Wireless charging system based on compact secondary circuit topology and power regulation and control method

Abstract

The invention provides a wireless charging system based on compact secondary circuit topology and a power regulation and control method. The wireless charging system comprises a direct-current voltage source, a full-bridge inverter, a compensation topology, a coupling mechanism, an integrated rectification and power regulation circuit IRPC and a system load. The IRPC provided by the invention only uses one diode, one switch tube and one filter capacitor, so that the compactness and the light weight of the secondary circuit topology are ensured to the maximum extent, and the IRPC is particularly suitable for wireless charging occasions needing miniaturized equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless power, and particularly relates to a wireless charging system based on a compact secondary side circuit topology and a power regulation method. BACKGROUND

[0002] Wireless power technology transmits energy across a large air gap with the help of coupling coils, and compared with the traditional conductive charging method, it successfully gets rid of the cable restriction. The wireless charging technology has many significant advantages: firstly, it is not easy to cause electric spark in harsh environmental conditions, effectively reduces the risk of electric shock and leakage, thereby greatly reduces the safety hazard; secondly, the power supply device has a larger range of movement during power supply, not only improves the flexibility of use, but also has aesthetic appearance; thirdly, it can provide continuous power support for miniature medical devices implanted in the human body and machines working in special environments.

[0003] Generally speaking, in order to meet the different charging needs of power supply devices, the wireless charging system should have high-efficiency constant current and constant voltage charging performance. However, the dynamic change of equivalent load resistance often leads to the fluctuation of charging current and voltage. Therefore, it is necessary to study the control method for maintaining constant current and constant voltage charging. From the closed-loop control strategy, the existing power regulation method for wireless charging system is as follows: As for the primary side power regulation method, the topology structure for power regulation mainly includes dc-dc converter and phase shift / frequency modulation inverter, and according to whether wireless communication is adopted, it can be further divided into charging information feedback type and parameter identification control type.

[0004] Charging information feedback type (need to use bilateral wireless communication): the prior art designs a lithium battery wireless charging system based on SS compensation topology, adopts a PI controller to adjust the operating frequency of the full-bridge inverter to realize constant voltage / constant current charging, and the disadvantage of this method is that when the system operating frequency deviates from the resonance frequency, the reactive power increases and the system efficiency decreases. The prior art proposes a phase-shift control method based on frequency tracking, adjusts the phase-shift angle to realize constant voltage charging when the system has optimal operating frequency, and although this method has a wide range of soft switching, thereby reducing the switching loss; however, the multi-resonance points of the resonance network affect the feasibility of the frequency tracking algorithm. The prior art adopts a fixed-frequency and variable-frequency asymmetric voltage control (AVC) method to adjust the phase-shift angle of the full-bridge inverter, realizes soft switching and constant current / voltage output in a wide load range, and the problem is that there is a lower limit for power regulation due to the control of only half a cycle. The prior art adopts a PI controller to adjust the duty cycle of the transmitting end Buck converter to realize constant current / voltage output, and the disadvantage is that the additional Buck converter increases the system volume, weight and cost, etc. The prior art proposes a charging control method based on pulse density modulation, which avoids the problems of weight and cost increase caused by the dc-dc converter. Disadvantage: not suitable for wireless charging occasions with large load quality factor and coupling coefficient. The prior art compares and analyzes different types of wireless feedback control methods, and summarizes the advantages and disadvantages of different methods.

[0005] Specifically, this type of method places the power regulation circuit in the primary side, thereby ensuring the compactness of the secondary circuit structure. However, since the secondary side charging information required for the primary side closed-loop control needs to be interacted through bilateral wireless communication, once the wireless communication is disturbed, the system may have abnormal operation problems, affecting the safety and stability of the system.

[0006] Parameter identification control type (does not use bilateral wireless communication): the prior art estimates the load power based on the output voltage and current of the full-bridge inverter, controls the duty cycle of the transmitting end Buck converter to regulate the load power. Disadvantage: unable to control the charging current / voltage. The prior art estimates the charging voltage based on the relationship between the resonance current in the transmitting coil and the resonance voltage of the compensation capacitor of the LCL-P compensation topology, and adjusts the phase-shift angle of the full-bridge inverter using a PI controller to realize constant voltage charging. Disadvantage: the accuracy of phase difference measurement affects the accuracy of charging voltage. The prior art estimates the charging voltage based on the equivalent load value and mutual inductance value estimated based on the output voltage and current of the full-bridge inverter, and adjusts the phase-shift angle of the full-bridge inverter using a PI controller to realize constant voltage charging. The prior art derives the relationship between the output voltage / current of the full-bridge inverter and the charging voltage, and adjusts the phase-shift angle of the full-bridge inverter using a PI controller to realize constant voltage charging. Disadvantage: the expression of the charging voltage is complex and difficult to apply to actual working conditions.

[0007] Specifically, this type of method puts the power regulation circuit on the primary side, thereby ensuring the compactness of the secondary side circuit structure. At the same time, although it is not necessary to use the secondary side charging information required for the bilateral wireless communication interaction primary side closed loop control, the secondary side charging information obtained through parameter identification will be affected by many factors (such as mutual inductance, self-inductance, etc. Parameter changes), thereby resulting in low parameter identification accuracy, further affecting the accuracy and stability of the primary side closed loop charging control.

[0008] As for the secondary side power regulation method, the topology structure for power regulation mainly includes controllable rectifier bridge, dc-dc converter and switching circuit, etc. The prior art uses different types of PI controllers to adjust the duty cycle of the Buck converter to realize constant current and constant voltage charging, the disadvantages: the volume, cost and weight of the receiving end are increased. The prior art uses a PI controller to adjust the phase shift angle of the half-controlled rectifier bridge to realize constant voltage charging, the disadvantage: the input voltage and input current of the half-controlled rectifier circuit are not in phase, resulting in the influence of the imaginary part of its input impedance on the system performance. The prior art increases a bidirectional switch before the receiving end rectifier circuit, controls the power received by the load through switching control, and realizes constant voltage charging. The prior art increases a unidirectional switch after the receiving end rectifier circuit, uses a hysteresis comparator to control the switching controller, and realizes constant voltage charging.

[0009] Specifically, this type of method puts the power regulation circuit on the secondary side, without using bilateral wireless communication to transmit charging information to the primary side, thereby avoiding the influence of unstable wireless communication. However, the power regulation circuit at the present stage usually uses more passive components and power devices, thereby occupying a large secondary side space, which seriously restricts its application in some occasions, for example: portable devices, for which the available space is usually strictly constrained. SUMMARY

[0010] The purpose of the present application is to overcome the deficiencies of the existing primary side and secondary side power regulation methods, and it is necessary to deeply study the compact design method of the secondary side circuit topology, and propose a wireless charging system and power regulation method based on a compact secondary side circuit topology.

[0011] This invention is achieved through the following technical solution: A wireless charging system based on a compact secondary-side circuit topology is proposed. The wireless charging system includes a DC voltage source, a full-bridge inverter, a compensation topology, a coupling mechanism, an integrated rectifier and power regulation circuit (IRPC), and a system load. The IRPC consists of a diode, a MOSFET, and a filter capacitor, and has both rectification and power regulation functions. The DC voltage is input to the full-bridge inverter and converted into high-frequency AC. Through the power transmission unit composed of the compensation topology and coupling mechanism, and in accordance with the law of electromagnetic induction, electrical energy is transmitted from the primary side to the secondary side. At this time, the IRPC not only rectifies the alternating current in the secondary-side resonant coil into DC, but also regulates the MOSFET... Q I1 The duty cycle of the PWM signal is used to further control the charging current and voltage of the system load.

[0012] The present invention also proposes a power regulation method for a wireless charging system based on the aforementioned compact secondary circuit topology, the power regulation method comprising four operating modes; First working mode, Q I1 The PWM drive signal is low. Q I1 When in an open-circuit state, the secondary resonant coil current... i s In the negative half-cycle, i s Inflow filter capacitor C o After the load is applied, the coil returns to the secondary resonant coil. Second working mode, Q I1 The PWM drive signal is low. Q I1 When in an open-circuit state, the secondary resonant coil current... i s In the positive half-cycle, i s Flowing Q I1 The current flows back to the secondary resonant coil after passing through the freewheeling diode, but does not flow into the filter capacitor. C o and load; Third working mode, Q I1 The PWM drive signal is high level. Q I1 When in a closed state, the secondary resonant coil current... i s In the positive half-cycle, i s Flowing QI1 The current flows back to the secondary resonant coil after passing through the freewheeling diode, but does not flow into the filter capacitor. C o and load; Fourth working mode, Q I1 The PWM drive signal is high level. Q I1 When in a closed state, the secondary resonant coil current... i s During the negative half-cycle, a portion of the current... i s Inflow Q I1 Then it returns to the secondary resonant coil, and another part of the current... i s Inflow filter capacitor C o After being loaded, it returns to the secondary resonant coil.

[0013] Furthermore, the charging current is obtained in the method. I o Duty cycle of the PWM signal D The relationship between them is as follows: Assume the expression for the resonant current of the secondary coil is: (1) Combining working modes, I o and The expression between them is formula (2); further, it is derived that T1 and T satisfy the expression (3); (2) (3) Combining formulas (2) and (3), we can obtain I o and D The expression between them is (4); obviously, control D Further adjustments are possible. I o or U o ; (4).

[0014] The beneficial effects of this invention are: 1. Compared with the commonly used secondary-side power regulation circuit topology, the IRPC proposed in this invention uses only one diode, one switching transistor and a filter capacitor, which maximizes the compactness and lightweight of the secondary-side circuit topology, making it particularly suitable for wireless charging applications that require miniaturized devices.

[0015] 2、The IRPC proposed in the application not only has a rectification function, but also has a power regulation function. Specifically, by controlling the duty cycle of the PWM signal through a simple PI algorithm, the constant current / constant voltage charging requirement of the load can be realized. In addition, the above process does not require complex signal acquisition or phase synchronization operations, thereby minimizing the control complexity.

[0016] 3、When a higher precision charging current is not required, even if closed-loop control is not used, the IRPC can still ensure that the equivalent load resistance changes within a certain range to approximate constant current charging, thereby further reducing the control complexity of the secondary side circuit topology. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a circuit topology diagram of a wireless charging system based on a compact secondary side circuit topology.

[0018] Figure 2 It is a working mode schematic diagram of a wireless charging system based on a compact secondary side circuit topology.

[0019] Figure 3 It is a simulation result schematic diagram between different equivalent load resistances, I o and D .

[0020] Figure 4 It is a simulation result schematic diagram of constant current charging.

[0021] Figure 5 It is a simulation result schematic diagram of constant voltage charging. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0023] As shown in Figure 1 , the application proposes a wireless charging system based on a compact secondary side circuit topology, which comprises a direct current voltage source, a full-bridge inverter, a compensation topology (IRPC) and a load. Figure 1The method is also applicable to other types of compensation topologies, such as: LCC-S, LCC-LCC, etc., coupling mechanisms, integrated rectifier and power control circuits (IRPC), and system loads. The IRPC is composed of a diode, a MOSFET, and a filter capacitor, and has the dual functions of rectification and power regulation. A direct-current voltage is input into a full-bridge inverter, becomes an alternating current with a high frequency (for example, 85 kHz), passes through a power transmission unit composed of a compensation topology and a coupling mechanism, and, in combination with the law of electromagnetic induction, the electric energy is transmitted from the primary side to the secondary side. At this time, the IRPC not only rectifies the alternating current in the secondary side resonant coil into a direct current, but also further controls the charging current and voltage of the system load by regulating the duty cycle of the PWM signal of the MOSFET. Q I1 .

[0024] In combination with the circuit topology shown in Figure 1 and the working waveform shown in Figure 2 , the application further provides a power regulation method for a wireless charging system based on the compact secondary side circuit topology. The power regulation method includes four working modes. The first working mode corresponds to Figure 2 I. Q I1 The PWM driving signal is at a low level, Q I1 is in an open circuit state, and the secondary side resonant coil current i s is in a negative half cycle, i s flows into the filter capacitor C o and the load and then returns to the secondary side resonant coil. The second working mode corresponds to Figure 2 II. Q I1 The PWM driving signal is at a low level, Q I1 is in an open circuit state, and the secondary side resonant coil current i s is in a positive half cycle, i s flows through the freewheeling diode of Q I1 and then returns to the secondary side resonant coil but does not flow into the filter capacitor C o and the load. The third working mode corresponds to Figure 2 III.Q I1 the PWM driving signal is high, Q I1 in the pass-through state, the secondary resonant coil current i s is in the positive half cycle, i s flows through Q I1 the freewheeling diode and returns to the secondary resonant coil, but will not flow into the filter capacitor C o and the load; the fourth working mode, corresponding to Figure 2 IV in FIG. 4. Q I1 the PWM driving signal is high, Q I1 in the pass-through state, the secondary resonant coil current i s is in the negative half cycle, a part of the current i s flows into Q I1 and returns to the secondary resonant coil, and another part of the current i s flows into the filter capacitor C o and the load and returns to the secondary resonant coil.

[0025] In summary, in the entire working process of the IRPC, the duty cycle D (the value range is 0-1) of the PWM signal of the fourth working mode is the core link for adjusting the charging current and voltage.

[0026] In the method, a relationship between the charging current I o and the duty cycle of the PWM signal D is obtained, and the relationship is specifically: assuming that the expression of the secondary coil resonant current is: (1) combined with the working mode, I o and the expression between is formula (2); further derivation is made to obtain that T1 and T satisfy expression (3); (2) (3) combined with formula (2) and (3), it can be obtained that I o and DThe expression between them is (4) ; obviously, the control D can be further adjusted I o or U o ; (4).

[0027] Circuit simulation verification: The core parameters of the simulation circuit of the wireless charging system based on the compact secondary side circuit topology are as follows: the DC bus voltage is 150 V, the self-inductance value of the primary side coil of the coupling mechanism is 110 μH, the self-inductance value of the secondary side coil is 85 μH, the mutual inductance value between the two is 35 μH, the equivalent load resistance changes in the range of 30 Ω to 42 Ω during the constant current charging process, and the equivalent load resistance changes in the range of 42 Ω to 125 Ω during the constant voltage charging process. The simulation data used here is only used as an example, and the method proposed in the application is also applicable to other parameter requirements.

[0028] 1. Open loop simulation verification: combined with the given parameters, the system is running in open loop and under different equivalent load resistances, I o and D The simulation results between them are plotted in Figure 3 . Obviously, the simulation results verify that the control D can adjust I o or U o In addition, the simulation results further verify that even if the closed loop control is not used, D a fixed value, I o The size of

[0029] 2. Constant current charging simulation: taking the charging current of 3 A as an example, the equivalent load resistance changes in the range of 30 Ω to 42 Ω, and the step is 4 Ω, and the simulation results are shown in Figure 4 . Obviously, adjusting the PWM signal duty cycle Q I1 of D (the change interval is 0.349, 0.348, 0.348, 0.349, respectively corresponding to four changes of the load) can realize stable constant current charging. In addition, according to the small change trend of the duty cycle D , it can be known that even if the closed loop control is not used, the IRPC still realizes approximate constant current charging. Of course, the charging current accuracy will be higher after the closed loop control is used.

[0030] 3. Constant voltage charging simulation: taking the charging voltage as 126 V as an example, the change range of the equivalent load resistance is 50 Ω to 125 Ω, and the step is 25 Ω, and the simulation result is shown in Figure 5 Obviously, the PWM signal duty cycle Q I1 of the constant voltage charging can be stabilized D (the change interval is 0.419, 0.512, 0.555, 0.581, respectively corresponding to four changes of the load).

[0031] The wireless charging system and power regulation method based on the compact secondary side circuit topology have the following technical advantages: first, the secondary side uses as few power devices as possible to realize the constant current and constant voltage output of the wireless charging system, ensuring the compactness and lightness of the secondary side circuit topology, and specific data comparison is shown in Table 1; second, since the power regulation is only completed by the secondary side circuit topology, it is not necessary to use wireless communication to interact the power regulation data between the primary side and the secondary side, thereby avoiding the problem of abnormal system operation when the wireless communication is disturbed.

[0032] Table 1 Comparison and analysis between the method proposed in the application and the existing secondary side power regulation method

[0033] Note: in Table 1, I 2 represents the effective value of the resonant current in the secondary side coil, I o represents the charging current, D represents the duty cycle of the PWM driving signal of the switch tube in the dc-dc converter, φ is the phase shift angle between the PWM driving signals of the switch tubes in the full-controlled / half-controlled rectifier circuit, β is the phase angle between the input voltage and the input current in the full-controlled / half-controlled rectifier circuit.

[0034] Although the application has been disclosed as above with reference to the preferred embodiments, it is not intended to limit the application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the application, therefore the protection scope of the application should be defined by the claims.

Claims

1. A wireless charging system based on a compact secondary side circuit topology, characterized by, The wireless charging system comprises a direct current voltage source, a full-bridge inverter, a compensation topology, a coupling mechanism, an integrated rectification and power regulation circuit (IRPC) and a system load; the IRPC is composed of a diode, a MOSFET and a filter capacitor, and has the dual functions of rectification and power regulation; the direct current voltage is input into the full-bridge inverter, becomes high-frequency alternating current, passes through the power transmission unit composed of the compensation topology and the coupling mechanism, and, in combination with the electromagnetic induction law, the electric energy is transmitted from the primary side to the secondary side; at this time, the IRPC not only rectifies the alternating current in the secondary side resonant coil into direct current, but also controls the charging current and voltage of the system load by regulating the duty cycle of the PWM signal of the MOSFET Q I1 .

2. A power regulation method for a wireless charging system based on the compact secondary side circuit topology of claim 1, characterized in that, The power regulation method comprises four working modes in total; The first working mode, Q I1 The PWM drive signal is low, Q I1 In the off state, the secondary resonant coil current i s In the negative half cycle, i s Flow into the filter capacitor C o And return to the secondary resonant coil after the load; the second working mode, Q I1 the PWM driving signal is low, Q I1 is in the open circuit state, the resonant coil current of the secondary side i s is in the positive half cycle, i s flows through Q I1 the freewheeling diode behind it returns to the resonant coil of the secondary side, but will not flow into the filter capacitor C o and the load; the third working mode, Q I1 the PWM driving signal is high level, Q I1 in the pass-through state, the secondary resonant coil current i s in the positive half cycle, i s flows back to the secondary resonant coil through Q I1 the freewheeling diode, but will not flow into the filter capacitor C o and the load; Fourth working mode, Q I1 The PWM drive signal is high level, Q I1 In the pass-through state, the secondary resonant coil current i s In the negative half cycle, a part of the current i s flows into Q I1 After returning to the secondary resonant coil, another part of the current i s flows into the filter capacitor C o And after the load returns to the secondary resonant coil.

3. The power regulation method of claim 2, wherein, In the method the charging current is obtained I o with the duty cycle of the PWM signal D a relationship between the duty cycle of the PWM signal and the charging current, in particular: Assuming the secondary coil resonant current is expressed as: (1) Combining working modes, I o and The expression between them is formula (2); further, it is derived that T1 and T satisfy the expression (3); (2) (3) Combining formulas (2) and (3), we can obtain I o and D The expression between them is (4); obviously, control D Further adjustments are possible. I o or U o ; (4)。

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