A power optimization method for an axial eccentric pendulum electromagnetic energy harvester

Abstract

The present invention proposes a power optimization method for an axial eccentric pendulum electromagnetic energy collector. The present invention adopts a two-dimensional section development method to convert the three-dimensional model of the axial energy collector into a two-dimensional model and then performs iterative calculations, which greatly reduces the model complexity and calculation freedom; at the same time, the model in the present invention adopts a steady-state solution method instead of a transient solution method, which can reduce the time steps required for the solution and further improve the solution speed. The optimization method proposed in the present invention can optimize the coil design parameters in the energy collector, and then realize the optimal design scheme for the output performance of the energy collector. It can maximize the output power of the energy collector in a limited space, which is of great significance for improving the output power density of the energy collector.

Description

Technical Field

[0001] The invention belongs to the technical field of coil design of energy collectors, and in particular relates to a power optimization method of an axial eccentric pendulum electromagnetic energy collector. Background Art

[0002] The eccentric pendulum low-frequency vibration energy collector with axial magnetic field distribution has the advantages of high power generation efficiency, low output impedance, and large output power. It has a simple structure and is easy to implement. It can be used in scenarios where low-frequency vibration energy is converted into electrical energy, such as wave energy collection and human kinetic energy collection. The core components of this energy collector are permanent magnets and coils, which rely on the change of equivalent magnetic flux in the coil to generate electric field power generation. For a coil of a given size, the larger the width and thickness of the coil, the more turns of the coil and the equivalent magnetic flux of the coil will increase. However, due to the internal resistance of the wire wound around the coil, the internal resistance of the coil will increase as the number of turns increases, which will lead to a decrease in output performance. At the same time, as the width of the coil increases, the coil area of ​​the inner circle will also decrease, resulting in an insignificant increase in magnetic flux; as the thickness of the coil increases, due to the magnetic field distribution characteristics of the permanent magnet, the increase in magnetic flux of the bottom coil layer far from the permanent magnet is also insignificant. At this time, as the internal resistance increases, the output power of the coil reaches a maximum value, which is of great significance for improving the output performance of the energy collector. Therefore, the present invention aims to propose a method for finding the optimal parameters of a coil, so as to provide an effective reference for the coil design parameters of an energy harvester. Summary of the invention

[0003] The purpose of the present invention is to solve the problems in the prior art and to provide a power optimization method for an axial eccentric pendulum electromagnetic energy collector.

[0004] The present invention is implemented by the following technical scheme. The present invention proposes a power optimization method for an axial eccentric pendulum electromagnetic energy collector, and the method is specifically as follows:

[0005] S1: Determine the design dimensions of the energy harvester and the coil diameter parameters as the geometric basis for establishing the 3D model;

[0006] S2: Determine the maximum swing angle of the eccentric pendulum through experiments or data manuals, and calculate the air gap;

[0007] S3: Establish a three-dimensional model of the electromagnetic field component of the energy harvester, intercept the mid-plane as the calculation area, and convert it into a two-dimensional calculation model;

[0008] S4: Use the Maxwell equations described by vector magnetic potential as the control equations of the calculation area and set the calculation conditions of the coil and permanent magnet;

[0009] S5: Calculate the rotor speed at the current time step and substitute it into the rotor region equations as the calculation condition and as the Lorentz term boundary condition;

[0010] S6: Calculate the rotor position at the current time step and update the rotor geometric position in the two-dimensional calculation model;

[0011] S7: dividing the two-dimensional computing model into computing networks and generating computing networks;

[0012] S8: solve the steady-state vector magnetic potential distribution at the current time step and calculate the output power of the coil group;

[0013] S9: Determine whether the next iteration time step exceeds the calculation cycle; if yes, go to S10; if not, increase the current time step by one time step as the next iteration time step, and re-execute S5 to S9;

[0014] S10: Calculate the effective value of the coil output power during the motion cycle;

[0015] S11: Compare other calculation results to determine whether the power reaches the maximum value; if yes, proceed to S12; if no, change the length and width geometric dimensions of the coil section and re-execute S3 to S11;

[0016] S12: Obtain the optimal design parameters of the energy harvester.

[0017] Furthermore, the energy collector described in step S1 is an eccentric pendulum low-frequency vibration energy collector with axial magnetic field distribution, in which a first coil layer, an eccentric pendulum layer and a second coil layer are distributed in sequence in the direction of the rotation axis; wherein the eccentric pendulum layer includes a supporting frame and a permanent magnet array; wherein the number of coils in the first coil layer and the second coil layer is the same, and the number of permanent magnets in the eccentric pendulum layer is half of the number of coils in the first coil layer.

[0018] Furthermore, the median surface described in step S3 is an annular cross-section, and its diameter is the average of the inner diameter and the outer diameter of the coil; the cross-section height is greater than the three-dimensional model height, and symmetrical blank areas are reserved above and below as air areas during calculation; it is axially expanded into a two-dimensional plane at the center of the side without the eccentric pendulum to form a two-dimensional calculation model.

[0019] Furthermore, the two-dimensional computing model is composed of multiple computing layers, including a first air epitaxial layer, a first coil layer, a first air gap layer, a permanent magnet layer, a second air gap layer, a second coil layer and a second air epitaxial layer; wherein the first coil layer and the second coil layer include coil areas and air areas; the permanent magnet layer includes a permanent magnet area and an air area.

[0020] Further, the rotor speed in step S5 is determined by the first-order derivative of the rotor displacement.

[0021] Furthermore, the rotor position in step S6 is determined by a rotor displacement function; the rotor displacement function is a periodic function that can describe the rotational displacement of the rotor within one energy conversion cycle.

[0022] Furthermore, the computing network division described in step S7 uses a triangular network or a rectangular network to divide the computing area into multiple computing nodes.

[0023] Further, in step S2, after determining the maximum swing angle, the minimum air gap is calculated using the following formula:

[0024] d AGM =R 0 sinθ B

[0025] In the formula, R 0 is the radius of the eccentric pendulum, θ B is the maximum swing angle, d AGM is the minimum air gap.

[0026] Furthermore, in step S4, the simplified Maxwell equations after quasi-static approximation are used as control equations, as shown in the following equation:

[0027]

[0028] Where D represents the electric displacement vector, E represents the electric field strength vector, B represents the magnetic flux density vector, and J represents the current density vector; the current density vector is solved by the electric field strength, and the electric field strength is solved by the rate of change of the vector magnetic potential A, satisfying the following equation:

[0029]

[0030] Where σ represents the conductivity.

[0031] Furthermore, in step S5, the permanent magnet group domain is set to have a Lorentz velocity condition, and the velocity value is specified using the following formula:

[0032]

[0033] In the formula, x′(t i ) represents the velocity at the current time step, θ′(t i ) is the rotor angular velocity at the current time step, which is obtained by taking the first-order derivative of the rotation angle function θ(t), R i Represents the inner radius of the coil group, R o Represents the outer radius of the coil group; thereby, the periodic rotation of the rotor in the energy harvester is converted into the Lorentz linear velocity condition at the current calculation time step, acting on the permanent magnet domain in the eccentric pendulum to simulate the relative motion between the permanent magnet and the coil.

[0034] The beneficial effects of the present invention are:

[0035] The present invention adopts a two-dimensional section development method to convert the three-dimensional model of the axial energy collector into a two-dimensional model and then perform iterative calculations, which greatly reduces the model complexity and calculation freedom; at the same time, the model in the present invention adopts a steady-state solution method instead of a transient solution method, which can reduce the time steps required for solution and further improve the solution speed. The optimization method proposed in the present invention can optimize the coil design parameters in the energy collector, and then realize the optimal design scheme of the output performance of the energy collector, and can maximize the output power of the energy collector in a limited space, which is of great significance for improving the output power density of the energy collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Attached Figure 1 It is a flow chart of the electromagnetic field optimization method of the present invention for a low-frequency vibration energy collector with axial magnetic field distribution.

[0037] Attached Figure 2 This is a schematic diagram for calculating the minimum air gap of an eccentric pendulum.

[0038] Attached Figure 3 It is a schematic diagram of the equivalent calculation model.

[0039] Attached Figure 4 It is a schematic diagram of the two-dimensional calculation model.

[0040] Attached Figure 5 This is a schematic diagram for calculating the number of coil turns. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1-Figure 5 The present invention proposes a power optimization method for an axial eccentric pendulum electromagnetic energy collector, and the method is specifically as follows:

[0043] S1: Determine the design dimensions of the energy harvester and the coil diameter parameters as the geometric basis for establishing the 3D model;

[0044] S2: Determine the maximum swing angle of the eccentric pendulum through experiments or data manuals, and calculate the air gap;

[0045] S3: Establish a three-dimensional model of the electromagnetic field component of the energy harvester, intercept the mid-plane as the calculation area, and convert it into a two-dimensional calculation model;

[0046] S4: Use the Maxwell equations described by vector magnetic potential as the control equations of the calculation area and set the calculation conditions of the coil and permanent magnet;

[0047] S5: Calculate the rotor speed at the current time step and substitute it into the rotor region equations as the calculation condition and as the Lorentz term boundary condition;

[0048] S6: Calculate the rotor position at the current time step and update the rotor geometric position in the two-dimensional calculation model;

[0049] S7: dividing the two-dimensional computing model into computing networks and generating computing networks;

[0050] S8: solve the steady-state vector magnetic potential distribution at the current time step and calculate the output power of the coil group;

[0051] S9: Determine whether the next iteration time step exceeds the calculation cycle; if yes, go to S10; if not, increase the current time step by one time step as the next iteration time step, and re-execute S5 to S9;

[0052] S10: Calculate the effective value of the coil output power during the motion cycle;

[0053] S11: Compare other calculation results to determine whether the power reaches the maximum value; if yes, proceed to S12; if no, change the length and width geometric dimensions of the coil section and re-execute S3 to S11;

[0054] S12: Obtain the optimal design parameters of the energy harvester.

[0055] The energy collector described in step S1 is an eccentric pendulum low-frequency vibration energy collector with axial magnetic field distribution, in which a first coil layer, an eccentric pendulum layer and a second coil layer are distributed in sequence in the direction of the rotation axis; the eccentric pendulum layer includes a supporting frame and a permanent magnet array; the number of coils in the first coil layer and the second coil layer is the same, and the number of permanent magnets in the eccentric pendulum layer is half of the number of coils in the first coil layer.

[0056] The median plane described in step S3 is an annular cross-section, and its diameter is the average of the inner diameter and the outer diameter of the coil; the cross-section height is greater than the three-dimensional model height, and symmetrical blank areas are reserved above and below as air areas during calculation; it is axially expanded into a two-dimensional plane at the center of the side without the eccentric pendulum to form a two-dimensional calculation model.

[0057] The two-dimensional computing model is composed of multiple computing layers, including a first air epitaxial layer, a first coil layer, a first air gap layer, a permanent magnet layer, a second air gap layer, a second coil layer and a second air epitaxial layer; wherein the first coil layer and the second coil layer include a coil area and an air area; the permanent magnet layer includes a permanent magnet area and an air area.

[0058] The rotor speed in step S5 is determined by the first-order derivative of the rotor displacement.

[0059] The rotor position in step S6 is determined by a rotor displacement function; the rotor displacement function is a periodic function that can describe the rotational displacement of the rotor within one energy conversion cycle.

[0060] The computing network division described in step S7 uses a triangular network or a rectangular network to divide the computing area into multiple computing nodes.

[0061] Example

[0062] The specific implementation of the present invention will be described below with reference to the accompanying drawings. Figure 1 The figure shows an electromagnetic field optimization method for an eccentric pendulum low-frequency vibration energy collector for axial magnetic field distribution proposed by the present invention, and the specific implementation method is as follows:

[0063] The first step is to use actual raw material parameters, application requirements, etc. as limiting conditions for the design of the energy harvester. These conditions include the outer diameter and thickness of the energy harvester, as well as parameters such as the wire diameter of the coil.

[0064] The second step is to determine the maximum axial swing angle of the eccentric pendulum. Since the eccentric pendulum is connected to the housing through bearings and other means, there is a certain tolerance in the connection between the bearing and the shaft, which will cause the eccentric pendulum to swing sideways. Figure 2 After determining the maximum swing angle, the minimum air gap is calculated using the following formula:

[0065] d AGM =R 0 sinθ B

[0066] In the formula, R 0 is the radius of the eccentric pendulum, θ B is the maximum swing angle, d AGM The minimum air gap calculated at this time is the minimum reserved distance that satisfies the eccentric pendulum so that it will not collide or rub against the side wall during actual operation. This value is used as the thickness of the first air gap and the second air gap in the model.

[0067] The third step is to build a three-dimensional model of the energy harvester, such as Figure 3As shown. The model contains components related to electromagnetic power generation of the energy collector, including the first coil layer, the eccentric pendulum layer and the second coil layer. There is an axial distance between the first coil layer and the eccentric pendulum layer, and there is an axial distance between the second coil layer and the eccentric pendulum layer. These two distances are equal and are the minimum air gaps calculated in the second step. The first coil layer and the second coil layer are evenly distributed with multiple coils in the radial direction, and the number of coils is related to the number of magnetic poles of the generator required in the actual design. The eccentric pendulum layer is distributed with multiple magnetic poles in the radial direction, and the number of magnetic poles is half of the number of the first coil inner layer or the second coil layer. The coils in the first coil layer and the second coil layer are distributed in the same position and have the same number of coils. The average value of the inner diameter and the outer diameter of the coil is used as the cross-sectional diameter, and a circular cross-section is established with the rotation axis as the center. The upper and lower heights of the cross-section are respectively higher than the first coil layer and the second coil layer, which is used to reserve the air domain. A section is made in the cross-section at a position symmetrical to the center line of the eccentric pendulum, and the circular surface is unfolded into a two-dimensional plane as a calculation model.

[0068] The fourth step is to use finite element analysis software such as COMSOL and ANSYS to set the control equations and boundary conditions of the two-dimensional calculation model, such as Figure 4 As shown. The two-dimensional calculation model includes a first air domain 31 (i.e., a first air epitaxial layer), a first coil layer 32, a first air gap layer 33, a permanent magnet layer 34, a second air gap layer 35, a second coil layer 36, and a second air domain 37 (i.e., a second air epitaxial layer), wherein the first coil layer includes a coil group domain 321 and an air domain 322, the permanent magnet layer includes a permanent magnet group domain 341 and an air domain 342, and the second coil layer includes a coil resistance domain 361 and an air domain 362. Since the relative rotation speed of the rotor and stator of the energy harvester is usually low, for the entire model, the simplified Maxwell equations after quasi-static approximation are used as the control equations, as shown below:

[0069]

[0070] Where D represents the electric displacement vector, E represents the electric field strength vector, B represents the magnetic flux density vector, and J represents the current density vector. The current density vector is solved by the electric field strength, and the electric field strength is solved by the rate of change of the vector magnetic potential A, satisfying the following equation:

[0071]

[0072] Where σ represents the conductivity.

[0073] For the coil group domain, set the number of turns of the coil and set the coil to be evenly distributed. The number of turns of the coil section is calculated as follows Figure 5 As shown, the coil is specified to be in a tightly wound mode, and the total number of turns of the coil is calculated as follows:

[0074]

[0075] In the formula, N represents the number of coil turns, H represents the coil thickness, W represents the coil width, and Φ represents the coil winding diameter. Thus, for a given coil width, thickness, and the diameter of the coil winding wire, the number of coil turns can be obtained as a setting condition. In the coil group domain, adjacent rectangular coil areas are set in opposite directions, that is, perpendicular to the 2D model plane, outward or inward.

[0076] For the permanent magnet group domain, each rectangular permanent magnet domain is set to have a residual magnetic flux density condition, that is, the permanent magnet condition is set. The residual magnetic flux density of adjacent rectangular permanent magnet domains is in opposite directions, and the residual magnetic flux density of each rectangular permanent magnet domain is the same, and the value is determined by the selected permanent magnet brand.

[0077] The fifth step is to specify the rotation angle function θ(t) within a complete motion cycle of the energy harvester, with the current time step t i As the time calculation condition (if it is the initial calculation state, it is 0). Set the permanent magnet group domain to have the Lorentz velocity condition, and use the following formula to specify the velocity value:

[0078]

[0079] In the formula, x′(t i ) represents the velocity at the current time step, θ′(t i ) is the rotor angular velocity at the current time step, which is obtained by taking the first-order derivative of the rotation angle function θ(t), R i Represents the inner radius of the coil group, R o Represents the outer radius of the coil group. This converts the periodic rotation of the rotor in the energy harvester into the Lorentz linear velocity condition at the current calculation time step, acting on the permanent magnet domain in the eccentric pendulum to simulate the relative motion between the permanent magnet and the coil.

[0080] The sixth step is to calculate the rotor geometric position in the horizontal direction according to the rotation angle function θ(t), and use the difference between this position and the initial position as the displacement value to move the permanent magnet group domain and update the two-dimensional geometric model. The position calculation method is as follows:

[0081]

[0082] In the formula, x(t i ) represents the equivalent two-dimensional position of the rotor at the current time step.

[0083] The seventh step is to divide the two-dimensional computing model into networks. The division method can be rectangular unit division or triangular division to generate a discretized computing network.

[0084] In the eighth step, the solver is used to calculate the steady-state vector magnetic potential distribution at the current time step, and the output voltage and output power of the coil are calculated. The coil output voltage is obtained by integrating the electric field vector over the length of the coil side wall. The maximum output power of the coil is the output power when the load impedance is equal to the internal resistance of the coil, and the calculation method is as follows:

[0085]

[0086] Where P(t i ) is the output power of the coil group at the current time step, U(t i ) is the output voltage of the coil group at the current time step, R c is the internal resistance of the coil group.

[0087] The ninth step is to determine whether the time step after the current time step is increased by one calculation time step has reached the rotor motion period of the energy collector. If not, the current time step is increased by one calculation time step as the time step for the next iterative calculation, and steps 5 to 9 are re-executed; if reached, proceed to step 10.

[0088] Step 10: Calculate the effective value of the output power of the energy harvester coil group in a complete motion cycle under the current coil geometry setting conditions. The calculation formula is as follows:

[0089]

[0090] Where N represents the number of discrete calculation points in a motion cycle, P RMs，j Represents the effective value of the energy harvester output power under the jth coil design parameters.

[0091] In the eleventh step, compare the calculated effective value results of the energy harvester output power under all different coil design parameter combinations to determine whether the effective value of the output power under the current design parameters has reached the maximum value. If not, change the design parameters of the coil, including geometric design parameters such as coil width and thickness, and re-execute steps 3 to 11; if yes, execute step 12.

[0092] In the twelfth step, the output power of the energy harvester has been maximized under the current coil design parameters, and the optimal design parameters are output as the design basis of the energy harvester.

Claims

1. A power optimization method for an axial eccentric pendulum electromagnetic energy collector, characterized in that: The method is specifically as follows: S1: Determine the design dimensions of the energy harvester and the coil diameter parameters as the geometric basis for establishing the 3D model; S2: Determine the maximum swing angle of the eccentric pendulum through experiments or data manuals, and calculate the air gap; S3: Establish a three-dimensional model of the electromagnetic field component of the energy harvester, intercept the mid-plane as the calculation area, and convert it into a two-dimensional calculation model; S4: Use the Maxwell equations described by vector magnetic potential as the control equations of the calculation area and set the calculation conditions of the coil and permanent magnet; S5: Calculate the rotor speed at the current time step and substitute it into the rotor region equations as the calculation condition and as the Lorentz term boundary condition; S6: Calculate the rotor position at the current time step and update the rotor geometric position in the two-dimensional calculation model; S7: dividing the two-dimensional computing model into computing networks to generate computing networks; S8: solve the steady-state vector magnetic potential distribution at the current time step and calculate the output power of the coil group; S9: Determine whether the next iteration time step exceeds the calculation cycle; If yes, go to S10; if no, increase the current time step by one time step as the time step of the next iteration, and re-execute S5 to S9; S10: Calculate the effective value of the coil output power during the motion cycle; S11: comparing other calculation results, determining whether the power reaches the maximum value; If yes, then enter S12; if no, then change the coil cross-sectional length and width geometric dimensions and re-execute S3 to S11; S12: Obtaining the optimal design parameters of the energy harvester; The energy collector described in step S1 is an eccentric pendulum low-frequency vibration energy collector with axial magnetic field distribution, in which a first coil layer, an eccentric pendulum layer and a second coil layer are distributed in sequence in the direction of the rotation axis; the eccentric pendulum layer includes a supporting frame and a permanent magnet array; the number of coils in the first coil layer and the second coil layer is the same, and the number of permanent magnets in the eccentric pendulum layer is half of the number of coils in the first coil layer.

2. The method according to claim 1, characterized in that The median plane described in step S3 is an annular cross-section, and its diameter is the average of the inner diameter and the outer diameter of the coil; the cross-section height is greater than the three-dimensional model height, and symmetrical blank areas are reserved above and below as air areas during calculation; it is axially expanded into a two-dimensional plane at the center of the side without the eccentric pendulum to form a two-dimensional calculation model.

3. The method according to claim 2, characterized in that The two-dimensional computing model is composed of multiple computing layers, including a first air epitaxial layer, a first coil layer, a first air gap layer, a permanent magnet layer, a second air gap layer, a second coil layer and a second air epitaxial layer; wherein the first coil layer and the second coil layer include a coil area and an air area; the permanent magnet layer includes a permanent magnet area and an air area.

4. The method according to claim 1, characterized in that: The rotor speed in step S5 is determined by the first-order derivative of the rotor displacement.

5. The method according to claim 1, characterized in that The rotor position in step S6 is determined by a rotor displacement function; the rotor displacement function is a periodic function that can describe the rotational displacement of the rotor within one energy conversion cycle.

6. The method according to claim 1, characterized in that The computing network division described in step S7 uses a triangular network or a rectangular network to divide the computing area into multiple computing nodes.

7. The method according to claim 1, characterized in that In step S2, after determining the maximum swing angle, the minimum air gap is calculated using the following formula: d AGM =R0·sinθ B Where R0 is the radius of the eccentric pendulum, θ B is the maximum swing angle, d AGM is the minimum air gap.

8. The method according to claim 1, characterized in that In step S4, the simplified Maxwell equations after quasi-static approximation are used as the control equations, as shown in the following equation: Where D represents the electric displacement vector, E represents the electric field strength vector, B represents the magnetic flux density vector, and J represents the current density vector; the current density vector is solved by the electric field strength, and the electric field strength is solved by the rate of change of the vector magnetic potential A, satisfying the following equation: Where σ represents the conductivity.

9. The method according to claim 1, characterized in that: In step S5, the permanent magnet group domain is set to have a Lorentz velocity condition, and the velocity value is specified using the following formula: In the formula, x′(t i ) represents the velocity at the current time step, θ′(t i ) is the rotor angular velocity at the current time step, which is obtained by taking the first-order derivative of the rotation angle function θ(t), R i Represents the inner radius of the coil group, R o Represents the outer radius of the coil group; thereby, the periodic rotation of the rotor in the energy harvester is converted into the Lorentz linear velocity condition at the current calculation time step, acting on the permanent magnet domain in the eccentric pendulum to simulate the relative motion between the permanent magnet and the coil.

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