High-voltage direct-coupled converter device electrical topology and modulation method thereof

Abstract

The application relates to a high-voltage direct-hanging type converter device electrical topology and a modulation method thereof. Each phase in the topology is composed of N-1 low-frequency power units and 1 high-frequency power unit in cascade. The low-frequency power unit adopts a three-level NPC full-bridge circuit, and the high-frequency power unit adopts a three-level ANPC full-bridge circuit. In the ANPC full-bridge circuit, the inner tube of the bridge arm adopts a wide-band semiconductor power device, and the outer tube of the bridge arm and the clamping tube adopt a silicon-based power semiconductor device. In the modulation method, the low-frequency power unit adopts a nearest level approximation modulation output step wave voltage, and the high-frequency power unit adopts a PWM modulation output shaping voltage. The two are superimposed to serve as a device output voltage. The application can reduce the number of series units, improve the system integration, concentrate high-frequency switching loss on low-loss devices, reduce device operation loss while controlling cost, and improve power density and operation efficiency.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to an electrical topology of a high-voltage direct-connect converter and its modulation method. Background Technology

[0002] The rapid increase in the proportion of new energy power generation, such as photovoltaic and wind power, poses severe challenges to the frequency stability, voltage support, and dynamic regulation capabilities of the power grid due to their inherent randomness and intermittency, as well as the continuous reduction in the spinning reserve capacity of traditional synchronous generators. The traditional method of connecting a large number of low-voltage converters in parallel to the medium- and high-voltage power grid via step-up transformers results in a large electrical distance from the grid and a slow system response, making it difficult to meet the rapid support requirements during rapid fluctuations in new energy power and grid faults. High-voltage direct-connected converters, with their multi-level, high-capacity power electronic topology, directly output AC voltage adapted to the voltage levels of medium- and high-voltage distribution networks, eliminating the need for bulky power frequency transformers and reducing parallel units, significantly improving dynamic response speed. They are core equipment supporting the safe operation of new power systems and enhancing grid flexibility.

[0003] Traditional high-voltage direct-connected converters mostly use a two-level full-bridge topology with all-Si devices as power submodules. Due to the limited voltage withstand capability of power devices and the difficulty in ensuring the series consistency of DC-side energy storage elements, high-voltage direct-connected converters have a large number of series power modules, resulting in problems such as high complexity of coordination and control, low system integration, and large footprint.

[0004] Existing patent document CN112737378A proposes a hybrid topology structure for a cascaded H-bridge multilevel converter. It utilizes hybrid frequency pulse width modulation to distinguish high-frequency and low-frequency modules, and unipolar modulation to separate the high-frequency module into corresponding high-frequency and power frequency branches. However, it uses a two-level topology as all power sub-modules, resulting in a high number of modules and poor system integration at voltage levels of 35kV and above. Its proposed control method balances the loss distribution of the low-frequency modules by performing a half-power frequency cycle timed rotation of the switching functions of each low-frequency module. That is, every half-power frequency cycle, the switching modes of each low-frequency module are sequentially pushed forward until a complete switching cycle is finished. This causes the operating frequency of the low-frequency modules to become twice the fundamental frequency, increasing system switching losses. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electrical topology and modulation method for a high-voltage direct-connected converter, which can achieve an optimal balance between system performance and cost.

[0006] The technical solution adopted by the present invention to solve its technical problem is as follows: providing an electrical topology of a high-voltage direct-connected converter, wherein each phase is composed of multiple low-frequency power units and one high-frequency power unit cascaded together, wherein the multiple low-frequency power units all adopt a three-level NPC full-bridge circuit, and the high-frequency power unit adopts a three-level ANPC full-bridge circuit; the inner tube of the bridge arm in the three-level ANPC full-bridge circuit adopts a wide bandgap semiconductor power device, and the outer tube of the bridge arm and the clamping tube in the three-level ANPC full-bridge circuit adopt silicon-based power semiconductor devices.

[0007] The power devices in the three-level NPC full-bridge circuit are silicon-based power semiconductor devices.

[0008] The technical solution adopted by this invention to solve its technical problem is: to provide a modulation method for the electrical topology of the above-mentioned high-voltage direct-connected converter, wherein the low-frequency power unit uses the nearest level approximation modulation to output a stepped wave voltage, the high-frequency power unit uses PWM modulation to output a shaped voltage, and the stepped wave voltage and the shaped voltage are superimposed to serve as the output voltage of the high-voltage direct-connected converter; wherein the low-frequency power unit can output five stepped wave voltages: +2E, +E, 0, -E, and -2E, where E is half of the DC side voltage of the low-frequency power unit.

[0009] The low-frequency power unit uses the nearest-level approximation modulation to output a stepped-wave voltage, specifically including:

[0010] Calculate the total output voltage of the low-frequency power unit based on the converter modulation wave signal;

[0011] Based on the sign of the converter modulation wave signal and the parity of the required number of levels, the total output voltage of the low-frequency power unit is distributed to each low-frequency power unit to ensure that each low-frequency power unit switches at most once within one grid fundamental frequency cycle.

[0012] The total output voltage of the low-frequency power unit is passed through The calculation yielded that, This is the total output voltage of the low-frequency power unit. The converter modulation wave signal, This is the function for rounding down to zero.

[0013] The method of distributing the total output voltage of the low-frequency power unit to each low-frequency power unit according to the sign of the converter modulation wave signal and the parity of the required number of levels is as follows:

[0014] When the converter modulation wave signal And the number of voltage levels required When the number is even, the number of low-frequency power units required is Furthermore, the output voltage of all activated low-frequency power units is +2E, while the output voltage of unactivated low-frequency power units is 0; when the converter modulation signal... And the number of voltage levels required When the number is odd, the number of low-frequency power units required is: Among them, the low-frequency power units that were put into operation The output voltage of one of the low-frequency power units is +2E, the output voltage of one of the low-frequency power units is +E, and the output voltage of the unused low-frequency power units is 0.

[0015] When the converter modulation wave signal And the number of voltage levels required When the number is even, the number of low-frequency power units required is Furthermore, the output voltage of all activated low-frequency power units is -2E, while the output voltage of unactivated low-frequency power units is 0; when the converter modulation signal... And the number of voltage levels required When the number is odd, the number of low-frequency power units required is: Among them, the low-frequency power units that were put into operation The output voltage of one of the low-frequency power units is -2E, the output voltage of one of the low-frequency power units is -E, and the output voltage of the low-frequency power units that are not in operation is 0.

[0016] Among them, the number of voltage levels that need to be invested , For the function that rounds down to zero, This is the function for taking the absolute value.

[0017] The high-frequency power unit uses PWM modulation to output a shaped voltage, specifically including:

[0018] Subtracting the total output voltage of the low-frequency power unit from the converter modulation wave signal yields the high-frequency power unit modulation wave signal.

[0019] The bridge arm modulation signal is determined based on the high-frequency power unit modulation signal.

[0020] The bridge arm output voltage is obtained by comparing the bridge arm modulated wave signal with the upper and lower triangular carrier signals respectively.

[0021] The output voltage is obtained by comparing the bridge arm modulated wave signal with the upper and lower triangular carrier signals, respectively. Specifically:

[0022] During the positive half-cycle of the bridge arm modulation signal, and when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, the bridge arm output voltage is +E; during the positive half-cycle of the bridge arm modulation signal, and when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal, the bridge arm output voltage is zero.

[0023] During the negative half-cycle of the bridge arm modulation signal, when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal, the bridge arm output voltage is -E; during the negative half-cycle of the bridge arm modulation signal, when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, the bridge arm output voltage is zero.

[0024] During the positive half-cycle of the bridge arm modulation signal, the upper bridge arm outer tube and lower clamping tube remain on, while the lower bridge arm outer tube and upper clamping tube remain off. The upper bridge arm inner tube turns on when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, and turns off when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal. The lower bridge arm inner tube turns off when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, and turns on when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal.

[0025] During the negative half-cycle of the bridge arm modulation signal, the upper bridge arm outer tube and lower clamping tube remain off, while the lower bridge arm outer tube and upper clamping tube remain on. The upper bridge arm inner tube turns on when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turns off when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal. The lower bridge arm inner tube turns off when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turns on when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal.

[0026] The technical solution adopted by the present invention to solve its technical problem is: to provide a computer-readable storage medium on which a computer program is stored, wherein the computer program, when executed by a processor, implements the steps of the above-mentioned modulation method.

[0027] Due to the adoption of the above-mentioned technical solution, this invention has the following advantages and positive effects compared with the prior art: This invention adopts a high-voltage direct-connection topology using a cascaded three-level NPC low-frequency unit and a three-level ANPC high-frequency unit. Compared with the traditional two-level H-bridge cascade scheme, the withstand voltage level of a single power unit is doubled, which can significantly reduce the number of series units, reduce the complexity of system coordination and control, improve device integration, reduce footprint, and increase system power density. Specifically, the high-frequency unit uses a hybrid device configuration, using SiC devices only in the inner tubes of the high-frequency operating bridge arms. This fully utilizes the low switching loss and high switching frequency characteristics of SiC devices while effectively controlling the overall device cost, achieving a balance between system performance and manufacturing cost. Combined with a high-low frequency hybrid modulation strategy, the low-frequency unit switches at the fundamental frequency with extremely low switching loss, while the high-frequency unit optimizes the output waveform quality through PWM modulation and concentrates high-frequency switching losses on the SiC devices, significantly reducing the total device loss and improving operating efficiency. The high switching frequency also reduces the size of the filter device, further increasing power density. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the electrical topology of the high-voltage direct-connected converter according to the first embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram illustrating the operation principle of each switching signal of the high-frequency power unit in the first embodiment of the present invention;

[0030] Figure 3 This is a voltage waveform diagram of each low-frequency power module output in an embodiment of the present invention;

[0031] Figure 4 This is a waveform diagram of the total output voltage of the low-frequency power module in an embodiment of the present invention;

[0032] Figure 5 This is a waveform diagram of the modulation signal of the high-frequency power module in an embodiment of the present invention;

[0033] Figure 6 This is a voltage waveform diagram output by the high-frequency power module in an embodiment of the present invention;

[0034] Figure 7 This is a PWM signal waveform diagram of each switching transistor of the high-frequency power module a and b bridge arms in an embodiment of the present invention;

[0035] Figure 8 This is a waveform diagram of the output phase voltage of the hybrid high-voltage direct-connected converter in an embodiment of the present invention. Detailed Implementation

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The first embodiment of the present invention relates to an electrical topology of a high-voltage direct-connected converter, such as... Figure 1 As shown, each phase consists of N-1 low-frequency power units. and one high-frequency power unit The circuit is cascaded. In this embodiment, all N-1 low-frequency power units adopt a three-level NPC full-bridge circuit, and the power devices used are silicon-based power semiconductor devices, such as Si IGBT power devices. The high-frequency power unit adopts a three-level ANPC full-bridge circuit. The inner transistors of the bridge arms of the three-level ANPC full-bridge circuit adopt wide-bandgap semiconductor power devices, such as SiC MOSFET power devices, while the outer transistors and clamping transistors of the bridge arms adopt silicon-based power semiconductor devices, such as Si IGBT power devices.

[0038] This embodiment proposes a high-low frequency hybrid modulation strategy to address the device distribution characteristics of this topology. Specifically, the low-frequency power unit uses nearest-level approximation modulation to output a stepped-wave voltage, while the high-frequency power unit uses PWM modulation to output a shaped voltage. The stepped-wave voltage and the shaped voltage are superimposed to serve as the output voltage of the hybrid high-voltage direct-connected converter. In this embodiment, the PWM modulation strategy of the high-frequency power unit concentrates the switching action on the inner transistor of the bridge arm, thus utilizing the high-frequency, low-switching-loss characteristics of wide-bandgap semiconductor power devices to minimize system switching losses.

[0039] In this embodiment, the low-frequency power unit uses the nearest-level approximation method for output level distribution and operates in stepped-wave mode. Each power module can output five stepped-wave voltages: +2E, +E, 0, -E, and -2E, where E is half of the DC-side voltage of the low-frequency power unit. When the low-frequency power unit uses the nearest-level approximation modulation to output stepped-wave voltage, it specifically includes:

[0040] The total output voltage of the low-frequency power unit is calculated based on the converter modulation wave signal, i.e., through... Calculate the total output voltage of the low-frequency power unit, where, This is the total output voltage of the low-frequency power unit. The converter modulation wave signal, This is a function that rounds down to zero.

[0041] Based on the converter modulation wave signal Positive and negative and the required number of levels The parity of the low-frequency power unit is determined by distributing the total output voltage of the low-frequency power unit to each low-frequency power unit to ensure that each low-frequency power unit switches at most once within one fundamental frequency cycle of the power grid. Specifically:

[0042] In the converter modulation wave signal And the number of voltage levels required When the number is even, the number of low-frequency power units required is Furthermore, the output voltage of all activated low-frequency power units is +2E, while the output voltage of unactivated low-frequency power units is 0; in the converter modulation wave signal And the number of voltage levels required When the number is odd, the number of low-frequency modules required And in the low-frequency power units that are put into use The output voltage of one of the low-frequency power units is +2E, the output voltage of one of the low-frequency power units is +E, and the output voltage of the low-frequency power units that are not in operation is 0.

[0043] In the converter modulation wave signal And the number of voltage levels required When the number is even, the number of low-frequency modules required is... Furthermore, the output voltage of all activated low-frequency power units is -2E, while the output voltage of unactivated low-frequency power units is 0; in the converter modulation wave signal And the number of voltage levels required When the number is odd, the number of low-frequency power units required is: And in the low-frequency power units that are put into use The output voltage of one of the low-frequency power units is -2E, the output voltage of one of the low-frequency power units is -E, and the output voltage of the low-frequency power units that are not in operation is 0.

[0044] Among them, the number of voltage levels that need to be invested It can be determined by the following formula:

[0045] ;

[0046] in, This is the function for taking the absolute value.

[0047] The total output voltage of the low-frequency power unit is the sum of the output voltages of all low-frequency power units, that is:

[0048]

[0049] These represent the output voltages of the first to the (N-1)th low-frequency power units, respectively.

[0050] In this embodiment, the high-frequency power unit operates in high-frequency PWM mode, using PWM modulation to output shaped voltage, specifically including:

[0051] Modulation wave signal of converter Subtract the total output voltage of the low-frequency power unit Obtain the high-frequency power unit modulated wave signal ,Right now ;

[0052] The modulation wave signal of the bridge arm is determined based on the modulation wave signal of the high-frequency power unit. In this embodiment, the high-frequency power unit adopts a three-level ANPC full-bridge circuit, which is divided into left and right bridge arms. In this embodiment, the left bridge arm is referred to as bridge arm a, and the right bridge arm is referred to as bridge arm b. The modulation wave signal of bridge arm a... It is a high-frequency power unit modulated wave signal, i.e. The modulated wave signal of the b-arm This is the inverse signal of the high-frequency power unit modulated wave signal, i.e. .

[0053] The bridge arm output voltage is obtained by comparing the bridge arm modulation signal with the upper and lower triangular carrier signals. In this embodiment, the modulation signal of bridge arm a... Modulation wave signal of bridge arm b respectively with the upper triangular carrier signal and lower triangular carrier signal By comparing the results, the corresponding bridge arm output voltages are obtained, as follows:

[0054] In bridge arm a: the modulated wave signal in bridge arm a If the positive half-cycle of the bridge arm a is the modulation signal The amplitude is greater than that of the upper triangular carrier signal. When the amplitude is [value missing], the output voltage of bridge arm a is +E; if the modulation wave signal of bridge arm a... The amplitude is less than or equal to the upper triangular carrier signal When the amplitude is [value missing], the output voltage of bridge arm a is 0. The modulation wave signal of bridge arm a... If the negative half-cycle of the modulation wave signal of bridge arm a is... The amplitude is less than that of the lower triangular carrier signal. When the amplitude is [value missing], the output voltage of bridge arm a is -E; if the modulation wave signal of bridge arm a... The amplitude is greater than or equal to the lower triangular carrier signal When the amplitude is 0, the output voltage of bridge arm a is 0.

[0055] In arm B: the modulated wave signal in arm B. If the positive half-cycle of the b-arm modulation signal is... The amplitude is greater than that of the upper triangular carrier signal. At that time, the output voltage of bridge arm b is +E; if the modulation signal of bridge arm b... The amplitude is less than or equal to the upper triangular carrier signal At that time, the output voltage of bridge arm B is 0. The modulation signal of bridge arm B... During the negative half-cycle, if the modulation signal of bridge arm b... The amplitude is less than that of the lower triangular carrier signal. When the amplitude is [value missing], the output voltage of bridge arm b is -E; if the modulation wave signal of bridge arm b... The amplitude is greater than or equal to the lower triangular carrier signal When the amplitude is 0, the output voltage of bridge arm b is 0.

[0056] To ensure that switching losses are concentrated on the SiC MOSFET device, such as Figure 2 As shown, the specific operating modes of each switching transistor are as follows:

[0057] During the positive half-cycle of the modulation wave signal of the bridge arm, the upper bridge arm outer tube S1 and the lower clamping tube S6 remain in the on state (see...). Figure 2 In The lower bridge arm outer tube S4 and the upper clamping tube S5 remain in the off state (see...). Figure 2 In The upper arm inner tube S2 is turned on when the amplitude of the bridge arm modulation wave signal is greater than the amplitude of the upper triangular carrier signal, and turned off when the amplitude of the bridge arm modulation wave signal is less than or equal to the amplitude of the upper triangular carrier signal (see...). Figure 2 In The lower arm inner tube S3 is turned off when the amplitude of the bridge arm modulation wave signal is greater than the amplitude of the upper triangular carrier signal, and turned on when the amplitude of the bridge arm modulation wave signal is less than or equal to the amplitude of the upper triangular carrier signal (see...). Figure 2 In );

[0058] During the negative half-cycle of the bridge arm modulation signal, the upper bridge arm outer tube S1 and the lower clamping tube S6 remain in the off state (see...). Figure 2 In The lower bridge arm outer tube S4 and the upper clamping tube S5 remain open (see...). Figure 2 In The upper arm inner tube S2 is turned on when the amplitude of the bridge arm modulation wave signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turned off when the amplitude of the bridge arm modulation wave signal is less than the amplitude of the lower triangular carrier signal (see...). Figure 2 In The lower arm inner tube S3 is turned off when the amplitude of the bridge arm modulation wave signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turned on when the amplitude of the bridge arm modulation wave signal is less than the amplitude of the lower triangular carrier signal (see...). Figure 2 In ).

[0059] It is easy to see that this implementation adopts a high-voltage direct-connection topology using a cascaded three-level NPC low-frequency unit and a three-level ANPC high-frequency unit. Compared with the traditional two-level H-bridge cascade scheme, the withstand voltage of a single power unit is doubled, which can significantly reduce the number of series units, reduce the complexity of system coordination and control, improve device integration, reduce footprint, and increase system power density. The high-frequency unit uses a hybrid configuration of Si IGBTs and SiC MOSFETs, using SiC devices only in the high-frequency operating bridge arm transistors. This fully utilizes the low switching loss and high switching frequency characteristics of SiC devices while effectively controlling the overall device cost, achieving a balance between system performance and manufacturing cost. Combined with a high-low frequency hybrid modulation strategy, the low-frequency unit switches at the fundamental frequency with extremely low switching losses, while the high-frequency unit optimizes the output waveform quality through PWM modulation and concentrates high-frequency switching losses on the SiC devices, significantly reducing the total device loss and improving operating efficiency. The high switching frequency also reduces the size of the filter device, further increasing power density.

[0060] The present invention will be further illustrated by a specific embodiment below.

[0061] In this embodiment, the high-voltage direct-connected converter has a total of 6 power modules, including 5 low-frequency power modules and 1 high-frequency power module. The DC side voltage of each power module is 2000V and the modulation ratio is 0.68. To ensure that the PWM switching signal of the high-frequency power module is clearly visible, the switching frequency of the high-frequency power module is only set to 2kHz.

[0062] Taking phase A as an example, the modulation signals of each low-frequency power module (sub-modules 1-5) are as follows: Figure 3 As shown, the modulation signals of each module are in the form of stepped waves. Within each fundamental frequency cycle, each output voltage level switches at most once; that is, the switching transistors of the low-frequency module switch at the fundamental frequency. The total output voltage of the low-frequency power module... like Figure 4 As shown, it is the result of the summation of the modulation signals of all low-frequency power modules, and the output level change step voltage is half of the DC side voltage of the power module.

[0063] The modulation signal of the high-frequency power module is as follows Figure 5 The image shows the converter modulation wave signal. Reduce the total output voltage of the low-frequency power module The result is that its output voltage is as follows: Figure 6As shown, its waveform is the result of high-frequency PWM modulation, and the output voltage switches levels at a carrier frequency of approximately 2kHz; the PWM signal waveforms of each switch transistor in the a-arm and b-arm of the high-frequency power module are as follows. Figure 7 As shown, where, These represent the switching states of each switching transistor. It can be seen that the eight Si IGBT devices (a bridge arm's upper bridge arm external transistor S) a1 The outer tube S of the upper bridge arm of bridge arm a a4 upper clamping tube S of bridge arm a a5 The lower clamping tube S of bridge arm a a6 、b bridge arm upper bridge arm outer tube S b1 、b bridge arm upper bridge arm outer tube S b4 upper clamping tube S of bridge arm B b5 The lower clamping tube S of the bridge arm b6 All four SiC MOSFET devices operate at the fundamental frequency, with only the upper bridge arm inner transistor S in bridge arm a being switched at that frequency. a2 The inner tube S of the lower bridge arm of bridge arm a a3 S, the inner tube of the upper arm of the bridge arm. b2 The lower bridge arm inner tube S of the b-arm b3 Switching is performed at a carrier frequency of 2kHz, which means that the switching loss is mainly concentrated on the SiC MOSFET device, effectively reducing the system switching loss.

[0064] The output phase voltage waveform of the hybrid high-voltage direct-connect converter is as follows: Figure 8 As shown, the output voltage is similar to that of traditional carrier phase-shift modulation, approximating an ideal modulated sine wave and exhibiting good output performance. Therefore, the electrical topology and modulation strategy of the high-voltage direct-connect converter involved in this invention can concentrate switching losses on the SiC MOSFET devices in the high-frequency power module while ensuring the quality of the converter output voltage waveform. This effectively reduces the number of switching operations of the Si IGBT devices, decreases device switching losses, and improves system efficiency.

[0065] A second embodiment of the present invention relates to a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the modulation method in the first embodiment.

[0066] 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 implemented on one or more computer-usable storage media (including, but not limited to, disk storage and optical storage) containing computer-usable program code.

[0067] 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.

[0068] 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 operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction methods implemented in a process. Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0069] 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.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electrical topology for a high-voltage direct-connected converter, characterized in that, Each phase consists of multiple low-frequency power units and one high-frequency power unit cascaded together. The multiple low-frequency power units all adopt a three-level NPC full-bridge circuit, and the high-frequency power unit adopts a three-level ANPC full-bridge circuit. The inner transistors of the bridge arms in the three-level ANPC full-bridge circuit adopt wide-bandgap semiconductor power devices, and the outer transistors and clamping transistors of the bridge arms in the three-level ANPC full-bridge circuit adopt silicon-based power semiconductor devices.

2. The electrical topology of the high-voltage direct-connected converter according to claim 1, characterized in that, The power devices in the three-level NPC full-bridge circuit are silicon-based power semiconductor devices.

3. A modulation method for the electrical topology of a high-voltage direct-connected converter as described in any one of claims 1-2, characterized in that, The low-frequency power unit uses the nearest-level approximation modulation to output a stepped wave voltage, and the high-frequency power unit uses PWM modulation to output a shaped voltage. The stepped wave voltage and the shaped voltage are superimposed to serve as the output voltage of the high-voltage direct-connected converter. The low-frequency power unit can output five stepped wave voltages: +2E, +E, 0, -E, and -2E, where E is half of the DC-side voltage of the low-frequency power unit.

4. The modulation method according to claim 3, characterized in that, The low-frequency power unit uses the nearest-level approximation modulation to output a stepped-wave voltage, specifically including: Calculate the total output voltage of the low-frequency power unit based on the converter modulation wave signal; Based on the sign of the converter modulation wave signal and the parity of the required number of levels, the total output voltage of the low-frequency power unit is distributed to each low-frequency power unit to ensure that each low-frequency power unit switches at most once within one grid fundamental frequency cycle.

5. The modulation method according to claim 4, characterized in that, The total output voltage of the low-frequency power unit is passed through The calculation yielded that, This is the total output voltage of the low-frequency power unit. The converter modulation wave signal, This is the function for rounding down to zero.

6. The modulation method according to claim 4, characterized in that, The method of distributing the sum of the output voltages to each low-frequency power unit based on the sign of the converter modulation signal and the parity of the required level number is as follows: When the converter modulation wave signal And the number of levels that need to be invested When the number is even, the number of low-frequency power units required is Furthermore, the output voltage of all activated low-frequency power units is +2E, while the output voltage of unactivated low-frequency power units is 0; when the converter modulation signal... And the number of levels that need to be invested When the number is odd, the number of low-frequency power units required is: Among them, the low-frequency power units that were put into operation The output voltage of one of the low-frequency power units is +2E, the output voltage of one of the low-frequency power units is +E, and the output voltage of the unused low-frequency power units is 0. When the converter modulation wave signal And the number of levels that need to be invested When the number is even, the number of low-frequency power units required is Furthermore, the output voltage of all activated low-frequency power units is -2E, while the output voltage of unactivated low-frequency power units is 0; when the converter modulation signal... And the number of levels that need to be invested When the number is odd, the number of low-frequency power units required is: Among them, the low-frequency power units that were put into operation The output voltage of one of the low-frequency power units is -2E, the output voltage of one of the low-frequency power units is -E, and the output voltage of the low-frequency power units that are not in operation is 0. Among them, the number of voltage levels that need to be invested , For the function that rounds down to zero, This is the function for taking the absolute value.

7. The modulation method according to claim 3, characterized in that, The high-frequency power unit uses PWM modulation to output a shaped voltage, specifically including: Subtracting the total output voltage of the low-frequency power unit from the converter modulation wave signal yields the high-frequency power unit modulation wave signal. The bridge arm modulation signal is determined based on the high-frequency power unit modulation signal. The bridge arm output voltage is obtained by comparing the bridge arm modulated wave signal with the upper and lower triangular carrier signals respectively.

8. The modulation method according to claim 7, characterized in that, The output voltage is obtained by comparing the bridge arm modulated wave signal with the upper and lower triangular carrier signals, specifically as follows: During the positive half-cycle of the bridge arm modulation signal, and when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, the bridge arm output voltage is +E; during the positive half-cycle of the bridge arm modulation signal, and when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal, the bridge arm output voltage is zero. During the negative half-cycle of the bridge arm modulation signal, when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal, the bridge arm output voltage is -E; during the negative half-cycle of the bridge arm modulation signal, when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, the bridge arm output voltage is zero.

9. The modulation method according to claim 8, characterized in that, During the positive half-cycle of the bridge arm modulation signal, the upper bridge arm outer tube and lower clamping tube remain on, while the lower bridge arm outer tube and upper clamping tube remain off. The upper bridge arm inner tube turns on when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, and turns off when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal. The lower bridge arm inner tube turns off when the amplitude of the bridge arm modulation signal is greater than the amplitude of the upper triangular carrier signal, and turns on when the amplitude of the bridge arm modulation signal is less than or equal to the amplitude of the upper triangular carrier signal. During the negative half-cycle of the bridge arm modulation signal, the upper bridge arm outer tube and lower clamping tube remain off, while the lower bridge arm outer tube and upper clamping tube remain on. The upper bridge arm inner tube turns on when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turns off when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal. The lower bridge arm inner tube turns off when the amplitude of the bridge arm modulation signal is greater than or equal to the amplitude of the lower triangular carrier signal, and turns on when the amplitude of the bridge arm modulation signal is less than the amplitude of the lower triangular carrier signal.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the modulation method as described in any one of claims 3-9.

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