A three-coil WPT system with constant-current S-S-N compensation

Abstract

The present invention discloses a three - coil WPT system with constant - current - type S - S - N compensation, which includes a transmitting side and a receiving side. The transmitting side includes a DC power supply U d , a high - frequency inverter H, a transmitting coil L p , a transmitting compensation capacitor C p , a relay coil L m and a relay compensation capacitor C m ; The receiving side includes a receiving coil L s , a rectifier D, a filter capacitor C F and a battery load R L . The relay coil and the transmitting coil are placed coplanarly to save space, and the transmitting coil, the receiving coil and the relay coil are coaxially symmetrically arranged to enhance coupling. The circuit structure of the present invention is simple. Under a fixed frequency, it can achieve constant - current output and soft - switching of the field - effect transistor in the inverter. Compared with the existing similar technologies, the receiving side of the system of the present invention does not require compensation components, ensuring the compactness, lightness and low cost of the receiving side of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless charging, and relates to a three-coil WPT system with constant-current type S-S-N compensation. Background Art

[0002] Since the traditional plug-in charging system limits the flexibility of electrical equipment and is prone to electrical hazards. Wireless power transfer (WPT) systems have received extensive attention from researchers due to their inherent advantages. The WPT system realizes contactless power transfer through electromagnetic coupling between terminal coils. It has the advantages of safety, flexibility, convenience, and the ability to work in special environments. Therefore, the WPT technology has developed rapidly and has gradually been integrated into various industrial applications. Currently, the WPT technology has been widely applied in fields such as light-emitting diode (LED) lighting, biomedical implants, portable electronic devices, and electric vehicles.

[0003] In the existing WPT compensation topologies, in order to achieve preset functions, it is usually necessary to introduce compensation elements on the receiving side. However, introducing compensation elements on the receiving side not only increases the occupied space on the receiving side of the electrical equipment, but also additionally increases the manufacturing cost of the product during mass production. Therefore, the present invention proposes a constant-current type three-coil WPT system based on S-S-N compensation. This system only has compensation elements on the transmitting side and does not require compensation elements to be installed on the receiving side, ensuring that the receiving side is compact and lightweight, while further reducing the manufacturing cost of the receiving side of the system. Summary of the Invention

[0004] The purpose of the present invention is to provide a WPT system with a low-cost, compact receiving side and realizing constant-current output, which has a simple structure and a low system cost.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] The present invention provides a three-coil WPT system with constant-current type S-S-N compensation, which is characterized in that it includes a transmitting side and a receiving side. The transmitting side includes a DC power supply U d , a high-frequency inverter H, a transmitting coil L p , a transmitting compensation capacitor C p , a relay coil L m and a relay compensation capacitor C m ; the receiving side includes a receiving coil L s , a full-bridge rectifier D, a filter capacitor C F and a battery load R L ; both ends of the output side of the DC power supply U d are connected to both ends of the input side of the high-frequency inverter H. One end of the output side of the high-frequency inverter H is connected to one end of the transmitting coil L p , and the transmitting coil Lp The other end is connected to the emission compensation capacitor C p at one end, and the other end of the emission compensation capacitor C p is connected to the other end of the output side of the high-frequency inverter H;

[0007] The receiving coil L s is connected to the input end of the full-bridge rectifier D, and the output end of the full-bridge rectifier D is filtered by the capacitor C F to supply power to the battery load R L ;

[0008] The relay coil L m has a relay compensation capacitor C connected in series at both ends m at both ends. The relay coil and the transmitting coil are placed coplanarly, and the transmitting coil, the receiving coil, and the relay coil are coaxially and symmetrically arranged.

[0009] The emission compensation capacitor C p has the following mathematical function relationship:

[0010]

[0011] The relay compensation capacitor C m has the following mathematical function relationship:

[0012]

[0013] In the above design equations, M pm is the mutual inductance between the transmitting coil L p and the relay coil L m , M ms is the mutual inductance between the receiving coil L s and the relay coil L m , and ω is the system operating angular frequency.

[0014] During the parameter design stage of the system, slightly increasing the emission compensation capacitor C p by 10% can make the output voltage of the inverter slightly lead the output current of the inverter, and basically does not affect the constant current output function of the system. Therefore, by slightly increasing the emission compensation capacitor C p by 10%, the zero-voltage turn-on of the field-effect transistor in the high-frequency inverter can be achieved, thereby improving the efficiency.

[0015] Advantages of the present invention:

[0016] 1. The present invention designs a constant-current type S-S-N compensated three-coil WPT system. This system only has compensation elements on the transmitting side and does not require compensation elements to be installed on the receiving side, ensuring that the receiving side is compact and lightweight, and at the same time further reducing the manufacturing cost of the receiving side of the system;

[0017] 2. In the present invention, the relay coil and the transmitting coil are placed coaxially and coplanarly. Compared with the structure in which the relay coil is placed between the transmitting side and the relay side, the present invention improves the space utilization rate of the system, makes the volume of the system smaller, and saves the occupied space.

[0018] 3. The present invention can achieve a constant current output independent of the load through the structural characteristics of the system itself without complex control techniques.

[0019] 4. The present invention can slightly increase the transmitting compensation capacitor C P by 10% to make the output voltage of the inverter slightly lead the output current of the inverter. This can not only make the system basically operate at a zero phase angle, but also achieve zero-voltage turn-on of the metal-oxide-semiconductor field-effect transistors (MOSFETs) in the high-frequency inverter, reduce the losses introduced by the reactive circulating current in the system, and effectively reduce the turn-on losses in the high-frequency inverter, thereby improving the overall efficiency of the system. In addition, slightly increasing the transmitting compensation capacitor C P by 10% will not affect the constant current output characteristics of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the overall circuit architecture diagram of the system involved in the present invention;

[0021] Figure 2 is the simplified circuit schematic diagram involved in the present invention;

[0022] Figure 3 is the experimental waveform diagram under the zero phase angle condition with a load of 10 Ω as an example in the embodiment of the present invention;

[0023] Figure 4 is the experimental waveform diagram under the zero-voltage turn-on condition with a load of 10 Ω as an example in the embodiment of the present invention;

[0024] Figure 5 is the experimental waveform diagram under the zero phase angle condition with a load of 20 Ω as an example in the embodiment of the present invention;

[0025] Figure 6 is the experimental waveform diagram under the zero-voltage turn-on condition with a load of 20 Ω as an example in the embodiment of the present invention;

[0026] Figure 7 is the experimental waveform diagram under the zero phase angle condition with a load of 30 Ω as an example in the embodiment of the present invention;

[0027] Figure 8 is the experimental waveform diagram under the zero-voltage turn-on condition with a load of 30 Ω as an example in the embodiment of the present invention;

[0028] Figure 9 is the model of the loosely coupled transformer constructed in the present invention;

[0029] Figure 10is the experimental coil at the transmitting end wound according to the present invention;

[0030] Figure 11 is the experimental coil at the receiving end wound according to the present invention. Detailed implementation manners

[0031] The implementation manners of the present invention will be described in detail below with reference to the accompanying drawings:

[0032] Figure 1 is the overall circuit architecture diagram of the embodiment system related to the present invention. As can be seen from the figure:

[0033] The system includes: a DC power supply U d , a high-frequency inverter H, a transmitting coil L p , a transmitting compensation capacitor C p , a relay coil L m , a relay compensation capacitor C m , a receiving coil L s , a full-bridge rectifier D, a filtering capacitor C F and a battery load R L .

[0034] The full-bridge rectifier D is composed of four diodes, and a filtering capacitor C is connected in parallel at the output end of the full-bridge rectifier D F , forming a rectifying circuit that can reduce the DC pulsation of the output of the high-frequency rectifier.

[0035] The two ends of the output side of the DC power supply U d are connected to the two ends of the input side of the high-frequency inverter H. One end of the output side of the high-frequency inverter H is connected to one end of the transmitting coil L p . The other end of the initial transmitting coil L p is connected to one end of the transmitting compensation capacitor C p . The other end of the transmitting compensation capacitor C p is connected to the other end of the output side of the high-frequency inverter H.

[0036] The receiving coil L s is connected to the input end of the full-bridge rectifier D. The output end of the full-bridge rectifier D supplies power to the battery load R F through the filtering capacitor C L .

[0037] The two ends of the relay coil L m are connected in series to the two ends of the relay compensation capacitor C m . The relay coil and the transmitting coil are placed coplanarly to save space. The transmitting coil, the receiving coil and the relay coil are coaxially symmetrically arranged.

[0038] Figure 2 is the simplified circuit schematic diagram of the topology embodiment related to the present invention. As can be seen from the figure, U inis the square-wave voltage generated by the high-frequency inverter H, R ac is the receiving coil L s is the equivalent AC load resistance of the backend components, and their values can be calculated by the following formula:

[0039]

[0040] As Figure 2 shown, the equivalent impedance of the coil is within the dashed box, and their values are given by the following formula:

[0041]

[0042] According to Kirchhoff's voltage law, the following system of equations can be listed.

[0043]

[0044] Among them, j represents the imaginary unit, I p 、I m and I s are the high-frequency currents flowing through the transmitting coil, the relay coil, and the secondary receiving coil respectively. Since the internal resistance values R p 、R s and R m are very small, they can be ignored. According to Equation (3), the currents flowing through the three coils can be calculated as follows:

[0045]

[0046] The expressions of A and B used to simplify the above formula are:

[0047]

[0048] Based on the above analysis, in order to achieve load-independent constant current output, that is, to satisfy that the output current I s is not affected by the load equivalent resistance R ac From (4), it can be seen that when B = 0, the output current I s is independent of the load, that is:

[0049]

[0050] From Equation (4) and Equation (6), the value of the equivalent input impedance when satisfying constant current output is:

[0051]

[0052] In order to satisfy the zero-phase angle operation of the system, it is necessary to make the value of Z in be purely resistive, that is, the value of Z in has no imaginary part and is only related to R acis related, that is, it needs to satisfy the following formula:

[0053]

[0054] At this time, an equation group that simultaneously satisfies constant current output and zero phase angle operation is obtained:

[0055]

[0056] Substituting Equation (9) into Equation (4) can further obtain the current expression of the coil:

[0057]

[0058] The equivalent input impedance at this time is simplified to:

[0059]

[0060] When Equation (9) holds, the system transconductance gain G can be obtained:

[0061]

[0062] Obviously, it can be seen from Equation (11) that Z in only has a real part. Therefore, the system can achieve a purely resistive input impedance and can achieve zero phase angle operation within the full load range. It can be seen from Equation (12) that the output current of the system is independent of the load resistance R ac , and the system realizes constant current output.

[0063] Since there are non-negligible parasitic capacitances in all four field-effect transistors that make up the high-frequency inverter, the input impedance angle of the system should be slightly inductive to achieve zero-voltage turn-on.

[0064] The input impedance angle of the system is defined as:

[0065]

[0066] From Equations (7) and (13), the expression of the input impedance angle of this system can be obtained as

[0067]

[0068] It can be seen from the above formula that when the parameters such as the self-inductance and mutual inductance of the system are determined, the magnitude of the input impedance angle can be changed by changing the values of the compensation capacitors C p and C m . However, the values of the compensation capacitors C p and C m are restricted by the constant current output characteristics. Therefore, it is necessary to consider whether the changes in C p and C m will affect the constant current output characteristics.

[0069] Finally, through analysis, it is found that slightly increasing the value of the emission compensation capacitor C p has almost no effect on the constant-current output characteristic. Therefore, the input impedance angle can be made slightly greater than zero by increasing the value of C p by 10%, so as to achieve zero-voltage turn-on.

[0070] Generally speaking, when the formula (9) is satisfied, the proposed system can obtain a stable constant-current output and can achieve a pure resistive input impedance; when the emitter compensation capacitor C p is increased by 10%, the field-effect transistor in the high-frequency inverter can achieve zero-voltage turn-on to improve the efficiency.

[0071] To experimentally verify the proposed constant-current type S-S-N compensated three-coil WPT system, Figure 9 the loose-coupled transformer model constructed by the present invention is shown. According to the constructed model, the experimental coils are wound as shown in Figure 10 and Figure 11 .

[0072] Figure 3 , Figure 5 and Figure 7 show the experimental waveform diagrams of the system when the load is 10Ω, 20Ω and 30Ω under the zero-phase angle working condition. It can be seen from the figure that the system realizes the load-independent constant-current output characteristic and zero-phase angle operation.

[0073] Figure 4 , Figure 6 and Figure 8 show the experimental waveform diagrams of the system when the load is 10Ω, 20Ω and 30Ω under the zero-voltage turn-on working condition after slightly increasing the emitter compensation capacitor C P by 10%. It can be seen from the figure that the field-effect transistor in the high-frequency inverter of the system realizes zero-voltage turn-on, improves the system efficiency, and slightly increasing the emitter compensation capacitor C P by 10% does not affect the constant-current output characteristic of the system.

[0074] It should be understood that the parts not elaborated in detail in this specification all belong to the prior art.

[0075] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, those of ordinary skill in the art should understand that these are only examples, and various deformations or modifications can be made to these embodiments without departing from the principles and essences of the present invention. The scope of the present invention is only defined by the appended claims.

Claims

1. A soft-switching implementation method for a three-coil WPT system for realizing constant-current S-S-N compensation, Characterized in that: The constant-current type S-S-N compensated three-coil WPT system includes a transmitting side and a receiving side. The transmitting side includes a DC power supply U d , a high-frequency inverter H, a transmitting coil L p , a transmitting compensation capacitor C p , a relay coil L m , and a relay compensation capacitor C m ; the receiving side includes a receiving coil L s , a full-bridge rectifier D, a filtering capacitor C F , and a battery load R L ; both ends of the output side of the DC power supply U d are connected to both ends of the input side of the high-frequency inverter H. One end of the output side of the high-frequency inverter H is connected to one end of the transmitting coil L p . The other end of the transmitting coil L p is connected to one end of the transmitting compensation capacitor C p . The other end of the transmitting compensation capacitor C p is connected to the other end of the output side of the high-frequency inverter H; The receiving coil L s is connected to the input end of the full-bridge rectifier D, and the output end of the full-bridge rectifier D passes through a filter capacitor C F to supply power to the battery load R L for power supply; The relay coil L m is connected in series with a relay compensation capacitor C at both ends m at both ends. The relay coil and the transmitting coil are placed coplanarly, and the transmitting coil, the receiving coil, and the relay coil are coaxially symmetrically arranged; The emission compensation capacitor C p has the following mathematical function relationship: The relay compensation capacitor C m has the following mathematical function relationship: Where: M pm is the mutual inductance between the transmitting coil L p and the relay coil L m , M ms is the mutual inductance between the receiving coil L s and the relay coil L m , and ω is the system operating angular frequency; During the parameter design phase of the system, the emission compensation capacitor C is slightly increased by 10% p to make the output voltage of the inverter slightly lead the output current of the inverter, so as to achieve zero-voltage turn-on of the field-effect transistor in the high-frequency inverter, thereby improving the efficiency.

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