Improved cascaded H-bridge modulation method and system based on carrier reconstruction, and terminal equipment

Abstract

The invention discloses an improved cascaded H-bridge modulation method and system based on carrier reconstruction and terminal equipment, and relates to the technical field of power electronic application. The method is suitable for a single-phase cascaded H-bridge converter with three sub-modules, each sub-module is powered by an independent direct-current power supply and has the same direct-current side voltage, the three sub-modules are connected in series and then are connected to an inductive impedance circuit, and the method comprises the following specific steps: taking a modulated wave as a constant wave in a carrier period; in order to balance the conduction loss between devices, based on carrier reconstruction, the optimal carrier arrangement for averaging the conduction loss of power devices is sought by traversing the carrier arrangement. According to the method, the influence of the modulation strategy on the service life of the converter is fully considered, the reliability requirement of the converter can be better met, on the premise that the high quality of a traditional IPD-PWM output waveform is kept, the thermal stress distribution of a power device is balanced, the influence of the modulation ratio on the reliability of the converter is more accurately evaluated, and the converter modulation strategy design under the specific working condition is guided.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power electronic applications, and particularly relates to an improved cascade H-bridge modulation method, system and terminal equipment based on carrier reconstruction. BACKGROUND

[0002] Multi-level converters are widely used in medium and high voltage and high power fields in recent years due to the advantages of small device stress, good output power quality and high conversion efficiency. The typical topological structure of the multi-level converter is divided into a diode clamping type (NPC type), a flying capacitor type (FC type) and a cascade H-bridge type (CHB type), wherein the CHB type multi-level converter is widely used in photovoltaic power generation, rail transit and reactive power compensation due to the advantages of modular structure, strong scalability and easy control.

[0003] With the wide application of power electronic devices, reliability has become an increasingly important factor. In large-scale industrial production and transportation, the reliability of power electronic devices is the core to ensure the safety of production and transportation. In the field of aerospace, due to the extremely high risk and huge loss of failure, the requirement for the reliability of power electronic devices is even higher. In addition, reliability also has an important influence on cost and economic benefit. In order to improve the reliability of power electronic devices, a large rated voltage and current margin are usually reserved, which greatly increases the manufacturing cost, and at the same time, causes redundancy and waste of resources. After the failure of the power electronic device, the maintenance of the system also consumes a large amount of cost and resources. Therefore, improving the reliability of the device, detecting the aging and falling of the device before the system fails, and replacing the low-reliability device in advance through reasonable reliability evaluation, become an effective method to improve economic benefit and ensure stable operation of the system. This requires us to conduct in-depth research on the reliability of a specific system.

[0004] The traditional modulation strategy of the CHB topology is carrier phase-shifted modulation (CPS-PWM) and in-phase disposition (IPD-PWM). CPS-PWM can realize natural power balance among sub-modules, but the THD of the output voltage is high; IPD-PWM has good output waveform quality but the power distribution among sub-modules is unbalanced, and the life of the converter is low.

[0005] At present, there are documents on the modulation strategy of the CHB topology. The existing document "Chen Z, Sun JB, Xu YM, et al. Power balancing method for cascade H-bridge inverter with output cycle pulse recycling [J]. Transactions of China Electrotechnical Society, 2020, 35(4): 827-838." improves the traditional CPS-PWM to improve the output waveform quality, but increases the total switching number of the converter, which increases the switching loss and is not conducive to the life of the converter.

[0006] The existing literature “Li Guohua, Li Yingdong, Wu Zehua. Dual-degree-of-freedom optimization control method for power and switching loss of cascaded H-bridge inverter [J]. Power System Technology, 2023, 47(6):2433-2442.DOI:10.13335 / j.1000-3673.pst.2022.2473” proposes that the switching loss can be optimized through spatial degrees of freedom, but it only balances the switching loss among sub-units, without considering the reliability of the entire converter to minimize the number of switching operations, and it does not consider the influence of the modulation ratio on the number of switching operations.

[0007] To this end, the present invention proposes an improved cascaded H-bridge modulation method, system, and terminal device based on carrier reconstruction. Summary of the Invention

[0008] The purpose of this invention is to provide an improved cascaded H-bridge modulation method, system, and terminal equipment based on carrier reconstruction. Based on the idea of ​​carrier reconstruction, it starts from the equalization of converter conduction loss and considers the influence of the modulation wave range under different modulation ratios on the conduction loss distribution. An improved IPD-PWM is proposed, which not only maintains the advantage of good harmonic quality of traditional IPD-PWM output waveform, but also significantly improves the converter lifespan.

[0009] According to a first aspect of the present invention, in order to achieve the above-mentioned objective, the present invention provides the following technical solution: an improved cascaded H-bridge modulation method based on carrier reconstruction, applicable to a cascaded H-bridge converter with three single-phase sub-modules, each sub-module being powered by an independent DC power supply with the same DC side voltage, the three sub-modules being connected in series and then connected to a variable inductive impedance circuit, the specific steps of which are as follows:

[0010] Define the modulated wave V m If the carrier frequency f m Greater than the modulation wave frequency f cr Then, within one carrier cycle, the modulated wave V will be m View it as a constant wave;

[0011] By reconstructing the carrier and traversing the conduction losses under different carrier arrangements, the optimal carrier arrangement that balances the conduction loss distribution among power devices is obtained, as follows:

[0012] Adjusting the carrier to distribute it evenly across multiple levels will balance the conduction losses of the upper and lower devices in a single bridge arm within the same submodule, where a single bridge arm is either the left or right bridge arm.

[0013] Phase shift the right bridge arm carrier relative to the left bridge arm within the same submodule Then the conduction loss between the left and right bridge arms within the same submodule is balanced;

[0014] For the carriers between different submodules, apply sequentially Phase shifting balances the conduction losses of power devices across submodules.

[0015] Furthermore, simplify the modulation wave V m The expression is as follows:

[0016] V m =m(-3E≤m≤3E)

[0017] In the formula, m is a constant and E is the submodule voltage.

[0018] Furthermore, for each submodule, the power device conduction time is made the same through carrier rearrangement, that is, the modulation wave is greater than the carrier for the same amount of time. For the CHB topology of three submodules in a single phase, this is specifically manifested as follows: the conduction time of the upper and lower devices of a single bridge arm within a submodule is the same; the conduction time of the corresponding devices of the left and right bridge arms within a submodule is the same; and the conduction time of the corresponding devices between submodules is the same.

[0019] Furthermore, based on carrier reconstruction, the spatial distribution of carriers across the three levels is adjusted, and the conduction loss under different arrangements is traversed to obtain the optimal carrier arrangement with balanced conduction loss distribution, as follows:

[0020] (41) The submodule includes four power devices, namely S 11 S 21 S 31 S 41 ;

[0021] (42) When the modulating wave is located at (2E, 3E), the conduction loss under all carrier arrangement schemes is calculated. When the modulating wave is in the positive half-cycle, the power device S... 11 The conduction time is as follows:

[0022]

[0023] In the formula, t on+ When S is the positive half-cycle of the modulated wave 11 The conduction time, |V ref | represents the amplitude of the modulated wave;

[0024] When the modulated wave is in the negative half-cycle, the power device S 11 The conduction time is as follows:

[0025]

[0026] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0027]

[0028] In the formula, t on For the total conduction time, t on+ t is the conduction time of the positive half-cycle of the modulated wave. on- The conduction time of the negative half-cycle of the modulated wave;

[0029] Power device S 41 With S 11 Complementary conduction, meaning the conduction time within one switching cycle is also... Due to the two power devices S on the right bridge arm of the submodule 41 S 11 Corresponding carrier and two power devices S in the left bridge arm 31 S 21 Symmetric about the x-axis, therefore the four devices in the current submodule have the same turn-on time;

[0030] (43) When the modulating wave is located at (E, 2E), and when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows:

[0031]

[0032] When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows:

[0033]

[0034] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0035]

[0036] (44) When the modulating wave is located at (0, E), and when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows:

[0037]

[0038] When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows:

[0039]

[0040] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0041]

[0042] In the formula, t on For the total conduction time, t on+ t is the conduction time of the positive half-cycle of the modulated wave. on- T is the conduction time of the negative half-cycle of the modulated wave.c The reconstructed carrier period.

[0043] Furthermore, in the stacked structure, each submodule in the cascaded H-bridge converter adopts a carrier configuration strategy with phase rotation characteristics. This degree of freedom is used to make the modulation carrier amplitude and period the same, with only a phase deviation, so that the left and right bridge arms within the submodule and the device characteristics between submodules are the same.

[0044] According to a second aspect of the present invention, the present invention provides an improved cascaded H-bridge modulation system based on carrier reconstruction for implementing the improved cascaded H-bridge modulation method based on carrier reconstruction described in the first aspect, comprising:

[0045] Modulation wave simplification module, used to define modulation wave V m If the carrier frequency f m Much greater than the modulation wave frequency f cr If so, the modulated wave is considered as a constant wave within one cycle.

[0046] The carrier reconfiguration module combines the characteristics of IPD-PWM and CPS-PWM, adjusts the spatial distribution of the simplified carrier between layers based on carrier reconfiguration, and traverses the conduction loss distribution under different arrangements to obtain the optimal carrier arrangement that balances the conduction loss of power devices.

[0047] According to a third aspect of the present invention, the present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor, wherein when the processor loads and executes the computer program, it employs an improved cascaded H-bridge modulation method based on carrier reconstruction as described in the first aspect.

[0048] According to a fourth aspect of the present invention, the present invention provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform an improved cascaded H-bridge modulation method based on carrier reconstruction as described in the first aspect.

[0049] The present invention has at least the following beneficial effects:

[0050] 1. Compared with the traditional cascaded H-bridge modulation strategy, this invention takes into account both the balance of device lifetime and the quality of output waveform. Specifically, compared with the traditional CPS-PWM, its output voltage harmonic content is small and the waveform quality is high; compared with the traditional IPD-PWM, it achieves natural balance between sub-modules, balances the conduction loss of power devices, and has a long system lifetime.

[0051] 2. Compared with the existing improved cascaded H-bridge modulation strategy, this invention aims to improve the overall reliability of the converter. It utilizes the amplitude and spatial degree of freedom of the modulation wave and the carrier wave, starting from the balance of conduction loss of power devices, and considers the influence of the modulation wave range under different modulation ratios on conduction loss. It proposes an improved IPD-PWM, which not only maintains the advantage of good harmonic quality of the output waveform of traditional IPD-PWM, but also significantly improves the lifespan of the converter.

[0052] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the topology of the single-phase three-submodule cascaded H-bridge converter of the present invention;

[0054] Figure 2 This is a modulation carrier diagram after carrier reconstruction in Embodiment 1 of the present invention, where (a) indicates that the modulation wave is in the positive half-cycle and (b) indicates that the modulation wave is in the negative half-cycle.

[0055] Figure 3 This is a comparison chart of the output waveform quality of the modulation method described in this invention with traditional carrier phase-shift modulation and carrier stacking modulation, where (a1), (a2), and (a3) ​​represent the CPS-PWM waveform, IPD-PWM waveform, and improved IPD-PWM waveform in the modulation method described in this invention, respectively; (b1), (b2), and (b3) represent the CPS-PWM THD&FFT, IPD-PWM THD&FFT, and improved IPD-PWM THD&FFT in the traditional method, respectively.

[0056] Figure 4 This is a comparison chart of the modulation method described in this invention and the traditional carrier stacked modulation lifetime, where (a) represents the CPS-PWM modulation lifetime, (b) represents the IPD-PWM modulation lifetime, and (c) represents the improved IPD-PWM modulation lifetime.

[0057] Figure 5 This is a schematic flowchart of the modulation method described in this invention. Detailed Implementation

[0058] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0059] Example 1:

[0060] Please see Figures 1-5 This invention provides a technical solution: an improved cascaded H-bridge modulation method based on carrier reconstruction, applicable to a cascaded H-bridge converter with three single-phase sub-modules. Each sub-module is powered by an independent DC power supply with the same DC-side voltage. The three sub-modules are connected in series to an inductive impedance circuit. The specific steps are as follows:

[0061] S1. Modulation Wave Simplification: Defining the Modulation Wave V m If the carrier frequency f m Much greater than the modulation wave frequency f cr Then, within one cycle, the modulated wave is regarded as a constant wave;

[0062] S2. Carrier Reconfiguration: Combining the characteristics of IPD-PWM and CPS-PWM, the carrier is reconfigured and its spatial distribution in multiple levels is adjusted. While maintaining the carrier spatial distribution of each submodule as equivalent to IPD-PWM, the fundamental amplitude and harmonic characteristics of the output voltage remain unchanged. By traversing the conduction losses under different carrier arrangements, the optimal carrier arrangement that balances the conduction loss distribution among power devices is obtained. Specific implementation includes:

[0063] First, the carrier is evenly distributed across each level to ensure that the conduction time of the devices above and below a single bridge arm is consistent.

[0064] Furthermore, the right bridge arm carrier is phase-shifted relative to the left bridge arm. Taking a single-phase three-sub-module topology as an example, the phase shift is 180° to achieve a balance of conduction losses between the left and right bridge arms;

[0065] For the carriers between different submodules, apply sequentially Phase shifting, taking a single-phase three-sub-module topology as an example, involves applying a 60° phase shift sequentially to ensure that the conduction losses of the corresponding devices in each sub-module are balanced.

[0066] like Figure 1 As shown, each submodule includes four power devices. For ease of description, the four power devices of the first submodule are denoted as S. 11 S 21 S 31 S 41 The four power devices in the second submodule are denoted as S. 12 S 22 S 32 S 42 The four power devices in the third submodule are denoted as S. 13 S 23 S 33 S 43 ;

[0067] This embodiment usesFigure 1 Taking the single-phase three-submodule cascaded H-bridge converter shown as the object, this paper utilizes the amplitude and spatial degrees of freedom of the modulation wave and carrier wave, starting from the equalization of power device conduction losses, and considering the impact of the modulation wave range under different modulation ratios on switching losses. An improved IPD-PWM is proposed. The specific modulation strategy is detailed in [link to specific modulation strategy]. Figure 2 :

[0068] When the modulated wave is located at (2E, 3E), the conduction loss is traversed across all carrier arrangements to obtain the following: Figure 1 Taking the first submodule as an example, the rest of the submodules are similar: For the left half-bridge device, when the modulated wave is greater than the carrier wave, the upper bridge arm is turned on (S 11 When the modulated wave is less than the carrier wave, the lower bridge arm is turned on (S). 41 (Conduction); For the right half-bridge device, when the modulating wave is greater than the carrier wave, the lower bridge arm conducts (S). 21 When the modulated wave is less than the carrier wave, the upper bridge arm is turned on (S). 31 (Conduction);

[0069] When the modulated wave is in the positive half-cycle, the power device S 11 The conduction time is as follows:

[0070]

[0071] When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows:

[0072]

[0073] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0074]

[0075] In the formula, t on For the total conduction time, t on+ t is the conduction time of the positive half-cycle of the modulated wave. on- T is the conduction time of the negative half-cycle of the modulated wave. c The reconstructed carrier period;

[0076] Power device S 41 With S 11 Complementary conduction, meaning the conduction time within one switching cycle is also... The right-arm devices correspond to carriers that are symmetrical about the x-axis to the left-arm devices, meaning the four devices in the first submodule have the same conduction time; the modulation carriers of the remaining submodules shift sequentially, similar to carrier phase-shift modulation.

[0077] When the modulating wave is located at (E, 2E), similarly to the above, when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows:

[0078]

[0079] When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows:

[0080]

[0081] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0082]

[0083] When the modulating wave is located at (0, E), similarly to the above, when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows:

[0084]

[0085] When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows:

[0086]

[0087] The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula:

[0088]

[0089] Regarding the technical solution of this embodiment, in the stacked structure, each sub-module in the cascaded H-bridge converter adopts a carrier configuration strategy with phase switching characteristics. This degree of freedom is used to make the modulation carrier amplitude and period the same, with only a phase deviation, so that the left and right bridge arms within the sub-module and the device characteristics between sub-modules are the same.

[0090] Regarding the technical solution of this embodiment, the modulation carrier is distributed at the same time across all levels within the same submodule; the modulation carriers corresponding to the left and right half-bridges within the same submodule are symmetrical about the x-axis, i.e., their phases are shifted by 180°; the carrier amplitude and frequency are the same between different submodules, with their phases shifted sequentially.

[0091] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0092] In this embodiment, a cascaded H-bridge converter with three single-phase sub-modules is used as the topology. The power devices are Infineon IKW50N65H5 IGBTs, which are powered by three DC power supplies. A thermal model is built using Simulink and PLECS joint thermal simulation.

[0093] The design conditions for the resistive-inductive circuitry include: a DC side voltage of 400V for a single submodule, an ambient temperature of 25℃, a load inductance of 3mH, a load resistance of 20Ω, an output frequency of 50Hz, a thermal resistance of 0.1K / W, and a duty cycle of 0.8.

[0094] Figure 3 This is a comparison chart of the output waveform quality of the modulation method in this embodiment with that of traditional carrier phase-shift modulation and carrier stacking modulation. (a1), (a2), and (a3) ​​represent the CPS-PWM waveform, IPD-PWM waveform, and improved IPD-PWM waveform in the modulation method described in this invention, respectively; (b1), (b2), and (b3) represent the CPS-PWM THD&FFT, IPD-PWM THD&FFT, and improved IPD-PWM THD&FFT in the traditional method, respectively; the output waveform quality is as follows: Figure 3 As shown, the output voltage THD (37.26%) of CPS-PWM is much higher than that of other modulation strategies. The spectrum and THD of the improved IPD-PWM are exactly the same as those of the traditional IPD-PWM, retaining the advantage of high output waveform quality of IPD-PWM.

[0095] The junction temperature is measured before and after the change in operating conditions, and the average junction temperature T within one transformation cycle t is compared. mean With respect to junction temperature fluctuation ΔT, the results are as follows Figure 4 As shown, Figure 4 This is a comparison chart of the lifetime of the modulation method in this embodiment and the traditional carrier stacked modulation, where (a) represents the lifetime of CPS-PWM modulation, (b) represents the lifetime of IPD-PWM modulation, and (c) represents the lifetime of improved IPD-PWM modulation. It can be seen that the traditional IPD-PWM has a high average junction temperature and junction temperature fluctuation before and after power conversion. The improved modulation strategy can reduce the junction temperature fluctuation within the cycle while reducing the average junction temperature, which helps to improve the reliability of the converter and increase the lifetime of the converter.

[0096] In summary, this invention fully considers the impact of modulation strategies on converter lifespan, better meets converter reliability requirements, balances the thermal stress distribution of power devices while retaining the high quality of traditional IPD-PWM output waveforms, more accurately evaluates the impact of modulation ratio on converter reliability, and guides the design of converter modulation strategies under specific operating conditions.

[0097] Example 2:

[0098] This embodiment provides an improved cascaded H-bridge modulation system based on carrier reconstruction, used to implement the improved cascaded H-bridge modulation method based on carrier reconstruction described in Embodiment 1, including:

[0099] Modulation wave simplification module, defines modulation wave V m If the carrier frequency f m Much greater than the modulation wave frequency f cr If so, the modulated wave is considered as a constant wave within one cycle.

[0100] The carrier reconstruction module combines the features of IPD-PWM and CPS-PWM. By reconstructing the carrier and adjusting its spatial distribution in multiple levels, it ensures that the fundamental amplitude and harmonic characteristics of the output voltage remain unchanged while maintaining the carrier spatial distribution of each submodule as equivalent to IPD-PWM. Furthermore, by traversing the conduction losses under different carrier arrangement methods, it obtains the optimal carrier arrangement method that balances the conduction loss distribution among power devices.

[0101] Example 3:

[0102] The present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores the computer program capable of running on the processor. When the processor loads and executes the computer program, it employs an improved cascaded H-bridge modulation method based on carrier reconstruction as described in Embodiment 1.

[0103] It should be noted that the terminal device can be a computer device such as a desktop computer, a laptop computer, or a cloud server, and the terminal device includes, but is not limited to, a processor and a memory. For example, the terminal device may also include input / output devices, network access devices, and buses.

[0104] Furthermore, the processor can be a central processing unit (CPU). Of course, depending on the actual use, other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. can also be used. The general-purpose processor can be a microprocessor or any conventional processor, etc., and this application does not limit it in this regard.

[0105] Example 4:

[0106] The present invention provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform an improved cascaded H-bridge modulation method based on carrier reconstruction as described in Embodiment 1.

[0107] The computer program can be stored in a computer-readable medium. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or certain middleware. The computer-readable medium includes any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the computer-readable medium includes, but is not limited to, the above-mentioned components.

[0108] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, 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.

[0109] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0110] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0111] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. An improved cascaded H-bridge modulation method based on carrier reconstruction, applicable to a cascaded H-bridge converter with three single-phase sub-modules, each sub-module being powered by an independent DC power supply with identical DC-side voltage, the three sub-modules being connected in series to a variable inductive impedance circuit, characterized in that... The specific steps are as follows: Define the modulated wave V m Due to the carrier frequency f m Greater than the modulation wave frequency f cr Then, within one carrier cycle, the modulated wave V will be m View it as a constant wave; By reconstructing the carrier and traversing the conduction losses under different carrier arrangements, the optimal carrier arrangement that balances the conduction loss distribution among power devices is obtained, as follows: Adjusting the carrier to distribute it evenly across multiple levels will balance the conduction losses of the upper and lower devices in a single bridge arm within the same submodule, where a single bridge arm is either the left or right bridge arm. Phase shift the right bridge arm carrier relative to the left bridge arm within the same submodule Then the conduction loss between the left and right bridge arms within the same submodule is balanced; For the carriers between different submodules, apply sequentially Phase shifting balances the conduction losses of power devices across submodules.

2. The improved cascaded H-bridge modulation method based on carrier reconstruction according to claim 1, characterized in that: Simplified modulated wave V m The expression is as follows: In m =m(-3E≤m≤3E) In the formula, m is a constant and E is the submodule voltage.

3. The improved cascaded H-bridge modulation method based on carrier reconstruction according to claim 2, characterized in that: For each submodule, carrier rearrangement ensures that the power devices have the same on-time, meaning the modulation wave is longer than the carrier wave for the same duration. The CHB topology for a single-phase three-submodule is specifically as follows: Within a submodule, the conduction time of the upper and lower devices of a single bridge arm is the same; the conduction time of the corresponding devices of the left and right bridge arms within a submodule is the same; and the conduction time of the corresponding devices between submodules is the same.

4. The improved cascaded H-bridge modulation method based on carrier reconstruction according to claim 3, characterized in that: The carriers are reconstructed and their spatial distribution across the three levels is adjusted. The conduction losses under different arrangements are traversed to obtain the optimal carrier arrangement with balanced conduction loss distribution, as follows: (41) The submodule includes four power devices, namely S 11 S 21 S 31 S 41 ; (42) When the modulating wave is located at (2E, 3E), the conduction loss under all carrier arrangement schemes is calculated. When the modulating wave is in the positive half-cycle, the power device S... 11 The conduction time is as follows: In the formula, t on+ When S is the positive half-cycle of the modulated wave 11 The conduction time, |V ref | represents the amplitude of the modulated wave; When the modulated wave is in the negative half-cycle, the power device S 11 The conduction time is as follows: The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula: In the formula, t on For the total conduction time, t on+ t is the conduction time of the positive half-cycle of the modulated wave. on- The conduction time of the negative half-cycle of the modulated wave; Power device S 41 With S 11 Complementary conduction, meaning the conduction time within one switching cycle is also... Due to the two power devices S on the right bridge arm of the submodule 41 S 11 Corresponding carrier and two power devices S in the left bridge arm 31 S 21 Symmetric about the x-axis, therefore the four devices in the current submodule have the same turn-on time; (43) When the modulating wave is located at (E, 2E), and when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows: When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows: The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula: (44) When the modulating wave is located at (0, E), and when the modulating wave is in the positive half-cycle, S 11 The conduction time is as follows: When the modulating wave is in the negative half-cycle, S 11 The conduction time is as follows: The modulation wave spends the same amount of time in both positive and negative periods, and the total conduction time is given by the following formula: In the formula, t on For the total conduction time, t on+ t is the conduction time of the positive half-cycle of the modulated wave. on- T is the conduction time of the negative half-cycle of the modulated wave. c The reconstructed carrier period.

5. The improved cascaded H-bridge modulation method based on carrier reconstruction according to claim 4, characterized in that: In the stacked structure, each submodule in the cascaded H-bridge converter adopts a carrier configuration strategy with phase rotation characteristics. This degree of freedom is used to make the modulation carrier amplitude and period the same, with only a phase deviation, so that the left and right bridge arms within the submodule and the device characteristics between submodules are the same.

6. An improved cascaded H-bridge modulation system based on carrier reconstruction, used to implement the improved cascaded H-bridge modulation method based on carrier reconstruction as described in any one of claims 1 to 5, characterized in that, include: Modulation wave simplification module, used to define modulation wave V m If the carrier frequency f m Much greater than the modulation wave frequency f cr Then, within one cycle, the modulated wave V m It can be viewed as a constant wave. The carrier reconstruction module combines the features of IPD-PWM and CPS-PWM. By reconstructing the carrier and adjusting its spatial distribution in multiple levels, it ensures that the fundamental amplitude and harmonic characteristics of the output voltage remain unchanged while maintaining the carrier spatial distribution of each submodule as equivalent to IPD-PWM. Furthermore, by traversing the conduction losses under different carrier arrangement methods, it obtains the optimal carrier arrangement method that balances the conduction loss distribution among power devices.

7. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, The memory stores a computer program that can run on the processor. When the processor loads and executes the computer program, it employs an improved cascaded H-bridge modulation method based on carrier reconstruction, as described in any one of claims 1 to 5.

8. A storage medium containing computer-executable instructions, characterized in that, The computer-executable instructions, when executed by a computer processor, are used to perform an improved cascaded H-bridge modulation method based on carrier reconstruction as described in any one of claims 1 to 5.

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