A medium-voltage power take-off auxiliary power supply circuit

Abstract

The application discloses a kind of medium voltage power supply circuit, including passive rectification unit, capacitive filter unit and isolation output unit;Passive rectification unit is used to connect the at least two-phase of medium voltage AC power grid, and the DC power of medium voltage AC is rectified;The capacitive filter unit is connected to the DC output end of passive rectification unit;The isolation output unit includes multiple isolation DC / DC converters and multiple control units, the input end of each isolation DC / DC converter is connected in series in turn and is connected in parallel to the both ends of the capacitive filter unit, and the output end of each isolation DC / DC converter is used to output at least one isolated DC voltage;And each control unit is powered from the input end of each isolation DC / DC converter, for each isolation DC / DC converter provides the operating power required for driving control.The application realizes the purpose of directly taking power from medium voltage power grid, and the circuit structure is simple and reliable, and the overall volume is smaller.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a medium-voltage power supply auxiliary power supply circuit. Background Technology

[0002] In solid-state transformers (SSTs) and medium-voltage power electronic equipment, auxiliary power supplies are used to provide operating voltage for control systems, drive circuits, etc. Currently, auxiliary power is mainly supplied in the following two ways: The first method draws power from the intermediate bus of the solid-state transformer. However, this method requires the auxiliary power supply to be powered on before the system is powered on, which is a forced power-on and cannot achieve pre-start self-test. To solve this problem, an external or internal integrated energy storage unit (such as a battery) is usually needed as a backup power source to supply power to the system before startup. However, external energy storage units limit their application scenarios and require mandatory storage; while internal integrated energy storage units have problems such as large size and the need for additional insulation design.

[0003] The second approach is to use a traditional voltage transformer (PT) to draw power directly from the medium-voltage AC grid. Although this solution has high reliability, voltage transformers are power frequency iron-core transformers, which are bulky and occupy a lot of equipment space. They also suffer from continuous reactive power losses during operation, which cannot meet the requirements of miniaturization and high integration of modern power electronic equipment.

[0004] Therefore, it is necessary to provide an auxiliary power supply circuit that can draw power directly from the medium-voltage power grid, is simple and reliable, and has a small size to solve the above-mentioned defects. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a medium-voltage power supply auxiliary power supply circuit that can directly draw power from the medium-voltage power grid, is simple and reliable, and has a small size.

[0006] In a first aspect, the present invention provides a medium-voltage power supply auxiliary power supply circuit, comprising: A passive rectifier unit, whose AC input terminal is used to connect to at least two phases of a medium-voltage AC power grid, is used to rectify medium-voltage AC power into DC power. A capacitive filter unit is connected to the DC output terminal of the passive rectifier unit; An isolated output unit includes multiple isolated DC / DC converters and multiple control units. The input terminals of each isolated DC / DC converter are connected in series and then in parallel across the capacitive filter unit. The output terminals of each isolated DC / DC converter are used to output at least one isolated DC voltage. Each of the control units draws power from the input terminal of each of the isolated DC / DC converters to provide the operating power required for drive control of each of the isolated DC / DC converters.

[0007] Compared with existing technologies, the medium-voltage power supply auxiliary power circuit of this invention rectifies medium-voltage AC power into DC power through a passive rectifier unit, filters and supports it through a capacitive filter unit, and uses a series structure on the input side of multiple isolated DC / DC converters to withstand the medium-voltage DC bus voltage, reducing the input voltage stress of a single converter. This allows for the use of low-voltage devices to achieve medium-voltage power supply, replacing the traditional bulky power frequency core PT transformer. The series voltage divider of semiconductor devices replaces the traditional power frequency core transformer structure of the PT voltage transformer, thus enabling the use of low-voltage devices to achieve medium-voltage power supply while meeting medium-voltage insulation requirements. On the one hand, it eliminates the need for the core and windings, reducing the size of the power supply device and avoiding the continuous reactive power loss of the PT scheme. Furthermore, the outputs of each isolated DC / DC converter are naturally isolated, allowing for the simultaneous acquisition of multiple isolated output voltages. On the other hand, passive rectification requires no external control or external power supply, making it simple and reliable. Each isolated DC / DC converter has a control unit that draws power from its own input, allowing the entire auxiliary power supply circuit to achieve self-powered startup and operation without external energy storage or backup power. It can be seen that the medium-voltage power supply auxiliary power supply circuit of the present invention can directly draw power from the medium-voltage power grid, obtain multiple isolated output voltages, eliminate the need for forced storage, and the overall circuit is simple, reliable, and small in size. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the first embodiment of the voltage-driven auxiliary power supply circuit in this invention.

[0009] Figure 2 yes Figure 1 The diagram shows the circuit connection structure of the rectifier bridge arm and the voltage equalization unit in the medium-voltage auxiliary power supply circuit.

[0010] Figure 3 yes Figure 1 The diagram shows the circuit connection structure of the isolated DC / DC converter and control unit in the medium-voltage auxiliary power supply circuit.

[0011] Figure 4 This is a circuit diagram of the second embodiment of the voltage-driven auxiliary power supply circuit in this invention.

[0012] Figure 5 This is a circuit diagram of the third embodiment of the voltage-driven auxiliary power supply circuit in this invention.

[0013] Figure 6 This is a circuit diagram of the fourth embodiment of the voltage-driven auxiliary power supply circuit in this invention.

[0014] Figure 7 This is a circuit diagram of the fifth embodiment of the voltage-driven auxiliary power supply circuit in this invention. Detailed Implementation

[0015] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below with reference to the schematic diagram, but it is not limited thereto.

[0016] Reference Figure 1 , Figure 1 This is a schematic diagram of the structure of a first embodiment of the medium-voltage auxiliary power supply circuit of the present invention. In the embodiment shown in the figure, the medium-voltage auxiliary power supply circuit of the present invention includes a passive rectifier unit 10, a capacitive filter unit 20, and an isolated output unit 30; wherein, the AC input terminal of the passive rectifier unit 10 is used to connect to at least two phases of the medium-voltage AC power grid, for rectifying the medium-voltage AC power into DC power; the capacitive filter unit 20 is connected to the DC output terminal of the passive rectifier unit 10; the isolated output unit 30 includes multiple isolated DC / DC converters 31 and multiple control units 40, the input terminals of each isolated DC / DC converter 31 are connected in series and then in parallel across the two ends of the capacitive filter unit 20, and the output terminal of each isolated DC / DC converter 31 is used to output at least one isolated DC voltage; and each control unit 40 draws power from the input terminal of each isolated DC / DC converter 31 to provide the operating power required for drive control of each isolated DC / DC converter 31.

[0017] In the present invention, a DC bus is formed at the DC output end of the passive rectification unit 10. The passive rectification unit 10 rectifies medium-voltage alternating current and outputs a DC voltage to the DC bus. A capacitive filtering unit 20 is connected to the DC bus, configured to filter and stabilize the rectified high-voltage direct current, and then a plurality of isolated DC / DC converters 31 with series-connected inputs perform isolation conversion to output isolated DC voltages, so as to supply power to the subsequent-stage load with multiple paths of isolated power supplies. During operation, the passive rectification unit 10 is used to rectify the medium-voltage alternating current without the intervention of external control and an external power supply, and the plurality of isolated DC / DC converters 31 have series-connected inputs, each isolated DC / DC converter 31 only bearing a part of the DC voltage, so that devices with lower withstand voltage can bear a higher DC bus voltage, thereby enabling direct power taking from the medium-voltage power grid and meeting medium-voltage insulation requirements, while outputting multiple paths of isolated DC voltages, replacing the traditional power frequency PT, reducing the volume and weight, and avoiding the continuous reactive power loss of the PT solution; meanwhile, each isolated DC / DC converter 31 is provided with a control unit 40 that takes power from its own input end. It can be understood that, to simplify the illustration, the control units 40 connected to each isolated DC / DC converter 31 are not all shown in the figure. As a result, the entire auxiliary power supply circuit can realize self-powered start-up and operation without an external energy storage or backup power supply, no mandatory energy storage configuration is required, and the overall circuit is simple and reliable.

[0018] In some embodiments, the passive rectification unit 10 includes at least two rectifier bridge arms 11 formed by a plurality of rectifier diodes D connected in series, and the number of rectifier diodes D connected in series in the rectifier bridge arm 11 is determined according to the voltage level of the medium-voltage AC power grid and the withstand voltage level of a single rectifier diode D. Specifically, the number of series-connected diodes is not less than the quotient of the DC side voltage divided by the product of the diode withstand voltage value and the margin coefficient, that is, the number N of series-connected rectifier diodes D satisfies: N≥Vdc / (Vr×k), where Vdc is the voltage across the capacitive filtering unit 20, which is determined after rectification according to the voltage level of the medium-voltage AC power grid, Vr is the rated withstand voltage of a single rectifier diode D, k is the margin coefficient and 0<k<1, and the smaller the margin coefficient and the voltage stress of the diode, the larger the number of series-connected diodes. Taking an AC input with a line voltage of 10kV as an example, the peak voltage at the DC output end after rectification is about 14.1kV. If diodes with a withstand voltage of 1700V are selected and the margin coefficient is 0.5, the number of series-connected diodes is not less than 14.1kV / (1700V×0.5)≈16.6, so 17 diodes connected in series can be selected.

[0019] In this embodiment, the AC input end of the passive rectification unit 10 is connected to three phase lines of the medium-voltage AC power grid, the passive rectification unit 10 includes three rectifier bridge arms 11, and each rectifier bridge arm 11 is formed by a plurality of rectifier diodes D connected in series. In conjunction with Figure 2Furthermore, to ensure that the rectifier diodes D connected in series maintain the same withstand voltage during operation, the medium-voltage auxiliary power supply circuit also includes multiple voltage equalization units 12 for balancing the voltage across each rectifier diode D. The voltage equalization units 12 can be large-value resistors R or other devices with similar voltage equalization functions. In terms of connection, one rectifier diode D can be connected in parallel with one voltage equalization unit 12, and / or two or more rectifier diodes D connected in series can share one voltage equalization unit 12. When multiple rectifier diodes D connected in series share one voltage equalization unit 12, the voltage equalization unit 12 should meet the withstand voltage levels of the multiple rectifier diodes D connected in parallel, and the parameters of each rectifier diode D sharing the same voltage equalization unit 12 should be close (e.g., the parameter difference between each rectifier diode D is less than a preset threshold, such as the reverse leakage current difference between each rectifier diode D at operating temperature not exceeding 10% (or the reverse recovery time difference is less than a preset threshold) to ensure voltage equalization. It can be understood that multiple rectifier diodes connected in series on the same rectifier bridge arm 11... The multiple rectifier diodes D can each be connected in parallel to a voltage equalization unit 12, or some rectifier diodes D can each be connected in parallel to a voltage equalization unit 12, while the other part of the rectifier diodes D connected in series (preferably devices from the same production batch and of the same model) share a voltage equalization unit 12; and the connection method of the rectifier diodes D and the voltage equalization unit 12 on different rectifier bridge arms 11 can be the same or different, depending on the actual needs. In addition, in some other embodiments, when the characteristics of the rectifier diodes D connected in series are relatively similar, or when the number of rectifier diodes D connected in series is large and the voltage stress of a single rectifier diode D is much less than its rated withstand voltage, the voltage equalization unit 12 may not be provided.

[0020] It should be noted that the large-value resistor mentioned in this embodiment is a high-resistance resistor element. Its resistance value must be selected to ensure that the voltage equalization current flowing through the resistor is significantly greater than the leakage current of the rectifier diode D itself, and that the larger the resistance value, the greater the resistive loss generated by the resistor itself (P=U). 2 The lower the R value, the better to meet the requirements of extremely low power consumption of the auxiliary power supply; at the same time, the withstand voltage rating of this resistor must be greater than the voltage it actually shares. As an example, in a 10kV medium-voltage system, the resistance value of this large-value resistor can range from hundreds of kiloohms (kΩ) to tens of megaohms (MΩ), for example, it can be 10MΩ. The specific value can also be determined according to the actual medium-voltage bus voltage level, the number of series diodes, and the allowable voltage equalization current or loss requirements.

[0021] Continue to refer to Figure 1In this embodiment, the capacitive filter unit 20 is composed of multiple capacitors C connected in series, and the number of capacitors C in the series-connected capacitive filter unit 20 is determined according to the capacitor's withstand voltage and the voltage across the capacitive filter unit 20. Further, a capacitor voltage equalization unit 22 is connected in parallel among the multiple capacitors C connected in series to equalize the voltage across each capacitor C. The capacitor voltage equalization unit 22 can also be a large-value resistor R or other devices with similar voltage equalization functions. In terms of connection method, one capacitor C can be connected in parallel with one capacitor voltage equalization unit 22, and / or two or more capacitors C connected in series (preferably devices from the same production batch and of the same model) share one capacitor voltage equalization unit 22. It can be understood that in this embodiment, the number of capacitors C connected in series and the connection method between the capacitor voltage equalization unit 22 and the series-connected capacitors C are the same as the aforementioned rules for determining the number of rectifier diodes D and the connection rules between the rectifier diodes D and the voltage equalization unit 12, and will not be repeated here. In addition, in some other embodiments, when a capacitor that meets both the voltage and capacitance requirements is available, the capacitive filter unit 20 can be supported and filtered using a single capacitor C.

[0022] Preferably, in some embodiments, the isolated DC / DC converter 31 can be an open-loop resonant converter and operates at a preset fixed frequency so that the voltage gain of the isolated DC / DC converter 31 does not change with the load. That is, the isolated DC / DC converter 31 can be a resonant converter operating in open loop at a preset fixed frequency, such as an LLC resonant converter or an LCC resonant converter. The preset fixed frequency corresponds to the operating point where the gain of the resonant converter does not change with the load. By fixing the switching frequency of the isolated DC / DC converter 31 at this operating point and setting an appropriate transformer ratio according to the required output voltage level, a stable target voltage gain can be obtained under open-loop conditions without closed-loop regulation and external intervention. The control is simple and the reliability is high.

[0023] Combination Figure 3The isolated DC / DC converter 31 achieves electrical isolation between the primary and secondary sides through a transformer T. The primary side can be connected to an H-bridge converter or a half-bridge converter, while the secondary side uses diodes for rectification. No control is required, enabling self-powering and open-loop operation. Specifically, the control unit 40 includes an auxiliary power supply module 41, a PWM module 42, and a drive module 43. The auxiliary power supply module 41 draws power from the DC side of the isolated DC / DC converter 31 to generate a stable low-voltage DC voltage, providing a stable operating voltage for the PWM module 42 and the drive module 43. After being powered, the PWM module 42 generates a square wave signal with a preset fixed frequency. The drive module 43 drives the switching transistors in the H-bridge or half-bridge converter on the primary side of the isolated DC / DC converter 31 to turn on and off according to the square wave signal.

[0024] In this embodiment, the capacitive filter unit 20 may further include an input capacitor C1 connected to the primary side of each isolated DC / DC converter 31. In some other embodiments, to further simplify the circuit structure, the input capacitor C1 on the primary side may be combined with the capacitor C on the DC bus used to support the bus voltage. That is, the primary side of the isolated DC / DC converter 31 and the DC bus share the same capacitor. This capacitor supports the DC bus voltage and also performs filtering and energy storage functions, thereby reducing the number of capacitors. Based on the above design, the control unit 40 draws power from the DC input terminal of each isolated DC / DC converter 31, generates a square wave signal of a fixed frequency through the PWM module 42, and then controls the primary side switching transistor through the drive module 43. This "self-powered" mode allows each isolated DC / DC converter 31 to be directly powered by its own input capacitor C1 / the capacitor C connected to the DC bus after medium voltage is applied, completing the voltage build-up process from 0 voltage to normal operation without the participation of an external energy storage unit.

[0025] Furthermore, the output terminals (secondary sides) of these multiple isolated DC / DC converters 31 are independent of each other, each providing multiple isolated DC voltages. Therefore, the required output voltage level and power of each isolated DC / DC converter 31 can be independently designed according to the downstream load. This output connection method is suitable for applications requiring multiple isolated power supplies with different voltage levels (such as +5V, ±15V, +24V) to provide independent power to controllers, sensors, fans, drive circuits, etc. The outputs do not interfere with each other, exhibiting extremely high electrical isolation and system redundancy.

[0026] Furthermore, in this embodiment, the transformer T in the isolated DC / DC converter 31 can be an air-core coil, or a structure where the primary and secondary magnetic cores are separated, to reduce the coupling capacitance between the primary and secondary windings and simplify the insulation design between the primary and secondary windings and the magnetic core. Additionally, at least one output terminal of the isolated DC / DC converter 31 can be equipped with a subsequent voltage regulator circuit (such as a linear regulator) as needed to improve the stability of the output voltage. Moreover, to reduce the insulation distance and module size, the medium-voltage auxiliary power supply circuit or part of its structure can be encapsulated with potting compound.

[0027] As can be seen from the above, in this embodiment, the auxiliary power supply circuit uses a passive rectifier unit 10 composed of multiple low-voltage diodes connected in series to rectify the medium-voltage AC power into DC power. After being filtered and supported by the capacitive filter unit 20, it is isolated and converted by multiple isolated DC / DC converters 31 connected in series to obtain isolated DC voltage. The DC voltage is then output through the naturally isolated output terminals of each isolated DC / DC converter 31, thus enabling the simultaneous acquisition of multiple isolated DC voltages. This eliminates the need for a bulky power frequency core PT transformer, replacing the traditional power frequency core transformer structure of the PT voltage transformer with a series voltage divider of semiconductor devices. As a result, low-voltage devices can be used to achieve medium-voltage power extraction while meeting medium-voltage insulation requirements, reducing the weight of the power extraction device. This design reduces quantity and size, avoids the continuous reactive power loss inherent in PT (Power Transmission) schemes, and features passive rectification that requires no external control or power supply, making it simple and reliable. Each isolated DC / DC converter 31 has a control unit 40 that draws power from its own input, allowing the entire auxiliary power supply circuit to achieve self-powered startup and operation without external energy storage or backup power. Furthermore, each isolated DC / DC converter 31 is an open-loop resonant converter operating at a preset fixed frequency. At this frequency, the voltage gain does not change with the load, eliminating the need for closed-loop control and enabling rapid establishment of auxiliary power after power-on. This results in simple control and high reliability. The multiple isolated DC / DC converters 31 are connected in series at their inputs, allowing them to withstand higher DC bus voltages with lower voltage-rated components. In addition, the transformer T in the isolated DC / DC converter 31 employs a specific structural design that effectively reduces the coupling capacitance between the primary and secondary sides, further improving the system's insulation reliability.

[0028] Reference Figure 4 , Figure 4This is a schematic diagram of the second embodiment of the voltage-driven auxiliary power supply circuit of the present invention. The difference between this embodiment and the first embodiment is that the voltage-driven auxiliary power supply circuit in this embodiment also includes a balancing resistor R1, and the specific connections of the output terminals of the multiple isolated DC / DC converters 31 are different, while the rest of the structure is the same or similar. In this embodiment, to further balance the voltage and power among the various isolated DC / DC converters 31, a balancing resistor R1 is connected in parallel at the output terminal of the isolated DC / DC converter 31 to prevent uneven voltage or power distribution caused by inconsistent parameters between modules; and as shown in the figure, the output terminals of the multiple isolated DC / DC converters 31 are connected in series sequentially. Through series combination, multiple low-voltage isolated DC voltages can be superimposed to obtain the required high-voltage output. This output terminal connection method is suitable for scenarios with high-voltage auxiliary equipment or where auxiliary power needs to be provided to a DC bus with a higher voltage level. In this embodiment, when using the series connection output mode, combined with the balancing resistor R1 connected to the output terminal of the isolated DC / DC converter 31, it can be ensured that the voltage distribution of each series-connected isolated DC / DC converter 31 is balanced when subjected to high voltage, avoiding breakdown due to excessive voltage. This embodiment can also achieve the purpose of directly drawing power from the medium-voltage power grid, and its circuit structure and control are simple, reliable, and have a small overall size. Understandably, in some other embodiments, the balancing resistor R1 may be set only at the input terminal of the isolated DC / DC converter 31, or the balancing resistor R1 may be set at both the input and output terminals of the isolated DC / DC converter 31. The output terminals of the isolated DC / DC converter 31 may also be independent outputs or connected in parallel, or other connection methods.

[0029] Reference Figure 5 , Figure 5 This is a schematic diagram of the third embodiment of the medium-voltage auxiliary power supply circuit of the present invention. The difference between this embodiment and the first embodiment lies in that the AC input terminal of the medium-voltage auxiliary power supply circuit is connected to two phase lines of the medium-voltage AC power grid, the number of rectifier bridge arms 11 in the passive rectifier unit 10 and the specific connection between the rectifier diode D and the voltage equalization unit 12 are different; the remaining structures are the same or similar. To more clearly illustrate the differences from the first embodiment, Figure 5 The intermediate isolation output unit is not shown; its specific structure can be found in [reference needed]. Figure 1In specific application scenarios, due to the very small power requirement of the auxiliary power supply, in order to further simplify the circuit, in this embodiment, the passive rectifier unit 10 is only connected to any two phases (such as phase a and phase b) of the medium-voltage three-phase AC power grid for rectification. The passive rectifier unit 10 includes two rectifier bridge arms 11, with the midpoints of the two rectifier bridge arms 11 respectively connected to any two phase lines of the three-phase power grid, rectifying the medium-voltage AC power into DC power. Each rectifier diode D in the rectifier bridge arm 11 is connected in parallel with a voltage equalization unit 12. This embodiment can also achieve the purpose of directly drawing power from the medium-voltage power grid, and the circuit structure and its control are simple and reliable, with a small overall size.

[0030] Reference Figure 6 , Figure 6 This is a schematic diagram of the fourth embodiment of the auxiliary power supply circuit for medium voltage power extraction according to the present invention. The difference between this embodiment and the first embodiment lies in the specific connections of the output terminals of the multiple isolated DC / DC converters 31; the remaining structures are the same or similar. In this embodiment, the output terminals of the multiple isolated DC / DC converters 31 are connected in parallel to output a single isolated DC voltage, thereby increasing the output isolated DC voltage. Through parallel connection, the output current capacity of the entire auxiliary power supply circuit can be effectively increased to meet the needs of high-power loads. This embodiment can also achieve the beneficial effects of low-voltage devices withstanding high voltage in series, rapid self-starting, simple and reliable control, and excellent insulation performance through a passive rectification and self-powered open-loop control architecture, while reducing size, avoiding PT losses, and eliminating the need for external energy storage.

[0031] Reference Figure 7 , Figure 7This is a schematic diagram of the fifth embodiment of the medium-voltage power supply auxiliary power supply circuit of the present invention. The difference between this embodiment and the first embodiment lies in the specific connections of the output terminals of the multiple isolated DC / DC converters 31; the remaining structures are the same or similar. In this embodiment, in the isolated output unit 30, the output terminals of some isolated DC / DC converters 31 are connected in series to increase the output voltage level, forming a first high-voltage power supply branch. The output terminals of some isolated DC / DC converters 31 are connected in series to form a second high-voltage power supply branch. The first high-voltage power supply branch, the second high-voltage power supply branch, and the output terminals of the remaining isolated DC / DC converters 31 are connected in parallel to independently output Von, Vo2, and Vo1, respectively, to provide multiple isolated DC voltages of different voltage levels. Through this series-parallel combination connection method, the auxiliary power supply circuit of the present invention can not only adapt to the high insulation voltage level requirements under medium-voltage environments but also output high power to meet the power supply requirements of multiple high-power auxiliary devices. This embodiment also utilizes a self-powered architecture that draws power from the input of the isolated DC / DC converter 31 through passive rectification. Combined with fixed-frequency open-loop resonant control and series connection of low-voltage device input, it effectively reduces the size and weight of the power-drawing device and avoids the continuous reactive power loss of the PT scheme. At the same time, it uses low-voltage devices to withstand the high-voltage DC bus and uses a specific transformer T structure to reduce the coupling capacitance between the primary and secondary sides. Ultimately, it achieves a comprehensive set of beneficial effects, including self-starting without external energy storage or backup power, simple and reliable control, and excellent system insulation performance.

[0032] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A medium-voltage power supply auxiliary power supply circuit, characterized in that, include: A passive rectifier unit, whose AC input terminal is used to connect to at least two phases of a medium-voltage AC power grid, is used to rectify medium-voltage AC power into DC power. A capacitive filter unit is connected to the DC output terminal of the passive rectifier unit; An isolated output unit includes multiple isolated DC / DC converters and multiple control units. The input terminals of each isolated DC / DC converter are connected in series and then in parallel across the capacitive filter unit. The output terminals of each isolated DC / DC converter are used to output at least one isolated DC voltage. Each of the control units draws power from the input terminal of each of the isolated DC / DC converters to provide the operating power required for drive control of each of the isolated DC / DC converters.

2. The medium-voltage auxiliary power supply circuit as described in claim 1, characterized in that, The passive rectifier unit includes at least two rectifier bridge arms formed by multiple rectifier diodes connected in series, and the number of rectifier diodes connected in series in the rectifier bridge arms is determined according to the voltage level of the medium-voltage AC power grid and the voltage rating of a single rectifier diode.

3. The medium-voltage power supply auxiliary power supply circuit as described in claim 2, characterized in that, A voltage equalization unit is connected in parallel between the rectifier diodes connected in series in the passive rectifier unit. The voltage equalization unit is used to equalize the voltage borne by each rectifier diode. Among them, one voltage equalization unit is connected in parallel with one rectifier diode, and / or, one voltage equalization unit is connected in parallel with multiple series rectifier diodes with similar parameters.

4. The medium-voltage power supply auxiliary power supply circuit as described in claim 3, characterized in that, The voltage equalization unit is a high-resistance resistor.

5. The medium-voltage auxiliary power supply circuit as described in claim 1, characterized in that, The capacitive filter unit is a single capacitor or is composed of multiple capacitors connected in series, and a capacitor voltage equalization unit is connected in parallel between the multiple capacitors connected in series to equalize the voltage borne by each capacitor.

6. The medium-voltage power supply auxiliary power supply circuit as described in claim 5, characterized in that, One of the capacitor voltage equalization units is connected in parallel with one of the capacitors, and / or, one of the capacitor voltage equalization units is connected in parallel with multiple series capacitors with similar parameters, and the number of series capacitors in the capacitive filter unit is determined according to the capacitor's withstand voltage and the voltage across the capacitive filter unit.

7. The medium-voltage auxiliary power supply circuit as described in claim 1, characterized in that, The isolated DC / DC converter is an open-loop resonant converter and operates at a preset fixed frequency so that the voltage gain of the isolated DC / DC converter does not change with the load.

8. The medium-voltage auxiliary power supply circuit as described in claim 1 or 7, characterized in that, The control unit includes an auxiliary power supply module, a PWM module, and a drive module; wherein... The auxiliary power supply module draws power from the DC side of the isolated DC / DC converter to generate a stable low-voltage DC voltage, thereby providing a stable operating voltage for the PWM module and the drive module. The PWM module is used to generate a square wave signal with a preset fixed frequency; The driving module is used to drive the primary-side switching transistor of the isolated DC / DC converter according to the square wave signal.

9. The medium-voltage auxiliary power supply circuit as described in claim 1 or 7, characterized in that, Each of the isolated DC / DC converters has a balancing resistor connected in parallel at its input and / or output terminals.

10. The medium-voltage auxiliary power supply circuit as described in claim 1 or 7, characterized in that, The output terminals of the multiple isolated DC / DC converters output the isolated DC voltage in a series connection, parallel connection, a mixed connection of series and parallel, or an independent output, so as to provide isolated DC voltages of different voltage levels.

11. The medium-voltage auxiliary power supply circuit as described in claim 1 or 7, characterized in that, The output of the isolated DC / DC converter is connected to a subsequent voltage regulator circuit.

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