Switched capacitor connected DC transformer and DC transformer control method

Abstract

The present application relates to a control method for a DC transformer, which is applied to a switched capacitor connected DC transformer, the method comprising: controlling the pre-charging of each DC conversion unit, and determining a first preset number of the DC conversion units as power transmission modules and a second preset number of the DC conversion units as redundant modules; wherein the sum of the first preset number and the second preset number is less than or equal to the preset number; and rotating and controlling each power transmission module and each redundant module in a preset rotation order, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switch capacitor of each redundant module is within a preset voltage range. The use of this method can make the SCDCT block capacitor voltage constant, ensuring the long-term operation safety of the SCDCT.

Description

Technical Field

[0001] The present application relates to the field of electric power technology, and in particular to a capacitor-connected DC transformer and a control method for the DC transformer. Background Art

[0002] The DC transformer is a key device for completing power transmission and voltage conversion in the medium-voltage DC distribution network. Conventional DC transformers are constructed using a dual-active full bridge (DAB) with series input and parallel output. However, due to the presence of capacitors on the DC side, the connection of online redundant modules cannot be achieved in the DAB type DC transformer, which reduces the reliability of the DC transformer and the DC distribution network. At the same time, when the DC bus fails, the capacitors in the DAB type DC transformer will have a large discharge current, affecting the fault handling speed of the DC distribution network. In view of the above background, in order to meet the needs of fault clearing of the DC distribution network and the design of redundant sub-modules of the DC transformer, the switched capacitor based DC transformer (Switched Capacitor based DC Transformer, SCDCT) was proposed and is considered to be a key topology that is promising for application in the actual engineering of medium-voltage DC distribution networks.

[0003] In traditional research on SCDCT, the focus is on the control analysis of the power transmission module in SCDCT, resulting in engineers' use of redundant modules in SCDCT remaining in the preliminary stage, that is, managing redundant submodules separately from power transmission modules. The above management method theoretically believes that due to the locking effect of the power electronic switch, the medium-voltage side capacitor of the redundant module does not have a charging and discharging process during the operation of the SCDCT, so the capacitor voltage of the redundant module can be maintained and can be directly put into operation when needed. However, when SCDCT is used in a DC distribution network, it usually runs continuously for several months or even years unless it is a maintenance period. Under such a long time scale, the locked switch tube will show a large resistance characteristic, that is, the capacitor voltage of the redundant module is actually discharging slowly, and may drop due to too long a time. In severe cases, it may be significantly different from the rated value, causing a current shock when it is put into operation, endangering the safe operation of the power electronic switch tube in the SCDCT. Summary of the invention

[0004] Based on this, it is necessary to provide a switch capacitor access DC transformer and a control method for the DC transformer to address the above technical problems, so that the capacitor voltage of the redundant module is constant and current shock can be avoided when it is put into use.

[0005] In order to achieve the above-mentioned purpose and other purposes, one aspect of the present application provides a control method of a DC transformer, which is applied to a switched capacitor connected DC transformer, wherein the switched capacitor connected DC transformer includes a preset number of DC conversion units, wherein the input end of each of the DC conversion units is electrically connected to a medium voltage DC bus, and the output end of each of the DC conversion units is electrically connected to a low voltage DC bus, wherein the method includes:

[0006] Controlling each of the DC conversion units to precharge, and determining a first preset number of the DC conversion units as power transmission modules and a second preset number of the DC conversion units as redundant modules; wherein the sum of the first preset number and the second preset number is less than or equal to the preset number;

[0007] The power transmission modules and the redundant modules are rotated and controlled according to a preset rotation order, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switching capacitor of each redundant module is within a preset voltage range.

[0008] In the control method of the DC transformer in the above embodiment, all DC conversion units in the SCDCT are first pre-charged and a first preset number of power transmission modules and a second preset number of redundant modules are determined, and then the power transmission modules and redundant modules are rotated and controlled according to the rotation sequence, so that the switching loss of each power transmission module is within the preset loss range, and the voltage change of the switch capacitor of each redundant module is within the preset voltage range. In this way, the capacitor voltage of each module of the SCDST is balanced, avoiding the occurrence of current shock when the redundant module is put into use.

[0009] In one embodiment, each of the DC conversion units is controlled to be precharged, and a first preset number N1 of the DC conversion units is determined as a power transmission module and a second preset number N2 of the DC conversion units is determined as a redundant module, N1+N2=N, N is less than or equal to the preset number, and the method includes:

[0010] Controlling each of the DC conversion units to operate in an initial stage after pre-charging;

[0011] During the initial stage, the 1st DC conversion unit to the N1th DC conversion unit are sequentially determined as power transmission modules, and the N1+1th DC conversion unit to the N1+N2th DC conversion unit are sequentially determined as redundant modules. The sequential determination facilitates the user's operation and enables the user to clearly distinguish the power transmission module and the redundant module.

[0012] In one embodiment, the step of performing rotation control on each of the power transmission modules and each of the redundant modules according to a preset rotation sequence includes:

[0013] Obtaining a rotation cycle, and controlling each of the redundant modules to be put into operation and each of the power transmission modules to be switched out within the rotation cycle;

[0014] At the end of the current rotation cycle, the switched capacitor DC transformer is controlled to operate in the next rotation cycle adjacent to the current rotation cycle. The power transmission module is controlled to be switched in and out within a rotation cycle, so as to achieve capacitor voltage balance of all DC conversion units.

[0015] In one embodiment, the control method of the DC transformer, when the current rotation cycle is the i-th rotation cycle:

[0016] When i∈[1, N2-1], the i+1th DC conversion unit to the i+N1th DC conversion unit are sequentially determined as power transmission modules, and the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0017] When i=N2, the i+1th DC conversion unit to the Nth DC conversion unit are sequentially determined as power transmission modules, and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0018] When i∈[N2+1, N-1], the DC conversion units i+1 to N and the DC conversion units 1 to N1-N+i are sequentially determined as power transmission modules, and the DC conversion units N1-N+i+1 to the DC conversion units i are sequentially determined as redundant modules, so as to achieve capacitor voltage balancing of all DC conversion units.

[0019] Another aspect of the present application provides a switched capacitor connected DC transformer, comprising a preset number of DC conversion units and a control module, wherein the input end of each of the DC conversion units is electrically connected to a medium voltage DC bus, and the output end of each of the DC conversion units is electrically connected in parallel to a low voltage DC bus;

[0020] The control module is configured to:

[0021] Controlling each of the DC conversion units to precharge, and determining a first preset number of the DC conversion units as power transmission modules and a second preset number of the DC conversion units as redundant modules; wherein the sum of the first preset number and the second preset number is less than or equal to the preset number;

[0022] The power transmission modules and the redundant modules are rotated and controlled according to a preset rotation order, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switching capacitor of each redundant module is within a preset voltage range.

[0023] In the switched capacitor connected DC transformer in the above embodiment, all DC conversion units in the SCDCT are first pre-charged and a first preset number of power transmission modules and a second preset number of redundant modules are determined, and then the power transmission modules and redundant modules are rotated and controlled according to the rotation sequence, so that the switching loss of each power transmission module is within the preset loss range, and the voltage change of the switched capacitor of each redundant module is within the preset voltage range. In this way, the capacitor voltage of each module of the SCDST is balanced, avoiding the occurrence of current shock when the redundant module is put into use.

[0024] In one embodiment, the control module is configured to:

[0025] Controlling each of the DC conversion units to operate in an initial stage after pre-charging;

[0026] During the initial stage, the first DC conversion unit to the N1th DC conversion unit are sequentially determined as power transmission modules, and the N1+1th DC conversion unit to the N1+N2th DC conversion unit are sequentially determined as redundant modules;

[0027] Obtaining a rotation cycle, and controlling each of the redundant modules to be put into operation and each of the power transmission modules to be switched out within the rotation cycle;

[0028] At the end of the current rotation cycle, the switch capacitor connected DC transformer is controlled to operate in the next rotation cycle adjacent to the current rotation cycle. The sequence is determined so that the user can operate conveniently and can clearly distinguish the power transmission module and the redundant module. The power transmission module is controlled to be switched on and off within a rotation cycle so as to achieve capacitor voltage balance of all DC conversion units.

[0029] In one embodiment, the control method of the DC transformer, when the current rotation cycle is the i-th rotation cycle:

[0030] When i∈[1, N2-1], the i+1th DC conversion unit to the i+N1th DC conversion unit are sequentially determined as power transmission modules, and the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0031] When i=N2, the i+1th DC conversion unit to the Nth DC conversion unit are sequentially determined as power transmission modules, and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0032] When i∈[N2+1, N-1], the DC conversion units i+1 to N and the DC conversion units 1 to N1-N+i are sequentially determined as power transmission modules, and the DC conversion units N1-N+i+1 to the DC conversion units i are sequentially determined as redundant modules, so as to achieve capacitor voltage balancing of all DC conversion units.

[0033] In one embodiment, the switched capacitor connected DC transformer further comprises:

[0034] The DC auxiliary inductor is configured as follows: an input end is electrically connected to the medium voltage DC bus, and an output end is electrically connected to the first power transmission module.

[0035] In one embodiment, the first power transmission module includes:

[0036] A first controllable switch unit is configured as follows: a first port is electrically connected to an output end of the DC auxiliary inductor;

[0037] The second controllable switch unit is configured as follows: a first port is connected to the next DC conversion unit adjacent to the first controllable switch unit, and a second port is electrically connected to the first port of the first controllable switch unit;

[0038] A third controllable switch unit is configured such that: a second port is electrically connected to the second port of the first controllable switch unit;

[0039] a fourth controllable switch unit, configured such that: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the first port of the third controllable switch unit;

[0040] A freewheeling inductor is configured such that: an input port is electrically connected to a first port of the third controllable switch unit;

[0041] A transformer is configured such that: a first port is electrically connected to an output port of the freewheeling inductor;

[0042] a fifth controllable switch unit, configured such that: a first port is electrically connected to the second port of the transformer, and a second port is electrically connected to the second port of the third controllable switch unit;

[0043] a sixth controllable switch unit, configured as follows: a first port electrically connected to the first port of the fourth controllable switch unit, and a second port electrically connected to the first port of the fifth controllable switch unit and the second port of the transformer;

[0044] The medium voltage side capacitor is configured as follows: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the second port of the first controllable switch unit. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the sixth controllable switch.

[0045] In one embodiment, the first power transmission module further includes:

[0046] a seventh controllable switch unit, configured as follows: a first port electrically connected to a third port of the transformer;

[0047] an eighth controllable switch unit, configured as follows: a first port is electrically connected to the low-voltage DC bus, and a second port is electrically connected to both the first port of the seventh controllable switch unit and the third port of the transformer;

[0048] a ninth controllable switch unit, configured as follows: a first port electrically connected to the fourth port of the transformer, and a second port electrically connected to the second port of the seventh controllable switch unit;

[0049] a tenth controllable switch unit, configured as follows: a first port electrically connected to the first port of the eighth controllable switch unit, and a second port electrically connected to the first port of the ninth controllable switch unit and the fourth port of the transformer;

[0050] The low-voltage side capacitor is configured as follows: the first port is electrically connected to the first port of the tenth controllable switch unit, and the second port is electrically connected to the second port of the ninth controllable switch unit. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the sixth controllable switch. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the tenth controllable switch.

[0051] In the above-mentioned switched capacitor-connected DC transformer and DC transformer control method, by managing the functional power transmission module and the redundant module together, a cyclic rotation switching algorithm is added without changing the original control architecture. No electrical measurement information is required, and the voltage balance of the capacitors on the medium-voltage side of all modules is achieved simply and efficiently, avoiding the occurrence of current shock when the redundant module is put into use. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments 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 creative work.

[0053] Figure 1 A schematic flow chart of a control method for a DC transformer provided in an embodiment of the present application;

[0054] Figure 2 A schematic flow chart of a control method for a DC transformer provided in another embodiment of the present application;

[0055] Figure 3 A schematic flow chart of a control method of a DC transformer provided in another embodiment of the present application;

[0056] Figure 4 A schematic flow chart of a control method for a DC transformer provided in yet another embodiment of the present application;

[0057] Figure 5 This is a structural diagram of a switched capacitor-connected DC transformer provided in one embodiment of the present application. DETAILED DESCRIPTION

[0058] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0060] It can be understood that the terms "first", "second", etc. used in the present application can be used in this article to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element.

[0061] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element, or connected to the other element through an intermediate element. In addition, the "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is transmission of electrical signals or data between the connected objects.

[0062] Switched Capacitor based DC Transformer (SCDCT) is considered to be a key converter that has the potential to be applied in practical medium-voltage DC distribution network projects due to its modular design, high power density, large transmission capacity, and the ability to implement redundant sub-module design and medium-voltage side DC fault blocking.

[0063] However, in the existing research on SCDCT, the existence of redundant submodules in SCDCT is ignored, and the research focuses on the control analysis of the power transmission submodule in SCDCT, which causes the use of redundant modules in SCDCT by engineers to remain in the preliminary stage, that is, the redundant submodules are managed separately from the power transmission modules. The above management method theoretically believes that due to the locking effect of the power electronic switch, the medium-voltage side capacitor of the redundant module does not have a charging and discharging process during the operation of the SCDCT, so the capacitor voltage of the redundant submodule can be maintained, and it can be directly put into use when it is needed. However, in practice, the locked power electronic switch is equivalent to a large resistor, so that during the long-term operation of the SCDCT (several months or even years), the capacitor voltage of the redundant submodule is actually slowly discharged, causing the capacitor voltage value to deviate far from the rated value at the moment of use, resulting in current shock, which endangers the safe operation of the power electronic switch tube in the SCDCT.

[0064] As described in the above background technology, in SCDCT, the traditional control method does not take into account the large resistance of the power electronic switch. In practical applications, the strategy of managing the redundant submodule separately from the power transmission module will cause the capacitor of the redundant submodule to not be charged for a long time, the capacitor voltage to drop, and seriously deviate from the rated value, so that it loses the online redundancy function. Therefore, a reasonable SCDCT redundant submodule management method is proposed to maintain the constant voltage of the redundant submodule capacitor, which is of great significance for improving the reliable operation of the SCDCT.

[0065] For the above reasons, please refer to Figure 1 In one embodiment of the present application, a control method for a DC transformer is provided, which is applied to a switched capacitor connected DC transformer, wherein the switched capacitor connected DC transformer comprises a preset number of DC conversion units, wherein the input end of each of the DC conversion units is electrically connected to a medium voltage DC bus, and the output end of each of the DC conversion units is electrically connected to a low voltage DC bus, and the method comprises the following steps:

[0066] Step 10: Control each of the DC conversion units to precharge, and determine a first preset number of the DC conversion units as power transmission modules and a second preset number of the DC conversion units as redundant modules; wherein the sum of the first preset number and the second preset number is less than or equal to the preset number;

[0067] Step 20: Rotate and control each of the power transmission modules and each of the redundant modules according to a preset rotation order, so that the switching loss of each of the power transmission modules is within a preset loss range, and the voltage change of the switching capacitor of each of the redundant modules is within a preset voltage range.

[0068] In the control method of the DC transformer in the above embodiment, all DC conversion units in the SCDCT are first pre-charged and a first preset number of power transmission modules and a second preset number of redundant modules are determined, and then the power transmission modules and redundant modules are rotated and controlled according to the rotation sequence, so that the switching loss of each power transmission module is within the preset loss range, and the voltage change of the switch capacitor of each redundant module is within the preset voltage range. In this way, the capacitor voltage of each module of the SCDST is balanced, avoiding the occurrence of current shock when the redundant module is put into use.

[0069] For further information, please refer to Figure 2 In one embodiment, each of the DC conversion units is controlled to be precharged, and a first preset number N1 of the DC conversion units is determined as a power transmission module and a second preset number N2 of the DC conversion units is determined as a redundant module, N1+N2=N, N is less than or equal to the preset number, and the method steps include:

[0070] Step 11: Control each of the DC conversion units to run in an initial stage after pre-charging;

[0071] Step 12: During the initial stage, the first DC conversion unit to the N1th DC conversion unit are sequentially determined as power transmission modules, and the N1+1th DC conversion unit to the N1+N2th DC conversion unit are sequentially determined as redundant modules. The sequential determination facilitates the user's operation and enables the user to clearly distinguish the power transmission module and the redundant module.

[0072] Please refer to Figure 3 In one embodiment, the step of performing rotation control on each of the power transmission modules and each of the redundant modules according to a preset rotation sequence includes:

[0073] Step 21: obtaining a rotation cycle, and controlling each redundant module to be put into operation and each power transmission module to be switched out within one rotation cycle;

[0074] Step 22: At the end of the current rotation cycle, the switched capacitor DC transformer is controlled to operate in the next rotation cycle adjacent to the current rotation cycle. The power transmission module is controlled to be switched on and off within a rotation cycle to achieve capacitor voltage balance of all DC conversion units.

[0075] Specifically, the rotation cycle is obtained. Since the switching device is turned on and off during the redundancy module and the power transmission module is switched off, it will cause switching losses, so the rotation cycle cannot be too short; at the same time, too long a rotation cycle may cause the capacitor voltage of the redundancy module to drop, so the rotation cycle cannot be too long. Therefore, it is most appropriate to choose tens of minutes to several hours as the rotation cycle of SCDCT.

[0076] Please refer to Figure 4 In one embodiment, the control method of the DC transformer includes:

[0077] Step 30: If the current rotation period is the i-th rotation period;

[0078] When i∈[1, N2-1], the i+1th DC conversion unit to the i+N1th DC conversion unit are sequentially determined as power transmission modules, and the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0079] When i=N2, the i+1th DC conversion unit to the Nth DC conversion unit are sequentially determined as power transmission modules, and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0080] When i∈[N2+1, N-1], the i+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the N1-[N-(i+1)+1]=N1-N+i are sequentially determined as power transmission modules, and the N1-N+i+1th DC conversion unit to the i-th DC conversion unit are sequentially determined as redundant modules.

[0081] Specifically, in the same rotation cycle, the submodules are not switched. When a rotation cycle ends, the submodule allocation state of SCDCT enters the next rotation cycle. After nN rotation cycles, SCDCT will be in the initial stage again.

[0082] For example, in some embodiments, if N=5, N1=3, and N2=2, the initial state is that the first DC conversion unit to the third DC conversion unit are power transmission modules, and the fourth to the fifth DC conversion units are redundant modules; after a rotation cycle, when it is in the first rotation cycle, the second DC conversion unit to the fourth DC conversion unit are power transmission modules, and the fifth DC conversion unit and the first DC conversion unit are redundant modules; after a rotation cycle, when it is in the second rotation cycle, at this time i=N2, the third DC conversion unit to the fifth DC conversion unit are power transmission modules, and the first DC conversion unit to the second DC conversion unit are redundant modules; after a rotation cycle, in During the third rotation cycle, the 4th DC conversion unit to the 5th DC conversion unit and the 1st DC conversion unit are power transmission modules, and the 2nd DC conversion unit to the 3rd DC conversion unit are redundant modules; after one rotation cycle, when in the 4th rotation cycle, the 5th DC conversion unit and the 1st DC conversion unit to the 2nd DC conversion unit are power transmission modules, and the 3rd DC conversion unit to the 4th DC conversion unit are redundant modules; after one rotation cycle, a total of 5 rotation cycles (n=1, nN=5) have passed, and it returns to the initial state, the 1st DC conversion unit to the 3rd DC conversion unit are power transmission modules, and the 4th to the 5th DC conversion units are redundant modules.

[0083] It should be understood that although Figure 1-Figure 4 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1-Figure 4 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0084] Please refer to Figure 5 Another aspect of the present application provides a switched capacitor connected DC transformer, comprising a preset number of DC conversion units and a control module, wherein the input end of each of the DC conversion units is electrically connected to a medium voltage DC bus, and the output end of each of the DC conversion units is electrically connected in parallel to a low voltage DC bus;

[0085] The control module is configured to:

[0086] Controlling each of the DC conversion units to precharge, and determining a first preset number of the DC conversion units as power transmission modules and a second preset number of the DC conversion units as redundant modules; wherein the sum of the first preset number and the second preset number is less than or equal to the preset number;

[0087] The power transmission modules and the redundant modules are rotated and controlled according to a preset rotation order, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switching capacitor of each redundant module is within a preset voltage range.

[0088] In the switched capacitor connected DC transformer in the above embodiment, all DC conversion units in the SCDCT are first pre-charged and a first preset number of power transmission modules and a second preset number of redundant modules are determined, and then the power transmission modules and redundant modules are rotated and controlled according to the rotation sequence, so that the switching loss of each power transmission module is within the preset loss range, and the voltage change of the switched capacitor of each redundant module is within the preset voltage range. In this way, the capacitor voltage of each module of the SCDST is balanced, avoiding the occurrence of current shock when the redundant module is put into use.

[0089] In one embodiment, the control module is configured to:

[0090] Controlling each of the DC conversion units to operate in an initial stage after pre-charging;

[0091] During the initial stage, the first DC conversion unit to the N1th DC conversion unit are sequentially determined as power transmission modules, and the N1+1th DC conversion unit to the N1+N2th DC conversion unit are sequentially determined as redundant modules;

[0092] Obtaining a rotation cycle, and controlling each of the redundant modules to be put into operation and each of the power transmission modules to be switched out within the rotation cycle;

[0093] At the end of the current rotation cycle, the switch capacitor connected DC transformer is controlled to operate in the next rotation cycle adjacent to the current rotation cycle. The sequence is determined so that the user can operate conveniently and can clearly distinguish the power transmission module and the redundant module. The power transmission module is controlled to be switched on and off within a rotation cycle so as to achieve capacitor voltage balance of all DC conversion units.

[0094] In one embodiment, the control module is configured to:

[0095] If the current rotation period is the i-th rotation period;

[0096] When i∈[1, N2-1], the i+1th DC conversion unit to the i+N1th DC conversion unit are sequentially determined as power transmission modules, and the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0097] When i=N2, the i+1th DC conversion unit to the Nth DC conversion unit are sequentially determined as power transmission modules, and the 1st DC conversion unit to the ith DC conversion unit are sequentially determined as redundant modules;

[0098] When i∈[N2+1, N-1], the DC conversion units i+1 to N and the DC conversion units 1 to N1-N+i are sequentially determined as power transmission modules, and the DC conversion units N1-N+i+1 to the DC conversion units i are sequentially determined as redundant modules, so as to achieve capacitor voltage balancing of all DC conversion units.

[0099] In one embodiment, the switched capacitor connected DC transformer further comprises:

[0100] The DC auxiliary inductor is configured as follows: an input end is electrically connected to the medium voltage DC bus, and an output end is electrically connected to the first power transmission module.

[0101] In one embodiment, the first power transmission module includes:

[0102] A first controllable switch unit is configured as follows: a first port is electrically connected to an output end of the DC auxiliary inductor;

[0103] The second controllable switch unit is configured as follows: a first port is connected to the next DC conversion unit adjacent to the first controllable switch unit, and a second port is electrically connected to the first port of the first controllable switch unit;

[0104] A third controllable switch unit is configured such that: a second port is electrically connected to the second port of the first controllable switch unit;

[0105] a fourth controllable switch unit, configured such that: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the first port of the third controllable switch unit;

[0106] A freewheeling inductor is configured such that: an input port is electrically connected to a first port of the third controllable switch unit;

[0107] A transformer is configured such that: a first port is electrically connected to an output port of the freewheeling inductor;

[0108] a fifth controllable switch unit, configured such that: a first port is electrically connected to the second port of the transformer, and a second port is electrically connected to the second port of the third controllable switch unit;

[0109] a sixth controllable switch unit, configured as follows: a first port electrically connected to the first port of the fourth controllable switch unit, and a second port electrically connected to the first port of the fifth controllable switch unit and the second port of the transformer;

[0110] The medium voltage side capacitor is configured as follows: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the second port of the first controllable switch unit. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the sixth controllable switch.

[0111] In one embodiment, the first power transmission module further includes:

[0112] a seventh controllable switch unit, configured as follows: a first port electrically connected to a third port of the transformer;

[0113] an eighth controllable switch unit, configured as follows: a first port is electrically connected to the low-voltage DC bus, and a second port is electrically connected to both the first port of the seventh controllable switch unit and the third port of the transformer;

[0114] a ninth controllable switch unit, configured as follows: a first port electrically connected to the fourth port of the transformer, and a second port electrically connected to the second port of the seventh controllable switch unit;

[0115] a tenth controllable switch unit, configured as follows: a first port electrically connected to the first port of the eighth controllable switch unit, and a second port electrically connected to the first port of the ninth controllable switch unit and the fourth port of the transformer;

[0116] The low-voltage side capacitor is configured as follows: the first port is electrically connected to the first port of the tenth controllable switch unit, and the second port is electrically connected to the second port of the ninth controllable switch unit. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the sixth controllable switch. The DC conversion unit is controlled to be a power transmission module or a redundant module by unlocking or locking the first controllable switch to the tenth controllable switch.

[0117] Specifically, for example, in some embodiments, if the first DC conversion unit is a power transmission module, the first controllable switch unit is in an unlocked state, the second controllable switch unit is in a locked state, and the remaining third to tenth controllable switch units are controlled according to the pulse signal generated by the system; if the first DC conversion unit is a redundant module, the first controllable switch unit is in a locked state, the second controllable switch unit is in an unlocked state, and the remaining third to tenth controllable switch units are all in a locked state.

[0118] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0119] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A control method for a DC transformer, characterized in that: Applied to a switched capacitor connected DC transformer, the switched capacitor connected DC transformer comprises a preset number of DC conversion units, the input end of each of the DC conversion units is electrically connected to a medium voltage DC bus, and the output end of each of the DC conversion units is electrically connected to a low voltage DC bus, the method comprises: Controlling the pre-charging of each of the DC conversion units; Controlling each of the DC changing units to operate in an initial stage; During the initial stage, a first preset number N1 of the DC conversion units is determined as a power transmission module and a second preset number N2 of the DC conversion units is determined as a redundant module; wherein the first preset number N1 of the DC conversion units includes the first DC conversion unit to the N1th DC conversion unit determined in sequence, and the second preset number N2 of the DC conversion units includes the N1+1th DC conversion unit to the N1+N2th DC conversion unit determined in sequence, N1+N2=N, N is less than or equal to the preset number; Obtain a rotation cycle, control each redundant module to be put into operation and each power transmission module to be cut out within one rotation cycle, and control the switched capacitor-connected DC transformer to operate in the next rotation cycle adjacent to the current rotation cycle at the end of the current rotation cycle, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switched capacitor of each redundant module is within a preset voltage range.

2. The control method of the DC transformer according to claim 1, characterized in that: During the current rotation period being the i-th rotation period: If i∈[1, N2-1], sequentially determine the i+1th DC conversion unit to the i+N1th DC conversion unit as power transmission modules, and sequentially determine the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit as redundant modules; If i=N2, sequentially determine the i+1th DC conversion unit to the Nth DC conversion unit as power transmission modules, and sequentially determine the 1st DC conversion unit to the ith DC conversion unit as redundant modules; If i∈[N2+1, N-1], the i+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the N1-N+ith DC conversion unit are sequentially determined as power transmission modules, and the N1-N+i+1th DC conversion unit to the i-th DC conversion unit are sequentially determined as redundant modules.

3. A switched capacitor connected DC transformer, characterized in that: It comprises a preset number of DC conversion units and a control module, wherein the input end of each DC conversion unit is electrically connected to a medium voltage DC bus, and the output end of each DC conversion unit is electrically connected to a low voltage DC bus in parallel; The control module is configured to: Controlling the pre-charging of each of the DC conversion units; Controlling each of the DC changing units to operate in an initial stage; During the initial stage, a first preset number N1 of the DC conversion units is determined as a power transmission module and a second preset number N2 of the DC conversion units is determined as a redundant module; wherein the first preset number N1 of the DC conversion units includes the first DC conversion unit to the N1th DC conversion unit determined in sequence, and the second preset number N2 of the DC conversion units includes the N1+1th DC conversion unit to the N1+N2th DC conversion unit determined in sequence, N1+N2=N, N is less than or equal to the preset number; Obtain a rotation cycle, control each redundant module to be put into operation and each power transmission module to be cut out within one rotation cycle, and control the switched capacitor-connected DC transformer to operate in the next rotation cycle adjacent to the current rotation cycle at the end of the current rotation cycle, so that the switching loss of each power transmission module is within a preset loss range, and the voltage change of the switched capacitor of each redundant module is within a preset voltage range.

4. The switched capacitor connected DC transformer according to claim 3, characterized in that: During the current rotation period being the i-th rotation period: If i∈[1, N2-1], sequentially determine the i+1th DC conversion unit to the i+N1th DC conversion unit as power transmission modules, and sequentially determine the i+N1+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the ith DC conversion unit as redundant modules; If i=N2, sequentially determine the i+1th DC conversion unit to the Nth DC conversion unit as power transmission modules, and sequentially determine the 1st DC conversion unit to the ith DC conversion unit as redundant modules; If i∈[N2+1, N-1], the i+1th DC conversion unit to the Nth DC conversion unit and the 1st DC conversion unit to the N1-N+ith DC conversion unit are sequentially determined as power transmission modules, and the N1-N+i+1th DC conversion unit to the i-th DC conversion unit are sequentially determined as redundant modules.

5. The switched capacitor connected DC transformer according to claim 3, characterized in that: Also includes: The DC auxiliary inductor is configured as follows: an input end is electrically connected to the medium voltage DC bus, and an output end is electrically connected to the first power transmission module.

6. The switched capacitor connected DC transformer according to claim 5, characterized in that: The first power transmission module comprises: A first controllable switch unit is configured as follows: a first port is electrically connected to an output end of the DC auxiliary inductor; The second controllable switch unit is configured as follows: a first port is connected to the next DC conversion unit adjacent to the first controllable switch unit, and a second port is electrically connected to the first port of the first controllable switch unit; A third controllable switch unit is configured such that: a second port is electrically connected to the second port of the first controllable switch unit; a fourth controllable switch unit, configured such that: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the first port of the third controllable switch unit; A freewheeling inductor is configured such that: an input port is electrically connected to a first port of the third controllable switch unit; A transformer is configured such that: a first port is electrically connected to an output port of the freewheeling inductor; a fifth controllable switch unit, configured such that: a first port is electrically connected to the second port of the transformer, and a second port is electrically connected to the second port of the third controllable switch unit; a sixth controllable switch unit, configured as follows: a first port electrically connected to the first port of the fourth controllable switch unit, and a second port electrically connected to the first port of the fifth controllable switch unit and the second port of the transformer; The medium-voltage side capacitor is configured as follows: a first port is electrically connected to the first port of the second controllable switch unit, and a second port is electrically connected to the second port of the first controllable switch unit.

7. The switched capacitor connected DC transformer according to claim 6, characterized in that: The first power transmission module further includes: a seventh controllable switch unit, configured as follows: a first port electrically connected to a third port of the transformer; an eighth controllable switch unit, configured as follows: a first port electrically connected to the low-voltage DC bus, and a second port electrically connected to both the first port of the seventh controllable switch unit and the third port of the transformer; a ninth controllable switch unit, configured as follows: a first port electrically connected to the fourth port of the transformer, and a second port electrically connected to the second port of the seventh controllable switch unit; a tenth controllable switch unit, configured as follows: a first port electrically connected to the first port of the eighth controllable switch unit, and a second port electrically connected to the first port of the ninth controllable switch unit and the fourth port of the transformer; The low-voltage side capacitor is configured as follows: a first port is electrically connected to the first port of the tenth controllable switch unit, and a second port is electrically connected to the second port of the ninth controllable switch unit.

8. The switched capacitor connected DC transformer according to claim 7, characterized in that: If the first DC conversion unit is the power transmission module, the first controllable switch unit is in an unlocked state, the second controllable switch unit is in a locked state, and the third controllable switch unit to the tenth controllable switch unit are controlled by a pulse signal; If the first DC conversion unit is a redundant module, the first controllable switch unit is in a locked state, the second controllable switch unit is in an unlocked state, and the third controllable switch unit to the tenth controllable switch unit are all in a locked state.

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