Medium-voltage input direct-current power supply system

Abstract

The invention discloses a medium-voltage input direct-current power supply system which comprises a phase-shifting transformer and at least one power conversion unit, the phase-shifting transformer comprises a plurality of secondary windings, each power conversion unit comprises at least one power conversion module, and each power conversion module comprises a rectifying unit and at least one direct-current conversion unit. The input end of the rectification unit is connected with one of the secondary windings, the at least one direct current conversion unit is connected to the output end of the rectification unit, each direct current conversion unit comprises a first power conversion circuit and a second power conversion circuit, the first power conversion circuit is a single-stage direct current conversion circuit, and the second power conversion circuit is a single-stage direct current conversion circuit. The second power conversion circuit is connected to the input end of the first power conversion circuit in parallel to suppress current oscillation of the input end of the first power conversion circuit, and each secondary winding is connected with a corresponding power conversion unit.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a medium voltage input direct current power supply system. Background Art

[0002] The DC / DC power conversion unit used in the existing medium voltage input DC power supply system usually adopts a Boost+Buck two-stage non-isolated architecture, such as Figure 1 As shown, the DC / DC power conversion unit 10 includes a Boost circuit 11 and a Buck circuit 12. The cost and efficiency of the two-stage non-isolated DC / DC power conversion unit are at a disadvantage compared to the single-stage DC / DC power conversion unit. In addition, the output connection method of the current medium voltage input DC power supply system is basically output parallel connection, such as Figure 2 As shown, the module M01 has input terminals A01 and A02, and the modules M01, M02 and M03 are connected in sequence. The connection method of the internal structure of the medium voltage input DC power supply system is single and has a limited scope of application.

[0003] Therefore, there is an urgent need to propose a medium voltage input DC power supply system with high working efficiency and adaptable to more different voltage applications through different connection schemes, thereby reducing the cost of the power supply system and improving the reliability of the power supply system. Summary of the invention

[0004] An object of the present invention is to provide a medium voltage input DC power supply system, which can solve one or more defects of the prior art.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a medium-voltage input DC power supply system, comprising a phase-shifting transformer, comprising multiple secondary windings; at least one power conversion unit, each power conversion unit comprising at least one power conversion module, each power conversion module comprising: a rectifier unit, the input end of the rectifier unit is connected to one of the multiple secondary windings; and at least one DC conversion unit, connected to the output end of the rectifier unit, each DC conversion unit comprises: a first power conversion circuit, the first power conversion circuit is a single-stage DC conversion circuit; a second power conversion circuit, connected in parallel to the input end of the first power conversion circuit to suppress current oscillation at the input end of the first power conversion circuit; wherein each secondary winding is connected to a corresponding power conversion unit.

[0006] In one embodiment of the present invention, the first power conversion circuit includes a first inductor and a second inductor, wherein the first terminal of the first inductor is connected in series with the first output terminal of the first power conversion circuit, and the first terminal of the second inductor is connected in series with the second output terminal of the first power conversion circuit.

[0007] In one embodiment of the present invention, a first power conversion circuit includes: a first bridge arm, including a third switch tube and a fifth switch tube connected in series, with a first output terminal between the third switch tube and the fifth switch tube; a second bridge arm, including a fourth switch tube and a sixth switch tube connected in series, with a second output terminal between the fifth switch tube and the sixth switch tube, and the fifth switch tube and the sixth switch tube are connected in series; a second capacitor, connected to both ends of the first bridge arm; a third capacitor, connected to both ends of the second bridge arm; and a fourth capacitor, with both ends of the fourth capacitor respectively connected to the second end of the first inductor and the second end of the second inductor.

[0008] In one embodiment of the present invention, a first power conversion circuit includes: a first bridge arm, including a third switch and a fifth switch connected in series, with a first output terminal between the third switch and the fifth switch; a second bridge arm, including a fourth switch and a sixth switch connected in series, with a second output terminal between the fifth switch and the sixth switch, the fifth switch and the sixth switch are connected in series, and a third node is provided between the fifth switch and the sixth switch; a second capacitor connected to both ends of the first bridge arm; a third capacitor connected to both ends of the second bridge arm; and a fourth capacitor and a fifth capacitor, with both ends of the fourth capacitor being connected to the second terminal and the third node of the first inductor respectively, and both ends of the fifth capacitor being connected to the second terminal and the third node of the second inductor respectively.

[0009] In an embodiment of the present invention, the fifth switch and the sixth switch are both diodes.

[0010] In one embodiment of the present invention, the first power conversion circuit further includes a first diode, an anode of the first diode is connected to the second output terminal, and a cathode of the first diode is connected to the first output terminal.

[0011] In one embodiment of the present invention, the voltage across the first bridge arm is equal to the voltage across the second bridge arm, and the third switch and the fourth switch have the same withstand voltage characteristics.

[0012] In one embodiment of the present invention, the voltages across the first bridge arm and the voltages across the second bridge arm are not equal, and the third switch and the fourth switch have different withstand voltage characteristics.

[0013] In one embodiment of the present invention, a ratio of a voltage across the first bridge arm to a voltage across the second bridge arm is greater than or equal to 1.5 and less than or equal to 10.

[0014] In an embodiment of the present invention, each power conversion module includes a plurality of DC conversion units whose input ends are connected in parallel, and the output ends of the plurality of DC conversion units are connected in parallel.

[0015] In one embodiment of the present invention, each power conversion unit includes a plurality of power conversion modules whose input ends are connected in parallel, and output ends of the plurality of power conversion modules are connected in parallel.

[0016] In one embodiment of the present invention, a plurality of power conversion units are included, and output ends of the plurality of power conversion units are connected in series.

[0017] In one embodiment of the present invention, a plurality of power conversion units are included, and output ends of the plurality of power conversion units are connected in parallel.

[0018] In one embodiment of the present invention, there are K secondary windings and K power conversion units corresponding one to one, and the voltage phases of the K secondary windings output are sequentially different by a phase shift angle; M groups of output busbars; wherein the K power conversion units are divided into L groups of output units according to a first order, each output unit includes M power conversion units, and the output ends of the M power conversion units in each output unit are sequentially connected in parallel one by one according to the first order to form M groups of output busbars, wherein K≥2, M≥2, L=K / M, and K is a multiple of M.

[0019] In one embodiment of the present invention, a first output unit and a second output unit, the first output unit includes I secondary windings and I power conversion units corresponding to each other, and the output ends of the I power modules are connected in parallel; the second output unit includes J secondary windings and J power conversion units corresponding to each other, and the output ends of the J power modules are connected in parallel, wherein I≥2, J≥2; the output end of the first output unit is connected in series with the output end of the second output unit.

[0020] In one embodiment of the present invention, a serial connection point between the output terminal of the first output unit and the output terminal of the second output unit is grounded.

[0021] In one embodiment of the present invention, there are four groups of output busbars.

[0022] In one embodiment of the present invention, the second power conversion circuit includes: a first port and a second port; a third inductor, a first switch tube and a second switch tube, the first switch tube and the second switch tube are connected in series, and there is a node between the first switch tube and the second switch tube; the third inductor is connected between the node and the first end of the first port of the second power conversion circuit.

[0023] In an embodiment of the present invention, the DC conversion unit further includes a first capacitor connected between the third inductor and the input terminal of the first power conversion circuit.

[0024] In one embodiment of the present invention, the medium voltage input DC power supply system also includes a first controller, which includes a voltage loop regulator, a current loop regulator, and a damping current generator; the voltage loop regulator outputs a first reference current based on the second port voltage of the second power conversion circuit and the first reference voltage; the damping current generator outputs a second reference current based on at least part of the AC component of the input voltage of the oscillation suppression module and the first coefficient; a third reference current is output based on the first reference current and the second reference current; the current loop regulator outputs a drive signal based on the third inductor current of the second power conversion circuit and the third reference current; and the duty cycle of the first switch tube and the duty cycle of the second switch tube are adjusted according to the drive signal.

[0025] In one embodiment of the present invention, the damping current generator outputs the second reference current according to at least part of the AC component of the input voltage of the oscillation suppression module and the first coefficient, combined with the output power of the first power conversion circuit.

[0026] The present invention provides a medium voltage input DC power supply system, which has high working efficiency and can adapt to more different voltage application occasions through different connection schemes, thereby reducing the cost of the system and improving the reliability of the power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions implemented in the present invention, the following briefly introduces the drawings required for use in the embodiments.

[0028] Figure 1 It is a structural schematic diagram of a DC / DC power conversion unit using a two-stage architecture in the prior art;

[0029] Figure 2 It is the connection method in the existing power supply system;

[0030] Figure 3A 1 is a schematic structural diagram of a non-isolated DC / DC power converter according to an embodiment of the present invention;

[0031] Figure 3B 1 is a schematic structural diagram of a non-isolated DC / DC power converter according to an embodiment of the present invention;

[0032] Figure 4 is a schematic structural diagram of an oscillation suppression module according to an embodiment of the present invention;

[0033] Figure 5 is a structural schematic diagram of an oscillation suppression module according to another embodiment of the present invention;

[0034] Figure 6 1 is a schematic structural diagram of a non-isolated DC / DC power converter according to an embodiment of the present invention;

[0035] Fig. 7A is a structural schematic diagram of a non-isolated DC / DC power converter according to another embodiment of the present invention;

[0036] Figure 7B is a structural schematic diagram of a non-isolated DC / DC power converter according to yet another embodiment of the present invention;

[0037] Figure 8 is an equivalent schematic diagram of a power conversion system including a power converter;

[0038] Fig. 9 is an equivalent schematic diagram of a power conversion system including a non-isolated DC / DC power converter of the present invention;

[0039] Fig.10 is based on Fig. 9 Equivalent circuit model of the power conversion system;

[0040] Fig.11 is based on Fig.10 Frequency domain control model of

[0041] Fig.12 is based on Fig.10 Schematic diagram of voltage simulation on the DC bus;

[0042] Fig.13 It is a schematic diagram of an embodiment of the oscillation suppression module control of the present invention;

[0043] Fig.14 yes Figure 4 The schematic diagram of the control embodiment of the oscillation suppression module shown;

[0044] Fig.15 yes Figure 4 A schematic diagram of another control embodiment of the oscillation suppression module shown;

[0045] Fig.16 yes Figure 5 The schematic diagram of the oscillation suppression module shown;

[0046] Fig.17 yes Figure 5 A schematic diagram of another control embodiment of the oscillation suppression module shown;

[0047] Fig.18A It is a schematic diagram of a three-phase rectifier circuit;

[0048] Fig.18B Yes Fig.18A Schematic diagram of output waveform of three-phase rectifier circuit shown;

[0049] Fig.18C It is a schematic diagram of the main AC harmonic components of the output voltage of the three-phase rectifier;

[0050] Fig.19A It is a schematic diagram of a single-phase diode rectifier circuit;

[0051] Fig.19B yes Fig.19A Schematic diagram of the output waveform of the single-phase diode rectifier circuit shown;

[0052] Fig.19C It is a schematic diagram of the main AC harmonic components of the output voltage of a single-phase diode rectifier;

[0053] Fig. 20A is based on Fig.17 A simulation model for computer simulation of the control embodiment shown;

[0054] Fig. 20B Based on Fig. 20A The simulation results of the simulation model shown;

[0055] Fig.21 is a simulation result of generating a damping current according to different first coefficients in a damping current generator;

[0056] Figures 22A-22B It is a simulation schematic diagram of optimizing damping current;

[0057] Fig.23 is a graph of the relationship between the DC bus voltage and the resonant frequency of the rectifier output impedance;

[0058] Fig.24 is a schematic structural diagram of a second controller according to an embodiment of the present invention;

[0059] Fig.25 is a schematic structural diagram of a second controller according to another embodiment of the present invention;

[0060] Fig.26 1 is a schematic structural diagram of a non-isolated DC / DC power converter according to an embodiment of the present invention;

[0061] Fig. 27 The structure of the power conversion unit is based on the present invention;

[0062] Fig.28 The structure of the medium voltage input DC power supply system is based on the present invention;

[0063] Fig.29 This is the structure of a DC conversion unit according to an embodiment of the present invention;

[0064] Fig.30 The structure of the medium voltage input DC power supply system is based on the present invention;

[0065] Fig.31 The structure of the medium voltage input DC power supply system is based on the present invention;

[0066] Fig.32 The structure of the medium voltage input DC power supply system is based on the present invention;

[0067] Fig.33 The structure of the medium voltage input DC power supply system is based on the present invention;

[0068] Fig.34 The invention is based on the structure of the medium voltage input DC power supply system.

[0069] Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. DETAILED DESCRIPTION

[0070] Example embodiments will now be described more fully with reference to the accompanying drawings, however, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; on the contrary, these embodiments are provided so that the present invention will be comprehensive and complete and will fully and completely convey the concept of the example embodiments to those skilled in the art.

[0071] When introducing the elements / components / etc. described and / or illustrated herein, the terms "one", "an", "the", "said" and "at least one" are used to indicate the presence of one or more elements / components / etc. The terms "comprise", "include" and "have" are used to indicate an open-ended inclusion and mean that additional elements / components / etc. may exist in addition to the listed elements / components / etc. In addition, the terms "first", "second", etc. in the claims are used only as marks and are not numerical limitations on their objects. The same numbers in the drawings represent the same or similar components. On the other hand, well-known components and steps are not described in the embodiments to avoid unnecessary limitations on the present invention. In addition, to simplify the drawings, some known and commonly used structures and elements will be illustrated in the drawings in a simple schematic manner.

[0072] Figure 3A FIG. 2 is a schematic diagram of a non-isolated DC / DC power converter 20 according to an embodiment of the present invention. Figure 3AAs shown, the non-isolated DC / DC power converter 20 includes a power module 21 and an oscillation suppression module 22. The power module 21 includes a first power conversion circuit 211. The first power conversion circuit 211 is a non-isolated DC / DC conversion circuit. The first output terminal A of the first power conversion circuit 211 is connected to the first inductor Lf1, and the second output terminal B of the first power conversion circuit 211 is connected to the second inductor Lf2. The oscillation suppression module 22 has a first input terminal P and a second input terminal N. There is an input voltage Vin between the first input terminal P and the second input terminal N. It includes a second power conversion circuit 221 inside. The first port of the second power conversion circuit 221 is connected in parallel to the input end of the first power conversion circuit 211. The current of the first port of the second power conversion circuit 221 is in phase with at least part of the AC voltage component of the input voltage Vin of the oscillation suppression module 22. The second power conversion circuit 221 can be a bidirectional DC / DC conversion circuit. It should be noted that, due to possible errors in practice, the current at the first port of the second power conversion circuit 221 and at least part of the AC voltage component of the input voltage Vin of the oscillation suppression module 22 have the same phase, but a phase error is allowed.

[0073] Figure 4 1 is a schematic diagram of the structure of an oscillation suppression module 22 according to an embodiment of the present invention. The oscillation suppression module 22 includes a second power conversion circuit 221, wherein the second power conversion circuit 221 may be a Boost circuit. In other embodiments, the second power conversion circuit 221 may be a bidirectional DC / DC conversion circuit such as Buck or Buck-Boost, but the present invention is not limited thereto. In this embodiment, the first port of the second power conversion circuit 221 includes a first terminal P and a second terminal N. The second power conversion circuit 221 includes a first switch Q1 and a second switch Q2, a third inductor Lf and a first capacitor C O There is a node O between the first switch Q1 and the second switch Q2, the third inductor Lf is connected between the node O and the first terminal P, and the second port of the second power conversion circuit 221 includes a first capacitor C O Two ends of the bridge arm are connected in parallel to the first switch Q1 and the second switch Q2 in series.

[0074] Furthermore, if Figure 5 As shown, the oscillation suppression module 22 may also include a DC blocking capacitor Cd, and the two ends of the DC blocking capacitor Cd are respectively connected to the first terminal P and the third inductor Lf. By connecting the DC blocking capacitor Cd in series with the second power conversion circuit 221, the voltage of the first port of the second power conversion circuit 221 can be reduced, thereby reducing the voltage stress on each switch of the second power conversion circuit, further reducing the loss of the second power conversion circuit 221, and selecting a switch with a lower withstand voltage rating when selecting components to reduce the cost of the oscillation suppression module.

[0075] The first power conversion circuit 211 may be a three-level Buck conversion circuit. Figure 3A In one embodiment shown, the first power conversion circuit 211 includes a first bridge arm and a second bridge arm, the first bridge arm includes a third switch Q3 and a fifth switch D2 connected in series, a first output terminal A is provided between the third switch Q3 and the fifth switch D2, the second bridge arm includes a fourth switch Q4 and a sixth switch D3 connected in series, a second output terminal B is provided between the fourth switch Q4 and the sixth switch D3, the fifth switch D2 and the sixth switch D3 are connected in series, a third node P3 is provided between the fifth switch D2 and the sixth switch D3. Figure 3B As shown, the fifth switch D2 and the sixth switch D3 may be, but are not limited to, diodes. When the fifth switch D2 is a diode, the cathode of the fifth switch D2 is connected to the first output terminal A. When the sixth switch D3 is a diode, the anode of the sixth switch D3 is connected to the second output terminal B. The first power conversion circuit 211 further includes a second capacitor V1 and a third capacitor V2. The second capacitor V1 is connected to both ends of the first bridge arm, and the third capacitor V2 is connected to both ends of the second bridge arm. The first power conversion circuit 211 may also include a first inductor Lf1 and a second inductor Lf2. The first end of the first inductor Lf1 is connected in series with the first output terminal A, and the first end of the second inductor Lf2 is connected in series with the second output terminal B. Figure 1Compared with the structure of the DC / DC power conversion module 10 shown in the figure, the first power conversion circuit 211 of this embodiment adopts a first inductor Lf1 and a second inductor Lf2 that are set separately on the positive output and the negative output. The second inductor Lf2 increases the controllability of the negative current, so that when multiple first power conversion circuits work in parallel, the positive current and the negative current at the output end of the first power conversion circuit are balanced, thereby effectively reducing the circulation between modules. In addition, when designing the magnetic component, the first inductor Lf1 and the second inductor Lf2 can be made into coupled inductors, and the DC magnetic flux can be offset through magnetic integration, thereby effectively reducing the inductor volume and reducing the manufacturing cost. The first power conversion circuit 211 also includes a fourth capacitor Cf, and the fourth capacitor Cf is connected in parallel to the second end of the first inductor Lf1 and the second end of the second inductor Lf2 of the first power conversion circuit 221. In some embodiments, the voltage at both ends of the first bridge arm and the voltage at both ends of the second bridge arm can be set according to actual applications. When the voltage across the first bridge arm is designed to be equal to the voltage across the second bridge arm, the third switch Q3 and the fourth switch Q4 of the first power conversion circuit 211 can use switches with consistent characteristics, such as switch devices with consistent withstand voltage characteristics, which use the same rated voltage between the drain and the source, but it should be understood that the voltage across the first bridge arm is equal to the voltage across the second bridge arm, and an error of 50% is allowed in the characteristic parameters of the switch device with consistent withstand voltage characteristics, but it is not limited to this. In other embodiments, when the voltage across the first bridge arm is designed to be unequal to the voltage across the second bridge arm, that is, the voltage across the second capacitor V1 and the voltage across the third capacitor V2 are designed to be different, switches with different characteristics can also be used. For example, the ratio between the voltage across the second capacitor V1 and the voltage across the third capacitor V2 can be set to any value between 1.5 and 10 times, but it is not limited to this. Specifically, the switch connected in parallel with the capacitor with lower voltage can adopt a switch with lower withstand voltage level, that is, a switch with lower rated voltage between drain and source, and the switch connected in parallel with the capacitor with higher voltage can adopt a switch with higher withstand voltage level, that is, a switch with higher rated voltage between drain and source, so as to make full use of the withstand voltage level of different switch devices and reduce loss and cost. At the same time, the characteristic selection of the fifth switch D2 and the sixth switch D3 can be adjusted accordingly according to the characteristics of the corresponding third switch Q3 and the fourth switch Q4. The second capacitor V1 and the third capacitor V2 can adopt capacitors with different capacities or different rated voltages, but are not limited to this.

[0076] Figure 6 FIG. 1 is a non-isolated DC / DC power converter 30 according to another embodiment of the present invention. The non-isolated DC / DC power converter 30 includes a power module 31 and an oscillation suppression module 32. The oscillation suppression module 32 includes a second power conversion circuit 321. The structure of the second power conversion circuit 321 can be similar to that of FIG. Figure 3BThe power module 31 includes a first power conversion circuit 311, and the structure of the first power conversion circuit 311 is the same as that of the second power conversion circuit 221 shown in FIG. Figure 3B Compared with the structure of the first power conversion circuit 211 shown in FIG. 1 , the difference is that the first power conversion circuit 311 further includes a first diode D1, the anode of D1 is connected to the second output terminal B, and the cathode of the first diode is connected to the first output terminal A. The setting of D1 can make the current in the first inductor Lf1 and the second inductor Lf2 flow through D1 when the third switch Q3 and the fourth switch Q4 are turned off at the same time, and the loss in this process will reduce the total loss of the current in the first inductor Lf1 and the second inductor Lf2 in the first power circuit flowing through the fifth diode D2 and the sixth diode D3. Figure 6 The architecture of the non-isolated DC / DC power converter shown can also operate in a 2-level mode. Since the sum of the voltage drops across D2 and D3 is greater than the voltage drop across D1, D2 and D3 are always bypassed by D1.

[0077] Fig. 7A FIG. 4 is a non-isolated DC / DC power converter 40 according to another embodiment of the present invention. The non-isolated DC / DC power converter 40 includes a power module 41 and an oscillation suppression module 42. The oscillation suppression module 42 includes a second power conversion circuit 421. The structure of the second power conversion circuit 421 can be similar to that of FIG. Figure 3A or Figure 3B The power module 41 includes a first power conversion circuit 411, and the first power conversion circuit 411 adopts the form of upper and lower Buck series connection. The structure of the first power conversion circuit 411 is the same as that of the second power conversion circuit 221, but is not limited thereto. Figure 3A Compared with the structure of the first power conversion circuit 211 shown in FIG. 4 , the difference is that in the first power conversion circuit 411, the fourth capacitor Cf is replaced by the first output capacitor Cf1 and the second output capacitor Cf2 connected in series, the two ends of the first output capacitor Cf1 are connected to the first inductor Lf1 and the third node P3 respectively, and the two ends of the second output capacitor Cf2 are connected to the second inductor Lf2 and the third node P3 respectively. Figure 6 Similar to the non-isolated DC / DC power converter 30 shown in FIG. 1 , the fifth switch D2 and the sixth switch D3 of the non-isolated DC / DC power converter 40 may be, but are not limited to, diodes. The non-isolated DC / DC power converter 40 may also include a first diode D1, such as Figure 7BAs shown, the anode of D1 is connected to the second output terminal B, and the cathode of the first diode is connected to the first output terminal A. In some embodiments, the voltage at both ends of the first bridge arm and the voltage at both ends of the second bridge arm can be set according to the actual application. When the voltage at both ends of the first bridge arm is designed to be equal to the voltage at both ends of the second bridge arm, the third switch Q3 and the fourth switch Q4 of the first power conversion circuit 211 can use switches with consistent characteristics, such as switch devices with consistent withstand voltage characteristics, which use the same rated voltage between the drain and the source, but it should be understood that the voltage at both ends of the first bridge arm is equal to the voltage at both ends of the second bridge arm. The characteristic parameters of the switch device with consistent withstand voltage characteristics allow an error of less than 50%, but are not limited to this. In other embodiments, when the voltage at both ends of the first bridge arm is designed to be unequal to the voltage at both ends of the second bridge arm, that is, the voltage at both ends of the second capacitor V1 and the voltage at both ends of the third capacitor V2 are designed to be different, switches with different characteristics can also be used. For example, the ratio between the voltage at both ends of the second capacitor V1 and the voltage at both ends of the third capacitor V2 can be set to any value between 1.5 and 10 times, but is not limited to this. Specifically, the switch connected in parallel with the capacitor with lower voltage can adopt a switch with lower withstand voltage level, that is, a switch with lower rated voltage between drain and source, and the switch connected in parallel with the capacitor with higher voltage can adopt a switch with higher withstand voltage level, that is, a switch with higher rated voltage between drain and source, so as to make full use of the withstand voltage level of different switch devices and reduce loss and cost. At the same time, the characteristic selection of the fifth switch D2 and the sixth switch D3 can be adjusted accordingly according to the characteristics of the corresponding third switch Q3 and the fourth switch Q4. The second capacitor V1 and the third capacitor V2 can adopt capacitors with different capacities or different rated voltages, and the voltage across the first output capacitor Cf1 and the second output capacitor Cf can be adjusted accordingly according to the voltage across the first bridge arm and the second bridge arm. When selecting the output capacitor, capacitor devices with equal or unequal rated voltages can be selected according to actual conditions, but are not limited to this.

[0078] The input end of any non-isolated DC / DC power converter including but not limited to the above embodiments can be connected to the output end of any rectifier circuit, i.e., the DC bus, and the rectifier circuit is connected to the AC power supply to form a power conversion system. Since the first power conversion circuit can be considered as a constant power load (CPL), Figure 8 As shown in , it exhibits negative resistance characteristics at its equivalent input impedance ZL(s). Fig. 9 As shown, a damper is added to the source side formed by, for example, an AC power supply and a rectifier circuit, such as any second power conversion circuit in the above embodiments, and its source side equivalent impedance is ZS(s). Fig.10 The equivalent circuit model shown and Fig.11The frequency domain control model shown in the figure shows that, according to the Nyquist stability criterion, if the equivalent impedance on the source side is not sufficiently damped, a DC bus or power supply will be Fig.12 Instability and oscillations shown.

[0079] Fig.13 for Figure 4 The control principle diagram of the first controller in the oscillation suppression module 22 shown in the figure, the first controller controls the current Ipn of the first port of the second power conversion circuit 221 of the oscillation suppression module 22 to be in phase with at least part of the AC component waveform of the port voltage Vpn, at which time the second power conversion circuit 221 presents the characteristics of an equivalent resistor at at least part of the frequency to suppress the oscillation of the input current of the first power conversion circuit 21. It should be noted that due to the error in actual control, the current Ipn of the first port of the second power conversion circuit 221 and at least part of the AC component waveform of the first port voltage Vpn should be considered to be in phase with each other, and an error of 30° leading or lagging is allowed.

[0080] Fig.14 for Figure 4 The control schematic diagram of the first controller in the oscillation suppression module 22 shown in the figure, wherein the dotted line part is the voltage control loop, and the solid line part is the current control loop, including a voltage loop regulator U1, a current loop regulator U2 and a damping current generator. The voltage loop regulator U1 outputs a first reference current Iref1 according to a second port voltage Vo of the second power conversion circuit 221 and a first reference voltage Vref; the damping current generator outputs a second reference current Iref2 according to the input port voltage Vin of the oscillation suppression module and a first coefficient k, wherein the first coefficient k can be a certain value or adjusted according to the system operating impedance. The first reference current Iref1 and the second reference current Iref2 are multiplied to output a third reference current Iref3, so that the waveform of Iref3 follows the waveform of an AC component Vin' of the input port current. The current loop regulator obtains a driving signal M according to a third inductor current iL of the second power conversion circuit 221 and a third reference current Iref3. For example, the modulator U3 obtains a driving signal M by converting an error amplified signal IE output by U2 according to the third inductor current iL and the third reference current Iref3 and a triangular wave Vramp, but the present invention is not limited thereto. The driving signal M is input to the first switch Q1 and the second switch Q2 to adjust the duty ratio of the first switch Q1 and the second switch Q2, so as to achieve the purpose of the third inductor current iL following the third reference current Iref3, that is, to control the third inductor current iL and avoid input current oscillation, wherein Q1 and Q2 are complementary turned on and a dead zone is left.

[0081] In other embodiments, Fig.14The difference of the control embodiment shown is that the second reference current Iref2 is determined by the input voltage Vin and the output power Po of the first power conversion circuit. Fig.15 As shown, the damping current generator can also output a second reference current Iref2 according to the input voltage Vin of the second power conversion circuit 221 and the output power Po of the first power conversion circuit 221 .

[0082] It should be noted that in the control method, U1, U2, and U3 can be implemented by analog or digital control or a mixture of the two. In addition, when the second power conversion circuit 221 is a bidirectional DC / DC conversion circuit such as Buck or Buck-Boost, the control idea of ​​the first controller is similar to the above control idea and will not be repeated here.

[0083] In some further embodiments, Fig.16 for Figure 5 The schematic diagram of the oscillation suppression module in the power conversion module shown includes a DC blocking capacitor connected in series with the second power conversion circuit to further reduce the rated voltage when the power semiconductor is selected in the second power conversion circuit. At the same time, since the DC blocking capacitor Cd blocks the DC voltage between the terminals P and N, and the second power conversion circuit is controlled so that the current of its first port is in phase with the AC component of the input voltage of the oscillation suppression module, it can be considered that the second power conversion circuit is controlled to dynamically simulate a resistor at a frequency other than DC. Therefore, at this time, the damping current provided by the second power conversion circuit can be an AC current at the system interference frequency, rather than a DC current, thereby further reducing the power loss and cost of the second power conversion circuit. Therefore, in order to realize that the second power conversion circuit provides an AC current at the system interference frequency, its second control implementation is as follows. Fig.17 As shown, including the second port voltage ( Fig.16 The VCd_dc in the circuit is composed of a control unit, a damping current generating unit, and an inductor current control unit. Among them, DFF is a duty cycle feedforward, BP is a bandpass filter, and LP is a low-pass filter. Due to the existence of the DC blocking capacitor Cd, the energy absorbed by the capacitor VCd_dc cannot be sent back to the DC bus through the DC blocking capacitor through the DC current. Fig.17 As shown, the second port voltage unit control unit includes a phase-locked loop (PLL) for tracking the AC component of the input voltage VPN of the oscillation suppression module and multiplying its unit waveform to generate a current reference to control the DC capacitor voltage (VCd_dc) of the second power conversion circuit to exchange energy with the DC bus connected to the input port of the oscillation suppression unit. For example, when the first power conversion circuit is connected to the DC bus after the three-phase AC source is rectified by six pulses, the phase-locked loop is used to track the main AC harmonic components on the DC bus voltage, including but not limited to the 6th harmonic component, the 12th harmonic component, the 18th harmonic component, etc. Figures 18A-18CAs shown. The damping energy absorbed by the capacitor VCd_dc can be sent back to the DC bus through the corresponding harmonic frequency through the second port voltage control unit to ensure the balance of the DC capacitor voltage of the second power conversion circuit. In other words, the control of the Cd_dc voltage can achieve energy exchange between Cd_dc and the DC bus by using the AC harmonics of the rectifier in the AC-DC energy conversion. Fig.16 The damping circuit shown in Fig.17 The control method proposed in the above can also be used in the case where the first power conversion circuit is connected to a single-phase diode rectifier. Fig.19A The single-phase diode rectifier circuit shown has two pulses in one line cycle, such as Fig.19B As shown, the first three significant AC harmonic components of the DC voltage of a single-phase diode rectifier are as follows Fig.19C As shown, at this time the PLL can track the 2 times harmonic frequency. Fig. 20A A simulation model of computer simulation according to the second control embodiment is shown in the case where a constant power load is supplied with power through a three-phase rectifier. Fig. 20B Based on Fig. 20A The simulation model performs simulation results. According to the simulation waveform, it can be seen that the voltage of VCd_dc is in a balanced state.

[0084] exist Fig.17 In the embodiment, the damping current generator is used to generate the damping current required by the system. The damping current generator includes generating the damping current according to the equivalent input impedance ZL of the constant power load and the input port voltage VPN of the oscillation suppression module. A low-pass filter is performed according to the load current at the input port of the oscillation suppression module and the input voltage VPN of the oscillation suppression module, and the cut-off frequency may be but is not limited to 100Hz, and a parameter reflecting the DC resistance of the load conversion circuit is obtained. Then, the parameter reflecting the DC resistance required by the system is scaled by the first coefficient K. In order to ensure that the second power conversion circuit generates sufficient damping, the first coefficient may be set but is not limited to 0.5. The simulation results when the first coefficient is equal to 0.5 are as shown in FIG. Fig.21 shown.

[0085] Furthermore, in some other embodiments, the damping current may be optimized by adjusting the first coefficient K. Based on the impedance stability analysis, the frequency of the damping current required by the second power conversion circuit depends on the frequency range where the source side equivalent impedance ZS and the load side equivalent impedance ZL intersect. Fig.22A As shown, since the output impedance of the source side including the AC power supply and the rectifier unit presents LC parallel resonance, when the inductance of the AC source side increases, the resonance frequency becomes smaller, and the VPN ripple frequency required by the damping generating unit is reduced, so the frequency range of VPN acquisition is wider. Fig. 22BIt can be seen that the frequency range corresponding to the damping current should be within the frequency range where the source side impedance ZS resonant frequency amplitude is larger than the load impedance ZL frequency amplitude. Therefore, when a constant first coefficient K is used, such as K = 0.5, the damping current generating unit will be injected into all frequencies above the VPN low-pass filter cutoff frequency, for example Fig.17 The frequency component is 100Hz, which may provide more damping current than actually required. In order to adaptively adjust the frequency of the AC component of the damping current injected by the second power conversion circuit with different grid inductances, the first coefficient K can be adaptively changed according to the required frequency range to adjust the source side equivalent impedance ZS. Since the load current and the DC bus capacitance can be preset, when the load current and the capacitance of the DC bus capacitance are known, the rectifier output impedance resonant frequency can be obtained according to the average value of the DC bus voltage, such as Fig.23 As shown in Figure 2. When the source side inductance increases, the output voltage of the rectifier ( Fig.23 The LC parallel resonant frequency is obtained according to the DC bus voltage, DC bus capacitance and load current (for example: Fig. 22B fr1 and fr2 in Fig.23 fr in the figure), thereby obtaining the required frequency component of the damping current, that is, the corresponding frequency range of the VPN to be collected. In this way, the damping current can be minimized, thereby minimizing the power of the second power conversion circuit and the efficiency of the entire system.

[0086] exist Fig.17 In the embodiment, the inductor current control unit is used to generate a current reference for controlling the current on the third inductor in the second power conversion circuit according to the current reference quantities generated by the second port voltage control unit and the damping current generating unit respectively, and further generate a duty cycle control signal for controlling the operation of the second power conversion circuit.

[0087] When the non-isolated DC / DC power conversion circuit 20 is, for example, Figure 3B The three-level BUCK conversion circuit shown in the figure, and when the voltages on the second capacitor V1 and the third capacitor V2 are equal, the positive and negative busbars of the output end are respectively provided with the first inductor Lf1 and the second inductor Lf2, so that the currents flowing through the positive and negative electrodes of the output end are substantially equal when the non-isolated DC / DC power conversion circuit 20 is working. When the voltages on the second capacitor V1 and the third capacitor V2 are not equal, and the characteristics of the third switch Q3 and the fourth switch Q4 used are greatly different, so that the conduction time of the two is inconsistent, then the currents of the positive and negative busbars of the output end will have a large difference and a circulating current will also be generated. Therefore, in another embodiment, as Fig.24As shown, the non-isolated DC / DC power converter 20 includes a second controller, which is configured to control the first power conversion circuit 211. The second controller includes a current control unit 2111, which obtains a first duty cycle variation △d according to the difference between the current Is+ of the first output terminal A and the current Is- of the second output terminal B of the first power conversion circuit 211, and the second controller adjusts a first duty cycle d1' of the third switch Q3 according to the first duty cycle variation △d to obtain a duty cycle d1; and adjusts a second duty cycle d2' of the fourth switch Q4 according to the first duty cycle variation △d to obtain a duty cycle d2. By increasing the on-time of Q3 and Q4 on the basis of the main control loop of the first power conversion circuit, the current values ​​flowing through the positive and negative bus bars tend to be equal. For example, if Q3 is on for a long time and Q4 is on for a short time, Is+ will be greater than Is- (the difference circulates in a circulating manner), and the control loop will produce a small duty cycle change △d, which will be superimposed on the duty cycle in the main control loop, ultimately reducing the duty cycle of Q3 and increasing the duty cycle of Q4.

[0088] In yet another embodiment, Fig.25 As shown, in order to balance and adjust the voltages of the second capacitor V1 and the third capacitor V2 of the first power conversion circuit 211, the second controller also includes a voltage control unit 2112. The voltage control unit 2112 obtains a second duty cycle change △d2 according to the difference between the voltage of the second capacitor V1 and the voltage of the third capacitor V2. The second controller adjusts the first duty cycle d1' of the third switch Q3 according to the second duty cycle change △d2 to obtain a duty cycle d1, and adjusts the second duty cycle d2' of the fourth switch Q4 according to the second duty cycle change to obtain a duty cycle d2. The duty cycles of the third switch Q3 and the fourth switch Q4 are fine-tuned according to the detected voltage difference between the second capacitor V1 and the third capacitor V2 on the basis of the main control loop of the first power conversion circuit, so that the voltages of the second capacitor V1 and the third capacitor V2 remain consistent.

[0089] Among them, the sampling of the voltage of the second capacitor V1 and the third capacitor V2 can perform differential sampling on the voltage of the second capacitor V1 and the third capacitor V2. In addition to analog control, digital control can also be used to fine-tune the duty cycle of the third switch Q3 and the fourth switch Q4 according to the voltage difference between the second capacitor V1 and the third capacitor V2 to achieve voltage balance on the second capacitor V1 and the third capacitor V2. When digital control is used, the voltage sampling can detect the total voltage in one way and detect the capacitor voltage on one side in another way, and the voltage difference between the second capacitor V1 and the third capacitor V2 is obtained by calculation.

[0090] In yet another embodiment of the present invention, Fig.26 As shown, it is Fig.25The difference is that the first power conversion circuit 211 also includes a second bidirectional DC / DC circuit 212, and the first port and the second port of the bidirectional DC / DC circuit 212 are respectively connected in parallel with the second capacitor V1 and the third capacitor V2 to balance the voltages of the upper and lower buses.

[0091] The non-isolated DC / DC power converter proposed by the present invention is provided with a second power conversion circuit in parallel with the first port of the first power conversion circuit, and the second power conversion circuit is controlled to form a resistance characteristic to form a damping to overcome the current oscillation caused by input or load fluctuation when the first conversion circuit presents a constant power load characteristic. Discrete inductors are provided at the positive and negative busbars of the second port of the first power conversion circuit to balance the current on the positive and negative busbars of the second port, thereby reducing the circulating current between modules. Further, considering the problem of uneven voltage and uneven current caused by the characteristic differences of the circuit components themselves in the actual circuit, the operating characteristics of the first power conversion circuit are further optimized by adding current sharing control and voltage sharing control to the main control circuit of the first power conversion circuit to increase the stability of its output. Further, the input voltage sharing of the first power conversion circuit can also be realized by a hardware circuit, that is, the voltage sharing control is independent of the original voltage loop and current loop, thereby simplifying the design of the voltage and current loop. Due to the high efficiency and low cost of the non-isolated DCDC power converter compared with the two-stage conversion circuit, it is particularly suitable for the medium voltage input DC power supply system of the data center or the drive of the AC motor.

[0092] like Fig. 27 As shown, it shows the structure of a power conversion module 60 based on the present invention. The power conversion module 60 includes N non-isolated DC / DC power converters 20 (20#1~20#N) and a rectifier unit 50, the input ends of the N non-isolated DC / DC power converters 20 are respectively connected to the rectifier unit 50, and the output ends of the N non-isolated DC / DC power converters 20 are connected in parallel, wherein N is greater than or equal to 1. Each power conversion module 60 can be applied to a modular power conversion device, including a rectifier and at least one non-isolated DC / DC power converter connected in sequence, wherein the structure of the rectifier unit 50 in the rectifier can be any rectifier circuit, and the non-isolated DC / DC conversion circuit includes but is not limited to any of the above embodiments.

[0093] like Fig.28 As shown, it shows the structure of the medium voltage input DC power supply system 100 based on the present invention. The medium voltage input DC power supply system 100 includes a phase-shifting transformer 70 and a plurality of power conversion units 80. The phase-shifting transformer 70 includes a plurality of secondary windings 71. Each secondary winding 71 is connected to a corresponding power conversion unit 80. Each power conversion unit 80 includes a plurality of Fig.13The power conversion modules 60 shown in the figure can be the same or different in number in each power conversion unit 80. In this embodiment, N=1 is taken as an example, that is, each power conversion module 60 can include the following: Fig. 27 The rectifier unit 50 and a non-isolated DC / DC power converter 20 are shown. The non-isolated DC / DC power converter 20 is connected to the output end of the rectifier unit 50. In each power conversion unit 80, the input ends of multiple power conversion modules 60 are connected in parallel, and the output ends of multiple power conversion modules 60 are connected in parallel to supply power to the load RLn, where n is greater than or equal to 1 and less than or equal to m. Each non-isolated DC / DC power converter 20 includes a first power conversion circuit 211 and a second power conversion circuit 221 of the present invention. The first power conversion circuit 211 and the second power conversion circuit 221 constitute a DC conversion unit. The first power conversion circuit 211 is a single-stage DC conversion circuit. The second power conversion circuit 221 is connected in parallel to the input end of the first power conversion circuit 211 to suppress the current oscillation at the input end of the first power conversion circuit 211.

[0094] Reference Fig.29 , Fig.29 The structure of the DC conversion unit is shown, wherein the output end of the first power conversion circuit 211 includes a first inductor Lf1, a second inductor Lf2 and an output capacitor Cf, the first end of the first inductor Lf1 and the first end of the second inductor Lf2 are respectively connected in series with the first node A and the second node B of the first power conversion circuit 211, and the output capacitor Cf is connected in parallel to the second end of the first inductor Lf1 and the second end of the second inductor Lf2.

[0095] like Fig.29 As shown, the first power conversion circuit 211 may further include a first diode D1 , and the first diode D1 is connected in parallel to a first end of the first inductor Lf1 and a first end of the second inductor Lf2 .

[0096] like Fig.30 As shown, it shows the structure of the medium voltage input DC power supply system 200 based on the present invention. The medium voltage input DC power supply system 200 includes a phase-shifting transformer 70 and a plurality of power conversion units 80'. The phase-shifting transformer 70 includes a plurality of secondary windings 71. Each secondary winding 71 is connected to a corresponding power conversion unit 80'. Each power conversion unit 80' includes Fig.13 The multiple power conversion modules 60 shown in FIG. 1 may each include a power conversion module 60 as shown in FIG. Fig. 27The rectifier unit 50 shown and N non-isolated DC / DC power converters 20 (20#1 to 20#N), N is greater than 1, wherein the input ends of the N non-isolated DC / DC power converters 20 are connected in parallel and connected to the output end of the rectifier unit 50, and the output ends of the N non-isolated DC / DC power converters 20 are connected in parallel. In each power conversion unit 80', the input ends of multiple power conversion modules 60 are connected in parallel, and the output ends are connected in parallel to supply power to a load. Each non-isolated DC / DC power converter 20 includes a first power conversion circuit 211 and a second power conversion circuit 221 of the present invention, and the first power conversion circuit 211 and the second power conversion circuit 221 constitute a DC conversion unit, and the structure of the DC conversion unit is as shown in FIG. Fig.15 As shown, the first power conversion circuit 211 is a single-stage DC conversion circuit, and the second power conversion circuit 221 is connected in parallel to the input end of the first power conversion circuit 211 to suppress current oscillation at the input end of the first power conversion circuit 211.

[0097] like Fig.31 As shown, it shows the structure of the medium voltage input DC power supply system 300 based on the present invention. The medium voltage input DC power supply system 300 includes a phase-shifting transformer 70 and a plurality of power conversion units 80'. The phase-shifting transformer 70 includes a plurality of secondary windings 71. Each secondary winding 71 is connected to a corresponding power conversion unit 80'. The difference between the medium voltage input DC power supply system 300 and the medium voltage input DC power supply system 200 is that the output ends of the plurality of power conversion units 80' are connected in series to supply power to the load RL. Since the outputs of the plurality of power conversion modules are connected in series, their output voltage is increased to be suitable for high voltage and high power loads, so that a low voltage power supply is used to supply power to a high voltage load.

[0098] like Fig.32 As shown, it shows the structure of the medium voltage input DC power supply system 400 based on the present invention. The medium voltage input DC power supply system 400 includes a phase-shifting transformer 70 and a plurality of power conversion units 80', the phase-shifting transformer 70 includes a plurality of secondary windings 71, each secondary winding 71 is connected to a corresponding power conversion unit 80', and the difference between the medium voltage input DC power supply system 400 and the medium voltage input DC power supply system 200 is that the output ends of the plurality of power conversion units 80' are connected in parallel to supply power to the load RL, so that a small current module supplies power to a large current load.

[0099] like Fig.33As shown, it shows the structure of the medium voltage input DC power supply system 500 based on the present invention. The phase-shifting transformer of the medium voltage input DC power supply system 500 includes 4+4n secondary windings (W1, W2...W(4+4n)), n is greater than or equal to 0, and the voltage phases output by the 4+4n secondary windings differ by a phase shift angle in sequence. Each secondary winding is connected to a power conversion unit 80', and the power conversion unit 80' corresponding to each secondary winding has an output end, and there are 4+4n output ends in total. In this embodiment, the 4+4n output ends are divided into 4 groups according to the first arrangement order, and the output ends of each group are respectively connected in parallel. The medium voltage input DC power supply system 600 has 4 groups of independent output busbars corresponding to the first arrangement order, namely Bus1, Bus2, Bus3 and Bus4. The winding corresponding to Bus1 is 1...1+4n (n≥0), the winding corresponding to Bus2 is 2...2+4n (n≥0), the winding corresponding to Bus3 is 3...3+4n (n≥0), and the winding corresponding to Bus4 is 4...4+4n (n≥0).

[0100] Further, in other embodiments, the medium voltage input DC power supply system 500 includes K secondary windings and K power conversion modules corresponding to each other, K≥2, the voltage phases of the outputs of the K secondary windings differ in sequence by a phase shift angle, and the medium voltage input DC power supply system 600 includes M groups of output busbars, M≥2, wherein the K power conversion modules are divided into L groups of output units according to a first sequence, each group of output units includes M power conversion modules, and the output ends of the M power conversion modules in each of the output units are connected in parallel one by one according to the first sequence to form the M groups of output busbars, wherein L=K / M, and K is a multiple of M. By such a setting, it can be achieved that when the output busbar power is unbalanced, the phase-shifting transformer has a high input power factor.

[0101] like Fig.34As shown, it shows the structure of the medium voltage input DC power supply system 600 based on the present invention. The medium voltage input DC power supply system 600 includes a first output unit 701 and a second output unit 702, the first output unit 702 includes I secondary windings and one-to-one corresponding I power conversion modules (80'#11~80'#n1), the output ends of the I power conversion modules are connected in parallel, the second output unit 702 includes J secondary windings and one-to-one corresponding J power conversion modules (80'#22~80'#m2), the output ends of the J power conversion modules are connected in parallel, wherein I≥2, J≥2, the output end put1 of the first output unit is connected in series with the output end put2 of the second output unit. Further, the series connection point between the output end put1 of the first output unit 701 and the output end put2 of the second output unit 702 is grounded. When the series connection point of the system architecture of the medium voltage input DC power supply system 600 is grounded, the safety distance between the positive and negative terminals of the module and the ground can be reduced, and the voltage level requirements for the safety capacitors can be reduced. Therefore, it can be used in charging piles, for example, to form an output of + / - 270V or + / - 400V, which is used to charge batteries of different voltage levels. In other embodiments, the series connection point may not be grounded, and in actual applications, the parallel and series connections of the outputs of the power conversion modules can be arbitrarily combined, and the present invention does not limit the number and order of series and parallel connections.

[0102] In each embodiment of the present invention, the phase shift angles between the secondary windings in the phase-shifting transformer may be equal or unequal, and there is no limitation on whether the primary and secondary windings of the transformer are triangular or Y-shaped. The rectification circuit in the power conversion module may be a diode rectification or a rectification performed by a switching element such as a thyristor.

[0103] The medium voltage input DC power supply system of the present invention adopts a single-stage power conversion unit and provides different connection schemes of the DC power supply system composed of the power conversion unit to adapt to more different voltage application scenarios, thereby reducing the cost of the system and improving the efficiency and reliability of the system.

[0104] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of protection of the present invention shall be subject to the scope defined by the appended claims.

Claims

1. A medium voltage input DC power supply system, characterized in that: Include: A phase-shifting transformer including a plurality of secondary windings; At least one power conversion unit, each of which comprises at least one power conversion module, each of which comprises: a rectifier unit, wherein an input end of the rectifier unit is connected to one of the plurality of secondary windings; and At least one DC conversion unit is connected to the output end of the rectification unit, and each of the DC conversion units includes: A first power conversion circuit, wherein the first power conversion circuit is a single-stage DC conversion circuit; a second power conversion circuit connected in parallel to the input end of the first power conversion circuit to suppress current oscillation at the input end of the first power conversion circuit; Wherein, each of the secondary windings is connected to a corresponding power conversion unit.

2. The medium voltage input DC power supply system according to claim 1, characterized in that: The first power conversion circuit includes a first inductor and a second inductor. The first terminal of the first inductor is connected in series with the first output terminal of the first power conversion circuit. The first terminal of the second inductor is connected in series with the second output terminal of the first power conversion circuit.

3. The medium voltage input DC power supply system according to claim 2, characterized in that: The first power conversion circuit comprises: A first bridge arm comprises a third switch and a fifth switch connected in series, wherein the first output terminal is provided between the third switch and the fifth switch; The second bridge arm comprises a fourth switch and a sixth switch connected in series, wherein the second output terminal is provided between the fifth switch and the sixth switch, and the fifth switch and the sixth switch are connected in series; A second capacitor is connected to two ends of the first bridge arm; A third capacitor is connected to two ends of the second bridge arm; as well as A fourth capacitor, wherein two ends of the fourth capacitor are respectively connected to the second terminal of the first inductor and the second terminal of the second inductor.

4. The medium voltage input DC power supply system according to claim 2, characterized in that: The first power conversion circuit comprises: A first bridge arm comprises a third switch and a fifth switch connected in series, wherein the first output terminal is provided between the third switch and the fifth switch; The second bridge arm comprises a fourth switch and a sixth switch connected in series, the second output terminal is provided between the fifth switch and the sixth switch, the fifth switch is connected in series with the sixth switch, and a third node is provided between the fifth switch and the sixth switch; A second capacitor is connected to two ends of the first bridge arm; A third capacitor is connected to two ends of the second bridge arm; as well as A fourth capacitor and a fifth capacitor, wherein two ends of the fourth capacitor are respectively connected to the second terminal and the third node of the first inductor, and two ends of the fifth capacitor are respectively connected to the second terminal and the third node of the second inductor.

5. The medium voltage input DC power supply system according to claim 3, characterized in that: The fifth switch and the sixth switch are both diodes.

6. The medium voltage input DC power supply system according to claim 4, characterized in that: The fifth switch and the sixth switch are both diodes.

7. The medium voltage input DC power supply system according to claim 5 or 6, characterized in that: The first power conversion circuit further includes a first diode, wherein an anode of the first diode is connected to the second output terminal, and a cathode of the first diode is connected to the first output terminal.

8. The medium voltage input DC power supply system according to claim 3, characterized in that , the voltage across the first bridge arm is equal to the voltage across the second bridge arm, and the third switch and the fourth switch have the same withstand voltage characteristics.

9. The medium voltage input DC power supply system according to claim 4, characterized in that , the voltage across the first bridge arm is equal to the voltage across the second bridge arm, and the third switch and the fourth switch have the same withstand voltage characteristics.

10. The medium voltage input DC power supply system according to claim 3, characterized in that: The voltages at both ends of the first bridge arm and the voltages at both ends of the second bridge arm are not equal, and the third switch and the fourth switch have different withstand voltage characteristics.

11. The medium voltage input DC power supply system according to claim 4, characterized in that: The voltages at both ends of the first bridge arm and the voltages at both ends of the second bridge arm are not equal, and the third switch and the fourth switch have different withstand voltage characteristics.

12. The medium voltage input DC power supply system according to claim 10, characterized in that: A ratio of a voltage across the first bridge arm to a voltage across the second bridge arm is greater than or equal to 1.5 and less than or equal to 10.

13. The medium voltage input DC power supply system according to claim 11, characterized in that: A ratio of a voltage across the first bridge arm to a voltage across the second bridge arm is greater than or equal to 1.5 and less than or equal to 10.

14. The medium voltage input DC power supply system according to claim 2, characterized in that: Each of the power conversion modules includes a plurality of DC conversion units with input ends connected in parallel, and output ends of the plurality of DC conversion units are connected in parallel.

15. The medium voltage input DC power supply system according to claim 2, characterized in that: Each of the power conversion units includes a plurality of power conversion modules whose input ends are connected in parallel, and output ends of the plurality of power conversion modules are connected in parallel.

16. The medium voltage input DC power supply system according to claim 15, characterized in that: It comprises a plurality of the power conversion units, and the output ends of the plurality of the power conversion units are connected in series.

17. The medium voltage input DC power supply system according to claim 15, characterized in that: It comprises a plurality of the power conversion units, and the output ends of the plurality of the power conversion units are connected in parallel.

18. The medium voltage input DC power supply system according to claim 15, characterized in that: Include: K secondary windings and K power conversion units corresponding to each other, wherein voltage phases output by the K secondary windings are sequentially different by a phase shift angle; M groups of output busbars; among them, The K power conversion units are divided into L groups of output units according to a first order, each of the output units includes M power conversion units, and the output ends of the M power conversion units in each of the output units are connected in parallel one by one according to the first order to form the M groups of output busbars, wherein K≥2, M≥2, L=K / M, and K is a multiple of M.

19. The medium voltage input DC power supply system according to claim 15, characterized in that: Include: A first output unit and a second output unit, wherein the first output unit includes I secondary windings and I power conversion units corresponding to each other, and the output ends of the I power modules are connected in parallel; The second output unit includes J secondary windings and J power conversion units corresponding to each other, and the output ends of the J power modules are connected in parallel, wherein I≥2, J≥2; The output terminal of the first output unit is connected in series with the output terminal of the second output unit.

20. The medium voltage input DC power supply system according to claim 19, characterized in that: A series connection point of an output terminal of the first output unit and an output terminal of the second output unit is grounded.

21. The medium voltage input DC power supply system according to claim 18, characterized in that: The output busbars are 4 groups.

22. The medium voltage input DC power supply system according to claim 1, characterized in that: The second power conversion circuit comprises: a first port and a second port; a third inductor, a first switch and a second switch, wherein the first switch and the second switch are connected in series, and a node is provided between the first switch and the second switch; The third inductor is connected between the node and a first end of the first port of the second power conversion circuit.

23. The medium voltage input DC power supply system according to claim 22, characterized in that: The DC conversion unit further includes a first capacitor connected between the third inductor and an input end of the first power conversion circuit.

24. The medium voltage input DC power supply system according to claim 1, characterized in that: Also includes a first controller, the first controller includes a voltage loop regulator, a current loop regulator, and a damping current generator; The voltage loop regulator outputs a first reference current according to the second port voltage of the second power conversion circuit and the first reference voltage; The damping current generator outputs a second reference current according to at least part of the AC component of the input voltage of the oscillation suppression module and the first coefficient; Outputting a third reference current according to the first reference current and the second reference current; The current loop regulator outputs a driving signal according to the third inductor current of the second power conversion circuit and the third reference current; The duty cycle of the first switch and the duty cycle of the second switch are adjusted according to the driving signal.

25. The medium voltage input DC power supply system according to claim 24, characterized in that: The damping current generator outputs the second reference current according to at least part of the AC component of the input voltage of the oscillation suppression module and the first coefficient, and in combination with the output power of the first power conversion circuit.

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