A high-capacity single-stage ac / dc converter and a control method thereof

Abstract

The application relates to a large-capacity single-stage AC / DC converter and a control method thereof, and belongs to the field of power electronics. The converter is composed of two same converters, and each converter is composed of a medium-voltage AC voltage regulation circuit, a single-phase medium-frequency transformer and a low-voltage rectifier circuit. The medium-voltage AC voltage regulation circuit and the low-voltage rectifier circuit use anti-parallel thyristor valve groups and diode valve groups respectively, so that the topological efficiency and reliability are improved; the single-phase medium-frequency transformer replaces multiple distributed high-frequency transformers, so that the topological cost is reduced; the voltage and current of the bridge arm series sub-modules of the medium-voltage AC voltage regulation circuit have high controllability, the output end can be connected to DC loads of different voltage grades, and the parallel connection structure of the two converters can significantly improve the transmission power of the power supply. The on-off sequence of the thyristor valve group period flip effectively reduces the voltage and current stress of the sub-module bridge arm. The converter has the advantages of few conversion stages, large power capacity, wide voltage output range and the like, and is suitable for large-capacity DC power supply scenes.

Description

Technical Field

[0001] This invention relates to the field of power electronics, specifically to a high-capacity single-stage AC / DC converter and its control method, applicable to fields requiring DC power supply, such as data center power supply and new energy vehicle charging stations. Background Technology

[0002] With the introduction of the "dual-carbon" strategy, new DC load industries such as data centers have developed rapidly. Their power supply method involves drawing power from medium-voltage AC (MVAC) buses and converting it into low-voltage DC (LVDC) to supply power to the loads. In 2022, global data center electricity consumption reached 460 billion kilowatt-hours, accounting for nearly 2% of global total electricity consumption, and is projected to grow to over 1 trillion kilowatt-hours by 2026. In 2023, my country's data center electricity consumption reached 150 billion kilowatt-hours, a year-on-year increase of 15.4%, accounting for 1.63% of total social electricity consumption.

[0003] Publication No. CN120033707A details a data center power supply system, proposing a data center power supply circuit based on multiple multi-port solid-state transformers. However, it suffers from problems such as a large number of components, power modules, and high-frequency transformers. Furthermore, the efficiency of the multi-stage rectification structure of the solid-state transformer is difficult to improve. Additionally, the insulation design of the high-frequency transformer in the DC / DC unit within the existing solid-state transformer is relatively difficult and costly, and its voltage regulation range is narrow.

[0004] As can be seen from the above, the application of CN120033707A is limited by factors such as technical economy, size, and reliability. In particular, for DC power supplies in the fields of data centers and electric vehicle charging stations, meeting the technical requirements of large capacity, wide output voltage range, controllable cost, high power density, and high reliability is a key research issue at present. Summary of the Invention

[0005] This invention addresses the problem that DC power supplies in data centers and electric vehicle charging stations cannot meet the technical requirements of large capacity, wide output voltage range, controllable cost, high power density, and high reliability. It provides a large-capacity single-stage AC / DC converter and its control method.

[0006] The technical solution adopted in this invention is:

[0007] A high-capacity single-stage AC / DC converter is provided, which is connected to a three-phase AC power grid, consisting of phases A, B, and C.

[0008] The converter contains two converters and an output filter capacitor C. o The two converters are converter number one and converter number two, and the output filter capacitor C... oThe two ends are the low-voltage DC output terminals Udc of the converter;

[0009] Converter No. 1 and Converter No. 2 use the same circuit topology. Each converter consists of a medium-voltage AC voltage regulation circuit, a single-phase intermediate frequency transformer and a low-voltage rectifier circuit.

[0010] The medium-voltage AC voltage regulating circuit in the No. 1 converter includes anti-parallel thyristor valve group T1, anti-parallel thyristor valve group T2, thyristor series inductor L1, thyristor series inductor L2, sub-module series bridge arm S1, and sub-module series bridge arm S2.

[0011] The single-phase intermediate frequency transformer operates at a frequency of 300 Hz. The single-phase intermediate frequency transformer consists of a transformer and a transformer leakage inductance L. k1 The transformer is composed of a primary side and a secondary side. The primary side includes a primary side first terminal and a primary side second terminal, and the secondary side includes a secondary side first terminal and a secondary side second terminal. The primary side first terminal and the secondary side first terminal are of the same name. The transformer's turns ratio is n:1, and the leakage inductance is L. k1 Where n and k are both real numbers;

[0012] The low-voltage rectifier circuit uses a diode rectifier bridge, and the diode rectifier bridge is a high-capacity voltage-connected structure, including diode D. L1 diode D L2 diode D L3 diode D L4 and the output filter capacitor C o ;

[0013] One end of each of the thyristor series inductors L1 and L2 is connected to phase A of the three-phase AC power grid. The other end of the thyristor series inductor L1 is connected to one end of the anti-parallel thyristor valve group T1, and the other end of the anti-parallel thyristor valve group T1 is connected to one end of the submodule bridge arm S1. The other end of the thyristor series inductor L2 is connected to one end of the anti-parallel thyristor valve group T2, and the other end of the anti-parallel thyristor valve group T2 is connected to one end of the submodule bridge arm S2. The other ends of each of the submodule bridge arms S1 and S2 are connected to phase B of the three-phase power grid.

[0014] The thyristor series inductor L1, the anti-parallel thyristor valve group T1, and the submodule bridge arm S1 constitute the first bridge arm on the medium voltage side of the first converter, and the thyristor series inductor L2, the anti-parallel thyristor valve group T2, and the submodule bridge arm S2 constitute the second bridge arm on the medium voltage side of the second converter.

[0015] The transformer leakage inductance L of the single-phase intermediate frequency transformer k1 One end is connected between the anti-parallel thyristor valve group T1 in the first bridge arm and the submodule bridge arm S1, and the transformer leakage inductance L k1The other end is connected to the first terminal of the primary side, and the second terminal of the primary side is connected between the anti-parallel thyristor valve group T2 and the submodule bridge arm S2 in the second bridge arm;

[0016] The diode D in the low-voltage rectifier circuit L1 D L3 The diodes are connected in series and form the first arm of the diode rectifier bridge. L2 D L4 The first arm of the diode rectifier bridge is connected in series and forms the second arm of the diode rectifier bridge; the second arm of the diode rectifier bridge is connected in parallel with the first arm of the diode rectifier bridge.

[0017] The first terminal of the secondary side of the single-phase intermediate frequency transformer is connected to the middle node of the first bridge arm of the diode rectifier bridge, and the second terminal of the secondary side of the single-phase intermediate frequency transformer is connected to the middle node of the second bridge arm of the diode rectifier bridge.

[0018] The medium-voltage AC voltage regulation circuit in the No. 2 converter includes anti-parallel thyristor valve group T3, anti-parallel thyristor valve group T4, thyristor series inductor L3, thyristor series inductor L4, sub-module series bridge arm S3, and sub-module series bridge arm S4.

[0019] The single-phase intermediate frequency transformer in converter No. 2 operates at a frequency of 300 Hz. The single-phase intermediate frequency transformer consists of a transformer and a transformer leakage inductance L. k2 The transformer is composed of a primary side and a secondary side. The primary side includes a primary side first terminal and a primary side second terminal, and the secondary side includes a secondary side first terminal and a secondary side second terminal. The primary side first terminal and the secondary side first terminal are of the same name. The transformer's turns ratio is n:1, and the leakage inductance is L. k2 Where n and k are both real numbers;

[0020] One end of each of the thyristor series inductors L3 and L4 is connected to phase A of the three-phase AC power grid. The other end of the thyristor series inductor L3 is connected to one end of the anti-parallel thyristor valve group T3, and the other end of the anti-parallel thyristor valve group T3 is connected to one end of the submodule bridge arm S3. The other end of the thyristor series inductor L4 is connected to one end of the anti-parallel thyristor valve group T4, and the other end of the anti-parallel thyristor valve group T4 is connected to one end of the submodule bridge arm S4. The other ends of each of the submodule bridge arms S3 and S4 are connected to phase C of the three-phase power grid.

[0021] The thyristor series inductor L3, the anti-parallel thyristor valve group T3, and the submodule bridge arm S3 constitute the first bridge arm on the medium voltage side of the second converter, and the thyristor series inductor L4, the anti-parallel thyristor valve group T4, and the submodule bridge arm S4 constitute the second bridge arm on the medium voltage side of the second converter.

[0022] The transformer leakage inductance L of the single-phase intermediate frequency transformer in converter No. 2 k2 One end is connected between the anti-parallel thyristor valve group T3 in the first bridge arm and the submodule bridge arm S3, and the transformer leakage inductance L k2 The other end is connected to the first terminal of the primary side, and the second terminal of the primary side is connected between the anti-parallel thyristor valve group T4 and the submodule bridge arm S4 in the second bridge arm;

[0023] Diode D in the low-voltage rectifier circuit of converter No. 2 L5 D L7 The diodes are connected in series and form the first arm of the diode rectifier bridge. L6 D L8 The first arm of the diode rectifier bridge is connected in series and forms the second arm of the diode rectifier bridge; the second arm of the diode rectifier bridge is connected in parallel with the first arm of the diode rectifier bridge.

[0024] In the No. 2 converter, the first terminal of the secondary side of the single-phase intermediate frequency transformer is connected to the middle node of the first arm of the diode rectifier bridge, and the second terminal of the secondary side of the single-phase intermediate frequency transformer is connected to the middle node of the second arm of the diode rectifier bridge.

[0025] Diode D of converter No. 1 L2 cathode and D L4 The anode of the diode is connected to the DC output terminal of converter number one; diode D of converter number two... L6 cathode and D L8 The anode of the first converter is connected to the DC output terminal of the second converter; the DC output terminals of the two converters are connected in parallel, and both are connected in parallel with a filter capacitor C. o Filter capacitor C o The two ends are the low-voltage DC output terminals Udc of the converter.

[0026] Furthermore, the control timing of the transformers in converter 1 and converter 2 differs by a quarter of a control cycle. That is, the trapezoidal current output by the two transformers and the double-frequency positive trapezoidal current output by the two converters after rectification by the low-voltage rectifier circuit differ in phase by a quarter of a transformer operating cycle. In other words, the phase difference satisfies...

[0027]

[0028] Among them, T φ It is the phase difference between the trapezoidal wave currents output by the two transformers, and also the phase difference between the double-frequency positive trapezoidal wave currents output by the two converters after rectification by the low-voltage rectifier circuit. T is the transformer operating cycle, Tz is the transformer zero-current time, and Tc is the transformer current adjustment time.

[0029] Furthermore, both the first converter and the second converter can operate independently.

[0030] Furthermore, the connection order of the No. 1 and No. 2 converters to the A-phase, B-phase, and C-phase terminals of the three-phase AC power grid can also be interchanged; the input terminal of the medium-voltage AC voltage regulating circuit can also adopt a three-phase angle connection method.

[0031] Furthermore, the operation of the aforementioned high-capacity single-stage AC / DC converter can be divided into six stages:

[0032] Phase 1 [t0~t1]: T1 is on, T2 is off, and the voltage of submodule bridge arm S1 is u. ac The current of T1 is controlled by submodule bridge arm S1 to be i ac Achieving unity power factor; the voltage of submodule bridge arm S2 is u ac -nU dc Apply voltage nU to the transformer dc The control transformer current is I dc / n, by actively adjusting the voltage applied to the transformer by the first and second bridge arms in the No. 1 transformer, a wide DC voltage range operation is achieved;

[0033] Phase 2 [t1~t2]: The voltage of submodule bridge arm S2 changes from u ac -nU dc Upgrade to u ac The voltage change time corresponding to the preparation for thyristor commutation is defined as T. u At time t2, the voltage across thyristor T2 is approximately zero, achieving zero-voltage turn-on; during this process, the transformer voltage amplitude is less than nU. dc The DC-side diode is in the off state, and the transformer current is zero. During the voltage rise of submodule bridge arm S2, submodule bridge arm S1 is sequentially switched on or off at short intervals to limit the du / dt generated on thyristor T2 and prevent false turn-on. du / dt is the voltage change per unit time.

[0034] Phase 3 [t2~t3]: This is the thyristor commutation phase. Both T1 and T2 are in the conducting state. By actively adjusting the voltages of the submodule bridge arms S1 and S2, commutation voltages U with opposite amplitudes are applied to the series inductors L1 and L2 of the two thyristors T1 and T2. T This causes the current in T1 to flow from i ac The current gradually decreases to zero, while the current in T2 gradually increases from zero to i. ac The di / dt current of thyristors T1 and T2 is limited to enable zero-current turn-off of T1. The time used in this stage is the commutation time T. c The current flowing through the thyristor is combined into i acTo ensure the continuity of the medium-voltage AC current, the transformer voltage amplitude is less than nU during this stage. dc The transformer current is zero; di / dt is the current changing per unit time.

[0035] Phase 4 [t3~t4]: After the current in T1 decreases to zero, adjust the voltage in S1 to u. ac +U R Actively apply back pressure U to T1 R The duration is T q T1 achieves reliable shutdown; at this time, the medium-voltage AC current is only borne by T2; T q Based on the thyristor turn-off time design, the turn-off time of ordinary thyristor modules is generally less than 400μs, while the turn-off time of fast-switching thyristors is generally between 25μs and 80μs.

[0036] Phase 5 [t4~t5]: T1 is off, T2 remains on; the voltage of submodule bridge arm S1 gradually decreases to u. ac -nU dc During the voltage drop, du / dt is constrained;

[0037] Phase 6 [t5~t6]: Submodule bridge arm S2 supports medium-voltage AC voltage, and the voltage of submodule bridge arm S1 is u. ac -nU dc The voltage difference between the bridge arms maintains the DC voltage and controls the DC current. By adjusting the voltage of the submodule bridge arm S1, the voltage amplitude of the transformer is changed, thus achieving wide voltage range operation.

[0038] A control method for a high-capacity single-stage AC / DC converter is proposed, which includes...

[0039] Phase 1 [t0~t1]: T1 is on, T2 is off, and the voltage of submodule bridge arm S1 is u. ac The current of T1 is controlled by submodule bridge arm S1 to be i ac Achieving unity power factor; the voltage of submodule bridge arm S2 is u ac -nU dc Apply voltage nU to the transformer dc The control transformer current is I dc / n, a method to achieve wide DC voltage range operation by actively adjusting the voltage applied to the transformer by the first and second bridge arms in the first transformer;

[0040] Phase 2 [t1~t2]: The voltage of submodule bridge arm S2 changes from u ac -nU dc Upgrade to u ac The voltage change time corresponding to the preparation for thyristor commutation is defined as T. uAt time t2, the voltage across thyristor T2 is approximately zero, achieving zero-voltage turn-on; during this process, the transformer voltage amplitude is less than nU. dc The DC-side diode is in the off state, and the transformer current is zero. During the voltage rise of submodule bridge arm S2, submodule bridge arm S1 is sequentially switched on or off at short intervals to limit the du / dt generated on thyristor T2 and prevent false turn-on. du / dt is the voltage change per unit time.

[0041] Phase 3 [t2~t3]: This is the thyristor commutation phase. Both T1 and T2 are in the conducting state. By actively adjusting the voltages of the submodule bridge arms S1 and S2, commutation voltages U with opposite amplitudes are applied to the series inductors L1 and L2 of the two thyristors T1 and T2. T This causes the current in T1 to flow from i ac The current gradually decreases to zero, while the current in T2 gradually increases from zero to i. ac The di / dt current of thyristors T1 and T2 is limited to enable zero-current turn-off of T1. The time used in this stage is the commutation time T. c The current flowing through the thyristor is combined into i ac To ensure the continuity of the medium-voltage AC current, the transformer voltage amplitude is less than nU during this stage. dc Methods to make the transformer current zero; di / dt is the current flowing per unit time;

[0042] Phase 4 [t3~t4]: After the current in T1 decreases to zero, adjust the voltage in S1 to u. ac +U R Actively apply back pressure U to T1 R The duration is T q T1 achieves reliable shutdown; at this time, the medium-voltage AC current is only borne by T2; T q Based on the thyristor turn-off time design, the turn-off time of ordinary thyristor modules is generally less than 400μs, while the turn-off time of fast-switching thyristors is generally between 25μs and 80μs.

[0043] Phase 5 [t4~t5]: T1 is off, T2 remains on; the voltage of submodule bridge arm S1 gradually decreases to u. ac -nU dc A method for constraining du / dt during voltage drop;

[0044] Phase 6 [t5~t6]: Submodule bridge arm S2 supports medium-voltage AC voltage, and the voltage of submodule bridge arm S1 is u. ac -nU dc The voltage difference between the bridge arms maintains the DC voltage and controls the DC current. By adjusting the voltage of the submodule bridge arm S1, the transformer voltage amplitude is changed, thus achieving a wide voltage range operation method.

[0045] Thyristor conduction mode 1: When the medium-voltage AC current is in the positive half-cycle of a power frequency cycle, the anti-parallel thyristor valve groups T1 and T2 are alternately turned on, and the number of turns is the same, alternately sharing the medium-voltage AC current; when the medium-voltage AC current drops to 0, the original forward conduction of T2 is naturally turned off, and T2 is turned on in reverse. The sub-module bridge arm S2 connected in series with T2 continues to support the medium-voltage AC voltage. In order to ensure continuous power transmission, the voltage of bridge arm S1 rises so that the voltage difference between the two bridge arms provides the transformer voltage. Thereafter, S1 and S2 alternately bear the medium-voltage AC voltage. Since the thyristor conduction sequence is reversed at the zero crossing of the medium-voltage AC current, the maximum voltage stress of the bridge arm is the medium-voltage AC voltage, and the maximum current stress is the transformer current.

[0046] Thyristor conduction mode two: The conduction timing of the thyristor valve group remains constant, that is, the anti-parallel thyristor valve groups T1 and T2 always maintain periodic alternating conduction. When the medium voltage AC current drops to 0, the original forward conduction of T2 naturally turns off, and T1 turns on in reverse to complete the switching. At this time, the sub-module bridge arm S1 connected in series with T1 supports the medium voltage AC voltage. In order to ensure continuous power transmission, the voltage of the S2 bridge arm drops, and the voltage difference between the two bridge arms provides the transformer voltage. Thereafter, S1 and S2 alternately bear the medium voltage AC voltage. The maximum voltage stress of the bridge arm is the medium voltage AC voltage plus the transformer voltage. When the bridge arm supports the medium voltage AC voltage, it also needs to provide transformer current. Therefore, under this thyristor switching logic, the maximum current stress of the bridge arm is the transformer current plus the medium voltage AC current.

[0047] Beneficial Effects: A high-capacity single-stage AC / DC converter and its control method mainly utilize anti-parallel thyristor valve groups and submodule bridge arms to achieve wide voltage output, requiring only one AC-DC conversion and fewer conversion stages. The periodic switching conduction timing of the thyristor valve groups effectively reduces the voltage and current stress on the submodule bridge arms. In summary, this invention has advantages such as fewer conversion stages, simple structure, large power capacity, low topology stress, direct connection to medium voltage, and wide voltage output range.

[0048] 1. This invention uses low-cost, high-capacity diodes and thyristors to construct the topology, resulting in a lower overall equipment cost and suitability for high-power applications.

[0049] 2. The present invention has fewer power conversion stages, eliminates the need for a medium-voltage side rectifier bridge, reduces one stage of AC / DC conversion, and also reduces the number of devices; the anti-parallel thyristor valve group is combined with the bridge arm submodule IGBT, allowing for flexible voltage regulation.

[0050] 3. Compared with the circuit topology based on solid-state transformer input series and output parallel design, the present invention uses a medium frequency transformer, which has fewer transformers and lower insulation cost; fewer modules and higher overall reliability.

[0051] 4. The present invention has smooth input and output current, low harmonic content, and high power quality.

[0052] 5. This invention has good output voltage regulation capability and can be used in DC power supply scenarios with different voltage levels.

[0053] 6. The thyristor turn-on timing logic used in this invention can reduce bridge arm voltage stress and bridge arm current stress, effectively reduce IGBT turn-on and switching losses, and protect the device from being easily damaged.

[0054] This invention utilizes anti-parallel thyristor valve groups and submodule bridge arms to achieve wide voltage output, requiring only one AC-DC conversion and fewer conversion stages. It meets the technical requirements of DC power supplies in data centers and electric vehicle charging stations in terms of large capacity, wide output voltage range, controllable cost, high power density, and high reliability. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the high-capacity single-stage AC / DC converter topology proposed in this invention;

[0056] Figure 2 This is a schematic diagram of a single-phase topology circuit for the high-capacity single-stage AC / DC converter proposed in this invention.

[0057] Figure 3 The thyristor switching timing and main voltage and current waveforms of the high-capacity single-stage AC / DC converter proposed in this invention are shown below.

[0058] Figure 4 This is a schematic diagram showing the phase shift of the intermediate frequency transformer current and the output current in the large-capacity single-stage AC / DC converter proposed in this invention;

[0059] Figure 5 The above are the bridge arm voltage waveforms of the large-capacity single-stage AC / DC converter proposed in this invention before and after thyristor commutation.

[0060] Figure 6 This is a schematic diagram of the current path in the first stage of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0061] Figure 7 This is a schematic diagram of the current path in the second stage of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0062] Figure 8 This is a schematic diagram of the current path in the third stage of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0063] Figure 9 This is a schematic diagram of the current path in the fourth stage of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0064] Figure 10 This is a schematic diagram of the current path in the fifth stage of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0065] Figure 11 This is a schematic diagram of the current path in stage six of operation of the high-capacity single-stage AC / DC converter proposed in this invention.

[0066] Figure 12 This is a schematic diagram of the bridge arm voltage and current waveforms when the thyristor conduction timing is constant in the large-capacity single-stage AC / DC converter proposed in this invention.

[0067] Figure 13 This is a schematic diagram of the bridge arm voltage and current waveforms when the thyristor conduction timing cycle of the large-capacity single-stage AC / DC converter proposed in this invention reverses. Detailed Implementation

[0068] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0069] The high-capacity single-stage AC / DC converter proposed in this invention comprises two identical converters, namely, converter one and converter two adopt the same circuit topology and are star-connected to the medium-voltage AC power grid. Both converters include a medium-voltage AC voltage regulating circuit composed of anti-parallel thyristor valve groups and submodule bridge arms, a single-phase intermediate frequency transformer, and a low-voltage rectifier circuit composed of press-fit diodes.

[0070] Introduction of components

[0071] Taking converter one as an example, the circuit components are as follows:

[0072] The medium-voltage AC voltage regulating circuit in this topology includes: anti-parallel thyristor valve group T1, anti-parallel thyristor valve group T2, thyristor branch series inductor L1, thyristor branch series inductor L2, submodule bridge arm S1, and submodule bridge arm S2. The anti-parallel thyristor valve group is composed of several anti-parallel thyristors connected in series, and the submodule bridge arm is composed of several submodules connected in series. The single-phase intermediate frequency transformer typically operates at 300 Hz and has a structure divided into a primary side and a secondary side. The primary side includes a first terminal and a second terminal, and the secondary side also includes a first terminal and a second terminal. The first terminal on the primary side and the first terminal on the secondary side of the transformer are of the same name. The transformer turns ratio is n:1, and the transformer leakage inductance is L. k1 The low-voltage rectifier circuit diodes adopt a high-capacity press-fit structure, including diode D. L1 diode D L2 diode D L3 diode DL4 and output filter capacitor C o ;

[0073] The second converter has the same circuits and components as the first converter.

[0074] Introduction to connection methods

[0075] The connection method for a high-capacity single-stage AC / DC converter is as follows: The upper terminals of the thyristor series inductors L1 and L2 are connected to phase A of the three-phase AC power grid, and the lower terminals of the thyristor series inductors L1 and L2 are connected to the anti-parallel thyristor valve groups T1 and T2, respectively. The lower terminals of the submodule bridge arms S1 and S2 are connected to phase B of the three-phase power grid. The thyristor series inductor L1, the anti-parallel thyristor valve group T1, and the submodule bridge arm S1 constitute the first bridge arm of the medium-voltage side of the converter, and the thyristor series inductor L2, the anti-parallel thyristor valve group T2, and the submodule bridge arm S2 constitute the second bridge arm of the medium-voltage side of the converter. The leakage inductance L of the intermediate frequency transformer... k1 According to the primary side, leakage inductance L k1 The left terminal is connected between the first bridge arm anti-parallel thyristor valve group T1 and the submodule bridge arm S1, with leakage inductance L k1 The right-side terminal is connected to the first terminal on the primary side, and the second terminal on the primary side is connected between the second bridge arm anti-parallel thyristor valve group T2 and the submodule bridge arm S2. The diode D on the low-voltage DC side... L1 D L3 The first arm of the diode rectifier bridge, diode D L2 D L4 This forms the second arm of the diode rectifier bridge. The first terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the first arm of the diode rectifier bridge, and the second terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the second arm of the diode rectifier bridge. The first terminals of the primary and secondary sides of the intermediate frequency transformer form the same-name terminals. The upper terminals of the thyristor series inductors L3 and L4 are connected to phase A of the three-phase AC power grid, and the lower terminals of the thyristor series inductors L3 and L4 are connected to the anti-parallel thyristor valve groups T3 and T4, respectively. The lower terminals of the submodule arms S3 and S4 are connected to phase C of the three-phase power grid. The thyristor series inductor L3, the anti-parallel thyristor valve group T3, and the submodule arm S3 form the first arm of the medium-voltage side of converter two, and the thyristor series inductor L4, the anti-parallel thyristor valve group T4, and the submodule arm S4 form the second arm of the medium-voltage side of converter two. The leakage inductance L of the intermediate frequency transformer... k2 According to the primary side, leakage inductance L k2 The left terminal is connected between the first bridge arm anti-parallel thyristor valve group T3 and the submodule bridge arm S3, with leakage inductance L k2The right-side terminal is connected to the first terminal on the primary side, and the second terminal on the primary side is connected between the second bridge arm anti-parallel thyristor valve group T4 and the submodule bridge arm S4. The diode D on the low-voltage DC side... L5 D L7 The first arm of the diode rectifier bridge, diode D L6 D L8 This forms the second arm of the diode rectifier bridge. The first terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the first arm of the diode rectifier bridge, and the second terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the second arm of the diode rectifier bridge. The first terminals of the primary and secondary sides of the intermediate frequency transformer form the same-name terminals. The DC output ports of the two converters are connected in parallel, along with a filter capacitor C. o .

[0076] Working principle:

[0077] The control method and working principle of a high-capacity single-stage AC / DC converter include the following parts:

[0078] Part 1: Taking a single converter as an example, within one power frequency cycle, the two bridge arms' anti-parallel thyristor valve groups alternately conduct, ensuring the continuity of the input medium-voltage AC current and cooperating with the sub-module bridge arms to generate a trapezoidal AC voltage on the transformer. Before the thyristor conducts, the corresponding bridge arm voltage rises to the medium-voltage AC voltage, ensuring the thyristor turns on under relatively low voltage stress and reducing thyristor turn-on stress. When the bridge arm thyristor conducts, the sub-module of the same bridge arm supports the input AC voltage and simultaneously controls the medium-voltage AC current. When the other bridge arm thyristor turns off, the voltage of the corresponding bridge arm is the difference between the medium-voltage AC voltage and the transformer primary voltage. After the thyristor turns off, the other bridge arm can also actively apply reverse voltage. The commutation process between the two bridge arms involves a certain commutation time to limit di / dt. By adjusting the transformer voltage amplitude, a wide range of DC-side voltage output can be achieved. The transformer current is controlled as a trapezoidal wave, and the rectified DC current becomes a trapezoidal wave with a frequency twice that of the transformer frequency. When both converters operate simultaneously, the superposition of the output trapezoidal waves results in a stable DC output.

[0079] Part Two: In the high-capacity single-stage AC / DC converter proposed in this invention, the transformer control timing of Converter 1 (Converter No. 1) and Converter 2 (Converter No. 2) differs by one-quarter of a control cycle. That is, the trapezoidal current output by the two transformers and the double-frequency positive trapezoidal current output by the two converters after rectification by the low-voltage rectifier circuit are phase-differentiated by one-quarter of a transformer operating cycle. In other words, the phase difference satisfies... Among them, T φIt is the phase difference between the trapezoidal wave currents output by the two transformers, and also the phase difference between the double-frequency positive trapezoidal wave currents output by the two converters after rectification by the low-voltage rectifier circuit. T is the transformer operating cycle, Tz is the transformer zero-current time, and Tc is the transformer current adjustment time.

[0080] Part Three: Specifically, taking a single converter as an example, the operation of this high-capacity single-stage AC / DC converter can be divided into six stages:

[0081] Phase 1 [t0~t1]: T1 is on, T2 is off, and the voltage of submodule bridge arm S1 is u. ac The current of T1 is controlled by submodule bridge arm S1 to be i ac Achieving unity power factor; the voltage of submodule bridge arm S2 is u ac -nU dc Apply voltage nU to the transformer dc The control transformer current is I dc / n, a method to achieve wide DC voltage range operation by actively adjusting the voltage applied to the transformer by the first and second bridge arms in the first transformer;

[0082] Phase 2 [t1~t2]: The voltage of submodule bridge arm S2 changes from u ac -nU dc Upgrade to u ac The voltage change time corresponding to the preparation for thyristor commutation is defined as T. u At time t2, the voltage across thyristor T2 is approximately zero, achieving zero-voltage turn-on; during this process, the transformer voltage amplitude is less than nU. dc The DC-side diode is in the off state, and the transformer current is zero. During the voltage rise of submodule bridge arm S2, submodule bridge arm S1 is sequentially switched on or off at short intervals to limit the du / dt generated on thyristor T2 and prevent false turn-on. du / dt is the voltage change per unit time.

[0083] Phase 3 [t2~t3]: This is the thyristor commutation phase. Both T1 and T2 are in the conducting state. By actively adjusting the voltages of the submodule bridge arms S1 and S2, commutation voltages U with opposite amplitudes are applied to the series inductors L1 and L2 of the two thyristors T1 and T2. T This causes the current in T1 to flow from i ac The current gradually decreases to zero, while the current in T2 gradually increases from zero to i. ac The di / dt current of thyristors T1 and T2 is limited to enable zero-current turn-off of T1. The time used in this stage is the commutation time T. c The current flowing through the thyristor is combined into i ac To ensure the continuity of the medium-voltage AC current, the transformer voltage amplitude is less than nU during this stage.dc Methods to make the transformer current zero; di / dt is the current flowing per unit time;

[0084] Phase 4 [t3~t4]: After the current in T1 decreases to zero, adjust the voltage in S1 to u. ac +U R Actively apply back pressure U to T1 R The duration is T q T1 achieves reliable shutdown; at this time, the medium-voltage AC current is only borne by T2; T q Based on the thyristor turn-off time design, the turn-off time of ordinary thyristor modules is generally less than 400μs, while the turn-off time of fast-switching thyristors is generally between 25μs and 80μs.

[0085] Phase 5 [t4~t5]: T1 is off, T2 remains on; the voltage of submodule bridge arm S1 gradually decreases to u. ac -nU dc A method for constraining du / dt during voltage drop;

[0086] Phase 6 [t5~t6]: Submodule bridge arm S2 supports medium-voltage AC voltage, and the voltage of submodule bridge arm S1 is u. ac -nU dc The voltage difference between the bridge arms maintains the DC voltage and controls the DC current. By adjusting the voltage of the submodule bridge arm S1, the transformer voltage amplitude is changed, thus achieving a wide voltage range operation method.

[0087] Part Four: The conduction timing of the anti-parallel thyristor valve group in a large-capacity single-stage AC / DC converter is divided into conduction mode one and conduction mode two. The voltage and current stress borne by the bridge arm is different in different conduction modes, as detailed below.

[0088] For thyristor conduction mode 1, please refer to [link / reference]. Figure 12 During the positive half-cycle of a power frequency cycle, the anti-parallel thyristor valve groups T1 and T2 alternately conduct, with the same number of conductions, alternately sharing the medium-voltage AC current. When the medium-voltage AC current drops to 0, the original forward-conducting T2 naturally turns off. At this time, T2 is reverse-conducting, and the sub-module bridge arm S2 connected in series with T2 continues to support the medium-voltage AC voltage. To ensure continuous power transmission, the voltage of bridge arm S1 rises, and the voltage difference between the two bridge arms provides the transformer voltage. Thereafter, S1 and S2 alternately bear the medium-voltage AC voltage. Since the thyristor conduction sequence reverses at the zero-crossing point of the medium-voltage AC current, the maximum voltage stress of the bridge arm is the medium-voltage AC voltage, and the maximum current stress is the transformer current.

[0089] Thyristor conduction mode two, please refer to Figure 13The conduction timing of the thyristor valve group remains constant; that is, the anti-parallel thyristor valve groups T1 and T2 maintain a periodic alternating conduction. When the medium-voltage AC current drops to 0, the original forward conduction of T2 naturally turns off, and T1 turns on in reverse, completing the switching. At this time, the sub-module arm S1, connected in series with T1, supports the medium-voltage AC voltage. To ensure continuous power transmission, the voltage of the S2 arm drops, and the voltage difference between the two arms provides the transformer voltage. Subsequently, S1 and S2 alternately bear the medium-voltage AC voltage, and the maximum voltage stress of the arm is the sum of the medium-voltage AC voltage and the transformer voltage. When the arm supports the medium-voltage AC voltage, it also needs to provide transformer current. Therefore, under this thyristor switching logic, the maximum current stress of the arm is the sum of the transformer current and the medium-voltage AC current.

[0090] Example 1:

[0091] The high-capacity single-stage AC / DC converter proposed in this invention comprises two identical converters, namely, converter one and converter two adopt the same circuit topology and are star-connected to the medium-voltage AC power grid. Both converters include a medium-voltage AC voltage regulating circuit composed of anti-parallel thyristor valve groups and submodule bridge arms, a single-phase intermediate frequency transformer, and a low-voltage rectifier circuit composed of press-fit diodes.

[0092] Taking a single converter as an example, such as Figure 2 As shown, the circuit components are as follows:

[0093] The medium-voltage AC voltage regulating circuit in this topology includes: anti-parallel thyristor valve group T1, anti-parallel thyristor valve group T2, thyristor series inductor L1, thyristor series inductor L2, submodule bridge arm S1, and submodule bridge arm S2. The anti-parallel thyristor valve group is composed of several anti-parallel thyristors connected in series, and the submodule bridge arm is composed of several submodules connected in series. The single-phase intermediate frequency transformer typically operates at 300 Hz and has a structure divided into a primary side and a secondary side. The primary side includes a first terminal and a second terminal, and the secondary side also includes a first terminal and a second terminal. The first terminal on the primary side and the first terminal on the secondary side of the transformer are of the same name. The transformer turns ratio is n:1, and the transformer leakage inductance is L. k1 The low-voltage rectifier circuit diodes adopt a high-capacity press-fit structure, including diode D. L1 diode D L2 diode D L3 diode D L4 Diode D L1 With diode D L3 The first arm of the diode rectifier bridge, diode D L2 With diode D L4 The second arm of the diode rectifier bridge, the output filter capacitor C o It is connected in parallel at both ends of the rectifier bridge arm.

[0094] The devices and components of the second converter are exactly the same as those of the first converter.

[0095] The connection method for a high-capacity single-stage AC / DC converter is as follows: The upper terminals of the thyristor series inductors L1 and L2 are connected to phase A of the three-phase AC power grid, and the lower terminals of the thyristor series inductors L1 and L2 are connected to the anti-parallel thyristor valve groups T1 and T2, respectively. The lower terminals of the submodule bridge arms S1 and S2 are connected to phase B of the three-phase power grid. The thyristor series inductor L1, the anti-parallel thyristor valve group T1, and the submodule bridge arm S1 constitute the first bridge arm of the medium-voltage side of the converter, and the thyristor series inductor L2, the anti-parallel thyristor valve group T2, and the submodule bridge arm S2 constitute the second bridge arm of the medium-voltage side of the converter. The leakage inductance L of the intermediate frequency transformer... k1 According to the primary side, leakage inductance L k1 The left terminal is connected between the first bridge arm anti-parallel thyristor valve group T1 and the submodule bridge arm S1, with leakage inductance L k1 The right-side terminal is connected to the first terminal on the primary side, and the second terminal on the primary side is connected between the second bridge arm anti-parallel thyristor valve group T2 and the submodule bridge arm S2. The diode D on the low-voltage DC side... L1 D L3 The first arm of the diode rectifier bridge, diode D L2 D L4 This forms the second arm of the diode rectifier bridge. The first terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the first arm of the diode rectifier bridge, and the second terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the second arm of the diode rectifier bridge. The first terminals of the primary and secondary sides of the intermediate frequency transformer form the same-name terminals. The upper terminals of the thyristor series inductors L3 and L4 are connected to phase A of the three-phase AC power grid, and the lower terminals of the thyristor series inductors L3 and L4 are connected to the anti-parallel thyristor valve groups T3 and T4, respectively. The lower terminals of the submodule arms S3 and S4 are connected to phase C of the three-phase power grid. The thyristor series inductor L3, the anti-parallel thyristor valve group T3, and the submodule arm S3 form the first arm of the medium-voltage side of converter two, and the thyristor series inductor L4, the anti-parallel thyristor valve group T4, and the submodule arm S4 form the second arm of the medium-voltage side of converter two. The leakage inductance L of the intermediate frequency transformer... k2 According to the primary side, leakage inductance L k2 The left terminal is connected between the first bridge arm anti-parallel thyristor valve group T3 and the submodule bridge arm S3, with leakage inductance L k2 The right-side terminal is connected to the first terminal on the primary side, and the second terminal on the primary side is connected between the second bridge arm anti-parallel thyristor valve group T4 and the submodule bridge arm S4. The diode D on the low-voltage DC side... L5 D L7 The first arm of the diode rectifier bridge, diode D L6 D L8This forms the second arm of the diode rectifier bridge. The first terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the first arm of the diode rectifier bridge, and the second terminal of the secondary side of the intermediate frequency transformer is connected to the middle node of the second arm of the diode rectifier bridge. The first terminals of the primary and secondary sides of the intermediate frequency transformer form the same-name terminals. The DC output ports of the two converters are connected in parallel, and a single filter capacitor C is used. o Replace the filter capacitors in converters one and two.

[0096] The thyristor valve group switching timing and main voltage and current waveforms of the high-capacity single-stage AC / DC converter proposed in this invention are as follows: Figure 3 As shown, the phase-shifting design of the two intermediate frequency transformers is as follows: Figure 4 As shown, the detailed waveform of the bridge arm voltage is as follows: Figure 5 As shown. Taking the mentioned converter one as an example, the operation process is divided into six stages, as follows: Figure 6 ~ Figure 11 As shown. The bridge arm voltage and current waveforms under thyristor conduction mode are as follows. Figure 12 As shown, the bridge arm voltage and current waveforms under thyristor conduction mode two are as follows: Figure 13 As shown. The working process of each stage has been mentioned in the working principle section, and will not be repeated here.

[0097] In the high-capacity single-stage AC / DC converter described in this invention, both converter one and converter two can operate independently.

[0098] The connection order of the input terminals of the high-capacity single-stage AC / DC converter described in this invention with the A-phase, B-phase, and C-phase terminals of the three-phase AC power grid can also be interchanged; the medium-voltage input terminal can also use the three-phase delta connection method.

[0099] The high-capacity single-stage AC / DC converter described in this invention can be extended to use multiple medium-voltage AC voltage regulating circuits connected in parallel, series, or a series-parallel hybrid connection, and connected to multiple medium-frequency transformers respectively; the secondary sides of multiple transformers can be connected in parallel, series, or a series-parallel hybrid connection, and multiple low-voltage rectifier circuits can also be connected in parallel, series, or a series-parallel hybrid connection.

[0100] This invention discloses a high-capacity single-stage AC / DC converter, consisting of two identical converters, Converter 1 and Converter 2, directly connected to a medium-voltage AC power grid. Each converter comprises an anti-parallel thyristor valve group, a submodule bridge arm, a single-phase intermediate frequency transformer, and a diode rectifier bridge. The medium-voltage AC voltage regulation circuit and the low-voltage rectifier circuit respectively utilize the low-cost anti-parallel thyristor valve group and diode valve group. The thyristors and diodes have low conduction losses, and the series connection technology is mature, improving topology efficiency and reliability. Two intermediate frequency transformers replace multiple distributed high-frequency transformers, further reducing topology costs. The voltage and current of the series-connected submodule bridge arm are highly controllable, and the output can be connected to DC loads of different voltage levels. The parallel connection structure of the two converter outputs significantly improves the power transmission capacity. The periodic switching conduction sequence of the thyristor valve group effectively reduces the voltage and current stress on the submodule bridge arm. Overall, this high-capacity single-stage AC / DC converter has advantages such as fewer conversion stages, simple structure, large power capacity, low topology stress, direct connection to medium voltage, and wide voltage output range, making it very suitable for high-capacity DC power supply scenarios.

[0101] This invention has been illustrated through several specific embodiments. Those skilled in the art will understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A large-capacity single-stage AC / DC converter, which is connected to a three-phase AC power grid, phase A, phase B, phase C; characterized in that, The converter comprises two converters and an output filter capacitor C o The two converters are a first converter and a second converter, and two ends of the output filter capacitor C o are low-voltage direct-current output ends Ud c； the first converter and the second converter adopt the same circuit topology, and each converter is composed of a medium-voltage AC voltage regulating circuit, a single-phase medium-frequency transformer and a low-voltage rectifier circuit; the medium-voltage AC voltage regulating circuit in the first converter comprises anti-parallel thyristor valve group T1, anti-parallel thyristor valve group T2, thyristor series inductance L1, thyristor series inductance L2, sub-module series bridge arm S1 and sub-module series bridge arm S2; The single-phase intermediate frequency transformer operates at a frequency of 300 Hz, and the single-phase intermediate frequency transformer is composed of a transformer and a transformer leakage inductance L k1 The transformer is divided into a primary side and a secondary side, wherein the primary side comprises a first terminal and a second terminal, the secondary side comprises a first terminal and a second terminal, and the first terminal of the primary side and the first terminal of the secondary side are the same name terminals; the transformer ratio of the transformer is n:1, and the transformer leakage inductance is L k1 ; wherein n, k are real numbers; The low-voltage rectifier circuit adopts a diode rectifier bridge, and the diode rectifier bridge is a large-capacity pressure contact structure, including diodes D L1 , diodes D L2 , diodes D L3 , diodes D L4 , and the output filter capacitor C o ; one end of the thyristor series inductance L1 and L2 is connected to phase A of the three-phase AC power grid, the other end of the thyristor series inductance L1 is connected to one end of the anti-parallel thyristor valve group T1, the other end of the anti-parallel thyristor valve group T1 is connected to one end of the sub-module bridge arm S1; the other end of the thyristor series inductance L2 is connected to one end of the anti-parallel thyristor valve group T2, the other end of the anti-parallel thyristor valve group T2 is connected to one end of the sub-module bridge arm S2; the other end of the sub-module bridge arm S1 and S2 is connected to phase B of the three-phase power grid; the thyristor series inductance L1, the anti-parallel thyristor valve group T1 and the sub-module bridge arm S1 constitute the first bridge arm of the medium-voltage side of the first converter, and the thyristor series inductance L2, the anti-parallel thyristor valve group T2 and the sub-module bridge arm S2 constitute the second bridge arm of the medium-voltage side of the second converter; The transformer leakage inductance L of the single-phase intermediate frequency transformer k1 One end of the transformer leakage inductance L is connected between the anti-parallel thyristor valve group T1 and the sub-module bridge arm S1 in the first bridge arm. k1 The other end of the transformer leakage inductance L is connected to the first terminal on the primary side, and the second terminal on the primary side is connected between the anti-parallel thyristor valve group T2 and the sub-module bridge arm S2 in the second bridge arm. the diodes D of the low-voltage rectifier circuit L1 , D L3 are connected in series and form a first bridge arm of a diode bridge, the diodes D L2 , D L4 are connected in series and form a second bridge arm of the diode bridge; the first bridge arm of the diode bridge and the second bridge arm of the diode bridge are connected in parallel; the first terminal of the transformer secondary side of the single-phase medium-frequency transformer is connected to the middle node of the first bridge arm of the diode rectifier bridge, and the second terminal of the transformer secondary side of the single-phase medium-frequency transformer is connected to the middle node of the second bridge arm of the diode rectifier bridge; the medium-voltage AC voltage regulating circuit in the second converter comprises anti-parallel thyristor valve group T3, anti-parallel thyristor valve group T4, thyristor series inductance L3, thyristor series inductance L4, sub-module series bridge arm S3 and sub-module series bridge arm S4; The single-phase intermediate frequency transformer in the second converter operates at a frequency of 300 Hz, and the single-phase intermediate frequency transformer is composed of a transformer and a transformer leakage inductance L k2 , wherein the primary side comprises a primary side first terminal and a primary side second terminal, the secondary side comprises a secondary side first terminal and a secondary side second terminal, and the primary side first terminal and the secondary side first terminal of the transformer are the same name terminals; the transformation ratio of the transformer is n:1, and the transformer leakage inductance is L k2 ; wherein n and k are real numbers. one end of the thyristor series inductance L3 and L4 is connected to phase A of the three-phase AC power grid, the other end of the thyristor series inductance L3 is connected to one end of the anti-parallel thyristor valve group T3, the other end of the anti-parallel thyristor valve group T3 is connected to one end of the sub-module bridge arm S3; the other end of the thyristor series inductance L4 is connected to one end of the anti-parallel thyristor valve group T4, the other end of the anti-parallel thyristor valve group T4 is connected to one end of the sub-module bridge arm S4; the other end of the sub-module bridge arm S3 and S4 is connected to phase C of the three-phase power grid; the thyristor series inductance L3, the anti-parallel thyristor valve group T3 and the sub-module bridge arm S3 constitute the first bridge arm of the medium-voltage side of the second converter, and the thyristor series inductance L4, the anti-parallel thyristor valve group T4 and the sub-module bridge arm S4 constitute the second bridge arm of the medium-voltage side of the second converter; The transformer leakage inductance L of the single-phase intermediate frequency transformer in the second converter k2 connects between the anti-parallel thyristor valve group T3 and the sub-module bridge arm S3 in the first bridge arm, one end of the transformer leakage inductance L k2 connects the primary side first terminal, and the primary side second terminal connects between the anti-parallel thyristor valve group T4 and the sub-module bridge arm S4 in the second bridge arm; Diode D of low voltage rectifier circuit in the second converter L5 , D L7 are connected in series and constitute a first bridge arm of a diode rectifier bridge L6 , D L8 are connected in series and constitute a second bridge arm of a diode rectifier bridge; the first bridge arm of the diode rectifier bridge and the second bridge arm of the diode rectifier bridge are connected in parallel the first terminal of the transformer secondary side of the single-phase medium-frequency transformer in the second converter is connected to the middle node of the first bridge arm of the diode rectifier bridge, and the second terminal of the transformer secondary side of the single-phase medium-frequency transformer is connected to the middle node of the second bridge arm of the diode rectifier bridge. the cathode of diode D L2 and the anode of diode D L4 are connected to the DC output terminal of the first converter; the cathode of diode D L6 and the anode of diode D L8 are connected to the DC output terminal of the second converter; the DC output terminals of the two converters are connected in parallel, and both are connected in parallel with a filter capacitor C o , the two ends of filter capacitor C o are the low-voltage DC output terminal Udc of the converter; The control timing of the transformer in the first converter and the second converter is different by one fourth of the control period, that is, the two transformers output trapezoidal wave currents, and the two converters output two times frequency positive trapezoidal wave currents after rectification by the low voltage rectification circuit, and the phase difference is one fourth of the transformer operation period, that is, the phase difference satisfies wherein, is the phase difference of the two transformer output trapezoidal wave currents, and is also the phase difference between the two times the frequency positive trapezoidal wave currents output by the low voltage rectifier circuit after rectification of the two transformers, T is the transformer operating period, Tz is the transformer zero current time, and Tc is the transformer current adjustment time.

2. A high-power single-stage AC / DC converter according to claim 1, characterized in that, The first converter and the second converter can be operated independently.

3. A high-power single-stage AC / DC converter according to claim 1, characterized in that, The connection mode of the first converter and the second converter with the A phase terminal, the B phase terminal and the C phase terminal of the three-phase alternating current grid can also be exchanged in order; the input end of the medium voltage alternating current voltage regulation circuit can also adopt a three-phase angle connection method.

4. A high-power single-stage AC / DC converter according to any one of claims 1, 2 or 3, characterized in that The operation process is divided into six stages: Phase one [t0~t1]: T1 is on, T2 is off, the voltage of submodule bridge arm S1 is u ac , the current of T1 is controlled by submodule bridge arm S1 as i ac , realizing unit power factor; the voltage of submodule bridge arm S2 is u ac -nU dc , the voltage nU is applied on the transformer dc , the current of the transformer is controlled as I dc / n, by actively adjusting the voltage applied on the transformer by the first bridge arm and the second bridge arm in the transformer, the wide DC voltage range operation is realized; Phase two [t1~t2]: the voltage of submodule bridge arm S2 rises from u ac -nU dc to u ac , preparing for thyristor commutation, the corresponding voltage variation time is defined as T u ; at t2, the voltage on thyristor T2 is approximately zero, realizing zero voltage turn-on; in this process, the transformer voltage amplitude is less than nU dc , the DC side diode is in the cut-off state, and the transformer current is zero; in the process of the voltage rise of the submodule bridge arm S2, the submodule bridge arm S1 is sequentially put into or cut off at a short interval to limit the du / dt generated on the thyristor T2, preventing false turn-on; du / dt is the voltage change per unit time; Phase three [t2~t3]: thyristor commutation phase, T1, T2 are in the on state, through the active regulation of sub-module bridge arm S1, S2 voltage, on two thyristor T1, T2 inductance L1, L2 are applied to the opposite amplitude commutation voltage U T , the T1 current from i ac Gradually reduced to zero, while the T2 current from zero gradually increases to i ac , limit the di / dt of thyristor T1, T2 current, T1 to achieve zero current turn-off, the time used in this stage is the commutation time T c , the current through the thyristor is i ac , to ensure the continuity of the medium voltage alternating current, the transformer voltage amplitude is less than nU dc , the transformer current is zero; di / dt is the current change per unit time; Phase four [t3-t4]: after T1 current is reduced to zero, S1 voltage is adjusted to u ac +U R , actively exerting counter pressure U on T1 R , with a duration of T q , T1 achieves reliable turn-off; at this time, the medium-voltage alternating current is only borne by T2; T q According to the thyristor turn-off time design, the turn-off time of ordinary thyristor modules is less than 400 μs, and the turn-off time of fast switching thyristors is between 25 μs and 80 μs; Phase five [t4~t5]: T1 is in off state, T2 keeps on; the voltage of submodule bridge arm S1 gradually decreases to u ac -nU dc , du / dt is constrained during voltage drop; Stage six [t5~t6]: submodule bridge arm S2 support medium voltage AC voltage, submodule bridge arm S1 voltage u ac -nU dc , the voltage difference between the bridge arms maintains the DC voltage and controls the DC current, by adjusting the voltage of the submodule bridge arm S1, the transformer voltage amplitude is changed, and wide voltage range operation is realized.

5. The control method of a high-capacity single-stage AC / DC converter according to claim 4, characterized by, The method comprises a method in which the operation process is divided into six stages: Phase one [t0~t1]: T1 is on, T2 is off, the voltage of submodule bridge arm S1 is u ac , the current of T1 is controlled by submodule bridge arm S1 as i ac , to achieve unit power factor; the voltage of submodule bridge arm S2 is u ac -nU dc , the voltage nU is applied on the transformer dc , the current of the transformer is controlled as I dc / n, the voltage applied on the transformer by actively adjusting the first bridge arm and the second bridge arm in the transformer, to achieve the method of working in a wide DC voltage range Phase two [t1~t2]: the voltage of submodule bridge arm S2 rises from u ac -nU dc to u ac , in preparation for thyristor commutation, the corresponding voltage variation time is defined as T u ; at t2, the voltage on thyristor T2 is approximately zero, realizing zero voltage turn-on; in this process, the transformer voltage amplitude is less than nU dc , the DC side diode is in the cut-off state, and the transformer current is zero; in the process of the voltage rise of the submodule bridge arm S2, the submodule bridge arm S1 is sequentially put into or cut off at a short interval to limit the du / dt generated on the thyristor T2, preventing the method of false turn-on; du / dt is the voltage change per unit time; Phase three [t2~t3]: thyristor commutation phase, T1, T2 are in the on state, through the active regulation of sub-module bridge arm S1, S2 voltage, on two thyristor T1, T2 inductance L1, L2 are applied to the opposite amplitude commutation voltage U T , make T1 current from i ac Gradually reduced to zero, while the T2 current gradually increases from zero to i ac , limit the di / dt of thyristor T1, T2 current, T1 realizes zero current off, the time used in this stage is the commutation time T c , the current through the thyristor is i ac , ensure the continuity of the medium voltage alternating current, the amplitude of the transformer voltage is less than nU dc , the transformer current is zero method; di / dt is the current flowing in unit time; Phase four [t3-t4]: after T1 current is reduced to zero, S1 voltage is adjusted to u ac +U R , actively on T1 to apply counter-pressure U R , duration T q , T1 to achieve reliable shutdown; at this time, the medium voltage AC current is only borne by T2; T q According to the thyristor turn-off time design, the ordinary thyristor module turn-off time is less than 400 μs, and the fast switch thyristor turn-off time is between 25 μs-80 μs. Phase five [t4~t5]: T1 is in off state, T2 remains on; the voltage of submodule bridge arm S1 gradually decreases to u ac -nU dc , the method of constraining du / dt during voltage drop; Phase six [t5~t6]: submodule bridge arm S2 support medium voltage AC voltage, submodule bridge arm S1 voltage u ac -nU dc , the voltage difference between the bridge arms maintains the DC voltage and controls the DC current, by adjusting the voltage of the submodule bridge arm S1, the transformer voltage amplitude is changed, and the method of wide voltage range operation is realized.

6. The control method of the large-capacity single-stage AC / DC converter according to claim 4, characterized in that, thyristor conduction mode one: when the medium voltage alternating current is in the positive half cycle within one power frequency cycle, the anti-parallel thyristor valve group T1 and T2 are alternately turned on, and the number of times of turning on is the same, and the medium voltage alternating current is alternately shared; when the medium voltage alternating current decreases to 0, the original T2 positive conduction occurs natural turn-off, at this time, T2 is allowed to be reversely turned on, and the sub-module bridge arm S2 in series with T2 continues to support the medium voltage alternating voltage, in order to ensure the continuous transmission of power, the voltage of S1 bridge arm rises to make the voltage difference of the two bridge arms provide the transformer voltage, thereafter, S1 and S2 alternately bear the medium voltage alternating voltage, since the thyristor conduction timing is reversed at the zero crossing of the medium voltage alternating current, the maximum voltage stress of the bridge arm is the medium voltage alternating voltage, and the maximum current stress is the transformer current.

7. The control method of the large-capacity single-stage AC / DC converter according to claim 4, characterized in that, thyristor conduction mode two: the conduction timing of the thyristor valve group is always constant, that is, the anti-parallel thyristor valve group T1 and T2 always maintain periodical alternate conduction, when the medium voltage alternating current decreases to 0, the original T2 positive conduction occurs natural turn-off, at this time, T1 is reversely turned on to complete switching; at this time, the sub-module bridge arm S1 in series with T1 supports the medium voltage alternating voltage, in order to ensure the continuous transmission of power, the voltage of S2 bridge arm decreases to make the voltage difference of the two bridge arms provide the transformer voltage, thereafter, S1 and S2 alternately bear the medium voltage alternating voltage, and the maximum voltage stress of the bridge arm is the medium voltage alternating voltage superimposed with the transformer voltage; when the bridge arm supports the medium voltage alternating voltage, the transformer current also needs to be provided, so that under the switching logic of the thyristor, the maximum current stress of the bridge arm is the transformer current superimposed with the medium voltage alternating current.

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