An automatic tuning method based on current and voltage detection at the transmitting end

Abstract

The present invention discloses an automatic tuning method based on current and voltage detection at the transmitting end. First, the transmitting end voltage, current amplitude and the phase difference between them are detected, and the mutual inductance estimation value between the transmitting end coil and the receiving end coil is obtained by calculating the detection values ​​of the amplitude and the phase difference; according to the relationship between the primary side capacitance equivalent value and the mutual inductance value when the series-parallel circuit topology resonates, the estimated value of the transmitting end equivalent capacitance is obtained; according to the relationship between the adjustment angle θ and the primary side equivalent capacitance value in the phase-controlled capacitor tuning method, the θ feedback value of the adjustment capacitance value is obtained; finally, a PWM wave is obtained, and then the required primary side equivalent capacitance value is obtained to compensate the circuit. The present invention can estimate the mutual inductance value in a non-resonant state, and then use the phase-controlled capacitor tuning method to adjust the circuit parameters, so that the system can restore the resonant state and maintain a high transmission efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of nonlinear control methods, and in particular relates to an automatic tuning method based on current and voltage detection at a transmitting end. Background Art

[0002] With the development of the times, more resources need to be explored to meet energy needs, such as oceans, mines, oil fields, etc. In order to meet the power supply needs of equipment under such environmental conditions, wireless power transmission will be an effective way of power supply. Wireless power transmission is a non-contact power transmission technology using magnetic fields, electric fields, microwaves, lasers, etc. as media.

[0003] Among them, the magnetic coupling resonance type overcomes the disadvantage of short transmission distance of electromagnetic induction type based on Faraday's law of electromagnetic induction, greatly increasing the transmission distance; it also overcomes the shortcomings of microwave radiation type, such as low efficiency and power, and the loss of energy transmission ability when encountering obstacles, and has the advantages of safety, high efficiency and no radiation. Therefore, magnetic coupling resonance type wireless power transmission has been deeply studied by all walks of life and has a wide range of applications.

[0004] Since the power transmission distance is long, the coupling coil generally forms a resonant circuit with the capacitor, and the transmission of power depends on the coupled resonant magnetic field between the transmitting coil and the receiving coil. The working conditions of the magnetic coupling resonant system are relatively strict. Slight changes in the circuit parameters of the transmitting and receiving coils will affect the working state of the system, and the transmission efficiency is easily affected by the change of the natural frequency. There are many factors that will cause changes in circuit parameters. For example, the temperature rise of the working circuit and the change of working conditions will cause changes in parasitic capacitance; the change of load and the offset of the coil will cause the reflected impedance of the secondary side equivalent to the primary side to change. In this way, the system will be in a detuned state, the transmission power and efficiency will be reduced, and the stability and controllability will be reduced.

[0005] Therefore, it is necessary to select a suitable tuning strategy so that the system can always return to the resonant state and maintain a high transmission efficiency regardless of changes in the load and coupling state. The present invention adopts a phase-controlled capacitive tuning strategy to adjust the circuit parameters (capacitance value) in real time so that the system is always in a resonant state. Summary of the invention

[0006] The purpose of the present invention is to provide an automatic tuning method based on current and voltage detection at the transmitting end, which can estimate the mutual inductance value in a non-resonant state, and then use a phase-controlled capacitive tuning method to adjust the circuit parameters so that the system can return to a resonant state and maintain a high transmission efficiency.

[0007] The technical solution adopted by the present invention is an automatic tuning method based on current and voltage detection at the transmitting end, which is characterized by being implemented in accordance with the following steps:

[0008] Step 1: Detect the voltage and current amplitudes at the transmitting end and the phase difference therebetween, and obtain an estimated value of the mutual inductance between the transmitting end coil and the receiving end coil by calculating the detected values ​​of the amplitude and the phase difference;

[0009] Step 2: After obtaining the estimated value of the mutual inductance between the two coils, the estimated value of the equivalent capacitance of the transmitting end is obtained according to the relationship between the equivalent value of the primary side capacitance and the mutual inductance when the series-parallel circuit topology resonates, that is, equation (14);

[0010] Step 3: After obtaining the estimated value of the equivalent capacitance of the transmitting end, the feedback value of θ for adjusting the capacitance value is obtained according to the relationship between the adjustment angle θ and the equivalent capacitance value of the primary side in the phase-controlled capacitance tuning method, i.e., equations (18) and (19);

[0011] Step 4: According to the obtained θ feedback value, it is converted into a certain voltage value through formula (15), and this voltage value, the opposite value of this voltage and the normalized sinusoidal voltage across the primary side capacitor are compared to obtain a specific PWM wave. This specific PWM wave is added to both ends of the switch tubes S5 and S6 to control their on and off, so as to obtain the required primary side equivalent capacitance value and compensate the circuit.

[0012] The present invention is also characterized in that:

[0013] Step 1 is implemented as follows:

[0014] Step 1.1: The initial state of the circuit is the resonant state, and the transmitter and receiver meet the following conditions:

[0015] ω 2 L2C2=1,ω 2 L1C1=1 (7)

[0016] The reflected impedance Z from the receiving end to the transmitting end is equivalent to r for:

[0017]

[0018] The total impedance Z at the transmitter is obtained 11 for

[0019]

[0020] Step 1.2: The total impedance of the transmitting side can also be obtained by measuring the input voltage u s The fundamental amplitude of the input voltage U on the transmitting side is obtained by adding the current i1 on the receiving coil s , the fundamental amplitude I1 of the current on the transmitting coil and the phase difference between the input voltage and the current on the transmitting coil Then the magnitude of the input impedance |Z11 |=U s / I1, impedance angle Then the transmitting end impedance Z 11 Another way to express this is:

[0021]

[0022] Step 1.3: Equivalently express the two expressions of the total impedance of the primary side, and combine equations (10) and (11) to obtain the relationship between the mutual inductance and the voltage and current amplitudes and the phase difference between them:

[0023]

[0024]

[0025] Therefore, the estimated value of mutual inductance based on transmitter detection is obtained:

[0026]

[0027] Step 2 is implemented as follows:

[0028] After obtaining the estimated value of mutual inductance, since the circuit topology is SP type, the equivalent capacitance value that makes the transmitting side resonate is obtained according to the formula, that is,

[0029]

[0030] Step 3 is implemented as follows:

[0031] Step 3.1, after obtaining the estimated value of the equivalent capacitance of the transmitter, use the phase-controlled capacitance tuning method to adjust the θ value so that the capacitance of the transmitter is adjusted to the estimated value of the equivalent capacitance. According to the absolute value of the charge of the capacitor in one working cycle is equal, C t satisfy:

[0032]

[0033] Where ω is the angular frequency, solve the above equation:

[0034]

[0035] From this we can get C cn The equivalent capacitance C t Capacitance:

[0036]

[0037] Step 3.2: The total equivalent capacitance value at the transmitter is:

[0038] C eq =C t +Cu (19)

[0039] According to the primary side equivalent capacitance value obtained in step 2, the feedback value of the adjustment angle θ can be obtained by obtaining the relationship between the adjustment angle θ and the primary side equivalent capacitance value.

[0040] Step 4 is implemented according to the following steps:

[0041] According to the obtained θ feedback value, it is converted into a voltage value through equation (15):

[0042]

[0043] By comparing this voltage value, the opposite value of this voltage and the normalized sinusoidal voltage across the primary capacitor, a PWM wave is obtained. By adding the PWM wave to both ends of the switch tubes S5 and S6 and controlling their on and off, the total capacitance value on the primary side is adjusted to near the capacitance value required to make the circuit resonate, thereby compensating the circuit and restoring the resonant state.

[0044] The beneficial effect of the present invention is that an automatic tuning system and tuning method based on current and voltage detection at the transmitting end controls the charging and discharging time of the capacitor by adjusting the on and off time of the switch tubes at both ends connected in series with the phase-controlled capacitor, thereby realizing stepless adjustment of the equivalent capacitance value of the phase-controlled capacitor, so that the equivalent capacitance value of the transmitting end can be changed within a certain range by adjustment. At this time, the capacitance is no longer a fixed value. By observing the current and voltage at the transmitting end, the estimated value of the mutual inductance in the non-resonant state can be obtained, and there is no need to measure the offset distance and offset angle between the coils. After obtaining the estimated value of the mutual inductance, the combined phase-controlled tuning method can realize automatic adjustment of the working state of the system to restore it to a resonant state. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the circuit diagram of SP type wireless power transmission system;

[0046] Figure 2 It is a phase-controlled capacitor tuning circuit;

[0047] Figure 3 It is the schematic diagram of the phase-controlled capacitor tuning circuit;

[0048] Figure 4 It is the control waveform diagram of the phase-controlled capacitor tuning circuit;

[0049] Figure 5 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0050] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] The circuit diagram of SP type wireless power transmission system is as follows Figure 1 As shown. DC power supply U d Converted into high-frequency AC power U through H-bridge inverter s , whose frequency is the same as the natural frequency of the system, so that both the transmitter and the receiver are in a resonant state, efficiently supplying power to the load R L Transfer energy. R1 and R2 are the equivalent series internal resistance of inductors L1 and L2 respectively, C1 and C2 are compensation capacitors, and M is the mutual inductance between the coils. Phase-controlled capacitor tuning circuit is shown in Figure 2 As shown, it includes two switching tubes connected in series with a capacitor. The schematic diagram of the phase-controlled capacitor tuning circuit is shown in Figure 3 As shown, switch tube S1 and switch tube S2 operate complementary, switch tube S3 and switch tube S4 operate complementary, when S1 and S4 are turned on, S2 and S3 are turned off, and vice versa, a square wave is generated. S5 and S6 jointly control the charging and discharging of the capacitor. The control waveform of the phase-controlled capacitor tuning circuit is shown in Figure 4 shown.

[0052] Combination Figure 5 , assuming the inherent resonant angular frequency is ω. The impedance Z1 of the transmitter loop of the series-parallel compensation network is:

[0053]

[0054] In formula (1), L1 is the inductance of the transmitting coil, C1 is the compensation capacitor value on the transmitting side, and R1 is the total resistance value on the transmitting side.

[0055] The receiving end loop impedance Z2 is:

[0056]

[0057] In formula (2), L2 is the inductance of the receiving coil, C2 is the compensation capacitor value of the receiving side, R2 is the total resistance value of the receiving side, and R L is the load value.

[0058] To make the receiving side in resonance, that is, ω 2 L2C2=1, then the reflected impedance Z of the primary side coupled to the secondary side r for:

[0059]

[0060] In formula (3), M is the mutual inductance between the transmitting and receiving coils.

[0061] To make the transmitting side also in resonance, it is necessary to make Im(Z 11 )=0, where Z 11 It is the total impedance value of the transmitting side after adding the reflected impedance.

[0062]

[0063] The compensation capacitance value G1 on the transmitter side is solved as:

[0064]

[0065] That is, the compensation capacitance value G1 satisfies the above formula to put the transmitter into a resonant state.

[0066] The system operating frequency is high, and the internal resistance of the primary and secondary inductors can be ignored to simplify the analysis. Formula (5) can be simplified as follows:

[0067]

[0068] When the resonant angular frequency, the inductance of the transmitting side and the inductance of the receiving side remain unchanged, the compensation capacitance value of the transmitting end to achieve resonance is only related to the mutual inductance value. According to the mutual inductance value of the coil in the resonant state, the compensation capacitance required by the transmitting side coil can be obtained. Therefore, a mutual inductance estimation method based on transmitting end detection is proposed.

[0069] In the resonant state, the transmitter and receiver satisfy:

[0070] ω 2 L2C2=1,ω 2 L1C1=1 (7)

[0071] The reflected impedance Z from the receiving end to the transmitting end is equivalent to r for:

[0072]

[0073] According to equations (1), (2), (7), and (8), the total input impedance Z at the transmitter can be obtained: 11 for

[0074]

[0075] Input impedance Z 11 It can be detected at the transmitter end and the input voltage u can be measured. s The fundamental amplitude of the input voltage U on the transmitting side can be obtained by adding the current i1 on the receiving coil s , the fundamental amplitude I1 of the current on the transmitting coil and the phase difference between the input voltage and the current on the transmitting coil Then the magnitude of the input impedance |Z 11 |=U s / I1, impedance angle Then Z 11 It can be expressed as:

[0076]

[0077] Combining equations 10 and 11, we can get

[0078]

[0079]

[0080] Therefore, the estimated value of mutual inductance based on transmitter detection can be obtained according to the formula:

[0081]

[0082] After obtaining the estimated value of mutual inductance, the equivalent capacitance value that makes the transmitting side resonate can be obtained.

[0083]

[0084] The essence of the phase-controlled capacitor tuning method is to make the fixed capacitor become an adjustable capacitor through a series switch tube, so that the capacitance value can be adjusted steplessly. Figure 1 As shown in Figure 1, the equivalent capacitance value can be controlled by controlling the on and off of the switch tube. The control waveform of the switch tube is as follows: Figure 2 shown.

[0085] The H-bridge inverter circuit generates an alternating square wave signal. This square wave voltage signal is applied to both ends of AB and passes through L d and C u After filtering, the voltage loaded on both ends of the phase-controlled capacitor tuning circuit A and C is a sinusoidal periodic voltage. Assuming that the amplitude of the sinusoidal voltage is U ac Let θ be the phase angle, which is mapped on the sinusoidal periodic voltage waveform at both ends of A and C as a comparison voltage U dc . in U ac Positive half cycle, when the phase angle mapping comparison voltage U dc Less than U ac At this time, the positive half cycle capacitor C cn The charging and discharging S5 is turned off, so the capacitor stops charging, and the voltage U across A and C ac Stable in U dc Similarly, in U ac Negative half cycle, U ac Less than voltage-U dc At this time, the negative half-cycle capacitor C cn The charging and discharging S6 is turned off, so the capacitor stops charging, and the voltage U across A and C ac Stable in -U dc constant.

[0086] The switch tube (including two switch tubes connected in series with the capacitor) in the present invention has four operating states:

[0087] State 1 (0-θ), such as Figure 4As shown, the switch tube S2 and the switch tube S3 are turned on, the switch tube S1 and the switch tube S4 are turned off, and the capacitor C cn The charge and discharge of is completely controlled by the switch tube S5. When the switch tube S5 is turned on, D6 is forward-conducted, and the capacitor C cn Charge;

[0088] State 2 (θ-π-θ), such as Figure 4 As shown, the switch tube S2 and the switch tube S3 are turned on, the switch tube S1 and the switch tube S4 are turned off, and the capacitor C cn The charge and discharge of is completely controlled by the switch tube S5. When the switch tube S5 is turned off, D6 is forward-conducted, and the capacitor C cn Stop charging, the voltage across the terminals is U dc ;

[0089] State 3 (π-π+θ), such as Figure 4 As shown, the switch tube S1 and the switch tube S4 are turned on, the switch tube S2 and the switch tube S3 are turned off, and the capacitor C cn The charge and discharge of is completely controlled by the switch tube S6. When the switch tube S6 is turned on, D5 is forward-conducted, and the capacitor C cn Charge;

[0090] State 4 (π+θ-2π-θ), such as Figure 4 As shown, the switch tube S1 and the switch tube S4 are turned on, the switch tube S2 and the switch tube S3 are turned off, and the capacitor C cn The charge and discharge of is completely controlled by the switch tube S6. When the switch tube S6 is turned off, D5 is forward-conducted, and the capacitor C cn Stop charging, the voltage across the terminals is -U dc ;

[0091] Since the voltage waveform is a sine wave, according to Figure 4 , phase angle θ and U dc , U ac The relationship between

[0092]

[0093] According to the absolute value of the charge of the capacitor in one working cycle is equal, C t satisfy:

[0094]

[0095] Where ω is the angular frequency. Solve the above equation:

[0096]

[0097] From this we can get C cn The equivalent capacitance C t Capacitance:

[0098]

[0099] Total equivalent capacitance value at the transmitter:

[0100] C eq =C t +C u (19)

[0101] In this way, the total equivalent capacitance on the primary side can be adjusted by adjusting the value of θ.

[0102] The research of the present invention is beneficial to solving two problems: one is to use a phase-controlled capacitor tuning method to make a fixed capacitor equivalent to a variable capacitor controlled by a switch tube to compensate for changes in the parameters of the transmitter circuit; the other is to use a mutual inductance estimation method based on current and voltage detection at the transmitter, and obtain an estimated value of the mutual inductance in the non-resonant state by detecting the current and voltage in the non-resonant state, and then use a phase-controlled capacitor tuning method based on the mutual inductance estimation value to put the system in a resonant state.

Claims

1. An automatic tuning method based on current and voltage detection at the transmitting end, characterized in that: Follow the steps below to implement it: Step 1: The compensation capacitor on the primary side of the wireless power transmission circuit is connected in series with the transmitting coil, and the compensation capacitor on the secondary side of the circuit is connected in parallel with the receiving coil. First, the DC power supply U d The output DC power passes through the H bridge formed by S1-S4. In the H bridge, S1 and S4 have the same drive signal 1, S2 and S3 have the same drive signal 2, and the drive signal 1 and the drive signal 2 are complementary. Therefore, the DC power U d In the H bridge, the alternating conduction is inverted to an amplitude of ±U d AC power supply U s , the AC power supply U s The frequency of the drive signal 1 and the drive signal 2 is the same; the AC power supply U s Then through the compensation network composed of R1, L1 and C1, R1 is the equivalent internal resistance of the line. When R1 is ignored, C1 and L1 form a series resonant circuit, and its inherent resonant frequency is equal to U s At the same frequency, the primary side circuit enters the resonant state. Similarly, in the secondary side circuit, when R2 is ignored, the receiving coil L2 and capacitor C2 form a parallel resonant circuit, and its inherent resonant frequency is also the same as U s At the same frequency, the secondary circuit is also in a resonant state. M is the mutual inductance between L1 and L2, and M represents the degree of magnetic field connection between the transmitting coil and the receiving coil; Using phase-controlled capacitor tuning circuit and resonant capacitor C u The capacitor C1 is connected in parallel, and the phase-controlled capacitor tuning circuit is composed of the switch tube S5, the capacitor C cn And switch tube S6 are connected in series in sequence, S5 and S6 are anti-series switch tubes, S5 and S6 are anti-parallel diodes D5 and D 6， S5 and S6 control capacitor C cn The time of input circuit, thus controlling C cn The equivalent capacitance value, DC U d The H bridge formed by S1-S4 becomes U s After,U s By S5, S6, D5, D6, C cn , C u And the transmitting coil L1 form a series resonant circuit. By adjusting the control signals of S5 and S6, C cn The time of accessing the circuit is changed, S5, S6 and C cn The equivalent capacitance value of the branch is changed; The voltage and current amplitudes at the transmitting end and the phase difference therebetween are detected, and the estimated value of the mutual inductance between the transmitting end coil and the receiving end coil is obtained by calculating the detected values ​​of the amplitude and the phase difference; The step 1 is specifically implemented according to the following steps: Step 1.1: The initial state of the circuit is the resonant state, and the transmitter and receiver meet the following conditions: oh 2 L2C2=1.ω 2 L1C1=1(7) The reflected impedance Z from the receiving end to the transmitting end is equivalent to r for: The total impedance Z at the transmitter is obtained 11 for Step 1.2: The total impedance of the transmitting side can also be obtained by measuring the input voltage u s The fundamental amplitude of the input voltage U on the transmitting side is obtained by adding the current i1 on the receiving coil s , the fundamental amplitude I1 of the current on the transmitting coil and the phase difference between the input voltage and the current on the transmitting coil Then the transmitting end impedance Z 11 =U s / I1, impedance angle Then the transmitting end impedance Z 11 Another way to express this is: Step 1.3: Equivalently express the two expressions of the total impedance of the primary side, and combine equations (10) and (11) to obtain the relationship between the mutual inductance and the voltage and current amplitudes and the phase difference between them: Therefore, the estimated value of mutual inductance based on transmitter detection is obtained: Step 2: After obtaining the estimated value of the mutual inductance between the two coils, obtain the estimated value of the equivalent capacitance of the transmitting end according to the relationship between the equivalent value of the primary side capacitance and the mutual inductance when resonance occurs in the series-parallel circuit topology; The step 2 is specifically implemented according to the following steps: After obtaining the estimated value of mutual inductance, since the circuit topology is SP type, the equivalent capacitance value that makes the transmitting side resonate is obtained according to the formula, that is, Step 3, according to the relationship between the adjustment angle θ and the primary side equivalent capacitance value in the phase-controlled capacitor tuning method, a θ feedback value of the adjustment capacitance value is obtained; Step 4: Convert the obtained θ feedback value into a certain voltage value, and compare the voltage value, the opposite value of the voltage and the normalized sinusoidal voltage across the primary capacitor to obtain a PWM wave. Add the PWM wave to the switch tubes S5 and S6 to control their on and off, and the required primary side equivalent capacitance value is obtained to compensate the circuit.

2. The automatic tuning method based on transmitting end current and voltage detection according to claim 1, characterized in that: The step 3 is specifically implemented according to the following steps: Step 3.1, after obtaining the estimated value of the equivalent capacitance of the transmitter, use the phase-controlled capacitance tuning method to adjust the θ value so that the capacitance of the transmitter is adjusted to the estimated value of the equivalent capacitance. According to the absolute value of the charge of the capacitor in one working cycle is equal, C t satisfy: Where ω is the angular frequency, solve the above equation: From this we can get C cn The equivalent capacitance C t Capacitance: Step 3.2: The total equivalent capacitance value at the transmitter is: C eq =C t +C u (19) According to the primary side equivalent capacitance value obtained in step 2, the feedback value of the adjustment angle θ can be obtained by obtaining the relationship between the adjustment angle θ and the primary side equivalent capacitance value.

3. The automatic tuning method based on transmitting end current and voltage detection according to claim 2, characterized in that: The step 4 is specifically implemented according to the following steps: According to the obtained θ feedback value, it is converted into a voltage value through equation (15): This voltage value, the opposite value of this voltage and the normalized sinusoidal voltage across the primary capacitor are compared to obtain a PWM wave. The PWM wave is added to both ends of the switch tubes S5 and S6 to control their on and off. This will adjust the total capacitance value on the primary side to near the capacitance value required to make the circuit resonate, compensate the circuit, and restore the circuit to a resonant state.

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