Patent Publication Number: US-2023133950-A1

Title: Power component of three-level converter, three-level converter and wind turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202010758876.8, filed on Jul. 31, 2020, and entitled “POWER COMPONENT OF THREE-LEVEL CONVERTER AND THREE-LEVEL CONVERTER”, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to the technical field of converter, and in particular, to a power component of a three-level converter, a three-level converter and a wind turbine. 
     A wind power converter can realize the alternating current—direct current—alternating current conversion between a wind turbine and a power grid, and is one of the important core components of the wind turbine. A neutral point clamped (NPC) three-level converter is one type of wind power converter, which can achieve an increase in a direct current bus voltage by using insulate gate bipolar transistor (IGBT) devices with a low blocking voltage, thereby increasing an alternating current output voltage and expanding a system power level; and therefore, it has been widely used. 
     However, in the existing NPC three-level converter, the losses of different IGBT devices are different, resulting in uneven distribution of losses of the IGBT devices of the NPC three-level converter, thereby increasing the design difficulty of a heat sink. 
     SUMMARY 
     Embodiments of the present application provide a power component of a three-level converter, a three-level converter, and a wind turbine, which can balance losses of NPC bridge arm units of the three-level converter, such that the losses of IGBT devices of the three-level converter are evenly distributed. 
     In a first aspect, an embodiment of the present application provides a power component of a three-level converter including: 
     a first NPC bridge arm unit, the first NPC bridge arm unit including a plurality of first NPC bridge arms connected in parallel, a first end of the first NPC bridge arm unit forming a direct current positive electrode end, and a second end of the first NPC bridge arm unit forming a direct current neutral point end; 
     a second NPC bridge arm unit, the second NPC bridge arm unit including a plurality of second NPC bridge arms connected in parallel, a first end of the second NPC bridge arm unit being connected to the second end of the first NPC bridge arm unit, and a second end of the second NPC bridge arm unit forming a direct current negative electrode end; 
     a third NPC bridge arm unit, the third NPC bridge arm unit including a plurality of third NPC bridge arms connected in parallel, a first end of the third NPC bridge arm unit being connected to a third end of the first NPC bridge arm unit, a second end of the third NPC bridge arm unit being connected to a third end of the second NPC bridge arm unit, and a third end of the third NPC bridge arm unit forming an alternating current end, 
     wherein the number of the second NPC bridge arms is the same as the number of the first NPC bridge arms, and the number of the third NPC bridge arms is determined based on a ratio of a loss of the first NPC bridge arm to a loss of the third NPC bridge arm. 
     In a second aspect, an embodiment of the present application provides a three-level converter including the power component of the three-level converter as described above. 
     In a third aspect, an embodiment of the present application provides a wind turbine including the three-level converter as described above. 
     In the power component of the three-level converter, the three-level converter, and the wind turbine according to the embodiments of the present application, for the power component, the number of the first NPC bridge arms in the first NPC bridge arm unit is the same as the number of the second NPC bridge arms in the second NPC bridge arm unit, and the number of the third NPC bridge arms in the third NPC bridge arm unit can be determined based on the ratio of the loss of the first NPC bridge arm to the loss of the third NPC bridge arm. Therefore, the number of the first NPC bridge arms, the number of the second NPC bridge arms and the number of the third NPC bridge arms can be adjusted based on the ratio between the losses, and then the number of IGBT devices controlled by each of the third NPC bridge arms can be adjusted, so as to adjust the loss corresponding to the switching action current of the IGBT device in each of the third NPC bridge arms and balance the losses of the IGBT devices in the NPC bridge arms, so that the losses of the IGBT devices of the three-level converter are evenly distributed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In order to illustrate technical solutions of embodiments of the present application more clearly, the drawings required for the embodiments of the present application will be briefly described. For those skilled in the art, other drawings can also be obtained from these drawings without any inventive effort. 
         FIG.  1    is a schematic topological diagram of a power component of a three-level converter in the related art. 
         FIG.  2    is a schematic diagram of an example of a commutation loop of the power component shown in  FIG.  1   . 
         FIG.  3    is a schematic diagram of another example of a commutation loop of the power component shown in  FIG.  1   . 
         FIG.  4    is a schematic diagram of yet another example of a commutation loop of the power component shown in  FIG.  1   . 
         FIG.  5    is a schematic diagram of yet another example of a commutation loop of the power component shown in  FIG.  1   . 
         FIG.  6    is a schematic pulse diagram of the power component shown in  FIG.  1   . 
         FIG.  7    is a schematic topological diagram of an NPC bridge arm in the related art. 
         FIG.  8    is a schematic topological diagram of another NPC bridge arm in the related art. 
         FIG.  9    is a schematic topological diagram of yet another NPC bridge arm in the related art. 
         FIG.  10    is a schematic diagram of a circuit structure of a power component of a three-level converter according to an embodiment of the present application. 
         FIG.  11    is a schematic topological diagram of a power component of a three-level converter according to an embodiment of the present application. 
         FIG.  12    is a schematic structural diagram of a power component of a three-level converter according to an embodiment of the present application. 
         FIG.  13    is a schematic diagram of electrical connections between various NPC bridge arm units according to an embodiment of the present application. 
         FIG.  14    is a schematic diagram of a connection structure according to an embodiment of the present application. 
         FIG.  15    is a schematic structural diagram of a power component of a three-level converter according to another embodiment of the present application. 
         FIG.  16    is a schematic diagram of electrical connections between a capacitor bank and NPC bridge arm units according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     Features of various aspects and exemplary embodiments of the present application will be described in detail below. In order to make objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and specific embodiments. It should be understood that, specific embodiments described herein are only for the illustration of the present application, not for limiting the present application. For those skilled in the art, the present application may be implemented without some of these specific details. The following description of the embodiments is only for providing a better understanding of the present application by illustrating examples of the present application. 
     In the description of the present application, it is noted that, unless otherwise specified, the meaning of “a plurality” is two or more; the terms “upper”, “lower”, “left”, “right” and the like indicate orientations or positional relationships merely to facilitate and simplify description of the present application, and do not indicate or imply that the apparatuses or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present application. In addition, terms “first”, “second”, and the like are merely used for the purpose of description and should not be understood as indicating or implying relative importance. 
     In the description of the present application, it should be further noted that, unless otherwise expressly specified and limited, the terms “installed”, “connected” and “connection” should be understood in a broad sense, for example, they may refer to a fixed connection, and may also refer to a detachable connection, or an integral connection; it may refer to a direct connection, and may also refer to an indirect connection through an intermediate medium. For those with ordinary skills in the field, the specific meanings of the terms mentioned above in the present application can be understood in accordance with specific conditions. A wind power converter can realize the alternating current—direct current—alternating current conversion between the wind turbine and the power grid, and is one of the important core components of the wind turbine. A neutral point clamped (NPC) three-level converter is one type of wind power converter, which can achieve an increase in a direct current bus voltage by using insulate gate bipolar transistor (IGBT) devices with a low blocking voltage, thereby increasing an AC output voltage and expanding a system power level; and therefore, it has been widely used. 
       FIG.  1    shows a schematic topological diagram of a power component of a three-level converter in the related art. As shown in  FIG.  1   , a power component of a three-level converter in the related art may include IGBT devices Q 1 -Q 6 . Each IGBT device may include one IGBT and one freewheeling diode. A collector of the IGBT may form a collector of the IGBT device, an emitter of the IGBT may form an emitter of the IGBT device, and a gate of the IGBT may form a gate of the IGBT device. The collector of the IGBT may be connected to a cathode of the freewheeling diode, and the emitter of the IGBT may be connected to an anode of the freewheeling diode. 
     The IGBT devices Q 1 , Q 2 , Q 3  and Q 4  may be sequentially connected in series. Specifically, a collector of the IGBT device Q 1  may form a direct current positive electrode end of the power component of the three-level converter for connecting with a positive electrode DC+ of the direct current bus of the three-level converter. An emitter of the IGBT device Q 1  may be connected to a collector of the IGBT device Q 2  to form a connection point A. An emitter of the IGBT device Q 2  may be connected to a collector of the IGBT device Q 3 . An emitter of the IGBT device Q 3  may be connected to a collector of the IGBT device Q 4  to form a connection point B. An emitter of the IGBT device Q 4  may form a direct current negative electrode end of the power component of the three-level converter for connecting with a negative electrode DC− of the direct current bus of the three-level converter. 
     In some embodiments, the emitter of the IGBT device Q 2  and the collector of the IGBT device Q 3  may form an alternating current end AC of the power component of the three-level converter. 
     The IGBT devices Q 5  and Q 6  may be sequentially connected in series. Specifically, a collector of the IGBT device Q 5  may be connected to the collector of the GBT device Q 2 . An emitter of the IGBT device Q 5  may be connected to a collector of the IGBT device Q 6 . An emitter of the IGBT device Q 6  may be connected to the emitter of the IGBT device Q 3 . The emitter of the IGBT device Q 5  and the collector of the IGBT device Q 6  may form a direct current neutral point end of the power component of the three-level converter for connecting with a direct current bus neutral point NP of the three-level converter. The IGBTs in the IGBT devices Q 5  and Q 6  are always in an off state, so that the IGBT devices Q 5  and Q 6  are used as diodes in the power component of the three-level converter. 
     In some embodiments, the power component of the three-level converter may further include capacitors Cl and C 2 . One end of the capacitor Cl is connected to the collector of the IGBT device Q 1 , and the other end of the capacitor Cl is connected to the emitter of the IGBT device Q 5  and the collector of the IGBT device Q 6 . One end of the capacitor C 2  is connected to the emitter of the IGBT device Q 4 , and the other end of the capacitor C 2  is connected to the emitter of the IGBT device Q 5  and the collector of the IGBT device Q 6 . 
     With reference to  FIG.  1   , when the IGBT in the IGBT device Q 2  is in an on state, the IGBT device Q 5  clamps a potential of the connection point A to the same potential as NP; and when the IGBT in the IGBT device Q 3  is in an on state, the IGBT device Q 6  clamps a potential of the connection point B to the same potential as NP. 
     For the power component of the three-level converter shown in  FIG.  1   , the applicant has found several problems during use, which will be described below. 
     First, the applicant has carefully studied the principle of the commutation process of the power component of the three-level converter shown in  FIG.  1   . 
       FIG.  2    shows a schematic diagram of an example of a commutation loop of the power component shown in  FIG.  1   .  FIG.  3    shows a schematic diagram of another example of a commutation loop of the power component shown in  FIG.  1   .  FIG.  4    shows a schematic diagram of yet another example of a commutation loop of the power component shown in  FIG.  1   .  FIG.  5    shows a schematic diagram of yet another example of a commutation loop of the power component shown in  FIG.  1   . 
     As shown in  FIG.  2   , the current can flow into the power component of the three-level converter from the alternating current end AC. When the IGBT in the IGBT device Q 3  is in the on state, the current can flow along a first path  210 , that is, the current can flow through the IGBT in the IGBT device Q 3  and the freewheeling diode in the IGBT device Q 6  in sequence, and finally flows to the neutral point NP of the direct current bus. When the IGBT in the IGBT device Q 3  is in the off state, the current can flow along a second path  220 , that is, the current can flow through the freewheeling diode in the IGBT device Q 2  and the freewheeling diode in the IGBT device Q 1  in sequence, and finally flows to the positive electrode DC+ of the direct current bus. 
     When a gate interlock circuit for the IGBT in the IGBT device Q 1  and the IGBT in the IGBT device Q 3  is turned on, and the IGBT in the IGBT device Q 2  is in a normally-on state, the current switches between the first path  210  and the second path  220 , and at the same time, when the current in the first path  210  reduces, the current in the second path  220  increases. In the first path  210 , the current flows to the NP potential, and the output current is at zero level. In the second path  220 , the current flows to the DC+ potential, and the output current is at a positive level. 
     As shown in  FIG.  5   , the flow path of the current is similar to that of  FIG.  2   . In a seventh path  510 , the current flows to the NP potential, and the output current is at zero level. In an eighth path  520 , the current flows to the DC− potential, and the output current is at a negative level, which is not further detailed here. 
     As shown in  FIG.  3   , the current can flow out of the power component of the three-level converter from the alternating current end AC. When the IGBT in the IGBT device Q 1  is in an on state, the current can flow along a third path  310 , that is, the current can flow through the positive electrode DC+ of the direct current bus, the IGBT in the IGBT device Q 1 , the IGBT in the IGBT device Q 2  in sequence, and finally flows to the alternating current end AC. When the IGBT in the IGBT device Q 1  is in an off state, the current can flow along a fourth path  320 , that is, the current can flow through the freewheeling diode in the IGBT device Q 5  and the IGBT device Q 2  in sequence, and finally flows to the alternating current end AC. 
     When a gate interlock circuit for the IGBT in the IGBT device Q 1  and the IGBT in the IGBT device Q 3  is turned on, and the IGBT in the IGBT device Q 2  is in the normally-on state, the current switches between the third path  310  and the fourth path  320 , and at the same time, when the current in the fourth path  320  reduces, the current in the third path  310  increases. In the third path  310 , the current flows out from the DC+ potential, and the output current is at a positive level. In the fourth path  320 , the current flows out from the NP potential, and the output current is at zero level. 
     As shown in  FIG.  4   , the flow path of the current is similar to that of  FIG.  3   . In a fifth path  410 , the current flows out from the DC− potential, and the output current is at a negative level. In a sixth path  420 , the current flows out from the NP potential, and the output current is at zero level. 
     It can be seen that, the above commutation process generates a pulse width modulation (PWM) output switching pulse of the power component. The switching pulse may have three states including positive level, zero level and negative level. When the switching pulse is at the positive level, the IGBT in the IGBT device Q 2  is normally on. When the switching pulse is at the negative level, the IGBT in the IGBT device Q 3  is normally on. When the switching pulse is at the zero level, the IGBT in the IGBT device Q 2  or the IGBT in the IGBT device Q 3  is kept at the on state, and a commutation switching action occurs between the IGBT in the IGBT device Q 1  or the IGBT in the IGBT device Q 4  and the IGBT in the IGBT device Q 5  or the IGBT in the IGBT device Q 6 . 
     From the above commutation process, the characteristics of the commutation process of the power component can be concluded. In the grid-side inversion process of direct current DC/alternating current AC, when the power factor is close to 1 (the phases of the grid-side phase voltage and grid-side phase current are substantially coincident), at the moment when the switching pulse is at the positive level, the current flows out of the AC, and at the moment when the switching pulse is at the negative level, the current flows into the AC. As such, the IGBT device Q 2  or the IGBT device Q 3  is always in the on state during half of a duty cycle, the IGBT device Q 2  and the IGBT device Q 3  are subject to only the conduction loss of the IGBTs, and the IGBT device Q 1 , the IGBT device Q 4 , the IGBT device Q 5  and the IGBT device Q 6  are subject to the conduction loss and the switching loss. 
     Then, the applicant has carefully studied a pulse control principle of the power component of the three-level converter shown in  FIG.  1   . 
       FIG.  6    shows a schematic pulse diagram of the power component shown in  FIG.  1   . 
     As shown in  FIG.  6   , in half of a cycle of the modulation wave (the modulation wave and the grid-side phase voltage are the same in frequency and phase), the IGBT in the IGBT device Q 2  or the IGBT in the IGBT device Q 3  is always in an on state, and there is no PWM switching action. In contrast, the IGBT in the IGBT device Q 1  or the IGBT in the IGBT device Q 4  is in a high frequency PWM switching action state. Due to the high frequency switching action of the IGBT in the IGBT device Q 1  and the IGBT in the IGBT device Q 4 , the losses of the IGBT in the IGBT device Q 1  and the IGBT in the IGBT device Q 4  are significantly higher than the losses of the IGBT in the IGBT device Q 2  and the IGBT in the IGBT device Q 3 . Given that the freewheeling diode in IGBT device Q 5  and the freewheeling diode in IGBT device Q 6  perform the switching action synchronously, and that the freewheeling diode in IGBT device Q 2  and the freewheeling diode in IGBT device Q 3  do not perform the switching action, the losses of the freewheeling diode in the IGBT device Q 5  and the freewheeling diode in the IGBT device Q 6  are significantly higher than the losses of the freewheeling diode in the IGBT device Q 2  and the freewheeling diode in the IGBT device Q 3 . It can be seen that, the losses of the IGBT device Q 1 , the IGBT device Q 4 , the IGBT device Q 5  and the IGBT device Q 6  are significantly higher than the losses of the IGBT device Q 2  and the IGBT device Q 3 . 
     Finally, in the related art, a plurality of packaged NPC bridge arms are generally fit together to form a power component of a three-level converter. Therefore, the applicant has carefully studied a topological structure of the NPC bridge arm that can form the power component of the three-level converter shown in  FIG.  1   . 
       FIG.  7    shows a schematic topological diagram of an NPC bridge arm in the related art.  FIG.  8    shows a schematic topological diagram of another NPC bridge arm in the related art.  FIG.  9    shows a schematic topological diagram of yet another NPC bridge arm in the related art. 
     As shown in  FIG.  7   , the NPC bridge arm may be a dual-transistor EconoDUAL package module, including the capacitor Cl, the IGBT device Q 1  and the IGBT device Q 5  shown in  FIG.  1   . As shown in  FIG.  8   , the NPC bridge arm may be a dual-transistor EconoDUAL package module, including the capacitor C 2 , the IGBT device Q 4  and the IGBT device Q 6  shown in  FIG.  1   . As shown in  FIG.  9   , the NPC bridge arm may be a dual-transistor EconoDUAL package module, including the IGBT device Q 2  and the IGBT device Q 3  shown in  FIG.  1   . 
     Therefore, according to the above analysis of the pulse control principle and the analysis of each NPC bridge arm, it can be known that the losses of the IGBT devices are significantly unevenly distributed in the NPC bridge arms. The losses to which the NPC bridge arms shown in  FIG.  7    and  FIG.  8    are subject are high, and the losses to which the NPC bridge arm shown in  FIG.  9    is subject are low. 
     In addition, in the related art, when the current outputting capability of the power component of the three-level converter shown in  FIG.  1    cannot meet the requirements of the wind power converter, a plurality of the power components of the three-level converter shown in  FIG.  1    are typically directly connected in hard-parallel to increase the output current, such that the gap of losses between different types of NPC bridge arms become larger. Due to the uneven loss distribution between different types of NPC bridge arms, separate designs of heat dissipation power for different NPC bridge arms are needed, which complicates the design of the heat sink responsible for cooling the IGBT devices. In addition, direct hard-parallel connection of multiple power components of the three-level converter shown in  FIG.  1    causes a waste on the number of IGBT devices used, and increase the cost of the power component of the three-level converter. 
     In addition, by simulating the losses of the IGBT devices in the power component of the three-level converter shown in  FIG.  1   , the applicant has found that when the IGBT devices are of the same model, the ratio of the loss of the IGBT device Q 1 , the IGBT device Q 4 , the IGBT device Q 5  or the IGBT device Q 6  to the loss of the IGBT device Q 2  or the IGBT device Q 3  is fixed. For example, in an inversion state with a power factor of  1 , the ratio between losses may be  1 . 55 . 
     In order to solve the above problems, embodiments of the present application provide a power component of a three-level converter and a three-level converter, which can determine the number of different NPC bridge arms based on the ratio between losses found above, so that losses of IGBT devices of the three-level converter are evenly distributed. The power component of the three-level converter according to the embodiments of the present application will be described first. 
       FIG.  10    shows a schematic diagram of a circuit structure of a power component of a three-level converter according to an embodiment of the present application. 
     As shown in  FIG.  10   , the power component of the three-level converter may include a first NPC bridge arm unit  1010 , a second NPC bridge arm unit  1020  and a third NPC bridge arm unit  1030 . 
     The first NPC bridge arm unit  1010  may include a plurality of first NPC bridge arms  1011  connected in parallel. First connection ends of the plurality of first NPC bridge arms  1011  are connected in parallel to form a first end of the first NPC bridge arm unit  1010 . The first end of the first NPC bridge arm unit  1010  forms a direct current positive electrode end and for connecting with the positive DC+ of the direct current bus of the three-level converter. Second connection ends of the plurality of first NPC bridge arms  1011  are connected in parallel to form a second end of the first NPC bridge arm unit  1010 . The second end of the first NPC bridge arm unit  1010  forms a direct current neutral point end for connecting with the neutral point NP of the direct current bus of the three-level converter. Third connection ends of the plurality of first NPC bridge arms  1011  are connected in parallel to form a third end of the first NPC bridge arm unit  1010 . 
     In some embodiments of the present application, each of the first NPC bridge arms  1011  may include a first IGBT unit, a second IGBT unit and a first capacitor unit. 
     A first end of the first IGBT unit forms the first connection end of the first NPC bridge arm  1011 . A second end of the first IGBT unit is connected to a first end of the second IGBT unit. A second end of the second IGBT unit forms the second connection end of the first NPC bridge arm  1011 . The second end of the first IGBT unit and the first end of the second IGBT unit each form a third connection end of the first NPC bridge arm  1011 . A first end of the first capacitor unit is connected to the first connection end of the first NPC bridge arm  1011 , and a second end of the first capacitor unit is connected to the second connection end of the first NPC bridge arm  1011 . 
     The first IGBT unit may include one IGBT device or two or more IGBT devices. In the case where the first IGBT unit includes one IGBT device, the collector of the IGBT device forms the first end of the first IGBT unit, and the emitter of the IGBT forms the second end of the first IGBT unit. In the case where the first IGBT unit includes two or more IGBT devices, the two or more IGBT devices may be connected in series or in parallel. When the IGBT devices are connected in series, the collector of a first one of the IGBT devices forms the first end of the first IGBT unit, and the emitter of the last one of the IGBTs forms the second end of the first IGBT unit. When the IGBT devices are connected in parallel, the collectors of two or more IGBT devices are connected in parallel to form the first end of the first IGBT unit, and the emitters of the two or more IGBTs are connected in parallel to form the second end of the first IGBT unit. It should be noted that, in the case where the first IGBT unit includes two or more IGBT devices, the two or more IGBT devices may be connected in a serial-parallel manner, and the specific connection manner of the two or more IGBT devices is not specifically limited. 
     Specifically, each IGBT device may include one IGBT and one freewheeling diode. The collector of the IGBT may form the collector of the IGBT device, the emitter of the IGBT may form the emitter of the IGBT device, and the gate of the IGBT may form the gate of the IGBT device. The collector of the IGBT may be connected to a cathode of the freewheeling diode, and the emitter of the IGBT may be connected to an anode of the freewheeling diode. 
     The structure of the second IGBT unit is similar to that of the first IGBT unit, and the details of which are not repeated here. 
     The first capacitor unit may include one first capacitor or two or more first capacitors. In the case where the first capacitor unit includes one first capacitor, a first end of the first capacitor forms the first end of the first capacitor unit, and a second end of the first capacitor forms the second end of the first capacitor unit. In the case where the first capacitor unit includes two or more first capacitors, the two or more first capacitors are connected in series, a first end of a first one of the first capacitors forms the first end of the first capacitor unit, and a second end of a last one of the first capacitors forms the second end of the first capacitor unit. It should be noted that, in the case where the first capacitor unit includes two or more first capacitors, the two or more first capacitors may be connected in parallel or in a serial-parallel manner, and the specific connection manner of the two or more first capacitor units is not specifically limited. 
     The second NPC bridge arm unit  1020  may include a plurality of second NPC bridge arms  1021  connected in parallel. First connection ends of the plurality of second NPC bridge arms  1021  are connected in parallel to form a first end of the second NPC bridge arm unit  1020 . The first end of the second NPC bridge arm unit  1020  may form the direct current neutral point end. The first end of the second NPC bridge arm unit  1020  is connected to the second end of the first NPC bridge arm unit  1010 . Second connection ends of the plurality of second NPC bridge arms  1021  are connected in parallel to form a second end of the second NPC bridge arm unit  1020 . The second end of the second NPC bridge arm unit  1020  forms the direct current negative electrode end for connecting with the negative electrode DC− of the direct current bus of the three-level converter. Third connection ends of the plurality of second NPC bridge arms  1021  are connected in parallel to form a third end of the second NPC bridge arm unit  1020 . 
     In some embodiments of the present application, each of the second NPC bridge arms  1021  may include a third IGBT unit, a fourth IGBT unit and a second capacitor unit. 
     A first end of the third IGBT unit forms the first connection end of the second NPC bridge arm  1021 . A second end of the third IGBT unit is connected to a first end of the fourth IGBT unit. A second end of the fourth IGBT unit forms the second connection end of the second NPC bridge arm  1021 . The second end of the third IGBT unit and the first end of the fourth IGBT unit each form the third connection end of the second NPC bridge arm  1021 . A first end of the second capacitor unit is connected to the first connection end of the second NPC bridge arm  1021 , and a second end of the second capacitor unit is connected to the second connection end of the second NPC bridge arm  1021 . 
     The structures of the third IGBT unit and the fourth IGBT unit are each similar to the structure of the first IGBT unit, and the details of which are not repeated here. The structure of the second capacitor unit is similar to that of the first capacitor unit, and the details of which are not repeated here. 
     The third NPC bridge arm unit  1030  may include a plurality of third NPC bridge arms  1031  connected in parallel. First connection ends of the plurality of third NPC bridge arms  1031  are connected in parallel to form a first end of the third NPC bridge arm unit  1030 . The first end of the third NPC bridge arm unit  1030  is connected to the third end of the first NPC bridge arm unit  1010 . A second end of the third NPC bridge arm unit  1030  is connected to the third end of the second NPC bridge arm unit  1010 . Third connection ends of the plurality of third NPC bridge arms  1031  are connected in parallel to form the third end of the third NPC bridge arm unit  1030 . The third end of the third NPC bridge arm unit  1030  forms an alternating current end for connecting with the AC bus of the three-level converter. 
     In some embodiments of the present application, each of the third NPC bridge arms  1031  may include a fifth IGBT unit and a sixth IGBT unit. 
     A first end of the fifth IGBT unit forms the first connection end of the third NPC bridge arm  1031 . A second end of the fifth IGBT unit is connected to a first end of the sixth IGBT unit. A second end of the sixth IGBT unit forms a second connection end of the third NPC bridge arm  1031 . The second end of the fifth IGBT unit and the first end of the sixth IGBT unit each form the third connection end of the third NPC bridge arm  1031 . 
     The structures of the fifth IGBT unit and the sixth IGBT unit are each similar to the structure of the first IGBT unit, and the details of which will not be repeated here. 
     In some embodiments of the present application, each of the above-mentioned NPC bridge arms may be a package module of any package type among EconoDUAL package module, IHM package module,  62 mm package module and PrimePACK package module. The package types of the NPC bridge arms are the same. 
     In the case where the NPC bridge arm is an EconoDUAL package module, the first NPC bridge arm  1011  may be the NPC bridge arm shown in  FIG.  7   , the second NPC bridge arm  1021  may be the NPC bridge arm shown in  FIG.  8   , and the third NPC bridge arm  1031  may be the NPC bridge arm shown in  FIG.  9   . 
     With reference to  FIG.  10   , the number of the second NPC bridge arms  1021  may be the same as the number of the first NPC bridge arms  1011 . The number of the third NPC bridge arms  1031  may be determined based on the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031 , so as to adjust the numbers of the first NPC bridge arms  1011 , the second NPC bridge arms  1021  and the third NPC bridge arms  1031  based on the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031 . 
     Taking the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031  being  1 . 55  as an example, the number of the third NPC bridge arms  1031  may be made less than the number of the first NPC bridge arms  1011  to increase the number of IGBT devices controlled by each of the third NPC bridge arms  1031 , which further increases the loss corresponding to the switching action current of the IGBT devices in each of the third NPC bridge arms  1031 , and increases the losses of the IGBT devices in each of the third NPC bridge arm  1031 , thereby balancing losses of IGBT devices in the first NPC bridge arms  1011 , the second NPC bridge arms  1021  and the third NPC bridge arms  1031 . 
     In embodiments of the present application, the power component includes a first NPC bridge arm unit  1010 , a second NPC bridge arm unit  1020  and a third NPC bridge arm unit  1030 . The number of the first NPC bridge arms  1011  in the first NPC bridge arm unit  1010  is the same as the number of the second NPC bridge arms  1021  in the second NPC bridge arm unit  1020 . The number of the third NPC bridge arms  1031  in the third NPC bridge arm unit  1030  can be determined based on the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031 . Therefore, the numbers of the first NPC bridge arms  1011 , the second NPC bridge arms  1021  and the third NPC bridge arms  1031  can be adjusted based on the ratio between losses, and then the number of IGBT devices controlled by each of the third NPC bridge arms  1031  can be adjusted to adjust the loss corresponding to the switching action current of the IGBT device in each of the third NPC bridge arms  1031 , which balances the losses of the IGBT devices in the NPC bridge arms, so that the losses of the IGBT devices of the three-level converter are evenly distributed. 
     In some embodiments of the present application, since ratios of the loss of any one of the IGBT device Q 1 , the IGBT device Q 4 , the IGBT device Q 5  and the IGBT device Q 6  to the loss of any one of the IGBT device Q 2  and the IGBT device Q 3  are the same, a simulation test is performed on each IGBT device in the power component of the three-level converter shown in  FIG.  1    to obtain a loss simulation result, and then the ratios of the loss of any one of the IGBT device Q 1 , the IGBT device Q 4 , the IGBT device Q 5  and the IGBT device Q 6  to the loss of any one of the IGBT device Q 2  and the IGBT device Q 3  is calculated. 
     The simulation test can be realized with the online simulation software IPOSIM of Infineon Technologies, Germany. 
     In some embodiments of the present application, the number of the third NPC bridge arms  1031  may be a value obtained by rounding up a quotient of the number of the first NPC bridge arms  1011  divided by the ratio. 
     Specifically, the number of the first NPC bridge arm  1011  may be divided by the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031 . Then the quotient obtained by the division operation is rounded up, and the value obtained by the rounding up is the number of the third NPC bridge arms  1031 . Therefore, based on the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031  and the number of the first NPC bridge arms  1011 , the number of the third NPC bridge arms  1031  can be determined, so as to adjust the number of the third NPC bridge arms  1031 . 
     Still taking the ratio of the loss of the first NPC bridge arm  1011  to the loss of the third NPC bridge arm  1031  being 1.55 as an example, if the number of the first NPC bridge arms  1011  is 4, then the number of the second NPC bridge arms  1021  is 4, and the number of the third NPC bridge arms  1031  is 3; if the number of the first NPC bridge arms  1011  is 3, then the number of the second NPC bridge arms  1021  is 3, and the number of the third NPC bridge arms  1031  is 2; if the number of the first NPC bridge arms  1011  is 5, then the number of the second NPC bridge arms  1021  is 5, and the number of the third NPC bridge arms  1031  is 4. 
     An example is used below to describe the topological structure of the power component of the three-level converter according to the embodiments of the present application. 
       FIG.  11    shows a schematic topological diagram of a power component of a three-level converter according to an embodiment of the present application. 
     As shown in  FIG.  11   , the power component of the three-level converter may include a first NPC bridge arm unit, a second NPC bridge arm unit and a third NPC bridge arm unit. The first NPC bridge arm unit may include four first NPC bridge arms connected in parallel. The second NPC bridge arm unit may include four second NPC bridge arms connected in parallel. The third NPC bridge arm unit may include four third NPC bridge arms connected in parallel. 
     Each of the first NPC bridge arms may be the NPC bridge arm shown in  FIG.  7   , each of the second NPC bridge arms may be the NPC bridge arm shown in  FIG.  8   , each of the third NPC bridge arms may be respectively the NPC bridge arm shown in  FIG.  9   , and the details of which will not be repeated here. 
     Specifically, the collectors of the IGBT devices Q 1  in the four NPC bridge arms shown in  FIG.  7    are connected in parallel, the emitters of the IGBT devices Q 1  in the four NPC bridge arms shown in  FIG.  7    are connected in parallel, and the emitters of the IGBT devices Q 5  in the NPC bridge arms shown in  FIG.  7    are connected in parallel. The collectors of the IGBT devices Q 6  in the four NPC bridge arms shown in  FIG.  8    are connected in parallel, the emitters of the IGBT devices Q 6  in the four NPC bridge arms shown in  FIG.  8    are connected in parallel, and the emitters of the IGBT devices Q 4  in the four NPC bridge arms shown in  FIG.  8    are connected in parallel. The collectors of the IGBT devices Q 2  in the four NPC bridge arms shown in  FIG.  9    are connected in parallel, the emitters of the IGBT devices Q 2  in the four NPC bridge arms shown in  FIG.  9    are connected in parallel, and the emitters of the IGBT devices Q 3  in the four NPC bridge arms shown in  FIG.  9    are connected in parallel. 
     Therefore, the topological structure of the power component of the three-level converter shown in  FIG.  11    can increase the number of IGBT devices controlled by each of the third NPC bridge arms, thereby increasing the loss corresponding to the switching action current of the IGBT devices in each of the third NPC bridge arms, and increasing the losses of the IGBT devices in each of the third NPC bridge arms, thereby balancing the losses of the IGBT devices in the first NPC bridge arms, the second NPC bridge arms and the third NPC bridge arms. 
     In some embodiments of the present application, in order to improve the reliability of the IGBT device, the power component of the three-level converter may further include a heat dissipation plate. The heat dissipation plate may include a first heat dissipation region and a second heat dissipation region. A plurality of first NPC bridge arms and a plurality of second NPC bridge arms may be alternately arranged in the first heat dissipation region, and a plurality of third NPC bridge arms may be linearly arranged in the second heat dissipation region along the arrangement direction of the plurality of first NPC bridge arms and the plurality of second NPC bridge arms. 
     In some embodiments, when the plurality of first NPC bridge arms and the plurality of second NPC bridge arms may be arranged along the width direction of the heat dissipation plate, the plurality of third NPC bridge arms may also be arranged along the width direction of the heat dissipation plate. 
     In some other embodiments, when the plurality of first NPC bridge arms and the plurality of second NPC bridge arms may be arranged along the length direction of the heat dissipation plate, the plurality of third NPC bridge arms may also be arranged along the length direction of the heat dissipation plate. 
     Therefore, in embodiments of the present application, the IGBT devices in the first NPC bridge arm, the second NPC bridge arm and the third NPC bridge arm may be dissipated through one piece of heat dissipation plate. Since the plurality of first NPC bridge arms and the plurality of second NPC bridge arms can be alternately arranged, the heat distribution of the heat dissipation plate can be even, and the difficulty of designing the heat dissipation plate can be reduced. 
       FIG.  12    shows a schematic structural diagram of a power component of a three-level converter according to an embodiment of the present application. As shown in  FIG.  12   , the power component of the three-level converter may include a heat dissipation plate  310 , four first NPC bridge arms  320 , four second NPC bridge arms  330  and three third NPC bridge arms  340 . 
     An upper half portion of the heat dissipation plate  310  may be the first heat dissipation region, and a lower half portion of the heat dissipation plate  310  may be the second heat dissipation region. The four first NPC bridge arms  320  and the four second NPC bridge arms  330  may be alternately arranged in the first heat dissipation region of the heat dissipation plate  310  in sequence along the width direction of the heat dissipation plate  310 , and the three third NPC bridge arms  340  may be linearly arranged in the second heat dissipation region of the heat dissipation plate  310  in sequence along the width direction of the heat dissipation plate  310 . Four corners of a packaging casing  321  of each of the first NPC bridge arms  320  are detachably connected to the heat dissipation plate  310  by bolts, so that the packaging casing  321  of the first NPC bridge arm  320  can be mounted on the heat dissipation plate  310 . Four corners of a packaging casing  331  of each of the second NPC bridge arms  330  are detachably connected to the heat dissipation plate  310  by bolts, so that the packaging casing  331  of the second NPC bridge arm  330  can be mounted on the heat dissipation plate  310 . Four corners of a packaging casing  341  of each of the third NPC bridge arms  340  are detachably connected to the heat dissipation plate  310  by bolts, so that the packaging casing  341  of the third NPC bridge arm  340  can be mounted on the heat dissipation plate  310 . 
     In some embodiments of the present application, the third end of the first NPC bridge arm unit may include the third connection ends of the plurality of first NPC bridge arms, and the third connection ends of the plurality of first NPC bridge arms are connected in parallel. The third end of the second NPC bridge arm unit may include third connection ends of the plurality of second NPC bridge arms, and the third connection ends of the plurality of second NPC bridge arms are connected in parallel. The first end of the third NPC bridge arm unit may include the first connection ends of the plurality of third NPC bridge arms, and the first connection ends of the plurality of third NPC bridge arms are connected in parallel. The second end of the third NPC bridge arm unit may include the second connection ends of the plurality of third NPC bridge arms, and the second connection ends of the plurality of third NPC bridge arms are connected in parallel. 
     Therefore, in the power component of the three-level converter shown in  FIG.  12   , the losses of the first NPC bridge arm  320 , the second NPC bridge arm  330  and the third NPC bridge arm  340  are similar, so that the heat dissipation plate  310  can be designed in a balanced way. 
       FIG.  13    shows a schematic diagram of electrical connections between various NPC bridge arm units according to an embodiment of the present application. 
     As shown in  FIG.  13   , four first NPC bridge arms (bridge arm I)  320  and four second NPC bridge arms (bridge arm II)  330  are alternately arranged. Three third NPC bridge arms (bridge arm III)  340  are arranged in parallel to four first NPC bridge arms  320  and four second NPC bridge arms  330 . Three third NPC bridge arms  340  are positioned below the four first NPC bridge arms  320  and the four second NPC bridge arms  330 . 
     The first connection end of the first NPC bridge arm  320  may be a direct current positive electrode end  322 . The second connection end of the first NPC bridge arm  320  may be a first direct current neutral point end  323 . The first NPC bridge arm  320  may include two third connection ends. Each of the third connection ends of the first NPC bridge arm  320  may be a first bridge arm connection end  324 . 
     In the case where the first NPC bridge arm  320  is the NPC bridge arm shown in  FIG.  7   , the collector of the IGBT device Q 1  shown in  FIG.  7    may form the direct current positive electrode end  322 . The emitter of the IGBT device Q 1  shown in  FIG.  7    may form one first bridge arm connection end  324 . The collector of the IGBT device Q 5  shown in  FIG.  7    may form another first bridge arm connection end  324 . The emitter of the IGBT device Q 5  shown in  FIG.  7    may form the first direct current neutral point end  323 . 
     The first connection end of the second NPC bridge arm  330  may be a second direct current neutral point end  332 . The second connection end of the second NPC bridge arm  330  may be the direct current negative electrode end  333 . The second NPC bridge arm  330  may include two third connection ends. Each of the third connection ends of the second NPC bridge arm  330  may be two second bridge arm connection ends  334  respectively. 
     In the case where the second NPC bridge arm  330  is the NPC bridge arm shown in  FIG.  8   , the collector of the IGBT device Q 6  shown in  FIG.  8    may form the second direct current neutral point end  332 . The emitter of the IGBT device Q 6  shown in  FIG.  8    may form one second bridge arm connection end  334 . The collector of the IGBT device Q 4  shown in  FIG.  8    may form another second bridge arm connection end  334 . The emitter of the IGBT device Q 4  shown in  FIG.  8    may form a direct current negative electrode end  333 . 
     The first connection end of the third NPC bridge arm  340  may be the third bridge arm connection end  342 . The second connection end of the third NPC bridge arm  340  may be the fourth bridge arm connection end  343 . The third NPC bridge arm  340  may include two third connection ends. Each of the third connection ends of the third NPC bridge arm  340  may be an alternating current end  344 . 
     In the case where the third NPC bridge arm  340  is the NPC bridge arm shown in  FIG.  9   , the collector of the IGBT device Q 2  shown in  FIG.  9    may form the third bridge arm connection end  342 . The emitter of the IGBT device Q 2  shown in  FIG.  9    may form one alternating current end  344 . The collector of the IGBT device Q 3  shown in  FIG.  9    may form another alternating current end  344 . The emitter of the IGBT device Q 3  shown in  FIG.  9    may form the fourth bridge arm connection end  343 . 
     Specifically, each of the first bridge arm connection ends  324  may be respectively connected in parallel with each of the third bridge arm connection ends  342 , and each of the second bridge arm connection ends  334  may be respectively connected in parallel with each of the fourth bridge arm connection ends  343 . 
     Therefore, in the embodiments of the present application, it can be realized that the four-element parallel connection structure in which the first NPC bridge arms  320  and the second NPC bridge arms  330  are connected is connected to the three-element parallel connection structure in which the third NPC bridge arms  340  are connected. 
     In the embodiments of the present application, each of the third bridge arm connection ends  342  may be respectively connected to a bus connection neutral point of two adjacent first bridge arm connection ends  324 . Each of the fourth bridge arm connection ends  343  may be respectively connected to the bus connection neutral point of the adjacent two second bridge arm connection ends  334 , such that each of the third NPC bridge arms  340  is at the neutral point position, thereby ensuring a desired current-sharing effect of the three-element parallel connection structure. 
     In some embodiments of the present application, the power component of the three-level converter may further include a first connection busbar, a second connection busbar and an insulation structure. The first connection busbar may connect the third connection ends of the plurality of first NPC bridge arms with the first connection ends of the plurality of third NPC bridge arms. The second connection busbar may connect the third connection ends of the plurality of second NPC bridge arms with the second connection ends of the plurality of third NPC bridge arms. The insulation structure may be arranged between the first connection busbar and the second connection busbar, so that the first connection busbar and the second connection busbar are arranged in insulation, thereby making full use of the space and reducing the volume of the power component of the three-level converter. 
     Specifically, the first connection busbar may be a metal conductive structure, and is connected to the third connection ends of the plurality of first NPC bridge arms and the first connection ends of the plurality of third NPC bridge arms respectively, so that the third connection ends of the plurality of first NPC bridge arms are connected in parallel with the first connection ends of the plurality of third NPC bridge arms. The second connection busbar may be a metal conductive structure, and is connected to the third connection ends of the plurality of second NPC bridge arms and the second connection ends of the plurality of third NPC bridge arms respectively, so that the third connection ends of the plurality of second NPC bridge arms are connected in parallel with the second connection ends of the plurality of third NPC bridge arms. 
     The metal conductive structure may be a metal sheet or a copper bar, or the metal conductive structure may be other metals with conductive function, and the specific metal type of the metal conductive structure is not limited in the embodiments of the present application. 
       FIG.  14    shows a schematic diagram of a connection structure according to an embodiment of the present application. As shown in  FIG.  14   , the first connection busbar  360  and the second connection busbar  370  may be metal sheets, respectively. The first connection busbar  360  is provided with four first concave portions  361 , four first convex portions  362 , three second concave portions  363  and three second convex portions  364 . The first concave portions  361  and the first convex portions  361  are alternately arranged on one side of the first connection busbar  360  along the length direction of the first connection busbar  360 . The second concave portions  363  and the second convex portions  364  are alternately arranged on the other side of the first connection busbar  360  along the length direction of the first connection busbar  360 . The second connection busbar  370  is provided with four third concave portions  371 , four third convex portions  372 , three fourth concave portions  373  and three fourth convex portions  374 . The third concave portions  371  and the third convex portions  372  are alternately arranged on one side of the second connection busbar  370  along the length direction of the second connection busbar  370 . The fourth concave portions  373  and the fourth convex portions  374  are alternately arranged on the other side of the second connection busbar  370  along the length direction of the second connection busbar  370 . The third concave portions  371  and the third convex portions  372  are arranged on the same side as the first concave portions  361  and the first convex portions  361 . The fourth concave portions  373  and the fourth convex portions  374  are arranged on the same side as the second concave portions  363  and the second convex portions  364 . 
     With reference to  FIG.  12   , each of the first convex portions  362  of the first connection busbar  360  may be connected with all of the third connection ends of one first NPC bridge arm  320  shown in  FIG.  12    by bolts respectively. The bolts penetrate through the third concave portions  371  of the second connection busbar  370  respectively. Each of the second convex portions  364  of the first connection busbar  360  may be connected with all of the first connection ends of one third NPC bridge arm  340  shown in  FIG.  12    by bolts respectively. The bolts penetrate through the fourth concave portions  373  of the second connection busbar  370  respectively. Each of the third convex portions  372  of the second connection busbar  370  may be connected with all of the third connection ends of one second NPC bridge arm  330  shown in  FIG.  12    by bolts respectively. The bolts penetrate through the first concave portions  361  of the first connection busbar  360  respectively. Each of the fourth convex portions  374  of the second connection busbar  370  may be connected with all of the second connection ends of one third NPC bridge arm  340  shown in  FIG.  12    by bolts respectively. The bolts penetrate through the second concave portions  363  of the first connection busbar  360  respectively. 
     In some embodiments of the present application, with reference to  FIG.  13   , the third end of the third NPC bridge arm unit may further include third connection ends of a plurality of third NPC bridge arms, and the third connection ends of the plurality of third NPC bridge arms are connected in parallel. 
     In some embodiments of the present application, the power component of the three-level converter may further include an alternating current busbar. The alternating current busbar may be a metal conductive structure. The alternating current busbar may be connected with the third connection ends of the plurality of third NPC bridge arms respectively. 
     With reference to  FIG.  12   , the alternating current busbar  350  may be a copper busbar. An obround through via  351  may be formed on the alternating current busbar  350  to ensure the current-sharing effect when the third connection ends are connected in parallel. 
     The alternating current busbar  350  may further include two fifth concave portions  352  and three fifth convex portions  353 . The fifth concave portions  352  and the fifth convex portions  353  are alternately arranged. Each of the fifth convex portions  353  is connected to all of the third connection ends of one third NPC bridge arm  340  by bolts respectively. 
     The alternating current busbar  350  may further include an alternating current end connection hole  354 . The alternating current end connection hole  354  may be configured to be connected with the alternating current busbar. 
     In some embodiments of the present application, the power component of the three-level converter may further include a direct current busbar. The direct current busbar may be connected to the first heat dissipation region of the heat dissipation plate. The direct current busbar may be positioned on a side of the first heat dissipation region away from the second heat dissipation region. The direct current busbar may include a positive electrode of the direct current busbar, a neutral point of the direct current busbar, and a negative electrode of the direct current busbar. The positive electrode of the direct current busbar, the neutral point of the direct current busbar and the negative electrode of the direct current busbar may be each formed of a metal conductive structure, such as a metal sheet or a copper bar. The positive electrode of the direct current busbar, the neutral point of the direct current busbar and the negative electrode of the direct current busbar may be stacked. For insulation between the positive electrode of the direct current busbar, the neutral point of the direct current busbar and the negative electrode of the direct current busbar, an insulating member may be arranged between the positive electrode of the direct current busbar and the neutral point of the direct current busbar, and an insulating member may be arranged between the neutral point of the direct current busbar and the negative electrode of the direct current busbar. 
     In some embodiments of the present application, the first end of the first NPC bridge arm unit may include the first connection ends of the plurality of first NPC bridge arms. The second end of the first NPC bridge arm unit may include the second connection ends of the plurality of first NPC bridge arms. The first end of the second NPC bridge arm unit may include the first connection ends of the plurality of second NPC bridge arms. The second end of the second NPC bridge arm unit may include the second connection ends of the plurality of second NPC bridge arms. The first connection ends of the plurality of first NPC bridge arms may be each connected to the positive electrode of the direct current bus. The second connection ends of the plurality of first NPC bridge arms and the first connection ends of the plurality of second NPC bridge arms may be each connected to the neutral point of the direct current busbar. The second connection ends of the plurality of second NPC bridge arms may be each connected to the negative electrode of the direct current busbar. 
     In some embodiments, the direct current busbar may be directly connected to each of the first NPC bridge arms and each of the second NPC bridge arms. 
     In some other embodiments, the direct current busbar may be connected to each of the first NPC bridge arms and each of the second NPC bridge arms by a capacitor bank, and at the same time, the direct current busbar may play a role of fixing each of the capacitors in the capacitor bank. 
     Optionally, the power component of the three-level converter may further include a capacitor bank. The capacitor bank may be arranged on the direct current busbar. The capacitor bank may include first capacitor units and second capacitor units. A first end of each of the first capacitor units may be connected to the positive electrode of the direct current busbar and a corresponding first connection end of the first connection ends of the plurality of first NPC bridge arms. A second end of each of the first capacitor units may be connected to the neutral point of the direct current busbar and a corresponding second connection end of the second connection ends of the plurality of first NPC bridge arms. A first end of each of the second capacitor units may be connected to the neutral point of the direct current busbar and a corresponding first connection end of the first connection ends of the plurality of second NPC bridge arms. A second end of each of the second capacitor units may be connected to the negative electrode of the direct current busbar and a corresponding second connection end of the second connection ends of the plurality of second NPC bridge arms. 
     Specifically, the first capacitor unit may include a plurality of first capacitors. The first end of each of the first capacitors may be connected in parallel to form the first end of the first capacitor unit. The second end of each of the first capacitors may be connected in parallel to form the second end of the first capacitor unit. In some embodiments, a first end of each of the first capacitors may be connected to the positive electrode of the direct current busbar, and a second end of each of the first capacitors may be connected to the neutral point of the direct current busbar. 
     The second capacitor unit may include a plurality of second capacitors. A first end of each of the second capacitors may be connected in parallel to form the first end of the second capacitor unit. A second end of each of the second capacitors may be connected in parallel to form the second end of the second capacitor unit. 
     In some embodiments, the first end of each of the second capacitors may be connected to the neutral point of the direct current busbar. The second end of each of the second capacitors may be connected to the negative electrode of the direct current busbar. 
       FIG.  15    shows a schematic structural diagram of a power component of a three-level converter according to another embodiment of the present application. As shown in  FIG.  15   , the power component of the three-level converter may further include a direct current busbar  380 . The direct current busbar  380  may be connected to the first heat dissipation region of the heat dissipation plate  310 . The direct current busbar  380  may be positioned on a side of the first heat dissipation region away from the second heat dissipation region. 
     The direct current busbar  380  may be provided with four first capacitors  381  and four second capacitors  382 . Since the number of the first capacitors  381  is the same as the number of the first NPC bridge arms  320 , and the number of the second capacitors  382  is the same as the number of the second NPC bridge arms  330 , so that a connection structure between the capacitors and the corresponding NPC bridge arms can be simplified. 
     In some embodiments, one first capacitor  381  and one second capacitor  382  are arranged along the vertical direction of the heat dissipation plate  310  and correspond to one first NPC bridge arm  320  and one second NPC bridge arm  330  adjacent thereto. 
       FIG.  16    shows a schematic diagram of electrical connections between the capacitor bank and the NPC bridge arm unit according to an embodiment of the present application. 
     As shown in  FIG.  16   , the first end of each of the first capacitors  381  may be connected to the direct current positive electrode end  322  of the adjacent first NPC bridge arm  320 . The second end of each of the first capacitors  381  may be connected to the first direct current neutral point end  323  of the adjacent first NPC bridge arm  320 . The first end of each of the second capacitors  382  may be connected to the second direct current neutral point end  332  of the adjacent second NPC bridge arm  330 . The second end of each of the two capacitors  382  may be connected to the direct current negative electrode end  333  of the adjacent second NPC bridge arm  330 . 
     Therefore, in embodiments of the present application, a symmetrical structural relationship of four groups of NPC bridge arms and direct current capacitors can be formed, and each of the direct current capacitors provides direct current support and ripple current to the corresponding NPC bridge arm respectively. When the IGBT device in the NPC bridge arm performs switching action and commutation, the direct current capacitor is charged or discharged synchronously. The charging and discharging paths of the direct current capacitor are shown by the arrows in  FIG.  16    above. Current paths are opposite and substantially coincide, which can offset stray inductance on the current path of the direct current capacitor, and reduce the voltage stress in the commutation process, so as to significantly improve the current-sharing of the part with direct current parallel connection. 
     With reference to  FIG.  15   , the first end of each of the first capacitors  381  may be connected to the first connection end of the adjacent first NPC bridge arm  320  by a metal conductive structure. The second end of each of the first capacitors  381  may be connected to the second connection end of the adjacent first NPC bridge arm  320  by a metal conductive structure. The first end of each of the second capacitors  382  may be connected to the first connection end of the adjacent second NPC bridge arm  330 . The second end of each of the second capacitors  382  may be connected to the second connection end of the adjacent second NPC bridge arm  330  by a metal conductive structure. 
     In some embodiments, the metal conductive structure may be a metal sheet or a copper bar. 
     In some embodiments of the present application, each of the first NPC bridge arms may include two or more IGBT devices connected in series. Each of the first NPC bridge arms is further provided with a gate connection end with each of the IGBT devices, respectively. The second NPC bridge arm may include two or more IGBT devices connected in series. Each of the second NPC bridge arms is further provided with a gate connection end with each of the IGBT devices, respectively. 
     In some embodiments of the present application, the power component of the three-level converter may further include a first driving board. The first driving board may be arranged on the first NPC bridge arm unit and the second NPC bridge arm unit. A first signal output end of the first driving board is connected with the gate of the first IGBT device. A second signal output end of the first driving board is connected with the gate of the second IGBT device. 
     Specifically, the first driving board may include a plurality of first signal output ends. One first signal output end corresponds to a gate of one IGBT device in one first NPC bridge arm. Each of the first signal output ends may be connected to the gate of the IGBT device through the gate connection end of the corresponding IGBT device. The first driving board may include a plurality of second signal output ends. One second signal output end corresponds to the gate of one IGBT device in one second NPC bridge arm. Each of the second signal output ends may be connected to the gate of the IGBT device through the gate connection end of the corresponding IGBT device. 
     With reference to  FIG.  15   , the power component of the three-level converter may further include a first driving board  391 . The first driving board  391  may be arranged on the first NPC bridge arms  320  and the second NPC bridge arms  330 . 
     In some embodiments of the present application, each of the third NPC bridge arms may include two or more IGBT devices connected in series. Each of the first NPC bridge arms is further provided with a gate connection end with each of the IGBT devices, respectively. 
     In some embodiments of the present application, the power component of the three-level converter may further include a second driving board. The second driving board may be arranged on the third NPC bridge arm unit. A signal output end of the second driving board is connected to the gates of the IGBT devices in the third NPC bridge arm. 
     Specifically, the second driving board may include a plurality of third signal output ends. One third signal output end corresponds to the gate of one IGBT device in one third NPC bridge arm. Each of the third signal output ends may be connected to the gate of the IGBT device through the gate connection end of the corresponding IGBT device. 
     With reference to  FIG.  15   , the power component of the three-level converter may further include a second driving board  392 . The second driving board  392  may be arranged on the third NPC bridge arms  340 . 
     To sum up, the power component of the three-level converter according to the embodiments of the present application achieves a balanced distribution of losses of the NPC bridge arms with an appropriate structural layout and an appropriate device configuration, and at the same time achieves a desired current-sharing effect and reduces the difficulty of designing the heat dissipation plate. In addition, the power component of the three-level converter can reduce the number of IGBTs used, thereby reducing the cost of the power component of the three-level converter. 
     The embodiments of the present application further provide a three-level converter. The three-level converter may include the power component of the three-level converter according to the embodiments of the present application. 
     In the embodiments of the present application, the power component of the three-level converter includes the first NPC bridge arm unit, the second NPC bridge arm unit and the third NPC bridge arm unit. The number of the first NPC bridge arms in the first NPC bridge arm unit is the same as the number of the second NPC bridge arms in the second NPC bridge arm unit, and the number of the third NPC bridge arms in the third NPC bridge arm unit can be determined based on the ratio of the loss of the first NPC bridge arm to the loss of the third NPC bridge arm. Therefore, the number of the first NPC bridge arms, the number of the second NPC bridge arms and the number of the third NPC bridge arms can be adjusted based on the ratio between the losses, and then the number of IGBT devices controlled by each of the third NPC bridge arms can be adjusted, so as to adjust the loss corresponding to the switching action current of the IGBT device in each of the third NPC bridge arms and balance the losses of the IGBT devices in the NPC bridge arms, so that the losses of the IGBT devices of the three-level converter are evenly distributed. 
     In some embodiments of the present application, the three-level converter may be any one of a wind power converter, a photovoltaic converter, an energy storage converter, and the like. 
     The embodiments of the present application further provide a wind turbine. The wind turbine may include the three-level converter according to the embodiments of the present application. 
     In some embodiments of the present application, the wind turbine may be any one of a direct-drive wind turbine, a doubly-fed wind turbine, a semi-direct-drive wind turbine, and the like. 
     It should be noted that the above are only specific implementations of the present application, those skilled in the art can clearly understand that the specific working processes of the above-described systems, modules and units can be referred to the corresponding processes in the foregoing method embodiments, for the convenience and brevity of the description, the details of which are not repeated here. It should be understood that the protection scope of the present application is not limited to the specific embodiments, any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should all fall within the protection scope of the present application.