Improved method for balancing the neutral point voltage of a three-level bidirectional DCDC converter
By sampling the capacitor voltage and inductor current of the three-level bidirectional DC-DC converter and reasonably adjusting the duty cycle of the switching transistor, the problem of midpoint voltage runaway was solved, and stable circuit control was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CRRC DALIAN R & D CO LTD
- Filing Date
- 2022-09-28
- Publication Date
- 2026-06-19
AI Technical Summary
In existing three-level bidirectional DC-DC circuits, the midpoint voltage is easily affected by zero drift of the current sensing circuit, leading to the problem of uncontrolled midpoint voltage.
By sampling the voltage of the supporting capacitor and the current of the inductor in the upper and lower bridge arms respectively, and selecting a switch with a reasonable duty cycle, the runaway midpoint voltage caused by current detection errors can be avoided.
Effective control of the midpoint voltage balance avoids the problem of midpoint voltage runaway caused by current detection errors, thus improving circuit stability.
Smart Images
Figure CN115411942B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fully automated products and relates to an improved method for neutral point voltage balance control of a three-level bidirectional DC-DC converter. Background Technology
[0002] For a type of three-level bidirectional DC-DC circuit with upper and lower bridge arm support capacitors on the high-voltage side, midpoint voltage balancing control of the upper and lower bridge arm support capacitors is required to avoid problems such as overvoltage and reduced lifespan caused by midpoint voltage deviation. Existing technology adjusts the midpoint voltage by introducing a differential-mode component to adjust the duty cycle of all switches in the upper and lower bridge arms. This method has the characteristic that the duty cycle needs to be adjusted in opposite directions when the current direction is different. Due to factors such as zero drift in the current detection circuit, under light load conditions, the detected current direction may be opposite to the actual current direction, causing the midpoint voltage to adjust in the wrong direction and resulting in midpoint voltage runaway.
[0003] The existing technology adjusts the midpoint voltage by introducing differential mode components to adjust the duty cycle of all switches in the upper and lower bridge arms, and selects the adjustment direction according to the current direction. When the current direction is different, the duty cycle needs to be adjusted in opposite directions.
[0004] One drawback of the existing technology is that when factors such as zero drift in the current detection circuit cause errors in the current direction judgment, it can lead to loss of control of the midpoint voltage. Summary of the Invention
[0005] To address the aforementioned problems, the present invention provides the following technical solution: an improved method for neutral point voltage balance control of a three-level bidirectional DC-DC converter, comprising the following steps:
[0006] Sample the voltage of the upper bridge arm supporting capacitor, the voltage of the lower bridge arm supporting capacitor, and the inductor current respectively;
[0007] Based on the relationship between the upper and lower bridge arm supporting capacitor voltages and the direction of the inductor current, the switching transistor with the adjusted duty cycle is selected to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter.
[0008] Furthermore, the specific scheme for selecting and adjusting the duty cycle of the switching transistor based on the relationship between the upper and lower bridge arm supporting capacitor voltages and the direction of the inductor current is as follows:
[0009] When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T4 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0010] When the voltage of the upper bridge arm supporting capacitor is less than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T1 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0011] When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T3 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0012] When the voltage of the upper bridge arm supporting capacitor is less than that of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T2 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0013] Furthermore, the inductor current can also be selected from the input current or output current in the DC-DC converter circuit to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter.
[0014] Furthermore: the selected switch can affect the midpoint current in the current inductor current direction, but will not affect the midpoint current when the inductor current direction is opposite to the current direction, and the required duty cycle adjustment direction will not cause the bridge arm where the selected switch is located to shoot through.
[0015] Furthermore, this method is applicable to situations where the detected current direction of a three-level bidirectional DC-DC converter is opposite to the actual current direction.
[0016] Furthermore, the method also includes filtering the inductor current.
[0017] This invention provides a method for balancing the midpoint voltage of a three-level bidirectional DC-DC converter. By rationally selecting and adjusting the duty cycle of the switching transistor, the method avoids the problem of uncontrolled midpoint voltage caused by factors such as zero drift in the current detection circuit. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 A schematic diagram of the main circuit of a three-level bidirectional DC-DC converter is provided for embodiments of the present invention. Detailed Implementation
[0020] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.
[0023] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.
[0024] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms 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, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.
[0025] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.
[0026] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.
[0027] Figure 1 The present invention provides a schematic diagram of the main circuit of a three-level bidirectional DC-DC converter. The main circuit of the three-level bidirectional DC-DC converter includes: voltage transformer TV1, voltage transformer TV2, capacitor C1, capacitor C2, switching transistor T1, switching transistor T2, switching transistor T3, switching transistor T4, capacitor C3, and inductor L.
[0028] The switching transistors T1, T2, T3, and T4 are connected in series from end to end.
[0029] One end of the inductor L is connected to the switching transistors T1 and T2;
[0030] The other end of the inductor L is connected to one end of the capacitor C3;
[0031] The other end of the capacitor C3 is connected to the switching transistors T3 and T4;
[0032] One end of the capacitor C1 is connected to one end of the switching transistor T1 and one end of the voltage transformer TV1;
[0033] The other end of the capacitor C1 is connected to one end of the switching transistor T2, the other end of the voltage transformer TV1, and one end of the voltage transformer TV2.
[0034] One end of the capacitor C2 is connected to one end of the switching transistor T2, the other end of the voltage transformer TV1, and one end of the voltage transformer TV2;
[0035] The other end of the capacitor C2 is connected to the other end of the switching transistor T4 and the other end of the voltage transformer TV2;
[0036] The following is combined Figure 1 The improved method for neutral point voltage balance control of a three-level bidirectional DC-DC converter provided in this embodiment of the invention includes the following steps:
[0037] S101: Samples the upper arm support capacitor voltage, lower arm support capacitor voltage, and inductor current of the three-level bidirectional DC-DC converter.
[0038] Optionally, the inductor current can be replaced by other physical quantities that can determine the direction of energy flow in the DC-DC converter circuit, such as input current and output current.
[0039] S102: Select the switching transistor with the adjusted duty cycle based on the relationship between the upper bridge arm support capacitor voltage and the lower bridge arm support capacitor voltage and the direction of the inductor current.
[0040] The selection criteria are as follows: the selected switch can affect the midpoint current in the current inductor current direction, but will not affect the midpoint current when the inductor current direction is opposite to the current direction, and the required duty cycle adjustment direction will not cause the bridge arm where the selected switch is located to shoot through.
[0041] Furthermore, it also includes filtering the inductor current.
[0042] Specifically, before adjustment, the duty cycle relationships of each switch were as follows: the duty cycles of switch T1 and switch T4 were equal, the duty cycles of switch T1 and switch T2 were complementary, and the duty cycles of switch T3 and switch T4 were complementary.
[0043] Inductor current I L Positive direction, such as Figure 1 As shown,
[0044] When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T4 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0045] When the voltage of the upper bridge arm supporting capacitor is less than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T1 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0046] When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T3 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0047] When the voltage of the upper bridge arm supporting capacitor is less than that of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T2 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged.
[0048] according to Figure 1 As can be seen from the circuit's operating principle, the shift in the midpoint voltage is caused by the non-zero cumulative charge of the midpoint current during the switching cycle.
[0049] When the inductor current is positive, the cumulative charge of the midpoint current during the switching cycle is related to the conduction time of switching transistors T1 and T4.
[0050] When the inductor current is negative, the cumulative charge of the midpoint current during the switching cycle is related to the turn-off time of switching transistors T2 and T3.
[0051] When the inductor current direction is different, the required adjustment direction of the duty cycle of the switching transistor is opposite. Existing technology adjusts the duty cycle of each switching transistor, which can lead to the midpoint voltage adjusting in the wrong direction if the inductor current direction is incorrectly determined. The improved midpoint voltage balance control method for a three-level bidirectional DC-DC converter provided in this invention only adjusts the duty cycle of the switching transistor that affects the midpoint current in the current inductor current direction. The selected switching transistor has no effect on the midpoint current when the inductor current direction is opposite, therefore, the midpoint voltage will not be adjusted in the wrong direction when the inductor current direction is incorrectly determined.
[0052] Compared with the prior art, the improved method for neutral point voltage balance control of a three-level bidirectional DC-DC converter provided in this embodiment of the invention avoids the problem of neutral point voltage runaway caused by factors such as zero drift of the current detection circuit by reasonably selecting and adjusting the switching transistor with the duty cycle.
[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A three-level bidirectional DCDC converter neutral point voltage balancing control method, characterized in that: Includes the following steps: Sample the voltage of the upper bridge arm supporting capacitor, the voltage of the lower bridge arm supporting capacitor, and the inductor current respectively; Based on the relationship between the upper and lower bridge arm supporting capacitor voltages and the direction of the inductor current, select the switching transistor with the adjusted duty cycle to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter. The specific scheme for selecting and adjusting the duty cycle of the switching transistor based on the relationship between the upper bridge arm support capacitor voltage and the lower bridge arm support capacitor voltage and the direction of the inductor current is as follows: When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T4 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged. When the voltage of the upper bridge arm supporting capacitor is less than the voltage of the lower bridge arm supporting capacitor and the inductor current is positive, the duty cycle of switch T1 is reduced by the duty cycle offset, while the duty cycles of other switches remain unchanged. When the voltage of the upper bridge arm supporting capacitor is greater than the voltage of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T3 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged. When the voltage of the upper bridge arm supporting capacitor is less than that of the lower bridge arm supporting capacitor and the inductor current is negative, the duty cycle of switch T2 is increased by the duty cycle offset, while the duty cycles of other switches remain unchanged.
2. The neutral-point voltage balancing control method of a three-level bidirectional DCDC converter according to claim 1, characterized in that: The inductor current is replaced by the input current or output current in the DC-DC converter circuit to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter.
3. The neutral-point voltage balancing control method of a three-level bidirectional DCDC converter according to claim 1, characterized in that: The selected switch can affect the midpoint current in the current inductor current direction, but will not affect the midpoint current when the inductor current direction is opposite to the current direction, and the required duty cycle adjustment direction will not cause the bridge arm containing the selected switch to shoot through.
4. The neutral-point voltage balancing control method of a three-level bidirectional DCDC converter according to claim 1, characterized in that: This method is applicable when the detected current direction of a three-level bidirectional DC-DC converter is opposite to the actual current direction.
5. The method for neutral point voltage balance control of a three-level bidirectional DC-DC converter according to claim 1, characterized in that: It also includes filtering the inductor current.