Self-coupling direct current transformer and control method thereof

Abstract

The invention provides a self-coupling direct current transformer and a control method thereof. Power transmission and energy transfer are achieved through the energy storage branches, multiplexing of the single energy storage branch is achieved through series connection of the first capacitor and the second capacitor, a primary side and a secondary side are formed, and the secondary side is formed through on-off of the first control switch and the second control switch and control over the voltage of the energy storage branches. And the current flow direction and the power transmission condition of each working mode are realized. In some embodiments, an energy storage bridge arm based on a half-bridge sub-module string is adopted as an energy transfer medium for self-coupling, so that the number of sub-modules is reduced, and thyristors which are low in cost and easy to connect in series are adopted as switching devices, so that the device cost is further reduced. Besides, the active characteristic of the energy storage bridge arm not only can actively construct a current waveform through a control signal to realize soft switching, but also can realize reliable turn-off of the thyristor, and is low in element loss and higher in control efficiency.

Description

Technical Field

[0001] The present application relates to the field of direct current (DC) grid control technology, and in particular to an auto-coupling DC transformer and a control method thereof. Background Art

[0002] In the transmission process of clean energy such as offshore wind power, the application of high-voltage DC transformers may be involved. For example, in deep sea application scenarios, the use of DC aggregation-transmission solutions can avoid reactive power loss, reduce the application of reactive power compensation equipment, and effectively solve the problems of multi-machine grid-connected stability control and wide-area interconnection of wind farm groups. For the application scenario of full DC transmission of deep offshore wind power, high-voltage and large-capacity DC transformers are the core link and key equipment for connecting DC systems of different voltage levels in offshore wind power aggregation and transmission networks.

[0003] However, compared with traditional low-voltage DC transformers, medium and high voltage application scenarios have restrictions on the device stress and device capacity of the transformer. Multiple transformers need to be connected in series or supporting modules need to be added to achieve high voltage applications. This brings about the problems of complex structure and high cost of the DC transformer. An autocoupled DC transformer can be used to simplify the structure and reduce device costs. Summary of the invention

[0004] The purpose of the present application is to solve at least one of the above-mentioned technical defects, especially the technical defects of the complex structure and high cost of the high-voltage DC transformer in the prior art.

[0005] In a first aspect, the present application provides an auto-coupling DC transformer, the transformer comprising:

[0006] A first DC capacitor, a second DC capacitor, an energy storage branch, a first control switch and a second control switch;

[0007] The first DC capacitor serves as the primary side of the transformer, the first DC capacitor and the second DC capacitor are connected in series as the secondary side of the transformer, and the energy storage branch, the first control switch and the second control switch are used to control the bridge arm voltage and the bridge arm current according to the preset working mode of the transformer to transmit power;

[0008] Furthermore, the first end of the first DC capacitor is connected to the first end of the energy storage branch and to the first end of the second DC capacitor, the second end of the energy storage branch is connected to the first end of the first control switch and the second end of the second control switch, the second end of the first DC capacitor is connected to the second end of the first control switch, and the second end of the second DC capacitor is connected to the first end of the first DC capacitor and the first end of the second control switch.

[0009] As an optional implementation manner, the first control switch includes a first thyristor module, and the second control switch includes a second thyristor module;

[0010] Among them, the anode of the first thyristor module serves as the first end of the first control switch, the cathode of the first thyristor module serves as the second end of the first control switch, the anode of the second thyristor module serves as the first end of the second control switch, and the cathode of the second thyristor module serves as the second end of the second control switch.

[0011] As an optional implementation manner, the first thyristor module and the second thyristor module include a plurality of thyristors connected in series, and the number of the thyristors is related to the capacity of the transformer.

[0012] As an optional implementation, the transformer further includes a first diode module and a second diode module;

[0013] Wherein, the first diode module and the second diode module are used to limit the current flow direction of the transformer in each working mode;

[0014] And, the first end of the first diode module is connected to the first end of the first capacitor, the second end of the first diode module is connected to the first end of the energy storage branch and the first end of the second diode module, and the second end of the second diode module is connected to the first end of the second capacitor.

[0015] As an optional implementation, the first diode module and the second diode module include a plurality of diodes connected in series, and the number of the diodes is related to the capacity of the transformer.

[0016] As an optional implementation, the energy storage branch includes a plurality of energy storage submodules connected in series, and an energy storage inductor connected in series with each of the energy storage submodules.

[0017] As an optional implementation, the energy storage submodule includes a half-bridge energy storage submodule.

[0018] As an optional implementation, the transformer also includes a first resistor, a first end of the first resistor is connected to the first end of the second capacitor, a second end of the first resistor is connected to the second end of the first capacitor, and the first resistor is used to sample and obtain the secondary side voltage of the transformer.

[0019] In a second aspect, the present application provides a method for controlling an auto-coupling DC transformer, the method being used for the auto-coupling DC transformer as described in the first aspect, the method comprising:

[0020] Generate a trigger pulse according to a preset switch cycle to drive the first control switch and the second control switch to be turned on alternately in a preset working mode;

[0021] According to the primary side voltage of the transformer, the bridge arm voltage of the energy storage branch is controlled to control the bridge arm current of the energy storage branch to perform power transmission between the first capacitor and the second capacitor.

[0022] As an optional implementation, the working modes include a first mode, a second mode, a third mode and a fourth mode;

[0023] The first mode includes: at the first moment, the first driving switch is triggered to turn on, and the bridge arm voltage is controlled to be less than the primary side voltage, so that the bridge arm current increases linearly; at the second moment, when the bridge arm current reaches the maximum value, the bridge arm voltage is controlled to be equal to the primary side voltage, so that the bridge arm current maintains the maximum value; at the third moment, the bridge arm voltage is controlled to be greater than the primary side voltage, so that the bridge arm current decays linearly, until the bridge arm current returns to zero at the fourth moment;

[0024] The second mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until the fifth moment, and the duration from the fourth moment to the fifth moment is greater than the turn-off time of the first control switch;

[0025] The third mode includes: at the fifth moment, the second driving switch is triggered to turn on, and the bridge arm voltage is controlled to be greater than the difference between the secondary side voltage and the primary side voltage, so that the direction of the bridge arm current is opposite to that in the first mode and increases linearly; at the sixth moment, when the bridge arm current reaches the reverse maximum value, the bridge arm voltage is controlled to be equal to the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current maintains the reverse maximum value; at the seventh moment, the bridge arm voltage is controlled to be less than the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current linearly decays until the bridge arm current returns to zero at the eighth moment;

[0026] The fourth mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until a ninth moment, and the duration from the eighth moment to the ninth moment is greater than the turn-off time of the second control switch.

[0027] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0028] Based on any of the above embodiments, the present application realizes power transmission and energy transfer through an energy storage branch, realizes the reuse of a single energy storage branch by connecting the first capacitor and the second capacitor in series, forms a primary side and a secondary side, and realizes the current flow and power transmission of each working mode by turning on and off the first control switch and the second control switch, and controlling the voltage of the energy storage branch. In some embodiments, an energy storage bridge arm based on a half-bridge sub-module string is used as an energy transfer medium autocoupling form, so that the number of sub-modules is reduced, and a low-cost and easy-to-connect thyristor is used as a switching device, thereby further reducing the device cost. In addition, the active characteristics of the energy storage bridge arm can not only realize soft switching by actively constructing a current waveform through a control signal, but also realize reliable shutdown of the thyristor, with low component loss and higher control efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A schematic diagram of the structure of an auto-DC transformer provided in one embodiment of the present application;

[0031] Figure 2 A schematic diagram of the structure of an auto-DC transformer provided in one embodiment of the present application;

[0032] Figure 3 A schematic diagram of a working scenario of an auto-coupling DC transformer provided in one embodiment of the present application;

[0033] Figure 4 A schematic diagram of a working scenario of an auto-coupling DC transformer provided in one embodiment of the present application;

[0034] Figure 5 A schematic diagram of the application effect of an auto-coupling DC transformer provided in one embodiment of the present application;

[0035] Figure 6 A schematic diagram of the simulation effect of an auto-DC transformer provided in one embodiment of the present application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] In view of the current energy shortage situation, non-polluting, renewable, environmentally friendly clean energy has attracted widespread attention. Among them, wind power generation has become the most promising renewable energy generation technology due to its low development cost and mature power generation technology.

[0038] The development of offshore wind power mainly adopts the AC convergence-AC transmission scheme, which has the advantages of low voltage boosting and networking costs. In deep sea application scenarios, due to problems such as cable network charging power, AC convergence-flexible DC transmission is the main solution. However, with the development trend of ultra-large capacity of single offshore wind power units, there are problems such as charging power in the wind farm convergence network. The use of DC convergence-transmission solutions can avoid reactive power loss or reactive power compensation equipment, and effectively solve the problems of multi-machine grid-connected stable control and wide-area interconnection networking of wind farm groups. For the application scenario of full DC transmission of deep offshore wind power, high-voltage and large-capacity DC transformers are the core link and key equipment for connecting DC systems of different voltage levels of offshore wind power convergence and transmission networks.

[0039] The traditional low-voltage DC transformer topology is limited by device stress and cannot be extended to the medium and high voltage fields. It can be directly applied to the medium and high voltage environment through device series connection technology, but the voltage balancing of the insulated gate bipolar transistor structure is difficult and cannot be widely used. The face-to-face topology is based on modular multi-level technology, which eliminates the problem of device series connection. The two-stage power conversion makes the loss larger, and there are half of the redundant modules in the work. A step-down multi-level modular dual active bridge converter has an autocoupling form, which not only eliminates the use of AC transformers, but also reduces the capacity of the transformer with the common part module, but requires the injection of AC circulating current to achieve the energy balance of the sub-modules, which makes the control complex and the loss increased. The hybrid DC transformer uses the energy storage bridge arm to replace the energy storage inductor, and realizes the active control of energy by controlling the bridge arm, but all the energy must be transferred through the energy storage bridge arm, so a large number of sub-modules are required. At present, it is still necessary to explore DC transformers suitable for high voltage and low cost.

[0040] In summary, compared with traditional low-voltage DC transformers, medium and high voltage application scenarios have restrictions on the device stress and device capacity of the transformer. Multiple transformers need to be connected in series or supporting modules need to be added to achieve high voltage applications. This brings about the problems of complex structure and high cost of the DC transformer. An autocoupled DC transformer can be used to simplify the structure and reduce device costs.

[0041] The technical concept of the present application is to realize power transmission and energy transfer through an energy storage branch, realize the reuse of a single energy storage branch by connecting the first capacitor and the second capacitor in series, form a primary side and a secondary side, and realize the current flow and power transmission of each working mode by turning on and off the first control switch and the second control switch, and controlling the voltage of the energy storage branch. In some embodiments, an energy storage bridge arm based on a half-bridge sub-module string is used as an energy transfer medium autocoupling form, so that the number of sub-modules is reduced, and at the same time, a low-cost and easy-to-connect thyristor is used as a switching device, thereby further reducing the device cost. In addition, the active characteristics of the energy storage bridge arm can not only realize soft switching by actively constructing a current waveform through a control signal, but also realize reliable shutdown of the thyristor, with low component loss and higher control efficiency.

[0042] See also Figure 1 , Figure 1 A schematic diagram of the structure of an auto-coupling DC transformer provided in one embodiment of the present application, an auto-coupling DC transformer, the transformer comprising:

[0043] A first DC capacitor, a second DC capacitor, an energy storage branch, a first control switch and a second control switch;

[0044] The first DC capacitor serves as the primary side of the transformer, the first DC capacitor and the second DC capacitor are connected in series as the secondary side of the transformer, and the energy storage branch, the first control switch and the second control switch are used to control the bridge arm voltage and the bridge arm current according to the preset working mode of the transformer to transmit power;

[0045] Furthermore, the first end of the first DC capacitor is connected to the first end of the energy storage branch and to the first end of the second DC capacitor, the second end of the energy storage branch is connected to the first end of the first control switch and the second end of the second control switch, the second end of the first DC capacitor is connected to the second end of the first control switch, and the second end of the second DC capacitor is connected to the first end of the first DC capacitor and the first end of the second control switch.

[0046] Power transmission and energy transfer are achieved through the energy storage branch, and the single energy storage branch is reused by connecting the first capacitor and the second capacitor in series to form a primary side and a secondary side, and the current flow and power transmission of each working mode are achieved by turning on and off the first control switch and the second control switch, as well as controlling the voltage of the energy storage branch. In some embodiments, an energy storage bridge arm based on a half-bridge sub-module string is used as an energy transfer medium autocoupling form, so that the number of sub-modules is reduced, and at the same time, a low-cost and easy-to-connect thyristor is used as a switching device, thereby further reducing the device cost. In addition, the active characteristics of the energy storage bridge arm can not only realize soft switching by actively constructing a current waveform through a control signal, but also realize reliable shutdown of the thyristor, with low component loss and higher control efficiency.

[0047] See also Figure 2 , Figure 2 A schematic diagram of the structure of an auto-DC transformer provided in one embodiment of the present application. As an optional implementation, the first control switch includes a first thyristor module, and the second control switch includes a second thyristor module;

[0048] Among them, the anode of the first thyristor module serves as the first end of the first control switch, the cathode of the first thyristor module serves as the second end of the first control switch, the anode of the second thyristor module serves as the first end of the second control switch, and the cathode of the second thyristor module serves as the second end of the second control switch.

[0049] This embodiment provides a first thyristor module and a second thyristor module as a specific implementation mode of two control switches, and utilizes the electrical characteristics of thyristors to realize the current control function in this application. In addition, thyristors are easy to expand and have low cost.

[0050] As an optional implementation manner, the first thyristor module and the second thyristor module include a plurality of thyristors connected in series, and the number of the thyristors is related to the capacity of the transformer.

[0051] In this embodiment, the thyristor module may specifically include multiple thyristors connected in series, and the number of thyristors is directly related to the capacity of the transformer, thereby reducing the cost caused by the need to connect multiple transformers in series or increase supporting modules in some embodiments. The number of thyristors connected in series depends on the electrical characteristics of the transformer itself and is easy to adjust.

[0052] like Figure 2 As shown, as an optional implementation, the transformer further includes a first diode module and a second diode module;

[0053] Wherein, the first diode module and the second diode module are used to limit the current flow direction of the transformer in each working mode;

[0054] And, the first end of the first diode module is connected to the first end of the first capacitor, the second end of the first diode module is connected to the first end of the energy storage branch and the first end of the second diode module, and the second end of the second diode module is connected to the first end of the second capacitor.

[0055] In this embodiment, a diode module is provided in the transformer to limit the flow direction of the current together with the control switch to achieve the expected effect of each working mode, thereby improving the stability and effectiveness of the transformer operation.

[0056] As an optional implementation, the first diode module and the second diode module include a plurality of diodes connected in series, and the number of the diodes is related to the capacity of the transformer.

[0057] In this embodiment, the diode module may specifically include a plurality of diodes connected in series, and the number of diodes is directly related to the capacity of the transformer, thereby reducing the cost caused by the need to connect multiple transformers in series or increase supporting modules in some embodiments. The number of diodes connected in series depends on the electrical characteristics of the transformer itself and is easy to adjust.

[0058] like Figure 2 As shown, as an optional implementation, the energy storage branch includes a plurality of energy storage submodules connected in series, and an energy storage inductor connected in series with each of the energy storage submodules.

[0059] The output voltage of the bridge arm can be controlled through a single energy storage branch with active characteristics to construct the output current of the bridge arm, control the waveform, and realize the power transmission process in each working mode. In addition, only a single energy storage branch is used for multiplexing in this application, which also reduces the hardware cost.

[0060] As an optional implementation, the energy storage submodule includes a half-bridge energy storage submodule.

[0061] By connecting half-bridge energy storage submodules in series, the structure of the energy storage branch is simplified, and the control process of the energy storage branch is made simpler and more efficient.

[0062] like Figure 2 As shown, as an optional implementation, the transformer also includes a first resistor, a first end of the first resistor is connected to the first end of the second capacitor, a second end of the first resistor is connected to the second end of the first capacitor, and the first resistor is used to sample and obtain the secondary side voltage of the transformer.

[0063] In the circuit provided in the present application, the first resistor can have both sampling and current limiting functions to ensure the safety inside the transformer.

[0064] The secondary side voltage is obtained by sampling the first resistor, thereby simplifying the parameter acquisition process of the transformer, improving the control efficiency, and improving the practicability of the transformer.

[0065] In fact, Figure 2 A landing scheme combining the above-mentioned embodiments is provided. Specifically, the voltage across the first capacitor C1 is used as the primary side voltage V1, and the voltage after the first capacitor C1 and the second capacitor C2 are connected in series is used as the secondary side voltage V2. The transformation ratio of the transformer The thyristor valves T1 and T2, and the diode valves D1 and D2 are composed of multiple devices connected in series. The number of devices connected in series can be adjusted to adapt to different voltage levels. a Half-bridge submodules and bridge arm inductor L a Composition. c1 and U c2 are the first capacitor C1, the voltage of the first capacitor C1, i1 and i2 are the primary and secondary currents, V arm and I arm are the output voltage and current of the bridge arm.

[0066] The working principle of the topology proposed in this application includes that the active characteristics of the energy storage bridge arm enable the flexible control of the output voltage of the bridge arm, thereby constructing any current waveform to achieve the control of the bridge arm interaction energy. s The bridge arm transfers energy between the first capacitor C1 and the second capacitor C2 by alternating conduction.

[0067] Specifically, based on this autotransformer topology, the present application also provides a corresponding control method to achieve the expected function. The method is used for the auto-coupling DC transformer as described in any embodiment, and the method includes:

[0068] Generate a trigger pulse according to a preset switch cycle to drive the first control switch and the second control switch to be turned on alternately in a preset working mode;

[0069] According to the primary side voltage of the transformer, the bridge arm voltage of the energy storage branch is controlled to control the bridge arm current of the energy storage branch to perform power transmission between the first capacitor and the second capacitor.

[0070] Power transmission and energy transfer are achieved through the energy storage branch, and the single energy storage branch is reused by connecting the first capacitor and the second capacitor in series to form the primary side and the secondary side. The current flow and power transmission of each working mode are achieved by turning on and off the first control switch and the second control switch, as well as controlling the voltage of the energy storage branch. In summary, the device structure is simplified by the reuse of the energy storage branch. In addition, due to the active characteristics of the energy storage bridge arm, not only can the current waveform be actively constructed through the control signal to achieve soft switching, but also the reliable shutdown of the thyristor can be achieved, with low component loss and higher control efficiency.

[0071] Specifically, the working modes include a first mode, a second mode, a third mode and a fourth mode. Figure 3 A schematic diagram of a working scenario of an auto-coupling DC transformer provided in one embodiment of the present application, Figure 4 A schematic diagram of a working scenario of an auto-coupling DC transformer provided in one embodiment of the present application, Figure 3 and Figure 4 It is used to illustrate the current flow direction of the transformer when the corresponding control method is executed.

[0072] In addition, it can also be combined with Figure 5 The waveforms in the figure illustrate the principles of each mode, such as Figure 5 As shown, Figure 5 A schematic diagram of the application effect of an auto-coupling DC transformer provided in one embodiment of the present application.

[0073] Figure 3 The current flow in the first mode is shown, wherein the first mode includes: at the first moment, the first driving switch is triggered to turn on, and the bridge arm voltage is controlled to be less than the primary side voltage, so that the bridge arm current increases linearly; at the second moment, when the bridge arm current reaches the maximum value, the bridge arm voltage is controlled to be equal to the primary side voltage, so that the bridge arm current maintains the maximum value; at the third moment, the bridge arm voltage is controlled to be greater than the primary side voltage, so that the bridge arm current decays linearly, until the bridge arm current returns to zero at the fourth moment;

[0074] After the current waveform is designed, the energy absorbed by the bridge arm is only equal to the maximum amplitude of the bridge arm current I arm1 Therefore, it can be controlled by I arm1 To control the energy absorbed by the bridge arm.

[0075] The second mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until the fifth moment, and the duration from the fourth moment to the fifth moment is greater than the turn-off time of the first control switch;

[0076] Since the diode and the thyristor are reverse blocked, there is a reverse voltage drop on the thyristor. In order to achieve reliable shutdown of the thyristor, it is necessary to ensure that the duration of the second mode is greater than the shutdown time of the corresponding thyristor.

[0077] Figure 4 The current flow in the third mode is shown, and the third mode includes: at the fifth moment, the second drive switch is triggered to turn on, and the bridge arm voltage is controlled to be greater than the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current direction is opposite to that in the first mode and increases linearly; at the sixth moment, when the bridge arm current reaches the reverse maximum value, the bridge arm voltage is controlled to be equal to the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current maintains the reverse maximum value; at the seventh moment, the bridge arm voltage is controlled to be less than the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current linearly decays until the bridge arm current returns to zero at the eighth moment;

[0078] The current of the third mode is actually a mirror image of the current of the first mode. Similarly, after the current waveform is designed, the energy released by the bridge arm and the maximum reverse amplitude of the bridge arm current I arm2 Therefore, it can be controlled by I arm2 To control the energy released by the bridge arm.

[0079] The fourth mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until a ninth moment, and the duration from the eighth moment to the ninth moment is greater than the turn-off time of the second control switch.

[0080] Similarly, since the diode and the thyristor are reversely blocked, there is a reverse voltage drop on the thyristor. In order to achieve reliable shutdown of the thyristor, it is necessary to ensure that the duration of the second mode is greater than the shutdown time of the corresponding thyristor.

[0081] This embodiment constructs the changes of bridge arm voltage and bridge arm current of four energy storage branches from the first mode to the fourth mode within one working cycle, and combines the on-off of the first control switch and the second control switch to achieve power transmission within one working cycle, thereby improving the efficiency and effectiveness of control while saving device costs, thereby improving the effectiveness of the autocoupled DC transformer provided in this application.

[0082] like Figure 6 As shown, Figure 6 A schematic diagram of the simulation effect of an auto-coupling DC transformer provided in an embodiment of the present application. The present application also provides a simulation process to illustrate the corresponding method, and the simulation waveform diagram can be used for reference.

[0083] based on Figure 1The DC transformer structure shown is constructed through a simulation platform, and simulation verification is performed for the topology. The simulation parameters are shown in Table 1 below;

[0084] Table 1: DC transformer simulation parameters

[0085]

[0086] Under the operating conditions shown in the table above, the input voltage is given to be 20kV, the output voltage is 36kV, and the overall transmission power is 10MW.

[0087] In the simulation results, V2 is the secondary voltage waveform, V sm is the submodule voltage waveform, i arm is the bridge arm current, V T1 and V T2 The voltage waveforms of thyristors T1 and T2 are shown. It can be seen that the voltage on the secondary side is stable at 36kV, and the voltage of all submodule capacitors is stable at 2kV. The bridge arm current changes in a trapezoidal wave. After the current returns to 0 in the forward direction, a stable reverse voltage drop appears on thyristor T1. After the current returns to 0 in the reverse direction, a stable reverse voltage drop appears on thyristor T2, which proves the effectiveness of the control strategy and the stable shutdown of the thyristor.

[0088] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0089] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can refer to each other.

[0090] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An auto-coupling DC transformer, characterized in that: The transformer comprises: A first DC capacitor, a second DC capacitor, an energy storage branch, a first control switch and a second control switch; The first DC capacitor serves as the primary side of the transformer, the first DC capacitor and the second DC capacitor are connected in series as the secondary side of the transformer, and the energy storage branch, the first control switch and the second control switch are used to control the bridge arm voltage and the bridge arm current according to the preset working mode of the transformer to transmit power; Furthermore, the first end of the first DC capacitor is connected to the first end of the energy storage branch and to the first end of the second DC capacitor, the second end of the energy storage branch is connected to the first end of the first control switch and the second end of the second control switch, the second end of the first DC capacitor is connected to the second end of the first control switch, and the second end of the second DC capacitor is connected to the first end of the first DC capacitor and the first end of the second control switch.

2. The transformer according to claim 1, characterized in that: The first control switch includes a first thyristor module, and the second control switch includes a second thyristor module; Among them, the anode of the first thyristor module serves as the first end of the first control switch, the cathode of the first thyristor module serves as the second end of the first control switch, the anode of the second thyristor module serves as the first end of the second control switch, and the cathode of the second thyristor module serves as the second end of the second control switch.

3. The transformer according to claim 2, characterized in that: The first thyristor module and the second thyristor module include a plurality of thyristors connected in series, and the number of the thyristors is related to the capacity of the transformer.

4. The transformer according to claim 1, characterized in that: The transformer also includes a first diode module and a second diode module; Wherein, the first diode module and the second diode module are used to limit the current flow direction of the transformer in each working mode; And, the first end of the first diode module is connected to the first end of the first capacitor, the second end of the first diode module is connected to the first end of the energy storage branch and the first end of the second diode module, and the second end of the second diode module is connected to the first end of the second capacitor.

5. The transformer according to claim 4, characterized in that: The first diode module and the second diode module include a plurality of diodes connected in series, and the number of the diodes is related to the capacity of the transformer.

6. The transformer according to claim 1, characterized in that: The energy storage branch includes a plurality of energy storage submodules connected in series, and an energy storage inductor connected in series with each of the energy storage submodules.

7. The transformer according to claim 6, characterized in that: The energy storage submodule includes a half-bridge energy storage submodule.

8. The transformer according to any one of claims 1 to 7, characterized in that: The transformer also includes a first resistor, a first end of the first resistor is connected to a first end of the second capacitor, a second end of the first resistor is connected to a second end of the first capacitor, and the first resistor is used to sample and obtain a secondary side voltage of the transformer.

9. A method for controlling an auto-coupling DC transformer, characterized in that: The method is used for the auto-DC transformer according to any one of claims 1 to 8, and the method comprises: Generate a trigger pulse according to a preset switch cycle to drive the first control switch and the second control switch to be turned on alternately in a preset working mode; According to the primary side voltage of the transformer, the bridge arm voltage of the energy storage branch is controlled to control the bridge arm current of the energy storage branch to perform power transmission between the first capacitor and the second capacitor.

10. The method according to claim 9, characterized in that The working modes include a first mode, a second mode, a third mode and a fourth mode; The first mode includes: at the first moment, the first driving switch is triggered to turn on, and the bridge arm voltage is controlled to be less than the primary side voltage, so that the bridge arm current increases linearly; at the second moment, when the bridge arm current reaches the maximum value, the bridge arm voltage is controlled to be equal to the primary side voltage, so that the bridge arm current maintains the maximum value; at the third moment, the bridge arm voltage is controlled to be greater than the primary side voltage, so that the bridge arm current decays linearly, until the bridge arm current returns to zero at the fourth moment; The second mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until the fifth moment, and the duration from the fourth moment to the fifth moment is greater than the turn-off time of the first control switch; The third mode includes: at the fifth moment, the second driving switch is triggered to turn on, and the bridge arm voltage is controlled to be greater than the difference between the secondary side voltage and the primary side voltage, so that the direction of the bridge arm current is opposite to that in the first mode and increases linearly; at the sixth moment, when the bridge arm current reaches the reverse maximum value, the bridge arm voltage is controlled to be equal to the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current maintains the reverse maximum value; at the seventh moment, the bridge arm voltage is controlled to be less than the difference between the secondary side voltage and the primary side voltage, so that the bridge arm current linearly decays until the bridge arm current returns to zero at the eighth moment; The fourth mode includes: when the bridge arm current returns to zero, controlling the bridge arm voltage to be greater than the primary side voltage until a ninth moment, and the duration from the eighth moment to the ninth moment is greater than the turn-off time of the second control switch.

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