Constant power multi-relay wireless power transmission system based on equivalent impedance regulation

Abstract

This application provides a constant power multi-relay wireless power transmission system based on equivalent impedance regulation. It addresses the problem of existing multi-relay WPT systems experiencing resonant matching issues due to drastic temperature fluctuations caused by external air temperature variations. The system includes a transmitting unit, a receiving unit, and a frequency controller, as well as at least one relay unit positioned between the transmitting and receiving units. The transmitting unit comprises a DC power supply, a high-frequency inverter, a primary-side compensation circuit, and a transmitting coil connected in sequence. The frequency controller calculates the input impedance and impedance angle based on the inverter output voltage and current, and controls the system frequency. This application dynamically maintains the overall equivalent input impedance of the system at a target constant value, thereby effectively ensuring stable constant power output even in complex external environments.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission, and in particular to a constant power multi-relay wireless power transmission system based on equivalent impedance regulation. Background Technology

[0002] Multi-relay architecture is a common implementation of magnetically coupled wireless power transfer (MC-WPT) technology, and powering online monitoring equipment on high-voltage transmission towers is a promising and typical application scenario. In this scenario, multi-relay MC-WPT systems are typically cascaded with inductively coupled current transformers (CTs). The CTs first draw energy from the high-voltage transmission line, then use this energy as the input source for the MC-WPT system, and finally transmit it wirelessly across insulation gaps to the end-user equipment. In this steady-state process, if the load current on the high-voltage transmission line remains constant, the port characteristics of the CT can be equivalent to an ideal constant current source, with its output current exhibiting a strictly linear relationship with the high-voltage line current. Based on the output characteristics of the constant current source, within the rated power capacity range of the CT, the higher the equivalent input impedance of the load, the higher the electromagnetic power output from the CT port. Therefore, analyzing and improving the overall equivalent input impedance of the multi-relay MC-WPT system is an effective way to maximize the energy extraction efficiency of the CT. Furthermore, if the overall equivalent impedance of the system can be increased, and closed-loop control is introduced to maintain the impedance constant when the external environment is disturbed, the output power of the power-taking CT can be locked; given that the overall transmission efficiency of the multi-relay system fluctuates less, the output power transmitted by the system to the terminal electrical equipment will also remain basically constant.

[0003] However, in actual outdoor applications of high-voltage transmission towers, multi-relay MC-WPT systems are exposed to complex and variable natural environments for extended periods. The system's operating temperature fluctuates drastically with the ambient temperature and cannot be artificially intervened. The wide range of ambient temperature changes causes temperature drift in the capacitance of the system's resonant compensation capacitor, thereby disrupting the system's original resonant matching state (causing detuning) and resulting in a significant shift in the overall equivalent impedance and a substantial drop in output power. Summary of the Invention

[0004] The purpose of this invention is to provide a constant power multi-relay wireless power transmission system based on equivalent impedance adjustment. This addresses the technical problem of existing multi-relay WPT systems where drastic temperature fluctuations with ambient air temperature cause temperature drift in the system's resonant compensation capacitor, thereby disrupting the system's original resonant matching state.

[0005] This application provides a constant power multi-relay wireless power transmission system based on equivalent impedance regulation, including a transmitting unit, a receiving unit, and a frequency controller, as well as at least one relay unit disposed between the transmitting unit and the receiving unit.

[0006] The transmitting unit includes a DC power supply, a high-frequency inverter, a primary-side compensation circuit, and a transmitting coil connected in sequence. The frequency controller is used to calculate the input impedance and impedance angle based on the inverter output voltage and current, and to control the system frequency.

[0007] Optionally, the specific steps for the frequency controller to control the system frequency are as follows:

[0008] S1: Calculate the maximum impedance point and frequency of the system when it operates at the optimal temperature m℃, and set the frequency at this point as the initial operating frequency of the system so that the system operates at the overall maximum impedance point.

[0009] S2: Real-time acquisition of inverter output voltage and current, and calculation of input impedance and impedance angle at the current moment;

[0010] S3: Determine whether the current input impedance is equal to the maximum impedance. If they are equal, return to step S2 to continue sampling. If they are not equal, proceed to step S4 to adjust the system frequency.

[0011] S4: Determine the frequency adjustment direction based on the impedance angle, and adjust the frequency every... Time adjustment After each adjustment, the input impedance and impedance angle of the system are measured until the system returns to the maximum impedance point.

[0012] Optionally, the optimal room temperature of the system in step S1 is 25°C.

[0013] Optionally, the impedance angle at the point of maximum system impedance is 0.

[0014] Optionally, in step S2, the input impedance Equal to the ratio of inverter output voltage to inverter output current, impedance angle for .

[0015] Optionally, the specific method in step S4 is as follows:

[0016] When the impedance angle is negative, it indicates a temperature rise; therefore, the frequency is adjusted every [number of intervals]. Time reduction The system continues operating until it returns to its maximum impedance point; when the impedance angle is positive, it is determined that the temperature has decreased, and the frequency is adjusted every [number] intervals. Time increase This continues until the system returns to its maximum impedance point.

[0017] Optionally, the relay unit includes a relay coil and a relay resonant capacitor connected in series.

[0018] Optionally, the receiving unit includes a receiving coil, a secondary compensation circuit, a rectifier, and a load connected in sequence.

[0019] Optionally, the primary-side compensation circuit and the secondary-side compensation circuit constitute an LCC-S topology.

[0020] Because of the adoption of the above technical solution, the present invention has the following advantages:

[0021] This application acquires the voltage and current signals of the primary side in real time and calculates the overall equivalent input impedance of the system online. When the overall impedance is detected to be drifting due to factors such as ambient temperature, the control system adaptively adjusts the operating frequency of the inverter to dynamically maintain the overall equivalent input impedance of the system at the target constant value, thereby effectively ensuring the constant power stable output of the system in complex external environments.

[0022] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0023] The accompanying drawings of this invention are described below.

[0024] Figure 1 This is a circuit diagram of the multi-relay wireless power transmission system of the present invention.

[0025] Figure 2 This is a flowchart of the method for controlling the system frequency using the frequency controller of the present invention.

[0026] Figure 3 The diagram shows the input impedance, impedance angle, and frequency variation of the system of this invention.

[0027] Figure 4 This is a comparison diagram of the overall system impedance changing with frequency before and after temperature changes in this invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" or "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, an integral connection, an electrical connection, or a signal connection; it can be a direct connection or an indirect connection through an intermediate medium.

[0029] like Figure 1 The constant power multi-relay wireless power transmission system based on equivalent impedance regulation shown includes a transmitting unit, a receiving unit, and a frequency controller, as well as at least one relay unit disposed between the transmitting unit and the receiving unit.

[0030] The transmitting unit includes a DC power supply (in this application, a power-supply CT), a high-frequency inverter, a primary-side compensation circuit, and a transmitting coil connected in sequence. The relay unit includes relay coils connected in series. and relay resonant capacitor ,in: The receiving unit includes a receiving coil. Secondary-side compensation circuit, rectifier and load .

[0031] In this embodiment, the high-frequency inverter is an H-type inverter, including... There are a total of 4 MOSFETs; the rectifier is a full-bridge rectifier, including... There are a total of 4 diodes and filter capacitors. The primary-side compensation circuit includes a primary-side compensation inductor. Primary-side series compensation capacitor Parallel compensation capacitor with primary side The secondary-side compensation circuit includes a secondary-side compensation capacitor. The primary-side compensation circuit and the secondary-side compensation circuit constitute an LCC-S topology; the frequency controller is used to calculate the input impedance and impedance angle based on the inverter output voltage and current, and to control the system frequency.

[0032] System Analysis:

[0033] Analysis of the system circuit using Kirchhoff's voltage law yields the following:

[0034] (1)

[0035] in, The system's resonant angular frequency, For the first The coil and the first Mutual inductance between coils ( ), and To separate the inverter output voltage and current, For the flow through the first The current in each coil, , .

[0036] The impedances of each circuit are expressed as follows:

[0037] (2)

[0038] in, For coil Parasitic resistance.

[0039] Simplify the coil circuits, retaining only the input and output circuit ports, and change the coil currents in the equations. Using the current in the transmitting coil loop and the current in the receiving coil circuit By representing the current loop model of the relay coil in equation (1), we can obtain:

[0040] (3)

[0041] By dividing the impedance matrix in equation (3) into blocks, we can obtain:

[0042] (4)

[0043] In equation (4), matrices A, B, and X, as well as the loop current vectors in each coil, are used. It can be represented as:

[0044] (5)

[0045] (6)

[0046] Based on equation (4), the relationships between the currents in each loop can be further obtained:

[0047] (7)

[0048] According to circuit theory, when U in equation (1) s When the impedance matrix parameters are determined, the current Since there is one and only one solution, the impedance matrix is ​​a non-singular matrix, and its submatrix X should also be a non-singular matrix, meaning that matrix X is invertible. From this, we can deduce that the relay coil circuit current is:

[0049] (8)

[0050] Next, we analyze the input coil loop and the output coil loop. From the KVL matrix equation of equation (1), we extract the voltage and current relationship between the input coil loop and the output coil loop, and obtain the following equation:

[0051] (9)

[0052] Substituting equations (8) and (5) into equation (9), we get:

[0053] (10)

[0054] in, and This is the transpose of matrices A and B, i.e., transforming column vectors A and B into row vectors. Combining equations (8) and (10), the two-port network model of the multi-relay MC-WPT system can be obtained as follows:

[0055] (11)

[0056] Among them, the coefficients in the Z impedance matrix , , , It can be represented as:

[0057] (12)

[0058] The inverter output current can be calculated. The expression is:

[0059] (13)

[0060] The input impedance can be obtained. The expression is:

[0061] (14)

[0062] Therefore, the phase angle of the transmitter voltage and current can be expressed as:

[0063] (15)

[0064] Therefore, the system input impedance is independent of the input and output, and is only related to the parameters in the impedance matrix. Changing the capacitance in the impedance matrix will affect the magnitude of the input impedance, and adjusting the frequency can also adjust the input impedance to meet the system specifications.

[0065] like Figure 2 As shown, the specific steps by which the frequency controller controls the system frequency are as follows:

[0066] S1: Calculate the maximum impedance point and frequency of the system when it is operating at the optimal temperature of 25℃. Set the frequency at this point as the initial operating frequency of the system so that the system operates at the overall maximum impedance point.

[0067] In this embodiment, a 5-coil system (including a transmitting coil) is constructed. Relay coil Receiver coil The parameters of the multi-relay WPT system are shown in Table 1.

[0068] Table 1 Parameter Table for Multi-Relay WPT System

[0069]

[0070] The input impedance and impedance angle of the system in the 85-115kHz range are calculated using equations (14) and (15) as follows: Figure 3 As shown, by Figure 3 It can be seen that the system's maximum impedance point occurs at 88.13kHz, with an impedance value of 35.3 and an impedance angle of 0. Therefore, the initial system frequency is set to 88.13kHz, at which point the overall system impedance is at its maximum, the power obtained from the power supply current transformer (CT) is also at its maximum, and the input terminal achieves ZPA (Zero Power Amplifier), maximizing power utilization.

[0071] S2: Real-time acquisition of inverter output voltage and current, and calculation of input impedance and impedance angle at the current moment;

[0072] In this embodiment, the input impedance and impedance angle at the current moment are calculated using equations (14) and (15).

[0073] S3: Determine whether the current input impedance is equal to the maximum impedance. If they are equal, return to step S2 to continue sampling. If they are not equal, proceed to step S4 to adjust the system frequency.

[0074] S4: Determine the frequency adjustment direction based on the impedance angle, and adjust the frequency every... Time adjustment After each adjustment, the input impedance and impedance angle of the system are measured until the system returns to the maximum impedance point.

[0075] In this embodiment, the system's resonant compensation capacitor ( If C0G capacitors are used, and the capacitance of the resonant compensation capacitors increases by 0.1% when the ambient temperature rises, the system impedance will change. Figure 4 As shown, by Figure 4 It can be seen that the overall impedance change curve of the system shifts to the left after the temperature rises. When the frequency remains constant, the overall impedance of the system decreases, leading to a decrease in output power. At this point, a frequency controller can be used to lower the frequency, causing the overall impedance of the system to rise until it returns to its original state, thus maintaining a constant output power. Simultaneously, from... Figure 4 It can be seen that when the temperature rises, the system input impedance angle shifts to the left in the frequency range of the optimal impedance, and the effect of temperature change on impedance and frequency is monotonically changing in a specific frequency range.

[0076] Therefore, it can be seen that when the temperature is constant, the impedance is at its maximum and the impedance angle is 0. When the temperature rises, the impedance angle shifts to the left in the optimal impedance frequency range, and the impedance angle becomes negative, indicating that the system exhibits weak inductance. At this time, reducing the frequency will return the system to the optimal impedance point. The same applies when the temperature drops. Therefore, by observing the sign of the impedance angle, the direction of the shift of the optimal impedance frequency point in a fixed frequency range can be determined, and the direction of frequency adjustment can be determined.

[0077] In summary, this application acquires the inverter voltage and current signals on the transmitting side in real time and calculates the overall equivalent input impedance of the system online. When the overall impedance is detected to be drifting due to factors such as ambient temperature, the control system adaptively adjusts the operating frequency of the inverter to dynamically maintain the overall equivalent input impedance of the system at the target constant value, thereby effectively ensuring the constant power stable output of the system in complex external environments.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A constant-power multi-relay wireless power transmission system based on equivalent impedance regulation, characterized in that, It includes a transmitting unit, a receiving unit, and a frequency controller, as well as at least one relay unit disposed between the transmitting unit and the receiving unit; The transmitting unit includes a DC power supply, a high-frequency inverter, a primary-side compensation circuit, and a transmitting coil connected in sequence. The frequency controller is used to calculate the input impedance and impedance angle based on the inverter output voltage and current, and to control the system frequency.

2. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment as described in claim 1, characterized in that, The specific steps by which the frequency controller controls the system frequency are as follows: S1: Calculate the maximum impedance point and frequency of the system when it operates at the optimal temperature m℃, and set the frequency at this point as the initial operating frequency of the system so that the system operates at the overall maximum impedance point. S2: Real-time acquisition of inverter output voltage and current, and calculation of input impedance and impedance angle at the current moment; S3: Determine whether the current input impedance is equal to the maximum impedance. If they are equal, return to step S2 to continue sampling. If they are not equal, proceed to step S4 to adjust the system frequency. S4: Determine the frequency adjustment direction based on the impedance angle, and adjust the frequency every... Time adjustment After each adjustment, the input impedance and impedance angle of the system are measured until the system returns to the maximum impedance point.

3. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 2, characterized in that, The optimal room temperature of the system in step S1 is 25°C.

4. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 2, characterized in that, The impedance angle at the point of maximum impedance of the system is 0.

5. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 4, characterized in that, In step S2, the input impedance Equal to the ratio of inverter output voltage to inverter output current, impedance angle for .

6. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 5, characterized in that, The specific method in step S4 is as follows: When the impedance angle is negative, it indicates a temperature rise; therefore, the frequency is adjusted every [number of intervals]. Time reduction The system continues operating until it returns to its maximum impedance point; when the impedance angle is positive, it is determined that the temperature has decreased, and the frequency is adjusted every [number] intervals. Time increase This continues until the system returns to its maximum impedance point.

7. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 1, characterized in that, The relay unit includes a relay coil and a relay resonant capacitor connected in series.

8. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 1, characterized in that, The receiving unit includes a receiving coil, a secondary compensation circuit, a rectifier, and a load connected in sequence.

9. A constant power multi-relay wireless power transmission system based on equivalent impedance adjustment according to claim 8, characterized in that, The primary-side compensation circuit and the secondary-side compensation circuit constitute an LCC-S topology.

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