CN110957796B - Wireless charging circuit and system - Google Patents

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 circuits and systems

Technical Field

The invention relates to a wireless charging circuit and system.

Background Art

Wireless inductive power transfer (IPT) is a growing technology that is generally used in applications where physical connection for power supply is inconvenient or impossible. It has the advantages of simplifying charging operations and eliminating safety issues associated with connecting electrical components. This technology is suitable for many different scenarios, such as consumer electronic devices, implantable human devices, and industrial electronic devices.

A new device and system are needed to improve the charging efficiency of IPT to meet market demand.

Summary of the invention

An exemplary embodiment provides a wireless power transmission circuit, which uses an alternating current (AC) power induced by a primary coil on the primary side of the circuit in a secondary coil on the secondary side of the circuit to supply power to a load of a variable resistor, and the wireless power transmission circuit includes: a controllable switched capacitor (SCC) connected to the AC power supply and a half-controlled rectifier bridge (SAR) connected to the output terminal of the SCC to rectify the output of the SCC. The SCC includes a first capacitor and two electrically controlled switches connected in parallel with the first capacitor, and the two electrically controlled switches are connected in series. The SAR includes a bridge circuit, which includes two electrically controlled switches. The two switches in the SCC are each turned on for half a cycle and are complementary to each other, and their off time has a time delay relative to the zero crossing point of the AC power supply, and the time delay is the control angle of the SCC. The two switches in the SAR are each turned on for half a cycle and are complementary to each other, and their off time has a time delay relative to the zero crossing point of the AC power supply, and the time delay is the conduction angle of the SAR. The wireless power transmission circuit provides a load impedance that matches the impedance of the coil by adjusting the control angle of the SCC and the conduction angle of the SAR, thereby providing a constant power output and improving the power transmission efficiency.

An exemplary embodiment also provides a wireless charging system for improving battery charging efficiency, which charges the battery through an AC power induced by a primary coil in the primary side of the circuit at a secondary coil in the secondary side of the circuit, and the wireless charging system includes: a controllable switched capacitor (SCC) connected to the secondary coil, a half-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 includes a bridge circuit, which includes two electrically controlled switches; a plurality of sensors for measuring the charging voltage and charging current of the battery; a controller for calculating the conduction angle of the SAR and the control angle of the SCC according to the measured values of the sensors and the predetermined 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 the SAR. The two switches in the SCC are each turned on for half a cycle and complement each other, and their disconnection time has a time delay relative to the zero crossing point of the AC power source, and the time delay is the control angle of the SCC; the two switches in the SAR are each turned on for half a cycle and complement each other, and their disconnection time has a time delay relative to the zero crossing point of the AC power source, and the time delay is the conduction angle of the SAR. The wireless power transmission circuit provides a load impedance that matches the coil impedance by adjusting the control angle of the SCC and the conduction angle of the SAR, thereby charging the battery at a constant power and improving the charging efficiency.

The exemplary embodiment also provides a wireless charging method for improving battery charging efficiency by a wireless charging system, wherein the battery is charged by an AC power source induced by a primary coil in the primary side of the circuit at a secondary coil in the 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), and the output end of the SAR is connected to a charging battery. The SCC includes a first capacitor and two series-connected electrically controlled switches connected in parallel with the first capacitor, and the SAR includes a bridge circuit, the bridge circuit includes two upper branches and two lower branches, each upper branch includes a diode, and each lower branch includes an electrically controlled switch. The wireless charging method comprises the following steps: the controller calculates the conduction angle of the SAR to provide a load resistance matching the impedance of the coil, wherein the conduction angle is the time delay of the disconnection time of the controllable switch of the SAR relative to the current zero crossing point of the AC power source; the controller calculates the control angle of the SCC to offset the reactance of the secondary side, wherein the control angle is the time delay of the disconnection time of the controllable switch of the SCC relative to the current zero crossing point of the AC power source; controls the switch in the SAR according to the conduction angle through a first control signal; and controls the switch in the SCC according to the control angle through a second control signal. The wireless charging method can charge the battery at a constant power, thereby improving the charging efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

FIG. 4 is a graph showing the relationship between the equivalent impedance and the controllable angle of an SCC according to an exemplary embodiment.

FIG. 5 is a diagram of an equivalent wireless power transmission circuit according to an exemplary embodiment.

FIG. 6A is a graph showing the relationship between a SAR conduction angle and an equivalent load impedance and a load resistance according to an exemplary embodiment.

6B is a graph showing the relationship between the SCC controllable angle and the impedance of the equivalent secondary-side capacitance and the SAR conduction angle according to an exemplary embodiment.

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

FIG. 8 is a diagram of an equivalent wireless charging circuit for constant power (CP) output and maximum efficiency according to an exemplary embodiment.

9 is a graph of output power and efficiency versus SAR conduction angle according to an exemplary embodiment.

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

FIG. 11 is a graph of SCC voltage stress according to an exemplary embodiment.

FIG. 12 is a graph showing the relationship between the loss resistance ratio and the charging efficiency and the internal resistance of the battery according to an exemplary embodiment.

FIG. 13 is a table of charging circuit parameters according to an exemplary embodiment.

FIG. 14 is a graph showing the relationship between the operating point and the battery resistance measurement results according to an exemplary embodiment.

15A is a graph showing the measured output current and voltage versus battery resistance of a system according to an exemplary embodiment.

15B is a graph showing measurement results of power and efficiency versus battery resistance according to an exemplary embodiment.

FIG. 16 is a transient waveform diagram of a circuit output parameter according to an 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 transmission circuit according to one embodiment.

DETAILED DESCRIPTION

An exemplary embodiment includes a wireless charging circuit that combines the advantages of load-independent transmission characteristics and matched load impedance by adopting a controllable switched capacitor (SCC) and a half-controlled rectifier (SAR) on 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 transmission 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 the smallest at the beginning of charging, and the charging power increases to the maximum value until the charging is completed. The charging time at a high power level is short, so the power capacity utilization rate of the charger using the constant current charging strategy is low.

In order to improve the utilization of the charging power capacity, the charger can control the output power to a predetermined maximum value, thereby providing constant power (CP) charging. For contact chargers, it is relatively easy to perform constant power charging in the battery management system. However, the inductive power transfer charger is required to operate at certain specific operating frequencies and needs to have load-independent transmission characteristics, thereby reducing control complexity and increasing maximum efficiency. In addition, the IPT converter needs to have load matching capabilities. In the case of load mismatch, the transmission efficiency may be significantly reduced. The existing single-stage IPT converters are difficult to achieve constant power charging and maintain maximum charging efficiency throughout the charging process.

One method to achieve constant power charging is through an IPT system with a multi-level converter cascade. For example,

The transmitter-side pre-stage converter is used to modulate the input amplitude, or the receiver-side post-stage converter is cascaded to the IPT converter for power regulation. However, due to the addition of additional converter stages, the power loss and control complexity will also increase accordingly. In addition, a wireless signal feedback device between the transmitter and receiver is also required.

In order to overcome the above-mentioned technical problems, an exemplary embodiment provides a wireless charging circuit, which includes a single-stage IPT converter, and the wireless charging circuit maintains a constant output power in the dominant stage of battery charging instead of providing a constant output current, so that its power capacity can be fully utilized to achieve a faster charging rate. The wireless charging circuit adopts series compensation, and adopts a controllable switched capacitor (SCC) and a half-controlled rectifier bridge (SAR) on the receiving side. By controlling the controllable angle of the SCC and the conduction angle of the SAR to simulate the optimal impedance and secondary load of the resonator, it combines the advantages of load-independent transmission characteristics and matching load impedance, so that constant power output can be achieved throughout the charger process and maximum transmission efficiency can be maintained.

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

(1) The charging circuit works under constant power conditions, which can give full play to its power usage and thus have a faster and safer charging rate.

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

(3) Fixed-frequency operation is achieved, and control is simple to implement. Control only needs to be implemented on the receiving side, without the need for wireless signal feedback between the transmitting side and the receiving side.

(4) A single-stage converter structure is adopted, and all switch tubes realize soft switching, thereby reducing losses.

The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. In the following description, X _subscript is used to express the impedance of the component indicated by its subscript.

FIG1 is a schematic diagram of a wireless charging circuit structure according to an exemplary embodiment. In FIG1 , the 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 DC source 111 connected in series, a full-bridge inverter 112 having four switches Q ₁ -Q ₄ , a primary compensation capacitor 113, and a primary coil 114. The DC source 111 has a voltage value of V _I , and 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, a SCC 121 and a SAR 122 connected in series. The secondary compensation capacitor 123 has a fixed capacitance C ₁ . The output filter capacitor C _f is connected in parallel with the SCC 121, the SAR 122 and the rechargeable battery 127 .

In FIG1 , the SCC 121 includes a capacitor 1211 and two electronically controlled switches 1212 connected in parallel. The capacitor 1211 has a fixed capacitance value C ₂ . The electronically controlled switch 1212 includes two metal oxide semiconductor field effect transistors (MOSFETs) connected in series, which are marked as Q _a and Q _b , respectively. The drains of Q _a and Q _b are connected, the sources are connected to the two ends of the capacitor 1211 , respectively, and the gates receive control signals. _{Q a} and Q _b are connected in anti-parallel with a diode, marked as _Da and D _{b ,} respectively. The voltage value across the SCC is represented as v _SCC , the current value flowing through the switch 1212 is represented as i _SCC , and the equivalent capacitance value of the SCC is represented as C _SCC . In the secondary circuit 120 , the series secondary compensation capacitor 123 is used to reduce the voltage stress of the switch in the SCC.

SAR122 includes two diodes 1221 in the upper branch, marked as _D5 and _D7 , and two electronically controlled switches 1222 in the lower branch. Each electronically controlled switch 1222 includes a MOSFET marked as _Q6 and _Q8 , wherein the drains of _Q6 and _Q8 are connected to the two upper branches respectively, and the sources are connected to each other.

Each MOSFET _Q6 and _Q8 includes an anti-parallel diode, labeled _D6 and _D8, respectively.

The primary coil 114 and the secondary coil 124 form a magnetic coupler 130, whose mutual inductance is M.

初级线圈114具有初级自感L_P和电阻R_P,w，其中电阻R_P,w为初级线圈损耗。次级线圈124具有次级自感L_S和电阻R_S,w，其中电阻R_S,w为次级线圈损耗。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 _LP and a resistance _RP,w , where the resistance _RP,w is the primary coil loss. The secondary coil 124 has a secondary self-inductance _LS and a resistance _RS,w , where the resistance _RS,w is the secondary coil loss.

In the wireless charging circuit 100, the DC source 111 converts the DC voltage _VI into an AC power with a voltage of _vp and an angular frequency of ω through the inverter 112, which is used to drive the primary coil 114 to induce an AC current i _S in the secondary coil 124, and then form an AC voltage v _S at the output end of the SCC. The induced voltage and induced current are input to the SAR 122 for rectification, and then filtered by the capacitor 126, and the output is a DC voltage V _O and a DC current I _O , that is, the charging voltage and charging current of the battery 127.

In one embodiment, switches _Q6 and _Q8 in SAR122 are turned on when their anti-parallel diodes are turned on, thereby achieving zero voltage switching (ZVS). Switches _Q6 and _Q8 are turned on for half a current cycle respectively and their turn-on times are complementary. Therefore, there is a time delay π-θ∈[0,π] between the turn-off time of _Q6 and _Q8 and the zero-crossing point of current i _S , and θ is defined as the conduction angle of SAR. The maximum value of the conduction angle θ is π and the minimum value is 0. The change of the conduction angle θ affects the phase angle between v _S and i _S.

开关Q_a和Q_b分别开通半个电流周期并且开通时间互补。例如，Q_a和Q_b在v_SCC零电压时开关，由此实现软开关以减少开关损耗。在半个电流周期内，电容C₂的充电时间(或放电时间)为

其随

的增大而减小，v_SCC的均方根值随之减小。由此，SCC的等效电容即C_SCC可以通过改变可控角

来进行调整。In one embodiment, switches _Qa and _Qb in the SCC are synchronized with the current _iS and have a controllable angle with the zero crossing of the current _iS .

Switches _Qa and _Qb are turned on for half a current cycle respectively and their on-times are complementary. For example, _Qa and _Qb are switched when v _SCC is zero voltage, thereby achieving soft switching to reduce switching losses. In half a current cycle, the charging time (or discharging time) of capacitor _C2 is

Its follow

As the controllable angle increases, the RMS value of v _SCC decreases accordingly. Therefore, the equivalent capacitance of SCC, i.e., C _SCC, can be changed by changing the controllable angle

to make adjustments.

In one embodiment, the conduction angle of the SAR 122 and the controllable angle of the SCC 121 are adjusted to provide matching load impedance, so that the wireless charging circuit 100 charges the battery 127 at a constant power, thereby improving the charging efficiency.

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

FIG. 2 is a switching sequence and operating waveform 200 of a half-controlled rectifier bridge (SAR) according to an exemplary embodiment. In FIG. 2 , the electrically controlled switches Q ₆ and Q ₈ of SAR122 are turned on when their anti-parallel diodes are turned on to achieve zero voltage switching. Q ₆ and Q ₈ are both turned on for half a current cycle and the turn-on time is complementary. Therefore, Q ₆ and Q ₈ have a time delay of π-θ∈[0,π] with the zero crossing point of i _s , where θ is the conduction angle of SAR122. v _s,1 is the basic component of v _s , which lags behind i _s , and its phase angle is given by γ=π-θ/2. Therefore, the equivalent load of the charging circuit is an impedance Z _eq instead of a pure resistance.

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

The equivalent fundamental impedance of the above SAR122 is:

Z _eq = R _eq + jX _eq , (1)

Where R _eq is the equivalent resistance, X _eq is the equivalent reactance,

Q_a和Q_b各开通半个周期，并且开通时间互补。由于Q_a和Q_b在v_SCC零电压下开通和关断，由此实现软开关以最小化开关损耗。FIG3 is a switching sequence and operating waveform 300 of an SCC according to an exemplary embodiment. In FIG3, the driving signals of the electronically controlled switches _Qa and _Qb are synchronized with _is and have a controllable angle with the zero crossing point of _is .

_Qa and _Qb are turned on for half a cycle each, and their turn-on times are complementary. Since _Qa and _Qb are turned on and off at zero voltage of v _SCC , soft switching is achieved to minimize switching losses.

The equivalent impedance of SCC, X _Cscc, can be expressed as formula (4), and simplified to formula (5) through quadratic curve fitting:

in

FIG. 4 is a graph 400 of equivalent impedance versus controllable angle of a SCC according to an exemplary embodiment.

从0.5π变化到π时，X_Cscc可以从标称电抗X_C2调制到零。As shown in FIG4 , the exact relationship between the equivalent impedance of the SCC and the controllable angle is represented by curve 401, and the approximate relationship is represented by curve 402.

When changing from 0.5π to π, X _Cscc can be modulated from the nominal reactance X _C2 to zero.

FIG. 5 is a diagram 500 of an equivalent charging circuit according to an exemplary embodiment.

FIG5 is an equivalent circuit diagram of the circuit shown in FIG1 . 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 connected in series. The resistor 512 has an equivalent resistance value R _p , which represents the loss on 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 inductor 524, a secondary compensation capacitor 523, a variable capacitor 521 and a load 522 connected in series. The capacitance value of the variable capacitor 521 is represented by C _scc , which is the equivalent capacitance of SCC121. The load 522 is represented by an equivalent impedance Z _eq , which includes a series resistance R _eq and a reactance X _eq , as shown in equation (1). The resistance R _S represents the sum of the losses of the secondary coil 124, SCC121 and SAR122.

For example, _Vp , _Ip , _Vs and _Is are used to represent the phasor representation of the fundamental components of variables _vp , _ip , _vs and _is respectively. _C1 , _CScc and _Xeq provide capacitive reactance in the secondary circuit, which can be represented by an equivalent secondary compensation capacitor _CS,eq as shown in formula (6):

By analyzing the equivalent circuit in Figure 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)

Where _XM is the mutual inductance of the primary coil and the secondary coil, _XLP is the inductive reactance of the primary circuit, and _XCP is the primary current.

X_Ls＝ωLs。The capacitive reactance of the circuit, X _M = ω M,

_XLs ＝ωLs.

The amplitudes of V _p , V _s and _Is are given by equations (9), (10) and (11) respectively:

The equivalent circuit efficiency of Figure 5 is shown in equation (12):

以及

在选定的工作频率ω下，当满足(13)和(14)时，传输效率最大，其表达式如式(15)所示，其中X_CS,eq,opt和R_eq,opt分别为使传输效率最大化的X_CS,eq和R_eq的优化值。Assumptions

as well as

At the selected operating frequency ω, when (13) and (14) are satisfied, the transmission efficiency is maximum, and its expression is shown in formula (15), where X _CS,eq,opt and R _eq,opt are the optimized values of X _CS,eq and R _eq that maximize the transmission efficiency, respectively.

X _Ls +X _{Cs, eq, opt} = 0 (13)

Since the battery internal resistance R _L varies greatly during the charging process, according to equation (14), the internal resistance needs to be converted into a matching resistance R _eq,opt via SAR to achieve the highest transmission efficiency. Therefore, according to equations (2) and (14), the conduction angle θ of SAR can be expressed as equation (16):

According to equation (3), the change of conduction angle θ will also affect the load reactance X _eq , which is expressed as equation (17):

The above analysis of the charging circuit of the exemplary embodiment is verified by simulation experiments. Unless otherwise specified, the parameters of the simulation experiments described below are all shown in the table of FIG. 7 .

Graph 600A in FIG6A shows the curve of the conduction angle θ changing with the load resistance. In FIG6A , curve 601 shows that the SAR conduction angle θ changes accordingly with the change of R _L , thereby achieving the optimized load resistance in the simulation. It can be seen from curve 603 that by controlling the conduction angle θ, the equivalent load resistance R _eq can be maintained at the optimized load resistance value R _eq,opt . However, curve 602 shows that as the conduction angle θ decreases, the magnitude of the reactance X _eq increases.

的大小，进而改变电抗X_Cscc，最终得到目标电抗X_{CS，eq，opt}＝-X_LS。结合式(5)，(6)和(17)，SCC的可控角

表达式如下：To ensure the condition in equation (14) to achieve the maximum charging efficiency, C _s,eq needs to be fully compensated to L _s at a fixed frequency. Therefore, the exemplary embodiment changes the controllable angle of SCC by

The size of the SCC is then changed to change the reactance X _Cscc , and finally the target reactance X _CS,eq,opt ＝-X _LS is obtained. Combining equations (5), (6) and (17), the controllable angle of SCC is

The expression is as follows:

Meeting the above analysis steps during the control process can enable the system to operate at maximum transmission efficiency.

导通角θ和等效次级侧补偿感抗X_CS,eq之间的关系图600B。在图6B中，曲线604显示了仿真实验中可控角

与导通角θ的联合控制。从曲线605可以看出，该联合控制使得等效次级补偿感抗X_CS,eq几乎恒定保持在优化值X_CS,eq,opt，由此能够实现最高效率。Figure 6B shows the controllable angle of SCC in the simulation experiment.

The relationship between the conduction angle θ and the equivalent secondary side compensation inductance X _CS,eq is shown in FIG600B. In FIG6B , curve 604 shows the controllable angle in the simulation experiment.

Combined control of the conduction angle θ. As can be seen from curve 605, the combined control makes the equivalent secondary compensation inductance _XCS,eq almost constant at the optimized value _XCS,eq,opt , thereby achieving the highest efficiency.

As described above, the wireless charging current of the exemplary embodiment can achieve the highest charging efficiency by matching and optimizing the load resistance in the secondary circuit and maintaining zero reactance. When the reactance is zero, the inductive energy transfer system can achieve load-independent output current. Therefore, by combining the above two points, constant power output and maximum efficiency can be achieved at the same time.

FIG8 shows an IPT circuit 800 that can achieve constant power output and maximum efficiency at the same time. 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 optimized value R _eq,opt . According to equation (14), the optimized load resistance R _eq,opt is approximately a constant value. Theoretically, if the loss on the electrical components is ignored, when the input voltage of the primary circuit is v _p , the output current amplitude of the secondary circuit that is independent of the load can be expressed as:

Therefore, during the entire charging process, for a fixed input voltage, the exemplary embodiment can ensure constant power output and maintain the highest efficiency, which is expressed as follows:

The subscript RMS represents the root mean square value.

Combining equations (9)-(11), (19), and (20), the constant charging power, the output DC voltage, and the DC current can be expressed as equations (21), (22), and (23), respectively:

Assuming that the equivalent load reactance _Xeq can be cancelled by properly controlling the reactance _XCSCC of the SCC,

Then the output power P _O is only related to the equivalent load resistance R _eq , and 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. Therefore, the output power P _O and the conduction angle θ have a monotonic relationship.

FIG. 9 illustrates a graph 900 of output power, efficiency, and SAR conduction angle in an exemplary embodiment.

In FIG9 , the relationship between the output power P _O and the conduction angle θ is represented by curves 910, 920 and 930, and the relationship between the efficiency η and the conduction angle θ is represented by curves 940, 950 and 960, and each group of curves corresponds to a battery resistance value _RL of 30Ω, 40Ω, and 50Ω, respectively. When P _O is a constant value in equation (20), the charging circuit efficiency is the highest, as shown by intersections 901, 902, and 903. Therefore, P _O,constant can be used as a reference value P _O,ref in the controller to achieve constant power output and maintain the highest efficiency.

FIG10 shows 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 output voltage and 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 FIG1 .

In one embodiment, the charging voltage Vo and the charging current Io are measured by the sensor 1020, and the measured values are input into the multiplier and the divider of the controller 1030, which are used to calculate the charging power and the load resistance, respectively. The controller further calculates the conduction angle of the SAR according to the difference between the measured value of the charging power and the reference value through PI control. At the same time, under the condition that the SAR conduction angle and the battery resistance are known, the control angle of the SCC is calculated according to formula (18). Thereafter, the signal generating unit 1040 generates the control signals of the SCC and the SAR respectively through the signal generator 1 and the signal generator 2 according to the calculated conduction angle and control angle. The signal generating unit 1040 also includes a zero-crossing detector for detecting the zero-crossing point of the coil current i _S in the secondary circuit and generating 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 of a proportional controller, an integral controller, and a differential controller, or a combination of two or more thereof.

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

In one embodiment, the control angle of the SCC is calculated based on the 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.

Since the operating frequency of the primary circuit is fixed, achieving constant power and highest efficiency charging only requires controlling the impedance of the secondary circuit. Therefore, the wireless charging system does not require 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 graph 1100 of the relationship between the voltage stress of the SCC and the secondary circuit compensation capacitance.

According to equations (3) and (5), |X _eq | changes with the battery resistance _RL , and its minimum value is represented by |X _eq | _min and its maximum value is |X _eq | _max . When the SCC control angle changes from π to 0.5π, |X _CSCC | changes from zero to |X _C2 |. X _CSCC is used to offset the change of X _eq , so that X _CS,eq can be maintained at the optimized value X _CS,eq,opt , thereby effectively compensating X _LS .

According to equation (14), _C1 needs to fully compensate the reactance of the secondary circuit, that is:

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

|V _SCC,max |＝|X _C2 ||I _S |. (26)

In order to reduce the voltage stress of the SCC switch, the |X _C2 | value should be minimized. Therefore, according to equation (24), the |X _C1 | value should be maximized. Combined with equation (25), the maximum value of |X _C1 | can be expressed as equation (27):

Curve 1110 in FIG. 11 shows the relationship between voltage stress |V _{SCC, max} | and reactance |X _C1 |. It can be seen that a larger value of |X _C1 | can reduce voltage stress |V _{SCC, max} |.

时，SCC的电流应力最大。因为此时，SCC中的电容C₂被开关Q_a和Q_b短路。由于根据式(19)，输出电流为恒值，SCC开关的最大电流应力可以表达为式(28)：When the control angle of SCC is maximum,

When , the current stress of SCC is the largest. Because at this time, the capacitor _C2 in SCC is short-circuited by switches _Qa and _Qb . Since according to equation (19), the output current is constant, the maximum current stress of SCC switch can be expressed as equation (28):

| _ISCC,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 in a state where the input voltage v _P and the input current i _P of the primary circuit are at a zero phase angle.

In one embodiment, the input impedance has a small inductance, so that the switches _Q1 - _Q4 achieve zero voltage switching to reduce switching losses. The primary frequency _ωP can be slightly reduced to meet the above requirements without significantly affecting the output power and efficiency. Therefore, the loss R _P of the primary circuit can be estimated by the primary coil resistance and the conduction loss of the inverter switch, as shown in equation (29):

R _P = R _{P, w} +2R _{on, 1} , (29)

Where R _on,1 is the on-resistance of the inverter switch. R _P can be regarded as a constant value.

Since both switches _Qa and _Qb of the SCC are soft switches, the switch conduction loss of the SCC can be estimated by equation (30):

Where R _on,2 and V _f,2 are the on-resistance and body diode forward voltage of switches Q _a and Q _b , respectively. The root mean square value _ISCC,RMS and the average value _ISCC,avg of the current flowing through Q _a and Q _b are calculated by equations (31) and (32), respectively:

Similarly, ignoring the small amount of switching loss caused by the ZVS of SAR switches Q ₆ and Q ₈ , the conduction loss of the SAR can be estimated as follows:

Where R _on,3 is the on-resistance of switches Q ₆ and Q ₈ , V _f,3 is the forward voltage of body diodes D ₅ -D _{8. i S,RMS} and i _S,avg are the root mean square value and average value of the current injected into SAR, respectively.

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

该比率随电池内阻R_L的变化而从1.1变化到1.3。根据式(15)，优化负载电阻R_eq,opt随

而变化，但是，轻微偏离该优化值对充电效率影响不大。在一个实施例中，R_eq,opt固定在如图7所示的值以简化计算。仿真实验的充电效率如曲线1220所示，其由于R_S的增加而稍微下降，但是在整个负载范围内大致上都保持在最大值。The loss resistivity is shown in FIG. 12 by curve 1210

This ratio changes from 1.1 to 1.3 as the battery internal resistance _RL changes. According to equation (15), the optimized load resistance R _eq,opt changes as

However, a slight deviation from the optimized value has little effect on the charging efficiency. In one embodiment, _Req,opt is fixed at the value shown in FIG7 to simplify the calculation. The charging efficiency of the simulation experiment is shown in curve 1220, which decreases slightly due to the increase of _RS , but remains at the maximum value in the entire load range.

The feasibility of the charging system is verified by circuit experiments. FIG13 is an experimental parameter table 1300 of a charging circuit according to an exemplary embodiment. According to table 1300, during the charging process, the equivalent battery internal resistance is simulated by an electronic load, and the variation range is approximately 18Ω to 50Ω. The input DC power and the output DC power are measured by a Yokogawa PX8000 precision power oscilloscope.

In the experiment, the inverter operating frequency is fixed at 85kHz, and constant power output and maximum efficiency are achieved by adjusting the conduction angle of the SAR and the control angle of the SCC. FIG14 shows a measured operating point diagram 1400, where the control angle of the SCC varies from 0.53π to 0.83π, and the conduction angle θ of the SAR varies from 0.95π to 0.57π.

FIG. 15A shows the relationship between the measured values of the output current and voltage and the battery resistance, FIG. 1500A. FIG. 15B shows the relationship between the measured values of the output power and efficiency and the battery resistance, FIG. 1500B. In FIG. 15A, curve 1501 shows the charging current, which changes in the opposite direction to the charging voltage shown by curve 1502. The output power represented by curve 1503 is basically stable at 147 watts, and the maximum efficiency is shown by curve 1504, which is maintained at about 88%. The experimental results shown in FIGS. 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, the waveforms of the inverter, SCC and SAR at the beginning, middle and end of charging are measured. The experimental results show that the inverter, SCC and SAR all achieve zero voltage switching. The maximum voltage stress of the SCC switch is about 55V, which is consistent with the analysis of formula (26).

In one embodiment, the wireless charging system uses a closed-loop control as shown in FIG10 in the secondary circuit, and the secondary impedance is controlled by a microprocessor to achieve constant power charging and maximum power. FIG16 shows the instantaneous waveform 1600 change of the step load resistance. The load resistance changes from 20Ω to 40Ω and then to 20Ω.

In FIG16 , the output voltage and the 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 in curve 1605. The output power is strictly controlled by the conduction angle of the SAR, while the control angle of the SCC is coordinated by the conduction angle and the battery load. No wireless feedback or wireless transmission is required in the system control process.

FIG17 is a schematic diagram of a wireless charging circuit according to an embodiment. In FIG17 , the wireless charging circuit 1700 includes an SCC 1721 and a SAR 1722. The SCC 1721 includes a fixed capacitor _C2 and two electrically controlled switches _Qa and _Qb , _Qa and _Qb are connected in series and then connected in parallel with the capacitor _C2 . After the SCC 1721 is connected in series with the fixed capacitor _C1 , it is connected in parallel with the secondary coil 1724.

The setting of SAR 1722 is the same as that of Figure 1. However, since the setting of SCC 1721 is different from that of Figure 1,

In the secondary circuit of circuit 1700, a filter inductor 1726 is connected in series with a battery 1727, rather than a filter capacitor connected in parallel with the battery in FIG. 1 .

FIG18 is a schematic diagram of an equivalent wireless power transmission circuit of FIG17. As shown in FIG18, the equivalent circuit 1800 includes an equivalent capacitor 1821 connected in parallel with an equivalent resistor 1822. By adjusting the conduction angle of the SAR and the control angle of the SCC, an optimized load resistance is achieved in the secondary circuit, and the capacitive 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 this specification and claims, "connected" means direct or indirect electrical connection.

Therefore, after introducing several embodiments, those skilled in the art will recognize that different modifications, other structures, equivalents, can be used without departing from the essence of the present invention. Accordingly, the above description should not be regarded as limiting the scope of the present invention as determined by the following claims.

Claims (20)

1. A wireless power transmission circuit that supplies power to a load of a variable resistor using an alternating current (AC) power source induced by a primary coil on a primary side of the circuit to a secondary coil on a secondary side of the circuit, the wireless power transmission circuit comprising: a controllable switched capacitor (SCC) connected to an 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 terminal 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 cycle and are complementary to each other. The off time thereof has a time delay relative to the zero crossing point of the AC power source. The time delay is the control angle of the SCC. The two switches in the SAR are each turned on for half a cycle and complement each other. The off time has a time delay relative to the zero crossing point of the AC power supply. The time delay is the conduction angle of the SAR. The wireless power transmission circuit provides a load impedance that matches the impedance of the coil by adjusting the control angle of the SCC and the conduction angle of the SAR, thereby providing a constant power output and improving the power transmission efficiency. 2. The wireless power transmission circuit according to claim 1, wherein the bridge circuit in the SAR has two upper branches and two lower branches, each upper branch includes a diode, each lower branch includes an electrically controlled switch, the electrically controlled switch includes a transistor and a diode anti-parallel to the transistor, the drain of each transistor is respectively connected to an upper branch, and the sources of the two transistors are connected to each other. 3 . The wireless power transmission 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 transmission 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 the conduction angle θ of the SAR is adjusted to

When , the power transmission efficiency is the highest, where _RL is the load resistance, _XM is the mutual inductance of the coil, _RS is the equivalent resistance of the secondary side loss, _RP is the equivalent resistance of the primary side loss, and _Req,opt is the optimized value of the SAR equivalent resistance that maximizes the transmission efficiency.

6. The wireless power transmission circuit according to 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 the highest, where X _CS,eq,opt is calculated as X _CS,eq,opt = -X _LS , X _LS is the self-inductance of the secondary coil, X _C1 is the reactance of the second capacitor, X _C2 is the reactance of the first capacitor, X _eq is the equivalent load reactance, and X _CS,eq,opt is the optimized value of the equivalent compensation capacitor reactance that maximizes the transmission efficiency. 7. The wireless power transmission circuit of claim 1, wherein the SCC is equivalent to a variable capacitor having a reactance X _CSCC , X _CSCC being calculated as

φ is the control angle of SCC, and X _C2 is the capacitive reactance of the first capacitor. The wireless power transmission circuit according to claim 1 , wherein the primary coil operates at a fixed frequency. 9. A wireless charging system for improving battery charging efficiency, wherein the battery is charged by an AC power 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 coil, comprising two electrically controlled switches connected in series and a first capacitor connected in parallel with the two electrically controlled switches; a half-controlled rectifier bridge (SAR) connected to the output terminal of the SCC to rectify the output of the SCC, wherein the SAR comprises a bridge circuit including two electrically controlled switches; Multiple sensors for measuring the battery's charging voltage and charging current; A controller, configured to calculate 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 according to the conduction angle and the control angle, and providing the control signal to the electrically controlled switches in the SCC and the SAR, The two switches in the SCC are each turned on for half a cycle and are complementary to each other. The off time thereof has a time delay relative to the zero crossing point of the AC power source. The time delay is the control angle of the SCC. The two switches in the SAR are each turned on for half a cycle and complement each other, and their off time has a time delay relative to the zero crossing point of the AC power supply, and the time delay is the conduction angle of the SAR. The wireless power transmission circuit provides a load impedance that matches the coil impedance by adjusting the control angle of the SCC and the conduction angle of the SAR, thereby charging the battery at a constant power and improving the charging efficiency. 10. The wireless charging system according to claim 9, wherein the bridge circuit in the SAR has two upper branches and two lower branches, each upper branch includes a diode, each lower branch includes an electrically controlled switch, the electrically controlled switch includes a transistor and a diode anti-parallel to the transistor, the drain of each transistor is respectively connected to an upper branch, and the sources of the two transistors are connected to each other. 11. The wireless charging system according to claim 9, wherein each electronically controlled switch of the SCC comprises a transistor, and drains of two transistors of the SCC are connected, and sources are respectively connected to two ends of the first capacitor. 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 according to claim 9, when the conduction angle θ of the SAR is adjusted to

When , the power transmission efficiency is the highest, where _RL is the load resistance, _XM is the mutual inductance of the coil, _RS is the equivalent resistance of the secondary side loss, _RP is the equivalent resistance of the primary side loss, and _Req,opt is the optimized value of the SAR equivalent resistance that maximizes the transmission efficiency.

15. The wireless charging system according to 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

When , the power transmission efficiency is the highest, where X _CS,eq,opt is calculated as X _CS,eq,opt = -X _LS , X _LS is the self-inductance of the secondary coil, X _C1 is the reactance of the second capacitor, X _C2 is the reactance of the first capacitor, X _eq is the equivalent load reactance, and X _CS,eq,opt is the optimized value of the equivalent compensation capacitor reactance that maximizes the transmission efficiency. 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, wherein the battery is charged by 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), and the output end of the SAR is connected to a rechargeable battery, wherein the SCC includes a first capacitor and two series-connected electrically controlled switches connected in parallel with the first capacitor, and the SAR includes a bridge circuit, the bridge circuit includes two upper branches and two lower branches, each upper branch includes a diode, and each lower branch includes an electrically controlled switch, and the wireless charging method includes the following steps: The controller calculates the conduction angle of the SAR to provide a load resistance that matches the impedance of the coil, wherein the conduction angle is a time delay of the disconnection time of the controllable switch of the SAR relative to a current zero crossing point of the AC power source; The controller calculates a control angle of the SCC to offset the reactance of the secondary side, wherein the control angle is a time delay of a disconnection time of a controllable switch of the SCC relative to a current zero crossing point of the AC power source; Controlling a switch in the SAR according to the conduction angle by a first control signal; and The switch in the SCC is controlled according to the control angle by the second control signal, so that the wireless charging system charges the battery at a constant power, thereby improving the charging efficiency. 18. The method of claim 17, wherein the conduction angle of the SAR is calculated by comparing the charging power with a predetermined reference power P _O ,

Wherein _VI is the charging voltage measured by the sensor, ω is the angular frequency of the AC power supply, M is the mutual inductance between the coils, _RS is the equivalent resistance of the secondary circuit loss, _RP is the equivalent resistance of the primary circuit loss, and _PO,constant is the constant charging power. 19. The method according to claim 17, further comprising: Measuring the charging voltage and charging current of the battery through a plurality of sensors; 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: Generate a first control signal according to the conduction angle of the SAR by a first signal generator; and The second control signal is generated by the second signal generator according to the control angle of the SCC.

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