A bridge arm flying span type modular multilevel converter topology and control method thereof

Abstract

The present invention discloses a bridge-arm flying-type modular multilevel converter topology and its control method. The proposed bridge-arm flying-type modular multilevel converter topology is composed of a three-phase AC system and a DC-side voltage stabilizing circuit. After the three-phase AC system is connected in parallel with the DC-side voltage stabilizing circuit, a DC port is obtained, and the DC voltage output by the DC port is V dc , where the three-phase AC system has a three-phase AC circuit structure. Each phase of the AC circuit is composed of an upper switching circuit, a lower switching circuit, a flying bridge arm, an AC-side filtering inductor, and an AC-side power supply. The bridge-arm flying-type modular multilevel converter topology and its control method of the present invention can simultaneously provide an AC port and a DC port for an AC-DC hybrid distribution network, and realize voltage conversion and power transfer between the AC port and the DC port of the converter, reducing the use of sub-modules, switching devices, and passive components, thereby further reducing the number of driving and sampling modules.

Description

Technical Field

[0001] The present invention relates to the technical field of power transformation, and in particular to a bridge arm flying span type modular multi-level converter topology and a control method thereof. Background Art

[0002] In order to meet the needs of renewable energy grid connection and power supply to DC loads, DC grid has received extensive attention and application, and cooperates with the existing AC grid to form an AC / DC hybrid distribution network. Therefore, it is necessary to introduce power electronic devices to provide an AC port and a DC port. Modular multilevel converter (MMC) is widely used in AC / DC hybrid distribution networks because of its advantages such as voltage-adjustable AC and DC ports, highly modular structure, high portability, and good harmonic characteristics.

[0003] However, the MMC topology uses a large number of half-bridge submodule circuits, which consumes a large number of switching devices and passive components, resulting in a high cost and large size of the MMC. At the same time, a large number of submodule circuits require a large number of driving and sampling modules, which further increases the cost of the MMC and increases the difficulty of designing the MMC control system. Therefore, a bridge arm switching converter (alternate arm converter, AAC) is proposed, which can reduce the number of submodules in the bridge arm and reduce the use of passive components. However, AAC needs to use a full-bridge circuit as a submodule circuit, and each bridge arm needs to add an additional set of switching circuits, resulting in the number of switching devices cannot be significantly reduced. At the same time, AAC can only work under a fixed modulation ratio condition, and the output DC voltage level is low, which seriously limits the performance and application of AAC. On this basis, patent CN110752763B proposes a modular multi-level converter topology and its modulation method. By improving the control strategy, this topology can replace the full-bridge sub-module in the AAC with a half-bridge sub-module, thereby further reducing the number of switching devices. At the same time, it has an adjustable modulation ratio and DC side voltage level, thereby reducing the cost of the converter and improving the performance of the converter.

[0004] The existing improved modular multi-level converter topology has made a great contribution to reducing the cost and volume of the converter, but these topologies are all based on three-phase six-bridge arms, and still use a large number of switching devices and passive components, which cannot significantly reduce the cost and volume of the converter, making the application of the converter difficult to popularize. Therefore, there is an urgent need for a modular multi-level converter topology that can not only realize the flexible conversion of voltage and flexible adjustment of power between the AC port and the DC port, but also greatly reduce the number of switching devices and passive components of the converter, thereby significantly reducing the cost and volume of the converter. At the same time, in order to cope with possible faults in the AC / DC hybrid distribution network, the topological structure of the converter needs to have a good fault ride-through capability, thereby improving the reliability of the converter and the AC / DC hybrid distribution network. Summary of the invention

[0005] The object of the present invention is to provide a bridge arm flying span type modular multi-level converter topology and a control method thereof, which can provide an AC port and a DC port at the same time, and is used in an AC / DC hybrid distribution network, and realizes voltage conversion and power transmission between the AC port and the DC port of the converter, reduces the use of submodules, switch devices and passive components, and further reduces the number of driving and sampling modules, thereby reducing the cost and volume of the converter, and improving the efficiency and power density of the converter. At the same time, the bridge arm flying span type modular multi-level converter topology has good fault ride-through capability, which can improve the reliability of the converter.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A bridge arm flying span modular multilevel converter topology is proposed. The bridge arm flying span modular multilevel converter topology is composed of a three-phase AC system and a DC side voltage stabilizing circuit. The three-phase AC system and the DC side voltage stabilizing circuit are connected in parallel to obtain a DC port. The DC port outputs a DC voltage of V dc The three-phase AC system is a three-phase AC circuit structure, and each phase AC circuit is composed of an upper switch circuit, a lower switch circuit, a flying bridge arm, an AC side filter inductor and an AC side power supply, wherein x = a, b, c phases.

[0008] The upper switch circuit is composed of a first switch device, a second switch device and an inductor connected in series, wherein x=a, b, c phase.

[0009] The lower switch circuit is composed of a third switch device, a fourth switch device and an inductor connected in series, and x=a, b, c phase.

[0010] The upper switch circuit and the lower switch circuit are connected in series, the connection point between the upper switch circuit and the lower switch circuit is connected to one end of the AC side filter inductor, and the other end of the AC side filter inductor is connected to the AC side power supply.

[0011] The first switch device is composed of at least one fully-controlled switch tube, and the second switch device is composed of at least one fully-controlled switch tube series structure. The fully-controlled switch tube series structure is composed of two fully-controlled switch tubes connected in reverse series. The two fully-controlled switch tubes connected in reverse series in the fully-controlled switch tube series structure have the same driving signal and are turned on and off at the same time.

[0012] The fourth switch device is composed of at least one fully-controlled switch tube, and the third switch device is composed of at least one fully-controlled switch tube in series.

[0013] Furthermore, the first switch device is composed of a fully-controlled switch tube, and the second switch device is composed of two fully-controlled switch tubes connected in reverse series. The two fully-controlled switch tubes connected in reverse series on the second switch device have the same driving signal and are turned on and off at the same time.

[0014] The collector of the first switching device is connected to the positive electrode of the DC port, the emitter of the first switching device is connected to the emitter of the fully-controlled switching tube located above in the second switching device, the collectors of the two fully-controlled switching tubes of the second switching device are connected, and the emitter of the fully-controlled switching tube located below in the second switching device is connected to the first inductor.

[0015] The fourth switch device is composed of a fully-controlled switch tube, and the third switch device is composed of two fully-controlled switch tubes connected in reverse series. The two fully-controlled switch tubes connected in reverse series in the third switch device have the same driving signal and are turned on and off at the same time.

[0016] The emitter of the upper fully-controlled switch tube in the third switch device is connected to the second inductor, the collectors of the two fully-controlled switch tubes on the third switch device are connected, and the emitter of the lower fully-controlled switch tube in the third switch device is connected to the collector of the fourth switch device.

[0017] The emitter of the fourth switch device is connected to the negative electrode of the DC port.

[0018] Furthermore, the flying bridge arm is composed of N cascaded full-bridge submodules, N=1, 2, 3..., and the input end of the N cascaded full-bridge submodule circuit is used as the input end F of the flying bridge arm. x1 , where x = a, b, c phase.

[0019] The output end of the N cascaded full-bridge sub-module circuit is used as the output end F of the flying bridge arm. x2 , where x = a, b, c phase.

[0020] The input end F of the flying bridge arm x1 The output terminal F of the bridge arm is connected to the connection point of the first switch device and the second switch device. x2Connected to a connection point between the third switching device and the fourth switching device.

[0021] Furthermore, the DC side voltage stabilizing circuit is composed of a first voltage stabilizing capacitor and a second voltage stabilizing capacitor, the positive electrode of the first voltage stabilizing capacitor is connected to the positive electrode of the DC port, the negative electrode of the first voltage stabilizing capacitor is connected to the positive electrode of the second voltage stabilizing capacitor, and the negative electrode of the second voltage stabilizing capacitor is connected to the negative electrode of the DC port.

[0022] Furthermore, the DC port is connected in series with a filter inductor for voltage stabilization and filtering.

[0023] Furthermore, the inductors in the upper switch circuit and the lower switch circuit and the AC side filter inductor are integrated into one inductor.

[0024] A control method for a bridge arm flying span modular multilevel converter topology, the control method is as follows:

[0025] When the x-phase AC voltage v is detected x When the value changes from negative to zero, the timing starts, and the delay is (θ / 2π)*T s After T s / 2, the first switch device and the third switch device are turned off, and the second switch device and the fourth switch device are triggered to turn on at the same time, where θ is the turn-on delay angle, T s is the AC voltage period at the AC port of the inverter.

[0026] When the x-phase AC voltage v is detected x When the positive value changes to zero, the timing starts, and the delay is (θ / 2π)*T s After T s After a turn-on time of / 2, the second switch device and the fourth switch device are turned off, and the first switch device and the third switch device are triggered to turn on.

[0027] When the first switch device and the third switch device are turned on, the input end of the flying bridge arm is connected to the positive electrode of the DC port through the first switch device, and the output end of the flying bridge arm is connected to the AC port of the converter through the third switch device. The voltage modulated by the flying bridge arm is as follows:

[0028]

[0029] When the second switch device and the fourth switch device are turned on, the input end of the flying bridge arm is connected to the AC port of the converter through the second switch device, and the output end of the flying bridge arm is connected to the negative electrode of the DC port through the fourth switch device. The voltage modulated by the flying bridge arm is as follows:

[0030]

[0031] Furthermore, the conduction delay angle θ is based on the power factor angle And the modulation index m is obtained, the power factor angle It is expressed as the phase difference between the voltage and current at the AC port of the inverter.

[0032] The modulation index m is the ratio of the peak value of the AC power phase voltage at the AC port of the converter to half of the DC port voltage. The value of the conduction delay angle θ can be obtained by the modulation index m, as shown in the following formula:

[0033]

[0034] Furthermore, when a short circuit fault is detected at the DC port of the converter, the AC side voltage v of the x phase is detected. x The value of v x When the value of is greater than or equal to zero, the first switch device and the third switch device are turned on, and the second switch device and the fourth switch device are turned off. At the same time, the voltage modulated by the flying bridge arm is as follows:

[0035] v Fx1Fx2 =-v x ,

[0036] When v x When the value of is less than zero, the second switch device and the fourth switch device are turned on, and the first switch device and the third switch device are turned off. At the same time, the voltage modulated by the flying bridge arm is as follows:

[0037] v Fx1Fx2 =v x ,

[0038] At this time, the converter works in static VAR compensator mode.

[0039] When it is detected that the short-circuit fault of the converter DC port has been cleared, the control method of the converter is switched to the control method before the short-circuit fault of the converter DC port is detected, so as to achieve fault ride-through.

[0040] Beneficial effects of the invention:

[0041] 1. The bridge arm flying span modular multi-level converter topology and control method thereof of the present invention can provide an AC port and a DC port at the same time, which is used in an AC / DC hybrid distribution network and realizes voltage conversion and power transmission between the AC port and the DC port of the converter;

[0042] 2. The bridge arm flying-span modular multilevel converter topology of the present invention adopts a three-phase three-bridge arm circuit structure, which reduces the use of submodules, switch devices and passive components, thereby further reducing the number of drive and sampling modules, thereby reducing the cost and volume of the converter and improving the efficiency and power density of the converter. At the same time, the bridge arm flying-span modular multilevel converter topology has good fault ride-through capability and improves the reliability of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with the accompanying drawings.

[0044] Figure 1 This is a topological diagram of a bridge arm flying span modular multi-level converter of the present invention;

[0045] Figure 2 It is a flow chart of a control method of a bridge arm flying span modular multi-level converter topology of the present invention;

[0046] Figure 3 It is a flow chart of a fault ride-through control method of a bridge arm flying span type modular multi-level converter topology of the present invention;

[0047] Figure 4 It is a simulation waveform diagram of the bridge arm flying span modular multi-level converter topology of the present invention;

[0048] Figure 4 (a) is the waveform of phase a voltage and three-phase current on the AC side;

[0049] (b) is the current waveform of the three-phase flying bridge arm;

[0050] (c) is the AC port voltage waveform of the a-phase inverter;

[0051] (d) is the voltage waveform of the flying bridge arm of phase a;

[0052] (e) is the capacitor voltage waveform of the a-phase flying bridge arm submodule;

[0053] (f) is the DC side current waveform. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] A bridge arm flying span modular multilevel converter topology is proposed. The bridge arm flying span modular multilevel converter topology is composed of a three-phase AC system 1 and a DC side voltage stabilizing circuit 2. The three-phase AC system 1 and the DC side voltage stabilizing circuit 2 are connected in parallel to obtain a DC port. The DC port outputs a DC voltage of V dc ,like Figure 1 shown.

[0056] The three-phase AC system 1 is a three-phase AC circuit structure. Each phase AC circuit consists of an upper switch circuit 11, a lower switch circuit 12, a flying bridge arm 13, an AC side filter inductor L f and AC side power supply v x Composition, where x = a, b, c phase.

[0057] The upper switch circuit 11 is composed of a first switch device S x1 , the second switching device S x2 It is connected in series with the first inductor L1, wherein x = a, b, c phase.

[0058] The first switching device S x1 It can be composed of a fully controlled switch tube, the second switch device S x2 It can be composed of two fully controlled switch tubes connected in reverse series, the second switch device S x2 The two fully-controlled switch tubes connected in reverse series have the same driving signal and are turned on and off at the same time.

[0059] The first switching device S x1 The collector of the first switching device S is connected to the positive electrode of the DC port. x1 The emitter and the second switching device S x2 The emitter of the fully controlled switch located at the top is connected, and the second switch device S x2 The collectors of the two fully controlled switch tubes on the x2 The emitter of the fully-controlled switch tube at the bottom is connected to the first inductor L1.

[0060] The lower switch circuit 12 is composed of a third switch device S x3 , the fourth switching device S x4 It is connected in series with the second inductor L2, and x=a, b, c phases.

[0061] The fourth switching device S x4 It can be composed of a fully controlled switch tube, and the third switch device S x3 It consists of two fully controlled switch tubes connected in reverse series, and the third switch device S x3 The two fully controlled switch tubes connected in reverse series have the same driving signal and are turned on and off at the same time.

[0062] The third switching device S x3The emitter of the fully controlled switch tube located at the top is connected to the second inductor L2, and the third switch device S x3 The collectors of the two fully controlled switch tubes on the x3 The emitter of the fully controlled switch tube at the bottom and the fourth switch device S x4 Collector connection.

[0063] The fourth switching device S x4 The emitter is connected to the negative pole of the DC port, the upper switch circuit 11 and the lower switch circuit 12 are connected in series, and the connection point between the upper switch circuit 11 and the lower switch circuit 12 is connected to the AC side filter inductor L f One end of the AC side filter inductor L f The other end is connected to the AC power supply v x connect.

[0064] The flying bridge arm 13 is composed of N cascaded full-bridge submodules, N=1, 2, 3..., and the input end of the N cascaded full-bridge submodule circuit is used as the input end F of the flying bridge arm 13. x1 , where x = a, b, c phase.

[0065] The output ends of the N cascaded full-bridge sub-module circuits are used as the output ends F of the flying bridge arm 13. x2 , where x = a, b, c phase.

[0066] Input terminal F of flying bridge arm 13 x1 With the first switching device S x1 and the second switching device S x2 The connecting point is connected to the output end F of the flying bridge arm 13 x2 The third switching device S x3 and the fourth switching device S x4 The connection points are connected.

[0067] The DC side voltage stabilizing circuit 22 is composed of a first voltage stabilizing capacitor C1 and a second voltage stabilizing capacitor C2. The positive electrode of the first voltage stabilizing capacitor C1 is connected to the positive electrode of the DC port, the negative electrode of the first voltage stabilizing capacitor C1 is connected to the positive electrode of the second voltage stabilizing capacitor C2, and the negative electrode of the second voltage stabilizing capacitor C2 is connected to the negative electrode of the DC port.

[0068] A set of filter inductors can be connected in series at the DC port to stabilize and filter the DC voltage.

[0069] The proposed flying-span modular multilevel converter topology can realize bidirectional power flow.

[0070] The first switch device S in the upper switch circuit 11 x1 and the third switch device S in the lower switch circuit 12 x3The second switch device S in the upper switch circuit 11 is turned on and off at the same time; x2 and the fourth switching device S in the lower switching circuit 12 x4 On at the same time and off at the same time.

[0071] The first switching device S x1 and the second switching device S x2 Complementary conduction, the third switch device S x3 and the fourth switching device S x4 Complementary conduction.

[0072] The first switching device S x1 and the fourth switching device S x4 Multiple fully controlled switching tubes can be connected in series.

[0073] When the first switching device S x1 and the fourth switching device S x4 When multiple fully-controlled switching tubes connected in series are used, the multiple fully-controlled switching tubes connected in series need to be turned on and off at the same time.

[0074] The second switching device S x2 and the third switching device S x3 Either a single set of reverse-series fully-controlled switch tubes can be used, or multiple sets of reverse-series fully-controlled switch tubes can be used, and the multiple sets of reverse-series fully-controlled switch tubes are connected in series.

[0075] When the second switching device S x2 and the third switching device S x3 When multiple groups of fully-controlled switch tubes connected in reverse series are used, the multiple groups of fully-controlled switch tubes connected in reverse series need to be turned on and off at the same time.

[0076] The first inductor L1 of the upper switch circuit 11 and the second inductor L2 of the lower switch circuit 12 and the AC side filter inductor L f Integrated into an inductor without affecting the operating performance of the inverter.

[0077] The control method of the bridge arm flying span modular multilevel converter topology is as follows: Figure 2 As shown, the control method is as follows:

[0078] When the x-phase AC side voltage v is detected x When the value changes from negative to zero, the timing starts, and the delay is (θ / 2π)*T s After a certain time, the first switch device S is turned on. x1 and the third switching device S x3 , after T s After a conduction time of / 2, the first switch device S x1 and the third switching device S x3Turn off, and trigger the second switch device S x2 and the fourth switching device S x4 conduction, where θ is the conduction delay angle, T s is the AC voltage period at the AC port of the inverter.

[0079] When the x-phase AC voltage v is detected x When the positive value changes to zero, the timing starts, and the delay is (θ / 2π)*T s After a certain time, the second switch device S is turned on. x2 and the fourth switching device S x4 , after T s After the on-time of / 2, the second switch device S x2 and the fourth switching device S x4 Turn off, and at the same time trigger the first switch device S x1 and the third switching device S x3 Conductivity.

[0080] When the first switching device S x1 and the third switching device S x3 When the switch is on, the input end of the flying bridge arm 13 is connected through the first switch device S x1 The output end of the flying bridge arm 13 is connected to the positive electrode of the DC port through the third switch device S x3 Connected to the AC port of the converter, the voltage modulated by the flying bridge arm 13 is:

[0081]

[0082] When the second switching device S x2 and the fourth switching device S x4 When the switch is on, the input end of the flying bridge arm 13 is connected through the second switch device S x2 The output end of the flying bridge arm 13 is connected to the AC port of the converter through the fourth switch device S x4 Connected to the negative pole of the DC port, the voltage modulated by the flying bridge arm 13 is

[0083]

[0084] The conduction delay angle θ is based on the power factor angle And the modulation index m is obtained, the power factor angle It is expressed as the phase difference between the voltage and current at the AC port of the converter, as shown in equations (3) and (4).

[0085] The modulation index m is the ratio of the peak value of the AC power phase voltage at the AC port of the converter to half of the DC port voltage, as shown in formula (5). The value of the conduction delay angle θ can be obtained by using the modulation index m, as shown in formula (6).

[0086]

[0087]

[0088]

[0089]

[0090] Fault ride-through control method for bridge arm flying span modular multilevel converter topology, such as Figure 3 As shown in the figure, when a short circuit fault is detected at the DC port of the converter, the AC side voltage v of the x phase is detected. x The value of v x When the value of is greater than or equal to zero, the first switch device S is turned on. x1 and the third switching device S x3 , turn off the second switch device S x2 and the fourth switching device S x4 At the same time, the voltage modulated by the flying bridge arm 13 is

[0091] v Fx1Fx2 =-v x (7)

[0092] When v x When the value of is less than zero, the second switch device S is turned on. x2 and the fourth switching device S x4 , turn off the first switching device S x1 and the third switching device S x3 At the same time, the voltage modulated by the flying bridge arm 13 is

[0093] v Fx1Fx2 =v x (8)

[0094] At this time, the converter operates in static VAR compensator (statcom) mode.

[0095] When it is detected that the short-circuit fault of the converter DC port has been cleared, the control method of the converter is switched to the control method under the non-fault condition shown in equations (1)-(6) to achieve fault ride-through.

[0096] In order to verify the effect of this topology and its control method, the proposed bridge arm flying span modular multilevel converter topology and its control method are simulated and verified. The simulation parameters are shown in Table 1.

[0097] Table 1 A set of simulation parameters of the bridge arm flying span modular multilevel converter topology

[0098]

[0099] According to the parameters in Table 1, the bridge arm flying span modular multilevel converter topology and its control method are simulated and verified. The simulation results are shown in Figure 4 shown.

[0100] from Figure 4 It can be seen from (a) that the phase a voltage and phase a current are in phase, achieving unity power factor operation, and the voltage and current on the AC side are both sinusoidal waves.

[0101] from Figure 4 It can be seen from (b) that the current of the three-phase flying bridge arm 13 has reached a balanced state.

[0102] from Figure 4 As can be seen in (c), the AC port voltage of the a-phase converter is a multi-level waveform.

[0103] from Figure 4 It can be seen from (d) that the voltage of the flying bridge arm 13 of phase a is consistent with the theoretical control result.

[0104] from Figure 4 As can be seen in (e), the submodule capacitor voltage fluctuates around 110V.

[0105] from Figure 4 It can be seen from (f) that the DC side current is a DC component superimposed on a six-fold frequency pulsation, and the current component of the six-fold frequency pulsation is smaller.

[0106] According to the simulation waveform of the bridge arm flying span modular multilevel converter topology with fault ride-through capability, the converter realizes the voltage conversion and power transmission between the AC port and the DC port of the converter, achieves the control purpose and the expected effect, and verifies the effectiveness and feasibility of the proposed bridge arm flying span modular multilevel converter topology and its control method.

[0107] The bridge arm flying span modular multilevel converter topology and control method thereof proposed in the present invention can provide an AC port and a DC port at the same time, which are used in an AC / DC hybrid distribution network, and realize voltage conversion and power transmission between the AC port and the DC port of the converter.

[0108] The flying-bridge modular multilevel converter topology adopts a three-phase three-bridge-bridge circuit structure, which reduces the use of sub-modules, switching devices and passive components, thereby further reducing the number of driving and sampling modules, thereby reducing the cost and volume of the converter and improving the efficiency and power density of the converter.

[0109] At the same time, the bridge arm flying span modular multilevel converter topology has good fault ride-through capability and improves the reliability of the converter.

[0110] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. A bridge arm flying span modular multilevel converter topology, the bridge arm flying span modular multilevel converter topology comprising a three-phase AC system (1) and a DC side voltage stabilizing circuit (2), wherein the three-phase AC system (1) and the DC side voltage stabilizing circuit (2) are connected in parallel to obtain a DC port, and the DC port outputs a DC voltage of V dc , characterized in that, The three-phase AC system (1) is a three-phase AC circuit structure, and each phase AC circuit is composed of an upper switch circuit (11), a lower switch circuit (12), a flying bridge arm (13), an AC side filter inductor (L f ) and AC power supply (v x ) wherein x = a, b, c phase; The upper switch circuit (11) is composed of a first switch device (S x1 ), the second switching device (S x2 ) and the first inductor L1 are connected in series, wherein x = a, b, c phase; The lower switch circuit (12) is composed of a third switch device (S x3 ), the fourth switching device (S x4 ) and the second inductor L2 are connected in series, x = a, b, c phase; The upper switch circuit (11) and the lower switch circuit (12) are connected in series, and the connection point between the upper switch circuit (11) and the lower switch circuit (12) is connected to the AC side filter inductor (L f ) is connected to one end of the AC side filter inductor (L f ) and the other end of the AC power supply (v x )connect; The first switching device (S x1 ) is composed of at least one fully controlled switch tube, the second switch device (S x2 ) is composed of at least one fully-controlled switch tube series structure, wherein the fully-controlled switch tube series structure is composed of two fully-controlled switch tubes connected in reverse series, and the two fully-controlled switch tubes connected in reverse series in the fully-controlled switch tube series structure have the same driving signal and are turned on and off at the same time; The fourth switching device (S x4 ) is composed of at least one fully controlled switch tube, and the third switch device (S x3 ) is composed of at least one fully controlled switch tube in series; The flying bridge arm (13) is composed of N cascaded full-bridge submodules, N=1, 2, 3..., and the input ends of the N cascaded full-bridge submodule circuits are used as the input ends F of the flying bridge arm (13). x1 , where x = a, b, c phase; The output ends of the N cascaded full-bridge submodule circuits are used as the output ends F of the flying bridge arms (13). x2 , where x = a, b, c phase; The input end F of the flying bridge arm (13) x1 With the first switching device (S x1 ) and the second switching device (S x2 ) is connected to the connection point, and the output end F of the flying bridge arm (13) is connected to the output end F of the flying bridge arm (13). x2 With the third switching device (S x3 ) and the fourth switching device (S x4 )’s connection points.

2. A bridge arm flying span modular multilevel converter topology according to claim 1, characterized in that: The first switching device (S x1 ) consists of a fully controlled switch tube, the second switch device (S x2 ) consists of two fully controlled switch tubes connected in reverse series, the second switch device S x2 The two reverse-series fully-controlled switch tubes have the same drive signal and are turned on and off at the same time; The first switching device (S x1 ) is connected to the positive electrode of the DC port, and the first switching device (S x1 ) and the emitter of the second switching device (S x2 ) is connected to the emitter of the fully controlled switch tube located at the top, and the second switch device (S x2 ) are connected to the collectors of the two fully controlled switch tubes, and the second switch device (S x2 ) wherein the emitter of the fully-controlled switch tube at the bottom is connected to the first inductor (L1); The fourth switching device (S x4 ) consists of a fully controlled switch tube, the third switch device (S x3 ) consists of two fully controlled switch tubes connected in reverse series, and the third switch device (S x3 ) in which two fully controlled switch tubes connected in reverse series have the same driving signal and are turned on and off at the same time; The third switching device (S x3 ) is connected to the emitter of the fully controlled switch tube at the top and the second inductor (L2). x3 ) are connected to the collectors of the two fully controlled switch tubes, and the third switch device (S x3 ) is located at the bottom of the emitter of the fully controlled switch tube and the fourth switch device (S x4 )’s collector connection; The fourth switching device (S x4 ) is connected to the negative terminal of the DC port.

3. The flying bridge type modular multilevel converter topology according to claim 1, characterized in that: The DC side voltage stabilizing circuit (2) is composed of a first voltage stabilizing capacitor (C1) and a second voltage stabilizing capacitor (C2), wherein the positive electrode of the first voltage stabilizing capacitor (C1) is connected to the positive electrode of the DC port, the negative electrode of the first voltage stabilizing capacitor (C1) is connected to the positive electrode of the second voltage stabilizing capacitor (C2), and the negative electrode of the second voltage stabilizing capacitor (C2) is connected to the negative electrode of the DC port.

4. A bridge arm flying span modular multilevel converter topology according to claim 3, characterized in that: The DC port is connected in series with a filter inductor for voltage stabilization and filtering.

5. The flying bridge type modular multilevel converter topology according to claim 1, characterized in that: The first inductor (L1) in the upper switch circuit (11), the second inductor (L2) in the lower switch circuit (12), and the AC side filter inductor (L f ) integrated into an inductor.

6. The control method of the bridge arm flying span modular multilevel converter topology according to any one of claims 1 to 5, characterized in that: The control method is as follows: When the x-phase AC side voltage v is detected x When the value changes from negative to zero, the timing starts, and the delay is (θ / 2π)*T s After a certain time, the first switch device (S x1 ) and the third switching device (S x3 ), after T s After a conduction time of / 2, the first switch device (S x1 ) and the third switching device (S x3 ) is turned off, and the second switch device (S x2 ) and the fourth switching device (S x4 ) is turned on, where θ is the conduction delay angle, T s is the AC voltage period of the AC port of the converter; When the x-phase AC side voltage v is detected x When the positive value changes to zero, the timing starts, and the delay is (θ / 2π)*T s After a certain time, the second switch device (S x2 ) and the fourth switching device (S x4 ), after T s After a conduction time of / 2, the second switch device (S x2 ) and the fourth switching device (S x4 ) is turned off, and the first switch device (S x1 ) and the third switching device (S x3 ) is turned on; When the first switching device (S x1 ) and the third switching device (S x3 ) is turned on, the input end of the flying bridge arm (13) is connected through the first switch device (S x1 ) is connected to the positive electrode of the DC port, and the output end of the flying bridge arm (13) is connected to the positive electrode of the DC port through the third switch device (S x3 ) is connected to the AC port of the converter, and the voltage modulated by the flying bridge arm (13) is as follows: When the second switching device (S x2 ) and the fourth switching device (S x4 ) is turned on, the input end of the flying bridge arm (13) is connected through the second switch device (S x2 ) is connected to the AC port of the converter, and the output end of the flying bridge arm (13) is connected to the AC port of the converter through the fourth switch device (S x4 ) is connected to the negative electrode of the DC port, and the voltage modulated by the flying bridge arm (13) is as follows:

7. The control method of the bridge arm flying span modular multilevel converter topology according to claim 6, characterized in that: The conduction delay angle θ is based on the power factor angle And the modulation index m is obtained, the power factor angle It is expressed as the phase difference between the voltage and current at the AC port of the converter; The modulation index m is the ratio of the peak value of the AC power phase voltage at the AC port of the converter to half of the DC port voltage. The value of the conduction delay angle θ can be obtained by the modulation index m, as shown in the following formula:

8. The control method of the bridge arm flying span modular multilevel converter topology according to claim 7, characterized in that: When a short circuit fault is detected at the DC port of the converter, the AC side voltage v of the x phase is detected. x The value of v x When the value of is greater than or equal to zero, the first switch device (S x1 ) and the third switching device (S x3 ), turn off the second switch device (S x2 ) and the fourth switching device (S x4 ), and at the same time, the voltage modulated by the flying bridge arm (13) is as follows: v Fx1Fx2 =-v x , When v x When the value of is less than zero, the second switch device (S x2 ) and the fourth switching device (S x4 ), turn off the first switch device (S x1 ) and the third switching device (S x3 ), and at the same time, the voltage modulated by the flying bridge arm (13) is as follows: v Fx1Fx2 =v x , At this time, the converter works in the static VAR compensator mode; When it is detected that the short-circuit fault of the converter DC port has been cleared, the control method of the converter is switched to the control method before the short-circuit fault of the converter DC port is detected, so as to achieve fault ride-through.

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