WPT system coupling coefficient estimation and control method based on dual-frequency tuning

Abstract

The invention provides a dual-frequency tuning method for estimating a coupling coefficient and an output voltage by measuring a transmitting current of a wireless power transmission system, which comprises the following steps of: additionally arranging an inductor and a capacitor parallel branch at a transmitting end and a receiving end, and measuring a fundamental wave and a seventh harmonic wave of an output current of an inverter; the coupling coefficient of the system and the magnitude of the output voltage are estimated, so that the transmitting end control of the output current and voltage can be realized. According to the method, wireless communication is not adopted, the problem of data packet loss is avoided, meanwhile, the receiving end does not need an additional DC-DC converter, and the hardware cost, the size and the weight of the receiving end can be greatly reduced. According to the method, the seventh harmonic current of the WPT system is amplified under the condition that the system efficiency is not reduced, then the coupling coefficient and the output voltage of the transmitting end can be estimated under the condition that wireless communication and a DC-DC converter of the receiving end are not adopted, closed-loop control is conducted on the output voltage and the output current, and the scheme is high in reliability and easy to achieve.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and particularly relates to a method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning. Background Art

[0002] Magnetic-coupled wireless power transmission is a technology that realizes non-contact power transmission by using the electromagnetic coupling principle of coils. Currently, it is widely used in devices such as smartphones, tablets, and smartwatches. With the development of technology, it is also gradually applied in application scenarios such as electric vehicles, robots, and implantable medical devices. The wireless power transmission system is divided into two parts: the transmitting end and the receiving end, and the two are completely electrically isolated. The transmitting end is powered by alternating current, and the mains power is converted into high-frequency alternating current through a rectifier-inverter two-stage topology and then connected to the transmitting coil. The receiving end obtains high-frequency alternating current through the receiving coil and converts it into direct current through rectification to supply power to the load. The transmitting coil and the receiving coil are coupled, and a matching compensation network is used to achieve resonance, improving the transmission power and efficiency. Generally, for devices such as electric vehicles and robots, the load is usually a battery, and the battery often charges in a constant current or constant voltage manner. In this case, the WPT system often adds DC-DC converters at the transmitting end and the receiving end to control the output current and voltage. The general topology of the WPT system is as Figure 1 shown.

[0003] In the field of high-power wireless power transmission such as electric vehicles, the transmitting-end device needs to collect data such as the output voltage and current of the receiving end to control (constant current, constant voltage, constant power) and protect (overvoltage, overcurrent) the charging voltage and current of the load. Further, maximum efficiency tracking can be achieved (this function is not essential). Currently, there are two ways to achieve the above functions:

[0004] Method 1: The receiving end collects data and uses wireless communication to send the data to the transmitting end, and the transmitting end controls the charging voltage and current and performs protection (i.e., transmitting-end control). The advantages are: compared with Method 2, the receiving end does not require a DC-DC converter, and the in-vehicle device is more lightweight; the disadvantages are that the wireless communication network is easily affected by electromagnetic interference and there are packet loss problems, which in turn affect the control accuracy, and the real-time performance of the protection function is average.

[0005] Method 2: Without using wireless communication, a DC-DC converter is added at the receiving end to control and protect the charging voltage and current (i.e., receiving-end control). The advantages are that the receiving end operates independently, there is no packet loss problem in wireless communication, the control accuracy is high, and real-time protection is provided; the disadvantages are that the receiving end needs to add a DC-DC converter, and the hardware cost and weight of the in-vehicle device are high.

[0006] Based on the above technical status quo, the present invention proposes a dual-frequency tuning method for estimating the coupling coefficient and output voltage by measuring the transmitted current of a wireless power transfer system. This method adds parallel branches of inductors and capacitors at the transmitting end and the receiving end, and estimates the coupling coefficient and the magnitude of the output voltage by measuring the fundamental wave and the seventh harmonic of the inverter output current, thereby enabling the control of the output current and voltage at the transmitting end. This method does not use wireless communication, avoiding the problem of data packet loss. At the same time, the receiving end does not require an additional DC-DC converter, which can also greatly reduce the hardware cost, volume, and weight of the receiving end. Summary of the Invention

[0007] In view of this, the present invention aims to overcome the deficiencies of the above problems in the prior art and proposes a method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning. This method adds parallel branches of inductors and capacitors at the transmitting end and the receiving end, and estimates the coupling coefficient and the magnitude of the output voltage by measuring the fundamental wave and the seventh harmonic of the inverter output current, thereby enabling the control of the output current and voltage at the transmitting end. This method does not use wireless communication, avoiding the problem of data packet loss. At the same time, the receiving end does not require an additional DC-DC converter, which can also greatly reduce the hardware cost, volume, and weight of the receiving end.

[0008] To achieve the above object, the technical solution of the present invention is realized as follows:

[0009] The first aspect of the present invention provides a method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning, including the following steps:

[0010] Step 1: Construct a wireless power transfer system, including a transmitting end, a transmitting end compensation network, a receiving end, a receiving end compensation network, a receiving end load, and a controller. The transmitting end includes a transmitting coil and an inverter, and the receiving end includes a receiving coil and a rectifier;

[0011] Step 2: Calculate the fundamental wave and the effective value of the seventh harmonic of the output voltage according to the effective angle of the voltage output by the inverter;

[0012] Step 3: Measure the effective values of the fundamental wave current and the seventh harmonic current output by the inverter;

[0013] Step 4: Calculate the coupling coefficient of the system;

[0014] Step 5: Calculate the voltage and current output at the receiving end of the system;

[0015] Step 6: Perform PI control according to the voltage and current set values and the magnitudes of the output voltage and current calculated in Step 5;

[0016] Step 7: Adjust the phase shift angle of the inverter according to the above PI control result, and then adjust the magnitudes of the system output voltage and current;

[0017] Step 8: Run Steps 2 to 7 in sequence to achieve closed-loop control of the output current and voltage at the transmitting end according to the coupling coefficient and the magnitude of the output voltage.

[0018] Further, the design formulas for the transmitting-end compensation network and the receiving-end compensation network are:

[0019]

[0020] where Z LC(7) is the impedance under the action of the 7th harmonic voltage, ω LC and ω (1) and ω (7) are the angular frequencies of the fundamental voltage and the 7th harmonic voltage respectively, and there is ω (7) = 7ω (1) , L b , C b , C s are the inductor and capacitor of the receiving-end compensation network respectively, and L s is the self-inductance of the receiving-end coil.

[0021] Further, in Step 4, the coupling coefficient of the system is:

[0022]

[0023] where |V ac7 | and |I p7 | are the amplitudes of the 7th harmonic voltage and current output by the inverter, |V ac7 | can be obtained through Fourier transform of the given DC voltage, and |I p7 | can be obtained by sampling and processing the current in the transmitting-end loop through a high-frequency ADC.

[0024] Further, in Step 5, the voltage output at the receiving end of the system is:

[0025]

[0026] where |I p1 | is the amplitude of the fundamental current output by the inverter.

[0027] Further, in Step 7, the magnitude of the inverter output voltage is adjusted by adjusting the phase angle between the two bridge arms of the inverter, and its fundamental wave and 7th harmonic voltages are:

[0028]

[0029] Combined with the voltage output by the system receiver, the magnitude of the current flowing through the load can be obtained as follows:

[0030]

[0031] The implementation of the transmitter control of the output current and voltage is carried out by using the combined coupling coefficient and output voltage estimation method.

[0032] The second aspect of the present invention provides an electronic device, including a processor and a memory communicatively connected to the processor and used for storing executable instructions of the processor. The processor is used to execute the above-mentioned method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning.

[0033] The third aspect of the present invention provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the above-mentioned method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning is implemented.

[0034] Compared with the prior art, the method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning of the present invention has the following advantages:

[0035] The method of the present invention amplifies the 7th harmonic current of the WPT system without reducing the system efficiency, and then can estimate the coupling coefficient and output voltage of the transmitter and perform closed-loop control on the output voltage and current without using wireless communication and the receiver DC-DC converter. This solution has high reliability, is easy to implement, and avoids the problem of data packet loss existing in traditional transmitter control methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0037] Figure 1 is a schematic diagram of the topology structure of a WPT system in the prior art;

[0038] Figure 2 is a schematic diagram of the topology structure of the WPT system of the present invention;

[0039] Figure 3 is a schematic diagram of the equivalent circuit under the fundamental wave and the 7th harmonic;

[0040] Figure 4 is a schematic diagram of the design flow of the compensation network of the present invention;

[0041] Figure 5 is a waveform diagram of the phase-shift control of the inverter of the present invention;

[0042] Figure 6 Topological diagram of the method of the present invention;

[0043] Figure 7 Schematic diagram of the closed-loop control process of the present invention;

[0044] Figure 8 Topological structure of the prototype built according to the present invention;

[0045] Figure 9 Schematic diagram of the experimental results of the estimation of the coupling coefficient and the output voltage under different coupling coefficients of the present invention;

[0046] Figure 10 Schematic diagram of the analysis of the estimation accuracy of the coupling coefficient and the output voltage under different coupling coefficients of the present invention. Detailed implementation manners

[0047] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0048] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0049] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "mounted", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0050] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0051] Embodiment 1:

[0052] The present invention provides a method for estimating and controlling the coupling coefficient of a WPT system based on dual - frequency tuning. The topology adopted by the WPT system is as shown in the appendix Figure 2 . At the transmitting end, a full - bridge or half - bridge inverter is used, which can output a high - frequency square - wave voltage with a frequency of f (the fundamental angular frequency is: ω (1) = 2πf); L p and L s are the self - inductances of the coils at the transmitting end and the receiving end respectively; L a , C a , and C p are the inductor and capacitor of the compensation network at the transmitting end respectively; L b , C b , and C s are the inductor and capacitor of the compensation network at the receiving end respectively. R a , R p , R s , and R b are the high - frequency internal resistances of L a , L p , L s , and L b respectively; R eq is the equivalent AC load at the receiving end; all the above system parameters can be measured by an impedance analyzer. M is the mutual inductance between the coils at the transmitting end and the receiving end, and its coupling coefficient is . It can be seen that the loop impedance Z Rx at the transmitting end is:

[0053]

[0054] where Z LC is the parallel impedance of L b , R b , and C b at the receiving end, and can be expressed as:

[0055]

[0056] In traditional wireless power transfer, energy transfer is mainly achieved by the action of the fundamental voltage output by the inverter. The impedance of higher - order harmonics is large, and their energy transfer effect can be ignored. As shown in Figure 3 . When designing the compensation network in the present invention, energy transfer is carried out with the fundamental voltage, and the 7th - harmonic voltage is selected for estimating the coupling coefficient. Therefore, this topology needs to achieve the following functions: (1) Under the fundamental - wave condition, the system needs to transfer energy smoothly to the receiving end and act on R eq ; (2) Under the 7th - harmonic condition, the system can transfer energy smoothly to the receiving end but does not act on R eq . Therefore, the following conditions need to be met:

[0057] (a) For the transmitter loop Tx, whether for the fundamental wave or the 7th harmonic, L a , C a , L p , C p and the corresponding reflection impedance can all achieve resonance;

[0058] (b) For the transmitter loop Rx, under the fundamental wave condition, the parallel impedance (Z b , C b ) is large enough to achieve an open circuit, while the series impedance of L LC(1) and L s , C s is 0. At this time, the fundamental wave can effectively act on R eq ; at this time, Z Rx = R eq

[0059] (c) For Rx, under the 7th harmonic condition, the parallel impedance (Z b , C b ) is 0, and at this time this branch is effectively short-circuited under the 7th harmonic; at the same time, the impedance of Cs is large enough to ensure that the 7th harmonic current does not flow through R LC(7) , and at this time, Z eq = jωL Rx s LC(7) .

[0060] Therefore, the design formula for the compensation network can be obtained as:

[0061]

[0062] where Z LC(7) is the impedance of Z LC under the action of the 7th harmonic voltage. ω (1) and ω (7) are the angular frequencies of the fundamental wave voltage and the 7th harmonic voltage respectively, and there is ω (7) = 7ω (1) . Under the fundamental wave and 7th harmonic conditions, the mapped impedance of the receiving end at the transmitting end is:

[0063]

[0064] In order to meet the double-resonance conditions of the Tx circuit at the fundamental frequency and the 7th harmonic, the following condition (a) must be satisfied, that is:

[0065]

[0066] The design process of the compensation network for the transmitter and receiver of the present invention is as follows:

[0067] Generally, the self-inductances L p of the transmitter and receiver coils of the WPT system and Ls is a known quantity, while the compensation capacitors C p and C s can be calculated according to the compensation network design formula. And L a and L b need to be reasonably designed. The compensation network design process designed by the present invention is as Figure 4 shown:

[0068] Step 1: Determine the self-inductance of the system coil: L p 、L s , and for the convenience of design, let L a = L p ;

[0069] Step 2: Design the resonant capacitor C a 、C p and C s parameters of the Tx loop through formulas (3) and (5);

[0070] Step 3: Select a suitable harmonic and fundamental impedance ratio β (about 1% - 4%) in the Rx loop, which satisfies formula (6);

[0071] Step 4: Design the resonant parameters L b and C b in the Rx loop through formulas (3) and (6).

[0072]

[0073] Combined with the reflection impedance principle, the estimated value of the coupling coefficient of the transmitter and receiver coils can be further obtained as:

[0074]

[0075] where, |V ac7 | and |I p7 | are the amplitudes of the 7th harmonic voltage and current output by the inverter. |V ac7 | can be obtained through Fourier transform of the given DC voltage. |I p7 | can be obtained by sampling and processing the current in the transmitter loop through a high-frequency ADC.

[0076] At this time, the fundamental voltage output by the system can also be obtained as:

[0077]

[0078] where, |I p1 | is the amplitude of the fundamental current output by the inverter, and can also be obtained by high-frequency sampling of the current in the transmitter loop. And L p 、L sParameters such as these can be obtained through measurement and are basically constant in magnitude.

[0079] By adopting the above strategy, the output voltage of the system and the coupling coefficient can be estimated without using wireless communication. At this time, the transmitter control of the output voltage and output current can be achieved through the phase-shift control of the inverter. The waveform of the inverter phase-shift control is as shown in the appendix Figure 5 as follows. Figure 5 Among them, Q1 and Q2 are the drive signals of the front bridge arm of the inverter; Q3 and Q4 are the drive signals of the rear bridge arm of the inverter, and v s is the actual voltage waveform output by the inverter, and v ac (1) is the fundamental voltage waveform output by the inverter, δ is the overlap angle of the drive signals of Q1 and Q4, and it is also the effective angle of the output voltage of the inverter. By adjusting the phase angle between the two bridge arms of the inverter, the magnitude of the output voltage of the inverter can be adjusted. Its fundamental wave and 7th harmonic voltages are respectively:

[0080]

[0081] Among them, V DC is the DC bus voltage of the front stage of the inverter. Combining formula (8), the magnitude of the current flowing through the load can be obtained as:

[0082]

[0083] At this time, the transmitter control of the output current and voltage can be realized by combining the above coupling coefficient and output voltage estimation methods. The topology diagram is as shown in the appendix Figure 6 as follows, and the control flow is as shown in the appendix Figure 7 as follows.

[0084] Step 1: First, after the system starts, it is made to operate at a normal low power through soft start.

[0085] Step 2: Calculate the fundamental wave and the effective value of the 7th harmonic of its output voltage according to the effective angle of the voltage output by the inverter;

[0086] Step 3: Measure the effective values of the fundamental wave current and the 7th harmonic current output by the inverter;

[0087] Step 4: Calculate the coupling coefficient of the system according to formula (7);

[0088] Step 5: Calculate the voltage and current output by the receiving end of the system;

[0089] Step 6: Perform PI control according to the voltage and current set values and the magnitudes of the output voltage and current calculated in Step 5 to obtain the δ value acting on the inverter;

[0090] Step 7: Adjust the inverter phase shift angle according to the above PI control result, and then adjust the magnitudes of the system output voltage and current;

[0091] According to the above steps, sequentially execute Step 2 to Step 7, and the closed-loop control of the output current and voltage at the transmitting end can be achieved according to the coupling coefficient and the magnitude of the output voltage.

[0092] Next, the effectiveness of the method of the present invention is verified through experiments.

[0093] The present invention builds a prototype with the following topological structure, as Figure 8 shown. The processor uses the dual-core DSP controller TMS320F28377 of TI, and while performing high-frequency current sampling and analysis, it collaboratively controls the output voltage. The parameters of the system are shown in Table 1.

[0094] Table 1

[0095]

[0096] To verify the effectiveness of the present invention, the following several experiments are respectively carried out.

[0097] 1. Ensure that there is no offset in the coil, adjust the distance between the coils to change the system coupling coefficient, and use an impedance analyzer to measure and record the distance between the coils under different coupling coefficients;

[0098] 2. Conduct experiments under different coupling coefficients, and record the calculated values of the coupling coefficient and the output voltage of the controller under different loads (R eq are 10 Ω, 30 Ω, and 50 Ω respectively). At the same time, record the actual output voltage of the system under the corresponding conditions.

[0099] Thus, the actual output voltage and the estimated voltage of the system under different loads and different coupling coefficients can be obtained, as Figure 9 shown. At the same time, under different coupling coefficients, use formula (7) to calculate the estimation deviation of the coupling coefficient and the output voltage to verify the accuracy of the coupling coefficient estimation, and the results are as Figure 10 shown. Analysis of the estimation accuracy of the coupling coefficient and the output voltage under different coupling coefficients:

[0100]

[0101] Among them, k act is the actual coupling coefficient of the coil in the experiment; k est is the coupling coefficient calculated by the coupling coefficient estimation method proposed by the present invention; V act is the actual output voltage on the load side in the experiment; V est is the output voltage on the load side calculated by the output voltage estimation method proposed by the present invention. kerr and V err are the coupling coefficient and the estimation accuracy of the output voltage, respectively.

[0102] The results show that the estimated value of the coupling coefficient is consistent with the actual measured value, and the output voltage and the estimated voltage also have good consistency under different coupling coefficients. The maximum experimental estimation errors of the coupling coefficient and the output voltage are 4% and 4.7%, respectively. Therefore, the system can effectively estimate the coupling coefficient and the output.

[0103] Embodiment 2:

[0104] An electronic device includes a processor and a memory communicatively connected to the processor and configured to store executable instructions of the processor. The processor is configured to execute the above-mentioned method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning.

[0105] Embodiment 3:

[0106] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for estimating and controlling coupling coefficient of a WPT system based on dual-frequency tuning, characterized in that: The steps include: Step 1: construct a wireless power transmission system, including a transmitter, a transmitter compensation network, a receiver, a receiver compensation network, a receiver load, and a controller, wherein the transmitter includes a transmitter coil and an inverter, and the receiver includes a receiver coil and a rectifier; Step 2: Calculate the effective value of the fundamental wave and the 7th harmonic of the output voltage according to the effective angle of the voltage output by the inverter; Step 3: Measure the effective value of the inverter output fundamental current and the 7th harmonic current; Step 4: Calculate the coupling coefficient of the system; Step 5: Calculate the voltage and current output by the receiving end of the system; Step 6: Perform PI control according to the voltage and current setting values, and the output voltage and current calculated in step 5; Step 7: According to the above PI control results, the inverter phase shift angle is adjusted to further adjust the system output voltage and current; Step 8: Run steps 2 to 7 in sequence to achieve closed-loop control of the output current and voltage at the transmitter according to the coupling coefficient and the output voltage.

2. According to a WPT system coupling coefficient estimation and control method based on dual-frequency tuning according to claim 1, it is characterized in that: The design formulas of the transmitter compensation network and the receiver compensation network are: Where Z LC(7) Z LC Impedance under the action of 7th harmonic voltage, ω (1) and ω (7) are the angular frequencies of the fundamental voltage and the 7th harmonic voltage respectively, and there exists ω (7) =7ω (1) , L b , C b , C s The three are the inductance and capacitance of the compensation network at the receiving end, L s is the self-inductance of the coil at the receiving end.

3. According to a WPT system coupling coefficient estimation and control method based on dual-frequency tuning according to claim 1, it is characterized in that: In step 4, the coupling coefficient of the system is: Among them, |V ac7 |and|I p7 |Amplitude of the seventh harmonic voltage and current output by the inverter, |V ac7 | can be obtained by Fourier transforming a given DC voltage, |I p7 |The transmitter loop current can be sampled and processed by a high-frequency ADC.

4. According to a WPT system coupling coefficient estimation and control method based on dual-frequency tuning according to claim 1, it is characterized in that: In step 5, the voltage output by the system receiving end is: Among them, |I p1 | is the fundamental current amplitude of the inverter output.

5. According to a method for estimating and controlling the coupling coefficient of a WPT system based on dual-frequency tuning according to claim 4, it is characterized in that: In step 7, the magnitude of the inverter output voltage is adjusted by adjusting the phase angle between the two bridge arms of the inverter, and the fundamental wave and the 7th harmonic voltage are respectively: Combined with the voltage output at the receiving end of the system, the current flowing through the load can be obtained as: The output current and voltage are controlled at the transmitter by combining the coupling coefficient and the output voltage estimation method.

6. An electronic device, comprising a processor and a memory connected to the processor for storing instructions executable by the processor, characterized in that: The processor is used to execute a WPT system coupling coefficient estimation and control method based on dual-frequency tuning as described in any one of claims 1-5 above.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, a WPT system coupling coefficient estimation and control method based on dual-frequency tuning as described in any one of claims 1 to 5 is implemented.

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