Multi-module flexible switching system for direct current power transmission based on expert decision

Abstract

The application belongs to the technical field of direct current transmission, and specifically discloses a multi-module direct current transmission flexible switching system based on expert decision-making. The scheme provided by the application mainly utilizes a fuzzy control algorithm to optimize the performance of the multi-module system in the switching process. In actual operation, the system can monitor the bus voltage difference between the current module and the reference module and the voltage mutation of the module in real time. After these data are sent to the fuzzy controller, the specific bus voltage compensation value is calculated. Then, the system adjusts the power distribution of the compensation module to offset the voltage impact generated during switching. The application can realize flexible switching of multi-module direct current transmission, effectively suppress voltage oscillation during switching, and balance system efficiency and dynamic characteristics.

Description

Technical Field

[0001] This application belongs to the field of DC power transmission technology, and more specifically, relates to a multi-module DC power transmission flexible switching system based on expert decision-making. Background Technology

[0002] As the core power supply for submarine cable-based observation networks and marine resource development equipment, the underwater multi-module constant current to constant voltage converter system features high efficiency, high reliability, and high anti-interference capabilities, enabling it to operate stably for extended periods in variable underwater environments. To enhance the overall system output power and reduce voltage stress on semiconductor components, this type of system commonly employs a multi-module input-series-output-parallel (ISOP) topology.

[0003] For power control of multiple modules, existing technologies are mainly divided into two categories: one is the power sharing control strategy, which is a linear control strategy with the advantages of simple control logic and high steady-state stability. However, the system efficiency is extremely low under light load conditions, which cannot meet the high-efficiency operation requirements of underwater power supply systems. The other is the power uneven sharing hard switching control strategy, which significantly improves light load efficiency by having several fully loaded modules and a compensation module work together to output power. However, it has a prominent drawback: power fluctuations can easily cause the compensation module to switch repeatedly, resulting in low-frequency oscillations and large overshoots in the system output voltage. Moreover, it is difficult to simultaneously take into account system efficiency and dynamic characteristics during hard switching: efficiency improvement is limited when there is low power oscillation, and voltage surges and poor dynamic characteristics occur when there is high power oscillation, which seriously affects the stability of the power supply system and the service life of components in complex underwater environments.

[0004] Existing flexible switching control strategies, such as master-slave control, voltage margin control, and traditional droop control, have attempted to solve the switching oscillation problem, but they have shortcomings such as low reliability, obvious switching oscillation, and large module power output error.

[0005] Therefore, how to achieve flexible switching of multi-module DC transmission, effectively suppress voltage oscillations during the switching process, and take into account both system efficiency and dynamic characteristics is an urgent problem to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this application is to provide a multi-module DC transmission flexible switching system based on expert decision-making, which can realize flexible switching of multi-module DC transmission, effectively suppress voltage oscillations during the switching process, and take into account both system efficiency and dynamic characteristics.

[0007] To achieve the above objectives, in a first aspect, this application provides a multi-module DC transmission flexible switching system based on expert decision-making, comprising: a multi-module transmission unit, a voltage acquisition module, a fuzzy controller, an integrator, and a limiting circuit;

[0008] The multi-module power transmission unit comprises multiple parallel modules, each used for DC power conversion. Its bus voltage is linearly related to the output power, satisfying the formula: ,in P Power is supplied to the module. This is the bus voltage when the module is fully loaded (the value can be 603.5V). This represents the bus voltage (in V) of the nth module. k The slope value (which can be 0.0446V / W) is used; among the multiple parallel modules, there is a preset reference full-load module, and the module with the largest bus voltage among the remaining modules is used as a compensation module. The input terminal of the voltage acquisition module is connected to the bus of each module of the multi-module power transmission unit, and is used to acquire the bus voltage of each module, and obtain the bus voltage difference between the current module and the reference full-load module, as well as the bus voltage change value of the current module itself. The output terminal of the voltage acquisition module is connected to the input terminal of the first quantization factor and the input terminal of the second quantization factor, respectively. The first quantization factor is used to quantize the bus voltage difference, and the second quantization factor is used to quantize the bus voltage abrupt change value. The output terminals of the first quantization factor and the second quantization factor are both connected to the input terminal of the fuzzy controller. The fuzzy controller is used to determine the bus voltage compensation value based on the input bus voltage difference and voltage mutation value, so as to adjust the power distribution of the compensation module. The output of the fuzzy controller is connected to the input of the scaling factor, the output of the scaling factor is connected to the input of the integrator, the output of the integrator is connected to the input of the limiting circuit, and the output of the limiting circuit is connected to the bus of the compensation module, for outputting a bus voltage compensation signal to the compensation module.

[0009] As a further preferred embodiment, the input of the fuzzy controller is the bus voltage difference U processed by the first quantization factor and the bus voltage mutation value K processed by the second quantization factor, and the output is the bus voltage compensation. Input quantities U, K and output quantities The basic domains of discourse are all (-3, -2, -1, 0, 1, 2, 3), and all of them divide the fuzzy set into 7 levels, namely positive large (PB), positive medium (PM), positive small (PS), zero (ZO), negative small (NS), negative medium (NM), and negative large (NB).

[0010] As a further preferred embodiment, the fuzzy controller uses a triangular membership function to characterize the degree to which an element belongs to a fuzzy set. This membership function can accurately describe the fuzzy correlation between the input and output quantities. The fuzzy inference uses the Mamdani inference algorithm and follows the minimax composition rule to ensure the rigor of the inference process. The defuzzification uses the region centroid method, which calculates the weighted average of the elements of the output quantity after fuzzy inference and their corresponding membership degrees, and rounds it to the nearest integer to obtain the accurate bus voltage compensation value, ensuring the executability of the control signal.

[0011] As a further preferred embodiment, the fuzzy controller pre-stores an expert decision table, which is formulated based on three aspects: stability, system efficiency, and dynamic characteristics. The stability constraint is that the action interval of the fuzzy controller is greater than the minimum system dwell time (experimentally verified to be 0.07s), ensuring that the system energy can sufficiently decay to a stable state during the switching process. The matching strategy for system efficiency and dynamic characteristics is as follows: when the compensation module oscillates at low power, a control logic with higher compensation power is used to improve system efficiency, while moderately sacrificing a small amount of dynamic characteristics; when the compensation module oscillates at high power, a control logic with lower compensation power is used to optimize dynamic characteristics while maintaining constant system efficiency.

[0012] As a further preferred embodiment, the expert decision table uses the bus voltage difference U as the row and the bus voltage mutation value K as the column, outputting the corresponding bus voltage compensation fuzzy level, with the specific rules as follows: When U is NB (negative large) or NM (negative medium), regardless of the level of K, the corresponding compensation level is ZO (zero). When U is NS (negative small), the compensation level corresponding to K is NM (negative medium) and NS (negative small) is NS (negative small), and the compensation level corresponding to the other K levels is ZO (zero). When U is ZO (zero), the compensation level corresponding to K being NB (negative large) is NS (negative small), the compensation level corresponding to K being NM (negative medium) is NM (negative medium), and the compensation level corresponding to the other K levels is ZO (zero). When U is PS (positive small), the compensation level corresponding to K being NB (negative large) is NS (negative small), the compensation level corresponding to K being NM (negative medium) is NM (negative medium), the compensation level corresponding to K being NS (negative small) is NB (negative large), the compensation level corresponding to K being PS (positive small) and PM (positive medium) is PS (positive small), and the compensation level corresponding to the other K levels is ZO (zero). When U is PM (center), the compensation level corresponding to K is PS (small) and PM (center) is PM (center), the compensation level corresponding to K is PB (large) is PS (small), and the compensation level corresponding to the other K levels is ZO (zero). When U is PB (positive large), the compensation level corresponding to K is PS (positive small) is PB (positive large), the compensation level corresponding to K is PM (positive medium), the compensation level corresponding to K is PS (positive small), and the compensation level corresponding to the other K levels is ZO (zero).

[0013] Secondly, this application provides a multi-module DC transmission flexible switching method based on expert decision-making, applied to a multi-module DC transmission flexible switching system based on expert decision-making as described in any of the above-mentioned methods, comprising the following steps: S1. The voltage acquisition module acquires the bus voltage of each module in the multi-module power transmission unit at a preset sampling frequency (preferably 100Hz). Based on the acquired voltage data, two core control signals are calculated: the bus voltage difference between the current module and module one, and the bus voltage change value of the current module itself (the voltage difference between adjacent sampling times). S2, after quantizing the bus voltage difference and bus voltage mutation value through quantization factors K1 and K2 respectively, convert them to the input domain of the fuzzy controller (-3,-2,-1,0,1,2,3) and input them to the fuzzy controller as fuzzy input quantities; S3, the fuzzy controller performs inference calculations on the fuzzy input quantity according to the pre-stored expert decision table, and uses the Mamdani fuzzy inference algorithm to perform defuzzification processing using the region centroid method, converting the fuzzy output quantity into an accurate initial value for bus voltage compensation. S4. The initial value of bus voltage compensation is proportionally adjusted by the proportional factor K0 and then sent to the integrator and the limiting circuit for processing in sequence: the integrator is used to eliminate static error, and the limiting circuit is used to limit the output range of the compensation value (preferably the limiting range is 0-50V) to avoid over-compensation and system oscillation, and finally obtain a stable bus voltage compensation value. S5 applies the final bus voltage compensation value to the compensation module bus of the multi-module transmission unit, accurately compensates the bus voltage of the compensation module, realizes the power redistribution between modules, and completes the flexible switching of multi-module DC transmission. S6 determines the power oscillation type of the compensation module. If it is low power oscillation, the bus voltage compensation value is increased; if it is high power oscillation, the bus voltage compensation value is decreased, adaptively adapting to the corresponding efficiency and dynamic characteristic control strategy.

[0014] As a further preferred embodiment, in step S6, low-power low-frequency oscillation is defined as the load power oscillating and switching between 980W and 1100W with a period of 0.1s. At this time, a 22V bus voltage compensation value is output to the compensation module, so that the compensation module remains in a continuously engaged state. The output voltage overshoot decreases from 1.8V in the hard switching to 1.1V, and the system efficiency increases from 93% to 94%. After bus voltage compensation, the bus voltage of the compensation module stabilizes at 590V, according to the formula. The calculated theoretical compensation power of the compensation module is 197.31W, and the actual compensation power is 195W. The deviation between the theoretical and actual values ​​is less than 1.2%, indicating high compensation accuracy.

[0015] As a further preferred embodiment, in step S6, high-power low-frequency oscillation is defined as the load power oscillating and switching between 480W and 900W with a period of 0.1s. At this time, a bus voltage compensation value of 14.4V is output to the compensation module, so that the compensation module remains in a continuously engaged state, and the output voltage overshoot drops from 4.6V in the hard switch to 3.2V, while the system efficiency remains unchanged at 91%-93%. After bus voltage compensation, the bus voltage of the compensation module stabilizes at 585V, according to the formula. The calculated theoretical compensation power of the compensation module is 85.20W, and the actual compensation power is 82W. The deviation between the theoretical and actual values ​​is less than 3.8%, which meets the requirements of engineering applications.

[0016] As a further preferred embodiment, the switching cycle of the multi-module DC transmission system is set to 0.1s, which is much larger than the minimum system dwell time (0.07s) to ensure the overall stability of the system; the bus voltage difference between adjacent modules is set to a fixed value ΔV=30V, and the fuzzy controller reduces the bus voltage difference between modules by adjusting the bus voltage of the compensation module, thereby effectively improving the dynamic characteristics of the system.

[0017] The multi-module DC transmission flexible switching system and method based on expert decision-making provided in this application have the following advantages compared with the prior art: (1) Effectively suppressing voltage oscillations and reducing voltage overshoot: This application uses a fuzzy controller to collect the bus voltage difference and voltage mutation value in real time, and accurately controls the bus voltage compensation value of the compensation module, thereby suppressing the low-frequency oscillation problem caused by power unevenness hard switching from the root cause. Under low power oscillation, the voltage overshoot is reduced from 1.8V to 1.1V, a reduction of 38.9%; under high power oscillation, the voltage overshoot is reduced from 4.6V to 3.2V, a reduction of 30.4%, and the dynamic characteristics of the system are significantly improved; (2) Achieving adaptive matching between efficiency and dynamic characteristics: Differentiated compensation strategies are designed for different power oscillation types. When the power oscillation is low, the compensation power is increased, and the system efficiency is improved from 93% to 94%. When the power oscillation is high, the compensation power is reduced. Under the premise of maintaining the system efficiency (91%-93%), the dynamic characteristics are optimized, which perfectly solves the technical problem that efficiency and dynamic characteristics are difficult to balance in the existing technology. (3) Ensure the overall stability of the system and avoid repeated switching of modules: The system switching cycle (0.1s) is much larger than the minimum dwell time (0.07s), and the action interval of the fuzzy controller meets the stability constraint. At the same time, the compensation module maintains a continuous switching state during the oscillation process, which avoids damage to components caused by repeated switching of modules and improves the reliability and service life of the system. (4) Strong robustness and adaptability to nonlinear switching characteristics: Fuzzy control does not require the establishment of an accurate mathematical model. It achieves control by transforming engineering experience into an expert decision table. It has high fault tolerance and strong robustness, and is perfectly adapted to the nonlinear switching characteristics of multi-module DC transmission. It is especially suitable for complex and changeable underwater working environments. (5) Accurate calculation of compensation power and high reproducibility of control: The bus voltage and output power of the multi-module transmission unit are strictly linearly related, which can be achieved by formula The theoretical compensation power of the compensation module can be calculated quickly and accurately, providing a quantitative basis for the design of compensation values ​​for fuzzy control, and making the entire flexible switching control process highly reproducible and scalable. (6) Simple topology and easy to integrate with existing systems: The system of this application only adds a voltage acquisition module, fuzzy controller, integrator and limiting circuit on the basis of the existing multi-module ISOP topology. There is no need to make major modifications to the original system. The components are mature, the engineering application cost is low, and it is easy to integrate with the existing underwater constant current to constant voltage conversion system. Attached Figure Description

[0018] Figure 1 This is a fuzzy control block diagram provided in the embodiments of this application; Figure 2 This is a triangular membership function diagram of fuzzy input and output quantities provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] It should be understood that, in the description of this application, the term "multiple" means two or more, unless otherwise explicitly specified; the terms "first" and "second," etc., are used to distinguish different objects, rather than to describe a specific order of objects.

[0021] To address the technical problems in existing multi-module DC transmission systems, such as low efficiency under light load in power-sharing control, low-frequency oscillations and large voltage overshoot in hard switching due to uneven power distribution, and the difficulty in balancing efficiency and dynamic characteristics, this application provides a flexible switching system and method for multi-module DC transmission based on expert decision-making. This application designs a dedicated fuzzy controller, combining quantization factors, proportional factors, integrators, and limiting circuits, to precisely adjust the bus voltage compensation value of the compensation module based on the bus voltage difference and voltage surge values. Furthermore, it designs differentiated compensation strategies for different power oscillation types, achieving flexible switching of multiple modules, effectively reducing voltage fluctuations, and balancing system global stability, operating efficiency, and dynamic characteristics. This system is suitable for the nonlinear switching characteristics and complex operating environment of underwater constant current to constant voltage conversion systems.

[0022] The multi-module DC transmission flexible switching system and method based on expert decision-making provided in this application are applicable to the multi-module input series output parallel (ISOP) topology of underwater constant current to constant voltage (CC-CV) converter systems. The minimum dwell time of the system has been experimentally verified to be 0.07s. The bus voltage difference between adjacent modules is fixed at ΔV=30V, and the switching cycle is set to 0.1s (which is much greater than the minimum dwell time), ensuring the global stability of the system.

[0023] As shown in Figure 1, this embodiment provides a multi-module DC transmission flexible switching system based on expert decision-making, including a multi-module transmission unit, a voltage acquisition module, a fuzzy controller, an integrator, and a limiting circuit. Each component is connected sequentially by wires to form a closed-loop control circuit: the input terminal of the voltage acquisition module is connected to each module bus of the multi-module transmission unit one by one; the output terminal of the voltage acquisition module is connected to the input terminals of quantization factors K1 and K2, respectively; the output terminals of quantization factors K1 and K2 are both connected to the input terminal of the fuzzy controller; the output terminal of the fuzzy controller is connected to the input terminal of the proportional factor K0; the output terminal of the proportional factor K0 is connected to the input terminal of the integrator; the output terminal of the integrator is connected to the input terminal of the limiting circuit; and the output terminal of the limiting circuit is connected to the compensation module bus of the multi-module transmission unit.

[0024] The multi-module transmission unit uses multiple identical modules to form an ISOP topology. Each module consists of a cascaded shunt regulator and an LLC resonant circuit. The bus voltage and output power of each module satisfy a linear formula. V bus1=603.5V (module full-load bus voltage), k=0.0446V / W, the compensation module is the module with the largest bus voltage except for the full-load module; the component selection of each module in the system is as follows: shunt regulator output capacitor C=44uF, excitation inductor Lm=800uH, resonant capacitor Cs=22nF, resonant inductor Ls=92.6uH, output capacitor Co=60uF, transformer turns ratio n (n1:n2)=1:1.25, output resistance Rld=281Ω.

[0025] The voltage acquisition module uses a high-precision voltage sensor (measurement accuracy ±0.1%) with a sampling frequency of 100Hz to acquire the bus voltage of each module of the multi-module power transmission unit in real time. It also uses the built-in computing unit to calculate the bus voltage difference between the current module and Module 1, as well as the sudden change value of the bus voltage of the current module itself (the voltage difference between adjacent sampling times).

[0026] Quantization factors K1=0.015 and K2=0.012 are used to accurately quantize the actual voltage signal to the input universe of discourse (-3,-2,-1,0,1,2,3) of the fuzzy controller; scaling factor K0=7.5 is used to restore the output of the fuzzy controller to the actual initial value of the bus voltage compensation.

[0027] The inputs to the fuzzy controller are the bus voltage difference U and the bus voltage jump value K after quantization by K1 and K2, and the output is the bus voltage compensation Ub; U, K, U b The basic universe of discourse is (-3, -2, -1, 0, 1, 2, 3), and the fuzzy sets are divided into 7 levels: PB (positive large), PM (positive medium), PS (positive small), ZO (zero), NS (negative small), NM (negative medium), and NB (negative large); the fuzzy controller adopts a triangular membership function (e.g., Figure 2 (As shown) represents the degree to which an element belongs to a fuzzy set. Fuzzy inference uses the Mamdani inference algorithm and follows the "maximum-minimal" composition rule. Defuzzification uses the region centroid method, through the formula... The weighted average value is calculated and rounded to obtain the accurate initial value of bus voltage compensation. The fuzzy controller has a pre-stored expert decision table, which is arranged with U as the row and K as the column, and outputs the corresponding fuzzy level of bus voltage compensation to ensure that the optimal compensation level is output according to different input combinations.

[0028] The integrator uses a first-order integrator (integration time constant τ=0.02s) to eliminate static error; the limiting range of the limiting circuit is set to 0-50V to avoid excessive compensation value leading to system over-adjustment.

[0029] The multi-module DC transmission flexible switching method based on expert decision-making provided in this embodiment is implemented based on the above system. The specific process is as follows: The voltage acquisition module acquires the bus voltage of each module in the multi-module transmission unit at a frequency of 100Hz, calculates the bus voltage difference between the current module and module one, and the sudden change value of the current module's own bus voltage; the two core control signals are quantized by quantization factors K1 and K2 respectively, and then input to the fuzzy controller; the fuzzy controller performs inference calculations based on the pre-stored expert decision table using the Mamdani fuzzy inference algorithm, and performs defuzzification processing using the region centroid method to obtain the initial value of bus voltage compensation; the initial value of bus voltage compensation is then proportionally factored by K0... After proportional adjustment, the voltage is sequentially fed into the integrator and limiting circuit to obtain the final bus voltage compensation value. This final bus voltage compensation value is then applied to the bus of the compensation module to accurately compensate the bus voltage of the compensation module, enabling power redistribution among the modules and facilitating flexible switching of multi-module DC transmission. Simultaneously, the voltage acquisition module monitors load power changes in real time to determine the power oscillation type of the compensation module. During low-power, low-frequency oscillations (load power 980W-1100W, period 0.1s), a 22V bus voltage compensation value is output, while during high-power, low-frequency oscillations (load power 480W-900W, period 0.1s), a 14.4V bus voltage compensation value is output, adaptively matching the corresponding efficiency and dynamic characteristic control strategies.

[0030] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A multi-module DC transmission flexible switching system based on expert decision-making, characterized in that, include: Multi-module power transmission unit, voltage acquisition module, fuzzy controller, integrator and limiting circuit; The multi-module power transmission unit comprises multiple parallel modules, each used for DC power conversion. Its bus voltage is linearly related to the output power, satisfying the formula: ,in P Power is supplied to the module. This is the bus voltage when the module is fully loaded. Let n be the bus voltage of the nth module. k The slope value is used; among the multiple parallel modules, there is a preset reference full-load module, and the module with the largest bus voltage among the remaining modules is used as a compensation module. The input terminal of the voltage acquisition module is connected to the bus of each module of the multi-module power transmission unit, and is used to acquire the bus voltage of each module, and obtain the bus voltage difference between the current module and the reference full-load module, as well as the bus voltage change value of the current module itself. The output terminal of the voltage acquisition module is connected to the input terminal of the first quantization factor and the input terminal of the second quantization factor, respectively. The first quantization factor is used to quantize the bus voltage difference, and the second quantization factor is used to quantize the bus voltage abrupt change value. The output terminals of the first quantization factor and the second quantization factor are both connected to the input terminal of the fuzzy controller. The fuzzy controller is used to determine the bus voltage compensation value based on the input bus voltage difference and voltage mutation value, so as to adjust the power distribution of the compensation module. The output of the fuzzy controller is connected to the input of the scaling factor, the output of the scaling factor is connected to the input of the integrator, the output of the integrator is connected to the input of the limiting circuit, and the output of the limiting circuit is connected to the bus of the compensation module, for outputting a bus voltage compensation signal to the compensation module.

2. The multi-module DC transmission flexible switching system based on expert decision-making as described in claim 1, characterized in that, The inputs of the fuzzy controller are the bus voltage difference U processed by the first quantization factor and the bus voltage mutation value K processed by the second quantization factor, and the output is the bus voltage compensation. Input quantities U, K and output quantities The basic domains of discourse are all (-3, -2, -1, 0, 1, 2, 3), and all of them divide the fuzzy set into 7 levels, namely positive large, positive medium, positive small, zero, negative small, negative medium, and negative large.

3. The multi-module DC transmission flexible switching system based on expert decision-making as described in claim 2, characterized in that, The fuzzy controller uses a triangular membership function to characterize the degree to which an element belongs to a fuzzy set. Fuzzy inference uses the Mamdani inference algorithm and follows the minimax composition rule. Defuzzification uses the region centroid method. After fuzzy inference, the elements of the output quantity and their corresponding membership degrees are weighted and averaged, and then rounded to the nearest integer to obtain the accurate bus voltage compensation value.

4. The multi-module DC transmission flexible switching system based on expert decision-making as described in claim 2, characterized in that, The fuzzy controller has a pre-stored expert decision table, which is formulated based on three aspects: stability, system efficiency, and dynamic characteristics. The stability is such that the action interval of the fuzzy controller is greater than the minimum dwell time of the system. The matching strategy between system efficiency and dynamic characteristics is as follows: when the compensation module oscillates at low power, more compensation power is used to improve system efficiency, while sacrificing a small amount of dynamic characteristics; when the compensation module oscillates at high power, less compensation power is used to optimize dynamic characteristics, while keeping system efficiency unchanged.

5. The multi-module DC transmission flexible switching system based on expert decision-making as described in claim 4, characterized in that, The expert decision table uses the bus voltage difference U as the row and the bus voltage mutation value K as the column, outputting the corresponding bus voltage compensation fuzzy level. The specific rules are as follows: When U is negative large or negative medium, the compensation level corresponding to all K is zero; When U is negative, the compensation level corresponding to K being negative medium or negative small is negative small, and the compensation level corresponding to the rest of K is zero. When U is zero, the compensation level corresponding to K being negative large is negative small, the compensation level corresponding to K being negative medium is negative medium, and the compensation level corresponding to the rest of K is zero. When U is positive, the compensation level corresponding to negative large is negative small, the compensation level corresponding to negative medium is negative medium, the compensation level corresponding to negative small is negative large, the compensation level corresponding to positive small or positive medium is positive small, and the compensation level corresponding to the rest of K is zero. When U is in the middle, the compensation level corresponding to K being either small or in the middle is in the middle, the compensation level corresponding to K being large is small, and the compensation level corresponding to the rest of K is zero. When U is positive, the compensation level corresponding to K being positive is positive, the compensation level corresponding to K being positive is positive, the compensation level corresponding to K being positive is positive, the compensation level corresponding to K being positive is positive, and the compensation level corresponding to the rest of K is zero.

6. A method for flexible switching of multi-module DC transmission based on expert decision-making, applied to a flexible switching system for multi-module DC transmission based on expert decision-making as described in any one of claims 1 to 5, characterized in that, It includes the following steps: S1, the bus voltage of each module in the multi-module power transmission unit is collected by the voltage acquisition module, and the bus voltage difference between the current module and the reference full-load module and the bus voltage change value of the current module are calculated. S2, after quantizing the bus voltage difference and the bus voltage sudden change value through the first quantization factor and the second quantization factor respectively, the values ​​are input to the fuzzy controller as fuzzy input quantities. S3, the fuzzy controller uses the Mamdani fuzzy inference algorithm to infer the fuzzy input based on the pre-stored expert decision table, and uses the region centroid method to defuzzify it to obtain the accurate initial value of bus voltage compensation. S4. The initial value of bus voltage compensation is adjusted by the proportional factor and then sent to the integrator and the limiting circuit for processing to obtain the final value of bus voltage compensation. S5 applies the bus voltage compensation value to the compensation module bus of the multi-module transmission unit to compensate the bus voltage of the compensation module, realize the power redistribution of each module, and complete the flexible switching of multi-module DC transmission. S6 determines the power oscillation type of the compensation module. If it is low power oscillation, the bus voltage compensation value is increased; if it is high power oscillation, the bus voltage compensation value is decreased, adapting to the corresponding efficiency and dynamic characteristic control strategy.

7. The multi-module DC transmission flexible switching method based on expert decision-making as described in claim 6, characterized in that, In step S6, the low-power low-frequency oscillation is the switching of load power between 980W and 1100W with a period of 0.1s. At this time, a 22V bus voltage compensation value is output to the compensation module to keep the compensation module in the switched-on state.

8. The multi-module DC transmission flexible switching method based on expert decision-making as described in claim 6, characterized in that, In step S6, the high-power low-frequency oscillation is the switching of the load power between 480W and 900W with a period of 0.1s. At this time, a bus voltage compensation value of 14.4V is output to the compensation module to keep the compensation module in the switched-on state.

9. The multi-module DC transmission flexible switching method based on expert decision-making as described in claim 6, characterized in that, The switching cycle of the system is 0.1s, which is greater than the minimum dwell time of the system of 0.07s; the bus voltage difference between adjacent modules is set to a fixed value ΔV=30V.

10. The multi-module DC transmission flexible switching method based on expert decision-making as described in claim 6, characterized in that, When the bus voltage of the compensation module reaches 590V, according to the formula... The calculated theoretical compensation power of the compensation module is 197.31W, and the actual compensation power is 195W. When the bus voltage of the compensation module reaches 585V, according to the formula... The calculated theoretical compensation power of the compensation module is 85.20W, while the actual compensation power is 82W; among which, P Power is supplied to the module. This is the bus voltage when the module is fully loaded. Let n be the bus voltage of the nth module. k This represents the slope value.

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