CN110957796B

CN110957796B - Wireless charging circuit and system

Info

Publication number: CN110957796B
Application number: CN201911279433.4A
Authority: CN
Inventors: 黄智聪; 林智声; 麦沛然; 马许愿
Original assignee: University of Macau
Current assignee: University of Macau
Priority date: 2019-12-12
Filing date: 2019-12-12
Publication date: 2023-05-02
Anticipated expiration: 2039-12-12
Also published as: CN110957796A

Abstract

Exemplary embodiments provide a wireless power transfer circuit for powering a variable resistive load with an Alternating Current (AC) power source induced by a primary coil of a primary side of the circuit in a secondary coil of the circuit, the wireless power transfer circuit comprising: a controllable switched capacitor (SCC) connected to the ac power supply and a half-controlled rectifier bridge (SAR) connected to an output of the SCC to rectify an output of the SCC. The wireless power transmission circuit provides a constant power output and improves power transmission efficiency by adjusting a control angle of the SCC and a conduction angle of the SAR to provide a load impedance matched with an impedance of the coil.

Description

Wireless charging circuit and system

Technical Field

The invention relates to a wireless charging circuit and a system.

Background

Wireless Inductive Power Transfer (IPT) is a continuously evolving technology, typically used in applications where it is inconvenient or impossible to achieve a physically connected power supply, with the advantage of simplifying the charging operation and eliminating the safety issues associated with the connection of electrical components. The technology is suitable for being applied to many different scenes, such as consumer electronic devices, implantable body devices, industrial electronic devices and the like.

There is a need for a new device and system that improves the charging efficiency of IPT to meet market demands.

Disclosure of Invention

Exemplary embodiments provide a wireless power transfer circuit for powering a variable resistive load with an Alternating Current (AC) power source induced by a primary coil of a primary side of the circuit in a secondary coil of the circuit, the wireless power transfer circuit comprising: a controllable switched capacitor (SCC) connected to the ac power supply and a half-controlled rectifier bridge (SAR) connected to an output of the SCC to rectify an output of the SCC. The SCC includes a first capacitor and two electrically controlled switches connected in parallel with the first capacitor, the two electrically controlled switches being connected in series. The SAR includes a bridge circuit that includes two electronically controlled switches. The two switches in the SCC are each turned on for half a period and are complementary to each other, and their off-times have a time delay relative to the zero crossing point of the ac power supply, which is the control angle of the SCC. Two switches in SAR are each turned on for half a period and are complementary to each other, with the off time having a time delay relative to the zero crossing of the ac power source, which is the conduction angle of SAR. The wireless power transmission circuit provides a constant power output and improves power transmission efficiency by adjusting a control angle of the SCC and a conduction angle of the SAR to provide a load impedance matched with an impedance of the coil.

The exemplary embodiments also provide a wireless charging system that improves battery charging efficiency by charging a battery with an ac power source induced by a primary coil in a primary side of a circuit at a secondary coil in a secondary side of the circuit, the wireless charging system comprising: a controllable switched capacitor (SCC), a half-controlled rectifier bridge (SAR), a sensor, a controller and a signal generator connected to the secondary winding. The SCC comprises two electrically controlled switches connected in series and a first capacitor connected in parallel with the two electrically controlled switches; the SAR is connected to the output end of the SCC to rectify the output of the SCC, and comprises a bridge circuit which comprises two electric control switches; a plurality of sensors for measuring a charging voltage and a charging current of the battery; the controller is used for calculating the conduction angle of the SAR and the control angle of the SCC according to the measured value of the sensor and the preset power value; and the at least one signal generator is used for generating a control signal according to the conduction angle and the control angle and providing the control signal to the electric control switches in the SCC and the SAR. Wherein the two switches in the SCC are each turned on for half a period and are complementary to each other, with an off time having a time delay relative to a zero crossing point of the ac power source, the time delay being a control angle of the SCC; two switches in SAR are each turned on for half a period and are complementary to each other, with the off time having a time delay relative to the zero crossing of the ac power source, which is the conduction angle of SAR. The wireless power transmission circuit provides load impedance matched with coil impedance by adjusting the control angle of SCC and the conduction angle of SAR, so as to charge the battery with constant power and improve charging efficiency.

Exemplary embodiments also provide a wireless charging method for improving battery charging efficiency by a wireless charging system, which charges a battery through an ac power source induced by a primary coil in a primary side of a circuit at a secondary coil in a secondary side of the circuit, wherein the ac power source is connected to a controllable switched capacitor (SCC) and then to a half-controlled rectifier bridge (SAR), an output of the SAR being connected to a rechargeable battery. Wherein the SCC comprises a first capacitor and two electrically controlled switches connected in series with the first capacitor, and the SAR comprises a bridge circuit comprising two upper branches and two lower branches, each upper branch comprising a diode and each lower branch comprising an electrically controlled switch. The wireless charging method comprises the following steps: calculating, by a controller, a conduction angle of SAR to provide a load resistance matched to an impedance of a coil, wherein the conduction angle is a time delay of an off time of a controllable switch of SAR relative to a current zero crossing of the ac power source; calculating, by a controller, a control angle of the SCC to cancel reactance of the secondary side, wherein the control angle is a time delay of an off time of a controllable switch of the SCC relative to a current zero crossing of the ac power source; controlling a switch in the SAR according to the conduction angle through a first control signal; and controlling a switch in the SCC according to the control angle through a second control signal. The wireless charging method can charge the battery with constant power, thereby improving the charging efficiency.

Drawings

Fig. 1 is a schematic diagram of a wireless charging circuit according to an exemplary embodiment.

Fig. 2 is a switching sequence and operating waveforms of a half-controlled rectifier bridge (SAR) according to an example embodiment.

Fig. 3 is a switching sequence and operating waveforms of a controllable switched capacitor (SCC) according to an exemplary embodiment.

FIG. 4 is a graph of equivalent impedance versus controllable angle for an SCC according to an exemplary embodiment.

Fig. 5 is an equivalent wireless power transfer circuit diagram according to one exemplary embodiment.

Fig. 6A is a graph of SAR conduction angle and equivalent load impedance versus load resistance, according to an example embodiment.

Fig. 6B is a graph of the SCC controllable angle and the impedance of the equivalent secondary side capacitance versus SAR conduction angle according to an example embodiment.

FIG. 7 is a table of simulation circuit parameters in accordance with an exemplary embodiment.

Fig. 8 is an equivalent wireless charging circuit diagram for Constant Power (CP) output and maximum efficiency according to an exemplary embodiment.

Fig. 9 is a graph of output power and efficiency versus SAR conduction angle in accordance with an exemplary embodiment.

Fig. 10 is a control block diagram of a wireless charging system according to an exemplary embodiment.

Fig. 11 is a SCC voltage stress graph according to an example embodiment.

Fig. 12 is a graph of loss resistance ratio and charge efficiency versus internal resistance of a battery according to an example embodiment.

Fig. 13 is a charging circuit parameter table according to an exemplary embodiment.

Fig. 14 is a graph of operating point versus battery resistance measurements according to an example embodiment.

Fig. 15A is a graph of the measurement of output current and voltage versus battery resistance for a system according to an example embodiment.

Fig. 15B is a graph of measured power and efficiency versus battery resistance according to an example embodiment.

Fig. 16 is a transient waveform diagram of circuit output parameters according to one embodiment.

Fig. 17 is a schematic diagram of a wireless charging circuit according to one embodiment.

Fig. 18 is an equivalent wireless power transfer circuit schematic diagram according to one embodiment.

Detailed Description

Exemplary embodiments include a wireless charging circuit that combines the advantages of load-independent transfer characteristics and matching load impedances by employing a controllable switched capacitor (SCC) and a half-controlled rectifier bridge (SAR) on the receiving side and by operating the SCC and SAR to simulate the optimal impedance of the resonator and the secondary load, thereby achieving constant power output throughout the charging process and maintaining maximum transfer efficiency.

The battery charging technology widely used at present is mainly constant Current Charging (CC). In the constant current charging process, the charging power is minimum when charging is started until the charging power is increased to the maximum value when charging is completed, and the charging duration time is shorter at a high power level, so that the power capacity utilization rate of the charger adopting the constant current charging strategy is lower.

In order to increase the utilization of the charge power capacity, the charger may control the output power to a predetermined maximum value, thereby providing Constant Power (CP) charging. For a contact charger, constant power charging in a battery management system is relatively easy, but an inductive power transfer charger is required to operate at some specific operating frequency and has a transfer characteristic independent of the load, thereby reducing control complexity and increasing maximum efficiency. In addition, IPT converters need to have load matching capability, and in the event of a load mismatch, transmission efficiency may be significantly reduced. Currently available single stage IPT converters have difficulty achieving constant power charging and maintaining maximum charging efficiency throughout the charging process.

One way to achieve constant power charging is an IPT system cascaded through multiple stages of converters. For example, the number of the cells to be processed,

the transmit side pre-stage converter is used for modulating the input amplitude or the receive side post-stage converter is cascaded to the IPT converter for power regulation. However, as additional converter stages are added, the power loss and control complexity increase accordingly. In addition, there is a need to add a wireless signal feedback device between the transmitting side and the receiving side.

To overcome the technical problems mentioned above, exemplary embodiments provide a wireless charging circuit comprising a single stage IPT converter that maintains a constant output power rather than providing a constant output current during the dominant phase of battery charging, thus fully exploiting its power capability and thus achieving a faster charging rate. The wireless charging circuit adopts series compensation, adopts a controllable switch capacitor (SCC) and a semi-controlled rectifier bridge (SAR) at a receiving side, simulates the optimal impedance and a secondary load of a resonator by controlling the controllable angle of the SCC and the conduction angle of the SAR, combines the advantages of load-independent transmission characteristics and matched load impedance, and can realize constant power output and maintain maximum transmission efficiency in the whole charger process.

Exemplary embodiments can achieve at least the following technical effects:

(1) The charging circuit works under the condition of constant power, and can fully exert the power consumption, thereby having faster and safer charging rate.

(2) The use of SCC and SAR to simulate the optimal impedance of the resonator and the secondary load achieves the advantages of load independent characteristics and matching the load impedance, thus maintaining maximum transmission efficiency throughout the charging process.

(3) The fixed frequency work is realized, the control is simple to realize, and the control is only realized on the receiving side without wireless signal feedback between the transmitting side and the receiving side.

(4) And a single-stage converter structure is adopted, and all switching tubes realize soft switching, so that the loss is reduced.

The invention is described in further detail below with reference to the drawings and the detailed description. In the following description, X _subscript For expressing the impedance of the component shown in its subscript.

Fig. 1 is a schematic diagram of a wireless charging circuit structure according to an exemplary embodiment. In fig. 1, a wireless charging circuit 100 includes a primary circuit 110 and a secondary circuit 120. The primary circuit 110 is a transmitting side circuit, and the secondary circuit 120 is a receiving side circuit. The primary circuit 110 includes a series connected DC source 111 having four switches Q ₁ -Q ₄ A full bridge inverter 112, a primary compensation capacitor 113, and a primary coil 114. Wherein the voltage value of the DC source 111 is V _I The primary compensation capacitor 113 has a fixed capacitance value C _P 。

The secondary circuit includes a secondary coil 124, a secondary compensation capacitor 123, an SCC121, and a SAR122 connected in series. Wherein the secondary compensation capacitor 123 has a fixed capacitance value C ₁ . Output filter capacitor C _f Is connected in parallel with the SCC121, the SAR122, and the rechargeable battery 127.

In FIG. 1, SCC121 includes a capacitor 1211 and two electronically controlled switches 1212 connected in parallel, capacitor 1211 has a fixed capacitance value C ₂ Electronically controlled switch 1212 includes two Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), labeled Q, respectively, connected in series _a And Q _b . Wherein Q is _a And Q _b The drains of which are connected to the two ends of the capacitor 1211, respectively, and the gate receives the control signal. Q (Q) _a And Q _b Respectively and reversely connected with a diode, which is marked as D _a And D _b . The voltage value across SCC is denoted as v _SCC The value of the current flowing through switch 1212 is denoted as i _SCC SCC equivalent capacitance is denoted as C _SCC . In the secondary circuit 120, a series secondary compensation capacitor 123 is used to reduce the voltage stress of the switches in the SCC.

SAR122 includes two diodes 1221 in the upper arm, labeled D respectively ₅ And D ₇ And two electronically controlled switches 1222 in the down leg. Each electronically controlled switch 1222 includes a MOSFET, labeled Q ₆ And Q ₈ Wherein Q is ₆ And Q ₈ The drains of which are connected to the two upper branches, respectively, and the sources are connected to each other.

Each MOSFET Q ₆ And Q ₈ Comprising an antiparallel diode, respectively designated D ₆ And D ₈ 。

Primary coil 114 and secondary coil 124 form a magnetic coupler 130, having a mutual inductance value of M,

for example, magnetic coupler 130 is a loosely coupled transformer. The coupling coefficient is defined as

The primary coil 114 has a primary self-inductance L _P And resistance R _P,w Wherein the resistance R _P,w Is the primary coil loss. The secondary coil 124 has a secondary self-inductance L _S And resistance R _S,w Wherein the resistance R _S,w Is the secondary coil loss.

In the wireless charging circuit 100, the dc source 111 supplies a dc voltage V via the inverter 112 _I Converted into voltage v _p An alternating current of angular frequency omega for driving the primary coil 114 to induce an alternating current i in the secondary coil 124 _S And further at SCThe output end of C forms alternating voltage v _S . The induced voltage and the induced current are input into SAR122 for rectification, and then filtered by capacitor 126 to be output as DC voltage V _O And direct current I _O I.e., the charging voltage and charging current of battery 127.

In one embodiment, switch Q in SAR122 ₆ And Q ₈ When the anti-parallel diode is on, a zero voltage switch (zero voltage switching, ZVS) is thereby realized. Switch Q ₆ And Q ₈ Half a current period is turned on and the on times are complementary, respectively. Thus Q ₆ And Q ₈ Turn-off time and current i of (2) _S There is a time delay pi-theta e 0 pi between zero crossings of (a)]θ is defined as the conduction angle of SAR. The conduction angle θ has a maximum value of pi and a minimum value of 0. The change in conduction angle θ affects v _S And i _S Phase angle between them.

In one embodiment, switch Q in SCC _a And Q _b And current i _S Synchronous with current i _S Is controllable in angle between zero crossing points of (a)

Switch Q _a And Q _b Half a current period is turned on and the on times are complementary, respectively. For example, Q _a And Q _b At v _SCC Switching at zero voltage, thereby implementing soft switching to reduce switching losses. Capacitor C during half a current period ₂ The charge time (or discharge time) of (a) is +.>

It is associated with->

Is increased and decreased, v _SCC The root mean square value of (c) decreases. Thereby, the equivalent capacitance of SCC, namely C _SCC By varying the controllable angle +.>

To make adjustments.

In one embodiment, the conduction angle of SAR122 and the controllable angle of SCC121 are adjusted to provide a matched load impedance such that wireless charging circuit 100 charges battery 127 at constant power, thereby improving charging efficiency.

In one embodiment, the electronically controlled switches in the SCC and SAR comprise MOSFET switches, and in other embodiments may be other transistor switches.

Fig. 2 is a switching sequence and operational waveform 200 of a half-controlled rectifier bridge (SAR) according to an example embodiment. In fig. 2, the electronically controlled switch Q of SAR122 ₆ And Q ₈ The anti-parallel diode is turned on when turned on to realize zero voltage switching. Q (Q) ₆ And Q ₈ Are turned on for half a current period and the on times are complementary. Thus Q ₆ And Q ₈ And i _s Has pi-theta E [0, pi ] between zero crossing points of (C)]θ is the conduction angle of SAR122. v _s,1 Is v _s Is delayed from i _s Its phase angle is given by γ=pi- θ/2. Therefore, the equivalent load of the charging circuit is the impedance Z _eq Rather than a pure resistor.

Battery charging is a slow process compared to the operating cycle of a wireless charging circuit, so the battery can be modeled as a resistor determined by the charging voltage and charging current, i.e

The equivalent fundamental impedance of the SAR122 is:

Z _eq ＝R _eq +jX _eq ， (1)

wherein R is _eq Is equivalent resistance X _eq In order to be an equivalent reactance,

fig. 3 is a switching sequence and operational waveform 300 of an SCC according to an exemplary embodiment. In fig. 3, an electrically controlled switch Q _a And Q _b Driving signal of (c) and i _s Synchronous with i _s With a controllable angle between zero crossings of (2)

Q _a And Q _b Each on for half a period and the on times are complementary. Due to Q _a And Q _b At v _SCC Turning on and off at zero voltage, thereby implementing soft switching to minimize switching losses.

Equivalent impedance of SCC, X _Cscc Can be expressed as formula (4) and reduced to formula (5) by quadratic curve fitting:

wherein the method comprises the steps of

Fig. 4 is a graph 400 of equivalent impedance versus controllable angle for an SCC according to an example embodiment.

As shown in fig. 4, the exact relationship of the equivalent impedance of the SCC to the controllable angle is represented as curve 401 and the approximate relationship is represented as curve 402. When (when)

X when changing from 0.5 pi to pi _Cscc Can be derived from nominal reactance X _C2 Modulated to zero.

Fig. 5 is an equivalent charging circuit diagram 500 according to an exemplary embodiment.

Fig. 5 is an equivalent circuit diagram of the circuit shown in fig. 1. The primary circuit includes a power source 511, a resistor 512, a primary compensation capacitor 513, an inductance 514, and a primary-side induced electromotive force 515 connected in series. Resistor 512 has an equivalent resistance R _p Which represents the primary coil 114 and the inverter 112. The capacitance value of the primary compensation capacitor 513 is denoted as C _p ，

The secondary circuit includes an equivalent induced ac current source 525, an inductance 524, a secondary compensation capacitance 523, a variable capacitance 521, and a load 522 connected in series with one another. The capacitance value of the variable capacitance 521 is denoted as C _scc I.e. the equivalent capacitance of SCC 121. The load 522 is defined by an equivalent impedance Z _eq Representation comprising resistors R in series _eq And reactance X _eq As shown in formula (1). Resistor R _S Representing the sum of the losses of the secondary coil 124, the scc121 and the SAR122.

For example, V _p ，I _p ，V _s And I _s Respectively for representing variable v _p ，i _p ，v _s And i _s Phasor representation of the fundamental component of (c). C (C) ₁ ，C _Scc And X _eq Providing capacitive reactance in the secondary circuit, which can be compensated with an equivalent secondary compensation capacitance C _S,eq Represented by the following formula (6):

by analyzing the equivalent circuit in fig. 5, the following relationship can be obtained:

(R _P +jX _Lp +jX _Cp )I _P -jX _M I _S ＝V _P (7)

-(R _S +R _eq +jX _LS +jX _Cs,eq )I _s -jX _M I _P ＝0 (8)

wherein X is _M X is the mutual inductance of the primary coil and the secondary coil _LP Is the inductance of the primary circuit, X _CP For primary electricity

Capacitive reactance of road X _M ＝ωM，

X _Ls ＝ωLs。

V _p 、V _s And I _s The magnitudes of (2) are given by equations (9) (10) and (11), respectively:

the equivalent circuit efficiency of fig. 5 is shown in formula (12):

assume that

And +.>

At the selected operating frequency ω, the transmission efficiency is maximized when (13) and (14) are satisfied, as shown in formula (15) where X _CS,eq,opt And R is _eq,opt X respectively maximizing transmission efficiency _CS,eq And R is _eq Is used for the optimization of the values of (a).

X _Ls +X _{Cs，eq，opt} ＝0 (13)

Due to the internal resistance R of the battery during charging _L The internal resistance is required to be converted into a matching resistance R via SAR according to equation (14) over a wide range _eq,opt To achieve the mostHigh transmission efficiency. Therefore, according to the formulas (2) and (14), the conduction angle θ of SAR can be expressed as formula (16):

according to equation (3), the variation of the conduction angle θ also affects the load reactance X _eq Which is represented by formula (17):

the above analysis of the charging circuit of the exemplary embodiment was verified by simulation experiments. The parameters of the simulation experiments described below are shown in the table of fig. 7 unless otherwise specified.

Graph 600A in fig. 6A shows the conduction angle θ as a function of load resistance. In FIG. 6A, curve 601 shows SAR conduction angle θ with R _L And accordingly, thereby achieving an optimized load resistance in the simulation. As can be seen from curve 603, by controlling the conduction angle θ, the equivalent load resistance R _eq Can be maintained at an optimized load resistance value R _eq,opt . However, curve 602 shows that as conduction angle θ becomes smaller, reactance X _eq Is increased.

To ensure the condition in formula (14) to achieve maximum charging efficiency, C _s,eq Needs to be fully compensated to L at a fixed frequency _s Thus, exemplary embodiments provide for controlling the angle of SCC by varying the angle of control

To change the reactance X _Cscc Finally, the target reactance X is obtained _{CS，eq，opt} ＝-X _LS . In combination with (5), (6) and (17), controllable angle of SCC +.>

The expression is as follows:

the analysis step is satisfied during the control process, so that the system can work at the maximum transmission efficiency.

FIG. 6B shows the controllable angle of SCC in simulation experiments

Conduction angle theta and equivalent secondary side compensation inductance X _CS,eq A relationship diagram 600B between. In FIG. 6B, curve 604 shows the controllable angle +.>

And the joint control of the conduction angle theta. As can be seen from curve 605, the combined control results in an equivalent secondary compensation inductance X _CS,eq Almost constantly maintained at the optimum value X _CS,eq,opt Thereby enabling the highest efficiency.

As described above, the wireless charging current of the exemplary embodiment can achieve the highest charging efficiency by matching the optimized load resistance in the secondary circuit and maintaining zero reactance. When the reactance is zero, the inductive energy transmission system can realize output current irrelevant to the load, so that the constant power output and the highest efficiency can be realized simultaneously by combining the two points.

Fig. 8 shows an IPT circuit 800 that enables both constant power output and maximum efficiency. In circuit 800, primary circuit 801 and secondary circuit 802 operate at a fixed resonant frequency ω. The reactance of the secondary circuit 802 is zero and the load resistance is maintained at the optimum value R _eq,opt . Optimizing the load resistance R according to equation (14) _eq,opt Is approximately constant. Theoretically, when the input voltage of the primary circuit is v, such as neglecting losses in the electrical components _p When the secondary circuit is independent of the load, the output current amplitude can be expressed as:

thus, the exemplary embodiment can guarantee a constant power output for a fixed input voltage throughout the charging process, and maintain the highest efficiency, expressed as follows:

where the subscript RMS represents the root mean square value.

In combination with formulas (9) - (11), (19), (20), constant charging power, output dc voltage and dc current can be expressed as formulas (21), (22) and (23), respectively:

assuming equivalent load reactance X _eq Can be controlled by appropriate control of the reactance X of SCC _CSCC But is to be counteracted and the result is that,

output power P _O Can be only equivalent to the load resistor R _eq In relation, the output power is expressed as

P _O ≈|I _S | ² _RMS R _eq 。

According to equation (2), the equivalent load resistance can be adjusted by controlling the conduction angle θ, and therefore, the output power P _O Has a monotonic relationship with the conduction angle θ (monotonic relationship).

Fig. 9 shows a plot 900 of output power, efficiency, and SAR conduction angle in an exemplary embodiment.

In fig. 9, the output power P _O The relationship with conduction angle θ is represented by

curves

910, 920 and 930, and the relationship of efficiency η with conduction angle θ is represented by

curves

940, 950 and 960, each set of curves corresponds to a battery resistance value R _L 30 omega, 40 omega, and 50 omega. When P _O At a constant value in equation (20), the charging circuit is most efficient, as indicated by

intersections

901, 902, 903. Therefore, P can be obtained by integrating P in the controller _O,constant As reference value P _O,ref To achieve constant power output and to maintain maximum efficiency.

Fig. 10 illustrates a wireless charging system 1000 of an exemplary embodiment. The wireless charging system 1000 includes a wireless charging circuit 1010 for charging a battery, a plurality of sensors 1020 for measuring an output voltage and an output current, a signal processing unit 1040 for providing a control signal to the wireless charging circuit 1010, and a controller 1030 for calculating a control angle for the control signal. The wireless charging circuit 1010 further includes SCC and SAR that can be adjusted by control signals. For example, wireless charging circuit 1010 is the wireless charging circuit shown in fig. 1.

In one embodiment, the charge voltage Vo and the charge current Io are measured by the sensor 1020, and the measured values are input to multipliers and dividers of the controller 1030 for calculating the charge power and the load resistance, respectively. The controller further calculates the conduction angle of the SAR according to the difference between the charging power measured value and the reference value through PI control. Meanwhile, under the condition that the SAR conduction angle and the battery resistance value are known, the control angle of SCC is calculated according to formula (18). Thereafter, the signal generation unit 1040 generates control signals of SCC and SAR by the signal generator 1 and the signal generator 2, respectively, according to the calculated conduction angle and control angle. The signal generating unit 1040 further includes a zero crossing detector for detecting the coil current i in the secondary circuit _S And generates a synchronization signal for the signal generator.

In one embodiment, the controller 1030 is a microcontroller or microprocessor capable of implementing a control algorithm.

In one embodiment, the controller 1030 includes any one or combination of two or more of a proportional controller, an integral controller, and a derivative controller.

In one embodiment, the power reference value P _O,ref Is determined as(21) Is a constant power value in the power supply.

In one embodiment, the control angle of the SCC is calculated from a relationship between the control angle of the SCC and a measured value of the conduction angle of the SAR.

In one embodiment, the control signals for the SCC and SAR are generated by more than one signal generator.

Because the working frequency of the primary circuit is fixed, the impedance of the secondary circuit is only required to be controlled to realize constant power and highest efficiency charging, and therefore, the wireless charging system does not need to carry out wireless communication between the primary circuit and the secondary circuit, thereby simplifying the circuit design and reducing the energy loss of the secondary circuit.

Fig. 11 shows a plot 1100 of voltage stress of SCC versus secondary circuit compensation capacitance.

According to formulas (3) and (5), |X _eq I is with battery resistance R _L Changes by a change, the minimum of which is denoted as |X _eq | _min Maximum value is |X _eq | _max . When the SCC control angle changes from pi to 0.5 pi, |x _CSCC Change from zero to |X _C2 |。X _CSCC For counteracting X _eq Is varied such that X _CS,eq Can be maintained at an optimal value X _CS,eq,opt Thereby effectively compensating X _LS 。

According to formula (14), C ₁ The reactance of the secondary circuit needs to be fully compensated, namely:

the voltage stress of the SCC switch is determined by the maximum voltage across the SCC, namely:

|V _SCC,max |＝|X _C2 ||I _S |. (26)

to reduce the voltage stress of the SCC switch, the |X should be minimized _C2 An i value. Thus, according to equation (24),should maximize |X _C1 An i value. Combined (25) |x _C1 The maximum value of i can be expressed as formula (27):

curve 1110 in fig. 11 shows the voltage stress V _SCC，max I and reactance I X _C1 The relation between I can be seen as larger I X _C1 The value can reduce the voltage stress |V _SCC，max |。

When the control angle of SCC is maximum, namely

When SCC current stress is greatest. Because at this time, the capacitance C in SCC ₂ Is switched Q _a And Q _b Short circuit. Since the output current is constant according to equation (19), the maximum current stress of the SCC switch can be expressed as equation (28):

|I _SCC，max |＝|I _S |. (28)

fig. 12 shows a plot 1200 of loss resistivity and efficiency versus equivalent cell resistance.

In one embodiment, the charging system operates on an input voltage v of the primary circuit _P And input current i _P In a zero phase angle state.

In one embodiment, the input impedance has a small inductance such that the switch Q ₁ -Q ₄ Zero voltage switching is implemented to reduce switching losses. The primary frequency omega can be slightly reduced _P To meet the above requirements without having a significant impact on output power and efficiency. Therefore, the loss R of the primary circuit _P The estimation can be made by the primary coil resistance and the conduction loss of the inverter switches as shown in equation (29):

R _P ＝R _P，w +2R _on，1 ， (29)

wherein R is _on,1 Is the on-resistance of the inverter switches. R is R _P Can be regarded as a constant value.

Two switches Q due to SCC _a And Q _b All soft switches, the switching conduction loss of SCC can be estimated by equation (30):

wherein R is _on,2 And V _f，2 Respectively is a switch Q _a And Q _b And the forward voltage of the body diode. Flow through Q _a And Q _b Current root mean square value I of (2) _SCC,RMS And mean value I _SCC,avg Calculated from equations (31) and (32), respectively:

/>

similarly, the SAR switch Q is ignored ₆ and Q ₈ The small switching loss due to ZVS, the on-loss of SAR can be estimated as equation (33):

wherein R is _on，3 Is a switch Q ₆ And Q ₈ On resistance of V _f，3 Body diode D ₅ -D ₈ Is a positive voltage of (a). i.e _S，RMS And i _S，avg Root mean square value and average value of current injected into SAR respectively, wherein

Combining losses in SCC and SAR, the equivalent resistance R of the secondary circuit losses can be calculated _S Expressed as:

the loss resistivity is shown by curve 1210 in FIG. 12

The ratio is dependent on the internal resistance R of the battery _L And from 1.1 to 1.3. Optimizing the load resistance R according to equation (15) _eq,opt Along with->

While varying, however, a slight deviation from this optimized value has little effect on the charging efficiency. In one embodiment, R _eq,opt Fixed at the values shown in fig. 7 to simplify the calculation. The charge efficiency of the simulation experiment is shown in curve 1220 due to R _S But remains at substantially the maximum value throughout the load range.

The feasibility of the charging system was verified by circuit experiments. Fig. 13 is an experimental parameter table 1300 of a charging circuit according to an exemplary embodiment. According to table 1300, during charging, the equivalent battery internal resistance is simulated by an electronic load, ranging from approximately 18Ω to 50Ω. The input dc power and the output dc power were measured by a Yokogawa PX8000 precision power oscilloscope.

In the experiment, the working frequency of the inverter is fixed at 85kHz, and constant power output and maximum efficiency are realized by adjusting the conduction angle of SAR and the control angle of SCC. Fig. 14 shows a measured plot 1400 of the control angle of SCC from 0.53 pi to 0.83 pi and the conduction angle θ of SAR from 0.95 pi to 0.57 pi.

Fig. 15A shows a graph 1500A of measured values of output current and voltage versus battery resistance. Fig. 15B shows a graph 1500B of measured output power and efficiency versus battery resistance. In fig. 15A, a curve 1501 shows a charging current, which is opposite to the charging voltage change direction shown by a curve 1502. The output power represented by curve 1503 is substantially stabilized at 147 watts and the maximum efficiency is maintained at around 88% as shown by curve 1504. The experimental results shown in fig. 15A and 15B confirm that the wireless charging circuit of the present invention can achieve constant power charging throughout the charging process and maintain the highest efficiency.

In one embodiment, waveforms of the inverter, SCC, and SAR at the start, middle, and end of charging are measured. Experimental results show that the inverter, SCC and SAR all achieve zero voltage switching. The maximum voltage stress of the SCC switch was about 55V, consistent with the analysis of equation (26).

In one embodiment, the wireless charging system employs closed loop control as shown in fig. 10 in the secondary circuit, with the secondary impedance controlled by the microprocessor, to achieve constant power charging and maximum power. Fig. 16 shows the instantaneous waveform 1600 variation of the ladder load resistance. Wherein the load resistance is changed from 20Ω to 40Ω to 20Ω.

In fig. 16, the output voltage and the output current are shown as

curves

1601 and 1602. The SAR conduction angle and SCC control angle are shown as

curves

1603 and 1604. The output power is calculated from the product of the output voltage and the output current, as shown by curve 1605, the output power is strictly controlled by the conduction angle of the SAR, while the control angle of the SCC is controlled by the conduction angle and the battery load coordination. No wireless feedback or wireless transmission is needed in the system control process.

Fig. 17 is a schematic diagram of a wireless charging circuit according to one embodiment. In fig. 17, the wireless charging circuit 1700 includes an SCC 1721 and a SAR 1722.SCC 1721 includes a fixed capacitance C ₂ And two electrically controlled switches Q _a And Q _b ，Q _a And Q _b Is connected in series with the capacitor C ₂ And are connected in parallel. SCC 1721 and fixed capacitor C ₁ After being connected in series, it is connected in parallel with the secondary coil 1724.

The arrangement of SAR 1722 is the same as in fig. 1. However, since the SCC 1721 is set differently from FIG. 1,

instead of using a filter capacitor in parallel with the battery in fig. 1, a filter inductor 1726 is used in the secondary circuit of circuit 1700 in series with battery 1727.

Fig. 18 is a schematic diagram of an equivalent wireless power transfer circuit of fig. 17. As shown in fig. 18, the equivalent circuit 1800 includes an equivalent capacitance 1821 in parallel with an equivalent resistance 1822. By adjusting the conduction angle of SAR and the control angle of SCC, an optimal load resistance is achieved in the secondary circuit, and the inductive reactance of the secondary coil is offset by the capacitive reactance of the equivalent capacitor 1821, so that the secondary circuit has zero reactance, thereby achieving constant power transmission and maximizing transmission efficiency.

In the present description and claims, "connected" is a direct or indirect electrical connection.

Thus, while several embodiments have been described, it will be understood by those skilled in the art that various changes, additional structures, equivalents may be used without departing from the spirit of the invention. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined in the following claims.

Claims

1. A wireless power transfer circuit for powering a variable resistive load with an Alternating Current (AC) power source induced by a primary coil of a primary side of the circuit in a secondary coil of the circuit, the wireless power transfer circuit comprising:

a controllable switched capacitor (SCC) connected to the ac power source, comprising a first capacitor and two electrically controlled switches connected in parallel with the first capacitor, the two electrically controlled switches being connected in series; and

a half-controlled rectifier bridge (SAR) connected to the output of the SCC to rectify the output of the SCC, comprising a bridge circuit including two electrically controlled switches,

the two switches in the SCC are each turned on for half a period and are complementary to each other, and their off-times have a time delay with respect to the zero-crossing point of the AC power source, the time delay being the control angle of the SCC,

two switches in SAR are each turned on for half a period and are complementary to each other, with an off time having a time delay relative to the zero crossing point of the ac power source, said time delay being the conduction angle of SAR,

the wireless power transmission circuit provides a constant power output and improves power transmission efficiency by adjusting a control angle of the SCC and a conduction angle of the SAR to provide a load impedance matched with an impedance of the coil.

2. The wireless power transfer circuit of claim 1 wherein the bridge circuit in the SAR has two upper branches and two lower branches, each upper branch comprising a diode and each lower branch comprising an electronically controlled switch comprising a transistor and a diode antiparallel to the transistor, the drain of each transistor being connected to one upper branch, respectively, and the sources of the two transistors being connected to each other.

3. The wireless power transfer circuit of claim 1, further comprising a filter capacitor connected in parallel with the load when the SCC is connected in series with the secondary coil.

4. The wireless power transfer circuit of claim 1, further comprising a filter inductor connected in series with the load when the SCC is connected in parallel with the secondary coil.

5. The wireless power transfer circuit of claim 1, when the SAR conduction angle θ is adjusted to be

When the power transmission efficiency is highest, wherein R _L Is a load resistance, X _M Is the mutual inductance of the coil, R _S Is equivalent resistance of secondary side loss, R _P R is the equivalent resistance of the primary side loss _eq,opt Optimized value of SAR equivalent resistance for maximizing transmission efficiency, wherein

6. The wireless power transfer circuit of claim 1, further comprising a second capacitor connected in series with the SCC, wherein when the control angle Φ of the SCC is adjusted to

When the power transmission efficiency is highest, wherein X _CS,eq,opt Calculated as X _CS,eq,opt ＝-X _LS ，X _LS X is the self-inductance of the secondary coil _C1 For reactance of the second capacitor, X _C2 For reactance of the first capacitor, X _eq For equivalent load reactance, X _CS,eq,opt An optimized value of equivalent compensation capacitance reactance to maximize transmission efficiency.

7. The wireless power transfer circuit of claim 1, wherein the SCC is equivalent to having a reactance X _CSCC Variable capacitor of X _CSCC Calculated as

Phi is the control angle of SCC, X _C2 Is the capacitive reactance of the first capacitor.

8. The wireless power transfer circuit of claim 1, wherein the primary coil operates at a fixed frequency.

9. A wireless charging system for improving battery charging efficiency by charging a battery from an ac power source induced by a primary coil in a primary side of a circuit at a secondary coil in a secondary side of the circuit, the wireless charging system comprising:

a controllable switched capacitor (SCC) connected to the secondary winding, comprising two electrically controlled switches in series and a first capacitor connected in parallel with the two electrically controlled switches;

a half-controlled rectifier bridge (SAR) connected to an output of the SCC to rectify an output of the SCC, wherein the SAR comprises a bridge circuit comprising two electronically controlled switches;

a plurality of sensors for measuring a charging voltage and a charging current of the battery;

the controller is used for calculating the conduction angle of the SAR and the control angle of the SCC according to the measured value of the sensor and the preset power value; and

at least one signal generator for generating a control signal according to the conduction angle and the control angle and providing the control signal to the electrically controlled switches in the SCC and SAR,

the two switches in the SAR are each turned on for half a period and are complementary to each other, the off-time of which has a time delay with respect to the zero crossing point of the ac power supply, said time delay being the conduction angle of the SAR,

the wireless power transmission circuit provides load impedance matched with coil impedance by adjusting the control angle of SCC and the conduction angle of SAR, so as to charge the battery with constant power and improve charging efficiency.

10. The wireless charging system of claim 9, wherein the bridge circuit in the SAR has two upper branches and two lower branches, each upper branch comprising a diode, each lower branch comprising an electronically controlled switch comprising a transistor and a diode antiparallel to the transistor, the drain of each transistor being connected to one of the upper branches, respectively, and the sources of the two transistors being connected to each other.

11. The wireless charging system of claim 9, wherein each electronically controlled switch of the SCC comprises a transistor, the drains of the two transistors of the SCC being connected, and the sources being connected across the first capacitor, respectively.

12. The wireless charging system of claim 9, further comprising a filter capacitor connected in parallel with the battery when the SCC is connected in series with the secondary coil.

13. The wireless charging system of claim 9, further comprising a filter inductor connected in series with the battery when the SCC is connected in parallel with the secondary coil.

14. The wireless charging system of claim 9, when the SAR conduction angle θ is adjusted to be

/>

15. The wireless charging system of claim 9, further comprising a second capacitor connected in series with the SCC, wherein when the control angle Φ of the SCC is adjusted to

16. The wireless charging system of claim 9, wherein the primary coil operates at one or more fixed frequencies.

17. A wireless charging method for improving battery charging efficiency by a wireless charging system, which charges a battery by an ac power source induced by a primary coil in a primary side of the circuit at a secondary coil in a secondary side of the circuit, wherein the ac power source is connected to a controllable switched capacitor (SCC) and then to a half-controlled rectifier bridge (SAR), an output of the SAR being connected to the rechargeable battery, wherein the SCC comprises a first capacitor and two electrically controlled switches connected in series in parallel with the first capacitor, the SAR comprising a bridge circuit comprising two upper branches and two lower branches, each upper branch comprising a diode, each lower branch comprising an electrically controlled switch, the wireless charging method comprising the steps of:

calculating, by a controller, a conduction angle of SAR to provide a load resistance matched to an impedance of a coil, wherein the conduction angle is a time delay of an off time of a controllable switch of SAR relative to a current zero crossing of the ac power source;

calculating, by a controller, a control angle of the SCC to cancel reactance of the secondary side, wherein the control angle is a time delay of an off time of a controllable switch of the SCC relative to a current zero crossing of the ac power source;

controlling a switch in the SAR according to the conduction angle through a first control signal; and

and controlling a switch in the SCC according to the control angle through a second control signal, so that the wireless charging system charges the battery with constant power, and the charging efficiency is improved.

18. The method of claim 17, wherein: by comparing the charging power with a predetermined reference power P _O A comparison is made to calculate the conduction angle of the SAR,

wherein V is _I For the charging voltage measured by the sensor, omega is the angular frequency of the alternating current power supply, M is the mutual inductance between coils, R _S Is the equivalent resistance of the secondary circuit loss, R _P Equivalent resistance to primary circuit loss, P _O,constant Is a constant charging power.

19. The method of claim 17, further comprising:

measuring a charging voltage and a charging current of the battery by a plurality of sensors; and

and the controller calculates the conduction angle of SAR according to the charging voltage and the charging current.

20. The method of claim 17, further comprising:

generating a first control signal according to the conduction angle of the SAR through a first signal generator; and

the second control signal is generated by a second signal generator according to the control angle of the SCC.