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

Abstract

The application discloses a control method and a control system of a three-level inverter under a low power factor, and comprises the following steps: obtaining operation state parameters containing a power factor angle phi and an electric angle theta; controlling the three-level inverter through small vectors based on an NTVV-SVPWM method in a gh coordinate system; introducing a neutral point balance control parameter l belonging to [0, 1] to adjust the action time of positive and negative small vectors, so as to balance the midpoint voltage; and detecting the power factor angle phi and the electric angle theta in real time, and performing a reverse compensation operation when a specific condition is met. The application overcomes the defect of losing the midpoint balance ability under an extremely low power factor, maintains the correct compensation current injection direction, prevents potential drift, reduces total harmonic distortion, and ensures high control precision.

Description

Technical Field

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

[0002] In the high-voltage electric drive systems of new energy vehicles, three-level motor controllers have become core components for high-performance drive control due to their excellent output waveform quality, extremely low switching losses, and good insulation performance for motors. Unlike traditional two-level topologies, three-level inverters generally employ split DC bus capacitors in their hardware architecture, thus physically forming a critical DC neutral point. Maintaining the dynamic balance of this neutral point potential during the actual operation of the motor controller is the cornerstone for ensuring the system's safe and stable output of high-quality AC voltage. If the neutral point voltage experiences continuous drift or severe oscillation, it will not only directly lead to uncontrollable errors in the modulated output voltage and significantly increase the total harmonic distortion of the motor traction current, affecting the vehicle's power smoothness and NVH performance, but may even trigger a fatal risk of overvoltage breakdown in power switching devices. Therefore, neutral point potential balance control has always been a core foundation in the field of automotive three-level motor controller technology.

[0003] Currently, the industry typically employs multi-level space vector pulse width modulation (MPPWM) technology. This involves flexibly controlling redundant small vectors that generate the same line voltage but exert opposite pulling effects on the neutral point current to achieve closed-loop compensation for neutral point voltage deviations. However, this traditional balance control strategy reveals serious limitations when facing complex real-world vehicle operating conditions. Especially when the motor operates under extremely low power factor conditions (such as low-speed, high-torque extreme escape or deep field weakening operation), the large phase difference between the motor stator voltage and current causes a nonlinear polarity deflection in the desired direction of the neutral point current in the underlying physical model. This results in the absence of any existing technology capable of stably regulating the neutral point current under low power factor conditions.

[0004] In summary, there is currently no technical solution that can accurately suppress neutral point voltage drift under all operating conditions. 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 and control system for a three-level inverter with low power factor.

[0006] This invention discloses a control method for a three-level inverter under low power factor conditions, comprising: Obtain the operating status parameters of the three-level inverter, including the power factor angle φ and electrical angle θ. In the gh coordinate system, the three-level inverter is controlled by a small vector based on the NTVV-SVPWM method. During the control process, a control parameter l is introduced to adjust the action time of the positive small vector and the negative small vector, where l∈[0,1]; so that a compensation current flows into the neutral point of the three-level inverter to balance the midpoint voltage of the neutral point; The current power factor angle φ and electrical angle θ are detected in real time. When the power factor angle φ and electrical angle θ meet specific conditions, the control parameter l is flipped to perform reverse compensation operation in order to maintain the correct injection direction of the neutral point compensation current of the three-level inverter.

[0007] Preferably, in the gh coordinate system, the control of the three-level inverter using a small vector based on the NTVV-SVPWM method includes: Based on the sector where the output voltage vector is located, one phase is configured as a split phase, and the other two phases are configured as non-split phases; When the output voltage vector is located in the first sector, phase B is configured as a split phase, and phases A and C are configured as non-split phases. The specific modulation voltage equation is configured as follows: The non-split phase A is: Phase B of the split phase is: The non-split phase C is: in, This is the modulation reference voltage for phase A. This is the modulation reference voltage for phase C; This is the positive periodic modulation reference voltage for phase B. This is the negative-cycle modulation reference voltage for phase B. This is the total voltage of the DC bus. and The coordinate components of the reference voltage in the gh coordinate system.

[0008] Preferably, the specific conditions are: the electrical angle θ satisfies θ<φ-π / 3, and the power factor angle φ>60°; Flipping control parameter l and performing reverse compensation operation includes: replacing control parameter l with a correction control parameter. , ; Utilizing modified control parameters The action time of the positive and negative small vectors is adjusted instead of the control parameter l.

[0009] Preferably, the initial value of the control parameter l is calculated by a PI controller.

[0010] Preferably, the input error signal of the PI controller is determined based on the midpoint potential deviation coefficient k of the DC bus, and the determination method includes: Obtain the voltage of the half-bridge capacitor on the DC bus and DC bus lower half-bridge capacitor voltage ; Calculate the midpoint potential deviation coefficient ; The difference between the preset target reference value and the midpoint potential deviation coefficient k is used as the initial error signal of the PI controller.

[0011] Preferably, the determination method further includes: The input error signal is normalized, including: Obtain the peak phase current under the current operating condition. The coordinate components g and h of the output voltage vector in the gh coordinate system, and the power factor angle. and electrical angle ; The normalized function value is calculated based on the obtained parameters, and the absolute value expression of the normalized function value is configured as follows: or The difference between the target reference value and the midpoint potential deviation coefficient k is used as the initial error signal; The initial error signal is divided by the absolute value of the normalized function to obtain the normalized error signal, which is then input to the PI controller as the input error signal of the PI controller.

[0012] Preferably, the control parameter l output by the PI controller is limited to a preset maximum value. and minimum value between.

[0013] Preferably, the PI controller is a PI controller with anti-saturation function.

[0014] A second aspect of this application provides a three-level inverter control system, comprising: a voltage and current acquisition unit, a control unit, and a three-level inverter; The voltage and current acquisition unit is used to acquire the output current and DC-side capacitor voltage in real time; The control unit receives voltage and current signals acquired by the voltage and current acquisition unit, and, in conjunction with preset system parameters, controls the three-level inverter by using the control method of the three-level inverter under any of the aforementioned low power factors.

[0015] Preferably, the three-level inverter is a three-level T-type inverter, a three-level neutral point clamping inverter, or an active neutral point clamping inverter.

[0016] Compared with existing technologies, the above technical solution has the following advantages: 1. The control method of this invention adjusts the action time of a small vector by introducing a control parameter l based on the NTVV-SVPWM method in the gh coordinate system. Its core technical advantage lies in addressing the problem of midpoint voltage drift in automotive three-level motor controllers under specific operating conditions. By real-time detection of the power factor angle φ and electrical angle θ, when a specific condition is identified where a low power factor leads to misjudgment of the neutral point current direction, the control parameter l is flipped to perform a reverse compensation operation. This scheme fundamentally overcomes the underlying physical defect of the motor controller completely losing its midpoint balance capability under extremely low power factors, effectively preventing continuous drift or AC oscillation of the neutral point potential, thereby completely eliminating the modulation alpha-beta voltage error, significantly reducing the total harmonic distortion (THD) of the output AC current, and ensuring high control accuracy of the traction motor drive. 2. At the underlying PWM generator level, this invention achieves the physical mapping of NTVV-SVPWM by precisely configuring the modulation voltage equations of the split-phase and non-split-phase. By independently adjusting the positive and negative periodic modulation reference voltages of the split-phase, the relative time of the three phases connecting to the neutral point is strictly equal, fundamentally reducing the basic average neutral point current to zero. Simultaneously, by embedding the control parameter l into the modulation equation of the non-split-phase, the conduction ratio of the positive and negative small vectors is precisely tilted, achieving unbiased injection of the compensation current. Combined with the precise determination of specific flip conditions, the system directly uses the modified control parameters to interchange the weighting of the positive and negative small vectors' action time configuration at the mathematical operation level. This technique can correct control direction errors under low power factor conditions with low computational cost without changing the overall architecture of the main control algorithm, ensuring that the neutral point balancing mechanism can still output the correct direction of the compensation current under extreme vehicle operating conditions. 3. Regarding closed-loop feedback regulation, this invention introduces a dynamic PI control loop and generates an initial error signal by calculating the midpoint potential deviation coefficient k based on the voltage of the upper and lower half-bridge capacitors on the DC bus. This dimensionless relative voltage deviation evaluation system successfully decouples the error signal from the large fluctuations in the total DC bus voltage of the automotive high-voltage battery pack, enhancing the system's anti-interference capability under different voltage levels. More importantly, the control system uses the phase current peak value, coordinate components g and h, power factor angle φ, and electrical angle θ to calculate the normalized function value and perform a division operation on the error signal. This normalization process dynamically offsets the physical differences in the sensitivity of different operating conditions to neutral point current regulation at the control theory level, allowing a single configured PI control parameter to perfectly adapt to all operating conditions of the motor controller, from low-speed high-torque start-up to high-speed weak-field cruise, greatly reducing the workload of multi-condition parameter matching in actual vehicle calibration. 4. To ensure the smoothness and NVH performance of the vehicle drive system, this invention establishes strict safety physical boundaries for the inverter's modulation process. By limiting the control parameter l output by the PI controller and immediately freezing the integral accumulation of the initial error signal when the boundary is reached using the anti-saturation function, the system forces a trade-off between quickly pulling back the midpoint voltage and ensuring high fidelity of the motor output voltage, completely avoiding phase lag and large overshoot oscillations caused by the long desaturation process of the control system. This allows the aforementioned method to be effectively used in onboard hardware architectures equipped with voltage and current acquisition units and control units. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the gh coordinate system; Figure 2 This is a schematic diagram of a three-level inverter. Figure 3 A flowchart illustrating the control method for the three-level inverter provided in this application; Figure 4 The control method for the three-level inverter provided in this application is based on a PI controller and is shown in the control flowchart. Figure 5 The control flowchart based on a PI controller after normalization of the control method for the three-level inverter provided in this application; Figure 6 A comparison diagram of the control results of the control method for the three-level inverter provided in this application and the control method in the prior art. Detailed Implementation

[0018] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0019] 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.

[0020] 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.

[0021] 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."

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Please see Figure 1 , Figure 1 This is a schematic diagram of the gh coordinate system.

[0026] like Figure 1 As shown, the basic background is introduced first: the so-called gh coordinate system is a coordinate system transformed from the αβ stationary coordinate system. In this system, the g-axis is aligned with the large vector PNN of the first sector, the h-axis is aligned with the large vector PPN, and the angle between the axes is 60°. The transformation matrix is: Taking the first sector as an example, in this coordinate system, the hexagonal boundary condition simplifies to g + h = 1. To achieve unified control across the entire sector, after determining the sector where the reference voltage vector is located, the system uses a rotation matrix to project the vectors of the other five sectors onto the first sector for equivalent calculation. This method reduces the amount of trigonometric functions such as cosine in actual control, thus greatly simplifying calculations and reducing control difficulty.

[0027] Based on the above background knowledge, this invention discloses a control method for a three-level inverter under low power factor.

[0028] Please see Figures 2-3 , Figure 2 This is a schematic diagram of a three-level inverter. Figure 3 A flowchart illustrating the control method for the three-level inverter provided in this application.

[0029] like Figures 2-3 As shown, this invention discloses a control method for a three-level inverter under low power factor conditions, comprising: Obtain the operating status parameters of the three-level inverter, including the power factor angle φ and electrical angle θ. In the gh coordinate system, the three-level inverter is controlled by a small vector based on the NTVV-SVPWM method. During the control process, a control parameter l is introduced to adjust the action time of the positive small vector and the negative small vector, where l∈[0,1]; so that a compensation current flows into the neutral point of the three-level inverter to balance the midpoint voltage of the neutral point; The current power factor angle φ and electrical angle θ are detected in real time. When the power factor angle φ and electrical angle θ meet specific conditions, the control parameter l is flipped to perform reverse compensation operation in order to maintain the correct injection direction of the neutral point compensation current of the three-level inverter.

[0030] This can be understood as follows: The control method of this invention adjusts the duration of the small vector by introducing a control parameter l based on the NTVV-SVPWM method in the gh coordinate system. Specifically, taking the positive small vector POO and the negative small vector ONN as examples, these two have the same driving effect, but their effects on the neutral point voltage are completely opposite. Assuming that the total time of the small vector in one switching cycle is T, then l∈[0,1] is the allocation parameter, and the duration of the positive small vector can be configured as follows: The duration of action of the negative small vector can be configured as follows: When l is 0.5, the positive and negative small vectors act for exactly the same duration, having no effect on the neutral point voltage. However, when l < 0.5, the negative small vector dominates, causing the neutral point voltage to decrease. The reverse is also true.

[0031] Therefore, based on the above control methods, the midpoint voltage of a three-level inverter can be balanced. However, this scheme is not feasible under low power factor conditions. This is because as the phase angle φ increases, the cosine term in the midpoint current formula changes sign within the sector. This not only results in the average midpoint current being zero over a fundamental cycle, but more importantly, it causes a reversal of the adjustment direction. Therefore, in certain specific ranges, this control method, due to this sign change, will lead to erroneous adjustment actions, causing the system to lose its balancing ability, and even further causing midpoint voltage drift due to the control.

[0032] Therefore, to address this problem, this application targets the issue of neutral point voltage drift that easily occurs in automotive three-level motor controllers under specific operating conditions. By real-time detection of the power factor angle φ and electrical angle θ, when a specific condition is identified where a low power factor leads to misjudgment of the neutral point current direction, the control parameter l is directly flipped to perform a reverse compensation operation. This method of manual correction within a specific range fundamentally overcomes the underlying physical defect of the motor controller completely losing its neutral point balance capability under extremely low power factors. It effectively prevents continuous drift or AC oscillation of the neutral point potential, thereby completely eliminating the modulation αβ voltage error, significantly reducing the total harmonic distortion (THD) of the output AC current, and ensuring high control accuracy of the traction motor drive. The above is an explanation of the basic concept of this application. The specific implementation of this application will be explained below.

[0033] In one possible implementation, in the gh coordinate system, the control of the three-level inverter via a small vector, based on the NTVV-SVPWM method, includes: Based on the sector where the output voltage vector is located, one phase is configured as a split phase, and the other two phases are configured as non-split phases; When the output voltage vector is located in the first sector, phase B is configured as a split phase, and phases A and C are configured as non-split phases. The specific modulation voltage equation is configured as follows: The non-split phase A is: Phase B of the split phase is: The non-split phase C is: in, This is the modulation reference voltage for phase A. This is the modulation reference voltage for phase C; This is the positive periodic modulation reference voltage for phase B. This is the negative-cycle modulation reference voltage for phase B. This is the total voltage of the DC bus. and The coordinate components of the reference voltage in the gh coordinate system.

[0034] The aforementioned method defines specific modulation voltage equations for configuring specific phases as split-phase and non-split-phase based on sector location. Its technical advantage lies in achieving precise physical mapping of NTVV-SVPWM at the underlying PWM generator level. By independently adjusting the positive and negative period modulation reference voltages of the split-phase, it ensures that the relative time for the three phases to connect to the neutral point within one switching cycle is strictly equal, fundamentally reducing the basic average neutral point current to zero. Simultaneously, embedding the control parameter l into the modulation equation of the non-split-phase allows for precise tilting of the positive and negative small vector conduction ratios without altering the fundamental amplitude of the line voltage output to the motor, achieving unbiased injection of compensation current without increasing additional hardware costs.

[0035] Of course, those skilled in the art will understand that this explanation uses phase B as an example. In actual control processes, the specific phase configured as the split phase depends strictly on the sector where the voltage reference vector is currently located. Similarly, when the voltage vector is in other sectors, phase A or phase C should be configured as the split phase, while the other two phases should be configured as non-split phases.

[0036] Furthermore, based on the above control methods, the specific location of the flip control parameter l can also be analyzed.

[0037] In one possible implementation, the specific conditions are: the electrical angle θ satisfies θ<φ-π / 3, and the power factor angle φ>60°; Flipping control parameter l and performing reverse compensation operation includes: replacing control parameter l with a correction control parameter. , ; Utilizing modified control parameters The action time of the positive and negative small vectors is adjusted instead of the control parameter l.

[0038] Based on the above explanation of the gh coordinate system, the control parameter l, power factor angle φ, and electrical angle θ relative to the midpoint voltage can be derived. The relevant formula for influence: Therefore, when PF=0 (i.e. φ=π / 2), if the midpoint voltage is still controlled according to the control parameter l, if φ>60°, for some cases where θ<φ-π / 3 is satisfied. The independent variable of the sine function in the formula will be <0. Therefore, the sine term will cause a sign change. This means that in the interval θ < φ - π / 3, the control system will generate a current flowing into the neutral point with incorrect polarity. When φ = 90°, this will occur within half a sector (0° < θ < 30°), resulting in an average current flowing into the neutral point within one sector / fundamental cycle. .

[0039] Therefore, specifically, given φ, if the electrical angle θ satisfies θ<φ-π / 3 and the power factor angle φ>60°, the control parameter l can be replaced with a correction control parameter. , The system directly swaps the weighting of the action time configurations of the positive and negative small vectors at the mathematical operation level. This technique can correct the regulator output direction error under low power factor conditions with low computing power cost without changing the original main closed-loop control algorithm architecture, effectively preventing the system from experiencing severe instability due to positive feedback of the midpoint voltage in this range.

[0040] Furthermore, to avoid determining the angle θ of the reference voltage in the αβ coordinate system and thus simplify the calculation, a simpler online detection criterion can be derived using trigonometric functions: Where c is a scaling factor (dependent on the scaling / normalization of the Park and Clarke transforms), but it is irrelevant here. Therefore, if the following conditions are met... Alternatively, the control parameter l can be replaced with a correction control parameter. , .

[0041] Based on the above specific control methods, the three-level inverter can be controlled to balance its midpoint voltage.

[0042] Please see Figure 4 , Figure 4 The control method for the three-level inverter provided in this application is based on the control flowchart of a PI controller.

[0043] like Figure 4 As shown, in one possible implementation, the initial value of the control parameter l is calculated by a PI controller.

[0044] By calculating the initial value of the control parameter l using a PI controller, a dynamic closed-loop feedback regulation loop is introduced into the neutral point voltage balancing mechanism. The PI controller can continuously and dynamically adjust the action time of small vectors based on the real-time offset of the neutral point potential. The proportional term provides a fast response to transient voltage offsets caused by vehicle acceleration or braking, while the integral term accumulates and eliminates steady-state errors caused by inverter hardware asymmetry. This ensures that the neutral point balancing control parameter l is always kept in an optimal dynamic adjustment state, effectively improving the voltage tracking speed of the motor controller when dealing with sudden load changes.

[0045] Of course, in another possible implementation, the above functions can also be achieved through software, and this application makes no restrictions on this.

[0046] Furthermore, in one possible implementation, the input error signal of the PI controller is determined based on the midpoint potential deviation coefficient k of the DC bus, and the determination method includes: Obtain the voltage of the half-bridge capacitor on the DC bus and DC bus lower half-bridge capacitor voltage ; Calculate the midpoint potential deviation coefficient ; The difference between the preset target reference value and the midpoint potential deviation coefficient k is used as the initial error signal of the PI controller.

[0047] A dimensionless relative voltage deviation evaluation system was constructed by calculating the midpoint potential deviation coefficient k based on the half-bridge capacitor voltage and the lower half-bridge capacitor voltage of the DC bus, and using this coefficient to generate the initial error signal. Compared with directly using the absolute voltage difference, the midpoint potential deviation coefficient k can decouple the error signal from the drastic fluctuations of the total DC bus voltage of the automotive high-voltage battery pack. When the battery pack voltage changes significantly due to rapid acceleration or energy recovery, this method can still provide stable and standardized error feedback for the PI controller, enhancing the anti-interference capability of the closed-loop control system under different bus voltage levels.

[0048] Please see Figure 5 , Figure 5 The control flowchart based on a PI controller after normalization of the control method for the three-level inverter provided in this application is shown.

[0049] like Figure 5 As shown, in one possible implementation, the determination method further includes: The input error signal is normalized, including: Obtain the peak phase current under the current operating condition. The coordinate components g and h of the output voltage vector in the gh coordinate system, and the power factor angle. and electrical angle ; The normalized function value is calculated based on the obtained parameters, and the absolute value expression of the normalized function value is configured as follows: or The difference between the target reference value and the midpoint potential deviation coefficient k is used as the initial error signal; The initial error signal is divided by the absolute value of the normalized function to obtain the normalized error signal, which is then input to the PI controller as the input error signal of the PI controller.

[0050] Normalization processing utilizes the peak phase current, coordinate components g and h, and power factor angle. The system calculates the normalized function value of the electrical angle θ and divides it by this value to obtain the normalized error signal. At the control theory level, this dynamically offsets the physical differences in the sensitivity of the automotive motor to neutral point current regulation under different operating conditions. Since the actual compensation current magnitude is highly dependent on the current phase current amplitude and power factor, the system physically flattens the system gain at different speeds and torques by performing division. This allows a single configured PI control parameter to perfectly adapt to all operating conditions of the motor controller, from low-speed, high-torque start-up to high-speed, weak-field cruise, greatly reducing the workload of multi-condition parameter matching in actual vehicle calibration.

[0051] It should be noted that the two normalization formulas above are essentially the same. When computing power is limited, or when extremely fast response is required, the normalization function expression can be selectively configured as follows: This reduces computing power requirements and improves response speed. In scenarios with ample computing power or high control precision requirements, the normalized function value expression can be selectively configured as follows: To meet the requirements, those skilled in the art can design their own solutions as needed, and this application makes no restrictions here.

[0052] It is understandable that the control parameter l directly affects the balancing rate of the midpoint voltage. However, if the control parameter l is set too far from the midpoint (l=0.5), excessive adjustment of the time allocation ratio of the small vector will introduce a large common-mode voltage. Furthermore, and more importantly, it will exacerbate the error in modulating the αβ voltage. Therefore, those skilled in the art need to design the value of the control parameter l appropriately according to the design requirements.

[0053] In one possible implementation, the control parameter l output by the PI controller is limited to a preset maximum value. and minimum value between.

[0054] By limiting the control parameters within the boundary range, the system forces a trade-off between rapidly pulling back the neutral point voltage and ensuring the high fidelity of the motor output voltage. This establishes a strict safety physical boundary for the inverter's modulation process, preventing severe distortion of the motor current waveform due to overcompensation and ensuring the smoothness and NVH performance of the vehicle drive system.

[0055] It should be noted that the preset maximum value mentioned here... and minimum value The specific value is not limited, and those skilled in the art can set it as needed; this application does not impose any restrictions here. For example, the maximum value... ∈[0,0.5], minimum value ∈[0.5,1].

[0056] Finally, in one possible implementation, the PI controller is a PI controller with anti-saturation function. This eliminates the integral saturation effect caused by the control parameter l reaching the physical limit boundary. When the system encounters a severe and sustained midpoint voltage imbalance, or when the controller output reaches its maximum or minimum value, the anti-saturation function immediately freezes the integral accumulation of the initial error signal. This ensures that when the external operating conditions causing the imbalance change or reverse, the PI controller can instantly escape the saturation state and adjust its output according to the normalized error signal, avoiding severe phase lag in the control system and preventing overshoot and large oscillations in the midpoint voltage when it returns to balance.

[0057] Please see Figure 6 , Figure 6 A comparison diagram of the control results of the control method for the three-level inverter provided in this application and the control method in the prior art.

[0058] like Figure 6 As shown, compared with the control methods in the prior art, the midpoint voltage of the three-level inverter under low power factor is better balanced after adopting this control method.

[0059] The above is a detailed description of the control method for a three-level inverter under low power factor provided in this application.

[0060] A second aspect of this application also provides a three-level inverter control system, comprising: a voltage and current acquisition unit, a control unit, and a three-level inverter; The voltage and current acquisition unit is used to acquire the output current and DC-side capacitor voltage in real time; The control unit receives voltage and current signals acquired by the voltage and current acquisition unit, and, in conjunction with preset system parameters, controls the three-level inverter by using the control method of the three-level inverter under any of the aforementioned low power factors.

[0061] This application also provides a complete onboard hardware execution architecture for executing the control method of the three-level inverter described in any of the preceding claims. The voltage and current acquisition unit provides high-precision physical quantity feedback for the underlying coordinate transformation and power factor angle calculation; the control unit transforms the abstract normalization algorithm and switching logic into the underlying drive duty cycle signal. The closed-loop collaboration of each unit ensures that the high-order midpoint balance control strategy can be reliably deployed in the automotive motor controller, continuously eliminating modulation αβ voltage errors and providing high-precision, low-harmonic drive current for the traction motor.

[0062] Finally, those skilled in the art will understand that the above control methods are applicable to various types of three-level inverters.

[0063] In one possible implementation, the three-level inverter is a three-level T-type inverter, a three-level neutral-point clamped inverter, or an active neutral-point clamped inverter.

[0064] While these topologies offer advantages such as low switching losses and good output waveforms, their split DC buses inherently carry the risk of neutral point potential drift. Applying this control method directly to the aforementioned specific hardware allows for the full utilization of its abundant redundant small vectors for precise charge transfer, completely suppressing the impact of AC oscillations on the DC-side capacitor. This ensures the safety of the switching devices while maximizing the efficiency advantages of the three-level motor controller in high-voltage electric drive systems.

[0065] 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, characterized in that, The control method includes: Obtain the operating status parameters of the three-level inverter, including the power factor angle φ and the electrical angle θ; In the gh coordinate system, the three-level inverter is controlled by a small vector based on the NTVV-SVPWM method. During the control process, a control parameter l is introduced to adjust the action time of the positive small vector and the negative small vector, where l∈[0,1]; so that a compensation current flows into the neutral point of the three-level inverter to balance the midpoint voltage of the neutral point; The current power factor angle φ and electrical angle θ are detected in real time. When the power factor angle φ and electrical angle θ meet specific conditions, the control parameter l is flipped to perform a reverse compensation operation to maintain the correct injection direction of the neutral point compensation current of the three-level inverter.

2. The control method for a three-level inverter as described in claim 1, characterized in that, The control of the three-level inverter using a small vector in the gh coordinate system, based on the NTVV-SVPWM method, includes: Based on the sector where the output voltage vector is located, one phase is configured as a split phase, and the other two phases are configured as non-split phases; When the output voltage vector is located in the first sector, phase B is configured as the split phase, and phases A and C are configured as the non-split phases. The specific modulation voltage equation is configured as follows: The non-split phase A is: Phase B of the split phase is: The non-split phase C is: in, This is the modulation reference voltage for phase A. This is the modulation reference voltage for phase C; This is the positive periodic modulation reference voltage for phase B. This is the negative-cycle modulation reference voltage for phase B. This is the total voltage of the DC bus. and The coordinate components of the reference voltage in the gh coordinate system.

3. The control method for a three-level inverter under low power factor as described in claim 1, characterized in that, The specific conditions are: the electrical angle θ satisfies θ<φ-π / 3, and the power factor angle φ>60°; The step of flipping the control parameter l and performing the reverse compensation operation includes: replacing the control parameter l with a correction control parameter. , ; using the aforementioned corrected control parameters The action time of the positive and negative small vectors is adjusted instead of the control parameter l.

4. The control method for a three-level inverter under low power factor as described in claim 1, characterized in that, The initial value of the control parameter l is calculated by a PI controller.

5. The control method for a three-level inverter under low power factor as described in claim 4, characterized in that, The input error signal of the PI controller is determined based on the midpoint potential deviation coefficient k of the DC bus, and the determination method includes: Obtain the voltage of the half-bridge capacitor on the DC bus and DC bus lower half-bridge capacitor voltage ; Calculate the midpoint potential deviation coefficient. ; The difference between the preset target reference value and the midpoint potential deviation coefficient k is used as the initial error signal of the PI controller.

6. The control method for a three-level inverter under low power factor as described in claim 5, characterized in that, The determination method further includes: Normalizing the input error signal includes: Obtain the peak phase current under the current operating condition. The coordinate components g and h of the output voltage vector in the gh coordinate system, and the power factor angle. and electrical angle ; The normalized function value is calculated based on the acquired parameters, and the absolute value expression of the normalized function value is configured as follows: or The difference between the target reference value and the midpoint potential deviation coefficient k is used as the initial error signal; The initial error signal is divided by the absolute value of the normalized function to obtain the normalized error signal, and the normalized error signal is input to the PI controller as the input error signal of the PI controller.

7. The control method for a three-level inverter under low power factor as described in claim 4, characterized in that, The control parameter l output by the PI controller is limited to a preset maximum value. and minimum value between.

8. The control method for a three-level inverter under low power factor as described in claim 7, characterized in that, The PI controller is a PI controller with anti-saturation function.

9. A three-level inverter control system, characterized in that, include: Voltage and current acquisition unit, control unit, and three-level inverter; The voltage and current acquisition unit is used to acquire the output current and DC-side capacitor voltage in real time. The control unit receives the voltage and current signals acquired by the voltage and current acquisition unit, and, in conjunction with preset system parameters, controls the three-level inverter by using the control method for a three-level inverter under low power factor as described in any one of claims 1-8.

10. The three-level inverter control system as described in claim 9, characterized in that, The three-level inverter is a three-level T-type inverter, a three-level neutral point clamping inverter, or an active neutral point clamping inverter.

Images