminal is used to drive the connected AC motor.

[0030] In the above implementation process, in scenarios requiring AC drive, multiple inverter units can convert the DC bus voltage signal on the common DC bus into an AC drive signal. The outputs of these multiple inverter units are connected in series to form a high-voltage AC output terminal, which drives the connected AC motor. Furthermore, when the AC motor decelerates, energy can be fed back to the common DC bus through the inverter units, achieving bidirectional energy transfer.

[0031] Optionally, the system further includes: a main controller; the main controller is connected to each of the power units, and the main controller is configured with a feedforward control strategy; The method further includes: The main controller determines the modulation command for each power unit; The power requirements of the connected loads are obtained through the main controller; The main controller adjusts the modulation command based on the power requirement and the feedforward control strategy.

[0032] In the above implementation process, in order to control the operation of multiple power units as a whole, a master controller can be set to determine the modulation command for controlling each power unit. Furthermore, the master controller is configured with a feedforward control strategy, which can obtain the actual power demand of the load connected to the common DC bus, and adjust the modulation command accordingly based on the power demand and the feedforward control strategy, so that each power unit can achieve its corresponding driving effect.

[0033] In summary, the embodiments of this application provide a high-voltage direct-connect power conversion system and method without a phase-shifting transformer. It eliminates the need for a power frequency phase-shifting transformer, effectively reducing the system size and improving the power supply and drive effect and efficiency. The output voltage of the common DC bus can be flexibly configured as AC (any voltage) or DC. It has advantages such as four-quadrant operation, modular hot-swappable design, and multi-source access. It is particularly suitable for high-power scenarios with extremely high requirements for size, efficiency, and reliability, such as oil and gas fracturing, data centers, energy storage, and rail transportation, meeting the usage needs of various high-power scenarios. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A schematic diagram of a high-voltage direct-connect power conversion system without a phase-shifting transformer provided in this application embodiment; Figure 2 A detailed structural schematic diagram of a high-voltage direct-connect power conversion system without a phase-shifting transformer provided in this application embodiment; Figure 3 A flowchart illustrating a high-voltage direct-connection power conversion method without a phase-shifting transformer provided in this application embodiment; Figure 4 This is a flowchart illustrating another high-voltage direct-connection power conversion method without a phase-shifting transformer provided in an embodiment of this application.

[0036] Icons: 110-Power unit; 120-High voltage AC grid; 111-Rectifier; 112-Isolation device; 130-Common DC bus; 131-Load; 140-Inverter unit; 141-AC motor; 132-External equipment; 151-Main controller; 152-Sub-controller. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of the embodiments of this application.

[0038] While existing phase-shifting transformer solutions are mature, they suffer from inherent drawbacks such as large size, low efficiency, and limited functionality. Non-isolated cascaded solutions, while eliminating the transformer, sacrifice electrical isolation and control reliability. Therefore, existing high-voltage, high-power motor drive systems are ineffective and cannot meet practical application requirements.

[0039] To address the aforementioned issues, this application provides a high-voltage direct-connect power conversion system and method without a phase-shifting transformer. This eliminates the need for a power frequency phase-shifting transformer, effectively reducing system size and improving power supply and drive performance and efficiency. The output voltage of the common DC bus can be flexibly configured as AC (any voltage) or DC, offering advantages such as four-quadrant operation, modular hot-swappable design, and multi-source access. It is particularly suitable for high-power scenarios with extremely high requirements for size, efficiency, and reliability, such as oil and gas fracturing, data centers, energy storage, and rail transportation, meeting the usage needs of various high-power applications.

[0040] Please see Figure 1 , Figure 1 This is a schematic diagram of a high-voltage direct-connected power conversion system without a phase-shifting transformer provided in an embodiment of this application. The system may include multiple cascaded power units 110.

[0041] Each power unit 110 includes a rectifier 111 and an isolation device 112. Power unit 110 is electrically isolated from other power units 110 based on the isolation device 112. The input terminal of the rectifier 111 is connected to a multi-phase high-voltage AC power grid 120, and the rectifier 111 is used to rectify the AC signal from the high-voltage AC power grid 120 into a DC signal. The input terminal of the isolation device 112 is connected to the output terminal of the rectifier 111, and the isolation device 112 is used to convert the DC signal into a common DC bus voltage signal. The output terminals of the isolation devices 112 in multiple power units 110 are connected in parallel to form a common DC bus 130, which is used to supply power to the connected load 131. The system comprises multiple cascaded power units 110, each including a rectifier 111 and an isolation device 112. Power units 110 are electrically isolated from other cascaded power units 110 based on their isolation devices 112, achieving a fusion system architecture of cascaded rectification and high-frequency isolation. The input of the rectifier 111 is connected to a multi-phase high-voltage AC power grid 120, converting the AC signal from the high-voltage AC power grid 120 into a DC signal. The input of the isolation device 112 is connected to the output of the rectifier 111, converting the DC signal output by the rectifier 111 into a voltage signal for a common DC bus 130. The outputs of multiple isolation devices 112 in the multiple power units 110 are connected in parallel to form a common DC bus 130, which supplies power to the connected load 131.

[0042] Optionally, in scenarios requiring DC drive, the load 131 can be a variety of different types of DC loads.

[0043] Optionally, the output interfaces of multiple isolation devices 112 are uniformly defined to form a standardized common DC bus 130 in parallel. The high-voltage AC power grid 120 can be a multiphase power grid, such as a three-phase power grid containing phases A, B, and C.

[0044] Optionally, the outputs of multiple isolation devices 112 can be connected in parallel to corresponding busbars to form a common DC bus 130. This common DC bus 130 can employ a multi-layer composite busbar structure with stray inductance <50nH. The common DC bus 130 can be equipped with multiple standardized interfaces, each including: DC positive and negative contacts; an optical fiber communication interface (for communication with the access unit); a liquid cooling interface (for connection to a cooling system); and an electronic tag identification contact (for automatic identification of the access module type). The mechanical dimensions and electrical definitions of the interfaces are completely consistent across all structures, supporting plug-and-play and hot-swapping. The voltage rating of the common DC bus 130 can be configured according to the voltage withstand capability of the power unit 110 devices and system requirements, preferably ranging from 600V to 1500V, with 800V being particularly preferred to match the optimal operating point of 1200V automotive-grade devices (with a 40% voltage margin).

[0045] It should be noted that the system does not require a power frequency phase-shifting transformer, which effectively reduces the system size and improves the power supply and drive effect and efficiency. The output voltage of the common DC bus 130 can be flexibly configured as AC (any voltage) or DC. It has the advantages of four-quadrant operation, modular hot-swappable, and multi-source access. It is particularly suitable for high-power scenarios with extremely high requirements for size, efficiency and reliability, such as oil and gas fracturing, data centers, energy storage, and rail transit, and meets the usage needs of a variety of high-power scenarios.

[0046] It should be noted that the number of various units and devices in the multiple figures of this application is only illustrative and does not impose specific limitations on the number.

[0047] Optionally, please refer to Figure 2 , Figure 2 This is a detailed structural diagram of a high-voltage direct-connected power conversion system without a phase-shifting transformer provided in an embodiment of this application. In scenarios with AC drive requirements, the system may also include: multiple inverter units 140.

[0048] In this system, the input terminals of multiple inverter units 140 are connected in parallel to a common DC bus 130. Each inverter unit 140 is used to invert the voltage signal of the common DC bus 130 into an AC drive signal. The output terminals of the multiple inverter units 140 are connected in series to form a high-voltage AC output terminal, which is used to drive the connected AC motor 141. Alternatively, the system may also include multiple inverter units 140, with their input terminals connected in parallel to the common DC bus 130. Each inverter unit 140 can invert the voltage signal of the common DC bus 130 into an AC drive signal. The output terminals of the multiple inverter units 140 are connected in series to form a high-voltage AC output terminal, which drives the connected AC motor 141 to operate.

[0049] It should be noted that when the AC motor 141 is decelerated, the energy can also be fed back to the common DC bus 130 through the inverter unit 140 to achieve bidirectional energy transfer.

[0050] For example, AC motor 141 can be a three-phase independent winding motor.

[0051] Optionally, the inverter unit 140 may also integrate a drive protection circuit and a local unit controller. The output of the inverter unit 140 is brought out through a standardized interface. Depending on the required output voltage (e.g., 3300V, 6000V, etc.), each phase winding is driven by m inverter unit 140 outputs connected in series (e.g., phase A is driven by m units connected in series). The unit controller receives modulation wave commands from the system controller and uses carrier phase-shift PWM to generate a multi-level stepped wave, making the synthesized voltage of the series output close to a sine wave with extremely small dv / dt.

[0052] Optionally, the inverter unit 140 can be an H-bridge structure or a three-level ANPC topology to further reduce dv / dt.

[0053] Optionally, the number m of the output terminals of the inverter units 140 in series in the high-voltage AC output terminal is determined according to the output voltage requirements of the corresponding phase windings, wherein the target line voltage in the output voltage requirements is determined based on the scenario requirements. The AC motor 141 includes a multi-phase independent winding motor, and the number of independent segments in each phase winding is equal to m. The number m of the output terminals of the inverter units 140 constituting the high-voltage AC output terminal in series is m, that is, the high-voltage AC output terminal is formed by the output terminals of m inverter units 140 in series. The specific value of m can be determined according to the output voltage requirements of the corresponding phase windings. The target line voltage in the output voltage requirements can be selected and determined based on the scenario requirements, and various high-voltage voltage levels such as 3300V, 6000V, or 10kV can be selected and determined accordingly. The AC motor 141 may include a multi-phase independent winding motor, and the number of independent segments of each phase winding is equal to m. That is, the number of series stages m of the inverter unit 140 matches the number of winding segments of the AC motor 141, forming an integrated "driver-motor" structure, which greatly shortens the required output cable length and allows the inverter unit 140 and the AC motor 141 to be installed close to each other, improving electromagnetic compatibility.

[0054] Alternatively, the outputs of multiple inverters can be connected in parallel first, and then connected to the corresponding AC motor 141 through a step-up transformer.

[0055] It should be noted that if there is no need for AC drive, the inverter unit 140 can be omitted, and the common DC bus 130 can directly output power to DC loads 131 such as data centers, electrolytic power supplies, and other DC equipment. The choice between installing the inverter unit 140 and the load 131 can be made based on the specific application requirements of the scenario.

[0056] Optionally, an external power interface is provided on the common DC bus 130; the external power interface is used to connect the common DC bus 130 and an external device 132; wherein the external device 132 includes an energy storage device or a power generation unit. The external power interface can connect the common DC bus 130 and the external device 132, such as an energy storage device or a power generation unit, to realize energy transfer between the external device 132 and the common DC bus 130, thereby achieving charging, energy storage, and other effects.

[0057] For example, the power generation unit may include corresponding photovoltaic devices and wind power devices, such as photovoltaic panels, wind turbines, and other devices that can realize power generation functions, such as hydropower generation, thermal power generation devices, etc. The power generation unit may include one or more devices of the same or different types. The photovoltaic devices can collect corresponding light energy, and the wind power devices can collect corresponding wind energy, so as to convert the light energy and / or wind energy into electrical energy through a converter, store the electrical energy in an energy storage device, or transmit the electrical energy to the common DC bus 130 for power supply.

[0058] Optionally, the external device 132 can be configured with a corresponding power conversion interface (such as a bidirectional DC / DC converter or a photovoltaic DC / DC converter) and interact with the main controller 151 set in the system through communication to realize multi-source coordinated power supply and energy management.

[0059] For example, the energy storage device can be a corresponding energy storage battery or other device, which can store the electrical energy generated by the power generation unit and the electrical energy transmitted by the common DC bus 130.

[0060] Optionally, the rectifier 111 may include a single-phase H-bridge topology, wherein the power switching devices in the single-phase H-bridge topology include IGBT (Insulated Gate Bipolar Transistor) or SiCMOSFET (Silicon Carbide MOSFET) to achieve efficient and independent rectification function.

[0061] Alternatively, power switching devices may also include other types of switching devices suitable for high-frequency applications, such as GaN (gallium nitride high electron mobility transistor) devices.

[0062] Alternatively, the rectifier 111 may also employ other devices such as a modular multilevel converter that enable high-voltage direct connection and bidirectional energy flow.

[0063] Optionally, the power switching device is integrated with anti-parallel diodes. The AC side of the rectifier 111 is connected to the corresponding phase (e.g., phase A) of the high-voltage AC grid 120 through a filter inductor, and the DC output is connected to the isolation device 112. The DC sides of each rectifier 111 are independent of each other, and together they withstand the high voltage of the high-voltage AC grid 120, such as 10kV line voltage. Each rectifier 111 can use carrier phase-shift PWM modulation to cancel out the switching harmonics of each power unit 110, and the grid-side current THD < 3%. At the same time, the sub-controller 152 can also detect the DC voltage inside the power unit 110 in real time and ensure the DC voltage balance inside each power unit 110 through a voltage equalization control algorithm (e.g., adjusting active power distribution).

[0064] For example, the power switching devices can be automotive-grade IGBTs or SiC MOSFETs, such as 600V-1700V automotive-grade IGBTs or SiC MOSFETs, using certified devices to meet the usage requirements of various application scenarios.

[0065] It should be noted that the system uses all automotive-grade components and provides engineering guidelines for voltage derating to 800V and current derating to 80%, ensuring high reliability while maintaining low cost.

[0066] Optionally, the isolation device 112 may include a dual active bridge converter, i.e., a DAB module. The dual active bridge converter may include components such as an input-side H-bridge, an output-side H-bridge, a high-frequency transformer, and a resonant inductor to achieve electrical isolation and signal conversion. The dual active bridge converter supports bidirectional energy flow. The dual active bridge converter can employ a phase-shift control strategy, adjusting the phase difference φ between the drive signals of the input-side H-bridge and the output-side H-bridge to control the magnitude and direction of power flow, thereby achieving four-quadrant operation and supporting bidirectional energy flow.

[0067] Alternatively, the isolation device 112 may also use other devices such as LLC resonant converters, CLLC resonant converters, or unidirectional DC / DC converters.

[0068] Optionally, the isolation device 112 consists of an input-side H-bridge, an output-side H-bridge, a high-frequency transformer T, and a resonant inductor Lr. The high-frequency transformer can use a nanocrystalline magnetic core, with a fixed operating frequency of 20kHz, and its insulation level meets the system requirements of the high-voltage AC power grid 120. The input-side H-bridge inverts the DC output from the rectifier device 111 into a 20kHz square wave, which is then isolated and transformed by the high-frequency transformer and rectified by the output-side H-bridge into a common DC bus voltage signal 130. The output terminals of all isolation devices 112 are connected in parallel to form a standardized common DC bus 130. Each isolation device 112 is controlled by a sub-controller 152, which can employ a phase-shift control strategy. By adjusting the phase difference φ between the input-side H-bridge and the output-side H-bridge drive signals, the magnitude and direction of power flow are controlled (φ>0 for forward flow, φ<0 for reverse feedback), thereby achieving four-quadrant operation.

[0069] Please continue reading. Figure 2 The system may further include a main controller 151, which is connected to each power unit 110 and is used to determine the modulation command for each power unit 110. In order to perform overall control of the operation of multiple power units 110, the system may be provided with a main controller 151, which is connected to each power unit 110 to determine the modulation command for controlling each power unit 110.

[0070] Please continue reading. Figure 2 To enable independent control of the internal operation of each power unit 110, a sub-controller 152 can be provided in each power unit 110. The sub-controller 152 is connected to the main controller 151 via optical fiber communication. The sub-controller 152 connects to the rectifier 111 and the isolation device 112, and controls the operation of the rectifier 111 and the isolation device 112 based on modulation commands. The sub-controller 152 and the main controller 151 can be connected via optical fiber communication to improve data transmission efficiency, thereby improving control response efficiency. The sub-controller 152, connected to the rectifier 111 and the isolation device 112, can control the operation of the rectifier 111 and the isolation device 112 based on the modulation commands received from the main controller 151, thereby achieving independent control of each power unit 110.

[0071] It should be noted that the main controller 151 is configured with a feedforward control strategy. The main controller 151 is also used to: acquire the power demand of the connected loads; and adjust the modulation command based on the power demand and the feedforward control strategy. The main controller 151 is configured with a feedforward control strategy, which enables it to acquire the actual power demand of the loads connected to the common DC bus 130, and adjust the modulation command accordingly based on the power demand and the feedforward control strategy, so that each power unit 110 can achieve its corresponding driving effect.

[0072] For example, feedforward control strategies may include model predictive control (MPC), which can incorporate the impulse response into the optimization objective, as well as various algorithms such as voltage equalization control algorithms and sorting-based capacitor voltage balancing algorithms (common in MMC).

[0073] Optionally, the multiple power units 110 include redundant units and working units. The main controller 151 is further configured to: determine the working status of each working unit; if the working status of any working unit is determined to be abnormal, isolate the abnormal working unit within a preset time, start the redundant unit to work, and adjust the working parameters of the normally working unit. Considering sudden abnormal situations, the multiple power units 110 can be divided into redundant units and working units. The main controller 151 can determine the working status of each working unit. When the working status of any working unit is abnormal, the abnormal working unit can be isolated within a preset event, and the shut-down redundant unit can be started to work. Since the working of the working unit has changed, the working parameters of the normally working unit can also be adjusted accordingly to ensure that the entire system can still operate normally in the event of an abnormal situation.

[0074] For example, the preset time can be set based on the actual communication situation, such as 2ms. The number of redundant units can be set based on the actual situation, such as setting one redundant unit. When all working units are working normally, the redundant unit is in a closed state. The main controller 151 can control the abnormal working unit to disconnect from the high-voltage AC power grid 120 to isolate the faulty unit.

[0075] Optionally, the main controller 151 can recalculate the PWM duty cycle and phase to determine new operating parameters, maintain a balanced electromagnetic torque so that the normal operating unit can perform amplification work, thereby ensuring stable system operation.

[0076] Optionally, the main controller 151 can be an electronic device with logic computing functions, such as a server, personal computer (PC), tablet computer, smartphone, or personal digital assistant (PDA). The main controller 151 can also be a processor installed in the system and connected via electrical cables or other devices. The processor may be an integrated circuit chip with signal processing capabilities, or a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0077] It should be noted that the system can adopt a hierarchical distributed control architecture: the main controller 151 can be based on ARM+FPGA and run the main control algorithm. Its main functions include: load feedforward control: acquiring real-time power demand from the load via a high-speed communication bus, adjusting the output of the rectifier and isolation stages in advance, and suppressing bus voltage fluctuations caused by impact loads (controlled within ±3%); voltage equalization control: dynamically adjusting the active power of each rectifier device 111 to ensure DC voltage balance in the series units; redundancy management: real-time monitoring of the operating status of all working units, and bypassing the abnormal working unit and taking over the redundant unit within 2ms when an abnormal fault is detected; multi-source coordination: when an external device 132 is connected, power can be allocated according to a preset strategy (such as green electricity priority); synchronization control: broadcasting a synchronization clock signal to the sub-controllers 152 of all power units 110 to ensure carrier phase consistency. The sub-controller 152 can be configured as an FPGA or MCU, capable of receiving modulation commands sent by the main controller 151 and performing local PWM generation, voltage and current sampling, fault detection, and fast protection. The sub-controller 152 and the main controller 151 communicate via optical fiber to achieve nanosecond-level synchronization.

[0078] For example, the system can operate under various conditions, including: Forward motoring (AC output): 10kV AC power is rectified into k independent DC signals by multiple cascaded rectifiers 111. Each DC signal is then isolated and converted at high frequency by isolation device 112 and connected in parallel to the common DC bus 130. Inverter unit 140 draws power from the common DC bus 130 and generates multi-level AC power via carrier phase-shifted PWM. The outputs of each inverter unit 140 are connected in series to drive the AC motor 141. The main controller 151 calculates the required voltage amplitude and frequency based on the motor speed command using vector control and sends modulated waves to each inverter unit 140. Braking energy feedback: When the AC motor 141 decelerates, energy is fed back to the common DC bus 130 via inverter unit 140, increasing the bus voltage. When isolator 112 detects a rise in bus voltage, it automatically enters reverse mode (phase shift angle φ < 0), feeding energy back to the DC side of rectifier 111. The cascaded H-bridge rectifier 111 (operating in active inverter mode at this time) then sends the energy back to the high-voltage AC grid 120. Pure DC output mode: When inverter unit 140 is not configured, the common DC bus 130 directly supplies power. The stable DC voltage formed by the parallel output of isolator 112 can be used by load 131. The main controller 151 can adjust the phase shift angle of isolator 112 according to the demand of load 131 to maintain stable bus voltage. Multi-source collaborative mode: When external devices such as energy storage devices or power generation units 132 are connected, the main controller 151 can dynamically allocate power according to the status of each source and the power demand of the load. For example, when photovoltaic power is sufficient, it is used first; when insufficient, it is supplemented by the grid; energy storage is used for peak shaving and valley filling or emergency support. Fault redundancy mode: When any working unit fails, the main controller 151 immediately instructs the abnormal working unit to stop and bypass, while adjusting the working parameters of other units (such as the phase shift angle of the isolation device 112) so that the remaining units can bear all the power, maintain the continuous operation of the system, and connect the redundant units to work.

[0079] Optionally, the system can also be equipped with cooling devices such as liquid cooling devices and air cooling devices connected to each structure, thereby reducing the high temperature of each structure during operation.

[0080] Please see Figure 3 , Figure 3 This is a flowchart illustrating a high-voltage direct-connection power conversion method without a phase-shifting transformer, provided in an embodiment of this application. The method is applied to the system in any of the above embodiments and may include steps S200-S300.

[0081] Step S200: The AC signal from the high-voltage AC power grid is rectified into a DC signal using a rectifier device.

[0082] In step S300, the DC signal is converted into a DC bus voltage signal using an isolation device.

[0083] In this system, the output terminals of the isolation devices in multiple power units are connected in parallel to form a common DC bus, which is used to supply power to the connected loads.

[0084] exist Figure 3 In the illustrated embodiment, the AC signal from the high-voltage AC power grid is rectified into a DC signal by a rectifier, and the DC signal output by the rectifier is converted into a DC bus voltage signal by an isolation device. The outputs of multiple isolation devices in multiple power units are connected in parallel to form a common DC bus, which can supply power to the connected loads.

[0085] Optionally, the system may further include: multiple inverter units, the input terminals of which are connected in parallel to a common DC bus. These inverter units can also convert the DC signal on the common DC bus into an AC signal. The output terminals of the multiple inverter units are connected in series to form a high-voltage AC output terminal, which is used to drive the connected AC motor. In scenarios requiring AC drive, multiple inverter units can convert the DC bus voltage signal on the common DC bus into an AC drive signal. The output terminals of these multiple inverter units, connected in series, can form a high-voltage AC output terminal to drive the connected AC motor. Furthermore, when the AC motor decelerates, energy can be fed back to the common DC bus through the inverter units, achieving bidirectional energy transfer.

[0086] Optionally, the system may further include: a main controller; the main controller is connected to each power unit and is configured with a feedforward control strategy. See also... Figure 4 , Figure 4 This is a flowchart illustrating another high-voltage direct-connection power conversion method without a phase-shifting transformer provided in an embodiment of this application. The method may further include steps S411-S413.

[0087] Step S411: The modulation command for each power unit is determined by the main controller.

[0088] Step S412: Obtain the power requirements of the connected load through the main controller.

[0089] Step S413: The modulation command is adjusted by the main controller based on power demand and feedforward control strategy.

[0090] exist Figure 4In the illustrated embodiment, to achieve overall control of the operation of multiple power units, a master controller can be configured to determine the modulation command for controlling each power unit. Furthermore, the master controller is equipped with a feedforward control strategy, enabling it to acquire the actual power demand of the load connected to the common DC bus and adjust the modulation command accordingly based on the power demand and the feedforward control strategy, so that each power unit can achieve its respective driving effect.

[0091] Since the principle of the method in this embodiment is similar to that of the aforementioned system embodiment, the implementation of the method in this embodiment can refer to the description in the above system embodiment, and the repeated parts will not be described again.

[0092] In summary, this application, through a system architecture of "cascaded rectification + high-frequency isolation," simultaneously achieves transformerless operation, isolation, high efficiency, high power density, four-quadrant operation, and modular design, demonstrating comprehensive advantages in technical performance. It can be widely applied in shale gas fracturing, mining crushing, data center power supply, rail transit traction, ship electric propulsion, and energy storage systems, and is particularly suitable for mobile or high-power-density scenarios with stringent requirements for equipment size, efficiency, and reliability. It has broad market prospects and significant economic value. It is especially suitable for the oil and gas extraction field, including but not limited to shale gas fracturing, submersible pump power supply, and offshore platform oil production—high-power applications with extremely high requirements for equipment size, efficiency, and reliability. Taking the submersible pump power supply scenario as an example, this application has unique advantages: multi-level output waveforms can effectively suppress voltage spikes caused by long cable reflections, avoiding damage to motor insulation; precise voltage regulation capabilities can automatically compensate for line voltage drops over thousands of meters of cable; and the transformerless design significantly reduces equipment size, making it particularly suitable for space-constrained environments such as offshore platforms.

[0093] This application achieves the following technical effects: Complete elimination of phase-shifting transformers: Through a system architecture of cascaded rectifier devices + isolation devices, no power frequency phase-shifting transformer is required. The system size and weight are reduced by more than 50% compared to traditional solutions, facilitating skid-mounted transportation and on-site layout. Significantly improved efficiency: Eliminating transformer losses (approximately 1.5%) and employing soft-switching technology in the isolation devices, the overall system efficiency reaches over 98.5%, an improvement of more than 1.5 percentage points compared to traditional solutions (≤97%). Based on a 20MW unit operating for 2000 hours annually, this translates to annual energy savings of over 600,000 kWh. High power density: High-frequency isolation reduces the size of the isolation devices to only 1 / 10 to 1 / 20 of a power frequency transformer, resulting in a power density 3 to 5 times higher than traditional solutions. Four-quadrant operation capability: The PWM rectification design allows for bidirectional energy flow, with braking energy fed back to the grid, making it suitable for frequent start-stop and rapid braking conditions. Flexible and adjustable output voltage: By adjusting the number of inverter units in series (m), it can cover any AC voltage level such as 3300V, 6000V, and 10kV; without inverter units, it can directly output 600V~1500V DC to meet various application needs. Standardized modular design: All isolation devices and inverter unit interfaces are unified and interchangeable, supporting hot-swappable maintenance, and reducing fault recovery time to within 2 hours; mass production of modules can significantly reduce costs. Optimized component costs: Using automotive-grade components in series, component costs are reduced by 60%~70% compared to high-voltage components of the same capacity, and the supply chain is stable and reliable. Superior output waveform quality: Multiple inverter units in series output achieve multi-level stepped waveforms with low dv / dt, allowing direct driving of AC motors without output filters, extending motor insulation life. Grid friendly: Carrier phase-shifted PWM results in grid-side current THD <3% and a power factor close to 1, eliminating the need for additional harmonic mitigation devices. Multi-source compatibility: Standardized common DC bus allows easy access to various external devices to form a smart microgrid, improving system energy self-sufficiency and power supply reliability.

[0094] In the several embodiments provided in this application, it should be understood that the disclosed device can also be implemented in other ways. The system embodiments described above are merely illustrative; for example, the block diagrams in the accompanying drawings show the architecture, functionality, and operation of possible implementations of the device according to various embodiments of this application. In this regard, each block in the block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagram, and combinations of block diagrams, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0095] In addition, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0096] If the aforementioned functions are implemented as software functional modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0097] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0098] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

[0099] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A high-voltage direct-connect power conversion system without a phase-shifting transformer, characterized in that, The system includes: multiple cascaded power units; Each of the power units includes a rectifier and an isolation device; the power unit is electrically isolated from other power units based on the isolation device. The input terminal of the rectifier is connected to a multiphase high-voltage AC power grid, and the rectifier is used to rectify the AC signal of the high-voltage AC power grid into a DC signal. The input terminal of the isolation device is connected to the output terminal of the rectifier device, and the isolation device is used to convert the DC signal into a DC bus voltage signal. The outputs of the isolation devices in multiple power units are connected in parallel to form a common DC bus, which is used to supply power to the connected loads.

2. The system according to claim 1, characterized in that, The system also includes: multiple inverter units; The input terminals of multiple inverter units are connected in parallel to the common DC bus; Each of the inverter units is used to invert the DC bus voltage signal on the common DC bus into an AC drive signal; The output terminals of multiple inverter units are connected in series to form a high-voltage AC output terminal; wherein, the high-voltage AC output terminal is used to drive the connected AC motor.

3. The system according to claim 2, characterized in that, in, The number m of the inverter units connected in series in the high-voltage AC output terminal is determined according to the output voltage requirements of the corresponding phase windings; wherein, the target line voltage in the output voltage requirements is determined based on the scenario requirements; the AC motor includes a multi-phase independent winding motor, and the number of independent segments of each phase winding is equal to m.

4. The system according to claim 1, characterized in that, An external power interface is provided on the common DC bus. The external power interface is used to connect the common DC bus and external equipment; wherein, the external equipment includes: energy storage equipment or power generation unit.

5. The system according to any one of claims 1-4, characterized in that, in, The rectifier includes a single-phase H-bridge topology, and the power switching devices in the single-phase H-bridge topology include IGBTs or SiC MOSFETs.

6. The system according to claim 5, characterized in that, in, The power switching device is an automotive-grade IGBT or SiC MOSFET.

7. The system according to any one of claims 1-4, characterized in that, in, The isolation device includes a dual active bridge converter, which includes an input-side H-bridge, an output-side H-bridge, a high-frequency transformer, and a resonant inductor; the dual active bridge converter supports bidirectional energy flow.

8. The system according to any one of claims 1-4, characterized in that, The system also includes: a main controller; The main controller is connected to each of the power units and is used to determine the modulation command for each of the power units.

9. The system according to claim 8, characterized in that, The power unit is also equipped with a sub-controller; The sub-controller is connected to the main controller via optical fiber communication; The sub-controller connects the rectifier and the isolation device, and is used to control the rectifier and the isolation device to operate based on the modulation command.

10. The system according to claim 8, characterized in that, in, The main controller is configured with a feedforward control strategy, and the main controller is also used to: obtain the power demand of the connected load; and adjust the modulation command based on the power demand and the feedforward control strategy.

11. The system according to claim 8, characterized in that, in, Multiple power units include redundant units and active units; The main controller is also configured to: determine the working status of each working unit; if it is determined that the working status of any working unit is abnormal, isolate the abnormal working unit within a preset time, start the redundant unit to work, and adjust the working parameters of the normal working unit.

12. A high-voltage direct-connection power conversion method without phase-shifting transformer, characterized in that, The method is applied to the system according to any one of claims 1-11, the system comprising: a plurality of cascaded power units; wherein each power unit comprises: a rectifier and an isolation device; the power unit is electrically isolated from other power units based on the isolation device; the input terminal of the rectifier is connected to a multiphase high-voltage AC power grid, and the input terminal of the isolation device is connected to the output terminal of the rectifier; The method includes: The rectifier device rectifies the AC signal from the high-voltage AC power grid into a DC signal. The isolation device converts the DC signal into a DC bus voltage signal. The output terminals of the isolation devices in the multiple power units are connected in parallel to form a common DC bus, which is used to supply power to the connected loads.

13. The method according to claim 12, characterized in that, in, The system also includes: multiple inverter units; The input terminals of multiple inverter units are connected in parallel to the common DC bus; The method further includes: The inverter unit converts the DC signal on the common DC bus into an AC drive signal. The output terminals of multiple inverter units are connected in series to form a high-voltage AC output terminal; wherein, the high-voltage AC output terminal is used to drive the connected AC motor.

14. The method according to claim 12 or 13, characterized in that, in, The system further includes: a main controller; the main controller is connected to each of the power units, and the main controller is configured with a feedforward control strategy; The method further includes: The main controller determines the modulation command for each power unit; The power requirements of the connected loads are obtained through the main controller; The main controller adjusts the modulation command based on the power requirement and the feedforward control strategy.

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