Three-level dc / dc converter and control system

Abstract

The utility model relates to a kind of three-level DC / DC converter and control system, three-level DC / DC converter includes input positive pole, input negative pole, output positive pole, output negative pole, output middle, control end, input positive pole is electrically connected with output positive pole, input negative pole is electrically connected with output negative pole, there is first switch tube and second switch tube in series between input positive pole and input negative pole, control end is electrically connected with first switch tube, second switch tube, there is first capacitor and second capacitor in series between output positive pole and output negative pole, output middle is electrically connected the midpoint of first capacitor and second capacitor, the midpoint of first switch tube and second switch tube in turn.The utility model uses three-level DC / DC topology to replace conventional balance circuit, so that the integration of system whole is higher, both can realize the power conversion of DC / DC, also can realize midpoint voltage balance by the wave mode of DC / DC, even in single-phase half-wave load condition also can work normally.

Description

Technical Field

[0001] This utility model relates to the field of power grid technology, and in particular to a three-level DC / DC converter and control system. Background Technology

[0002] Currently, the DC / DC converters on both the photovoltaic and battery sides of three-phase photovoltaic-storage inverters employ a two-level topology, using 1200V IGBTs or 1200V silicon carbide MOSFETs as switching transistors. Furthermore, a balancing circuit is added to the bus to handle unbalanced loads. Because three-phase photovoltaic-storage inverters all have off-grid load capability, and customers' off-grid loads are diverse—some are directly connected to single-phase loads, causing significant fluctuations in the positive and negative voltages of the bus; others are single-phase half-wave loads, leading to voltage offsets on the bus and affecting the normal operation of the system—it's quite difficult to optimize the inverter's performance solely through software control, as both single-phase and half-wave loads require 100% long-term load capacity.

[0003] To accommodate most customer application scenarios, the current solution for three-phase photovoltaic-storage inverters is to add a balancing circuit to the bus to ensure the balance of positive and negative voltages. However, adding an extra balancing circuit to suppress the deviation of positive and negative voltages on the bus results in poor overall integration. Furthermore, in pursuit of high frequency, the switching transistors of the photovoltaic-side DC / DC converter need to use silicon carbide MOSFETs. However, the voltage drop of the body diode of a silicon carbide MOSFET is 3 to 5 times that of a regular diode. If the customer reverses the positive and negative terminals on the photovoltaic side, the silicon carbide MOSFET may burn out in a short time, affecting its use.

[0004] Therefore, there is a need for a three-level DC / DC converter and control system that does not require an external balancing circuit, achieves high system integration, and enables midpoint voltage balancing. Utility Model Content

[0005] In order to overcome the shortcomings of the prior art, this utility model provides a three-level DC / DC converter and control system.

[0006] The technical solution of this utility model is as follows: A three-level DC / DC converter includes an input positive terminal Vi+, an input negative terminal Vi-, an output positive terminal Vo+, an output negative terminal Vo-, an output neutral terminal VoN, and a control terminal. The input positive terminal Vi+ is electrically connected to the output positive terminal Vo+, and the input negative terminal Vi- is electrically connected to the output negative terminal Vo-. A first switch Q1 and a second switch Q2 are connected in series between the input positive terminal Vi+ and the input negative terminal Vi-. The control terminal is electrically connected to both the first switch Q1 and the second switch Q2. A first capacitor C1 and a second capacitor C2 are connected in series between the output positive terminal Vo+ and the output negative terminal Vo-. The output neutral terminal VoN is sequentially connected to the midpoint between the first capacitor C1 and the second capacitor C2, and the midpoint between the first switch Q1 and the second switch Q2.

[0007] As a further improvement of this utility model, the positive input Vi+ and / or the negative input Vi- are provided with a voltage-regulating inductor.

[0008] As a further improvement of this utility model, the first switching transistor Q1 has a first body diode D1, the second switching transistor Q2 has a second body diode D2, the anode of the first body diode D1 is electrically connected to the cathode of the second body diode D2, the cathode of the first body diode D1 is electrically connected to the input positive terminal Vi+, and the anode of the second body diode D2 is electrically connected to the input negative terminal Vi-.

[0009] A control system includes an energy storage module BAT, a photovoltaic module PV, a three-level DC / AC converter, and an output module. The energy storage module BAT and the photovoltaic module PV are connected in parallel and electrically connected to the input terminal of the three-level DC / AC converter. A first DC / DC converter is provided between the photovoltaic module PV and the three-level DC / AC converter, and a second DC / DC converter is provided between the energy storage module BAT and the three-level DC / AC converter. The first DC / DC converter and / or the second DC / DC converter are the aforementioned three-level DC / DC converters. The live wire of the output module is electrically connected to the output terminal of the three-level DC / AC converter, and the neutral wire N of the output module is electrically connected to the output neutral VoN of the three-level DC / AC converter.

[0010] As a further improvement of this utility model, the first DC / DC converter has a first positive input V1i+ and a first negative input V1i-, and the second DC / DC converter has a second positive input V2i+ and a second negative input V2i-. The first positive input V1i+ and the second positive input V2i+ intersect at point X. A third diode D3 is provided between the first positive input V1i+ and point X. The anode of the third diode D3 is electrically connected to the first positive input V1i+, and the cathode of the third diode D3 is electrically connected to point X. The first negative input V1i- and the second negative input V2i- intersect at point Y. A fourth diode D4 is provided between the first negative input V1i- and the Y point. The anode of the fourth diode D4 is electrically connected to the Y point, and the cathode of the fourth diode D4 is electrically connected to the first negative input V2i-.

[0011] As a further improvement of this utility model, a seventh switch Q7 is provided between the second input positive terminal V2i+ and the X point, and an eighth switch Q8 is provided between the second input negative terminal V2i- and the Y point.

[0012] As a further improvement of this utility model, the seventh switch Q7 has a seventh body diode D7, the anode of the seventh body diode D7 is electrically connected to the second input positive terminal V2i+, and the cathode of the seventh body diode D7 is electrically connected to point X. The eighth switch Q8 has an eighth body diode D8, the anode of the eighth body diode D8 is electrically connected to point Y, and the cathode of the eighth body diode D8 is electrically connected to the second input negative terminal V2i-.

[0013] As a further improvement of this utility model, both the first DC / DC converter and the second DC / DC converter are three-level DC / DC converters, the first capacitor C1 of the two three-level DC / DC converters is the same, the second capacitor C2 of the two three-level DC / DC converters is the same, and the control terminal of the two three-level DC / DC converters is the same.

[0014] As a further improvement of this utility model, there are three live wires, namely the first live wire A, the second live wire B, and the third live wire C. A fifth filter inductor L5 is provided between the three-level DC / AC converter and the first live wire A, a sixth filter inductor L6 is provided between the three-level DC / AC converter and the second live wire B, and a seventh filter inductor L7 is provided between the three-level DC / AC converter and the third live wire C.

[0015] As a further improvement of this utility model, a third filter capacitor C3 is provided between the first live wire A and the neutral wire N, a fourth filter capacitor C4 is provided between the second live wire B and the neutral wire N, and a fifth filter capacitor C5 is provided between the third live wire C and the neutral wire N.

[0016] According to the above-described solution, the beneficial effects of this utility model are as follows: 1. This utility model adopts a three-level DC / DC topology to replace the conventional balanced circuit, which makes the overall system more integrated. It can realize DC / DC power conversion and achieve neutral point voltage balance through DC / DC wave generation. It can work normally even under single-phase half-wave load. 2. The three-level DC / DC topology of this utility model uses two series-connected switching transistors, which adds one more switching transistor compared with the two-level DC / DC topology. This allows the original 1200V silicon carbide MOS to be replaced with a 600V silicon MOS, thereby reducing the on-state voltage drop of the switching transistor. Even if the photovoltaic side is connected incorrectly, it is not easy to burn out the switching transistor, effectively improving the fault tolerance and safety of the system. 3. This utility model can also use switching transistors with slightly larger voltage specifications, such as 650V silicon MOS, and the diodes can also be 650V silicon carbide or silicon diodes. While taking into account size and efficiency, the system cost will also have advantages in special application scenarios, and a larger voltage margin will be left for power devices. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 This is a schematic diagram of the structure of the first embodiment of the control system of this utility model; Figure 3 This is a schematic diagram of the structure of the second embodiment of the control system of this utility model; Figure 4 This is a structural schematic diagram of the third embodiment of the control system of this utility model. Detailed Implementation

[0018] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0019] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0021] See Figure 1 This utility model provides a three-level DC / DC converter, including an input positive terminal Vi+, an input negative terminal Vi-, an output positive terminal Vo+, an output negative terminal Vo-, an output neutral terminal VoN, and a control terminal. The input positive terminal Vi+ is electrically connected to the output positive terminal Vo+, and the input negative terminal Vi- is electrically connected to the output negative terminal Vo-. A first switch Q1 and a second switch Q2 are connected in series between the input positive terminal Vi+ and the input negative terminal Vi-. The control terminal is electrically connected to both the first switch Q1 and the second switch Q2. The control terminal outputs two independent drive signals to the first switch Q1 and the second switch Q2 respectively. The drive signals for switch Q2 are two independent drive signals that do not affect each other. The duty cycles of the first switch Q1 and the second switch Q2 can be the same or different, depending on their respective drive signals. A first capacitor C1 and a second capacitor C2 are connected in series between the positive output Vo+ and the negative output Vo-. The midpoint of the output VoN is connected in sequence to the midpoint of the first capacitor C1 and the second capacitor C2, and the midpoint of the first switch Q1 and the second switch Q2. The difference between the positive output Vo+ and the midpoint output VoN is the positive half-bus voltage, and the difference between the midpoint output VoN and the negative output Vo- is the negative half-bus voltage. Dynamic pressure equalization principle: Assume the positive half-bus voltage is Uc1, the negative half-bus voltage is Uc2, and the switching period is Ts. When Uc1=Uc2, the duty cycles of the first switch Q1 and the second switch Q2 are the same, both being D, meaning that the first switch Q1 and the second switch Q2 are turned on and off at the same time. When Uc1 > Uc2, the duty cycle of the first switch Q1 becomes D + deltaD, and the duty cycle of the second switch Q2 becomes D - deltaD. At this time, the turn-on time of the first switch Q1 is 2 × deltaD longer than the turn-on time of the second switch Q2. Therefore, the positive input Vi+ has 2 × deltaD time to charge the second capacitor C2, thereby realizing the dynamic adjustment of the output midpoint VoN voltage. When Uc1 < Uc2, the duty cycle of the first switch Q1 becomes D - deltaD, and the duty cycle of the second switch Q2 becomes D + deltaD. At this time, the turn-on time of the first switch Q1 is 2 × deltaD less than the turn-on time of the second switch Q2. Therefore, the positive input Vi+ has 2 × deltaD time to charge the first capacitor C1, thereby realizing the dynamic adjustment of the voltage of the output midpoint VoN.

[0022] In this invention's three-level DC / DC topology, a first switch Q1 and a second switch Q2 are connected in series. By adjusting the duty cycle of the first switch Q1 and the second switch Q2, the first capacitor C1 or the second capacitor C2 is selectively charged, thereby achieving the output midpoint VoN voltage. The control is simple and the cost is low. At the same time, compared with the two-level DC / DC topology, the three-level DC / DC topology adds a switch, which can replace the original 1200V silicon carbide MOS with a 600V silicon MOS, thereby reducing the on-state voltage drop of the switch. Even if the photovoltaic side is connected incorrectly, it is not easy to burn out the switch, effectively improving the fault tolerance and safety of the system.

[0023] In one embodiment of this utility model, a voltage regulator inductor is provided at the positive input terminal Vi+ and / or the negative input terminal Vi-. The voltage regulator inductor stabilizes the input voltage at the input terminal, thereby improving the stability of the input voltage. Specifically, the voltage regulator inductor can adopt the following three structures: Structure 1: The positive input terminal Vi+ is equipped with a voltage regulator inductor L1; Structure 2: The negative input terminal Vi- is equipped with a voltage regulator inductor L2; Structure 3: The positive input Vi+ is equipped with a Zener inductor L1, and the negative input Vi- is equipped with a Zener inductor L2. Optionally, the Zener inductors L1 and L2 can be two independent inductors, or they can be coupled inductors.

[0024] In one embodiment of this utility model, the first switching transistor Q1 has a first body diode D1, and the second switching transistor Q2 has a second body diode D2. The anode of the first body diode D1 is electrically connected to the cathode of the second body diode D2, the cathode of the first body diode D1 is electrically connected to the positive input Vi+, and the anode of the second body diode D2 is electrically connected to the negative input Vi-. That is, the anode voltage of the first body diode D1 is always lower than the cathode voltage, and the anode voltage of the second body diode D2 is always lower than the cathode voltage, so that the first body diode D1 and the second body diode D2 are always in the off state.

[0025] This utility model provides a control system including an energy storage module BAT, a photovoltaic module PV, a three-level DC / AC converter, and an output module. The energy storage module BAT and the photovoltaic module PV are connected in parallel and electrically connected to the input terminal of the three-level DC / AC converter. A first DC / DC converter is provided between the photovoltaic module PV and the three-level DC / AC converter, and a second DC / DC converter is provided between the energy storage module BAT and the three-level DC / AC converter. The first DC / DC converter and / or the second DC / DC converter are the aforementioned three-level DC / AC converters. The input terminal of the three-level DC / AC converter is connected to a DC bus. Therefore, the three voltage values ​​output by the three-level DC / AC converter... These are the three voltage values ​​of the DC bus: the positive terminal BUS+, the midpoint BUSN, and the negative terminal BUS-. The live wire of the output module is electrically connected to the output terminal of the three-level DC / AC converter, and the neutral wire N of the output module is electrically connected to the output midpoint VoN of the three-level DC / DC converter. The energy storage module BAT and the photovoltaic module PV provide suitable DC power to the three-level DC / AC converter through the first DC / DC converter and the second DC / DC converter, respectively. The three-level DC / AC converter converts the acquired DC power into AC power and provides it to the output module. The first DC / DC converter and the second DC / DC converter can adopt the following three structures: Structure 1: See Figure 2 Both the first and second DC / DC converters are three-level DC / DC converters, meaning that the energy storage module BAT and the photovoltaic module PV can dynamically adjust the output midpoint VoN potential through their respective connected three-level DC / DC converters. Structure 2: See Figure 3 The first DC / DC converter is a two-level DC / DC converter, and the second DC / DC converter is a three-level DC / DC converter. Structure 3: See Figure 4 The first DC / DC converter is a three-level DC / DC converter, and the second DC / DC converter is a two-level DC / DC converter.

[0026] This invention allows for the selection and adjustment of the number of three-level DC / DC converters according to specific application scenarios and usage requirements. For example, in structures two and three mentioned above, a three-level DC / DC converter is selectively provided in the energy storage module BAT and the photovoltaic module PV. This ensures dynamic adjustment of the output mid-voltage (VoN) while effectively reducing the system's operating cost.

[0027] This invention uses a three-level DC / DC topology to replace the conventional balanced circuit, resulting in a higher overall system integration. It can achieve both DC / DC power conversion and midpoint voltage balancing through DC / DC waveform generation, and can operate normally even under single-phase half-wave load conditions. In addition, it can use switching transistors with slightly larger voltage specifications, such as 650V silicon MOSFETs. While balancing size and efficiency, it also offers advantages in system cost for special application scenarios, and provides a larger voltage margin for power devices.

[0028] As one embodiment of the present invention, the first DC / DC converter has a first positive input V1i+ and a first negative input V1i-, and the second DC / DC converter has a second positive input V2i+ and a second negative input V2i-. The first positive input V1i+ and the second positive input V2i+ intersect at point X. A third diode D3 is provided between the first positive input V1i+ and point X. The anode of the third diode D3 is electrically connected to the first positive input V1i+, and the cathode of the third diode D3 is electrically connected to point X. The first negative input V1i- and the second negative input V2i- intersect at point Y. A fourth diode D4 is provided between the first negative input V1i- and point Y. The anode of the fourth diode D4 is electrically connected to point Y, and the cathode of the fourth diode D4 is electrically connected to the first negative input V2i-. By cooperating with the third diode D3 and the fourth diode D4, it can be ensured that the current at both ends of the photovoltaic module PV flows in one direction, that is, the current at both ends of the photovoltaic module PV can only flow from the first input positive terminal V1i+ to the first input negative terminal V1i-, thereby improving the stability of the photovoltaic module PV power supply.

[0029] As one embodiment of this utility model, a seventh switch Q7 is provided between the second input positive terminal V2i+ and point X, and an eighth switch Q8 is provided between the second input negative terminal V2i- and point Y. Through the cooperation of the seventh switch Q7 and the eighth switch Q8, the energy storage module BAT can be connected or disconnected, and the staff can select the appropriate power supply mode according to the specific usage requirements.

[0030] In one embodiment of this utility model, the seventh switch Q7 has a seventh body diode D7, the anode of which is connected to the second input positive terminal V2i+, and the cathode of which is connected to point X. The eighth switch Q8 has an eighth body diode D8, the anode of which is connected to point Y, and the cathode of which is connected to the second input negative terminal V2i-. When the seventh switch Q7 and the eighth switch Q8 are turned on, the energy storage module BAT can discharge to supply power to the DC bus, and the photovoltaic module PV can also charge the energy storage module BAT. When the seventh switch Q7 and the eighth switch Q8 are turned off, the current cannot flow into the second input positive terminal V2i+ of the energy storage module BAT. Therefore, the photovoltaic module PV cannot charge the energy storage module BAT. However, under the action of the seventh body diode D7 and the eighth body diode D8, when the energy storage module BAT has sufficient internal charge, it can still discharge.

[0031] As one embodiment of this utility model, both the first DC / DC converter and the second DC / DC converter are three-level DC / DC converters. The first capacitor C1 of the two three-level DC / DC converters is the same, the second capacitor C2 of the two three-level DC / DC converters is the same, and the control terminal of the two three-level DC / DC converters is the same. This can effectively reduce the number of capacitors and control terminals, making the overall system more integrated and reducing the cost of use.

[0032] In one embodiment of this utility model, there are three live wires: a first live wire A, a second live wire B, and a third live wire C. A fifth filter inductor L5 is provided between the three-level DC / AC converter and the first live wire A, a sixth filter inductor L6 is provided between the three-level DC / AC converter and the second live wire B, and a seventh filter inductor L7 is provided between the three-level DC / AC converter and the third live wire C. A third filter capacitor C3 is provided between the first live wire A and the neutral wire N, a fourth filter capacitor C4 is provided between the second live wire B and the neutral wire N, and a fifth filter capacitor C5 is provided between the third live wire C and the neutral wire N, which can ensure the stability of the output module.

[0033] In summary, this invention provides a three-level DC / DC converter and control system. It employs a first switch Q1 and a second switch Q2 connected in series. By adjusting the duty cycle of the first switch Q1 and the second switch Q2, the first capacitor C1 or the second capacitor C2 is selectively charged, thereby achieving the output midpoint VoN voltage. The control is simple and cost-effective. Furthermore, compared to a two-level DC / DC topology, the three-level DC / DC topology adds one more switch, allowing the original 1200V silicon carbide MOS to be replaced with a 600V silicon MOS, thus reducing the on-state voltage drop of the switch and enabling photovoltaic... Even with incorrect polarity connection, the switching transistor is less likely to burn out, effectively improving the system's fault tolerance and operational safety. The adoption of a three-level DC / DC topology instead of the conventional balanced circuit results in higher overall system integration. It enables both DC / DC power conversion and midpoint voltage balancing through DC / DC waveform generation, allowing normal operation even under single-phase half-wave load conditions. Furthermore, it allows the use of higher voltage switching transistors, such as 650V silicon MOSFETs, balancing size and efficiency while offering cost advantages in specific applications and providing greater voltage margin for power devices.

[0034] It should be emphasized that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A three-level DC / DC converter, characterized in that, The device includes an input positive terminal Vi+, an input negative terminal Vi-, an output positive terminal Vo+, an output negative terminal Vo-, an output neutral terminal VoN, and a control terminal. The input positive terminal Vi+ is electrically connected to the output positive terminal Vo+, and the input negative terminal Vi- is electrically connected to the output negative terminal Vo-. A first switch Q1 and a second switch Q2 are connected in series between the input positive terminal Vi+ and the input negative terminal Vi-. The control terminal is electrically connected to both the first switch Q1 and the second switch Q2. A first capacitor C1 and a second capacitor C2 are connected in series between the output positive terminal Vo+ and the output negative terminal Vo-. The output neutral terminal VoN is sequentially connected to the midpoint between the first capacitor C1 and the second capacitor C2, and the midpoint between the first switch Q1 and the second switch Q2. The first switch Q1 has a first body diode D1, and the second switch Q2 has a second body diode D2. The anode of the first body diode D1 is electrically connected to the cathode of the second body diode D2, the cathode of the first body diode D1 is electrically connected to the positive input Vi+, and the anode of the second body diode D2 is electrically connected to the negative input Vi-.

2. The three-level DC / DC converter according to claim 1, characterized in that, The positive input Vi+ and / or the negative input Vi- are provided with a voltage-regulating inductor.

3. A control system, characterized in that, The device includes an energy storage module BAT, a photovoltaic module PV, a three-level DC / AC converter, and an output module. The energy storage module BAT and the photovoltaic module PV are connected in parallel and electrically connected to the input terminal of the three-level DC / AC converter. A first DC / DC converter is provided between the photovoltaic module PV and the three-level DC / AC converter, and a second DC / DC converter is provided between the energy storage module BAT and the three-level DC / AC converter. The first DC / DC converter and / or the second DC / DC converter are three-level DC / DC converters as described in any one of claims 1-2. The live wire of the output module is electrically connected to the output terminal of the three-level DC / AC converter, and the neutral wire N of the output module is electrically connected to the output neutral VoN of the three-level DC / AC converter.

4. The control system according to claim 3, characterized in that, The first DC / DC converter has a first positive input V1i+ and a first negative input V1i-, and the second DC / DC converter has a second positive input V2i+ and a second negative input V2i-. The first positive input V1i+ and the second positive input V2i+ intersect at point X. A third diode D3 is provided between the first positive input V1i+ and point X. The anode of the third diode D3 is electrically connected to the first positive input V1i+, and the cathode of the third diode D3 is electrically connected to point X. The first negative input V1i- and the second negative input V2i- intersect at point Y. A fourth diode D4 is provided between the first negative input V1i- and the Y point. The anode of the fourth diode D4 is electrically connected to the Y point, and the cathode of the fourth diode D4 is electrically connected to the first negative input V2i-.

5. The control system according to claim 4, characterized in that, A seventh switch Q7 is provided between the second positive input V2i+ and point X, and an eighth switch Q8 is provided between the second negative input V2i- and point Y.

6. The control system according to claim 5, characterized in that, The seventh switch Q7 has a seventh body diode D7, the anode of which is electrically connected to the second input positive terminal V2i+, and the cathode of which is electrically connected to point X. The eighth switch Q8 has an eighth body diode D8, the anode of which is electrically connected to point Y, and the cathode of which is electrically connected to the second input negative terminal V2i-.

7. The control system according to claim 3, characterized in that, Both the first DC / DC converter and the second DC / DC converter are three-level DC / DC converters. The first capacitor C1 of the two three-level DC / DC converters is the same, the second capacitor C2 of the two three-level DC / DC converters is the same, and the control terminal of the two three-level DC / DC converters is the same.

8. The control system according to claim 3, characterized in that, There are three live wires: a first live wire A, a second live wire B, and a third live wire C. A fifth filter inductor L5 is provided between the three-level DC / AC converter and the first live wire A. A sixth filter inductor L6 is provided between the three-level DC / AC converter and the second live wire B. A seventh filter inductor L7 is provided between the three-level DC / AC converter and the third live wire C.

9. The control system according to claim 8, characterized in that, A third filter capacitor C3 is provided between the first live wire A and the neutral wire N, a fourth filter capacitor C4 is provided between the second live wire B and the neutral wire N, and a fifth filter capacitor C5 is provided between the third live wire C and the neutral wire N.

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