CN110957796A

CN110957796A - Wireless charging circuit and system

Info

Publication number: CN110957796A
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: 2020-04-03
Anticipated expiration: 2039-12-12
Also published as: CN110957796B

Abstract

An exemplary embodiment provides a wireless power transmission circuit that supplies power to a load of a variable resistance using an Alternating Current (AC) power source induced in a secondary coil in a secondary side of the circuit by a primary coil in a primary side of the circuit, the wireless power transmission circuit including: a controllable switched capacitor (SCC) connected to an alternating current 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 an SCC and a conduction angle of an SAR to provide a load impedance matched with an impedance of a coil.

Description

Wireless charging circuit and system

Technical Field

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

Background

Wireless Inductive Power Transfer (IPT) is a constantly developing technology, generally used for applications where it is inconvenient or impossible to physically connect the power supply, with the advantages of simplifying the charging operation and eliminating safety issues associated with the connection of electrical components. The technology is suitable for being applied to many different scenes, such as consumer electronics equipment, implanted human body equipment, industrial electronic equipment and the like.

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

Disclosure of Invention

An exemplary embodiment provides a wireless power transmission circuit that supplies power to a load of a variable resistance using an Alternating Current (AC) power source induced in a secondary coil in a secondary side of the circuit by a primary coil in a primary side of the circuit, the wireless power transmission circuit including: a controllable switched capacitor (SCC) connected to an alternating current 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 comprises a bridge circuit comprising two electrically controlled switches. Two switches in the SCC are each on for half a cycle and are complementary to each other, with their off-times having a time delay relative to the zero crossing of the ac power source, which is the control angle of the SCC. The two switches in the SAR are each on for half a cycle and complementary to each other, with their off times having a time delay relative to the zero crossing of the ac power source, which is the conduction angle of the SAR. The wireless power transmission circuit provides a constant power output and improves power transmission efficiency by adjusting a control angle of an SCC and a conduction angle of an SAR to provide a load impedance matched with an impedance of a coil.

Exemplary embodiments also provide a wireless charging system for improving battery charging efficiency, which charges a battery by an alternating current power induced at a secondary coil in a secondary side of a circuit by a primary coil in the primary side of the circuit, the wireless charging system including: a controllable switched capacitor (SCC) connected to the secondary winding, a semi-controlled rectifier bridge (SAR), a sensor, a controller, and a signal generator. The SCC includes 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, wherein the bridge circuit comprises two electrically controlled switches; a plurality of sensors for measuring a charging voltage and a charging current of the battery; a controller for calculating a conduction angle of the SAR and a control angle of the SCC according to a measurement value of the sensor and a predetermined power value; at least one signal generator for generating a control signal based on the conduction angle and the control angle and providing the control signal to the electrically controlled switches in the SCC and SAR. Wherein two switches in the SCC are each on for half a cycle and complementary to each other, with their off-times having a time delay relative to a zero crossing of the AC power source, the time delay being a control angle of the SCC; the two switches in the SAR are each on for half a cycle and complementary to each other, with their off times having a time delay relative to the zero crossing of the ac power source, which is the conduction angle of the SAR. The wireless power transmission circuit provides load impedance matched with coil impedance by adjusting a control angle of an SCC and a conduction angle of an SAR, so that a battery is charged at constant power, and charging efficiency is improved.

Exemplary embodiments also provide a wireless charging method for improving battery charging efficiency implemented by a wireless charging system, which charges a battery by an ac power source induced at a secondary coil in a secondary side of a circuit by a primary coil in the primary 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), and an output terminal of the SAR is connected to the charged battery. Wherein the SCC comprises a first capacitor and two electrically controlled switches connected in series in parallel with the first capacitor, 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 the 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 the SAR relative to a current zero crossing of the AC power source; calculating, by a controller, a control angle of an SCC to cancel a reactance of a 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 by a second control signal. The wireless charging method can charge the battery with constant power, thereby improving charging efficiency.

Drawings

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

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

Fig. 3 illustrates a switching sequence and operating waveforms for a controllable switched capacitor (SCC) according to an example embodiment.

FIG. 4 is a graph of equivalent impedance versus controllable angle for an SCC in accordance with an exemplary embodiment.

Fig. 5 is an equivalent wireless power transmission circuit diagram according to an example 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 in accordance with an example embodiment.

FIG. 7 is a table of simulation circuit parameters according to an example embodiment.

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

Fig. 11 is a SCC voltage stress diagram in accordance with an example embodiment.

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

Fig. 13 is a table of parameters for a charging circuit according to an example embodiment.

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

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

FIG. 15B is a graph of measurement results of power and efficiency versus battery resistance, according to an example embodiment.

FIG. 16 is a graph of transient waveforms of circuit output parameters, according to one embodiment.

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

Fig. 18 is a schematic diagram of an equivalent wireless power transfer circuit 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 impedance by employing a controllable switched capacitor (SCC) and a half-controlled rectifier bridge (SAR) at the receiving side and operating the SCC and SAR to simulate the optimal impedance and secondary load of the resonator, 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 when charging is completed, and the charging duration time under the high-power level is short, so that the power capacity utilization rate of the charger adopting the constant-current charging strategy is low.

To improve the utilization of the charging power capacity, the charger may control the output power to a predetermined maximum value, thereby providing Constant Power (CP) charging. For contact chargers, constant power charging is relatively easy in a battery management system, but inductive power transfer chargers are required to operate at certain specific operating frequencies and have load-independent transfer characteristics, thereby reducing control complexity and increasing peak efficiency. In addition, the IPT converter needs to have load matching capability, and in case of load mismatch, the transmission efficiency may be significantly reduced. The existing single-stage IPT converter is difficult to realize constant-power charging and keeps the maximum charging efficiency in the whole charging process.

One method of achieving constant power charging is through an IPT system with cascaded multi-level converters. For example, a transmit side pre-converter is used for modulating the input amplitude, or a receive side post-converter is cascaded to the IPT converter for power regulation. However, as additional converter stages are added, power consumption and control complexity are increased. In addition, a wireless signal feedback device between the transmitting side and the receiving side needs to be added.

To overcome the above-mentioned technical problems, exemplary embodiments provide a wireless charging circuit including a single-stage IPT converter that maintains a constant output power rather than providing a constant output current during a dominant phase of battery charging, and thus can leverage its power capabilities to achieve faster charging rates. The wireless charging circuit adopts series compensation, a controllable switch capacitor (SCC) and a semi-controlled rectifier bridge (SAR) are adopted on a receiving side, the optimal impedance and the secondary load of a resonator are simulated by controlling the controllable angle of the SCC and the conduction angle of the SAR, and the advantages of load-independent transmission characteristic and matched load impedance are combined, so that constant power output can be realized in the whole charger process and the maximum transmission efficiency can be maintained.

The exemplary embodiments can achieve at least the following technical effects:

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

(2) The use of SCC and SAR to model the optimal impedance of the resonator and secondary load achieves the advantages of load independent behavior and matching load impedance to maintain maximum transfer efficiency throughout the charging process.

(3) The fixed frequency work is realized, the control is simple, the control is realized only on the receiving side, and the wireless signal feedback between the transmitting side and the receiving side is not needed.

(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 further described in the following with reference to the accompanying drawings and the detailed descriptionThe steps are described in detail. In the following description, X_subscriptFor expressing the impedance of the component shown in its subscript (script).

Fig. 1 is a schematic diagram of a wireless charging circuit according to an exemplary embodiment. In fig. 1, the wireless charging circuit 100 includes a primary circuit 110 and a secondary circuit 120. The primary circuit 110 is a transmit side circuit and the secondary circuit 120 is a receive side circuit. The primary circuit 110 comprises a series connection of a dc source 111 with four switches Q₁-Q₄ Full bridge inverter 112, primary compensation capacitor 113, and primary coil 114. Wherein the voltage value of the direct current source 111 is V_IThe primary compensation capacitor 113 has a fixed capacitance value C_P. The secondary circuit includes a secondary coil 124, a secondary compensation capacitance 123, an SCC121, and a SAR122 connected in series. Wherein the secondary compensation capacitor 123 has a fixed capacitance value C₁. Output end filter capacitor C_fConnected in parallel with the SCC121, SAR122, and charging battery 127.

In fig. 1, the SCC121 includes a capacitor 1211 and two electrically controlled switches 1212 connected in parallel, where the capacitor 1211 has a fixed capacitance value C₂The electronically controlled switch 1212 includes two Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), respectively designated as Q, connected in series_aAnd Q_b. Wherein Q_aAnd Q_bThe source is connected to two ends of the capacitor 1211, and the gate receives the control signal. Q_aAnd Q_bEach antiparallel-connected to a diode, denoted by D_aAnd D_b. The voltage value across the SCC is denoted v_SCCThe value of the current flowing through the switch 1212 is represented as i_SCCSCC equivalent capacitance value is represented as C_SCC. In the secondary circuit 120, a series secondary compensation capacitance 123 is used to reduce the voltage stress of the switches in the SCC.

SAR122 includes two diodes 1221 in the upper branch, labeled D respectively₅And D₇And two electrically controlled switches 1222 in the lower branch. Each electronically controlled switch 1222 includes a MOSFET, respectively designated Q₆And Q₈Wherein Q is₆And Q₈The drains are connected to the two upper branches, respectively, and the sources are connected to each other. Each MOSFET Q₆And Q₈Comprising an anti-parallel diode, respectively denoted by D₆And D₈。

The primary coil 114 and the secondary coil 124 form a magnetic coupler 130 having a mutual inductance value M, for example, the magnetic coupler 130 is a loosely coupled transformer. The coupling coefficient is defined as

The primary coil 114 has a primary self-inductance and a resistance R_P,wWherein the resistance R_P,wIs the primary coil loss. The secondary coil 124 has a secondary self-inductance L_SAnd a resistance R_S,wWherein the resistance R_P,wIs the secondary winding loss.

In the wireless charging circuit 100, the dc source 111 supplies the dc voltage V via the inverter 112_IConverted to a voltage v_pAlternating current of angular frequency ω for driving the primary coil 114 to induce an alternating current i in the secondary coil 124_SFurther, an AC voltage v is formed at the SCC output terminal_S. The induced voltage and the induced current are input into the SAR122 for rectification, filtered by the capacitor 126 and output as a direct current voltage V_OAnd a direct current I_OI.e., the charging voltage and charging current of the battery 127.

In one embodiment, switch Q in SAR122₆And Q₈It is switched on when its anti-parallel diode is conducting, thus realizing Zero Voltage Switching (ZVS). Switch Q₆And Q₈Half current cycles are turned on respectively and the turn-on times are complementary. Thus, Q₆And Q₈Off time and current i_SHas a time delay of pi-theta epsilon [0, pi ] between zero-crossing points]θ is defined as the conduction angle of the SAR. The conduction angle θ has a maximum value of π and a minimum value of 0. Influence v of variation of conduction angle theta_SAnd i_SThe phase angle therebetween.

In one embodiment, switch Q in SCC_aAnd Q_bAnd current i_SIn synchronism with the current i_SHas a controllable angle between zero crossings

Switch Q_aAnd Q_bHalf current cycles are turned on respectively and the turn-on times are complementary. For example, Q_aAnd Q_bAt v_SCCAnd switching at zero voltage, thereby realizing soft switching to reduce switching loss. In half current period, the capacitor C₂Has a charging time (or discharging time) of

Which follow

Increase and decrease of v_SCCThe root mean square value of (d) is reduced. Thus, the equivalent capacitance of SCC, namely C_SCCCan be controlled by changing the controllable angle

To make the adjustment.

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 a constant power, thereby improving charging efficiency.

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

Fig. 2 is a switching sequence and operating waveform 200 for a half-controlled rectifier bridge (SAR) according to an exemplary embodiment. In fig. 2, an electrically controlled switch Q of SAR122₆And Q₈And when the anti-parallel diode is conducted, the switch is switched on to realize zero-voltage switching. Q₆And Q₈Both turn on for half a current period and the turn on times are complementary. Thus, Q₆And Q₈And i_sHas pi-theta epsilon [0, pi ] between zero-crossing points]θ is the conduction angle of SAR 122. v. of_s,1Is v_sOf a basic component which lags behind i_sThe phase angle is given by γ ═ π - θ/2. Therefore, the temperature of the molten metal is controlled,

the equivalent load of the charging circuit being the impedance Z_eqRather than a pure resistor.

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

The equivalent fundamental impedance of the SAR122 is:

Z_eq＝R_eq+jX_eq， (1)

wherein R is_eqIs an equivalent resistance, X_eqIn order to be an equivalent reactance,

FIG. 3 is a switching sequence and operating waveform 300 for an SCC according to an exemplary embodiment. In FIG. 3, the switch Q is controlled electrically_aAnd Q_bDrive signal of and i_sIs synchronized with i_sHave a controllable angle between zero crossings

Q_aAnd Q_bEach on half a cycle and the on times are complementary. Due to Q_aAnd Q_bAt v_SCCSwitching on and off at zero voltage, thereby enabling soft switching to minimize switching losses.

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

wherein

FIG. 4 is a graph 400 of equivalent impedance versus controllable angle for an SCC in accordance with an exemplary 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 in use

When changing from 0.5 pi to pi, X_CsccCan be derived from the nominal reactance X_C2Modulated to zero.

Fig. 5 is an equivalent charging circuit diagram 500 in accordance with an example embodiment.

Fig. 5 is an equivalent circuit diagram of the circuit shown in fig. 1. The primary circuit includes a power supply 511, a resistor 512, a primary compensation capacitor 513, an inductor 514, and a primary side induced electromotive force 515, which are connected in series. The resistor 512 has an equivalent resistance R_pWhich represents losses in the primary coil 114 and the inverter 112. The capacitance value of the primary compensation capacitor 513 is denoted C_p，

The secondary circuit includes an equivalent induced ac current source 525, an inductor 524, a secondary compensation capacitor 523, a variable capacitor 521, and a load 522 connected in series with each other. The capacitance value of the variable capacitor 521 is represented as C_sccI.e., the equivalent capacitance of SCC 121. The load 522 is composed of an equivalent impedance Z_eqIs represented by including a series-connected resistor R_eqAnd reactance X_eqAs shown in formula (1). Resistance R_SRepresenting the sum of the losses of the secondary coil 124, SCC121 and SAR 122.

For example, V_p，I_p，V_sAnd I_sRespectively for representing variable v_p，i_p，v_sAnd i_sPhasor representation of the fundamental component of (a). C₁，C_SccAnd X_eqProviding a capacitive reactance in the secondary circuit, which may be of equivalent secondary

Compensation capacitor C_S,eqExpressed as 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_MI_S＝V_P(7)

-(R_S+R_eq+jX_LS+jX_Cs,eq)I_s-jX_MI_P＝0 (8)

wherein X_MFor mutual inductance of primary and secondary coils, X_LPIs the inductive reactance of the primary circuit, X_CPIs the capacitive reactance of the primary circuit,

X_Ls＝ωLs

V_p、V_sand I_sAre given by equations (9), (10) and (11), respectively:

the equivalent circuit efficiency of fig. 5 is shown by equation (12):

suppose that

And

at a selected operating frequency omegaWhen (13) and (14) are satisfied, the transmission efficiency is maximized, and the expression thereof is as shown in formula (15), wherein X is_CS,eq,optAnd R_eq,optX respectively for maximizing transmission efficiency_CS,eqAnd R_eqThe optimum value of (c).

X_Ls+X_{Cs，eq，opt}＝0 (13)

Due to the internal resistance R of the battery during charging_LThe variation range is large, and according to equation (14), the internal resistance needs to be converted into a matching resistance R via SAR_eq,optTo achieve maximum transmission efficiency. Therefore, according to equations (2) and (14), the conduction angle θ of the SAR can be expressed as equation (16):

according to the formula (3), the change in the conduction angle θ also affects the load reactance X_eqRepresented 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 variation of the conduction angle theta with load resistance. In FIG. 6A, curve 601 represents SAR conduction angle θ as a function of R_LIs changed 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_eqCan be maintained at the optimal load resistance value R_eq,opt. However, the curve 602 shows that the reactance X decreases as the conduction angle θ decreases_eqIncreases in amplitude.

The condition in the formula (14) is ensured to achieve the maximum charging efficiency, C_s,eqNeeds to be adequately compensated to L at a fixed frequency_sAccordingly, the exemplary embodiments change the controllable angle of the SCC by changing

By the size of (2), thereby varying the reactance X_CsccFinally, the target reactance X is obtained_{CS，eq，opt}＝-X_LS. Controllable angle of combination of formulas (5), (6) and (17), SCC

The expression is as follows:

satisfying the above analysis steps in the control process enables the system to operate at maximum transmission efficiency.

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

Conduction angle theta and equivalent secondary side compensation inductive reactance X_CS,eqThe relationship diagram 600B between. In FIG. 6B, curve 604 shows the controllable angle in the simulation experiment

In conjunction with the conduction angle theta. As can be seen from curve 605, the joint control results in an equivalent secondary compensation inductive reactance X_CS,eqIs maintained almost constant at an optimum value X_CS,eq,optThereby enabling maximum efficiency to be achieved.

As described above, the wireless charging current of the exemplary embodiment can achieve the highest charging efficiency by matching the optimized load resistance and maintaining zero reactance in the secondary circuit. When the reactance is zero, the inductive energy transmission system can realize the 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.

Figure 8 shows an IPT circuit 800 that achieves both constant power output and maximum efficiency. In the circuit 800, the primary circuit 801 and the 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,optIs substantially constant. Theoretically, when the input voltage of the primary circuit is v, the losses in the electrical components are ignored_pThe load-independent output current amplitude of the secondary circuit can be expressed as:

thus, the exemplary embodiments ensure constant work for a fixed input voltage throughout the charging process

The rate is output and maintained at the highest efficiency, and the expression is as follows:

where the subscript RMS represents the root mean square value.

Combined formulas (9) - (11), (19) and (20), constant charging power and output direct current

Voltage and DC current may be expressed as equations (21), (22) and (23), respectively:

assuming equivalent load reactance X_eqThe reactance X of SCC can be controlled appropriately_CSCCAnd is counteracted, the output power P is_OCan be only equal toEffective load resistance R_eqIn relation, the output power is denoted as P_O≈|I_S|² _RMSR_eq。

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

Fig. 9 shows a graph 900 of output power, efficiency, and SAR conduction angle in an exemplary embodiment. In FIG. 9, the output power P_OThe relationship with conduction angle theta is represented by

curves

910, 920 and 930, and the relationship with conduction angle theta for efficiency η is represented by

curves

940, 950 and 960, each set of curves corresponding to cell resistance value R, respectively_L30 Ω, 40 Ω, and 50 Ω. When P is present_OAt a constant value in equation (20), the charging circuit efficiency is highest, as indicated by the

intersections

901, 902, 903. Therefore, P can be controlled by the controller_O,constantAs a reference value P_O,refTo achieve constant power output and 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 an SCC and a SAR that can be adjusted by a control signal. For example, the wireless charging circuit 1010 is the wireless charging circuit shown in fig. 1.

In one embodiment, the charging voltage Vo and the charging current Io are measured by the sensor 1020, and the measured values are input to a multiplier and divider of the controller 1030 for calculating the charging power and the load resistance value, respectively. The controller further calculates the conduction angle of the SAR according to the difference value 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 the SCC is calculated according to equation (18). Thereafter, the signal generating unit 1040 passes the signal generator 1 and the signal generator 2, respectively, based on the calculated conduction angle and control angleControl signals for the SCC and SAR are generated. The signal generation unit 1040 further comprises a zero crossing detector for detecting the coil current i in the secondary circuit_SAnd generating a synchronization signal for the signal generator.

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

In one embodiment, controller 1030 comprises 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,refIs determined as the constant power value in equation (21).

In one embodiment, the control angle of the SCC is calculated from a relationship between the control angle of the SCC and the 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 for realizing 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, the circuit design is simplified, and the energy loss of the secondary circuit is reduced.

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

According to formula (14), C₁The reactance of the secondary circuit needs to be fully compensated, i.e.:

the voltage stress of the SCC switch is determined by the maximum voltage across the SCC, i.e.:

|V_SCC，max|＝|X_C2||I_S|. (26)

When the control angle of SCC is maximum

The current stress of SCC is the largest. Because at this time, the capacitance C in SCC₂Is switched on and off Q_aAnd Q_bAnd (4) short-circuiting. 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|＝|Is|. (28)

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

In one embodiment, the charging system operates on the input voltage v of the primary circuit_PAnd an input current i_PIn a state of zero phase angle.

In one embodiment, the input impedance has a small inductance, such that the switch Q₁–Q₄Zero voltage switching is implemented to reduce switching losses. Can slightly lower the primaryFrequency omega_PTo meet the above requirements without having a significant impact on output power and efficiency. Therefore, the loss R of the primary circuit_PCan pass through the primary line

The turn resistance and the conduction loss of the inverter switch are estimated as shown in equation (29):

R_P＝R_P，w+2R_on，1， (29)

wherein R is_on,1Is the on-resistance of the inverter switch. R_PCan be regarded as a constant value.

Two switches Q due to SCC_aAnd Q_bAll soft switching, the switching turn-on loss of the SCC can be estimated by equation (30):

wherein R is_on,2And V_f,2Are respectively a switch Q_aAnd Q_bThe on resistance of the body diode and the body diode forward voltage. Flows through Q_aAnd Q_bCurrent root mean square value of_SCC,RMSSum mean I_SCC,avgCalculated by equations (31) and (32), respectively:

similarly, omitting the SAR switch Q₆and Q₈The conduction loss of SAR, a small amount of switching loss due to ZVS, can be estimated as equation (33):

wherein R is_on,3Is a switch Q₆And Q₈On resistance of V_f,3Is a body diode D₅-D₈The forward voltage of (2). i.e. i_S,RMSAnd i_S,avgRespectively currents injected into SARRoot mean square value and mean value, wherein

The equivalent resistance R of the secondary circuit loss can be combined with the loss in SCC and SAR_SExpressed as:

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

The ratio is a function of the internal resistance R of the cell_LFrom 1.1 to 1.3. According to the formula (15), the load resistance R is optimized_eq,optFollowed by

But slightly off the optimum value does not greatly affect the charging efficiency. In one embodiment, R_eq,optFixed at the values shown in fig. 7 to simplify the calculation. The charge efficiency of the simulation experiment is shown as curve 1220, which is due to R_SBut is slightly decreased but remains at a substantially maximum value throughout the load range.

The feasibility of the charging system was verified by circuit experiments. Fig. 13 is a table 1300 of experimental parameters for a charging circuit, according to an example embodiment. According to table 1300, the equivalent battery internal resistance is simulated by the electronic load during charging, and the range of variation is approximately 18 Ω to 50 Ω. 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 the SAR and the control angle of the SCC. FIG. 14 shows a measured working point diagram 1400 where the control angle of SCC varies from 0.53 π to 0.83 π and the conduction angle of SAR varies from 0.95 π to 0.57 π.

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 values of output power and efficiency versus battery resistance. In fig. 15A, a curve 1501 shows a charging current, which is opposite to the charging voltage variation shown by a curve 1502. The output power represented by curve 1503 substantially stabilizes at 147 watts, and the maximum efficiency remains around 88% as represented 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 zero voltage switching is achieved for the inverter, SCC and SAR. The maximum voltage stress of the SCC switch is about 55V, which is consistent with the analysis of equation (26).

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

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

curves

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

curves

1603 and 1604. The output power is calculated by the product of the output voltage and the output current, as shown by curve 1605, the output power is tightly controlled by the conduction angle of the SAR, while the control angle of the SCC is coordinately controlled by the conduction angle and the battery load. Wireless feedback or wireless transmission is not needed in the system control process.

Fig. 17 is a schematic diagram of a wireless charging circuit according to an embodiment. In fig. 17, the wireless charging circuit 1700 includes an SCC 1721 and a SAR 1722. SCC 1721 includes a fixed capacitor C₂And two electrically controlled switches Q_aAnd Q_b，Q_aAnd Q_bConnected in series with a capacitor C₂And (4) connecting in parallel. SCC 1721 and fixed capacitor C₁After being connected in series, the secondary coil 1724 is connected in parallel.

The arrangement of SAR 1722 is the same as in fig. 1. However, since the SCC 1721 is arranged differently from that of fig. 1, the secondary circuit of the circuit 1700 employs a filter inductor 1726 in series with the battery 1727 instead of the filter capacitor in parallel with the battery in fig. 1.

Fig. 18 is a schematic diagram of an equivalent wireless power transmission circuit of fig. 17. As shown in fig. 18, equivalent circuit 1800 includes an equivalent capacitor 1821 in parallel with an equivalent resistor 1822. By adjusting the conduction angle of the SAR and the control angle of the SCC, the optimized load resistance is realized in the secondary circuit, and the inductive reactance of the secondary coil is counteracted through the capacitive reactance of the equivalent capacitor 1821, so that the secondary circuit has zero reactance, thereby realizing constant power transmission and maximizing transmission efficiency.

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

Thus, having described several embodiments, it will be recognized by those of skill in the art that various modifications, additional structures, and 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 by the following claims.

Claims

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

a controllable switched capacitor (SCC) connected to an alternating current 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 an output of the SCC for rectifying an output of the SCC, including a bridge circuit including two electrically controlled switches,

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

the two switches in the SAR are each conducting for half a period and complementary to each other, and the off-time thereof has a time delay relative to the zero-crossing point of the alternating current power source, the time delay being the conduction angle of the SAR,

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

2. The wireless power transmission 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, each lower branch comprising an electrically controlled switch comprising a transistor and a diode connected in anti-parallel with the transistor, the drain of each transistor being connected to one upper branch, 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 transmission circuit according to claim 1, when a conduction angle θ of the SAR is adjusted to be

When the power transmission efficiency is the highest, R is_LIs a load resistance, X_MIs the mutual inductance of the coil, R_SEquivalent resistance for secondary side losses, R_PIs the equivalent resistance of the primary side loss.

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 of the SCC is adjusted to

In which X is_CS,eq,optIs calculated as X_CS,eq,opt＝-X_LS，X_LSFor self-inductance of the secondary coil, X_C1Is the reactance of a second capacitor, X_C2Is the reactance of the first capacitor, X_eqIs the equivalent load reactance.

7. The wireless power transmission circuit of claim 1, wherein the SCC is equivalent to having a reactance X_CCSSVariable capacitor of, X_CCSSIs calculated as

Phi is the control angle of SCC, X_C2Is 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 with an alternating current power induced at a secondary coil in a secondary side of a circuit by a primary coil in the primary 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 semi-controlled rectifier bridge (SAR) connected to an output of the SCC to rectify an output of the SCC, wherein the SAR includes a bridge circuit including two electrically controlled switches;

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

a controller for calculating a conduction angle of the SAR and a control angle of the SCC according to a measurement value of the sensor and a predetermined power value; and

at least one signal generator for generating a control signal based on 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 conducting for half a period and complementary to each other, and the off-time thereof has a time delay relative to the zero-crossing point of the AC power source, the time delay being the conduction angle of the SAR,

the wireless power transmission circuit provides load impedance matched with coil impedance by adjusting a control angle of an SCC and a conduction angle of an SAR, so that a battery is charged at constant power, and charging efficiency is improved.

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 electrically controlled switch comprising a transistor and a diode connected in anti-parallel with the transistor, the drain of each transistor being connected to one upper branch, 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 two transistors of the SCC being connected and the sources being connected to two ends of 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 conduction angle θ of the SAR is adjusted to

15. The wireless charging system of claim 9, further comprising a second capacitor connected in series with the SCC, wherein when the control angle 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 induced at a secondary coil in a secondary side of a circuit by a primary coil in a primary side of the circuit, wherein the ac power is connected to a controllable switched capacitor (SCC) and then to a semi-controlled rectifier bridge (SAR), an output of the SAR being connected to the charged battery, wherein the SCC includes a first capacitor and two electrically controlled switches connected in series in parallel with the first capacitor, the SAR includes a bridge circuit including two upper legs and two lower legs, each upper leg including a diode, and each lower leg including an electrically controlled switch, the wireless charging method comprising the steps of:

calculating, by a controller, a conduction angle of the 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 the SAR relative to a current zero crossing of the AC power source;

calculating, by a controller, a control angle of an SCC to cancel a reactance of a 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 a battery with constant power, thereby improving the charging efficiency.

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

wherein V_IThe charging voltage measured for the sensor, ω is the angular frequency of the AC source, M is the mutual inductance between the coils, R_SEquivalent resistance, R, for secondary circuit losses_PIs the equivalent resistance of the primary circuit losses.

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 the 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

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