A constant voltage control method and system for wireless power transmission

Abstract

The present application relates to the field of wireless power transmission, and provides a constant voltage control method and system for wireless power transmission. The method comprises: approximating the primary side resonant circuit of the wireless power transmission system to an S-S topology fundamental equivalent circuit based on the fundamental wave, obtaining a primary side fundamental equivalent model; performing coordinate transformation processing on the primary side fundamental equivalent model, converting from the stationary coordinate system to the rotating coordinate system, and obtaining an S-S topology state equation in the dq rotating coordinate system; inputting the S-S topology state equation into a cascade observer, estimating the state of the primary side resonant current, and obtaining an estimated value of the rectifier side load voltage; subtracting the estimated value of the rectifier side load voltage from the target voltage reference value, calculating the control quantity through the controller, and applying the control quantity to the duty cycle of the BUCK step-down circuit to continuously optimize and adjust the rectifier side load voltage, and complete the constant voltage control. The present application improves the control accuracy and response speed of the constant voltage power supply under the condition of rapid load change.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, and in particular to a constant voltage control method and system for wireless power transmission. Background Technology

[0002] Non-contact power transfer technology has been widely used in recent years in scenarios such as rotating machinery, implantable medical devices, smart terminals, and the Internet of Things (IoT) in the home. Taking rotating testing equipment as an example, the rotating testing equipment is installed on the secondary side of the wireless power supply. Its internal equivalent load often changes according to the testing needs of the secondary side. This change will affect the output voltage of the wireless power supply system, ultimately affecting the normal operation of the secondary circuit and even causing damage to electronic components. Therefore, a fast and accurate constant voltage control method is crucial to ensuring the reliable operation of the wireless power supply system.

[0003] Existing primary-side control technologies typically require establishing an additional wireless communication link between the primary and secondary sides to transmit secondary-side load voltage information back to the primary-side controller in real time, thereby achieving closed-loop regulation of the output voltage. However, the transmission delay and bit error rate introduced by the communication link can adversely affect the stability of the control system, especially under conditions of rapid load changes, making it difficult to meet the requirements of real-time constant voltage control for response speed and control accuracy. Summary of the Invention

[0004] This invention provides a constant voltage control method and system for wireless power transmission to overcome the shortcomings of the prior art.

[0005] This invention provides a constant voltage control method for wireless power transmission, comprising: S1: The primary-side resonant circuit of the wireless power transmission system is approximated as the SS topology equivalent circuit based on the fundamental wave, thus obtaining the primary-side fundamental wave equivalent model. S2: Perform coordinate transformation on the original fundamental wave equivalent model, transforming it from a stationary coordinate system to a rotating coordinate system, to obtain the SS topological state equation in the dq rotating coordinate system; S3: Input the SS topology state equation into the cascade observer, and obtain the estimated value of the rectifier-side load voltage by performing state estimation on the primary side resonant current; S4: The difference between the estimated value of the rectifier-side load voltage and the target voltage reference value is calculated by the controller to obtain the control quantity, and the control quantity is applied to the duty cycle of the BUCK step-down circuit to continuously optimize and adjust the rectifier-side load voltage, thereby completing the constant voltage control of wireless power transmission.

[0006] According to the constant voltage control method for wireless power transmission provided by the present invention, step S1 further includes: S11: Treat the wireless power transmission system as a frequency selector that ignores harmonic components but retains the fundamental frequency component, and obtain the SS topology fundamental equivalent circuit; S12: Lag the phase of the SS topology fundamental equivalent circuit by 90° to obtain a virtual circuit; S13: The SS topology fundamental equivalent circuit and the virtual circuit are respectively used as the α-axis component and β-axis component of the stationary coordinate system to obtain the primary-side fundamental equivalent model in the αβ stationary coordinate system.

[0007] According to the constant voltage control method for wireless power transmission provided by the present invention, step S2 further includes: S21: For the primary-side fundamental equivalent model, establish the voltage equation in the αβ stationary coordinate system according to Kirchhoff's voltage law. The voltage equation corresponds to the circuit equation of the α axis and the circuit equation of the β axis, respectively. S22: Transform the voltage equation into the dq rotating coordinate system using a coordinate transformation matrix to obtain the SS topological state equation in the dq rotating coordinate system.

[0008] According to the constant voltage control method for wireless power transmission provided by the present invention, the expression of the coordinate transformation matrix in step S22 is as follows:

[0009] in, The component of the primary resonant current on the d-axis in the dq rotating coordinate system. Let be the component of the primary resonant current along the q-axis in the dq rotating coordinate system. The component of the primary resonant current on the α-axis in the αβ stationary coordinate system. Let be the component of the primary resonant current along the β axis in the αβ stationary coordinate system. It is the resonant angular frequency. This is the current control moment; The state equations include the primary-side voltage equation and the secondary-side voltage equation, expressed as follows:

[0010]

[0011] in, Let dq be the primary current d-axis component vector. The dq-axis component vector of the primary current The first derivative with respect to time, Let dq be the d-axis component vector of the secondary current. The dq-axis component vector of the secondary current The first derivative with respect to time, For the input voltage vector, For load voltage vector, The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. The system matrix of the secondary voltage equation is... This is the mutual inductance coupling matrix of the secondary voltage equation.

[0012] According to the constant voltage control method for wireless power transfer provided by the present invention, the cascaded observer in step S3 is a two-stage observer, specifically including: The first-stage observer takes the primary-side resonant current measurement and the primary-side voltage as inputs, and based on the SS topological state equation, performs a joint estimation of the primary-side current and the secondary-side current to obtain the estimated value of the secondary-side resonant current. The state equation of the first-stage observer is:

[0013]

[0014]

[0015] in, Let dq be the primary current d-axis component vector. This is the estimate of the dq-axis component vector of the primary current by the first-stage observer. This is the first derivative of the estimate of the primary current dq-axis component vector by the first-stage observer. This is the estimate of the dq-axis component vector of the secondary current by the first-stage observer. This is the first derivative of the estimate of the secondary current dq-axis component vector by the first-stage observer. The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. This represents the fundamental amplitude of the primary-side inverter output voltage. The first gain parameter of the first-stage observer, This is the second gain parameter of the first-stage observer. The first correction factor for the first-stage observer, This is the second correction factor for the first-stage observer. It is a 2×2 zero matrix. It is a 2×2 identity matrix. This is the vector of the higher-order sliding mode correction term for the first-stage observer. This is the primary current estimation error. For the design coefficient of the sliding surface, For symbolic functions, For the sliding surface variables of the first-level observer; The second-stage observer takes the estimated value of the secondary resonant current as input and combines it with the secondary voltage equation to jointly estimate the secondary current and the load voltage, thereby obtaining the estimated value of the rectifier-side load voltage. The state equation of the second-stage observer is:

[0016]

[0017]

[0018] in, This is the first derivative of the second-stage observer's estimate of the rectifier-side load voltage vector. The system matrix of the secondary voltage equation is... The mutual inductance coupling matrix of the secondary voltage equation is... This indicates that the corresponding vector is taken from the estimation result output by the first-level observer. It is a 2×1 zero matrix. The first gain parameter of the second-stage observer, This is the second gain parameter for the second-stage observer. The first correction factor for the second-stage observer, This is the second correction factor for the second-stage observer. For the secondary current estimation error, This is the vector of the higher-order sliding mode correction term for the second-stage observer. For the sliding surface variables of the second-level observer, This is the dq-axis component vector of the secondary current.

[0019] According to the constant voltage control method for wireless power transmission provided by the present invention, step S3 further includes: The stability of the first-stage observer is verified using Lyapunov stability theory, specifically including: S311: Define the error variable and construct the error equation; S312: Select a positive definite matrix, solve for the construction matrix that satisfies the first preset condition, and construct the Lyapunov function through the construction matrix; S313: By selecting a gain parameter that satisfies the second preset condition, the first derivative of the Lyapunov function is made less than 0, so as to confirm that the first-stage observer is asymptotically stable.

[0020] According to the constant voltage control method for wireless power transmission provided by the present invention, in step S312, the expression of the first preset condition is:

[0021] in, The system matrix of the error equation, Indicates matrix transpose. The matrix to be solved is a positive definite symmetric matrix. This is a pre-selected positive definite symmetric matrix in the Lyapunov stability analysis; In step S313, the expression for the second preset condition is:

[0022] in, This is the input matrix for the error equation. This is the vector of the higher-order sliding mode correction term for the first-level observer.

[0023] According to the constant voltage control method for wireless power transmission provided by the present invention, in step S4, the controller adopts a PID control algorithm, and the expression of the control quantity of the controller is:

[0024] in, The control quantity output by the PID controller. This refers to the DC bus voltage at the input of the BUCK circuit. For rectifier-side filter capacitors, The difference between the target voltage reference value and the estimated value of the rectifier-side load voltage. This is the proportionality coefficient. The differential coefficients are... The integral coefficient is... To control the start time, This is the current control moment.

[0025] According to the constant voltage control method for wireless power transmission provided by the present invention, in step S4, the continuous domain algorithm of the cascaded observer and the controller is discretized by the forward Euler method to obtain the discretized observer equation and the discretized controller equation. The discretized observer equation and the discretized controller equation are written into the DSP control module to continuously update the estimated value of the rectifier-side load voltage and the control quantity with a fixed step size, thereby realizing real-time constant voltage control of the rectifier-side load voltage.

[0026] The present invention also provides a constant voltage control system for wireless power transfer, for executing a constant voltage control method for wireless power transfer as described in any of the preceding claims, comprising: DC power supply, used to provide DC input voltage to the system; The BUCK step-down circuit is connected to the DC power supply and adjusts the DC input voltage according to the duty cycle control quantity output by the controller to obtain an adjustable DC bus voltage. The full-bridge topology high-frequency inverter module, composed of multiple MOSFETs, is used to invert the adjustable DC bus voltage into a high-frequency AC voltage. The dual-sided energy resonant unit consists of a primary-side inductor, a primary-side capacitor, a secondary-side inductor, a secondary-side capacitor, and mutual inductance forming an SS resonant topology. It is used to transmit the high-frequency AC voltage to the secondary side via resonant coupling, generating primary-side resonant current and secondary-side resonant current. The full-bridge rectifier unit, consisting of multiple diodes and filter capacitors, is used to rectify and filter the secondary resonant current to obtain the rectified load voltage. A resistive load is connected to the output terminal of the full-bridge rectifier unit; The primary side current acquisition circuit uses a fluxgate current sensor to sample the primary side resonant current to obtain the primary side resonant current sampling signal; The DSP control module includes: The coordinate transformation unit is used to perform coordinate transformation processing on the primary side resonant current sampling signal to obtain the dq axis current component. A cascaded observer unit is used to perform state estimation of the rectifier-side load voltage using the dq-axis current component and the primary-side voltage as inputs, and to obtain the estimated value of the rectifier-side load voltage. The controller unit is used to calculate the difference between the estimated value of the rectifier-side load voltage and the target voltage reference value, and output the calculated duty cycle control quantity to the BUCK step-down circuit.

[0027] This invention provides a constant voltage control method and system for wireless power transfer. By constructing a state equation based on a dq rotating coordinate system and combining a cascaded observer with feedforward regulation using a BUCK step-down circuit, it breaks the hardware dependence on direct sampling of the secondary load voltage in traditional wireless power transfer systems. This not only significantly eliminates the need for complex secondary communication links and high-precision voltage sensors, greatly reducing system hardware costs and topology complexity, but also fundamentally eliminates the negative impact of communication delay and signal interference on control accuracy. Furthermore, the high-order sliding mode correction mechanism introduced in the cascaded observer, combined with strict parameter constraints based on Lyapunov stability theory, endows the system with the ability to operate under strong electromagnetic coupling environments. The extremely high state estimation immunity and convergence accuracy ensure that the load voltage estimate can quickly and without steady-state error approximate the real state, thus providing an extremely reliable control feedback reference for the back-end controller. In addition, this invention discretizes the continuous domain algorithm using the forward Euler method and writes it into the DSP module, realizing high dynamic real-time calculation with a fixed step size. This effectively suppresses the truncation error and phase shift caused by digital discretization, enabling the entire closed-loop system to still exhibit excellent transient response recovery capability and voltage regulation robustness by continuously optimizing the duty cycle when facing load changes or coupling shifts. Finally, high-quality and high-precision constant voltage output is achieved in a minimalist hardware architecture that does not require cross-side information interaction. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of a constant voltage control method for wireless power transmission provided in an embodiment of the present invention; Figure 2 A schematic diagram of the DSP module in a constant voltage control system for wireless power transmission provided in an embodiment of the present invention; Figure 3 A schematic diagram illustrating the control principle of a constant voltage control method for wireless power transmission provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the SS topology fundamental equivalent circuit established under the fundamental approximation assumption, provided in an embodiment of the present invention. Figure 5 A schematic diagram of the equivalent circuit model in a stationary coordinate system provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the equivalent circuit model in a rotating coordinate system provided in an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the verification results of a constant voltage control method for wireless power transmission provided in an embodiment of the present invention in discrete simulation. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, embodiments of this invention, and should not be construed as limiting the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. In the description of this invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] The embodiments of the present invention are described below with reference to the figures.

[0032] like Figure 1 As shown, the present invention provides a constant voltage control method for wireless power transmission, comprising: S1: The primary-side resonant circuit of the wireless power transmission system is approximated as the fundamental wave equivalent circuit of the SS topology, thus obtaining the primary-side fundamental wave equivalent model.

[0033] Step S1 further includes: S11: Treat the wireless power transmission system as a frequency selector that ignores harmonic components but retains the fundamental frequency component, and obtain the SS topology fundamental equivalent circuit.

[0034] Furthermore, based on the working principle of wireless power transmission systems, this invention considers it essentially to be a frequency selector, meaning that the system's energy transfer efficiency at the resonant frequency is much higher than at other frequencies. Based on this, this invention ignores higher harmonic components in the circuit, retaining only the fundamental resonant component for modeling, and equates the primary-side resonant circuit to an SS topology fundamental equivalent circuit, i.e., a resonant compensation structure where both the primary and secondary sides use series compensation capacitors, with the primary side consisting of an inductor. ,capacitance Equivalent resistance The series circuit forms a resonant circuit, with the secondary side consisting of an inductor. ,capacitance Equivalent resistance and load resistance A series connection forms a resonant circuit, with the primary and secondary sides connected by mutual inductance. Achieve energy coupling.

[0035] S12: Lag the phase of the SS topology fundamental equivalent circuit by 90° to obtain a virtual circuit.

[0036] In step S12, to construct a biaxial model in a stationary coordinate system, the present invention lags the phase of all electrical quantities of the SS topology fundamental equivalent circuit obtained in step S11 by 90° to obtain a virtual circuit. The obtained virtual circuit is not a physically independent circuit, but a mathematical mirror image obtained by phase shifting the original circuit. Its current and voltage maintain the same amplitude as the original circuit, only the phase differs by 90°.

[0037] S13: The SS topology fundamental equivalent circuit and the virtual circuit are respectively used as the α-axis component and β-axis component of the stationary coordinate system to obtain the primary-side fundamental equivalent model in the αβ stationary coordinate system.

[0038] In step S13, the present invention defines the electrical quantities of the fundamental equivalent circuit of the original SS topology as follows: Axial components define the electrical quantities of a virtual circuit as... The two components together constitute the primary-side fundamental wave equivalent model in the αβ stationary coordinate system, that is, the real circuit and the virtual circuit, which are 90° out of phase, respectively represent the two orthogonal axes of the stationary coordinate system.

[0039] S2: Perform coordinate transformation on the original fundamental wave equivalent model, transforming it from a stationary coordinate system to a rotating coordinate system, to obtain the SS topological state equation in the dq rotating coordinate system.

[0040] Step S2 further includes: S21: For the primary-side fundamental equivalent model, establish the voltage equations in the αβ stationary coordinate system according to Kirchhoff's voltage law. The voltage equations correspond to the circuit equations of the α-axis and the β-axis, respectively.

[0041] In step S21, after obtaining the equivalent model of the primary fundamental wave in the αβ stationary coordinate system, this invention applies Kirchhoff's voltage law to the primary and secondary circuits respectively, that is, the sum of the voltages of each component in the circuit equals the circuit excitation voltage, to establish the voltage equations corresponding to the α-axis and β-axis. Specifically, this invention first applies Kirchhoff's voltage law to the primary circuit, stating that the sum of the inductor voltage, capacitor voltage, resistor voltage drop, and mutual inductance coupling voltage equals the inverter output voltage. For the secondary circuit, the sum of the voltage drops of each component and the sum of the mutual inductance coupling terms equal zero. Since the electrical quantities in the αβ coordinate system still change sinusoidally with time, it is relatively complex to design the controller directly based on this coordinate system. Therefore, in the subsequent step S22, the present invention further transforms it to a rotating coordinate system.

[0042] S22: Transform the voltage equation into the dq rotating coordinate system using a coordinate transformation matrix to obtain the SS topological state equation in the dq rotating coordinate system.

[0043] The expression for the coordinate transformation matrix in step S22 is as follows:

[0044] in, The component of the primary resonant current on the d-axis in the dq rotating coordinate system. Let be the component of the primary resonant current along the q-axis in the dq rotating coordinate system. The component of the primary resonant current on the α-axis in the αβ stationary coordinate system. Let be the component of the primary resonant current along the β axis in the αβ stationary coordinate system. It is the resonant angular frequency. This is the current control moment; The state equations include the primary-side voltage equation and the secondary-side voltage equation, expressed as follows:

[0045]

[0046] in, Let dq be the primary current d-axis component vector. The dq-axis component vector of the primary current The first derivative with respect to time, Let dq be the d-axis component vector of the secondary current. The dq-axis component vector of the secondary current The first derivative with respect to time, For the input voltage vector, For load voltage vector, The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. The system matrix of the secondary voltage equation is... This is the mutual inductance coupling matrix of the secondary voltage equation.

[0047] This invention uses a coordinate transformation matrix to transform the primary resonant current components in the αβ stationary coordinate system. Components converted to dq rotating coordinate system Transformation based on resonant angular frequency The rotational speed is used to make the dq coordinate system rotate synchronously with the resonant frequency, thereby transforming the originally sinusoidal AC quantity that varies with time into an approximate DC quantity, significantly reducing the difficulty of solving the subsequent state equations. In the DSP implementation, Axial components This is achieved by reading historical sampling data from the storage array one-quarter of the resonance period before the current moment. Specifically, it utilizes the timing relationship between the sine signal and its cosine signal, which lags it by 90°, to directly extract the signal from the time-domain sampling data without requiring additional hardware. Axial components.

[0048] After coordinate transformation, this invention obtains the SS topological state equations in the dq rotating coordinate system, which include the primary-side voltage equations and secondary-side voltage equations from the above expressions. Wherein, As the system matrix in the primary-side voltage equation, it describes the impedance characteristics of the primary-side circuit itself. As the mutual inductance coupling matrix in the primary-side voltage equation, it describes the coupling effect of the secondary-side current on the primary side. As the input matrix for the primary voltage equation; The system matrix of the secondary voltage equation is... This is the mutual inductance coupling matrix of the secondary voltage equation, describing the coupling effect of the primary current on the secondary side. The specific definition of the coefficient matrix is ​​as follows:

[0049]

[0050]

[0051]

[0052]

[0053] in:

[0054]

[0055]

[0056]

[0057] in, This is the equivalent series resistance of the primary resonant circuit. This is the frequency correction term for the rotating coordinate system of the primary resonant circuit. The equivalent inductance in the rotating coordinate system of the primary resonant circuit is... For mutual intuition, This represents the equivalent gain of mutual inductance coupling in the dq coordinate system. The equivalent inductance in the rotating coordinate system of the secondary resonant circuit is... This is the equivalent series resistance of the secondary resonant circuit. This is the frequency correction term in the rotating coordinate system for the secondary resonant circuit. The self-inductance of the primary resonant coil, This is a primary-side series compensation capacitor. The self-inductance of the secondary resonant coil, It is a secondary-side series compensation capacitor.

[0058] The above state equations fully express the electrical coupling relationship between the primary and secondary sides in matrix form, providing a mathematical basis for the design of subsequent cascaded observers.

[0059] S3: Input the SS topology state equation into the cascade observer, and obtain the estimated value of the rectifier-side load voltage by performing state estimation on the primary side resonant current.

[0060] The cascaded observer in step S3 is a two-stage observer, specifically including: The first-stage observer takes the primary-side resonant current measurement and the primary-side voltage as inputs, and based on the SS topological state equation, performs a joint estimation of the primary-side current and the secondary-side current to obtain the estimated value of the secondary-side resonant current. The state equation of the first-stage observer is:

[0061]

[0062]

[0063] in, Let dq be the primary current d-axis component vector. This is the estimate of the dq-axis component vector of the primary current by the first-stage observer. This is the first derivative of the estimate of the primary current dq-axis component vector by the first-stage observer. This is the estimate of the dq-axis component vector of the secondary current by the first-stage observer. This is the first derivative of the estimate of the secondary current dq-axis component vector by the first-stage observer. The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. This represents the fundamental amplitude of the primary-side inverter output voltage. The first gain parameter of the first-stage observer, This is the second gain parameter of the first-stage observer. The first correction factor for the first-stage observer, This is the second correction factor for the first-stage observer. It is a 2×2 zero matrix. It is a 2×2 identity matrix. This is the vector of the higher-order sliding mode correction term for the first-stage observer. This is the primary current estimation error. For the design coefficient of the sliding surface, For symbolic functions, For the sliding surface variables of the first-level observer.

[0064] After obtaining the SS topological state equation in the dq rotating coordinate system, this invention constructs a two-stage cascaded observer to measure the primary-side resonant current. and the fundamental amplitude of the primary inverter output voltage Given the input, estimate the secondary resonant current and the rectifier-side load voltage step by step.

[0065] Furthermore, the first-stage observer receives... and Based on the primary-side voltage equation and secondary-side voltage equation in the SS topology state equations, a system is constructed to... and The joint estimation equations are as follows. The higher-order sliding mode observer is a state observation method based on the sliding mode control concept, aiming to construct the sliding surface variables. That is, the measured value of the primary current. Compared with the estimated value The difference multiplied by the sliding surface design coefficient get Subsequently, the present invention will Substitute the sign function The sign function outputs positive values. Output for negative values Outputting zero values This is used to construct the higher-order sliding mode correction term vector. , The two lines are respectively and ,in , This is the gain parameter.

[0066] The state equation of the first-level observer will (Obtained by multiplying the coefficient matrix of the state equation with the current estimated current vector) (Input matrix multiplied by known voltage), correction term and (Estimation error based on primary current) (Multiplied by their respective correction factors) and Add them together to get and Then, the integral is updated by discretizing the integral using the forward Euler method. and .along with Driven to approach zero, Convergence, estimated value of secondary resonant current It then converges to the true value.

[0067] Step S3 also includes: The stability of the first-stage observer is verified using Lyapunov stability theory, specifically including: S311: Define the error variable and construct the error equation.

[0068] S312: Select a positive definite matrix, solve for the construction matrix that satisfies the first preset condition, and construct the Lyapunov function through the construction matrix.

[0069] In step S312, the expression for the first preset condition is:

[0070] in, The system matrix of the error equation, Indicates matrix transpose. The matrix to be solved is a positive definite symmetric matrix. This is a pre-selected positive definite symmetric matrix in the Lyapunov stability analysis.

[0071] S313: By selecting a gain parameter that satisfies the second preset condition, the first derivative of the Lyapunov function is made less than 0, so as to confirm that the first-stage observer is asymptotically stable.

[0072] In step S313, the expression for the second preset condition is:

[0073] in, This is the input matrix for the error equation. This is the vector of the higher-order sliding mode correction term for the first-level observer.

[0074] Furthermore, for the first-stage observer, this invention verifies its stability using Lyapunov stability theory. Specifically, with... and Construct error variables and establish error equations, where the system matrix of the error equations is... The input matrix is Then, a positive definite symmetric matrix is ​​selected. Solve for the condition that satisfies Positive definite symmetric matrix ,by Construct the Lyapunov function. In the... After finding the first derivative, this invention selects the option that satisfies... Gain parameters , Ultimately This confirms that the first-stage observer is asymptotically stable.

[0075] The second-stage observer takes the estimated value of the secondary resonant current as input and combines it with the secondary voltage equation to jointly estimate the secondary current and the load voltage, thereby obtaining the estimated value of the rectifier-side load voltage. The state equation of the second-stage observer is:

[0076]

[0077]

[0078] in, This is the first derivative of the second-stage observer's estimate of the rectifier-side load voltage vector. The system matrix of the secondary voltage equation is... The mutual inductance coupling matrix of the secondary voltage equation is... This indicates that the corresponding vector is taken from the estimation result output by the first-level observer. It is a 2×1 zero matrix. The first gain parameter of the second-stage observer, This is the second gain parameter for the second-stage observer. The first correction factor for the second-stage observer, This is the second correction factor for the second-stage observer. For the secondary current estimation error, This is the vector of the higher-order sliding mode correction term for the second-stage observer. For the sliding surface variables of the second-level observer, This is the dq-axis component vector of the secondary current.

[0079] For the second-stage observer of this invention, the output of the first stage is used as the reference. As input, and combining the secondary voltage equation, the relationship between the secondary current and the rectifier-side load voltage is analyzed. Joint estimation is performed. Specifically, this invention constructs sliding surface variables. That is, the error is estimated based on the secondary current. Multiply get Then Substituting the sign function, construct the second-order higher-order sliding mode correction term vector. The two lines are respectively and , , This is the second-stage gain parameter.

[0080] The state equation of the second-level observer will (Taken from the first-level estimation results, subscript) This indicates that the vector originates from the output of the first-level observer, and the correction term. and as well as Add them together to get and The estimated value of the rectifier-side load voltage is obtained by discrete integration using the forward Euler method. .

[0081] The final calculation result is that when the error approaches zero, it satisfies... , , , This allows for the observation of the load voltage on the rectifier side.

[0082] S4: The difference between the estimated value of the rectifier-side load voltage and the target voltage reference value is calculated by the controller to obtain the control quantity, and the control quantity is applied to the duty cycle of the BUCK step-down circuit to continuously optimize and adjust the rectifier-side load voltage, thereby completing the constant voltage control of wireless power transmission.

[0083] In step S4, the controller employs a PID control algorithm, and the expression for the controller's control quantity is:

[0084] in, The control quantity output by the PID controller. This refers to the DC bus voltage at the input of the BUCK circuit. For rectifier-side filter capacitors, The difference between the target voltage reference value and the estimated value of the rectifier-side load voltage. This is the proportionality coefficient. The differential coefficients are... The integral coefficient is... To control the start time, This is the current control moment.

[0085] Furthermore, in step S3, we obtain Then, the present invention compares it with the target voltage reference value. The difference is used to obtain the control error. Then will Input to PID controller, PID controller to Perform proportional calculations separately ( Multiply by the proportionality factor Differential operations () Multiply by the differential coefficient after taking the time derivative ), integration operations ( From the start of control Up to the current moment Multiply by the integral coefficient after integration ), add the three results and divide by To obtain the control quantity Control quantity Duty cycle directly affecting the BUCK step-down circuit Adjusting the output voltage of the BUCK circuit changes the input voltage of the full-bridge inverter, thus driving it. Towards convergence.

[0086] In step S4, the continuous domain algorithm of the cascaded observer and the controller is discretized by the forward Euler method to obtain the discretized observer equation and the discretized controller equation. The discretized observer equation and the discretized controller equation are written into the DSP control module to continuously update the estimated value of the rectifier-side load voltage and the control quantity with a fixed step size, so as to realize the real-time constant voltage control of the rectifier-side load voltage.

[0087] The continuous domain equations of the aforementioned cascaded observer and PID controller are both discretized using the forward Euler method. The forward Euler method approximates the state variables at the next time step by multiplying the derivative value at the current time step by a fixed step size. , , and The continuous differential equation is transformed into a stepwise recursive difference equation. After being written into the DSP control module, the DSP completes current sampling, coordinate transformation, observer recursion, controller calculation, and duty cycle output in sequence with a fixed step size, thereby realizing real-time constant voltage control of the rectifier-side load voltage.

[0088] The present invention also provides a constant voltage control system for wireless power transfer, for executing a constant voltage control method for wireless power transfer as described in any of the preceding claims, comprising: DC power supply, used to provide DC input voltage to the system; The BUCK step-down circuit is connected to the DC power supply and adjusts the DC input voltage according to the duty cycle control quantity output by the controller to obtain an adjustable DC bus voltage. The full-bridge topology high-frequency inverter module, composed of multiple MOSFETs, is used to invert the adjustable DC bus voltage into a high-frequency AC voltage. The dual-sided energy resonant unit consists of a primary-side inductor, a primary-side capacitor, a secondary-side inductor, a secondary-side capacitor, and mutual inductance forming an SS resonant topology. It is used to transmit the high-frequency AC voltage to the secondary side via resonant coupling, generating primary-side resonant current and secondary-side resonant current. The full-bridge rectifier unit, consisting of multiple diodes and filter capacitors, is used to rectify and filter the secondary resonant current to obtain the rectified load voltage. A resistive load is connected to the output terminal of the full-bridge rectifier unit; The primary side current acquisition circuit uses a fluxgate current sensor to sample the primary side resonant current to obtain the primary side resonant current sampling signal; like Figure 2 As shown, the DSP control module includes: The coordinate transformation unit is used to perform coordinate transformation processing on the primary side resonant current sampling signal to obtain the dq axis current component. A cascaded observer unit is used to perform state estimation of the rectifier-side load voltage using the dq-axis current component and the primary-side voltage as inputs, and to obtain the estimated value of the rectifier-side load voltage. The controller unit is used to calculate the difference between the estimated value of the rectifier-side load voltage and the target voltage reference value, and output the calculated duty cycle control quantity to the BUCK step-down circuit.

[0089] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0090] The following description, in conjunction with the illustrations, illustrates a constant voltage control method and system for wireless power transmission according to the present invention, and its control principle.

[0091] like Figure 3 As shown, the overall system framework of the wireless power transmission constant voltage control method of the present invention is illustrated, which is divided into the upper WPT topology hardware part and the lower DSP control part.

[0092] The WPT topology consists of DC power supplies. BUCK step-down circuit (composed of) , (and inductors), full-bridge inverter (composed of MOSFETs) - Composition), primary resonant circuit ( , Secondary resonant circuit ( , ), full-bridge rectifier circuit (composed of diodes) - (Composition) and filter capacitors With load The output voltage is Primary resonant current The current is collected by the current sensor and then sent to the DSP control section.

[0093] The data flow of the DSP control section is as follows: the acquired primary resonant current. First, we enter the dq-to-αβ module, which constructs a structure by combining historical data from 1 / 4 of a period ago in the storage array. Axis components, then transformed by coordinate transformation matrix Converted to dq axis current components , And thus obtain , The aforementioned dq-axis components are then input into a higher-order sliding mode observer, which combines the system parameters (including those pre-stored in Circuit Parameter Table 1) with the parameters stored in Table 1. , , , , , , (etc.) and primary voltage The secondary resonant current is estimated sequentially according to the two-stage cascaded structure. With rectifier side load voltage Output , To the observer. The observer's output. (i.e., in the diagram) The data is sent to the controller, and the controller will... The control quantity is obtained by subtracting the target reference voltage from the PID controller, and the output duty cycle is then calculated. The step-down circuit adjusts the inverter input voltage to form a complete closed-loop control circuit.

[0094] Figure 4 This paper demonstrates the SS topology fundamental equivalent circuit established under the fundamental wave approximation assumption, which forms the basis for coordinate transformation modeling.

[0095] The circuit is divided into two parts from left to right: the primary circuit and the secondary circuit, which are connected by mutual inductance. Coupling. The primary circuit is supplied by an AC voltage source. Primary-side series capacitor Primary resonant inductor Primary-side equivalent resistance The series connection has a primary resonant current of... ,in This represents the phase difference between the primary current and the excitation voltage. The secondary circuit consists of a secondary-side capacitor connected in series. Secondary resonant inductor Secondary equivalent resistance and load resistance The series connection has a secondary resonant current of ,in This represents the phase difference of the secondary current.

[0096] This equivalent circuit ignores the higher harmonics generated by the inverter, retaining only the fundamental component for modeling. Based on this circuit, Kirchhoff's voltage law is applied to the primary and secondary loops respectively, allowing the establishment of voltage equations with the fundamental current as the state variable, providing a circuit basis for subsequent αβ coordinate system modeling.

[0097] Figure 5 A schematic diagram of modeling the αβ stationary coordinate system shows that... Figure 4 The process of extending the fundamental equivalent circuit of the SS topology to the αβ biaxial model. Figure 5 In the middle, the original side loop is For excitation, the current is The circuit contains a primary-side capacitor. ,inductance With resistance It also includes a mutually inducted voltage source from the secondary side. The secondary loop current is Includes secondary capacitors ,inductance ,resistance and load and the mutually inductively coupled voltage source from the primary side. . Figure 5 In the model, the electrical quantities of the original circuit constitute the α-axis component, and the virtual circuit obtained by lagging the overall phase of the original circuit by 90° constitutes the β-axis component. The two circuits together constitute a complete biaxial model in the αβ stationary coordinate system. The voltage sources, controlled sources and impedance elements in the circuit are all expressed in complex form, reflecting the coupling relationship between the α and β axes.

[0098] Figure 6 A schematic diagram of the dq rotating coordinate system model is provided, illustrating the equivalent circuit in the dq rotating coordinate system obtained after coordinate transformation of the circuit equations in the αβ stationary coordinate system. The primary loop is powered by a DC voltage. For excitation, series equivalent inductance (Right now ) and equivalent resistance It contains two controlled voltage sources: (Right now (reflecting the cross coupling of the dq axes) and (This reflects the coupling of the secondary current to the primary side through the mutual inductance). The secondary circuit uses the rectifier-side load voltage. (Equivalent to a controlled source) as the terminal, series equivalent inductance (Right now ) and equivalent resistance and includes a controlled voltage source (Right now )and (The primary current couples to the secondary side through mutual inductance). After dq transformation, the AC quantity that originally varied sinusoidally with time is transformed into an approximate DC quantity. The circuit equations are simplified from time-varying differential equations to constant coefficient matrix equations, i.e., SS topology state equations, providing a direct mathematical model for the design of cascaded observers.

[0099] The following describes a specific embodiment of a constant voltage control method and system for wireless power transmission according to the present invention, with reference to the accompanying drawings.

[0100] To further verify the effectiveness of this method, in a specific embodiment, the present invention builds a discrete simulation in MATLAB / Simulink with a fixed simulation step size of 1e-6s, and the circuit parameters are shown in Table 1.

[0101] Table 1 System Simulation Parameters

[0102] This example simulates the constant voltage control method for wireless power transfer of the present invention. Figure 7 The verification results of the control method of this invention in MATLAB / Simulink discrete simulation are shown. Figure 7 The horizontal axis represents time (in milliseconds, ranging from 0 to 0.15 ms), and the vertical axis represents voltage (in voltage, ranging from -1 to 10 V). The red curve in the graph represents the target reference voltage. The blue curve represents the actual value of the load voltage on the rectifier side. The control algorithm is labeled as GHDSMO+SMBPID (i.e., high-order sliding mode observer combined with state matrix compensation PID controller).

[0103] Two sets of tests were executed in the simulation: Group 1, Load At the initial time It mutated at approximately 0.03 ms. It then recovered to its previous state in approximately 0.06 ms. Target reference voltage Maintain a constant voltage of 6V during this phase. Figure 7 It can be seen that during load mutation After a brief fluctuation, it quickly recovers to 6V with minimal tracking error.

[0104] The second group, target reference voltage The voltage jumped from 6V to 5V in approximately 0.09ms, and then recovered from 5V to 6V in approximately 0.125ms. Maintain at this stage Unchanged. By Figure 7 visible, It quickly tracks the new target value after a step change in the reference voltage, with minimal overshoot and fast response during the adjustment process.

[0105] The above two sets of simulation results show that the present invention can withstand two operating conditions: sudden load change and reference voltage step change. All can track quickly and accurately This verified the estimation accuracy of the cascaded observer for the rectifier-side load voltage and the effectiveness of the PID controller in adjusting the duty cycle.

[0106] Compared with existing technologies, the control method of this invention does not require an additional communication link. It only needs to collect the primary resonant current information and design the observer and controller algorithms through a rotating coordinate model. This effectively avoids control problems caused by communication delays and bit errors, and reduces the number of modules for additional communication links, saving space, especially for the secondary circuit. Secondly, compared with traditional data-driven or multi-stage circuit modeling methods, the control method of this invention requires less computation, is more adaptable to conditions such as sudden load changes, and has low algorithm design complexity. In addition, the control method of this invention can respond to changes in circuit state more quickly, thus responding to load changes faster and achieving high control accuracy.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A constant voltage control method for wireless power transmission, characterized in that, include: S1: The primary-side resonant circuit of the wireless power transmission system is approximated as the SS topology equivalent circuit based on the fundamental wave, thus obtaining the primary-side fundamental wave equivalent model. S2: Perform coordinate transformation on the original fundamental wave equivalent model, transforming it from a stationary coordinate system to a rotating coordinate system, to obtain the SS topological state equation in the dq rotating coordinate system; S3: Input the SS topology state equation into the cascade observer, and obtain the estimated value of the rectifier-side load voltage by performing state estimation on the primary side resonant current; S4: The difference between the estimated value of the rectifier-side load voltage and the target voltage reference value is calculated by the controller to obtain the control quantity, and the control quantity is applied to the duty cycle of the BUCK step-down circuit to continuously optimize and adjust the rectifier-side load voltage, thereby completing the constant voltage control of wireless power transmission.

2. The constant voltage control method for wireless power transmission according to claim 1, characterized in that, Step S1 further includes: S11: Treat the wireless power transmission system as a frequency selector that ignores harmonic components but retains the fundamental frequency component, and obtain the SS topology fundamental equivalent circuit; S12: Lag the phase of the SS topology fundamental equivalent circuit by 90° to obtain a virtual circuit; S13: The SS topology fundamental equivalent circuit and the virtual circuit are respectively used as the α-axis component and β-axis component of the stationary coordinate system to obtain the primary-side fundamental equivalent model in the αβ stationary coordinate system.

3. The constant voltage control method for wireless power transmission according to claim 1, characterized in that, Step S2 further includes: S21: For the primary-side fundamental equivalent model, establish the voltage equation in the αβ stationary coordinate system according to Kirchhoff's voltage law. The voltage equation corresponds to the circuit equation of the α axis and the circuit equation of the β axis, respectively. S22: Transform the voltage equation into the dq rotating coordinate system using a coordinate transformation matrix to obtain the SS topological state equation in the dq rotating coordinate system.

4. The constant voltage control method for wireless power transmission according to claim 3, characterized in that, The expression for the coordinate transformation matrix in step S22 is: in, The component of the primary resonant current on the d-axis in the dq rotating coordinate system. Let be the component of the primary resonant current along the q-axis in the dq rotating coordinate system. The component of the primary resonant current on the α-axis in the αβ stationary coordinate system. Let be the component of the primary resonant current along the β axis in the αβ stationary coordinate system. The resonant angular frequency, This is the current control moment; The state equations include the primary-side voltage equation and the secondary-side voltage equation, expressed as follows: in, Let dq be the dq-axis component vector of the primary current. The dq-axis component vector of the primary current The first derivative with respect to time, Let dq be the d-axis component vector of the secondary current. The dq-axis component vector of the secondary current The first derivative with respect to time, For the input voltage vector, For load voltage vector, The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. The system matrix of the secondary voltage equation is... This is the mutual inductance coupling matrix of the secondary voltage equation.

5. The constant voltage control method for wireless power transmission according to claim 1, characterized in that, The cascaded observer in step S3 is a two-stage observer, specifically including: The first-stage observer takes the primary-side resonant current measurement and the primary-side voltage as inputs, and based on the SS topological state equation, performs a joint estimation of the primary-side current and the secondary-side current to obtain the estimated value of the secondary-side resonant current. The state equation of the first-stage observer is: in, Let dq be the dq-axis component vector of the primary current. This is the estimate of the dq-axis component vector of the primary current by the first-stage observer. This is the first derivative of the estimate of the primary current dq-axis component vector by the first-stage observer. This is the estimate of the dq-axis component vector of the secondary current by the first-stage observer. This is the first derivative of the estimate of the secondary current dq-axis component vector by the first-stage observer. The system matrix of the primary voltage equation is... The mutual inductance coupling matrix of the primary voltage equation is... This is the input matrix for the primary voltage equation. This represents the fundamental amplitude of the primary-side inverter output voltage. The first gain parameter of the first-stage observer, This is the second gain parameter of the first-stage observer. The first correction factor for the first-stage observer, This is the second correction factor for the first-stage observer. It is a 2×2 zero matrix. It is a 2×2 identity matrix. This is the vector of the higher-order sliding mode correction term for the first-level observer. This is the primary current estimation error. For the design coefficient of the sliding surface, For symbolic functions, For the sliding surface variables of the first-level observer; The second-stage observer takes the estimated value of the secondary resonant current as input and combines it with the secondary voltage equation to jointly estimate the secondary current and the load voltage, thereby obtaining the estimated value of the rectifier-side load voltage. The state equation of the second-stage observer is: in, This is the first derivative of the second-stage observer's estimate of the rectifier-side load voltage vector. The system matrix of the secondary voltage equation is... The mutual inductance coupling matrix of the secondary voltage equation is... This indicates that the corresponding vector is taken from the estimation result output by the first-level observer. It is a 2×1 zero matrix. The first gain parameter of the second-stage observer, This is the second gain parameter for the second-stage observer. The first correction factor for the second-stage observer, This is the second correction factor for the second-stage observer. For the secondary current estimation error, This is the vector of the higher-order sliding mode correction term for the second-stage observer. For the sliding surface variables of the second-level observer, This is the dq-axis component vector of the secondary current.

6. The constant voltage control method for wireless power transmission according to claim 5, characterized in that, Step S3 also includes: The stability of the first-stage observer is verified using Lyapunov stability theory, specifically including: S311: Define the error variable and construct the error equation; S312: Select a positive definite matrix, solve for the construction matrix that satisfies the first preset condition, and construct the Lyapunov function through the construction matrix; S313: By selecting a gain parameter that satisfies the second preset condition, the first derivative of the Lyapunov function is made less than 0, so as to confirm that the first-stage observer is asymptotically stable.

7. The constant voltage control method for wireless power transmission according to claim 6, characterized in that, In step S312, the expression for the first preset condition is: in, The system matrix of the error equation, Indicates matrix transpose. The matrix to be solved is a positive definite symmetric matrix. This is a pre-selected positive definite symmetric matrix in the Lyapunov stability analysis; In step S313, the expression for the second preset condition is: in, This is the input matrix for the error equation. This is the vector of the higher-order sliding mode correction term for the first-level observer.

8. The constant voltage control method for wireless power transmission according to claim 1, characterized in that, In step S4, the controller employs a PID control algorithm, and the expression for the controller's control quantity is: in, The control quantity output by the PID controller. This refers to the DC bus voltage at the input terminal of the BUCK circuit. For rectifier-side filter capacitors, The difference between the target voltage reference value and the estimated value of the rectifier-side load voltage. This is the proportionality coefficient. The differential coefficients are... The integral coefficient is... To control the start time, This is the current control moment.

9. The constant voltage control method for wireless power transmission according to claim 1, characterized in that, In step S4, the continuous domain algorithm of the cascaded observer and the controller is discretized by the forward Euler method to obtain the discretized observer equation and the discretized controller equation. The discretized observer equation and the discretized controller equation are written into the DSP control module to continuously update the estimated value of the rectifier-side load voltage and the control quantity with a fixed step size, so as to realize the real-time constant voltage control of the rectifier-side load voltage.

10. A constant voltage control system for wireless power transfer, used to execute a constant voltage control method for wireless power transfer as described in any one of claims 1 to 9, characterized in that, include: DC power supply, used to provide DC input voltage to the system; The BUCK step-down circuit is connected to the DC power supply and adjusts the DC input voltage according to the duty cycle control quantity output by the controller to obtain an adjustable DC bus voltage. The full-bridge topology high-frequency inverter module, composed of multiple MOSFETs, is used to invert the adjustable DC bus voltage into a high-frequency AC voltage. The dual-sided energy resonant unit consists of a primary-side inductor, a primary-side capacitor, a secondary-side inductor, a secondary-side capacitor, and mutual inductance forming an SS resonant topology. It is used to transmit the high-frequency AC voltage to the secondary side via resonant coupling, generating primary-side resonant current and secondary-side resonant current. The full-bridge rectifier unit, consisting of multiple diodes and filter capacitors, is used to rectify and filter the secondary resonant current to obtain the rectified load voltage. A resistive load is connected to the output terminal of the full-bridge rectifier unit; The primary side current acquisition circuit uses a fluxgate current sensor to sample the primary side resonant current to obtain the primary side resonant current sampling signal; The DSP control module includes: The coordinate transformation unit is used to perform coordinate transformation processing on the primary side resonant current sampling signal to obtain the dq axis current component. A cascaded observer unit is used to perform state estimation of the rectifier-side load voltage using the dq-axis current component and the primary-side voltage as inputs, and to obtain the estimated value of the rectifier-side load voltage. The controller unit is used to calculate the difference between the estimated value of the rectifier-side load voltage and the target voltage reference value, and output the calculated duty cycle control quantity to the BUCK step-down circuit.

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