A control method, control system and driving system of a three-level inverter under low power factor

Abstract

The application provides a control method, a control system and a driving system of a three-level inverter under low power factor, the method comprising: obtaining a voltage reference vector and a neutral point voltage of the inverter in a current control period; determining a sector where the voltage reference vector is located and a target phase corresponding to the sector according to the voltage reference vector; judging whether the direction of the neutral point current generated by the neutral vector in the current sector is conducive to reducing the offset value of the neutral point voltage according to the offset value of the neutral point voltage; and injecting a control parameter Delta into the calculation of the modulation reference instruction of the target phase according to whether the direction of the neutral point current is conducive to reducing the offset value, so that the modulation instruction of the target phase controls the target phase corresponding bridge arm to switch to a two-level working mode or maintain a three-level working mode. The application completely cuts off the current path of the continuously deteriorating neutral point voltage from the physical source, effectively suppresses the neutral point potential drift, and significantly improves the output accuracy and stability of the three-level inverter.

Description

Technical Field

[0001] This invention relates to the field of three-level inverters, and more particularly to a control method, control system, and drive system for a three-level inverter under low power factor conditions. Background Technology

[0002] With the rapid development of new energy vehicles and industrial drive technologies, the requirements for power conversion efficiency and output waveform quality in motor drive systems are increasing. Three-level inverters, with their multi-stage voltage output characteristics, lower harmonic distortion, and reduced voltage stress on switching devices, occupy a crucial position in high-performance motor drive control. As the core hub connecting the DC power supply and the AC load, the quality of the inverter's space vector modulation strategy directly determines the accuracy of the power output to the motor, thus affecting the operational stability and reliability of the entire drive system.

[0003] However, mainstream three-level inverters generally employ a split DC bus topology, resulting in a midpoint with an unstable physical potential in the hardware structure. In actual operation, especially under extreme conditions such as low power factor, traditional space vector modulation algorithms inevitably inject a large unbalanced current into this midpoint when calling certain voltage vectors (such as the midpoint vector). This current surge disrupts the original charge balance, causing severe drift and low-frequency AC oscillations at the midpoint potential. This leads to inverter output command distortion and current distortion, and in severe cases, can even compromise the voltage equalization safety of power devices, significantly reducing equipment lifespan.

[0004] In summary, how to effectively overcome the midpoint potential instability problem under specific low power factors without increasing additional hardware costs or changing the original topology has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In order to overcome the above-mentioned technical defects, the purpose of this invention is to provide a control method, control system and drive system for a three-level inverter under low power factor conditions.

[0006] This invention discloses a control method for a three-level inverter under low power factor conditions, comprising: Obtain the voltage reference vector and midpoint voltage of the inverter in the current control cycle; The sector in which it is located is determined based on the voltage reference vector, and the target phase corresponding to that sector is determined; Based on the offset value of the midpoint voltage, determine whether the direction of the midpoint current generated by the midpoint vector in the current sector is conducive to reducing the offset value; Depending on whether it is beneficial to reduce the offset value, when calculating the modulation reference command of the target phase, the control parameter Δ is injected so that the modulation command of the target phase controls the corresponding bridge arm to switch to a two-level working mode or maintain a three-level working mode.

[0007] Preferably, determining whether the direction of the midpoint current generated by the midpoint vector within the current sector is conducive to reducing the offset value specifically includes: Obtain the direction of the midpoint current required to reduce the offset value of the midpoint voltage; divide the rotation region of the midpoint vector into 6 sectors; If the required midpoint current direction is positive, then the direction of the midpoint current generated by the midpoint vector in odd-numbered sectors is not conducive to reducing the offset value, while the direction of the midpoint current generated by the midpoint vector in even-numbered sectors is conducive to reducing the offset value. If the required midpoint current direction is negative, then the direction of the midpoint current generated by the midpoint vector in even-numbered sectors is not conducive to reducing the offset value, while the direction of the midpoint current generated by the midpoint vector in odd-numbered sectors is conducive to reducing the offset value.

[0008] Preferably, injecting control parameter Δ to cause the modulation command of the target phase to control the corresponding bridge arm to switch to a two-level operating mode or maintain a three-level operating mode includes: When it is determined that this is beneficial to reducing the offset value, the control parameter Δ is set to 0 to maintain the three-level working mode; When it is determined that it is not conducive to reducing the offset value, the control parameter Δ is set to a preset value. The preset value is equal to the relative time of connection between the target phase and the midpoint level in the current switching cycle, so that the target phase is not connected to the midpoint level in the switching cycle, thereby returning to the two-level working mode.

[0009] Preferably, the calculation method for the control parameter Δ includes: Transform the voltage reference vector to the normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system; control parameter Δ = 1 - gh.

[0010] Preferably, the injected control parameter Δ specifically includes: The modulation reference command of the target phase is decomposed into a positive reference signal. and negative reference signal ; The control parameter Δ is divided into a positive control parameter and a negative control parameter, each with an amplitude of Δ / 2, and is superimposed on the positive reference signal. and negative reference signal The superimposed reference signal correction value is: Positive reference signal correction value = +Δ / 2; Negative reference signal correction value = -Δ / 2.

[0011] Preferably, the bridge arm corresponding to the target generates the drive pulse through a dual-carrier comparison method: The positive reference signal correction value is compared with a positive carrier with an amplitude range of [0,1] to generate a pulse width modulation signal for controlling the upper arm switch of the target phase; The negative reference signal correction value is compared with a negative carrier with an amplitude range of [-1, 0] to generate a pulse width modulation signal for controlling the target phase lower arm switch.

[0012] Preferably, the voltage reference vector is transformed to the normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system, specifically including: Obtain the components α and β of the voltage reference vector in the stationary αβ coordinate system; The current sector where the voltage reference vector is located is determined by comparing the magnitude and sign of components α and β. Based on the determined current sector, components α and β are mapped to the first sector using a rotation matrix to obtain the mapped components. and ; Using mapping components and The components g and h in the gh coordinate system are calculated.

[0013] A second aspect of this application also provides a control system for a three-level inverter under low power factor conditions, comprising: a memory for storing a computer program; A processor for executing computer programs to implement control methods for a three-level inverter under low power factor conditions, as described above.

[0014] A third aspect of this application provides a drive system comprising: a three-level inverter, a motor, and the aforementioned control system; The control system is communicatively connected to the three-level inverter and is used to control the three-level inverter; the three-level inverter is electrically connected to the motor and is used to drive the motor.

[0015] Compared with existing technologies, the above technical solution has the following advantages: 1. The technical solution provided in this application mainly addresses the problems of midpoint voltage drift and AC oscillation that easily occur in three-level inverters under low power factor. During the control process, the system acquires the voltage reference vector and midpoint voltage of the inverter in the current control cycle. Since the midpoint vector injects a large amount of current into the midpoint under low power factor, severely disrupting the balance, the algorithm needs to dynamically determine whether the direction of the midpoint current generated by the midpoint vector in the current sector is beneficial or detrimental based on the offset value of the midpoint voltage. For adverse operating conditions, the system controls the parameter Δ when calculating the modulation reference command of the target phase. This proactive intervention can forcibly command the corresponding bridge arm of the target to skip the midpoint and directly switch to the two-level operating mode without changing the underlying hardware topology. This completely cuts off the current path that continuously deteriorates the midpoint voltage from the physical source, effectively suppresses midpoint potential drift under low power factor, and significantly improves the overall output power quality of the inverter. 2. After establishing the active switching strategy, the system precisely implements the control intent through a deterministic sector screening mechanism and a time stripping algorithm. The system first obtains the target compensation current direction required to reduce the offset value and compares it in real time with the inherent alternation characteristics of the center vectors in the six sector divisions, accurately locking down and eliminating harmful center vectors that would worsen the offset. If an unfavorable condition is determined, the system introduces a normalized gh coordinate system to calculate the degree to which the target phase deviates from the outer boundary of the space vector hexagon, thus accurately representing the relative time at which the phase should have been connected to the midpoint level. By precisely setting the control parameter Δ to this relative time, the system actively strips this midpoint dwell time at the algorithm level, forcing the target phase to directly cross the midpoint within the switching cycle, completing precise two-level degradation. Simultaneously, the relatively simple calculation significantly reduces the chip's computational burden. 3. To ensure the accuracy of the output voltage is not lost when executing a two-level backoff command, this application employs a symmetrical injection and hardware / software command mapping mechanism: the system divides the control parameter Δ into two equal halves, which are then symmetrically superimposed onto the positive and negative reference signals of the target phase. These halves are perfectly canceled out when the potential difference is subtracted at the final physical output, thus strictly ensuring that the average output voltage of the target phase is equal to the initial command, completely eliminating the risk of motor torque pulsation caused by drastic switching of the internal modulation mode. The corrected reference signal is sent to an independent dual-carrier comparison architecture to ensure that the mathematical correction intention is accurately mapped to the underlying drive pulse. Furthermore, through a full-sector rotating mapping strategy, the inverter can reuse the same simplified operational model in all sectors, achieving a significant reduction in the underlying control code and a leap in anti-interference capabilities. 4. Finally, this method was implemented in the control and drive systems of the three-level inverter, thereby preventing the risk of overvoltage breakdown of the power devices of the three-level inverter itself due to the imbalance of the midpoint potential, while ensuring that the waveform of the electrical energy delivered to the traction motor has extremely high smoothness and consistency, which is more suitable for the driving scenarios of new energy vehicles with more stringent requirements for the electrical reliability of the system. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the control method for a three-level inverter under low power factor conditions provided in this application. Detailed Implementation

[0017] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0018] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0019] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0021] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0023] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.

[0024] Please see Figure 1 This is a flowchart illustrating the control method for a three-level inverter under low power factor conditions provided in this application.

[0025] like Figure 1 As shown, this invention discloses a control method for a three-level inverter under low power factor conditions, comprising: Obtain the voltage reference vector and midpoint voltage of the inverter in the current control cycle; The sector in which it is located is determined based on the voltage reference vector, and the target phase corresponding to that sector is determined; Based on the offset value of the midpoint voltage, determine whether the direction of the midpoint current generated by the midpoint vector in the current sector is conducive to reducing the offset value; Depending on whether it is beneficial to reduce the offset value, when calculating the modulation reference command of the target phase, the control parameter Δ is injected so that the modulation command of the target phase controls the corresponding bridge arm to switch to a two-level working mode or maintain a three-level working mode.

[0026] This can be understood as follows: The main purpose of this application is to solve the problems of midpoint voltage drift and AC oscillation that are prone to occur in three-level inverters under low power factor conditions. In the specific control process, the system first obtains the voltage reference vector and midpoint voltage within the current control cycle of the inverter. Since the midpoint vector injects a large amount of current into the midpoint under low power factor conditions, severely disrupting the balance, the algorithm needs to determine whether the direction of the midpoint current generated by the midpoint vector in the current sector is beneficial or detrimental based on the offset value of the midpoint voltage at this time. For adverse operating conditions, the system injects the control parameter Δ when calculating the modulation reference command of the target phase. This approach can forcibly command the corresponding bridge arm of the target to skip the midpoint and directly switch to the two-level operating mode without changing the underlying hardware topology. Through this dynamic intervention, the system completely cuts off the current path that continuously deteriorates the midpoint voltage from the physical source, thereby effectively suppressing midpoint potential drift under low power factor conditions and significantly improving the overall output power quality of the inverter.

[0027] The above is an explanation of the basic concept of this application. The following is a description of the specific implementation methods of each step of this application.

[0028] In one possible implementation, determining whether the direction of the midpoint current generated by the mid-vector within the current sector is conducive to reducing the offset value specifically includes: Obtain the direction of the midpoint current required to reduce the offset value of the midpoint voltage; divide the rotation region of the midpoint vector into 6 sectors; If the required midpoint current direction is positive, then the direction of the midpoint current generated by the midpoint vector in odd-numbered sectors is not conducive to reducing the offset value, while the direction of the midpoint current generated by the midpoint vector in even-numbered sectors is conducive to reducing the offset value. If the required midpoint current direction is negative, then the direction of the midpoint current generated by the midpoint vector in even-numbered sectors is not conducive to reducing the offset value, while the direction of the midpoint current generated by the midpoint vector in odd-numbered sectors is conducive to reducing the offset value.

[0029] This can be understood as follows: From the perspective of space vector modulation, as the voltage reference vector rotates in different regions, the direction of the midpoint current caused by the midpoint vector exhibits a strict alternating change characteristic between adjacent sectors. Based on this pattern, the system first obtains the target compensation current direction required to reduce the current midpoint voltage offset and compares it in real time with the inherent current polarity of the midpoint vector in the six divided sectors. For example, when the system urgently needs a positive midpoint current to pull back the potential, the midpoint vector in odd-numbered sectors often has a counterproductive effect, while even-numbered sectors can provide positive assistance. With the help of this highly deterministic sector screening mechanism, the control system can use software to lock and eliminate midpoint vectors that will further worsen the midpoint voltage offset, while retaining midpoint vectors that can restore midpoint voltage balance, thus truly achieving active, fast, and smooth regulation and control of the midpoint voltage under low power factor conditions.

[0030] Correspondingly, in one possible implementation, injecting a control parameter Δ to cause the modulation command of the target phase to control the corresponding bridge arm to switch to a two-level operating mode or maintain a three-level operating mode includes: When it is determined that this is beneficial to reducing the offset value, the control parameter Δ is set to 0 to maintain the three-level working mode; When it is determined that it is not conducive to reducing the offset value, the control parameter Δ is set to a preset value. The preset value is equal to the relative time of connection between the target phase and the midpoint level in the current switching cycle, so that the target phase is not connected to the midpoint level in the switching cycle, thereby returning to the two-level working mode.

[0031] After establishing the screening logic, the operation of a phase in three-level mode can be flexibly controlled by adjusting the control parameter Δ. This achieves extremely precise physical-level degradation to two-level operation mode, providing a solid foundation for cutting off harmful currents.

[0032] Furthermore, in one possible implementation, the calculation of the control parameter Δ includes: Transform the voltage reference vector to the normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system; control parameter Δ = 1 - gh.

[0033] To ensure the efficient implementation of the aforementioned time stripping strategy in engineering, this application also provides a specific mathematical calculation model for the control parameter Δ. For ease of calculation, a normalized gh coordinate system is introduced. The voltage reference vector is first transformed to this special non-orthogonal coordinate system to extract components g and h. In the geometric space of the gh coordinate system, the system boundary exhibits a high degree of linear symmetry. Therefore, formula 1-gh mathematically precisely characterizes the degree to which the target phase deviates from the outer boundary of the hexagonal spatial vector, which is equivalent to the relative time proportion at which the phase needs to be connected to the midpoint level. This mathematical modeling greatly simplifies the solution process for Δ. By transforming the originally complex spatial geometric projection and duty cycle calculation into a basic linear algebraic subtraction operation, not only is the absolute accuracy of the relative time calculation fundamentally guaranteed, but the computational burden on the digital signal processor is also significantly reduced, effectively improving the real-time dynamic response capability of the inverter control algorithm.

[0034] Once the specific control parameter Δ is obtained, it can be injected.

[0035] In one possible implementation, the control parameter Δ is injected, specifically including: The modulation reference command of the target phase is decomposed into a positive reference signal. and negative reference signal ; The control parameter Δ is divided into a positive control parameter and a negative control parameter, each with an amplitude of Δ / 2, and is superimposed on the positive reference signal. and negative reference signal The superimposed reference signal correction value is: Positive reference signal correction value = +Δ / 2; Negative reference signal correction value = -Δ / 2.

[0036] The principle needs to be explained here: By splitting the modulation reference command of the target phase in two, and dividing the calculated control parameter Δ equally into two halves, these halves are symmetrically superimposed onto the positive and negative reference signals in the forms of +Δ / 2 and -Δ / 2, respectively. According to the basic principle of carrier modulation, the final actual output phase voltage of the target phase is determined by the differential mode components of its positive and negative commands. When +Δ / 2 and -Δ / 2 are injected simultaneously as common-mode compensation quantities into the control commands of the upper and lower bridge arms, these two parts are perfectly canceled out during the subtraction of potential differences at the physical output terminals. This ensures that while the system successfully changes the internal operating trajectory of the power switch and smoothly skips the midpoint, it strictly guarantees that the average output voltage of the target phase within one switching cycle is consistent with the initial command voltage, thereby preventing the potential risks of motor torque pulsation and current distortion caused by drastic switching of internal modulation modes.

[0037] For example, taking the need to split phase B at this time as an example, the three-phase reference signals at this time are: Furthermore, in one possible implementation, the target-corresponding bridge arm specifically generates the drive pulse via a dual-carrier comparison method: The positive reference signal correction value is compared with a positive carrier with an amplitude range of [0,1] to generate a pulse width modulation signal for controlling the upper arm switch of the target phase; The negative reference signal correction value is compared with a negative carrier with an amplitude range of [-1, 0] to generate a pulse width modulation signal for controlling the target phase lower arm switch.

[0038] The independent operation of dual-carrier partitions not only ensures that the two-level working mode can be safely and stably activated at the physical layer, but also greatly improves the anti-interference capability of the entire driver module in complex electromagnetic environments.

[0039] The above is a complete description of the midpoint voltage balancing method for a three-level inverter under low power factor conditions provided in this application. Those skilled in the art will understand that further mathematical modifications can be made to achieve better simplification and facilitate implementation. This application makes no limitations herein.

[0040] In one possible implementation, the voltage reference vector is transformed to a normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system, specifically including: Obtain the components α and β of the voltage reference vector in the stationary αβ coordinate system; The current sector where the voltage reference vector is located is determined by comparing the magnitude and sign of components α and β. Based on the determined current sector, components α and β are mapped to the first sector using a rotation matrix to obtain the mapped components. and ; Using mapping components and The components g and h in the gh coordinate system are calculated.

[0041] For example, this application also provides a normalized coordinate transformation and sector determination optimization strategy that avoids complex trigonometric function calculations. In traditional processes, the system often relies on inverse trigonometric functions to calculate spatial angles in a stationary αβ coordinate system to lock the sector, which is an extremely time-consuming nonlinear operation for the underlying chip. This solution, however, directly extracts the numerical values ​​and signs of components α and β for algebraic comparison, instantly determining the current sector. Subsequently, the system uses a rotation matrix to uniformly force-map the components of any sector to the first sector to obtain intermediate components, and finally performs a gh coordinate system transformation. This process not only completely eliminates the cumbersome angle calculation task and removes algorithm jitter caused by singularities, but more importantly, the full-sector normalized mapping allows the inverter to perfectly reuse the same simplified gh coordinate mathematical operation model in six different sectors, thereby significantly simplifying the underlying control code and improving execution efficiency.

[0042] A second aspect of this application also provides a control system for a three-level inverter under low power factor conditions, comprising: a memory for storing a computer program; A processor for executing computer programs to implement control methods for a three-level inverter under low power factor conditions, as described above.

[0043] This enables the three-level inverter to actively suppress midpoint voltage instability when dealing with extremely low power factor conditions.

[0044] A third aspect of this application provides a drive system comprising: a three-level inverter, a motor, and the aforementioned control system; The control system is communicatively connected to the three-level inverter and is used to control the three-level inverter; the three-level inverter is electrically connected to the motor and is used to drive the motor.

[0045] By applying the above control system to the drive system to drive the motor, the risk of overvoltage breakdown of the power devices of the three-level inverter caused by midpoint potential imbalance is fundamentally eliminated, the service life of the hardware is extended, and the waveform of the electrical energy delivered to the traction motor has extremely high smoothness and consistency, which perfectly meets the requirements of the new energy vehicle drive scenario with extremely stringent requirements for system electrical reliability and smoothness.

[0046] It should be noted that the embodiments of the present invention have better implementability and are not intended to limit the present invention in any way. Any person skilled in the art may use the above-disclosed technical content to change or modify it into equivalent effective embodiments. However, any modifications or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A control method for a three-level inverter under low power factor conditions, characterized in that, The control method includes: Obtain the voltage reference vector and midpoint voltage of the inverter in the current control cycle; The sector in which the voltage reference vector is located is determined based on the voltage reference vector, and the target phase corresponding to that sector is determined. Based on the offset value of the midpoint voltage, determine whether the direction of the midpoint current generated by the midpoint vector in the current sector is conducive to reducing the offset value; Depending on whether it is beneficial to reduce the offset value, when calculating the modulation reference command of the target phase, a control parameter Δ is injected so that the modulation command of the target phase controls the corresponding bridge arm to switch to a two-level operating mode or maintain a three-level operating mode.

2. The control method for a three-level inverter under low power factor as described in claim 1, characterized in that, The determination of whether the direction of the midpoint current generated by the midvector in the current sector is conducive to reducing the offset value specifically includes: Obtain the direction of the midpoint current required to reduce the offset value of the midpoint voltage; divide the rotation region of the midpoint vector into 6 sectors; If the required midpoint current direction is positive, then it is determined that the midpoint current direction generated by the midpoint vector in odd-numbered sectors is not conducive to reducing the offset value, while the midpoint current direction generated by the midpoint vector in even-numbered sectors is conducive to reducing the offset value. If the required midpoint current direction is negative, then the direction of the midpoint current generated by the midpoint vector in even-numbered sectors is not conducive to reducing the offset value, while the direction of the midpoint current generated by the midpoint vector in odd-numbered sectors is conducive to reducing the offset value.

3. The control method for a three-level inverter under low power factor as described in claim 2, characterized in that, The injection control parameter Δ causes the modulation command of the target phase to control the corresponding bridge arm to switch to a two-level operating mode or maintain a three-level operating mode, including: When it is determined that it is beneficial to reduce the offset value, the control parameter Δ is set to 0 to maintain the three-level working mode; When it is determined that it is not conducive to reducing the offset value, the control parameter Δ is set to a preset value, which is equal to the relative time that the target phase is connected to the midpoint level in the current switching cycle, so that the target phase is not connected to the midpoint level in the switching cycle, thereby returning to the two-level working mode.

4. The control method for a three-level inverter under low power factor as described in claim 3, characterized in that, The calculation method for the control parameter Δ includes: The voltage reference vector is transformed to the normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system; the control parameter Δ = 1 - gh.

5. The control method for a three-level inverter under low power factor as described in claim 4, characterized in that, The injection control parameter Δ specifically includes: The modulation reference command of the target phase is split into a positive reference signal. and negative reference signal ; The control parameter Δ is divided into a positive control parameter and a negative control parameter, both with an amplitude of Δ / 2, which are respectively superimposed on the positive reference signal. and the negative reference signal The superimposed reference signal correction value is: Positive reference signal correction value = +Δ / 2; Negative reference signal correction value = -Δ / 2.

6. The control method for a three-level inverter under low power factor as described in claim 5, characterized in that, The bridge arm corresponding to the target specifically generates a drive pulse through a dual-carrier comparison method: The positive reference signal correction value is compared with a positive carrier with an amplitude range of [0,1] to generate a pulse width modulation signal for controlling the upper bridge arm switch of the target phase; The negative reference signal correction value is compared with a negative carrier with an amplitude range of [-1, 0] to generate a pulse width modulation signal for controlling the target phase lower arm switch.

7. The control method for a three-level inverter under low power factor as described in claim 4, characterized in that, The step of transforming the voltage reference vector to the normalized gh coordinate system to obtain the components g and h of the voltage reference vector in the gh coordinate system specifically includes: Obtain the components α and β of the voltage reference vector in the stationary αβ coordinate system; The current sector where the voltage reference vector is located is determined by comparing the magnitude and sign of component α and component β. Based on the determined current sector, components α and β are mapped to the first sector using a rotation matrix to obtain the mapped components. and ; Using the mapping components and The components g and h in the gh coordinate system are calculated.

8. A control system for a three-level inverter under low power factor conditions, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the control method for a three-level inverter under low power factor as described in any one of claims 1-7.

9. A drive system, characterized in that, include: A three-level inverter, a motor, and a control system as described in claim 8; The control system is communicatively connected to the three-level inverter and is used to control the three-level inverter; the three-level inverter is electrically connected to the motor and is used to drive the motor.

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