Converter, control method and related products

Abstract

The application discloses a converter, a control method and related products. The converter comprises a three-phase bridge arm circuit, each phase bridge arm circuit in the three-phase bridge arm circuit comprising a series connection of an upper half bridge arm and a lower half bridge arm; the upper half bridge arm and the lower half bridge arm comprising a sub-module module and a single switch circuit module connected in series, the sub-module module being connected close to a direct current side, and the single switch circuit module being connected close to an alternating current side; the sub-module module comprising a plurality of sub-modules connected in series, and the single switch circuit module comprising a plurality of single switch circuits connected in series; wherein the single switch circuit comprises a controllable switch tube, a diode, an absorption circuit and a lightning arrester; the diode is connected in antiparallel across the controllable switch tube, the absorption circuit is connected in parallel across the controllable switch tube, and the lightning arrester is connected in parallel across the controllable switch tube. In the embodiment of the application, the single switch circuit module and the sub-module module are connected in series, the number of sub-modules and the volume of the capacitor in the sub-module are reduced, and the power density of the converter valve body is increased.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a converter, a control method, and related products. Background Art

[0002] HVDC Flexible is a next-generation transmission technology, following AC and conventional (UHV) DC transmission. While inheriting the inherent advantages of DC transmission, HVDC Flexible utilizes voltage source converters (VSCs), DC capacitors for voltage support, and fully controlled power electronic devices with controllable on / off switching to control the output waveform, enabling independent control of active and reactive power.

[0003] In related technologies, VSCs typically use a modular multilevel converter (MMC) topology, achieving AC / DC conversion by controlling the submodules within the MMC. However, in HVDC transmission scenarios, the large number of submodules within the MMC and the large volume of capacitors within the submodules result in low power density within the converter valve body. Summary of the Invention

[0004] Based on the above problems, the present application provides a converter, a control method and related products to increase the power density of the converter valve body.

[0005] The embodiments of this application disclose the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a converter, comprising: a three-phase bridge arm circuit, wherein each phase bridge arm circuit in the three-phase bridge arm circuit includes an upper half bridge arm and a lower half bridge arm connected in series; the upper half bridge arm and the lower half bridge arm include a sub-module module and a single switch circuit module connected in series, the sub-module module is connected close to the DC side, and the single switch circuit module is connected close to the AC side;

[0007] The sub-module module includes multiple sub-modules connected in series, and the single-switch circuit module includes multiple single-switch circuits connected in series; wherein, the single-switch circuit includes a controllable switch tube, a diode, an absorption circuit and a lightning arrester; the diode is connected in anti-parallel at both ends of the controllable switch tube, the absorption circuit is connected in parallel at both ends of the controllable switch tube, and the lightning arrester is connected in parallel at both ends of the controllable switch tube.

[0008] In a possible embodiment, the invention further includes: a controller;

[0009] The controller is used to obtain a trigger angle of the upper half bridge arm according to the power factor angle of the bridge arm circuit when the upper half bridge arm and the lower half bridge arm in the bridge arm circuit are alternately turned on; and control the phase of the current of the upper half bridge arm according to the trigger angle to turn off the diode soft switch or turn off the controllable switch tube hard switch.

[0010] In one possible embodiment, the controller is specifically configured to, when the bridge arm circuit is operating in the rectification and reactive power absorption mode, obtain a first trigger angle of the upper half bridge arm based on the power factor angle if the power factor angle of the bridge arm circuit is within a first interval; control the phase of the current of the upper half bridge arm based on the first trigger angle to cause the diode soft switch to be turned off; wherein the lower limit value of the first interval is 0, and the upper limit value of the first interval is π / 2.

[0011] In a possible embodiment, the controller is specifically used to, when the bridge arm circuit is operating in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, obtain the second trigger angle of the upper half bridge arm according to the power factor angle; control the phase of the current of the upper half bridge arm according to the second trigger angle to turn off the diode soft switch; if the power factor angle of the bridge arm circuit exceeds the second interval, obtain the third trigger angle of the upper half bridge arm according to the power factor angle; control the phase of the current of the upper half bridge arm according to the third trigger angle to turn off the controllable switch tube hard switch; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit value of the second interval is 0.

[0012] In one possible embodiment, the controller is specifically configured to, when the bridge arm circuit operates in an inverter to absorb reactive power, obtain a fourth trigger angle of the upper half bridge arm based on the power factor angle if the power factor angle of the bridge arm circuit is within a third interval; control the phase of the current of the upper half bridge arm based on the fourth trigger angle to cause the diode soft switch to be turned off; wherein the lower limit value of the third interval is π / 2, and the upper limit value of the third interval is π.

[0013] In a possible embodiment, the controller is specifically used to, when the bridge arm circuit operates in the inverter to transmit reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, obtain the fifth trigger angle of the upper half bridge arm according to the power factor angle; control the phase of the current of the upper half bridge arm according to the fifth trigger angle to cause the diode to be soft-switched off; if the power factor angle of the bridge arm circuit exceeds the fourth interval, obtain the sixth trigger angle of the upper half bridge arm according to the power factor angle; control the phase of the current of the upper half bridge arm according to the sixth trigger angle to cause the controllable switch tube to be hard-switched off; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , m R is the rated modulation ratio.

[0014] In a possible embodiment, the controller is further configured to control the switching frequency of the controllable switch tube in the upper half bridge arm to be less than a preset threshold.

[0015] In a possible embodiment, the absorption circuit includes a resistor and a capacitor connected in series.

[0016] In a second aspect, an embodiment of the present application provides a control method for a converter, wherein the converter includes a three-phase bridge arm circuit, wherein each phase bridge arm circuit in the three-phase bridge arm circuit includes an upper half bridge arm and a lower half bridge arm connected in series; the upper half bridge arm and the lower half bridge arm include a sub-module module and a single switch circuit module connected in series, wherein the sub-module module is connected close to the DC side, and the single switch circuit module is connected close to the AC side; the sub-module module includes a plurality of sub-modules connected in series, and the single switch circuit module includes a plurality of single switch circuits connected in series; wherein the single switch circuit includes a controllable switch tube, a diode, an absorption circuit, and a lightning arrester; the diode is connected in anti-parallel at both ends of the controllable switch tube, the absorption circuit is connected in parallel at both ends of the controllable switch tube, and the lightning arrester is connected in parallel at both ends of the controllable switch tube;

[0017] Methods include:

[0018] When the upper half bridge arm and the lower half bridge arm in the bridge arm circuit are alternately turned on, the trigger angle of the upper half bridge arm is obtained according to the power factor angle of the bridge arm circuit;

[0019] The phase of the current in the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off.

[0020] In a possible embodiment, the phase of the current in the upper half bridge arm is controlled according to the trigger angle to turn off the diode soft switch or the controllable switch tube hard switch, including: when the bridge arm circuit operates in the rectification and absorption of reactive power, if the power factor angle of the bridge arm circuit is within a first interval, obtaining a first trigger angle of the upper half bridge arm according to the power factor angle; controlling the phase of the current in the upper half bridge arm according to the first trigger angle to turn off the diode soft switch; wherein the lower limit value of the first interval is 0, and the upper limit value of the first interval is π / 2.

[0021] In a possible embodiment, the phase of the current of the upper half bridge arm is controlled according to the trigger angle to turn off the diode soft switch or turn off the controllable switch tube hard switch, including: when the bridge arm circuit operates in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, the second trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the second trigger angle to turn off the diode soft switch; if the power factor angle of the bridge arm circuit exceeds the second interval, the third trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the third trigger angle to turn off the controllable switch tube hard switch; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit value of the second interval is 0.

[0022] In a possible embodiment, the phase of the current in the upper half bridge arm is controlled according to the trigger angle to turn off the diode soft switch or turn off the controllable switch tube hard switch, including: when the bridge arm circuit operates in the inverter to absorb reactive power, if the power factor angle of the bridge arm circuit is within a third interval, obtaining a fourth trigger angle of the upper half bridge arm according to the power factor angle; controlling the phase of the current in the upper half bridge arm according to the fourth trigger angle to turn off the diode soft switch; wherein the lower limit value of the third interval is π / 2, and the upper limit value of the third interval is π.

[0023] In a possible embodiment, the phase of the current of the upper half bridge arm is controlled according to the trigger angle to turn off the diode soft switch or turn off the controllable switch tube hard switch, including: when the bridge arm circuit operates in the inverter to send reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, the fifth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fifth trigger angle to turn off the diode soft switch; if the power factor angle of the bridge arm circuit exceeds the fourth interval, the sixth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the sixth trigger angle to turn off the controllable switch tube hard switch; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , m R is the rated modulation ratio.

[0024] In a possible embodiment, the method further includes: controlling the switching frequency of the controllable switch tube in the upper half bridge arm to be less than a preset threshold.

[0025] In a possible embodiment, the absorption circuit includes a resistor and a capacitor connected in series.

[0026] In a third aspect, an embodiment of the present application provides a control device comprising a processor and a memory, wherein the memory is used to store programs, instructions or codes, and the processor is used to execute the programs, instructions or codes in the memory to complete the control method of the converter as in the embodiment of the second aspect.

[0027] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium storing a computer program, wherein the computer program is loaded by a processor to execute the control method of the converter as in the embodiment of the second aspect.

[0028] To increase the power density of the MMC valve body, an embodiment of the present application provides a converter that connects a submodule module in series via a single switch circuit module, thereby reducing the number of submodules and the volume of the capacitor within the submodule, and increasing the power density of the converter valve body. Furthermore, the converter in the embodiment of the present application allows the modulation ratio of the converter to be greater than 1 during overmodulation operation, enabling overmodulation operation of the converter without relying on the injection of external harmonics, thereby increasing the converter's transmission capacity and improving the converter's reactive power support capability during transient operation. Furthermore, the single switch circuit in the embodiment of the present application connects an absorption circuit and a lightning arrester in parallel at both ends of the diode and the controllable switch tube. When the diode is soft-switched off or the controllable switch tube is hard-switched off, series voltage balancing between the single switch circuits is achieved through the absorption circuit and the lightning arrester. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 is a schematic diagram of an inverter;

[0031] Figure 2 A schematic diagram of a single switch circuit provided in an embodiment of the present application;

[0032] Figure 3 A schematic diagram of a diode soft switch shutdown provided in an embodiment of the present application;

[0033] Figure 4 A schematic diagram of an absorption circuit provided in an embodiment of the present application;

[0034] Figure 5 A schematic diagram of a hard-switching shutdown of a controllable switch tube provided in an embodiment of the present application;

[0035] Figure 6 A schematic diagram of a half-bridge submodule provided in an embodiment of the present application;

[0036] Figure 7 A schematic diagram of another half-bridge submodule provided in an embodiment of the present application;

[0037] Figure 8 A schematic diagram of a full-bridge submodule provided in an embodiment of the present application;

[0038] Figure 9 A schematic diagram of another full-bridge submodule provided in an embodiment of the present application;

[0039] Figure 10 A flowchart of a method for controlling a converter provided in an embodiment of the present application;

[0040] Figure 11 A schematic diagram of a control device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to help those skilled in the art better understand the present invention, the following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings of 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 those skilled in the art without creative work are within the scope of protection of the present invention.

[0042] In the specification and claims of this application, the terms "first" and "second" are used to distinguish different objects, rather than to describe a specific order of objects. For example, "a first single switch circuit" and "a second single switch circuit" are used to distinguish different single switch circuits, rather than to describe a specific order of the single switch circuits.

[0043] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0044] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, for example, multiple processing units means two or more processing units, etc.; multiple elements means two or more elements, etc.

[0045] Currently, flexible DC converters are primarily categorized as two-level voltage source converters (VSCs) and modular multilevel VSCs. In two-level VSCs, the bridge arms consist solely of switching devices, with the upper and lower arms of each phase alternately conducting. The output voltage consists of only two levels (positive and negative). Consequently, the switching frequency of the switching devices exceeds 1kHz, resulting in high losses in the valve body. In modular multilevel VSCs, the bridge arms consist solely of submodules, with the upper and lower arms of each phase conducting simultaneously. AC / DC conversion is achieved by controlling the switching of submodules. This results in a high number of output levels and a low switching frequency, allowing for flexible expansion of voltage levels by increasing the number of submodules. However, when modular multilevel VSCs are applied in HVDC transmission scenarios, the large number of submodules and the significant volumetric volume of the capacitors within the submodules result in low converter valve power density and high construction costs.

[0046] Based on this, in an embodiment of the present application, the upper and lower bridge arms of each phase bridge arm circuit in the converter each include a series-connected submodule module and a single switch circuit module; wherein the submodule module includes multiple series-connected submodules, and the single switch circuit module includes multiple series-connected single switch circuits. Compared to a two-level current source converter, the converter in this embodiment of the present application can reduce valve body losses; compared to a modular multi-level voltage source converter, the converter in this embodiment of the present application can increase the valve body's power density.

[0047] In order to enable those skilled in the art to better understand and implement the technical solutions provided in the embodiments of the present application, the architecture of the converter is first introduced below with reference to the accompanying drawings.

[0048] See also Figure 1 , which is a schematic diagram of a converter.

[0049] like Figure 1 As shown, the converter includes a three-phase bridge arm circuit, and each phase bridge arm circuit includes an upper half bridge arm and a lower half bridge arm connected in series; the upper half bridge arm and the lower half bridge arm include a sub-module module and a single switch circuit module connected in series, the sub-module module is connected close to the DC side, and the single switch circuit module is connected close to the AC side; the sub-module module includes multiple sub-modules connected in series, and the single switch circuit module includes multiple single switch circuits connected in series.

[0050] It should be understood that the AC side in the embodiment of the present application includes a three-phase power grid, namely phase A, phase B and phase C, and the three-phase voltages of the power grid are ua, ub and uc respectively.

[0051] For the A-phase bridge arm circuit, the first end of the sub-module module in the upper half bridge arm (the sub-module module includes a first sub-module SM11, a second sub-module SM12... and an n-th sub-module SM1n connected in series) is used to connect to the DC positive pole DC+, the second end of the sub-module module is connected to the first end of the single-switch circuit module (the single-switch circuit module includes a first single-switch circuit SDM11, a second single-switch circuit SDM12... and an m-th single-switch circuit SDM1m connected in series), and the second end of the single-switch circuit module is used to connect to the A-phase voltage ua; the first end of the single-switch circuit module in the lower half bridge arm (the single-switch circuit module includes a first single-switch circuit SDM21, a second single-switch circuit SDM22... and an m-th single-switch circuit SDM2m connected in series) is used to connect to the A-phase voltage ua, the second end of the single-switch circuit module is connected to the first end of the sub-module module (the sub-module module includes a first sub-module SM21, a second sub-module SM22... and an n-th sub-module SM2n connected in series), and the second end of the sub-module module is connected to the DC negative pole DC-. Wherein, n is an integer greater than or equal to 2, and m is an integer greater than or equal to 2.

[0052] For the B-phase bridge arm circuit, the first end of the sub-module module in the upper half bridge arm (the sub-module module includes a first sub-module SM31, a second sub-module SM32... and an n-th sub-module SM3n connected in series) is used to connect to the DC positive pole DC+, the second end of the sub-module module is connected to the first end of the single switch circuit module (the single switch circuit module includes a first single switch circuit SDM31, a second single switch circuit SDM32... and an m-th single switch circuit SDM3m connected in series), and the second end of the single switch circuit module is used to connect to the B-phase voltage ub; the first end of the single switch circuit module in the lower half bridge arm (the single switch circuit module includes a first single switch circuit SDM41, a second single switch circuit SDM42... and an m-th single switch circuit SDM4m connected in series) is used to connect to the B-phase voltage ub, the second end of the single switch circuit module is connected to the first end of the sub-module module (the sub-module module includes a first sub-module SM41, a second sub-module SM42... and an n-th sub-module SM4n connected in series), and the second end of the sub-module module is connected to the DC negative pole DC-. Wherein, n is an integer greater than or equal to 2, and m is an integer greater than or equal to 2.

[0053] For the C-phase bridge arm circuit, the first end of the sub-module module in the upper half bridge arm (the sub-module module includes a first sub-module SM51, a second sub-module SM52... and an n-th sub-module SM5n connected in series) is used to connect to the DC positive pole DC+, the second end of the sub-module module is connected to the first end of the single switch circuit module (the single switch circuit module includes a first single switch circuit SDM51, a second single switch circuit SDM52... and an m-th single switch circuit SDM5m connected in series), and the second end of the single switch circuit module is used to connect to the C-phase voltage uc; the first end of the single switch circuit module in the lower half bridge arm (the single switch circuit module includes a first single switch circuit SDM61, a second single switch circuit SDM62... and an m-th single switch circuit SDM6m connected in series) is used to connect to the C-phase voltage uc, the second end of the single switch circuit module is connected to the first end of the sub-module module (the sub-module module includes a first sub-module SM61, a second sub-module SM62... and an n-th sub-module SM6n connected in series), and the second end of the sub-module module is connected to the DC negative pole DC-. Wherein, n is an integer greater than or equal to 2, and m is an integer greater than or equal to 2.

[0054] It should be noted that in the embodiment of the present application, the number of sub-modules in the sub-module module is determined by the voltage level of the AC side and the voltage level of the DC side. The higher the voltage level of the AC side and the voltage level of the DC side, the greater the number of sub-modules; the number of single-switch circuits in the single-switch circuit module is determined by the voltage level of the DC side. The higher the voltage level of the DC side, the greater the number of single-switch circuits.

[0055] In the case where the converter is applied to a high-voltage direct current transmission scenario, since the submodule module includes many controllable switch tubes connected in series, there is a problem of series voltage balancing, which in turn causes damage to the controllable switch tube. In order to solve the above technical problems, the embodiment of the present application connects an absorption circuit and a lightning arrester in series at both ends of the controllable switch tube and the diode. When the diode is soft-switched off, the absorption circuit absorbs energy and slows down the rate of change of the voltage, thereby achieving dynamic voltage balancing; when the controllable switch tube is hard-switched off, the lightning arrester clamps the overshoot voltage, thereby achieving dynamic voltage balancing. In addition, the converter in the embodiment of the present application allows the modulation ratio of the converter to be greater than 1 when in overmodulation operation, and the overmodulation operation of the converter can be achieved without relying on the injection of external harmonics, thereby increasing the transmission capacity of the converter and improving the reactive support capability of the converter during transient operation.

[0056] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0057] See also Figure 2 , which is a schematic diagram of a single switch circuit provided in an embodiment of the present application.

[0058] like Figure 2 As shown, the single switch circuit SDM includes a first controllable switch transistor G1, a first diode D1, an absorption circuit 100, and a lightning arrester MOV. The first diode D1 is connected in antiparallel to both ends of the controllable switch transistor G1, the absorption circuit 100 is connected in parallel to both ends of the first controllable switch transistor G1, and the lightning arrester MOV is connected in parallel to both ends of the first controllable switch transistor G1.

[0059] The type of the controllable switch tube is not specifically limited in the embodiments of the present application. For example, the controllable switch tube can be a controllable switch tube such as an integrated gate-commutated thyristor (IGCT) and an insulated-gate bipolar transistor (IGBT).

[0060] Because the single switch circuit provided in the embodiment of the present application includes a first controllable switch tube G1 and a first diode D1, the single switch circuit in the embodiment of the present application corresponds to two different shutdown modes, namely, a hard switching shutdown mode of the first controllable switch tube G1 and a soft switching shutdown mode of the first diode D1.

[0061] For ease of understanding, the present application provides a schematic diagram of a diode soft switch shutoff, see Figure 3 .

[0062] like Figure 3 As shown, θ represents the trigger angle of the upper half bridge arm, ua represents the phase voltage of the bridge arm circuit, ia represents the phase current of the bridge arm circuit, and i D represents the diode current, i G Represents the controllable switch current. The trigger angle is used to control the phase of the current in the upper half bridge arm, so that the diode is commutated at the current zero crossing point, that is, the diode is soft-switched off.

[0063] For the diodes connected in series in the bridge arm circuit, due to differences in parameters such as the junction capacitance, internal resistance and reverse recovery time of the diodes, there will be an uneven voltage distribution during the shutdown process and the blocking state. This may cause some diodes to withstand excessive voltage and break down, endangering the safe and stable operation of the circuit.

[0064] To this end, in this embodiment of the present application, an absorption circuit is connected in parallel across the first diode D1. When the first diode D1 is soft-switched off, the absorption circuit absorbs the voltage spike across the first diode D1 and dissipates the energy as heat. This energy dissipation by the absorption circuit smoothes the voltage variation across the first diode D1, thereby achieving series voltage balancing.

[0065] For example, Figure 4As shown, the absorption circuit includes a first resistor R1 and a first capacitor C1 connected in series. When the first diode D1 is turned off, the first capacitor C1 absorbs the voltage spike across the first diode D1, while the first resistor R1 dissipates energy to prevent resonance between the first capacitor C1 and the inductor in the circuit. The energy storage of the first capacitor C1 and the energy dissipation of the first resistor R1 smooth the voltage across the first diode D1, thus achieving series voltage balancing.

[0066] For ease of understanding, the present application embodiment provides a schematic diagram of a hard switch shutdown of a controllable switch tube, see Figure 5 .

[0067] like Figure 5 As shown, θ represents the trigger angle of the upper half bridge arm, ua represents the phase voltage of the bridge arm circuit, ia represents the phase current of the bridge arm circuit, and i D represents the diode current, i G Indicates the controllable switch tube current, u G Represents the voltage of the controllable switch. By controlling the phase of the current in the upper half-bridge arm through the trigger angle, the controllable switch is actively turned off, that is, the controllable switch is hard-switched off.

[0068] Hard-switching of a controlled switch occurs when the current rapidly drops to zero while the voltage rapidly rises to the power supply voltage or higher. During this process, factors such as the switch's junction capacitance and line inductance can generate large voltage spikes and electromagnetic interference, potentially causing the switch to experience excessive voltage stress or even damage.

[0069] To this end, in this embodiment of the present application, a lightning arrester (MOV) is connected in parallel across the first controllable switch G1. When the controllable switch G1 is turned off and an overvoltage is generated, the MOV quickly turns on, limiting the voltage to below its protection level, thereby protecting the controllable switch from excessive voltage. For the controllable switches connected in series in the bridge arm circuit, the lightning arrester ensures that the voltage across each controllable switch does not exceed its withstand voltage, thereby achieving series voltage balancing.

[0070] In the embodiment of the present application, for the soft switch shutdown of the first diode D1, series voltage balancing is achieved through the absorption circuit; for the hard switch shutdown of the first controllable switch tube G1, series voltage balancing is achieved through the lightning arrester MOV.

[0071] The following will introduce the methods of controlling the soft switching turn-off of the diode and the hard switching turn-off of the controllable switch tube in the converter based on the single switch circuit in the aforementioned embodiment.

[0072] In one possible implementation, when the upper half bridge arm and the lower half bridge arm in the bridge arm circuit are alternately turned on, the trigger angle of the upper half bridge arm is obtained according to the power factor angle of the bridge arm circuit; the phase of the current of the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off.

[0073] It should be understood that the upper and lower arms of the same phase bridge circuit alternately conduct within a cycle to ensure continuous phase current. If the trigger angle of the upper arm is θ, the trigger angle of the lower arm is π-θ. The following describes the control of the upper arm, and the control of the lower arm corresponds to it.

[0074] Based on the converter in the above embodiment, the voltage u of the upper half bridge arm of any phase bridge arm circuit in the converter is u and current i u The following formulas (1) and (2) are satisfied respectively:

[0075] (1)

[0076] (2)

[0077] Among them, U dc is the DC voltage, m is the modulation ratio, is the phase current peak value, ω is the power frequency angular frequency, φ is the power factor angle, and θ is the trigger angle of the upper half bridge arm in the bridge arm circuit.

[0078] It should be noted that the modulation ratio m in the embodiment of the present application has an adjustment range of the rated modulation ratio m. R ±10% of the surrounding area.

[0079] The energy E of the bridge arm circuit satisfies the following formula (3):

[0080] (3)

[0081] According to the above formulas (1), (2) and (3), it can be deduced that the converter energy balance constraint must satisfy the following formula (4):

[0082] (4)

[0083] According to the above formula (4), the expression of the trigger angle θ of the upper half bridge arm can be further obtained. The expression of the trigger angle θ is shown in the following formula (5):

[0084] (5)

[0085] In an embodiment of the present application, it is necessary to control the phase of the current of the upper half bridge arm accordingly according to the operating conditions of the bridge arm circuit (rectification absorption of reactive power, rectification transmission of reactive power, inversion absorption of reactive power and inversion transmission of reactive power).

[0086] The operating conditions of the bridge arm circuit can be determined according to the following formula (6):

[0087] (6)

[0088] If the power factor angle of the bridge arm circuit φ In the first quadrant, the bridge arm circuit operates in the condition of rectifying and absorbing reactive power; if the power factor angle of the bridge arm circuit is φ In the fourth quadrant, the bridge arm circuit operates in the condition of rectifying and sending reactive power; if the power factor angle of the bridge arm circuit is φ In the second quadrant, the bridge arm circuit operates in the condition of inverter absorption of reactive power; if the power factor angle of the bridge arm circuit is φ In the third quadrant, the bridge arm circuit operates in the condition of inverter sending reactive power.

[0089] In one possible implementation, when the bridge arm circuit operates in the rectification and reactive power absorption mode, if the power factor angle of the bridge arm circuit is within a first interval, a first trigger angle of the upper half bridge arm is obtained based on the power factor angle; the phase of the current of the upper half bridge arm is controlled based on the first trigger angle to turn off the diode soft switch; wherein the lower limit value of the first interval is 0, and the upper limit value of the first interval is π / 2.

[0090] The expression of the first trigger angle of the upper half bridge arm is shown in the following formula (7):

[0091] (7)

[0092] Among them, the boundary of the power factor angle φ 1 Satisfies the following formula (8)

[0093] (8)

[0094] When rectifying and absorbing reactive power, if the power factor angle of the bridge arm circuit is less than or equal to the corresponding boundary φ 1 , then through θ 1 The expression of the first trigger angle of the upper half bridge arm is obtained; if the power factor angle of the bridge arm circuit is greater than the corresponding boundary φ 1 , then through θ 2The first trigger angle of the upper half bridge arm is obtained from the expression. The phase of the current in the upper half bridge arm is controlled according to the first trigger angle to cause the diode to be soft-switched off. When the diode is soft-switched off, the absorption circuit in the aforementioned embodiment is used to achieve series voltage balancing between the single switch circuits.

[0095] In another possible implementation, when the bridge arm circuit operates in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, the second trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the second trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the second interval, the third trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the third trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit value of the second interval is 0.

[0096] The expression of the second trigger angle of the upper half bridge arm is shown in the following formula (9):

[0097] (9)

[0098] The power factor angle boundary φ2 satisfies the following formula (10):

[0099] (10)

[0100] When rectifying and transmitting reactive power, if the power factor angle of the bridge arm circuit is greater than or equal to the corresponding boundary φ 2 ,pass θ 2 The second trigger angle of the upper half bridge arm is obtained from the expression; the phase of the current in the upper half bridge arm is controlled according to the second trigger angle to cause the diode to be soft-switched off. When the diode is soft-switched off, the series voltage balancing between the single switch circuits is achieved by the absorption circuit in the aforementioned embodiment.

[0101] If the power factor angle of the bridge arm circuit is less than the corresponding boundary φ 2 ,pass θ 2 The expression (ignoring θ 2 The third trigger angle of the upper half bridge arm is obtained by controlling the phase of the current in the upper half bridge arm according to the third trigger angle, thereby causing the controllable switch to be hard-switched off. When the controllable switch is hard-switched off, the arrester in the aforementioned embodiment is used to achieve series voltage balancing between the single switch circuits.

[0102] Furthermore, in the process of controlling the phase of the current of the upper half bridge arm through the third trigger angle of the bridge arm circuit, the embodiment of the present application can also control the switching frequency of the controllable switch tube so that the switching frequency of the controllable switch tube is less than the preset threshold, thereby enabling the lightning arrester to clamp the overshoot voltage when the controllable switch tube is hard-switched off as much as possible, and further realize the series voltage equalization between the controllable switch tubes connected in series.

[0103] In another possible implementation, when the bridge arm circuit operates in the inverter to absorb reactive power, if the power factor angle of the bridge arm circuit is within a third interval, the fourth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fourth trigger angle to turn off the diode soft switch; wherein the lower limit value of the third interval is π / 2, and the upper limit value of the third interval is π.

[0104] The expression of the fourth trigger angle of the upper half bridge arm is shown in the following formula (11):

[0105] (11)

[0106] The power factor angle boundary φ3 satisfies the following formula (12):

[0107] (12)

[0108] When the inverter absorbs reactive power, if the power factor angle of the bridge arm circuit is less than or equal to the corresponding boundary φ 3 , then through θ 1 The expression of the fourth trigger angle of the upper half bridge arm is obtained; if the power factor angle of the bridge arm circuit is greater than the corresponding boundary φ 3 , then through θ 2 The fourth trigger angle of the upper half bridge arm is obtained from the expression. The phase of the current in the upper half bridge arm is controlled according to the fourth trigger angle to cause the diode to softly switch off. When the diode is softly switched off, the absorption circuit in the aforementioned embodiment is used to achieve series voltage balancing between the single switch circuits.

[0109] In another possible implementation, when the bridge arm circuit operates in the inverter to transmit reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, the fifth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fifth trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the fourth interval, the sixth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the sixth trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , mR is the rated modulation ratio.

[0110] The expression of the fifth trigger angle of the upper half bridge arm is shown in the following formula (13):

[0111] (13)

[0112] The power factor angle boundary φ4 satisfies the following formula (14):

[0113] (14)

[0114] When the inverter sends reactive power, if the power factor angle of the bridge arm circuit is less than or equal to the corresponding boundary φ 4 ,pass θ 1 The fifth trigger angle of the upper half bridge arm is obtained from the expression; the phase of the current in the upper half bridge arm is controlled according to the fifth trigger angle to cause the diode to be softly switched off. When the diode is softly switched off, the snubber circuit in the aforementioned embodiment achieves series voltage balancing between the single switch circuits.

[0115] If the power factor angle of the bridge arm circuit is greater than the corresponding boundary φ 4 ,pass θ 1 The expression (ignoring θ 1 The sixth trigger angle of the upper half bridge arm is obtained by controlling the phase of the current in the upper half bridge arm according to the sixth trigger angle, thereby causing the controllable switch to be hard-switched off. When the controllable switch is hard-switched off, the arrester in the aforementioned embodiment is used to achieve series voltage balancing between the single switch circuits.

[0116] Furthermore, in the process of controlling the phase of the current of the upper half bridge arm through the sixth trigger angle of the bridge arm circuit, the embodiment of the present application can also control the switching frequency of the controllable switch tube so that the switching frequency of the controllable switch tube is less than the preset threshold, thereby enabling the lightning arrester to clamp the overshoot voltage when the controllable switch tube is hard-switched off as much as possible, and further realize the series voltage equalization between the controllable switch tubes connected in series.

[0117] In an embodiment of the present application, on the basis of connecting the absorption circuit and the lightning arrester in series at both ends of the controllable switch tube, by controlling the phase of the current, the diode in the upper half bridge arm is soft-switched off, and then the energy is absorbed by the absorption circuit to slow down the rate of change of the voltage, thereby achieving dynamic voltage balancing; by controlling the phase of the current, the controllable switch tube in the upper half bridge arm is hard-switched off, and then the overshoot voltage is clamped by the lightning arrester, thereby achieving dynamic voltage balancing.

[0118] On the basis of achieving series voltage balancing between single-switch circuit modules, the embodiment of the present application connects the single-switch circuit module in series with the sub-module module, thereby reducing the number of sub-modules and the volume of the capacitor within the sub-module, and increasing the power density of the converter valve body; and the converter in the embodiment of the present application allows the modulation ratio of the converter to be greater than 1 under the condition of overmodulation operation, and the overmodulation operation of the converter can be achieved without relying on the injection of external harmonics, thereby increasing the transmission capacity of the converter and improving the reactive support capability of the converter during transient operation.

[0119] It should be noted that the specific form of the sub-module SM is not specifically limited in the embodiments of the present application. For example, the sub-module can be a half-bridge sub-module or a full-bridge sub-module.

[0120] When the controllable switch tube is IGCT, the schematic diagram of the half-bridge submodule can be found in Figure 6 .like Figure 6 As shown, the half-bridge submodule includes a second controllable switch G2, a third controllable switch G3, a second diode D2, a third diode D3, a sixth diode D6, a second capacitor C2, a third capacitor C3, a first inductor L1 and a second resistor R2. The half-bridge submodule includes three parallel branches. In the first branch, the cathode of the second controllable switch tube G2 is connected to the anode of the third controllable switch tube G3, the second diode D2 is connected in anti-parallel to the second controllable switch tube G2, and the third diode D3 is connected in anti-parallel to the third controllable switch tube G3; in the second branch, the anode of the sixth diode D6 is connected to the anode of the second controllable switch tube G2, the cathode of the sixth diode D6 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the cathode of the third controllable switch tube G3; the second branch is connected to the third branch through the first inductor L1, and the first end of the first inductor L1 is connected to the anode of the sixth diode D6, and the second end of the first inductor L1 is connected to the cathode of the sixth diode D6 through the second resistor R2; in the third branch, the first end of the third capacitor C3 is connected to the second end of the first inductor L1, and the second end of the third capacitor C3 is connected to the cathode of the third controllable switch tube G3.

[0121] The following will introduce the operation of the submodule in terms of its locked state, switched-on state and cut-off state.

[0122] In the locked state, both the second and third controllable switches G2 and G3 are off, putting the submodule in an abnormal operating state. This state can be used to charge the submodule's capacitors during startup. In the event of a fault, the submodule's capacitors can be bypassed to prevent further damage.

[0123] In the active state, the second controllable switch G2 of the upper bridge arm is turned on, the third controllable switch G3 of the lower bridge arm is turned off, and the third capacitor C3 is connected to the circuit. At this point, the third capacitor C3 can be in either a charging or discharging state, depending on the direction of the current. If the bridge arm current flows into the submodule, the third capacitor C3 is in a charging state; if the bridge arm current flows out of the submodule, the third capacitor C3 is in a discharging state, outputting energy to the circuit.

[0124] In the cut-off state, the second controllable switch tube G2 of the upper half bridge arm is turned off, the second controllable switch tube G3 of the lower half bridge arm is turned on, and the third capacitor C3 is cut out of the circuit. At this time, the output voltage of the submodule is zero.

[0125] In the embodiment of the present application, by controlling the on and off states of the half-bridge submodule and cascading multiple submodules, a multi-level waveform can be obtained at the output end to achieve DC to AC conversion or AC to DC conversion.

[0126] In order to further reduce the harmonic content in the output voltage of the submodule, in the embodiment of the present application, a filtering circuit composed of a first inductor L1, a sixth diode D6, a second resistor R2 and a second capacitor C2 is used to reduce the harmonic content in the output voltage of the submodule and improve the power quality.

[0127] When the controllable switch tube is an IGBT, the schematic diagram of the half-bridge submodule can be found in Figure 7 .like Figure 7 As shown, the half-bridge submodule includes a second controllable switch G2, a third controllable switch G3, a second diode D2, a third diode D3, and a second capacitor C2. The cathode of the second controllable switch G2 is connected to the anode of the third controllable switch G3, the second diode D2 is connected in anti-parallel to the second controllable switch G2, and the third diode D3 is connected in anti-parallel to the third controllable switch G3. The anode of the second controllable switch G2 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the cathode of the third controllable switch G3.

[0128] It should be understood that the controllable switch tube is a half-bridge sub-module of IGBT, and the principle is the same as that of the half-bridge sub-module of IGCT, which will not be repeated here.

[0129] When the controllable switch tube is IGCT, the schematic diagram of the full-bridge submodule can be found in Figure 8 .like Figure 8As shown, the full-bridge submodule includes a second controllable switch tube G2, a third controllable switch tube G3, a fourth controllable switch tube G4, a fifth controllable switch tube G5, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a second capacitor C2, a third capacitor C3, a first inductor L1, and a second resistor R2. The full-bridge submodule includes four parallel branches. In the first branch, the cathode of the second controllable switch tube G2 is connected to the anode of the third controllable switch tube G3, the second diode D2 is connected in anti-parallel to the second controllable switch tube G2, and the third diode D3 is connected in anti-parallel to the third controllable switch tube G3; in the second branch, the anode of the sixth diode D6 is connected to the anode of the second controllable switch tube G2, the cathode of the sixth diode D6 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the cathode of the third controllable switch tube G3; the second branch is connected to the third branch through the first inductor L1. In the third branch, a first end of the first inductor L1 is connected to the anode of the sixth diode D6, and a second end of the first inductor L1 is connected to the cathode of the sixth diode D6 via a second resistor R2; in the third branch, a first end of the third capacitor C3 is connected to the second end of the first inductor L1, and a second end of the third capacitor C3 is connected to the cathode of the third controllable switch tube G3; in the fourth branch, the cathode of the fourth controllable switch tube G4 is connected to the anode of the fifth controllable switch tube G5, the fourth diode D4 is connected in anti-parallel to the second controllable switch tube G4, and the fifth diode D5 is connected in anti-parallel to the third controllable switch tube G5.

[0130] The following will introduce the operation of the submodule with respect to the locked state, positive input state, negative input state and cut-off state.

[0131] In the blocking state, the second controllable switch G2, the third controllable switch G3, the fourth controllable switch G4 and the fifth controllable switch G5 are all turned off. In this state, the submodule can use the third capacitor C3 to absorb the fault current, clear the fault current and avoid oscillation.

[0132] In the positive input state, when the second controllable switch tube G2 is turned on, the third controllable switch tube G3 is turned off, the fourth controllable switch tube G4 is turned off, and the fifth controllable switch tube G5 is turned on, the current flows out from the positive electrode of the power supply, passes through the second controllable switch tube G2, the first capacitor C1 and the fifth controllable switch tube G5, and returns to the negative electrode of the power supply.

[0133] In the negative input state, when the second controllable switch tube G2 is turned off, the third controllable switch tube G3 is turned on, the fourth controllable switch tube G4 is turned on, and the fifth controllable switch tube G5 is turned off, the current flows out from the negative electrode of the power supply, passes through the fourth controllable switch tube G4, the first capacitor C1 and the third controllable switch tube G3, and returns to the positive electrode of the power supply.

[0134] In the cut-off state, there are two implementation situations: in the first situation, the second controllable switch tube G2 is turned on, the third controllable switch tube G3 is turned on, the fourth controllable switch tube G4 is turned off, and the fifth controllable switch tube G5 is turned off. At this time, the current can flow from the second controllable switch tube G2 to the third controllable switch tube G3, but will not pass through the first capacitor C1; in the second situation, the second controllable switch tube G2 is turned off, the third controllable switch tube G3 is turned off, the fourth controllable switch tube G4 is turned on, and the fifth controllable switch tube G5 is turned on. The current flows from the fourth controllable switch tube G4 to the fifth controllable switch tube G5, and also does not pass through the first capacitor C1. In both situations, the output voltage is 0.

[0135] In the embodiment of the present application, by controlling the on and off states of the full-bridge submodule and cascading multiple submodules, a multi-level waveform can be obtained at the output end to achieve DC to AC conversion or AC to DC conversion.

[0136] In order to further reduce the harmonic content in the output voltage of the submodule, in the embodiment of the present application, a filtering circuit composed of a first inductor L1, a sixth diode D6, a second resistor R2 and a second capacitor C2 is used to reduce the harmonic content in the output voltage of the submodule and improve the power quality.

[0137] When the controllable switch tube is IGBT, the schematic diagram of the full-bridge submodule can be found in Figure 9 .like Figure 9 As shown, the full-bridge submodule includes a second controllable switch transistor G2, a third controllable switch transistor G3, a fourth controllable switch transistor G4, a fifth controllable switch transistor G5, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, and a second capacitor C2. The cathode of the second controllable switch transistor G2 is connected to the anode of the third controllable switch transistor G3, the second diode D2 is connected in anti-parallel to the second controllable switch transistor G2, and the third diode D3 is connected in anti-parallel to the third controllable switch transistor G3; the cathode of the fourth controllable switch transistor G4 is connected to the anode of the fifth controllable switch transistor G5, the fourth diode D4 is connected in anti-parallel to the second controllable switch transistor G4, and the fifth diode D5 is connected in anti-parallel to the third controllable switch transistor G5; the anode of the second controllable switch transistor G2 is connected to the first end of the second capacitor C2, the second end of the second capacitor C2 is connected to the cathode of the third controllable switch transistor G3, the anode of the fourth controllable switch transistor G4 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the cathode of the fifth controllable switch transistor G5.

[0138] It should be understood that the controllable switch tube is a full-bridge sub-module of IGBT, and the principle is the same as that of the full-bridge sub-module of IGCT, which will not be repeated here.

[0139] Based on the converter provided in the above embodiments, an embodiment of the present application further provides a method for controlling the converter, which is described in detail below with reference to the accompanying drawings.

[0140] The converter comprises three-phase bridge arm circuits, each of the three-phase bridge arm circuits comprises an upper half bridge arm and a lower half bridge arm connected in series, the upper half bridge arm and the lower half bridge arm comprise a sub-module module and a single-switch circuit module connected in series, the sub-module module is connected close to a direct current side, and the single-switch circuit module is connected close to an alternating current side; the sub-module module comprises a plurality of sub-modules connected in series, and the single-switch circuit module comprises a plurality of single-switch circuits connected in series; wherein the single-switch circuit comprises a controllable switch tube, a diode, an absorption circuit and a lightning arrester; the diode is connected in antiparallel across the controllable switch tube, the absorption circuit is connected in parallel across the controllable switch tube, and the lightning arrester is connected in parallel across the controllable switch tube.

[0141] The method comprises:

[0142] S100: obtaining a trigger angle of the upper half bridge arm according to a power factor angle of the bridge arm circuit in a case where the upper half bridge arm and the lower half bridge arm in the bridge arm circuit are alternately turned on.

[0143] S200: controlling a phase of a current of the upper half bridge arm according to the trigger angle, so that the diode is soft switched off or the controllable switch tube is hard switched off.

[0144] In the embodiments of the present application, the upper half bridge arm and the lower half bridge arm of each phase bridge arm circuit in the converter each comprise a sub-module module and a single-switch circuit module connected in series. The sub-module module comprises a plurality of sub-modules connected in series, and the single-switch circuit module comprises a plurality of single-switch circuits connected in series. Compared with a two-level current source converter, the converter in the embodiments of the present application can reduce the loss of the valve body; compared with a modular multilevel voltage source converter, the converter in the embodiments of the present application can improve the power density of the valve body.

[0145] The absorption circuit and the lightning arrester are connected in series across the controllable switch tube. In a case where the antiparallel diode of the controllable switch tube is soft switched off, the absorption circuit absorbs energy to slow down the rate of change of voltage, thereby achieving dynamic voltage sharing. In a case where the controllable switch tube is hard switched off, the lightning arrester clamps the overshoot voltage, thereby achieving dynamic voltage sharing. In addition, in a case where the converter in the embodiments of the present application is over-modulated, the modulation ratio of the converter is allowed to be greater than 1, the over-modulation operation of the converter can be achieved without relying on the injection of external harmonics, the transmission capacity of the converter is increased, and the reactive power support capability of the converter during transient operation is improved.

[0146] In one possible implementation, the phase of the current in the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off, including: when the bridge arm circuit operates in rectification and reactive power absorption, if the power factor angle of the bridge arm circuit is within a first interval, obtaining the first trigger angle of the upper half bridge arm according to the power factor angle; controlling the phase of the current in the upper half bridge arm according to the first trigger angle, so that the diode is soft-switched off; wherein the lower limit value of the first interval is 0, and the upper limit value of the first interval is π / 2.

[0147] In one possible implementation, the phase of the current of the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off, including: when the bridge arm circuit operates in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, the second trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the second trigger angle, so that the diode is soft-switched off; if the power factor angle of the bridge arm circuit exceeds the second interval, the third trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the third trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit value of the second interval is 0.

[0148] In one possible implementation, the phase of the current in the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off, including: when the bridge arm circuit operates in the inverter to absorb reactive power, if the power factor angle of the bridge arm circuit is within the third interval, obtaining the fourth trigger angle of the upper half bridge arm according to the power factor angle; controlling the phase of the current in the upper half bridge arm according to the fourth trigger angle, so that the diode is soft-switched off; wherein the lower limit value of the third interval is π / 2, and the upper limit value of the third interval is π.

[0149] In one possible implementation, the phase of the current of the upper half bridge arm is controlled according to the trigger angle, so that the diode is soft-switched off or the controllable switch tube is hard-switched off, including: when the bridge arm circuit operates in the inverter to send reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, the fifth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fifth trigger angle, so that the diode is soft-switched off; if the power factor angle of the bridge arm circuit exceeds the fourth interval, the sixth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the sixth trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , m R is the rated modulation ratio.

[0150] In a possible implementation, the method for controlling the converter further includes controlling the switching frequency of the controllable switch tube in the upper half bridge arm to be less than a preset threshold.

[0151] In one possible implementation, see Figure 11 , which is a schematic diagram of a control device provided in an embodiment of the present application.

[0152] The control device may include a memory 1011 and a processor 1012. The processor 1012 may be connected to the converter and may drive switches in each bridge arm circuit in the converter. Figure 11 As shown, the memory can be a random access memory (RAM), a flash memory, a read only memory (ROM), an EPROM memory, an Electronic Programmable ROM (EPROM), a register, a hard disk, a removable disk, etc.

[0153] The memory 1011 can store computer instructions. When the computer instructions stored in the memory 1011 are executed by the processor 1012, the processor 1012 can be used to execute the inverter control method. The memory 1011 can also store data, such as the preset range, preset threshold, and other information involved in the above embodiments.

[0154] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function according to the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), or a semiconductor medium (e.g., a solid-state drive (SSD)).

[0155] The present application also provides a readable storage medium for storing the methods provided in the above embodiments, such as a random access memory (RAM), flash memory, read-only memory (ROM), EPROM, electronic programmable ROM (EPROM), register, hard disk, removable disk, or any other form of storage medium known in the art.

[0156] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from the other embodiments. Similar or identical parts between the various embodiments can be referred to in conjunction with each other. The methods disclosed in the embodiments are described briefly because they correspond to the product embodiments disclosed in the embodiments. For relevant details, refer to the description of the product embodiments.

[0157] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A converter, characterized in that: include: A three-phase bridge arm circuit and a controller, wherein each phase bridge arm circuit in the three-phase bridge arm circuit includes an upper half bridge arm and a lower half bridge arm connected in series; the upper half bridge arm and the lower half bridge arm include a submodule module and a single switch circuit module connected in series, the submodule module is connected close to the DC side, and the single switch circuit module is connected close to the AC side; The submodule module includes multiple submodules connected in series, and the single switch circuit module includes multiple single switch circuits connected in series; wherein the single switch circuit includes a controllable switch tube, a diode, an absorption circuit and a lightning arrester; the diode is connected in anti-parallel to both ends of the controllable switch tube, the absorption circuit is connected in parallel to both ends of the controllable switch tube, and the lightning arrester is connected in parallel to both ends of the controllable switch tube; The controller is configured to, when the bridge arm circuit operates in a rectification and reactive power absorption mode, determine a first trigger angle of the upper half bridge arm based on a power factor angle of the bridge arm circuit within a first interval; and control a phase of a current in the upper half bridge arm based on the first trigger angle to cause the diode soft switch to be turned off; wherein a lower limit value of the first interval is 0, and an upper limit value of the first interval is π / 2; When the bridge arm circuit operates in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, the second trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the second trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the second interval, the third trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the third trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit of the second interval is 0; When the bridge arm circuit operates in an inverter mode to absorb reactive power, if the power factor angle of the bridge arm circuit is within a third interval, a fourth trigger angle of the upper half bridge arm is obtained based on the power factor angle; a phase of the current of the upper half bridge arm is controlled based on the fourth trigger angle to cause the diode soft switch to be turned off; wherein a lower limit value of the third interval is π / 2, and an upper limit value of the third interval is π; When the bridge arm circuit operates in the inverter to transmit reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, the fifth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fifth trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the fourth interval, the sixth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the sixth trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , m R is the rated modulation ratio.

2. The converter according to claim 1, characterized in that The controller is further configured to control the switching frequency of the controllable switch tube in the upper half bridge arm to be less than a preset threshold.

3. The converter according to claim 1 or 2, characterized in that: The absorption circuit includes a resistor and a capacitor connected in series.

4. A method for controlling a converter, characterized in that: The converter includes a three-phase bridge arm circuit, each phase bridge arm circuit in the three-phase bridge arm circuit includes an upper half bridge arm and a lower half bridge arm connected in series; the upper half bridge arm and the lower half bridge arm include a sub-module module and a single switch circuit module connected in series, the sub-module module is connected close to the DC side, and the single switch circuit module is connected close to the AC side; the sub-module module includes multiple sub-modules connected in series, and the single switch circuit module includes multiple single switch circuits connected in series; wherein the single switch circuit includes a controllable switch tube, a diode, an absorption circuit and a lightning arrester; the diode is connected in anti-parallel to both ends of the controllable switch tube, the absorption circuit is connected in parallel to both ends of the controllable switch tube, and the lightning arrester is connected in parallel to both ends of the controllable switch tube; Methods include: When the bridge arm circuit operates in a rectification and reactive power absorption mode, if the power factor angle of the bridge arm circuit is within a first interval, a first trigger angle of the upper half bridge arm is obtained based on the power factor angle; a phase of the current of the upper half bridge arm is controlled based on the first trigger angle to cause the diode soft switch to be turned off; wherein the lower limit value of the first interval is 0, and the upper limit value of the first interval is π / 2; When the bridge arm circuit operates in the rectification and transmission of reactive power, if the power factor angle of the bridge arm circuit is within the second interval, the second trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the second trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the second interval, the third trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the third trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the second interval is , m R is the rated modulation ratio, and the upper limit of the second interval is 0; When the bridge arm circuit operates in an inverter mode to absorb reactive power, if the power factor angle of the bridge arm circuit is within a third interval, a fourth trigger angle of the upper half bridge arm is obtained based on the power factor angle; a phase of the current of the upper half bridge arm is controlled based on the fourth trigger angle to cause the diode soft switch to be turned off; wherein a lower limit value of the third interval is π / 2, and an upper limit value of the third interval is π; When the bridge arm circuit operates in the inverter to transmit reactive power, if the power factor angle of the bridge arm circuit is within the fourth interval, the fifth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the fifth trigger angle, so that the diode soft switch is turned off; if the power factor angle of the bridge arm circuit exceeds the fourth interval, the sixth trigger angle of the upper half bridge arm is obtained according to the power factor angle; the phase of the current of the upper half bridge arm is controlled according to the sixth trigger angle, so that the controllable switch tube is hard-switched off; wherein the lower limit value of the fourth interval is π, and the upper limit value of the fourth interval is , m R is the rated modulation ratio.

5. A control device, characterized in that: The system comprises a processor and a memory, wherein the memory is used to store programs, instructions or codes, and the processor is used to execute the programs, instructions or codes in the memory to complete the control method of the converter as claimed in claim 4.

6. A computer-readable storage medium, characterized in that A computer program is stored, and the computer program is loaded by a processor to execute the control method of the converter according to claim 4.

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