Lunar flexible power transmission and transformation system

Abstract

The invention provides a lunar surface flexible power transmission and transformation system, and relates to the technical field of lunar surface microgrids, the lunar surface flexible power transmission and transformation system comprises a first Z-source network, the first end of the first Z-source network is connected with a first DC power supply; the direct current end of the first inverter is connected with the second end of the first Z-source network; the first end of the first high-frequency transformer is connected with the alternating current end of the first inverter; the first controller is connected with the control end of the first inverter, and the first controller is used for modulating the direct connection state of the first inverter within a time period according to the output current and the output voltage of the first inverter, so that the direct connection state of the first inverter is adjusted; and the first inverter is controlled to be alternately switched between the direct connection state and the non-direct connection state according to the direct connection state. The lunar surface flexible power transmission and transformation system provided by the invention can improve the operation efficiency and reduce the equipment cost.

Description

Technical Field

[0001] The present invention relates to the technical field of lunar microgrids, and in particular to a lunar flexible power transmission and transformation system. Background Art

[0002] The energy system is the basic guarantee for the lunar scientific research station. The lunar energy system has the characteristics of many energy types, a wide range of load power levels, and complex electricity usage scenarios, showing a trend of comprehensive energy utilization. The energy types mainly include photovoltaics, small nuclear power, isotope power supplies, fuel cells, energy storage and other forms. Technologies such as efficient power conversion of multiple energy forms, long-distance power transmission, power supply adaptation of multiple types of loads, and multi-source collaborative optimization management are all key scientific issues to be solved in the construction of the lunar energy system. The lunar power supply system is different from the ground power system. It is a smaller-scale independent energy system that uses in-situ energy on the lunar surface to generate electricity and maintain the supply and demand balance of system energy. At the same time, since the lunar scientific research station is far away from the earth and needs to maintain normal operation without human supervision, its power system needs to have strong autonomous operation management and self-maintenance functions. The microgrid system is a small power generation and consumption network architecture with self-control, self-protection and self-management capabilities that can integrate multiple energy forms and loads for comprehensive management.

[0003] As the scale of microgrid systems expands, the geographical scope of their distribution will also become larger and larger, and microgrids that are far apart will need longer transmission lines to interconnect. Higher voltages are more suitable for long-distance power transmission, which can effectively reduce wire costs and transmission losses, but the vacuum environment on the lunar surface places higher requirements on the insulation of cables. However, unlike the application scenarios of spacecraft and space stations, lunar microgrids have the need for long-distance power transmission. When transmitting power over long distances, the power loss and voltage drop of the transmission lines are serious, but increasing the wire diameter will increase the weight and volume of the transmission lines. Moreover, since the voltage levels of current power generation and power-consuming equipment are generally low, the bus voltage of small microgrid systems generally adopts the 100V DC standard. In addition, after the voltage level is increased to 3kV, the impact of the increase in transmission voltage on the total amount of equipment is reduced. Taking all factors into consideration, it is believed that 3kV AC transmission is the best choice for all factors. Therefore, when using AC transmission, it is necessary to first convert 100V DC into 3kV AC. The topology structure for boosting low-voltage DC to high-voltage AC is currently mainly a two-stage structure, one stage DC boost and one stage inverter. Due to the high AC voltage, the inverter adopts a multi-level topology or a module cascade topology. The two-stage conversion structure has low efficiency. In addition, the multi-level or module cascade topology uses more power devices and capacitors, the converter is larger in size, and the reliability of the equipment is low. Summary of the invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a lunar flexible power transmission and transformation system, which is used to solve the problems in the prior art that during long-distance power transmission, the power loss and voltage drop of the transmission line are serious, the inverter adopts a multi-level topology or a modular cascaded topology, the two-stage conversion structure has a low efficiency, in addition, the multi-level or modular cascaded topology uses more power devices and capacitors, the volume of the converter is large, and the reliability of the equipment is low.

[0005] To achieve the above object and other related objects, the present invention provides a lunar flexible power transmission and transformation system, including: a first Z-source network, the first end of the first Z-source network is connected to a first DC power supply; a first inverter, the DC end of the first inverter is connected to the second end of the first Z-source network; a first high-frequency transformer, the first end of the first high-frequency transformer is connected to the AC end of the first inverter; a first controller, the first controller is connected to the control end of the first inverter, and the first controller is used to modulate the direct-conduction state of the first inverter according to the output current and output voltage of the first inverter within a time period, and control the first inverter to alternately switch between the direct-conduction state and the non-direct-conduction state according to the direct-conduction state; wherein, when the first inverter is in the direct-conduction state, the first DC power input is boosted to a second DC power through the first Z-source network; when the first inverter is in the non-direct-conduction state, the second DC power is converted into a first AC power through the first inverter, and the first AC power is boosted to a second AC power through the first high-frequency transformer and then output.

[0006] In an embodiment of the present invention, the first inverter is a three-phase inverter, the first inverter includes three bridge arms, the first end of each bridge arm is connected to the positive extreme of the first Z-source network, and the second end of each bridge arm is connected to the negative extreme of the first Z-source network.

[0007] In an embodiment of the present invention, the first Z-source network includes: a first capacitor, a second capacitor, a first inductor and a second inductor; the positive extreme of the first capacitor and the negative extreme of the second capacitor are connected to the positive extreme of the first inductor, and the positive extreme of the first inverter is connected between the negative extreme of the first inductor and the positive extreme of the second capacitor; the positive extreme of the first capacitor and the negative extreme of the second capacitor are connected to the positive extreme of the second inductor, and the negative extreme of the first inverter is connected between the negative extreme of the first capacitor and the positive extreme of the second inductor, the positive extreme of the first capacitor and the positive extreme of the first inductor are connected to the positive extreme of the first DC power supply, and the negative extreme of the second capacitor and the negative extreme of the second inductor are connected to the negative extreme of the first DC power supply.

[0008] In an embodiment of the present invention, the AC end of the first inverter is connected to the first end of the first high-frequency transformer through a first filter network.

[0009] In an embodiment of the present invention, the lunar flexible power transmission and transformation system further includes a seventh switching tube. The first end of the seventh switching tube is connected to the positive terminal of the first DC power supply, the second end of the seventh switching tube is connected to the positive terminal of the first Z-source network, and the control end of the seventh switching tube is connected to the first controller.

[0010] In an embodiment of the present invention, the first controller includes: a modulation unit for modulating the on-duty ratio of the first inverter in the on-state within a time period through SPWM modulation and according to two set constant voltage values whose absolute values are greater than or equal to the peak value of the sine wave; and a control unit for obtaining a corresponding modulation signal according to the given voltage and current, calculating the corresponding on-duty ratio, and controlling the first inverter to alternately switch between the on-state and the off-state according to the on-state corresponding to the on-duty ratio.

[0011] In an embodiment of the present invention, the first direct current is 100V; the first alternating current is 300V, 1kHz; the second alternating current is 3kV, 1kHz.

[0012] In an embodiment of the present invention, the lunar flexible power transmission and transformation system further includes: a second Z-source network, the first end of the second Z-source network is connected to the second DC power supply; a second inverter, the DC terminal of the second inverter is connected to the second end of the second Z-source network; a second high-frequency transformer, the first end of the second high-frequency transformer is connected to the AC terminal of the second inverter, and the second end of the second high-frequency transformer is connected to the second end of the first high-frequency transformer; a second controller, the second controller is connected to the control end of the second inverter.

[0013] In an embodiment of the present invention, the first DC power supply is the first microgrid; the second DC power supply is the second microgrid.

[0014] In an embodiment of the present invention, the first microgrid includes a photovoltaic unit, a small nuclear power unit, an energy storage unit, and a lunar base living load; the second microgrid includes an energy storage unit, a photovoltaic unit, a fuel cell, a lunar rover, a scientific research load, and a communication load.

[0015] As described above, a lunar flexible power transmission and transformation system and a microgrid system of the present invention have the following beneficial effects: By using a Z-source inverter composed of a Z-source network and an inverter, it is possible to realize boosting a low-voltage DC to a high-voltage AC first alternating current through a single-stage conversion, avoiding the need for additional boosting devices. After the Z-source inverter, a high-frequency transformer can be used to boost the first alternating current to a higher voltage level to meet the application scenario requirements of using a 3kV / 1kHz AC transmission mode for long-distance lunar environment long-distance power transmission. Furthermore, through the above-mentioned single-stage power conversion topology structure, compared with the traditional two-stage solution of DC boosting and then inversion, the operation efficiency can be improved and the equipment cost can be reduced. Brief Description of the Drawings

[0016] Figure 1 It shows a structural block diagram of a lunar surface flexible power transmission and transformation system provided by an embodiment of the present invention.

[0017] Figure 2 It shows a flowchart of a current loop control and a voltage loop control process provided by an embodiment of the present invention.

[0018] Figure 3 It shows a schematic diagram of the topology structure of a first Z-source network and a first inverter provided by an embodiment of the present invention.

[0019] Figure 4 It shows a schematic diagram of an equivalent circuit of a direct-through state of a first inverter provided by an embodiment of the present invention.

[0020] Figure 5 It shows a schematic diagram of an equivalent circuit of a non-direct-through state of a first inverter provided by an embodiment of the present invention.

[0021] Figure 6 It shows a schematic diagram of waveforms of a boost SPWM modulation process and modulation pulses in corresponding sections provided by an embodiment of the present invention.

[0022] Figure 7 It shows a schematic diagram of pulse waveforms of a first switching modulation tube provided by an embodiment of the present invention.

[0023] Figure 8 It shows a schematic diagram of the output voltage of a first switched Z-source inverter provided by an embodiment of the present invention.

[0024] Figure 9 It shows a schematic diagram of the line voltage waveform of an AC transmission line provided by an embodiment of the present invention.

[0025] Figure 10 It shows a schematic diagram of the three-phase current waveforms on the converter side provided by an embodiment of the present invention.

[0026] Figure 11 It shows a schematic diagram of the d-axis current waveform on the converter side provided by an embodiment of the present invention.

[0027] Figure 12 It shows a schematic diagram of the q-axis current waveform on the converter side provided by an embodiment of the present invention.

[0028] Figure 13 It shows a structural block diagram of a power transmission system topology provided by an embodiment of the present invention.

[0029] Figure 14 It shows a specific structural schematic diagram of a power transmission system topology provided by an embodiment of the present invention.

[0030] Figure 15 Shown is a structural diagram of a lunar microgrid system provided by an embodiment of the present invention.

[0031] Description of component labels

[0032] The first Z-source network 10; the first inverter 20; the first high-frequency transformer 30; the first controller 40; the first DC power supply 50; the first filter network 60; the second Z-source network 11; the second inverter 21; the second high-frequency transformer 31; the second controller 41; the second DC power supply 51, the second filter network 61. Detailed implementation manners

[0033] The following uses specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0034] It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0035] In the following description, a large number of details are explored to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0036] The construction progress of the lunar microgrid system that provides power supply for the lunar scientific research station should be synchronized with the construction progress of the lunar scientific research station and should be scalable. Therefore, the structure of the lunar microgrid system adopts a multi-microgrid interconnection structure, which is interconnected and expanded by small microgrid systems. Multiple small microgrid systems in different regions such as resource power generation, habitats, and scientific research stations are linked to build a medium-sized or large-scale microgrid of a larger scale. In the most basic topological structure, a basic microgrid unit can include various energy forms such as photovoltaic, small nuclear power, fuel cell power generation systems, thermoelectric power generation, and energy storage, as well as various load types such as lunar rovers, communication equipment, scientific research equipment, life support systems, and domestic loads. When selecting the voltage levels of various parts of the microgrid, various factors need to be comprehensively considered, such as the compatibility with the power supply standards of various types of aerospace power levels in operation, technical continuity, the radiation hardening problem of devices in a strong radiation environment, and the weight of equipment. The voltage levels used in the International Space Station currently include the 120V part built by the United States and the 120V and 28V hybrid part built by Russia. The voltage levels adopted by Chinese spacecraft and space stations are mainly 100V and 28V. Different from the application scenarios of spacecraft and space stations, the lunar microgrid has a demand for long-distance power transmission. During long-distance power transmission, the power loss and voltage drop of the transmission line are serious. However, increasing the wire diameter will increase the weight and volume of the transmission line. To improve this problem, the method of increasing the voltage can be adopted, but the increase in the voltage level is limited by the radiation resistance of device materials. In addition, after the voltage level is increased to 3kV, the impact of increasing the transmission voltage on the total amount of equipment decreases. Considering all aspects of factors, it is recommended that the 3kV / 1kHz AC transmission mode be used for long-distance transmission, which is the best choice considering all aspects of factors.

[0037] Please refer to Figure 1 , the present invention provides a lunar flexible power transmission and transformation system, including: a first Z-source network 10, a first end of the first Z-source network 10 is connected to a first DC power supply 50; a first inverter 20, a DC end of the first inverter 20 is connected to a second end of the first Z-source network 10; a first high-frequency transformer 30, a first end of the first high-frequency transformer 30 is connected to an AC end of the first inverter 20; a first controller 40, the first controller 40 is connected to a control end of the first inverter 20, and the first controller 40 is used to modulate the direct-conduction state of the first inverter 20 according to the output current and output voltage of the first inverter 20 within a time period, and control the first inverter 20 to alternately switch between the direct-conduction state and the non-direct-conduction state according to the direct-conduction state; wherein, when the first inverter 20 is in the direct-conduction state, the first DC power input is boosted to a second DC power through the first Z-source network 10; when the first inverter 20 is in the non-direct-conduction state, the second DC power is converted into a first AC power through the first inverter 20, and the first AC power is boosted to a second AC power through the first high-frequency transformer 30 and then output.

[0038] In this embodiment, in the lunar surface flexible power transmission and transformation system of the present invention, through the first Z-source network 10 disposed between the first DC power supply 50 and the first inverter 20, it is possible to achieve energy storage and conversion by the first Z-source network when the first inverter 20 is in the through state, so as to boost the DC bus voltage and realize the voltage boosting function, that is, to boost the input first direct current to the second direct current through the first Z-source network 10. By the first inverter 20 being in this through state, the system can store energy and increase the output voltage, avoiding the need for additional voltage boosting components. It should be noted that in the through state of the first inverter 20, the switching tubes of each arm of the first inverter 20 are simultaneously turned on to form a short-circuit state. After the first direct current is boosted to the second direct current, the first inverter 20 will alternately switch to the non-through state within a time period, that is, under the control of the first controller 40 for the first inverter 20, the switching tubes of each arm of the first inverter 20 work according to the conventional SPWM control strategy to perform DC-AC conversion, transfer the energy stored in the first Z-source network 10 to the load, and generate an output AC voltage, that is, convert from the second direct current to the first alternating current. In this non-through state, the first Z-source network 10 does not perform voltage boosting, and the first inverter 20 mainly performs the inversion function to convert direct current into alternating current for output. In order to be able to change the voltage level of this first alternating current, by adding the first high-frequency transformer 30 after the first inverter 20, it is possible to achieve the conversion of the voltage level of the first alternating current to the second alternating current. The lunar surface flexible power transmission and transformation system of the present invention mainly aims at the application scenario of the lunar microgrid with high specific power and high efficiency requirements for long-distance power transmission systems. By adopting the series structure of the first Z-source network 10, the first inverter 20, and the first high-frequency transformer 30, compared with the traditional two-stage solution of DC boosting and then inversion, the operation efficiency can be improved and the equipment cost can be reduced.

[0039] In an embodiment of the present invention, the first inverter 20 is a three-phase inverter. The first inverter 20 includes three arms, the first end of each arm is connected to the positive extreme of the first Z-source network 10, and the second end of each arm is connected to the negative extreme of the first Z-source network 10.

[0040] Please refer to FIGS. 2 and Figure 3 , the three arms are respectively denoted as the first arm, the second arm, and the third arm. The first arm includes the first switching tube S 1 and the second switching tube S 4 , the second arm includes the third switching tube S 2 and the fourth switching tube S 5 , the third arm includes the fifth switching tube S 3 and the sixth switching tube S 6 . Among them, the first switching tube S 1The first end of 1 is connected to the positive terminal of the first Z-source network 10 as the first end of the first bridge arm, and the second end of the first switching tube S 4 is connected to the first end of the second switching tube S 4 ; the second end of the second switching tube S 2 is connected to the negative terminal of the first Z-source network 10 as the second end of the first bridge arm; the first end of the third switching tube S 2 is connected to the positive terminal of the first Z-source network 10 as the first end of the second bridge arm, and the second end of the third switching tube S 5 is connected to the first end of the fourth switching tube S 5 ; the second end of the fourth switching tube S 3 is connected to the negative terminal of the first Z-source network 10 as the second end of the second bridge arm; the first end of the fifth switching tube S 3 is connected to the positive terminal of the first Z-source network 10 as the first end of the third bridge arm, and the second end of the fifth switching tube S 6 is connected to the first end of the sixth switching tube S 6 ; the second end of the sixth switching tube S 1 is connected to the negative terminal of the first Z-source network 10 as the second end of the second bridge arm. Among them, the control terminals of the first switching tube S 4 , the second switching tube S 2 , the third switching tube S 5 , the fourth switching tube S 3 , the fifth switching tube S 6 and the sixth switching tube S

[0041] In an embodiment of the present invention, the first Z-source network 10 includes: a first capacitor C 1 , a second capacitor C 2 , a first inductor L 1 and a second inductor L 2 ; the positive terminal of the first capacitor C 1 and the negative terminal of the second capacitor C 2 are connected to the positive terminal of the first inductor L 1 , and the positive terminal of the first inverter 20 is connected between the negative terminal of the first inductor L 1 and the positive terminal of the second capacitor C 2 ; the positive terminal of the first capacitor C 1 and the negative terminal of the second capacitor C 2 are connected to the positive terminal of the second inductor L 2 , and the negative terminal of the first inverter 20 is connected between the negative terminal of the first capacitor C 1 and the positive terminal of the second inductor L 2 ; the positive terminal of the first capacitor C 1 and the positive terminal of the first inductor L 2The positive terminal is connected to the positive terminal of the first DC power supply 50, and the negative terminal of the second capacitor C 2 and the negative terminal of the second inductor L 2 The negative terminal is connected to the negative terminal of the first DC power supply 50.

[0042] Please refer to Figure 4 and Figure 5 , assuming a cycle time of T, where the time in the direct-conduction state is T 0 , and the time in the non-direct-conduction state is T 1 . From the equivalent circuit in the direct-conduction state of Figure 4 , we get: u L =u C , u d =2u C , u i =0. From the equivalent current in the non-direct-conduction state of Figure 5 , we get: u L =u 0 -u C , u d =u 0 , u i =2u C -u 0 . According to the volt-second balance principle of the inductor, we get: The peak value of the inverter output phase voltage is: where, u i is the average voltage applied to the inverter bridge, is the peak voltage applied to the inverter bridge, B is the boost factor, D is the direct-conduction duty cycle, D = T 0 / T, M is the modulation index. From the above formula, it can be seen that by changing the direct-conduction duty cycle and the modulation index, boost can be achieved.

[0043] However, too high a boost ratio will lead to excessive voltage stress. In order to achieve a boost to the second AC voltage level, such as 3 kV, a first high-frequency transformer 30 needs to be added after the Z-source inverter composed of the first Z-source network 10 and the first inverter 20 to achieve a higher voltage level, as Figure 2 shown.

[0044] Furthermore, the AC terminal of the first inverter 20 is connected to the first end of the first high-frequency transformer 30 through the first filter network 60. The first filter network 60 includes three third inductors L f1 , three fourth inductors L f2 and three third capacitors C f , the first end of each third inductor L f1 is connected to the midpoint of each bridge arm, and the second end of each third inductor L f1 is connected to the corresponding fourth inductor L f2is connected to the first end, and each fourth inductor L f2 's second end is respectively connected to the first end of the first high-frequency transformer 30. Each third capacitor C f 's first end is connected to the third inductor L f1 's second end and the fourth inductor L f2 's first end, and the second ends of the respective third capacitors C f are connected to each other.

[0045] In an embodiment of the present invention, the lunar surface flexible power transmission and transformation system further includes a seventh switching tube S 7 , and the first end of the seventh switching tube S 7 is connected to the positive terminal of the first DC power supply 50, the second end of the seventh switching tube S 7 is connected to the positive terminal of the first Z-source network 10, and the control end of the seventh switching tube S 7 is connected to the first controller 40. In this embodiment, the seventh switching tube S 7 can be used to control the direct-conduction state, that is, when the seventh switching tube S 7 is turned off, the first inverter 20 is in the direct-conduction state, and when the seventh switching tube S 7 is turned on, the first inverter 20 is in the non-direct-conduction state.

[0046] In an embodiment of the present invention, the first controller 40 includes: a modulation unit for modulating the direct-conduction duty cycle of the first inverter 20 in a direct-conduction state within a time period through SPWM modulation and according to two set constant voltage values whose absolute values are greater than or equal to the peak value of the sine wave; and a control unit for obtaining a corresponding modulation signal according to the given voltage and current, calculating the corresponding direct-conduction duty cycle to achieve the stability of the output voltage and current, and then controlling the first inverter 20 to alternately switch between the direct-conduction state and the non-direct-conduction state according to the direct-conduction state corresponding to the direct-conduction duty cycle.

[0047] In an embodiment of the present invention, SPWM is one of the common modulation strategies in Z-source inverters. Combining with the boost characteristic of the first Z-source network 10, it can achieve voltage regulation and boost of the output voltage. For Z-source inverters, in addition to the traditional zero-vector state and effective-vector state, there is also a unique direct-conduction zero-vector state. When working in the direct-conduction zero-vector state and the traditional zero-vector state, the load is short-circuited, and the action time of the effective vector remains unchanged. According to this principle, simple boost can be achieved by replacing part of the traditional zero-vector state with the direct-conduction zero-vector state during SPWM modulation.

[0048] Please refer to Figure 6, the direct-through duty ratio is controlled by introducing two constant voltage values Vp or Vn whose absolute values are greater than or equal to the peak value of the sine wave. When the amplitude of the carrier wave is greater than Vp or less than Vn, all switches are closed and enter the direct-through state. When the carrier wave is greater than Vp, the modulation pulses in the corresponding section jump from 0 to 1, as shown in the red part of the figure. When the carrier wave is less than Vn, the modulation pulses in the corresponding section remain 1 unchanged. The rest of the time is in the traditional SPWM modulation state. And within each modulation period, the direct-through zero vector is evenly inserted in the middle of the traditional zero vectors, avoiding the negative impact on the output voltage waveform caused by the asymmetry introduced by the direct-through state. In this modulation mode, there is a relationship between the modulation degree and the direct-through duty ratio. As can be seen from Figure 6 , when the modulation degree M increases, the amplitude of the modulation wave increases, the absolute values of Vp and Vn also increase, and the direct-through duty ratio decreases. At this time, the relationship between the two is D = 1 - M. At this time, the calculation formulas for the boost factor B and the voltage gain G are as follows:

[0049]

[0050] Please refer to Figure 2 , the three-phase current i output by the inverter is collected abc , and after dq transformation, i d and i q are obtained. They are compared with the given values, and the calculated error is superimposed with the dq-axis components of the phase voltage and the decoupling voltage signal after passing through the PI regulator, and then transformed into the abc coordinate system to obtain the voltage given value U ref . After Z-source SPWM modulation, the SPWM signal is obtained, and the switching tubes can be controlled to achieve current closed-loop control. The current-loop control method not only ensures the rapid correction of the current error but also improves the dynamic response ability of the system, ensuring accurate current control under load changes or interference conditions.

[0051] In Figure 2 , it can be seen that a double-loop control mode of voltage outer loop - current inner loop is adopted. The specific control process is as follows: First, the output voltage u of the inverter is collected abc and the output current i abc . After dq transformation, the corresponding dq-axis components of the voltage and current are obtained. The error between the output voltage of the inverter and the given value is adjusted by PI to obtain the current given values i d * and i q *These two current set values represent the desired current targets of the system and will serve as the inputs for the inner-loop current control. After decoupling processing and PI regulation, the compensated control quantity is obtained. This control quantity is then transformed back to the abc coordinate system through the inverse dq coordinate transformation to obtain the reference values Uref of the three-phase voltages for the generation of pulse signals. Through Z-source SPWM modulation, the reference voltage Uref is converted into pulse signals for controlling the on and off of the inverter switching tubes, thereby achieving closed-loop voltage control. This modulation method can flexibly generate pulse signals according to the given reference voltages (i.e., ud* and uq*), ensuring the stability of the output voltage of the inverter and reaching the predetermined target. Through this dual-loop control strategy, the voltage outer loop ensures the precise stability of the output voltage and adapts to different load changes; while the current inner loop improves the dynamic response ability, quickly adjusts the current, and prevents current overshoot and overpunch phenomena.

[0052] Preferably, the first direct current is 100V; the first alternating current is 300V, 1kHz; the second alternating current is 3kV, 1kHz.

[0053] Please refer to Figures 7 to 12 , to verify the correctness of the topology and control strategy proposed in this paper, a simulation model of a Z-source based flexible DC power transmission system is built in Matlab / Simulink. The designed power of the converter is 10kVA, the rated operating frequency is 1kHz, and the transformer step-up ratio is 1:10. In this simulation platform, the modulation strategy of the converter and the power transmission control strategy are respectively simulated and analyzed.

[0054] During the simulation process of the modulation strategy, to verify the correctness under SPWM modulation, by setting the DC side voltage to 100V, the switching frequency to 50kHz, the modulation index M = 0.556, and the shoot-through duty ratio D = 0.444, after boosting by the Z-source inverter, the corresponding modulation waveform of switch S1 is as Figure 7 shown, and the output line voltage is as Figure 8 shown. From the waveforms of Figure 8 and Figure 9 , it can be seen that after boosting by the Z-source inverter, the peak value of the output line voltage is approximately U ab = 424V, the frequency is at 1kHz, and its effective value is approximately 300V, which is almost the same as the theoretical value. After passing through a high-frequency transformer with a turns ratio of 1:10 and a frequency of 1kHz, 3kV high-frequency alternating current can be obtained. The simulation results can verify the effectiveness and stability of the Z-source inverter under SPWM modulation during the boosting process. The results show that the inverter can not only convert a low-voltage DC power supply into a high-voltage alternating current, but also achieve an ideal voltage gain and frequency output.

[0055] During the simulation of the power transmission control strategy, the symmetric Z-source power transmission structure can be equivalent to an AC bus under voltage control, and power transmission simulation tests can be further carried out by changing the current. During the simulation, when starting to work, the power delivered by the converter is set to 5 kW. At the moment of 0.01 s, the active current delivered is changed from 5 A to 10 A, and at 0.015 s, the delivered power is changed to 0 A. The reactive current is set to 0 at the initial moment, set to 2 A at 0.0125 s, and changed to 0 A at 0.0175 s. In the simulation waveforms, Figure 9 is the AC bus voltage waveform, Figure 10 is the three-phase current waveform on the converter side, Figure 11 and Figure 12 are the d-axis and q-axis components of the current on the converter side respectively. It can be seen from the simulation results that the topological structure and control strategy of the lunar flexible power transmission and transformation system of the present invention can achieve stable control of the AC voltage of the flexible power transmission system and power transmission control.

[0056] Such as Figure 13 and Figure 14 , in an embodiment of the present invention, the lunar flexible power transmission and transformation system further includes: a second Z-source network 11, the first end of the second Z-source network 11 is connected to the second DC power supply 51; a second inverter 21, the DC end of the second inverter 21 is connected to the second end of the second Z-source network 11; a second high-frequency transformer 31, the first end of the second high-frequency transformer 31 is connected to the AC end of the second inverter 21, and the second end of the second high-frequency transformer 31 is connected to the second end of the first high-frequency transformer 30; a second controller 41, the second controller 41 is connected to the control end of the second inverter 21.

[0057] In this embodiment, in the lunar flexible power transmission and transformation system of the present invention, by connecting the first DC power supply 50 to the first end of the first Z-source network 10, the second end of the first Z-source network 10 is connected to the DC end of the first inverter 20, and the AC end of the first inverter 20 is connected to the first end of the first high-frequency transformer 30; then through the second end of the first high-frequency transformer 30 is connected to the second end of the second high-frequency transformer 31, the first end of the second high-frequency transformer 31 is connected to the AC end of the second inverter 21, the DC end of the second inverter 21 is connected to the second end of the second Z-source network 11, and the first end of the second Z-source network 11 is connected to the second DC power supply 51. Thus, bidirectional flow of energy from the first Z-source network 10 → the first inverter 20 → the first high-frequency transformer 30 → the second high-frequency transformer 31 → the second inverter 21 → the second Z-source network 11, and from the second Z-source network 11 → the second inverter 21 → the second high-frequency transformer 31 → the first high-frequency transformer 30 → the first inverter 20 → the first Z-source network 10 can be achieved.

[0058] For example, after converting the 100V DC power of the first DC power supply 50 into 300V, 1kHz high-frequency AC power through the Z-source inverter composed of the first Z-source network 10 and the first inverter 20, the alternating current of 3kV can be obtained through the high-frequency transformer with a turns ratio of 1:10 of the second high-frequency transformer 31. Further, according to the bidirectional flow of energy, the symmetric structure of the second high-frequency transformer 31, the second inverter 21, and the second Z-source network 11 can be sequentially passed through to convert 3kV alternating current into 100V DC power and then output it.

[0059] In an embodiment of the present invention, the second Z-source network 11 may adopt the same structure as the first Z-source network 10, the second inverter 21 may adopt the same structure as the first inverter 20, and the second high-frequency transformer 31 may adopt the same structure as the first high-frequency transformer 30, which will not be elaborated here.

[0060] In an embodiment of the present invention, the first controller 40 is used to modulate the direct-conduction state of the first inverter 20 according to the output current and output voltage of the first inverter 20 within a time period, and control the first inverter 20 to alternately switch between the direct-conduction state and the non-direct-conduction state according to the direct-conduction state. Similarly, the second controller 41 also adopts the same control method as the first controller 41, which will not be elaborated here.

[0061] Preferably, in order to ensure the structural symmetry with the first filter network 60, the AC terminal of the second inverter 21 is connected to the first end of the second high-frequency transformer 31 through the second filter network 61. The second filter network 61 may adopt the same structure as the first filter network 60, which will not be elaborated here.

[0062] Further, in order to achieve bidirectional controllability when realizing the bidirectional flow of energy between the first microgrid and the second microgrid, the lunar flexible power transmission and transformation system further includes an eighth switching tube. The first end of the eighth switching tube is connected to the positive terminal of the second DC power supply 51, the second end of the eighth switching tube is connected to the positive terminal of the second Z-source network 11, and the control terminal of the eighth switching tube is connected to the second controller 41. The control process of the eighth switching tube is the same as that of the seventh switching tube S 7 which will not be elaborated here.

[0063] Please refer to Figure 15, in an embodiment of the present invention, the first DC power supply 50 is the first microgrid; the second DC power supply 51 is the second microgrid. Among them, the first microgrid includes a photovoltaic unit, a small nuclear power unit, an energy storage unit, and the living load of the lunar base; the second microgrid includes an energy storage unit, a photovoltaic unit, a fuel cell, a lunar rover, a scientific research load, and a communication load. The first microgrid, that is, microgrid A, outputs alternating current through the power router A, and the second microgrid, that is, microgrid B, outputs alternating current through the power router B, and they are interconnected through the power router A and the power router B to form a two-way flow of energy. Specifically, the power router A can output alternating current through the first Z-source network 10, the first inverter 20, the first high-frequency transformer 30 and under the control of the first controller 40, and the power router B can output alternating current through the second Z-source network 11, the second inverter 21, the second high-frequency transformer 31 and under the control of the second controller 41.

[0064] In summary, a lunar flexible power transmission and transformation system disclosed by the present invention can, by using a Z-source inverter composed of a Z-source network and an inverter, realize boosting a low-voltage DC to a high-voltage AC first alternating current through a single-stage conversion, avoiding the need for additional boosting devices. After the Z-source inverter, through a high-frequency transformer, the first alternating current can be boosted to a higher voltage level to meet the application scenario requirements of using a 3kV / 1kHz AC transmission mode for long-distance power transmission in the lunar environment, and then through the single-stage power conversion topology structure adopted above, compared with the traditional two-stage solution of DC boosting and then inversion, the operation efficiency can be improved and the equipment cost can be reduced. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0065] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A lunar flexible power transmission and transformation system, characterized in that: include: A first Z source network, wherein a first end of the first Z source network is connected to a first DC power source; A first inverter, wherein a DC terminal of the first inverter is connected to a second terminal of the first Z source network; a first high-frequency transformer, wherein a first end of the first high-frequency transformer is connected to an AC end of the first inverter; a first controller connected to a control end of the first inverter, the first controller being used to modulate a through state of the first inverter according to an output current and an output voltage of the first inverter within a time period, and to control the first inverter to alternately switch between the through state and the non-through state according to the through state; Among them, when the first inverter is in a direct-flow state, the first input direct current is boosted to a second direct current through the first Z source network; when the first inverter is in a non-direct-flow state, the second direct current is converted into a first alternating current through the first inverter, and the first alternating current is boosted to a second alternating current through the first high-frequency transformer and then output.

2. The lunar surface flexible power transmission and transformation system according to claim 1 is characterized in that: The first inverter is a three-phase inverter, and the first inverter includes three bridge arms, a first end of each bridge arm is connected to the positive terminal of the first Z source network, and a second end of each bridge arm is connected to the negative terminal of the first Z source network.

3. The lunar surface flexible power transmission and transformation system according to claim 2 is characterized in that: The first Z source network comprises: A first capacitor, a second capacitor, a first inductor, and a second inductor; The positive terminal of the first capacitor and the negative terminal of the second capacitor are connected to the positive terminal of the first inductor, and the positive terminal of the first inverter is connected between the negative terminal of the first inductor and the positive terminal of the second capacitor; the positive terminal of the first capacitor and the negative terminal of the second capacitor are connected to the positive terminal of the second inductor, the negative terminal of the first inverter is connected between the negative terminal of the first capacitor and the positive terminal of the second inductor, the positive terminal of the first capacitor and the positive terminal of the first inductor are connected to the positive terminal of the first DC power supply, and the negative terminal of the second capacitor and the negative terminal of the second inductor are connected to the negative terminal of the first DC power supply.

4. The lunar surface flexible power transmission and transformation system according to claim 2 is characterized in that: The AC end of the first inverter is connected to the first end of the first high-frequency transformer through a first filtering network.

5. The lunar surface flexible power transmission and transformation system according to claim 1 is characterized in that: The lunar flexible power transmission and transformation system also includes a seventh switch tube, a first end of the seventh switch tube is connected to the positive end of the first DC power supply, a second end of the seventh switch tube is connected to the positive end of the first Z source network, and a control end of the seventh switch tube is connected to the first controller.

6. The lunar surface flexible power transmission and transformation system according to claim 1 is characterized by: The first controller comprises: a modulation unit, configured to modulate a through duty ratio of the first inverter in a through state within a time period by SPWM modulation according to two set constant voltage values ​​whose absolute values ​​are greater than or equal to the peak value of the sine wave; and A control unit is used to obtain a corresponding modulation signal according to a given voltage and current, calculate a corresponding through-duty ratio, and control the first inverter to switch alternately between a through-state and a non-through-state according to a through-state corresponding to the through-duty ratio.

7. The lunar surface flexible power transmission and transformation system according to claim 1 is characterized in that: The first direct current is 100V; the first alternating current is 300V, 1kHz; the second alternating current is 3kV, 1kHz.

8. The lunar surface flexible power transmission and transformation system according to claim 1 is characterized by: The lunar surface flexible power transmission and transformation system also includes: a second Z source network, wherein a first end of the second Z source network is connected to a second DC power source; a second inverter, wherein a DC terminal of the second inverter is connected to a second terminal of the second Z source network; a second high-frequency transformer, wherein a first end of the second high-frequency transformer is connected to an AC end of the second inverter, and a second end of the second high-frequency transformer is connected to a second end of the first high-frequency transformer; A second controller is connected to a control end of the second inverter.

9. The lunar surface flexible power transmission and transformation system according to claim 8 is characterized in that: The first DC power supply is a first microgrid; the second DC power supply is a second microgrid.

10. The lunar surface flexible power transmission and transformation system according to claim 9, characterized in that: The first microgrid includes photovoltaic units, small nuclear power units, energy storage units and living loads of the lunar base; the second microgrid includes energy storage units, photovoltaic units, fuel cells, lunar rovers, scientific research loads and communication loads.

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