LCC-S type wireless power transmission system modeling and parameter identification method

Abstract

The application relates to an LCC-S type wireless power transmission system modeling and parameter identification method and belongs to the wireless charging field. The modeling and parameter identification method accurately analyzes and calculates the influence of a receiving end rectifier circuit of a wireless power transmission system on a load impedance, combines a high-order harmonic mathematical model of the wireless power transmission system, collects inverter bridge output voltage, current and energy receiving coil output voltage, and realizes high-precision identification of mutual inductance and load resistance by using a genetic algorithm. The application establishes a related model of the rectifier circuit, completes parameter identification under the premise of not increasing the circuit complexity, and is convenient for further optimization design of wireless power transmission system parameters and control.

Description

Technical Field

[0001] This invention relates to the field of wireless charging, and more particularly to a method for modeling and parameter identification of an LCC-S type wireless power transmission system. Background Technology

[0002] Wireless Power Transfer (WPT) eliminates the need for contactless power supply, increasing the portability of charging devices. It is convenient, durable, and safer and more reliable due to the absence of wear and sparks. It also saves on maintenance costs and is easier to design for sealed, waterproof, and dustproof systems, making it a promising technology with excellent development prospects.

[0003] In wireless power transfer technology, a resonant compensation network is needed to compensate for reactive power in the coupling coil and improve system efficiency. In wireless charging applications such as for watches, headphones, and tablets, users place different power receiving devices on the wireless charging pad. Since the distance between the devices changes relatively little, the distance between the coupling coils remains essentially constant, so the mutual inductance can be considered fixed. Different load devices will cause changes in the system's equivalent load impedance. Therefore, a parameter identification method is needed to address load changes. In wireless charging applications for electric vehicles, different brands and types of vehicles have different chassis heights, materials, and parking positions, leading to height and positional shifts in the relative positions of the power receiver and transmitter. This causes changes in the mutual inductance of the wireless power transfer system's coupling mechanism, and the equivalent impedance of the batteries in different vehicles varies at different charging stages. These parameter changes cause the system to deviate from its rated operating point, reducing system output power and energy transfer efficiency, and increasing the complexity of controller design. When the load or mutual inductance in the wireless power transfer system changes, the system needs to adjust its control strategy promptly to maintain ideal operating conditions under complex circumstances and improve transmission efficiency. In summary, load and mutual inductance identification methods for wireless power transmission systems are extremely important.

[0004] When the system transmission distance or other parameters change, the system needs to be adjusted and controlled. Currently, there are three main control methods: ① control at the transmitting end; ② control at the receiving end; ③ simultaneous control at both the transmitting and receiving ends. These three methods adjust and control the system by adding auxiliary means such as additional communication equipment, Buck converters, and controllable switches at the receiving end. While they have a certain effect on improving system performance, they cannot fundamentally solve the problems of system operating frequency drift and changes in operating characteristics caused by wide-range variations in load and mutual inductance. Therefore, in wireless power transmission systems, when the load and mutual inductance change, the system needs to accurately obtain load and mutual inductance parameter information to take more effective measures to control the system and ensure stable and efficient operation. Therefore, this invention proposes a modeling and parameter identification method for an LCC-S type wireless power transmission system. Summary of the Invention

[0005] When the equivalent impedance of the load equipment and the relative position of the coupling coils change in a wireless power transfer system, the system operation deviates from its rated operating point, reducing the system output power and energy transfer efficiency. Therefore, for wireless power transfer systems, obtaining load and mutual inductance parameter information to adjust system power and improve system efficiency—that is, a parameter identification method—is extremely important. This invention ① addresses the problem of inaccurate mathematical model establishment in LCC-S type compensation parameter identification methods by establishing a more accurate mathematical model based on higher harmonics. ② To address the limitation of current parameter identification methods that can only identify the equivalent resistance value of the AC side of the rectifier circuit, it accurately analyzes and calculates the impact of the receiving end rectifier circuit on the impedance. This invention proposes a modeling and parameter identification method for LCC-S type wireless power transfer systems based on higher harmonic calculations. By acquiring the inverter bridge output voltage and current, as well as the receiving end coil output voltage, it achieves high-precision identification of load and mutual inductance parameters.

[0006] The shortcomings of existing technologies are: ① The model is not accurate enough, resulting in reduced recognition accuracy. ② Only the parameters of the equivalent load are identified; the influence of the rectifier circuit on the amplitude and phase of the load impedance is not accurately considered during model building. ③ Numerical optimization algorithms are prone to getting trapped in local optima and have low search efficiency.

[0007] To address these shortcomings, this invention proposes a modeling and parameter identification method for LCC-S type wireless power transfer systems.

[0008] The wireless power transmission system consists of an energy transmitter and an energy receiver.

[0009] The energy transmitter consists of a DC power supply, a high-frequency inverter circuit, a transmitter resonant compensation circuit, and an energy transfer coil connected in sequence to form a series circuit.

[0010] The energy receiving end is composed of an energy receiving coil, a receiving end resonant compensation circuit, a rectifier circuit, and a load connected in sequence to form a series circuit.

[0011] The genetic algorithm parameter identification method includes the following steps:

[0012] Step 1: Based on the derivation of the relationship between the output voltage and current of the inverter circuit and the equivalent impedance of the system in the wireless power transmission system, establish a mathematical model of the LCC-S type system with rectifier circuit considering higher harmonics.

[0013] Step 2: By calculating the output voltage of the receiving end, a constraint relationship between resistance and mutual inductance is introduced. After other system parameters are determined, there is a unique mapping relationship between the resistance value and the mutual inductance value, thereby reducing the number of parameters to be identified.

[0014] Step 3: Construct a suitable objective function for the mathematical model of the wireless power transmission system described in Step 1, and introduce a genetic algorithm to transform the parameter identification problem of the load and mutual inductance of the wireless power transmission system into an objective function optimization problem. Introduce the constraint relationship described in Step 2 into the algorithm operation process to reduce the possibility of the algorithm getting trapped in local optima.

[0015] Step 4: When the operating status of the wireless power transmission system changes or the load and mutual inductance parameters are unknown, i.e., when the identification of load and mutual inductance parameters is involved, the load R and mutual inductance M of the system are identified by the modeling and parameter identification method of this invention. Based on the identification results, the specific parameters of the wireless power transmission system can be determined for subsequent control work, so that the system can be maintained in a more ideal operating state.

[0016] The mathematical model of the LCC-S type system with rectifier circuit considering higher harmonics described in step 1 is as follows:

[0017] The impedance reflected at the transmitting end by the receiving end:

[0018] Where ω is the system operating frequency, n is the harmonic order, M is the mutual inductance, and Z is the system operating frequency. s_n This is the series impedance of the receiving circuit.

[0019] System input impedance:

[0020] Where ω is the system operating frequency, n is the harmonic order, and α n Let β be the resistance of the system input impedance under the nth harmonic. n Let L be the reactance of the system input impedance under the nth harmonic. f For the transmitter resonant inductance, C f For the transmitter resonant capacitor, C p L is the compensation capacitor for the transmitter. p R is the self-inductance of the transmitting coil.p Z is the internal resistance of the transmitting coil. r_n This is the impedance reflected at the transmitting end by the receiving end.

[0021] The system input current amplitude is:

[0022] Where n is the harmonic order, E dc This is the DC power supply voltage.

[0023] The phase of the system input current is:

[0024] When calculating the impedance of a rectifier circuit, the equivalent impedance of the nth harmonic of the rectifier circuit load is:

[0025]

[0026] Where ω is the system operating frequency, n is the harmonic order, M is the mutual inductance, and L is the system operating frequency. f For the transmitter resonant inductance, C f C1 is the resonant capacitor at the transmitting end, C2 is the compensation capacitor at the transmitting end, L1 is the self-inductance of the transmitting coil, and C2 is the compensation capacitor at the transmitting end. This represents the fundamental phase of the rectifier circuit load.

[0027] The fundamental impedance of the rectifier circuit load is:

[0028]

[0029] Where R is the load resistance, Z o_n The amplitude of the nth harmonic impedance of the rectifier circuit load. The fundamental phase of the rectifier circuit load. The nth harmonic phase of the rectifier circuit load.

[0030] The rectifier circuit model described in the mathematical model contains the fundamental impedance in the load harmonic impedance of the rectifier circuit. The model uses harmonic analysis and iterative method to calculate the equivalent impedance of the fundamental and each harmonic of the rectifier circuit load.

[0031] The iterative method can obtain a more accurate equivalent impedance of the rectifier load. The smaller the iteration error set by the iterative method, the higher the accuracy of the load equivalent impedance calculation. However, the calculation time increases, and the error requirement and calculation time need to be considered comprehensively.

[0032] The constraint function relationship between the mutual inductance and the resistance introduced by the output voltage of the receiving end in step 2 is as follows:

[0033] Transmitter coil current: i p =(1-ω 2 L f C f)i in -jωC f u in

[0034] Where ω is the system operating frequency, L f For the transmitter resonant inductance, C f For the resonant capacitor at the transmitter, i in To provide the system with input current, u in This is the DC power supply voltage.

[0035] Receiver coil output voltage:

[0036] Where ω is the system operating frequency, L s For the self-inductance of the receiving coil, C s R is the compensation capacitor for the receiving end. s R is the internal resistance of the receiving coil, M is the mutual inductance, and R is the internal resistance of the receiving coil. e i is the equivalent impedance of the rectifier circuit. p This represents the current in the transmitting coil.

[0037] The objective function expression in step 3 is:

[0038] Among them, i f_mea (T0) and i f_mea (T0+T) represent the sampled values ​​of the inverter output current at time T0 and time T0+T, respectively, after the system has reached steady-state operation. f (T0) and i f (T0+T) represents the calculated values ​​at times T0 and T0+T obtained using a mathematical model.

[0039] After qualitative analysis of the relationship between load and system input current, the value of 1 / 4 of the time after the stabilization period is selected for time T0. At time 1 / 4, the system input current is more sensitive to load changes, and load changes can effectively cause changes in the fitness function value, thereby improving recognition efficiency and accuracy.

[0040] This invention provides a modeling and parameter identification method for an LCC-S type wireless power transmission system. The method includes: establishing a mathematical model of the wireless power transmission system based on higher harmonics, improving model accuracy; considering the existence of the rectifier circuit during modeling, using higher harmonic analysis and iterative methods to obtain a more accurate equivalent impedance of the rectifier load, with the calculation accuracy determined by the iteration error set by the iterative method; using this mathematical model to identify the load resistance value connected after the rectifier circuit; introducing the load and mutual inductance relationship from the receiver output voltage calculation formula, reducing the variables of the parameters to be identified, and obtaining the corresponding mutual inductance value by searching and optimizing the load value; qualitatively analyzing the relationship between the instantaneous value of the system input current and the load resistance in the genetic algorithm constraint relationship, finding that the system input current is more sensitive to load changes at 1 / 4 of a cycle, and load changes can effectively cause changes in the fitness function value, thereby improving identification accuracy and effectively avoiding multivariate search getting trapped in local optima and improving algorithm search efficiency. Attached Figure Description

[0041] Figure 1 : Circuit diagram of the LCC-S type compensation network wireless power transmission system described in this invention.

[0042] Figure 2 The equivalent circuit of the LCC-S type wireless power transmission system described in this invention.

[0043] Figure 3 The flowchart of the rectifier circuit impedance calculation based on the iterative method described in this invention.

[0044] Figure 4 : Flowchart of the genetic algorithm described in this invention.

[0045] Figure 5 A qualitative analysis diagram of system input current and load in one specific embodiment.

[0046] Figure 6 A convergence result diagram of parameter identification based on a higher harmonic mathematical model in one specific implementation. Detailed Implementation

[0047] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey the scope of the invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention.

[0048] Unless otherwise stated, the terms used herein have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0049] Figure 1 This is a circuit diagram of an LCC-S type compensation network wireless power transmission system according to an embodiment of the present invention.

[0050] The wireless power transmission system consists of an energy transmitter and an energy receiver.

[0051] The energy transmitter consists of a DC power supply, a high-frequency inverter circuit, a transmitter resonant compensation circuit, and an energy transfer coil connected in sequence to form a series circuit.

[0052] The energy receiving end is composed of an energy receiving coil, a receiving end resonant compensation circuit, a rectifier circuit, a filter capacitor, and a load connected in sequence to form a series circuit.

[0053] In the LCC-S compensation topology described above, the first resonant cavity is composed of an inductor L f With capacitor C f Composition, in which capacitor C f And with capacitor C p The self-inductance L of the common and transmitting coils p The resonance forms a second resonant cavity. The self-inductance L of the receiving coil... s With capacitor C s The resonance forms a third resonant cavity. The reactive power in the coupling coil is compensated by the resonance of the above three resonant cavities, thereby improving the system power factor and increasing system efficiency.

[0054] The system circuit parameters used in this invention satisfy the following relationship:

[0055] Where ω is the system operating frequency, L f For the transmitter resonant inductance, C f L is the resonant capacitor at the transmitter. p For the self-inductance of the transmitting coil, C p L is the compensation capacitor for the transmitter. s For the self-inductance of the receiving coil, C s This is a compensation capacitor for the receiving end.

[0056] The square wave voltage u output by the system inverter circuit in The Fourier transform expansion of (t) is as follows:

[0057]

[0058] Where ω is the system operating frequency, n is the harmonic order, and E dc This is the system input voltage.

[0059] The inverter output current is the steady-state current i generated by the system input current under the excitation of the square wave voltage. in (t) can be expressed as:

[0060]

[0061] Where ω is the system operating frequency, n is the harmonic order, and I n This represents the amplitude of the harmonic current.

[0062] The system input current can be expressed as:

[0063] The impedance reflected at the transmitting end by the receiver circuit impedance is: Z s_n =jμ s +R s +R e

[0064] Among them, R e R is the equivalent impedance before the rectifier circuit. s This is the internal resistance of the receiving coil.

[0065] In the above formula,

[0066] make

[0067] Where ω is the system operating frequency, n is the harmonic order, M is the mutual inductance, and Z is the system operating frequency. s_n This is the series impedance of the receiving circuit.

[0068] The system input impedance is:

[0069]

[0070] Where ω is the system operating frequency, n is the harmonic order, and L f For the transmitter resonant inductance, C f For the transmitter resonant capacitor, C p L is the compensation capacitor for the transmitter. p R is the self-inductance of the transmitting coil. p Z is the internal resistance of the transmitting coil. r_n This is the impedance reflected at the transmitting end by the receiving end.

[0071] The above equation can be simplified to obtain: Z in_n =α n +jβ n

[0072]

[0073] in,

[0074] From the above derivation, the amplitude and phase of the system input current can be obtained as follows:

[0075]

[0076] Based on circuit principles, the current i in the receiving coil can be obtained. p With system input current i in The relation is:

[0077] i p =(1-ω 2 L f C f )i in -jωC f u in

[0078] Where ω is the system operating frequency, L f For the transmitter resonant inductance, C f For the resonant capacitor at the transmitter, i in To provide the system with input current, u in This is the DC power supply voltage;

[0079] The induced voltage of the receiving coil is: u s =jωMi p

[0080] The input voltage of the rectifier circuit is:

[0081] Where ω is the system operating frequency, L s For the self-inductance of the receiving coil, C s R is the compensation capacitor for the receiving end. s R is the internal resistance of the receiving coil, M is the mutual inductance, and R is the internal resistance of the receiving coil. e i is the equivalent impedance of the rectifier circuit. p This represents the current in the transmitting coil.

[0082] The formula for calculating the output voltage at the receiving end introduces a constraint relationship between resistance and mutual inductance. Then, a genetic algorithm is introduced to transform the parameter identification problem into an optimization problem that minimizes the objective function value.

[0083] against Figure 2 The equivalent circuit of the wireless power transfer system is calculated using the rectifier circuit impedance based on an iterative method, by... Figure 3 The calculation flowchart can calculate the equivalent load R. e The relationship between the load resistance R and the load resistance R.

[0084] The formula in the flowchart for calculating the impedance of a rectifier circuit based on the iterative method is shown below, with the derivation process omitted.

[0085]

[0086]

[0087] Z o_n =a / / b

[0088]

[0089] This completes the establishment of the mathematical model for the wireless power transfer system considering the rectifier circuit.

[0090] The mathematical model shows that the wireless power transmission system is a high-order multivariable coupled nonlinear system. Therefore, a genetic algorithm is introduced to transform the parameter identification and solution process into a parameter optimization process.

[0091] The flowchart of the genetic algorithm used in this invention is as follows: Figure 4 As shown, the algorithm steps are as follows:

[0092] Step 1: After determining the input system parameters of the LCC-S type compensation system, detect the amplitude E of the square wave of the system input voltage. dc The effective value of the inverter output current I1 and the instantaneous value of the inverter output current I f_mea .

[0093] Step 2: Generate the initial population using binary encoding.

[0094] Step 3: Calculate the mutual inductance and the rectifier circuit impedance R e .

[0095] Step 4: Calculate the fitness function value, where the fitness function formula is:

[0096]

[0097] Among them, i f_mea (T0) and i f_mea (T0+T) represent the sampled values ​​of the inverter output current at time T0 and time T0+T, respectively, after the system has reached steady-state operation. f (T0) and i f (T0+T) represents the calculated values ​​at times T0 and T0+T obtained using a mathematical model.

[0098] Step 5: Evaluate the fitness function based on its value and select offspring populations using the survival of the fittest principle.

[0099] Step Six: Perform the crossover and mutation steps in the genetic algorithm on the individuals selected in Step Four.

[0100] Step 7: Update the population and determine if the termination condition has been met. If it has, end the iteration and obtain the parameter identification values ​​for load R and mutual inductance M. Otherwise, continue the iteration.

Claims

1. A method for modeling and parameter identification of an LCC-S type wireless power transfer system, characterized in that: The wireless power transmission system consists of an energy transmitter and an energy receiver. The energy transmitter consists of a DC power supply, a high-frequency inverter circuit, a transmitter resonant compensation circuit, and an energy transfer coil connected in sequence to form a series circuit. The energy receiving end is composed of an energy receiving coil, a receiving end resonant compensation circuit, a rectifier circuit, a filter capacitor, and a load connected in sequence to form a series circuit. The modeling and parameter identification method includes the following steps: Step 1: Based on the derivation of the relationship between the output voltage and current of the inverter circuit and the equivalent impedance of the system in the wireless power transmission system, establish a mathematical model of the LCC-S type wireless power transmission system with rectifier circuit considering higher harmonics. Step 2: By using the formula for calculating the output voltage at the receiving end, a constraint relationship between resistance and mutual inductance is introduced. After other system parameters are determined, there is a unique mapping relationship between the resistance value and the mutual inductance value, thereby reducing the number of parameters to be identified. Step 3: Construct a suitable objective function for the mathematical model of the wireless power transmission system described in Step 1, and introduce a genetic algorithm to transform the parameter identification problem of the load and mutual inductance of the wireless power transmission system into an objective function optimization problem. Introduce the constraint relationship described in Step 2 into the algorithm operation process to reduce the possibility of the algorithm getting trapped in local optima. Step 4: When the operating status of the wireless power transmission system changes or the load and mutual inductance parameters are unknown, i.e., when the identification of load and mutual inductance parameters is involved, the load R and mutual inductance M of the system are identified using the modeling and parameter identification method. Based on the identification results, the specific parameters of the wireless power transmission system can be determined for subsequent control work, so that the system can be maintained in a relatively ideal operating state.

2. The modeling and parameter identification method for the LCC-S type wireless power transmission system according to claim 1, characterized in that: The mathematical model of the LCC-S type wireless power transfer system with rectifier circuit considering higher harmonics, as described in step 1, is as follows: The impedance reflected at the transmitting end by the receiving end: Where ω is the system operating frequency, n is the harmonic order, M is the mutual inductance, and Z is the system operating frequency. s_n The series impedance of the receiving circuit; System input impedance: Where ω is the system operating frequency, n is the harmonic order, and α n Let β be the resistance of the system input impedance under the nth harmonic. n Let L be the reactance of the system input impedance under the nth harmonic. f For the transmitter resonant inductance, C f For the transmitter resonant capacitor, C p L is the compensation capacitor for the transmitter. p R is the self-inductance of the transmitting coil. p Z is the internal resistance of the transmitting coil. r_n This is the impedance reflected at the transmitting end by the receiving end; The system input current amplitude is: Where n is the harmonic order, E dc This is the DC power supply voltage; The phase of the system input current is: When calculating the impedance of a rectifier circuit, the equivalent impedance of the nth harmonic of the rectifier circuit load is: Where ω is the system operating frequency, n is the harmonic order, M is the mutual inductance, and L is the system operating frequency. f For the transmitter resonant inductance, C f C1 is the resonant capacitor at the transmitting end, C2 is the compensation capacitor at the transmitting end, L1 is the self-inductance of the transmitting coil, and C2 is the compensation capacitor at the transmitting end. The fundamental phase of the rectifier circuit load; The fundamental impedance of the rectifier circuit load is: Where R is the load resistance, Z o_n The amplitude of the nth harmonic impedance of the rectifier circuit load. The fundamental phase of the rectifier circuit load. The nth harmonic phase of the rectifier circuit load; The rectifier circuit load harmonic impedance in the mathematical model of the LCC-S type wireless power transmission system with rectifier circuit considering higher harmonics described in step 1 contains the fundamental impedance. The model uses harmonic analysis and iterative methods to calculate the fundamental and equivalent impedances of each harmonic of the rectifier circuit load. The iterative method can obtain a more accurate equivalent impedance of the rectifier circuit load. The smaller the set iteration error, the higher the accuracy of the load equivalent impedance calculation, but the calculation time increases. Therefore, it is necessary to comprehensively consider the error requirements and the calculation time.

3. The modeling and parameter identification method for the LCC-S type wireless power transfer system according to claim 1, characterized in that: The constraint relationship between resistance and mutual inductance mentioned in step 2 includes the formula for the current of the transmitting coil and the formula for the output voltage of the receiving coil; Transmitter coil current: i p =(1-ω 2 L f C f )i in -jωC f u in ; Where ω is the system operating frequency, L f For the transmitter resonant inductance, C f For the resonant capacitor at the transmitter, i in For the system input current, u in This is the DC power supply voltage; Receiver coil output voltage: Where ω is the system operating frequency, L s For the self-inductance of the receiving coil, C s R is the compensation capacitor for the receiving end. s R is the internal resistance of the receiving coil, M is the mutual inductance, and R is the internal resistance of the receiving coil. e To avoid controlling the equivalent impedance of the rectifier bridge, i p This represents the current in the transmitting coil.

4. The modeling and parameter identification method for the LCC-S type wireless power transmission system according to claim 1, characterized in that: The objective function expression in step 3 is: Among them, i f_mea (T0) and i f_mea (T0+T) represent the sampled values ​​of the inverter output current at time T0 and time T0+T, respectively, after the system has reached steady-state operation. f (T0) and i f (T0+T) represents the calculated values ​​at times T0 and T0+T obtained using a mathematical model. After a qualitative analysis of the relationship between the load and the system input current, the value of T0 is selected as the value of 1 / 4 of the stable period. At 1 / 4 of the time, the system input current is more sensitive to load changes, and load changes can effectively cause changes in the fitness function value, thereby improving recognition efficiency and accuracy.

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