A robust autonomous fractional-order bidirectional wireless charging and discharging system

Abstract

The present invention relates to a highly robust autonomous fractional-order bidirectional wireless charging and discharging system, comprising a fractional-order primary circuit and a fractional-order secondary circuit, wherein the fractional-order primary circuit comprises a dual-port primary fractional-order capacitor, a primary inductor and a power grid, wherein the first port of the dual-port primary fractional-order capacitor is connected to the power grid, and the second port is connected to the primary inductor; the fractional-order secondary circuit comprises a dual-port secondary fractional-order capacitor, a secondary inductor and a battery, wherein the first port of the dual-port secondary fractional-order capacitor is connected to the battery, and the second port is connected to the secondary inductor; the primary inductor and the secondary inductor realize wireless power transmission by magnetic field coupling. The system improves the robustness of the bidirectional wireless charging and discharging system.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and in particular relates to a highly robust autonomous fractional-order bidirectional wireless charging and discharging system. Background Art

[0002] In recent years, my country has vigorously developed new energy sources, and the market share of electric vehicles has increased year by year, and bidirectional wireless power transmission technology has become more and more popular. In a typical electric vehicle magnetic coupling bidirectional wireless charging and discharging system, both the primary and secondary sides need to use bidirectional converters, and the end connected to the power grid's industrial frequency AC power requires a two-stage bidirectional converter. Different coupling mechanisms, resonant networks, and bidirectional converters will affect the performance of the system. When the relative position of the coil, the load size, the passive parameters, and the resonant frequency are offset, the power transmission direction and size of the electric vehicle bidirectional wireless charging and discharging system will become unstable, and the transmission efficiency will also be reduced, which greatly hinders the application and promotion of electric vehicle bidirectional wireless charging and discharging technology. Summary of the invention

[0003] The object of the present invention is to provide a highly robust autonomous fractional-order bidirectional wireless charging and discharging system, which improves the robustness of the bidirectional wireless charging and discharging system.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a highly robust autonomous fractional-order bidirectional wireless charging and discharging system, including a fractional-order primary circuit and a fractional-order secondary circuit, the fractional-order primary circuit includes a dual-port primary fractional-order capacitor, a primary inductor and a power grid, the first port of the dual-port primary fractional-order capacitor is connected to the power grid, and the second port is connected to the primary inductor; the fractional-order secondary circuit includes a dual-port secondary fractional-order capacitor, a secondary inductor and a battery, the first port of the dual-port secondary fractional-order capacitor is connected to the battery, and the second port is connected to the secondary inductor; the primary inductor and the secondary inductor realize wireless power transmission by magnetic field coupling.

[0005] Furthermore, the dual-port primary fractional-order capacitor C α1 and the two-port secondary side fractional capacitor C α2 The differential relationship between the voltage and current at the second port of satisfies:

[0006]

[0007] Among them, i Cn is the instantaneous value of the current at the second port of the two-port fractional capacitor, v Cn is the instantaneous voltage value of the second port of the two-port fractional capacitor, C αn is the capacitance of the two-port fractional capacitor, α n is the order of the two-port fractional capacitor, 0<αn <2 and α n ≠1, n=1, 2 represent the two-port primary fractional-order capacitor and the two-port secondary fractional-order capacitor respectively;

[0008] The phase relationship satisfies:

[0009]

[0010] in, is the phase difference between the current and voltage at the second port of the two-port fractional-order capacitor.

[0011] Furthermore, the first port of the two-port fractional capacitor serves as both an energy injection port and an energy absorption port. When the order α of the fractional capacitor is greater than 1, its first port is an energy injection port, and the injected power P1 satisfies:

[0012] P1=-V C I C cos(0.5πα)

[0013] When the order α of the fractional capacitor is less than 1, its first port is an energy absorption port, and the absorbed power P2 satisfies:

[0014] P2=V C I C cos(0.5πα)

[0015] Among them, V C and I C are the average values ​​of the voltage and current at the second port of the two-port fractional capacitor, respectively.

[0016] Furthermore, when the order of the dual-port primary fractional-order capacitor is greater than 1 and the order of the dual-port secondary fractional-order capacitor is less than 1, the fractional-order primary circuit serves as a transmitting end, the fractional-order secondary circuit serves as a receiving end, and the power grid charges the battery; when the order of the dual-port primary fractional-order capacitor is less than 1 and the order of the dual-port secondary fractional-order capacitor is greater than 1, the fractional-order secondary circuit serves as a transmitting end, the fractional-order primary circuit serves as a receiving end, and the battery discharges to the power grid.

[0017] Furthermore, a first resistor is connected in series on a connection line between the dual-port primary fractional-order capacitor and the primary inductor, and a second resistor is connected in series on a connection line between the dual-port secondary fractional-order capacitor and the secondary inductor.

[0018] Furthermore, an autonomous system is formed by using a two-port fractional-order capacitor with an order greater than 1 and an inductor coil, so that the parameters of the two-port fractional-order capacitor with an order greater than 1 automatically follow the changes of system parameters to achieve constant system transmission efficiency and output power.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the system has a simple structure, does not require a high-frequency voltage source, and the transmission efficiency and output power of the system can automatically adapt to changes in the coupling coefficient and the resonant frequency. The present invention is based on the negative resistance characteristics of the fractional-order capacitor when the order is greater than 1 and the positive resistance characteristics when the order is less than 1. By changing the order, the fractional-order primary circuit can be used as both a transmitter and a receiver. At the same time, the autonomous circuit based on the negative resistance characteristics of the fractional-order capacitor enables the system to have a constant transmission efficiency and output power, which solves the problem of efficiency reduction or unstable output power caused by the resonant frequency offset and the change of the coupling coefficient in the traditional two-way wireless charging and discharging system, and improves the robustness of the two-way wireless charging and discharging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the system structure of an embodiment of the present invention;

[0021] Figure 2 is a curve showing the relationship between the transmission efficiency and the coupling coefficient of the system in the embodiment of the present invention;

[0022] Figure 3 is a curve showing the relationship between the system output power and the coupling coefficient in an embodiment of the present invention;

[0023] Figure 4 is a curve showing the relationship between the transmission efficiency of the system and the resonant frequency offset of the receiving end in the embodiment of the present invention;

[0024] Figure 5 is a curve showing the relationship between the system output power and the resonant frequency offset of the receiving end in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] like Figure 1As shown, this embodiment provides a highly robust autonomous fractional-order bidirectional wireless charging and discharging system, including a fractional-order primary circuit and a fractional-order secondary circuit, wherein the fractional-order primary circuit includes a dual-port primary fractional-order capacitor C α1 , the primary inductor L1 and the power grid, the dual-port primary fractional capacitor C α1 The first port is connected to the power grid, and the second port is connected to the primary inductor L1; the fractional-order secondary circuit includes a dual-port secondary fractional-order capacitor C α2 , the secondary inductor L2 and the battery, the dual-port secondary fractional capacitor C α2 The first port is connected to the battery, and the second port is connected to the secondary inductor L2; the dual-port primary fractional-order capacitor C α1 A first resistor R is connected in series with the connection line of the primary inductor L1. S1 , the dual-port secondary side fractional capacitor C α2 A second resistor R is connected in series with the connection line of the secondary inductor L2. S1 The primary inductor L1 and the secondary inductor L2 realize wireless power transmission through magnetic field coupling.

[0029] The dual-port primary side fractional capacitor C α1 and the two-port secondary side fractional capacitor C α2 The differential relationship between the voltage and current at the second port of satisfies:

[0030]

[0031] The phase relationship satisfies:

[0032]

[0033] The impedance is:

[0034]

[0035] Among them, i Cn is the instantaneous value of the current at the second port of the two-port fractional capacitor, v Cn is the instantaneous voltage value of the second port of the two-port fractional capacitor, C αn is the capacitance of the two-port fractional capacitor, α n is the order of the two-port fractional capacitor, 0<α n <2 and α n ≠1, n=1, 2 represent the two-port primary fractional-order capacitor and the two-port secondary fractional-order capacitor respectively; is the phase difference between the current and voltage of the second port of the two-port fractional-order capacitor; ω is the operating angular frequency of the two-port fractional-order capacitor.

[0036] The first port of the two-port fractional capacitor can be used as both an energy injection port and an energy absorption port. When the order α of the fractional capacitor is greater than 1, its first port is an energy injection port, and the injected power P1 satisfies:

[0037] P1=-V C I C cos(0.5πα)

[0038] When the order α of the fractional capacitor is less than 1, its first port is an energy absorption port, and the absorbed power P2 satisfies:

[0039] P2=V C I C cos(0.5πα)

[0040] Among them, V C and I C are the average values ​​of the voltage and current at the second port of the two-port fractional capacitor, respectively.

[0041] The working principle of this system is: using a two-port fractional capacitor with an order greater than 1 and an inductor coil to form an autonomous system, so that the parameters of the two-port fractional capacitor with an order greater than 1 can automatically follow the changes in the system parameters to achieve constant system transmission efficiency and output power. The two-port fractional capacitor with an order greater than 1 has a negative resistance characteristic, provides energy for the circuit, and automatically selects the operating frequency and capacitance to maintain stable operation. When the system parameters change, the operating frequency and capacitance of the two-port fractional capacitor with an order greater than 1 will automatically follow the system changes and automatically keep the system transmission efficiency and output power constant.

[0042] The dual-port primary side fractional capacitor C α1 The order is greater than 1 and the two-port secondary side fractional capacitor C α2 When the order is less than 1, the fractional-order primary circuit acts as the transmitting end, the fractional-order secondary circuit acts as the receiving end, and the power grid charges the battery; the dual-port primary fractional-order capacitor C α1 The order is less than 1 and the two-port secondary side fractional capacitor C α2 When the order is greater than 1, the fractional-order secondary circuit acts as the transmitting end, the fractional-order primary circuit acts as the receiving end, and the battery discharges to the grid.

[0043] When the fractional-order primary circuit is used as the transmitter and the fractional-order secondary circuit is used as the receiver, the order of the dual-port primary fractional-order capacitor is greater than 1, providing energy for the circuit. According to the coupled mode theory, Figure 1 The coupled mode equations for the system shown are:

[0044]

[0045] Where a1 and a2 are the energy representations of the fractional-order primary and secondary circuits, respectively, g1 = -(τ Cα1 +τ S1 ) is the total energy gain term of the fractional-order primary circuit, τ2=τ Cα2 +τ S2 is the total energy loss term of the fractional-order secondary circuit, is the energy coupling coefficient, where k is the mutual inductance coupling coefficient, ω1 and ω2 are the resonant angular frequencies of the fractional-order primary and secondary circuits, respectively. The expression is as follows:

[0046]

[0047] τ Cα1 , τ S1 , τ Cα2 and τ S2 Respectively characterize the loss coefficient of each component in the circuit, the specific expression is as follows:

[0048]

[0049]

[0050]

[0051]

[0052] From the formula, we can get the condition for the system to have a steady-state solution:

[0053]

[0054] And from the formula and formula we can get:

[0055]

[0056] The general formula of system transmission efficiency is:

[0057]

[0058] System output power general formula:

[0059]

[0060] in,

[0061]

[0062] Where V Cα1 is the effective value of the voltage of the primary fractional-order capacitor of the two-port.

[0063] Substituting the formula and into the formula, using the Taylor series, By performing a first-order Taylor series expansion approximation at ω1 / ω=1, eliminating ω1 from the simultaneous equations, and considering the parameter characteristics of weak coupling and high quality factor of the wireless power transmission system, the approximate analytical solution of the system operating frequency can be obtained as follows:

[0064]

[0065] When the order of the two-port primary fractional-order capacitor is a fixed value, that is, let α1 = α0 be a constant, the above formula can be used to calculate that when the system operating frequency is a real number, the mutual inductance coupling coefficient must satisfy:

[0066]

[0067] In the formula, k C is the critical operating point of the system.

[0068] When k ≥ k C , when α1=α0, the transmission efficiency of the system can be approximated as:

[0069]

[0070] The output power is approximately:

[0071]

[0072] In the formula, S Cα1 is the apparent power of the two-port primary fractional-order capacitor. From the above formula, we can see that k ≥ k C The transmission efficiency and output power of the system are independent of the mutual inductance coefficient and the resonant frequency of the secondary circuit.

[0073] When the fractional-order primary circuit is used as the receiving end and the fractional-order secondary circuit is used as the transmitting end, according to the coupled mode theory, Figure 1 The coupled mode equations of the system shown can be expressed as:

[0074]

[0075] In the formula, g2=-(τ Cα2 +τ S2 ) is the total energy gain term of the fractional-order secondary circuit, τ1=τ Cα1 +τ S1 It is the total energy loss term of the fractional-order primary circuit.

[0076] The expressions related to g2 and τ1 are as follows:

[0077]

[0078]

[0079] From the formula, we can get the condition for the system to have a steady-state solution:

[0080]

[0081] And from the formula we can get:

[0082]

[0083] The general formula of system transmission efficiency is:

[0084]

[0085] System output power general formula:

[0086]

[0087] in,

[0088]

[0089] Where V Cα2 is the effective value of the voltage of the fractional-order capacitor on the secondary side of the two-port.

[0090] Based on the Taylor series expansion method, Perform a first-order Taylor series expansion approximation at ω2 / ω=1, and eliminate ω2 from the parallel equations. Considering the parameter characteristics of the wireless power transmission system with weak coupling and high quality factor, the approximate analytical solution of the system's operating frequency can be obtained as:

[0091]

[0092] When the order of the fractional-order capacitors on the secondary side of the two-port is fixed, let α2 = α0 be a constant. From the above formula, it can be calculated that when the system operating frequency is a real number, the range of the mutual inductance coupling coefficient is:

[0093]

[0094] In the formula, k C is the critical operating point of the system.

[0095] When k ≥ k C , when α2=α0, the transmission efficiency of the system can be approximated as:

[0096]

[0097] The output power is approximately:

[0098]

[0099] In the formula, S Cα2 is the apparent power of the fractional-order capacitor on the secondary side of the two-port. From the above formula, we can see that k ≥ kC The transmission efficiency and output power of the system are independent of the mutual inductance coefficient and the resonant frequency of the primary circuit.

[0100] Taking the fractional-order primary circuit as the transmitter and the fractional-order secondary circuit as the receiver as an example, the inductance of the inductor coil is set to L1 = L2 = 100μH, the order of the two-port secondary fractional capacitor is set to α2 = 0.98, and the rated resonant frequency of the fractional-order secondary circuit is ω 20 =2π*500kHz. If the critical value of the mutual inductance coupling coefficient is required to meet k in practical applications C =0.039, then according to the formula, the order of the required two-port primary fractional capacitor can be determined to be α0 = 1.03. When the resonant frequency of the fractional secondary circuit is not offset, the relationship curves of the system's transmission efficiency and output power with the mutual inductance coupling coefficient are as follows: Figure 2 and Figure 3 As shown. Figure 2 and Figure 3 It can be seen that when k ≥ k C When the resonant frequency of the fractional-order secondary circuit is offset, taking k = 0.05 as an example, the relationship curve between the transmission efficiency and output power of the system and the resonant frequency offset of the fractional-order secondary circuit is as follows: Figure 4 and Figure 5 As shown, it can be seen that the transmission efficiency and output power of the system do not change with the shift of the resonant frequency.

[0101] From the above analysis, it can be seen that the highly robust autonomous fractional-order bidirectional wireless charging and discharging system proposed in the present invention can achieve efficient bidirectional transmission with constant transmission efficiency and output power within the designed mutual inductance coupling coefficient range, regardless of changes in the mutual inductance coupling coefficient and shifts in the resonant frequency of the receiving end. This is quite different from the traditional two-way wireless power transmission system and is difficult to achieve in the traditional two-way wireless charging and discharging system. The advantages of the system of the present invention are obvious.

[0102] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A highly robust autonomous fractional-order bidirectional wireless charging and discharging system, characterized in that: It comprises a fractional-order primary circuit and a fractional-order secondary circuit, wherein the fractional-order primary circuit comprises a dual-port primary fractional-order capacitor, a primary inductor and a power grid, wherein a first port of the dual-port primary fractional-order capacitor is connected to the power grid, and a second port is connected to the primary inductor; the fractional-order secondary circuit comprises a dual-port secondary fractional-order capacitor, a secondary inductor and a battery, wherein a first port of the dual-port secondary fractional-order capacitor is connected to the battery, and a second port is connected to the secondary inductor; the primary inductor and the secondary inductor realize wireless power transmission by means of magnetic field coupling; The dual-port primary side fractional capacitor C α1 and the two-port secondary fractional capacitor C α2 The differential relationship between the voltage and current at the second port of satisfies: Among them, i Cn is the instantaneous value of the current at the second port of the two-port fractional capacitor, v Cn is the instantaneous voltage value of the second port of the two-port fractional capacitor, C αn is the capacitance of the two-port fractional capacitor, α n is the order of the two-port fractional capacitor, 0<α n <2 and α n ≠1, n=1, 2 represent the two-port primary fractional-order capacitor and the two-port secondary fractional-order capacitor respectively; The phase relationship satisfies: Among them, φ Cn is the phase difference between the current and voltage at the second port of the two-port fractional capacitor; The first port of the two-port fractional capacitor serves as both an energy injection port and an energy absorption port. When the order α of the fractional capacitor is greater than 1, its first port is an energy injection port, and the injected power P1 satisfies: P1=-V C I C cos(0.5πα) When the order α of the fractional capacitor is less than 1, its first port is an energy absorption port, and the absorbed power P2 satisfies: P2=V C I C cos(0.5πα) Among them, V C and I C are the average values ​​of the voltage and current of the second port of the two-port fractional capacitor, respectively; When the order of the dual-port primary fractional-order capacitor is greater than 1 and the order of the dual-port secondary fractional-order capacitor is less than 1, the fractional-order primary circuit serves as a transmitting end, the fractional-order secondary circuit serves as a receiving end, and the power grid charges the battery; when the order of the dual-port primary fractional-order capacitor is less than 1 and the order of the dual-port secondary fractional-order capacitor is greater than 1, the fractional-order secondary circuit serves as a transmitting end, the fractional-order primary circuit serves as a receiving end, and the battery discharges to the power grid.

2. According to claim 1, a highly robust autonomous fractional-order bidirectional wireless charging and discharging system is characterized in that: A first resistor is connected in series to the connection line between the dual-port primary fractional-order capacitor and the primary inductor coil, and a second resistor is connected in series to the connection line between the dual-port secondary fractional-order capacitor and the secondary inductor coil.

3. The highly robust autonomous fractional-order bidirectional wireless charging and discharging system according to claim 1, characterized in that: An autonomous system is formed by using a two-port fractional-order capacitor with an order greater than 1 and an inductor coil, so that the parameters of the two-port fractional-order capacitor with an order greater than 1 automatically follow the changes of system parameters to achieve constant system transmission efficiency and output power.

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