A high-efficiency modulation method for network-structured three-level neutral-point clamped SVG

Abstract

The application discloses a kind of network type three-level midpoint clamping SVG high efficiency modulation method, belong to network type power electronic equipment modulation technical field, comprising the following steps: S1, based on the value range division of zero sequence voltage fundamental wave period is midpoint voltage controllable interval and midpoint voltage uncontrollable interval, the midpoint voltage uncontrollable interval is subdivided and set extension interval;S2, the influence of different distribution mode of extension interval on SVG DC side midpoint voltage is analyzed, and the optimal extension interval distribution mode is determined;S3, the width of extension interval and the extension proportion of two sides are optimized, and the mixed modulation strategy with optimal extension interval is formed;S4, modulation wave is generated based on mixed modulation strategy, and PWM driving signal is obtained by comparing modulation wave and carrier signal, to drive SVG power device to work to suppress midpoint voltage fluctuation.The application reduces switching loss and electromagnetic noise, improves equipment operating efficiency and reliability.

Description

Technical Field

[0001] This invention relates to the field of modulation technology for grid-type power electronic equipment, and in particular to a high-efficiency modulation method for grid-type three-level midpoint clamped SVG. Background Technology

[0002] With the rapid development of new energy power generation technology, problems such as voltage fluctuations and frequency instability caused by high-penetration new energy grid connection are becoming increasingly prominent. As a new generation of power electronic equipment, grid-type SVG, with its voltage source characteristics, can actively establish voltage and frequency references, provide reliable voltage and inertia support in weak grid scenarios, effectively improve the system's anti-disturbance capability, and has become a key device for building new power systems.

[0003] The three-level neutral-point clamp (NPC) topology is widely used in medium- and high-voltage, high-capacity SVG products due to its significant advantages of high output voltage and low device voltage stress. However, this topology has an inherent technical bottleneck: the midpoint voltage of the two voltage divider capacitors on the DC side is prone to imbalance, resulting in low-frequency harmonics in the SVG output voltage. This causes voltage distortion at the grid connection point, severely affecting the SVG's ability to accurately support the grid voltage. Under extreme conditions such as grid faults or sudden load changes, it may exacerbate voltage flicker or even trigger transient instability.

[0004] To address the midpoint voltage imbalance problem, existing technologies primarily employ zero-sequence voltage injection carrier modulation strategies. The SVG (Video Stabilizer) achieves midpoint voltage balance by injecting zero-sequence voltage into the modulated wave to regulate the midpoint current. However, this strategy is limited to the controllable range of the midpoint voltage. When the modulation index is high or the power factor is low, a large uncontrollable range of midpoint voltage appears, leading to aggravated midpoint voltage fluctuations. If the midpoint voltage fluctuations in the uncontrollable range are suppressed by increasing the switching frequency, it will significantly increase the switching losses of the SVG power devices, causing severe electromagnetic noise and reducing the stability and reliability of the equipment. Traditional hybrid modulation strategies employ... With dual-modulation wave carrier modulation strategy ( The simple combination of these two methods fails to fully utilize the modulation potential of the uncontrollable range and cannot achieve synergistic optimization of switching losses and midpoint voltage fluctuations.

[0005] Therefore, there is an urgent need for a high-efficiency modulation method that can break through the limitations of traditional modulation strategies, expand the effective modulation range, and reduce the switching frequency and suppress the midpoint voltage fluctuation, so as to meet the operation requirements of medium- and high-voltage large-capacity grid-type SVG under complex working conditions. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a high-efficiency modulation method for mesh-type three-level midpoint clamped SVG, by extending... The effective range of the strategy is determined so that the SVG output voltage is clamped to the positive and negative DC buses within the extended range, reducing the SVG switching frequency, and thus determining the optimal extended range distribution.

[0007] The technical solution adopted in the high-efficiency modulation method of SVG with mesh-type three-level midpoint clamping in this invention is as follows:

[0008] A high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping includes the following steps:

[0009] S1. Based on the range of zero-sequence voltage, the fundamental period is divided into a controllable range of midpoint voltage and an uncontrollable range of midpoint voltage. The uncontrollable range of midpoint voltage is further subdivided and an extended range is set.

[0010] S2. Analyze the impact of different distribution patterns of the extended interval on the DC side midpoint voltage of the SVG, and determine the optimal distribution pattern of the extended interval;

[0011] S3. Optimize the width of the extended range and the extension ratio on both sides to form a hybrid modulation strategy with the optimal extended range;

[0012] S4. A modulation wave is generated based on a hybrid modulation strategy. The PWM drive signal is obtained by comparing the modulation wave with the carrier signal, which drives the SVG power device to work in order to suppress the midpoint voltage fluctuation.

[0013] A further improvement to the technical solution of the present invention lies in that the specific process of dividing the interval based on the zero-sequence voltage value range in step S1 is as follows: a zero-sequence voltage injection carrier modulation strategy is adopted ( The system determines whether the injected zero-sequence voltage exceeds the maximum range that satisfies the midpoint voltage balance. If it does, the corresponding interval is the uncontrollable interval of the midpoint voltage; otherwise, it is the controllable interval of the midpoint voltage.

[0014] A further improvement to the technical solution of the present invention lies in that the process of subdividing the uncontrollable interval of the midpoint voltage in step S1 is as follows: the uncontrollable interval of the midpoint voltage is subdivided into an extended interval and a non-extended interval, and then solved... The position angle of the uncontrollable interval of the midpoint voltage is used to calculate the width of the uncontrollable interval, and the initial range of the extended interval is set based on the width of the uncontrollable interval.

[0015] A further improvement of the technical solution of the present invention is that: the distribution of the extended interval in step S2 includes left extension, right extension, and optimal extension; wherein, the extended interval of left extension is the left segment of the uncontrollable interval. The right-extended range is the right-side segment of the uncontrollable range. The optimal expansion interval is the set of the left and right segments of the uncontrollable interval. , , The two endpoints of the uncontrollable interval are the position angles. , The internal boundary position angle of the extended interval.

[0016] A further improvement of the technical solution of the present invention is that the specific process of determining the optimal expansion interval distribution mode in step S2 is as follows: matching the corresponding modulation strategies for the three distribution modes of left expansion, right expansion and optimal expansion respectively, and selecting the distribution mode with the smallest fluctuation amplitude as the optimal expansion interval distribution mode by comparing the fluctuation amplitude of the DC side midpoint voltage of the SVG under the three distribution modes.

[0017] A further improvement to the technical solution of the present invention is that the specific process of optimizing the width of the extended interval and the ratio of both sides in step S3 is as follows: determine the total width of the extended interval according to the loss control requirements of the SVG. By adjusting the width of the left extended interval Width of the extended interval on the right The ratio is used to achieve the lowest possible midpoint voltage fluctuation amplitude; among which, .

[0018] A further improvement to the technical solution of this invention lies in the fact that the specific process of generating the PWM drive signal in step S4 is as follows: the modulated waves of each phase output by the hybrid modulation strategy are compared with the upper and lower symmetrically set triangular carrier signals respectively, and the PWM signal of the three-level midpoint clamped SVG power device is generated according to the comparison result. ;in, Corresponding to the three-phase bridge arm.

[0019] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0020] This invention will The operating range is extended to the uncontrollable range of the midpoint voltage. By clamping the SVG output voltage to the positive and negative DC buses within the extended range, the switching frequency of the SVG power device under high regulation or low power factor conditions is reduced, switching losses and electromagnetic noise are reduced, and the operating efficiency and reliability of the equipment are improved.

[0021] This invention analyzes the impact of three expansion interval distribution methods—left expansion, right expansion, and optimal expansion—on the midpoint voltage. By quantitatively comparing the midpoint voltage fluctuation amplitude under different distribution methods, the optimal expansion distribution method is determined.

[0022] Based on the optimal expansion method, this invention further quantifies and analyzes the impact of the ratio of the expansion intervals on the DC-side midpoint voltage of the SVG, determines the optimal ratio of the expansion intervals on the left and right sides, and finally forms a hybrid modulation strategy with the optimal expansion interval, which effectively suppresses the fluctuation of the DC-side midpoint voltage of the SVG. Attached Figure Description

[0023] Figure 1 This is a control flowchart of a high-efficiency modulation method for a three-level midpoint clamped SVG in a mesh-type configuration according to the present invention.

[0024] Figure 2 This is a diagram of the three-level midpoint clamped SVG topology to which this invention applies;

[0025] Figure 3 A diagram showing the width of the uncontrollable range of midpoint voltage under different modulation schemes and power factors;

[0026] Figure 4 Map showing the location distribution of the three extended regions;

[0027] Figure 5 for and , and Change diagram;

[0028] Figure 6 for , The magnitude of the capacitor voltage deviation as m changes. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of this invention.

[0030] like Figure 1 As shown, this embodiment discloses a high-efficiency modulation method for mesh-type three-level midpoint clamped SVG, including the following steps:

[0031] S1. Based on the range of zero-sequence voltage, the fundamental period is divided into a controllable range of midpoint voltage and an uncontrollable range of midpoint voltage. The uncontrollable range of midpoint voltage is further subdivided and an extended range is set.

[0032] In this embodiment, the three-level midpoint clamped SVG topology is as follows: Figure 2 As shown, it includes a DC-side voltage source, two voltage-regulating capacitors, and a three-level neutral-point clamped SVG power device. Three-phase sinusoidal modulation wave. , It can be represented as:

[0033]

[0034] Where m represents the modulation index. This refers to the phase of the modulating wave. To improve DC voltage utilization, a zero-sequence voltage can be injected into the modulating wave. This yields zero-sequence voltage injection carrier modulation. To ensure the average midpoint current is zero, the zero-sequence voltage v is... 0z Set to:

[0035]

[0036] in The power factor angle, for:

[0037]

[0038] When the modulation index m is greater than the maximum modulation index for maintaining the neutral point voltage balance hour, The zero-sequence voltage of the strategy intersects with the boundary of the range of possible zero-sequence voltages, let , We can obtain:

[0039]

[0040] Further calculation yields the position angle of the uncontrollable interval of the midpoint voltage as follows: Width is . , The trend of power factor and modulation degree change is as follows Figure 3 As shown. The size of the uncontrollable range of the midpoint voltage is affected by the modulation index and power factor. The width of the extended range is adjusted according to the midpoint voltage fluctuation amplitude or the SVG switching frequency limit. The present invention is based on (The uncontrollable range width at the midpoint voltage is 0.57 rad), extended range width Let's take an example for analysis.

[0041] S2. After calculating the width of the uncontrollable interval and setting the extended interval, analyze the impact of three distribution methods—left extension, right extension, and optimal extension—on the midpoint voltage within the extended interval, and determine the corresponding distribution methods. and dual-modulation wave carrier modulation strategy ( The allocation strategy for the three extended regions. and Distribution as follows Figure 4 As shown, the corresponding extended intervals are: left extended interval Right-side extended interval Optimal expansion interval ;Will Figure 4 The modulation strategies corresponding to the distribution methods in (a) to (c) are respectively defined as follows: , and . Figure 5 As shown hour, and , and By comparing the voltage fluctuation of the DC-side capacitor of the SVG under the action of three distribution methods, the midpoint voltage fluctuation amplitude corresponding to the three distribution methods is compared, so as to determine the optimal extended range distribution method.

[0042] S3, when the interval width is expanded Once determined, adjust the width of the left and right extended intervals. and To achieve the lowest possible amplitude of midpoint voltage fluctuation. (Regulation) Expand the interval width Under certain conditions, the amplitude of capacitor voltage fluctuation varies with and Trend of change Figure 6 As shown in (a). With As m increases, the amplitude of the midpoint voltage fluctuation first decreases and then increases. When m is... As the power factor increases, the amplitude of the capacitor voltage fluctuation also increases. and Expand the interval width Under certain conditions, the amplitude of capacitor voltage fluctuation varies with m and Trend of change Figure 6 As shown in (b). When As the voltage increases, the voltage fluctuation amplitude also decreases first and then increases. Figure 6 Connecting the points with the lowest voltage fluctuation amplitude on the inner surfaces of (a) and (b) yields the curve of the minimum voltage fluctuation amplitude at the midpoint (purple dashed line). Then, when the width of the left and right expansion intervals... When the midpoint voltage fluctuation amplitude is minimized, and the width ratio of this extended range is not affected by the modulation index and power factor, the optimal extension method and the corresponding hybrid modulation strategy (OEHPWM) are determined.

[0043] S4. By summarizing the previous steps, the optimal extended range hybrid modulation strategy is obtained. By executing this strategy, the modulated waves of each phase are compared with the upper and lower carrier signals to obtain the PWM signal of the three-level midpoint clamped SVG power device, which drives the SVG of each phase bridge arm to work, thereby realizing the suppression of voltage fluctuation at the midpoint of the SVG capacitor.

[0044] In the above embodiments, a high-efficiency modulation method for mesh-type three-level midpoint clamped SVG is provided. This invention will... The effective range of the SVG is extended to the uncontrollable range of the midpoint voltage. By clamping the SVG output voltage to the positive and negative DC buses within the extended range, the switching frequency of the SVG power devices under high modulation or low power factor conditions is reduced, thereby reducing switching losses and electromagnetic noise and improving equipment operating efficiency and reliability. This invention analyzes the impact of three extended range distribution methods—left extension, right extension, and optimal extension—on the midpoint voltage. By quantitatively comparing the midpoint voltage fluctuation amplitude under different distribution methods, the optimal extended distribution method is determined. Based on the optimal extension method, this invention further quantitatively analyzes the impact of the ratio of the two extended ranges on the SVG DC side midpoint voltage, determines the optimal ratio of the left and right extended ranges, and finally forms a hybrid modulation strategy with the optimal extended range, effectively suppressing the SVG DC side midpoint voltage fluctuation.

[0045] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the inventive concept should fall within the protection scope of the present invention. All technical contents for which protection is sought in this invention are fully described in the claims.

Claims

1. A high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping, characterized in that, Includes the following steps: S1. Based on the range of zero-sequence voltage, the fundamental period is divided into a controllable range of midpoint voltage and an uncontrollable range of midpoint voltage. The uncontrollable range of midpoint voltage is further subdivided and an extended range is set. S2. Analyze the impact of different distribution patterns of the extended interval on the DC side midpoint voltage of the SVG, and determine the optimal distribution pattern of the extended interval. S3. Optimize the width of the extended range and the extension ratio on both sides to form a hybrid modulation strategy with the optimal extended range; S4. A modulation wave is generated based on a hybrid modulation strategy. The PWM drive signal is obtained by comparing the modulation wave with the carrier signal, which drives the SVG power device to work in order to suppress the midpoint voltage fluctuation.

2. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 1, characterized in that, The specific process of dividing the interval based on the zero-sequence voltage value range in step S1 is as follows: using a zero-sequence voltage injection carrier modulation strategy (ZVI-PWM), it is determined whether the injected zero-sequence voltage exceeds the maximum value range that satisfies the midpoint voltage balance. If it exceeds, the corresponding interval is the uncontrollable interval of the midpoint voltage; if it does not exceed, it is the controllable interval of the midpoint voltage.

3. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 2, characterized in that, The process of subdividing the uncontrollable interval of the midpoint voltage in step S1 is as follows: the uncontrollable interval of the midpoint voltage is subdivided into an extended interval and a non-extended interval. The width of the uncontrollable interval is calculated by solving the position angle of the uncontrollable interval of the midpoint voltage in ZVI-PWM. The initial range of the extended interval is set based on the width of the uncontrollable interval.

4. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 1, characterized in that: The distribution of the extended interval in step S2 includes left extension, right extension, and optimal extension; wherein, the extended interval of left extension is the left segment of the uncontrollable interval. θ 1, θ 3], the right-extended range is the right-side segment of the uncontrollable range. θ 4, θ [2] The optimal expansion interval is the set of the left and right segments of the uncontrollable interval. , θ 1. θ 2 represents the position angles of the two endpoints of the uncontrollable interval. θ 3. θ 4 is the internal boundary angle of the extended interval.

5. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 4, characterized in that, The specific process for determining the optimal expansion interval distribution mode in step S2 is as follows: matching the corresponding modulation strategies for the three distribution modes of left expansion, right expansion and optimal expansion, and selecting the distribution mode with the smallest fluctuation amplitude as the optimal expansion interval distribution mode by comparing the fluctuation amplitude of the DC side midpoint voltage of the SVG under the three distribution modes.

6. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 1, characterized in that, The specific process of optimizing the width of the extended interval and the ratio of both sides in step S3 is as follows: determine the total width Δ of the extended interval according to the loss control requirements of the SVG. θ By adjusting the width Δ of the left-side extended interval θ 1 and the width Δ of the right-side extended interval θ A ratio of 2 achieves the lowest possible midpoint voltage fluctuation amplitude; Among them, D θ =D θ 1+D θ 2.

7. The high-efficiency modulation method for SVG with mesh-type three-level midpoint clamping according to claim 1, characterized in that, The specific process of generating the PWM drive signal in step S4 is as follows: The modulated waves output by the hybrid modulation strategy are compared with the upper and lower symmetrically set triangular carrier signals respectively. Based on the comparison results, a PWM signal S for the three-level midpoint clamped SVG power device is generated. x1 -S x4 Where x∈{A,B,C} corresponds to a three-phase bridge arm.

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