Energy management strategy of system-level model based on vibration energy collection

Abstract

The invention discloses an energy management strategy of a system-level model based on vibration energy collection. The energy management strategy comprises the following steps: S1, constructing a vibration energy collector model, an interface circuit model and an energy storage device model; s2, constructing a system-level model of vibration energy collection based on the vibration energy collector model, the interface circuit model and the energy storage device model constructed in the step S1, and performing simulation; and S3, designing an energy management strategy according to the vibration energy collection system-level model constructed in the step S2. The flow rule of the collected vibration environment energy in each energy collection module is accurately described through the vibration energy collection system-level model, and a corresponding energy management strategy is formulated according to the simulation result of the vibration energy collection system-level model. Under different environment inputs, the energy management strategy can achieve performance superior to existing maximum power point tracking (MPPT).

Description

Technical Field

[0001] The present invention relates to the field of energy harvesting system modeling, and particularly to an energy management strategy for a system-level model based on vibration energy harvesting. Background Art

[0002] In recent years, micro-systems represented by wireless sensor nodes have been widely used in the environment to perform monitoring tasks. Constrained by the environment, cost, volume, etc., the solution of using a large-capacity battery as a stable power source for micro-systems cannot solve the power supply problems of these micro-systems. Therefore, micro-systems need to solve their own power problems through other technologies. Energy harvesting technology is a feasible power supply solution for micro-systems. Energy harvesting technology refers to collecting and utilizing various forms of weak energy existing in the environment to supply power to micro-systems, such as solar energy, thermal energy, mechanical vibration energy, etc. Among them, vibration energy is widely distributed and often appears in various energy harvesting modules.

[0003] Currently, when constructing an energy harvesting module in a micro-system, it mainly consists of a simple combination of independent devices, lacking an overall analysis of the energy harvesting module, resulting in the design of the energy harvesting module of the micro-system being highly dependent on the design experience of the designer. Moreover, energy management strategies represented by the maximum power point tracking (MPPT) technology only perform energy management optimization from the device or circuit level, lacking a system-level analysis. This phenomenon leads to the optimization of only the efficiency of the energy harvester when optimizing the energy harvesting module, while ignoring the management and utilization efficiency of energy in the micro-system, significantly reducing the actually available energy of the system. Summary of the Invention

[0004] The purpose of the present invention is to provide an energy management strategy for a system-level model based on vibration energy harvesting, accurately describe the flow law of the collected environmental energy in the energy harvesting module through the system-level model, and formulate corresponding energy management strategies according to the simulation results of the system-level model. Under different environmental inputs and control strategies, this energy management strategy can achieve better performance than MPPT.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] An energy management strategy for a system-level model based on vibration energy harvesting, comprising the following steps:

[0007] Step S1, construct a vibration energy harvester model, an interface circuit model, and an energy storage device model;

[0008] Step S2, based on the vibration energy harvester model, interface circuit model, and energy storage device model constructed in Step S1, construct a system-level model of vibration energy harvesting and perform simulation;

[0009] Step S3: Design an energy management strategy based on the system-level model of vibration energy harvesting constructed in Step S2.

[0010] Furthermore, the vibration energy harvester adopts a piezoelectric energy harvester, and the piezoelectric energy harvester adopts a single-ended fixed cantilever beam structure.

[0011] Furthermore, the interface circuit consists of a full-bridge rectifier circuit and a Buck circuit.

[0012] Furthermore, the Buck circuit receives the signal input generated by the control unit, and the control unit provides different control modes for the Buck circuit through the MOS switch in the Buck circuit, namely the MOS switch frequency and the duty cycle.

[0013] Furthermore, the energy storage device adopts a secondary solid-state lithium-ion battery.

[0014] Furthermore, in Step S2, the simulation process of the system-level model of vibration energy harvesting is as follows:

[0015] (1) Initialize the parameters of the entire system-level model of vibration energy harvesting;

[0016] (2) Obtain the environmental parameters and input them into the system-level model of vibration energy harvesting to obtain the parameters of the system-level model of vibration energy harvesting;

[0017] (3) The full-bridge rectifier circuit model obtains the corresponding output voltage according to the parameters of the system-level model of vibration energy harvesting;

[0018] (4) The signal generated by the control unit is input into the Buck circuit model to obtain the output current and energy transfer efficiency of the Buck circuit;

[0019] (5) Update the power and terminal voltage of the energy storage device according to the output current and output duration of the Buck circuit.

[0020] Furthermore, different vibration environment inputs correspond to different energy management strategies, and the energy management strategies are realized by the control unit changing the control signals.

[0021] Among them, the energy management strategy is obtained according to the simulation results of the system-level model of vibration energy harvesting.

[0022] Among them, select the control signal corresponding to the maximum energy output as the energy management strategy.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0024] 1. Compared with the prior art, the present invention proposes a system-level model for vibration energy harvesting and realizes the modeling and simulation of each module in the vibration energy harvesting system on a unified platform.

[0025] 2. An energy management strategy based on the system-level model of vibration energy harvesting proposed by the present invention takes into account the parameters of all modules in the vibration energy harvesting system to optimize the system output energy. Compared with the traditional MPPT strategy, it has higher output energy under the same test conditions.

[0026] 3. Similar to the existing MPPT technology, the energy management strategy proposed by the present invention does not change the existing control mode, that is, by adjusting the frequency and duty cycle of the control signal (only the values are different, and the adjusted parameters are the same) to regulate the output energy of the vibration energy harvesting system. Therefore, this method can be applied and popularized without changing the existing hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the vibration energy harvesting system of the present invention;

[0028] Figure 2 is the equivalent circuit model of the piezoelectric energy harvester;

[0029] Figure 3 is the working waveform of the Buck circuit in the interface circuit;

[0030] Figure 4 is the working schematic diagram of the secondary solid-state lithium-ion battery;

[0031] Figure 5 is the relationship diagram between the power output by the vibration energy harvesting system and the duty cycle of the control signal when the vibration acceleration is 1g and the control signal period is 0.005s;

[0032] Figure 6 is the output power of the vibration energy harvesting system corresponding to the MPPT strategy and the energy management strategy based on the system-level model and the proportion of the optimized improvement of the output power under different test conditions. DETAILED DESCRIPTION OF THE INVENTION

[0033] The following further explains the present invention with reference to the accompanying drawings.

[0034] The energy collected from environmental vibration in the energy flow and modeling interface of the energy harvesting module is as Figure 1 shown.

[0035] An energy management strategy based on the system-level model of vibration energy harvesting includes the following steps:

[0036] Step S1, construct a vibration energy harvester model, an interface circuit model, and an energy storage device model;

[0037] Step S11, construct a vibration energy harvester model:

[0038] The vibration energy harvester is described by the following control equations

[0039]

[0040]

[0041] where C p is the capacitance of the piezoelectric layer, R l is the load resistance, v p is the output voltage of the vibration energy harvester; η r , ξ r , ω r , N r are respectively the modal coordinate, damping ratio, resonance frequency, modal electromechanical coupling term, and applied force of the single - end fixed cantilever beam at the r - th order resonance.

[0042] By solving equations (1) and (2), the output voltage and current of the vibration energy harvester are expressed as

[0043]

[0044]

[0045] where v p (t) represents the output voltage of the vibration energy harvester, i p (t) represents the output current of the vibration energy harvester, W0 is the amplitude of the base end in the transverse direction, which depends on the acceleration and excitation frequency of the vibration input, ω is the excitation frequency, is the unit imaginary number, and |V0| is the amplitude of v p .

[0046] Therefore, the model of the vibration energy harvester can be equivalent to Figure 2 the circuit model shown.

[0047] Step S12, establish a system - level model of the interface circuit:

[0048] The energy collected by the vibration energy harvester first enters the full - bridge rectifier circuit. In the full - bridge rectifier circuit, part of the energy is lost in the form of charge during the AC - DC process, resulting in a decrease in the output power. This process is expressed as

[0049]

[0050] Q F= Q tot -2(V rect +2V D )C p #(6)

[0051] where Q tot is the total charge generated by the vibration energy harvester in half a vibration cycle, Q F is the output charge of the full-bridge rectifier circuit, |I p | is Figure 2 the amplitude of the AC current source in rect V is the output voltage of the full-bridge rectifier circuit, V D is the forward conduction voltage of diode D.

[0052] According to Equation (6), the output power of the full-bridge rectifier circuit can be expressed as

[0053]

[0054] where E F is the energy output in half a vibration cycle; C p is the piezoelectric layer capacitance of the vibration energy harvester, as Figure 2 shown; ω is the vibration frequency; |I p | is Figure 2 the amplitude of the AC current source in rect V is the rectified voltage; V D is the forward voltage of diode D.

[0055] The energy output by the full-bridge rectifier circuit then enters the Buck circuit. Combining Figure 3 with the working waveform of the Buck circuit in

[0056]

[0057]

[0058] where the waveform of Figure 3 is as shown; I M is the maximum inductor current, as Figure 3 shown; D1T, D2T are the charging and discharging durations of inductor L in one cycle T, as Figure 3 shown; is the forward conduction voltage of the freewheeling diode D F in the Buck circuit; V bat is the battery terminal voltage.

[0059] In addition, the Buck circuit will generate corresponding energy losses during operation, and this part of the energy is expressed as

[0060]

[0061]

[0062] Among them, and P M are the conduction loss of the freewheeling diode D F and the MOS switch loss respectively; C gs , C gd are the gate-source and gate-drain capacitances respectively.

[0063] Therefore, combining Equation (9), Equation (10) and Equation (11), the energy transfer efficiency of the Buck circuit is expressed as

[0064]

[0065] Among them, P out is the output power of the Buck circuit; is the conduction loss of the freewheeling diode D F in the Buck circuit; P M is the MOS switch loss in the Buck circuit.

[0066] Step S13, construct an energy storage device model:

[0067] The output energy of the interface circuit then enters the energy storage device. The energy storage device in this example is a secondary solid-state lithium-ion battery, and its internal structure and particle migration under the charging working state are as Figure 4 shown. The secondary battery model is described by the drift and diffusion of particles in the battery electrolyte and the positive electrode, and is expressed as follows

[0068]

[0069] a(y, 0) = δa0 #(13.2)

[0070]

[0071]

[0072] and

[0073]

[0074] c(y, 0) = C eq #(14.2)

[0075]

[0076]

[0077] Among them, a is Li+ concentration, It's Li + Diffusion coefficient, a0 is the active Li + The total amount of Li + The percentage of, N is the electrolyte thickness, I is the charging current, F is the Faraday constant, A is the interface area; c is Li ⊕ The concentration of It's Li ⊕ The diffusion coefficient, Yes - The diffusion coefficient, c eq is the initial time Li ⊕ The equilibrium concentration of M is the thickness of the positive electrode.

[0078] Under the description of equations (13) and (14), the polarization voltage inside the secondary battery is expressed as

[0079]

[0080]

[0081] Where E is Li + The built-in electric field generated by drift, R is the gas constant, T w is the battery operating temperature; k is the electrochemical reaction constant, and The electrolyte and electrode interface treatment Li ⊕ and Li + concentration.

[0082] Therefore, the interface voltage of the secondary battery model is expressed as

[0083] V bat =E eq +η mt +η ct #(17)

[0084] Among them, P out Output power for the Buck circuit; is the freewheeling diode D in the Buck circuit F Conduction loss; P M is the MOS switch loss in the Buck circuit.

[0085] Step S2, through the modeling interface, the vibration energy harvester model, the interface circuit model, and the energy storage device model constructed in step S1 are combined to construct a system-level model for energy harvesting. The constructed system-level model for vibration energy harvesting is described by a unified physical language, so it can be simulated on a unified platform. The specific details of the implementation are shown in Table 1.

[0086] Table 1

[0087]

[0088] Table 1 describes the simulation process of the system - level model for vibration energy harvesting. The control signal frequency and duty cycle obtained in the simulation process are for obtaining the energy management strategy.

[0089] The simulation process is as follows:

[0090] (1) Initialize the parameters of the system - level model for the entire vibration energy harvesting;

[0091] (2) Obtain the vibration environment parameters and input them into the vibration energy harvester model;

[0092] (3) The full - bridge rectifier circuit obtains the corresponding output voltage according to the output of the vibration energy harvester model;

[0093] (4) The signal generated by the control unit is input into the Buck circuit to obtain the output current and energy transfer efficiency of the Buck circuit;

[0094] (5) Update the power and terminal voltage of the secondary solid - state lithium - ion battery according to the output current and output duration of the Buck circuit.

[0095] After completing the system - level model simulation, corresponding experiments are carried out to verify the accuracy of the system - level model. The results are as Figure 5 shown.

[0096] Figure 5 The experimental data and simulation data in [] are basically the same, indicating the accuracy of the system - level model.

[0097] Step S3: Design the energy management strategy according to the system - level model proposed in step S2.

[0098] According to the simulation results of the system - level model, the corresponding energy management strategy can be obtained. Specifically, select the control signal corresponding to the maximum energy output as the energy management strategy.

[0099] Figure 5 The output power obtained by the MPPT technology in [] is not the maximum energy that the system can obtain, while the energy management strategy obtained according to the system - level model simulation can enable the system to obtain the maximum energy.

[0100] Different vibration environment inputs correspond to different energy management strategies. The energy management strategy is realized by the control unit changing the control signal. To test the performance of the vibration energy harvesting system under different energy management strategies with different vibration environment inputs, the vibration environment inputs in Table 1 can be adjusted. The comparison between the system - level energy management strategy and MPPT under different vibration environment inputs is as Figure 6 shown.

[0101] In Figure 6 , the difference in output power obtained by applying the MPPT strategy and the system-level strategy illustrates that the system-level strategy has at least a 7% improvement in the vibration energy harvesting module compared to the traditional MPPT technology under different environmental vibration inputs (see η eff ).

[0102] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An energy management strategy based on a system-level model of vibration energy harvesting, characterized by: The following steps are involved: Step S1, constructing a vibration energy harvester model, an interface circuit model, and an energy storage device model; Step S2, based on the vibration energy harvester model, interface circuit model, and energy storage device model constructed in step S1, a system-level model for vibration energy harvesting is constructed, and simulation is performed; Step S3, designing an energy management strategy based on the system-level model of vibration energy harvesting constructed in step S2.

2. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 1, characterized in that: The vibration energy collector adopts a piezoelectric energy collector, and the piezoelectric energy collector adopts a cantilever beam structure with a single end fixed.

3. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 1, characterized in that: The interface circuit consists of a full-bridge rectifier circuit and a Buck circuit.

4. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 3, characterized in that: The Buck circuit receives a signal input generated by a control unit, and the control unit provides different control modes, namely, MOS switching frequency and duty cycle, for the Buck circuit through a MOS switch in the Buck circuit.

5. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 1, characterized in that: The energy storage device adopts a secondary solid-state lithium-ion battery.

6. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 1, characterized in that: In step S2, the simulation process of the system-level model of vibration energy harvesting is as follows: (1) Initialize the system-level model parameters of the entire vibration energy harvesting; (2) Obtaining environmental parameters and inputting them into a system-level model of vibration energy harvesting to obtain system-level model parameters of vibration energy harvesting; (3) The full-bridge rectifier circuit model obtains the corresponding output voltage based on the system-level model parameters of vibration energy harvesting; (4) The signal generated by the control unit is input into the Buck circuit model to obtain the output current and energy transfer efficiency of the Buck circuit; (5) Update the power and terminal voltage of the energy storage device according to the output current and output duration of the Buck circuit.

7. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 6, characterized in that: Different vibration environment inputs correspond to different energy management strategies, and the energy management strategies are implemented by changing the control signal through the control unit.

8. An energy management strategy based on a system-level model of vibration energy harvesting according to claim 1 or 6, characterized in that: The energy management strategy is derived from the simulation results of a system-level model of vibration energy harvesting.

9. The energy management strategy of a system-level model based on vibration energy harvesting according to claim 8, characterized in that: The control signal corresponding to the maximum energy output is selected as the energy management strategy.

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