A direct current transformer sub-module voltage control method and device

Abstract

The present application relates to a kind of direct-current transformer submodule voltage control method and device, by obtaining each submodule voltage of direct-current transformer, the hysteresis control of each submodule voltage of direct-current transformer is carried out, and the duty cycle of each submodule is adjusted using the result of hysteresis control, to solve the problem that submodule voltage is not uniform voltage and overvoltage due to the nonlinear gain of resonant converter in the starting process of direct-current transformer device.The technical scheme of the present application, by using duty cycle dynamic adjustment control algorithm, i.e.the module with high submodule voltage is controlled by hysteresis+slope, to adjust its duty cycle, and lower submodule voltage, to achieve better submodule voltage equalization effect, ensure the safe and stable operation of device, can effectively solve the problem that submodule voltage is not uniform and overvoltage due to the nonlinear gain of resonant converter in the starting process of direct current transformer device, control logic is simple, easy to realize.

Description

Technical Field

[0001] This invention relates to the field of power system voltage monitoring technology, and in particular to a method and device for voltage control of a DC transformer submodule. Background Technology

[0002] DC transformer devices can realize functions such as DC voltage transformation, bidirectional power transmission, and electrical isolation, and are key equipment in DC distribution networks. The bidirectional LLC resonant DC transformer based on the ISOP structure is generally composed of multiple power submodules connected in series on the input side and parallel on the output side. It can effectively improve the voltage level and capacity of DC transformers and has now become a common technical solution.

[0003] Submodule overvoltage control is a key technology in the research of DC transformer devices, and its control characteristics directly affect the safe and reliable operation of the DC transformer device. Bidirectional LLC resonant DC transformers based on the ISOP structure mainly consider maintaining a constant voltage transformation ratio for each power submodule, thus achieving voltage equalization among the submodules. However, during the startup process of a DC transformer device, voltage unevenness and overvoltage problems often arise in the submodules due to the nonlinearity of the resonant converter gain. Therefore, how to effectively suppress submodule overvoltage during the startup condition of a DC transformer device has become an urgent problem to be solved in this field. Summary of the Invention

[0004] Based on the above-mentioned situation of the prior art, the purpose of the present invention is to provide a DC transformer submodule voltage control method and device. By performing hysteresis control on the voltage of each submodule of the DC transformer and adjusting the duty cycle of each submodule using the result of hysteresis control, the problem of uneven voltage and overvoltage of submodules caused by the nonlinearity of the resonant converter gain during the startup process of the DC transformer device is solved.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for controlling the voltage of a DC transformer submodule is provided, comprising the steps of:

[0006] Obtain the output voltage of each submodule when the DC transformer starts up;

[0007] Hysteresis control is applied to the output voltage of each submodule. The upper voltage threshold of this hysteresis control is U1, and the lower voltage threshold is U0.

[0008] The duty cycle of each submodule is adjusted based on the results of hysteresis control.

[0009] Furthermore, adjusting the duty cycle of each submodule based on the hysteresis control results includes:

[0010] If the output voltage of the submodule is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the submodule with the first duty cycle change slope K.

[0011] If the output voltage of the submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the corresponding submodule is raised to the rated duty cycle with the second duty cycle change slope k.

[0012] Furthermore, reducing the duty cycle of the submodule with a first duty cycle change slope K includes:

[0013] K = (D min -D n )*f / N

[0014] Among them, D min For the minimum duty cycle, D n The current duty cycle is given, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction phase.

[0015] Furthermore, the step of raising the duty cycle of the corresponding sub-module to the rated duty cycle with the second duty cycle change slope k includes:

[0016] k=(D e -D n )*f / M

[0017] Among them, D e N is the rated duty cycle, M is the number of cycles set for the stage of restoring the rated duty cycle, and M is greater than N.

[0018] Furthermore, the submodule includes an LLC resonant converter power submodule.

[0019] According to another aspect of the present invention, a voltage control device for a DC transformer submodule is provided, comprising a voltage acquisition module, a hysteresis control module, and a duty cycle adjustment module; wherein,

[0020] The voltage acquisition module is used to acquire the output voltage of each sub-module when the DC transformer starts up.

[0021] The hysteresis control module is used to perform hysteresis control on the output voltage of each submodule. The upper voltage threshold of the hysteresis control is U1, and the lower voltage threshold is U0.

[0022] The duty cycle adjustment module is used to adjust the duty cycle of each sub-module based on the results of hysteresis control.

[0023] Furthermore, the duty cycle adjustment module adjusts the duty cycle of each submodule based on the hysteresis control results, including:

[0024] If the output voltage of the submodule is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the submodule with the first duty cycle change slope K.

[0025] If the output voltage of the submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the corresponding submodule is raised to the rated duty cycle with the second duty cycle change slope k.

[0026] Furthermore, reducing the duty cycle of the submodule with a first duty cycle change slope K includes:

[0027] K = (D min -D n )*f / N

[0028] Among them, D min For the minimum duty cycle, D n The current duty cycle is given, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction phase.

[0029] Furthermore, the step of raising the duty cycle of the corresponding sub-module to the rated duty cycle with the second duty cycle change slope k includes:

[0030] k=(D e -D n )*f / M

[0031] Among them, D e N is the rated duty cycle, M is the number of cycles set for the stage of restoring the rated duty cycle, and M is greater than N.

[0032] Furthermore, the submodule includes an LLC resonant converter power submodule.

[0033] In summary, this invention provides a method and apparatus for controlling the voltage of DC transformer submodules. By acquiring the voltage of each submodule of the DC transformer, hysteresis control is performed on the voltage of each submodule, and the duty cycle of each submodule is adjusted using the results of the hysteresis control. This addresses the problem of uneven voltage distribution and overvoltage in the submodules caused by the nonlinear gain of the resonant converter during the startup of the DC transformer device. The technical solution of this invention employs a dynamic duty cycle adjustment control algorithm. Specifically, the module with the high voltage is controlled through hysteresis and ramp control to adjust its duty cycle, thereby lowering the submodule voltage and achieving better voltage equalization. This ensures the safe and stable operation of the device and effectively solves the problem of uneven voltage distribution and overvoltage in the submodules caused by the nonlinear gain of the resonant converter during the startup of the DC transformer device. The control logic is simple and easy to implement. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the topology of a DC transformer device.

[0035] Figure 2 This is a flowchart of the DC transformer submodule voltage control method of the present invention;

[0036] Figure 3 This is a block diagram of the DC transformer submodule voltage control device of the present invention. Detailed Implementation

[0037] 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 the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0038] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings. According to one embodiment of the present invention, a method for controlling the voltage of a DC transformer submodule is provided. Figure 1 The diagram shows a schematic of the topology of a DC transformer device, such as... Figure 1 As shown, the DC transformer includes multiple power submodules, which are connected in series on the input side and in parallel on the output side. Each submodule adopts an LLC resonant converter topology. Due to the inherent characteristics of LLC resonant circuits, the transformer's no-load gain varies significantly, making it prone to overvoltage and voltage imbalance. This embodiment addresses these issues by providing a DC transformer submodule voltage control method, the flowchart of which is shown below. Figure 2 As shown, it includes the following steps:

[0039] S1. Obtain the output voltage of each submodule when the DC transformer starts up. Establish a submodule voltage library and perform initialization, enabling the submodule voltage cyclic detection function. For example, the submodule voltage values ​​can be collected and stored in a storage space to establish the submodule voltage library.

[0040] S2. Perform hysteresis control on the output voltage of each submodule. The upper voltage threshold of this hysteresis control is U1, and the lower voltage threshold is U0. For example, a commonly used hysteresis control algorithm in this field can be used to implement hysteresis control.

[0041] S3. Adjust the duty cycle of each submodule based on the hysteresis control results. Duty cycle refers to the percentage of on-time to the switching cycle for power electronic switching devices, such as IGBTs, on the high-voltage side of the power submodule. In this embodiment, for example, for… Figure 1 The power electronic switching devices on the high-voltage side are adjusted as shown. Specifically, the following methods can be used:

[0042] If the output voltage of the submodule is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the submodule with the first duty cycle change slope K.

[0043] If the output voltage of the submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the corresponding submodule is raised to the rated duty cycle with the second duty cycle change slope k.

[0044] In this embodiment, ramp control is used primarily to smooth the input or output. Considering that the output voltage of the power submodule is greater than the upper voltage threshold U1, it is necessary to reduce the submodule voltage as quickly as possible and rapidly reduce the duty cycle of the high-voltage side submodule. Here, the minimum duty cycle can be set to D. min The duty cycle of this submodule can be reduced by the following formula, using the slope K of the first duty cycle change:

[0045] K = (D min -D n )*f / N

[0046] Among them, D n The current duty cycle is given, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction phase.

[0047] If the output voltage of the power submodule is less than the lower voltage threshold U0, the duty cycle of the corresponding submodule can be increased to the rated duty cycle with the second duty cycle change slope k according to the following formula:

[0048] k=(D e -D n )*f / M

[0049] Among them, D e M is the rated duty cycle, and M is the number of cycles set for the stage of restoring the rated duty cycle. M is generally greater than N.

[0050] According to another embodiment of the present invention, a DC transformer submodule voltage control device is provided, the block diagram of which is shown below. Figure 3 As shown, it includes a voltage acquisition module, a hysteresis control module, and a duty cycle adjustment module.

[0051] The voltage acquisition module is used to acquire the output voltage of each sub-module when the DC transformer starts up.

[0052] The hysteresis control module is used to perform hysteresis control on the output voltage of each submodule. The upper voltage threshold of the hysteresis control is U1, and the lower voltage threshold is U0.

[0053] The duty cycle adjustment module is used to adjust the duty cycle of each sub-module according to the result of hysteresis control: if the output voltage of the sub-module is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the sub-module by the first duty cycle change slope K.

[0054] If the output voltage of a submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the submodule is increased by the duty cycle change slope K, and the duty cycle of the corresponding submodule is increased to the rated duty cycle by the second duty cycle change slope k.

[0055] The reduction of the duty cycle of this sub-module by the first duty cycle change slope K includes:

[0056] K = (D min -D n )*f / N

[0057] Among them, D n The current duty cycle is given, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction phase.

[0058] Increasing the duty cycle of the corresponding submodule to the rated duty cycle using the second duty cycle change slope k includes:

[0059] k=(D e -D n )*f / M

[0060] Among them, D e M is the rated duty cycle, and M is the number of cycles set for the stage of restoring the rated duty cycle. M is generally greater than N.

[0061] The other specific steps for each module in the device to achieve its corresponding function are the same as those provided in the first embodiment of the present invention, and will not be repeated here.

[0062] In summary, this invention relates to a method and apparatus for controlling the voltage of submodules of a DC transformer. By acquiring the voltage of each submodule of the DC transformer, hysteresis control is applied to the voltage of each submodule, and the duty cycle of each submodule is adjusted using the results of the hysteresis control. This addresses the problem of uneven voltage distribution and overvoltage in the submodules caused by the nonlinear gain of the resonant converter during the startup of the DC transformer device. The technical solution of this invention employs a dynamic duty cycle adjustment control algorithm. Specifically, the module with the high voltage is controlled through hysteresis and ramp control to adjust its duty cycle, thereby lowering the submodule voltage and achieving better voltage equalization. This ensures the safe and stable operation of the device and effectively solves the problem of uneven voltage distribution and overvoltage in the submodules caused by the nonlinear gain of the resonant converter during the startup of the DC transformer device. The control logic is simple and easy to implement.

[0063] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for voltage control of a DC transformer submodule, characterized in that, Including the following steps: Obtain the output voltage of each submodule when the DC transformer starts up; Hysteresis control is applied to the output voltage of each submodule. The upper voltage threshold of this hysteresis control is U1, and the lower voltage threshold is U0. The duty cycle of each submodule is adjusted based on the results of hysteresis control. If the output voltage of the submodule is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the submodule with the first duty cycle change slope K. K = (Dmin - Dn) * f / N; Where Dmin is the minimum duty cycle, Dn is the current duty cycle, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction stage; If the output voltage of the submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the corresponding submodule is raised to the rated duty cycle with the second duty cycle change slope k. k = (De - Dn) * f / M Where De is the rated duty cycle, M is the number of cycles set for the stage of restoring the rated duty cycle, and M is greater than N.

2. The method according to claim 1, characterized in that, The submodule includes an LLC resonant converter power submodule.

3. A voltage control device for a DC transformer submodule, characterized in that, It includes a voltage acquisition module, a hysteresis control module, and a duty cycle adjustment module; among which, The voltage acquisition module is used to acquire the output voltage of each sub-module when the DC transformer starts up. The hysteresis control module is used to perform hysteresis control on the output voltage of each submodule. The upper voltage threshold of the hysteresis control is U1, and the lower voltage threshold is U0. The duty cycle adjustment module is used to adjust the duty cycle of each sub-module based on the results of hysteresis control. If the output voltage of the submodule is greater than the upper voltage threshold U1, ramp control is enabled to reduce the duty cycle of the submodule with the first duty cycle change slope K. K = (Dmin - Dn) * f / N Where Dmin is the minimum duty cycle, Dn is the current duty cycle, f is the switching frequency, and N is the number of cycles set for the duty cycle reduction stage; If the output voltage of the submodule is less than the lower voltage threshold U0, ramp control is enabled, and the duty cycle of the corresponding submodule is raised to the rated duty cycle with the second duty cycle change slope k. k = (De - Dn) * f / M Where De is the rated duty cycle, M is the number of cycles set for the stage of restoring the rated duty cycle, and M is greater than N.

4. The apparatus according to claim 3, characterized in that, The submodule includes an LLC resonant converter power submodule.

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