An ec-wpt system with constant current output characteristic resistant to coupling mechanism offset

Abstract

The application relates to the technical field of electric field coupling type wireless power transmission (EC-WPT), and particularly discloses an EC-WPT system with constant current output characteristics and anti-coupling mechanism offset, wherein a primary side resonance network adopts an LC resonance network composed of an inductor L1 and a capacitor C1, and a secondary side resonance network adopts a П type resonance network composed of a capacitor C2, an inductor L2 and an inductor L3. The system adopts an LC-CLL resonance network, and based on the same, network parameters are designed to make the system have anti-offset characteristics and constant current output characteristics, so that constant current output can be realized under the condition of load change, and constant current output can still be realized under the condition of coupling mechanism offset. Under the condition that the coupling mechanism does not offset, the system can realize ZPA operation, and under the condition that the coupling mechanism offsets greatly, the input impedance angle of the system is small, so that the system can have a high power factor and reduce reactive power loss.

Description

Technical Field

[0001] This invention relates to the field of electric-field coupled wireless power transfer (EC-WPT) technology, and more particularly to an EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment. Background Technology

[0002] Wireless Power Transfer (WPT) refers to the comprehensive application of power electronics and control theories and technologies to transmit electrical energy from the power grid or battery to electrical devices through a carrier (such as an electric field, magnetic field, microwave, or laser) in a non-electrical contact mode. Based on different transmission mechanisms, it can be divided into several types, including Magnetic Coupling Wireless Power Transfer (MC-WPT), Electric-field Coupled Wireless Power Transfer (EC-WPT), Microwave Power Transfer (MPT), and Laser Power Transfer (LPT). Among these, the EC-WPT system has the following advantages: the coupling mechanism is simple, lightweight, and flexible in shape, resulting in low overall cost; during operation, most of the electrical flux of the electric field coupling mechanism is distributed between the electrodes, minimizing electromagnetic interference to the surrounding environment; and when there are metal conductors between or around the electric field coupling mechanism, eddy current losses are minimal. Therefore, EC-WPT technology has attracted widespread attention from experts both domestically and internationally.

[0003] In EC-WPT technology applications, most wireless power supply devices, such as electric vehicles, require a constant output current to ensure performance and safety. However, during charging, the movement of the device can cause offsets in the coupling mechanism or changes in transmission distance, affecting the coupling capacitance. Furthermore, the load on the device is not constant during operation. Therefore, the output current of the EC-WPT system must not change significantly with variations in coupling capacitance and load.

[0004] To address the above requirements, reference [1] proposes a parameter design method based on a bilateral LC resonant network that enables the system to achieve constant current output; reference [2] proposes an FT resonant network, which enables the system to have constant current output characteristics through reasonable parameter configuration. Reference [3] proposes a parameter design method based on an LC-LCLC resonant network that enables constant current output. The methods proposed in the above references can only guarantee constant current output under load changes. When the coupling mechanism is offset, it will seriously affect its constant current output characteristics.

[0005] [1] Lian J, Qu

[0006] [2] Su Yugang, Xie Shiyun, Wang Zhihui, et al. Constant voltage-constant current electric field coupled power transmission system based on FF / T variable structure resonant network [J]. Journal of Electrical Engineering, 2019, 34(06):1127-1136.

[0007] [3] Liao Zhijuan, Zhou Lei, Wu Zhen, Wei Guoyu, Xia Chenyang. Variable structure LC-CLCL topology constant voltage constant current electric field coupled power transmission system [J]. Proceedings of the CSEE, 2021, 41(17):6039-6050. Summary of the Invention

[0008] This invention provides an EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment. The technical problem it solves is that existing methods can ensure constant current output of the EC-WPT system under load changes, but when the coupling mechanism is misaligned, it cannot simultaneously maintain its constant current output characteristics and high power factor.

[0009] To address the above technical problems, this invention provides an EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment. The system includes a DC source, an inverter, a primary-side resonant network, a coupling mechanism, a secondary-side resonant network, a rectifier and filter circuit, and a load equivalent resistance R. LThe coupling mechanism includes opposing emitting plates P1 and receiving plates P3, as well as opposing emitting plates P2 and receiving plates P4. The primary side resonant network is an LC resonant network composed of inductor L1 and capacitor C1, and the secondary side resonant network is a П-type resonant network composed of capacitor C2, inductor L2 and inductor L3. Inductor L2 is connected between capacitor C2 and inductor L3.

[0010] Inductor L1, capacitor C1, capacitor C2, inductor L2, and inductor L3 satisfy the following:

[0011] ω 2 L1C1=1,ω 2 C2(L2+L3)=1,

[0012] Neglecting the internal resistance of the inductor and the equivalent series resistance of the capacitor, These represent the impedances of inductor L1 and capacitor C1, respectively. ω represents the impedance of capacitor C2, inductor L2 and inductor L3 respectively, and ω represents the operating angular frequency of the system.

[0013] Specifically, assume C1 = αC s C2 = βC s L2 = γL3, α represents the capacitance C1 and the equivalent capacitance C s The proportionality coefficient between them, β, represents the ratio of capacitance C2 to equivalent capacitance C. s The proportionality coefficients α, β, and γ represent the proportionality coefficients between inductors L2 and L3. Then, the proportionality coefficients α, β, and γ satisfy (β-γ)α+β=0.

[0014] Specifically, the system parameter design process includes the following steps:

[0015] S1. Set the system's operating frequency based on engineering experience;

[0016] S2. Determine the system input voltage E according to actual requirements. dc With system output current I L The set value, and the equivalent capacitance C of the coupling mechanism determined according to the coupling mechanism. s Size;

[0017] S3, according to E dc I L as well as Determine the relationship between α and γ, u in This represents the instantaneous output voltage of the inverter. I represents the output current vector of the П-type resonant network. o express The effective value, The inverter's output voltage vector is represented by t, which represents time.

[0018] S4. According to (β-γ)α+β=0 and Analysis of equivalent capacitance C s α and the system's input impedance angle The relationship between C s =C s +ΔC represents the equivalent capacitance when the coupling mechanism shifts, and ΔC represents the shift of the coupling capacitance. At this time, α becomes... β becomes Rectifier filter and load equivalent resistance R L Equivalent resistance R eq ;

[0019] S5. Select the value of α according to the input impedance angle requirements;

[0020] S6. Obtain a set of parameter values ​​for L1, C1, C2, L2, and L3 that satisfy the conditions.

[0021] Specifically, C s =C s1 C s2 / (C s1 +C s2 ), C s1 C represents the coupling capacitance formed between the opposite emitting plate P1 and the receiving plate P3. s2 This represents the coupling capacitance formed between the emitting plate P2 and the receiving plate P4 that are facing each other.

[0022] Specifically, R eq =8R L / π 2 .

[0023] Specifically, the system output current is constant:

[0024] Specifically, the full-bridge inverter circuit consists of four MOSFETs.

[0025] Specifically, the rectifier-filter circuit consists of four diodes and a filter capacitor C. f composition.

[0026] This invention provides an EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment. It employs an LC-CLL resonant network and, based on this, designs network parameters that enable the system to simultaneously resist misalignment and possess constant current output characteristics. Compared with other resonant networks with constant current output characteristics, this invention has the following advantages:

[0027] 1) It can achieve constant current output not only under load changes, but also under the condition that the coupling mechanism is offset.

[0028] 2) When the coupling mechanism does not shift, the system can achieve ZPA operation. When the coupling mechanism shifts significantly, the system's input impedance angle is small, which can ensure that the system has a high power factor and reduce reactive power loss. Attached Figure Description

[0029] Figure 1 This is a topology diagram of an EC-WPT system with constant current output characteristics that resists coupling mechanism offset, provided by an embodiment of the present invention.

[0030] Figure 2 This is provided by the embodiments of the present invention. Figure 1 The system equivalent circuit diagram;

[0031] Figure 3 This is a prominent LC resonant network provided in the embodiments of the present invention. Figure 2 The system equivalent circuit diagram;

[0032] Figure 4 This is a prominent CLL resonant network provided in the embodiments of the present invention. Figure 2 The system equivalent circuit diagram;

[0033] Figure 5 This is a parameter design flowchart of an EC-WPT system with constant current output characteristics that resists coupling mechanism offset, provided by an embodiment of the present invention.

[0034] Figure 6 The parameters α and C provided in the embodiments of the present invention are s Relationship between input impedance angle and input impedance angle;

[0035] Figure 7 When the coupling mechanism provided in the embodiment of the present invention is facing (C) s =200pF) Output voltage and current waveform diagram;

[0036] Figure 8 This is a waveform diagram of the inverter output voltage and current of the system provided in an embodiment of the present invention;

[0037] Figure 9 This is a waveform diagram of the output current when the coupling mechanism is offset according to an embodiment of the present invention;

[0038] Figure 10 This is a waveform diagram of the inverter output voltage and current of the system under the condition of coupling mechanism offset provided in the embodiment of the present invention. Detailed Implementation

[0039] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0040] This invention provides an EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment, such as... Figure 1 The circuit diagram shown includes a DC source (E dc The circuit consists of a DC input voltage, an inverter (composed of four MOSFETs S1-S4), a primary-side resonant network, a coupling mechanism, a secondary-side resonant network, and a rectifier and filter circuit (composed of four diodes D1-D4 and a filter capacitor C). f (Composition) and load equivalent resistance R L The coupling mechanism includes opposing emitter plates P1 and P3, and opposing emitter plates P2 and P4. The two opposing plates P1-P3 and P2-P4 respectively form coupling capacitors C. s1 and C s2 The primary resonant network is an LC resonant network composed of inductor L1 and capacitor C1, and the secondary resonant network is a П-type resonant network composed of capacitor C2, inductor L2 and inductor L3, with inductor L2 connected between capacitor C2 and inductor L3.

[0041] The DC power supply generates a high-frequency voltage through a high-frequency inverter. This voltage is then filtered by an LC network at the transmitting end and simultaneously pumped up to the high excitation voltage required by the coupling mechanism. When the receiving plate of the coupling mechanism is placed near the transmitting plate, an interactive electric field is generated between the two plates. Under the influence of this interactive electric field, a displacement current "flows" through the plates, enabling wireless power transmission. The rectifier filter converts the AC power into DC power to supply the electrical equipment.

[0042] exist Figure 1 In the topology shown, the internal resistance of the inductor and the equivalent series resistance of the capacitor are usually small compared to their own impedance. To simplify the analysis, the internal resistance of the inductor and the equivalent series resistance of the capacitor can be ignored, and the system can be equivalent to... Figure 2 The circuit shown. Figure 1 The rectifier filter and load R in L It can be equivalent to a resistor R eq Satisfying R eq =8R L / π 2 The equivalent capacitance C of the coupling mechanism s =C s1 C s2 / (C s1 +C s2 ), u inIt is the instantaneous output voltage of the inverter, i1, i s i2, i o These are respectively the current flowing through inductor L1 and capacitor C s Inductor L2 and resistor R eq The current, u o This represents the system's output voltage.

[0043] Since the system's resonance compensation network can filter out most of the higher harmonics, the fundamental frequency approximation method can be used to simplify the analysis, resulting in:

[0044]

[0045] Where ω is the system's operating angular frequency, and it satisfies the relationship ω = 2πf with the operating frequency f. Similarly, the effective value I of the input current of the rectifier and filter circuits... o With output current I L The valid values ​​have the following relationship:

[0046]

[0047] The system's transmitter is an LC resonant network, as shown in the schematic diagram below. Figure 3 As shown. The inverter output voltage serves as the input u of the LC resonant network. in R in the figure o1 This represents the equivalent input impedance of the subsequent circuit.

[0048] According to Kirchhoff's voltage law, the relationship between the output current and the input voltage of this circuit is as follows:

[0049]

[0050] in These represent the impedances of inductor L1 and capacitor C1, respectively. and When equation (4) is satisfied,

[0051]

[0052] From equation (3), we can obtain:

[0053]

[0054] From equation (5), it can be seen that, given a constant pressure source Under excitation, when the parameters satisfy the resonance condition in equation (4), the output current of the LC resonant network is... The output current is independent of the subsequent circuitry and is determined by the input voltage and the impedance of inductor L1.

[0055] The receiver CLL resonant network is as follows Figure 4 As shown.

[0056] Analyzing this circuit, neglecting the internal resistance of the inductor and the equivalent series resistance of the capacitor, we can obtain... Figure 4 Output current With input current The relationships are:

[0057]

[0058] in These represent the impedances of capacitor C2, inductor L2, and inductor L3, respectively. and When equation (7) is satisfied,

[0059]

[0060] From equation (6), we can obtain:

[0061]

[0062] As can be seen from equation (8), when the CLL resonant network (P-type resonant network) at the receiving end is excited by a given constant current source, and when the parameters satisfy the resonance condition in equation (7), its output current is... Size is independent of load.

[0063] Based on the above analysis, assuming the operating frequency of the entire system is ω, and the system simultaneously satisfies the resonance conditions in equations (4) and (7), that is, the parameters satisfy...

[0064] ω 2 L1C1=1 (9)

[0065] ω 2 C2(L2+L3)=1 (10)

[0066] The system output current is:

[0067]

[0068] As can be seen from equation (11), the system output current is related to the equivalent capacitance C of the system coupling mechanism. s It is unrelated to, and also unrelated to, the load resistance R. eq It is unrelated, so the system can achieve constant current output when the coupling mechanism is offset and the load changes.

[0069] The input impedance angle in this embodiment is: Figure 2 The equivalent circuit shown has an input port impedance angle. In practical applications, if the system input impedance angle is too large, the power factor will be small, resulting in greater reactive power loss and lower transmission efficiency. Therefore, the system input impedance angle is analyzed to ensure that the system operates with a smaller input impedance angle.

[0070] Assume C1 = αC s C2 = βC s L2 = γL3, according to equations (9) and (10):

[0071]

[0072]

[0073]

[0074] α represents the difference between capacitance C1 and equivalent capacitance C. s The proportionality coefficient between them, β, represents the ratio of capacitance C2 to equivalent capacitance C. s The proportionality coefficient between inductors L2 and L3 is γ, which represents the proportionality coefficient between inductors L2 and L3.

[0075] Substituting equations (12), (13), and (14) into equation (10), we can obtain...

[0076]

[0077] Using Kirchhoff's voltage law to analyze the entire circuit, we can find:

[0078]

[0079] Solving for:

[0080]

[0081] When the imaginary part of equation (17) is 0, the input impedance angle is 0, and the entire system operates in ZPA state. At this time, the relationship between α, β, and γ is:

[0082] (β-γ)α+β=0 (18)

[0083] Based on the above analysis, it can be seen that when the system coupling mechanism is aligned and all parameters satisfy the conditions of equations (12), (13), and (18), the system operates under ZPA. However, when the coupling mechanism is offset, the equivalent capacitance of the coupling mechanism becomes C. s =C s +ΔC, where ΔC represents the offset of the coupling capacitor. At this point:

[0084]

[0085]

[0086] (β'-γ)α'+β'=0 no longer holds true, the system cannot achieve ZPA, and its input impedance angle is:

[0087]

[0088] As the above analysis shows, when the coupling mechanism shifts, the system cannot be guaranteed to operate in ZPA mode. A larger input impedance angle increases the volt-ampere rating of components, increases reactive power loss, and reduces transmission efficiency. To ensure system performance, the system parameter design process described below should ensure that the system input impedance angle is as small as possible when the coupling mechanism shifts.

[0089] This paper determines the system input voltage and output current based on the application scenario, and determines the equivalent coupling capacitance of the coupling mechanism based on its dimensions. Currently, most EC-WPT systems operate in the range of 500kHz to 2MHz. Excessive operating frequency leads to higher dynamic losses and electromagnetic interference, while insufficient frequency results in a larger compensation inductance, lower system quality factor, and lower power density. Furthermore, a larger equivalent coupling capacitance allows for a lower operating frequency, while a smaller equivalent coupling capacitance necessitates a higher operating frequency. Based on the above analysis and specific engineering requirements, a reasonable frequency value is selected within the 500kHz to 2MHz range. The system parameter design flowchart is shown below. Figure 5 As shown.

[0090] Currently, the rated input and output of lithium batteries are mostly 96V / 2A, 72V / 2A, and 48V / 2A. Taking a system input voltage of 72V and a constant output current of 2A as an example, the coupling mechanism capacitor parameter is taken as 200pF, and the system operating frequency is taken as f = 1MHz based on engineering experience. According to equations (2)(15)(18)(21), the parameters α and C can be obtained. s The relationship with the input impedance angle is as follows: Figure 6 As shown, according to Figure 6 It can be observed that when α≤3, the coupling mechanism capacitance varies within the range of 200pF±50%, and the system input impedance angle only varies between -5° and 5°, which is within an acceptable range. Furthermore, if C1 is too small, the compensation inductance L1 at the transmitter will be large, increasing the system size and reducing power density. Therefore, it is desirable that C1 is sufficiently large under the given conditions. Also, because C1=αC s Therefore, we take α = 3.

[0091] Based on the aforementioned parameter design method, a set of system simulation parameters can be obtained as shown in Table 1.

[0092] Table 1 System Simulation Parameters

[0093]

[0094] Based on the parameters in Table 1, a system simulation model was established using the MATLAB / Simulink platform. When the coupling mechanism has no offset, i.e., C... s=200pF, the simulation results obtained by varying the load resistance during the simulation process are as follows: Figure 7 As shown in the figure, during the switch from load resistance of 30Ω to 60Ω, the load current changes from 1.991A to 1.893A; during the switch from load resistance of 60Ω to 30Ω, the load current changes from 1.893A to 2.023A. Therefore, when the load resistance changes by 50%, the load current changes by only 6.5%, demonstrating good constant current performance. The inverter output current and voltage waveforms corresponding to a load resistance of 30Ω are shown in the figure. Figure 8 As shown in (a), the inverter output current and voltage waveforms are as follows when the load resistance is 60Ω. Figure 8 As shown in (b). Figure 8 It can be seen that the system is in the ZPA state under varying resistance, which is consistent with the aforementioned theoretical analysis.

[0095] When the coupling mechanism experiences a deviation of ±25%, i.e., the equivalent coupling capacitance C s The values ​​are 250pF and 150pF, respectively. Figure 9 The output current i is calculated for three cases with equivalent coupling capacitances of 250pF, 200pF, and 150pF. L The simulation waveforms show the load resistance changing from 30Ω to 60Ω at 0.01s and from 60Ω to 30Ω at 0.025s. From... Figure 9 It can be seen that the simulated waveforms almost overlap in the three cases. A magnified view from the lower right corner, showing the time from 0.016s to 0.017s, reveals that the current difference is only 5% in all three cases. Therefore, the offset of the coupling mechanism has a very small impact on the output current, and the system exhibits strong anti-offset performance. Table 2 lists the output current magnitudes corresponding to the load resistance changing from 30Ω to 60Ω and then back to 30Ω in the three cases of coupling mechanism offset by -25%, facing directly, and offset by +25%. The maximum current change is only 7.25%.

[0096] Table 2 Output current values ​​for different coupling mechanism parameters under different loads

[0097]

[0098] The inverter output voltage and current waveforms when the coupling mechanism is offset by ±25% are as follows: Figure 10 As shown, where Figure 10 (a) C S =150pF, Figure 10 (b) C S =250pF. It can be seen that even with a ±25% offset in the coupling mechanism, the phase difference between the inverter output voltage and current changes by less than 5°, which is consistent with the theoretical value.

[0099] In summary, the EC-WPT system with constant current output characteristics that resists coupling mechanism misalignment provided by the embodiments of the present invention employs an LC-CLL resonant network, and based on this, network parameters are designed to enable the system to simultaneously resist misalignment and possess constant current output characteristics. Compared with other resonant networks with constant current output characteristics, the present invention has the following advantages:

[0100] 1) It can achieve constant current output not only under load changes, but also under the condition that the coupling mechanism is offset.

[0101] 2) When the coupling mechanism does not shift, the system can achieve ZPA operation. When the coupling mechanism shifts significantly, the system's input impedance angle is small, which can ensure that the system has a high power factor and reduce reactive power loss.

[0102] Simulation results using MATLAB / Simulink show that the system model still exhibits good constant current performance even when the load is disturbed by 50% and the coupling mechanism is offset by 25%.

[0103] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An EC-WPT system with constant current output characteristic and anti-coupling mechanism offset, comprising a DC source, an inverter, a primary side resonant network, a coupling mechanism, a secondary side resonant network, a rectification filter circuit and a load equivalent resistance R L , the coupling mechanism comprises opposite emitter plates P1 and receiver plates P3 and opposite emitter plates P2 and receiver plates P4, characterized in that: The primary side resonant network adopts an LC resonant network composed of an inductor L1 and a capacitor C1, and the secondary side resonant network adopts a П type resonant network composed of a capacitor C2, an inductor L2 and an inductor L3, and the inductor L2 is connected between the capacitor C2 and the inductor L3; The inductor L1, the capacitor C1, the capacitor C2, the inductor L2 and the inductor L3 satisfy: ， ， ， ， , represent the impedance of the inductance L1 and the capacitance C1, respectively, , , represent the impedance of the capacitance C2, the inductance L2 and the inductance L3, respectively, represents the operating angular frequency of the system; Let , , , represent the proportional coefficient between the capacitance C1 and the equivalent capacitance C s , represent the proportional coefficient between the capacitance C2 and the equivalent capacitance C s , represent the proportional coefficient between the inductance L2 and the inductance L3, then the proportional coefficient , , satisfies ; The parameter design process of the system comprises the following steps: S1, setting the working frequency of the system according to engineering experience; S2, determining the system input voltage E according to actual requirements dc and the set value of the system output current I L , and determining the size of the equivalent capacitance C s of the coupling mechanism according to the coupling mechanism S3. According to E dc , L and , , determining a relationship between , represents an instantaneous output voltage of the inverter, represents an output current vector of the П resonant network, represents a root mean square value of represents an output voltage vector of the inverter, t represents time; S4. The method of S3, wherein the coupling mechanism is a transformer. And The relationship between the equivalent capacitance C s , and the input impedance angle of the system , representing the equivalent capacitance when the coupling mechanism is offset, representing the coupling capacitance offset amount, at which becomes , becomes , the rectifier filter and load equivalent resistance R L is equivalent to resistance R eq ; S5. Taking the value of the input impedance angle according to the demand of the input impedance angle ; S6, obtaining a group of parameter values of L1, C1, C2, L2 and L3 satisfying the condition.

2. The EC-WPT system with constant current output characteristic and anti- coupling mechanism offset according to claim 1, characterized in that: , C s1 represents the coupling capacitance formed between the facing emitter plate P1 and the receiver plate P3, C s2 represents the coupling capacitance formed between the facing emitter plate P2 and the receiver plate P4.

3. The EC-WPT system with constant current output characteristic and anti-coupling mechanism offset according to claim 1, characterized in that: 。 4. The EC-WPT system with constant current output characteristic and anti- coupling mechanism offset according to claim 2, wherein, The system output current is constant: 。 5. The EC-WPT system with constant current output characteristic and anti- coupling mechanism offset according to claim 1, characterized in that: The full-bridge type inverter circuit is composed of four MOSFETs.

6. The EC-WPT system with constant current output characteristic and anti- coupling mechanism offset according to claim 1, characterized in that: The rectifier filter circuit is composed of four diodes and a filter capacitor C f Composition.

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