Optimized carrier modulation method and system considering oscillations and unbalanced midpoint voltage

Abstract

The application belongs to the technical field of power electronics, and discloses an optimal carrier modulation method and system considering oscillation and unbalanced midpoint voltage. The method obtains normalized sinusoidal waves of phase A, phase B and phase C according to a three-phase normalization formula of a SPWM modulation strategy of a three-level Vienna rectifier; calculates a modulation signal correction variable and an unbalanced coefficient of a midpoint voltage; calculates a zero sequence voltage u z.ICB considering oscillation and unbalanced midpoint voltage, and injects the zero sequence voltage into the three-phase normalized sinusoidal waves to obtain intermittent modulation waves of the three-level Vienna rectifier of phase A, phase B and phase C considering oscillation and unbalanced midpoint voltage. The application can greatly reduce switching loss and improve the efficiency of the converter under the working condition of oscillation and unbalanced midpoint voltage, and can suppress low-frequency harmonics and eliminate current zero-crossing distortion. The application does not need sector judgment and only needs to inject a zero sequence component, and is simple and convenient to implement.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular relates to an optimized carrier modulation method and system that takes into account oscillations and unbalanced midpoint voltage. Background Technology

[0002] Compared to traditional two-level converters, three-level Vienna rectifiers offer advantages such as higher efficiency, higher voltage capability, and lower dv / dt. Therefore, three-level Vienna rectifiers have been widely used in industrial applications such as aircraft systems, hybrid energy storage systems, and electric vehicle charging systems. Three-level Vienna rectifiers are typically used as the front-end power factor correction converter in two-stage AC / DC power systems, providing the required DC output voltage to the DC / DC stage. For example, in data center power systems and electric vehicle charging systems, Vienna rectifiers need to provide dual voltages for series / parallel DC / DC converters to reduce costs and achieve a flexible output voltage range.

[0003] Under oscillating and unbalanced NP voltages, traditional modulation methods suffer from vector synthesis errors, inevitably increasing the total harmonic distortion (THD) of the input current. In the literature Z. Zhang, G. Zhang, G. Wang, J. Wang, D. Ding, and D. Xu, “A Hybrid Modulation Strategy With Neutral Point Voltage Balance Capability for Electrolytic Capacitorless Vienna Rectifiers,” IEEE Trans. Power Electron., pp. 1-11, 2022, a hybrid modulation scheme combining redundant vectors and compressed vectors is proposed to balance the NP voltage and reduce current THD. However, the hybrid discontinuous modulation method primarily utilizes redundant vectors to regulate the NP voltage, resulting in higher switching losses.

[0004] In the paper "A Hybrid Carrier-Based DPWM With Controllable NP Voltage for Three-Phase Vienna Rectifiers," by Y. Ming, L. Zhang, Y. Zou, Y. Xing, H. Zhao, Z. Zhang, T. Wang, and Y. Wang, "A Hybrid Carrier-Based DPWM With Controllable NP Voltage for Three-Phase Vienna Rectifiers," IEEE Trans. Transp. Electrification., vol. 8, no. 2, pp. 1874-1884, Jun. 2022, a hybrid carrier-based discontinuous modulation method is proposed, which can achieve redundant clamping modes. When the NP voltage exceeds the upper and lower limits, the clamping mode is changed to raise or lower the NP voltage. However, switching the redundant clamping mode causes a step change in the modulated waveform, resulting in additional switching losses. Meanwhile, some discontinuous modulation methods for three-level midpoint clamping do not consider the current zero-crossing distortion problem, leading to an increase in input current harmonics. Moreover, if the space vector method is used, the calculation of sub-sector division and vector action time becomes complex when considering oscillations and unbalanced midpoint voltages. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the embodiments disclosed in this invention provide an optimized carrier modulation method and system that considers oscillations and unbalanced midpoint voltage. Specifically, it relates to an optimized carrier discontinuous modulation method for a three-level Vienna rectifier that considers oscillations and unbalanced midpoint voltage.

[0006] The technical solution is as follows: an optimized carrier modulation method considering oscillation and unbalanced midpoint voltage, the method comprising the following steps:

[0007] S1, based on the three-phase normalization formula of the SPWM modulation strategy of the three-level Vienna rectifier, the normalized sine waves of phases A, B, and C are obtained as u ma u mb u mc ;

[0008] S2, calculate the modulation signal correction variable and the midpoint voltage imbalance coefficient;

[0009] S3, Calculate the zero-sequence voltage u considering oscillations and the unbalanced midpoint voltage. z.ICB and the zero-sequence voltage u z.ICB Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation of the neutral point voltage, considering oscillations and imbalances. ref_x x = a, b, and c.

[0010] In step S1, the normalized sine waves of phases A, B, and C are obtained from the three-phase normalization formula as u ma u mb u mc The method for determining it is as follows:

[0011]

[0012]

[0013] In the formula, u ma For phase A normalized sine wave, u mb For the normalized sine wave of phase B, u mc For a C-phase normalized sine wave, f g U is the power grid frequency, m is the modulation ratio, m∈(0,1); m U is the amplitude of the AC reference phase voltage. dc This is the DC-side bus voltage.

[0014] In step S2, the modulation signal correction variable is calculated according to the following formula:

[0015]

[0016] In the formula, u mx x = a, b, and c are the normalized sine waves u of phases A, B, and C, respectively. ma u mb u mc , These are the modulation signal correction variables, δ is the midpoint voltage imbalance coefficient, and u z1 This is a peak clamping correction variable.

[0017] Furthermore, the midpoint voltage imbalance coefficient δ is calculated according to the following formula:

[0018]

[0019] In the formula, δ is the midpoint voltage imbalance coefficient, U dc1 U is the voltage of the capacitor on the DC bus. dc2 This is the voltage of the capacitor below the DC bus.

[0020] In step S3, the zero-sequence voltage u considering oscillations and the unbalanced midpoint voltage is calculated. z.ICB The method for determining is shown in the following formula:

[0021]

[0022] In the formula, for The maximum value, for The minimum value, for The minimum value, u max u min u mid Normalized sine waves u for phases A, B, and C respectively ma u mb u mc The maximum, minimum, and median values ​​of u th To correct the variable, u z1 This is a peak clamping correction variable.

[0023] Furthermore, the variable u is modified. th and the clamping coefficient k of the variable interval VAC Calculate according to the following formula:

[0024]

[0025] In the formula, The zero-crossing clamping angle is set.

[0026] In step S3, the zero-sequence voltage u z.ICB Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation of the neutral point voltage, considering oscillations and imbalances. ref_x The method for determining x = a, b, and c is as follows:

[0027]

[0028] In the formula, u ref_x x = a, b, and c represent a low-switching-loss three-phase discontinuous carrier modulation wave under neutral-point voltage imbalance conditions, u ma For phase A normalized sine wave, u mb For the normalized sine wave of phase B, u mc For the C-phase normalized sine wave, u z.ICB The zero-sequence voltage is injected to account for the discontinuous modulation wave of the oscillation and unbalanced midpoint voltage.

[0029] Another object of the present invention is to provide an optimized carrier modulation system that considers oscillations and unbalanced midpoint voltage, the system implementing the optimized carrier modulation method considering oscillations and unbalanced midpoint voltage, the system comprising:

[0030] The three-phase normalization module is used to obtain the normalized sine waves of phases A, B, and C, respectively, based on the three-phase normalization of the SPWM modulation strategy of the three-level Vienna rectifier. ma u mb u mc ;

[0031] The module for calculating modulation signal correction variables and midpoint voltage imbalance coefficients is used to calculate modulation signal correction variables and midpoint voltage imbalance coefficients using the modulation signal correction variable calculation formula and the midpoint voltage imbalance coefficient calculation formula.

[0032] The discontinuous modulation wave acquisition module is used to calculate the zero-sequence voltage u considering oscillations and the unbalanced midpoint voltage. z.ICB and the zero-sequence voltage u z.ICB Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation of the neutral point voltage, considering oscillations and imbalances. ref_x x = a, b, and c.

[0033] Furthermore, the system is mounted on a three-level Vienna rectifier to perform optimized carrier modulation of oscillation and unbalanced midpoint voltage.

[0034] Furthermore, the three-level Vienna rectifier is installed in aircraft systems, hybrid energy storage systems, and electric vehicle charging systems to perform optimized carrier modulation of oscillation and unbalanced midpoint voltage.

[0035] Combining all the above technical solutions, the beneficial effects of this invention are as follows: Compared with traditional modulation methods, this invention can significantly reduce switching losses and improve converter efficiency under oscillating and unbalanced midpoint voltage conditions, while simultaneously suppressing low-frequency harmonics and eliminating current zero-crossing distortion. This invention requires no sector judgment and only needs to inject a zero-sequence component once, making engineering implementation simple and convenient.

[0036] This invention reduces the need for high-end controllers, thereby lowering the hardware cost of controllers used in fast charging systems for electric vehicles; it also improves power quality and reduces harmonic pollution to the power grid. Under conditions of oscillation and unbalanced midpoint voltage, it can simultaneously reduce switching losses and eliminate current zero-crossing distortion, achieved through a carrier wave method, significantly reducing the modulation signal calculation time. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure;

[0038] Figure 1 This is a schematic diagram of a common three-level Vienna rectifier main circuit topology and its oscillation and unbalanced midpoint voltage in the prior art provided by the embodiments of the present invention;

[0039] Figure 2 This is a flowchart of the optimized carrier modulation method considering oscillation and unbalanced midpoint voltage provided in an embodiment of the present invention;

[0040] Figure 3This is the zero-crossing clamping region of the optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage provided in the embodiments of the present invention;

[0041] Figure 4 These are the experimental results of the DC-side upper bus capacitor voltage, DC-side lower bus capacitor voltage, A-phase bridge arm voltage, and A-phase current under the oscillation midpoint voltage condition provided by the embodiments of the present invention.

[0042] Figure 5 This is an experimental result diagram of the DC side upper bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.4 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0043] Figure 6 This is an experimental result diagram of the DC side lower bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.4 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0044] Figure 7 This is an experimental result diagram of the DC side upper bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.7 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0045] Figure 8 This is an experimental result diagram of the DC side lower bus capacitor voltage, A-phase bridge arm voltage, and A-phase current when the modulation ratio m = 0.7 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention. Detailed Implementation

[0046] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0047] The innovative aspects of the optimized carrier modulation method and system considering oscillation and unbalanced midpoint voltage provided in this invention are as follows: The discontinuous modulation method considering oscillation and unbalanced midpoint voltage proposed in this invention can not only significantly reduce switching losses and improve converter efficiency under oscillation and unbalanced midpoint voltage conditions, but also suppress low-frequency harmonics of the input current, eliminate current zero-crossing distortion, effectively improve the quality of the input current, and has the advantage of low digital computation burden.

[0048] Example 1, Figure 1This diagram illustrates a common three-level Vienna rectifier main circuit topology and its oscillation and unbalanced midpoint voltage. The three-phase Vienna rectifier includes three-phase AC power supplies ea, eb, ec, three-phase input filter inductors La, Lb, Lc, first to sixth power diodes D1-D6, first to sixth power switches S1-S6, first DC bus filter capacitor C1 and second DC bus filter capacitor C2, first DC load R1 and second DC load R2. The six power diodes are connected in pairs to form three-phase bridge arms, and the six power switches are connected in pairs to form three-phase bridge arms. The first DC bus filter capacitor and the second DC bus filter capacitor are respectively connected to the two ends of the midpoint of the DC side.

[0049] like Figure 2 As shown, the optimized carrier modulation method considering oscillation and unbalanced midpoint voltage provided in this embodiment of the invention includes the following steps:

[0050] S1, based on the three-phase normalization formula of the SPWM modulation strategy of the three-level Vienna rectifier, the normalized sine waves of phases A, B, and C are obtained as u ma u mb u mc ;

[0051] S2, calculate the modulation signal correction variable and the midpoint voltage imbalance coefficient;

[0052] S3, Calculate the zero-sequence voltage u considering oscillations and the unbalanced midpoint voltage. z.ICB and the zero-sequence voltage u z.ICB Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation of the neutral point voltage, considering oscillations and imbalances. ref_x x = a, b, and c.

[0053] The modulated wave is compared with the triangular carrier wave to generate the switching signal for the three-phase power switching device.

[0054] Example 2, as another embodiment of the present invention, provides an optimized carrier modulation method considering oscillations and unbalanced midpoint voltage, comprising:

[0055] Step 1: Based on the three-phase normalization formula of the three-level Vienna rectifier SPWM modulation strategy, the normalized sine waves of phases A, B, and C are obtained as u... ma u mb u mc The method for determining the three-phase normalized sine wave is as follows:

[0056]

[0057]

[0058] In the formula, u ma For phase A normalized sine wave, u mb For the normalized sine wave of phase B, u mc For a C-phase normalized sine wave, f g U is the power grid frequency, m is the modulation ratio, m∈(0,1); m U is the amplitude of the AC reference phase voltage. dc This is the DC-side bus voltage.

[0059] Step 2, calculate the imbalance coefficient between the modulation signal and the midpoint voltage:

[0060] The modified modulation signal of the optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage is calculated according to equation (2):

[0061]

[0062] In the formula, u mx x = a, b, and c are the normalized sine waves u of phases A, B, and C, respectively. ma u mb u mc , These are the modulation signal correction variables, δ is the midpoint voltage imbalance coefficient, and u z1 This is a peak clamping correction variable.

[0063] The midpoint voltage imbalance coefficient is calculated according to equation (3):

[0064]

[0065] In the formula, δ is the midpoint voltage imbalance coefficient, U dc1 U is the voltage of the capacitor on the DC bus. dc2 This is the voltage of the capacitor below the DC bus.

[0066] The main circuit topology of a three-level Vienna rectifier and its oscillation and unbalanced midpoint voltage are as follows: Figure 1 As shown.

[0067] Step 3, Zero-sequence voltage calculation:

[0068] Define the zero-sequence voltage u considering oscillations and the voltage at the midpoint of imbalance. z.ICB This invention relates to u z.ICB The method for determining is shown in equation (4):

[0069]

[0070] In the formula, for The maximum value, for The minimum value, for The minimum value, u max u min u mid Normalized sine waves u for phases A, B, and C respectively ma u mb u mc The maximum, minimum, and median values ​​of u th To correct the variable, u z1 This is a peak clamping correction variable.

[0071] Correction variable u th and the clamping coefficient k of the variable interval VAC Calculate according to the following formula:

[0072]

[0073] In the formula, The zero-crossing clamping angle is set.

[0074] Among them, the zero-crossing clamping region of the optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage is as follows: Figure 3 As shown, the shaded area represents the adjustable zero-clamping region. (From...) Figure 3 It can be seen that under different modulation ratios m and midpoint voltage imbalance coefficients δ, the adjustment variable u th Different zero-crossing clamping angles can be set.

[0075] Step 4, to obtain the modulated wave of the optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage:

[0076] Define the three-phase discontinuous carrier modulated wave considering oscillation and unbalanced midpoint voltage as u ref_x x = a, b, and c, this invention relates to u ref_x The method for determining x = a, b, and c is as shown in equation (6):

[0077]

[0078] In the formula, u ref_x x = a, b, and c represent a low-switching-loss three-phase discontinuous carrier modulation wave under neutral-point voltage imbalance conditions, u ma For phase A normalized sine wave, u mb For the normalized sine wave of phase B, u mc For the C-phase normalized sine wave, u z.ICB The zero-sequence voltage is injected to account for the discontinuous modulation wave of the oscillation and unbalanced midpoint voltage.

[0079] As can be seen from the above embodiments, the present invention can significantly reduce switching losses and improve converter efficiency under oscillating and unbalanced midpoint voltage conditions.

[0080] This invention can suppress low-frequency harmonics in the input current caused by oscillations and unbalanced midpoint voltage, and can also eliminate current zero-crossing distortion, effectively improving the quality of the input current.

[0081] This invention eliminates the need for sector determination and vector action time calculation, and is implemented via carrier wave, simplifying the calculation and reducing the computational burden on digital controllers.

[0082] Example 3: This invention provides an optimized carrier modulation system considering oscillations and unbalanced midpoint voltage, comprising:

[0083] The three-phase normalization module is used to obtain the normalized sine waves of phases A, B, and C, respectively, based on the three-phase normalization of the SPWM modulation strategy of the three-level Vienna rectifier. ma u mb u mc ;

[0084] The module for calculating modulation signal correction variables and midpoint voltage imbalance coefficients is used to calculate modulation signal correction variables and midpoint voltage imbalance coefficients using the modulation signal correction variable calculation formula and the midpoint voltage imbalance coefficient calculation formula.

[0085] The discontinuous modulation wave acquisition module is used to calculate the zero-sequence voltage u considering oscillations and the unbalanced midpoint voltage. z.ICB and the zero-sequence voltage u z.ICB Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation of the neutral point voltage, considering oscillations and imbalances. ref_x x = a, b, and c.

[0086] Example 4: The optimized carrier modulation system considering oscillation and unbalanced midpoint voltage is mounted on a three-level Vienna rectifier to perform optimized carrier modulation of oscillation and unbalanced midpoint voltage.

[0087] Example 5: A three-level Vienna rectifier is used in aircraft systems, hybrid energy storage systems, and electric vehicle charging systems to perform optimized carrier modulation of oscillation and unbalanced midpoint voltage.

[0088] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0089] To further illustrate the effects of the embodiments of the present invention, the following experiments were conducted.

[0090] The experiment used a Vienna rectifier prototype to verify the invented optimized carrier discontinuous modulation method that filters oscillations and unbalanced midpoint voltage. The prototype's input voltage was 115V / 65V, the output voltage was 400V, and the power was 2.5kW. Figure 4 These are the experimental results of the DC-side upper bus capacitor voltage, DC-side lower bus capacitor voltage, A-phase bridge arm voltage, and A-phase current under the oscillation midpoint voltage condition provided by the embodiments of the present invention.

[0091] Figure 5 This is an experimental result diagram of the DC side upper bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.4 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0092] Figure 6 This is an experimental result diagram of the DC side lower bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.4 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0093] Figure 7 This is an experimental result diagram of the DC side upper bus capacitor voltage, A-phase bridge arm voltage and A-phase current when the modulation ratio m = 0.7 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0094] Figure 8 This is an experimental result diagram of the DC side lower bus capacitor voltage, A-phase bridge arm voltage, and A-phase current when the modulation ratio m = 0.7 under unbalanced neutral point voltage conditions, provided by an embodiment of the present invention.

[0095] Figures 4-8 Middle U dc1 and U dc2 These are the voltages of the upper and lower filter capacitors on the DC bus, U. AO Let i be the voltage of phase A bridge arm. a This is the input current for phase A. Figures 5-8 In the diagram, AP, AO, and AN represent the voltage clamping and P, O, and N states of phase A bridge arm, respectively. Figures 4-8 As can be seen, when using the optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage of this invention, under the condition of oscillation and unbalanced midpoint voltage, the bridge arm voltage is clamped near the current peak, which can effectively reduce switching losses. The bridge arm voltage is clamped near the current zero-crossing point, the input current has no zero-crossing distortion, and the AC current waveform quality is good, demonstrating the correctness of the proposed optimized carrier discontinuous modulation method considering oscillation and unbalanced midpoint voltage.

[0096] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An optimized carrier modulation method considering oscillation and unbalanced midpoint voltage, characterized in that, The method includes the following steps: S1, the normalized sine waves of phases A, B, and C are obtained according to the three-phase normalization formula of the SPWM modulation strategy of the three-level Vienna rectifier, which are respectively... ; S2, calculate the modulation signal correction variable and the midpoint voltage imbalance coefficient; S3, Calculate the zero-sequence voltage considering oscillations and the unbalanced midpoint voltage. and zero-sequence voltage Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation considering oscillations and unbalanced midpoint voltage. ; In step S1, the normalized sine waves of phases A, B, and C are obtained by the three-phase normalization formula. The method for determining it is as follows: In the formula, For phase A, normalized sine wave, For phase B, normalized sine wave, For the C-phase normalized sine wave, For the power grid frequency, The modulation ratio, ; The amplitude of the AC reference phase voltage, This refers to the DC-side bus voltage. In step S2, the modulation signal correction variable is calculated according to the following formula: In the formula, Normalized sine waves for phases A, B, and C , These are the modulation signal correction variables, This is the midpoint voltage imbalance coefficient. For peak clamping correction variables, Normalized sine waves for phases A, B, and C, respectively. The maximum, minimum, and median values; Midpoint voltage imbalance coefficient Calculate according to the following formula: In the formula, This is the midpoint voltage imbalance coefficient. This is the voltage of the capacitor on the upper side of the DC bus. This refers to the capacitor voltage below the DC bus. In step S3, the zero-sequence voltage considering oscillations and the unbalanced midpoint voltage is calculated. The method for determining is shown in the following formula: In the formula, It is the zero-sequence voltage. for The maximum value, for The minimum value, for The minimum value, Normalized sine waves for phases A, B, and C, respectively. The maximum, minimum, and median values. This is the midpoint voltage imbalance coefficient. To correct the variables, This is a peak clamping correction variable.

2. The optimized carrier modulation method considering oscillation and unbalanced midpoint voltage according to claim 1, characterized in that, Correction variables and the clamping coefficient of the variable interval Calculate according to the following formula: In the formula, The zero-crossing clamping angle is set.

3. The optimized carrier modulation method considering oscillation and unbalanced midpoint voltage according to claim 1, characterized in that, In step S3, the zero-sequence voltage is... Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation considering oscillations and unbalanced midpoint voltage. The method for determining it is as follows: In the formula, This represents a low-switching-loss three-phase discontinuous carrier modulation wave under neutral-point voltage imbalance conditions. For phase A, normalized sine wave, For phase B, normalized sine wave, For the C-phase normalized sine wave, The zero-sequence voltage is injected to account for the discontinuous modulation wave of the oscillation and unbalanced midpoint voltage.

4. An optimized carrier modulation system considering oscillation and unbalanced midpoint voltage, characterized in that, The system implements the optimized carrier modulation method considering oscillations and unbalanced midpoint voltage as described in any one of claims 1-3, and the system comprises: The three-phase normalization module is used to obtain the normalized sine waves of phases A, B, and C based on the three-phase normalization of the SPWM modulation strategy of the three-level Vienna rectifier. ; The module for calculating modulation signal correction variables and midpoint voltage imbalance coefficients is used to calculate modulation signal correction variables and midpoint voltage imbalance coefficients using the modulation signal correction variable calculation formula and the midpoint voltage imbalance coefficient calculation formula. The discontinuous modulation wave acquisition module is used to calculate the zero-sequence voltage considering oscillations and the unbalanced midpoint voltage. and zero-sequence voltage Injecting a three-phase normalized sine wave yields a three-level Vienna rectifier (phases A, B, and C) with discontinuous modulation considering oscillations and unbalanced midpoint voltage. .

5. The optimized carrier modulation system considering oscillation and unbalanced midpoint voltage according to claim 4, characterized in that, The system is mounted on a three-level Vienna rectifier for optimized carrier modulation of oscillation and unbalanced midpoint voltage.

6. The optimized carrier modulation system considering oscillation and unbalanced midpoint voltage according to claim 4, characterized in that, The three-level Vienna rectifier is used in aircraft systems, hybrid energy storage systems, and electric vehicle charging systems to perform optimized carrier modulation of oscillation and unbalanced midpoint voltage.

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