Three-phase wireless electric energy transmission device and load power adjusting method

Abstract

A three-phase wireless electric energy transmission device disclosed by the present invention comprises a three-phase inverter, a three-phase switch capacitor, a coil magnetic field coupling structure and a rectifier, the coil magnetic field coupling structure comprises a primary coil and a secondary coil which are arranged in mirror symmetry, the primary coil is provided with two layers, each layer comprises a three-phase coil, each phase coil occupies a 120-degree angle range of the circumference, and the rectifier is connected with the primary coil and the secondary coil. The two layers of coils form a staggered angle, each phase of switched capacitor of the three-phase switched capacitor comprises a first capacitor branch and a second capacitor branch which are arranged in parallel, the first capacitor branch is provided with a first capacitor, and the second capacitor branch comprises a second capacitor and a switch module which are arranged in series; the switch module adjusts the equivalent capacitance value of the second capacitor branch through the duty ratio and adjusts the transmission power of the three-phase wireless power transmission device. The invention further discloses a load power adjusting method of the three-phase wireless power transmission device, the transmission efficiency can be kept unchanged within the adjusting range, and soft switching can be achieved within the adjusting range.

Description

Technical Field

[0001] This invention relates to the field of wireless power supply technology, and in particular to a three-phase wireless power transmission device and a load power regulation method. Background Technology

[0002] Wireless power transfer (WPT) enables efficient power transfer between devices. Compared to single-phase systems, three-phase WPT systems offer significant advantages, such as effectively reducing current ripple and thus decreasing the capacitance requirements of the DC-side capacitors. Furthermore, at the same power rating, the switching devices in a three-phase system experience less current stress, making it more suitable for high-power applications such as fast charging of electric vehicles.

[0003] For the power flow of a WPT (Wide-Plank Power Adapter), existing technology controls it by adjusting the phase difference between the primary and secondary six-switch inverters in a wye-wye connected bidirectional WPT system. However, this method increases the inverter's volt-ampere-second compression (VAS) under light load conditions, leading to a decrease in efficiency. Duty cycle modulation schemes are also used for phase difference control to regulate power flow, but these methods suffer from high harmonic content at low duty cycles and the inability to achieve soft switching across the entire regulation range.

[0004] Considering the limitations of traditional three-phase voltage source inverters in high-power applications, multilevel converters are also used for load power regulation in WPT systems. Multilevel topologies include diode-clamped converters, flying capacitor converters, cascaded full-bridge converters, and modular multilevel converters. These topologies can significantly reduce the voltage stress on switching devices, making it possible to use power devices with lower rated voltages; however, the series connection of multiple switches also introduces more switching losses. Summary of the Invention

[0005] To address the aforementioned deficiencies in the prior art, the present invention aims to provide a three-phase wireless power transmission device that solves the problem of reduced transmission efficiency in three-phase WPT circuits within the power regulation range. Another objective of the present invention is to provide a load power regulation method for the three-phase wireless power transmission device.

[0006] The technical solution of this invention is as follows: A three-phase wireless power transmission device includes a three-phase inverter, a three-phase switched capacitor, a coil magnetic field coupling structure, and a rectifier. The coil magnetic field coupling structure includes a primary coil and a secondary coil, which are arranged in a mirror-symmetrical manner. The primary coil has two layers, each layer including three-phase coils, each phase coil occupying a 120° angular range of the circumference. The corresponding phase coils of the upper and lower three-phase coils form an interleaved angle. The three-phase switched capacitor is connected between the output terminal of the three-phase inverter and the primary coil. Each phase of the three-phase switched capacitor includes a first capacitor branch and a second capacitor branch connected in parallel. The first capacitor branch includes a first capacitor, and the second capacitor branch includes a second capacitor and a switching module connected in series. The switching module adjusts the equivalent capacitance value of the second capacitor branch and adjusts the transmission power of the three-phase wireless power transmission device by adjusting the duty cycle.

[0007] Furthermore, the corresponding phase coils of the upper three-phase coil and the lower three-phase coil are interleaved at an angle of 110° to 140°, preferably 120°.

[0008] Furthermore, the switching module consists of a switching transistor and a diode connected in parallel.

[0009] Furthermore, each phase coil is wound in a sector-shaped structure with a central angle of 120°, and the three phase coils are staggered by 120°.

[0010] Furthermore, to address the challenge of achieving soft switching across the entire regulation range, the equivalent primary side cross-inductance coefficient of the three-phase switching capacitor and coil magnetic field coupling structure is greater than the value calculated by the following formula:

[0011] ,

[0012] in, , For the system operating frequency, Let be the mutual inductance coefficient between the in-phase coils of the primary and secondary windings. The cross-inductance coefficient is the coefficient of cross-inductance on the opposite side. R is the cross-inductance coefficient on the same side of the secondary side, and R is the load resistance.

[0013] Furthermore, in order to increase the load current adjustment range, the capacitance value of the second capacitor is greater than the critical capacitance value between the undercompensated and overcompensated regions of the cross-coupling.

[0014] Furthermore, the formula for calculating the critical capacity is:

[0015] ,

[0016] Where L is the inductance of a single-phase coil in the primary winding. The cross-inductance coefficient on the same side of the original edge is the coefficient of mutual inductance. This is the capacitance value of the first capacitor.

[0017] Another technical solution of the present invention is a load power adjustment method for a three-phase wireless power transmission device, based on the aforementioned three-phase wireless power transmission device, adjusting the duty cycle according to the required load power using the following formula:

[0018] ,

[0019] in, To meet the required load power, This represents the fundamental amplitude of the inverter's output voltage. The cross-inductance coefficient on the same side of the secondary side. The cross-inductance coefficient is the coefficient of cross-inductance on the opposite side. , For the system operating frequency, Let be the mutual inductance coefficient between the in-phase coils of the primary and secondary windings, i be the imaginary unit, R be the load resistance, and L be the inductance of a single-phase coil in the primary winding. This is the capacitance value of the first capacitor. Let be the capacitance value of the second capacitor, and D be the duty cycle.

[0020] Furthermore, when the duty cycle controls the switching module, the switching module is activated at the moment when the current crosses zero.

[0021] Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

[0022] Three-phase wireless power transmission devices do not rely on high-order topologies, do not require increased size and weight on the receiving side, maintain constant transmission efficiency within the power regulation range, and can also achieve soft switching across the entire current regulation range. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the circuit structure of the three-phase wireless power transmission device of the present invention.

[0024] Figure 2 This is a schematic diagram of the upper and lower three-phase coils of the coil magnetic field coupling structure, which are staggered at different angles.

[0025] Figure 3 This is a diagram of a switched capacitor structure.

[0026] Figure 4 for , , The relationship between the current gain Gia and the current gain Gia.

[0027] Figure 5 for , , With impedance angle Relationship diagram.

[0028] Figure 6 for , , With transmission efficiency Relationship diagram.

[0029] Figure 7 This is a diagram showing the relationship between the current adjustment range Gr and the angle between the upper and lower layers.

[0030] Figure 8 This is a diagram showing the relationship between transmission efficiency and the angle between the upper and lower layers.

[0031] Figure 9 This is the timing diagram for switched capacitor control.

[0032] Figure 10 This is a graph showing the relationship between the duty cycle and the equivalent capacitance of the switched capacitor.

[0033] Figure 11 This is a graph showing the relationship between the duty cycle of the switched capacitor and the load current.

[0034] Figure 12 This is a graph showing the relationship between the duty cycle of the switched capacitor and the transmission efficiency.

[0035] Figure 13 The inverter output voltage and current waveforms are shown at the lowest duty cycle.

[0036] Figure 14 The inverter output voltage and current waveforms are shown at the highest duty cycle. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments, but these are not intended to limit the scope of the invention.

[0038] like Figure 1 As shown, an embodiment of the present invention provides a three-phase wireless power transmission device, comprising a three-phase inverter 1, a three-phase switched capacitor 2, a coil magnetic field coupling structure 3, and a rectifier 4. Figure 2As shown, the coil magnetic field coupling structure 3 includes a primary coil 301 and a secondary coil 302, with the primary coil 301 on top and the secondary coil 302 on the bottom. The primary coil 301 and the secondary coil 302 are arranged in a mirror-symmetrical configuration, and their structures are identical. Taking the primary coil 301 as an example, the structure of the primary coil 301 and the secondary coil 302 is explained. The primary coil 301 has two layers, each layer including three-phase coils. Each phase coil 301a (red phase A, yellow phase B, and blue phase C) occupies a 120° angular range around the circumference. Specifically, each phase coil 301a is wound into a fan-shaped structure with a central angle of 120°, and the three phase coils are staggered by 120° to form a circle. The corresponding phase coils of the upper-layer three-phase coil and the lower-layer three-phase coil are connected in series and form an interleaved angle (angle), as shown below. Figure 2 The primary side upper A-phase coil 301a and the primary side lower A-phase coil 301a are interleaved at an angle of 30°.

[0039] Three-phase switched capacitor 2 is connected between the output terminal of three-phase inverter 1 and the primary winding 301. A switched capacitor is connected in series before each phase winding 301a. Please refer to... Figure 3 As shown, each phase switching capacitor 201 of the three-phase switching capacitor 2 (a switching capacitor connected in series before a phase coil) includes a first capacitor branch 201a and a second capacitor branch 201b connected in parallel. The first capacitor branch 201a is provided with a first capacitor 201c, and the second capacitor branch 201b is composed of a second capacitor 201d connected in series and a switching module. The switching module consists of a switching transistor 201e and a diode 201f connected in parallel.

[0040] The mathematical model of the entire three-phase wireless power transmission device is as follows:

[0041]

[0042]

[0043] in The fundamental voltage amplitude of the inverter output is given by i, where i is the imaginary unit. , For the system operating frequency, It is a three-phase equivalent AC load. , and These represent the parasitic resistances of the primary three-phase circuits A, B, and C, respectively. L is the mutual inductance coefficient of the in-phase coils of the primary and secondary coils, C is the inductance, I is the capacitance, and A, B, C are uppercase subscripts indicating the phase sequence of the primary (transmitter) side, and a, b, c are lowercase subscripts indicating the phase sequence of the secondary (receiver) side.

[0044] In a three-phase wireless power transfer device, there is cross-coupling between coils on the same side; therefore, the same-side cross-coupling is defined as follows:

[0045] ;

[0046] ;

[0047] ;

[0048] .

[0049] This refers to the cross-inductance coefficient on the same side of the original edge, i.e., the cross-inductance coefficient on the same side of the initial coupled structure. The cross-inductance coefficient on the same side of the secondary side. is the cross-inductance coefficient on the opposite sides.

[0050] To ensure soft switching within the regulation range, the overall equivalent coefficient after the three-phase switching capacitor and the coil magnetic field coupling structure are connected in series is... It should be slightly larger than the equivalent value corresponding to pure resistivity. As shown in the following formula

[0051] .

[0052] Since the three phases are symmetrical and their angles differ by 120°, the current gain Gia of phase A is calculated as follows, taking phase A as an example.

[0053] .

[0054] Based on the above relationship, we can derive different loads and The current gain curve at the value is as follows Figure 4 As shown in the figure Here is the normalized load resistance, where As can be seen from the figure, The larger the current gain, the less sensitive the output current gain is to changes in cross-coupling on the same side, and the lower the current gain, the smoother the overall waveform. The smaller the value, the larger the range of current gain variation. The range of current gain variation is mainly concentrated in... Within the range of (0-3), the current gain is divided into a rising segment and a falling segment; Within the range, The smaller the value, the greater the current gain under high compensation.

[0055] The impedance angle of phase A is shown in the following formula.

[0056] .

[0057] Based on the above relationship, we can derive different loads and The impedance angle variation curve under the value is as follows: Figure 5 As shown, with the increase of R / Rb, in Within the range of variation, the input impedance gradually shifts towards capacitive; The input impedance is almost capacitive within the 0-2 range, which is not conducive to achieving ZVS; when the coupling coefficient increases, the impedance angle remains almost unchanged. The larger, The larger the range of sensory experiences, the better.

[0058] The expression for the transmission efficiency of phase A is as follows:

[0059] .

[0060] Based on the above relationship, a 3D graph of transmission efficiency under different load values ​​can be obtained as follows: Figure 6 As shown in the figure, the transmission efficiency is related to... Irrelevant, related This means that same-side cross-coupling on the primary side will not affect transmission efficiency; Within a certain range, transmission efficiency increases with... Increased with the increase, At that time, the overall maximum efficiency shifts to the right; by adjusting... Adjusting the current gain will not affect the transmission efficiency. The transmission efficiency versus duty cycle curve is shown below. Figure 12 As shown.

[0061] The structural diagrams of the coil magnetic field coupling structure at different angles are shown below. Figure 2 As shown, the angle between the upper and lower three-phase coils 301a of the three-phase double-layer coil is scanned using finite element simulation software. This angle represents the angle between coils of the same phase on the same side. The current adjustment range and transmission efficiency show opposite trends with respect to the angle. Figure 7 , 8 Considering both factors, maximizing the desired effect, an angle between the upper and lower in-phase coils on the same side is preferred, ideally between 100° and 140°, with 120° being optimal. Gr is defined as follows:

[0062] Gr = Peak current gain / Current gain at full compensation

[0063] The load factor is defined as follows:

[0064] .

[0065] By changing the duty cycle of the switching transistors, the equivalent capacitance of the three-phase switched capacitors is altered, thereby changing the cross-coupling compensation coefficient. This allows for adjustment of the transmission power. Since the switched capacitor is connected in series in the constant voltage circuit, to maintain soft switching of the switching transistor when the duty cycle changes, the zero-crossing detection circuit must accurately activate the switching transistor at the moment the current crosses zero. The control timing diagram for the three-phase switched capacitor is as follows: Figure 9 As shown, Figure 9 middle, This is the drive signal for the switching transistor in the switched capacitor. The voltage across the switching transistor. This indicates that the switch is on. The diode representing the parallel connection of the switching transistors is turned on. Represents the first capacitor The voltage at both ends, Represents the flow through the first capacitor The current, Represents the flow through the second capacitor The current, This represents the total current flowing through a single-phase switched capacitor.

[0066] The sum of the currents in the first and second capacitor branches of the switched capacitor is shown below.

[0067] .

[0068] The current in the first branch is

[0069] ,

[0070] Where T is the period, D is the duty cycle of the switching transistor, and the Fourier decomposition is shown in the following equation.

[0071] , .

[0072] The current after decomposition is

[0073] ,

[0074] The relationship between the equivalent capacitance and duty cycle of the second capacitor branch is expressed by the following formula:

[0075] .

[0076] After substituting the values, the relationship between the equivalent capacitance and the duty cycle can be obtained as shown in the following expression.

[0077] .

[0078] To ensure that the load power can be adjusted across the entire duty cycle range of 0-50%, and that soft switching is still achieved with maximum current gain when the duty cycle is zero, the first capacitor of the first capacitor branch... The following conditions must be met. The inductance of phase A in the primary winding

[0079] .

[0080] Critical capacitance between undercompensated and overcompensated regions of cross-coupling As shown in the following formula

[0081] .

[0082] When the value is lower than the above formula, the load power regulation range can only operate in the cross-coupling undercompensated region, while When the value is greater than the above formula, the load power regulation range can operate in the cross-coupling undercompensated region and the cross-coupling overcompensated region. The existence of cross-coupling is equivalent to increasing the load current regulation range.

[0083] Based on the above expression, establish the transmission power. The expression chain relating the duty cycle D to the following is shown below. In other words, based on this expression chain, the required transmission power can be determined. The duty cycle D of the switching transistor is obtained, thereby adjusting the load power of the three-phase wireless power transmission device.

[0084] ,

[0085] The relationship between equivalent capacitance and duty cycle of the switching transistor is shown in the figure below. Figure 10 As shown in the figure, the theoretical capacitance curve is basically consistent with the simulated capacitance curve. Figure 11 The figure shows the relationship between the switching transistor's duty cycle and the load current. As can be seen from the figure, the load current can be continuously adjusted within a certain range by changing the duty cycle. The current adjustment range is 3.8-10.5A, and the transmission efficiency remains consistently around 89%. The inverter output voltage and current waveforms corresponding to the minimum and maximum duty cycles are shown below. Figure 13 , 14 As shown in the figure, the input impedance remains inductive within the adjustment range.

Claims

1. A three-phase wireless power transfer apparatus, characterized by, The three-phase inverter, the three-phase switch capacitor, the coil magnetic field coupling structure and the rectifier, the coil magnetic field coupling structure includes a primary coil and a secondary coil, the primary coil and the secondary coil are mirror symmetrically arranged, the primary coil is provided with two layers, each layer includes three-phase coils, each phase coil occupies a 120° angle range of circumference, the corresponding phase coils of the upper three-phase coils and the lower three-phase coils form staggered angles, the three-phase switch capacitor is connected between the output end of the three-phase inverter and the primary coil, each phase switch capacitor of the three-phase switch capacitor includes a first capacitor branch and a second capacitor branch arranged in parallel, the first capacitor branch is provided with a first capacitor, the second capacitor branch includes a second capacitor and a switch module arranged in series, the switch module adjusts the equivalent capacitance value of the second capacitor branch and the transmission power of the three-phase wireless power transmission device through duty ratio adjustment.

2. The three-phase wireless power transfer device of claim 1, wherein, The corresponding phase coils of the upper three-phase coils and the lower three-phase coils form staggered angles of 110°-140°.

3. The three-phase wireless power transfer device of claim 1, wherein, The corresponding phase coils of the upper three-phase coils and the lower three-phase coils form staggered angles of 120°.

4. The three-phase wireless power transfer apparatus of claim 1, wherein, The switch module is a parallel-connected switch tube and diode.

5. The three-phase wireless power transfer apparatus of claim 1, wherein, Each phase coil is arranged in a fan-shaped structure with a central angle of 120°, and the three-phase coils are staggered by 120°.

6. The three-phase wireless power transfer apparatus of claim 1, wherein, The equivalent primary side cross mutual inductance coefficient of the three-phase switch capacitor and the coil magnetic field coupling structure as a whole is greater than the calculated value of the following formula: ， wherein, , is the system operating frequency, is the mutual inductance coefficient of the primary coil and the same side coil of the secondary coil, is the opposite side cross mutual inductance coefficient, is the secondary side same side cross mutual inductance coefficient, and R is the load resistance.

7. The three-phase wireless power transfer device of claim 1, wherein, The capacitance value of the second capacitor is greater than the critical capacitance value of the cross-coupling under-compensation region and the over-compensation region.

8. A three-phase wireless power transfer apparatus according to claim 7, characterised in that, The calculation formula of the critical capacitance value is: ， Wherein, L is the single-phase inductance of the primary side coil, is the same side cross mutual inductance coefficient of the primary side, is the capacitance value of the first capacitor.

9. A load power regulation method of a three-phase wireless power transfer apparatus, characterized by, The three-phase wireless power transmission device according to any one of claims 1-8, the duty ratio is adjusted according to the required load power according to the following formula: ， wherein, is the demand load power, is the inverter output voltage fundamental amplitude, is the same side cross mutual inductance coefficient of the secondary side, is the different side cross mutual inductance coefficient, , is the system operating frequency, is the mutual inductance coefficient of the same phase coil of the primary side coil and the secondary side coil, i is the imaginary unit, R is the load resistance, L is the single-phase coil inductance in the primary side coil, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, D is the duty cycle.

10. The method of load power regulation for a three-phase wireless power transfer apparatus of claim 9, wherein, When the switch module is controlled by the duty ratio, the switch module is actuated at the current zero-crossing time.

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