Wireless power transmission system for realizing resonant tracking by means of low-frequency pulse control

Abstract

The present invention belongs to the technical field of wireless power transmission, and in particular to a wireless power transmission system for realizing resonant tracking by means of low-frequency pulse control. The wireless power transmission system comprises a power source, a transmitting end and a receiving end, wherein the transmitting end has a compensation circuit composed of a resonant capacitor and a transmitting coil that are connected to each other in series, the receiving end has a receiving coil, and the transmitting end also comprises a bridge inverter. The wireless power transmission system in the present invention implements resonant tracking by means of low-frequency pulse control of an inverter, and realizes current self-oscillation by means of voltage pulse charging. Compared with the traditional method for realizing self-oscillation by means of a negative resistor, the present invention does not require an additional complex negative resistor design, and realizes self-oscillation simply by changing an inverter control signal, thereby having a superior application cost efficiency; and the absence of extra circuits also makes the expansion of system functions more flexible.

Description

Wireless power transmission system realizing resonance tracking through low-frequency pulse control Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and in particular relates to a wireless power transmission system that realizes resonance tracking through low-frequency pulse control. Background Art

[0002] Wireless power transmission (WPT) technology, which transmits energy through circuit resonance, has advantages such as convenience and safety, which has led to its widespread use and research.

[0003] As the fundamental function for AC / DC conversion, inverter control is a key research area in WPT. Examples include basic pulse width modulation (PWM) power control strategies, using on-off keying modulation to achieve impedance conversion without a DC / DC converter under capacitive loads, pulse frequency modulation (PFM) technology that utilizes energy density regulation to achieve power control under soft switching, and inverter phase control technology that enables wireless energy beamforming using cross-antennas.

[0004] WPT uses resonance as an energy transmission mode to improve efficiency. Precisely matching the coil current frequency with the resonant frequency is crucial for effective resonant operation. However, the resonant frequency of WPT is variable due to factors such as measurement accuracy, ambient temperature, and component tolerances. This is particularly true due to impedance changes caused by varying charging distances. Deviations between the operating frequency and the resonant frequency can cause detuning, which increases system reactive power losses and reduces energy efficiency. Therefore, resonant tracking is a research hotspot in WPT.

[0005] Feedback control based on circuit resonance information is a straightforward approach to achieving resonance tracking. Depending on the target, feedback control schemes can be categorized into two types: input frequency modification and resonance parameter switching. Parameter switching is primarily achieved through controlling array coils and adjustable capacitors. The additional switching devices introduce operating losses, and the discontinuity of device parameters makes accurate resonance tracking difficult, making this approach unsuitable for practicality and cost. Compared to parameter switching, frequency modification tracks the resonance frequency by controlling the inverter frequency. This approach eliminates the need for additional components, resulting in improved efficiency. Furthermore, inverter-based control offers greater flexibility for functional expansion. However, both approaches essentially involve designing a feedback control system to achieve resonance tracking. Because the resonance state of WPT is volatile and difficult to detect, resonance tracking requires not only precise detection circuitry to obtain resonance information but also complex control algorithms. This increases cost and creates bottlenecks in the system's real-time performance and robustness.

[0006] Resonance in WPT can be generated not only by external periodic AC energy drive, but also by self-oscillation. The resonant frequency of the circuit generated by self-oscillation is only related to the internal resonant parameters. Compared with the feedback control scheme, resonance tracking achieved through self-oscillation does not require any resonance information feedback and algorithm control, has better cost, and solves the bottleneck of feedback control scheme in real-time and robustness. S. Assawaworrarit et al. proposed a parity asymmetric circuit in Nature to improve the robustness of WPT. Its essence is to construct a symmetrical circuit by canceling the equivalent negative resistance to achieve self-oscillation resonant tracking. In this way, although self-oscillation resonant tracking has better robustness and real-time performance, the design of negative resistance is very complicated, which will bring additional costs and reduce the redundancy of the system. In addition, the complicated circuit structure will also limit the expansion of system functions.

[0007] Summary of the Invention

[0008] The present invention addresses the technical problems in the prior art of achieving self-oscillation resonant tracking by constructing a symmetrical circuit with negative resistance, which has high costs, reduced system redundancy and limited system function expansion. The purpose of the present invention is to provide a wireless power transmission system that achieves resonant tracking through low-frequency pulse control.

[0009] To solve the aforementioned technical problems, one aspect of the present invention provides a wireless power transmission system that implements resonance tracking through low-frequency pulse control, comprising a power supply, a transmitter, and a receiver. The transmitter comprises a compensation circuit consisting of a resonant capacitor and a transmitter coil connected in series, and the receiver comprises a receiver coil that generates a magnetic field coupling with the transmitter coil.

[0010] The transmitting end further includes a bridge inverter, and the bridge inverter includes:

[0011] a first MOS transistor, wherein a drain of the first MOS transistor is connected to the positive electrode of the power supply, a source of the first MOS transistor is connected to an end of the resonant capacitor away from the transmitting coil, and a gate of the first MOS transistor is a driving end;

[0012] a second MOS transistor, wherein a source of the second MOS transistor is respectively connected to the negative electrode of the power supply and an end of the transmitting coil away from the resonant capacitor, a drain of the second MOS transistor is connected to the source of the first MOS transistor, and a gate of the second MOS transistor is the other driving end.

[0013] Optionally, in the wireless power transmission system for achieving resonance tracking through low-frequency pulse control as described above, the first MOS transistor and the second MOS transistor are N-channel MOSFETs.

[0014] Optionally, in the wireless power transmission system for achieving resonance tracking through low-frequency pulse control as described above, when the first MOS transistor is controlled to be turned on and the second MOS transistor is turned off, the transmitter is in a charging stage, and the transmitter is connected to the power supply and charged;

[0015] When the first MOS transistor is controlled to be disconnected and the second MOS transistor is turned on, a low-frequency pulse control signal is continuously provided to the driving end of the second MOS transistor, and the second MOS transistor outputs a low-frequency pulse voltage. The transmitting end forms a closed resonant loop and generates self-oscillation. The transmitting coil generates an induced magnetic field, and the receiving coil at the receiving end obtains energy, thereby realizing wireless power transmission.

[0016] Optionally, in the wireless power transmission system for realizing resonance tracking by low-frequency pulse control as described above, the pulse time τ and the control frequency f of the low-frequency pulse control signal are c With the oscillation period T o The relationship between them is: τ=T o / 2

[0017] Where n≥1, n∈Z +

[0018] Then, the duty cycle D of the low-frequency pulse control signal is:

[0019] Optionally, in the aforementioned wireless power transmission system for achieving resonance tracking through low-frequency pulse control, the wireless power transmission system for achieving resonance tracking through low-frequency pulse control includes a control circuit, and the control circuit includes:

[0020] a controller, the controller being connected to a driving end of the first MOS transistor and a driving end of the second MOS transistor respectively;

[0021] a measuring circuit, the measuring circuit being used to obtain an oscillation period of the closed resonant loop formed by the transmitting end, the output end of the measuring circuit being connected to the signal input end of the controller;

[0022] After initialization, the controller controls the second MOS tube to output a fixed low-frequency pulse voltage for oscillation, and the controller obtains the oscillation period T through the measurement circuit. o , according to the oscillation period T o With pulse time τ, control frequency f c The relationship between the pulse time τ and the control frequency f of the low-frequency pulse control signal is adjusted c .

[0023] Optionally, in the wireless power transmission system for achieving resonance tracking through low-frequency pulse control as described above, when the controller controls the second MOS transistor to output a fixed low-frequency pulse voltage for oscillation, the control parameter of the low-frequency pulse control signal is:

[0024] Control frequency f c The frequency is 40Khz, the duty cycle D is 10%, and the pulse time τ is 10% of the charging cycle T c .

[0025] Optionally, in the wireless power transmission system for realizing resonance tracking by low-frequency pulse control as described above, according to the oscillation period T o With pulse time τ, control frequency f c The relationship between the pulse time τ and the control frequency f of the low-frequency pulse control signal is adjusted c When n is 1, the control frequency f c is the oscillation period T o The duty cycle D is fixed at 25%.

[0026] Optionally, in the wireless power transmission system for achieving resonance tracking through low-frequency pulse control as described above, the measurement circuit adopts a zero-crossing current detection circuit.

[0027] The positive progress effect of the present invention is:

[0028] 1. The wireless power transmission system of the present invention achieves resonance tracking through low-frequency pulse control of the inverter and realizes current self-oscillation through pulsed voltage charging. Compared with traditional negative resistance self-oscillation methods, the present invention does not require additional complex negative resistance design. To achieve self-oscillation, the present invention only needs to change the inverter control signal, resulting in a more cost-effective application. The lack of additional circuitry also makes the system more flexible in expanding its functions.

[0029] 2. The control circuit for resonant tracking in this invention has the expanded capability to achieve soft switching across the entire operating range. Compared to conventional WPTs with fixed control frequencies, this invention achieves higher efficiency and power gain under strong coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The disclosure of the present invention will become more apparent with reference to the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. In the drawings:

[0031] FIG1( a ) is a schematic diagram of a circuit of the present invention;

[0032] Figure 1(b) shows w under different coupling degrees r With w LC Ratio diagram;

[0033] Figure 2(a) u of the inverter of the present invention under traditional control signal P 、i P Synchronous waveform diagram;

[0034] Figure 2(b) u of the inverter of the present invention under low-frequency pulse control signal P 、i P Asynchronous waveforms;

[0035] FIG3( a ) is a schematic diagram of a circuit in the voltage pulse charging stage of the present invention;

[0036] FIG3( b ) is a schematic diagram of a circuit in the current self-oscillation stage of the present invention;

[0037] FIG4 is a waveform diagram of the relationship between τ and To under different conditions of the present invention;

[0038] FIG5 shows different f c i P Waveform diagram of changes;

[0039] Figure 6 shows the u under traditional square wave signal and pulse signal P bilateral spectrum;

[0040] Figure 7 shows the i under different signals P Spectrum and Z P Normalized curve of

[0041] FIG8 is another circuit diagram of the present invention;

[0042] FIG9 is a flow chart of system control of the present invention;

[0043] Figure 10(a) shows the coil resonant voltage and control signal test waveforms under initial 10% duty cycle pulse control;

[0044] Figure 10(b) shows the coil resonant voltage and control signal test waveforms under 25% duty cycle pulse control during operation;

[0045] FIG11 is a graph showing the relationship between the coupling coefficient and the oscillation frequency at different charging distances;

[0046] Figure 12 is a diagram of power transmission capabilities under different control systems;

[0047] Figure 13 shows the efficiency diagram under different control systems. DETAILED DESCRIPTION

[0048] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different perspectives and applications without departing from the spirit of the present invention.

[0049] It should be noted that, unless there is any conflict, the following embodiments and features therein may be combined with each other.

[0050] In the description of the present invention, it should be noted that, for directional words, such as the terms "outside", "middle", "inside", "outside", etc., the directions and positional relationships indicated are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. Therefore, the terms "first" and "second" may explicitly or implicitly refer to one or more of these features. Throughout the description of the present invention, "several" and "a number" mean two or more, unless otherwise specifically defined.

[0052] The embodiment of the present invention provides a wireless power transmission system for realizing resonance tracking by low-frequency pulse control, comprising a power supply U IN , transmitter and receiver, the transmitter has a resonant capacitor C connected in series with each other P and the transmitting coil L P The compensation circuit is composed of a receiving coil L at the receiving end. S , receiving coil L S With the transmitting coil L P Generate magnetic field coupling to achieve wireless power transmission.

[0053] 1( a ), the transmitting end further includes a bridge inverter, and the bridge inverter includes a first MOS transistor S1 and a second MOS transistor S2 .

[0054] The drain of the first MOS tube S1 is connected to the power supply U IN The positive electrode of the first MOS tube S1 is connected to the resonant capacitor C P Keep away from the transmitting coil L P One end of the first MOS transistor S1 is the gate of the first MOS transistor S1, and the gate of the first MOS transistor S1 is the driving end of the first MOS transistor S1.

[0055] The source of the second MOS tube S2 is connected to the power supply UIN The negative pole, transmitting coil L P Keep away from the resonant capacitor C P The drain of the second MOS transistor S2 is connected to the source of the first MOS transistor S1, and the gate of the second MOS transistor S2 is the driving end of the second MOS transistor S2.

[0056] The transmitter of the present invention adopts a series-parallel compensation circuit (SP) as the basic topology of WPT. The imaginary part of its reflected impedance changes under different mutual inductances, which makes the resonant frequency f of SP at different charging distances r The present invention is combined with SP to form a bridge inverter, which is actually a half-bridge inverter. As shown in Figure 1(a), the power supply U IN is the DC voltage input to the bridge inverter, k is the coupling coefficient, u P 、i P is the output voltage and current of the bridge inverter. P The first MOS tube S1 and the second MOS tube S2 serve as switches to form the upper arm and lower arm of the half-bridge inverter. P is the transmitting coil, C P is the resonant capacitor, L S is the receiving coil, C S is the receiving capacitor (L P *C P =L S *C S ).

[0057] Output reactance Z of half-bridge inverter for WPT P The loop reactance Ztx at the transmitting end and the reflected impedance Z at the receiving end ref The composition can be inductive, capacitive, and resistive as shown in the following values:

[0058] For the WPT circuit with series series (SS) compensation, the parameter angular frequency Z ref The imaginary part is always zero, so the w of the SS topology under different k r Just for w LC Unlike SS, SP's Im(Z ref ) in w LC The imaginary part below is non-zero and has the following values:

[0059] Formula (2) shows that the SP topology is LC Z refIt is capacitive and increases with the increase of mutual inductance M, which will increase the reactive loss of the circuit and thus deteriorate the working condition of the inverter. Increasing the operating frequency can make the transmitter loop reactance Ztx inductive to compensate for the capacitive reactance, which can be expressed by the following formula:

[0060] Formula (3) can be used to obtain w r , the w r It can be obtained that Im(Z P ) is zero. r With w LC Comparison can be obtained as shown in Figure 2(b). From Figure 2(b), it can be seen that as k increases, w r The higher the value, the higher the value. ref ) becomes larger, resulting in the transmitter requiring a higher inductive reactance to compensate for the capacitive reactance; and the smaller k is, the smaller w r The closer to w LC , this is due to the low coupling Im(Z ref ) influence decreases. Since obtaining k and solving Equation (3) are very troublesome, traditional feedback control schemes require a large amount of information and complex calculations to achieve resonance tracking, which increases the cost and leads to bottlenecks in the real-time and robustness of the system.

[0061] Resonance, as a circuit phenomenon, can be generated not only through alternating current modulated by an external feedback control system, but also through self-oscillation. Resonance generated by self-oscillation is unaffected by external disturbances, depends solely on internal resonant parameters, and exhibits no latency. Therefore, it overcomes the robustness and real-time performance bottlenecks of traditional feedback control schemes while offering a more cost-effective solution.

[0062] Therefore, the present invention adopts a design that realizes self-oscillation only through low-frequency pulse control of the inverter, which realizes current self-oscillation by utilizing voltage pulse charging.

[0063] As shown in Figure 2(a), it is the ideal waveform of the output voltage and current of the bridge inverter corresponding to the traditional control signal. P The waveform of is determined only by the control signal, and i P by u P It is determined by the inverter output load. Since the WPT equivalent load is a series inductor and capacitor, its DC isolation characteristics make it P It can only be an AC with periodic symmetrical changes. P When the change is symmetrical within a resonant cycle, it matches the resonant load characteristics. P with i P They are synchronous, that is, under traditional signals, the control frequency of the bridge inverter is equal to the system operating frequency.

[0064] As shown in Figure 2(b), it is the ideal waveform under the control signal proposed by the present invention. When the bridge inverter control signal is a low-frequency pulse, u P It does not change within one resonant cycle. However, i P Affected by the resonant load, it will not stop changing. P with i P will lose synchronization (f UP ≠f IP ). After the loss of step i P It will self-oscillate, and its frequency is determined only by the resonance parameters. Therefore, under the low-frequency pulse control signal proposed by the present invention, the operating frequency of the system can automatically track the resonance frequency.

[0065] In some embodiments, the first MOS transistor S1 and the second MOS transistor S2 are N-channel MOSFETs.

[0066] In some embodiments, as shown in FIG3( a ) and FIG3 ( b ), they are schematic diagrams of circuit operation when the bridge inverter control signal is a low-frequency pulse.

[0067] 3(a), when the first MOS tube S1 is turned on and the second MOS tube S2 is turned off, the transmitter is in the charging stage, and the transmitter is connected to the power supply U IN Connected and charged. Of course, in this stage, a low-frequency pulse control signal is provided to the driving end of the first MOS tube S1. The energy input to the system is related to the state of the resonance part. When the resonance is at the negative voltage peak, the voltage difference between the power supply and the resonance end is the largest, and the input power is the largest at this time. Conversely, when the resonance is at the positive voltage peak, the input energy is the smallest.

[0068] 3(b), when the first MOS transistor S1 is turned off and the second MOS transistor S2 is turned on, a low-frequency pulse control signal is continuously provided to the driving end of the second MOS transistor S2, and the second MOS transistor S2 outputs a low-frequency pulse voltage. The transmitting end forms a closed resonant loop and generates self-oscillation, and the transmitting coil L P Generate an induced magnetic field, the receiving coil L at the receiving end S Energy is obtained to realize wireless power transmission. In this stage, since the low-frequency pulse control signal does not change in one resonant cycle, i P It will oscillate freely at the transmitting end and P An induced magnetic field is generated on the load, thereby transferring energy to the load. P The oscillation angular frequency w o Is it equal to the resonant angular frequency w r This is the key to the establishment of the above-mentioned design theory proposed by the present invention, and their relationship can be solved through the distributed circuit charging oscillation model.

[0069] According to Kirchhoff's law, the transmitter loop voltage equation in Figure 3(b) can be written as follows:

[0070] where R P is the equivalent resonant resistance (R P =Re(Z ref )), L P 'For L P and Im(Z ref ) is an equivalent resonant inductor. The parameters in the above formula can be expressed as:

[0071] Substituting the above equation into equation (4) yields the following second-order linear differential equation with constant coefficients:

[0072] Solving the above formula we can get u cp for:

[0073] Where A1 and A2 are constants. P is the characteristic root of the equation as shown below:

[0074] in,

[0075] Analyzing the above formula, we can see that when Q<0.5, there are two unequal negative real roots. At this time, the circuit decays exponentially and does not have oscillation characteristics. When Q>0.5, u cp It consists of a pair of conjugate complex roots, which can be expressed as follows after merging:

[0076] Among them U P,M is the initial oscillation voltage, which is also the maximum instantaneous voltage when the system is running.

[0077] Substituting equation (5) into equation (9) yields the i in the oscillation phase: P :

[0078] Now we can extract the oscillation frequency w o With w r The relationship is as follows:

[0079] In WPT, energy is usually transmitted through coil magnetic induction. In order to ensure the transmission capacity, it is necessary to set |L|>>|C|, so Q>>0.5 in formula (11). o =w r, thus supporting the theoretical feasibility of the proposed invention. At the same time, because self-oscillation is a spontaneous response state, the current at the resonant end will continue to oscillate throughout the entire operating cycle (including the charging cycle). Compared to the method of using a negative resistance to construct a symmetrical circuit to achieve self-oscillation resonance tracking, the self-oscillation achieved by the present invention through low-frequency pulse control has greater advantages in terms of cost and system flexibility.

[0080] In some embodiments, the pulse time τ and the control frequency f of the low-frequency pulse control signal are c With the oscillation period T o The relationship between them is: τ=T o / 2 (12)

[0081] Where n≥1, n∈Z +

[0082] Then, the duty cycle D of the low-frequency pulse control signal is:

[0083] The bridge inverter outputs low-frequency pulse voltage to directly achieve resonance tracking, but different control parameters will affect the operation of the bridge inverter. The control parameters of the low-frequency pulse control signal of the present invention are pulse time τ and control frequency f c , they are related to the oscillation period T o The relationship determines the switching moment of the switch tube during circuit operation, which greatly affects the switching loss of the inverter.

[0084] Referring to Figure 4, there are four different pulse times (pulse widths) τ and oscillation periods T. o u under the relationship P with i P waveform.

[0085] When τ>T o / 2 or τ <T o / 2 hours P with i P The phases are inconsistent, and the switching action cannot be completed at zero current, resulting in switching losses and reduced efficiency.

[0086] When τ=T o When P During the negative half cycle, the resonant end is still connected to the power supply, which causes the current to be reversely charged and thus reduces the system power transmission capability.

[0087] When τ=T o / 2, u P in i PThe pulse charging is completed in the positive half cycle, and the switching action of the first MOS tube S1 and the second MOS tube S2 is completed at zero current. At this time, the working condition of the system is optimal, and the bridge inverter has the maximum output power and the lowest switching loss.

[0088] Similar to the analysis of τ, for the system single control charging cycle T c In terms of (f c =1 / T c ), in order to ensure u P with i P The same phase, T c Must be T o Integer multiples of T, and in order to ensure that the current can oscillate completely during the non-charging time, c Must be T o more than twice.

[0089] Therefore, the optimal low-frequency pulse control parameters can be summarized as Equations (12) and (13).

[0090] Formula (14) shows that the optimal control parameter duty cycle D of the low-frequency pulse has a specific value, the maximum value of which does not exceed 25% and is only related to power, which greatly simplifies the control design process of the present invention.

[0091] In some embodiments, n is 1, and the control frequency f c is the oscillation period T o The duty cycle D is fixed at 25%.

[0092] For the control frequency f in formula (13) c As for the proportional coefficient n, the larger n is, the shorter the single charging cycle T c The longer the oscillation time, the longer the oscillation time. According to formula (10), the i P So e -σt It decreases exponentially, so the larger n is, the larger i is. P The smaller the average current is, the lower the system output power is, which is also intuitively shown in Figure 5. Therefore, by controlling n, power control based on low-frequency pulse signal system can be achieved.

[0093] In order to ensure the output power and simplify the control process, n is preferably the minimum value, that is, n = 1. At this time, according to formula (13) and formula (14), the control frequency f c is the oscillation period T o The duty cycle D is fixed at 25%.

[0094] The present invention also analyzes and simulates the circuit characteristics under different control parameters. P The time domain expression within a control cycle can be written as:

[0095] u in the frequency domain can be obtained by exponential Fourier transform P for:

[0096] Where Sa is the sampling function, and u P The spectrum lines are also roughly distributed according to the shape of the sampling function.

[0097] When τ=T o / 2, u P is a traditional symmetrical square wave signal (D=50%), and its Fourier expansion is:

[0098] After obtaining the corresponding mathematical expression of the low-frequency pulse control signal, the system output power formula can be obtained similarly to the traditional WPT calculation method as follows:

[0099] where Z RX is the loop impedance at the receiving end. out and apparent power The resonant end efficiency η can be obtained by comparing the real part of Q , which is mainly affected by the quality factor of the resonant end. The efficiency η of the system inverter inv It is mainly affected by switching loss, which is related to many factors. P ) and perform data fitting to obtain the relevant inverter efficiency formula. So far, the system efficiency η sys It can be written as follows: η sys =η Q η inv (19)

[0100] Among them, η Q =P OUT / Re(S P ), η inv =f[ang(S P )]

[0101] After obtaining the simulation formulas for the system's output power and efficiency, relevant experimental verification can be carried out, which will optimize the system design process and improve model accuracy.

[0102] Equation (18) shows that the traditional square wave signal has no even harmonics, which will limit the frequency conversion of the signal at high frequencies. Simulating Equations (16) and (17) can yield the u under the traditional square wave signal and the pulse signal (D = 10%). P The double-sided spectrum is shown in Figure 6. The figure clearly shows that compared to the traditional signal which only has odd harmonics that drop rapidly, the pulse signal has a large number of odd and even harmonics.P It can be understood as an LCR filter with frequency-selective characteristics. These rich high-frequency components are loaded on the Z filter with frequency-selective characteristics. P It will enhance w r The current components near the input are converted into the required current with resonant frequency and self-oscillation resonant tracking is achieved. Figure 7 also shows this process, where i P With Z P All were normalized.

[0103] In some embodiments, referring to FIG8 and FIG9 , the wireless power transmission system for achieving resonance tracking through low-frequency pulse control of the present invention includes a control circuit, which includes a controller (Control module) and a measuring circuit (Measuring module).

[0104] The controller is connected to the driver terminals of the first MOS transistor S1 and the second MOS transistor S2. It provides low-frequency pulse control signals to control the first and second MOS transistors S1 and S2. A measurement circuit is used to obtain the oscillation period of the closed resonant loop formed by the transmitter. The output of the measurement circuit is connected to the signal input of the controller.

[0105] Although the use of low-frequency pulse control signals can directly achieve self-oscillation resonance tracking without the need to detect resonance information and feedback control, the oscillation frequency varies under different charging distances, and fixed low-frequency pulse control parameters cannot achieve soft switching operation in the entire operating range. Therefore, this embodiment designs a low-frequency pulse control system with additional soft switching functions as shown in Figure 8, which can be used to achieve full-range soft switching and resonance tracking under unknown coupling coefficients and variable loads. The system is used to obtain the oscillation period T o The device consists of a measuring circuit and a controller that outputs a low-frequency pulse control signal.

[0106] The control process is shown in Figure 9. After the system is initialized, the controller controls the bridge inverter to output a fixed low-frequency pulse voltage for WPT circuit oscillation. After the initial signal is output, the circuit will oscillate. At this time, the oscillation period T can be extracted through the measurement circuit. o , according to the oscillation period T o and the pulse time τ, adjust τ to T o The power control of the system can be achieved by adjusting n in equation (13).

[0107] In some embodiments, when a fixed low-frequency pulse voltage is used for oscillation, the control parameters of the low-frequency pulse control signal are: control frequency f c The frequency is 40Khz, the duty cycle D is 10%, and the pulse time τ is 10% of the charging cycle Tc .

[0108] In some embodiments, in order to ensure the output power and simplify the control process, n is 1 and the control frequency f c is the oscillation period T o The duty cycle D is fixed at 25%.

[0109] In some embodiments, the oscillation period T o There are many measurement schemes, and any measurement circuit in the prior art can be used. For example, the measurement circuit of this embodiment uses a zero-crossing current detection circuit.

[0110] The zero current detection circuit is a circuit that outputs a current sampling resistor and a zero voltage comparator with T o The time square wave signal is then measured by the controller's counter.

[0111] Example 1:

[0112] The system circuit and control method adopt the control circuit of Figure 1(a) combined with Figure 8 and the control method of Figure 9. The system parameters are shown in Table 1 below:

[0113] Table 1

[0114] In Table 1, r P and r S Not shown, r P As an equivalent resistance to the transmitting coil L P Series, same, r S As the receiving resistor and the receiving coil C S The MOSFETs are connected in series: a first MOS tube S1 and a second MOS tube S2.

[0115] The transmitting coil uses a Qi standard coil. In order to prevent the interaction between ferrites at close distances and increase self-inductance, no ferrite is used on the back of the receiving coil.

[0116] The controller uses an STM32G474 as the MCU, the measurement circuit uses an INA214 as the current sampling chip, and an LM293 as the voltage comparator. The receiving-end rectifier circuit uses an active bridge rectifier scheme, and the rest of the design is similar to traditional WPT.

[0117] Figure 10(a) and Figure 10(b) are the experimental waveforms of the resonant voltage and the control signal under the 5mm coil charging distance, which are the initial signal (D = 10%, f c =40kHz) and working signal (D = 25%, f c =1 / 2f o ). From the comparison of the two figures, we can find that under the initial signal, due to iP The transient change of L P The voltage has a higher peak, while under the working pulse, due to the realization of ZCS, the L P The voltage is very flat. Note that L S The voltage on the L has a certain oscillation. After frequency analysis, it is found that this is due to the S The oscillation of the rectifier pF capacitor Crect is caused by the oscillation, and its impact on system efficiency and power can be ignored. S It can be found that the oscillation frequencies are the same, which verifies that low-frequency pulse control of any parameters can achieve self-oscillation resonant tracking.

[0118] Figure 11 shows the relationship between k and f at different charging distances. o Since the spectrum at the receiving end is clearer than that at the transmitting end, f o The test object is the receiving coil to improve the measurement accuracy. The figure also simulates the system f through formula (3) r , and f o The comparison shows that the deviation is within 1%, which also verifies the accuracy of low-frequency pulse control in achieving resonance tracking. The test found that as k decreases, the oscillation frequency is closer to f LC , which is consistent with the analysis of Figure 1(b).

[0119] This embodiment also tests the output power capacity and efficiency of two systems: the traditional fixed frequency control system (f = f LC ,D=50%) and the low-frequency pulse control system proposed in this paper (f=f o / 2, D = 25%). Voltage gain G under different systems V (G V =U OUT / U IN ) is shown in Figure 12, where the simulation uses Equation (18). From the figure, it can be seen that the traditional signal has a higher G than the low-frequency pulse control signal when the coupling is strong (k>0.3). V Low, this is because Im(Z P ,w LC ) is too large under strong coupling and reduces the system active power. In contrast, under weak coupling (k<0.3)Im(Z P ,w LC ) will become smaller, and the lower duty cycle of the low-frequency pulse control signal makes its equivalent input voltage smaller than the traditional signal, which leads to the G V It is even smaller under weak coupling. As for the power simulation results, the variation pattern is the same as that of the test results.

[0120] The efficiency under different control systems is shown in Figure 13, where the simulation in the figure is based on formula (19), and high-frequency loss is also added in the simulation for more accurate simulation. It can be seen from the figure that the efficiency based on low-frequency pulse control under strong coupling is higher than that of constant frequency control, which confirms the effectiveness of the present invention in resonance tracking and efficiency optimization. However, under weak coupling, due to the low resonance deviation, the improvement in efficiency is not obvious. The figure shows that the efficiency of the two control systems under extremely strong coupling (k>0.8) has decreased. The f under this coupling r is very high (f r >250kHz), while high frequencies reduce C S The equivalent reactance reduces the active power on the parallel load, so the low-frequency pulse control that can achieve resonant high-frequency operation under strong coupling will have power loss. For a fixed control frequency system, f under strong coupling LC With f r Excessive deviation increases the system reactive power and thus increases the inverter loss.

[0121] In summary, this embodiment experimentally verifies that the wireless power transmission system based on low-frequency pulse control signals to achieve resonance tracking has better system characteristics than the traditional fixed-frequency system under strong coupling, indicating the effectiveness of the present invention.

[0122] The present invention has been described in detail above with reference to the embodiments of the accompanying drawings. A person skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention. The scope of protection of the present invention shall be determined by the scope defined by the appended claims.

Claims

1. A wireless power transmission system for realizing resonance tracking through low-frequency pulse control, comprising a power supply, a transmitting end and a receiving end, wherein the transmitting end has a compensation circuit composed of a resonant capacitor and a transmitting coil connected in series, and the receiving end has a receiving coil; It is characterized in that The transmitting end further includes a bridge inverter, and the bridge inverter includes: a first MOS transistor, wherein the drain of the first MOS transistor is connected to the positive electrode of the power supply, the source of the first MOS transistor is connected to an end of the resonant capacitor away from the transmitting coil, and the gate of the first MOS transistor is a driving end; a second MOS tube, wherein the source of the second MOS tube is respectively connected to the negative electrode of the power supply and one end of the transmitting coil away from the resonant capacitor, the drain of the second MOS tube is connected to the source of the first MOS tube, and the gate of the second MOS tube is the other driving end.

2. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 1, characterized in that: The first MOS transistor and the second MOS transistor are N-channel MOSFETs.

3. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 1, characterized in that: When the first MOS tube is controlled to be turned on and the second MOS tube is turned off, the transmitting end is in a charging stage, and the transmitting end is connected to the power supply and charged; When the first MOS tube is controlled to be disconnected and the second MOS tube is turned on, a low-frequency pulse control signal is continuously provided to the driving end of the second MOS tube, the second MOS tube outputs a low-frequency pulse voltage, the transmitting end forms a closed resonant loop and generates self-oscillation, the transmitting coil generates an induced magnetic field, and the receiving coil of the receiving end obtains energy to realize wireless power transmission.

4. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 3, characterized in that: The pulse time τ and control frequency f of the low-frequency pulse control signal c With the oscillation period T o The relationship between is: τ=T o / 2 Then, the duty cycle D of the low-frequency pulse control signal is: Where n ≥ 1, n ∈ Z + .

5. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control according to any one of claims 1 to 4, characterized in that: The wireless power transmission system for realizing resonance tracking through low-frequency pulse control comprises a control circuit, and the control circuit comprises: a controller, wherein the controller is connected to a driving end of the first MOS tube and a driving end of the second MOS tube respectively; a measuring circuit, the measuring circuit being used to obtain the oscillation period of the closed resonant loop formed by the transmitting end, the output end of the measuring circuit being connected to the signal input end of the controller; After initialization, the controller controls the second MOS tube to output a fixed low-frequency pulse voltage for oscillation, and the controller obtains the oscillation period T through the measurement circuit. o , according to the oscillation period T o With pulse time τ, control frequency f c The relationship between the pulse time τ and the control frequency f of the low-frequency pulse control signal is adjusted c .

6. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 5, characterized in that: When the controller controls the second MOS tube to output a fixed low-frequency pulse voltage for oscillation, the control parameter of the low-frequency pulse control signal is: Control frequency f c The charging cycle T is 40Khz, the duty cycle D is 10%, and the pulse time τ is 10%. c .

7. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 5, characterized in that: According to the oscillation period T o With pulse time τ, control frequency f c The relationship between the pulse time τ and the control frequency f of the low-frequency pulse control signal is adjusted c When n is 1, the control frequency f c is the oscillation period T o The duty cycle D is fixed at 25%.

8. The wireless power transmission system for realizing resonance tracking by low-frequency pulse control as claimed in claim 5, characterized in that: The measuring circuit adopts a zero-crossing current detection circuit.

Images