Three-switch sub-module, operation method thereof and three-phase modular multilevel converter

Abstract

The invention relates to a three-switch sub-module, an operation method thereof and a three-phase modular multilevel converter, the three-switch sub-module comprises a first switch tube, a second switch tube, a third switch tube, a direct current capacitor, an energy storage unit and a direct current filter inductor, the first end of the first switch tube is connected with the positive electrode of the direct current capacitor, and the second end of the first switch tube is connected with the negative electrode of the direct current capacitor; the second end of the first switch tube is connected with the first output port and the first end of the second switch tube, the second end of the second switch tube is connected with the second end of the direct current filter inductor and the first end of the third switch tube, and the second end of the third switch tube is connected with the energy storage unit, the direct current capacitor and the second output port. The energy storage unit is further connected with the first end of the direct-current filter inductor. Compared with an existing two-stage sub-module topology suitable for energy storage access, the three-switch sub-module is only provided with three switch tubes, the manufacturing cost and the loss of the switch tubes are reduced, the voltage of an energy storage unit is low, the balancing problem caused by series connection of a large number of energy storage monomers is avoided, and the operation reliability is improved.

Description

Technical Field

[0001] The present application relates to the technical field of converters, and particularly to a three-switch sub-module, an operation method thereof, and a three-phase modular multilevel converter. Background Art

[0002] Modular multilevel converters have broad application prospects in medium and high voltage large-capacity fields such as flexible DC power transmission, new energy power generation, and electric drive due to advantages such as modular structure, good output harmonic characteristics, and bidirectional power flow.

[0003] Connecting an energy storage unit (such as battery energy storage, supercapacitor, etc.) to the DC side of the sub-module of a modular multilevel converter through a specific interface circuit can further improve the flexibility of the power flow direction of the converter and expand the functions and application scenarios of the converter topology.

[0004] There are currently two ways to connect an energy storage unit (such as battery energy storage, supercapacitor, etc.) to the DC side of the sub-module of a modular multilevel converter through a specific interface circuit. One way is to directly connect the energy storage unit or connect it in parallel with the DC capacitor of the sub-module of the converter through a passive filter. At this time, the energy storage unit needs to reach the same voltage level as the DC capacitor of the sub-module of the converter, which puts high requirements on the voltage level and series balance of the energy storage unit. Moreover, the energy storage unit needs to bear the fundamental frequency, second harmonic frequency and other low-frequency voltage ripples at both ends of the DC capacitor of the sub-module of the converter, which has a negative impact on its operating efficiency and life. Another way is to connect the energy storage unit in parallel with the DC capacitor of the sub-module of the converter through a bidirectional DC / DC converter, that is, to form a two-stage sub-module topology. Compared with the first way, this way can realize independent control of the charge and discharge current and power of each energy storage unit and avoid it from bearing the low-frequency ripple at both ends of the sub-module capacitor. Therefore, it is more friendly to the energy storage unit, but the additional bidirectional DC / DC converter will greatly increase the number of power electronic switching devices in the entire converter and reduce the operating reliability and efficiency of the power system. Summary of the Invention

[0005] The present application provides a three-switch sub-module, an operation method thereof, and a three-phase modular multilevel converter, which are used to solve the technical problem that the existing topological structure of connecting an energy storage unit to a modular multilevel converter has low operating reliability and efficiency.

[0006] In order to achieve the above object, the present application provides the following technical solutions:

[0007] On the one hand, a three-switch sub-module is provided, including a first switch tube, a second switch tube, a third switch tube, a DC capacitor, an energy storage unit, and a DC filter inductor. The first end of the first switch tube is connected to the positive electrode of the DC capacitor. The second end of the first switch tube is respectively connected to a first output port and the first end of the second switch tube. The second end of the second switch tube is respectively connected to the second end of the DC filter inductor and the first end of the third switch tube. The second end of the third switch tube is respectively connected to the negative electrode of the energy storage unit, the negative electrode of the DC capacitor, and a second output port. The positive electrode of the energy storage unit is connected to the first end of the DC filter inductor; the voltage of the energy storage unit is lower than the voltage of the DC capacitor.

[0008] Preferably, the third ends of the first switch tube, the second switch tube, and the third switch tube are all connected to a control module, and the control module is used to control the operation of the first switch tube, the second switch tube, and the third switch tube.

[0009] Preferably, the control module is used to control the operation of the first switch tube, the second switch tube, and the third switch tube according to a first working mode, a second working mode, or a third working mode;

[0010] The content of the first working mode includes: controlling the first switch tube to be turned off, the second switch tube to be turned on, the third switch tube to be turned on, removing the DC capacitor and discharging the energy storage unit, so that the output voltage between the first output port and the second output port is 0;

[0011] The content of the second working mode includes: controlling the first switch tube to be turned on, the second switch tube to be turned off, the third switch tube to be turned on, connecting the DC capacitor and discharging the energy storage unit, so that the output voltage between the first output port and the second output port is the voltage of the DC capacitor;

[0012] The content of the third working mode includes: controlling the first switch tube to be turned on, the second switch tube to be turned on, the third switch tube to be turned off, connecting the DC capacitor and charging the energy storage unit, so that the output voltage between the first output port and the second output port is the voltage of the DC capacitor.

[0013] Preferably, the control module includes a first modulation signal for controlling the connection or disconnection of the DC capacitor, a second modulation signal for controlling the charging or discharging of the energy storage unit, a first switching signal for controlling the on or off operation of the first switching tube, a second switching signal for controlling the on or off operation of the second switching tube, and a third switching signal for controlling the on or off operation of the third switching tube. The first modulation signal is processed by pulse width modulation technology to obtain the first switching signal. The second modulation signal is obtained by inverting the signal processed by the pulse width modulation technology to obtain the third switching signal. The second switching signal is obtained by performing a logical exclusive OR operation on the first switching signal and the third switching signal.

[0014] Preferably, the first switching tube, the second switching tube, and the third switching tube are all MOS tubes, IGBT tubes, or other fully controlled power electronic switching devices; and / or, the energy storage unit includes one energy storage element or a plurality of energy storage elements connected in series, and the energy storage element is a battery or a supercapacitor.

[0015] In another aspect, a method for operating a three-switch sub-module is provided, which is applied to the above-mentioned three-switch sub-module. The operating method includes the following steps:

[0016] Obtain the output voltage required by the three-switch sub-module;

[0017] Determine the working mode according to the output voltage;

[0018] Control the operation of the three-switch sub-module according to the working mode.

[0019] Preferably, controlling the operation of the three-switch sub-module according to the working mode includes:

[0020] If the working mode is the first working mode, control the first switching tube of the three-switch sub-module to be disconnected, the second switching tube to be turned on, the third switching tube to be turned on, the DC capacitor to be disconnected, and the energy storage unit to discharge;

[0021] If the working mode is the second working mode, control the first switching tube to be turned on, the second switching tube to be disconnected, the third switching tube to be turned on, the DC capacitor to be connected, and the energy storage unit to discharge;

[0022] If the working mode is the third working mode, control the first switching tube to be turned on, the second switching tube to be turned on, the third switching tube to be disconnected, the DC capacitor to be connected, and the energy storage unit to charge.

[0023] Preferably, determining the operating mode according to the output voltage includes: if the output voltage is 0, the operating mode is the first operating mode; if the output voltage is the voltage of the DC capacitor in the three-switch sub-module, the operating mode is the second operating mode or the third operating mode.

[0024] In another aspect, a three-phase modular multilevel converter is provided, which includes three-phase bridge arms and a controller for controlling the operation of each phase of the bridge arms. Each phase of the bridge arms includes an upper bridge arm and a lower bridge arm, and both the upper bridge arm and the lower bridge arm include N series-connected three-switch sub-modules as described above.

[0025] Preferably, the content of the controller includes:

[0026] Obtain the fundamental angular frequency of the three-phase bridge arms, the DC bus voltage input to the three-phase bridge arms, and the AC voltage output by the three-phase bridge arms, and obtain the energy storage voltage and capacitor voltage of the three-switch sub-module;

[0027] Calculate according to the DC bus voltage and the AC voltage to obtain the AC modulation ratio of the three-phase bridge arms; calculate according to the energy storage voltage and the capacitor voltage to obtain the DC modulation ratio of the three-switch sub-module;

[0028] Calculate according to the fundamental angular frequency and the AC modulation ratio to obtain a first modulation signal for controlling the connection or disconnection of the DC capacitor in the three-switch sub-module; and determine a second modulation signal for controlling the charging or discharging of the energy storage unit in the three-switch sub-module according to the DC modulation ratio;

[0029] Calculate according to the first modulation signal and the capacitor voltage to obtain the output voltage between the first output port and the second output port of the three-switch sub-module.

[0030] The three-switch sub-module, its operation method, and the three-phase modular multilevel converter. The three-switch sub-module includes a first switch tube, a second switch tube, a third switch tube, a DC capacitor, an energy storage unit, and a DC filter inductor. The first end of the first switch tube is connected to the positive pole of the DC capacitor. The second end of the first switch tube is respectively connected to the first output port and the first end of the second switch tube. The second end of the second switch tube is respectively connected to the second end of the DC filter inductor and the first end of the third switch tube. The second end of the third switch tube is respectively connected to the negative pole of the energy storage unit, the negative pole of the DC capacitor, and the second output port. The positive pole of the energy storage unit is connected to the first end of the DC filter inductor; the voltage of the energy storage unit is lower than the voltage of the DC capacitor.

[0031] As can be seen from the above technical solutions, the present application has the following advantages: The energy storage unit is connected to both ends of the DC capacitor of the three-switch sub-module via a power conversion circuit composed of power electronic switching devices (such as switching tubes). Therefore, it has the ability to independently control the charge and discharge current and power of each energy storage unit, and can avoid each energy storage unit from bearing low-frequency voltage ripples such as fundamental frequency and second harmonic frequency at both ends of the DC capacitor of the three-switch sub-module. Compared with the existing two-level sub-module topology suitable for energy storage access, this three-switch sub-module only has 3 switching tubes, which reduces the manufacturing cost and switching tube loss. The voltage required for the energy storage unit it sets is relatively low, far lower than the voltage of the DC capacitor, greatly reducing the number of series-connected battery monomers or supercapacitor monomers in the energy storage unit, avoiding the balancing problem brought about by a large number of series-connected battery monomers or supercapacitor monomers, improving the operating reliability of the energy storage unit, and solving the technical problems of low operating reliability and efficiency existing in the topology structure of the existing energy storage unit accessing a modular multilevel converter.

[0032] The operation method of this three-switch sub-module determines the working mode according to the output voltage obtained for the three-switch sub-module, and controls the operation of the three-switch sub-module according to the working mode, improving the operating reliability of the energy storage unit in the three-switch sub-module.

[0033] This three-phase modular multilevel converter improves the operating reliability of the energy storage unit accessing the modular multilevel converter through the three switching tubes and the energy storage unit set in the three-switch sub-module SM. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a schematic diagram of the topology structure of the three-switch sub-module described in the embodiment of the present application;

[0036] Figure 2 It is a schematic diagram of the topology structure of the three-switch sub-module in the first working mode described in the embodiment of the present application;

[0037] Figure 3 It is a schematic diagram of the topology structure of the three-switch sub-module in the second working mode described in the embodiment of the present application;

[0038] Figure 4 It is a schematic diagram of the topology structure of the three-switch sub-module in the third working mode described in the embodiment of the present application;

[0039] Figure 5 It is a flowchart of the steps of the operation method of the three-switch sub-module described in the embodiments of the present application;

[0040] Figure 6 It is a topological schematic diagram of the three-phase modular multilevel converter described in the embodiments of the present application;

[0041] Figure 7 It is a schematic diagram of the switching drive signals of the three-phase modular multilevel converter described in the embodiments of the present application. Detailed implementation manners

[0042] To make the objectives, features, and advantages of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the embodiments described below are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0043] In the description of the embodiments of the present application, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present application, "a plurality of" means two or more unless otherwise specifically defined.

[0044] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0045] The embodiments of the present application provide a three-switch sub-module, its operation method, and a three-phase modular multilevel converter, which solve the technical problems of low operation reliability and efficiency in the topological structure of the existing energy storage unit connected to the modular multilevel converter.

[0046] Embodiment 1:

[0047] Figure 1 It is a topological structure schematic diagram of the three-switch sub-module described in the embodiments of the present application.

[0048] As Figure 1As shown in the figure, an embodiment of the present application provides a three-switch sub-module, including a first switch tube S1, a second switch tube S2, a third switch tube S3, a DC capacitor C, an energy storage unit 101, and a DC filter inductor L b , the first end of the first switch tube S1 is connected to the positive electrode of the DC capacitor C, the second end of the first switch tube S1 is respectively connected to the first output port X and the first end of the second switch tube S2, and the second end of the second switch tube S2 is respectively connected to the DC filter inductor L b 's second end and the first end of the third switch tube S3, the second end of the third switch tube S3 is respectively connected to the negative electrode of the energy storage unit 101, the negative electrode of the DC capacitor C, and the second output port Y, and the positive electrode of the energy storage unit 101 is connected to the DC filter inductor L b 's first end; the voltage of the energy storage unit 101 is lower than the voltage of the DC capacitor C.

[0049] It should be noted that the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all MOS tubes, IGBT tubes, or other fully controlled power electronic switch devices (such as triodes); and / or, the energy storage unit 101 includes one energy storage element or multiple energy storage elements connected in series, and the energy storage element is a battery or a supercapacitor. In this embodiment, if the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all IGBT tubes, the first ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the collectors of the IGBT tubes, the second ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the emitters of the IGBT tubes, and the third ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the bases of the IGBT tubes. If the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all MOS tubes, the first ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the sources of the MOS tubes, the second ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the drains of the MOS tubes, and the third ends of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all the gates or control ends of the MOS tubes.

[0050] In the embodiment of the present application, the number of power electronic switch devices provided in the three-switch sub-module is only 3 (such as the first switch tube S1, the second switch tube S2, and the third switch tube S3). The two-level sub-module of the existing modular multilevel converter with energy storage access contains at least 4 power electronic switch devices. Therefore, compared with the existing solution, the number of power electronic switch devices in the three-switch sub-module is reduced by 25%, reducing the cost of the power electronic switch devices and the losses of the power electronic switch devices in the three-switch sub-module. The voltage required for the energy storage unit of the three-switch sub-module is relatively low, far lower than the voltage of the DC capacitor, greatly reducing the number of series-connected battery monomers or supercapacitor monomers that make up the energy storage unit, avoiding the balancing problem caused by a large number of series-connected battery monomers or supercapacitor monomers, and improving the operating reliability of the energy storage unit.

[0051] In the embodiment of the present application, the three-switch sub-module includes an energy storage port formed by an energy storage unit, a DC port formed by a DC capacitor, and an AC port formed by a first output port X and a second output port Y. The power can flow freely among the three ports of the energy storage port, the DC port, and the AC port. The three-switch sub-module has an energy storage function and can be applied to a flexible DC transmission system with energy storage.

[0052] A three-switch sub-module provided in the present application includes a first switch tube, a second switch tube, a third switch tube, a DC capacitor, an energy storage unit, and a DC filter inductor. The first end of the first switch tube is connected to the positive pole of the DC capacitor. The second end of the first switch tube is respectively connected to the first output port and the first end of the second switch tube. The second end of the second switch tube is respectively connected to the second end of the DC filter inductor and the first end of the third switch tube. The second end of the third switch tube is respectively connected to the negative pole of the energy storage unit, the negative pole of the DC capacitor, and the second output port. The positive pole of the energy storage unit is connected to the first end of the DC filter inductor. Compared with the existing two-level sub-module topology suitable for energy storage access, the three-switch sub-module reduces the manufacturing cost and switch tube losses by only having 3 switch tubes. The voltage required for the energy storage unit it sets is relatively low, far lower than the voltage of the DC capacitor, greatly reducing the number of series-connected battery monomers or supercapacitor monomers that make up the energy storage unit, avoiding the balancing problem caused by a large number of series-connected battery monomers or supercapacitor monomers, improving the operating reliability of the energy storage unit, and solving the technical problems of low operating reliability and efficiency existing in the topology structure of the existing energy storage unit accessing the modular multilevel converter.

[0053] Figure 2 It is a schematic diagram of the topology structure of the three-switch sub-module in the first working mode described in the embodiment of the present application. Figure 3 It is a schematic diagram of the topology structure of the three-switch sub-module in the second working mode described in the embodiment of the present application. Figure 4Schematic diagram of the topological structure of the three-switch sub-module in the third working mode according to the embodiments of the present application.

[0054] In an embodiment of the present application, the third terminals of the first switch tube S1, the second switch tube S2, and the third switch tube S3 are all connected to the control module, and the control module is used to control the operation of the first switch tube S1, the second switch tube S2, and the third switch tube S3. The control module is used to control the operation of the first switch tube S1, the second switch tube S2, and the third switch tube S3 according to the first working mode, the second working mode, or the third working mode.

[0055] As Figures 2 to 4 shown, in the embodiments of the present application, the content of the first working mode includes: controlling the first switch tube S1 to be turned off, the second switch tube S2 to be turned on, the third switch tube S3 to be turned on, removing the DC capacitor C, and the energy storage unit 101 discharging, so that the output voltage U xy between the first output port X and the second output port Y is 0; the content of the second working mode includes: controlling the first switch tube S1 to be turned on, the second switch tube S2 to be turned off, the third switch tube S3 to be turned on, connecting the DC capacitor C, and the energy storage unit 101 discharging, so that the output voltage U xy between the first output port X and the second output port Y is the voltage U C of the DC capacitor C; the content of the third working mode includes: controlling the first switch tube S1 to be turned on, the second switch tube S2 to be turned on, the third switch tube S3 to be turned off, connecting the DC capacitor C, and the energy storage unit 101 charging, so that the output voltage U xy between the first output port X and the second output port Y is the voltage U C of the DC capacitor C.

[0056] It should be noted that, as shown in Table 1, the switch state of the switch tube being 0 means turned off, and the switch state of the switch tube being 1 means turned on; the first modulation signal H c being 1 means the DC capacitor is connected, and the first modulation signal H c being 0 means the DC capacitor is removed; the second modulation signal H b being 1 means the energy storage unit is charging, and the second modulation signal H b being 0 means the energy storage unit is discharging. In each working mode, there must be and only 2 power electronic switch devices in the on state, and the remaining power electronic switch devices are in the off state.

[0057] Table 1 shows the 3 working modes of the three-switch sub-module

[0058]

[0059] In one embodiment of the present application, the control module includes a first modulation signal for controlling the connection or disconnection of the DC capacitor, a second modulation signal for controlling the charging or discharging of the energy storage unit, a first switch signal for controlling the on or off operation of the first switch tube, a second switch signal for controlling the on or off operation of the second switch tube, and a third switch signal for controlling the on or off operation of the third switch tube. The first modulation signal is processed using pulse width modulation technology to obtain the first switch signal. The second modulation signal is inverted after being processed by pulse width modulation technology to obtain the third switch signal. The second switch signal is obtained by performing a logical exclusive OR operation on the first switch signal and the third switch signal.

[0060] It should be noted that, as shown in Table 1, the logical relationship between the switching states of each switch tube and the first modulation signal H c and the second modulation signal H b is represented by the first formula, where "¬" represents logical negation and "⊕" represents logical exclusive OR. The first formula is:

[0061]

[0062] According to the first formula, in the process of obtaining the first switch signal and the third switch signal using pulse width modulation technology, the first modulation signal is directly compared with the triangular carrier wave set in the pulse width modulation technology to obtain the first switch signal, and the signal obtained by comparing the second modulation signal with the triangular carrier wave set in the pulse width modulation technology is inverted to obtain the third switch signal. In this embodiment, the pulse width modulation (PWM) technology is a relatively mature technology in the art. For example, pulse width modulation is an analog control method that modulates the bias of the base of a transistor or the gate of a MOS transistor according to the change of the corresponding load to change the conduction time of the transistor or MOS transistor, thereby changing the output of the switching regulated power supply.

[0063] Embodiment 2:

[0064] Figure 5 This is a flowchart of the steps of the operation method of the three-switch sub-module described in the embodiments of the present application.

[0065] As Figure 5 shown, the embodiments of the present application provide an operation method for a three-switch sub-module, which is applied to the above three-switch sub-module. The operation method includes the following steps:

[0066] S1. Obtain the output voltage required by the three-switch sub-module;

[0067] S2. Determine the working mode according to the output voltage;

[0068] S3. Control the operation of the three-switch sub-module according to the working mode.

[0069] It should be noted that the content of the three-switch sub-module in this embodiment has been described in Embodiment 1, and the content of the three-switch sub-module will not be repeated in this embodiment. The operation method of the three-switch sub-module improves the operation reliability of the energy storage unit in the three-switch sub-module by obtaining the output voltage required by the three-switch sub-module, determining the working mode according to the output voltage, and controlling the operation of the three-switch sub-module according to the working mode.

[0070] In the embodiment of the present application, controlling the operation of the three-switch sub-module according to the working mode includes:

[0071] If the working mode is the first working mode, control the first switch tube of the three-switch sub-module to be turned off, the second switch tube to be turned on, the third switch tube to be turned on, remove the DC capacitor, and discharge the energy storage unit;

[0072] If the working mode is the second working mode, control the first switch tube to be turned on, the second switch tube to be turned off, the third switch tube to be turned on, connect the DC capacitor, and discharge the energy storage unit;

[0073] If the working mode is the third working mode, control the first switch tube to be turned on, the second switch tube to be turned on, the third switch tube to be turned off, connect the DC capacitor, and charge the energy storage unit.

[0074] If the working mode is the first working mode, control the first switch tube of the three-switch sub-module to be turned off, the second switch tube to be turned on, the third switch tube to be turned on, remove the DC capacitor, and discharge the energy storage unit;

[0075] If the working mode is the second working mode, control the first switch tube to be turned on, the second switch tube to be turned off, the third switch tube to be turned on, connect the DC capacitor, and discharge the energy storage unit;

[0076] If the working mode is the third working mode, control the first switch tube to be turned on, the second switch tube to be turned on, the third switch tube to be turned off, connect the DC capacitor, and charge the energy storage unit.

[0077] Embodiment 3:

[0078] Figure 6 It is a topological schematic diagram of the three-phase modular multilevel converter described in the embodiment of the present application.

[0079] As Figure 6 shown, the embodiment of the present application provides a three-phase modular multilevel converter, including three-phase bridge arms and a controller for controlling the operation of each phase bridge arm. Each phase bridge arm includes an upper bridge arm and a lower bridge arm. Both the upper bridge arm and the lower bridge arm include N series-connected three-switch sub-modules SM as described above.

[0080] It should be noted that the content of the three-switch sub-module SM in the third embodiment has been described in the first embodiment, and the content of the three-switch sub-module SM will not be repeated in this embodiment. In this embodiment, the three-phase modular multilevel converter improves the operation reliability of the energy storage unit connected to the modular multilevel converter through three switching tubes and the energy storage unit arranged in the three-switch sub-module SM.

[0081] Figure 7 This is a schematic diagram of the switching drive signals of the three-phase modular multilevel converter described in the embodiments of the present application. In Figure 7 , Cr is a triangular carrier wave.

[0082] As Figure 7 shown, in the embodiments of the present application, the content of the controller includes:

[0083] Obtain the fundamental angular frequency ω of the three-phase bridge arm, the DC bus voltage U dc input to the three-phase bridge arm, and the AC voltage U m output by the three-phase bridge arm, and obtain the energy storage voltage U b of the three-switch sub-module and the capacitor voltage U C ;

[0084] Calculate according to the DC bus voltage and the AC voltage to obtain the AC modulation ratio of the three-phase bridge arm; calculate according to the energy storage voltage and the capacitor voltage to obtain the DC modulation ratio of the three-switch sub-module;

[0085] Calculate according to the fundamental angular frequency and the AC modulation ratio to obtain a first modulation signal for controlling the charging or discharging of the DC capacitor in the three-switch sub-module; and determine a second modulation signal for controlling the charging or discharging of the energy storage unit in the three-switch sub-module according to the DC modulation ratio;

[0086] Calculate according to the first modulation signal and the capacitor voltage to obtain the output voltage between the first output port and the second output port in the three-switch sub-module.

[0087] It should be noted that according to the DC bus voltage and the AC voltage, the AC modulation ratio formula is used for calculation to obtain the AC modulation ratio m ac of the three-phase bridge arm. The AC modulation ratio formula is m ac =2U m / U dc . The DC modulation ratio m b of the three-switch sub-module is calculated according to the energy storage voltage and the capacitor voltage using the DC modulation ratio formula. The DC modulation ratio formula is m b =U b / U C .

[0088] In the embodiments of the present application, the first modulation signal H c and the second modulation signal Hb It is represented by the second formula respectively. The second formula is:

[0089] .

[0090] In the embodiment of the present application, only the DC and fundamental components are considered, and the high-frequency harmonic components are ignored. The voltage U of the energy storage unit of the three-switch sub-module b , the output voltage U xy and the relationship with the first modulation signal H c and the second modulation signal H b is represented by the third formula. The third formula is:

[0091] .

[0092] Exemplarily, the computer program can be divided into one or more modules / units. One or more modules / units are stored in the memory and executed by the processor to complete the present application. One or more modules / units can be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in the terminal device.

[0093] The terminal device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art can understand that it does not constitute a limitation on the terminal device, and it may include more or fewer components than shown in the figure, or combine certain components, or different components. For example, the terminal device may also include input / output devices, network access devices, a bus, etc.

[0094] The so-called processor may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0095] The memory can be an internal storage unit of the terminal device, such as the hard disk or memory of the terminal device. The memory can also be an external storage device of the terminal device, such as a plug-in hard disk equipped on the terminal device, a SmartMedia Card (SMC), a Secure Digital (SD) card, a Flash Card, etc. Further, the memory can also include both the internal storage unit and the external storage device of the terminal device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory can also be used to temporarily store the data that has been output or will be output.

[0096] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0097] In several embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there can be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces, and the indirect couplings or communication connections of the devices or units can be in electrical, mechanical, or other forms.

[0098] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0099] In addition, in each embodiment of the present invention, the functional units can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated units can be implemented in the form of hardware or in the form of software functional units.

[0100] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0101] As described above, the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present application.

Claims

1. A three-switch sub-module, characterized in that, It includes a first switching tube, a second switching tube, a third switching tube, a DC capacitor, an energy storage unit and a DC filter inductor. The first end of the first switching tube is connected to the positive pole of the DC capacitor. The second end of the first switching tube is respectively connected to a first output port and the first end of the second switching tube. The second end of the second switching tube is respectively connected to the second end of the DC filter inductor and the first end of the third switching tube. The second end of the third switching tube is respectively connected to the negative pole of the energy storage unit, the negative pole of the DC capacitor and a second output port. The positive pole of the energy storage unit is connected to the first end of the DC filter inductor; the voltage of the energy storage unit is lower than the voltage of the DC capacitor.

2. The three-switch sub-module according to claim 1, wherein The third ends of the first switching tube, the second switching tube and the third switching tube are all connected to a control module, and the control module is used to control the operation of the first switching tube, the second switching tube and the third switching tube.

3. The three-switch sub-module according to claim 2, wherein The control module is used to control the operation of the first switching tube, the second switching tube and the third switching tube according to a first working mode, a second working mode or a third working mode; The content of the first working mode includes: controlling the first switching tube to be turned off, the second switching tube to be turned on, the third switching tube to be turned on, removing the DC capacitor and the energy storage unit to discharge, so that the output voltage between the first output port and the second output port is 0; The content of the second working mode includes: controlling the first switching tube to be turned on, the second switching tube to be turned off, the third switching tube to be turned on, connecting the DC capacitor and the energy storage unit to discharge, so that the output voltage between the first output port and the second output port is the voltage of the DC capacitor; The content of the third working mode includes: controlling the first switching tube to be turned on, the second switching tube to be turned on, the third switching tube to be turned off, connecting the DC capacitor and the energy storage unit to charge, so that the output voltage between the first output port and the second output port is the voltage of the DC capacitor.

4. The three-switch sub-module according to claim 2, wherein The control module includes a first modulation signal for controlling the connection or removal of the DC capacitor, a second modulation signal for controlling the charging or discharging of the energy storage unit, a first switching signal for controlling the conduction or cut-off operation of the first switching tube, a second switching signal for controlling the conduction or cut-off operation of the second switching tube, and a third switching signal for controlling the conduction or cut-off operation of the third switching tube. The first modulation signal is processed by pulse width modulation technology to obtain the first switching signal. The second modulation signal is obtained by taking the inverse of the signal after being processed by the pulse width modulation technology to obtain the third switching signal. The second switching signal is obtained by performing a logical exclusive OR operation on the first switching signal and the third switching signal.

5. The three-switch sub-module according to any one of claims 1-4, characterized in that, The energy storage unit includes one energy storage element or a plurality of energy storage elements connected in series, and the energy storage element is a battery or a supercapacitor.

6. A running method of a three-switch sub-module, which is applied to the three-switch sub-module described in any one of claims 1-5, and is characterized in that, The operation method includes the following steps: Obtain the output voltage required by the three-switch sub-module; Determine the working mode according to the output voltage; Control the operation of the three-switch sub-module according to the working mode.

7. The operating method of the three-switch sub-module according to claim 6, characterized in that, Controlling the operation of the three-switch sub-module according to the working mode includes: If the working mode is the first working mode, control the first switch tube of the three-switch sub-module to be turned off, the second switch tube to be turned on, the third switch tube to be turned on, cut off the DC capacitor and discharge the energy storage unit; If the working mode is the second working mode, control the first switch tube to be turned on, the second switch tube to be turned off, the third switch tube to be turned on, connect the DC capacitor and discharge the energy storage unit; If the working mode is the third working mode, control the first switch tube to be turned on, the second switch tube to be turned on, the third switch tube to be turned off, connect the DC capacitor and charge the energy storage unit.

8. The operating method of the three-switch sub-module according to claim 6, characterized in that Determining the working mode according to the output voltage includes: if the output voltage is 0, the working mode is the first working mode; if the output voltage is the voltage of the DC capacitor in the three-switch sub-module, the working mode is the second working mode or the third working mode.

9. A three-phase modular multilevel converter, comprising three-phase bridge arms and a controller for controlling the operation of each phase of the bridge arms. Each phase of the bridge arms includes an upper bridge arm and a lower bridge arm, characterized in that, Both the upper bridge arm and the lower bridge arm include N three-switch sub-modules connected in series as described in any one of claims 1-5.

10. The three-phase modular multilevel converter according to claim 9, characterized in that, The content of the controller includes: Obtain the fundamental angular frequency of the three-phase bridge arm, the DC bus voltage input to the three-phase bridge arm, and the AC voltage output by the three-phase bridge arm, and obtain the energy storage voltage and capacitor voltage of the three-switch sub-module; Calculate according to the DC bus voltage and the AC voltage to obtain the AC modulation ratio of the three-phase bridge arm; calculate according to the energy storage voltage and the capacitor voltage to obtain the DC modulation ratio of the three-switch sub-module; Calculate according to the fundamental angular frequency and the AC modulation ratio to obtain a first modulation signal for controlling the connection or disconnection of the DC capacitor in the three-switch sub-module; and determine a second modulation signal for controlling the charging or discharging of the energy storage unit in the three-switch sub-module according to the DC modulation ratio; Calculate according to the first modulation signal and the capacitor voltage to obtain the output voltage between the first output port and the second output port in the three-switch sub-module.

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