Converter, control method thereof, storage medium and flexible direct current power transmission system

Abstract

The invention provides a current converter, a control method thereof, a storage medium and a flexible DC power transmission system, the current converter comprises a plurality of phases of bridge arms, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm which are connected in series, each of the upper bridge arm and the lower bridge arm comprises a switching circuit and a plurality of sub-modules which are connected in series, the switching circuit comprises a reactor and a plurality of switching modules, each switch module comprises a first controllable switch tube, a first diode and a first energy absorption module, the first controllable switch tube is reversely connected with the first diode in parallel, the first energy absorption module is connected with the first controllable switch tube in parallel, the reactor is sequentially connected with the first controllable switch tubes of the plurality of switch modules in series, and the upper bridge arm and the lower bridge arm do not comprise lightning arresters. The current converter at least solves the problem of high loss of the current converter in the prior art.

Description

Technical Field

[0001] This application relates to the field of power electronic conversion technology, and more specifically, to a converter, its control method, a computer-readable storage medium, and a flexible DC transmission system. Background Technology

[0002] Currently, flexible high-voltage direct current (VSC-HVDC) transmission technology based on voltage source converters has become an important technical means for the high-proportion consumption of renewable energy in the future due to the absence of commutation failure problems and the ability to achieve decoupled control of active and reactive power. Existing flexible DC converters are modular multilevel converters (MMCs), with bridge arms consisting only of sub-modules. The upper and lower bridge arms of each phase are simultaneously turned on. By controlling the switching and modulation of AC voltage and supporting DC voltage by controlling the sub-modules, a large number of output levels can be achieved. The switching frequency of the devices is relatively low, and the voltage level can be flexibly expanded by increasing the number of sub-modules.

[0003] However, each phase arm of the converter has a circulating DC current. This circulating DC current not only increases system losses but can also cause overheating of switching devices and capacitors, affecting the stability of the entire system. To eliminate the circulating DC current, large arm reactors are required on the arm, resulting in higher converter losses. Summary of the Invention

[0004] The main objective of this application is to provide a converter, its control method, a computer-readable storage medium, and a flexible DC transmission system to at least solve the problem of high losses in prior art converters.

[0005] To achieve the above objectives, according to one aspect of this application, a converter is provided, comprising: a multi-phase bridge arm, each phase bridge arm including an upper bridge arm and a lower bridge arm connected in series, each upper bridge arm and the lower bridge arm including a series-connected switching circuit and a plurality of sub-modules, each switching circuit including a reactor and a plurality of switching modules, each switching module including a first controllable switch transistor, a first diode and a first energy absorption module, the first controllable switch transistor and the first diode being connected in reverse parallel, the first energy absorption module being connected in parallel with the first controllable switch transistor, the reactor being connected in series with the first controllable switch transistors of the plurality of switching modules, and neither the upper bridge arm nor the lower bridge arm including a surge arrester.

[0006] Optionally, the first energy absorption module includes: a second diode, the anode of which is electrically connected to the cathode of the first diode; a first energy storage device, one end of which is electrically connected to the cathode of the second diode and the other end of which is electrically connected to the anode of the first diode; and a discharge device connected in parallel with the first energy storage device.

[0007] Optionally, the first energy storage device includes a capacitor, and the discharge device includes a resistor.

[0008] Optionally, the first controllable switch is an IGCT (Integrated Gate-Commutated Thyristor) switch or an IGBT (Insulated Gate Bipolar Transistor) switch.

[0009] Optionally, the submodule includes: a second energy storage device; a second energy absorption module including three terminals, wherein a first terminal of the second energy absorption module is electrically connected to one terminal of the second energy storage device, and a second terminal of the second energy absorption module is electrically connected to the other terminal of the second energy storage device; a second controllable switch, wherein one terminal of the second controllable switch is electrically connected to the third terminal of the second energy absorption module; a third diode, connected in reverse parallel across the two ends of the second controllable switch; a third controllable switch, wherein one terminal of the third controllable switch is electrically connected to the other terminal of the second controllable switch, and the other terminal of the third controllable switch is electrically connected to the other end of the second energy storage device; and a fourth diode, connected in reverse parallel across the two ends of the third controllable switch.

[0010] Optionally, the second controllable switch and the third controllable switch are respectively an IGCT switch or an IGBT switch.

[0011] Optionally, the submodule includes a second energy storage device, and the maximum number of the switching modules in the bridge arm is [number missing]. The maximum number of the submodules is ,in, The function is a floor function, where M is the maximum number of switch modules and N is the maximum number of sub-modules. This refers to the DC bus voltage of the converter. The voltage stored in the second energy storage device.

[0012] According to another aspect of this application, a control method for a converter is provided for controlling any of the converters described above, comprising: using a power frequency square wave to alternately turn on and off the switching circuits of the upper and lower bridge arms; based on a half-wave modulation strategy and the on and off strategy of the switching circuits, alternately engaging and disengaging the sub-modules of the upper and lower bridge arms, such that when the switching circuit is on, the corresponding sub-module of the upper or lower bridge arm is engaged, and when the switching circuit is off, the corresponding sub-module of the upper or lower bridge arm is disengaged.

[0013] Optionally, using a power frequency square wave to alternately turn the switching circuits of the upper and lower bridge arms on and off includes: determining the control function of the switching circuit based on the power frequency square wave. ,in, The control function is... Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the symbol function is 1, in When the sign function is 0, the control function is used to control the switching circuit, such that when the control function is 1, the switching circuit of the upper bridge arm is turned on and the switching circuit of the lower bridge arm is turned off, and when the control function is 0, the switching circuit of the upper bridge arm is turned off and the switching circuit of the lower bridge arm is turned on.

[0014] Optionally, based on the half-wave modulation strategy and the on / off strategy of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, including: generating a current reference value based on an active power reference value, a reactive power reference value, and a DC voltage; generating a reference voltage waveform for the sub-modules of the upper bridge arm and the lower bridge arm for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms; and generating control signals for the sub-modules of the upper and lower bridge arms using a nearest-level approximation modulation method based on the reference voltage waveform and the on / off strategy, so that the sub-module of the upper bridge arm is engaged and the sub-module of the lower bridge arm is disengaged, or the sub-module of the lower bridge arm is engaged and the sub-module of the upper bridge arm is disengaged.

[0015] Optionally, generating a reference voltage waveform for the submodule of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms includes: generating a reference voltage waveform for the submodule of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms. ,in, The reference voltage waveform of the submodule of the upper bridge arm. The reference voltage waveform of the submodule of the lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

[0016] Optionally, based on the reference voltage waveform and the turn-on and turn-off strategy, a nearest-level approximation modulation method is used to generate control signals for the submodules of the upper and lower bridge arms, including: determining the number of submodules in operation for the upper and lower bridge arms using the nearest-level approximation modulation method based on the reference voltage waveform and the turn-on and turn-off strategy. ,in, The number of sub-modules deployed in the upper bridge arm. The number of sub-modules deployed in the lower bridge arm. =0 or 1, When =1, it indicates that the turn-on and turn-off strategy is to turn on the switching circuit of the upper bridge arm. When = 0, it indicates that the turn-on and turn-off strategy is to turn on the switching circuit of the lower bridge arm. The reference voltage waveform of the submodule of the upper bridge arm. The reference voltage waveform is provided for the submodule of the lower bridge arm, and the submodule includes a second energy storage device. The ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device; and the corresponding control signal for the sub-module is generated based on the number of sub-modules deployed in the upper and lower bridge arms.

[0017] According to another aspect of this application, a computer-readable storage medium is provided, the computer-readable storage medium including a stored program, wherein, when the program is executed, it controls the device on which the computer-readable storage medium is located to perform any of the methods described.

[0018] According to another aspect of this application, a flexible DC transmission system is provided, comprising: any of the converters described above; and electronic equipment including: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including methods for performing any of the methods described above.

[0019] Using the technical solution of this application, in the upper and lower arms of the converter, the switching circuit and multiple sub-modules are connected in series. The switching circuit includes a reactor, multiple switching modules including a first controllable switch, a first diode and a first energy absorption module. The first controllable switch and the first diode are connected in reverse parallel. The first energy absorption module is connected in parallel across the first controllable switch. The reactor and multiple first controllable switches are connected in series in sequence. No surge arresters are installed in either the upper or lower arms. This application incorporates switching circuits in the upper and lower arms of the converter. Through coordinated control, the switching states of the upper and lower arms and the switching of submodules are managed. When the switching circuit is on, the submodule on the corresponding arm is engaged; when the switching circuit is off, the submodule on the corresponding arm is locked. This allows the upper and lower arms to alternately conduct within different half-cycles of the power frequency cycle. Consequently, DC circulating current cannot form a complete loop between the upper and lower arms within half a power frequency cycle, thus suppressing the formation of DC circulating current in the upper and lower arms. This means that the reactor does not need to bear excessive DC circulating current suppression, thus reducing the inductance requirement of the reactor in the arms. Lower inductance not only reduces overall system losses and response time but also helps to reduce reactor cost and physical size. Furthermore, because the required inductance of the inductors in this application is low, the resulting overvoltage level is also correspondingly reduced. Therefore, surge arresters are no longer necessary in this case. Thus, the converter in this application does not require surge arresters, which not only significantly reduces the overall losses of the converter but also reduces its cost and size. In addition, a first energy absorption module is set in the upper and lower bridge arms to absorb excess energy. This can quickly absorb energy, clamp the voltage within a safe range, and protect the controllable switching transistor. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 A schematic diagram of the structure of a converter according to an embodiment of this application is shown;

[0022] Figure 2 A hardware structure block diagram of a mobile terminal for performing a control method for an inverter according to an embodiment of this application is shown;

[0023] Figure 3 A schematic flowchart of a control method for a converter according to an embodiment of this application is shown;

[0024] Figure 4 A control block diagram of a converter provided according to an embodiment of this application is shown.

[0025] The above figures include the following reference numerals:

[0026] 10. Switching circuit; 101. Reactor; 102. First controllable switch transistor; 103. First diode; 104. Second diode; 105. First energy storage device; 106. Discharge device; 20. Submodule; 201. Second energy storage device; 202. Second controllable switch transistor; 203. Third diode; 204. Third controllable switch transistor; 205. Fourth diode; 206. Third energy storage device; 207. Fifth diode; 208. Resistive element; 209. Inductive element; 30. DC capacitor; 40. Smoothing reactor; 502. Processor; 504. Memory; 506. Transmission device; 508. Input / output device. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0029] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0030] As described in the background section, existing converters suffer from high losses, which limits their engineering applications. To address these technical problems, embodiments of this application provide a converter, its control method, a computer-readable storage medium, and a flexible DC transmission system.

[0031] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0032] This application provides a converter. Figure 1 An exemplary schematic diagram of a converter according to an embodiment of this application is shown, such as... Figure 1 As shown, the converter described above includes:

[0033] The multi-phase bridge arm includes an upper bridge arm and a lower bridge arm connected in series. Each upper bridge arm and the lower bridge arm includes a series-connected switching circuit 10 and multiple sub-modules 20. The switching circuit 10 includes a reactor 101 and multiple switching modules. Each switching module includes a first controllable switch transistor 102, a first diode 103, and a first energy absorption module. The first controllable switch transistor 102 and the first diode 103 are connected in reverse parallel. The first energy absorption module is connected in parallel with the first controllable switch transistor 102. The reactor 101 and the first controllable switch transistors 102 of the multiple switching modules are connected in series. Neither the upper bridge arm nor the lower bridge arm includes a surge arrester.

[0034] Specifically, the reactor 101 is connected in series with multiple of the aforementioned switching modules. A first diode 103 is connected in reverse parallel across the first controllable switch 102, and this first diode 103 serves a protective function.

[0035] In the above embodiments, in the upper and lower arms of the converter, the switching circuit and multiple sub-modules are connected in series. The switching circuit includes a reactor, multiple switching modules including a first controllable switch, a first diode and a first energy absorption module. The first controllable switch and the first diode are connected in reverse parallel. The first energy absorption module is connected in parallel across the first controllable switch. The reactor and multiple first controllable switches are connected in series in sequence. No surge arresters are installed in either the upper or lower arms. This application incorporates switching circuits in the upper and lower arms of the converter. Through coordinated control, the switching states of the upper and lower arms and the switching of submodules are managed. When the switching circuit is on, the submodule on the corresponding arm is engaged; when the switching circuit is off, the submodule on the corresponding arm is locked. This allows the upper and lower arms to alternately conduct within different half-cycles of the power frequency cycle. Consequently, DC circulating current cannot form a complete loop between the upper and lower arms within half a power frequency cycle, thus suppressing the formation of DC circulating current in the upper and lower arms. This means that the reactor does not need to bear excessive DC circulating current suppression, thus reducing the inductance requirement of the reactor in the arms. Lower inductance not only reduces overall system losses and response time but also helps to reduce reactor cost and physical size. Furthermore, because the required inductance of the inductors in this application is low, the resulting overvoltage level is also correspondingly reduced. Therefore, surge arresters are no longer necessary in this case. Thus, the converter in this application does not require surge arresters, which not only significantly reduces the overall losses of the converter but also reduces its cost and size. In addition, a first energy absorption module is set in the upper and lower bridge arms to absorb excess energy. This can quickly absorb energy, clamp the voltage within a safe range, and protect the controllable switching transistor.

[0036] In practical applications, when the first controllable switch 102 is turned off, due to the induced load in submodule 20, these loads generate back electromotive force, attempting to maintain a constant current. At this time, the first diode 103 connected in reverse parallel can act as a freewheeling path, allowing the current to continue flowing instead of being suddenly interrupted, preventing excessively high reverse voltage. This phenomenon is called "freewheeling," effectively preventing damage to the switch caused by energy not being released at the moment of turn-off. Therefore, the first diode 103 connected in reverse parallel across the first controllable switch 102 plays a certain protective role. At the moment of switching, especially under rapidly changing conditions, voltage spikes may occur because the energy stored in the induced load needs to find a way to release. The first diode 103 provides this path, effectively clamping the voltage and preventing damage to the first controllable switch 102. Furthermore, the first diode 103 connected in reverse parallel can also assist in implementing soft-switching technology, that is, when the first controllable switch 102 is turned on or off, it operates in a zero-voltage or zero-current state, thereby greatly reducing switching losses and switching stress, and improving system efficiency and reliability.

[0037] In some embodiments, the first energy absorption module includes: a second diode 104, the anode of which is electrically connected to the cathode of the first diode 103; a first energy storage device 105, one end of which is electrically connected to the cathode of the second diode 104, and the other end of which is electrically connected to the anode of the first diode 103; and a discharge device 106 connected in parallel with the first energy storage device 105. In this embodiment, when the first controllable switch 102 is turned off, the second diode 104 is in a forward conducting state, allowing energy to flow from the high-voltage region across the first controllable switch 102 to the first energy storage device 105 in the first energy absorption module. When the first controllable switch 102 is turned on, the second diode 104 is in a reverse cutoff state, preventing energy from flowing back from the first energy storage device 105 to the first controllable switch 102. This protects the first controllable switch 102 from the influence of reverse voltage and avoids potential damage. During the switching process, the first energy storage device 105 can absorb and store transient energy, further suppressing DC circulating current to prevent this energy from damaging the first controllable switch 102 or other circuit parts. The first energy storage device 105 can also prevent the voltage across the first controllable switch 102 from having an excessively high peak value at the moment of switching. By limiting the rate of voltage change, the first controllable switch 102 is protected from overvoltage impact. When the energy in the first energy storage device 105 is no longer needed, the discharge device 106 can convert this energy into heat energy and consume it, or release it in other ways, to prevent excessive energy accumulation in the first energy storage device 105. After the first controllable switch 102 is turned off, the energy in the first energy storage device 105 can be quickly discharged through the discharge device to help speed up the preparation for the next switching operation, reduce the waiting time during the switching process, and improve the system's response speed and efficiency. In addition, by controlling the resistance or conduction time of the discharge device 106, the protection capability of the first energy absorption module can be adjusted to prevent the first energy storage device 105 from overvoltage or overheating, thereby protecting the entire converter from damage caused by energy surges.

[0038] For example, the first energy storage device 105 includes a capacitor, and the discharge device 106 includes a resistor. This embodiment uses a capacitor and a resistor connected in parallel to construct a first energy absorption module. The capacitor absorbs energy, and the resistor discharges energy when appropriate, further ensuring the energy absorption and discharge of the switching module when the upper and lower bridge arms are alternately turned on.

[0039] Furthermore, the first energy storage device 105 is a capacitor, and the discharge device 106 is a resistor.

[0040] Those skilled in the art can ensure the stability and reliability of the energy absorption circuit by properly matching the values ​​of capacitors and resistors.

[0041] In some other exemplary embodiments, the first energy storage device 105 may also be a supercapacitor. The discharge device 106 may also be a transistor, a thyristor, or other energy discharge device 106 or energy discharge circuit that can convert electrical energy into thermal energy, mechanical energy, or chemical energy.

[0042] In another exemplary embodiment, the first controllable switch 102 is either an IGCT switch or an IGBT switch. This embodiment provides a choice of two controllable switches to meet the needs of different application scenarios.

[0043] In the case where the first controllable switch 102 is an IGCT switch, the IGCT switch is a highly efficient power switching device in high-voltage, high-current power electronic applications. Its internal structure and operating principle have significant characteristics, particularly the latch-up effect, which results in an extremely low voltage drop in the IGCT during conduction, thus greatly reducing conduction losses. Furthermore, due to the low on-state voltage drop of the IGCT switch, its power loss is also low during conduction. Since most of the losses occur when the switch is on, the low conduction loss characteristic reduces the need for large-capacity buffer energy storage devices; therefore, a μF-level capacitor is sufficient to handle the energy generated during switching.

[0044] When the first controllable switch 102 is an IGBT switch, by introducing IGBT-type solid-state switches in the upper and lower arms of the converter, the conduction cycle of the upper and lower arms can be precisely controlled, and the alternating conduction of the upper and lower arms of each phase can be achieved. The control of the sub-module 20 on the arm is not affected by the IGBT-type solid-state switch, so that the control strategy of the switching circuit 10 and the sub-module 20 can be consistent. Through the alternating conduction method, the fundamental frequency energy fluctuation in the sub-module 20 can be significantly reduced, thereby reducing the demand for energy storage devices in the sub-module 20 and making the device size of the energy storage devices in the sub-module 20 significantly smaller.

[0045] Optionally, the reactor 101 mentioned above in this application can be an anode reactor 101 with an inductance of μH, and the first energy storage device 105 mentioned above in this application can be a buffer capacitor with a capacitance of μF, to protect the upper and lower bridge arms, so that the overall loss of the converter is low and the converter meets the operation requirements of existing flexible DC projects.

[0046] For example, the first diode 103 described above can be a fast recovery diode. By selecting a fast recovery diode as the first diode 103, efficient and low-loss current rectification and freewheeling can be achieved in high-speed switching converter circuits, while minimizing switching noise and losses.

[0047] According to some alternative embodiments of this application, the submodule 20 includes: a second energy storage device 201; a second energy absorption module including three terminals, wherein a first terminal of the second energy absorption module is electrically connected to one terminal of the second energy storage device 201, and a second terminal of the second energy absorption module is electrically connected to the other terminal of the second energy storage device 201; a second controllable switch 202, wherein one terminal of the second controllable switch 202 is electrically connected to the third terminal of the second energy absorption module; a third diode 203, connected in reverse parallel across the two terminals of the second controllable switch 202; a third controllable switch 204, wherein one terminal of the third controllable switch 204 is electrically connected to the other terminal of the second controllable switch 202, and the other terminal of the third controllable switch 204 is electrically connected to the other terminal of the second energy storage device 201; and a fourth diode 205, connected in reverse parallel across the two terminals of the third controllable switch 204. This embodiment integrates a second energy storage device 201, a second energy absorption module, and a switching device into submodule 20, achieving flexible control and energy management of the bridge arm submodule 20. Each second energy storage device 201 in submodule 20 contributes a fixed level to the output voltage of the entire converter when activated. The sum of the voltages of all activated second energy storage devices 201 constitutes the instantaneous output voltage of the bridge arm. Furthermore, the charging and discharging of the second energy storage devices 201 in submodule 20 absorbs and releases fluctuating bridge arm power on the AC side, preventing these fluctuations from penetrating to the DC side. The second energy absorption module buffers and absorbs energy, protecting the controllable switching transistors from transient energy impacts. The switching device controls the activation and deactivation of submodule 20. Through the coordinated operation of the second energy storage device 201, the second energy absorption module, and the switching device, the control accuracy and response speed of submodule 20 are improved, enabling the converter to achieve high-efficiency, high-quality, and highly controllable high-power energy conversion.

[0048] In one specific embodiment, the second energy absorption module includes: a third energy storage device 206, one end of which is the second terminal of the second energy absorption module; a fifth diode 207, the cathode of which is electrically connected to the other end of the third energy storage device 206, and the anode of which is the third terminal of the second energy absorption module; a resistor 208, one end of which is the first terminal of the second energy absorption module, and the other end of which is electrically connected to the cathode of the fifth diode 207; and an inductor 209, one end of which is electrically connected to one end of the resistor 208, and the other end of which is electrically connected to the anode of the fifth diode 207. In this embodiment, the inductor 209 can limit the rate of change of the current of the controllable switch, and the third energy storage device 206 and the resistor 208 can absorb and dissipate the energy on the inductor, thereby protecting the device from overvoltage damage.

[0049] For example, the third energy storage device 206 described above can be a capacitor or a supercapacitor. In an optional embodiment of this application, the third energy storage device 206 is a capacitor.

[0050] For example, the third diode 203 and the fourth diode 205 described above can be fast recovery diodes. By selecting fast recovery diodes as the third diode 203 and the fourth diode 205, efficient and low-loss current rectification and freewheeling can be achieved in high-speed switching converter circuits, while minimizing switching noise and losses.

[0051] In practical applications, the aforementioned submodule 20 can be as follows: Figure 1 The half-bridge submodule shown is an example. Submodule 20 can also be a full-bridge submodule. Those skilled in the art can flexibly choose the type of submodule 20 according to the actual situation.

[0052] Optionally, the second controllable switch 202 and the third controllable switch 204 are respectively an IGCT switch or an IGBT switch. This embodiment provides a choice of two controllable switches to meet the needs of different application scenarios. IGCT has a lower on-state voltage drop and is more suitable for high power density and low loss scenarios, while IGBT may be more cost-effective under certain specific conditions.

[0053] In other embodiments, losses and costs can be balanced by using a combination of IGCT and IGBT.

[0054] like Figure 1 As shown, in a specific implementation, the submodule 20 includes a second energy storage device 201, and the maximum number of the switch modules in the bridge arm is [number missing]. The maximum number of the above submodules 20 is ,in, The function is the floor function, where M is the maximum number of the aforementioned switch modules, and N is the maximum number of the aforementioned sub-modules 20. This refers to the DC bus voltage of the aforementioned converter. The voltage stored in the second energy storage device 201 mentioned above.

[0055] The above embodiment calculates the ratio between the DC bus voltage and the voltage of sub-module 20 to determine the maximum number of sub-module 20 and switch modules in order to achieve the optimal operating state. By reasonably configuring the number of sub-module 20 and switch modules, the efficiency and reliability of the converter are improved, and the stable operation and energy management of the converter are further ensured.

[0056] In some other embodiments of this application, the first energy storage device 105, the discharge device 106, and the reactor 101 can be configured as devices with adjustable parameters. At least one of the following values ​​can be adjusted in real time according to the converter's operating conditions (including load demand and grid voltage fluctuations): the capacitance of the first energy storage device 105, the resistance of the discharge device 106, and the inductance of the reactor 101. Specifically, when the load demand exceeds a first threshold or the grid voltage fluctuation is greater than a second threshold, the capacitance, resistance, and inductance are increased; when the load demand is less than or equal to the first threshold or the grid voltage fluctuation is less than or equal to the second threshold, the capacitance, resistance, and inductance are decreased. This helps to further optimize the converter's performance, improve its adaptability to complex operating environments, and reduce its losses.

[0057] The methods and embodiments provided in this application can be executed on a mobile terminal, computer terminal, or similar computing device. Taking running on a mobile terminal as an example, Figure 2 This is a hardware structure block diagram of a mobile terminal for a converter control method according to an embodiment of this application. Figure 2 As shown, a mobile terminal may include one or more ( Figure 2 Only one is shown in the diagram. A processor 502 (which may include, but is not limited to, a microprocessor MCU or a programmable logic device FPGA, etc.) and a memory 504 for storing data are also shown. The mobile terminal may further include a transmission device 506 for communication functions and an input / output device 508. Those skilled in the art will understand that... Figure 2 The structure shown is for illustrative purposes only and does not limit the structure of the mobile terminal described above. For example, the mobile terminal may also include components that are more... Figure 2 The more or fewer components shown, or having the same Figure 2 The different configurations shown.

[0058] The memory 504 can be used to store computer programs, such as application software programs and modules, like the computer program corresponding to the converter control method in this embodiment. The processor 502 executes various functional applications and data processing by running the computer program stored in the memory 504, thus implementing the above-described method. The memory 504 may include high-speed random access memory and non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 504 may further include memory remotely located relative to the processor 502, and these remote memories can be connected to the mobile terminal via a network. Examples of the aforementioned networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof. The transmission device 506 is used to receive or send data via a network. Specific examples of the aforementioned networks may include wireless networks provided by the mobile terminal's communication provider. In one example, the transmission device 506 includes a network interface controller (NIC), which can be connected to other network devices via a base station to communicate with the Internet. In one example, the transmission device 506 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0059] This embodiment provides a control method for a converter operating on a mobile terminal, computer terminal, or similar computing device, for controlling any of the aforementioned converters. It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0060] Figure 3 This is a flowchart of a control method for a converter according to an embodiment of this application. Figure 3 As shown, the method includes the following steps:

[0061] Step S601: Use a power frequency square wave to alternately turn on and off the switching circuits of the upper and lower bridge arms;

[0062] Specifically, the aforementioned power frequency square wave refers to a square wave signal synchronized with the local power system standard frequency (also known as the grid frequency). When the upper bridge arm's switching circuit is on, the lower bridge arm's switching circuit is off; when the upper bridge arm's switching circuit is off, the lower bridge arm's switching circuit is on.

[0063] Step S602: Based on the half-wave modulation strategy and the on and off strategies of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, such that when the switching circuit is engaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is engaged, and when the switching circuit is disengaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is disengaged.

[0064] Specifically, the aforementioned switching circuits and sub-modules located in the same bridge arm have a corresponding relationship. The switching circuit's on and off strategy is the same as the strategy of alternately turning on and off the switching circuits of the upper and lower bridge arms in step S601.

[0065] In this embodiment, firstly, the power frequency square wave is used to alternately turn on and off the switching circuits of the upper and lower bridge arms; then, based on the half-wave modulation strategy and the on and off strategy of the switching circuits, the sub-modules of the upper and lower bridge arms are alternately turned on and off, so that the switching circuits and sub-modules on the same bridge arm are turned on or off synchronously. This application achieves coordinated control of the switching states of the upper and lower bridge arms and the switching of submodules through power frequency square wave control and half-wave modulation strategies. Specifically, when the switching circuit is on, the submodule on the corresponding bridge arm is engaged; when the switching circuit is off, the submodule on the corresponding bridge arm is locked. This allows the upper and lower bridge arms to alternately conduct within different half-cycles of the power frequency cycle. Therefore, DC circulating current cannot form a complete loop between the upper and lower bridge arms within half a power frequency cycle, thus suppressing the formation of DC circulating current in the upper and lower bridge arms. This means that the reactor does not need to bear excessive DC circulating current suppression tasks, thus reducing the inductance requirement of the reactor in the bridge arm. Lower inductance not only reduces the overall system loss and response time but also helps to reduce the cost and physical size of the reactor, solving the problem of high converter losses caused by DC circulating current. Furthermore, because the inductance required by this application is low, the resulting overvoltage level is also correspondingly reduced. Therefore, the installation of surge arresters is no longer necessary in this case. Thus, the converter in this application does not require surge arresters, which not only greatly reduces the overall loss of the converter but also reduces the cost and size of the converter.

[0066] In addition to half-wave modulation strategies, multi-level modulation techniques, such as space vector modulation (SVM) or carrier phase-shift PWM (CPS-PWM), can be combined to further optimize the output waveform quality, reduce THD (total harmonic distortion), and reduce the switching frequency of IGCT devices, thereby reducing switching losses.

[0067] In some embodiments, using a power frequency square wave to alternately turn the switching circuits of the upper and lower bridge arms on and off includes: determining the control function of the switching circuits based on the power frequency square wave. ,in, For the above control function, Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the above symbolic function is 1, that is, in hour ,exist When the above symbolic function is 0, that is, in hour The aforementioned control function controls the switching circuits such that when the control function is 1, the switching circuit of the upper bridge arm is on and the switching circuit of the lower bridge arm is off; when the control function is 0, the switching circuit of the upper bridge arm is off and the switching circuit of the lower bridge arm is on. In this embodiment, the control function is determined using a power frequency square wave signal. Based on the positive and negative half-cycles of the power frequency square wave, the control function alternately turns the switching circuits of the upper and lower bridge arms on and off, achieving precise control of the bridge arm switching circuits and ensuring the stability and reliability of the alternating on / off state of the bridge arms.

[0068] In other alternative solutions, based on a half-wave modulation strategy and the on / off strategy of the aforementioned switching circuit, the sub-modules of the upper and lower bridge arms are alternately engaged and disengaged. This includes: generating a current reference value based on an active power reference value, a reactive power reference value, and a DC voltage; generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms; and generating control signals for the sub-modules of the upper and lower bridge arms using the Nearest Level Modulation (NLM) method based on the reference voltage waveform and the aforementioned on / off strategy, so that the sub-modules of the upper bridge arm are engaged and the sub-modules of the lower bridge arm are disengaged, or the sub-modules of the lower bridge arm are engaged and the sub-modules of the upper bridge arm are disengaged. In this embodiment, the half-wave modulation strategy generates the reference voltage waveform of the submodule based on the conduction state of the switching circuits of the upper and lower bridge arms, while the nearest level approximation modulation method is used to generate the control signal of the submodule. Through the half-wave modulation strategy and the nearest level approximation modulation method, the alternating engagement and locking of the upper and lower bridge arms are precisely controlled, further improving the efficiency and reliability of the converter.

[0069] Specifically, generating a current reference value based on the active power reference value, the reactive power reference value, and the DC voltage includes: sending the aforementioned active power reference value, the aforementioned reactive power reference value, and the aforementioned DC voltage into a PI controller to generate the aforementioned current reference value in a two-phase rotating coordinate system (dq).

[0070] Optionally, generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms includes: generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms. ,in, The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform is for the aforementioned submodule of the aforementioned lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

[0071] In the above embodiments, the generated reference voltage waveform is based on the actual bridge arm current and the expected current reference value. By comparing the two and generating the corresponding voltage waveform, the deviation between the actual current and the target current can be corrected, which helps to improve the current quality, reduce harmonics, and make the current closer to a sine wave, meeting the standard requirements of the power system. By adopting a half-wave modulation strategy, combined with factors such as modulation ratio and power frequency angular frequency, the switching mode of the submodule can be optimized, reducing unnecessary switching actions. This not only reduces switching losses but also indirectly reduces the losses of energy storage devices by reducing the fundamental frequency energy ripple of the submodules in the bridge arm, thereby reducing the overall operating losses of the converter and improving the system energy efficiency. Compared to traditional modulation methods such as carrier stacking modulation and nearest-level approximation modulation, half-wave modulation strategies are often simpler and more intuitive. Based on the periodicity of the power frequency, by controlling the alternating conduction of the upper and lower bridge arm submodules, it can effectively suppress DC circulating current in the DC converter, thereby eliminating the need for bridge arm surge arresters and simplifying the design of control logic and hardware requirements. By updating and generating a reference voltage waveform in real time, the system can quickly adjust the conduction state of the bridge arm submodules according to the phase changes of the AC phase voltage, which is crucial for improving the dynamic response capability of the converter. Accurate reference voltage waveforms and real-time monitoring of actual bridge arm currents help maintain the stability of DC voltage.

[0072] According to further embodiments of this application, based on the aforementioned reference voltage waveform and the aforementioned on / off strategy, a nearest-level approximation modulation method is used to generate control signals for the sub-modules of the upper and lower bridge arms, including: determining the number of sub-modules engaged in the upper and lower bridge arms using the nearest-level approximation modulation method based on the aforementioned reference voltage waveform and the aforementioned on / off strategy. ,in, The number of the aforementioned sub-modules deployed in the aforementioned upper bridge arm. This refers to the number of sub-modules deployed in the aforementioned lower bridge arm. =0 or 1, When =1, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the upper bridge arm. When =0, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the lower bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned lower bridge arm, wherein the aforementioned submodule includes a second energy storage device, is provided. The ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device is used; the control signal for the corresponding sub-module is generated based on the number of sub-modules deployed in the upper and lower bridge arms.

[0073] In the above embodiments, the NLM method utilizes the number of submodules engaged to approximate the reference voltage waveform, thereby achieving precise control of the converter output voltage. This generates an output voltage that most closely resembles the reference voltage waveform, reducing voltage deviation, improving voltage quality, and ensuring voltage stability in the power system. The NLM method also simplifies the control logic, avoiding complex multi-level PWM modulation strategies. Selectively turning on the switching circuits of the upper or lower bridge arm based on the turn-on / turn-off strategy avoids unnecessary submodule switching actions, thus significantly reducing switching losses. Using the reference voltage waveform to guide the engagement of submodules effectively suppresses energy pulsation in the second energy storage devices in the upper and lower bridge arms. Under the alternating turn-on strategy, the charging and discharging processes of the second energy storage devices in the upper and lower bridge arms are evenly distributed, reducing energy fluctuations in the second energy storage devices and extending their service life.

[0074] According to further embodiments of this application, a multi-objective optimization control strategy can also be introduced to control the converter. This multi-objective optimization control strategy includes: determining the control objectives of the converter, which include at least some of power factor correction (PFC), harmonic suppression, voltage stability, and energy recovery efficiency; based on the converter's dynamic model, converting each control objective into a mathematical expression as an objective function to obtain a set of objective functions. For example, the objective functions may include minimizing the deviation between the instantaneous power factor and the ideal value, which, in the dq coordinate system, is expressed as minimizing the deviation of the d-axis component; or, for example, the objective functions may include minimizing the harmonic content of the output current or voltage, by establishing an objective decomposition based on Fourier technology. Functions are used to quantify harmonic distortion; for example, the objective function can include voltage stability, which is expressed as minimizing the deviation between the voltage and the set reference value; constraints that meet the safety and physical limitations of the converter are defined, including but not limited to current and voltage limits, IGCT switch conduction time limits, etc.; the search space is determined, that is, the range of the control parameters, which can include modulation ratio, carrier frequency, switching action threshold, etc.; then an optimization algorithm is selected, such as particle swarm optimization, genetic algorithm, differential evolution, or multi-objective optimization variants such as NSGA-II, MOEA / D, etc., and the optimization algorithm is executed to iteratively find the optimal solution set that satisfies the objective function set, and the operation of the converter is controlled according to the optimal solution set.

[0075] To enable those skilled in the art to better understand the technical solution of this application, the implementation process of the converter control method of this application will be described in detail below with reference to specific embodiments.

[0076] This embodiment relates to a specific control method for a converter, the specific structure of which is as follows: Figure 1 As shown, Figure 1As shown, the converter described above has a three-phase six-arm topology, meaning the converter includes six arms. Each arm is equipped with a series-connected switching circuit 10 and N sub-modules 20. The switching circuit 10 includes a series-connected reactor 101 and M switching modules. Each of the aforementioned switching modules includes a first controllable switch 102, a first diode 103, a second diode 104, a first energy storage device 105, and a discharge device 106. The first controllable switch 102 is connected in reverse parallel with the first diode 103. The anode of the second diode 104 is electrically connected to the cathode of the first diode 103. The cathode of the second diode 104 is electrically connected to one end of the first energy storage device 105, and the other end of the first energy storage device 105 is electrically connected to the anode of the first diode 103. The discharge device 106 is connected in parallel across the first energy storage device 105. Each submodule 20 includes a second energy storage device 201, a third energy storage device 206, a second controllable switch 202, a third diode 203, a third controllable switch 204, a fourth diode 205, a fifth diode 207, a resistor 208, and an inductor 209. The second and third controllable switches 202 and 204 are connected in series. The third diode 203 is connected in reverse parallel across the second controllable switch 202. The fourth diode 205 is connected in reverse parallel across the third controllable switch 204. The anode of the fifth diode 207 is electrically connected to the cathode of the third diode 203, and the cathode of the fifth diode 207 is electrically connected to... One end of the third energy storage device 206 is electrically connected, and the other end of the third energy storage device 206 is electrically connected to the anode of the fourth diode 205. One end of the inductor 209 is electrically connected to the anode of the fifth diode 207, and the other end of the inductor 209 is electrically connected to one end of the second energy storage device 201. The other end of the second energy storage device 201 is electrically connected to the anode of the fourth diode 205. One end of the resistor 208 is electrically connected to the cathode of the fifth diode 207 and one end of the third energy storage device 206, respectively, and the other end of the resistor 208 is electrically connected to the other end of the inductor 209 and one end of the second energy storage device 201, respectively. The DC terminal of the converter includes a DC capacitor 30 and a smoothing reactor 40. Among them, the first controllable switch 102, the second controllable switch 202 and the third controllable switch 204 are all IGCTs, the first diode 103, the third diode 203 and the fourth diode 205 are all fast recovery diodes, the second energy storage device 201 is a DC capacitor 30, the inductor 209 and the reactor 101 are all anode reactors, the first energy storage device 105 and the third energy storage device 206 are both absorption capacitors, and the discharge device 106 is an absorption resistor.

[0077] Where M and N satisfy the following equation:

[0078] , .

[0079] The control block diagram of the above converter is as follows: Figure 4 As shown, this embodiment provides a converter control method based on a half-wave modulation strategy for alternating conduction of the upper and lower bridge arms of an IGCT type converter. In the above converter, the IGCT type switching circuits 10 of the upper and lower bridge arms are controlled by a power frequency square wave. The control function of the IGCT type switching circuit 10 of the j-th (j=a, b, c) phase unit bridge arm is: ,when When the first controllable switch 102 of the upper bridge arm is turned on, the first controllable switch 102 of the lower bridge arm is turned off; when The first controllable switch 102 of the current bridge arm is turned on, and the first controllable switch 102 of the upper bridge arm is turned off.

[0080] The control function of the IGCT type switching circuit 10 of the j-th phase unit bridge arm satisfy:

[0081] ,in, For the sign function, in The sign function is 1 at time. The sign function is 0 at that time;

[0082] The IGCT-type submodule 20 of the aforementioned converter bridge arm adopts a control method based on a half-wave modulation strategy, such as... Figure 4 As shown, based on the active power reference value reactive power and reference DC bus voltage Using outer loop power P / Q (or voltage) Control the generation of dq-axis current reference values , Then, based on the current reference value , and each phase reference wave Reference waves for the upper and lower bridge arms of the IGCT type submodule 20 of each phase unit are generated through inner loop current control. and The reference wave satisfies the following equation:

[0083] ;

[0084] If the control function of the IGCT type switching circuit 10 of the phase unit is If the IGCT type submodule 20 of the upper bridge arm of the phase unit generates a control signal according to the nearest level approximation modulation method, the IGCT type submodule 20 of the lower bridge arm will be locked; conversely, when At that time, the IGCT type submodule 20 of the lower bridge arm of the phase unit generates a control signal according to the NLM modulation method, and the IGCT type submodule 20 of the upper bridge arm is locked.

[0085] The number of IGCT-type sub-modules deployed in each phase unit's upper and lower bridge arms is 20. and Satisfaction formula:

[0086] Where N0=U dc / U SM U dc U is the DC bus voltage of the aforementioned converter. SM The voltage stored in the second energy storage device 201 is also the average voltage of the second energy storage device 201 in each submodule 20;

[0087] Control function of IGCT type switching circuit 10 per phase unit Using a square wave at power frequency, each IGCT-type submodule 20 of the bridge arm is only allowed to be engaged during the half-cycle of the IGCT-type switching circuit 10 of that bridge arm being turned on, and is locked out during the half-cycle of the off period. Therefore, the DC circulating current between phase units and between phase units and the DC-side capacitor is blocked, thereby suppressing DC circulating current. The bridge arm reactor 101 and surge arrester can be eliminated on the bridge arm. The aforementioned topology and control method of the converter with alternating conduction of IGCT-type bridge arm submodules 20 significantly reduces the converter's size, increases the valve body power density, reduces the maximum fundamental frequency energy pulsation of the bridge arm submodule 20 by approximately 2 / 3, and solves the problem of high losses in existing bridge arm alternating conduction converters, meeting the operational requirements of flexible DC projects. In addition, the controllable switching transistors in the sub-module 20 of the converter and the switching circuit 10 are all IGCT devices, resulting in lower conduction losses. Since the bridge arm reactor 101 is eliminated, the switching circuit 10 only needs to be equipped with a μF-level buffer capacitor and a μH-level anode reactor, resulting in lower losses during the switching process. Therefore, the overall loss of the converter is lower than that of the existing MMC, meeting the operational requirements of flexible DC projects.

[0088] This application also provides a control device for a converter. It should be noted that the control device for the converter in this application can be used to execute the control method for a converter provided in this application. This device is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0089] The control device for the aforementioned converter includes a processor and a memory. Units for running the control method of the converter are stored as program units in the memory, and the processor executes these program units to implement the corresponding functions. All of the above modules reside in the same processor; alternatively, the modules may be located in different processors in any combination.

[0090] The processor contains a core, which retrieves the corresponding program units from memory. One or more cores can be configured, and adjusting core parameters can at least address the problem of high losses in existing converters.

[0091] The memory may include non-permanent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0092] This application also provides a flexible DC transmission system, including:

[0093] Any of the above-mentioned converters;

[0094] An electronic device includes: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include methods for performing any of the methods described above.

[0095] Through the above embodiments, in the flexible DC transmission system, switching circuits are set in the upper and lower arms of the converter, and the control method of the converter described above is operated by electronic equipment. This method realizes the linkage control of the switching state of the upper and lower arms and the switching of sub-modules through power frequency square wave control and half-wave modulation strategy. That is, when the switching circuit is turned on, the sub-module on the corresponding arm is turned on, and when the switching circuit is turned off, the sub-module on the corresponding arm is locked. This allows the upper and lower arms to alternately conduct in different half-cycles of the power frequency cycle. As a result, the DC circulating current cannot form a complete loop between the upper and lower arms within half a power frequency cycle, thereby suppressing the formation of DC circulating current in the upper and lower arms. This means that the reactor does not need to bear too much DC circulating current suppression task. Therefore, the inductance requirement of the reactor in the arm can be reduced. The lower inductance not only reduces the loss and response time of the entire system, but also helps to reduce the cost and physical size of the reactor, solving the problem of high converter loss caused by DC circulating current. Furthermore, since the inductance required by this application is low, the resulting overvoltage level is also reduced accordingly. Therefore, the installation of surge arresters is no longer necessary in this case. Thus, there is no need to install surge arresters in the converter of this application, which not only greatly reduces the overall loss of the converter, but also reduces the cost and size of the converter.

[0096] This application provides a computer-readable storage medium including a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the control method of the converter.

[0097] Specifically, the control methods for the converter include:

[0098] Step S601: Use a power frequency square wave to alternately turn on and off the switching circuits of the upper and lower bridge arms;

[0099] Specifically, the aforementioned power frequency square wave refers to a square wave signal synchronized with the local power system standard frequency (also known as the grid frequency). When the upper bridge arm's switching circuit is on, the lower bridge arm's switching circuit is off; when the upper bridge arm's switching circuit is off, the lower bridge arm's switching circuit is on.

[0100] Step S602: Based on the half-wave modulation strategy and the on / off strategy of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, such that when the switching circuit is engaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is engaged, and when the switching circuit is disengaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is disengaged.

[0101] Specifically, the aforementioned switching circuits and sub-modules located in the same bridge arm have a corresponding relationship. The switching circuit's on and off strategy is the same as the strategy of alternately turning on and off the switching circuits of the upper and lower bridge arms in step S601.

[0102] Optionally, using a power frequency square wave, the switching circuits of the upper and lower bridge arms are alternately turned on and off, including: determining the control function of the switching circuits based on the aforementioned power frequency square wave. ,in, For the above control function, Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the above symbolic function is 1, in When the above symbol function is 0, the above control function is used to control the above switching circuit, such that when the above control function is 1, the above switching circuit of the above upper bridge arm is turned on and the above switching circuit of the above lower bridge arm is turned off, and when the above control function is 0, the above switching circuit of the above upper bridge arm is turned off and the above switching circuit of the above lower bridge arm is turned on.

[0103] Optionally, based on the half-wave modulation strategy and the on / off strategy of the aforementioned switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, including: generating a current reference value based on the active power reference value, the reactive power reference value, and the DC voltage; generating a reference voltage waveform for the sub-modules of the upper bridge arm and the lower bridge arm for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms; and generating control signals for the sub-modules of the upper and lower bridge arms using a nearest-level approximation modulation method based on the reference voltage waveform and the aforementioned on / off strategy, so as to engage the sub-modules of the upper bridge arm and disengage the sub-modules of the lower bridge arm, or engage the sub-modules of the lower bridge arm and disengage the sub-modules of the upper bridge arm.

[0104] Optionally, generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms includes: generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms. ,in, The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform is for the aforementioned submodule of the aforementioned lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

[0105] Optionally, based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies, a nearest-level approximation modulation method is used to generate control signals for the sub-modules of the upper and lower bridge arms, including: determining the number of sub-modules in operation for the upper and lower bridge arms based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies using the nearest-level approximation modulation method. ,in, The number of the aforementioned sub-modules deployed in the aforementioned upper bridge arm. This refers to the number of sub-modules deployed in the aforementioned lower bridge arm. =0 or 1, When =1, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the upper bridge arm. When =0, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the lower bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned lower bridge arm, wherein the aforementioned submodule includes a second energy storage device, is provided. The ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device is used; the control signal for the corresponding sub-module is generated based on the number of sub-modules deployed in the upper and lower bridge arms.

[0106] This application provides a processor for running a program, wherein the program executes the control method of the converter.

[0107] This application provides a device, which includes a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it performs at least the following steps:

[0108] Step S601: Use a power frequency square wave to alternately turn on and off the switching circuits of the upper and lower bridge arms;

[0109] Specifically, the aforementioned power frequency square wave refers to a square wave signal synchronized with the local power system standard frequency (also known as the grid frequency). When the upper bridge arm's switching circuit is on, the lower bridge arm's switching circuit is off; when the upper bridge arm's switching circuit is off, the lower bridge arm's switching circuit is on.

[0110] Step S602: Based on the half-wave modulation strategy and the on and off strategies of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, such that when the switching circuit is engaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is engaged, and when the switching circuit is disengaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is disengaged.

[0111] Specifically, the aforementioned switching circuits and sub-modules located in the same bridge arm have a corresponding relationship. The switching circuit's on and off strategy is the same as the strategy of alternately turning on and off the switching circuits of the upper and lower bridge arms in step S601.

[0112] The devices mentioned in this article can be servers, PCs, tablets, mobile phones, etc.

[0113] Optionally, using a power frequency square wave, the switching circuits of the upper and lower bridge arms are alternately turned on and off, including: determining the control function of the switching circuits based on the aforementioned power frequency square wave. ,in, For the above control function, Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the above symbolic function is 1, in When the above symbol function is 0; the above control function is used to control the above switching circuit, such that when the above control function is 1, the above switching circuit of the above upper bridge arm is turned on and the above switching circuit of the above lower bridge arm is turned off, and when the above control function is 0, the above switching circuit of the above upper bridge arm is turned off and the above switching circuit of the above lower bridge arm is turned on.

[0114] Optionally, based on the half-wave modulation strategy and the on / off strategy of the aforementioned switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, including: generating a current reference value based on the active power reference value, the reactive power reference value, and the DC voltage; generating a reference voltage waveform for the sub-modules of the upper bridge arm and the lower bridge arm for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms; and generating control signals for the sub-modules of the upper and lower bridge arms using a nearest-level approximation modulation method based on the reference voltage waveform and the aforementioned on / off strategy, so as to engage the sub-modules of the upper bridge arm and disengage the sub-modules of the lower bridge arm, or engage the sub-modules of the lower bridge arm and disengage the sub-modules of the upper bridge arm.

[0115] Optionally, generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms includes: generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms. ,in, The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform is for the aforementioned submodule of the aforementioned lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

[0116] Optionally, based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies, a nearest-level approximation modulation method is used to generate control signals for the sub-modules of the upper and lower bridge arms, including: determining the number of sub-modules in operation for the upper and lower bridge arms based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies using the nearest-level approximation modulation method. ,in, The number of the aforementioned sub-modules deployed in the aforementioned upper bridge arm. This refers to the number of sub-modules deployed in the aforementioned lower bridge arm. =0 or 1, When =1, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the upper bridge arm. When =0, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the lower bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned lower bridge arm, wherein the aforementioned submodule includes a second energy storage device, is provided. The ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device is used; the control signal for the corresponding sub-module is generated based on the number of sub-modules deployed in the upper and lower bridge arms.

[0117] This application also provides a computer program product, which, when executed on a data processing device, is suitable for executing an initialization program having at least the following method steps:

[0118] Step S601: Use a power frequency square wave to alternately turn on and off the switching circuits of the upper and lower bridge arms;

[0119] Specifically, the aforementioned power frequency square wave refers to a square wave signal synchronized with the local power system standard frequency (also known as the grid frequency). When the upper bridge arm's switching circuit is on, the lower bridge arm's switching circuit is off; when the upper bridge arm's switching circuit is off, the lower bridge arm's switching circuit is on.

[0120] Step S602: Based on the half-wave modulation strategy and the on and off strategies of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, such that when the switching circuit is engaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is engaged, and when the switching circuit is disengaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is disengaged.

[0121] Specifically, the aforementioned switching circuits and sub-modules located in the same bridge arm have a corresponding relationship. The switching circuit's on and off strategy is the same as the strategy of alternately turning on and off the switching circuits of the upper and lower bridge arms in step S601.

[0122] Optionally, using a power frequency square wave, the switching circuits of the upper and lower bridge arms are alternately turned on and off, including: determining the control function of the switching circuits based on the aforementioned power frequency square wave. ,in, For the above control function, Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the above symbolic function is 1, in When the above symbol function is 0; the above control function is used to control the above switching circuit, such that when the above control function is 1, the above switching circuit of the above upper bridge arm is turned on and the above switching circuit of the above lower bridge arm is turned off, and when the above control function is 0, the above switching circuit of the above upper bridge arm is turned off and the above switching circuit of the above lower bridge arm is turned on.

[0123] Optionally, based on the half-wave modulation strategy and the on / off strategy of the aforementioned switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, including: generating a current reference value based on the active power reference value, the reactive power reference value, and the DC voltage; generating a reference voltage waveform for the sub-modules of the upper bridge arm and the lower bridge arm for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms; and generating control signals for the sub-modules of the upper and lower bridge arms using a nearest-level approximation modulation method based on the reference voltage waveform and the aforementioned on / off strategy, so as to engage the sub-modules of the upper bridge arm and disengage the sub-modules of the lower bridge arm, or engage the sub-modules of the lower bridge arm and disengage the sub-modules of the upper bridge arm.

[0124] Optionally, generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms includes: generating a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms. ,in, The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform is for the aforementioned submodule of the aforementioned lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

[0125] Optionally, based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies, a nearest-level approximation modulation method is used to generate control signals for the sub-modules of the upper and lower bridge arms, including: determining the number of sub-modules in operation for the upper and lower bridge arms based on the aforementioned reference voltage waveform and the aforementioned turn-on and turn-off strategies using the nearest-level approximation modulation method. ,in, The number of the aforementioned sub-modules deployed in the aforementioned upper bridge arm. This refers to the number of sub-modules deployed in the aforementioned lower bridge arm. =0 or 1, When =1, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the upper bridge arm. When =0, it indicates that the above-mentioned turn-on and turn-off strategy is to turn on the above-mentioned switching circuit of the lower bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned upper bridge arm. The reference voltage waveform of the aforementioned submodule of the aforementioned lower bridge arm, wherein the aforementioned submodule includes a second energy storage device, is provided. The ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device is used; the control signal for the corresponding sub-module is generated based on the number of sub-modules deployed in the upper and lower bridge arms.

[0126] Obviously, those skilled in the art should understand that the modules or steps of this application described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. They can be implemented using computer-executable program code, and thus can be stored in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those presented here, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, this application is not limited to any particular combination of hardware and software.

[0127] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0128] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0129] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0130] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0131] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0132] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0133] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0136] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0137] In the upper and lower bridge arms of the converter in this application, the switching circuit and multiple sub-modules are connected in series. The switching circuit includes a reactor, multiple switching modules including a first controllable switch, a first diode and a first energy absorption module. The first controllable switch and the first diode are connected in reverse parallel. The first energy absorption module is connected in parallel across the first controllable switch. The reactor and multiple first controllable switches are connected in series in sequence. No surge arresters are installed in either the upper or lower bridge arms. This application incorporates switching circuits in the upper and lower arms of the converter. Through coordinated control, the switching states of the upper and lower arms and the switching of submodules are managed. When the switching circuit is on, the submodule on the corresponding arm is engaged; when the switching circuit is off, the submodule on the corresponding arm is locked. This allows the upper and lower arms to alternately conduct within different half-cycles of the power frequency cycle. Consequently, DC circulating current cannot form a complete loop between the upper and lower arms within half a power frequency cycle, thus suppressing the formation of DC circulating current in the upper and lower arms. This means that the reactor does not need to bear excessive DC circulating current suppression, thus reducing the inductance requirement of the reactor in the arms. Lower inductance not only reduces overall system losses and response time but also helps to reduce reactor cost and physical size. Furthermore, because the required inductance of the inductors in this application is low, the resulting overvoltage level is also correspondingly reduced. Therefore, surge arresters are no longer necessary in this case. Thus, the converter in this application does not require surge arresters, which not only significantly reduces the overall losses of the converter but also reduces its cost and size. In addition, a first energy absorption module is set in the upper and lower bridge arms to absorb excess energy. This can quickly absorb energy, clamp the voltage within a safe range, and protect the controllable switching transistor.

[0138] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A converter, characterized in that, include: The multi-phase bridge arm includes an upper bridge arm and a lower bridge arm connected in series in each phase. Each upper bridge arm and the lower bridge arm includes a series-connected switching circuit and multiple sub-modules. The switching circuit includes a reactor and multiple switching modules. Each switching module includes a first controllable switching transistor, a first diode, and a first energy absorption module. The first controllable switching transistor and the first diode are connected in reverse parallel. The first energy absorption module is connected in parallel with the first controllable switching transistor. The reactor and the first controllable switching transistors of the multiple switching modules are connected in series in sequence. Neither the upper bridge arm nor the lower bridge arm includes a surge arrester.

2. The converter according to claim 1, characterized in that, The first energy absorption module includes: The anode of the second diode is electrically connected to the cathode of the first diode; A first energy storage device, one end of which is electrically connected to the cathode of the second diode, and the other end of which is electrically connected to the anode of the first diode; The discharge device is connected in parallel with the first energy storage device.

3. The converter according to claim 2, characterized in that, The first energy storage device includes a capacitor, and the discharge device includes a resistor.

4. The converter according to claim 1, characterized in that, The first controllable switch is an IGCT switch or an IGBT switch.

5. The converter according to claim 1, characterized in that, The submodule includes: Second energy storage device; The second energy absorption module includes three terminals. The first terminal of the second energy absorption module is electrically connected to one end of the second energy storage device, and the second terminal of the second energy absorption module is electrically connected to the other end of the second energy storage device. The second controllable switch has one end electrically connected to the third end of the second energy absorption module; The third diode is connected in reverse parallel across the two ends of the second controllable switch. A third controllable switch, one end of which is electrically connected to the other end of the second controllable switch, and the other end of which is electrically connected to the other end of the second energy storage device; The fourth diode is connected in reverse parallel across the third controllable switch.

6. The converter according to claim 5, characterized in that, The second controllable switch and the third controllable switch are respectively an IGCT switch or an IGBT switch.

7. The converter according to claim 1, characterized in that, The submodule includes a second energy storage device, and the maximum number of the switch modules in the bridge arm is [number missing]. The maximum number of the submodules is ,in, The function is a floor function, where M is the maximum number of switch modules and N is the maximum number of sub-modules. This refers to the DC bus voltage of the converter. The voltage stored in the second energy storage device.

8. A control method for a converter, used to control the converter according to any one of claims 1 to 7, characterized in that, include: The switching circuits of the upper and lower bridge arms are alternately turned on and off using power frequency square waves; Based on the half-wave modulation strategy and the on / off strategy of the switching circuit, the sub-modules of the upper bridge arm and the lower bridge arm are alternately engaged and disengaged, such that when the switching circuit is engaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is engaged, and when the switching circuit is disengaged, the corresponding sub-module of the upper bridge arm or the lower bridge arm is disengaged.

9. The method according to claim 8, characterized in that, A switching circuit that uses a power frequency square wave to alternately turn the upper and lower bridge arms on and off includes: Based on the power frequency square wave, the control function of the switching circuit is determined as follows: ,in, The control function is... Where t is the power frequency angular frequency, and t is the time. For power frequency phase, For the sign function, in When the symbol function is 1, in The symbol function is 0 at that time; The control function is used to control the switching circuit such that when the control function is 1, the switching circuit of the upper bridge arm is turned on and the switching circuit of the lower bridge arm is turned off, and when the control function is 0, the switching circuit of the upper bridge arm is turned off and the switching circuit of the lower bridge arm is turned on.

10. The method according to claim 8, characterized in that, Based on the half-wave modulation strategy and the switching circuit's on / off strategy, the sub-modules of the upper and lower bridge arms are alternately switched on and off, including: Based on the active power reference value, reactive power reference value, and DC voltage, a current reference value is generated. Based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms, a reference voltage waveform for the sub-modules of the upper and lower bridge arms for half-wave modulation is generated. Based on the reference voltage waveform and the turn-on and turn-off strategies, the control signals for the sub-modules of the upper bridge arm and the lower bridge arm are generated using the nearest level approximation modulation method, so as to enable the sub-module of the upper bridge arm to be engaged and the sub-module of the lower bridge arm to be locked, or enable the sub-module of the lower bridge arm to be engaged and the sub-module of the upper bridge arm to be locked.

11. The method according to claim 10, characterized in that, Based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms, a reference voltage waveform for the submodules of the upper and lower bridge arms used for half-wave modulation is generated, including: Based on the current reference value and the actual bridge arm currents of the upper and lower bridge arms, a reference voltage waveform for the sub-modules of the upper and lower bridge arms used for half-wave modulation is generated. ,in, The reference voltage waveform of the submodule of the upper bridge arm. The reference voltage waveform of the submodule of the lower bridge arm. The modulation ratio, Where t is the power frequency angular frequency, and t is the time. Let j be the phase of the AC phase voltage.

12. The method according to claim 10, characterized in that, Based on the reference voltage waveform and the turn-on and turn-off strategies, control signals for the submodules of the upper and lower bridge arms are generated using a nearest-level approximation modulation method, including: Based on the reference voltage waveform and the turn-on and turn-off strategies, the number of sub-modules deployed in the upper and lower bridge arms is determined using the nearest-level approximation modulation method. ,in, The number of sub-modules deployed in the upper bridge arm. The number of sub-modules deployed in the lower bridge arm. =0 or 1, When =1, it indicates that the turn-on and turn-off strategy is to turn on the switching circuit of the upper bridge arm. When = 0, it indicates that the turn-on and turn-off strategy is to turn on the switching circuit of the lower bridge arm. The reference voltage waveform of the submodule of the upper bridge arm. The reference voltage waveform is provided for the submodule of the lower bridge arm, and the submodule includes a second energy storage device. It is the ratio of the DC bus voltage of the converter to the voltage stored in the second energy storage device; Based on the number of sub-modules deployed in the upper and lower bridge arms, the corresponding control signal for each sub-module is generated.

13. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device on which the computer-readable storage medium is located to perform the method according to any one of claims 8 to 12.

14. A flexible DC transmission system, characterized in that, include: The converter according to any one of claims 1 to 7; An electronic device includes: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including methods for performing any one of claims 8 to 12.

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