Chain converter

Abstract

The invention provides a chain-type converter which comprises a first node, a second node and a plurality of switch sub-modules, the switch sub-modules are connected in series and electrically connected between the first node and the second node, and the switching time of at least one switch sub-module is longer than that of other switch sub-modules. According to the chain-type converter, the common-mode current is effectively inhibited by prolonging the switching time of the at least one switch sub-module.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to a chain converter. Background Art

[0002] The chain converter is composed of multiple sub-modules connected in series. Due to the large size of the battery in the chain energy storage system and the large distributed capacitance of the battery to the ground, a large common-mode current will be generated. The common-mode current affects EM I and increases system losses. It must be processed to ensure the normal operation of the system. At the same time, the common-mode voltage flows through the distributed capacitance between the battery and the ground, which will damage the insulation of the battery cell. In addition, standards such as VDE 4105 also have strict requirements on the common-mode current of photovoltaic systems, requiring that the ground leakage current must be below the standard when it involves personal safety, fire problems and EMI problems, that is, the photovoltaic contact leakage current is required to be below 30mA and the fire leakage current is required to be below 300mA.

[0003] At present, the commonly used DC / DC isolation topology can increase the common-mode impedance and reduce the common-mode current, but it increases the system cost and reduces the system efficiency. In addition, patent CN105610343B provides a modulation method for suppressing the leakage current of the H-bridge cascade inverter. In this method, two sub-modules are grouped and a specific modulation method is used to make the parasitic capacitor voltage and constant to achieve the effect of suppressing the common-mode current. However, although this modulation method can effectively reduce the effective value of the common-mode voltage to ground, the specific switch modulation state will affect other indicators such as ripple current, and it is impossible to eliminate the common-mode current peak caused by inconsistent switching transients. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a chain converter which can effectively reduce the common-mode current.

[0005] In order to achieve the above object, the present invention provides a chain converter, comprising:

[0006] First node;

[0007] Second node;

[0008] A plurality of switch submodules, wherein the plurality of switch submodules are connected in series and electrically connected between a first node and a second node, and a switch switching time of at least one switch submodule is greater than a switch switching time of other switch submodules.

[0009] Optionally, a switching time of at least one switch submodule is greater than twice a switching time of other switch submodules.

[0010] Optionally, the multiple switch sub-modules include multiple low-frequency sub-modules and a first high-frequency sub-module.

[0011] Optionally, a ground terminal is electrically connected to the second node, wherein a low-frequency submodule is electrically connected to the second node.

[0012] Optionally, the first high-frequency submodule is electrically connected to the first node.

[0013] Optionally, a distributed capacitance of any low-frequency submodule to ground is greater than a distributed capacitance of the first high-frequency submodule to ground.

[0014] Optionally, a ground terminal is electrically connected between two adjacent low-frequency sub-modules.

[0015] Optionally, the first high-frequency submodule is electrically connected to the first node or the second node.

[0016] Optionally, the chain converter further comprises:

[0017] The second high frequency submodule is electrically connected to the first node and the second high frequency submodule is electrically connected to the second node.

[0018] Optionally, the phase difference between the first port voltage of the first high frequency submodule and the second port voltage of the second high frequency submodule is 180°, so that the common mode currents of the first high frequency submodule and the second high frequency submodule flowing through the multiple low frequency submodules cancel each other.

[0019] Optionally, the first high-frequency submodule and the second high-frequency submodule adopt a two-level topology or a three-level topology.

[0020] Optionally, the first high-frequency submodule includes a first full-bridge circuit, the first full-bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a first switch and a second switch connected in series, and the second bridge arm includes a third switch and a fourth switch connected in series, wherein the first midpoint of the first bridge arm is a first jump point, the second midpoint of the second bridge arm is a second jump point, and there is a first port voltage between the first jump point and the second jump point;

[0021] The second high-frequency submodule includes a second full-bridge circuit, the second full-bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, the third bridge arm includes a fifth switch and a sixth switch connected in series, and the fourth bridge arm includes a seventh switch and an eighth switch connected in series, wherein the third midpoint of the third bridge arm is a third jump point, the fourth midpoint of the fourth bridge arm is a fourth jump point, and there is a second port voltage between the third jump point and the fourth jump point.

[0022] Optionally, when the first switch and the fourth switch are turned on, the first full-bridge circuit is in the first mode; when the first switch and the third switch are turned on, the first full-bridge circuit is in the second mode; when the second switch and the third switch are turned on, the first full-bridge circuit is in the third mode; when the second switch and the fourth switch are turned on, the first full-bridge circuit is in the fourth mode;

[0023] When the fifth switch and the eighth switch are turned on, the second full-bridge circuit is in the first mode; when the fifth switch and the seventh switch are turned on, the second full-bridge circuit is in the second mode; when the sixth switch and the seventh switch are turned on, the second full-bridge circuit is in the third mode; when the sixth switch and the eighth switch are turned on, the second full-bridge circuit is in the fourth mode.

[0024] Optionally, when the first full-bridge circuit switches from the fourth mode to the first mode, the potential of the first jump point becomes higher, and when the second full-bridge circuit switches from the first mode to the second mode, the potential of the fourth jump point becomes higher;

[0025] When the first full-bridge circuit switches from the first mode to the second mode, the potential of the second trip point becomes higher, and when the second full-bridge circuit switches from the fourth mode to the first mode, the potential of the third trip point becomes higher;

[0026] When the first full-bridge circuit switches from the second mode to the third mode, the potential of the first trip point becomes lower, and when the second full-bridge circuit switches from the third mode to the fourth mode, the potential of the fourth trip point becomes lower;

[0027] When the first full-bridge circuit switches from the third mode to the fourth mode, the potential of the second trip point becomes lower; when the second full-bridge circuit switches from the second mode to the third mode, the potential of the third trip point becomes lower.

[0028] Optionally, the first high-frequency submodule includes a first full-bridge circuit and a first energy storage element and a second energy storage element, the first full-bridge circuit includes a first upper bridge arm and a first lower bridge arm connected in series, the first upper bridge arm includes a first switch and a second switch connected in series with each other, and the first lower bridge arm includes a third switch and a fourth switch connected in series with each other, wherein the first midpoint between the first upper bridge arm and the first lower bridge arm is a first jump point; the first full-bridge circuit also includes a first diode and a second diode connected in series between a first node between the first switch and the second switch of the first upper bridge arm and a second node between the third switch and the fourth switch of the first lower bridge arm, and the second midpoint between the first diode and the second diode is a second jump point; both ends of the first energy storage element and the second energy storage element after the series connection are connected in parallel to the first full-bridge circuit, and the third node between the first energy storage element and the second energy storage element is connected to the second midpoint; there is a first port voltage between the first jump point and the second jump point;

[0029] The second high-frequency submodule includes a second full-bridge circuit and a third energy storage element and a fourth energy storage element. The second full-bridge circuit includes a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes a fifth switch and a sixth switch connected in series with each other. The second lower bridge arm includes a seventh switch and an eighth switch connected in series with each other, wherein a third midpoint between the second upper bridge arm and the second lower bridge arm is a third jump point. The second full-bridge circuit also includes a third diode and a fourth diode connected in series between a fourth node between the fifth switch and the sixth switch of the second upper bridge arm and a fifth node between the seventh switch and the eighth switch of the second lower bridge arm, and a fourth midpoint between the third diode and the fourth diode is a fourth jump point. Both ends of the third energy storage element and the fourth energy storage element connected in series are connected in parallel to the second full-bridge circuit, and the sixth node between the third energy storage element and the fourth energy storage element is connected to the fourth midpoint. There is a second port voltage between the third jump point and the fourth jump point.

[0030] Optionally, a switching time of at least one low-frequency submodule is greater than a switching time of other low-frequency submodules.

[0031] Optionally, the chain converter further comprises:

[0032] The power source or the load is electrically connected between the first node and the second node.

[0033] Optionally, the power supply is a DC power supply or an AC power supply, the first high-frequency submodule includes a first switch circuit and a first energy storage element connected in parallel, and the low-frequency submodule includes a second switch circuit and a second energy storage element connected in parallel.

[0034] Optionally, the first switching circuit includes a half-bridge inverter circuit or a full-bridge circuit.

[0035] Optionally, when the power supply is a DC power supply, the second switching circuit includes a half-bridge circuit or a full-bridge circuit.

[0036] Optionally, when the power source is an AC power source, the second switching circuit includes a full-bridge circuit.

[0037] The present invention further provides a three-phase chain converter, comprising:

[0038] Three-phase power supply;

[0039] High frequency submodule;

[0040] Multiple low-frequency sub-modules, wherein each phase of the three-phase chain converter includes multiple low-frequency sub-modules connected in series, the three phases of the three-phase chain converter share the same high-frequency sub-module, and the switching time of at least one low-frequency sub-module is greater than the switching time of other low-frequency sub-modules.

[0041] Optionally, the high-frequency submodule includes a two-level topology or a three-level topology.

[0042] Optionally, the low-frequency submodule includes a full-bridge circuit and an energy storage element connected in parallel.

[0043] It can be seen from the above scheme that the advantages of the present invention are:

[0044] The chain converter provided by the present invention effectively reduces the common mode current by extending the switching time of some switch submodules or reducing the frequency of the switch submodules. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A circuit topology diagram of a chain converter in the prior art;

[0046] Figure 2 is a circuit topology diagram of the chain converter of the first embodiment;

[0047] Figure 3A The simulation effect diagram when the switching time is 20ns is shown;

[0048] Figure 3B The simulation effect diagram is shown when the switching time is 200ns;

[0049] Figure 4 is a circuit topology diagram of a chain-link converter according to Embodiment 2;

[0050] Figure 5A This is the simulation effect diagram of 2.5KHZ high frequency working state;

[0051] Figure 5B This is the simulation effect diagram of 25HZ low-frequency working state;

[0052] Figure 6 is a circuit topology diagram of a chain-link converter of Embodiment 3;

[0053] Figure 7 is a circuit topology diagram of a chain-link converter according to Embodiment 4;

[0054] Figure 8 is a common-mode current path diagram of the chain converter shown in the fourth embodiment;

[0055] Fig. 9A The simulation effect diagram of the third embodiment is shown;

[0056] Fig. 9B The simulation effect diagram of the fourth embodiment is shown;

[0057] Fig.10 The circuit topology diagram of the chain converter of the fifth embodiment is shown;

[0058] Fig.11 The circuit topology diagram of the chain-link converter of the sixth embodiment is shown;

[0059] Fig. 12A This is another simulation effect diagram of the chain converter of the fourth embodiment;

[0060] Fig. 12B This is a simulation effect diagram of the chain converter of Example 6;

[0061] Fig.13 is a circuit topology diagram of a chain-link converter according to Embodiment 7;

[0062] Fig.14 is a circuit topology diagram of the chain converter shown in the eighth embodiment;

[0063] Fig.15A A first schematic common-mode current path diagram of the chain-link converter shown in the eighth embodiment;

[0064] Fig. 15B A second schematic common-mode current path diagram of the chain-link converter shown in the eighth embodiment;

[0065] Fig.16 is a circuit topology diagram of a chain-link converter according to Embodiment 9;

[0066] Fig.17 is a circuit topology diagram of a chain-link converter according to Embodiment 10;

[0067] Fig.18 is a circuit topology diagram of a chain-link converter according to the eleventh embodiment;

[0068] Fig.19 This is a circuit topology diagram of the chain-link converter of the twelfth embodiment. DETAILED DESCRIPTION

[0069] The terms "first", "second", etc. used in this application do not specifically refer to the order or sequence, nor are they used to limit the present invention. They are only used to distinguish between elements or operations described with the same technical terms. Secondly, the terms "comprise", "include", "have", "contain", etc. used in this application are all open terms, which mean including but not limited to. In addition, "coupled" or "electrically connected" used in this application may refer to two or more elements making direct physical or electrical contact, or making indirect physical or electrical contact with each other. In addition, in this application, unless the text specifically limits the articles, "one" and "the" may refer to a single or multiple.

[0070] As mentioned above, in the prior art, although the modulation method can effectively reduce the effective value of the common-mode voltage to ground, it does not involve the adjustment of the switching times and switching time, and cannot eliminate the common-mode current peak caused by the switching transient inconsistency.

[0071] Based on this, the present invention adopts solutions such as extending the switch switching time of the chain converter, lowering the frequency of the submodule or optimizing the grounding point, so as to effectively suppress the common mode current.

[0072] Figure 1 A circuit topology diagram of a conventional chain converter in the prior art is shown, which includes a power supply or load 1, a first node P1, a second node P2, and a plurality of high-frequency sub-modules HF i (i takes a value of 1....N), wherein the plurality of high-frequency sub-modules HF i are connected in series and electrically connected between the first node P1 and the second node P2.

[0073] Figure 2 The circuit topology diagram of the chain converter of the first embodiment of the present invention is shown, and the chain converter comprises a power source or load 1, a first node P1, a second node P2, and a plurality of switch submodules SM i (i is 1...N), wherein the plurality of switch submodules SM i are connected in series and electrically connected between the first node P1 and the second node P2. Figure 2 As shown, each switch submodule Smi includes a switch circuit Us i (i takes a value of 1....n) and an energy storage element connected in parallel. The switch circuit Us i may be a half-bridge circuit or a full-bridge circuit, and the energy storage element includes a capacitor or a battery. In this embodiment, the switch switching time of at least one switch submodule is greater than the switch switching time of other switch submodules. The so-called switch switching time refers to the time required for the switch to change from the "on" state to the "off" state or from the "off" state to the "on" state. Since multiple switch submodules are in a series structure, by increasing the switch switching time of at least one switch submodule, the du / dt value of the entire series branch can be reduced, thereby reducing the peak value of the common mode current.

[0074] In some embodiments, the switching time of at least one switch sub-module is greater than twice the switching time of other switch sub-modules.

[0075] In some embodiments, considering the deviation of the circuit components themselves, such as the deviation of the driving and the deviation of the circuit parameters, the switching time of at least one switch submodule is more than three times the switching time of other switch submodules.

[0076] In some embodiments, when the switch submodule is used in low-power applications, when the switch device is a MOSFET, the switch switching time is in nanoseconds; when the switch submodule is used in high-power applications, the switch switching time is in microseconds.

[0077] Figure 3A , Figure 3B , Figure 5A , Figure 5B , Fig. 9A , Fig. 9B , Fig. 12A as well as Fig. 12B These are all simulation renderings when the switching device is MOSFET.

[0078] Figure 3A and Figure 3B The simulation effect diagrams of different switch switching times of the chain converter of the first embodiment are shown respectively, wherein: Figure 3A This is the simulation effect diagram when the switch switching time is 20ns. Figure 3A The output voltage waveforms and common-mode current waveforms of four different switch submodules are shown from top to bottom; Figure 3B This is the simulation effect diagram when the switch switching time is extended to 200ns. Figure 3B From top to bottom, the output voltage waveforms and common-mode current waveforms of the corresponding four different switch submodules are shown. By comparison, it can be found that when the switch switching time increases from 20ns to 200ns, the common-mode current peak value decreases from 18A to 2A. Therefore, extending the switch switching time of some switch submodules effectively reduces the common-mode current peak value.

[0079] Since traditional chain converters are all high-frequency submodules, their batteries are bulky, and the distributed capacitance of the batteries to the ground is large, which will generate large common-mode currents. Therefore, it is necessary to reduce the frequency of the switch submodules of traditional chain converters. Figure 4 As shown, Figure 4 The circuit topology diagram of the chain converter of the second embodiment is shown. In this embodiment, the multiple switch submodules are set as multiple low-frequency submodules LFSM i and a high-frequency submodule HFSM1, and the high-frequency submodule compensates the voltage difference between the bus and the low-frequency submodule, wherein the frequency of the high-frequency submodule is greater than twice the frequency of the low-frequency submodule. Generally speaking, since the number of common-mode voltage jumps of the low-frequency submodule to the ground is much lower than the number of common-mode voltage jumps of the high-frequency submodule to the ground, after the chain converter is low-frequencyed, the number of common-mode voltage jumps of the entire series branch of the mixed high- and low-frequency submodules to the ground is greatly reduced, which effectively reduces the common-mode current.

[0080] Since the frequency of the low-frequency sub-module is very low and the switching loss ratio is also very low, the conditions for increasing the switching time are met. Therefore, configuring the switching time of the low-frequency sub-module to be greater than the switching time of the high-frequency sub-module can also effectively reduce the peak value of the common-mode current.

[0081] Please refer to Figure 4 The power supply includes an AC power supply or a DC power supply, the high-frequency submodule includes a first switch circuit UH1 and a first energy storage element connected in parallel, and the low-frequency submodule includes a second switch circuit UL i (i takes a value of 1....n) and a second energy storage element connected in parallel.

[0082] In some embodiments, when the power source is an AC power source or a DC power source, the first switch circuit UH1 includes a half-bridge inverter circuit or a full-bridge circuit, and the first energy storage element includes a capacitor.

[0083] In some embodiments, when the power source is a DC power source, the second switch circuit UL i includes a half-bridge circuit or a full-bridge circuit, and the second energy storage element includes a capacitor or a battery.

[0084] In some embodiments, when the power source is an AC power source, the second switch circuit UL i includes a full-bridge circuit, and the second energy storage element includes a capacitor or a battery.

[0085] Figure 5A and Figure 5B The simulation effect diagrams of the chain converter of the first embodiment in the high frequency or low frequency working state are shown respectively. Figure 5A This is a simulation effect diagram of the chain converter of Example 1 in a 2.5KHZ high frequency working state. Figure 5A The output voltage waveforms and common-mode current waveforms of four different sub-modules are displayed from top to bottom; Figure 5B This is a simulation effect diagram of the chain converter of Example 1 in a 25HZ low-frequency working state. Figure 5B From top to bottom are the output voltage waveforms and common-mode current waveforms of the four different sub-modules. Figure 2 It can be seen that for the same chain converter, when it is in high-frequency working mode, the instantaneous value of the common-mode current of the submodule to the ground is larger; when it is in low-frequency working mode, the instantaneous value of the common-mode current of the submodule to the ground is greatly reduced. Therefore, setting multiple submodules as low-frequency submodules can realize the low-frequency of the chain converter and effectively reduce the common-mode current.

[0086] Figure 6 The circuit topology diagram of the chain converter of the third embodiment is shown. In this embodiment, a low-frequency submodule is placed at the second node P2, and the second node P2 is grounded through the impedance Z, and the high-frequency submodule is electrically connected to any low-frequency submodule, that is, the high-frequency submodule is placed at a non-grounded node. If the placement position of the high-frequency submodule is not selected, the rapid voltage jump of the high-frequency submodule will affect a large number of low-frequency submodules. On the contrary, if the high-frequency submodule is placed far away from the ground node, the number of low-frequency submodules affected by it will be reduced, and the farther away from the ground node, the fewer the number of low-frequency submodules affected by the high-frequency submodule, and the better the suppression effect on the common-mode current.

[0087] In some embodiments, the switching time of at least one low-frequency sub-module is greater than the switching time of other low-frequency sub-modules, that is, the switching time of some low-frequency sub-modules can be extended to suppress the common-mode current, wherein extending the switching time of the low-frequency sub-module at the ground node has the best effect on suppressing the common-mode current.

[0088] Figure 7 The circuit topology diagram of the chain converter of the fourth embodiment is shown. Figure 7 As shown, the high-frequency submodule is placed at the first node P1. At this time, the common-mode voltage jump of the high-frequency submodule will not affect the low-frequency submodule. In addition, since the volume of the high-frequency submodule is much smaller than that of the battery, after the distance from the ground node is increased, the distributed capacitance of the high-frequency submodule can be further reduced. If the distributed capacitance of the high-frequency submodule to the ground is small enough, it can be considered to be approximately disconnected, and the common-mode current generated by the high-frequency submodule to the ground has approximately no effect, so the common-mode current can be better suppressed.

[0089] In some embodiments, the distributed capacitance of any low-frequency submodule to ground is greater than the distributed capacitance of the high-frequency submodule to ground.

[0090] Figure 8 The common-mode current path diagram of the chain converter of the fourth embodiment is shown. Assuming that the distributed capacitance of the high-frequency submodule to the ground is small enough to be ignored, the common-mode current flows into the ground point through each low-frequency submodule. Therefore, the high-frequency submodule is set at a position far away from the ground node to minimize the influence of the high-frequency submodule on the low-frequency submodule, thereby effectively suppressing the common-mode current.

[0091] See also Fig. 9A and Fig. 9B ,in, Fig. 9A The simulation effect diagram of the chain converter shown in the third embodiment is shown. Fig. 9A From top to bottom are the positive-to-ground voltage waveforms and common-mode current instantaneous value waveforms of four different submodules. Fig. 9B The simulation effect diagram of the chain converter shown in the fourth embodiment is shown. Fig. 9B From top to bottom, the waveforms of the positive-to-ground voltage and the instantaneous value of the common-mode current of four different submodules are shown. Fig. 9A and Fig. 9B It can be seen that when the high-frequency submodule is placed at the first node P1, the common-mode current is greatly reduced and the suppression effect is obvious.

[0092] Fig.10 The circuit topology diagram of the chain converter of the fifth embodiment is shown. In this embodiment, the ground terminal is placed between two low-frequency submodules, and the high-frequency submodule is electrically connected to any low-frequency submodule. In other embodiments, the high-frequency submodule is placed at the first node P1 or the second node P2.

[0093] In this embodiment, the ground terminal is set between two low-frequency sub-modules. The ground terminal can be placed at the midpoint of the low-frequency sub-module or at other positions except the midpoint of the low-frequency sub-module. The so-called midpoint of the low-frequency sub-module refers to the point where the number of low-frequency sub-modules above and below the point is equal. By placing the ground terminal between the two low-frequency sub-modules, this embodiment can achieve decoupling between the voltage jumps of the low-frequency sub-modules above and below the ground terminal, effectively reducing the common-mode current. At the same time, when the ground terminal is located at or close to the midpoint of the low-frequency sub-module, the insulation voltage is lower and the common-mode current suppression effect is better. In other words, the closer the ground terminal is to the midpoint of the low-frequency sub-module, the better the suppression effect on the common-mode current.

[0094] Fig.11 The circuit topology diagram of the chain converter of the sixth embodiment is shown as follows: Fig.11 As shown, the series branch has a total of N+1 sub-modules, including N low-frequency sub-modules and one high-frequency sub-module. When N is an even number, when the grounding terminal is located at the midpoint P0 of the low-frequency sub-module, the maximum number of sub-modules affected by the common-mode voltage jump of the low-frequency sub-module at the grounding node is N / 2, which further reduces the common-mode current peak and is also beneficial to the insulation design of the system.

[0095] Fig. 12A and Fig. 12B The simulation results of different grounding points are shown respectively. Fig. 12A is another simulation effect diagram of the chain converter of the fourth embodiment, Fig. 12A The waveforms of the positive-to-ground voltage and the instantaneous value of the common-mode current of different submodules in four embodiments are shown from top to bottom; Fig. 12B This is a simulation effect diagram of the chain converter of Example 6. Fig. 12B From top to bottom, the voltage waveforms to ground and the instantaneous value waveforms of common-mode current of four different submodules are shown. By comparison, it can be found that when the ground terminal is located at the midpoint of the low-frequency submodule, the common-mode current peak value is reduced from 2.2A to 1.8A due to the reduction in the number of submodules that jump at the same time, which effectively suppresses the common-mode current.

[0096] Fig.13 The circuit topology diagram of the chain converter of the seventh embodiment is shown. In this embodiment, the chain converter includes a plurality of high-frequency submodules, for example, two high-frequency submodules, namely, a first high-frequency submodule HFSM1 and a second high-frequency submodule HFSM2, wherein the first high-frequency submodule HFSM1 is electrically connected to the first node P1, and the second high-frequency submodule HFSM2 is electrically connected to the second node P2. In this embodiment, the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 are redundantly arranged, and in the case of a high-frequency submodule failure, another high-frequency submodule can be substituted, and at the same time, the common-mode current can be effectively reduced.

[0097] Fig.14 The circuit structure diagram of the chain converter of the eighth embodiment is shown. Figures 15A to 15B Several schematic common-mode current path diagrams of the chain-link converter of the eighth embodiment are shown respectively.

[0098] In this embodiment, when the common-mode current of the high-frequency sub-module cannot be ignored, two high-frequency sub-modules can be set in the chain converter, and the common-mode currents of the two high-frequency sub-modules offset each other, thereby eliminating the influence of the common-mode current of the high-frequency sub-module on the common-mode current path of the low-frequency sub-module.

[0099] In this embodiment, the chain-link converter includes a first high frequency submodule HFSM1, a second high frequency submodule HFSM2 and a plurality of low frequency submodules LFSM i (i is 1...n). Figures 15A to 15B When considering the influence of the common-mode current of the high-frequency sub-module, all low-frequency sub-modules are equivalent to a capacitor C L总 , that is, C L总 is the total parasitic capacitance of all low-frequency submodules to ground. In addition, C H1 is the parasitic capacitance of the first high frequency submodule HFSM1 to ground, C H2 is the parasitic capacitance of the second high frequency submodule HFSM2 to ground. V A1B1 is the port voltage of the first high-frequency submodule HFSM1, V A2B2 is the port voltage of the second high-frequency submodule HFSM2.

[0100] In this embodiment, the switching of each switch in the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 can be controlled so that the working modes of the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 differ by 180°, that is, the port voltage V A1B1 The port voltage V A2B2 The phase difference is 180°. Since the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 have the same structure, the common-mode currents of the two high-frequency submodules flowing through the low-frequency submodule cancel each other out at this time, thereby eliminating the influence of the common-mode current of the high-frequency submodule on the common-mode current path of the low-frequency submodule. And it can be understood that in the present invention, in a two-level topology circuit or a three-level topology circuit, the cancellation of common-mode current can be achieved in this way.

[0101] More specifically, Fig.15A The first schematic common-mode current path diagram of the chain-link converter shown in the eighth embodiment is shown. Fig.15AIt can be seen that in this exemplary embodiment, the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 can be respectively set at the first node P1 and the second node P2, and can be controlled by adopting a two-level topology. The first high-frequency submodule HFSM1 can include a first full-bridge circuit UH1 and a first energy storage element C electrically connected to each other. f1 The first full-bridge circuit UH1 may include a first bridge arm and a second bridge arm, the first bridge arm may include a first switch S1 and a second switch S2 connected in series, the second bridge arm may include a third switch S3 and a fourth switch S4 connected in series, wherein the first midpoint A1 of the first bridge arm is a first jump point, and the second midpoint B1 of the second bridge arm is a second jump point. The second high-frequency submodule HFSM2 may include a second full-bridge circuit UH2 and a second energy storage element C electrically connected to each other. f2 , the second full-bridge circuit UH2 may include a third bridge arm and a fourth bridge arm, the third bridge arm may include a fifth switch S5 and a sixth switch S6 connected in series, the fourth bridge arm may include a seventh switch S7 and an eighth switch S8 connected in series, wherein the third midpoint A2 of the third bridge arm is the third jump point, and the fourth midpoint B2 of the fourth bridge arm is the fourth jump point. Fig.15A As shown in the figure, the common mode current path is taken as an example, in which each switch in the first high frequency submodule HFSM1 can be controlled to make its port voltage V A1B1 With a first phase, the common mode current of the first high frequency submodule HFSM1 to the ground is, for example, a total parasitic capacitance C of the plurality of low frequency submodules. L总 Outflow (For specific current flow direction, see Fig.15A At this time, the switches in the second high-frequency submodule HFSM2 can be controlled to make its port voltage V A2B2 The second phase is 180° different from the first phase. At this time, the common mode current of the second high frequency submodule HFSM2 to the ground flows into (the specific current flow direction can be seen in Fig.15A The total parasitic capacitance C of the plurality of low-frequency sub-modules is shown by the arrows around the second high-frequency sub-module HFSM2. L总 Since the first high-frequency submodule HFSM1 is identical to the second high-frequency submodule HFSM2 and the port voltage V A1B1 The port voltage V A2B2 The phase difference is 180°, so at this time the common-mode currents of the two high-frequency sub-modules flowing through the low-frequency sub-module can cancel each other, thereby eliminating the influence of the common-mode current of the high-frequency sub-module on the common-mode current path of the low-frequency sub-module.

[0102] exist Fig.15AIn the embodiment shown, the working modes of the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 can be changed by controlling the switching of each switch in the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2, that is, by changing the potential of the jump point, the common-mode currents of the two high-frequency submodules flowing through the low-frequency submodule can be offset. For the convenience of description, the following definitions are made:

[0103] When the first switch S1 is turned on, the second switch S2 is turned off, the third switch S3 is turned off, and the fourth switch S4 is turned on, the first full-bridge circuit UH1 is in the first mode; when the first switch S1 is turned on, the second switch S2 is turned off, the third switch S3 is turned on, and the fourth switch S4 is turned off, the first full-bridge circuit UH1 is in the second mode; when the first switch S1 is turned off, the second switch S2 is turned on, the third switch S3 is turned on, and the fourth switch S4 is turned off, the first full-bridge circuit UH1 is in the third mode; when the first switch S1 is turned off, the second switch S2 is turned on, the third switch S3 is turned off, and the fourth switch S4 is turned on, the first full-bridge circuit UH1 is in the fourth mode.

[0104] When the first full-bridge circuit UH1 switches from the fourth mode to the first mode, the potential of the first jump point A1 becomes higher; when the first full-bridge circuit UH1 switches from the first mode to the second mode, the potential of the second jump point B1 becomes higher; when the first full-bridge circuit UH1 switches from the second mode to the third mode, the potential of the first jump point A1 becomes lower; when the first full-bridge circuit UH1 switches from the third mode to the fourth mode, the potential of the second jump point B1 becomes lower.

[0105] The second high frequency submodule HFSM2 comprises a second full bridge circuit UH2 and a second energy storage element C which are electrically connected to each other. f2 , the second full-bridge circuit UH2 includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a fifth switch S5 and a sixth switch S6 connected in series, the fourth bridge arm includes a seventh switch S7 and an eighth switch S8 connected in series, wherein the third midpoint A2 of the third bridge arm is the third jump point, and the fourth midpoint B2 of the fourth bridge arm is the fourth jump point. For the convenience of description, the following definitions are made:

[0106] When the fifth switch S5 is turned on, the sixth switch S6 is turned off, the seventh switch S7 is turned off, and the eighth switch S8 is turned on, the second full-bridge circuit UH2 is in the first mode; when the fifth switch S5 is turned on, the sixth switch S6 is turned off, the seventh switch S7 is turned on, and the eighth switch S8 is turned off, the second full-bridge circuit UH2 is in the second mode; when the fifth switch S5 is turned off, the sixth switch S6 is turned on, the seventh switch S7 is turned on, and the eighth switch S8 is turned off, the second full-bridge circuit UH2 is in the third mode; when the fifth switch S5 is turned off, the sixth switch S6 is turned on, the seventh switch S7 is turned off, and the eighth switch S8 is turned on, the second full-bridge circuit UH2 is in the fourth mode.

[0107] When the second full-bridge circuit UH2 switches from the fourth mode to the first mode, the potential of the third jump point A2 becomes higher; when the second full-bridge circuit UH2 switches from the first mode to the second mode, the potential of the fourth jump point B2 becomes higher; when the second full-bridge circuit UH2 switches from the second mode to the third mode, the potential of the third jump point A2 becomes lower; when the second full-bridge circuit UH2 switches from the third mode to the fourth mode, the potential of the fourth jump point B2 becomes lower.

[0108] In order to make the common mode currents of the first high frequency submodule HFSM1 and the second high frequency submodule HFSM2 flowing through the common mode current path of the low frequency submodule cancel each other, the following control method may be adopted:

[0109] When the first full-bridge circuit UH1 switches from the fourth mode to the first mode, the potential of the first jump point A1 becomes higher. At this time, the second full-bridge circuit UH2 switches from the first mode to the second mode, so that the potential of the fourth jump point B2 becomes higher.

[0110] When the first full-bridge circuit UH1 switches from the first mode to the second mode, the potential of the second jump point B1 becomes higher. At this time, the second full-bridge circuit UH2 switches from the fourth mode to the first mode, and the potential of the third jump point A2 becomes higher.

[0111] When the first full-bridge circuit UH1 switches from the second mode to the third mode, the potential of the first jump point A1 becomes low. At this time, the second full-bridge circuit UH2 switches from the third mode to the fourth mode, and the potential of the fourth jump point B2 becomes low.

[0112] When the first full-bridge circuit UH1 switches from the third mode to the fourth mode, the potential of the second jump point B1 becomes lower. At this time, the second full-bridge circuit UH2 switches from the second mode to the third mode, and the potential of the third jump point A2 becomes lower.

[0113] Depend on Fig.15A It can be seen that the first high frequency submodule HFSM1 and the second high frequency submodule HFSM2 are respectively arranged at the first node P1 and the second node P2. When the potential of the first jump point A1 becomes high, the common mode current of the first high frequency submodule HFSM1 to the ground is from the total parasitic capacitance C L总 At this time, the potential of the fourth jump point B2 of the second high-frequency submodule HFSM2 is controlled to become high, and the common-mode current of the second high-frequency submodule HFSM2 to the ground flows into the total parasitic capacitance C of the multiple low-frequency submodules. L总 Since the first high frequency submodule HFSM1 is the same as the second high frequency submodule HFSM2, the common mode currents of the two high frequency submodules flowing through the low frequency submodule cancel each other out, thereby eliminating the influence of the common mode current of the high frequency submodule on the common mode current path of the low frequency submodule.

[0114] Fig. 15B A second schematic common-mode current path diagram of the chain-link converter shown in the eighth embodiment is shown. Fig. 15B It can be seen that in this exemplary embodiment, the structures of the first high frequency submodule HFSM1 and the second high frequency submodule HFSM2 are similar to those of Fig.15A The embodiment shown is different in that: the first high frequency submodule HFSM1 may include a first full bridge circuit UH1 and a first energy storage element Cf1 and a second energy storage element Cf2, the first full bridge circuit UH1 may include an upper bridge arm and a lower bridge arm connected in series, the upper bridge arm may include a first switch S1 and a second switch S2 connected in series, the lower bridge arm may include a third switch S3 and a fourth switch S4 connected in series, wherein the first midpoint A1 between the upper bridge arm and the lower bridge arm is the first jump point. The first full bridge circuit UH1 also includes a first diode D1 and a second diode D2 connected in series between a first node between the first switch S1 and the second switch S2 of the upper bridge arm and a second node between the third switch S3 and the fourth switch S4 of the lower bridge arm, and a second midpoint B1 between the first diode D1 and the second diode D2 is the second jump point. The two ends of the first energy storage element Cf1 and the second energy storage element Cf2 connected in series are connected in parallel with the first full-bridge circuit UH1, and the third node between the first energy storage element Cf1 and the second energy storage element Cf2 is connected to the second midpoint B1. The second high-frequency submodule HFSM2 may include a second full-bridge circuit UH2, a third energy storage element Cf3, and a fourth energy storage element Cf4. The second full-bridge circuit UH2 may include an upper bridge arm and a lower bridge arm connected in series. The upper bridge arm may include a fifth switch S5 and a sixth switch S6 connected in series, and the lower bridge arm may include a seventh switch S7 and an eighth switch S8 connected in series, wherein the third midpoint A2 between the upper bridge arm and the lower bridge arm is the third jump point. The second full-bridge circuit UH2 also includes a third diode D3 and a fourth diode D4 between the fourth node connected in series between the fifth switch S5 and the sixth switch S6 of the upper bridge arm and the fifth node between the seventh switch S7 and the eighth switch S8 of the lower bridge arm, and the fourth midpoint B2 between the third diode D3 and the fourth diode D4 is the fourth jump point. The two ends of the third energy storage element Cf3 and the fourth energy storage element Cf4 connected in series are connected in parallel to the second full-bridge circuit UH2, and the sixth node between the third energy storage element Cf3 and the fourth energy storage element Cf4 is connected to the fourth midpoint B2. In this exemplary embodiment, the first high-frequency submodule HFSM1 and the second high-frequency submodule HFSM2 can be controlled using a three-level topology, that is, by controlling each switch in the first high-frequency submodule HFSM1 so that its port voltage VA1 B1 has a first phase, at which time the common-mode current of the first high-frequency submodule HFSM1 to the ground, for example, flows out from the total parasitic capacitance CL of the plurality of low-frequency submodules (for specific current flow direction, see Fig. 15BAt this time, the switches in the second high-frequency submodule HFSM2 can be controlled so that its port voltage VA2B2 has a second phase, and the second phase is 180° different from the first phase. At this time, the common-mode current of the second high-frequency submodule HFSM2 to the ground flows into (the specific current flow direction can be seen in Fig. 15B The total parasitic capacitance CL of the plurality of low-frequency submodules is shown in the arrow flow direction around the second high-frequency submodule HFSM2. Since the first high-frequency submodule HFSM1 is the same as the second high-frequency submodule HFSM2 and the phase difference between the port voltage VA1B1 of the first high-frequency submodule HFSM1 and the port voltage VA2B2 of the second high-frequency submodule HFSM2 is 180°, the common-mode currents of the two high-frequency submodules flowing through the low-frequency submodule can cancel each other, thereby eliminating the influence of the common-mode current of the high-frequency submodule on the common-mode current path of the low-frequency submodule.

[0115] Fig.16 The circuit topology diagram of the chain converter of the ninth embodiment is shown. In this embodiment, the power source is an AC power source, the high frequency submodule HFSM1 includes a full bridge circuit and a capacitor connected in parallel, and the low frequency submodule includes a full bridge circuit and a battery connected in parallel.

[0116] Fig.17 The circuit topology diagram of the chain converter of the tenth embodiment is shown. In this embodiment, the power supply is an AC power supply, and the high-frequency submodule HFSM1 includes a half-bridge inverter circuit, wherein the half-bridge inverter circuit includes a switch bridge arm and a capacitor bridge arm connected in parallel, the switch bridge arm includes two switches connected in series, and the capacitor bridge arm includes two capacitors connected in series. The low-frequency submodule includes a full-bridge circuit and a battery connected in parallel.

[0117] Fig.18 The circuit topology diagram of the chain converter of the eleventh embodiment is shown. In this embodiment, the power supply is a three-phase AC power supply, each phase of the three-phase chain converter includes a plurality of low-frequency submodules connected in series, each low-frequency submodule includes a full-bridge circuit and an energy storage element, and the high-frequency submodule HFSM1 includes a two-level topology. The switching time of at least one low-frequency submodule is greater than the switching time of other low-frequency submodules.

[0118] In some embodiments, the energy storage element may be a battery. The high frequency submodule includes three switch bridge arms connected in parallel and a capacitor bridge arm, each switch bridge arm includes two switches connected in series, and the capacitor bridge arm includes two capacitors connected in series.

[0119] Fig.19The circuit topology diagram of the chain converter of the twelfth embodiment is shown. In this embodiment, the power supply is a three-phase AC power supply, each phase of the three-phase chain converter includes a plurality of low-frequency submodules connected in series, each low-frequency submodule includes a full-bridge circuit and an energy storage element, and the high-frequency submodule HFSM1 includes a three-level topology. The switching time of at least one low-frequency submodule is greater than the switching time of other low-frequency submodules.

[0120] In some embodiments, the energy storage element may be a battery, and the high frequency submodule HFSM1 includes a mid-point clamped three-level topology.

[0121] In addition, in a specific implementation, the chain converter provided by the above-mentioned embodiments of the present invention can be applied to a high-voltage direct-hung AC chain energy storage system. In a high-voltage direct-hung AC chain energy storage system, the distributed capacitance to the ground of the long cable between the battery cabinet and the converter will increase the common-mode current, and the distributed capacitance to the ground of the bulky battery will also increase the common-mode current. Therefore, by extending the switching time of the chain converter of the present invention, lowering the frequency of the submodules, and optimizing the grounding, the common-mode current problem of the high-voltage direct-hung AC chain energy storage system can be effectively solved.

[0122] In addition, the chain converters of the above embodiments of the present invention can also be applied to MMC flexible DC systems. Since the MMC system is a series architecture, the voltage jump of the submodule near the ground potential point has the greatest impact on the common mode current. By extending the switching time of some submodules near the ground potential point, the common mode current can be greatly reduced.

[0123] It should be noted that, in this article, the terms "comprise", "include" 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, an element defined by the sentence "comprises one..." does not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the method and device in the embodiment of the present invention is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be applied, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0124] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A chain converter, characterized in that: include: First node; Second node; A plurality of switch submodules, wherein the plurality of switch submodules are connected in series and electrically connected between the first node and the second node, and a switch switching time of at least one of the switch submodules is greater than the switch switching time of other switch submodules.

2. The chain-link converter according to claim 1, characterized in that: The switching time of at least one of the switch submodules is greater than twice the switching time of the other switch submodules.

3. The chain-link converter according to claim 1, characterized in that: The plurality of switch sub-modules include a plurality of low-frequency sub-modules and a first high-frequency sub-module.

4. The chain-link converter according to claim 3, characterized in that: A ground terminal is electrically connected to the second node, wherein one of the low-frequency submodules is electrically connected to the second node.

5. The chain-link converter according to claim 4, characterized in that: The first high-frequency submodule is electrically connected to the first node.

6. The chain-link converter according to claim 3, characterized in that: A distributed capacitance of any of the low-frequency submodules to the ground is greater than a distributed capacitance of the first high-frequency submodule to the ground.

7. The chain-link converter according to claim 3, characterized in that: A ground terminal is electrically connected between two adjacent low-frequency sub-modules.

8. The chain-link converter according to claim 7, characterized in that: The first high-frequency submodule is electrically connected to the first node or the second node.

9. The chain-link converter according to claim 3, characterized in that: Also includes: The second high-frequency submodule is electrically connected to the first node and the second high-frequency submodule is electrically connected to the second node.

10. The chain-link converter according to claim 9, characterized in that: The phase difference between the first port voltage of the first high frequency submodule and the second port voltage of the second high frequency submodule is 180°, so that the common mode currents of the first high frequency submodule and the second high frequency submodule flowing through the multiple low frequency submodules cancel each other.

11. The chain-link converter according to claim 10, characterized in that: The first high-frequency submodule and the second high-frequency submodule adopt a two-level topology or a three-level topology.

12. The chain-link converter according to claim 10, characterized in that: The first high-frequency submodule includes a first full-bridge circuit, the first full-bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a first switch and a second switch connected in series, the second bridge arm includes a third switch and a fourth switch connected in series, wherein a first midpoint of the first bridge arm is a first jump point, a second midpoint of the second bridge arm is a second jump point, and the first port voltage exists between the first jump point and the second jump point; The second high-frequency submodule includes a second full-bridge circuit, the second full-bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, the third bridge arm includes a fifth switch and a sixth switch connected in series, and the fourth bridge arm includes a seventh switch and an eighth switch connected in series, wherein the third midpoint of the third bridge arm is a third jump point, the fourth midpoint of the fourth bridge arm is a fourth jump point, and the second port voltage exists between the third jump point and the fourth jump point.

13. The chain-link converter according to claim 12, characterized in that: When the first switch and the fourth switch are turned on, the first full-bridge circuit is in a first mode; when the first switch and the third switch are turned on, the first full-bridge circuit is in a second mode; when the second switch and the third switch are turned on, the first full-bridge circuit is in a third mode; when the second switch and the fourth switch are turned on, the first full-bridge circuit is in a fourth mode; When the fifth switch and the eighth switch are turned on, the second full-bridge circuit is in the first mode; when the fifth switch and the seventh switch are turned on, the second full-bridge circuit is in the second mode; when the sixth switch and the seventh switch are turned on, the second full-bridge circuit is in the third mode; when the sixth switch and the eighth switch are turned on, the second full-bridge circuit is in the fourth mode.

14. The chain-link converter according to claim 13, characterized in that: When the first full-bridge circuit switches from the fourth mode to the first mode, the potential of the first trip point becomes higher, and when the second full-bridge circuit switches from the first mode to the second mode, the potential of the fourth trip point becomes higher; When the first full-bridge circuit switches from the first mode to the second mode, the potential of the second trip point becomes higher, and when the second full-bridge circuit switches from the fourth mode to the first mode, the potential of the third trip point becomes higher; When the first full-bridge circuit switches from the second mode to the third mode, the potential of the first trip point becomes lower, and when the second full-bridge circuit switches from the third mode to the fourth mode, the potential of the fourth trip point becomes lower; When the first full-bridge circuit switches from the third mode to the fourth mode, the potential of the second trip point becomes lower, and when the second full-bridge circuit switches from the second mode to the third mode, the potential of the third trip point becomes lower.

15. The chain-link converter according to claim 10, characterized in that: The first high-frequency submodule includes a first full-bridge circuit and a first energy storage element and a second energy storage element. The first full-bridge circuit includes a first upper bridge arm and a first lower bridge arm connected in series. The first upper bridge arm includes a first switch and a second switch connected in series with each other. The first lower bridge arm includes a third switch and a fourth switch connected in series with each other, wherein the first midpoint between the first upper bridge arm and the first lower bridge arm is a first jump point; the first full-bridge circuit also includes a first diode and a second diode connected in series between a first node between the first switch and the second switch of the first upper bridge arm and a second node between the third switch and the fourth switch of the first lower bridge arm, and the second midpoint between the first diode and the second diode is a second jump point; the two ends of the first energy storage element and the second energy storage element connected in series are connected in parallel with the first full-bridge circuit, and the third node between the first energy storage element and the second energy storage element is connected to the second midpoint; there is the first port voltage between the first jump point and the second jump point; The second high-frequency submodule includes a second full-bridge circuit and a third energy storage element and a fourth energy storage element. The second full-bridge circuit includes a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes a fifth switch and a sixth switch connected in series with each other. The second lower bridge arm includes a seventh switch and an eighth switch connected in series with each other, wherein the third midpoint between the second upper bridge arm and the second lower bridge arm is a third jump point. The second full-bridge circuit also includes a third diode and a fourth diode connected in series between a fourth node between the fifth switch and the sixth switch of the second upper bridge arm and a fifth node between the seventh switch and the eighth switch of the second lower bridge arm, and the fourth midpoint between the third diode and the fourth diode is a fourth jump point. Both ends of the third energy storage element and the fourth energy storage element connected in series are connected in parallel to the second full-bridge circuit, and the sixth node between the third energy storage element and the fourth energy storage element is connected to the fourth midpoint. There is a second port voltage between the third jump point and the fourth jump point.

16. The chain-link converter according to claim 3, characterized in that: The switch switching time of at least one of the low-frequency sub-modules is greater than the switch switching time of the other low-frequency sub-modules.

17. The chain-link converter according to claim 3, characterized in that: The chain converter further comprises: A power source or a load is electrically connected between the first node and the second node.

18. The chain-link converter according to claim 17, characterized in that: The power supply is a DC power supply or an AC power supply, the first high-frequency submodule includes a first switch circuit and a first energy storage element connected in parallel, and the low-frequency submodule includes a second switch circuit and a second energy storage element connected in parallel.

19. The chain-link converter according to claim 18, characterized in that: The first switching circuit includes a half-bridge inverter circuit or a full-bridge circuit.

20. The chain-link converter according to claim 18, characterized in that When the power source is the DC power source, the second switch circuit includes a half-bridge circuit or a full-bridge circuit.

21. The chain-link converter according to claim 18, characterized in that When the power source is the AC power source, the second switch circuit includes a full-bridge circuit.

22. A three-phase chain converter, characterized in that: Include: Three-phase power supply; High frequency submodule; Multiple low-frequency sub-modules, wherein each phase of the three-phase chain converter includes multiple low-frequency sub-modules connected in series, the three phases of the three-phase chain converter share the same high-frequency sub-module, and the switching time of at least one low-frequency sub-module is greater than the switching time of other low-frequency sub-modules.

23. The three-phase chain-link converter according to claim 22, characterized in that: The high-frequency submodule includes a two-level topology or a three-level topology.

24. The three-phase chain-link converter according to claim 22, characterized in that: The low-frequency submodule includes a full-bridge circuit and an energy storage element connected in parallel.

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