A maximum power point tracking method for energy harvesters and its application

Abstract

This invention discloses a maximum power point tracking (MPPT) method and its application for energy harvesters, belonging to the field of energy harvesting technology. Based on the gradient of the objective function T, representing the phasor difference between the load voltage and the open-circuit voltage and the magnitude difference of the load voltage, with respect to the load voltage magnitude, the perturbation direction of the load voltage magnitude is determined. Based on the phase difference, the perturbation direction of the load voltage phase is determined, and the load voltage magnitude and phase of the energy harvester are simultaneously adjusted in the corresponding perturbation direction, ensuring that the load impedance and the equivalent internal impedance of the energy harvester maintain a conjugate match, enabling accurate tracking of the maximum power of the energy harvester. Furthermore, during the perturbation process, the perturbation direction at the previous moment is used to correct the perturbation direction at the current moment to accelerate the perturbation. In addition, an adaptive perturbation step size is designed to achieve large step perturbation in the early stages and small step perturbation near the maximum power point, improving the matching rate while reducing perturbation oscillations.

Description

Technical Field

[0001] This invention belongs to the field of energy harvesting technology, and more specifically, relates to a maximum power point tracking method and its application for energy harvesters. Background Technology

[0002] With the development of the Internet of Things (IoT), the demand for wireless sensors is increasing. However, for suburban applications far from cities, current power supply methods, primarily based on batteries or wires, suffer from drawbacks such as limited lifespan and high maintenance costs. To address these issues, many energy harvesters have been proposed to convert environmental vibration energy, electromagnetic energy, and thermal energy into electrical energy to power wireless sensors. Since wireless sensors operate intermittently, it is not necessary to design energy harvesters to provide a large operating current. Instead, small energy harvesters combined with energy storage capacitors can be selected to store sufficient energy during the sensor's intermittent operation to power its operation. To store sufficient energy as quickly as possible, maximum power point tracking (MPPT) is required for the energy harvester. Therefore, researching a MPPT method for energy harvesters is of great significance.

[0003] When the internal impedance parameters of an energy harvester are unknown, there are two main methods for achieving maximum power point tracking (MPPT): the open-circuit voltage method and the perturbation-observation method. The open-circuit voltage method controls the input voltage of the power conversion circuit to half the open-circuit voltage of the energy harvester to achieve MPPT. While it can quickly locate the maximum power point, it only achieves resistance matching and does not match the reactance. It only works well for energy harvesters in resonant states; for non-resonant energy harvesters, it cannot accurately track the maximum power. The perturbation-observation method observes power changes by perturbing the input resistance of the circuit to achieve MPPT. Similarly, it only achieves resistance matching and suffers from inaccurate maximum power point location for non-resonant energy harvesters. Furthermore, the perturbation step size and direction of this method have a certain degree of randomness, easily leading to problems such as slow perturbation speed and large perturbation oscillations. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a maximum power point tracking method and application for energy harvesters. Its purpose is to solve the technical problem that the prior art cannot accurately track the maximum power of the energy harvester in the non-resonant state when the internal impedance of the energy harvester is unknown.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a maximum power point tracking method for an energy harvester, comprising:

[0006] S1. Acquire the zero-crossing time of the load current of the energy harvester, and calculate the phase difference between the load current and the open-circuit voltage based on the zero-crossing time and frequency of the open-circuit voltage of the energy harvester.

[0007] S2, Calculate the open-circuit voltage amplitude and phase difference Substitute the values ​​into the objective function T and calculate the gradient of the objective function T with respect to the load voltage magnitude. Adjust the load voltage magnitude of the energy harvester in the direction opposite to the gradient direction.

[0008] Based on phase difference Adjusting the phase of the energy harvester load voltage: when the phase difference When the phase difference is greater than 0, increase the phase of the load voltage; when the phase difference is greater than 0, increase the phase of the load voltage. When the value is less than 0, decrease the phase of the load voltage;

[0009] S3. Repeat steps S1-S2 at preset time intervals to iterate until the objective function T and the phase difference are satisfied. The absolute values ​​of all values ​​are less than the corresponding preset values; at this time, the output power of the energy harvester is at its maximum.

[0010] Here, the objective function T represents the phasor difference between the load voltage and the open-circuit voltage and the magnitude difference of the load voltage.

[0011] More preferably, step S2 includes: converting the open-circuit voltage amplitude and phase difference. Substitute these values ​​into the objective function T, and calculate the gradient w of the objective function T with respect to the load voltage magnitude. u Based on gradient w u The direction of the disturbance to the load voltage amplitude v u The update is performed, and then based on the updated perturbation direction v u Adjust the load voltage amplitude of the energy harvester;

[0012] Based on phase difference The direction of the disturbance to the phase angle of the load voltage v θ The update is performed, and then based on the updated perturbation direction v θ Adjust the phase of the energy harvester load voltage;

[0013] Among them, the direction of the disturbance of the load voltage amplitude v u The direction of the disturbance of the phase angle of the load voltage v θ The initial values ​​are all initialized to 0 before step S1.

[0014] More preferably, in the t-th iteration, based on gradient w u The direction of the disturbance to the load voltage amplitude v u The updated formula is as follows:

[0015] v u (t)=v u (t-1)+w u

[0016] In the t-th iteration, based on the phase difference The direction of the disturbance to the phase angle of the load voltage v θ The updated formula is as follows:

[0017]

[0018] Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ .

[0019] More preferably, in the t-th iteration, the perturbation direction v of the load voltage amplitude u The updated formula is as follows:

[0020] v u (t)=β u v u (t-1)+(1-β u )w u (t)

[0021] In the t-th iteration, the perturbation direction v of the load voltage phase angle θ The updated formula is as follows:

[0022]

[0023] Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;w u (t) represents the gradient w in the t-th iteration. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ ; The phase difference in the t-th iteration β u and β θ All are weighting coefficients greater than 0 and less than 1.

[0024] More preferably, in the t-th iteration, based on the updated perturbation direction v u The formula for adjusting the load voltage amplitude of the energy harvester is:

[0025] u L (t)=u L (t-1)+γ u v u (t)

[0026] In the t-th iteration, based on the updated perturbation direction v θ The formula for adjusting the phase of the energy harvester load voltage is:

[0027] θ(t)=θ(t-1)+γ θ v θ (t)

[0028] Among them, u L (t) and u L (t-1) represent the load voltage amplitudes in the t-th and t-1-th iterations, respectively; γ u This is the adjustment step size for the load voltage amplitude; v u (t) represents the perturbation direction v in the t-th iteration. u θ(t) and θ(t-1) are the load voltage phases in the t-th and t-1-th iterations, respectively; v θ (t) represents the perturbation direction v in the t-th iteration. θ ;γ θ This is the adjustment step size for the load voltage phase.

[0029] More preferably, in the t-th iteration, the adjustment step size of the load voltage amplitude is:

[0030]

[0031] In the t-th iteration, the adjustment step size of the load voltage phase is:

[0032]

[0033] Where, α u The basic adjustment step size for the load voltage amplitude; s u (t)=β u '·s u (t-1)+(1-β u ')·w u (t) 2 ;s u (t) and s u (t-1) are the adjustment parameters for the load voltage amplitude in the t-th and t-1th iterations, respectively; w u (t) represents the gradient w in the t-th iteration.u ε is a preset coefficient; α θ The basic adjustment step size for the load voltage phase; s θ (t) and s θ (t-1) are the adjustment parameters of the load voltage phase in the t-th and t-1-th iterations, respectively; The phase difference in the t-th iteration β u 'and β θ All are weighting coefficients greater than 0 and less than 1.

[0034] More preferably, the objective function T is:

[0035]

[0036] Among them, u oc The open-circuit voltage amplitude; u L θ represents the load voltage amplitude; θ represents the load voltage phase.

[0037] In a second aspect, the present invention provides a self-powered sensor system, comprising: an energy harvester, an energy conversion circuit, and a sensor;

[0038] The power conversion circuit is used to execute the maximum power point tracking method provided in the first aspect of the present invention to obtain the maximum power output of the energy harvester for use by the sensor.

[0039] Thirdly, the present invention provides a maximum power point tracking system for an energy harvester, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the maximum power point tracking method provided in the first aspect of the present invention when executing the computer program.

[0040] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device in which the storage medium is located to perform the maximum power point tracking method provided in the first aspect of the present invention.

[0041] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0042] 1. This invention provides a maximum power point tracking (MPPT) method for energy harvesters. Based on the gradient of the objective function T, representing the phasor difference between the load voltage and the open-circuit voltage and the magnitude difference of the load voltage, with respect to the load voltage magnitude, the perturbation direction of the load voltage magnitude is determined, based on the phase difference. The direction of the disturbance of the load voltage phase is determined, and the amplitude and phase of the load voltage of the energy harvester are simultaneously adjusted in the corresponding direction of the disturbance. This ensures that the load impedance and the equivalent internal impedance of the energy harvester are kept in conjugate matching, rather than just achieving resistance matching. Whether the energy harvester is in a resonant state or a non-resonant state, its maximum power can be accurately tracked.

[0043] 2. Furthermore, the maximum power point tracking method for energy harvesters provided by this invention ensures that each perturbation direction during the perturbation process is the direction that minimizes the objective function the fastest. The perturbation direction at the current moment is corrected using the perturbation direction at the previous moment. This means that if the gradient direction at the current moment is the same as the previous gradient direction, the perturbation amplitude is increased; if it is opposite to the previous gradient direction, the perturbation is reduced. This accelerates the perturbation process of the load voltage amplitude and phase, thereby enabling the energy harvester to track the maximum power accurately in a shorter time.

[0044] 3. Furthermore, the maximum power tracking method for energy harvesters provided by this invention adds weight to the perturbation direction at each moment, so that the gradient direction closer to the current moment has a greater influence on the current perturbation direction, and the gradient direction farther away has a smaller influence on the current perturbation direction, so as to avoid the gradient direction that is far away from the current moment still having a large influence on the current perturbation, thereby improving the tracking accuracy while improving the tracking efficiency.

[0045] 4. Furthermore, the maximum power point tracking method for energy harvesters provided by this invention is designed with an adaptive perturbation step size, which enables the method to quickly approach the true maximum power point with a large perturbation step size in the early stage of perturbation, and then approach the true maximum power point with a small perturbation step size after approaching the true maximum power point, thereby improving the matching rate while reducing perturbation oscillation. Attached Figure Description

[0046] Figure 1 A flowchart of a maximum power point tracking method for an energy harvester is provided for Embodiment 1 of the present invention;

[0047] Figure 2 This is a schematic diagram of the equivalent circuit model of the electromagnetic vibration energy harvester provided in Embodiment 1 of the present invention;

[0048] Figure 3 Thevenin equivalent circuit diagram of the electromagnetic vibration energy harvester provided in Embodiment 1 of the present invention;

[0049] Figure 4 The phasor relationship diagram of load voltage and open-circuit voltage in the Thevenin equivalent circuit of the energy harvester provided in Embodiment 1 of the present invention;

[0050] Figure 5 Here is a block diagram of a complex impedance matching circuit system based on the maximum power point tracking method provided by this invention;

[0051] Figure 6 The graph shows the output power and output voltage during a disturbance using the maximum power point tracking method provided by this invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0053] Example 1

[0054] A maximum power point tracking method for energy harvesters, such as Figure 1 As shown, it includes:

[0055] S1. Acquire the zero-crossing time of the load current of the energy harvester, and calculate the phase difference between the load current and the open-circuit voltage based on the zero-crossing time and frequency of the open-circuit voltage of the energy harvester.

[0056] Specifically, phase difference The calculation formula is as follows:

[0057]

[0058] Where t1 is the zero-crossing moment of the open-circuit voltage, t2 is the zero-crossing moment of the load current, and f is the frequency of the open-circuit voltage.

[0059] S2, Calculate the open-circuit voltage amplitude and phase difference Substitute these values ​​into the objective function T and calculate the gradient of the objective function T with respect to the load voltage magnitude. Adjust the load voltage magnitude of the energy harvester in the direction opposite to the gradient direction. Simultaneously, based on the phase difference... Adjusting the phase of the energy harvester load voltage: when the phase difference When the phase difference is greater than 0, increase the phase of the load voltage; when the phase difference is greater than 0, increase the phase of the load voltage. When the value is less than 0, decrease the phase of the load voltage;

[0060] Wherein, the objective function T represents the phasor difference between the load voltage and the open-circuit voltage and the magnitude difference of the load voltage; the phasor difference is obtained based on the phasor relationship between the load voltage and the open-circuit voltage in the Thevenin equivalent circuit of the energy harvester.

[0061] It should be noted that the energy harvester refers to an energy harvester with AC output, including magnetic field energy harvesters, piezoelectric vibratory energy harvesters, and electromagnetic vibratory energy harvesters (EVEH). Since the internal impedance of an AC-output energy harvester is not purely resistive—for example, the internal impedance of a magnetic field energy harvester is inductive, while that of a piezoelectric vibratory energy harvester is capacitive—the equivalent impedance of an EVEH will exhibit different states at different vibration frequencies, and deviation from the resonant frequency will lead to an increase in inductive or capacitive impedance. The inductive or capacitive nature of the energy harvester's internal impedance is not negligible. Therefore, to maximize the power absorbed by the load and achieve maximum power point tracking (MPPT), conjugate impedance matching should be implemented. The two necessary conditions for achieving conjugate impedance matching are that the amplitude of the input voltage of the power conversion circuit is half the amplitude of the energy harvester's open-circuit voltage, and the phase of the input current of the power conversion circuit is the same as the phase of the energy harvester's open-circuit voltage. Specifically, an EVEH will be used as an example for detailed explanation below:

[0062] EVEHs possess advantages such as simple structure, small size, low cost, high reliability, and wide applicability, making them suitable for supporting the widespread deployment of sensors. An EVEH mainly consists of a spring, a magnet, and a coil. External vibrations cause relative motion between the magnet and coil via the spring, thereby generating an induced electromotive force. The equivalent circuit model derived from the equations of motion is as follows: Figure 2 As shown. Where y(t) is the vibration displacement caused by the external excitation. That is, the vibration acceleration caused by external excitation, k e is the electromagnetic induction constant, which is determined by the relative position of the coil and the magnet; k is the spring constant; m is the weight of the mass block including the magnet and connecting parts; c mech R is the system's mechanical damping coefficient. c and L c These represent the resistance and inductance of the coil, Z. L This is the load impedance. When the EVEH is in a resonant state, its internal virtual capacitance... and virtual inductance k s When in resonance, it appears as an open circuit to the outside; at this time, the equivalent internal impedance of EVEH will exhibit slightly less inductance, mainly due to the coil inductance L. cThis is caused by the following: When the vibration frequency is higher than the resonant frequency, the parallel circuit composed of the internal virtual capacitor and internal virtual inductor behaves inductively to the outside; at this time, the equivalent internal impedance of the EVEH will exhibit a large inductive characteristic. Conversely, when the vibration frequency is lower than the resonant frequency, the parallel circuit composed of the internal virtual capacitor and internal virtual inductor behaves capacitively to the outside; at this time, the equivalent internal impedance of the EVEH will exhibit a large capacitive characteristic. Therefore, the internal equivalent impedance of the EVEH will exhibit different characteristics depending on its vibration state. Furthermore, the increase in inductive or capacitive characteristics due to deviation from the resonant frequency is not negligible. Therefore, to maximize the power absorbed by the load, the load impedance Z should be... L It maintains conjugate matching with the equivalent internal impedance of EVEH.

[0063] The Thevenin equivalent circuit of EVEH's equivalent circuit model is as follows: Figure 3 As shown (it should be noted that the Thevenin equivalent circuit of all energy harvesters with AC output is as follows). Figure 3 The circuit structure shown is not limited to EVEH; this description uses EVEH as an example only. The open-circuit voltage U... oc Load current I L Load voltage U L The following relationship must be satisfied:

[0064] U oc =u oc sin(ωt)

[0065]

[0066]

[0067] Among them, I L with U oc The phase difference is U L with U oc The phase difference is U L with U oc phasor relations such as Figure 4 As shown, the phasor difference between the load voltage and the open-circuit voltage

[0068] According to the complex impedance matching condition, the amplitude of the input voltage of the power conversion circuit is half the amplitude of the open-circuit voltage of the energy harvester, that is... Let the objective function T be as follows:

[0069]

[0070] As can be seen from the above equation, T is not a function that is always greater than zero, which is not conducive to solving for extrema. Therefore, The final objective function T is as follows:

[0071]

[0072] The objective function T with respect to u L The gradient is as follows:

[0073]

[0074] The directional derivative of a function is the direction in which the function increases most rapidly, and its opposite direction is the direction in which the function decreases most rapidly. Therefore, the opposite direction of the above equation is chosen as u. L The perturbation direction ensures that each perturbation step is in the direction that minimizes T to zero most quickly. Then u L The direction of the disturbance w u as follows:

[0075]

[0076] This is another necessary condition for complex impedance matching. Analysis shows that when... At that time, the load current I L Leading open circuit voltage U oc Inductive load matching is required to achieve complex impedance matching; therefore, the load voltage U needs to be increased in this case. L The phase angle θ. When At that time, the load current I L Lagging open-circuit voltage U oc A capacitive load is required to achieve complex impedance matching, which necessitates reducing the load voltage U. L The phase angle θ. Therefore, the perturbation direction w is chosen for θ. θ as follows:

[0077]

[0078] Preferably, in order to accelerate u L And the θ perturbation process, introducing v u and v θ As you accelerate u L and the θ perturbation process. Specifically, in one optional implementation, step S2 includes: converting the open-circuit voltage amplitude and phase difference... Substitute these values ​​into the objective function T, and calculate the gradient w of the objective function T with respect to the load voltage magnitude. u Based on gradient w u The direction of the disturbance to the load voltage amplitude v u The update is performed, and then based on the updated perturbation direction v u Adjust the load voltage amplitude of the energy harvester;

[0079] At the same time, based on phase difference The direction of the disturbance to the phase angle of the load voltage v θ The update is performed, and then based on the updated perturbation direction v θ Adjust the phase of the energy harvester load voltage.

[0080] Among them, the direction of the disturbance of the load voltage amplitude v u The direction of the disturbance of the phase angle of the load voltage v θ The initial values ​​are all initialized to 0 before step S1.

[0081] In one alternative implementation, the disturbance direction v of the load voltage amplitude is... u Update it to its gradient w u The sum; the direction of the disturbance of the load voltage phase angle v θ Update it to phase difference The summation is used to increase the perturbation magnitude if the current gradient direction is the same as the previous gradient direction, and decrease the perturbation if it is opposite to the previous gradient direction, thereby accelerating u. L and the θ perturbation process. Specifically, in the t-th iteration, based on the gradient w u The direction of the disturbance to the load voltage amplitude v u The updated formula is as follows:

[0082] v u (t)=v u (t-1)+w u

[0083] In the t-th iteration, based on the phase difference The direction of the disturbance to the phase angle of the load voltage v θ The updated formula is as follows:

[0084]

[0085] Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ .

[0086] Furthermore, to avoid gradient directions that are far from the current time still having a significant impact on the current disturbance, preferably, in one optional implementation, the disturbance direction v of the load voltage amplitude is... u Update it to its gradient w u The weighted summation result β u ·v u+(1-β u )·w u The direction of the disturbance of the load voltage phase angle v θ Update it to phase difference The weighted summation result

[0087] Specifically, in the t-th iteration, the perturbation direction v of the load voltage amplitude... u The updated formula is as follows:

[0088] v u (t)=β u v u (t-1)+(1-β u )w u (t)

[0089] In the t-th iteration, the perturbation direction v of the load voltage phase angle θ The updated formula is as follows:

[0090]

[0091] Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;w u (t) represents the gradient w in the t-th iteration. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ ; The phase difference in the t-th iteration β u and β θ All are weighting coefficients greater than 0 and less than 1, and in this embodiment, they are all taken as 0.9.

[0092] The above method uses a moving weighted average to add weight to the perturbation direction at each time step, so that the gradient direction closer to the current time step has a greater impact on the current perturbation direction, and the gradient direction farther away has a smaller impact on the current perturbation direction.

[0093] Furthermore, in one alternative implementation, in the t-th iteration, based on the updated perturbation direction v u The formula for adjusting the load voltage amplitude of the energy harvester is:

[0094] u L (t)=u L (t-1)+γ u v u(t)

[0095] In the t-th iteration, based on the updated perturbation direction v θ The formula for adjusting the phase of the energy harvester load voltage is:

[0096] θ(t)=θ(t-1)+γ θ v θ (t)

[0097] Among them, u L (t) and u L (t-1) represent the load voltage amplitudes in the t-th and t-1-th iterations, respectively; γ u This is the adjustment step size for the load voltage amplitude; v u (t) represents the perturbation direction v in the t-th iteration. u θ(t) and θ(t-1) are the load voltage phases in the t-th and t-1-th iterations, respectively; v θ (t) represents the perturbation direction v in the t-th iteration. θ ;γ θ This is the adjustment step size for the load voltage phase.

[0098] It should be noted that the adjustment step size γ of the load voltage amplitude u Adjustment step size γ of load voltage phase θ All values ​​can be preset; however, to achieve a larger disturbance step size when the distance is greater and a smaller step size when the distance to the maximum power point is less, thereby improving the matching rate and reducing disturbance oscillations, preferably, in one optional implementation, the square of the disturbance direction at each moment is accumulated by a moving weighted average to serve as the adjustment parameter for the disturbance step size, thus correcting the disturbance step size. Specifically, in the t-th iteration, the adjustment step size of the load voltage amplitude is:

[0099]

[0100] In the t-th iteration, the adjustment step size of the load voltage phase is:

[0101]

[0102] Where, α u The basic adjustment step size for the load voltage amplitude is set to 0.18 in this embodiment; s u (t)=β u '·s u (t-1)+(1-β u ')·w u (t) 2 ;s u (t) and s u(t-1) are the adjustment parameters for the load voltage amplitude in the t-th and t-1th iterations, respectively; w u (t) represents the gradient w in the t-th iteration. u ε is a preset coefficient, which is a very small value to avoid the denominator being zero; α θ The basic adjustment step size for the load voltage phase is set to 0.1 in this embodiment; s θ (t) and s θ (t-1) are the adjustment parameters of the load voltage phase in the t-th and t-1-th iterations, respectively; The phase difference in the t-th iteration β u 'and β θ All are weighting coefficients greater than 0 and less than 1, and in this embodiment, they are all taken as 0.9.

[0103] S3. Repeat steps S1-S2 at preset time intervals (0.5s in this embodiment) until the objective function T and the phase difference are equal. The absolute values ​​of all values ​​are less than the corresponding preset values; at this time, the output power of the energy harvester is at its maximum.

[0104] In this embodiment, the preset value of the objective function T is 0.1; phase difference The corresponding preset value is 0.02.

[0105] In summary, the maximum power point tracking method for energy harvesters provided by this invention ensures that each perturbation direction during the perturbation process is the direction that minimizes the objective function the fastest, and the perturbation direction at the current moment is corrected using the perturbation direction at the previous moment to accelerate the perturbation; the perturbation step size is also adjusted by adding a corrected adaptive algorithm to achieve large step size perturbation in the early stage of perturbation and small step size perturbation when approaching the maximum power point, thereby improving the matching rate while reducing perturbation oscillation.

[0106] Furthermore, the performance of the maximum power point tracking method provided by this invention is verified using EVEH as an example; specifically, the block diagram of the complex impedance matching circuit system based on the maximum power point tracking method provided by this invention is as follows: Figure 5 As shown. The main circuit is an H-bridge, with a PMOS transistor at the top and a GAN HEMT transistor at the bottom. The control method is unipolar frequency-doubled sinusoidal pulse width modulation, and the modulated wave is obtained by sampling the input current and controlling its amplitude and phase. The open-circuit voltage U is sampled. oc and load current I L To obtain reference information about the disturbance. oc u L and This information is sent to a microcontroller (MCU), which performs logic operations and then synchronizes the result to the modulation wave v via SPI communication. s In the control circuit, this design reduces the MCU's operating time, thereby decreasing power consumption. Modulated wave v s The input to the control circuit is the load current i L At the same time, it can control i under the MCU. L Phase and amplitude adjustments are made. The generated modulated wave v s It is fed into the drive circuit, where it generates the switching signal for the switching transistor.

[0107] Since the equivalent circuit model of EVEH is a second-order system, it takes a long time for EVEH to stabilize after the command is issued. In order to avoid sampling incorrect signals and issuing incorrect commands before EVEH has stabilized, the time interval of the disturbance is selected to be 0.5s (i.e. the preset time interval in step S3). The parameters of the equivalent circuit of EVEH are shown in Table 1.

[0108] Table 1

[0109]

[0110] The resonant frequency of the EVEH is 120Hz. Therefore, the vibration frequency was set to 119Hz to measure the maximum power point tracking effect of the present invention when the EVEH deviates from the resonant frequency. The output power and output voltage during the disturbance process are as follows: Figure 6As shown in the figure, the theoretical maximum output power of this parameter's EVEH at a vibration frequency of 119Hz is 6.13mW. As can be seen from the figure, the fast P&O method proposed in this invention can achieve an output power of 6mW within 4 seconds, with a maximum power matching degree of 97.9%. Compared to Reference 1 (G. Szarka, S. Burrow, P. Proynov and B. Stark, "Maximum power transfer tracking for ultralow-power electromagnetic energy harvesters", IEEE Trans. Power Electron., vol. 29, no. 1, pp. 201-212, Jan. 2014), which achieved a maximum power matching degree of 78.5% within 8 seconds, and Reference 2 (L. Costanzo and M. Vitelli, "Resonant electromagnetic vibration harvesters applications: Optimization of P&O MPPT technique parameters", Proc. 13th Int. Conf. Ecol. Veh. Renew. Energys, pp. 1-8, 2018), which achieved a maximum power matching degree of 96.9% within 26 seconds, this invention has a higher maximum power matching degree and requires less time, enabling accurate tracking of the maximum power of the energy harvester in a shorter time.

[0111] Example 2

[0112] A self-powered sensor system includes: an energy harvester, an energy conversion circuit, and a sensor;

[0113] The power conversion circuit is used to execute the maximum power point tracking method provided in Embodiment 1 of the present invention to obtain the maximum power output of the energy harvester for use by the sensor.

[0114] The relevant technical solutions are the same as in Embodiment 1, and will not be repeated here.

[0115] Example 3

[0116] A maximum power point tracking (MPPT) system for an energy harvester includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to perform the MPPT method provided in Embodiment 1 of the present invention.

[0117] The relevant technical solutions are the same as in Embodiment 1, and will not be repeated here.

[0118] Example 4

[0119] A computer-readable storage medium includes a stored computer program, wherein when the computer program is run by a processor, it controls the device where the storage medium is located to execute the maximum power point tracking method provided in Embodiment 1 of the present invention.

[0120] The relevant technical solutions are the same as in Embodiment 1, and will not be repeated here.

[0121] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A maximum power point tracking method for energy harvesters, characterized in that, include: S1. Acquire the zero-crossing time of the load current of the energy harvester, and calculate the phase difference between the load current and the open-circuit voltage based on the zero-crossing time and frequency of the open-circuit voltage of the energy harvester. S2, Calculate the open-circuit voltage amplitude and phase difference Substitute the values ​​into the objective function T, calculate the gradient of the objective function T with respect to the load voltage magnitude, and adjust the load voltage magnitude of the energy harvester in the direction opposite to the gradient direction; Based on the phase difference Adjusting the phase of the energy harvester load voltage: when the phase difference When the phase difference is greater than 0, increase the phase of the load voltage; when the phase difference... When the value is less than 0, decrease the phase of the load voltage; S3. Repeat steps S1-S2 at preset time intervals for iteration until the objective function T and the phase difference are equal. The absolute values ​​of all values ​​are less than the corresponding preset values; at this time, the output power of the energy harvester is at its maximum. Wherein, the objective function T represents the phasor difference between the load voltage and the open-circuit voltage and the magnitude difference of the load voltage.

2. The maximum power point tracking method according to claim 1, characterized in that, Step S2 includes: [comparing the open-circuit voltage amplitude and the phase difference] Substitute these values ​​into the objective function T, and calculate the gradient w of the objective function T with respect to the load voltage magnitude. u Based on gradient w u The direction of the disturbance to the load voltage amplitude v u The update is performed, and then based on the updated perturbation direction v u Adjust the load voltage amplitude of the energy harvester; Based on the phase difference The direction of the disturbance to the phase angle of the load voltage v θ The update is performed, and then based on the updated perturbation direction v θ Adjust the phase of the energy harvester load voltage; Among them, the direction of the disturbance of the load voltage amplitude v u The direction of the disturbance of the phase angle of the load voltage v θ The initial values ​​of all are initialized to 0 before step S1.

3. The maximum power point tracking method according to claim 2, characterized in that, In the t-th iteration, based on gradient w u The direction of the disturbance to the load voltage amplitude v u The updated formula is as follows: v u (t)=v u (t-1)+w u In the t-th iteration, based on the phase difference The direction of the disturbance to the phase angle of the load voltage v θ The updated formula is as follows: Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ .

4. The maximum power point tracking method according to claim 2, characterized in that, In the t-th iteration, the direction of the disturbance v of the load voltage amplitude u The updated formula is as follows: v u (t)=β u v u (t-1)+(1-β u )w u (t) In the t-th iteration, the perturbation direction v of the load voltage phase angle θ The updated formula is as follows: Among them, v u (t) and v u (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. u ;w u (t) represents the gradient w in the t-th iteration. u ;v θ (t) and v θ (t-1) represent the perturbation directions v in the t-th and t-1-th iterations, respectively. θ ; The phase difference in the t-th iteration β u and β θ All are weighting coefficients greater than 0 and less than 1.

5. The maximum power point tracking method according to any one of claims 2-4, characterized in that, In the t-th iteration, based on the updated perturbation direction v u The formula for adjusting the load voltage amplitude of the energy harvester is: u L (t)=u L (t-1)+γ u v u (t) In the t-th iteration, based on the updated perturbation direction v θ The formula for adjusting the phase of the energy harvester load voltage is: θ(t)=θ(t-1)+γ θ v θ (t) Among them, u L (t) and u L (t-1) represent the load voltage amplitudes in the t-th and t-1-th iterations, respectively; γ u This is the adjustment step size for the load voltage amplitude; v u (t) represents the perturbation direction v in the t-th iteration. u θ(t) and θ(t-1) are the load voltage phases in the t-th and t-1-th iterations, respectively; v θ (t) represents the perturbation direction v in the t-th iteration. θ ;γ θ This is the adjustment step size for the load voltage phase.

6. The maximum power point tracking method according to claim 5, characterized in that, In the t-th iteration, the adjustment step size of the load voltage amplitude is: In the t-th iteration, the adjustment step size of the load voltage phase is: Where, α u The basic adjustment step size for the load voltage amplitude; s u (t)=β u '·s u (t-1)+(1-β u ')·w u (t) 2 ;s u (t) and s u (t-1) are the adjustment parameters for the load voltage amplitude in the t-th and t-1th iterations, respectively; w u (t) represents the gradient w in the t-th iteration. u ε is a preset coefficient; α θ The basic adjustment step size for the load voltage phase; s θ (t) and s θ (t-1) are the adjustment parameters of the load voltage phase in the t-th and t-1-th iterations, respectively; The phase difference in the t-th iteration β u 'and β θ All are weighting coefficients greater than 0 and less than 1.

7. The maximum power point tracking method according to any one of claims 1-4, characterized in that, The objective function T is: Among them, u oc The open-circuit voltage amplitude; u L θ represents the load voltage amplitude; θ represents the load voltage phase.

8. A self-powered sensor system, characterized in that, include: Energy harvesters, power conversion circuits, and sensors; The power conversion circuit is used to execute the maximum power point tracking method according to any one of claims 1-7 to obtain the maximum power output by the energy harvester for use by the sensor.

9. A maximum power point tracking system for an energy harvester, characterized in that, include: A memory and a processor, the memory storing a computer program, the processor executing the computer program to perform the maximum power point tracking method according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, it controls the device in which the storage medium is located to perform the maximum power point tracking method according to any one of claims 1-7.

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