A microwave rectifier terminal energy management method based on GMPPT technology

Abstract

The present invention discloses a method for energy management at the microwave rectifier end based on GMPPT technology, belonging to the technical field of computing, extrapolating or counting. The method includes the following steps: analyzing the output external characteristics of a single microwave rectifier circuit to establish a voltage source model; paralleling multiple microwave rectifier circuits and analyzing the relationship between the total power and the output voltage; based on the electrical characteristics after paralleling multiple microwave rectifier circuits, proposing to add GMPPT technology to the microwave DC energy management to achieve the effect of optimizing the overall efficiency. The present invention realizes the optimized management of DC energy at the microwave rectifier end, reduces the volume and complexity, lowers the cost, and improves the system efficiency.

Description

Technical Field

[0001] The present invention discloses a microwave rectifier terminal energy management method based on GMPPT (Global Maximum Power Point Tracking) technology, belonging to the technical field of calculation, extrapolation or counting. Background Art

[0002] Microwave power transmission (MPT) is a technology for transmitting electrical energy through electromagnetic waves in free space. It is the key to the research of space solar power stations and also has application prospects in powering high-altitude aircraft such as stratospheric airships and unmanned aerial vehicles, as well as micro and small robots. Since microwave electrical energy is wirelessly transmitted in free space with relatively small transmission losses, and the only losses affecting the transmission efficiency are natural losses such as the atmosphere, microwave technology is currently one of the research hotspots at home and abroad and has broad development prospects in the military, aerospace and other fields.

[0003] A microwave power transmission system mainly consists of three parts: a microwave transmitting end, free space, and a microwave receiving end. The microwave receiving end is an important part of the MPT system, used to realize the conversion of microwave to direct current electrical energy and the subsequent stage energy management. Its efficiency is crucial for the entire system. The general structure is as Figure 1 shown, mainly including: a receiving antenna, a rectifying circuit, a direct current energy management circuit, and a direct current load. Since most receiving antennas are array-type, a rectifying circuit board is connected behind each antenna to convert microwave into direct current, and then power needs to be supplied to the direct current load. Currently, most research focuses on how to improve the efficiency of the rectifying circuit, and there is less research on the subsequent stage direct current energy management, and most of them are distributed management, that is, a management module is added behind each receiving rectifying circuit, often with a large structure and complex algorithms. Therefore, there is an urgent need for a centralized microwave rectifier terminal energy management method applicable to multiple outputs to realize the optimization management of the subsequent stage energy, thereby further improving the overall efficiency of the receiving end. Summary of the Invention

[0004] The invention purpose of the present invention is to address the deficiencies of the above background art and propose a microwave rectifier terminal energy management method based on GMPPT technology. This method establishes a model through the analysis of the external characteristics of a single rectifying circuit, analyzes the overall law of power characteristics when multiple circuits are connected in parallel, and finally adds GMPPT technology to seek the optimal output power point in the case of multiple peaks, thereby forming a direct current energy management circuit, improving the rectifier terminal efficiency, and solving the technical problems of the large circuit structure and complex algorithm of the existing distributed energy management method for microwave receiving ends.

[0005] The present invention adopts the following technical solutions to solve its technical problems:

[0006] A microwave rectifier terminal energy management method based on GMPPT technology includes the following three steps.

[0007] (1) Analyze the output external characteristics of a single microwave rectifier circuit to establish a voltage source model:

[0008] Use the experimental data of the rectifier circuit obtained by testing to plot the external characteristic curve of the circuit. After analyzing its electrical characteristics, the microwave rectifier circuit is equivalent to a voltage source, that is, equivalent to a structure in which an ideal voltage source is connected in series with the internal resistance of the voltage source.

[0009] (2) Parallel multiple microwave rectifier circuits and analyze the relationship between the total power and the output voltage:

[0010] Adopt a structure in which diodes are connected in series on different branches and then the branches are paralleled to automatically adapt to the load change. Combining MATLAB simulation, the output voltage range can be divided into several intervals, and there is exactly one peak point in each interval.

[0011] (3) Based on the electrical characteristics after parallel connection of multiple microwave rectifier circuits, propose to add GMPPT technology to the microwave DC energy management. First, track the local maximum power point in each interval of the output voltage, and then track the global maximum power point to achieve the effect of optimizing the overall efficiency.

[0012] According to the characteristic analysis after parallel connection of multiple rectifier circuits, adopt a centralized management method. Add an active control Buck converter after the circuit, and use a chip to implement the global maximum power point tracking technology from interval to overall.

[0013] The present invention adopts the above technical solutions and has the following beneficial effects:

[0014] (1) Cost advantage: Compared with the distributed DC energy management, the present invention adopts a centralized parallel rectifier circuit structure, reduces the number of converters, saves redundant electrical components, and greatly reduces the size and complexity of the structure, thereby reducing the cost.

[0015] (2) Performance advantage: Compared with the traditional microwave rectification method that does not manage the multiple DC energies, resulting in energy waste and design difficulties, the present invention optimizes the management by paralleling multiple rectifier circuits. The present invention controls the output power by adding an active converter, which is more universal than the traditional single power point design. Adding the idea of GMPPT to the microwave rectifier terminal has innovation and development.

[0016] (3) Modular and easy to integrate: The solution given by the present invention is conducive to modular implementation. The specific implemented hardware circuits, chips, etc. are relatively mature in the communication field, and subsequent chip design is easy to achieve. Description of the Drawings

[0017] Figure 1 It is the general structure diagram of the microwave wireless power transmission receiving - end system.

[0018] Figure 2 It is the overall block diagram of the microwave rectifier - end energy management method based on GMPPT proposed by the present invention.

[0019] Figure 3 It is the external characteristic curve of the microwave rectifier circuit obtained by testing.

[0020] Figure 4 It is the external characteristic curve of the ideal voltage source.

[0021] Figure 5 It is the equivalent circuit model of a single - piece microwave rectifier circuit.

[0022] Figure 6 It is the topological schematic diagram of the parallel rectifier circuit.

[0023] Figure 7 It is the P - V relationship curve of a single rectifier board and the overall P - V relationship curve after parallel connection.

[0024] Figure 8 It is the centralized energy management structure diagram.

[0025] Figure 9 It is the schematic diagram of finding the maximum power point by the perturbation and observation method.

[0026] Figure 10 It is the algorithm flowchart of the local maximum power point tracking technology.

[0027] Figure 11 It is the algorithm flowchart of the global maximum power point tracking technology. Specific implementation manner

[0028] A microwave rectifier - end energy management method based on GMPPT technology proposed by the present invention. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention will be further described in detail with reference to the accompanying drawings. 1. Modeling of a single rectifier circuit at the receiving end

[0029] To combine the energies of each microwave rectifier circuit to form a centralized management, it is necessary to study the DC external characteristics of a single - piece microwave rectifier circuit. The external characteristics of the rectifier circuit are tested by adjusting the load of the rectifier circuit at the same power level, and the obtained results are as Figure 3 shown. From this external characteristic curve, it can be seen that the output voltage U o and the output current I o can be approximately fitted into a straight line with a fixed slope. Therefore, the external characteristics of the microwave rectifier circuit to the outside can be equivalent to a DC voltage source. The external characteristic curve of the ideal voltage source model is as Figure 4 shown, and the intersection point of the curve and the vertical axis is the no - load voltage US As the load current increases, the voltage loss across the internal resistance increases, and the load voltage will continuously decrease until it reaches 0. At this time, the circuit is in a short - circuit state. Therefore, the intersection point of the curve and the abscissa is the short - circuit current I S , and the slope of the curve is the internal resistance R of the voltage source S , R s =U s / I s . According to this rule, a single - block microwave rectification circuit can be equivalent to a voltage - source model in which an ideal voltage source and an internal resistance are connected in series as shown in Figure 5 . The voltage of the voltage source is U S , and the internal resistance is R S , U S is related to R S and the parameters of the microwave rectification circuit itself. These parameters of different circuits can be measured through experiments. The rectification circuit is connected in series with the load R L , so the current in the circuit is all I S . The established single - block rectification circuit board model provides a theoretical basis for the analysis of the total power characteristics after parallel connection in the following text.

[0030] 2. Analysis of the power characteristics after parallel connection of rectification circuit boards

[0031] (1) Analysis of the parallel - circuit connection method: Since the energy received by each antenna is different and it is impossible to achieve a completely balanced effect, the voltages obtained after each rectification circuit board connected to the antenna are also different. Therefore, parallel operation cannot be directly carried out, otherwise it will cause a short - circuit between power supplies. In the present invention, a structure of adding diodes on different branches is adopted, as shown in Figure 6 . This structure can automatically adapt to load changes, that is, when the load current is low, only the branch with the maximum received power conducts to supply power. As the load current increases, due to the load effect of the voltage source, the output voltage decreases. When the load current increases to make the output voltage decrease to the open - circuit voltage of the second - highest - power path, as shown in Figure 6 , the diode of this path conducts, and the two branches jointly provide energy for the load. Similarly, when the load further increases and the output voltage further decreases, new series branches will conduct. Through such a parallel connection method, the receiving end can automatically adjust the number of parallel branches according to the load needs, achieving the purpose of automatically adapting to the load needs.

[0032] (2) Analysis of the power characteristics of the parallel circuit: Derive the power formula of each rectification circuit board from the equivalent voltage - source model of a single - block rectification circuit board. Given that the rectification board is a voltage source, the relationship between the output voltage and the output current forms equation (1):

[0033] U i =-R Si *I i +U Si(1)

[0034] Let I i be represented by U i for the convenience of simplifying calculations, as shown in Equation (2):

[0035]

[0036] After multiplying the voltage and current, the power formula of a single rectifier plate is obtained, as shown in Equation (3):

[0037]

[0038] Among them, U i represents the output voltage of the i-th rectifier plate, I i represents the output current of the i-th rectifier plate, P i represents the output power of the i-th rectifier plate, U Si represents the open-circuit voltage of the equivalent voltage source of the i-th rectifier plate, I si represents the short-circuit current of the equivalent voltage source of the i-th rectifier plate, R Si represents the internal resistance of the equivalent voltage source of the i-th rectifier plate, i = 0, 1, 2,... n, and n represents the number of blocks of the receiving antenna array.

[0039] To facilitate the analysis of the total power of the parallel rectifier circuit, the total power P is calculated by taking the m-th, p-th, and k-th rectifier plates among n rectifier plates total (m, p, k = 0, 1, 2,... n, and m ≠ p ≠ k), as shown in Equation (4):

[0040]

[0041] Assume U Sm > U Sp > U Sk , the power (P i )-voltage (V) curves of each rectifier plate and the overall power (P total )-voltage (V) curve after parallel connection are plotted in the MATLAB software as Figure 7 shown.

[0042] From Equations (3) and (4), it can be seen that the P i -V curves of each rectifier plate are quadratic curves, and the intersection points with the abscissa are (0, 0), (U Si , 0), Figure 7 Among them, the P i -V simulation curves of the m-th, p-th, and k-th rectifier plates are represented by diamond, triangle, and square curves respectively, which are consistent with the formula analysis. The circular curve represents the P-V curve of the sum of the three rectifier plates, and the abscissas are U Sk and U SpAn inflection point occurs, and the changing trend of the curve can be divided into three parts according to the abscissa range: (0, U Sk ), (U Sk , U Sp ), and (U Sp , U Sm ). Each part of the curve has exactly one peak point, and the total power curve has three peak points. By comparing these three peak points, the maximum power point of the curve can be obtained.

[0043] 3. Analysis of the global maximum power point tracking algorithm

[0044] Based on simulation and experimental experience, the present invention uses a Buck circuit as an active DC-DC converter to regulate the final output power. The present invention performs energy management after all rectifier circuits are connected in parallel. Therefore, a centralized circuit topology is adopted as shown in Figure 8 . The multiple microwave rectifier circuits shown in Figure 2 are equivalent to a voltage source model in series with a diode and then connected in parallel to the input end of the Buck circuit. The output end of the Buck circuit is connected to the final DC load R L . The voltage and current at the input and output ends of the Buck circuit are collected respectively, and algorithms and PI regulation are performed in a DSP (Digital Signal Processing) controller. Finally, the overall circuit can be adjusted to the maximum power transfer point, realizing the optimization management of the energy after the rectifier stage.

[0045] As analyzed above, the power characteristic curve of the overall rectifier circuit after parallel connection may have multiple peak points. However, the region can be divided according to the abscissa, and the local maximum power points can be found in different regions in turn. Then, by comparing them in turn, the global maximum power point can be obtained.

[0046] The present invention uses the perturbation and observation method to find the local maximum power point. The perturbation and observation method, as the name implies, requires applying an external perturbation to the controlled circuit to cause a corresponding change in its output voltage. Then, the output voltage and output power of the circuit after applying the external perturbation are sampled, and the next judgment is made after observing the changing trends of both. Its working principle is as shown in Figure 9 . The specific idea is: by adjusting the number of branches connected to the input end of the Buck converter to apply a perturbation to the input signal of the Buck converter. If the applied perturbation causes the output voltage to increase and the output power also increases accordingly, as shown in the process from P a to P b in the figure, then it is considered that the direction of the perturbation is correct. Therefore, continue to apply the perturbation in the same direction to make the output voltage continue to increase. If the applied perturbation causes the output voltage to increase, but the output power decreases accordingly, as shown in the process from P c to P dIf the process is such that the disturbance direction is considered incorrect, the disturbance is applied in the reverse direction to reduce the output voltage; and vice versa. Following this idea, the values of the output voltage and output current are detected at fixed time intervals, and the next control direction is determined based on the results of observation and comparison. The above process is repeated until the output power approaches the maximum power point.

[0047] In the continuous inductor current state of the Buck converter, the input-output relationship is as shown in Equation (5):

[0048]

[0049] Among them, U o is the output voltage, I o is the output current, U in is the input voltage, I in is the input current, and D is the duty cycle of the converter. Only by obtaining U in and I in of the converter through the sampling circuit can its P in be calculated. Then, U in is sent to the DSP chip and compared with the reference value U in_ref . Subsequently, after PI regulation, the required duty cycle signal is output to the switching tube of the converter, thereby completing the closed-loop control of U in .

[0050] U in_ref is obtained by the DSP through algorithm calculation, and its specific algorithm flow is as shown in Figure 10 and Figure 11 . First, calculate the maximum power points in the three intervals of the abscissa (0, U Sk ), (U Sk , U Sp ), (U Sp , U Sm ) respectively, as shown in Figure 10 : Set the initial search range (U min , U max ) of the input voltage and the initial step size step, and assume that the optimization order is from small to large for search. Then, starting from the minimum value U min , compare the magnitudes of the output power P corresponding to U i and U (i-1) Ui and P U(i-1) . If P U(i-1) is less than P Ui , then increment i by one, that is, replace U i with U (i-1) , replace U (i+1) with U i , and continue to compare P U(i+1) with PUi The size changes in a cycle, and its subsequent idea is basically the same as that of the perturbation observation method. However, different from the traditional perturbation observation method, if the change in the input voltage value causes the operating point of the rectifier circuit to cross the maximum power point, such as Figure 9 P in e changes to P f In the case of, U min =U (i-2) , U max =U (i-1) , step = step / 10, then the search range of the input voltage will be reduced to between the previous two search values, and the search step size will be correspondingly reduced to improve the search accuracy. When the difference between the upper and lower limits of the search range is less than 3, it can be considered that half of the sum of the previous two voltage search values is the optimal voltage U optimal of the pre-stage rectifier circuit, U optimal = 0.5*(U max +U min ) = 0.5*(U (i-1) +U (i-2) ), U optimal is the final given value of the input voltage of the Buck converter, thus ending this search. Compared with the traditional perturbation observation method, the algorithm adopted in the present invention will reduce the search range and step size of the maximum power point as the maximum power point is approached, and will end the search when the control accuracy requirement is met, so the control accuracy is relatively high and there is no problem of power oscillation. The three maximum power point coordinates obtained by this algorithm are (U1, P1), (U2, P2), (U3, P3). Input these three sets of data into the Figure 11 algorithm shown, and after pairwise comparison of the powers, the voltage value corresponding to the maximum power point is obtained, that is, the reference value U in_ref required for PI regulation.

[0051] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A microwave rectifier terminal energy management method based on GMPPT technology, characterized in that Analyze the electrical characteristics of the microwave rectifier circuit, equivalently represent multiple microwave rectifier circuits as a voltage source model branch respectively, analyze the parallel voltage source model branches to obtain the relationship between the total output power of the parallel branches and the output voltage of each branch, and connect each voltage source model branch in parallel at the input end of the Buck converter; According to the relationship between the total output power of the parallel branches and the output voltage of each branch, and adopt the maximum power point tracking technology to adjust the number of voltage source model branches connected to the input end of the Buck converter. The specific method is: obtain the division of the output voltage range of the Buck converter by the open-circuit voltage of each branch according to the relationship between the total output power of the parallel branches and the output voltage of each branch, divide the output voltage range of the voltage Buck converter into intervals corresponding to the number of branches according to the open-circuit voltage of the connected branches, search for the given value of the input voltage of the Buck converter corresponding to the maximum power point of each interval, and select the maximum value among the given values of the input voltage of the Buck converter corresponding to the maximum power point of each interval as the given value of the input voltage of the Buck converter; Among them, the specific method for searching for the given value of the input voltage of the Buck converter corresponding to the maximum power point of each interval is: starting from the minimum value of the input voltage of the Buck converter, gradually increase the number of voltage source model branches connected in parallel at the input end of the Buck converter. For each increase in a voltage source model branch, compare the current output voltage of the Buck converter with the output voltage of the Buck converter after the previous adjustment of the number of voltage source model branches, and compare the current output power of the Buck converter with the output power of the Buck converter after the previous adjustment of the number of voltage source model branches. When the output power of the Buck converter after the previous adjustment of the number of voltage source model branches is less than the current output power of the Buck converter, continue to increase the number of voltage source model branches connected in parallel at the input end of the Buck converter. When the output power of the Buck converter exceeds the maximum power point, search for the given value of the input voltage of the Buck converter between the output voltages of the Buck converter after the previous two adjustments of the number of voltage source model branches; The specific method for searching for the given value of the input voltage of the Buck converter between the output voltages of the Buck converter after the previous two adjustments of the number of voltage source model branches is: When the difference between the output voltages of the Buck converter after the previous two adjustments of the number of voltage source model branches is less than 3, take half of the sum of the output voltages of the Buck converter after the previous two adjustments of the number of voltage source model branches as the given value of the input voltage of the Buck converter, When the difference between the output voltages of the Buck converter after the previous two adjustments of the number of voltage source model branches is greater than or equal to 3, reduce the search step size, start from the minimum value of the input voltage of the Buck converter, and readjust the number of voltage source model branches connected to the input end of the Buck converter.

2. The method for microwave rectifier end energy management based on the GMPPT technology according to claim 1, wherein The voltage source model branch is a branch where a voltage source is connected in series with its internal resistance, and the parameters of the voltage source and its internal resistance are measured through experiments.

3. The method for microwave rectifier terminal energy management based on the GMPPT technology according to claim 1, characterized in that, The voltage source model branch is connected in series with a short-circuit prevention diode.

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