A self-balanced DC / DC conversion system

Abstract

The present invention provides a self-equalized voltage DC / DC conversion system, comprising: a high-voltage DC port, a low-voltage DC port, a port inductor, a controller and at least one conversion unit, wherein each conversion unit comprises an energy balancing circuit and a plurality of power sub-modules. The adjacent power sub-module capacitors in the cut-off state form a loop through the energy balancing circuit, the series capacitors automatically equalize the voltage, and the power sub-module with a high capacitor voltage will discharge to the power sub-module with a low capacitor voltage. Energy can be transferred between power sub-modules through a simple control strategy, thereby achieving continuous energy transfer between the high-voltage DC port and the low-voltage DC port. The present invention has the advantages of a small number of IGBTs, low cost, simple insulation design, high power quality, and fast restart speed after a fault.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a self-balanced voltage DC / DC conversion system. Background Art

[0002] With the continuous increase in the scale and penetration of renewable energy power generation, the existing large-scale renewable energy AC grid-connected technology has become increasingly prominent, with problems such as high active and reactive coupling, complex transient and steady-state interaction mechanisms, and high oscillation risks. New energy DC grid-connected technology has technical advantages such as fewer control dimensions, high collection efficiency, and good system stability. It has become an important development direction for large-scale renewable energy grid-connected technology. Since the output DC voltage level of renewable energy is relatively low and the voltage of the collection and transmission system is relatively high, high-voltage and high-ratio DC / DC converters with DC voltage conversion, system flow control, and fault current limiting functions have become the core equipment for all-DC grid-connected renewable energy such as offshore wind power and large-scale photovoltaic power generation, and have broad application prospects.

[0003] Due to the limitations of electrical topology and switching device capabilities, traditional Buck, Boost and other DC / DC converters have shortcomings in operating voltage, capacity, efficiency and voltage transformation ratio. Based on this, the prior art proposes several converters: ISOP (Input Series Output Parallel) DC / DC converter based on DAB (Dual Active Bridge), LC resonant boost DC / DC converter, and modular resonant non-isolated DC / DC converter without active switch and other electrical topologies to meet the engineering application requirements of high voltage, high power and high transformation ratio of DC / DC converters.

[0004] However, the above converters have different technical problems, specifically: the ISOP DC / DC converter based on DAB, in order to meet the needs of high-voltage and large-capacity applications, adopts multiple small-capacity DC / DC converters connected in parallel on the input side and in series on the output side, thereby effectively reducing the capacity and port voltage of each DCDC converter. However, each isolation transformer needs to isolate the DC high-voltage system voltage, which makes the insulation design difficult and the insulation cost high; the LC resonant boost DC / DC converter realizes the boost function through LC resonance, without the need for a transformer, but the waveform of the converter input and output current is poor, and a larger filtering device is required. In addition, due to the shared resonant capacitor, high and low The insulation level on the high-voltage side is the same, and the high- and low-voltage thyristors need to be selected according to the same voltage level. Considering that the resonant capacitor voltage is usually 1.2 to 1.4 times the rated voltage on the high-voltage side, a larger number of power devices are required. The modular resonant non-isolated DC / DC converter without active switches uses a cascaded LC resonant circuit to achieve step-by-step voltage increase and energy transmission. When the switching frequency is lower than the resonant frequency, the LC resonant circuit can be used to achieve zero-current switching of the switching device to reduce switching losses. However, when a short-circuit fault occurs in the DC collection system of this electrical topology, the resonant capacitor will discharge the short-circuit fault point to zero, increasing the system fault current and not conducive to the rapid restart of the new energy station after a fault. Summary of the invention

[0005] Therefore, in order to solve the problems of fault current, difficulty in rapid recovery, complex control strategy and high equipment cost in the prior art, the present invention provides a self-balanced DC / DC conversion system.

[0006] The present invention provides a self-balanced DC / DC conversion system, comprising: a high-voltage DC port, a low-voltage DC port, a port inductor, a controller and at least one conversion unit, wherein each conversion unit comprises an energy balancing circuit and a plurality of power submodules.

[0007] When there are multiple conversion units, each conversion unit is connected in parallel via a DC port;

[0008] The port inductors are arranged at the high voltage DC port and the low voltage DC port;

[0009] Each power submodule is connected in series, and two adjacent power submodules are connected through diodes to form an energy balancing circuit. The adjacent power submodule capacitors in the cut-off state form a loop through the energy balancing circuit. The two power submodule capacitors are connected in series and automatically equalize the voltage. Therefore, the power submodule capacitor with a high voltage will discharge to the power submodule capacitor with a low voltage.

[0010] The controller is connected to the control end of the conversion unit and is used to cyclically control the input and removal states of multiple power sub-modules according to a preset rule. The power sub-modules transfer energy between the high-voltage DC port and the low-voltage DC port through the energy balancing circuit.

[0011] Optionally, the power submodule includes: a power transfer circuit, a DC support capacitor, two main circuit terminals and two auxiliary terminals; wherein:

[0012] The power transfer circuit is connected in parallel with the DC support capacitor; wherein the power transfer circuit is a full-bridge circuit or a half-bridge circuit;

[0013] When the power transfer circuit is a half-bridge circuit, the neutral point of the half-bridge circuit and the positive or negative electrode of the DC support capacitor serve as the main circuit terminals of the power submodule;

[0014] When the power transfer circuit is a full-bridge circuit, the two neutral points of the full-bridge circuit serve as the main circuit terminals of the power submodule;

[0015] The main circuit terminals of adjacent power submodules are connected in series;

[0016] The positive and negative electrodes of the DC link capacitor are connected to the auxiliary terminals of the power submodule.

[0017] Optionally, the energy balancing circuit is a diode unidirectional balancing circuit or a diode bidirectional balancing circuit.

[0018] Optionally, the positive electrodes of the DC support capacitors in two adjacent power sub-modules are connected through diodes, or the negative electrodes of the DC support capacitors in two adjacent power sub-modules are connected through diodes, and all diodes are connected in series in the same direction to form a diode unidirectional balancing circuit.

[0019] Optionally, the positive electrodes of the DC support capacitors in two adjacent power sub-modules and the negative electrodes of the DC support capacitors are connected through diodes, the diodes connected to the positive electrodes are connected in series in the same direction, and the diodes connected to the negative electrodes are connected in series in the same direction to form a diode bidirectional balancing circuit.

[0020] Optionally, the main circuit terminals of each power submodule are connected in series in sequence, and the positive and negative electrodes of the series connection serve as two terminals of the high-voltage DC port;

[0021] The series connection point between the series-connected negative electrode and any two adjacent power sub-modules serves as two terminals of the low-voltage DC port.

[0022] Optionally, the terminals of the high voltage DC port and the low voltage DC port are respectively connected in series with port inductors.

[0023] The technical solution of the present invention has the following advantages:

[0024] The self-equalizing DC / DC conversion system provided by the invention has a DC port connected to a power supply and a load. After the DC port is connected to the power supply and the load, the sub-module capacitor connected to the power supply increases in voltage due to charging, and the sub-module capacitor connected to the load decreases in voltage due to discharging. The voltages of the power sub-module capacitors in the conversion unit are arranged in descending or ascending order. Through the control strategy, energy can be transferred from the high-voltage power sub-module to the low-voltage power sub-module in sequence, thereby realizing continuous energy transfer between the high-voltage DC port and the low-voltage DC port. There is no need to introduce a complex control system or to collect capacitor voltage information in real time, thus avoiding massive calculations on the collected information, reducing the equipment cost of the system, and not adding fault current to the system. It can be quickly restarted after a new energy station fails. At the same time, it has the advantages of a small number of IGBTs, a simple insulation design, and high power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A schematic diagram of the structure of a self-balanced DC / DC conversion system provided by an embodiment of the present invention;

[0027] Figure 2-Figure 6 They are schematic diagrams of the structures of the self-balanced voltage DC / DC conversion system provided by the embodiments of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The self-balanced voltage DC / DC conversion system provided by the embodiment of the present invention has a structural schematic diagram as shown in FIG. Figure 1 As shown, including: high voltage DC port (such as Figure 1 Middle U DCA As shown), low voltage DC port (as Figure 1 Middle U DCB As shown), a port inductor, a controller and at least one conversion unit 1, Figure 1Taking one conversion unit 1 as an example, when the self-balanced voltage DC / DC conversion system includes multiple conversion units, each conversion unit is connected in parallel, and its structural schematic diagram is as shown in FIG. Figure 2 As shown, the specific number of conversion units is not limited and can be adjusted according to actual application conditions; each conversion unit includes an energy balancing circuit 11 and a plurality of power sub-modules 12.

[0031] like Figure 1 As shown, the port inductor is arranged at the high-voltage DC port and the low-voltage DC port, each power sub-module 12 is connected in series, and two adjacent power sub-modules are connected through diodes to form an energy balancing circuit 11. The controller is connected to the control end of the conversion unit 1, and then cyclically controls the input and removal states of multiple power sub-modules 12 according to a preset rule, so that each power sub-module 12 is arranged in descending order or ascending order, and the capacitors in the adjacent power sub-modules 12 in the removal state form a loop through the energy balancing circuit. The capacitors of the two power sub-modules 12 are connected in series and automatically equalize the voltage. The capacitor of the power sub-module 12 with a high voltage will discharge to the capacitor of the power sub-module 12 with a low voltage, so as to realize continuous energy transfer between the high-voltage DC port and the low-voltage DC port, so as to balance the capacitor voltages in each power sub-module 12. The specific working principle can be found in the following embodiments Figure 5 and Figure 6 Demonstration of control process.

[0032] It is worth noting that the preset rules for controlling the input and removal states of the power submodule 12, including the number of input submodules in the high-voltage DC port and the low-voltage DC port loop, the direction of energy transfer, etc., can be adjusted according to the actual application scenario without specific limitation, and can refer to the following embodiments. Figure 5 and Figure 6 Demonstration of control process.

[0033] The self-equalizing DC / DC conversion system provided in this embodiment constructs an energy balancing circuit between submodules, so that the adjacent power submodule capacitors in the removed state form a loop through the energy balancing circuit, and the series capacitors automatically equalize the voltage, and the power submodule with a high capacitor voltage will discharge to the power submodule with a low capacitor voltage. After the DC port is connected to the power supply and the load, the submodule capacitor connected to the power supply increases due to the charging voltage, and the submodule capacitor connected to the load decreases due to the discharge voltage. According to the preset rules, the input and removal of the power submodules are cyclically controlled, and the capacitor voltages of the power submodules in the conversion unit are arranged in descending or ascending order, and the energy is transferred from the high-voltage power submodule to the low-voltage power submodule in turn, and finally the continuous energy transfer between the high-voltage DC port and the low-voltage DC port is realized.

[0034] In a specific embodiment, the power submodule 12 includes: a power transfer circuit (such as Figure 1T3, T4), DC support capacitor (such as Figure 1 Middle C SM As shown), two main circuit terminals (as Figure 1 n1, n2) and two auxiliary terminals (as shown in Figure 1 (shown as a1 and a2 in the figure).

[0035] like Figure 1 As shown, the power transfer circuit is connected in parallel with the DC support capacitor; the main circuit terminals of adjacent power sub-modules are connected in series; the positive and negative electrodes of the DC support capacitor serve as auxiliary terminals of the power sub-module. That is, the main circuit terminals of each power sub-module are connected in series in sequence, and the positive and negative electrodes after series connection serve as two terminals of the high-voltage DC port; the series connection point of the negative electrode after series connection and any two adjacent power sub-modules serve as two terminals of the low-voltage DC port; the terminals of the high-voltage DC port and the low-voltage DC port are each connected in series with a port inductor.

[0036] It is worth noting that the power transfer circuit can be a half-bridge circuit, such as Figure 1 As shown, it can also be a full-bridge circuit, such as Figure 2 and Figure 3 shown.

[0037] When the power transfer circuit is a half-bridge circuit, the neutral point of the half-bridge circuit and the positive electrode of the DC support capacitor serve as the main circuit terminals of the power submodule 12. Figure 1 As shown in n1 and n2, the neutral point of the half-bridge circuit and the negative electrode of the DC support capacitor serve as the main circuit terminals of the power submodule 12, as shown in FIG. Figure 4 As shown in n1 and n2.

[0038] When the power transfer circuit is a full-bridge circuit, the two neutral points of the full-bridge circuit serve as the main circuit terminals of the power submodule, such as Figure 3 As shown in n1 and n2.

[0039] like Figure 1-4 As shown, the half-bridge circuit and the full-bridge circuit are composed of IGBT switch tubes, and each IGBT switch tube is reversely connected in parallel with a diode. The specific process of controlling the switching state of multiple power sub-modules 12 is as follows: controlling the on and off states of the IGBT switch tubes in the power sub-modules 12 to achieve the switching state of the power sub-modules 12. That is, by controlling the switching of the DC support capacitor, the required output voltage and the port voltage of the DC / DC conversion system are formed to complete the system power transmission.

[0040] In a specific embodiment, the energy balancing circuit 11 may be a diode unidirectional balancing circuit. In this case, the negative electrodes of the DC support capacitors in two adjacent power submodules 12 are connected via a diode to form a diode unidirectional balancing circuit. The schematic diagram of the structure is shown in FIG. Figure 1 As shown, the negative electrodes of the DC support capacitors in two adjacent power submodules 12 are connected through diodes, and all diodes are connected in series in the same direction to form a diode unidirectional balancing circuit to achieve energy transfer from the high-voltage DC port to the low-voltage DC port, that is, a step-down self-balancing DC / DC conversion system; or, as Figure 4 As shown, the positive electrodes of the DC support capacitors in two adjacent power submodules 12 are connected through diodes, and all diodes are connected in series in the same direction to form a diode unidirectional balancing circuit, so as to realize the energy transfer of the conversion system from the low-voltage DC port to the high-voltage DC port, that is, a boost self-balanced DC / DC conversion system. In actual application, in a conversion unit composed of N modules, N-1 diodes are required to form an energy balancing circuit 11.

[0041] The energy balancing circuit 11 may also be a diode bidirectional balancing circuit, and its structural diagram is shown in FIG. Figure 2 As shown, the positive poles of the DC support capacitors in two adjacent power sub-modules 12, and the negative poles of the DC support capacitors are connected through diodes, the diodes connected to the positive poles of the DC support capacitors are connected in series in the same direction, and the diodes connected to the negative poles of the DC support capacitors are connected in series in the same direction, forming a diode bidirectional balancing circuit, realizing bidirectional energy transfer between the high-voltage DC port and the low-voltage DC port of the conversion system, that is, a step-up and step-down self-balancing DC / DC conversion system. Therefore, in a conversion unit composed of N power sub-modules 12, N-1 diodes are required to form the first group of diodes, each diode is connected in parallel between the negative poles of the DC support capacitors of two adjacent power sub-modules 12, and N-1 diodes are required to form the second group of diodes, each diode is connected in parallel between the positive poles of the DC support capacitors of two adjacent power sub-modules 12, and an energy balancing circuit is formed by two groups of diodes.

[0042] In a specific embodiment, the number of the conversion units in the above conversion system and the number of the power sub-modules 12 in the conversion units can be determined according to specific circumstances.

[0043] For example, Figure 5 As shown, the step-down self-equalizing DC / DC conversion system includes a high-voltage DC port, a low-voltage DC port, a port inductor, a controller and a conversion unit. Among them, the conversion unit includes an energy balancing circuit and 8 power sub-modules. Its energy balancing circuit is a diode unidirectional balancing circuit, which is provided with 7 diodes, each diode is connected in parallel between the negative poles of the DC support capacitors of two adjacent power sub-modules, and all diodes are connected in series in the same direction in sequence; the power sub-module includes: a power transfer circuit, a 0.5kV DC support capacitor, two main circuit terminals and two auxiliary terminals; the power transfer circuit is connected in parallel with the DC support capacitor, and the power transfer circuit adopts a half-bridge circuit. The self-equalizing DC / DC conversion system is suitable for DC high transformation ratio step-down output occasions.

[0044] like Figure 5 As shown, the main circuit terminals of the eight power submodules are connected in series in sequence, and the two terminals after the series connection are respectively connected in series with the port inductor to form a 2kV high-voltage DC port; the negative pole after the series connection, and the connection points of the main circuit terminals of the middle submodule 4 and submodule 5 are respectively connected in series with the port inductor to form a 1kV low-voltage DC port.

[0045] At this time, the controller is used to cyclically control the input and removal states of multiple power sub-modules according to a preset rule, and the specific process of balancing the capacitor voltage in each power sub-module is as follows: the DC / DC conversion system forms a DC port voltage by controlling the switching of the DC support capacitor. There are 4 power sub-modules in the internal loop of the high-voltage DC port, and the high-voltage DC port voltage is 2kV. There are 2 power sub-modules in the internal loop of the low-voltage DC port, and the low-voltage DC port voltage is 1kV. By controlling the on and off states of the corresponding IGBTs in the power sub-modules, the input and removal of the power sub-modules are realized, and whether the power sub-module capacitors are used as support for the output voltage is controlled. Among the 8 power sub-modules of the conversion unit, 4 power sub-modules are always in the input state and 4 power sub-modules are in the removal state. The power sub-module in the closed state cooperates with the energy balancing circuit to realize the transfer of sub-module capacitor energy to the adjacent lower sub-module, and by changing the position of the removed sub-module in turn, the energy is transferred from the high-voltage DC port to the low-voltage DC port, and the sub-module capacitor voltage is balanced at the same time.

[0046] For example, at time t1, control Figure 5 The middle switch tubes T13, T23, T53, and T63 are closed, and T14, T24, T54, and T64 are disconnected, then submodules 1, 2, 5, and 6 are in the cut-off state; the control switch tubes T34, T44, T74, and T84 are closed, and T33, T43, T73, and T83 are disconnected, then submodules 3, 4, 7, and 8 are in the input state; at this time, the DC support capacitor C of submodule 1 SM1 Through the energy balancing circuit to the sub-module 2 DC support capacitor C SM2 Discharge, realize the energy transfer from submodule 1 to submodule 2, submodule 5 DC support capacitor C SM5 Through the energy balancing circuit to the sub-module 6 DC support capacitor C SM6 Discharge, to achieve energy transfer from submodule 5 to submodule 6, the energy transfer path is as follows Figure 5 Indicated by the dashed line with arrow.

[0047] At time t2, the control switch tubes T23, T33, T63, and T73 are closed, and T24, T34, T64, and T74 are disconnected, then submodule 2, submodule 3, submodule 6, and submodule 7 are in the cut-off state; the control switch tubes T44, T54, T84, and T14 are closed, and T43, T53, T83, and T13 are disconnected, then submodule 4, submodule 5, submodule 8, and submodule 1 are in the input state; at this time, the DC support capacitor C of submodule 2 SM2 Through the energy balancing circuit to the sub-module 3 DC support capacitor C SM3 Discharge, realize the energy transfer from submodule 2 to submodule 3, submodule 6 DC support capacitor C SM6 Through the energy balancing circuit to the sub-module 7 DC support capacitor C SM7 Discharging to achieve energy transfer from submodule 6 to submodule 7.

[0048] At time t3, the control switch tubes T33, T43, T73, and T83 are closed, and T34, T44, T74, and T84 are disconnected, then submodules 3, 4, 7, and 8 are in the cut-off state; the control switch tubes T54, T64, T14, and T24 are closed, and T53, T63, T13, and T23 are disconnected, then submodules 5, 6, 1, and 2 are in the input state; at this time, the DC support capacitor C of submodule 3 SM3 Through the energy balancing circuit to the sub-module 4 DC support capacitor C SM4 Discharge, realize the energy transfer from submodule 3 to submodule 4, submodule 7 DC support capacitor C SM7 Through the energy balancing circuit to the sub-module 8 DC support capacitor C SM8 Discharging to achieve energy transfer from submodule 7 to submodule 8.

[0049] At time t4, the control switch tubes T43, T53, T83, and T13 are closed, and T44, T54, T84, and T14 are disconnected, then submodule 4, submodule 5, submodule 8, and submodule 1 are in the cut-off state; the control switch tubes T64, T74, T24, and T34 are closed, and T63, T73, T23, and T33 are disconnected, then submodule 7, submodule 7, submodule 2, and submodule 3 are in the input state; at this time, the DC support capacitor C of submodule 4 SM4 Through the energy balancing circuit to the sub-module 5 DC support capacitor C SM5 Discharging to achieve energy transfer from submodule 4 to submodule 5.

[0050] Therefore, by looping the above process from t1 to t4, Figure 5 The energy transfer from the high voltage side to the low voltage side of the self-voltage-balanced DC / DC conversion system is shown.

[0051] Or, if Figure 6As shown, the boost self-equalizing DC / DC conversion system includes: a high-voltage DC port, a low-voltage DC port, a port inductor, a controller and a conversion unit. Among them, the conversion unit includes an energy balancing circuit and 9 power sub-modules. Its energy balancing circuit is a diode unidirectional balancing circuit, which is equipped with 8 diodes, each diode is connected in parallel between the negative poles of the DC support capacitors of two adjacent power sub-modules, and all diodes are connected in series in the same direction in sequence; the power sub-module includes: a power transfer circuit, a 1kV DC support capacitor, two main circuit terminals and two auxiliary terminals; the power transfer circuit is connected in parallel with the DC support capacitor, and the power transfer circuit adopts a half-bridge circuit. This self-equalizing DC / DC conversion system is suitable for DC high-ratio boost output occasions.

[0052] like Figure 6 As shown, the main circuit terminals of the 9 power sub-modules are connected in series in sequence, and the two terminals after the series connection are respectively connected in series with the port inductor to form a 5kV high-voltage DC port; the negative pole after the series connection, and the connection points of the main circuit terminals of the two middle sub-modules 4 and 5 are respectively connected in series with the port inductor to form a 2kV low-voltage DC port.

[0053] At this time, the controller is used to cyclically control the input and removal states of multiple power sub-modules according to a preset rule, and the specific process of balancing the capacitor voltage in each power sub-module is as follows: the DC / DC conversion system forms a DC port voltage by controlling the switching of the DC support capacitor. There are 5 power sub-modules in the internal loop of the high-voltage DC port, and the high-voltage DC port voltage is 5kV. There are 2 power sub-modules in the internal loop of the low-voltage DC port, and the low-voltage DC port voltage is 2kV. By controlling the on and off states of the corresponding IGBTs in the power sub-modules, the input and removal of the power sub-modules are realized, and whether the power sub-module capacitors are used as support for the output voltage is controlled. Among the 9 power sub-modules of the conversion unit, 5 power sub-modules are always in the input state and 4 power sub-modules are in the removal state. The power sub-module in the closed state cooperates with the energy balancing circuit to realize the transfer of sub-module capacitor energy to the adjacent lower sub-module. By changing the position of the removed sub-module in turn, the energy is transferred from the low-voltage DC port to the high-voltage DC port, and the sub-module capacitor voltage is balanced at the same time.

[0054] Specifically, similar to the above control process, that is, at time t1, submodule 1, submodule 2, submodule 6, and submodule 7 are removed, and submodule 3, submodule 4, submodule 5, submodule 8, and submodule 9 are put into operation; at this time, the DC support capacitor C of module 1 SM1 Through the energy balancing circuit to the sub-module 2 DC support capacitor C SM2 Discharge to achieve energy transfer from submodule 1 to submodule 2; submodule 6 DC support capacitor C SM6 Through the energy balancing circuit to the sub-module 7 DC support capacitor CSM7 Discharge, to achieve energy transfer from submodule 6 to submodule 7, the energy transfer path is as follows Figure 6 At time t2, control submodule 2, submodule 3, submodule 7, and submodule 8 are removed, and submodule 1, submodule 4, submodule 5, submodule 6, and submodule 9 are put into operation. At this time, the DC support capacitor C SM2 Through the energy balancing circuit to the sub-module 3 DC support capacitor C SM3 Discharge, to achieve energy transfer from submodule 2 to submodule 3, submodule 7 DC support capacitor C SM7 Through the energy balancing circuit to the sub-module 8 DC support capacitor C SM8 Discharge, to achieve energy transfer from submodule 7 to submodule 8. At t3, control submodule 3, submodule 4, submodule 8, submodule 9 to be removed, submodule 1, submodule 2, submodule 5, submodule 6, submodule 7 to be put into operation. At this time, the DC support capacitor C SM3 Through the energy balancing circuit to the sub-module 4 DC support capacitor C SM4 Discharge, realize the energy transfer from submodule 3 to submodule 4, submodule 8 DC support capacitor C SM8 Through the energy balancing circuit to the sub-module 9 DC support capacitor C SM9 Discharge, to achieve energy transfer from submodule 8 to submodule 9. At t4, control submodule 4, submodule 5, submodule 9, submodule 1 are removed, and submodule 2, submodule 3, submodule 6, submodule 7, and submodule 8 are put into operation. At this time, the DC support capacitor C of module 4 SM4 Through the energy balancing circuit to the sub-module 5 DC support capacitor C SM5 Discharge, to achieve energy transfer from submodule 4 to submodule 5. At t5, control submodule 5, submodule 6, submodule 1, submodule 2 are removed, and submodule 3, submodule 4, submodule 7, submodule 8, and submodule 9 are put into operation. At this time, the DC support capacitor C of module 5 SM5 Through the energy balancing circuit to the sub-module 6 DC support capacitor C SM6 Discharge, to achieve energy transfer from submodule 5 to submodule 6, module 1 DC support capacitor C SM1 Through the energy balancing circuit to the sub-module 2 DC support capacitor C SM2 Discharge, to achieve energy transfer from submodule 1 to submodule 2. At t6, control submodule 6, submodule 7, submodule 2, submodule 3 are removed, and submodule 1, submodule 4, submodule 5, submodule 8, and submodule 9 are put into operation. At this time, the DC support capacitor C of module 6 SM6 Through the energy balancing circuit to the sub-module 7 DC support capacitor C SM7 Discharge, to achieve energy transfer from submodule 6 to submodule 7, module 2 DC support capacitor C SM2 Through the energy balancing circuit to the sub-module 3 DC support capacitor CSM3 Discharge, to achieve energy transfer from submodule 2 to submodule 3. At t7, submodule 7, submodule 8, submodule 3, and submodule 4 are removed, and submodule 1, submodule 2, submodule 5, submodule 6, and submodule 9 are put into operation. The DC support capacitor C of module 7 SM7 Through the energy balancing circuit to the sub-module 8 DC support capacitor C SM8 Discharge, realize the energy transfer from submodule 7 to submodule 8, module 3 DC support capacitor C SM3 Through the energy balancing circuit to the sub-module 4 DC support capacitor C SM4 Discharge, to achieve energy transfer from submodule 3 to submodule 4. At t8, control submodule 8, submodule 9, submodule 4, submodule 5 are removed, and submodule 1, submodule 2, submodule 3, submodule 6, and submodule 7 are put into operation. At this time, the DC support capacitor C of module 8 SM8 Through the energy balancing circuit to the sub-module 9 DC support capacitor C SM9 Discharge, realize the energy transfer from submodule 8 to submodule 9, module 4 DC support capacitor C SM4 Through the energy balancing circuit to the sub-module 5 DC support capacitor C SM5 Discharge to achieve energy transfer from submodule 4 to submodule 5. At T9, submodule 9, submodule 1, submodule 5, and submodule 6 are controlled to be removed, and submodule 2, submodule 3, submodule 4, submodule 7, and submodule 8 are put into operation. At this time, the DC support capacitor C SM5 Through the energy balancing circuit to the sub-module 6 DC support capacitor C SM6 Discharge, to achieve energy transfer from submodule 5 to submodule 6. By repeating the above process from t1 to t9, Figure 6 The energy transfer from the low voltage side to the high voltage side of the self-voltage-balanced DC / DC conversion system is shown.

[0055] It should be noted that when the conversion system is provided with other numbers of conversion units, or when there are other numbers of sub-modules in the conversion unit, the control principle is similar to the above process. The number of sub-modules put into the high-voltage DC port loop and the low-voltage DC port loop can be determined according to the actual application situation, and it is sufficient to be able to realize energy transfer between two adjacent sub-modules. No more examples are given one by one.

[0056] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A self-balanced DC / DC conversion system, characterized in that: include: A high-voltage DC port, a low-voltage DC port, a port inductor, a controller and at least one conversion unit, wherein each conversion unit includes an energy balancing circuit and a plurality of power sub-modules; When there are multiple conversion units, each of the conversion units is connected in parallel via a DC port; The port inductor is arranged at the high voltage DC port and the low voltage DC port; Each of the power sub-modules is connected in series to form a conversion unit, and two adjacent power sub-modules are connected through diodes to form the energy balancing circuit, wherein the energy balancing circuit is a diode bidirectional balancing circuit, between the positive electrodes of the DC support capacitors in the two adjacent power sub-modules, so as to realize the energy transfer of the conversion system from the low-voltage DC port to the high-voltage DC port, and the negative electrodes of the DC support capacitors are connected through diodes to realize the energy transfer from the high-voltage DC port to the low-voltage DC port, the diodes connected to the positive electrodes of the DC support capacitors are connected in series in the same direction, and the diodes connected to the negative electrodes of the DC support capacitors are connected in series in the same direction, so as to form a diode bidirectional balancing circuit; The controller is connected to the control end of the conversion unit and is used to cyclically control the input and removal states of multiple power sub-modules according to a preset rule. The power sub-modules transfer energy between the high-voltage DC port and the low-voltage DC port through the energy balancing circuit.

2. The self-voltage-balanced DC / DC conversion system according to claim 1, characterized in that: The power submodule includes: a power transfer circuit, a DC support capacitor, two main circuit terminals and two auxiliary terminals; wherein: The power transfer circuit is connected in parallel with the DC support capacitor; wherein the power transfer circuit is a full-bridge circuit or a half-bridge circuit; When the power transfer circuit is a half-bridge circuit, the neutral point of the half-bridge circuit and the positive electrode or negative electrode of the DC support capacitor serve as the main circuit terminals of the power submodule; When the power transfer circuit is a full-bridge circuit, two neutral points of the full-bridge circuit serve as main circuit terminals of the power submodule; The main circuit terminals of adjacent power submodules are connected in series; The positive electrode and the negative electrode of the DC support capacitor are connected to the auxiliary terminal of the power submodule.

3. The self-voltage-balanced DC / DC conversion system according to claim 2, characterized in that: The main circuit terminals of the power submodules are connected in series in sequence, and the positive and negative electrodes connected in series serve as two terminals of the high-voltage DC port; The series connection point between the series-connected negative electrode and any two adjacent power submodules serves as two terminals of the low-voltage DC port.

4. The self-balanced DC / DC conversion system according to claim 3, characterized in that: Terminals of the high-voltage DC port and the low-voltage DC port are respectively connected in series with port inductors.

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