Energy management circuit for vibration energy collector

Abstract

An energy management circuit for a vibration energy collector comprises an impedance matching circuit, a charging circuit, an energy storage module composed of a super capacitor and a lithium battery, a discharging circuit controlled by a power management chip and a post-stage load. The impedance matching circuit performs optimal impedance matching; the charging circuit is used for rectifying and converting the small-voltage electric energy of the alternating current output by the energy collector, so that the energy is stored in an energy storage module formed by a super capacitor and a lithium battery; the discharging circuit manages energy release of the energy storage module, prolongs the service life of the energy storage module by setting a charging and discharging hysteresis interval of the energy storage unit, and is used for supplying energy to a rear-end node. The output energy of the energy collector is taken as a main power supply, and the lithium battery is taken as a standby power supply, so that stable power supply for a rear-end sensor node in an unstable environment is realized, and the problem that continuous power supply cannot be realized because the power of the vibration energy collector is generally relatively small and the energy taking efficiency of a standard energy collection circuit is relatively low is solved.

Description

Technical Field

[0001] The utility model relates to the field of vibration energy harvesting technology and electric energy management technology, and in particular to an energy management circuit for a vibration energy harvester, which is mainly a circuit for matching a charging circuit with high energy efficiency and switching between a main and auxiliary energy storage modules and stably supplying power to a subsequent load. Background Art

[0002] The purpose of energy harvesting is to collect various forms of relatively weak energy that is difficult to directly use in the environment to provide a reliable power supply for electronic systems. Energy harvesting technology avoids the problem of difficult replacement of traditional batteries and environmental pollution, and is in line with the concept of sustainable development. Vibration energy is ubiquitous and can be easily found in hard-to-reach places. Therefore, vibration energy harvesting methods may have many advantages over other energy harvesting methods, such as cleanliness, stability, small size, and can be used in many specific fields.

[0003] In the field of energy management circuits for energy harvesting, the main problem currently exists is that the energy collected by the energy harvester is affected by environmental factors and the output is unstable. It is possible that the energy collected by the energy harvester is less than the consumption of the back-end equipment or that the peak period of energy collection does not match the peak period of power consumption. Patent application 201310257373.2 discloses a power generation device that generates voltage by rolling over a piezoelectric transducer by a car. In the device, a multi-voltage rectifier circuit multiplies the voltage and rectifies it, and then charges the supercapacitor and rechargeable battery through a voltage-stabilizing charging circuit, but does not involve a complete discharge circuit. Patent application 201680001810.6 provides a power management method, device and micro-energy power supply based on micro-energy harvesting. The method is based on SOC execution and has the disadvantages of high MCU power consumption, which will reduce energy extraction efficiency. Patent application 202310763112.1 discloses a battery-free self-powered leg movement EMG signal monitoring system based on energy harvesting technology. The energy management circuit in the system adopts power management using undervoltage and overvoltage locking circuits to maintain the output voltage between 3.3-5V. The input voltage range of this circuit is between 10-20V, which is not suitable for the use scenario of energy harvesters with small voltage output. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the purpose of the utility model is to provide an energy management circuit for a vibration energy harvester, which uses the energy output of the energy harvester as the main power supply and a lithium battery as a backup power supply to achieve stable power supply for the back-end sensor nodes in an unstable environment, solving the problem that the power of the vibration energy harvester is generally small, the energy extraction efficiency of the standard energy harvesting circuit is low, and continuous power supply cannot be achieved.

[0005] In order to achieve the above object, the technical solution of the utility model is:

[0006] An energy management circuit for a vibration energy harvester comprises an impedance matching circuit 2, a charging circuit 3, an energy storage module 8 consisting of a super capacitor 4 and a lithium battery 6, a discharge circuit 5 controlled by a power management chip, and a post-stage load 7; the impedance matching circuit 2 performs optimal impedance matching; the charging circuit 3 is used to rectify and convert the low-voltage AC electric energy output by the energy harvester 1, so that the energy is stored in the energy storage module 8 consisting of the super capacitor 4 and the lithium battery 6; the discharge circuit 5 manages the energy release of the energy storage module 8 to supply energy to the back-end node.

[0007] The impedance matching circuit 2 is a T-type LCC impedance matching network, including three branches. The first branch is a capacitor C1 connected in series with the power supply AC of the energy harvester 1 and the coil self-inductance L1 inside the energy harvester 1; the second branch is the actual load R1 and the inductor L2 connected in series; the third branch includes a capacitor C2, which is connected in parallel with the first and second branches.

[0008] The charging circuit 3 is a self-powered synchronous charge extraction circuit, including a switch S1 for monitoring positive and negative peak values, a switch S2, a source-end capacitor C3, a positive voltage detection switch S3, an energy storage capacitor C4, a freewheeling diode D1, an energy storage inductor L3 and a load R2; the source-end capacitor C3 is used as a detection capacitor, and the switch function is realized by detecting the voltage across it. When the capacitor C3 reaches a positive peak value, the switch S1 is closed, and the capacitor C3 and the parallel energy storage inductor L3 form an LC oscillation circuit. The source-end capacitor C3 stores charge and passes The energy storage inductor L3 is transmitted to the other direction; when the voltage on the capacitor C3 reaches the negative peak value, the switches S2 and S3 are closed, the charge stored on the energy storage inductor C3 is extracted by the energy storage inductor L3, the current is collected by the energy storage inductor L3, and the current energy is stored in the energy storage inductor L3; at this time, the switch S2 is disconnected, and the charge on the energy storage inductor L3 flows to the energy storage capacitor C4 through the freewheeling diode D1 and the switch S2. The circuit uses the positive and negative peak values ​​as the boundary, sets the positive and negative cycle charging process, and finally completes the charge extraction process through the inductor freewheeling.

[0009] The supercapacitor 4 of the energy storage module 8 serves as the main power source to store the energy collected by the charging circuit 3 from the energy harvester; the lithium battery 6 of the energy storage module 8 serves as a backup power source, and when the energy output of the supercapacitor 4 is insufficient, it quickly switches to a stable power supply for the back end; when the energy harvester 1 collects sufficient energy, the lithium battery 6 is trickle charged.

[0010] The discharge circuit 5 uses LTC3106 as the power management chip. The lithium battery 6 is connected to the Vstore port through a filter ceramic capacitor. The Vcap and EnVstr ports monitor and control the upper and lower thresholds of the voltage of the lithium battery 6 respectively. The Vin port is connected to the super capacitor 4. The voltage of the super capacitor 4 is divided by the resistors R3 and R4 connected on both sides of the RUN port. The internal comparator of the power management chip compares the divided voltage value with the internal rated voltage value, and controls the discharge interval of the super capacitor 4 through the resistance ratio of the RUN port; the V of the discharge circuit 5 is changed by configuring the SS1 and SS2 ports. OUT , through the configuration of OS1 and OS2 ports, the discharge interval of the rechargeable lithium battery 6 is determined; SW1 and SW2 are connected to the BUCK-BOOST circuit inside the inductor control chip to work; the Vaux port outputs a fixed voltage, that is, the rated working voltage inside the chip.

[0011] Compared with the prior art, the utility model has the following beneficial effects:

[0012] 1. The impedance matching circuit 2 of the utility model is a T-type LCC impedance matching network, which determines a capacitor-inductor combination with higher charging efficiency. At the same time, the inductance and capacitance of the T-type LCC impedance network effectively adjust the circuit capacitive reactance and inductive reactance, thereby weakening the inductive reactance inside the energy harvester coil.

[0013] 2. The charging circuit 3 of the utility model uses a self-powered synchronous charge extraction circuit. This technology combines voltage inversion, rectification and synchronous charge extraction to improve energy extraction efficiency and output power. When the parasitic capacitor voltage inside the energy harvester reaches a positive peak, an LC path is formed by closing the switch, and the charge is transported through the inductor L to complete the voltage inversion. When the output of the energy harvester reaches a negative peak, the switch is closed, and the charge on the inductor flows to the storage capacitor through the diode. The circuit realizes the use of no rectifier bridge and inductor multiplexing, which improves efficiency and reduces costs.

[0014] 3. The discharge circuit 5 of the utility model uses the power management chip LTC3106. LTC3106 is used as a control chip and has automatic power switching management optimized for multi-source low-power systems. When the main power supply is unavailable, LTC3106 can seamlessly switch to the backup power supply, and the backup power supply supplies power to the power management chip and the back end; when the main power supply is available and there is surplus energy, the backup battery can be trickle charged.

[0015] 4. The utility model can provide stable power supply for the back-end load 7 such as wireless accelerometer sensor node and thermometer and hygrometer; when the output of the energy harvester is insufficient, the lithium battery can be switched to provide stable power supply for the back-end load.

[0016] In summary, the utility model is aimed at a vibration energy harvester and designs a method that uses the energy output of the energy harvester as the main power supply and a lithium battery as the backup power supply. The management chip controls the supercapacitor and the backup lithium battery to quickly switch to provide stable power supply for the subsequent load. The circuit design has the characteristics of a wide input voltage range, high energy extraction efficiency, switching between main and auxiliary power supplies, and good output stability, thereby realizing an energy management circuit that provides stable power supply to the back-end sensor nodes in an unstable environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the overall structural diagram of the utility model.

[0018] Figure 2 It is a schematic diagram of the impedance matching circuit 2 of the present invention.

[0019] Figure 3 This is the topological structure of the charging circuit 3 of the present utility model.

[0020] Figure 4 This is a schematic diagram of a discharge circuit controlled by a power management chip LTC3106 of the discharge circuit 5 of the present invention.

[0021] Figure 5 This is a simulation test result diagram of the utility model.

[0022] Figure 6 This is a test result diagram of the prototype of the utility model.

[0023] Figure 7 This is a physical diagram of the utility model. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

[0025] refer to Figure 1 , an energy management circuit for a vibration energy harvester, comprising an impedance matching circuit 2, a charging circuit 3, an energy storage module 8 consisting of a super capacitor 4 and a lithium battery 6, a discharge circuit 5 controlled by a power management chip, and a post-stage load 7; the impedance matching circuit 2 performs optimal impedance matching to improve charging efficiency; the charging circuit 3 is used to rectify and convert the low-voltage AC electric energy output by the energy harvester 1, so that the energy is stored in the energy storage module 8 consisting of the super capacitor 4 and the lithium battery 6; the discharge circuit 5 manages the energy release of the energy storage module, and by setting the charging and discharging hysteresis interval of the energy storage unit, the service life of the energy storage module is extended, and it is used to supply energy to the back-end node.

[0026] refer to Figure 2 The impedance matching circuit 2 is a T-type LCC impedance matching network, which includes three branches. The first branch is a capacitor C1 connected in series with the power supply AC of the energy harvester 1 and the coil self-inductance L1 inside the energy harvester 1; the second branch is the actual load R1 and the inductor L2 connected in series; the third branch includes a capacitor C2 connected in parallel with the first and second branches. The goal of load matching is to maximize the energy conversion efficiency. Assume R s is the internal impedance of the power supply, R L is the load impedance, if and only if R L =R S When the load obtains the maximum output power, the state at this time is the matching state. The impedance of the supercapacitor during the charging process is nonlinear, and its capacitive impedance is constantly changing. Therefore, it is optimized and the discharge interval of the supercapacitor is set through the discharge circuit controlled by the power management chip. The back-end impedance of the charging process is tested in this discharge interval. Impedance matching is performed to improve the charging efficiency. The impedance matching circuit has a simple structure and stable performance. Through impedance matching of inductors and capacitors, the energy extraction efficiency is improved.

[0027] Reference Image Figure 3 The charging circuit 3 is a self-powered synchronous charge extraction circuit, which is intended to increase the open circuit voltage and thus improve the output power of the circuit, and includes a switch S1 for monitoring positive and negative peak values, a switch S2, a source-end capacitor C3, a positive voltage detection switch S3, an energy storage capacitor C4, a freewheeling diode D1, an energy storage inductor L3 and a load R2; the source-end capacitor C3 is used as a detection capacitor, and the switching function is realized by controlling the on-off of the transistor by detecting the voltage across the two ends of the capacitor C3. When the capacitor C3 reaches the positive peak value, the switch S1 is closed, and the capacitor C3 and the parallel energy storage inductor L3 form an LC oscillation circuit. The source capacitor C3 stores the charge and transmits it to the other direction through the energy storage inductor L3; when the voltage on the capacitor C3 reaches the negative peak value, the switches S2 and S3 are closed, the charge stored on the energy storage inductor C3 is extracted by the energy storage inductor L3, the current is collected by the energy storage inductor L3, and the current energy is stored in the energy storage inductor L3; at this time, the switch S2 is disconnected, and the charge on the energy storage inductor L3 flows to the energy storage capacitor C4 through the freewheeling diode D1 and the switch S2. The circuit uses the positive and negative peak values ​​as the boundary, sets the positive and negative cycle charging process, and finally completes the charge extraction process through the inductor freewheeling.

[0028] Figure 4This is the schematic diagram of the discharge circuit 5 controlled by the power management chip LTC3106. The discharge circuit 5 uses the LTC3106 of Analog Devices as the power management chip. The lithium battery 6 is connected to the Vstore port through a filter ceramic capacitor. The Vcap and EnVstr ports respectively monitor and control the upper and lower thresholds of the voltage of the lithium battery 6 to prevent overcharging and over-discharging of the battery, greatly extending the life of the rechargeable lithium battery. Vin is connected to the supercapacitor 4, and the voltage of the supercapacitor 4 is divided by the resistors R3 and R4 connected on both sides of the RUN port. The internal comparator of the power management chip compares the divided voltage value with the internal rated voltage value, and controls the discharge interval of the supercapacitor through the resistance ratio of the RUN port; the V of the discharge circuit 5 is changed through the port configuration of the SS1 and SS2 ports. OUT , the circuit shown in the figure outputs 3.3V. The discharge interval of the rechargeable lithium battery 6 is determined by the configuration of the OS1 and OS2 ports; the SW1 and SW2 terminals are connected to the BUCK-BOOST circuit inside the inductor control chip to work. The Vaux port outputs a fixed voltage, which is the rated working voltage inside the chip.

[0029] The working principle of the utility model is:

[0030] The impedance matching circuit 2 of the utility model performs optimal impedance matching; the charging circuit 3 is used to rectify and convert the low-voltage AC electric energy output by the energy harvester 1, so that the energy is stored in the energy storage module 8 composed of a supercapacitor and a lithium battery; the energy output by the energy harvester is used as the main power supply, and the backup lithium battery is used as the backup power supply; the discharge circuit 5 manages the energy release of the energy storage module, and extends the service life of the energy storage module by setting the charging and discharging hysteresis interval of the energy storage unit, which is used to supply energy to the back-end node, realize stable power supply to the subsequent load in an unstable environment, realize the collection of vibration energy, and then use the collected energy to power the subsequent load.

[0031] The charging circuit 3 combines voltage inversion, rectification and synchronous charge extraction. By detecting capacitors, transistors as switch controls, diodes and inductors, the positive and negative peak values ​​of the voltage of the energy harvester are monitored to control the on and off of the circuit branches, and the positive and negative cycle charging process is set with the positive and negative peak values ​​as the boundaries. Finally, the charge extraction process is completed by inductor continuous current.

[0032] The function of the impedance matching circuit 2 is to perform impedance matching, thereby improving charging efficiency. The impedance matching circuit has a simple structure and stable performance, and improves energy extraction efficiency through impedance matching of inductance and capacitance.

[0033] The discharge circuit 5 uses the LTC3106 of Analog Devices as the power management chip. The LTC3106 provides a RUN pin for resistance programming. Figure 4R3 and R2 are used to control the input voltage to start the chip. When the input voltage reaches the startup voltage threshold, the LTC3106 starts to work and the back-end outputs 3.3V. When the input voltage drops to the lower threshold voltage, the LTC3106 can seamlessly switch to the backup power supply. And the main power supply can choose to trickle charge the battery and power the load when there is enough remaining energy.

[0034] Use LT SPICE software to perform circuit simulation, such as Figure 5 shown. Figure 5 The horizontal axis is time and the vertical axis is voltage. When the voltage of the storage capacitor reaches the upper voltage limit, the discharge circuit controlled by the power management chip is turned on, and the capacitor is discharged. As the load consumes power, the voltage across the capacitor drops rapidly. When it is lower than the lower threshold voltage, the discharge circuit is disconnected, so the capacitor is charged and the capacitor voltage starts to rise again, and the cycle repeats. According to the output voltage of the energy storage module, the load works intermittently. Figure 6 The output of the vibration energy harvester, the output of the lithium battery Vstore, and the voltage output of the discharge circuit of the energy management circuit are monitored by an oscilloscope.

[0035] Figure 7 This is a physical picture of the utility model. The irregular board size is only 46*32mm, which can be placed inside a small energy harvester. M2 screw holes are left around it, which can be effectively fixed to the energy harvester without being affected by external vibrations. The FPC socket on the back of the circuit board can be connected to the input energy from the energy harvester. The FPC soft cable is used, which is beneficial for assembly and placement. The 4 holes on the left can be connected to external switches and LED indicators, and the internal working status is indicated by the LED light. The upper hole on the right can be connected to a backup battery, and the lower hole on the right can be connected to a supercapacitor for energy storage. The two middle holes can be output through leads, so that the internal energy of the energy harvester can be rectified and stored, and then output to the outside to adapt to the voltage level of different application scenarios.

[0036] The above only illustrates several specific embodiments of the present invention, but cannot be regarded as the protection scope of the present invention. Any equivalent changes or modifications or proportional enlargement or reduction made according to the design spirit of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. An energy management circuit for a vibration energy harvester, characterized in that: The invention comprises an impedance matching circuit (2), a charging circuit (3), an energy storage module (8) composed of a super capacitor (4) and a lithium battery (6), a discharge circuit (5) controlled by a power management chip, and a back-end load (7); the impedance matching circuit (2) performs optimal impedance matching; the charging circuit (3) is used to rectify and convert the low-voltage AC electric energy output by the energy harvester (1) so that the energy is stored in the energy storage module (8) composed of the super capacitor (4) and the lithium battery (6); the discharge circuit (5) manages the energy release of the energy storage module (8) to supply energy to the back-end node; The impedance matching circuit (2) is a T-type LCC impedance matching network, comprising three branches, wherein the first branch is a capacitor C1 connected in series with the power source AC of the energy harvester (1) and the coil self-inductance L1 inside the energy harvester (1); the second branch is an actual load R1 and an inductor L2 connected in series; and the third branch comprises a capacitor C2 connected in parallel with the first and second branches.

2. The energy management circuit for a vibration energy harvester according to claim 1, characterized in that: The charging circuit (3) is a self-powered synchronous charge extraction circuit, comprising a switch S1 for monitoring positive and negative peak values, a switch S2, a source-end capacitor C3, a positive voltage detection switch S3, an energy storage capacitor C4, a freewheeling diode D1, an energy storage inductor L3 and a load R2; the source-end capacitor C3 is used as a detection capacitor, and the switch function is realized by detecting the voltage across the capacitor C3. When the capacitor C3 reaches a positive peak value, the switch S1 is closed, and the capacitor C3 and the parallel energy storage inductor L3 form an LC oscillation circuit. The source-end capacitor C3 stores charge and passes The energy stored in the energy storage inductor L3 is then transferred to the other direction; when the voltage on the capacitor C3 reaches a negative peak value, the switches S2 and S3 are closed, the charge stored on the energy storage inductor C3 is extracted by the energy storage inductor L3, the current is collected by the energy storage inductor L3, and the current energy is stored in the energy storage inductor L3; at this time, the switch S2 is disconnected, and the charge on the energy storage inductor L3 flows to the energy storage capacitor C4 through the freewheeling diode D1 and the switch S2. The circuit uses the positive and negative peak values ​​as the boundary, sets the positive and negative cycle charging process, and finally completes the charge extraction process through the inductor freewheeling.

3. The energy management circuit for a vibration energy harvester according to claim 1, characterized in that: The supercapacitor (4) of the energy storage module (8) serves as a main power source to store energy collected by the charging circuit (3) from the energy collector; the lithium battery (6) of the energy storage module (8) serves as a backup power source, and when the energy output of the supercapacitor (4) is insufficient, it quickly switches to a stable power supply for the back end; when the energy collected by the energy collector (1) is sufficient, the lithium battery (6) is trickle charged.

4. The energy management circuit for a vibration energy harvester according to claim 1, characterized in that: The discharge circuit (5) uses LTC3106 as a power management chip, the lithium battery (6) is connected to the Vstore port through a filter ceramic capacitor, the Vcap and EnVstr ports respectively monitor and control the upper and lower thresholds of the voltage of the lithium battery (6), the Vin port is connected to the supercapacitor (4), the voltage of the supercapacitor (4) is divided by resistors R3 and R4 connected to both sides of the RUN port, the internal comparator of the power management chip compares the divided voltage value with the internal rated voltage value, and controls the discharge interval of the supercapacitor through the resistance ratio of the RUN port; the V of the discharge circuit (5) is changed through the configuration of the SS1 and SS2 ports. OUT The discharge interval of the rechargeable lithium battery (6) is determined by configuring the OS1 and OS2 ports; the SW1 and SW2 terminals are connected to the BUCK-BOOST circuit inside the inductor control chip to operate; the Vaux port outputs a fixed voltage, i.e., the rated working voltage inside the chip.

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