Voltage Tracking Method for Wireless Power Transfer Systems Based on Two-Degree-of-Freedom H2 Control

Abstract

This invention relates to the field of wireless power transfer technology, specifically disclosing a voltage tracking method for wireless power transfer systems based on two-degree-of-freedom H2 control. Traditional PID controllers are low-order controllers, limiting their impact on the zero-pole distribution of the closed-loop WPT system and thus restricting its dynamic performance. This new method, based on two-degree-of-freedom H2 control, includes the following steps: establishing a large-signal model of the WPT system; sampling the output signal of the WPT system to identify the large-signal model, obtaining the identified model G of the system. W (s), where s is the Laplace operator; based on the identification model G W (s) Construct a closed-loop WPT system control model, and obtain the system's input-output relationship based on the closed-loop WPT system control model; construct an evaluation function based on the closed-loop WPT system control model; and obtain the controller K(s). This invention uses a high-order H2 controller and calculates the optimal controller based on the system model, which can significantly improve the system's performance in tracking the reference signal and meet the constantly changing power demands of the load side.

Description

Technical Field

[0001] This invention relates to the field of wireless power transfer technology, and in particular to a voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control. Background Technology

[0002] With increasing demands for flexibility and safety in charging electrical equipment, wireless power transfer (WPT) technology is finding wider application in electric vehicles, drones, rail transportation, and underwater unmanned equipment. It establishes an energy transfer mode from the primary to the secondary side by constructing a paired energy coupling mechanism with a primary and secondary side, using a high-frequency magnetic field as the energy transfer medium. A wireless charging (WPT) system mainly consists of the following components:

[0003] Primary energy transformation section

[0004] The WPT system is powered by mains frequency power. After being rectified and filtered by a rectifier and filter circuit to form the desired input DC power, it enters the high-frequency inverter section, where it is converted into a high-frequency square wave signal to drive the resonant circuit to generate a high-frequency energy-transferring magnetic field. The high-frequency inverter stage typically consists of a full-bridge inverter or a half-bridge inverter. To achieve soft-switching in the high-frequency inverter stage and to generate an alternating magnetic field, a resonant circuit needs to be added to the primary side of the WPT system. Furthermore, the resonant frequency of the resonant circuit should be consistent with the inverter's operating frequency during use.

[0005] Coupled magnetic field section

[0006] As the most critical energy transmission component of a wireless power transmission system, the coupling coil converts high-frequency alternating current into a high-frequency magnetic field to achieve medium-free energy transmission.

[0007] Secondary side energy transformation section

[0008] To improve the energy reception efficiency of the secondary coil, the secondary side of the WPT system should also be equipped with a resonant circuit. Parallel resonance can be used when the secondary load requires an equivalent current source; series resonance can be used when the secondary load requires an equivalent voltage source. The electrical energy picked up by the resonant circuit is still in AC form, requiring rectifiers and filter circuits to shape the voltage and current so that the system output is DC.

[0009] WPT systems typically use sensors at the system output voltage location to wirelessly feed the output voltage back to the primary-side controller for adjustment, thus maintaining a stable output voltage.

[0010] Currently, in applications, devices to be charged typically have different charging power requirements (e.g., 5kW, 10kW, and 15kW), each corresponding to a different output voltage. During different time periods of the same charging process, the WPT system transmitter needs to provide different voltages in real time according to the varying power demands of the device being charged. This requirement for dynamically switching output voltage places certain demands on the WPT system's ability to track the set voltage. When the charging demand of the device changes, the WPT system needs to quickly track the new reference voltage without any tracking error.

[0011] Currently, the industrial sector typically uses PID controllers to control WPT systems, enabling them to track different setpoint voltages. PID stands for Proportional, Integral, and Differential. The PID control algorithm combines proportional, integral, and derivative components into a single control algorithm. It is the most mature and widely used control algorithm for continuous circuits. This algorithm emerged in the 1930s and 40s and is suitable for situations where the model of the controlled object is unclear. Essentially, PID control calculates the output signal based on the deviation from the reference signal according to the proportional, integral, and derivative functional relationship. The result is used to control the output, enabling the system to track the setpoint. However, PID control also presents some performance challenges in WPT systems:

[0012] (1) The PID controller is a low-order controller, while the WPT system is a high-order system. Therefore, the PID controller cannot significantly affect the zero-pole distribution of the WPT system (the zero-pole distribution is related to the convergence speed of the system). As a result, the tracking performance of the system will be limited and the response speed will not be fast enough.

[0013] (2) PID controller parameter tuning requires extensive engineering experience. When the system has nonlinear characteristics, multiple sets of PID parameters need to be determined for the same system under different operating conditions. Good control performance can only be achieved by switching the PID parameters, which brings complexity and uncertainty to the implementation of the control system. Summary of the Invention

[0014] This invention provides a voltage tracking method for wireless power transfer systems based on two-degree-of-freedom H2 control. The technical problem it solves is that PID control in WPT systems has insufficient response speed, requires the determination of multiple sets of PID parameters for tuning, and its tracking performance is limited, which brings complexity and uncertainty to the implementation of the control system.

[0015] To address the above technical problems, this invention provides a voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control, comprising the following steps:

[0016] S1. Establish a large-signal model of the wireless power transmission system, i.e., the WPT system;

[0017] S2. Sample the output signal of the WPT system to identify the large-signal model and obtain the system's identification model. , For the Laplace operator;

[0018] S3. Based on the identification model Construct a closed-loop WPT system control model, and obtain the system's input-output relationship based on the closed-loop WPT system control model:

[0019]

[0020] in, It is a reference input. yes The output, It is an error signal. It is a control input. To control the sensitivity weighting function, The error sensitivity weighting function is... For feedforward circuit, For the output feedback link, For controller vectors, For the generalized control object, It is the identity matrix. It is defined as;

[0021] S4. Construct an evaluation function based on the closed-loop WPT system control model. , Represent the lower linear fractional transformation;

[0022] S5, Determine if controller that reaches the minimum value , This represents the 2-norm.

[0023] Furthermore, step S5 specifically includes the following steps:

[0024] S51. Obtaining the generalized control object State space implementation:

[0025]

[0026] in, It is a broadly defined object of control. The state space implements the corresponding system parameter matrix. For the system matrix, To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, This is the output matrix; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, This is the output matrix;

[0027] S52. Define the matrix variables to be solved. for:

[0028]

[0029] in, Representing the algebraic Riccati equation The solution, , , All are satisfied A general matrix of appropriate dimension for constraints;

[0030] S53. Define two Hamiltonian matrices as follows:

[0031]

[0032] S54, Define the matrix for:

[0033]

[0034] S55. Define the stable transfer function matrix. They are respectively:

[0035]

[0036] S56, Define the matrix :

[0037]

[0038] in, The transfer function matrix is ​​defined;

[0039] S57, Controller Convert to:

[0040]

[0041] S58, Based on the converted Conversion ;

[0042] S59, Output Enable controller that reaches the minimum value .

[0043] Further, in step S58, based on the converted , Convert to:

[0044]

[0045] Where the matrix Defined as:

[0046] .

[0047] Furthermore, Expand and substitute into the transfer function matrix ,get The final expression is:

[0048] .

[0049] Further, in step S59, hour, It reaches the minimum value.

[0050] Further, in step S59, When the minimum value is reached Represented as:

[0051] .

[0052] Further, in step S2, Represented as:

[0053]

[0054] in, To identify parameters for the system.

[0055] Further, in step S2, the output signal of the WPT system is sampled, specifically as follows:

[0056] A random square wave signal is input to excite the WPT system, and the equivalent input voltage of the inverter is sampled. The voltage across the load resistor is sampled as the input signal. As the output signal, the sampling time is 0.5ms.

[0057] As an example, the WPT system is an LCC-S-WPT system.

[0058] The voltage tracking method for wireless power transfer systems based on two-degree-of-freedom H2 control provided by this invention employs high-order... The controller, which calculates the optimal controller based on the system model, can significantly improve the system's performance in tracking the reference signal and meet the ever-changing power demands of the load side. Attached Figure Description

[0059] Figure 1 This is a circuit model diagram of the LCC-S-WPT system provided in an embodiment of the present invention;

[0060] Figure 2 This is a closed-loop WPT system model diagram provided in an embodiment of the present invention;

[0061] Figure 3 This is a two-degree-of-freedom-based embodiment of the present invention. Simulink simulation diagram of the closed-loop WPT system under control;

[0062] Figure 4 This is a two-degree-of-freedom embodiment of the present invention. A comparison of the noise signal of the WPT system between the control method and the PID control method. Detailed Implementation

[0063] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0064] In application, wireless charging systems need to provide different output voltages according to the constantly changing power demands of the load. This requires the system to respond quickly to different power demands and achieve error-free tracking. Traditional PID controllers are low-order controllers, which have limited impact on the zero-pole distribution of the closed-loop WPT system, thus limiting their dynamic performance.

[0065] Robust control theory is a new modern control theory that emerged in the 1980s. It arose to address the overly mathematical tendencies of modern control theory and adapt to the needs of practical engineering. Its core design principle involves shaping the frequency domain characteristics of the system. This method of obtaining desired characteristics by adjusting the system's frequency domain characteristics is a familiar technique to engineers and is fundamental to classical control theory. Robust control theory can be divided into two main branches based on different control objectives: one is robust control technology based on the H-norm analysis method, which handles parameter uncertainties and disturbance rejection; the other focuses on improving system response speed and tracking performance. (norm) control technology.

[0066] Control has the following advantages:

[0067] First, The norm represents the product of the squares of the signals, and the system's norm is... The smaller the norm, the faster the response speed, achieved by minimizing the closed-loop WPT system. Using norms to derive the controller allows us to directly obtain the optimal controller for improving system tracking performance.

[0068] second, The controller is a high-order controller designed based on the system model. It can significantly affect the zero-pole distribution of the system. By selecting appropriate controller parameters, the closed-loop system may be made to have both speed and robustness.

[0069] third, The control design process is clearly defined and easy to adjust, reducing reliance on experience in system parameter tuning.

[0070] based on The advantages of (norm) control technology, and embodiments of the present invention provide a method based on two degrees of freedom H2 (norm) control technology. A voltage tracking method for a wireless power transfer system controlled by a wireless power transfer system includes steps S1 to S6.

[0071] (1) Step S1: Establish a large-signal model of the wireless power transmission system, i.e., the WPT system.

[0072] This example uses an LCC-S type WPT system for modeling. The system structure is as follows: Figure 1 As shown. Among them, It is a DC input voltage source; It is the inductance on the original side. It is a secondary inductor; and It is a resonant capacitor; Mutual inductance between coils; For inverter switching transistors; It is a rectifier bridge diode. For filtering capacitors, For load, This is the load voltage.

[0073] (2) Step S2: Model Identification

[0074] S2. Sample the output signal of the WPT system to identify the large-signal model and obtain the system's identification model. , For the Laplace operator.

[0075] A large-signal model of the WPT system is established by collecting input and output data, with the input signal being the inverter's equivalent input voltage. The output is the voltage across the load resistor. The sampling time is 0.5 ms, and a random square wave signal is used to excite the system. After obtaining the system's output signal, the System Identification toolbox in Matlab is used for identification. A continuous second-order transfer function is selected as the identification model. The final system model is then obtained. as follows:

[0076] (1)

[0077] in Here, s represents the system identification parameters, and s is the Laplace operator.

[0078] (3) S3. Construct a closed-loop WPT system control model and obtain the input-output relationship.

[0079] S3. Based on the identification model Construct a closed-loop WPT system control model, and obtain the input-output relationship of the system based on the closed-loop WPT system control model.

[0080] The control block diagram of a closed-loop system is as follows: Figure 2 As shown. Among them It is a reference input. yes The output, It is an error signal. It is a control input. The sensitivity weighting function is used to suppress excessive changes in the control input. This is the error sensitivity weighting function, used to adjust the tracking performance of the system; This is a feedforward element (first degree of freedom). This is the output feedback loop (second degree of freedom). Since a vector controller is used, it is a two-degree-of-freedom control structure. For an identity matrix of appropriate dimensions, The definition is as follows: Define the evaluation signal. , For the input evaluation function, This is the error evaluation function.

[0081] based on Figure 2 The input-output relationship of the system can be expressed as:

[0082] (2)

[0083] in The representation is defined as follows: It refers to the object of control in a broad sense.

[0084] (4) S4. Constructing the evaluation function

[0085] S4. Construct an evaluation function based on the closed-loop WPT system control model. .

[0086] First of all, The following blocks can be used for partitioning:

[0087] (3)

[0088] Define generalized objects With controller The lower linear fractional transformation (LFT) is as follows:

[0089] (4)

[0090] From reference input To the evaluation function The transfer function can be written as

[0091] (5)

[0092] (5) S5, find the one that makes controller that reaches the minimum value , This represents the 2-norm.

[0093] Will Redefining , The goal of control is to find a regular controller. This ensures the stability of the closed-loop system and makes... It reaches a minimum value.

[0094] Step S5 specifically includes the following steps:

[0095] S51. Obtaining the generalized control object State space implementation:

[0096] (6)

[0097] in It is a broadly defined object of control. The state space implements the corresponding system parameter matrix. For the system matrix, To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, This is the output matrix; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, For the output matrix, For direct matrix transmission; It is a generalized control object block. The state space implements the corresponding system parameter matrix. To control the input matrix, This is the output matrix;

[0098] S52. Define the matrix variables to be solved. for:

[0099] (7)

[0100] in, Representing the algebraic Riccati equation The solution, , , All are satisfied A general matrix of appropriate dimension for constraints;

[0101] S53. Define two Hamiltonian matrices as follows:

[0102] (8)

[0103] S54, Define the matrix for:

[0104] (9)

[0105] S55. Define the stable transfer function matrix. They are respectively:

[0106] (10)

[0107] S56, Define the matrix :

[0108] (11)

[0109] in, The transfer function matrix is ​​defined;

[0110] S57, Controller Convert to:

[0111] (12)

[0112] S58, Based on the converted Conversion for:

[0113] (13)

[0114] Where the matrix Defined as:

[0115] (14)

[0116] S59, Output Enable controller that reaches the minimum value .

[0117] Step S59 specifically includes:

[0118] Will Expand and substitute into the transfer function matrix We can obtain:

[0119] (15)

[0120] Using the orthogonality between stable and completely unstable transfer function matrices, we have:

[0121] (16)

[0122] In order to make To reach the minimum value, let That's it. The optimal controller is:

[0123] (17)

[0124] The voltage tracking method for wireless power transfer systems based on two-degree-of-freedom H2 control provided in this invention employs a high-order... The controller, which calculates the optimal controller based on the system model, can significantly improve the system's performance in tracking the reference signal and meet the ever-changing power demands of the load side.

[0125] The following experiment will verify this.

[0126] Based on two degrees of freedom The SIMULINK simulation block diagram of the controlled WPT system is as follows: Figure 3 As shown. The reference voltage signal was set to 200V-300V-400V, with a switching interval of 0.02s. A PID control scheme was used for comparison. The PID parameters were provided by Matlab PID Tuner. The comparison results are as follows. Figure 4 As shown in the figure. It can be seen that the WPT system has two degrees of freedom. Under the control of the controller, it has a faster tracking speed compared to the PID controller, and has two degrees of freedom. The controller's settling time is 8ms, while the PID controller's is 15ms, representing an 87.5% improvement in response speed. Therefore, it is a two-degree-of-freedom controller. The controller can respond to changes in the reference input more quickly.

[0127] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control, characterized in that, Including the following steps: S1. Establish a large-signal model of the wireless power transmission system, i.e., the WPT system; S2. Sample the output signal of the WPT system to identify the large-signal model, and obtain the system identification model G. W (s), where s is the Laplace operator; S3, Based on the identification model G W (s) Construct a closed-loop WPT system control model, and obtain the system's input-output relationship based on the closed-loop WPT system control model: ， Where r is the reference input, and y is G. W The output of (s), z u For the input evaluation function, z e Let e ​​be the error evaluation function, u be the control input, and W be the error signal. u To control the sensitivity weighting function, W e K is the error sensitivity weighting function. p For the feedforward stage, K f For the output feedback loop, K=[K p -K f [I] represents the controller vector, P represents the generalized controlled object, and I represents the identity matrix. It is defined as; S4. Construct an evaluation function based on the closed-loop WPT system control model. , Represent the lower linear fractional transformation; S5, Determine if The controller K(s) that reaches the minimum value. This represents the 2-norm.

2. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 1, characterized in that, Step S5 specifically includes the following steps: S51. Obtaining the state space of the generalized control object P: ， Where {A,B,C,D} is the system parameter matrix corresponding to the state-space implementation of the generalized control object P, where A is the system matrix, B is the control input matrix, C is the output matrix, and D is the direct transfer matrix; {A,B1,C1,0} is the block of the generalized control object. The state space implementation corresponds to the system parameter matrix, where B1 is the control input matrix and C1 is the output matrix; {A,B2,C1,D} 12 } is a generalized control object block. The state space implementation corresponds to the system parameter matrix, B2 is the control input matrix, C1 is the output matrix, and D... 12 For direct transmission of the matrix; {A,B1,C2,D 21 } is a generalized control object block. The state space implementation corresponds to the system parameter matrix, B1 is the control input matrix, C2 is the output matrix, and D... 21 For direct transmission of the matrix; {A,B2,C2,0} is a block of the generalized control object. The state space implements the corresponding system parameter matrix, B2 is the control input matrix, and C2 is the output matrix; S52. Define the matrix variable X to be solved as: ， in, Representing the algebraic Riccati equation E T The solutions to X + XE - XWX + Q = 0 all satisfy E, W, and Q. T The general matrix of the constraint X+XE-XWX+Q=0; S53. Define two Hamiltonian matrices as follows: ； S54. Define matrices X1, Y1, F2, L2. for: ； S55. Define the stable transfer function matrices U, V, G c G f They are respectively: ； S56, Define the matrix : ， Among them, M, M 11 M 12 M 21 M 22 The transfer function matrix is ​​defined; S57. Convert controller K(s) to: ； S58, Based on the transformed K(s) transform H zr (s); S59, Output Enable The controller K(s) reaches the minimum value.

3. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 2, characterized in that, In step S58, based on the transformed K(s), H zr (s) is converted to: ， Where matrix N is defined as: 。 4. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 3, characterized in that, H zr (s) Expand and substitute into the transfer function matrices U, V, G c G f H zr The final expression of (s) is: 。 5. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 4, characterized in that: In step S59, when Q=0, It reaches the minimum value.

6. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 5, characterized in that, In step S59, The value of K(s) at its minimum is expressed as: 。 7. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to any one of claims 1 to 6, characterized in that, In step S2, G W (s) is represented as: ， Where {a0, a1, b0, b1} are the system identification parameters.

8. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 7, characterized in that, In step S2, the output signal of the WPT system is sampled, specifically as follows: A random square wave signal is input to excite the WPT system. The equivalent input voltage u of the inverter is sampled as the input signal, and the voltage vo across the load resistor is sampled as the output signal. The sampling time is 0.5ms.

9. The voltage tracking method for a wireless power transfer system based on two-degree-of-freedom H2 control according to claim 8, characterized in that: The WPT system is the LCC-S-WPT system.

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