Wireless electric energy transmission system suitable for industrial environment

Abstract

The invention provides a wireless electric energy transmission system suitable for an industrial environment, and solves the limitation of an industrial sensor in traditional wired charging and complex industrial environments. According to the system, constant voltage output and maximum efficiency tracking (MET) control are realized under the conditions of load change and coupling coefficient fluctuation by accurately adjusting the duty ratio D of a DC-DC converter at a transmitting end and the phase shift angle alpha of a semi-active rectifier (SAR) at a receiving end. The optimized control strategy enables the system to stably operate in a dynamic environment, ensures efficient and stable charging, and reduces the risks of wired interface damage and unstable charging. Compared with traditional wired charging, the wireless charging device overcomes the adaptability problem in severe environments such as high temperature, high humidity, high vibration and narrow space, avoids complex cable layout and maintenance cost, is widely applied to the fields of industrial sensors, power equipment and the like, is particularly suitable for scenes needing efficient wireless charging and constant voltage output, and has wide application prospects. The equipment operation stability and the production efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission. More specifically, a wireless power transmission system applicable to industrial environments is disclosed. Background Art

[0002] With the continuous improvement of industrial automation and intelligence, more and more industrial equipment and sensors require stable and efficient power supply, especially the application requirements in harsh environments such as high temperature, high humidity, and vibration are becoming more prominent. Although traditional wired charging systems have certain advantages in terms of stability, they have many disadvantages in industrial environments. First of all, due to the harsh working environment, traditional wired charging systems are prone to problems such as cable damage, interface loosening, or voltage instability, resulting in system failures or downtime, seriously affecting the continuity of production and the stability of equipment. Especially in high-temperature and high-humidity environments, cables will age faster due to overheating or moisture, resulting in unstable electrical connections and increasing the risk of equipment failures. In addition, high temperatures will cause an increase in the internal resistance of the battery, a decrease in charging efficiency, and even lead to battery overheating or safety accidents. High-humidity environments will cause internal corrosion of the battery, an increase in the risk of electrolyte leakage or short circuits. Secondly, the wiring of wired charging systems is cumbersome, and the installation and maintenance costs are high. Especially in scenarios where charging equipment needs to be adjusted or replaced frequently, the management difficulty increases. Moreover, in high-temperature and high-humidity environments, cables and connectors will be damaged, further increasing the frequency of maintenance and replacement, and further increasing the operating costs of the system.

[0003] In recent years, wireless power transmission (WPT) technology, as an emerging energy transmission method, has gradually received attention in industrial applications. WPT systems transmit energy through electromagnetic waves, which can avoid many problems brought by traditional wired charging methods. Especially in harsh industrial environments, it can effectively reduce equipment failure rates and maintenance costs. However, most existing WPT systems have a problem: when the load resistance or coupling coefficient changes, how to simultaneously achieve constant voltage output and maximum efficiency transmission is still a technical problem. Existing WPT systems often cannot achieve a balance between efficiency and stability when dealing with load changes or coupling coefficient fluctuations, resulting in low charging efficiency or unstable voltage, affecting the normal operation of industrial equipment. In addition, when the load is damaged, wired charging is difficult to ensure the stability and integrity of the charging system, which will lead to power transmission interruption or equipment damage. Summary of the Invention

[0004] To solve the above problems, how to provide a stable voltage output without affecting the system efficiency and adapt to the changes in different industrial environments has become the key technology that the wireless power transmission system needs to overcome. In response to this challenge, the present invention proposes a bilateral control scheme, which combines synchronous rectification (DC-DC) at the transmitting end and a semi-active rectifier (SAR) at the receiving end. By precisely controlling the duty cycle and phase shift angle, a constant voltage output and maximum efficiency transmission are always maintained under load changes and coupling coefficient fluctuations. Specifically, the present invention adjusts the phase shift angle of the SAR α to maintain a constant voltage output, thereby ensuring the stability of the system; at the same time, by adjusting the duty cycle of the DC-DC converter at the transmitting end D , the system can maintain an optimal match between the input power and the output power, maximizing the system transmission efficiency.

[0005] To achieve the above object, the present invention adopts the following technical solutions: a wireless power transmission system applicable to industrial environments. The method includes the following steps: S1. Establish a mathematical model according to the proposed wireless power transmission system; S2. Analyze the system efficiency according to the mathematical model obtained in S1; S3. Implement MET control analysis on the system according to the efficiency analysis result obtained in S2; S4. Propose a bilateral control scheme according to the MET control analysis result obtained in S3; Further, the establishment of the mathematical model described in S1 includes the following steps: S11. Based on the topological principle, the output voltage of the high-frequency inverter (HFI) U i and the input voltage of the semi-active rectifier (SAR) U O The effective values can be expressed as: ;

[0006] In the formula: θ , α , are the conduction angles of the high-frequency inverter (HFI) and the semi-active rectifier (SAR) respectively, D , U dc and U D are the duty cycle, output voltage and input voltage of the DC-DC converter respectively. In order to make the transmitting end of the system work in the quasi-resonant state, the conduction angle θ of the HFI takes 180°, so .

[0007] S12. R OFor the equivalent resistance of the SAR and the load ( R B ), it can be expressed as: ;

[0008] S13. According to Kirchhoff's law, the mathematical model of the SS compensation network can be obtained: ; In the formula: L P , L S are the self - inductances of the coupling coils, M is the mutual inductance of the coupling coils; C P , C S are the compensation capacitors in the SS compensation network, R P , R S are the parasitic resistances in the coupling coils, I i is the effective value of the input current of the primary coil, I O is the effective value of the output current of the secondary coil, where , f is the power transmission frequency.

[0009] Furthermore, the analysis of the system efficiency described in S2 includes the following steps: S21. To make the system work in the resonant state, the parameter design of the SS compensation network should meet the following requirements:

[0010] S22. Substituting the mathematical model described in S21 into S13, the expression of the effective values of the input and output currents of the coil can be obtained as: ; S23. The input - output power of the coupling mechanism can be expressed as: ; where P i is the input power, P O is the output power.

[0011] S24. Based on the power expression, the power transmission efficiency of the electric energy can be obtained as: ; S25. Based on the efficiency formula, for the equivalent impedance R OBy taking the derivative and setting it to zero, the optimal equivalent impedance corresponding to the maximum efficiency point of the system can be obtained. R O -opt, Its expression is: ; From the above formula, it can be seen that when the parameters of the coupled coils are determined, the optimal equivalent load impedance corresponding to the maximum efficiency of the system R O -opt will change with the mutual inductance M . This means that due to the offset of the coupled coils or other factors, the mutual inductance M changes, R O -opt it will no longer remain constant. Therefore, in order to make the system always work at the optimal efficiency state, it is necessary to continuously track the optimal equivalent load impedance.

[0012] Furthermore, the steps for MET control analysis of the system according to S3 are as follows: S31. Based on the SAR topology, the following equation should be satisfied according to the principle of power conservation: ; In the formula: U B is the output voltage of SAR.

[0013] S32. According to S22 and S31, the effective value of the HFI output voltage can be expressed as: ; S33. Substituting S12 into S32, we can get U i and U B The relationship between them is: ; S34. Substituting S11 into S33, we can get D and The relationship between them is: ; S35. By differentiating D with respect to the following equation can be obtained: ; S36. When the system works at the optimal equivalent load point, combining S12 and S25, the that makes the system work at the maximum efficiency point can be deduced: ; S37. Substituting S36 into S35 gives the duty cycle of the transmitter - side DC - DC converter at the maximum efficiency point D and the conduction angle of the receiver - side SAR α The mathematical expression of the optimal functional relationship between them is as follows: ; S38. As can be seen from S37, the derivative at the optimal equivalent impedance point where the system operates at maximum efficiency is R B independent of the load Therefore, the mathematical expression can be approximately simplified to: ; Therefore, from the mathematical expression, it can be concluded that the derivative at the maximum efficiency point of the system is related to the input and output DC voltages and the parasitic resistance of the coupling coil. When the system input DC voltage U D is kept constant, by adjusting the phase - shift angle α of the receiver - side SAR, the output DC voltage U B of the system can be kept constant, where R P , R S are also constant. Therefore, for the system proposed in the present invention, when the system transmission efficiency reaches the maximum value, the derivative is always a fixed value δ and is not affected by the changes in mutual inductance and load resistance.

[0014] Furthermore, the introduction of the bilateral control scheme described in S4 includes the following steps: S41. Further The second - order derivative of can be derived as: ; S42. As can be seen from S35, the derivative is always negative, which means D decreases as monotonically increases. And it can be clearly seen from S41 that the second - order derivative is always positive, which indicates increases as monotonically increases. Therefore, to meet the maximum efficiency tracking requirement of the system, it is only necessary to coordinate the duty cycle of the transmitter - side DC - DC converter and the phase - shift angle of the receiver - side SAR, that is, by gradually increasing the phase - shift angle α and comparing the derivative with the fixed value δ and continuously tracking the optimal value δ .

[0015] S43. Receiver - side control of CV output: By introducing two controllable switching tubes into the uncontrolled rectifier device Q 7 , Q 8 , another controllable degree of freedom is introduced into the system, that is, the phase - shift angle of SAR α . Based on S11, it can be known that the output voltage of the wireless power transfer (WPT) system can be adjusted by adjusting the phase - shift angle α . The switching states of the controllable switching tubes Q 7 and Q 8 determine the power flowing to the load. Therefore, the receiving side of the WPT system can be considered to be composed of an uncontrolled rectifier plus a DC - DC converter.

[0016] S44. Transmitter - side MET control: According to the above analysis, the system can maintain the CV output by automatically adjusting the phase - shift angle of SAR α . However, in the case where the DC - DC controller at the transmitter end does not participate in the regulation, the input power of the system will deviate from the optimal value due to the change of the output power, resulting in significant power loss and further reducing the transmission efficiency of the system. To solve this problem, the present invention introduces a mechanism to optimize the system efficiency by adjusting the duty cycle of the DC - DC converter, enabling the system to dynamically match the best operating point. By precisely adjusting the duty cycle D , the best matching point between D and α can be found, thereby maximizing the transmission efficiency of the system.

[0017] Compared with the prior art, the present invention has the following technical effects: 1. The WPT system proposed by the present invention adopts an SS compensation network, which has excellent bandwidth capabilities, stability, and strong anti - interference ability. In addition, the SS compensation network does not require complex compensation circuit devices, which not only reduces the system cost but also effectively reduces the volume of the device. At the same time, the use of passive devices is reduced, further reducing the circuit loss and thus improving the overall energy efficiency. With these advantages, the system can be used for large loads and is also suitable for providing wireless power transfer for small sensors or mobile robots.

[0018] 2. The present invention adopts the duty cycle D and the phase - shift angle αAs a key control variable, it is not necessary to rely on complex calculations to evaluate the coupling coefficient in real time. This control method can simultaneously achieve constant voltage (CV) output and maximum efficiency transfer (MET) control under the conditions of changing load resistance and coupling coefficient. Since these parameters are easy to obtain and there is no need to additionally configure expensive power, voltage or current sensors, the system structure is made more concise and efficient. This control strategy not only enhances the stability and reliability of the system, but also effectively reduces the system volume, lowers the hardware cost, and significantly improves the overall economy and practicality.

[0019] 3. The system used in the present invention does not require additional power conversion circuits at the receiving and transmitting ends, but directly regulates based on the parameters of the essential power circuit. This method not only saves space, reduces the system volume, and lowers the manufacturing and maintenance costs, but also reduces the number of power devices used, further reducing the system loss, thus significantly improving the energy efficiency. Brief Description of the Drawings

[0020] Figure 1 is the system circuit diagram of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention; Figure 2 is the closed-loop block diagram of a bilateral control scheme of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention; Figure 3 is the equivalent circuit diagram of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention in an SS compensated WPT system; Figure 4 is for a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention under different equivalent loads R O and mutual inductance M under the efficiency curve; Figure 5 is for four working modes of SAR in a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention. (a) Mode 1, (b) Mode 2, (c) Mode 3, (d) Mode 4; Figure 6 is the bilateral MET control flowchart of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention; Figure 7 is the experimental verification device diagram of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention; Figure 8 is the mutual inductance change trend diagram of a wireless power transmission system applicable to an industrial environment in a specific embodiment of the present invention. (a) The mutual inductance change trend caused by the misalignment of the horizontal x-axis and y-axis, (b) The mutual inductance change trend caused by the vertical distance; Figure 9 Experimental waveforms of a wireless power transfer system applicable to industrial environment in a specific embodiment of the present invention under different R B conditions. (a) R B = 20, (b) R B = 35; Figure 10 Experimental waveforms of a wireless power transfer system applicable to industrial environment in a specific embodiment of the present invention under different offset degrees. (a) Horizontal misalignment of 10 cm, (b) vertical misalignment of 10 cm; Figure 11 A specific relationship diagram among the duty cycle D , phase shift angle α and efficiency in a wireless power transfer system applicable to industrial environment in a specific embodiment of the present invention ( R B = 30); Figure 12 At the actual maximum system efficiency point of a wireless power transfer system applicable to industrial environment in a specific embodiment of the present invention, the derivative versus the relationship curves between (a) different load resistances (without misalignment) and (b) different mutual inductances; Figure 13 Efficiency comparison curves of a wireless power transfer system applicable to industrial environment in a specific embodiment of the present invention under different conditions. (a) Different loads (without misalignment), (b) different vertical distances, (c) different horizontal misalignments; Detailed implementation manners

[0021] A wireless power transfer (WPT) system applicable to industrial environment in this embodiment is as Figure 1 shown. The present invention selects the SS resonant compensation network with the simplest structure, the most space-saving, the smallest loss and the lowest cost as the analysis object. In a complete wireless charging system, first a rectifier is needed to convert the mains power into direct current, then the direct current is converted into the DC voltage level required by the system through a DC-DC converter, and then the direct current is converted into high-frequency alternating current through a high-frequency inverter circuit. The high-frequency alternating current then passes through the coupling coil, and wireless power transfer is achieved through the principle of Faraday electromagnetic induction. Finally, the high-frequency alternating current is converted into direct current through a rectifying device to supply power to the load. Among them U D is the input voltage source of the DC-DC converter; U dc is the output voltage source of the DC-DC; Q1 ~Q 4 It is a high-frequency inverter circuit composed of four power MOSFETs, which is responsible for converting U dc into a high-frequency square-wave voltage U i to drive the SS resonance tank; two Schottky diodes D5, D6 and two power MOSFETs ( Q 7~ Q 8) form a semi-active rectifier (SAR), which is responsible for converting the high-frequency voltage U O into direct current to supply power to the load; R B is the load; U B is the battery charging voltage; C B is an electrolytic capacitor, which is used for filtering and smoothing U B ; where L P , L S are the self-inductances of the coupling coils, M is the mutual inductance of the coils; C P , C S are the SS compensation capacitors, R P , R S are the parasitic resistances of the coupling coils.

[0022] In this embodiment, based on the proposed WPT system, as Figure 2 shown, the present invention proposes a bilateral control scheme, which combines the transmitter DC-DC converter and the receiver semi-active rectifier (SAR). By precisely controlling the duty cycle and phase shift angle, under the conditions of load variation and coupling coefficient fluctuation, a constant voltage output and maximum efficiency transmission are always maintained. Specifically, the present invention adjusts the phase shift angle α of the SAR to maintain a constant voltage output, thereby ensuring the stability of the system; at the same time, by adjusting the duty cycle D of the transmitter DC-DC converter, the system can maintain an optimal match between the input power and the output power, maximizing the system transmission efficiency.

[0023] In a specific embodiment, the wireless power transfer system applicable to the industrial environment includes the following steps: S1. Establish a mathematical model according to the proposed wireless power transfer system; Furthermore, S1 includes the following steps: S11. Since the SS compensation network has a bandwidth characteristic and high-order harmonics can be neglected, for the sake of easy analysis, only the fundamental wave is analyzed. Based on the topological principle, the output voltage of the high-frequency inverter (HFI) U i and the input voltage of the semi-active rectifier U O effective values can be expressed as: ; where θ , α , are the conduction angles of the HFI and SAR respectively, U dc is the output voltage of the DC-DC converter, U B is the effective value of the output voltage of the semi-active rectifier. In order to make the system work in the quasi-resonant state, the conduction angle θ of the HFI takes 180°, so .

[0024] S12. According to the law of conservation of energy, the relationship between the input voltage U D and the output voltage U dc of the DC-DC converter can be expressed as:

[0025] S13. R O is the equivalent resistance of the SAR and the load ( R B ), which can be expressed as:

[0026] S14. According to the Figure 3 equivalent circuit diagram, the mathematical model of the SS compensation network can be obtained by Kirchhoff's law:

[0027] In the formula: L P , L S are the self-inductances of the coupling coils, M is the mutual inductance of the coupling coils; C P , C S are the compensation capacitors in the SS compensation network, R P , R S are the parasitic resistances in the coupling coils; Ii is the effective value of the input current of the primary side coil, I O is the effective value of the output current of the secondary side coil, where , f is the power transmission frequency of the electric energy.

[0028] S2. Analyze the system efficiency based on the mathematical model described in S2; Furthermore, the efficiency analysis described in S2 includes the following steps: S21. To make the system work in the resonance state, the parameter design of the SS compensation network should meet the following requirements: ; Substituting S21 into the mathematical model described in S14, the expression for the effective values of the input and output currents of the coil can be obtained as: ; The input and output power of the coupling mechanism can be expressed as: ; where P i is the input power, P O is the output power.

[0029] S24. Based on the power expression, the power transmission efficiency of the system can be obtained as: ; It can be seen from the system efficiency formula S23 that, when the frequency remains unchanged, the system efficiency is only related to the mutual inductance M and the equivalent load impedance R O These two variables. This indicates that the coupling coefficient K ( ) and the load resistance R B are the key factors affecting the system efficiency. Further analysis shows that the system efficiency increases with the increase of the coupling coefficient K because stronger coupling is beneficial to power transmission. At the same time, the derivative of the efficiency with respect to M is always positive, indicating that increasing the coupling degree can improve the system efficiency. However, the second derivative of the efficiency with respect to R O is negative, which means that there is an optimal equivalent load resistance R O -opt that makes the system efficiency reach the maximum value. This is because too large or too small load impedance will reduce the system efficiency. To make the analysis results more intuitive, in Figure 4The relationship between the system transmission efficiency and different equivalent load resistances and mutual inductances is plotted M Therefore, for a wireless charging system constructed by an SS compensation network, not only the coupling coefficient needs to be optimized K , but also the equivalent load impedance needs to be precisely designed R O , in order to maximize the system efficiency. This provides an important theoretical basis for the design and optimization of the present invention.

[0030] S25. Differentiate the equivalent impedance R O with respect to the efficiency formula, and set its derivative to zero, the optimal equivalent impedance corresponding to the maximum efficiency point of the system can be obtained R O -opt, Its expression is: ; S26. Since , S25 can be expressed as: ; As can be seen from S26, when the parameters of the coupling coil are determined, the optimal equivalent load impedance R O -opt corresponding to the maximum system efficiency M will change with the change of the mutual inductance M . This means that due to the offset of the coupling coil or other factors, the mutual inductance coefficient R O -opt will no longer remain constant. Therefore, in order to keep the system always working at the best efficiency state, it is necessary to continuously track the optimal equivalent load impedance.

[0031] S3. Conduct MET control analysis on the system according to the efficiency analysis results obtained in S2; Furthermore, the control analysis described in S3 is as follows: S31. In the actual charging environment, the equivalent impedance of the battery and the coupling coefficient of the coil will continuously fluctuate with the change of external conditions. Especially in a complex industrial environment, the change of these parameters will significantly reduce the transmission efficiency of the entire charging system. Therefore, how to track and optimize these key parameters in real time has become the key to ensuring efficient charging. Next, the present invention will focus on discussing how to track the optimal equivalent impedance of the load in real time during the charging process to ensure the maximum efficiency of the system throughout the charging process.

[0032] S32. Based on the SAR topology, the following equation should be satisfied according to the principle of power conservation:

[0033] S33. According to S22 and S32, the effective value of the HFI output voltage can be expressed as: ; S34. Substituting S13 into S33 gives U i and U B The relational expression between them is:

[0034] S35. Substituting S11 into S34 gives D and The relational expression between them is:

[0035] where D and are the duty cycle of the DC-DC converter on the transmitting side and the phase shift angle of the SAR on the receiving side respectively. These two parameters can be obtained and measured relatively easily. Therefore, if we can find the functional relational expression between D and at the optimal equivalent impedance state, then we can successfully make the entire system reach the maximum transmission efficiency by adjusting the parameters in this relational expression.

[0036] S36. By differentiating D with respect to the following equation can be obtained: ; S37. When the system operates at the optimal equivalent load point, combining S13 and S25 can deduce for the system to operate at the maximum efficiency point: ; S38. Substituting S37 into S36 can obtain the mathematical expression of the optimal functional relationship between the duty cycle D of the DC-DC converter on the transmitting side and the conduction angle α of the SAR on the receiving side at the maximum efficiency point: ; S39. As can be seen from S38, the derivative at the optimal equivalent impedance point for the system to operate at the maximum efficiency is independent of the load R B and since , the mathematical expression can be simplified to: ; Therefore, it can be concluded from the mathematical expressions that the derivative of the system operating at the maximum efficiency point is related to the input and output DC voltages and the parasitic resistance of the coupling coil. When the system input DC voltage U D remains constant, by adjusting the phase shift angle of the SAR on the receiver side α , the output DC voltage of the system can be made U B remain constant, where R P and R S are also constant. Therefore, for the system proposed in the present invention, when the system transmission efficiency reaches the maximum value, the derivative is always a fixed value δ , and is not affected by changes in mutual inductance and load resistance.

[0037] S310. In fact, the load modulation range of the SAR is limited. According to S13 and S25, when the inequality is satisfied, regardless of how the phase shift angle α varies, the equivalent resistance R O cannot reach the optimal value, so MET control cannot be achieved. Therefore, to achieve MET control, the following equation needs to be satisfied: ; Therefore, when designing a WPT system with a constant voltage (CV) output, the following design criteria are usually followed: To ensure that the system can operate at the maximum efficiency point, we should select the minimum equivalent load resistance of the battery R B _min greater than or equal to the maximum value. With this design method, it can be ensured that the system can operate at the maximum efficiency point even when the equivalent load resistance of the battery reaches the minimum value.

[0038] S4. According to the MET control analysis results obtained in S3, a bilateral control scheme is proposed; Furthermore, the bilateral control scheme described in S4 is as follows: S41. Further the second derivative of can be derived as: ; S42. It can be seen from S36 that the derivative is always negative, which means D decreases as monotonically increases. And it can be clearly seen from S41 that the second derivative is always positive, which indicates increase with the monotonic increase. Therefore, to meet the maximum efficiency tracking requirement of the system, it is only necessary to coordinate the duty cycle of the transmitter DC-DC converter and the phase shift angle of the receiver-side SAR, that is, by gradually increasing α and comparing the derivative with the fixed value δ and continuously tracking the optimal value δ .

[0039] S43. Receiver-side control CV output: By introducing two controllable switch tubes Q 7 , Q 8 into the uncontrolled rectifier device, another controllable degree of freedom is introduced into the system, that is, the phase shift angle α of the SAR. Based on S11, it can be known that the output voltage of the wireless power transfer (WPT) system can be adjusted by adjusting the phase shift angle α . The switching states of the controllable switch tubes Q 7 and Q 8 determine the power flowing to the load. Therefore, the receiver side of the WPT system can be considered to be composed of an uncontrolled rectifier plus a DC-DC converter. The working process of the SAR is as shown in Figure 5 and the operation sequence is detailed as follows: Mode 1: In Mode 1, Q 7 and Q 8 are turned on, while D 5 and D 6 are turned off. The output current of the SS resonant network flows through Q 7 and Q 8 . The load R B obtains energy from the filter capacitor C B .

[0040] Mode 2: D 5 and Q 8 are both turned on, and D 6 and Q 7 are turned off during this period. The output current of the SS resonant network flows through D 5 and Q 8 , and the energy is transferred to the load R B .

[0041] Mode 3: In this case,Q 7 and Q 8 is turned on, while D 5 and D 6 is turned off. Similar to Mode 1, the load R B obtains energy from C B .

[0042] Mode 4: D 6 and Q 7 are both turned on, and D 5 and D 8 are turned off during this period. The output current of the SS resonant network flows through D 6 and Q 7 , and energy is transferred to the load R B .

[0043] S44. Transmitter MET control: According to the above analysis, the system can maintain the CV output by automatically adjusting the phase shift angle of the SAR α without being affected by the mutual inductance and load resistance. However, in the case where the transmitter DC-DC controller does not participate in the regulation, the input power of the system will deviate from the optimal value due to the change in the output power, resulting in significant power loss and thus reducing the transmission efficiency of the system. To solve this problem, the present invention introduces a mechanism to optimize the system efficiency by adjusting the duty cycle of the DC-DC converter, enabling the system to dynamically match the best operating point. By precisely adjusting the duty cycle D , the best matching point between D and α can be found, thereby maximizing the transmission efficiency of the system. The specific functional relationship between the duty cycle D and the phase shift angle α is represented by Equation S39. The flowchart of the MET control proposed by the present invention is presented in Figure 6 , and the detailed process is described as follows.

[0044] The first step: Determine the relevant system parameters, such as the system input and output DC voltages U D and U B , as well as the parasitic resistances of the coils R P and R S . Finally, calculate δ according to S39.

[0045] The second step: Initialize the duty cycle D=1. Automatically adjust the phase shift angle α to make the output voltage reach the preset CV value U B .

[0046] Step 3: Record the duty cycle at this time D and the phase shift angle α , which are respectively denoted as D 0 and α 0 .

[0047] Step 4: Slightly adjust the duty cycle to , and then record the phase shift angle α 1 .

[0048] Step 5: Based on the two adjacent points recorded in Step 3 and Step 4 ( D 0 and α 0 , D 1 and α 1 ), the derivative can be obtained based on the equation . .

[0049] Step 6: Judge whether the equation satisfies the equality , where δ is the allowable error component range. If the equation is satisfied, it proves that the system realizes MET control at ( D 0 and α 0 ). If the equation does not hold, it proves that the system has not reached the optimal load point, and D will continue to be slightly reduced to search for the maximum efficiency point. Repeat Step 4 until the equation satisfies where k = 1, 2, 3,..., the maximum efficiency point of the system can be determined at ( D k and α k ), and then record this point ( D k and α k ). Obviously, the proposed MET control strategy can be easily implemented with only two adjustment parameters D and α . The derivative can be easily and quickly calculated by the transmitter-side controller. In addition, these two adjustment parameters D andα It can be easily obtained without any measuring devices (such as power sensors, current sensors, etc.).

[0050] The above embodiments will be further described below in conjunction with specific simulations and experiments.

[0051] To verify the correctness and effectiveness of the proposed control system of the invention, a verification experimental prototype was built to provide an output voltage of 48V. The experimental verification device based on the circuit parameters listed in Table I is as Figure 7 shown. Since the polypropylene film capacitor has the advantages of small volume and low dielectric loss, it is used in the SS resonant circuit in this study. Six MOSFETs (IRFP250N) with low drain-source on-resistance are selected for the transmitter DC-DC converter and HFI. Two MOSFETs (IRFP250N) and two fast recovery diodes (MBR16100CT) are used to construct the receiver SAR. The proposed MET method is implemented in the transmitter-side controller STM32F334C8T6. The receiver-side controller DSP (TMS320F28335) is responsible for adjusting the output voltage. Table II lists the specific specifications of each electrical component to improve visibility.

[0052] Table I

[0053]

[0054] Table II

[0055]

[0056] To verify the performance of the proposed method under different offset conditions, the change of the coupling coefficient when the receiving device is misaligned was studied. As Figure 8 shown, two inevitable offset states in practical applications are mainly discussed in the present invention: horizontal misalignment and vertical misalignment, and the influence of these situations on the coupling performance needs to be particularly concerned in dynamic charging applications.

[0057] Figure 9 The experimental waveforms under different load conditions (20Ω and 35Ω) are shown. It should be particularly noted that during the system voltage adjustment process, the transmitter controller automatically adjusts the duty cycle α according to the change of the phase shift angle D to achieve the maximum transmission efficiency of the system. It can be clearly seen that Figure 9 the system output voltages in (a) and (b) always remain at 48V, while the phase shift angles of the receiver SAR are 73.2° and 48.3° respectively. It can be intuitively judged from this that the proposed method can effectively maintain a stable CV output by adjusting α and is not affected by the change of the load resistance.

[0058] In addition, Figure 10 experimental waveforms under different offset conditions are shown. Figure 10 (a) and (b) respectively show the experimental results when the load resistance is 35 Ω under horizontal misalignment and vertical misalignment. The horizontal offset is 10 cm and the vertical offset is 10 cm. It can be clearly seen that Figure 10 the system output voltages in (a) and (b) are always stable at 48 V. In addition, the phase shift angles α of the receiver SAR are 43.3° and 39.3° respectively. These results verify that the proposed method can effectively maintain the stability of the output voltage under different offset conditions by adjusting the α value.

[0059] When the load resistance is 30 Ω and there is no offset in the horizontal and vertical directions of the charging pad, Figure 11 shows the D , α specific relationship with the system efficiency. It can be clearly observed that as D increases, α shows a downward trend. At the same time, the system efficiency first increases and then gradually decreases as α decreases. The system efficiency reaches the maximum at a specific D value, and there is a specific α value corresponding to the constant voltage (CV) output. This result effectively verifies the correctness and rationality of the theoretical analysis in the present invention.

[0060] Under the condition that the phase shift angle α is automatically adjusted to obtain a constant voltage (CV) output, by manually adjusting the duty cycle D , the minimum input power at any given output power can be obtained, thereby determining the actual maximum system efficiency. The actual derivative can be calculated by measuring the phase shift angle α and the duty cycle D , and the calculated derivative is compared with δ to judge the effectiveness of the proposed method. Figure 12 (a) and (b) respectively show the derivative change curves of the actual maximum system efficiency points under different load resistances (without misalignment) and different mutual inductances caused by horizontal / vertical misalignment (load resistance is 30 Ω). It can be clearly seen from Figure 12 that regardless of the changes in the load resistance and mutual inductance, the derivative always tracks the δ value at the maximum efficiency point. This phenomenon fully verifies the rationality of the basic theory of the proposed MET method.

[0061] To further verify the tracking performance of the proposed maximum efficiency transfer (MET) method, Figure 13 comparative experimental results under different load and charging pad misalignment conditions are presented. The orange curve represents the efficiency measured using the proposed MET method, while the red curve is the efficiency obtained by manually adjusting the duty cycle D to search for the minimum input power at a given output power. Figure 13 (a) shows the efficiency curves under different loads (no misalignment); Figure 13 (b) and (c) respectively show the comparative efficiency curves under different vertical distances (no horizontal misalignment) and horizontal misalignments (no vertical misalignment) when the load resistance is fixed at 30 Ω. It can be clearly seen from Figure 13 that the efficiency measured using the proposed MET method is always slightly higher than the actual maximum efficiency. This is mainly because the method does not consider the losses of the high-frequency inverter (HFI), semi-active rectifier (SAR), and related compensation components. However, the impact of these losses on the system performance is negligible because the efficiency measured by the proposed method is always close to the actual maximum efficiency. The above results intuitively prove that the proposed method can effectively track the maximum efficiency of the system regardless of the change in load resistance or the change in coupling coefficient caused by vertical / horizontal misalignment.

Claims

1. A wireless power transmission system suitable for industrial environments: comprising the following steps: S1. Establish a mathematical model based on the proposed wireless power transmission system; S2, analyzing the system efficiency based on the mathematical model obtained in S1; S3, perform MET control analysis on the system according to the efficiency analysis results obtained in S2; S4. Propose a bilateral control scheme based on the MET control analysis results obtained in S3.

2. A wireless power transmission system suitable for industrial environments according to claim 1, characterized in that: Further, S1 includes the following steps: S5. Based on the topological principle, the output voltage of the high-frequency inverter (HFI) U i and Semi-Active Rectifier (SAR) input voltage U O The valid values ​​can be expressed as: ； Where: θ , α , are the conduction angles of the high frequency inverter (HFI) and the semi-active rectifier (SAR), D , U dc and U D are the duty cycle, output voltage and input voltage of the DC-DC converter respectively. In order to make the system transmitter work in a quasi-resonant state, the conduction angle of HFI θ Take 180°, so ; S6, R O for SAR and load ( R B ) can be expressed as: ； S7. The mathematical model of SS compensation network can be obtained from Kirchhoff's law: ； Where: L P , L S is the self-inductance of the coupling coil, M is the mutual inductance of the coupled coils; C P , C S is the compensation capacitor in the SS compensation network, R P , R S is the parasitic resistance in the coupling coil, I i is the effective value of the primary coil input current, I O is the effective value of the secondary coil output current, where , f The frequency of power transmission.

3. A wireless power transmission system suitable for industrial environments according to claim 1, characterized in that: The analysis of system efficiency according to the mathematical model obtained in S1 described in S2 includes the following steps: S8. In order to make the system work in a resonant state, the parameter design of the SS compensation network should meet the following requirements: ； S9. Substituting S8 into the mathematical model described in S7, the effective value expression of the current input and output of the original secondary coil can be obtained as follows: ； S10, the input and output power of the coupling mechanism can be expressed as: ； in P i Input power P O is the output power; S11. Based on the power expression, the power transmission efficiency of the system can be obtained as: ； S12. Equivalent impedance based on efficiency formula R O Taking the derivative and setting it to zero, we can get the optimal equivalent impedance corresponding to the maximum efficiency point of the system. R O -opt, Its expression is: ； From the above formula, we can know that when the coupling coil parameters and transmission frequency are determined, the optimal equivalent load impedance corresponding to the maximum system efficiency is R O -opt With mutual induction M This means that the mutual inductance changes with the change of the coupling coil offset or other factors. M changes have occurred, R O -opt Will no longer remain constant, so in order to make the system always work at the best efficiency, it is necessary to constantly track the optimal equivalent load impedance.

4. A wireless power transmission system suitable for industrial environments according to claim 1, characterized in that: The steps for MET control analysis of the system based on the efficiency analysis results obtained from S2 are as follows: S13. Based on the SAR topology, the following equation should be satisfied according to the power conservation principle: ； S14, based on S9 and S13, the effective value of the HFI output voltage U i It can be expressed as: ； S15, Substituting S6 into S14, we get U i and U B The relationship between them is: ； S16, Substituting S5 into S15, we get D and The relationship between them is: ； S17, by D At Differentiation yields the following equation: ； S18. When the system works at the optimal equivalent load point, due to the parasitic resistance R s , R p Combining S6 and S12, it can be deduced that the system works at the maximum efficiency point. for: ； S19, Substituting S18 into S17 can obtain the duty cycle of the primary DC-DC converter at the maximum efficiency point D and the conduction angle of the secondary SAR α The mathematical expression of the optimal functional relationship between is: ； S20, from S19, we can know that the derivative of the optimal equivalent impedance point that makes the system work at maximum efficiency With load R B is irrelevant, and because , so the mathematical expression can be simplified to: ； It can be seen from the mathematical expression that the derivative of the system working at the maximum efficiency point is It is related to the input and output DC voltage and the parasitic resistance of the coupling coil. U D By adjusting the phase shift angle of the SAR at the receiver side, α , the system's output DC voltage U B Keep constant, where R P , R S is also constant; therefore, for the system proposed in the present invention, when the system transmission efficiency reaches the maximum value, the derivative Always fixed value δ , and is not affected by changes in mutual inductance and load resistance.

5. The wireless power transmission system suitable for industrial environment according to claim 1, characterized in that: Based on the MET control analysis results obtained from S3, a two-sided control solution is proposed, which includes the following steps: S21. Further The second-order derivative of can be derived as: ； S22, from S17, we can see that the derivative is always negative, which means D Follow increases monotonically and decreases, and it can be clearly seen from S21 that the second-order derivative is always positive, which indicates Therefore, in order to meet the system's maximum efficiency tracking requirements, it is only necessary to coordinate the duty cycle of the DC-DC converter at the transmitter and the phase shift angle of the SAR at the receiver, that is, to gradually increase α , and the derivative With fixed value δ Compare and keep track of the best value δ, S23, receiving side controls CV output: by introducing two controllable switch tubes in the uncontrolled rectifier device Q 7. Q 8. Another controllable degree of freedom is introduced into the system, namely the SAR phase shift angle α Based on S5, the output voltage of the wireless power transmission (WPT) system can be adjusted by adjusting the phase shift angle α To adjust, controllable switch Q 7 and Q The switching state of 8 determines the power flowing to the load; therefore, the receiving side of the WPT system can be considered to be composed of an uncontrolled rectifier plus a DC-DC converter.

6. S24, MET control at the transmitter: Based on the above analysis, the system can automatically adjust the phase shift angle of SAR α To maintain CV output, however, when the DC-DC controller at the transmitter is not involved in the regulation, the input power of the system will deviate from the optimal value due to the change in output power, resulting in significant power loss, thereby reducing the transmission efficiency of the system. To solve this problem, a mechanism for optimizing system efficiency by adjusting the duty cycle of the DC-DC converter is introduced, so that the system can dynamically match the optimal operating point and accurately adjust the duty cycle. D , you can find D and α The best matching point between them can maximize the transmission efficiency of the system.

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