Constant voltage output control method of double-pickup wireless power transmission system

Abstract

A constant voltage output control method of a dual-pickup wireless power transmission system adopts a single-emission dual-pickup magnetic coupling mechanism, and a pickup end adopts mutually overlapped Double D coils to eliminate mutual inductance between pickup coils; the rectification module of each pickup circuit is independently connected to a Buck circuit, the two Buck circuits are connected in series, and the output voltage of the load of the dual-pickup wireless power transmission system is the sum of the output voltages of the two Buck circuits; and through a constant-voltage control method for model prediction control of the sliding-mode observer, the sliding-mode observer is used to avoid measurement of inductive current by model prediction control, and the model prediction control is used to control constant-voltage output of the system. Compared with traditional model prediction control, the control method used by the invention reduces acquisition of inductive current, and has very strong robustness for mutual inductance change and reference voltage jump.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless power transmission systems, and in particular to a constant voltage output control method for a dual-pickup wireless power transmission system. Background Art

[0002] Wireless power transmission technology overcomes the safety hazards of traditional wired charging methods in harsh environments and has the advantages of strong portability and high reliability. Among them, dynamic wireless power transmission technology has been widely used in application scenarios such as underwater robots, biomedicine, and electric vehicles due to its advantages such as saving charging time and space, and has become a research hotspot in the field of wireless power transmission.

[0003] Adding dual pickup coils to the pickup end of a wireless power transfer system effectively reduces the voltage and current borne by a single pickup coil, improving the system's robustness against offset. Therefore, dual-pickup wireless power transfer systems offer unique advantages in electrified transportation. A key challenge for dynamic wireless power transfer systems is maintaining a constant voltage output even when the dual pickup ends are moving rapidly.

[0004] Conventional PI control is currently used to achieve constant load-side voltage output. However, PI control produces a certain amount of overshoot during the regulation process, and this control method requires complex wireless communication between the transmitter and the pickup. Poor PI control results in voltage fluctuations on the system load side, failing to meet the system load's requirement for output voltage stability. This complex wireless communication between the transmitter and the pickup not only increases the system's hardware cost, but also makes the wireless communication information transmission susceptible to electromagnetic interference, further causing system load voltage fluctuations.

[0005] A method for dynamically allocating power at dual pickup ends has also been proposed in the prior art, but the constant power wireless power transmission system is rarely used in practice. This method does not achieve constant voltage output of the load. In real life, it is more necessary to achieve constant voltage output on the load side. Therefore, this method has great limitations in application scenarios. In addition, this method does not take system efficiency issues into consideration, which can easily lead to low transmission efficiency of the system.

[0006] Since the dual-pickup wireless power transmission system has two pickup coils, mutual inductance will inevitably be generated between the two pickup coils, which will affect the stable voltage output of the system to a certain extent. Summary of the Invention

[0007] In response to the above-mentioned technical problems of how to eliminate the mutual inductance between the dual pickup coils and how to achieve constant voltage output of the dual pickup wireless power transmission system, the present technical solution provides a constant voltage output control method for a dual pickup wireless power transmission system. The method proposes a single-transmitter dual-pickup magnetic coupling mechanism, and the pickup end uses overlapping DD coils to eliminate the mutual inductance between the pickup coils; the rectifier module of each pickup circuit is independently connected to the Buck circuit, and the two Buck circuits are connected in series. The output voltage of the dual pickup wireless power transmission system load is the sum of the output voltages of the two Buck circuits; a constant voltage control method of sliding mode observer-model predictive control is also proposed, which uses a sliding mode observer to avoid the measurement of the inductor current by model predictive control, and uses model predictive control to control the constant voltage output of the system; effectively solving the above-mentioned problems.

[0008] The present invention is achieved through the following technical solutions:

[0009] A constant voltage output control method for a dual-pickup wireless power transmission system, comprising the steps of:

[0010] Step 1: Use a single-transmitter dual-pickup magnetic coupling mechanism. The dual-pickup coils use overlapping DD coils. The magnetic coupling mechanism coils have a reasonable size and number of turns. When the two pickup coils reach a fixed overlapping distance, the mutual inductance between the dual pickup coils is close to 0.

[0011] Step 2: Analyze the transmission characteristics of the dual-pickup wireless power transmission system. Use an LCC resonant compensation network as the topology of the transmitting coil and an S-type compensation network as the compensation topology of the pickup coil. The rectifier module of each pickup circuit is independently connected to the Buck circuit, and the two Buck circuits are connected in series.

[0012] Step 3: For the dual-pickup wireless power transfer system, an output voltage distribution strategy based on optimal efficiency is proposed. By dynamically adjusting the output voltages of the two pickup circuits, the two pickup circuits cooperate with each other to achieve a constant voltage output of the system.

[0013] Step 4: Use the load voltage control method that combines a sliding mode observer and model predictive control to establish the state space equation of the secondary-side Buck circuit. Based on this model, design a model predictive controller and combine it with a sliding mode observer to achieve stable control of the load voltage.

[0014] Furthermore, the DD coil described in step 1 is a double D-shaped symmetrical coil for a wireless power transmission system, which is composed of an orthogonal combination of two semicircular windings. A superimposed magnetic field is formed in the central area by the same-phase current, and its orthogonal structure can reduce cross-coupling; when the winding directions of the DD coils are consistent, as the distance between the two pickup coils changes, the mutual inductance has a zero-crossing point, that is, the magnetic flux entering each pickup coil is equal to the magnetic flux passing out; the mutual inductance between the transmitting coil and the pickup coil 1 is M1, the mutual inductance between the transmitting coil and the pickup coil 2 is M2, and the mutual inductance between the pickup coil 1 and the pickup coil 2 is M3. When M3 is close to 0, the two pickup coils can be regarded as decoupled.

[0015] Furthermore, the dual-pickup wireless power transmission system described in step 2 includes: a DC input power supply U in MOSFET and diodes are connected in parallel to form switching devices S1-S4, and compensation inductor L p , parallel compensation capacitor C p , series compensation capacitor C1, transmitting coil internal resistance r1, transmitting coil self-inductance L1, pickup coil 1 self-inductance L2, pickup coil 2 self-inductance L3, pickup coil 1 compensation capacitor C2, pickup coil 2 compensation capacitor C3, pickup coil 1 internal resistance r2 and pickup coil 2 internal resistance r3, pickup circuit 1 rectifier circuit, pickup circuit 1 Buck circuit capacitor C4, pickup circuit 1 Buck circuit inductor L4, pickup circuit 1 filter capacitor C f1 , the rectifier circuit of the pickup circuit 2, the Buck circuit capacitor C5 in the pickup circuit 2, the Buck circuit inductor L5 in the pickup circuit 2, the filter capacitor C of the pickup circuit 2 f2 , R L is the system load resistance.

[0016] Furthermore, the dual-pickup wireless power transmission system is simplified, and the simplified operation method is: the DC input power supply U in And the switching devices S1-S4 are equivalent to the AC power supply U o , the rectifier circuit and Buck circuit in the pickup circuit 1 are equivalent to the resistor R1, the rectifier circuit and Buck circuit in the pickup circuit 2 are equivalent to the resistor R2, I1 is the current through the inductor L p I2 is the transmitting current of the primary transmitting coil, I3 is the pickup current of the pickup coil 1, and I4 is the pickup current of the pickup coil 2.

[0017] Furthermore, the efficiency expression of the dual-pickup wireless power transmission system described in step 2 is:

[0018]

[0019] In the above formula, η is the efficiency of the wireless power transmission system, P L0is the active power loss of the transmitting coil, P L1 is the active power loss on pickup coil 1, P L2 To pick up the active power loss on coil 2, the output power of the wireless power transmission system is P out .

[0020] Furthermore, the specific operation steps of step three include:

[0021] Step 3.1: Let the duty cycle of the Buck circuit in pickup circuit 1 be D1, the duty cycle of the Buck circuit in pickup circuit 2 be D2, and let the ratio of the Buck module duty cycles of pickup circuit 1 and pickup circuit 2 be β, then

[0022]

[0023] Step 3.2: Let the active power loss on the pickup coil 1 be P L1 , the active power loss on the pickup coil 2 is P L2 , the output power of the dual-pickup wireless power transmission system is P out , r2 is the internal resistance of pickup coil 1, r3 is the internal resistance of pickup coil 2, I2 is the transmitting current of the primary transmitting coil, ω is the angular frequency, M1 is the mutual inductance between the transmitting coil and pickup coil 1, M2 is the mutual inductance between the transmitting coil and pickup coil 2, then the total pickup coil loss P of the dual pickup wireless power transmission system is LOSS for:

[0024]

[0025] Step 3.3: When P LOSS When it is minimum, the transmission efficiency of the dual pickup wireless power transmission is the highest, and the total power loss of the pickup coil P LOSS Derivative of the duty cycle ratio β, β max is the ratio of the Buck circuit duty cycle corresponding to the optimal transmission efficiency of the dual-pickup wireless power transmission system:

[0026]

[0027] Step 3.4: To optimize the transmission efficiency of the dual-pickup wireless power transmission system, the duty cycle ratio β should be equal to β max , assuming the output voltage target value of the dual-pickup wireless power transmission system is U T , the voltage target value of pickup coil 1 is U T1 , the voltage target value of pickup coil 2 is U T2 , then the voltage target value of each pickup coil is:

[0028]

[0029] Step 3.5: Assume that the actual output voltages of pickup circuit 1 and pickup circuit 2 are U R1 and U R2 , load R L The voltage on the R , so that the actual output voltage of the dual-pickup wireless power transmission system and the set voltage value are always kept equal, the load voltage U R Equal to U T , the output voltage U of the pickup coil 1 R1 Equal to the voltage target value U of the pickup coil 1 T1 , the output voltage U of the pickup coil 2 R2 Equal to the voltage target value U of the pickup coil 2 T2 , that is, constant voltage output under optimal efficiency can be achieved;

[0030]

[0031] Furthermore, the specific operation steps of step 4 are:

[0032] Step 4.1: Discretize the continuous-time model using the Buck circuit to obtain a discrete model of the Buck circuit, and analyze the state update equation and output equation of the discrete model of the Buck circuit; the state update equation and output equation of the discrete model of the Buck circuit are:

[0033]

[0034] In the above formula, k represents the kth sampling moment, which is used to mark the discretized time series, and k+1 corresponds to the next sampling moment; T s is the sampling period, i.e., the discretized time interval; L is the Buck circuit inductance, C is the Buck circuit capacitance, and R is the load resistance; S(k) is the switch state function at the kth moment, i L (k) is the inductor current at the kth moment; i L (k+1) is the inductor current at the k+1th moment, V out (k) is the output voltage at the kth moment, V out (k+1) is the output voltage at the k+1th moment, V in Input voltage for the Buck circuit;

[0035] Step 4.2: Model the sliding-mode observer based on the Buck circuit and analyze the inductor current observation value in the Buck circuit. Use the fourth-order Runge-Kutta method to integrate the state variables to update the observation value. Calculate k1 and k2 for the inductor current observation value, which is shown in the following formula:

[0036]

[0037] In the above formula, di L / dt represents the instantaneous rate of change of the inductor current at the kth moment, k1 represents the contribution of the derivative to the inductor current at the kth moment, and k2 represents the k+T s / 2The contribution of the derivative to the inductor current;

[0038] Step 4.3: Pass the observed Buck circuit inductor current to the model predictive controller to reduce the need for model predictive control to measure the inductor current.

[0039] Step 4.4: Based on the model predictive control constant voltage control method of the Buck circuit, the model predictive control adjusts the duty cycle of the Buck circuit.

[0040] Furthermore, the model predictive control described in step 4.4 uses the system's mathematical model to predict system behavior and make adjustments. First, the system model is predicted, then the system is optimized in a rolling manner, and finally the system is corrected by feedback. Model predictive control can accurately predict the dynamic response of the system and exhibit greater robustness to internal and external disturbances.

[0041] The discretized output voltage prediction equation is:

[0042]

[0043] In the above formula, It is the output voltage predicted for the next step, with a duty cycle range of [0,1], S test is the duty cycle of the current test, V out is the output voltage;

[0044] The voltage tracking error term is:

[0045]

[0046] In the above formula, e(k) represents the voltage tracking error, Indicates the output voltage predicted at the k+1th moment, U ref Indicates the reference voltage value;

[0047] γ is the penalty coefficient, and the penalty term for control quantity change is:

[0048] Δμ(k)=γ|S test -S(k-1)|;

[0049] In the above formula, △μ(k) represents the penalty term for control variable change, and S(k-1) is the actual switching state;

[0050] The comprehensive objective function balances voltage tracking performance and control smoothness, and the total cost function is set to J(k):

[0051] J(k)=e(k)+Δu(k);

[0052] In the above formula, J(k) is the total cost function;

[0053] Among all the test duty cycles, select the duty cycle S with the smallest total cost J(k) test (arg) is used as the optimal duty cycle of the Buck circuit, and we get:

[0054] S test (arg) = argminJ(k);

[0055] In the above formula, S test (arg) represents the duty cycle with the minimum total cost, and argmin represents the minimization function.

[0056] Beneficial effects

[0057] The constant voltage output control method for a dual-pickup wireless power transmission system proposed in the present invention has the following beneficial effects compared with the prior art:

[0058] (1) The present invention proposes a single-transmitter dual-pickup magnetic coupling mechanism, and the pickup end adopts overlapping DD coils to achieve decoupling between the dual pickup coils and eliminate the mutual inductance between the pickup coils; the rectifier module of each pickup circuit is independently connected to the Buck circuit, and the two Buck circuits are connected in series. The output voltage of the dual-pickup wireless power transmission system load is the sum of the output voltages of the two Buck circuits; a sliding mode observer-model predictive control constant voltage control method is also proposed, which uses a sliding mode observer to avoid the measurement of the inductor current by the model predictive control, and uses the model predictive control to control the system constant voltage output; compared with the traditional model predictive control, the method used by the present invention reduces the acquisition of the inductor current, not only has no overshoot, but also has a fast adjustment speed, and has strong robustness to changes in mutual inductance and sudden changes in reference voltage.

[0059] (2) The technology of the present invention can not only realize the constant voltage output of the dual-pickup wireless power transmission system, but also propose a voltage distribution strategy based on optimal efficiency. While realizing the constant voltage output of the system, the efficiency optimum point is analyzed to obtain the ratio of the Buck circuit duty cycles in the two pick-up circuits when the efficiency is optimal, and the corresponding pick-up circuit output voltage is calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a coupling structure diagram of the dual-pickup wireless power transmission system in the present invention.

[0061] Figure 2 This is a position distribution diagram of each coil in the dual-pickup wireless power transmission system of the present invention.

[0062] Figure 3This is a structural diagram of the dual-pickup wireless power transmission system in the present invention.

[0063] Figure 4 FIG. 4 is an equivalent circuit diagram of the dual-pickup wireless power transmission system of the present invention.

[0064] Figure 5 This is a block diagram of the Buck circuit based on sliding mode observer-model predictive control in the present invention.

[0065] Figure 6 This is the voltage waveform output by the pickup circuit 1 when the reference voltage suddenly changes.

[0066] Figure 7 This is the voltage waveform output by the pickup circuit 2 when the reference voltage suddenly changes. DETAILED DESCRIPTION

[0067] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Under the premise of not departing from the design concept of the present invention, various modifications and improvements made by ordinary persons in this field to the technical solutions of the present invention should fall within the scope of protection of the present invention.

[0068] Example 1:

[0069] A constant voltage output control method for a dual-pickup wireless power transmission system, comprising the steps of:

[0070] Step 1: Use a single-transmitter, dual-pickup magnetic coupling mechanism. The dual-pickup coils use overlapping DD coils. DD coils are double D-shaped symmetrical coils used in wireless power transmission systems. They are composed of two orthogonal semicircular windings. They form a superimposed magnetic field in the center area through in-phase currents. Their orthogonal structure can reduce cross-coupling. The magnetic coupling mechanism coils use a reasonable size and number of turns. When the two pickup coils achieve a fixed overlapping distance, the mutual inductance between the dual pickup coils is close to zero.

[0071] When the winding directions of the DD coils are consistent, as the distance between the two pickup coils changes, the mutual inductance between the DD coils has a zero-crossing point, that is, the magnetic flux entering each pickup coil is equal to the magnetic flux passing out; Figure 1 The figure below shows the coupled structure of a dual-pickup wireless power transfer system. The mutual inductance between the transmitting coil and pickup coil 1 is M1, the mutual inductance between the transmitting coil and pickup coil 2 is M2, and the mutual inductance between pickup coil 1 and pickup coil 2 is M3. When M3 approaches zero, the two pickup coils are considered decoupled. The parameters of the transmitting and pickup coils are shown in Table 1. Given the coil dimensions and number of turns, the decoupling overlap length between the two pickup coils is 0.045m.

[0072] Table 1 Simulation parameters of electromagnetic coupling mechanism

[0073] parameter Numerical Transmitting coil size / m 0.2×0.2 Transmitting coil turns 16 Receiving coil 1 size / m 0.2×0.2 Receiving coil 2 size / m 0.2×0.2 Receiving coil 1 turns 16 Receiving coil 2 turns 16 Air gap / m 0.06 Overlap distance / m 0.045

[0074] When the air gap between the transmitting coil and the pickup coil is 0.06m, the distribution positions of the coils are as follows: Figure 2 As shown, the self-inductance and mutual inductance of each coil are shown in Table 2.

[0075] Table 2 Self-inductance and mutual inductance of each coil in the simulation model

[0076] parameter Numerical <![CDATA[L P1 / μH]]> 80.6802 <![CDATA[L P2 / μH]]> 80.6821 <![CDATA[M1 / μH]]> 13.6472 <![CDATA[M2 / μH]]> 17.3762 <![CDATA[M3 / μH]]> 0.039

[0077] In the table, L P1 is the self-inductance of pickup coil 1, L P2 is the self-inductance of the pickup coil 2, M1 is the mutual inductance between the pickup coil 1 and the transmitting coil, M2 is the mutual inductance between the pickup coil 1 and the transmitting coil, and M3 is the mutual inductance between the pickup coil 1 and the pickup coil 2. As shown in Table 2, the mutual inductance M3 between the pickup coils is almost 0, which means that the two pickup coils are decoupled from each other.

[0078] Step 2: Analyze the transmission characteristics of the dual-pickup wireless power transmission system, use the LCC resonant compensation network as the topology of the transmitting coil, and the S-type compensation network as the compensation topology of the pickup coil. The rectifier module of each pickup circuit is independently connected to the Buck circuit, and the two Buck circuits are connected in series. The structural block diagram of the dual-pickup wireless power transmission system is as follows: Figure 3 shown.

[0079] like Figure 3 As shown, the dual-pickup wireless power transmission system includes: a DC input power supply U in MOSFET and diodes are connected in parallel to form switching devices S1-S4, and compensation inductor L p , parallel compensation capacitor C p , series compensation capacitor C1, primary coil internal resistance r1, transmitting coil self-inductance L1, pickup coil 1 self-inductance L2, pickup coil 2 self-inductance L3, pickup coil 1 compensation capacitor C2, pickup coil 2 compensation capacitor C3, pickup coil 1 internal resistance r2 and pickup coil 2 internal resistance r3, pickup circuit 1 rectifier circuit, pickup circuit 1 Buck circuit capacitor C4, pickup circuit 1 Buck circuit inductor L4, pickup circuit 1 filter capacitor C f1 , the rectifier circuit of the pickup circuit 2, the Buck circuit capacitor C5 in the pickup circuit 2, the Buck circuit inductor L5 in the pickup circuit 2, the filter capacitor C of the pickup circuit 2 f2 , R L is the system load resistance.

[0080] System DC input power supply U inThe high-frequency inverter network uses switching devices S1-S4 composed of MOSFET tubes and diodes in parallel. The output current of the high-frequency inverter network passes through the LCC composite resonant compensation network to form a constant current on the transmitting coil L1. The internal resistance of the transmitting coil is r1. The LCC composite resonant compensation network consists of the compensation inductor L p , parallel compensation capacitor C p , composed of series compensation capacitor C1.

[0081] The self-inductance L2 of the pickup coil 1 is connected in series with the compensation capacitor C2, and the self-inductance L3 of the pickup coil 2 is connected in series with the compensation capacitor C3. The two pickup coils are used to couple the magnetic field energy of the transmitting coil. The internal resistance of the pickup coil 1 is r3, and the internal resistance of the pickup coil 2 is r3.

[0082] The AC induced voltage picked up by the pickup coil 1 is converted into DC power through the rectifier circuit of the pickup circuit 1. The DC power is connected to the input side of the Buck circuit. The Buck circuit of the pickup circuit 1 consists of capacitor C4, inductor L4 and filter capacitor C f1 The AC induced voltage picked up by the pickup coil 2 is converted into DC power through the rectifier circuit of the pickup circuit 2. The DC power is connected to the input side of the Buck circuit. The Buck circuit of the pickup circuit 2 consists of capacitor C5, inductor L5 and filter capacitor C f2 The Buck circuit outputs of pickup circuit 1 and pickup circuit 2 are connected in series to the system load resistor R L , that is, the output voltage of the two parts is the load resistance R L powered by.

[0083] The double-pickup wireless power transmission system is simplified equivalently. The equivalent simplified circuit diagram of the double-pickup wireless power transmission system is as follows: Figure 4 As shown, the DC input power supply U in And the switching devices S1-S4 are equivalent to the AC power supply U o , the rectifier circuit and Buck circuit in the pickup circuit 1 are equivalent to the resistor R1, the rectifier circuit and Buck circuit in the pickup circuit 2 are equivalent to the resistor R2, I1 is the current through the inductor L p I2 is the transmitting current of the primary transmitting coil, I3 is the pickup current of the pickup coil 1, and I4 is the pickup current of the pickup coil 2.

[0084] According to the KVL law, Figure 4 The circuit shown in the figure lists the fundamental circuit equation, which is:

[0085]

[0086] In the above formula, ω is the angular frequency and j represents an imaginary number.

[0087] The current flowing through each inductor in the resonant state of the system is:

[0088]

[0089] Input voltage U of the rectifier module of the pickup circuit 1 Z0 And the input voltage U of the rectifier module of the pickup circuit 2 Z1 They are:

[0090]

[0091] Output voltage U of the rectifier module of the pickup circuit 1 Z2 And the output voltage U of the rectifier module of the pickup circuit 2 Z3 They are:

[0092]

[0093] Using Buck step-down circuit, let the output voltages of pickup circuit 1 and pickup circuit 2 be U R1 and U R2 , then the following relationship is satisfied:

[0094]

[0095] Wherein, D1 is the duty cycle of the Buck circuit in pickup circuit 1, and D2 is the duty cycle of the Buck circuit in pickup circuit 2.

[0096] Since the two pickup circuits are connected in series, the voltage on the load should be the sum of the output voltages of the two pickup circuits. L Voltage U on R for:

[0097]

[0098] Assume that the ratio of the Buck module duty cycles of pickup circuit 1 and pickup circuit 2 is β, then:

[0099]

[0100] The output powers P1 and P2 of pickup circuit 1 and pickup circuit 2 are:

[0101]

[0102] The total output power of the system is the sum of the output powers of the two pickup circuits. The total output power of the system is P out for:

[0103]

[0104] Assume that the active power loss on the transmitting coil is P L0 , the active power loss on the pickup coil 1 is PL1 , the active power loss on the pickup coil 2 is P L2 , then the active power loss on each coil is:

[0105]

[0106] The efficiency expression of the dual-pickup wireless power transmission system is obtained as:

[0107]

[0108] In the above formula, η is the efficiency of the wireless power transmission system.

[0109] Step 3: For the dual-pickup wireless power transfer system, an output voltage distribution strategy based on optimal efficiency is proposed. By dynamically adjusting the output voltages of the two pickup circuits, the two pickup circuits cooperate with each other to achieve a constant voltage output of the system.

[0110] For a dual-pickup wireless power transfer system, the output voltages of the two pickup circuits can be dynamically adjusted to coordinate with each other, achieving a constant voltage output. However, for a given output voltage target, there are countless possible combinations of the output voltages of the two pickup circuits. These different output voltage combinations result in different system transmission efficiencies, meaning that each β value corresponds to a different system transmission efficiency.

[0111] An output voltage distribution strategy is proposed for a dual-pickup wireless power transmission system to ensure that the system always maintains a constant voltage output. The total power of the system is mainly composed of three parts: output power, transmission rail loss power, and pickup coil loss power. Among them, the only variable loss of the system is the loss of the pickup coil. To maximize the system's transmission efficiency, the loss of the two pickup coils should be minimized. The specific operation steps include:

[0112] Step 3.1: Let the duty cycle of the Buck circuit in pickup circuit 1 be D1, the duty cycle of the Buck circuit in pickup circuit 2 be D2, and let the ratio of the Buck module duty cycles of pickup circuit 1 and pickup circuit 2 be β. Then:

[0113]

[0114] Step 3.2: Let the active power loss on the pickup coil 1 be P L1 , the active power loss on the pickup coil 2 is P L2 , the output power of the dual-pickup wireless power transmission system is P out, r2 is the internal resistance of pickup coil 1, r3 is the internal resistance of pickup coil 2, I2 is the transmitting current of the primary transmitting coil, ω is the angular frequency, M1 is the mutual inductance between the transmitting coil and pickup coil 1, M2 is the mutual inductance between the transmitting coil and pickup coil 2, then the total pickup coil loss P of the dual pickup wireless power transmission system is LOSS for:

[0115]

[0116] Step 3.3: When P LOSS When it is minimum, the transmission efficiency of the dual pickup wireless power transmission is the highest, and the total power loss of the pickup coil P LOSS Derivative of the duty cycle ratio β,

[0117]

[0118] In the above formula, d represents the differential operation;

[0119] β max is the ratio of the Buck circuit duty cycles corresponding to the optimal transmission efficiency of the dual-pickup wireless power transmission system; the expression for the ratio of the Buck module duty cycles of the pickup circuit βmax that optimizes the system transmission efficiency is:

[0120]

[0121] Step 3.4: To optimize the transmission efficiency of the dual-pickup wireless power transmission system, the duty cycle ratio β should be equal to β max , assuming the output voltage target value of the dual-pickup wireless power transmission system is U T , the voltage target value of pickup coil 1 is U T1 , the voltage target value of pickup coil 2 is U T2 , then the voltage target value of each pickup coil is:

[0122]

[0123] If different pickup circuits are to output the set voltage target value at all times, the mutual inductance M1 and M2 of the system in each state must be known. Therefore, M1 and M2 need to be estimated; the estimation formula is:

[0124]

[0125] To know the magnitude of mutual inductance M1 and M2, you only need to measure the output voltage and current I2 of the two rectifier modules. Current I2 is the current of the system's transmitting coil, which basically does not change after the system parameters are fixed. It can be measured in the initial state of operation to avoid wireless communication between the transmitter and the receiver.

[0126] Step 3.5: Assume that the actual output voltages of pickup circuit 1 and pickup circuit 2 are U R1 and U R2 , load R L The voltage on the R , so that the actual output voltage of the dual-pickup wireless power transmission system and the set voltage value are always kept equal, the load voltage U R Equal to U T , the output voltage U of the pickup coil 1 R1 Equal to the voltage target value U of the pickup coil 1 T1 , the output voltage U of the pickup coil 2 R2 Equal to the voltage target value U of the pickup coil 2 T2 , that is, constant voltage output under optimal efficiency can be achieved;

[0127]

[0128] Step 4: Use the load voltage control method that combines a sliding mode observer and model predictive control to establish the state space equation of the secondary-side Buck circuit. Based on this model, design a model predictive controller and combine it with a sliding mode observer to achieve stable control of the load voltage.

[0129] Use the sliding mode observer-model predictive control method to adjust the Buck circuit duty cycle to achieve the load voltage U R Equal to the output voltage target value U T , the output voltage U of the pickup coil 1 R1 Equal to the voltage target value U of the pickup coil 1 T1 , the output voltage U of the pickup coil 2 R2 Equal to the voltage target value U of the pickup coil 2 T2 .

[0130] The load voltage U R Equal to the output voltage target value U T As the control target, the U is controlled by adjusting the duty cycle of the Buck circuit. R1 and U R2 control, and finally achieve U R Equal to U T To implement model predictive control to adjust the Buck circuit duty cycle, it is first necessary to establish a mathematical model of the controlled object. The specific steps are:

[0131] Step 4.1: Discretize the continuous-time model through the Buck circuit to obtain the discrete model of the Buck circuit, and analyze the state update equation and output equation of the discrete model of the Buck circuit. The discrete model of the Buck circuit can be obtained by discretizing the continuous-time model, where the continuous-time model is composed of the inductor current i L(t) and output voltage V out (t) is described by the dynamic equation.

[0132]

[0133] Among them, V in is the Buck circuit input voltage, i L is the inductor current, V out is the output voltage of the Buck circuit, S(t) is the switch state function; di L (t) / dt represents the rate of change of the inductor current with time t; dV out (t) / dt represents the rate of change of output voltage with time t.

[0134] Applying the forward Euler method to the continuous-time model of the Buck circuit, we obtain the discretization equations for the inductor current and the output voltage:

[0135]

[0136] In the above formula, k represents the kth sampling moment, which is used to mark the discretized time series, and k+1 corresponds to the next sampling moment. s is the sampling period, i.e. the discretized time interval; S(k) is the switch state function at the kth moment, i L (k) is the inductor current at the kth moment; i L (k+1) is the inductor current at the k+1th moment, V out (k) is the output voltage at the kth moment, V out (k+1) is the output voltage at the k+1th moment. Figure 5 As shown, L is the Buck circuit inductor, C is the Buck circuit capacitor, and R is the load resistance.

[0137] Write the above discretization results into state space form to obtain the state variable X(k) and the state update equation X(k+1);

[0138]

[0139] Among them, the state matrix A and input matrix B are:

[0140]

[0141] The state update equation and output equation of the discrete model of the Buck circuit are:

[0142]

[0143] Step 4.2: Model the sliding mode observer based on the Buck circuit and analyze the observed value of the inductor current in the Buck circuit;

[0144] Define state variables X and observation state variables for:

[0145]

[0146] The observation error e of the output voltage is defined as:

[0147]

[0148] Define the smoothing function sgn, where δ is the sliding mode smoothing coefficient:

[0149]

[0150] The derivative of the inductor current observation and the derivative of the output voltage observation are:

[0151]

[0152] Where K is the sliding mode gain.

[0153] The fourth-order Runge-Kutta method is used to integrate the state variables to update the observation value. For the inductor current observation value, k1 and k2 are calculated, where T S is the control period, and the inductor current observation value is:

[0154]

[0155] In the above formula, di L / dt represents the instantaneous rate of change of the inductor current at the kth moment, k1 represents the contribution of the derivative to the inductor current at the kth moment, and k2 represents the k+T s / 2 is the contribution of the derivative to the inductor current.

[0156] Step 4.3: Pass the observed Buck circuit inductor current to the model predictive controller to reduce the measurement of the inductor current by the model predictive controller.

[0157] Step 4.4: Based on the model predictive control constant voltage control method of the Buck circuit, the model predictive control adjusts the duty cycle of the Buck circuit.

[0158] Model predictive control uses the mathematical model of the system to predict system behavior and make adjustments. First, the system model is predicted, then the system is rolled optimized, and finally the system is feedback corrected. Model predictive control can accurately predict the dynamic response of the system and show greater robustness when disturbances occur inside and outside the system.

[0159] It is the output voltage predicted for the next step, with a duty cycle range of [0,1], Stest is the duty cycle of the current test, T s is the system control period, and the discretized output voltage prediction equation is:

[0160]

[0161] In the above formula, It is the output voltage predicted for the next step, with a duty cycle range of [0,1], S test is the duty cycle of the current test, T s is the system sampling period; i L is the inductor current.

[0162] The voltage tracking error term is:

[0163]

[0164] In the above formula, represents the output voltage predicted at the k+1th moment; e(k) represents the voltage tracking error, U ref Indicates the reference voltage value.

[0165] γ is the penalty coefficient, and the penalty term for control quantity change is:

[0166] Δμ(k)=γ|S test -S(k-1)|;

[0167] In the above formula, △μ(k) represents the penalty term for control quantity change, and S(k-1) is the actual switching state.

[0168] The comprehensive objective function balances voltage tracking performance and control smoothness, and the total cost function is set to J(k):

[0169] J(k)=e(k)+Δu(k);

[0170] In the above formula, J(k) is the total cost function, e(k) represents the voltage tracking error, and △μ(k) represents the penalty term for control quantity change.

[0171] Among all the test duty cycles, select the duty cycle S with the smallest total cost J(k) test (arg) is used as the optimal duty cycle of the Buck circuit, and we get:

[0172] S test (arg) = argminJ(k);

[0173] In the above formula, S test (arg) represents the duty cycle with the minimum total cost, and argmin represents the minimization function.

[0174] In order to verify the superiority of the improved sliding mode observer-model predictive control of the dual-pickup wireless power transfer system, the inventors conducted simulation verification and analysis. The specific process is as follows:

[0175] A simulation model was built in Matlab / Simulink, and the simulation parameters are shown in Table 3. The model predictive control method was compared with two PI controllers with different parameters: the PI_1 controller parameters were set to P = 1.225 and I = 1750, and the PI_2 controller parameters were set to P = 0.57 and I = 156. The sliding mode gain K and the sliding mode smoothing coefficient δ affect the observation effect of the sliding mode observer, while the penalty coefficient γ affects the control effect of the model predictive controller.

[0176] Table 3 Circuit simulation parameters of LCC-S dual-pickup WPT system

[0177] parameter Numerical DC power supply / V 200 System natural resonant frequency f / kHz 85 <![CDATA[Self-inductance L1 of transmitting coil / μH]]> 166.9 <![CDATA[Self-inductance L2 / μH of pick-up coil 1]]> 80.68 <![CDATA[Self-inductance L3 / μH of pick-up coil 2]]> 81.54 <![CDATA[Transmitter compensation inductance L p / μH]]> 22 <![CDATA[Parallel compensation capacitor C at the transmitting end p / nF]]> 159.36 <![CDATA[Series compensation capacitor C1 at the transmitting end / nF]]> 24.17 <![CDATA[Pickup end 1 series compensation capacitor C2 / nF]]> 53.01 <![CDATA[Pickup terminal 2 series compensation capacitor C3 / nF]]> 51.38 <![CDATA[Filter capacitor C4 / nF]]> 50 <![CDATA[Filter capacitor C5 / nF]]> 50 <![CDATA[Filter capacitor C f1 / μF]]> 27 <![CDATA[Filter capacitor C f2 / μF]]> 27 <![CDATA[Filter Inductor L4 / μH]]> 120 <![CDATA[Filter Inductor L5 / μH]]> 120 <![CDATA[Load resistance R L / Ω]]> 10 <![CDATA[Internal resistance r1 of the transmitting coil / Ω]]> 0.195 <![CDATA[Internal resistance r2 / Ω of pickup coil 1]]> 0.1826 <![CDATA[Internal resistance r3 / Ω of pickup coil 2]]> 0.1875 Sliding mode gain K 500 Sliding mode smoothing coefficient δ 0.1 Control period Ts 1 / 85000 Penalty coefficient γ 0.01

[0178] Simulation results of reference voltage mutation: Assuming the total system output voltage is 100V, the output voltages of pickup circuit 1 and pickup circuit 2 are evenly distributed before 0.05S, both are 50V. At 0.05S, the mutual inductances M1 and M2 change. It can be calculated that the reference voltage of pickup circuit 1 is 62V, and the reference voltage of pickup circuit 2 is 38V. At this time, this voltage distribution method achieves the best system efficiency. The output voltage waveform of pickup circuit 1 is as follows: Figure 6 As shown, the output voltage waveform of the pickup circuit 2 is as follows Figure 7 shown.

[0179] Conclusion: In order to meet the rapid response requirements of the dual-pickup wireless power transmission system for stable output voltage, the dual-pickup wireless power transmission system is designed and modeled. Overlapping DD coils are proposed to eliminate the mutual inductance between the pickup coils. The output voltage characteristics and transmission efficiency of the system are analyzed, and a constant voltage control strategy based on optimal efficiency is proposed. While achieving constant voltage output of the system, the efficiency optimum point is analyzed, and the ratio of the duty cycles of the two pickup circuit Buck models when the efficiency is optimal is obtained. The corresponding pickup circuit output voltage is calculated.

[0180] Using a load voltage control strategy that combines a sliding-mode observer with model predictive control (MPC), the state-space equations for the secondary-side Buck circuit were established. A MPC was designed based on the Buck circuit, and the sliding-mode observer was used to estimate the Buck circuit's inductor current, eliminating the need for MPC to measure the inductor current. The MPC approach was compared with traditional PI control methods. The results showed that the MPC did not produce overshoot, had significantly faster response than the PI controller, and was more robust to variations in reference voltage and mutual inductance.

[0181] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention shall be covered by the present invention.

Claims

1. A constant voltage output control method for a dual-pickup wireless power transmission system, characterized by: Including steps: Step 1: Use a single-transmitter dual-pickup magnetic coupling mechanism. The dual-pickup coils use overlapping DD coils. The magnetic coupling mechanism coils have a reasonable size and number of turns. When the two pickup coils reach a fixed overlapping distance, the mutual inductance between the dual pickup coils is close to 0. Step 2: Analyze the transmission characteristics of the dual-pickup wireless power transmission system. Use an LCC resonant compensation network as the topology of the transmitting coil and an S-type compensation network as the compensation topology of the pickup coil. The rectifier module of each pickup circuit is independently connected to the Buck circuit, and the two Buck circuits are connected in series. Step 3: For the dual-pickup wireless power transfer system, an output voltage distribution strategy based on optimal efficiency is proposed. By dynamically adjusting the output voltages of the two pickup circuits, the two pickup circuits cooperate with each other to achieve a constant voltage output of the system. Step 4: Use the load voltage control method that combines a sliding mode observer and model predictive control to establish the state space equation of the secondary-side Buck circuit. Based on this model, design a model predictive controller and combine it with a sliding mode observer to achieve stable control of the load voltage.

2. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 1, characterized in that: The DD coil described in step 1 is a double D-shaped symmetrical coil used in wireless power transmission systems. It is composed of two semicircular windings in an orthogonal combination. A superimposed magnetic field is formed in the central area by the same-phase current. Its orthogonal structure can reduce cross-coupling. When the winding directions of the DD coils are consistent, as the distance between the two pickup coils changes, the mutual inductance has a zero-crossing point, that is, the magnetic flux entering each pickup coil is equal to the magnetic flux passing out. The mutual inductance between the transmitting coil and the pickup coil 1 is M1, the mutual inductance between the transmitting coil and the pickup coil 2 is M2, and the mutual inductance between the pickup coil 1 and the pickup coil 2 is M3. When M3 is close to 0, the two pickup coils can be regarded as decoupled.

3. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 1, characterized in that: The dual-pickup wireless power transmission system described in step 2 includes: a DC input power supply U in MOSFET and diodes are connected in parallel to form switching devices S1-S4, and compensation inductor L p , parallel compensation capacitor C p , series compensation capacitor C1, transmitting coil internal resistance r1, transmitting coil self-inductance L1, pickup coil 1 self-inductance L2, pickup coil 2 self-inductance L3, pickup coil 1 compensation capacitor C2, pickup coil 2 compensation capacitor C3, pickup coil 1 internal resistance r2 and pickup coil 2 internal resistance r3, pickup circuit 1 rectifier circuit, pickup circuit 1 Buck circuit capacitor C4, pickup circuit 1 Buck circuit inductor L4, pickup circuit 1 filter capacitor C f1 , the rectifier circuit of the pickup circuit 2, the Buck circuit capacitor C5 in the pickup circuit 2, the Buck circuit inductor L5 in the pickup circuit 2, the filter capacitor C of the pickup circuit 2 f2 , R L is the system load resistance.

4. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 3, characterized in that: The dual-pickup wireless power transmission system is simplified, and the simplified operation method is: the DC input power supply U in And the switching devices S1-S4 are equivalent to the AC power supply U o , the rectifier circuit and Buck circuit in the pickup circuit 1 are equivalent to the resistor R1, the rectifier circuit and Buck circuit in the pickup circuit 2 are equivalent to the resistor R2, I1 is the current through the inductor L p I2 is the transmitting current of the primary transmitting coil, I3 is the pickup current of the pickup coil 1, and I4 is the pickup current of the pickup coil 2.

5. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 1, 3 or 4, characterized in that: The efficiency expression of the dual-pickup wireless power transmission system described in step 2 is: In the above formula, η is the efficiency of the wireless power transmission system, P L0 is the active power loss of the transmitting coil, P L1 is the active power loss on pickup coil 1, P L2 To pick up the active power loss on coil 2, P out is the output power of the wireless power transmission system.

6. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 3, characterized in that: The specific steps of step three include: Step 3.1: Let the duty cycle of the Buck circuit in pickup circuit 1 be D1, the duty cycle of the Buck circuit in pickup circuit 2 be D2, and let the ratio of the Buck module duty cycles of pickup circuit 1 and pickup circuit 2 be β, then Step 3.2: Let the active power loss on the pickup coil 1 be P L1 , the active power loss on the pickup coil 2 is P L2 , the output power of the dual-pickup wireless power transmission system is P out , r2 is the internal resistance of pickup coil 1, r3 is the internal resistance of pickup coil 2, I2 is the transmitting current of the primary transmitting coil, ω is the angular frequency, M1 is the mutual inductance between the transmitting coil and pickup coil 1, M2 is the mutual inductance between the transmitting coil and pickup coil 2, then the total pickup coil loss P of the dual pickup wireless power transmission system is LOSS for: Step 3.3: When P LOSS When it is minimum, the transmission efficiency of the dual pickup wireless power transmission is the highest, and the total power loss of the pickup coil P LOSS Derivative of the duty cycle ratio β, β max is the ratio of the Buck circuit duty cycle corresponding to the optimal transmission efficiency of the dual-pickup wireless power transmission system: Step 3.4: To optimize the transmission efficiency of the dual-pickup wireless power transmission system, the duty cycle ratio β should be equal to β max , assuming the output voltage target value of the dual-pickup wireless power transmission system is U T , the voltage target value of pickup coil 1 is U T1 , the voltage target value of pickup coil 2 is U T2 , then the voltage target value of each pickup coil is: Step 3.5: Assume that the actual output voltages of pickup circuit 1 and pickup circuit 2 are U R1 and U R2 , load R L The voltage on the R , so that the actual output voltage of the dual-pickup wireless power transmission system and the set voltage value are always kept equal, the load voltage U R Equal to U T , the output voltage U of the pickup coil 1 R1 Equal to the voltage target value U of the pickup coil 1 T1 , the output voltage U of the pickup coil 2 R2 Equal to the voltage target value U of the pickup coil 2 T2 , that is, constant voltage output under optimal efficiency can be achieved; 7. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 1, characterized in that: The specific operation steps of step 4 are: Step 4.1: Discretize the continuous-time model using the Buck circuit to obtain a discrete model of the Buck circuit, and analyze the state update equation and output equation of the discrete model of the Buck circuit; the state update equation and output equation of the discrete model of the Buck circuit are: In the above formula, k represents the kth sampling moment, which is used to mark the discretized time series, and k+1 corresponds to the next sampling moment; T s is the sampling period, i.e., the discretized time interval; L is the Buck circuit inductance, C is the Buck circuit capacitance, and R is the load resistance; S(k) is the switch state function at the kth moment, i L (k) is the inductor current at the kth moment; i L (k+1) is the inductor current at the k+1th moment, V out (k) is the output voltage at the kth moment, V out (k+1) is the output voltage at the k+1th moment, V in Input voltage for the Buck circuit; Step 4.2: Model the sliding mode observer based on the Buck circuit and analyze the observed value of the inductor current in the Buck circuit; The state variables are integrated using the fourth-order Runge-Kutta method to update the observation value. k1 and k2 are calculated for the inductor current observation value, which is shown in the following formula: In the above formula, di L / dt represents the instantaneous rate of change of the inductor current at the kth moment, k1 represents the contribution of the derivative to the inductor current at the kth moment, and k2 represents the k+T s / 2The contribution of the derivative to the inductor current; Step 4.3: Pass the observed Buck circuit inductor current to the model predictive controller to reduce the need for model predictive control to measure the inductor current. Step 4.4: Based on the model predictive control constant voltage control method of the Buck circuit, the model predictive control adjusts the duty cycle of the Buck circuit.

8. The constant voltage output control method of a dual-pickup wireless power transmission system according to claim 7, characterized in that: The model predictive control described in step 4.4 uses the system's mathematical model to predict system behavior and make adjustments. First, the system model is predicted, followed by rolling optimization, and finally feedback correction. Model predictive control can accurately predict the system's dynamic response and demonstrate greater robustness to internal and external disturbances. The discretized output voltage prediction equation is: In the above formula, It is the output voltage predicted for the next step, with a duty cycle range of [0,1], S test is the duty cycle of the current test, V out is the output voltage; The voltage tracking error term is: In the above formula, e(k) represents the voltage tracking error, Indicates the output voltage predicted at the k+1th moment, U ref Indicates the reference voltage value; γ is the penalty coefficient, and the penalty term for control quantity change is: Δμ(k)=γ|S test -S(k-1)|; In the above formula, △μ(k) represents the penalty term for control variable change, and S(k-1) is the actual switching state; The comprehensive objective function balances voltage tracking performance and control smoothness, and the total cost function is set to J(k): J(k)=e(k)+Δu(k); Among all the test duty cycles, select the duty cycle S with the smallest total cost J(k) test (arg) is used as the optimal duty cycle of the Buck circuit, and we get: S test (arg)=argminJ(k); In the above formula, S test (arg) represents the duty cycle with the minimum total cost, and argmin represents the minimization function.

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