A maximum power point tracking and synchronization method for LCC wireless power transfer system based on perturb and observe method

Abstract

The application provides a maximum power point tracking and synchronization method for an LCC wireless power transmission system based on a disturbance observation method, which is low in communication speed requirement, convenient in structure, good in reliability and low in cost. In the application, the input of a pulse width modulation generation module at a vehicle end is a phase shift angle beta s and a system phase angle theta, and the pulse width modulation generation module generates corresponding PWM driving signals according to the two quantities, and the signals are used for operating a phase shift full bridge converter at the vehicle end; an output voltage Vds at the vehicle end is transmitted to a ground end of the wireless power transmission system through wireless communication, and the output voltage Vds and a resonance current ILrp of a compensation network enter a double-loop PI controller, and finally a ground end phase shift angle beta p is calculated and output to the pulse width modulation generation module at the ground end; the pulse width modulation generation module at the ground end generates corresponding PWM driving signals according to the ground end phase shift angle beta p, and the PWM driving signals are used for operating a phase shift full bridge converter at the ground end. The application can be applied to the field of power electronics.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to vehicle-side synchronous rectification for wireless power transmission. This method enables phase control even when communication delays between the vehicle and ground are severe (or even when there is no communication). In particular, it relates to a maximum power point tracking and synchronization method for LCC wireless power transmission systems based on the perturbation observation method. Background Technology

[0002] Maximum Power Point Tracking (MPPT) technology is commonly used in wind and solar power generation because the energy input of the system is unstable in these applications. For example, a major drawback of solar power systems is that their output power is significantly affected by weather conditions, such as changes in sunlight intensity and ambient temperature. Wind turbines also encounter complex wind conditions, such as unstable wind volume and changing wind direction. This constantly changing energy input places certain demands on the converter.

[0003] Maximum power point tracking (MPPT) of a solar cell array aims to adjust the operating point of the array according to external environmental conditions, ensuring maximum power output at any given time. One method is the perturbation-observation technique (also known as perturbation-observation).

[0004] The perturbation and observation method (P&O) is a commonly used maximum power point tracking algorithm. Also known as the hill-climbing method, it involves applying a forward or backward perturbation to the voltage, comparing the magnitude of the two perturbations, and then using feedback control. In photovoltaic power generation, the perturbation and observation method primarily controls the voltage and current at the output port.

[0005] In wireless power transfer systems, the vehicle-side (receiving end) exhibits characteristics similar to those of wind or solar power generation when receiving energy input. The magnetically coupled resonant energy received at the vehicle-side is unstable, constantly changing with variations in coil state, position, and resonant cavity parameter misalignment. Furthermore, to ensure smooth transfer of electromagnetic energy from the ground to the vehicle-side (and vice versa in a BWPT system), a phase difference must be maintained between the systems at the ground and vehicle-side. This phase difference, assuming negligible internal resistance, is 90°, but in most cases, it exhibits a complex relationship with system efficiency and various input parameters (voltage ratio, ground phase shift angle, vehicle-side phase shift, coupling coefficient, and system phase angle, among others). Therefore, synchronizing the two systems in practical applications is a very challenging task.

[0006] The phase-shifted full-bridge converter is a commonly used type in wireless power transfer systems. A phase-shifted full-bridge is a bidirectional topology (LCC topology), and its output / input power is related to the phase shift angle. Traditional synchronization methods used in wireless power transfer systems employing phase-shifted full-bridges typically involve real-time communication to transmit control and measurement parameters for synchronization. This method places high demands on communication speed; significant delays can directly lead to system misalignment. The LCC topology, a commonly used topology in wireless power transfer systems, operates at a fixed frequency. It possesses the characteristic of achieving natural constant current, but the LCC resonant cavity has extremely high parameter sensitivity. In other words, the LCC parameters need to be quite precise, otherwise misalignment will occur. In practical applications, due to changes in component temperature characteristics and natural coil losses, the LCC parameters can change, leading to misalignment. A common method to suppress this type of misalignment is vector control, which overcomes parameter misalignment by neutralizing the deviated current and voltage vectors. However, this requires certain computing resources and specialized computing hardware circuits (common types include arithmetic logic units (ALUs) and application-specific integrated circuits (ASICs)).

[0007] However, traditional synchronization methods typically transmit control and measurement parameters via real-time communication for synchronized control. This method places high demands on communication speed; significant delays can directly lead to system misalignment. Furthermore, the latency of wireless communication and the intervals between data transmissions severely impact control performance. In addition, traditional synchronization methods require complex detection circuits, the detection of multiple analog quantities, and sophisticated algorithms for computation. They also cannot suppress parameter misalignment in LCC (Limited Computation Center) topologies, which exhibit strong parameter sensitivity, thus requiring substantial computational resources and additional hardware circuitry. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a maximum power point tracking and synchronization method for LCC wireless power transmission system based on the perturbation observation method, which has low requirements for communication speed, convenient construction structure, good reliability and low cost.

[0009] The technical solution adopted in this invention is as follows: In this invention, electrical energy is transmitted from the ground to the vehicle. Both the ground and vehicle converters are phase-shifted full-bridge converters. The ground and vehicle converters form a wireless power transmission system with an LCC compensation network structure. The sampled analog quantity at the ground is the resonant current ILrp of the LCC compensation network, and the sampled analog quantities at the vehicle are the output voltage Vds and the output current Ids. The method includes the following steps:

[0010] Step a: Divide the sampled output voltage Vds with the target power Pref to obtain the target current Iref. This algebraic loop is expressed as: Iref = Pref / Vds;

[0011] Step b: Subtract the set target current Iref from the output current Ids to obtain the current error Ierr;

[0012] Step c: Input the current error Ierr into the proportional-integral controller PI for proportional and integral control. The proportional part P performs proportional calculation on the signal, and the integral part I is the sum of the differences between the measured value and the expected value. The sum of P and I is used as the control output to control the change of current. By adjusting the coefficients of P and I, the output current Ids can be made to reach and stabilize at the set target power Pref as quickly and stably as possible.

[0013] Step d: The output of the proportional-integral controller (PI) is the phase shift angle βs at the vehicle end. This signal is input to the pulse width modulation generation module at the vehicle end and to the disturbance observation module on the other hand.

[0014] Step e: The disturbance observation method module determines the direction of change of the system phase angle θ in the next cycle based on the change of the phase shift angle βs at the vehicle end and the direction of change of the current system phase angle θ. Finally, it outputs the calculated system phase angle θ to the pulse width calibration generation module at the vehicle end.

[0015] Step f: The pulse width modulation generation module at the vehicle end receives the vehicle end phase shift angle βs and the system phase angle θ as inputs. The pulse width modulation generation module generates corresponding PWM drive signals based on these two quantities. These signals are used to operate the phase-shifting full-bridge converter at the vehicle end.

[0016] Step g: The output voltage Vds at the vehicle end is transmitted to the ground end of the wireless power transmission system via wireless communication. The output voltage Vds and the resonant current ILrp of the compensation network enter a dual-loop PI controller together. Finally, the ground end phase shift angle βp is calculated and output to the pulse width modulation generation module at the ground end.

[0017] In step h, the pulse width modulation generation module at the ground end generates corresponding PWM drive signals based on the phase shift angle βp at the ground end. These PWM drive signals are used to operate the phase-shifted full-bridge converter at the ground end.

[0018] Furthermore, in step e, the specific steps for detection using the perturbation-observation method through the perturbation-observation method module are as follows:

[0019] Step e1: First, determine whether the target power Pref this time and the target power Pref last time exceed the set power margin ε. If they do not exceed the power margin ε, the system phase angle θ does not change.

[0020] Step e2: If the change in target power Pref exceeds the set power margin ε, determine the direction of change of the system phase angle θ this time and the previous time, and decide the next step based on whether the change is positive or negative.

[0021] Step e3: Then determine the direction of change of the vehicle-end phase shift angle βs between this time and the previous time, and then increase or decrease the system phase angle θ by the change amount Δθ based on the determination result, so that the direction of change of the system phase angle θ and the input target power Pref have a negative feedback relationship.

[0022] Step e4: Finally, output the system phase angle θ.

[0023] Furthermore, the wireless power transmission operates at a fixed frequency of 80kHz to 90kHz.

[0024] More specifically, in step g, the wireless communication method is WiFi communication, Bluetooth, or Zigbee.

[0025] The beneficial effects of this invention are as follows: In the method of this invention, it is set that: electrical energy is transmitted from the ground end to the vehicle end; the converters at both the ground end and the vehicle end are phase-shifted full-bridge converters; the ground end and the vehicle end form a wireless power transmission system with an LCC compensation network structure; the sampled analog quantity at the ground end is the resonant current ILrp of the LCC compensation network; and the sampled analog quantities at the vehicle end are the output voltage Vds and the output current Ids. The steps are: dividing the sampled output voltage Vds by the target power Pref to obtain the target current Iref, which is expressed as: Iref = Pref / V The target current Iref is subtracted from the output current Ids to obtain the current error Ierr. The current error Ierr is then input into a proportional-integral (PI) controller for proportional and integral control. The proportional component P performs proportional calculations on the signal, while the integral component I is the sum of the differences between each measured value and the desired value. The sum of P and I serves as the control output to control the current change. By adjusting the coefficients of P and I, the output current Ids is made to reach and stabilize at the set target power Pref as quickly and stably as possible. The output of the PI controller is the vehicle-end phase shift angle βs. This signal is input to both the vehicle-end pulse width modulation (PWM) generation module and the disturbance observation module. The disturbance observation module determines the direction of the system phase angle θ for the next cycle based on the changes in the vehicle-end phase shift angle βs and the current system phase angle θ, and finally outputs the calculated system phase angle θ to the vehicle-end PWM generation module. The vehicle-end PWM generation module receives the vehicle-end phase shift angle βs and the system phase angle θ as inputs, and generates the corresponding PWM drive signals based on these two values. The signal is used to operate the phase-shifted full-bridge converter at the vehicle end; the output voltage Vds at the vehicle end is transmitted to the ground end of the wireless power transmission system via wireless communication. The output voltage Vds and the resonant current ILrp of the compensation network enter a dual-loop PI controller together, and finally the ground-end phase shift angle βp is calculated and output to the pulse width modulation generation module at the ground end; the pulse width modulation generation module at the ground end generates corresponding PWM drive signals according to the ground-end phase shift angle βp. These PWM drive signals are used to operate the phase-shifted full-bridge converter at the ground end. The method of the present invention has the following advantages:

[0026] (1) For the two converters in a wireless power transmission system, phase synchronization between them is necessary, but it is difficult to achieve through wireless communication between the two sides because it has high real-time requirements. Commonly used wireless communication methods, such as Bluetooth, ZigBee, and Wi-Fi, all have problems with latency, connection interval, and transmission speed. For example, the minimum connection interval of Bluetooth 5.0 is 7.5ms, the maximum data transmission rate of ZigBee is 250kbps, and Wi-Fi has limitations on distributed inter-frame space and transmission interval. In addition, due to the strong electromagnetic interference generated by the coupled magnetic field, the introduction of real-time wireless communication will weaken the robustness of the control system. The problems mentioned above have a significant impact on the performance of the system. However, the present invention is insensitive to the communication latency and interference of such a two-side system.

[0027] (2) The present invention requires the detection of only a few analog quantities, and only three analog quantities need to be measured, each using a different sampling and conditioning circuit. Moreover, these conditioning circuits are not too complex.

[0028] (3) The present invention can suppress the parameter misalignment of LCC within a certain range, alleviate the parameter sensitivity of LCC topology, and does not require large computing resources and additional computing hardware circuits. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a wireless power transmission system with an LCC compensation network architecture. The symbols in the diagram represent the following: Vdp is the input voltage, Vp is the full-bridge output voltage at ground, Lrp is the resonant inductance at ground, Cp is the parallel compensation capacitor at ground, Cps is the series compensation capacitor at ground, Lp is the self-inductance at ground, ILrp is the resonant current of the LCC compensation network, M is the mutual inductance coefficient, Ls is the self-inductance at the vehicle end, Css is the series compensation capacitor at the vehicle end, Cs is the parallel compensation capacitor at the vehicle end, Lrs is the resonant inductance at the vehicle end, Vs is the full-bridge output voltage at the vehicle end, Vds is the output voltage, and Ids is the output current.

[0030] Figure 2 This is a schematic diagram of the control strategy of the present invention;

[0031] Figure 3 This is the algorithm flowchart of the perturbation-observation method module;

[0032] Figure 4 This is a schematic diagram of the resonant current coil current is sampling and conditioning circuit.

[0033] Figure 5 This is the schematic diagram of the output DC voltage sampling and conditioning circuit;

[0034] Figure 6 This is the schematic diagram of the output DC current sampling and conditioning circuit;

[0035] Figure 7 This is a flowchart of the perturbation observation algorithm implemented in Simulink in an embodiment of the present invention;

[0036] Figure 8 This is a simplified structural diagram of the algebraic ring on the vehicle side implemented using Simulink in an embodiment of the present invention;

[0037] Figure 9 This is a diagram of the simulation system implemented using Simulink in this embodiment of the invention;

[0038] Figure 10 This is a simulation effect diagram implemented using Simulink in the embodiment. Detailed Implementation

[0039] In this invention, the method is configured such that electrical energy is transmitted from the ground terminal to the vehicle terminal. Both the ground and vehicle terminals use phase-shifted full-bridge converters, forming a wireless power transmission system with an LCC compensation network structure. The sampled analog quantity at the ground terminal is the resonant current ILrp of the LCC compensation network, and the sampled analog quantities at the vehicle terminal are the output voltage Vds and the output current Ids. Their sampling circuits are respectively... Figures 4-6 As shown. The sampling circuit for the resonant current ILrp of the LCC compensation network is an improved peak hold circuit, essentially similar to a diode connected across a capacitor. This circuit can record peak changes in rapidly changing signals. The sampling circuit for the output voltage Vds is a combination of a proportional operational circuit and a voltage follower. The sampling circuit for the output current Ids is also a combination of a proportional operational circuit and a voltage follower; unlike the output voltage Vds, its input is a differential-mode signal. The wireless power transfer operates at a fixed frequency of 80kHz to 90kHz. The ground control loop for the wireless power transfer of this invention is a dual-loop PI controller.

[0040] The method includes the following steps:

[0041] Step a: Divide the sampled output voltage Vds with the target power Pref to obtain the target current Iref. This algebraic loop is expressed as: Iref = Pref / Vds;

[0042] Step b: Subtract the set target current Iref from the output current Ids to obtain the current error Ierr;

[0043] Step c: Input the current error Ierr into the proportional-integral controller PI for proportional and integral control. The proportional part P performs proportional calculation on the signal, and the integral part I is the sum of the differences between the measured value and the expected value. The sum of P and I is used as the control output to control the change of current. By adjusting the coefficients of P and I, the output current Ids can be made to reach and stabilize at the set target power Pref as quickly and stably as possible.

[0044] Step d: The output of the proportional-integral controller (PI) is the phase shift angle βs at the vehicle end. This signal is input to the pulse width modulation generation module at the vehicle end on one side and to the disturbance observation method module (P&O algorithm in the figure, where n is the number of Fourier series expansions).

[0045] Step e: The disturbance observation module determines the direction of the change (disturbance) of the system phase angle θ in the next cycle based on the change of the phase shift angle βs at the vehicle end and the change direction of the current system phase angle θ. Finally, it outputs the calculated system phase angle θ to the pulse width calibration generation module at the vehicle end.

[0046] Step f: The pulse width modulation generation module at the vehicle end receives the vehicle end phase shift angle βs and the system phase angle θ as inputs. The pulse width modulation generation module generates corresponding PWM drive signals based on these two quantities. These signals are used to operate the phase-shifting full-bridge converter at the vehicle end.

[0047] Step g: The output voltage Vds at the vehicle end is transmitted to the ground end of the wireless power transmission system via wireless communication (common communication methods are WiFi, Bluetooth and Zigbee, etc.). The output voltage Vds and the resonant current ILrp of the compensation network enter a dual-loop PI controller together. Finally, the ground end phase shift angle βp is calculated and output to the pulse width modulation generation module at the ground end.

[0048] In step h, the pulse width modulation generation module at the ground end generates corresponding PWM drive signals based on the phase shift angle βp at the ground end. These PWM drive signals are used to operate the phase-shifted full-bridge converter at the ground end.

[0049] Specifically, such as Figure 3 The diagram shows the flowchart of the P&O algorithm (i.e., perturbation and observation method). It includes three data quantities: system phase angle θ, vehicle-end phase shift angle βs, system phase angle change Δθ, power margin ε, and target power Pref. The numbers above these numbers indicate which P&O algorithm iteration this data belongs to; n-1 represents the previous iteration, n represents the current iteration, and n+1 represents the next iteration. Specifically, in step e, the perturbation and observation method module performs the perturbation and observation detection as follows:

[0050] Step e1: First, determine whether the target power Pref this time and the target power Pref last time exceed the set power margin ε (this value is a set value, representing the allowable power error). If it does not exceed the power margin ε, the system phase angle θ does not change.

[0051] Step e2: If the change in target power Pref exceeds the set power margin ε, determine the direction of change of the system phase angle θ this time and the previous time, and decide the next step based on whether the change is positive or negative.

[0052] Step e3: Then determine the direction of change of the vehicle-end phase shift angle βs between this time and the previous time, and then increase or decrease the system phase angle θ by the change amount Δθ based on the determination result, so that the direction of change of the system phase angle θ and the input target power Pref have a negative feedback relationship.

[0053] Step e4: Finally, output the system phase angle θ.

[0054] like Figures 7 to 10 As shown, in this invention, Simulink is specifically used to implement the algorithm part, and PSpice is used to simulate the sampling circuit part. The P&O algorithm is implemented in Simulink as follows: Figure 7 As shown. Besides the perturbation-observation algorithm, it also includes the division calculation process for Vds and Pref, the operation process for Iref and Ids, and a PI controller. The part following the PI controller is the implementation. Figure 3 The algorithm flow is described. This part is encapsulated into a submodule named MPPT (meaning Maximum Power Point Tracking). Figure 8 This is an example of implementing the vehicle-side control loop in Simulink. The MPPT submodule in the diagram is... Figure 7 The P&O algorithm and other calculation processes. The output control quantity is adjusted by a VCO (voltage-controlled oscillator) to change the output frequency accordingly. The following describes the pulse width modulation generation method at the vehicle end. This is a fixed-frequency phase-shifted full-bridge PWM generation method. The entire Simulink simulation implementation is as follows: Figure 9 As shown. Figure 8 This is its vehicle-side control algebraic loop. The ground terminal does not perform control but instead provides a fixed output for ease of observation. The simulation results implemented using Simulink in this example are as follows: Figure 10 As shown, the output voltage and output power can be controlled, and synchronization between the two systems can be achieved without very strict communication requirements.

[0055] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A maximum power point tracking and synchronization method for LCC wireless power transfer system based on perturb and observe method, characterized in that, In this method, the following settings are established: electrical energy is transmitted from the ground terminal to the vehicle terminal; both the ground terminal and the vehicle terminal use phase-shifted full-bridge converters; the ground terminal and the vehicle terminal form a wireless power transmission system with an LCC compensation network structure; the sampled analog quantity at the ground terminal is the resonant current ILrp of the LCC compensation network; and the sampled analog quantities at the vehicle terminal are the output voltage Vds and the output current Ids. The method includes the following steps: Step a: Divide the sampled output voltage Vds with the target power Pref to obtain the target current Iref. This algebraic loop is expressed as: Iref = Pref / Vds; Step b: Subtract the set target current Iref from the output current Ids to obtain the current error Ierr; Step c: Input the current error Ierr into the proportional-integral controller PI for proportional and integral control; Step d: The output of the proportional-integral controller (PI) is the phase shift angle βs at the vehicle end. This signal is input to the pulse width modulation generation module at the vehicle end and to the disturbance observation module on the other hand. Step e: The disturbance observation method module determines the direction of change of the system phase angle θ in the next cycle based on the change of the phase shift angle βs at the vehicle end and the direction of change of the current system phase angle θ. Finally, it outputs the calculated system phase angle θ to the pulse width calibration generation module at the vehicle end. Step f: The pulse width modulation generation module at the vehicle end receives the vehicle end phase shift angle βs and the system phase angle θ as inputs. The pulse width modulation generation module generates corresponding PWM drive signals based on these two quantities. These signals are used to operate the phase-shifting full-bridge converter at the vehicle end. Step g: The output voltage Vds at the vehicle end is transmitted to the ground end of the wireless power transmission system via wireless communication. The output voltage Vds and the resonant current ILrp of the compensation network enter a dual-loop PI controller together. Finally, the ground end phase shift angle βp is calculated and output to the pulse width modulation generation module at the ground end. Step h: The pulse width modulation generation module at the ground end generates corresponding PWM drive signals based on the phase shift angle βp at the ground end. These PWM drive signals are used to operate the phase-shifted full-bridge converter at the ground end. In step e, the specific steps for detection using the perturbation-observation method through the perturbation-observation method module are as follows: Step e1: First, determine whether the target power Pref this time and the target power Pref last time exceed the set power margin ε. If they do not exceed the power margin ε, the system phase angle θ does not change. Step e2: If the change in target power Pref exceeds the set power margin ε, determine the direction of change of the system phase angle θ this time and the previous time, and decide the next step based on whether the change is positive or negative. Step e3: Then determine the direction of change of the vehicle-end phase shift angle βs between this time and the previous time, and then increase or decrease the system phase angle θ by the change amount Δθ based on the determination result, so that the direction of change of the system phase angle θ and the input target power Pref have a negative feedback relationship. Step e4: Finally, output the system phase angle θ.

2. The maximum power point tracking and synchronization method for LCC wireless power transfer system based on perturb and observe method according to claim 1, characterized in that, The wireless power transmission works in a fixed frequency mode, and the frequency is 80-90 kHz.

3. The maximum power point tracking and synchronization method for LCC wireless power transfer systems based on the perturbation-observation method according to claim 1, characterized in that, In step g, the wireless communication mode is WiFi communication, Bluetooth or Zigbee.

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